Themistoklis Venianakis

Carob leaves have gained attention for their bioactive properties and traditional medicinal uses, including as treatment for diabetes, digestive disorders, and microbial infections. The aim of this study was to explore the phytochemical composition of carob leaf acetone extracts using advanced spectroscopic techniques. The combined use of heteronuclear nuclear magnetic resonance (NMR) experiments with 1D selective nuclear Overhauser effect spectroscopy (NOESY) offers detailed structural insights and enables the direct identification and quantification of key bioactive constituents in carob leaf extract. In particular, the NMR and mass spectrometry techniques revealed the presence of myricitrin as a predominant flavonoid, as well as a variety of glycosylated derivatives of myricetin and quercetin, in acetone extract. Furthermore, siliquapyranone and related gallotannins are essential constituents of the extract. The potent inhibitory effects of the carob leaf extract on Staphylococcus aureus (MIC = 50 μg mL⁻¹) and a-glucosidase enzyme (IC₅₀ = 67.5 ± 2.4 μg mL⁻¹) were also evaluated. Finally, the antibacterial potency of carob leaf constituents were calculated in silico; digalloyl-parasorboside and gallic acid 4-O-glucoside exert a stronger bactericidal activity than the well-known myricitrin and related flavonoids. In summary, our findings provide valuable insights into the bioactive composition and health-promoting properties of carob leaves and highlight their potential for pharmaceutical and nutraceutical applications.

Saturation transfer difference (STD), inter-ligand NOEs (INPHARMA NMR), and docking calculations are reported for investigating specific binding sites of the high-affinity synthetic 7-nitrobenz-2-oxa-1,3-diazoyl-4-C₁₂ fatty acid (NBD-C₁₂ FA) with non-labeled human serum albumin (HSA) and in competition with the drugs warfarin and ibuprofen. A limited number of negative interligand NOEs between NBD-C₁₂ FA and warfarin were interpreted in terms of a short-range allosteric competitive binding in the wide Sudlow’s binding site II (FA7) of NBD-C₁₂ FA with Ser-202, Lys-199, and Trp-214 and warfarin with Arg-218 and Arg-222. In contrast, the significant number of interligand NOEs between NBD-C₁₂ FA and ibuprofen were interpreted in terms of a competitive binding mode in Sudlow’s binding site I (FA3 and FA4) with Ser-342, Arg-348, Arg-485, Arg-410, and Tyr-411. NBD-C₁₂ FA has the unique structural properties, compared to short-, medium-, and long-chain saturated and unsaturated natural free fatty acids, of interacting with well-defined structures with amino acids of both the internal and external polar anchor sites in Sudlow’s binding site I and with amino acids in both FA3 and FA4 in Sudlow’s binding site II. The NBD-C₁₂ FA, therefore, interacts with novel structural characteristics in the drug binding sites I and II and can be regarded as a prototype molecule for drug development.

Colocasia esculenta L. leaves are considered a by-product of taro cultivation and are discarded as environmental waste, despite their valuable phenolic composition. Their valorization to obtain value-added substances for medicinal, food, and cosmetic applications is the aim of the current work. An ultrasound-assisted extraction was developed for the environmentally friendly and sustainable isolation of taro leaf antioxidants using natural deep eutectic solvents (NaDESs). Among the utilized solvents, the NaDES based on betaine and ethylene glycol provided the best extraction efficiencies in terms of polyphenolic content and antioxidant activity. Multi-response optimization suggested a solvent-to-solid ratio of 10 mL g⁻¹, a processing time of 60 min, an extraction temperature of 60 °C, and a water content of 33.8% (w/w) as optimal extraction parameters. Leaf extract obtained under these optimum operational parameters demonstrated a strong radical scavenging activity against 2,2-diphenyl-1-picrylhydrazyl (65.80 ± 0.87%), a high ferric reducing antioxidant power (126.62 ± 1.92 μmol TE g⁻¹ sample), and significant protection against oxidative stress-induced DNA damage. The chromatographic characterization of the optimum extract revealed its richness in flavonoids (flavones and flavonols). The outcomes of the present study suggest that the proposed method could serve as a highly efficient and green alternative for the recovery of polyphenols from agricultural wastes.

Molecular structures, in chloroform and DMSO solution, of the free fatty acids (FFAs) caproleic acid, oleic acid, α-linolenic acid, eicosapentanoic acid (EPA) and docosahexaenoic acid (DHA) are reported with the combined use of NMR and DFT calculations. Variable temperature and concentration chemical shifts of the COOH protons, transient 1D NOE experiments and DFT calculations demonstrate the major contribution of low molecular weight aggregates of dimerized fatty acids through intermolecular hydrogen bond interactions of the carboxylic groups, with parallel and antiparallel interdigitated structures even at the low concentration of 20 mM in CDCl₃. For the dimeric DHA, a structural model of an intermolecular hydrogen bond through carboxylic groups and an intermolecular hydrogen bond between the carboxylic group of one molecule and the ω-3 double bond of a second molecule is shown to play a role. In DMSO-d₆ solution, NMR and DFT studies show that the carboxylic groups form strong intermolecular hydrogen bond interactions with a single discrete solvation molecule of DMSO. These solvation species form parallel and antiparallel interdigitated structures of low molecular weight, as in chloroform solution. This structural motif, therefore, is an intrinsic property of the FFAs, which is not strongly affected by the length and degree of unsaturation of the chain and the hydrogen bond ability of the solvent.

Molecular structures, in chloroform and DMSO solution, of the monounsaturated free fatty acids (FFAs) caproleic acid (dec-9-enoic acid) and oleic acid (octadec-9-enoic acid) and the ω-3 FFAs α-linolenic acid (9Z,12Z,15Z)-octadeca-9,12,15-trienoic acid ALA), eicosapentanoic acid (5Z,8Z,11Z,14Z,17Z)-icosa-5,8,11,14,17-pentaenoic acid) and docosahexaenoic acid (4Z,7Z,10Z,13Z,16Z,19Z)-docosa-4,7,10,13,16,19-hexaenoic acid), are reported with the combined use of NMR and DFT calculations. Variable temperature and concentration chemical shifts of the COOH protons and transient 1D NOE experiments, in CDCl3, demonstrate the major contribution of low molecular weight aggregates of dimerized fatty acids, through intermolecular hydrogen bond interactions of the carboxylic groups, with parallel and antiparallel interdigitated structures, even at the low concentration of 20 mM. For the dimeric DHA, a structural model of an intermolecular hydrogen bond through carboxylic groups and an intermolecular hydrogen bond between the carboxylic group of one molecule and the ω-3 double bond of a second molecule, is shown to play a role. In DMSO-d6 solution the centro-symmetric hydrogen bond interactions are broken and the carboxylic groups form strong intermolecular hydrogen bond interactions with a discrete solvation molecule of DMSO. These solvation species form parallel and antiparallel interdigitated structures of low molecular weight. DFT structural models in CHCl3 and DMSO, in agreement with the NMR data, are compared with the structures in the liquid state

Medium- and long-chain saturated and unsaturated free fatty acids (FFAs) are known to bind to human serum albumin (HSA), the main plasma carrier protein. Atomic-level structural data regarding the binding mode in Sudlow’s sites I (FA7) and II (FA4, FA3) of the polyunsaturated ω-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), however, are largely unknown. Herein, we report the combined use of saturation transfer difference (STD) and Interligand NOEs for Pharmacophore Mapping (INPHARMA) NMR techniques and molecular docking calculations to investigate the binding mode of DHA and EPA in Sudlow’s sites Ι and ΙΙ of HSA. The docking calculations and the significant number of interligand NOEs between DHA and EPA and the drugs warfarin and ibuprofen, which are stereotypical ligands for Sudlow’s sites I and II, respectively, were interpreted in terms of competitive binding modes and the presence of two orientations of DHA and EPA at the binding sites FA7 and FA4. The exceptional flexibility of the long-chain DHA and EPA and the formation of strongly folded structural motives are the key properties of HSA–PUFA complexes.

Artemisinin is known to bind to the main plasma protein carrier serum albumin (SA); however, there are no atomic level structural data regarding its binding mode with serum albumin. Herein, we employed a combined strategy of saturation transfer difference (STD), transfer nuclear Overhauser effect spectroscopy (TR-NOESY), STD–total correlation spectroscopy (STD-TOCSY), and Interligand Noes for PHArmacophore Mapping (INPHARMA) NMR methods and molecular docking calculations to investigate the structural basis of the interaction of artemisinin with human and bovine serum albumin (HSA/BSA). A significant number of inter-ligand NOEs between artemisinin and the drugs warfarin and ibuprofen as well as docking calculations were interpreted in terms of competitive binding modes of artemisinin in the warfarin (FA7) and ibuprofen (FA4) binding sites. STD NMR experiments demonstrate that artemisinin is the main analyte for the interaction of the A. annua extract with BSA. The combined strategy of NMR and docking calculations of the present work could be of general interest in the identification of the molecular basis of the interactions of natural products with their receptors even within a complex crude extract.

A density functional theory (DFT) study of the ¹H- and ¹³C-NMR chemical shifts of the geometric isomers of 18:2 ω-7 conjugated linoleic acid (CLA) and nine model compounds is presented, using five functionals and two basis sets. The results are compared with available experimental data from solution high resolution nuclear magnetic resonance (NMR). The experimental ¹H chemical shifts exhibit highly diagnostic resonances due to the olefinic protons of the conjugated double bonds. The “inside” olefinic protons of the conjugated double bonds are deshielded than those of the “outside” protons. Furthermore, in the cis/trans isomers, the signals of the cis bonds are more deshielded than those of the trans bonds. These regularities of the experimental ¹H chemical shifts of the olefinic protons of the conjugated double bonds are reproduced very accurately for the lowest energy DFT optimized single conformer, for all functionals and basis sets used. The other low energy conformers have negligible effects on the computational ¹H-NMR chemical shifts. We conclude that proton NMR chemical shifts are more discriminating than carbon, and DFT calculations can provide a valuable tool for (i) the accurate prediction of ¹H-NMR chemical shifts even with less demanding functionals and basis sets; (ii) the unequivocal identification of geometric isomerism of CLAs that occur in nature, and (iii) to derive high resolution structures in solution.