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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Molecular Structure".

Deadline for manuscript submissions: 30 April 2024 | Viewed by 3959

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Prof. Dr. Chan Kyung Kim

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Department of Chemistry and Chemical Engineering, Inha University, 100 Inha-ro, Michuhol-gu, Inchenon 22212, Republic of Korea
Interests: computational chemistry; high-energy density material design; computer-aided materials; drug design
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Dear Colleagues,

We are pleased to announce the new Special Issue entitled “Exclusive Feature Papers on Molecular Structure”. This is a collection of important high-quality papers (original research articles or comprehensive reviews) published in open access format by Editorial Board Members or prominent scholars invited by the Editorial Office and the Guest Editors. We aim to gather state-of-the-art or new cutting-edge developments that cover all kinds of topics in the physical chemistry field through selected works, in the hope of making a great contribution to the community. We intend for this Special Issue to serve as a forum for disseminating excellent research findings, as well as sharing innovative ideas in the field.

Prof. Dr. Chan Kyung Kim
Guest Editor

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (6 papers)

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Research

11 pages, 1796 KiB

Open AccessArticle

Synthesis, Structure, and Characterizations of a Volatile/Soluble Heterometallic Hexanuclear Precursor [NaMn₂(thd)₄(OAc)]₂

Yuxuan Zhang

Zheng Wei

and

Evgeny V. Dikarev

Molecules 2023, 28(23), 7795; https://doi.org/10.3390/molecules28237795 - 27 Nov 2023

Viewed by 237

Abstract

The paper describes a heterobimetallic mixed-ligand hexanuclear precursor [NaMn₂(thd)₄(OAc)]₂ (1) (thd = 2,2,6,6-tetramethyl-3,5-heptadionate; OAc = acetate) that was designed based on its lithium homoleptic analogue, [LiMn₂(thd)₅], by replacing one of the thd ligands with an acetate group in order to accommodate 5-coordinated sodium instead of tetrahedral lithium ion. The complex, which is highly volatile and soluble in a variety of common solvents, has been synthesized by both the solid-state and solution methods. The unique “dimer-of-trimers” heterometallic structure consists of two trinuclear [NaMn^II₂(thd)₄]⁺ units firmly bridged by two acetate ligands. X-ray diffraction techniques, DART mass spectrometry, ICP-OES analysis, and IR spectroscopy have been employed to confirm the structure and composition of the hexanuclear complex. Similar to the Li counterpart forming LiMn₂O₄ spinel material upon thermal decomposition, the title Na:Mn = 1:2 compound was utilized as the first single-source precursor for the low-temperature preparation of Na₄Mn₉O₁₈ tunnel oxide. Importantly, four Mn sites in the hexanuclear molecule can be potentially partially substituted by other transition metals, leading to heterotri- and tetrametallic precursors for the advanced quaternary and quinary Na-ion oxide cathode materials. Full article

(This article belongs to the Special Issue Exclusive Feature Papers on Molecular Structure)

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19 pages, 3156 KiB

Open AccessArticle

NMR “Finger Prints” of N-Heterocyclic Carbenes, DFT Analysis: Scopes and Limitations

Svetlana A. Kondrashova

and

Shamil K. Latypov

Molecules 2023, 28(23), 7729; https://doi.org/10.3390/molecules28237729 - 23 Nov 2023

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Abstract

The scopes and limitations of theoretical methods for estimating various NMR metrics of NHCs are considered on a wide range of model NHCs and their derivatives, using a number of computational approximations. On the whole, the most reliable, from the point of view of predictability and insusceptibility to additional effects, are ³¹P/¹³C NMR shifts of NHC–phosphinidene adducts and ¹³C CSs of carbenes themselves. The method based on the analysis of ⁷⁷Se CS NHC–selenoureas has some limitations since the observed NMR parameters can also be modulated by exchange effects due to their formation with non-classical hydrogen bonds. As for HEP, since the delicate balance of electron distribution between Pd and two carbon centers can nonlinearly affect relativistic spin–orbit effects, the accuracy of the estimation of this metric may still be limited. ¹³C CSs of NHC–azolium salts do not seem to be reliable, since the observed values are strongly influenced by the effects of the exchange between different forms with counterions, which are difficult to estimate correctly. Full article

(This article belongs to the Special Issue Exclusive Feature Papers on Molecular Structure)

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8 pages, 3369 KiB

Open AccessCommunication

Directional Crystallization of Conjugated Molecules during Coating Processes

Detlef-M. Smilgies

and

Ruipeng Li

Molecules 2023, 28(14), 5371; https://doi.org/10.3390/molecules28145371 - 13 Jul 2023

Viewed by 389

Abstract

The coating of organic molecules from the solution phase can result in directional crystal growth under certain conditions, even on a smooth isotropic surface and without the need of any kind of graphoexpitaxial preparation of the substrate. Based on reviewing the results from a variety of coating techniques and coating parameters, we identified that it is crucial for the coating speed to match the growth speed of the fastest growing crystal plane to achieve a high degree of directional crystallization. Full article

(This article belongs to the Special Issue Exclusive Feature Papers on Molecular Structure)

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17 pages, 2505 KiB

Open AccessArticle

Silver Ion High-Performance Liquid Chromatography—Atmospheric Pressure Chemical Ionization Mass Spectrometry: A Tool for Analyzing Cuticular Hydrocarbons

and

Molecules 2023, 28(9), 3794; https://doi.org/10.3390/molecules28093794 - 28 Apr 2023

Cited by 1 | Viewed by 1133

Abstract

Aliphatic hydrocarbons (HCs) are usually analyzed by gas chromatography (GC) or matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. However, analyzing long-chain HCs by GC is difficult because of their low volatility and the risk of decomposition at high temperatures. MALDI cannot distinguish between isomeric HCs. An alternative approach based on silver ion high-performance liquid chromatography (Ag-HPLC) is shown here. The separation of HC standards and cuticular HCs was accomplished using two ChromSpher Lipids columns connected in series. A gradient elution of the analytes was optimized using mobile phases prepared from hexane (or isooctane) and acetonitrile, 2-propanol, or toluene. HCs were detected by atmospheric pressure chemical ionization mass spectrometry (APCI-MS). Good separation of the analytes according to the number of double bonds, cis/trans geometry, and position of double bonds was achieved. The retention times increased with the number of double bonds, and trans isomers eluted ahead of cis isomers. The mobile phase significantly affected the mass spectra of HCs. Depending on the mobile phase composition, deprotonated molecules, molecular ions, protonated molecules, and various solvent-related adducts of HCs were observed. The optimized Ag-HPLC/APCI-MS was applied for characterizing cuticular HCs from a flesh fly, Neobellieria bullata, and cockroach, Periplaneta americana. The method made it possible to detect a significantly higher number of HCs than previously reported for GC or MALDI-MS. Unsaturated HCs were frequently detected as isomers differing by double-bond position(s). Minor HCs with trans double bonds were found beside the prevailing cis isomers. Ag-HPLC/APCI-MS has great potential to become a new tool in chemical ecology for studying cuticular HCs. Full article

(This article belongs to the Special Issue Exclusive Feature Papers on Molecular Structure)

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13 pages, 1506 KiB

Open AccessArticle

Size–Pore-Dependent Methanol Sequestration from Water–Methanol Mixtures by an Embedded Graphene Slit

Roger Bellido-Peralta

Fabio Leoni

Carles Calero

and

Giancarlo Franzese

Molecules 2023, 28(9), 3697; https://doi.org/10.3390/molecules28093697 - 25 Apr 2023

Cited by 1 | Viewed by 717

Abstract

The separation of liquid mixture components is relevant to many applications—ranging from water purification to biofuel production—and is a growing concern related to the UN Sustainable Development Goals (SDGs), such as “Clean water and Sanitation” and “Affordable and clean energy”. One promising technique is using graphene slit-pores as filters, or sponges, because the confinement potentially affects the properties of the mixture components in different ways, favoring their separation. However, no systematic study has shown how the size of a pore changes the thermodynamics of the surrounding mixture. Here, we focus on water–methanol mixtures and explore, using Molecular Dynamics simulations, the effects of a graphene pore, with size ranging from 6.5 to 13 Å, for three compositions: pure water, 90%–10%, and 75%–25% water–methanol. We show that tuning the pore size can change the mixture pressure, density and composition in bulk due to the size-dependent methanol sequestration within the pore. Our results can help in optimizing the graphene pore size for filtering applications. Full article

(This article belongs to the Special Issue Exclusive Feature Papers on Molecular Structure)

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11 pages, 4496 KiB

Open AccessArticle

Inclusion Complexes of 3,4-Ethylenedioxythiophene with Per-Modified β- and γ-Cyclodextrins

Aurica Farcas

Ana-Maria Resmerita

Mihaela Balan-Porcarasu

Corneliu Cojocaru

Cristian Peptu

and

Ion Sava

Molecules 2023, 28(8), 3404; https://doi.org/10.3390/molecules28083404 - 12 Apr 2023

Cited by 4 | Viewed by 813

Abstract

Herein, we report the synthesis of inclusion complexes (ICs) based on 3,4-ethylenedioxythiophene (EDOT) with permethylated β-cyclodextrins (TMe-βCD) and permethylated γ-cyclodextrins (TMe-γCD) host molecules. To prove the synthesis of such ICs, molecular docking simulation, UV-vis titrations in water, ¹H-NMR, and H-H ROESY, as well as matrix-assisted laser desorption ionization mass spectroscopy (MALDI TOF MS) and thermogravimetric analysis (TGA) were carried out on each of the EDOT∙TMe-βCD and EDOT∙TMe-γCD samples. The results of computational investigations reveal the occurrence of hydrophobic interactions, which contribute to the insertion of the EDOT guest inside the macrocyclic cavities and a better binding of the neutral EDOT to TMe-βCD. The H-H ROESY spectra show correlation peaks between H-3 and H-5 of hosts and the protons of the guest EDOT, suggesting that the EDOT molecule is included inside the cavities. The MALDI TOF MS analysis of the EDOT∙TMe-βCD solutions clearly reveals the presence of MS peaks corresponding to sodium adducts of the species associated with the complex formation. The IC preparation shows remarkable improvements in the physical properties of EDOT, rendering it a plausible alternative to increasing its aqueous solubility and thermal stability. Full article

(This article belongs to the Special Issue Exclusive Feature Papers on Molecular Structure)

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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Five and Six-Coordinated Zinc Isomers in the Heterometallic Cyclic Molecular Tetramer
Authors: Yuxuan Zhang; Haixiang Han; Zheng Wei; Evgeny V. Dikarev
Affiliation: a. Department of Chemistry, University at Albany, Albany, NY 12222, United States b. School of Materials Science and Engineering, Tongji University, Shanghai, 201804, China
Abstract: The manuscript describes the synthesis of two heterometallic Li-Zn isomers. Both structures are cyclic tetranuclear molecules that differ by coordination number of Zn ions, which are either 5- or 6-coordinated. X-ray structural analysis, powder diffraction pattern, multinuclear NMR, IR, mass-spectrometry, and TGA have been used for characterization of two isomers. The transformation in different solvents from 5- to 6-coordinated Zn species and vice-versa is also described.

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