Chemistry, Volume 3, Issue 4 (December 2021) – 25 articles

The production of biocomposites based on natural fiber waste and biopolymers is constantly increasing because of their renewability, biodegradability, and the accordance with the circular economy principles. The aim of this work is to contrast the disadvantages in the production of biocomposites, such as reduction of molecular weight through the use of biobased chain extenders. For this purpose, epoxidized soybean oil (ESO) and dicarboxylic acids (DCAs) were used to contrast the slight chain scission observed in a poly(lactic acid) (PLA)/poly(butylene succinate-co-adipate) (PBSA) binary blend caused by the melt mixing with hazelnut shell powder (HSP). Two different dimensions of HSPs were considered in this study as well as different concentrations of the ESO/DCA system, comparing succinic acid and malic acid as dicarboxylic acids. Melt viscosity parameters, such as torque and melt volume rate (MVR), were measured to investigate the chain extender effect during the extrusion. In addition, the reactivity of the ESO/DCA system was investigated through infrared spectroscopy. The effect of chain extenders on thermal properties, in particular on the crystallinity of PLA, and on mechanical properties of final biocomposites was investigated to understand their potentialities in industrial application. Results of this study evidenced a modest increase in melt viscosity due to ESO/malic acid chain extension system, but only for the HSP with the lower dimension (so the higher surface area) and adding 0.5 wt.% of ESO/malic acid. Thus, the slight chain scission of polyesters, not significantly affecting the final properties of these biocomposites, is the most relevant effect that was revealed in this complex reactive system. Full article

The fragrance field of perfumes has attracted considerable scientific, industrial, cultural, and civilizational interest. The marine odor is characterized by the specific smell of sea breeze, seashore, algae, and oyster, among others. Marine odor is a more recent fragrance and is considered as one of the green and modern fragrances. The smells reproducing the marine environment are described due to their content of Calone 1951 (7-methyl-2H-1,5-benzodioxepin-3(4H)-one), which is a synthetic compound. In addition to the synthetic group of benzodioxepanes, such as Calone 51 and its derivatives, three other groups of chemical compounds seem to represent the marine smell. The first group includes the polyunsaturated cyclic ((+)-Dictyopterene A) and acyclic (giffordene) hydrocarbons, acting as pheromones. The second group corresponds to polyunsaturated aldehydes, such as the (Z,Z)-3,6-nonadienal, (E,Z)-2,6-nonadienal, which are most likely derived from the degradation of polyunsaturated fatty acids. The third group is represented by small molecules such as sulfur compounds and halogenated phenols which are regarded as the main flavor compounds of many types of seafood. This review exposes, most notably, the knowledge state on the occurrence of marine ingredients in fragrance. We also provide a detailed discussion on several aspects of essential oils, which are the most natural ingredients from various marine sources used in fragrance and cosmetics, including synthetic and natural marine ingredients. Full article

This review summarizes the results on the aromaticity of a series of synthesized and hypothetical neutral heterocirculene molecules and their double charged ions. The aromaticity of heterocirculenes is a direct reflection of their electronic structure responsible for the specific optoelectronic and photophysical properties. We show how the presence of a heteroatom in the outer macrocycle affects the aromaticity of hetero[8]circulenes. In addition, we also describe the change in aromaticity and strain energy for a series of the “lower” (n < 8) and “higher” (n > 8) hetero[n]circulenes. It was demonstrated that the loss of planarity with increased strain leads to an increased antiaromaticity of the lower hetero[n]circulenes, whereas higher hetero[n]circulenes demonstrate a more pronounced aromatic nature because of the small departure from planarity of each heteroarene ring in hetero[n]circulene molecule. Finally, we discuss the aromatic nature of the first examples of π-extended hetero[8]circulenes. Full article

The on-surface synthesis of boroxine-containing molecules can be a convenient method of introducing specific functionalities. Here, we show the validity of a previously described synthesis protocol on the Au (111) surface by applying it to a different molecular precursor. We study in detail the assembly of the precursor, highlighting possible intermediate stages of the condensation process. We combine scanning tunneling microscopy and X-ray spectroscopies to fully characterize both the morphology and the electronic properties of the system. DFT calculations are presented to assign the main electronic transitions originating the B K-edge absorption spectrum. The study paves the way to a facile strategy for functionalizing a surface with molecules of tailored sizes and compositions. Full article

Population growth and the way resources are being exploited are directly affecting the environment. The natural fiber market, for example, is worth billions of dollars and a huge amount of the fibers becomes waste. This considerable amount of waste motivates the study of the fibers as a reinforcement in polymeric matrix, which benefits both the environmental sustainability and technical-commercial development of new materials with good properties and reduced cost. In this study, jute fiber-reinforced composites previously manufactured from an industrial waste (W), polypropylene, compatibilizer, and nano-calcium carbonate (N), were exposed to natural and accelerated aging. The composites were tested by infrared spectroscopy, contact angle (CA) measurement, and tensile test. Infrared analysis showed greater oxidative degradation after accelerated aging. All CA values continued above 90° after natural aging. Among all compositions, the ones with the presence of N had the highest CA values, showing that N acted as a waterproofing agent. After accelerated aging, a significant decrease in all CA values was observed. The composites did not show significant variation in the elastic modulus after either aging. Deformation at break decreased significantly for compositions with no jute fiber in both aging programs. No remarkable reduction was observed in the compositions with jute fibers. Full article

The aromaticity of [n]starphenes (n = 1, 4, 7, 10, 13, 16), as well as starphene-based [19]dendriphene, is addressed by calculating the magnetically induced current density and the induced magnetic field, using the pseudo-π model. When an external magnetic field is applied, these systems create diatropic currents that split into a global peripheral current surrounding the starphene skeleton and several local currents in the acene-based arms, resulting in large shielding cones above the arms. In particular, the arm currents are smaller than their linear analogs, and in general, the strengths of the ring currents tend to weaken as the starphene get larger. Full article

In this study, the effect of these variables on commercial silica NP retention was presented in a fabricated flow model considering only the physical adsorption aspects of silica NP retention. From our observations, it was established that while silica NP concentration, flow rate and salt are key variables in influencing silica NP agglomeration and retention, the effect of temperature was highly subdued. The effect of salt-induced agglomeration was particularly severe at moderate salinity (≈4 wt% NaCl). To mitigate the effect of salt-induced agglomeration, a commonly used anionic surfactant, sodium dodecyl sulfate (SDS) was added to the solution and the silica NP retention was tabulated. An amount of 0.3 wt% SDS was found to negate salt-induced agglomeration significantly, paving the way for use of silica NP solutions, even in the presence of saline conditions. A section on the prospective use of artificial intelligence for this purpose has been included. This study is useful for understanding NP retention behaviour, especially in the presence of salinity and its mitigation using surfactants, in flow applications. Full article

The experimentally characterized hexamethylbenzene dication C₆(CH₃)₆²⁺ shows a pentagonal-pyramidal structure involving a carbon-capped five-membered ring. The structural characterization of this hypercoordination (or hypervalency) gives rise if the aromatic behavior remains in the resulting pentagon ring. Here, we investigated the induced magnetic field of C₆(CH₃)₆²⁺ to gain a deeper understanding of the resulting non-classical structural situation in a representative pentagonal-pyramidal structure. Our results support the view of a C₅(CH₃)₅⁻/CCH₃³⁺ structure, depicting a π-aromatic pentamethylcyclopentadienyl anion with a 6π-electron kernel, with a capped carbon which does not decrease the characteristic shielding cone property of the aromatic ring. Hence, carbon-capped rings are suggested to retain the aromatic behavior from the former aromatic ring. We expect that the analysis of both the overall magnetic response and NMR chemical shifts may be informative to unravel the characteristic patterns in the formation of hypervalent carbon atoms involving non-classical chemical environments. Full article

The development of biodegradable materials as food packaging material is important not only due to the reduction in environmental pollution but also because of an improvement in the functionality. Rice husk-reinforced biopolymers have offered a possible solution to waste-disposal problems associated with traditional petroleum-derived plastics. Rice husk-reinforced low density polyethylene (LDPE)-based biocomposites have been of great interest for their use as food packaging material. In this work, the LDPE/RH biocomposites with different rice husk (RH) content (10, 20, 30, 40 and 50 wt.%) were prepared by the melt mixing process in a laboratory Brabender mixer. The effect of RH content on the physical, thermal and mechanical properties of LDPE was investigated. More importantly, this work aimed to research the biodegradation of the LDPE/RH biocomposites as well as their effect on ‘Granny Smith’ apples’ respiration. The results showed that the incorporation of RH into the LDPE decreased the thermal stability of LDPE, increased water vapour permeability and water absorption, and increased the degree of crystallinity. The incorporation of RH increased the biodegradability of LDPE as well as the postharvest quality of ‘Granny Smith’ apples. The addition of RH in LDPE film significantly decreased fruit respiration and increased firmness as compared to LDPE film. The composting results showed that after the LDPE/RH biocomposite films were biodegraded for 21 days, the biocomposite films with the highest content of rice husks were the most degraded. Full article

In recent years, 2D materials have been implemented in several applications due to their unique and unprecedented properties. Several examples can be named, from the very first, graphene, to transition-metal dichalcogenides (TMDs, e.g., MoS₂), two-dimensional inorganic compounds (MXenes), hexagonal boron nitride (h-BN), or black phosphorus (BP). On the other hand, the accessible and low-cost 3D printers and design software converted the 3D printing methods into affordable fabrication tools worldwide. The implementation of this technique for the preparation of new composites based on 2D materials provides an excellent platform for next-generation technologies. This review focuses on the recent advances of 3D printing of the 2D materials family and its applications; the newly created printed materials demonstrated significant advances in sensors, biomedical, and electrical applications. Full article

Even though metallacyclopentadienes (MCPs) are among the most common metallacycles, their electron delocalization (aromaticity) has received far less attention than other metallacycles, such as metallabenzenes. We systematically studied the aromaticity of MCPs with energetic (isomerization stabilization energy), density (delocalization index) and magnetic (current density) aromaticity indices. The indices agree that metallacyclopentadienes are, in general, weakly aromatic at most. The 18$e^{-}$ complexes showed the expected weak aromaticity, and only the $d^8$ molecules are somewhat anti-aromatic. However, the theoretical account of the aromaticity of the 16$e^{-}$ MCPs is more convoluted. We find that the aromatic criteria for a 16$e^{-}$$d^4$ ruthenacyclopentadiene disagree. The lack of agreement shows that significant electron delocalization is not always related to great stability or to strong diatropic currents. Full article

The mechanism of aromatic nitration is critically reviewed with particular emphasis on the paradox of the high positional selectivity of substitution in spite of low substrate selectivity. Early quantum chemical computations in the gas phase have suggested that the retention of positional selectivity at encounter-limited rates could be ascribed to the formation of a radical pair via an electron transfer step occurring before the formation of the Wheland intermediate, but calculations which account for the effects of solvent polarization and the presence of counterion do not support that point of view. Here we report a brief survey of the available experimental and theoretical data, adding a few more computations for better clarifying the role of electron transfer for regioselectivity. Full article

Microbial technology offers a green alternative for the synthesis of value-added nanomaterials. In particular, fungal compounds can improve silver nanoparticle production, stabilizing colloidal nanoparticles. Based on a previous study by our group, silver nanoparticles obtained using the extracellular cell-free extracts of Phanerochaete chrysosporium (PchNPs) have shown antimicrobial and antibiofilm activity against Gram-negative bacteria. Moreover, nisin—a bacteriocin widely used as a natural food preservative—has recently gained much attention due its antimicrobial action against Gram-positive bacteria in biomedical applications. Therefore, the aim of this work was to conjugate biogenic silver nanoparticles (PchNPs) with nisin to obtain nanoconjugates (PchNPs@nis) with enhanced antimicrobial properties. Characterization assays were conducted to determine physicochemical properties of PchNPs@nis, and also their antibacterial and antibiofilm activities were studied. The formation of PchNPs@nis was confirmed by UV-Vis, TEM, and Raman spectroscopy analysis. Different PchNPs@nis nanobioconjugates showed diameter values in the range of 60–130 nm by DLS and surface charge values between −20 and −13 mV. Nisin showed an excellent affinity to PchNPs, with binding efficiencies higher than 75%. Stable synthesized PchNPs@nis nanobioconjugates were not only able to inhibit biofilm formation by S. aureus, but also showed inhibition of the planktonic cell growth of Staphyloccocus aureus and Escherichia coli, broadening the spectrum of action of the unconjugated antimicrobials against Gram-positive and Gram-negative bacteria. In conclusion, these results show the promising application of PchNPs@nis, prepared via green technology, as potential antimicrobial nanomaterials. Full article

The aim of the present study was to investigate the effects of fiber content and then silane treatment on the mechanical performance of the natural fiber composites of recycled acrylonitrile–butadiene–styrene (ABS) provided by the automotive sector. Wood and palmyra fibers were used as fillers in 10% and 20% fiber content composites. The fibers were treated with N-(2-Aminoethyl)-3-aminopropyltrimethoxysilane to improve the interfacial adhesion between fibers and polymer matrices. The mechanical properties of the composites were determined by tensile and impact tests. Morphological analysis was later performed using a scanning electron microscope (SEM). According to the experiment results, the tensile and impact strength of both wood and palmyra fibers increase after silane treatment. However, for the low-wood-fiber-content composite, the tensile and impact strength decrease after silane treatment due to the presence of an excess amount of silane relative to fiber content. The addition of wood and palmyra fibers significantly improved the tensile modulus of composite material and further increases slightly after silane treatment. Finally, SEM analysis shows a homogenous mix of fibers and polymer matrices with fewer voids after silane treatment, thereby improving interfacial adhesion. Full article

In this work, we describe a user-friendly procedure for the preparation of all the isomeric forms of the terpene linalool oxide. The presented method is based on the transformation of the linalool enantiomers into the corresponding diastereoisomeric mixtures of the two furanoid oxides and two pyranoid oxides. Taking advantage of the different steric hindrance of the hydroxyl functional groups, the pyranoid forms were separated as a diastereoisomeric mixtures of their benzoate esters. Conversely, the cis- and trans-furanoid isomers were transformed in the corresponding acetates, which were directly separated by chromatography. The hydrolysis of the latter esters afforded cis- and trans-furanoid linalool oxides whereas the same reaction performed on the benzoates mixture afforded a separable mixture of cis- and trans-pyranoid linalool oxide. Overall, the method features, as a unique mandatory requirement, the availability of both linalool enantiomers, and can be conveniently performed from a milligram to a multigram scale. Full article

Lithium-ion capacitors (LICs) are considered to be one of the most promising energy storage devices which have the potential of integrating high energy of lithium-ion batteries and high power and long cycling life of supercapacitors into one system. However, the current LICs could only provide high power density at the cost of low energy density due to the sluggish Li⁺ diffusion and/or low electrical conductivity of the anode materials. Moreover, the serious capacity and kinetics imbalances between anode and cathode result in not only inferior rate performance but also unsatisfactory cycling stability. Therefore, designing high-power and structure stable anode materials is of great significance for practical LICs. Under this circumstance, graphene-based materials have been intensively explored as anodes in LICs due to their unique structure and outstanding electrochemical properties and attractive achievements have been made. In this review, the recent progresses of graphene-based anode materials for LICs are systematically summarized. Their synthesis procedure, structure and electrochemical performance are discussed with a special focus on the role of graphene. Finally, the outlook and remaining challenges are presented with some constructive guidelines for future research. Full article

New synthetic routes are presented to derivatives of a (known) M₈L₁₂ cubic coordination cage in which a range of different substituents are attached at the C⁴ position of the pyridyl rings at either end of the bis(pyrazolyl-pyridine) bridging ligands. The substituents are (i) –CN groups (new ligand L^CN), (ii) –CH₂OCH₂–CCH (containing a terminal alkyne) groups (new ligand L^CC); and (iii) –(CH₂OCH₂)₃CH₂OMe (tri-ethyleneglycol monomethyl ether) groups (new ligand L^PEG). The resulting functionalised ligands combine with M²⁺ ions (particularly Co²⁺, Ni²⁺, Cd²⁺) to give isostructural [M₈L₁₂]¹⁶⁺ cage cores bearing 24 external functional groups; the cages based on L^CN (with M²⁺ = Cd²⁺) and L^CC (with M²⁺ = Ni²⁺) have been crystallographically characterised. The value of these is twofold: (i) exterior nitrile or alkene substituents can provide a basis for further synthetic opportunities via ‘Click’ reactions allowing in principle a diverse range of functionalisation of the cage exterior surface; (ii) the exterior –(CH₂OCH₂)₃CH₂OMe groups substantially increase cage solubility in both water and in organic solvents, allowing binding constants of cavity-binding guests to be measured under an increased range of conditions. Full article

There is a demand for renewable resources, such as biomass, to produce compounds considered as platform molecules. This study deals with dehydration of fructose for the formation of 5-hydroxymethylfurfural (HMF), a feedstock molecule. Different catalysts (aluminosilicates, niobic acid, 12-tungstophosphoric acid—HPW, and supported HPW/Niobia) were studied for this reaction in an aqueous medium. The catalysts were characterized by XRD, FT-IR, N₂ sorption at −196 °C and pyridine adsorption. It was evident that the nature of the sites (Brønsted and Lewis), strength, quantity and accessibility to the acidic sites are critical to the conversion and yield results. A synergic effect of acidity and mesoporous area are key factors affecting the activity and selectivity of the solid acids. Niobic acid (Nb₂O₅·nH₂O) revealed the best efficiency (highest TON, yield, selectivity and conversion). It was determined that the optimum acidity strength of catalysts should be between 80 to 100 kJ mol⁻¹, with about 0.20 to 0.30 mmol g⁻¹ of acid sites, density about 1 site nm⁻² and mesoporous area about 100 m² g⁻¹. These values fit well within the general order of the observed selectivity (i.e., Nb₂O₅ > HZSM-5 > 20%HPW/Nb₂O₅ > SiO₂-Al₂O₃ > HY > HBEA). Full article

Several metal diimine complexes have been reported to possess anticancer properties. To evaluate the anticancer properties of tetrahedral zinc(II) diimine complexes, six complexes were synthesized with the general formula M(N^N)Cl₂ {where M = Zn, Pt and N^N = 2,2’-biquinoline (1), 2,2’-dipyridylketone (2) and 4-((pyridine-2-ylmethylene)amino)phenol (3)}. In general, the intrinsic DNA-binding constants for the different compounds exhibited values within close proximity; the changes in the viscosity of the CT-DNA upon binding to the compounds suggest intercalation-binding mode. Molecular docking study predicted that complexes containing the highly planar ligand 2,2’-biquinoline are capable to establish π–π interactions with nucleobases of the DNA; the other four complexes engaged in donor–acceptor interactions with DNA nucleobases. The six complexes and two reference drugs (cisplatin and sunitinib) were tested against two cancer cell lines (COLO 205 and RCC-PR) and one normal cell line (LLC-MK2), highlighting the better performance of the zinc(II) complexes compared to their platinum(II) analogues. Moreover, zinc(II) complexes have higher selectivity index values than the reference drugs, with promising anticancer properties. Full article

Concrete sewer pipes can be corroded by the biogenic sulfuric acid (H₂SO₄) generated from microbiological activities in a process called biocorrosion or microbiologically induced corrosion (MIC). In this study, inhibitors that can reduce Acidithiobacillus thiooxidans growth and thus may reduce the accumulation of biofilm components responsible for the biodegradation of concrete were used. D-tyrosine, tetrakis hydroxymethyl phosphonium sulfate (THPS) and TiO₂ nanoparticles were investigated as potential inhibitors of sulfur-oxidizing bacteria (SOB) growth. Results showed that most of the chemicals used can inhibit SOB growth at a concentration lower than 100 mg/L. TiO₂ nanoparticles exhibited the highest biocide effect and potential biocorrosion mitigation activity, followed by D-tyrosine and THPS. Full article

In situ characterization of catalysts provides important information on the catalyst and the understanding of its activity and selectivity for a specific reaction. TPX techniques for catalyst characterization reveal the role of the support on the stabilization and dispersion of the active sites. However, these can be altered at high temperature since sintering of active species can occur as well as possible carbon deposition through the Bosch reaction, which hinders the active species and deactivates the catalyst. In situ characterization of the spent catalyst, however, may expose the causes for catalyst deactivation. For example, a simple TPO analysis on the spent catalyst may produce CO and CO₂ via a reaction with O₂ at high temperature and this is a strong indication that deactivation may be due to the deposition of carbon during the Sabatier reaction. Other TPX techniques such as TPR and pulse chemisorption are also valuable techniques when they are applied in situ to the fresh catalyst and then to the catalyst upon deactivation. Full article

Ring-current maps give a direct pictorial representation of molecular aromaticity. They can be computed at levels ranging from empirical to full ab initio and DFT. For benzenoid hydrocarbons, Hückel–London (HL) theory gives a remarkably good qualitative picture of overall current patterns, and a useful basis for their interpretation. This paper describes an implemention of Aihara’s algorithm for computing HL currents for a benzenoid (for example) by partitioning total current into its constituent cycle currents. The Aihara approach can be used as an alternative way of calculating Hückel–London current maps, but more significantly as a tool for analysing other empirical models of induced current based on conjugated circuits. We outline an application where examination of cycle contributions to HL total current led to a simple graph-theoretical approach for cycle currents, which gives a better approximation to the HL currents for Kekulean benzenoids than any of the existing conjugated-circuit models, and unlike these models it also gives predictions of the HL currents in non-Kekulean benzenoids that are of similar quality. Full article

In this paper, a simple and clean process for the alkylation and arylation of nitrogen-containing heterocycles is reported. The reactions were conducted using the Q-tube® as a non-conventional technology, in water as a green solvent, at overboiling temperature. The developed strategy was used to improve two steps in the total synthesis of caffeine, as reported by Narayan, and then extended to the preparation of N-decorated xanthines. Finally, piperidine, methyl piperazine, and isatine were proven to be suitable substrates for the protocol proposed herein. Full article

Polymer microspheres with inter-connecting pores are widely used as microsphere materials. In the study, the ethyl cellulose microspheres (ECM) were prepared by using the solvent-evaporation method. Based on that, a method for the separation and purification of benzoic acid from crude extract of Cyclocarya paliurus was established by the ECM and high performance liquid chromatography (HPLC). The ECM after the sorption equilibrium was desorbed by using 40% methanol as the analytical solvent. The content of benzoic acid in eluent is up to 0.0216 mg/mL, and the benzoic acid can be obtained with a high purity of 82.22%. Furthermore, the adsorption-desorption behavior of benzoic acid onto ECM was investigated. The results of adsorption kinetics of benzoic acid showed that the adsorption followed the pseudo-first-order kinetic model. The ECM was characterized by using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscope (SEM), and X-ray diffraction (XRD). The results showed that the ECM has a high adsorption property due to its more porous structure, phenolic hydroxyl group, and other oxygen-containing functional groups. This method and the ECM can be used stably, continuously, and efficiently to purify the benzoic acid from the methanol extract of C. paliurus on a large scale. Full article

The minimum energy structures of the Si₃C₅ and Si₄C₈ clusters are planar and contain planar tetracoordinate carbons (ptCs). These species have been classified, qualitatively, as global (π) and local (σ) aromatics according to the adaptive natural density partitioning (AdNDP) method, which is an orbital localization method. This work evaluates these species’ aromaticity, focusing on confirming and quantifying their global and local aromatic character. For this purpose, we use an orbital localization method based on the partitioning of the molecular space according to the topology of the electronic localization function (LOC-ELF). In addition, the magnetically induced current density is analyzed. The LOC-ELF-based analysis coincides with the AdNDP study (double aromaticity, global, and local). Moreover, the current density analysis detects global and local ring currents. The strength of the global and local current circuit is significant, involving 4n + 2 π- and σ-electrons, respectively. The latter implicates the Si-ptC-Si fragment, which would be related to the 3c-2e σ-bond detected by the orbital localization methods in this fragment. Full article