Spatial structure, thermodynamics and kinetics of formation of hydrazones derived from pyridoxal 5′-phosphate and 2-furoic, thiophene-2-carboxylic hydrazides in solution

Influence of Solvent Polarity on the Conformer Ratio of Bicalutamide in Saturated Solutions: Insights from NOESY NMR Analysis and Quantum-Chemical Calculations

The study presents a thorough and detailed analysis of bicalutamide's structural and conformational properties. Quantum chemical calculations were employed to explore the conformational properties of the molecule, identifying significant energy differences between conformers. Analysis revealed that hydrogen bonds stabilise the conformers, with notable variations in torsion angles. Conformers were classified into 'closed' and 'open' types based on the relative orientation of the cyclic fragments. NOE spectroscopy in different solvents (CDCl3 and DMSO-d6) was used to study the conformational preferences of the molecule. NOESY experiments provided the predominance of 'closed' conformers in non-polar solvents and a significant presence of 'open' conformers in polar solvents. The proportions of open conformers were 22.7 ± 3.7% in CDCl3 and 59.8 ± 6.2% in DMSO-d6, while closed conformers accounted for 77.3 ± 3.7% and 40.2 ± 6.2%, respectively. This comprehensive study underscores the solvent environment's impact on its structural behaviour. The findings significantly contribute to a deeper understanding of conformational dynamics, stimulating further exploration in drug development.

Cuminaldehyde-3-hydroxy-2-napthoichydrazone: Synthesis, effect of solvents, nonlinear optical activity, antioxidant activity, antimicrobial activity, and DFT analysis

Hydrazones derived from essential oil components have attracted considerable interest because of their antimicrobial, antioxidant, and nonlinear optical applications. In the present work, a new essential oil component derivative (EOCD), cuminaldehyde-3-hydroxy-2-napthoichydrazone (CHNH), was synthesized. EOCD was characterized by Fourier transform infrared spectroscopy, mass spectrometry, nuclear magnetic resonance (1H and 13C) spectroscopy, elemental analysis, ultraviolet-visible absorption spectroscopy, and field-emission scanning electron microscopy. Thermogravimetric analysis and X-ray diffraction showed a higher stability, phase-pure, and non-existent isomorphic phase transition in EOCD. Solvent studies indicated that the normal emission band was caused by the locally excited state and the large Stokes shifted emission originated because of the twisted intramolecular charge transfer. The EOCD possessed higher direct and indirect band gap energies of 3.05 eV and 2.90 eV respectively, as determined by the Kubelka-Munk algorithm. The outcomes of frontier molecular orbitals, global reactivity descriptors, Mulliken, and molecular electrostatic potential surface by density functional theory calculations revealed high intramolecular charge transfer, good realistic stability, and high reactiveness of EOCD. The hydrazone EOCD exhibited higher hyperpolarizability (18.248 × 10-30 esu) in comparison to urea. Antioxidant test results indicated that EOCD showed significant antioxidant activity (p < 0.05), as determined by the DPPH radical scavenging assay. The newly synthesized EOCD showed no antifungal activity against Aspergillus flavus. Additionally, the EOCD showed good antibacterial activity against Escherichia coli and Bacillus subtilis.

Vitamin B6-based fluorescence chemosensor for selective detection of F- ions: design, synthesis, and characterization

The present paper reports on the synthesis and characterization of a new chemosensor for fluoride ions, a hydrazone derived from pyridoxal 5'-phosphate and benzothiazole. The structure of the chemosensor was confirmed using 1H and 13C NMR, FT-IR and mass spectroscopy. The conformational diversity of the chemosensor influencing the sensor activity was studied by the quantum chemistry methods on the B3LYP/6-311++G(d, p) (H, C, N, O, P, S) level, and the optimal structure of the chemosensor was chosen. The selective capability of detecting F- in the aqueous solution, which also contains Cl-, Br-, I-, NCS-, ClO4-, HSO4-, and NO3- was demonstrated. The detection limit (LOD) for fluoride ions was 0.22 µM as determined by the 3σ method. The turn-on effect in the presence of fluoride ions is based on the deprotonation of the chemosensor and its subsequent aggregation in DMSO. In addition, the chemosensor was used for the detection and estimation of F- in real samples using fluorescence spectroscopy.

Investigation of the Spatial Structure of Flufenamic Acid in Supercritical Carbon Dioxide Media via 2D NOESY

The search for new forms of already known drug compounds is an urgent problem of high relevance as more potent drugs with fewer side effects are needed. The trifluoromethyl group in flufenamic acid renders its chemical structure differently from other fenamates. This modification is responsible for a large number of conformational polymorphs. Therefore, flufenamic acid is a promising structural modification of well-known drug molecules. An effective approach in this field is micronization, employing "green" supercritical fluid technologies. This research raises some key questions to be answered on how to control polymorphic forms during the micronization of drug compounds. The results presented in this work demonstrate the ability of two-dimensional nuclear Overhauser effect spectroscopy to determine conformational preferences of small molecular weight drug compounds in solutions and fluids, which can be used to predict the polymorphic form during the micronization. Quantitative analysis was carried out to identify the conformational preferences of flufenamic acid molecules in dimethyl sulfoxide-d6 medium at 25 °C and 0.1 MPa, and in mixed solvent medium containing supercritical carbon dioxide at 45 °C and 9 MPa. The data presented allows predictions of the flufenamic acid conformational preferences of poorly soluble drug compounds to obtain new micronized forms.

Conformational Screening of Arbidol Solvates: Investigation via 2D NOESY

Understanding of the nucleation process's fundamental principles in saturated solutions is an urgent task. To do this task, it is necessary to control the formation of polymorphic forms of biologically active compounds. In certain cases, a compound can exist in a single polymorphic form, but have several solvates which can appear in different crystal forms, depending on the medium and conditions of formation, and show different pharmaceutical activity. In the present paper, we report on the analysis of Arbidol conformational preferences in two solvents of different polarities-deuterated chloroform and dimethyl sulfoxide-at 25 °C, using the 2D NOESY method. The Arbidol molecule has various solvate forms depending on the molecular conformation. The method based on the nuclear Overhauser effect spectroscopy was shown to be efficient in the analysis of complex heterocyclic compounds possessing conformation-dependent pseudo-polymorphism. It is one of the types of polymorphism observed in compounds forming crystal solvates. Combined use of NMR methods and X-ray data allowed determining of conformer populations of Arbidol in CDCl₃ and DMSO-d₆ which were found to be 8/92% and 37/63%, respectively. The preferred conformation in solution is the same that appears in stable crystal solvates of Arbidol.

Acylhydrazones and Their Biological Activity: A Review

Due to the structure of acylhydrazones both by the pharmacophore -CO-NH-N= group and by the different substituents present in the molecules of compounds of this class, various pharmacological activities were reported, including antitumor, antimicrobial, antiviral, antiparasitic, anti-inflammatory, immunomodulatory, antiedematous, antiglaucomatous, antidiabetic, antioxidant, and actions on the central nervous system and on the cardiovascular system. This fragment is found in the structure of several drugs used in the therapy of some diseases that are at the top of public health problems, like microbial infections and cardiovascular diseases. Moreover, the acylhydrazone moiety is present in the structure of some compounds with possible applications in the treatment of other different pathologies, such as schizophrenia, Parkinson's disease, Alzheimer's disease, and Huntington's disease. Considering these aspects, we consider that a study of the literature data regarding the structural and biological properties of these compounds is useful.

The Role of Hidden Conformers in Determination of Conformational Preferences of Mefenamic Acid by NOESY Spectroscopy

Mefenamic acid has been used as a non-steroidal anti-inflammatory drug for a long time. However, its practical use is quite limited due to a number of side effects on the intestinal organs. Conformational polymorphism provides mefenamic acid with unique properties regarding possible modifications obtained during the micronization process, which can improve pharmacokinetics and minimize side effects. Micronization can be performed by decompression of supercritical fluids; methods such as rapid expansion of the supercritical solution have proven their efficiency. However, this group of methods is poorly applicable for compounds with low solubility, and the modification of the method using a pharmaceutically suitable co-solvent may be useful. In our case, addition of only 2 mol% dimethyl sulfoxide increased the solubility remarkably. Information on the conformational state may be critically important for carrying out micronization. In this work, structural analysis and estimate of conformational preferences of mefenamic acid in dimethyl sulfoxide-d6 (at 25 °C and 0.1 MPa) and in a mixed solvent supercritical carbon dioxide + dimethyl sulfoxide-d6 (45 °C, 9 MPa) were performed based on nuclear Overhauser effect spectroscopy. Results show changes in the conformation fractions depending on the medium used. The importance of allowing for hidden conformers in estimating the conformational state was demonstrated in the analysis. Obtained results may be useful for improving micronization parameters.

Exposing Hidden Conformations of Carbamazepine Appearing Due to Interaction With the Solid Phase by 2D 1H-15N HMBC NMR Spectroscopy

Two-dimensional ¹H-¹⁵N HMBC NMR spectra of the well-known anticonvulsant carbamazepine dissolved in different organic solvents, recorded on an NMR spectrometer prove the existence of hidden conformers in saturated solutions. Obtained conformer distribution arises due to the presence of the solid phase in saturated solution. A weak influence of ring currents was revealed for different molecular conformations of carbamazepine dissolved in a saturated solution, which provides a simple approach to discovering hidden conformations. Hidden conformers were found in three different solvents: dimethyl sulfoxide, chloroform, and dichloromethane.

Binding of pyridoxal, pyridoxal 5'-phosphate and derived hydrazones to bovine serum albumin in aqueous solution

In the present paper, the kinetics of a reaction between bovine serum albumin (BSA) and pyridoxal, pyridoxal 5'-phosphate was studied, apparent rate constant of product formation and dissociation as well as binding constants were determined. Pyridoxal 5'-phosphate hydrazones of isonicotinic, picolinic, 2-furoic, thiophene-2-carboxylic, pyrazinoic acids binding to BSA was studied by spectrofluorimetry, stability constants of the associates were calculated from experimental data using maximal likelihood approach. The changes in the secondary structure of BSA induced by hydrazones addition were studied by IR spectroscopy. New freely available software for curve fitting was developed as a part of the software kit designed for the solution chemistry and used for a specific problem of this study, IR spectra processing.