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Exclusive Feature Papers in Analytical Chemistry
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Exclusive Feature Papers in Analytical Chemistry

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

Deadline for manuscript submissions: 31 August 2025 | Viewed by 521

Special Issue Editors

Dr. João Pinto da Costa

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Guest Editor
Centre for Environmental and Marine Studies (CESAM) & Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal
Interests: analytical chemistry; nanoplastics; microplastics; bioremediation
Special Issues, Collections and Topics in MDPI journals
Dr. Teresa A. P. Rocha-Santos

grade E-Mail Website
Guest Editor
Centre for Environmental and Marine Studies (CESAM) & Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal
Interests: development of analytical methodologies fit for purpose; (bio)sensors; plastics; microplastics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue aims to highlight cutting-edge research and innovative advancements in the field of analytical chemistry. Featuring a diverse collection of articles from leading experts, this Issue will cover the latest methodologies, techniques, and applications that push the boundaries of analytical science. They address challenges in diverse areas such as environmental analysis, food safety studies, material characterization, and pharmaceutical analysis. Topics include but are not limited to the following:

  • Novel analytical methods and instrumentation;
  • Advances in chromatography, spectroscopy, and mass spectrometry;
  • Applications of analytical chemistry in environmental, pharmaceutical, and industrial contexts;
  • Emerging trends in data analysis and chemical informatics;
  • Green and sustainable analytical practices.

This Special Issue provides a valuable resource for analytical chemists, researchers in various scientific fields, and those seeking to stay abreast of the latest developments. Researchers and practitioners are invited to contribute their most impactful work, offering insights into the dynamic and evolving landscape of analytical chemistry.

Dr. João Pinto da Costa
Dr. Teresa A. P. Rocha-Santos
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

  • analytical chemistry
  • instrumentation
  • environment and food
  • pharmaceutical industry
  • green chemistry

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  • e-Book format: Special Issues with more than 10 articles can be published as dedicated e-books, ensuring wide and rapid dissemination.

Further information on MDPI's Special Issue policies can be found here.

Published Papers (2 papers)

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Research

13 pages, 5633 KiB  
Article
Mechanistic Study of L-Rhamnose Monohydrate Dehydration Using Terahertz Spectroscopy and Density Functional Theory
by Bingxin Yan, Zeyu Hou, Yuhan Zhao, Bo Su, Cunlin Zhang and Kai Li
Molecules 2025, 30(5), 1189; https://doi.org/10.3390/molecules30051189 - 6 Mar 2025
Viewed by 160
Abstract
L-rhamnose has recently gained attention for its potential to enhance vaccine antigenicity. To optimize its use as a vaccine adjuvant, it is important to understand the dehydration behavior of L-rhamnose monohydrate, which plays a critical role in modifying its physicochemical properties. This study [...] Read more.
L-rhamnose has recently gained attention for its potential to enhance vaccine antigenicity. To optimize its use as a vaccine adjuvant, it is important to understand the dehydration behavior of L-rhamnose monohydrate, which plays a critical role in modifying its physicochemical properties. This study investigated the spectroscopic characteristics of L-rhamnose and its monohydrate using terahertz time-domain spectroscopy (THz-TDS), Raman spectroscopy, and powder X-ray diffraction (PXRD). The results indicate that THz-TDS can more effectively distinguish the spectral features of these two compounds and can be used to reflect the structural changes in L-rhamnose monohydrate before and after dehydration. THz spectral data show that dehydration of L-rhamnose occurs at 100 °C, and continuous heating at 100 °C can complete the dehydration process within 6 min. Density functional theory (DFT) calculations revealed that water molecule vibrations significantly affect the THz absorption peaks. These findings indicate that removing water during dehydration causes substantial changes in molecular structure and dynamics. Overall, this study highlights the value of combining THz-TDS with DFT calculations to investigate the structures of carbohydrates and their hydrates, providing an accurate method for understanding the dehydration process and molecular interactions in hydrated systems. This approach holds significant importance for the development of effective vaccine adjuvants. Full article
(This article belongs to the Special Issue Exclusive Feature Papers in Analytical Chemistry)
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Figure 1

Figure 1
<p>Molecular structure diagrams of L-rhamnose (<b>a</b>) and rhamnose monohydrate (<b>b</b>), and unit cell diagrams of L-rhamnose (<b>c</b>) and L-rhamnose monohydrate (<b>d</b>). The white, gray, and red spheres represent hydrogen (H) atoms, carbon (C) atoms, and oxygen (O) atoms, respectively. ABC represents the unit cell parameters.</p> Full article ">Figure 2
<p>THz experimental absorption spectra and error bars of L-rhamnose (<b>a</b>) and L-rhamnose monohydrate (<b>b</b>) at 25 °C.</p> Full article ">Figure 3
<p>Comparison between experimental and calculated Raman spectra of L-rhamnose (<b>a</b>) and L-rhamnose monohydrate (<b>b</b>). Spectra are vertically offset for clarity.</p> Full article ">Figure 4
<p>Comparison of PXRD experiment and calculated diffraction patterns of L-rhamnose (<b>a</b>) and L-rhamnose monohydrate (<b>b</b>) (with vertical spectral shift for clarity).</p> Full article ">Figure 5
<p>(<b>a</b>) THz spectra of L-rhamnose monohydrate at different temperatures (spectra are vertically offset for clarity); (<b>b</b>) TGA curve of L-rhamnose monohydrate.</p> Full article ">Figure 6
<p>THz spectra of L-rhamnose monohydrate at different times at 100 °C (for clarity, the spectra are vertically shifted).</p> Full article ">Figure 7
<p>Experimental (<b>a</b>) and calculated (<b>b</b>) THz spectra, and vibrational modes of L-rhamnose at 2.13 THz (<b>c</b>) and 2.44 THz (<b>d</b>). ABC represents the unit cell parameters, and the green arrow indicates the vibrational direction at the corresponding THz frequency.</p> Full article ">Figure 8
<p>Experimental (<b>a</b>) and calculated (<b>b</b>) THz spectra, and vibrational modes of L-rhamnose monohydrate at 2.12 THz (<b>c</b>), 2.38 THz (<b>d</b>), and 2.68 THz (<b>e</b>). ABC represents the unit cell parameters, and the green arrow indicates the vibrational direction at the corresponding THz frequency.</p> Full article ">Figure 9
<p>Schematic diagram of THz-TDS system optical path.</p> Full article ">
13 pages, 1755 KiB  
Article
Determination of the Enantiomerization Barrier of Midazolam in Aqueous Conditions by Electronic Circular Dichroism and Dynamic Enantioselective HPLC/UHPLC
by Francesca Romana Mammone, Daniele Sadutto, Eleonora Antoniella, Marco Pierini and Roberto Cirilli
Molecules 2025, 30(5), 1108; https://doi.org/10.3390/molecules30051108 - 28 Feb 2025
Viewed by 119
Abstract
Midazolam is a benzodiazepine that is utilized for the induction of anesthesia and the facilitation of procedural sedation. Despite the absence of stereogenic centers, the non-planar seven-membered ring devoid of reflection symmetry elements confers planar stereogenicity to the molecule. Due to the rapid [...] Read more.
Midazolam is a benzodiazepine that is utilized for the induction of anesthesia and the facilitation of procedural sedation. Despite the absence of stereogenic centers, the non-planar seven-membered ring devoid of reflection symmetry elements confers planar stereogenicity to the molecule. Due to the rapid conformational inversion of the Rp and Sp enantiomers, which occurs via a simple ring flip, high-performance liquid chromatography (HPLC) enantiomeric separation is restricted to sub-room temperature conditions. In this study, the energy barriers for the racemization of midazolam at five distinct temperatures and in acetonitrile/water mixtures were determined by monitoring the decay of the circular dichroism signal at a specific wavelength over time. The kinetic and thermodynamic data obtained were compared with those determined by dynamic enantioselective high-performance liquid chromatography using the Chiralpak IG-3 chiral stationary phase, which contains the amylose tris(3-chloro-5-methylphenylcarbamate) as the selector. The temperature-dependent dynamic HPLC of midazolam was carried out at the same temperatures and with the same aqueous mixtures used in parallel kinetic off-column experiments. To simulate dynamic chromatographic profiles, a lab-made computer program based on a stochastic model was utilized. The results indicated that the moderate influence of the stationary phase resulted in a slight increase in the activation barriers, which was more pronounced as the time spent in the column increased. This phenomenon was found to be mitigated when switching from a 250 mm × 4.6 mm, 3 µm, Chiralpak IG-3 column to a 50 mm × 4.6 mm, 1.6 µm, Chiralpak IG-U UHPLC column. The outcomes obtained under UHPLC conditions were found to be more closely aligned with those obtained through the ECD technique, with a discrepancy of only 0.1 kcal/mol or less, indicating a high degree of concordance between the two methods. Full article
(This article belongs to the Special Issue Exclusive Feature Papers in Analytical Chemistry)
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Figure 1

Figure 1
<p>Structure of midazolam (<b>left</b>) and polytube model of the interconversion process of its conformational enantiomers (<b>right</b>).</p> Full article ">Figure 2
<p>Plots of the retention factors (<span class="html-italic">k</span><sub>1</sub> and <span class="html-italic">k</span><sub>2</sub>) of the enantiomers of midazolam as a function of the water content in the acetonitrile–aqueous mode. Chromatographic conditions: column, Chiralpak IG-3 (250 mm × 4.6 mm, 3 μm); temperature, 5 °C; flow rate, 1.0 mL/min (from 5 to 30% of water in acetonitrile) and 0.7 mL/min (40% and of 50% water in acetonitrile); detection, UV at 254 nm.</p> Full article ">Figure 3
<p>Off-column racemization of midazolam monitored by enantioselective ECD methods. (<b>a</b>) HPLC enantioseparation of 0.33 mg of midazolam. Chromatographic conditions: column, Chiralpak IG-3 (250 mm × 4.6 mm, 3 μm); temperature, 5 °C; mobile phase, acetonitrile/water 80:20 (<span class="html-italic">v</span>/<span class="html-italic">v</span>); flow rate, 1.3 mL/min; detection, UV at 280 nm. (<b>b</b>) ECD spectrum of the first eluted enantiomer collected under the same conditions as in (<b>a</b>) and recorded at 5 °C; (<b>c</b>) ECD signal decay at 264 nm of the first eluted enantiomer monitored at 5–25 °C.</p> Full article ">Figure 4
<p>An illustrative example of dynamic enantioselective HPLC determinations pertinent to the enantiomerization process of midazolam from 5 to 25 °C. The simulated dynamic chromatograms (gray traces) are superimposed on the corresponding experimental ones (colored traces). Chromatographic conditions: column, Chiralpak IG-3 (250 mm × 4.6 mm, 3 μm); mobile phase, acetonitrile/water 80:20 (<span class="html-italic">v</span>/<span class="html-italic">v</span>); flow rate, 1 mL/min; detection, UV at 254 nm.</p> Full article ">Figure 5
<p>UHPLC traces for the enantioseparation of midazolam from 5 to 37 °C. Chromatographic conditions: column, Chiralpak IG-U (50 mm × 3.0 mm, 1.6 μm); mobile phase, acetonitrile/water 90:10 (<span class="html-italic">v</span>/<span class="html-italic">v</span>); flow rate, 1.5 mL/min; detection, UV at 254 nm.</p> Full article ">
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