1
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Payam AF, Khalil S, Chakrabarti S. Synthesis and Characterization of MOF-Derived Structures: Recent Advances and Future Perspectives. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2024:e2310348. [PMID: 38660830 DOI: 10.1002/smll.202310348] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2023] [Revised: 03/11/2024] [Indexed: 04/26/2024]
Abstract
Due to their facile tunability, metal-organic frameworks (MOFs) are employed as precursors and templates to construct advanced functional materials with unique and desired chemical, physical, mechanical, and morphological properties. By tuning MOF precursor composition and manipulating conversion processes, various MOF-derived materials commonly known as MOF derivatives can be constructed. The possibility of controlled and predictable properties makes MOF derivatives a preferred choice for numerous advanced technological applications. The innovative synthetic designs besides the plethora of interdisciplinary characterization approaches applicable to MOF derivatives provide the opportunity to perform a myriad of experiments to explore the performance and offer key insight to develop the next generation of advanced materials. Though there are many published works of literature describing various synthesis and characterization techniques of MOF derivatives, it is still not clear how the synthesis mechanism works and what are the best techniques to characterize these materials to probe their properties accurately. In this review, the recent development in synthesis techniques and mechanisms for a variety of MOF derivates such as MOF-derived metal oxides, porous carbon, composites/hybrids, and sulfides is summarized. Furthermore, the details of characterization techniques and fundamental working principles are summarized to probe the structural, mechanical, physiochemical, electrochemical, and electronic properties of MOF and MOF derivatives. The future trends and some remaining challenges in the synthesis and characterization of MOF derivatives are also discussed.
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Affiliation(s)
- Amir Farokh Payam
- Nanotechnology and Integrated Bioengineering Centre (NIBEC), School of Engineering, Ulster University, 2-24 York Street, Belfast, BT15 1AP, UK
| | - Sameh Khalil
- Nanotechnology and Integrated Bioengineering Centre (NIBEC), School of Engineering, Ulster University, 2-24 York Street, Belfast, BT15 1AP, UK
| | - Supriya Chakrabarti
- Nanotechnology and Integrated Bioengineering Centre (NIBEC), School of Engineering, Ulster University, 2-24 York Street, Belfast, BT15 1AP, UK
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2
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Daniels R, Yassin OA, Toribio JM, Gascón JA, Sotzing G. Re-Examining Cannabidiol: Conversion to Tetrahydrocannabinol Using Only Heat. Cannabis Cannabinoid Res 2024; 9:486-494. [PMID: 36516105 DOI: 10.1089/can.2022.0235] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Introduction: In the last decade, the market for Cannabidiol (CBD) has grown to become a near $2 billion dollar industry in the United States alone. This growth can be attributed to a growing social acceptance of marijuana, a more detailed understanding of many health benefits attributed to cannabinoids, and the low cost and wide availibility of hemp-derived cannabinoids. Due to the complex legal histories of marijuana and cannabinoids, the stability and safety of CBD is still an area of interest as research has been restricted globally. Conversion of CBD to its psychoactive isomers, most notably delta-9-Tetrahydrocannabinol (Δ9-THC), presents a significant safety issue for consumers and producers of CBD products. Methods: Previous studies investigating the stability of CBD have focused mainly on replicating conditions experienced during long-term storage at room temperature or lower. Here, we report the thermal stability of CBD at 175°C. Dynamic 1H-NMR experiments and computational electronic structure calculations were used to characterize possible reaction paths from CBD to THC. Results: After 30 minutes of heating, Δ9-THC was produced in detectable amounts in aerobic and anaerobic conditions without an acid catalyst. Conclusions: Our findings support an energetically feasible reaction route that is favorable due to both an increase in phenol acidity at high temperatures and the presence of intramolecular OH-π hydrogen bonding.
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Affiliation(s)
- Robert Daniels
- Department of Chemistry, University of Connecticut, Storrs, Connecticut, USA
| | - Omer A Yassin
- Department of Chemistry, University of Connecticut, Storrs, Connecticut, USA
| | - John M Toribio
- Department of Chemistry, University of Connecticut, Storrs, Connecticut, USA
| | - José A Gascón
- Department of Chemistry, University of Connecticut, Storrs, Connecticut, USA
| | - Gregory Sotzing
- Department of Chemistry, University of Connecticut, Storrs, Connecticut, USA
- Polymer Program, University of Connecticut, Storrs, Connecticut, USA
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3
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Morrelli D, Maitra S, Krishnan VV. To flame-seal or not to flame-seal NMR tubes: The role of liquid-vapor equilibria on the accuracy of variable temperature experiments. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2024; 62:19-27. [PMID: 37994184 DOI: 10.1002/mrc.5411] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2023] [Revised: 10/23/2023] [Accepted: 10/24/2023] [Indexed: 11/24/2023]
Abstract
In NMR experiments, it is crucial to control the temperature of the sample, especially when measuring kinetic parameters. Usually, it takes 2 to 5 min for the temperature of the sample inside the NMR probe to stabilize at a fixed value set for the experiment. However, the NMR sample tubes are flame-sealed in some cases, such as when working with volatile solvents, atmosphere-sensitive samples, or calibration samples for long-term use. When these samples are placed inside the NMR probe, the spectrometer controls the lower portion (liquid phase) of the NMR sample tube with a gas flow at a fixed temperature, while the upper portion (vapor) is at ambient temperature. This probe design creates a unique temperature gradient across the sample, leading to vapor pressure build-up, particularly inside a sealed NMR tube. By analyzing the temperature-dependent spectral line shape changes of a chemical exchange process, we report that under standard experimental conditions, the sample temperature can take up to 2 to 3 h (instead of minutes) to stabilize. The time scale of the liquid-vapor equilibrium process is much slower, with a half-life exceeding 35 min, in contrast to the 2-min duration required to obtain each spectrum. This phenomenon is exclusively due to the liquid-vapor equilibrium process of the flame-sealed NMR tube and is not observable otherwise.
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Affiliation(s)
- Derek Morrelli
- Department of Chemistry and Biochemistry, California State University Fresno, Fresno, California, USA
- Department of Chemistry, Southwestern Oregon Community College, Coos Bay, Oregon, USA
| | - Santanu Maitra
- Department of Chemistry and Biochemistry, California State University Fresno, Fresno, California, USA
| | - V V Krishnan
- Department of Chemistry and Biochemistry, California State University Fresno, Fresno, California, USA
- Department of Pathology and Molecular Medicine, University of California Davis School of Medicine, Sacramento, California, USA
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Knight AL, Widjaja V, Lisi GP. Temperature as a modulator of allosteric motions and crosstalk in mesophilic and thermophilic enzymes. Front Mol Biosci 2023; 10:1281062. [PMID: 37877120 PMCID: PMC10591084 DOI: 10.3389/fmolb.2023.1281062] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Accepted: 09/27/2023] [Indexed: 10/26/2023] Open
Abstract
Mesophilic and thermophilic enzyme counterparts are often studied to understand how proteins function under harsh conditions. To function well outside of standard temperature ranges, thermophiles often tightly regulate their structural ensemble through intra-protein communication (via allostery) and altered interactions with ligands. It has also become apparent in recent years that the enhancement or diminution of allosteric crosstalk can be temperature-dependent and distinguish thermophilic enzymes from their mesophilic paralogs. Since most studies of allostery utilize chemical modifications from pH, mutations, or ligands, the impact of temperature on allosteric function is comparatively understudied. Here, we discuss the biophysical methods, as well as critical case studies, that dissect temperature-dependent function of mesophilic-thermophilic enzyme pairs and their allosteric regulation across a range of temperatures.
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Affiliation(s)
| | | | - George P. Lisi
- Department of Molecular Biology, Cell Biology and Biochemistry, Brown University, Providence, RI, United States
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5
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Ramírez-García JC, Vázquez-Ramírez R, Patiño ME, Aguirre-Cabrera C, Carranza V, Álvarez CMG. Theoretical study of Gibbs free energy and NMR chemical shifts, of the effect of methyl substituents on the isomers of (E)-1-(α,Ꞵ-Dimethylbenzyliden)-2,2-diphenylhydrazine. AN ACAD BRAS CIENC 2023; 95:e20220766. [PMID: 37466538 DOI: 10.1590/0001-3765202320220766] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2022] [Accepted: 02/27/2023] [Indexed: 07/20/2023] Open
Abstract
A theoretical analysis of free Gibbs Energy and NMR 1H 13C chemical shifts of the effect of introduce methyl groups on diphenyl rings, to produce different isomers of (E)-1-(α,Ꞵ-dimethylbenzylidene)-2,2-diphenylhydrazine, is presented. IR vibrational frequencies, Mulliken charges, molecular electrostatic potential (MEP), Gibbs free energy (G) and 1H- and 13C-NMR chemical shifts were obtained by theoretical calculations. In this analysis it was found that the position of the methyl group affects the values of the 1H- and 13C-NMR chemical shifts and the ∆G and ∆H thermodynamic properties of formation and reaction, these properties vary with the same trend, for the isomers studied. Gibbs free energy calculations show that the theoretical (E)-1-(3,4-Dimethylbenzylidene)-2,2-diphenylhydrazine isomer is the most stable, which explains the success of the experimental synthesis of this compound among the other isomers. For this molecule, the C of the HC=N group is the most nucleophilic and the H is the least acidic. The 1H-NMR chemical shifts of protons show a strong correlation with the C=N distance. It was also observed that methyl affects the ν(C=N) frequencies, the C=N distance increases when the inductive effect of the methyl groups is in the structure.
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Affiliation(s)
- Juan Carlos Ramírez-García
- Facultad de Ciencias Químicas, Benemérita Universidad Autónoma de Puebla, Av. 14 Sur Col. San Manuel, Ciudad Universitaria, Puebla, C.P. 72592 México
| | - Ricardo Vázquez-Ramírez
- Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, D.F. 04510, México
| | - María Eugenia Patiño
- Centro de Química, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, Av. 14 Sur Col. Jardines de San Manuel, Ciudad Universitaria, Puebla, P.O. Box 1067, C.P. 72001 México
| | - Carla Aguirre-Cabrera
- Facultad de Ciencias Químicas, Benemérita Universidad Autónoma de Puebla, Av. 14 Sur Col. San Manuel, Ciudad Universitaria, Puebla, C.P. 72592 México
| | - Vladimir Carranza
- Centro de Química, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, Av. 14 Sur Col. Jardines de San Manuel, Ciudad Universitaria, Puebla, P.O. Box 1067, C.P. 72001 México
| | - Carmen Mária González Álvarez
- Facultad de Ciencias Químicas, Benemérita Universidad Autónoma de Puebla, Av. 14 Sur Col. San Manuel, Ciudad Universitaria, Puebla, C.P. 72592 México
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6
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Gieroba B, Kalisz G, Krysa M, Khalavka M, Przekora A. Application of Vibrational Spectroscopic Techniques in the Study of the Natural Polysaccharides and Their Cross-Linking Process. Int J Mol Sci 2023; 24:ijms24032630. [PMID: 36768949 PMCID: PMC9916414 DOI: 10.3390/ijms24032630] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2022] [Revised: 01/24/2023] [Accepted: 01/27/2023] [Indexed: 02/03/2023] Open
Abstract
Polysaccharides are one of the most abundant natural polymers and their molecular structure influences many crucial characteristics-inter alia hydrophobicity, mechanical, and physicochemical properties. Vibrational spectroscopic techniques, such as infrared (IR) and Raman spectroscopies are excellent tools to study their arrangement during polymerization and cross-linking processes. This review paper summarizes the application of the above-mentioned analytical methods to track the structure of natural polysaccharides, such as cellulose, hemicellulose, glucan, starch, chitosan, dextran, and their derivatives, which affects their industrial and medical use.
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Affiliation(s)
- Barbara Gieroba
- Independent Unit of Spectroscopy and Chemical Imaging, Medical University of Lublin, Chodźki 4a Street, 20-093 Lublin, Poland
- Correspondence:
| | - Grzegorz Kalisz
- Independent Unit of Spectroscopy and Chemical Imaging, Medical University of Lublin, Chodźki 4a Street, 20-093 Lublin, Poland
| | - Mikolaj Krysa
- Independent Unit of Spectroscopy and Chemical Imaging, Medical University of Lublin, Chodźki 4a Street, 20-093 Lublin, Poland
| | - Maryna Khalavka
- Independent Unit of Spectroscopy and Chemical Imaging, Medical University of Lublin, Chodźki 4a Street, 20-093 Lublin, Poland
- Department of Industrial Technology of Drugs, National University of Pharmacy, Pushkins’ka 63 Street, 61002 Kharkiv, Ukraine
| | - Agata Przekora
- Independent Unit of Tissue Engineering and Regenerative Medicine, Medical University of Lublin, Chodźki 1 Street, 20-093 Lublin, Poland
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Hand AT, Lamb AC, Richmond MG, Wang X, Steren CA, Xue ZL. Syntheses of Group 5 Amide Amidinates and Their Reactions with Water: Different Reactivities of Nb(V) and Ta(V) Complexes. Inorg Chem 2022; 61:19075-19087. [DOI: 10.1021/acs.inorgchem.2c02365] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Affiliation(s)
- Adam T. Hand
- Department of Chemistry, The University of Tennessee, Knoxville, Tennessee 37996, United States
| | - Adam C. Lamb
- Department of Chemistry, The University of Tennessee, Knoxville, Tennessee 37996, United States
| | - Michael G. Richmond
- Department of Chemistry, The University of North Texas, Denton, Texas 76203, United States
| | - Xiaoping Wang
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Carlos A. Steren
- Department of Chemistry, The University of Tennessee, Knoxville, Tennessee 37996, United States
| | - Zi-Ling Xue
- Department of Chemistry, The University of Tennessee, Knoxville, Tennessee 37996, United States
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8
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Oluwafemi KA, Klein R, Lobb KA, Tshiwawa T, Isaacs M, Hoppe HC, Kaye PT. Synthesis and Conformational Studies of 5-bromo-1-[(N-substituted-carbamoyl)methyl]-7-azabenzimidazoles. J Mol Struct 2022. [DOI: 10.1016/j.molstruc.2022.133811] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
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9
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Westwood MN, Johnson CC, Oyler NA, Meints GA. Kinetics and thermodynamics of BI-BII interconversion altered by T:G mismatches in DNA. Biophys J 2022; 121:1691-1703. [PMID: 35367235 PMCID: PMC9117933 DOI: 10.1016/j.bpj.2022.03.031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2021] [Revised: 10/26/2021] [Accepted: 03/28/2022] [Indexed: 11/19/2022] Open
Abstract
T:G mismatches in DNA result in humans primarily from deamination of methylated CpG sites. They are repaired by redundant systems, such as thymine DNA glycosylase (TDG) and methyl-binding domain enzyme (MBD4), and maintenance of these sites has been implicated in epigenetic processes. The process by which these enzymes identify a canonical DNA base in the incorrect basepairing context remains a mystery. However, the conserved contacts of the repair enzymes with the DNA backbone suggests a role for protein-phosphate interaction in the recognition and repair processes. We have used 31P NMR to investigate the energetics of DNA backbone BI-BII interconversion, and for this work have focused on alterations to the activation barriers to interconversion and the effect of a mismatch compared with canonical DNA. We have found that alterations to the ΔG of interconversion for T:G basepairs are remarkably similar to U:G basepairs in the form of stepwise differences in ΔG of 1-2 kcal/mol greater than equivalent steps in unmodified DNA, suggesting a universality of this result for TDG substrates. Likewise, we see perturbations to the free energy (∼1 kcal/mol) and enthalpy (2-5 kcal/mol) of activation for the BI-BII interconversion localized to the phosphates flanking the mismatch. Overall our results strongly suggest that the perturbed backbone energetics in T:G basepairs play a significant role in the recognition process of DNA repair enzymes.
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Affiliation(s)
- M N Westwood
- Department of Chemistry and Biochemistry, Missouri State University, Springfield, Missouri
| | - C C Johnson
- Department of Chemistry and Biochemistry, Missouri State University, Springfield, Missouri
| | - Nathan A Oyler
- Department of Chemistry, University of Missouri-Kansas City, Kansas City, Missouri
| | - Gary A Meints
- Department of Chemistry and Biochemistry, Missouri State University, Springfield, Missouri.
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10
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Morrelli D, Guerra JG, Kumar P, Bajwa B, Krishnan V, Maitra S. Role of solvent dielectric constant on the enthalpy-entropy compensation in the hindered amide bond rotation. Chem Phys Lett 2022. [DOI: 10.1016/j.cplett.2022.139412] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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11
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Emwas AH, Szczepski K, Poulson BG, Chandra K, McKay RT, Dhahri M, Alahmari F, Jaremko L, Lachowicz JI, Jaremko M. NMR as a "Gold Standard" Method in Drug Design and Discovery. Molecules 2020; 25:E4597. [PMID: 33050240 PMCID: PMC7594251 DOI: 10.3390/molecules25204597] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2020] [Revised: 10/05/2020] [Accepted: 10/06/2020] [Indexed: 12/11/2022] Open
Abstract
Studying disease models at the molecular level is vital for drug development in order to improve treatment and prevent a wide range of human pathologies. Microbial infections are still a major challenge because pathogens rapidly and continually evolve developing drug resistance. Cancer cells also change genetically, and current therapeutic techniques may be (or may become) ineffective in many cases. The pathology of many neurological diseases remains an enigma, and the exact etiology and underlying mechanisms are still largely unknown. Viral infections spread and develop much more quickly than does the corresponding research needed to prevent and combat these infections; the present and most relevant outbreak of SARS-CoV-2, which originated in Wuhan, China, illustrates the critical and immediate need to improve drug design and development techniques. Modern day drug discovery is a time-consuming, expensive process. Each new drug takes in excess of 10 years to develop and costs on average more than a billion US dollars. This demonstrates the need of a complete redesign or novel strategies. Nuclear Magnetic Resonance (NMR) has played a critical role in drug discovery ever since its introduction several decades ago. In just three decades, NMR has become a "gold standard" platform technology in medical and pharmacology studies. In this review, we present the major applications of NMR spectroscopy in medical drug discovery and development. The basic concepts, theories, and applications of the most commonly used NMR techniques are presented. We also summarize the advantages and limitations of the primary NMR methods in drug development.
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Affiliation(s)
- Abdul-Hamid Emwas
- Core Labs, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
| | - Kacper Szczepski
- Biological and Environmental Sciences & Engineering Division (BESE), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia; (K.S.); (B.G.P.); (K.C.); (L.J.)
| | - Benjamin Gabriel Poulson
- Biological and Environmental Sciences & Engineering Division (BESE), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia; (K.S.); (B.G.P.); (K.C.); (L.J.)
| | - Kousik Chandra
- Biological and Environmental Sciences & Engineering Division (BESE), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia; (K.S.); (B.G.P.); (K.C.); (L.J.)
| | - Ryan T. McKay
- Department of Chemistry, University of Alberta, Edmonton, AB T6G 2W2, Canada;
| | - Manel Dhahri
- Biology Department, Faculty of Science, Taibah University, Yanbu El-Bahr 46423, Saudi Arabia;
| | - Fatimah Alahmari
- Nanomedicine Department, Institute for Research and Medical, Consultations (IRMC), Imam Abdulrahman Bin Faisal University (IAU), Dammam 31441, Saudi Arabia;
| | - Lukasz Jaremko
- Biological and Environmental Sciences & Engineering Division (BESE), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia; (K.S.); (B.G.P.); (K.C.); (L.J.)
| | - Joanna Izabela Lachowicz
- Department of Medical Sciences and Public Health, Università di Cagliari, Cittadella Universitaria, 09042 Monserrato, Italy
| | - Mariusz Jaremko
- Biological and Environmental Sciences & Engineering Division (BESE), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia; (K.S.); (B.G.P.); (K.C.); (L.J.)
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12
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Zenkevich IG, Lukina VM. Characteristic Features of the Gas Chromatographic Separation of Tautomers of Ethyl Acetoacetate. RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A 2020. [DOI: 10.1134/s0036024420060357] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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13
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Babailov SP, Zapolotsky EN. A new approach to determining the structure of lanthanide complexes in solution according to the Curie-spin contribution to the paramagnetic spin-spin relaxation rate enhancements: Ho-DOTA. Polyhedron 2020. [DOI: 10.1016/j.poly.2020.114487] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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14
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Guerra J, Bajwa B, Kumar P, Vazquez S, Krishnan VV, Maitra S. Validation of Enthalpy-Entropy Compensation Mechanism in Partial Amide Bond Rotation. ACS OMEGA 2020; 5:9348-9355. [PMID: 32363286 PMCID: PMC7191833 DOI: 10.1021/acsomega.0c00332] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/23/2020] [Accepted: 03/27/2020] [Indexed: 06/11/2023]
Abstract
The concept of enthalpy-entropy compensation (EEC) is one of the highly debated areas of thermodynamics. The conformational change due to restricted double-bond rotation shows a classic two-site chemical exchange phenomenon and has been extensively studied. Fifty-four analogs of N,N-diethyl-m-toluamide (DEET) as a model system were synthesized to study the thermodynamics of the partial amide bond character using nuclear magnetic resonance (NMR) spectroscopy. Line-shape analysis as a function of temperature is used to estimate the chemical exchange. Eyring analysis was then used to convert the chemical exchange rates to determine the transition state enthalpy and entropy of the molecules. The experimental design follows selective variations that perturb one aspect of the molecular system and its influence on the observed thermodynamic effect. The results of the study demonstrate that amide bond resonance in analogs of DEET follows an EEC mechanism. Simple modifications made to DEET's structural motif alter both the enthalpy and entropy of the system and were limited overall to a temperature compensation factor, T β = 292.20 K, 95% CI [290.66, 293.73]. We suggest EEC as a model to describe the kinetic compensation seen in chemical exchange phenomena in analogs of DEET.
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Affiliation(s)
- Jacob Guerra
- Department
of Chemistry, California State University, Fresno, California 93740, United States
| | - Bhvandip Bajwa
- Department
of Chemistry, California State University, Fresno, California 93740, United States
| | - Prarthana Kumar
- Department
of Chemistry, California State University, Fresno, California 93740, United States
| | - Salvador Vazquez
- Department
of Chemistry, California State University, Fresno, California 93740, United States
| | - Viswanathan V. Krishnan
- Department
of Chemistry, California State University, Fresno, California 93740, United States
- Department
of Pathology & Laboratory
Medicine, University of California Davis, Davis, California 95616, United States
| | - Santanu Maitra
- Department
of Chemistry, California State University, Fresno, California 93740, United States
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