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The substituent and solvent effect on intramolecular charge transfer (ICT) of twelve monocarbohydrazones (mCHs) were studied using experimental and theoretical methodology. The effects of specific and non-specific solvent–solute interactions on the UV–Vis absorption maxima shifts were evaluated using linear free energy relationships (LFERs) principles, i.e. using the Kamlet-Taft and Catalán models. Linear free energy relationships in the form of single substituent parameter equation (SSP) was used to analyze substituent effect on UV–Vis, NMR and pKa change. According to crystallographic data and quantum chemical calculations, the trans (E) form was found to be more stable. A photochromism of compounds with 2-hydroxyphenyl and 2-pyridylimino groups substituted at imine carbon atom results in E/Z isomerization due to creation of intermolecular hydrogen bond in E and Z form, respectively. Multiple stage mass spectrometry (MS-MSn) analysis was applied to define main fragmentation pathways. Furthermore, the experimental findings were interpreted with the aid of ab initio MP2/6–311 G(d,p) and time-dependent density functional (TD-DFT) methods. TD-DFT calculations were performed to quantify the efficiency of intramolecular charge transfer (ICT) with the aid of the charge-transfer distance (DCT) and the amount of transferred charge (QCT) calculation. It was found that both substituents and solvents influence electron density shift i.e. extent of conjugation, and affect ICT character in the course of excitation. Keywords: Solvatochromism, LSER, Photoisomerization, Intramolecular charge transfer, Quantum chemical calculation

© 2020, Institute of Chemistry, Slovak Academy of Sciences. Abstract: Carbohydrazones are compounds that are increasingly studied due to their wide potential biological activity. Monocarbohydrazones (mCHs), as one of the carbohydrazone derivatives, so far have been poorly investigated. For a more detailed study, in this paper, eighteen compounds of monocarbohydrazones (eight known and ten newly synthesized derivatives) were synthesized and characterized using NMR and IR spectroscopy. As carbohydrazones show E/Z isomerization caused by the presence of the imino group, some of the synthesized mCHs are in the form of a mixture of these two isomers. The effects of specific and nonspecific solvent–solute interactions on the UV absorption maxima shifts were evaluated using linear free energy relationships principles, i.e., using Kamlet–Taft’s and Catalan’s models. For more information about interactions between dissolved substance and the surrounding medium, correlations have been made with Hansen’s solubility parameters. The influence of the structure on the spectral behavior of the compounds tested was interpreted using Hammett’s equation. Experimentally obtained physicochemical properties of mCHs were compared to and confirmed with computational methods that included TD-DFT calculations and MP2 geometry optimizations. Graphic abstract: [Figure not available: see fulltext.].

Fourteen mono- and bis-carbohydrazone ligands have been synthesized and characterized. Antioxidant activity of the substances was investigated together with possible (E)/(Z) isomerization, and explained on the most active antioxidant compound 4 in various dimethyl sulphoxide–water mixtures. The addition of water to the system was involved in the formation of hydrated molecules which was confirmed in NMR after the addition of D2O. The ligands were tested in vitro against Gram-positive and Gram-negative bacteria and fungi, and their activity was discussed in relation to the structure of investigated carbohydrazone. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 172013]

Thiocarbohydrazones (TCHs) and structurally related molecules are versatile organic compounds which exert antioxidant, anticancer, and other beneficial health effects. The combination of UV/Vis, NMR spectroscopy, and quantum chemical calculations was used to rationalize the experimentally observed increase in the radical scavenging activity upon the addition of water in DMSO solution of TCHs. Mono- and bis(salicylaldehyde) TCHs (compounds 1 and 2) undergo water-induced E-to-Z isomerization which is followed by disruption of intramolecular hydrogen bond, ground state destabilization, and 11 kcal/mol decrease in the bond dissociation enthalpy (BDE). Electron spin delocalization is more pronounced in Z-isomers of 1 and 2. On the other hand, 2-acetylpyridine TCHs (compounds 3 and 4) undergo thione-to-thiol tautomerism which also decreases the BDE and facilitates the hydrogen atom transfer to 2,2-diphenyl-1-picrylhydrazyl radical (DPPH∙). The appearance of thiolic –SH group as another reactive site toward free radicals improves the antioxidant activity of 3 and 4. The spin density of 3- and 4-thiol radicals is delocalized over the entire thiocarbohydrazide moiety compared to more localized spin of thione radicals. Additional stabilization of thiol radicals corroborates with the increased antioxidant activity. This study provides the new insights on the solution structure of TCHs, and also highlights the importance of solution structure determination when studying the structure-antioxidant relationships of isomerizable compounds. Supplementary material: [http://cherry.chem.bg.ac.rs/handle/123456789/3848]

Synthesis of high-performance alkyd resins (ARs) based on waste poly(ethylene terephthalate) (PET) glycolyzates is presented. PET glycolyzates were synthesized by catalytic depolymerization with trimethylolpropane (TMP) and trimethylolethane (TME) and used as replacement of polyhydroxylic component during the ARs synthesis. The obtained glycolyzates and produced ARs were analyzed using FTIR, 1H and 13C NMR spectroscopy and acid, iodine, and hydroxyl value were determined. Rheological properties of the synthesized ARs, as well as, thickness, adhesion, hardness and the gloss values were determined. All synthesized ARs show good adhesion and hardness and the gloss values are greater than 95%. The influence of the addition of vinyl modified nanosilica Aerosil® R380, functionalized with 3-(trimethoxysilyl)propyl methacrylate (TMSPM) and tris(2-methoxyethoxy)(vinyl)silane (TMEVS), on the mechanical and anticorrosive characteristics of the prepared nanocomposite coatings, based on ARs, was investigated. U ovom radu prikazana je sinteza alkidnih smola visokih performansi baziranih na otpadnim poli(etilentereftalat) (PET) glikolizatima. PET glikolizati su sintetisani katalitičkom depolimerizacijom sa trimetilolpropanom (TMP) i trimetiloletanom (TME) koji su korišćeni za zamenu polihidroksilne komponente u toku sinteze alkidnih smola. Dobijeni glikolizati i alkidne smole u velikom prinosu su okarakterisane FTIR i 1HNMR spektroskopijom, kiselinskim, jodnim i hidroksilnim brojem. Određena su reološka svojstva sintetisanih alkidnih smola kao što su debljina, athezija, tvrdoća i sjaj i sve sintetisane alkidne smole su pokazale veliku adeziju i tvrdoću i sjaj veći od 98%. Ispitivan je uticaj dodatka modifikovanih silika Aerosil® R380 nanočestica na mehaničke I antikorozivne karakteristike dobijenih nanokompozitnih premaza na bazi alkidnih smola.

Due to the rise of microbial strains resistant to conventional therapies, there is an urgent need for finding the new antimicrobial chemotypes. Heterocyclic compounds such as thiocarbohydrazones (TCHs) are able to interact with many metalloenzymes essential for microbes, while sulfur atom increases lipophilicity which is generally positively correlated with potency. In this paper, we report antibacterial and antifungal activity of twenty-two TCHs toward eight bacterial and three fungal strains. Furthermore, three alignment independent 3D QSAR models based on descriptors derived from molecular interaction fields (MIFs) are developed in order to rationalize structure-activity relationships for activities of TCHs toward S. aureus, P. aeruginosa and C. albicans. Several structural fragments important for biological activity are recognized in each model, and structural modifications which could lead to increased potency are suggested. Designed structures will be synthesized accordingly and tested toward the same microbial strains in order to obtain more potent derivatives. The supporting information: [https://cer.ihtm.bg.ac.rs/handle/123456789/4480]

The ratios of E/Z isomers of sixteen synthesized 1,3-dihydro-3-(substituted phenylimino)-2H-indol-2-one were studied using experimental and theoretical methodology. Linear solvation energy relationships (LSER) rationalized solvent influence of the solvent-solute interactions on the UV-Vis absorption maxima shifts (v(max)) of both geometrical isomers using the Kamlet-Taft equation. Linear free energy relationships (LEER) in the form of single substituent parameter equation (SSP) was used to analyze substituent effect on pK(a), NMR chemical shifts and v(max) values. Electron charge density was obtained by the use of Quantum Theory of Atoms in Molecules, i.e. Bader's analysis. The substituent and solvent effect on intramolecular charge transfer (ICT) were interpreted with the aid of time-dependent density functional (TD-DFT) method. Additionally, the results of TD-DFT calculations quantified the efficiency of ICT from the calculated charge-transfer distance (D-CT) and amount of transferred charge (Q(CT)). The antimicrobial activity was evaluated using broth microdilution method. 3D QSAR modeling was used to demonstrate the influence of substituents effect as well as molecule geometry on antimicrobial activity. (C) 2018 Elsevier B.V. All rights reserved. This is peer-reviewed version of the following article: Brkić, D. R.; Božić, A. R.; Marinković, A. D.; Milčić, M. K.; Prlainović, N. Ž.; Assaleh, F. H.; Cvijetić, I. N.; Nikolić, J. B.; Drmanić, S. Ž. Detailed Solvent, Structural, Quantum Chemical Study and Antimicrobial Activity of Isatin Schiff Base. Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy 2018, 196, 16–30. [https://doi.org/10.1016/j.saa.2018.01.080] Supplementary material: [http://cherry.chem.bg.ac.rs/handle/123456789/3197]

15 symmetric 1-methyl-2,6-bis[2-(substituted phenyl)ethenyl]pyridinium iodides were synthesized in this work. Their structures were characterized using IR, H-1 and C-13 NMR, and UV-Vis spectroscopy. DFT calculations indicated that s-trans/s-trans conformation prevail in all compounds. The effects of specific and non-specific solvent-solute interactions on the UV-Vis absorption maxima shifts were evaluated using linear solvation-free energy relationships (LSER), i.e., Kamlet-Taft and Catalan models. A linear free energy relationship (LFER) in the form of single substituent parameter equations (SSP) was used to postulate quantitative structure-property relations of substituent effect on NMR data. TD-DFT results showed dependence of electronic transition on the substituent effects. The push-pull character of these compounds was analyzed by differences in C-13 chemical shift of the ethylenic double bond in 2- and 6-positions of cross-conjugated with pyridinum central ring. Also, the quotient of the occupations for the bonding pi and anti-bonding pi* orbitals of this bond was considered. Good correlations of the selected parameter between double bond lengths with pi*/pi and C-13 chemical shift differences of the bridging group proved them to be adequate descriptor of push-pull character. Synthesized compounds were screened for the antioxidant activity, using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical methods, and results demonstrated moderate antioxidant potential. Supplementary material: [http://cherry.chem.bg.ac.rs/handle/123456789/3255]

Production of high-performance nanocomposite materials obtained from unsaturated polyester resin, based on products of the waste poly(ethylene terephthalate) recycling, and modified multi-walled carbon nanotubes is presented. Di-hydroxy functional glycolysates, synthesized by catalytic depolymerization of poly(ethylene terephthalate) with propylene glycol, were used for the unsaturated polyester resin synthesis. The structure of the obtained glycolysis product and unsaturated polyester resin were characterized by using FTIR and NMR spectroscopy, and by acid, iodine, and hydroxyl value. Nanofillers were prepared by direct and two-step amidation of oxidized multi-walled carbon nanotubes. Direct amidation with diallylamine produced multi-walled carbon nanotube-diallylamine reactive nanofiller. Two-step modification with diamines: hexamethylenediamine and p-phenylenediamine gave multi-walled carbon nanotube-hexamethylenediamine and multi-walled carbon nanotube- p-phenylenediamine nanofiller, respectively, whose amidation with methyl ester of linseed oil fatty acids gave multi-walled carbon nanotube-hexamethylenediamine/methyl ester of linseed oil fatty acid and multi-walled carbon nanotube- p-phenylenediamine/methyl ester of linseed oil fatty acid nanofiller, respectively. Influences of vinyl functionalities on mechanical properties of nanocomposite were analyzed from tensile strength ( σb), elongation ( ɛb) and Young’s modulus ( E) determination. An increase of 97.4, 119 and 139% of σb was obtained for nanocomposites with addition of 0.25 wt.% of diallylamine, p-phenylenediamine/methyl ester of linseed oil fatty acid and hexamethylenediamine/methyl ester of linseed oil fatty acid multi-walled carbon nanotubes, respectively. Short techno-economic analysis, performed on the basis of fixed and variable unsaturated polyester resin production costs, showed satisfactory potential profit, which could be realized by the implementation of the presented technology.