Search

The paper presents the results and interpretation of theoretical calculations for the progesterone-β-cyclodextrin (P@β-CD; G4MP2) and progesterone-β-cyclodextrin-β-cyclodextrin (P@β-CD-β-CD; G2) systems. The geometry of the progesterone molecule was optimized on basis of the DFT theory using the B3LYP, PBE1PBE and M06-2X functionals, for selected Pople basis sets [6-31G, 6-31++G, 6-31++G(d,p), 6-311G, 6-311++G, 6-311++G(d,p)] and the Dunning basis set (aug-cc-pVDZ). Presented results of theoretical calculations provide insight into the mechanism of formation of supramolecular systems of progesterone and β-cyclodextrin, allowing us to understand the impact of differences in the polarizability of specific fragments of the "guest" molecule, through the analysis of the Mulliken population distribution, on the tendency for equilibrium inclusion by "host" molecules characterized by selective affinity towards hydrophilic and hydrophobic molecular systems. The comparison of model structures of "guest-host" systems with 1:1 and 1:2 stoichiometry allows us to assess the contribution of a given type of non-covalent interactions (hydrogen bonds, van der Waals interactions, London dispersion forces) in the formation of supramolecular complexes. Due to the complexity of the real research object, including interactions between large molecules in solution, in this work it was decided to choose an approximation that reflects only the key effects. The results presented in this paper constitute a starting point for both theoretical research on analogous supramolecular systems based on β-cyclodextrin derivatives, as well as instrumental studies (NMR, FT-IR, HPLC) of preparations of real inclusion complexes. The approach adopted now can contribute to a better understanding of the phenomenon used in the development of water purification technologies., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Jakub reports equipment, drugs, or supplies was provided by PL-Grid Consortium. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

This paper discusses the state of advancement in the development of spectroscopic methods based on the use of mid (proper) infrared radiation in the context of applications in various fields of science and technology. The authors drew attention to the most important solutions specific to both spectroscopy itself (ATR technique) and chemometric data processing tools (PCA and PLS models). The objective of the current paper is to collect and consistently present information on various aspects of FT-IR spectroscopy, which is not only a well-known and well-established method but is also continuously developing. The innovative aspect of the current review is to show FT-IR's great versatility that allows its applications to solve and explain issues from both the scientific domain (e.g., hydrogen bonds) and practical ones (e.g., technological processes, medicine, environmental protection, and food analysis). Particular attention was paid to the issue of hydrogen bonds as key non-covalent interactions, conditioning the existence of living matter and determining the number of physicochemical properties of various materials. Since the role of FT-IR spectroscopy in the field of hydrogen bond research has great significance, a historical outline of the most important qualitative and quantitative hydrogen bond theories is provided. In addition, research on selected unconventional spectral effects resulting from the substitution of protons with deuterons in hydrogen bridges is presented. The state-of-the-art and originality of the current review are that it presents a combination of uses of FT-IR spectroscopy to explain the way molecules vibrate and the effects of those vibrations on macroscopic properties, hence practical applications of given substances.

Herein, the infrared spectroscopic properties of molecular succinic acid crystals (SA) and their four isotopic analogs [C 2 H 4 (COOH) 2 , h 6 -SA; C 2 H 4 (COOD) 2 , d 2 -SA; C 2 D 4 (COOH) 2 , d 4 -SA; C 2 D 4 (COOD) 2 , d 6 -SA] are reported. The correlation between the structure of succinic acid molecules and their corresponding hydrogen bond energies is elucidated. The effects related to the isotopic dilution as well as the changes in the spectrum recording temperature on the fine structures of the v O-H and v O-D bands are interpreted. The infrared spectral anomalies detected in the spectra of isotopically neat succinic nanocrystal acids are confirmed by theoretical calculations using density functional theory (DFT). According to previous spectroscopic studies of succinic acid and those carried out for α,ω-dicarboxylic acids, a decent agreement between the experimental results and the theoretical DFT simulations is obtained. Moreover, the spectra of single crystals of the h 6 and d 4 succinic acid variants prove that the vibrational coupling mechanism between the (COOH) 2 cycles is rigorously convergent to that detected in the spectra of aromatic carboxylic acids, suggesting thereby that the promotion of symmetry-forbidden high stretching IR transitions plays a crucial role. Furthermore, the obtained experimental results reveal that the succinic acid shows a spectral behavior significantly different from that characteristic of hydrogen associations of other acids of homologous series, such as the glutaric, adipic, malonic, and pimelic acid crystals. The results obtained herein shed light on the way to explore the revealed structure of isotopic derivatives of succinic acid crystals and may prove to be useful results for understanding the nature of unconventional interactions as well as the macroscopic energy effects directing the development of hydrogen associations.

The paper explains the relationship between the energy of hydrogen bonds and the distance between associated carboxyl groups of malonic acid (MA) molecules by means of infrared spectroscopic studies of crystals of its four isotopic varieties [CH 2 (COOH) 2 , h 4 -MA; CH 2 (COOD) 2 , d 2 c -MA; CD 2 (COOH) 2 , d 2 m -MA; CD 2 (COOD) 2 , d 4 -MA]. The effects associated with impact on the isotopic dilution and changes in the temperature of spectrum registration on the fine structures of the ν O-H and ν O-D bands were analyzed. MA molecular crystals are characterized by a tendency to spontaneous H/D isotopic exchange both within centrosymmetric hydrogen bond cycles and methylene groups. The mono- and polycrystalline spectra obtained in the infrared range of isotopically neat and isotopically diluted by deuterons do not indicate the occurrence of anomalous temperature evolution in the course of lowering their registration temperature to 77 K. Theoretical calculations did not give clear confirmation of the nature of the phenomena analyzed., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

This paper deals with the experimental and theoretical studies of abnormal properties of terephthalic acid (TAC) and phthalic acid (PAC) crystals manifested in the H/D isotopic exchange. The widely utilized deuteration routine appeared to be insufficiently effective in the case of the h 6 -TAC isotopomer. In the case of the d 4 -TAC derivative the isotopic exchange process occurred noticeably more effectively. In contrast, both isotopomers of PAC, h 6 and d 4 , appeared much more susceptible for deuteration. A theoretical model was elaborated describing "long-distance" dynamical co-operative interactions involving hydrogen bonds in TAC and PAC crystals. The model assumes extremely strong dynamical co-operative interactions of hydrogen bonds from the adjacent (COOH) 2 cycles. This leads to an additional stabilization of h 6 -TAC molecular chains. The interaction energies affect the chemical equilibrium of the H/D isotopic exchange. The model predicts a differentiated influence of the H and D atoms linked to the aromatic rings on to the process. In this approach the totally-symmetric CH bond stretching vibrations and the proton stretching totally symmetric vibrations couple with the π-electronic motions. It was also shown that identical hydrogen isotope atoms, H or D, in whole TAC molecules, noticeably enlarge the energy of the dynamical co-operative interactions in the crystals, in contrast to the case of different hydrogen isotopes present in the carboxyl groups and linked to the aromatic rings. The "long-distance" dynamical co-operative interactions in PAC crystals were found of a minor importance due to the electronic properties of PAC molecules., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The spectral properties of four different crystalline succinic acid (HOOC-(CH2)2-COOH) (SAC) isotopomer systems, h6, d2, d4 and d6, were examined by means of the IR spectroscopy in polarized light aided by numerical simulations of the νO-H and νO-D band contour shapes on utilizing the "strong-coupling" model. The abnormal IR spectral properties of SAC crystals in relation to the corresponding properties of glutaric, pimelic and adipic acid crystals were ascribed to the hyperconjugation electronic effects in the acid associated molecules. A vibronic coupling mechanism involving the proton stretching vibrations in the (COOH)2 cycles and the electronic motions in the molecular skeletons, the isotopic "H/D self-organization" mechanisms and a long-distance vibrational exciton coupling between the adjacent (COOH)2 cycles in the molecular chains are mainly responsible for the generation of the temperature effects in the crystalline IR spectra., (Copyright © 2015 Elsevier B.V. All rights reserved.)