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13 pages, 5859 KiB

Open AccessArticle

CO₂-Driven N-Formylation/N-Methylation of Amines Using C-Scorpionate Metal Complexes

by Inês A. S. Matias, Anna M. Trzeciak, Paulina Pąchalska, Ana P. C. Ribeiro and Luísa M. D. R. S. Martins

Molecules 2024, 29(4), 870; https://doi.org/10.3390/molecules29040870 - 16 Feb 2024

Viewed by 544

Abstract

C-scorpionate metal complexes, specifically, [NiCl₂(tpm)]·3H₂O, [CoCl₂(tpm)]·3H₂O and [PdCl₂(tpm)] [tpm = hydrotris(1H-pyrazol-1-yl)methane], were effective in the N-formylation and N-methylation of amines using carbon dioxide, as carbon source, in the presence of sodium borohydride. Various [...] Read more.

C-scorpionate metal complexes, specifically, [NiCl₂(tpm)]·3H₂O, [CoCl₂(tpm)]·3H₂O and [PdCl₂(tpm)] [tpm = hydrotris(1H-pyrazol-1-yl)methane], were effective in the N-formylation and N-methylation of amines using carbon dioxide, as carbon source, in the presence of sodium borohydride. Various parameters were studied, including reaction time, temperature, solvent volume, presence of additives, and catalyst amount. These parameters were found to have a significant impact on the selectivity of the product. [NiCl₂(tpm)]·3H₂O exhibited good conversion at 80 °C, but its selectivity towards formamide decreased with prolonged reaction time. Increasing the amount of [NiCl₂(tpm)]·3H₂O, the selectivity changed. [PdCl₂(tpm)] showed different selectivity compared to [NiCl₂(tpm)]·3H₂O, while [CoCl₂(tpm)]·3H₂O presented poor results. Monitoring the reaction course by ¹H NMR revealed the presence of an intermediate species that influenced product formation. These results highlight the versatility and catalytic potential of C-scorpionate metal complexes in the N-formylation/N-methylation of amines in the catalytic system (NaBH₄/MeCN/CO₂). Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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10 pages, 678 KiB

Open AccessArticle

Arabinoxylan from Corn Fiber Obtained through Alkaline Extraction and Membrane Purification: Relating Bioactivities with the Phenolic Compounds

by Verónica Weng, Martim Cardeira, Andreia Bento-Silva, Ana Teresa Serra, Carla Brazinha and Maria Rosário Bronze

Molecules 2023, 28(15), 5621; https://doi.org/10.3390/molecules28155621 - 25 Jul 2023

Cited by 2 | Viewed by 1028

Abstract

Arabinoxylan has prebiotic properties, as it is able to resist digestion in the small intestine and undergoes fermentation in the large intestine. In this work, arabinoxylan was extracted from corn fiber using an alkaline solution and further purified with membrane processing. It was [...] Read more.

Arabinoxylan has prebiotic properties, as it is able to resist digestion in the small intestine and undergoes fermentation in the large intestine. In this work, arabinoxylan was extracted from corn fiber using an alkaline solution and further purified with membrane processing. It was found that the extracts were mainly composed of xylose (50–52%), arabinose (37–39%), galactose (9%) and glucose (1–4%), with an A/X ratio of 0.72–0.77. All the extracts were composed of phenolic compounds, including ferulic acid derivatives such as dimers, trimers and tetramers. The purified extract had a lower concentration of ferulic and p-coumaric acid (0.004 and 0.02 mg/mg_{dry_weight}, respectively) when compared to raw extract (19.30 and 2.74 mg/mg_{dry_weight}, respectively). The same effect was observed for the antioxidant activity, with purified extracts having a lower value (0.17 ± 0.02 µmol TEAC/mg) when compared to the raw extract (2.20 ± 0.35 µmol TEAC/mg). The purified extract showed a greater antiproliferative effect against the HT29 cell line with EC₅₀ = 0.12 ± 0.02 mg/mL when compared to the raw extract (EC₅₀ = 5.60 ± 1.6 mg/mL). Both raw and purified extracts did not show any cytotoxicity to the Caco-2 cell line in the maximum concentration tested (10 mg/mL). Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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14 pages, 585 KiB

Open AccessArticle

Application of Green Technology to Extract Clean and Safe Bioactive Compounds from Tetradesmus obliquus Biomass Grown in Poultry Wastewater

by Jelena Vladić, Jelena Molnar Jazić, Alice Ferreira, Snežana Maletić, Dragoljub Cvetković, Jasmina Agbaba, Senka Vidović and Luisa Gouveia

Molecules 2023, 28(5), 2397; https://doi.org/10.3390/molecules28052397 - 06 Mar 2023

Cited by 3 | Viewed by 2166

Abstract

Microalgae are capable of assimilating nutrients from wastewater (WW), producing clean water and biomass rich in bioactive compounds that need to be recovered from inside the microalgal cell. This work investigated subcritical water (SW) extraction to collect high-value compounds from the microalga Tetradesmus [...] Read more.

Microalgae are capable of assimilating nutrients from wastewater (WW), producing clean water and biomass rich in bioactive compounds that need to be recovered from inside the microalgal cell. This work investigated subcritical water (SW) extraction to collect high-value compounds from the microalga Tetradesmus obliquus after treating poultry WW. The treatment efficiency was evaluated in terms of total Kjeldahl nitrogen (TKN), phosphate, chemical oxygen demand (COD) and metals. T. obliquus was able to remove 77% TKN, 50% phosphate, 84% COD, and metals (48–89%) within legislation values. SW extraction was performed at 170 °C and 30 bar for 10 min. SW allowed the extraction of total phenols (1.073 mg GAE/mL extract) and total flavonoids (0.111 mg CAT/mL extract) with high antioxidant activity (IC₅₀ value, 7.18 µg/mL). The microalga was shown to be a source of organic compounds of commercial value (e.g., squalene). Finally, the SW conditions allowed the removal of pathogens and metals in the extracts and residues to values in accordance with legislation, assuring their safety for feed or agriculture applications. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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15 pages, 948 KiB

Open AccessArticle

Novel Organic Salts Based on Mefloquine: Synthesis, Solubility, Permeability, and In Vitro Activity against Mycobacterium tuberculosis

by Dário Silva, Márcio V. C. Lopes, Željko Petrovski, Miguel M. Santos, Jussevania P. Santos, Sueli F. Yamada-Ogatta, Marcelle L. F. Bispo, Marcus V. N. de Souza, Ana Rita C. Duarte, Maria C. S. Lourenço, Raoni Schroeder B. Gonçalves and Luis C. Branco

Molecules 2022, 27(16), 5167; https://doi.org/10.3390/molecules27165167 - 13 Aug 2022

Cited by 3 | Viewed by 1581

Abstract

The development of novel pharmaceutical tools to efficiently tackle tuberculosis is the order of the day due to the rapid development of resistant strains of Mycobacterium tuberculosis. Herein, we report novel potential formulations of a repurposed drug, the antimalarial mefloquine (MFL), which [...] Read more.

The development of novel pharmaceutical tools to efficiently tackle tuberculosis is the order of the day due to the rapid development of resistant strains of Mycobacterium tuberculosis. Herein, we report novel potential formulations of a repurposed drug, the antimalarial mefloquine (MFL), which was combined with organic anions as chemical adjuvants. Eight mefloquine organic salts were obtained by ion metathesis reaction between mefloquine hydrochloride ([MFLH][Cl]) and several organic acid sodium salts in high yields. One of the salts, mefloquine mesylate ([MFLH][MsO]), presented increased water solubility in comparison with [MFLH][Cl]. Moreover, all salts with the exception of mefloquine docusate ([MFLH][AOT]) showed improved permeability and diffusion through synthetic membranes. Finally, in vitro activity studies against Mycobacterium tuberculosis revealed that these ionic formulations exhibited up to 1.5-times lower MIC values when compared with [MFLH][Cl], particularly mefloquine camphorsulfonates ([MFLH][(1R)-CSA], [MFLH][(1S)-CSA]) and mefloquine HEPES ([MFLH][HEPES]). Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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12 pages, 2014 KiB

Open AccessArticle

Preparation of Thioaminals in Water

by Lídia A. S. Cavaca, Rafael F. A. Gomes and Carlos A. M. Afonso

Molecules 2022, 27(5), 1673; https://doi.org/10.3390/molecules27051673 - 03 Mar 2022

Cited by 3 | Viewed by 2279

Abstract

The presence of sulfur–carbon bonds is transversal to several areas of chemistry, e.g., drug discovery, materials, and chemical biology. However, a lack of efficient and sustainable procedures for the preparation of thioaminals, the N,S-analogues of O,O-acetals, contributes to this functional group [...] Read more.

The presence of sulfur–carbon bonds is transversal to several areas of chemistry, e.g., drug discovery, materials, and chemical biology. However, a lack of efficient and sustainable procedures for the preparation of thioaminals, the N,S-analogues of O,O-acetals, contributes to this functional group often being overlooked by the scientific community. In this work is described the formation of thioaminals in water promoted by copper(II) triflate. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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12 pages, 2334 KiB

Open AccessArticle

Synthesis of Vitamin B3 through a Heterogeneous Photocatalytic Approach Using Metal-Free Carbon Nitride-Based Catalysts

by Raquel A. Fernandes, Maria J. Sampaio, Joaquim L. Faria and Cláudia G. Silva

Molecules 2022, 27(4), 1295; https://doi.org/10.3390/molecules27041295 - 15 Feb 2022

Cited by 4 | Viewed by 2457

Abstract

Vitamin B3 (nicotinic acid, VB3) was synthesized through the photocatalytic oxidation of 3-pyridinemethanol (3PM) under visible-light-emitting diode (LED) irradiation using metal-free graphitic carbon nitride (GCN) - based materials. A bulk (GCN) material was prepared by a simple thermal treatment using dicyandiamide as the [...] Read more.

Vitamin B3 (nicotinic acid, VB3) was synthesized through the photocatalytic oxidation of 3-pyridinemethanol (3PM) under visible-light-emitting diode (LED) irradiation using metal-free graphitic carbon nitride (GCN) - based materials. A bulk (GCN) material was prepared by a simple thermal treatment using dicyandiamide as the precursor. A post-thermal treatment under static air and nitrogen flow was employed to obtain the GCN-T and GCN-T-N materials, respectively. The conditions adopted during the post-treatment revealed differences in the resulting materials’ morphological, electronic, and optical properties. The post-treated photocatalysts revealed an enhanced efficiency in the oxidation of 3PM into VB3, with the GCN-T-N photocatalyst being the best-performing material. The defective surface, reduced crystallinity, and superior photoabsorption of GCN-T-N account for this material’s improved performance in the production of VB3. Nevertheless, the presence of nitrogen vacancies in the carbon nitride structure and, consequently, the creation of mid-gap states also accounts to its highly oxidative ability. The immobilization of GCN-T-N in sodium alginate hydrogel was revealed as a promising strategy to produce VB3, avoiding the need for the photocatalyst separation step. Concerning the mechanism of synthesis of VB3 through the photocatalytic oxidation of 3PM, it was possible to identify the presence of 3-pyridinecarboxaldehyde (3PC) as the intermediary product. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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21 pages, 8653 KiB

Open AccessArticle

Enhanced Enzyme Reuse through the Bioconjugation of L-Asparaginase and Silica-Based Supported Ionic Liquid-like Phase Materials

by João C. F. Nunes, Mafalda R. Almeida, Rui M. F. Bento, Matheus M. Pereira, Valéria C. Santos-Ebinuma, Márcia C. Neves, Mara G. Freire and Ana P. M. Tavares

Molecules 2022, 27(3), 929; https://doi.org/10.3390/molecules27030929 - 29 Jan 2022

Cited by 5 | Viewed by 2240

Abstract

L-asparaginase (ASNase) is an amidohydrolase that can be used as a biopharmaceutical, as an agent for acrylamide reduction, and as an active molecule for L-asparagine detection. However, its free form displays some limitations, such as the enzyme’s single use and low stability. Hence, [...] Read more.

L-asparaginase (ASNase) is an amidohydrolase that can be used as a biopharmaceutical, as an agent for acrylamide reduction, and as an active molecule for L-asparagine detection. However, its free form displays some limitations, such as the enzyme’s single use and low stability. Hence, immobilization is one of the most effective tools for enzyme recovery and reuse. Silica is a promising material due to its low-cost, biological compatibility, and tunable physicochemical characteristics if properly functionalized. Ionic liquids (ILs) are designer compounds that allow the tailoring of their physicochemical properties for a given task. If properly designed, bioconjugates combine the features of the selected ILs with those of the support used, enabling the simple recovery and reuse of the enzyme. In this work, silica-based supported ionic liquid-like phase (SSILLP) materials with quaternary ammoniums and chloride as the counterion were studied as novel supports for ASNase immobilization since it has been reported that ammonium ILs have beneficial effects on enzyme stability. SSILLP materials were characterized by elemental analysis and zeta potential. The immobilization process was studied and the pH effect, enzyme/support ratio, and contact time were optimized regarding the ASNase enzymatic activity. ASNase–SSILLP bioconjugates were characterized by ATR-FTIR. The bioconjugates displayed promising potential since [Si][N₃₄₄₄]Cl, [Si][N₃₆₆₆]Cl, and [Si][N₃₈₈₈]Cl recovered more than 92% of the initial ASNase activity under the optimized immobilization conditions (pH 8, 6 × 10⁻³ mg of ASNase per mg of SSILLP material, and 60 min). The ASNase–SSILLP bioconjugates showed more enhanced enzyme reuse than reported for other materials and immobilization methods, allowing five cycles of reaction while keeping more than 75% of the initial immobilized ASNase activity. According to molecular docking studies, the main interactions established between ASNase and SSILLP materials correspond to hydrophobic interactions. Overall, it is here demonstrated that SSILLP materials are efficient supports for ASNase, paving the way for their use in the pharmaceutical and food industries. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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23 pages, 2529 KiB

Open AccessArticle

Tunning CO₂ Separation Performance of Ionic Liquids through Asymmetric Anions

by Bruna F. Soares, Daniil R. Nosov, José M. Pires, Andrey A. Tyutyunov, Elena I. Lozinskaya, Dmitrii Y. Antonov, Alexander S. Shaplov and Isabel M. Marrucho

Molecules 2022, 27(2), 413; https://doi.org/10.3390/molecules27020413 - 09 Jan 2022

Cited by 3 | Viewed by 2609

Abstract

This work aims to explore the gas permeation performance of two newly-designed ionic liquids, [C₂mim][CF₃BF₃] and [C₂mim][CF₃SO₂C(CN)₂], in supported ionic liquid membranes (SILM) configuration, as another effort to provide [...] Read more.

This work aims to explore the gas permeation performance of two newly-designed ionic liquids, [C₂mim][CF₃BF₃] and [C₂mim][CF₃SO₂C(CN)₂], in supported ionic liquid membranes (SILM) configuration, as another effort to provide an overall insight on the gas permeation performance of functionalized-ionic liquids with the [C₂mim]⁺ cation. [C₂mim][CF₃BF₃] and [C₂mim][CF₃SO₂C(CN)₂] single gas separation performance towards CO₂, N₂, and CH₄ at T = 293 K and T = 308 K were measured using the time-lag method. Assessing the CO₂ permeation results, [C₂mim][CF₃BF₃] showed an undermined value of 710 Barrer at 293.15 K and 1 bar of feed pressure when compared to [C₂mim][BF₄], whereas for the [C₂mim][CF₃SO₂C(CN)₂] IL an unexpected CO₂ permeability of 1095 Barrer was attained at the same experimental conditions, overcoming the results for the remaining ILs used for comparison. The prepared membranes exhibited diverse permselectivities, varying from 16.9 to 22.2 for CO₂/CH₄ and 37.0 to 44.4 for CO₂/N₂ gas pairs. The thermophysical properties of the [C₂mim][CF₃BF₃] and [C₂mim][CF₃SO₂C(CN)₂] ILs were also determined in the range of T = 293.15 K up to T = 353.15 K at atmospheric pressure and compared with those for other ILs with the same cation and anion’s with similar chemical moieties. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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15 pages, 2596 KiB

Open AccessArticle

Impact of Eutectic Solvents Utilization in the Microwave Assisted Extraction of Proanthocyanidins from Grape Pomace

by Rodrigo T. Neto, Sónia A. O. Santos, Joana Oliveira and Armando J. D. Silvestre

Molecules 2022, 27(1), 246; https://doi.org/10.3390/molecules27010246 - 31 Dec 2021

Cited by 8 | Viewed by 1958

Abstract

The extraction of proanthocyanidins (PACs), despite being an important and limiting aspect of their industrial application, is still largely unexplored. Herein, the possibility of combining eutectic solvents (ESs) with microwave assisted extraction (MAE) in the extraction of PACs from grape pomace (GP) is [...] Read more.

The extraction of proanthocyanidins (PACs), despite being an important and limiting aspect of their industrial application, is still largely unexplored. Herein, the possibility of combining eutectic solvents (ESs) with microwave assisted extraction (MAE) in the extraction of PACs from grape pomace (GP) is explored, aiming to improve not only the extraction yield but also the mean degree of polymerization (mDP). The combination of choline chloride with lactic acid was shown to be the most effective combination for PACs extraction yield (135 mg_PAC/g_GP) and, despite the occurrence of some depolymerization, also enabled us to achieve the highest mDP (7.13). Additionally, the combination with MAE enabled the process to be completed in 3.56 min, resulting in a considerably reduced extraction time. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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18 pages, 5445 KiB

Open AccessFeature PaperArticle

Pretreatment of Plastic Waste: Removal of Colorants from HDPE Using Biosolvents

by Ana M. Ferreira, Isa Sucena, Vanessa Otero, Eva Mariasole Angelin, Maria João Melo and João A. P. Coutinho

Molecules 2022, 27(1), 98; https://doi.org/10.3390/molecules27010098 - 24 Dec 2021

Cited by 18 | Viewed by 5245

Abstract

Plastics recycling remains a challenge due to the relatively low quality of the recycled material, since most of the developed recycling processes cannot deal with the additives present in the plastic matrix, so the recycled products end up in lower-grade applications. The application [...] Read more.

Plastics recycling remains a challenge due to the relatively low quality of the recycled material, since most of the developed recycling processes cannot deal with the additives present in the plastic matrix, so the recycled products end up in lower-grade applications. The application of volatile organic solvents for additives removal is the preferred choice. In this study, pretreatment of plastic packaging waste to remove additives using biosolvents was investigated. The plastic waste used was high-density polyethylene (HDPE) with blue and orange colorants (pigment and/or dye). The first step was to identify the type of colorants present in the HDPE, and we found that both plastics presented only one colorant that was actually a pigment. Then, limonene, a renewable solvent, was used to solubilize HDPE. After HDPE dissolution, a wide range of alcohols (mono-, di-, and tri-alcohols) was evaluated as antisolvents in order to selectively precipitate the polymer and maximize its purity. The use of limonene as solvent for plastic dissolution, in combination with poly-alcohols with an intermediate alkyl chain length and a large number of hydroxyl (OH) groups, was found to work best as an antisolvent (1,2,3-propanetriol and 1,2,4-butanetriol), leading to a removal of up to 94% and 100% of the blue and orange pigments, respectively. Finally, three cycles of extraction were carried out, proving the capability of the solvent and antisolvent to be recovered and reused, ensuring the economic viability and sustainability of the process. This pretreatment provides a secondary source of raw materials and revenue for the recycling process, which may lead to an increase in the quality of recycled polymers, contributing to the development of an economical and sustainable recycling process. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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23 pages, 3675 KiB

Open AccessArticle

Catalytic Transfer Hydrogenation and Acid Reactions of Furfural and 5-(Hydroxymethyl)furfural over Hf-TUD-1 Type Catalysts

by Margarida M. Antunes, Andreia F. Silva, Carolina D. Bernardino, Auguste Fernandes, Filipa Ribeiro and Anabela A. Valente

Molecules 2021, 26(23), 7203; https://doi.org/10.3390/molecules26237203 - 27 Nov 2021

Cited by 6 | Viewed by 2569

Abstract

Heterogeneous catalysis, which has served well the petrochemical industry, may valuably contribute towards a bio-based economy by sustainably enabling selective reactions to renewable chemicals. Carbohydrate-containing matter may be obtained from various widespread sources and selectively converted to furanic platform chemicals: furfural (Fur) and [...] Read more.

Heterogeneous catalysis, which has served well the petrochemical industry, may valuably contribute towards a bio-based economy by sustainably enabling selective reactions to renewable chemicals. Carbohydrate-containing matter may be obtained from various widespread sources and selectively converted to furanic platform chemicals: furfural (Fur) and 5-(hydroxymethyl)furfural (Hmf). Valuable bioproducts may be obtained from these aldehydes via catalytic transfer hydrogenation (CTH) using alcohols as H-donors under relatively moderate reaction conditions. Hafnium-containing TUD-1 type catalysts were the first of ordered mesoporous silicates explored for the conversion of Fur and Hmf via CTH/alcohol strategies. The materials promoted CTH and acid reactions leading to the furanic ethers. The bioproducts spectrum was broader for the reaction of Fur than of Hmf. A Fur reaction mechanism based on literature data was discussed and supported by kinetic modelling. The influence of the Hf loading and reaction conditions (catalyst load, type of alcohol H-donor, temperature, initial substrate concentration) on the reaction kinetics was studied. The reaction conditions were optimized to maximize the yields of 2-(alkoxymethyl)furan ethers formed from Fur; up to 63% yield was reached at 88% Fur conversion, 4 h/150 °C, using Hf-TUD-1(75), which was a stable catalyst. The Hf-TUD-1(x) catalysts promoted the selective conversion of Hmf to bis(2-alkoxymethyl)furan; e.g., 96% selectivity at 98% Hmf conversion, 3 h/170 °C for Hf-TUD-1(50). Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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23 pages, 15320 KiB

Open AccessArticle

Ionic Liquids and Water: Hydrophobicity vs. Hydrophilicity

by Rita F. Rodrigues, Adilson A. Freitas, José N. Canongia Lopes and Karina Shimizu

Molecules 2021, 26(23), 7159; https://doi.org/10.3390/molecules26237159 - 26 Nov 2021

Cited by 20 | Viewed by 2673

Abstract

Many chemical processes rely extensively on organic solvents posing safety and environmental concerns. For a successful transfer of some of those chemical processes and reactions to aqueous media, agents acting as solubilizers, or phase-modifiers, are of central importance. In the present work, the [...] Read more.

Many chemical processes rely extensively on organic solvents posing safety and environmental concerns. For a successful transfer of some of those chemical processes and reactions to aqueous media, agents acting as solubilizers, or phase-modifiers, are of central importance. In the present work, the structure of aqueous solutions of several ionic liquid systems capable of forming multiple solubilizing environments were modeled by molecular dynamics simulations. The effect of small aliphatic chains on solutions of hydrophobic 1-alkyl-3-methylimidazolium bis(trifluoromethyl)sulfonylimide ionic liquids (with alkyl = propyl [C₃C₁im][NTf₂], butyl [C₄C₁im][NTf₂] and isobutyl [iC₄C₁im][NTf₂]) are covered first. Next, we focus on the interactions of sulphonate- and carboxylate-based anions with different hydrogenated and perfluorinated alkyl side chains in solutions of [C₂C₁im][C_nF_2n+1SO₃], [C₂C₁im][C_nH_2n+1SO₃], [C₂C₁im][CF₃CO₂] and [C₂C₁im][CH₃CO₂] (n = 1, 4, 8). The last system considered is an ionic liquid completely miscible with water that combines the cation N-methyl-N,N,N-tris(2-hydroxyethyl)ammonium [N_{1 2OH 2OH 2OH}]⁺, with high hydrogen-bonding capability, and the hydrophobic anion [NTf₂]^–. The interplay between short- and long-range interactions, clustering of alkyl and perfluoroalkyl tails, and hydrogen bonding enables a wealth of possibilities in tailoring an ionic liquid solution according to the needs. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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13 pages, 2601 KiB

Open AccessArticle

Modern Methods for the Sustainable Synthesis of Metalloporphyrins

by Carla Gomes, Mariana Peixoto and Marta Pineiro

Molecules 2021, 26(21), 6652; https://doi.org/10.3390/molecules26216652 - 02 Nov 2021

Cited by 7 | Viewed by 2665

Abstract

Metalloporphyrins are involved in many and diverse applications that require the preparation of these compounds in an efficient manner, which nowadays, also involves taking into consideration sustainability issues. In this context, we use ball milling mechanochemistry and sonochemistry for the rational development of [...] Read more.

Metalloporphyrins are involved in many and diverse applications that require the preparation of these compounds in an efficient manner, which nowadays, also involves taking into consideration sustainability issues. In this context, we use ball milling mechanochemistry and sonochemistry for the rational development of synthetic strategies for the sustainable preparation of metalloporphyrins. Zinc, copper, cobalt and palladium complexes of hydrophobic porphyrins were obtained in high yields and under mechanical action with a moderate excess of the metal salt, without any solvent or additive. Sonochemistry prove to be a good alternative for the preparation of metal complexes of water-soluble porphyrins in good yields and short reaction times. Both strategies have good sustainability scores, close to the ideal values, which is useful in comparing and helping to choose the more adequate method. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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10 pages, 1158 KiB

Open AccessArticle

Thermal Analysis of Binary Mixtures of Imidazolium, Pyridinium, Pyrrolidinium, and Piperidinium Ionic Liquids

by Elena Gómez, Pedro Velho, Ángeles Domínguez and Eugénia A. Macedo

Molecules 2021, 26(21), 6383; https://doi.org/10.3390/molecules26216383 - 22 Oct 2021

Cited by 1 | Viewed by 1901

Abstract

Ionic liquids (ILs) are being widely studied due to their unique properties, which make them potential candidates for conventional solvents. To study whether binary mixtures of pure ionic liquids provide a viable alternative to pure ionic liquids for different applications, in this work, [...] Read more.

Ionic liquids (ILs) are being widely studied due to their unique properties, which make them potential candidates for conventional solvents. To study whether binary mixtures of pure ionic liquids provide a viable alternative to pure ionic liquids for different applications, in this work, the thermal analysis and molar heat capacities of five equimolar binary mixtures of ionic liquids based on imidazolium, pyridinium, pyrrolidinium, and piperidinium cations with dicyanamide, trifluoromethanesulfonate, and bis(trifluoromethylsulfonyl)imide anions have been performed. Furthermore, two pure ionic liquids based on piperidinium cation have been thermally characterized and the heat capacity of one of them has been measured. The determination and evaluation of both the transition temperatures and the molar heat capacities was carried out using differential scanning calorimetry (DSC). It was observed that the thermal behavior of the mixtures was completely different than the thermal behavior of the pure ionic liquids present, while the molar heat capacities of the binary mixtures were very similar to the value of the average of molar heat capacities of the two pure ionic liquids. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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13 pages, 1463 KiB

Open AccessArticle

Click-Derived Triazoles and Triazolylidenes of Manganese for Electrocatalytic Reduction of CO₂

by Sofia Friães, Sara Realista, Clara S. B. Gomes, Paulo N. Martinho and Beatriz Royo

Molecules 2021, 26(21), 6325; https://doi.org/10.3390/molecules26216325 - 20 Oct 2021

Cited by 13 | Viewed by 2250

Abstract

A series of new fac-[Mn(L)(CO)₃Br] complexes where L is a bidentate chelating ligand containing mixed mesoionic triazolylidene-pyridine (MIC^py, 1), triazolylidene-triazole (MIC^trz, 2), and triazole-pyridine (trz^py, 3) ligands have been prepared and fully characterized, including the single crystal [...] Read more.

A series of new fac-[Mn(L)(CO)₃Br] complexes where L is a bidentate chelating ligand containing mixed mesoionic triazolylidene-pyridine (MIC^py, 1), triazolylidene-triazole (MIC^trz, 2), and triazole-pyridine (trz^py, 3) ligands have been prepared and fully characterized, including the single crystal X-ray diffraction studies of 1 and 2. The abilities of 1–3 and complex fac-[Mn(MIC^MIC)(CO)₃Br] (4) to catalyze the electroreduction of CO₂ has been assessed for the first time. It was found that all complexes displayed a current increase under CO₂ atmosphere, being 3 and 4 the most active complexes. Complex 3, bearing a N^N-based ligand exhibited a good efficiency and an excellent selectivity for reducing CO₂ to CO in the presence of 1.0 M of water, at low overpotential. Interestingly, complex 4 containing the strongly electron donating di-imidazolylidene ligand exhibited comparable activity to 3, when the experiments were performed in neat acetonitrile at slightly higher overpotential (−1.86 vs. −2.14 V). Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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15 pages, 18392 KiB

Open AccessArticle

Stable and Oriented Liquid Crystal Droplets Stabilized by Imidazolium Ionic Liquids

by Efthymia Ramou, Guilherme Rebordão, Susana I. C. J. Palma and Ana C. A. Roque

Molecules 2021, 26(19), 6044; https://doi.org/10.3390/molecules26196044 - 05 Oct 2021

Cited by 10 | Viewed by 2219

Abstract

Liquid crystals represent a fascinating intermediate state of matter, with dynamic yet organized molecular features and untapped opportunities in sensing. Several works report the use of liquid crystal droplets formed by microfluidics and stabilized by surfactants such as sodium dodecyl sulfate (SDS). In [...] Read more.

Liquid crystals represent a fascinating intermediate state of matter, with dynamic yet organized molecular features and untapped opportunities in sensing. Several works report the use of liquid crystal droplets formed by microfluidics and stabilized by surfactants such as sodium dodecyl sulfate (SDS). In this work, we explore, for the first time, the potential of surface-active ionic liquids of the imidazolium family as surfactants to generate in high yield, stable and oriented liquid crystal droplets. Our results show that [C₁₂MIM][Cl], in particular, yields stable, uniform and monodisperse droplets (diameter 74 ± 6 µm; PDI = 8%) with the liquid crystal in a radial configuration, even when compared with the standard SDS surfactant. These findings reveal an additional application for ionic liquids in the field of soft matter. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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12 pages, 1793 KiB

Open AccessArticle

Supercritical CO₂ Assisted Impregnation of Ibuprofen on Medium-Chain-Length Polyhydroxyalkanoates (mcl-PHA)

by Liane Meneses, Rita Craveiro, Ana Rita Jesus, Maria A. M. Reis, Filomena Freitas and Alexandre Paiva

Molecules 2021, 26(16), 4772; https://doi.org/10.3390/molecules26164772 - 06 Aug 2021

Cited by 7 | Viewed by 2096

Abstract

In this work, we propose the utilization of scCO₂ to impregnate ibuprofen into the mcl-PHA matrix produced by Pseudomonas chlororaphis subs. aurantiaca (DSM 19603). The biopolymer has adhesive properties, is biocompatible and has a melting temperature of 45 °C. Several conditions, namely, [...] Read more.

In this work, we propose the utilization of scCO₂ to impregnate ibuprofen into the mcl-PHA matrix produced by Pseudomonas chlororaphis subs. aurantiaca (DSM 19603). The biopolymer has adhesive properties, is biocompatible and has a melting temperature of 45 °C. Several conditions, namely, pressure (15 and 20 MPa) and impregnation time (30 min, 1 h and 3 h) were tested. The highest ibuprofen content (90.8 ± 6.5 mg of ibuprofen/g_PHA) was obtained at 20 MPa and 40 °C, for 1 h, with an impregnation rate of 89 mg/(g·h). The processed mcl-PHA samples suffered a plasticization, as shown by the decrease of 6.5 °C in the T_g, at 20 MPa. The polymer’s crystallinity was also affected concomitantly with the matrices’ ibuprofen content. For all the impregnation conditions tested the release of ibuprofen from the biopolymer followed a type II release profile. This study has demonstrated that the mcl-PHA produced by P. chlororaphis has a great potential for the development of novel topical drug delivery systems. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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17 pages, 3799 KiB

Open AccessArticle

Supercritical CO₂ Extraction as a Tool to Isolate Anti-Inflammatory Sesquiterpene Lactones from Cichorium intybus L. Roots

by João P. Baixinho, José D. Anastácio, Viktoriya Ivasiv, Katarina Cankar, Dirk Bosch, Regina Menezes, Matthew de Roode, Cláudia Nunes dos Santos, Ana A. Matias and Naiara Fernández

Molecules 2021, 26(9), 2583; https://doi.org/10.3390/molecules26092583 - 28 Apr 2021

Cited by 11 | Viewed by 3158

Abstract

Cichorium intybus L. or chicory plants are a natural source of health-promoting compounds in the form of supplements such as inulin, as well as other bioactive compounds such as sesquiterpene lactones (SLs). After inulin extraction, chicory roots are considered waste, with most SLs [...] Read more.

Cichorium intybus L. or chicory plants are a natural source of health-promoting compounds in the form of supplements such as inulin, as well as other bioactive compounds such as sesquiterpene lactones (SLs). After inulin extraction, chicory roots are considered waste, with most SLs not being harnessed. We developed and optimized a new strategy for SL extraction that can contribute to the conversion of chicory root waste into valuable products to be used in human health-promoting applications. In our work, rich fractions of SLs were recovered from chicory roots using supercritical CO₂. A response surface methodology was used to optimize the process parameters (pressure, temperature, flow rate, and co-solvent percentage) for the extraction performance. The best operating conditions were achieved at 350 bar, 40 °C, and 10% EtOH as a co-solvent in a 15 g/min flow rate for 120 min. The extraction with supercritical CO₂ revealed to be more selective for the SLs than the conventional solid–liquid extraction with ethyl acetate. In our work, 1.68% mass and a 0.09% sesquiterpenes yield extraction were obtained, including the recovery of two sesquiterpene lactones (8-deoxylactucin and 11β,13-dihydro-8-deoxylactucin), which, to the best of our knowledge, are not commercially available. A mixture of the abovementioned compounds were tested at different concentrations for their toxic profile and anti-inflammatory potential towards a human calcineurin/NFAT orthologue pathway in a yeast model, the calcineurin/Crz1 pathway. The SFE extract obtained, rich in SLs, yielded results of inhibition of 61.74 ± 6.87% with 50 µg/mL, and the purified fraction containing 8-deoxylactucin and 11β,13-dihydro-8-deoxylactucin inhibited the activation of the reporter gene up to 53.38 ± 3.9% at 10 µg/mL. The potential activity of the purified fraction was also validated by the ability to inhibit Crz1 nuclear translocation and accumulation. These results reveal a possible exploitable green technology to recover potential anti-inflammatory compounds from chicory roots waste after inulin extraction. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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Review

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26 pages, 1154 KiB

Open AccessReview

Hydrothermal Liquefaction: How the Holistic Approach by Nature Will Help Solve the Environmental Conundrum

by Saeed Ranjbar and Francisco Xavier Malcata

Molecules 2023, 28(24), 8127; https://doi.org/10.3390/molecules28248127 - 16 Dec 2023

Cited by 1 | Viewed by 1726

Abstract

Hydrothermal liquefaction (HTL) represents a beacon of scientific innovation, which unlocks nature’s alchemical wonders while reshaping the waste-to-energy platform. This transformative technology offers sustainable solutions for converting a variety of waste materials to valuable energy products and chemicals—thus addressing environmental concerns, inefficiencies, and [...] Read more.

Hydrothermal liquefaction (HTL) represents a beacon of scientific innovation, which unlocks nature’s alchemical wonders while reshaping the waste-to-energy platform. This transformative technology offers sustainable solutions for converting a variety of waste materials to valuable energy products and chemicals—thus addressing environmental concerns, inefficiencies, and high costs associated with conventional waste-management practices. By operating under high temperature and pressure conditions, HTL efficiently reduces waste volume, mitigates harmful pollutant release, and extracts valuable energy from organic waste materials. This comprehensive review delves into the intricacies of the HTL process and explores its applications. Key process parameters, diverse feedstocks, various reactor designs, and recent advancements in HTL technology are thoroughly discussed. Diverse applications of HTL products are examined, and their economic viability toward integration in the market is assessed. Knowledge gaps and opportunities for further exploration are accordingly identified, with a focus on optimizing and scaling up the HTL process for commercial applications. In conclusion, HTL holds great promise as a sustainable technology for waste management, chemical synthesis, and energy production, thus making a significant contribution to a more sustainable future. Its potential to foster a circular economy and its versatility in producing valuable products underscore its transformative role in shaping a more sustainable world. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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14 pages, 1361 KiB

Open AccessReview

Polyelectrolyte Precipitation: A New Green Chemistry Approach to Recover Value-Added Proteins from Different Sources in a Circular Economy Context

by Ricardo Gómez-García, Ana A. Vilas-Boas, Ana Martins Vilas-Boas, Débora A. Campos and Manuela Pintado

Molecules 2022, 27(16), 5115; https://doi.org/10.3390/molecules27165115 - 11 Aug 2022

Cited by 3 | Viewed by 2503

Abstract

Proteins have always been vital biological molecules used for industrial purposes, human nutrition and health. Nowadays, seeking new alternatives and sources of these biomolecules is becoming an increasing research trend derived from the present consumer awareness between food consumption and health promotion, but [...] Read more.

Proteins have always been vital biological molecules used for industrial purposes, human nutrition and health. Nowadays, seeking new alternatives and sources of these biomolecules is becoming an increasing research trend derived from the present consumer awareness between food consumption and health promotion, but also on environmental sustainability. Although there are different consolidated/traditional downstream processes to obtain proteins, such as chromatography tools, alkali hydrolysis, precipitation by inorganic salts and organic solvents, their industrial-scale application still demands urgent innovation due to the poor recovery yields, high costs and time-consuming steps, environmental impact as well as some toxic concerns. Polyelectrolyte precipitation represents a green, innovative alternative for protein recovery; however, there are reduced data regarding its pilot or industrial-scale application. In this literature work, the action mechanism and principles with regards to its functionality and insights for its application on a big scale are reviewed. Overall, this review discusses the novelty and sustainability of protein precipitation by polyelectrolytes from different sources against traditional techniques as well as highlights the relationship between protein source, production relevance and bioactive properties that are key factors to maximize the application of this extractive method on a circular economy context. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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25 pages, 1857 KiB

Open AccessReview

Carotenoid Production from Microalgae: The Portuguese Scenario

by Mariam Kholany, João A. P. Coutinho and Sónia P. M. Ventura

Molecules 2022, 27(8), 2540; https://doi.org/10.3390/molecules27082540 - 14 Apr 2022

Cited by 11 | Viewed by 3267

Abstract

Microalgae have an outstanding capacity to efficiently produce value-added compounds. They have been inspiring researchers worldwide to develop a blue biorefinery, supporting the development of the bioeconomy, tackling the environmental crisis, and mitigating the depletion of natural resources. In this review, the characteristics [...] Read more.

Microalgae have an outstanding capacity to efficiently produce value-added compounds. They have been inspiring researchers worldwide to develop a blue biorefinery, supporting the development of the bioeconomy, tackling the environmental crisis, and mitigating the depletion of natural resources. In this review, the characteristics of the carotenoids produced by microalgae are presented and the downstream processes developed to recover and purify them are analyzed, considering their main applications. The ongoing activities and initiatives taking place in Portugal regarding not only research, but also industrialization under the blue biorefinery concept are also discussed. The situation reported here shows that new techniques must be developed to make microalgae production more competitive. Downstream pigment purification technologies must be developed as they may have a considerable impact on the economic viability of the process. Government incentives are needed to encourage a constructive interaction between academics and businesses in order to develop a biorefinery that focuses on high-grade chemicals. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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24 pages, 1513 KiB

Open AccessReview

Supported Ionic Liquids Used as Chromatographic Matrices in Bioseparation—An Overview

by Sandra C. Bernardo, Rita Carapito, Márcia C. Neves, Mara G. Freire and Fani Sousa

Molecules 2022, 27(5), 1618; https://doi.org/10.3390/molecules27051618 - 28 Feb 2022

Cited by 7 | Viewed by 2652

Abstract

Liquid chromatography plays a central role in biomanufacturing, and, apart from its use as a preparative purification strategy, either in biopharmaceuticals or in fine chemicals industries, it is also very useful as an analytical tool for monitoring, assessing, and characterizing diverse samples. The [...] Read more.

Liquid chromatography plays a central role in biomanufacturing, and, apart from its use as a preparative purification strategy, either in biopharmaceuticals or in fine chemicals industries, it is also very useful as an analytical tool for monitoring, assessing, and characterizing diverse samples. The present review gives an overview of the progress of the chromatographic supports that have been used in the purification of high-value products (e.g., small molecules, organic compounds, proteins, and nucleic acids). Despite the diversity of currently available chromatographic matrices, the interest in innovative biomolecules emphasizes the need for novel, robust, and more efficient supports and ligands with improved selectivity. Accordingly, ionic liquids (ILs) have been investigated as novel ligands in chromatographic matrices. Given herein is an extensive review regarding the different immobilization strategies of ILs in several types of supports, namely in silica, Sepharose, and polymers. In addition to depicting their synthesis, the main application examples of these supports are also presented. The multiple interactions promoted by ILs are critically discussed concerning the improved selectivity towards target molecules. Overall, the versatility of supported ILs is here considered a critical point to their exploitation as alternatives to the more conventional liquid chromatographic matrices used in bioseparation processes. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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21 pages, 5086 KiB

Open AccessReview

Mechanochemistry in Portugal—A Step towards Sustainable Chemical Synthesis

by Vânia André, M. Teresa Duarte, Clara S. B. Gomes and Mafalda C. Sarraguça

Molecules 2022, 27(1), 241; https://doi.org/10.3390/molecules27010241 - 31 Dec 2021

Cited by 7 | Viewed by 3443

Abstract

In Portugal, publications with mechanochemical methods date back to 2009, with the report on mechanochemical strategies for the synthesis of metallopharmaceuticals. Since then, mechanochemical applications have grown in Portugal, spanning several fields, mainly crystal engineering and supramolecular chemistry, catalysis, and organic and inorganic [...] Read more.

In Portugal, publications with mechanochemical methods date back to 2009, with the report on mechanochemical strategies for the synthesis of metallopharmaceuticals. Since then, mechanochemical applications have grown in Portugal, spanning several fields, mainly crystal engineering and supramolecular chemistry, catalysis, and organic and inorganic chemistry. The area with the most increased development is the synthesis of multicomponent crystal forms, with several groups synthesizing solvates, salts, and cocrystals in which the main objective was to improve physical properties of the active pharmaceutical ingredients. Recently, non-crystalline materials, such as ionic liquids and amorphous solid dispersions, have also been studied using mechanochemical methods. An area that is in expansion is the use of mechanochemical synthesis of bioinspired metal-organic frameworks with an emphasis in antibiotic coordination frameworks. The use of mechanochemistry for catalysis and organic and inorganic synthesis has also grown due to the synthetic advantages, ease of synthesis, scalability, sustainability, and, in the majority of cases, the superior properties of the synthesized materials. It can be easily concluded that mechanochemistry is expanding in Portugal in diverse research areas. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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24 pages, 3005 KiB

Open AccessFeature PaperReview

Natural Polymers-Based Materials: A Contribution to a Greener Future

by Ana C. Q. Silva, Armando J. D. Silvestre, Carla Vilela and Carmen S. R. Freire

Molecules 2022, 27(1), 94; https://doi.org/10.3390/molecules27010094 - 24 Dec 2021

Cited by 35 | Viewed by 11710

Abstract

Natural polymers have emerged as promising candidates for the sustainable development of materials in areas ranging from food packaging and biomedicine to energy storage and electronics. In tandem, there is a growing interest in the design of advanced materials devised from naturally abundant [...] Read more.

Natural polymers have emerged as promising candidates for the sustainable development of materials in areas ranging from food packaging and biomedicine to energy storage and electronics. In tandem, there is a growing interest in the design of advanced materials devised from naturally abundant and renewable feedstocks, in alignment with the principles of Green Chemistry and the 2030 Agenda for Sustainable Development. This review aims to highlight some examples of the research efforts conducted at the Research Team BioPol4fun, Innovation in BioPolymer-based Functional Materials and Bioactive Compounds, from the Portuguese Associate Laboratory CICECO–Aveiro Institute of Materials at the University of Aveiro, regarding the exploitation of natural polymers (and derivatives thereof) for the development of distinct sustainable biobased materials. In particular, focus will be given to the use of polysaccharides (cellulose, chitosan, pullulan, hyaluronic acid, fucoidan, alginate, and agar) and proteins (lysozyme and gelatin) for the assembly of composites, coatings, films, membranes, patches, nanosystems, and microneedles using environmentally friendly strategies, and to address their main domains of application. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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19 pages, 2022 KiB

Open AccessFeature PaperReview

Solid Dosage Forms of Biopharmaceuticals in Drug Delivery Systems Using Sustainable Strategies

by Clarinda Costa, Teresa Casimiro, Maria Luísa Corvo and Ana Aguiar-Ricardo

Molecules 2021, 26(24), 7653; https://doi.org/10.3390/molecules26247653 - 17 Dec 2021

Cited by 5 | Viewed by 3252

Abstract

Drug delivery systems (DDS) often comprise biopharmaceuticals in aqueous form, making them susceptible to physical and chemical degradation, and therefore requiring low temperature storage in cold supply and distribution chains. Freeze-drying, spray-drying, and spray-freeze-drying are some of the techniques used to convert biopharmaceuticals-loaded [...] Read more.

Drug delivery systems (DDS) often comprise biopharmaceuticals in aqueous form, making them susceptible to physical and chemical degradation, and therefore requiring low temperature storage in cold supply and distribution chains. Freeze-drying, spray-drying, and spray-freeze-drying are some of the techniques used to convert biopharmaceuticals-loaded DDS from aqueous to solid dosage forms. However, the risk exists that shear and heat stress during processing may provoke DDS damage and efficacy loss. Supercritical fluids (SCF), specifically, supercritical carbon dioxide (scCO₂), is a sustainable alternative to common techniques. Due to its moderately critical and tunable properties and thermodynamic behavior, scCO₂ has aroused scientific and industrial interest. Therefore, this article reviews scCO₂-based techniques used over the year in the production of solid biopharmaceutical dosage forms. Looking particularly at the use of scCO₂ in each of its potential roles—as a solvent, co-solvent, anti-solvent, or co-solute. It ends with a comparison between the compound’s stability using supercritical CO₂-assisted atomization/spray-drying and conventional drying. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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11 pages, 710 KiB

Open AccessReview

Therapeutic Deep Eutectic Systems towards the Treatment of Tuberculosis and Colorectal Cancer: Opportunities and Challenges

by Filipe Oliveira, Filipa Santos and Ana Rita C. Duarte

Molecules 2021, 26(22), 7022; https://doi.org/10.3390/molecules26227022 - 20 Nov 2021

Cited by 12 | Viewed by 2715

Abstract

What if a new technology based on therapeutic deep eutectic systems would disrupt the current treatment of major economic and socially burden diseases? The classical definition of eutectic systems is that they are the combination of two or more compounds that interact via [...] Read more.

What if a new technology based on therapeutic deep eutectic systems would disrupt the current treatment of major economic and socially burden diseases? The classical definition of eutectic systems is that they are the combination of two or more compounds that interact via hydrogen bonds, from which results a melting temperature depression in comparison with that of its individual components. Therapeutic deep eutectic systems are defined as eutectic systems in which at least one of the individual components is an active pharmaceutical ingredient, or a eutectic system in which the active pharmaceutical ingredient is dissolved. Current literature reports on tuberculosis have been mostly based on the most common anti-tuberculosis drugs prescribed. Using eutectic systems based on naturally occurring molecules known for their anti-microbial activity may also present a promising therapeutic strategy able to cope with the prevalence of Mycobacterium tuberculosis and prevent the appearance of multidrug resistance strains. With regards to colorectal cancer, literature has been unravelling combinations of terpenes with anti-inflammatory drugs that are selectively cytotoxic towards colorectal cancer cells and do not compromise the viability of normal intestinal cells. This technology could contribute to preventing tumor growth and metastasis while providing a patient compliance therapeutics, which will be crucial to the success of overcoming the challenges presented by cancers. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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15 pages, 3415 KiB

Open AccessReview

Microwave Irradiation: Alternative Heating Process for the Synthesis of Biologically Applicable Chromones, Quinolones, and Their Precursors

by Hélio M. T. Albuquerque, Diana C. G. A. Pinto and Artur M. S. Silva

Molecules 2021, 26(20), 6293; https://doi.org/10.3390/molecules26206293 - 18 Oct 2021

Cited by 22 | Viewed by 2744

Abstract

Microwave irradiation has become a popular heating technique in organic synthesis, mainly due to its short reaction times, solventless reactions, and, sometimes, higher yields. Additionally, microwave irradiation lowers energy consumption and, consequently, is ideal for optimization processes. Moreover, there is evidence that microwave [...] Read more.

Microwave irradiation has become a popular heating technique in organic synthesis, mainly due to its short reaction times, solventless reactions, and, sometimes, higher yields. Additionally, microwave irradiation lowers energy consumption and, consequently, is ideal for optimization processes. Moreover, there is evidence that microwave irradiation can improve the regioselectivity and stereoselectivity aspects of vital importance in synthesizing bioactive compounds. These crucial features of microwave irradiation contribute to its inclusion in green chemistry procedures. Since 2003, the use of microwave-assisted organic synthesis has become common in our laboratory, making our group one of the first Portuguese research groups to implement this heating source in organic synthesis. Our achievements in the transformation of heterocyclic compounds, such as (E/Z)-3-styryl-4H-chromen-4-ones, (E)-3-(2-hydroxyphenyl)-4-styryl-1H-pyrazole, (E)-2-(4-arylbut-1-en-3-yn-1-yl)-4H-chromen-4-ones, or (E)-2-[2-(5-aryl-2-methyl-2H-1,2,3-triazol-4-yl)vinyl]-4H-chromen-4-ones, will be discussed in this review, highlighting the benefits of microwave irradiation use in organic synthesis. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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21 pages, 3917 KiB

Open AccessReview

Added-Value Chemicals from Lignin Oxidation

by Carina A. Esteves Costa, Carlos A. Vega-Aguilar and Alírio E. Rodrigues

Molecules 2021, 26(15), 4602; https://doi.org/10.3390/molecules26154602 - 29 Jul 2021

Cited by 20 | Viewed by 5142

Abstract

Lignin is the second most abundant component, next to cellulose, in lignocellulosic biomass. Large amounts of this polymer are produced annually in the pulp and paper industries as a coproduct from the cooking process—most of it burned as fuel for energy. Strategies regarding [...] Read more.

Lignin is the second most abundant component, next to cellulose, in lignocellulosic biomass. Large amounts of this polymer are produced annually in the pulp and paper industries as a coproduct from the cooking process—most of it burned as fuel for energy. Strategies regarding lignin valorization have attracted significant attention over the recent decades due to lignin’s aromatic structure. Oxidative depolymerization allows converting lignin into added-value compounds, as phenolic monomers and/or dicarboxylic acids, which could be an excellent alternative to aromatic petrochemicals. However, the major challenge is to enhance the reactivity and selectivity of the lignin structure towards depolymerization and prevent condensation reactions. This review includes a comprehensive overview of the main contributions of lignin valorization through oxidative depolymerization to produce added-value compounds (vanillin and syringaldehyde) that have been developed over the recent decades in the LSRE group. An evaluation of the valuable products obtained from oxidation in an alkaline medium with oxygen of lignins and liquors from different sources and delignification processes is also provided. A review of C₄ dicarboxylic acids obtained from lignin oxidation is also included, emphasizing catalytic conversion by O₂ or H₂O₂ oxidation. Full article

(This article belongs to the Special Issue Green Chemistry in Portugal)

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