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Spectroscopic and Spectrometric Techniques for Structural Analysis
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Spectroscopic and Spectrometric Techniques for Structural Analysis

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

Deadline for manuscript submissions: closed (31 January 2023) | Viewed by 28914

Special Issue Editors

Prof. Dr. Nives Galić

E-Mail Website
Guest Editor
Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102a, 10000 Zagreb, Croatia
Interests: mass spectroscopy; UV-Vis spectroscopy; spectrofluorimetry
Special Issues, Collections and Topics in MDPI journals
Dr. Ana Čikoš

E-Mail Website
Guest Editor
Ruđer Bošković Institute, Bijenička 54, HR-10000 Zagreb, Croatia
Interests: NMR spectroscopy; structure elucidation; drug discovery; natural products; macrocycles; fragment-based drug discovery (NMR screening); protein-ligand interactions; solution-state conformation; degradation Products; impurities; complexes

Special Issue Information

Dear Colleagues,

The aim of this Special Issue is to discuss different spectroscopic and spectrometric techniques and their application in structural studies of various compounds and systems. Spectroscopy and spectrometry cover many instrumental techniques which are widely used not only for elucidating structures (new chemical entities, isolated impurities, natural products, fermentation and degradation products, etc.) but also as tools to probe the interactions between various chemical species (macromolecules and their ligands, inclusion complexes, metal complexes etc.), discovering what the molecules look like in three-dimensional space, how they interact with their environment, how they are made and what in their structure is responsible for their biological activity, as well as the physical or chemical properties that they exhibit. All of this can be carried out in solid state, solution and gaseous phase.

In this Special Issue, the emphasis will be placed on technical advancement or novel application of one particular technique, or a combination of several methods, leading to reliable scientific conclusions. Papers can cover the application of spectroscopic methods in different areas of research, such as drug design and development, organic and inorganic synthesis, physical and chemical properties, natural product research and non-target analysis. Molecular modelling articles are welcome if presented in combination with spectroscopic and spectrometric experimental data. The abovementioned techniques can be used in both fundamental and applied research. Both original research and review articles will be considered.

Prof. Dr. Nives Galić
Dr. Ana Čikoš
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

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.

Keywords

  • NMR spectroscopy
  • mass spectrometry
  • vibrational spectroscopy
  • UV-Vis spectroscopy
  • spectrofluorimetry
  • EPR spectroscopy
  • structural analysis

Published Papers (14 papers)

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Research

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24 pages, 6122 KiB  
Article
Infrared Spectral Classification of Natural Bitumens for Their Rheological and Thermophysical Characterization
by Anastasiya Y. Yadykova, Larisa A. Strelets and Sergey O. Ilyin
Molecules 2023, 28(5), 2065; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules28052065 - 22 Feb 2023
Cited by 18 | Viewed by 1549
Abstract
Natural bitumens consist of many molecules whose chemical composition depends on the oilfield and determines the physicochemical properties of the bitumens as materials. Infrared (IR) spectroscopy is the fastest and least expensive method to assess the chemical structure of organic molecules, which makes [...] Read more.
Natural bitumens consist of many molecules whose chemical composition depends on the oilfield and determines the physicochemical properties of the bitumens as materials. Infrared (IR) spectroscopy is the fastest and least expensive method to assess the chemical structure of organic molecules, which makes it attractive in terms of rapid prediction of the properties of natural bitumens based on their composition evaluated in this way. In this work, IR spectra were measured for ten samples of natural bitumens significantly different in properties and origin. Based on the ratios of certain IR absorption bands, bitumens are proposed to be divided into paraffinic, aromatic, and resinous. In addition, the internal relationship between IR spectral characteristics of bitumens, such as polarity, paraffinicity, branchiness, and aromaticity, is shown. A study of phase transitions in bitumens by differential scanning calorimetry was carried out, and the use of a heat flow differential to find hidden points of bitumens’ glass transitions is proposed. Furthermore, the dependences of the total melting enthalpy of crystallizable paraffinic compounds on the aromaticity and branchiness of bitumens are demonstrated. A detailed study of bitumens’ rheology in a wide temperature range was carried out, and characteristic features of rheological behavior for different bitumen classes are revealed. Based on the viscous properties of bitumens, their glass transition points were found and compared with the calorimetric glass transition temperatures and nominal solid–liquid transition points obtained from temperature dependences of bitumens’ storage and loss moduli. The dependences of viscosity, flow activation energy, and glass transition temperature of bitumens on their IR spectral characteristics are shown, which can be used to predict the rheological properties of bitumens. Full article
(This article belongs to the Special Issue Spectroscopic and Spectrometric Techniques for Structural Analysis)
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10 pages, 1226 KiB  
Communication
Quantifying Microalgae Growth by the Optical Detection of Glucose in the NIR Waveband
by Vimal Angela Thiviyanathan, Pin Jern Ker, Eric P. P. Amin, Shirley Gee Hoon Tang, Willy Yee and M. Z. Jamaludin
Molecules 2023, 28(3), 1318; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules28031318 - 30 Jan 2023
Cited by 2 | Viewed by 2108
Abstract
Microalgae have become a popular area of research over the past few decades due to their enormous benefits to various sectors, such as pharmaceuticals, biofuels, and food and feed. Nevertheless, the benefits of microalgae cannot be fully exploited without the optimization of their [...] Read more.
Microalgae have become a popular area of research over the past few decades due to their enormous benefits to various sectors, such as pharmaceuticals, biofuels, and food and feed. Nevertheless, the benefits of microalgae cannot be fully exploited without the optimization of their upstream production. The growth of microalgae is commonly measured based on the optical density of the sample. However, the presence of debris in the culture and the optical absorption of the intercellular components affect the accuracy of this measurement. As a solution, this paper introduces the direct optical detection of glucose molecules at 940–960 nm to accurately measure the growth of microalgae. In addition, this paper also discusses the effects of the presence of glucose on the absorption of free water molecules in the culture. The potential of the optical detection of glucose as a complement to the commonly used optical density measurement at 680 nm is discussed in this paper. Lastly, a few recommendations for future works are presented to further verify the credibility of glucose detection for the accurate determination of microalgae’s growth. Full article
(This article belongs to the Special Issue Spectroscopic and Spectrometric Techniques for Structural Analysis)
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21 pages, 1628 KiB  
Article
Computational Studies on Selected Macrolides Active against Escherichia coli Combined with the NMR Study of Tylosin A in Deuterated Chloroform
by Biljana Arsic, Jill Barber, Ana Cikos, Manikandan Kadirvel, Emilija Kostic, Andrew J. McBain, Jelena Milicevic, Angela Oates and Andrew Regan
Molecules 2022, 27(21), 7280; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27217280 - 26 Oct 2022
Cited by 1 | Viewed by 1601
Abstract
Although many antibiotics are active against Gram-positive bacteria, fewer also show activity against Gram-negative bacteria. Here, we present a combination of in silico (electron ion-interaction potential, molecular docking, ADMET), NMR, and microbiological investigations of selected macrolides (14-membered, 15-membered, and 16-membered), aiming to discover [...] Read more.
Although many antibiotics are active against Gram-positive bacteria, fewer also show activity against Gram-negative bacteria. Here, we present a combination of in silico (electron ion-interaction potential, molecular docking, ADMET), NMR, and microbiological investigations of selected macrolides (14-membered, 15-membered, and 16-membered), aiming to discover the pattern of design for macrolides active against Gram-negative bacteria. Although the conformational studies of 14-membered and 15-membered macrolides are abundant in the literature, 16-membered macrolides, and their most prominent representative tylosin A, have received relatively little research attention. We therefore report the complete 1H and 13C NMR assignment of tylosin A in deuterated chloroform, as well as its 3D solution structure determined through molecular modelling (conformational search) and 2D ROESY NMR. Additionally, due to the degradation of tylosin A in deuterated chloroform, other species were also detected in 1D and 2D NMR spectra. We additionally studied the anti-bacterial activity of tylosin A and B against selected Gram-positive and Gram-negative bacteria. Full article
(This article belongs to the Special Issue Spectroscopic and Spectrometric Techniques for Structural Analysis)
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10 pages, 1728 KiB  
Article
A Simple Elimination of the Thermal Convection Effect in NMR Diffusiometry Experiments
by Dávid Nyul, Levente Novák, Mónika Kéri and István Bányai
Molecules 2022, 27(19), 6399; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27196399 - 27 Sep 2022
Viewed by 1298
Abstract
Thermal convection is always present when the temperature of an NMR experiment is different from the ambient one. Most often, it falsifies the value of the diffusion coefficient determined by NMR diffusiometry using a PGSE NMR experiment. In spite of common belief, it [...] Read more.
Thermal convection is always present when the temperature of an NMR experiment is different from the ambient one. Most often, it falsifies the value of the diffusion coefficient determined by NMR diffusiometry using a PGSE NMR experiment. In spite of common belief, it acts not only at higher temperatures but also at temperatures lower than in the laboratory. Sodium alkyl-sulfate monomers and micelles in D2O solvent were used as model molecules measured at T = 319 K in order to show that thermal convection sometimes remains hidden in experiments. In this paper, we demonstrate that the increase in apparent diffusion coefficient with increasing diffusion time is a definite indicator of thermal convection. Extrapolation to zero diffusion time can also be used to obtain the real diffusion coefficient, likewise applying the less sensitive pulse sequences designed for flow compensation or the expensive hardware, e.g., sapphire or Shigemi NMR tubes, to decrease the temperature gradient. Further, we show experiments illustrating the effect of a long diffusion time in which the periodic changes of the echo intensity with gradient strength appear as predicted by theories. Full article
(This article belongs to the Special Issue Spectroscopic and Spectrometric Techniques for Structural Analysis)
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12 pages, 3285 KiB  
Communication
Detection and Verification of a Key Intermediate in an Enantioselective Peptide Catalyzed Acylation Reaction
by Matthias Brauser, Tim Heymann and Christina Marie Thiele
Molecules 2022, 27(19), 6351; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27196351 - 26 Sep 2022
Cited by 2 | Viewed by 1499
Abstract
Until now, the intermediate responsible for the acyl transfer of a highly enantioselective tetrapeptide organocatalyst for the kinetic resolution of trans-cycloalkane-1,2-diols has never been directly observed. It was proposed computationally that a π-methylhistidine moiety is acylated as an intermediate step in the catalytic [...] Read more.
Until now, the intermediate responsible for the acyl transfer of a highly enantioselective tetrapeptide organocatalyst for the kinetic resolution of trans-cycloalkane-1,2-diols has never been directly observed. It was proposed computationally that a π-methylhistidine moiety is acylated as an intermediate step in the catalytic cycle. In this study we set out to investigate whether we can detect and characterize this key intermediate using NMR-spectroscopy and mass spectrometry. Different mass spectrometric experiments using a nano-ElectroSpray Ionization (ESI) source and tandem MS-techniques allowed the identification of tetrapeptide acylium ions using different acylation reagents. The complexes of trans-cyclohexane-1,2-diols with the tetrapeptide were also detected. Additionally, we were able to detect acylated tetrapeptides in solution using NMR-spectroscopy and monitor the acetylation reaction of a trans-cyclohexane-1,2-diol. These findings are important steps towards the understanding of this highly enantioselective organocatalyst. Full article
(This article belongs to the Special Issue Spectroscopic and Spectrometric Techniques for Structural Analysis)
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14 pages, 3585 KiB  
Article
Identification of Photocatalytic Alkaloids from Coptidis Rhizome by an Offline HPLC/CC/SCD Approach
by Shu-Qin Qin, Jun Ma, Qi-Qi Wang, Wei Xu, Wen-Cai Ye and Ren-Wang Jiang
Molecules 2022, 27(19), 6179; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27196179 - 21 Sep 2022
Cited by 2 | Viewed by 1447
Abstract
Natural products continue to be a valuable source of active metabolites; however, researchers of natural products are mostly focused on the biological effects, and their chemical utility has been less explored. Furthermore, low throughput is a bottleneck for classical natural product research. In [...] Read more.
Natural products continue to be a valuable source of active metabolites; however, researchers of natural products are mostly focused on the biological effects, and their chemical utility has been less explored. Furthermore, low throughput is a bottleneck for classical natural product research. In this work, a new offline HPLC/CC/SCD (high performance liquid chromatography followed by co-crystallization and single crystal diffraction) workflow was developed that greatly expedites the discovery of active compounds from crude natural product extracts. The photoactive total alkaloids of the herbal medicine Coptidis rhizome were firstly separated by HPLC, and the individual peaks were collected. A suitable coformer was screened by adding it to the individual peak solution and observing the precipitation, which was then redissolved and used for co-crystallization. Seven new co-crystals were obtained, and all the single crystals were subjected to X-ray diffraction analysis. The molecular structures of seven alkaloids from milligrams of crude extract were resolved within three days. NDS greatly decreases the required crystallization amounts of alkaloids to the nanoscale and enables rapid stoichiometric inclusion of all the major alkaloids with full occupancy, typically without disorder, affording well-refined structures. It is noteworthy that anomalous scattering by the coformer sulfur atoms enables reliable assignment of absolute configuration of stereogenic centers. Moreover, the identified alkaloids were firstly found to be photocatalysts for the green synthesis of benzimidazoles. This study demonstrates a new and green phytochemical workflow that can greatly accelerate natural product discovery from complex samples. Full article
(This article belongs to the Special Issue Spectroscopic and Spectrometric Techniques for Structural Analysis)
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15 pages, 2951 KiB  
Article
Quality Assessment of Apple and Grape Juices from Serbian and German Markets by Planar Chromatography—Chemometrics
by Đurđa Krstić, Petar Ristivojević, Filip Andrić, Dušanka Milojković-Opsenica and Gertrud E. Morlock
Molecules 2022, 27(12), 3933; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27123933 - 19 Jun 2022
Viewed by 1975
Abstract
The high consumption of plant-based foods on a global scale has increased the number of adulterations in the food industry. Along with this, analytical approaches to fraud detection need to be further developed. A nontargeted effect-directed profiling by high-performance thin-layer chromatography hyphenated with [...] Read more.
The high consumption of plant-based foods on a global scale has increased the number of adulterations in the food industry. Along with this, analytical approaches to fraud detection need to be further developed. A nontargeted effect-directed profiling by high-performance thin-layer chromatography hyphenated with five effect-directed assays (free radical scavenging assay, Aliivibrio fischeri bioassay, and acetylcholinesterase, butyrylcholinesterase, and tyrosinase inhibition assays) and multi-imaging provided additional information on the antioxidative, antimicrobial, and enzyme inhibition activities for 18 apple and 18 grape juices from markets in Serbia and Germany. Bioactive zones of interest were eluted using an elution head-based interface and further characterized by electrospray ionization high-resolution mass spectrometry. The different profiles were evaluated chemometrically, and several compounds, which were characteristic of samples from different markets located in Serbia and Germany, were identified in apple juice (such as chlorogenic acid, phloridzin, epicatechin, and caffeic acid) and grape juice (such as chlorogenic acid, epicatechin, and quercetin). The developed rapid and simple method for the quality assessment of fruit juices coming from different (geographic) markets showed clear quality differences. Thus, it could be used to learn more about quality differences, to detect fraud in fruit juice production, and to verify the authenticity of the origin. Full article
(This article belongs to the Special Issue Spectroscopic and Spectrometric Techniques for Structural Analysis)
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12 pages, 1481 KiB  
Article
Unprecedented Epimerization of an Azithromycin Analogue: Synthesis, Structure and Biological Activity of 2′-Dehydroxy-5″-Epi-Azithromycin
by Goran Kragol, Victoria A. Steadman, Zorica Marušić Ištuk, Ana Čikoš, Martina Bosnar, Dubravko Jelić, Gabrijela Ergović, Marija Trzun, Berislav Bošnjak, Ana Bokulić, Jasna Padovan, Ines Glojnarić and Vesna Eraković Haber
Molecules 2022, 27(3), 1034; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27031034 - 03 Feb 2022
Cited by 1 | Viewed by 2127
Abstract
Certain macrolide antibiotics, azithromycin included, possess anti-inflammatory properties that are considered fundamental for their efficacy in the treatment of chronic inflammatory diseases, such as diffuse pan-bronchiolitis and cystic fibrosis. In this study, we disclose a novel azithromycin analog obtained via Barton–McCombie oxidation during [...] Read more.
Certain macrolide antibiotics, azithromycin included, possess anti-inflammatory properties that are considered fundamental for their efficacy in the treatment of chronic inflammatory diseases, such as diffuse pan-bronchiolitis and cystic fibrosis. In this study, we disclose a novel azithromycin analog obtained via Barton–McCombie oxidation during which an unprecedented epimerization on the cladinose sugar occurs. Its structure was thoroughly investigated using NMR spectroscopy and compared to the natural epimer, revealing how the change in configuration of one single stereocenter (out of 16) profoundly diminished the antimicrobial activity through spatial manipulation of ribosome binding epitopes. At the same time, the anti-inflammatory properties of parent macrolide were retained, as demonstrated by inhibition of LPS- and cigarette-smoke-induced pulmonary inflammation. Not surprisingly, the compound has promising developable properties including good oral bioavailability and a half-life that supports once-daily dosing. This novel anti-inflammatory candidate has significant potential to fill the gap in existing anti-inflammatory agents and broaden treatment possibilities. Full article
(This article belongs to the Special Issue Spectroscopic and Spectrometric Techniques for Structural Analysis)
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14 pages, 2510 KiB  
Article
New Bicyclic Azalide Macrolides Obtained by Tandem Palladium Catalyzed Allylic Alkylation/Conjugated Addition Reaction
by Sulejman Alihodžić, Hana Čipčić Paljetak, Ana Čikoš and Ivaylo Jivkov Elenkov
Molecules 2022, 27(2), 432; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27020432 - 10 Jan 2022
Viewed by 2145
Abstract
Unprecedented tandem allylic alkylation/intermolecular Michael addition was used in the preparation of novel bicyclic azalides. NMR spectroscopy was used not only to unambiguously determine and characterize the structures of these unexpected products of chemical reaction but also to investigate the effect the rigid [...] Read more.
Unprecedented tandem allylic alkylation/intermolecular Michael addition was used in the preparation of novel bicyclic azalides. NMR spectroscopy was used not only to unambiguously determine and characterize the structures of these unexpected products of chemical reaction but also to investigate the effect the rigid bicyclic modification has on the conformation of the whole molecule. Thus, some of the macrolides prepared showed antibacterial activity in the range of well-known antibiotic drug azithromycin. Full article
(This article belongs to the Special Issue Spectroscopic and Spectrometric Techniques for Structural Analysis)
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10 pages, 1327 KiB  
Article
Identification and Quantification of Hydrocarbon Functional Groups in Gasoline Using 1H-NMR Spectroscopy for Property Prediction
by Abdul Gani Abdul Jameel
Molecules 2021, 26(22), 6989; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26226989 - 19 Nov 2021
Cited by 8 | Viewed by 2024
Abstract
Gasoline is one of the most important distillate fuels obtained from crude refining; it is mainly used as an automotive fuel to propel spark-ignited (SI) engines. It is a complex hydrocarbon fuel that is known to possess several hundred individual molecules of varying [...] Read more.
Gasoline is one of the most important distillate fuels obtained from crude refining; it is mainly used as an automotive fuel to propel spark-ignited (SI) engines. It is a complex hydrocarbon fuel that is known to possess several hundred individual molecules of varying sizes and chemical classes. These large numbers of individual molecules can be assembled into a finite set of molecular moieties or functional groups that can independently represent the chemical composition. Identification and quantification of groups enables the prediction of many fuel properties that otherwise may be difficult and expensive to measure experimentally. In the present work, high resolution 1H nuclear magnetic resonance (NMR) spectroscopy, an advanced structure elucidation technique, was employed for the molecular characterization of a gasoline sample in order to analyze the functional groups. The chemical composition of the gasoline sample was then expressed using six hydrocarbon functional groups, as follows: paraffinic groups (CH, CH2 and CH3), naphthenic CH-CH2 groups and aromatic C-CH groups. The obtained functional groups were then used to predict a number of fuel properties, including research octane number (RON), motor octane number (MON), derived cetane number (DCN), threshold sooting index (TSI) and yield sooting index (YSI). Full article
(This article belongs to the Special Issue Spectroscopic and Spectrometric Techniques for Structural Analysis)
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11 pages, 1531 KiB  
Article
Rapid Structure Determination of Bioactive 4″-Tetrahydrofurfuryl Macrozone Reaction Mixture Components by LC-SPE/Cryo NMR and MS
by Iva Habinovec, Ivana Mikulandra, Lucia Ema Sekula, Jana Gašperov, Saša Kazazić and Predrag Novak
Molecules 2021, 26(20), 6316; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26206316 - 19 Oct 2021
Cited by 2 | Viewed by 1857
Abstract
LC-SPE/cryo NMR and MS methodologies have been developed and employed for a rapid structure determination of 4″-tetrahydrofurfuryl macrozone reaction mixture components. Macrozones, novel conjugates of azithromycin, and thiosemicarbazones have shown very good in vitro antibacterial activities against susceptible and some resistant bacterial strains [...] Read more.
LC-SPE/cryo NMR and MS methodologies have been developed and employed for a rapid structure determination of 4″-tetrahydrofurfuryl macrozone reaction mixture components. Macrozones, novel conjugates of azithromycin, and thiosemicarbazones have shown very good in vitro antibacterial activities against susceptible and some resistant bacterial strains and are promising agents for further development. The post-column multiple trapping of the chromatographically separated reaction mixture components on the SPE cartridges increased the sensitivity and together with cryogenically cooled NMR probe made it possible to identify and structurally characterize main 4″-tetrahydrofurfuryl macrozone reaction mixture compounds including those present at very low concentration level. This approach has several advantages over a classical off-line procedure, efficiency and low solvent consumption being the two most important ones. All identified components were process-related. It has been demonstrated that two different kinds of compounds with respect to structure were identified, i.e., macrolide-related and thiosemicarbazone-related ones. This methodology can serve as a platform for reliable and effective macrolides reaction components structure profiling, serving as both isolation and identification tools. Full article
(This article belongs to the Special Issue Spectroscopic and Spectrometric Techniques for Structural Analysis)
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10 pages, 1694 KiB  
Communication
Validation of Structural Grounds for Anomalous Molecular Mobility in Ionic Liquid Glasses
by Mikhail Yu. Ivanov, Sergey A. Prikhod’ko, Olga D. Bakulina, Alexey S. Kiryutin, Nicolay Yu. Adonin and Matvey V. Fedin
Molecules 2021, 26(19), 5828; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26195828 - 26 Sep 2021
Cited by 8 | Viewed by 1637
Abstract
Ionic liquid (IL) glasses have recently drawn much interest as unusual media with unique physicochemical properties. In particular, anomalous suppression of molecular mobility in imidazolium IL glasses vs. increasing temperature was evidenced by pulse Electron Paramagnetic Resonance (EPR) spectroscopy. Although such behavior has [...] Read more.
Ionic liquid (IL) glasses have recently drawn much interest as unusual media with unique physicochemical properties. In particular, anomalous suppression of molecular mobility in imidazolium IL glasses vs. increasing temperature was evidenced by pulse Electron Paramagnetic Resonance (EPR) spectroscopy. Although such behavior has been proven to originate from dynamics of alkyl chains of IL cations, the role of electron spin relaxation induced by surrounding protons still remains unclear. In this work we synthesized two deuterated imidazolium-based ILs to reduce electron–nuclear couplings between radical probe and alkyl chains of IL, and investigated molecular mobility in these glasses. The obtained trends were found closely similar for deuterated and protonated analogs, thus excluding the relaxation-induced artifacts and reliably demonstrating structural grounds of the observed anomalies in heterogeneous IL glasses. Full article
(This article belongs to the Special Issue Spectroscopic and Spectrometric Techniques for Structural Analysis)
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Review

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28 pages, 4645 KiB  
Review
Recent Advances in Mass Spectrometry-Based Structural Elucidation Techniques
by Xin Ma
Molecules 2022, 27(19), 6466; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27196466 - 30 Sep 2022
Cited by 8 | Viewed by 3584
Abstract
Mass spectrometry (MS) has become the central technique that is extensively used for the analysis of molecular structures of unknown compounds in the gas phase. It manipulates the molecules by converting them into ions using various ionization sources. With high-resolution MS, accurate molecular [...] Read more.
Mass spectrometry (MS) has become the central technique that is extensively used for the analysis of molecular structures of unknown compounds in the gas phase. It manipulates the molecules by converting them into ions using various ionization sources. With high-resolution MS, accurate molecular weights (MW) of the intact molecular ions can be measured so that they can be assigned a molecular formula with high confidence. Furthermore, the application of tandem MS has enabled detailed structural characterization by breaking the intact molecular ions and protonated or deprotonated molecules into key fragment ions. This approach is not only used for the structural elucidation of small molecules (MW < 2000 Da), but also crucial biopolymers such as proteins and polypeptides; therefore, MS has been extensively used in multiomics studies for revealing the structures and functions of important biomolecules and their interactions with each other. The high sensitivity of MS has enabled the analysis of low-level analytes in complex matrices. It is also a versatile technique that can be coupled with separation techniques, including chromatography and ion mobility, and many other analytical instruments such as NMR. In this review, we aim to focus on the technical advances of MS-based structural elucidation methods over the past five years, and provide an overview of their applications in complex mixture analysis. We hope this review can be of interest for a wide range of audiences who may not have extensive experience in MS-based techniques. Full article
(This article belongs to the Special Issue Spectroscopic and Spectrometric Techniques for Structural Analysis)
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Other

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9 pages, 617 KiB  
Brief Report
Extraction of the Anticancer and Antimicrobial Agent, Prodigiosin, from Vibrio gazogenes PB1 and Its Identification by 1D and 2D NMR
by Dhanya Vijay, Nassra S. Alshamsi, Ziad Moussa and M. Kalim Akhtar
Molecules 2022, 27(18), 6030; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27186030 - 16 Sep 2022
Cited by 7 | Viewed by 2014
Abstract
Prodigiosin is a secondary metabolite produced in several species of bacteria. It exhibits antimicrobial and anticancer properties. Methods for the extraction and identification of prodigiosin and their related derivatives from bacterial cultures typically depend on solvent-based extractions followed by NMR spectroscopy. The estuarine [...] Read more.
Prodigiosin is a secondary metabolite produced in several species of bacteria. It exhibits antimicrobial and anticancer properties. Methods for the extraction and identification of prodigiosin and their related derivatives from bacterial cultures typically depend on solvent-based extractions followed by NMR spectroscopy. The estuarine bacterium, V. gazogenes PB1, was previously shown to produce prodigiosin. This conclusion, however, was based on analytical data obtained from ultraviolet-visible absorption spectrophotometry and infrared spectroscopy. Complete dependence on these techniques would be considered inadequate for the accurate identification of the various members of the prodiginine family of compounds, which possess very similar chemical structures and near-identical optical properties. In this study, we extracted prodigiosin from a culture of Vibrio gazogenes PB1 cultivated in minimal media, and for the first time, confirmed the synthesis of prodigiosin Vibrio gazogenes PB1 using NMR techniques. The chemical structure was validated by 1H and 13C NMR spectroscopy, and further corroborated by 2D NMR, which included 1H-1H-gDQFCOSY, 1H-13C-gHSQC, and 1H-13C-gHMBC, as well as 1H-1H-homonuclear decoupling experiments. Based on this data, previous NMR spectral assignments of prodigiosin are reaffirmed and in some cases, corrected. The findings will be particularly relevant for experimental work relating to the use of V. gazogenes PB1 as a host for the synthesis of prodigiosin. Full article
(This article belongs to the Special Issue Spectroscopic and Spectrometric Techniques for Structural Analysis)
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