Silver Nanoparticles from Tabernaemontana Divaricate leaf extract: Mechanism of action and Bio-application for photo degradation of 4-Aminopyridine.

Silver nanoparticles (Ag NPs) were synthesised by the reduction of Ag+ to Ag0 in the presence of enol form of flavonoids present in plant extract of Tabernaemontana Divaricate (T. Divaricate). Prepared Ag NPs were characterized using UV-Vis, XRD, HR-TEM with EDX and XPS techniques. XPS spectra exhibited peaks at 366 eV and 373 eV, which specified spin orbits for Ag 3d3/2, and Ag 3d5/2 that confirmed the formation of Ag NPs. Ag NPs were spherical in shape with an average size of 30 nm as revealed by HR-TEM and FE-SEM techniques. EDX studies verified the high purity of Ag NPs with silver 46.96 %, carbon 16.35 %, oxygen 16.22 %, nitrogen 20.25 % and sulphur 0.21%. LC-MS analysis of plant extract confirmed the qualitative presence of alkaloids, tannins, flavonoids, phenols, and carbohydrates. Prepared Ag NPs showed good photocatalytic activity towards degradation of 4-Amniopyridine with 61% degradation efficiency at optimum conditions in 2 hrs of reaction time under visible light. The number of intermediates were found were ten within the mass number of 0–450. Ag NPs synthesized using bio-extract have also showed good inactivation against Escherichia Coli (E. Coli) and Bacillus Subtilis (B. Subtilis) bacteria due to availability of free radicals.

Curcumin analogues for possible cancer treatment A QSAR and partial ordering study

The possible effect of curcumin as a potential natural cancer treatment drug has been intensively discussed. In the present study the probabilities of a series of curcumin analogues to possess potential as antineoplastic, prostate cancer treatment and anticarcinogenic agents has been studied theoretically applying a selection of quantitative structure-activity relation and absorption, distribution, metabolism, and excretion (ADME) approaches. From spectroscopic studies it is evident that these compounds can be found in both enol and diketo forms, the former in general the more predominant in non-polar solvents, whereas in polar solvents, like water an increasing amount of the diketo form can be noted. Hence, the probabilities for both the enols and diketo forms to possess the above-mentioned effects were studied. In most cases the enol form shows the highest probabilities for being effective although the differences are not significant. Thus, it is suggested to look at the sum of effects of the keto and the enol forms in relation to the possible therapeutic effects of the compounds here studied.

New Precursors to 3-Sulfanylhexan-1-ol? Investigating the Keto–Enol Tautomerism of 3-S-Glutathionylhexanal

The volatile thiol compound 3-sulfanylhexan-1-ol (3SH) is a key impact odorant of white wines such as Sauvignon Blanc. 3SH is produced during fermentation by metabolism of non-volatile precursors such as 3-S-gluthathionylhexanal (glut-3SH-al). The biogenesis of 3SH is not fully understood, and the role of glut-3SH-al in this pathway is yet to be elucidated. The aldehyde functional group of glut-3SH-al is known to make this compound more reactive than other precursors to 3SH, and we are reporting for the first time that glut-3SH-al can exist in both keto and enol forms in aqueous solutions. At wine typical pH (~3.5), glut-3SH-al exists predominantly as the enol form. The dominance of the enol form over the keto form has implications in terms of potential consumption/conversion of glut-3SH-al by previously unidentified pathways. Therefore, this work will aid in the further elucidation of the role of glut-3SH-al towards 3SH formation in wine, with significant implications for the study and analysis of analogous compounds.

Crystal structure of 1,1′-{(1E,1′E)-[4,4′-(9H-fluorene-9,9-diyl)bis(4,1-phenylene)]bis(azanylylidene)bis(methanylylidene)}bis(naphthalen-2-ol) dichlorobenzene monosolvate

The bis(anil) molecule of the title compound, C47H32N2O2·C6H4Cl2, contains two anil fragments in the enol–enol form, exhibiting intramolecular O—H...N hydrogen bonds. The two hydroxynaphthalene ring systems are approximately parallel to each other with a dihedral angle of 4.67 (8)° between them, and each ring system makes a large dihedral angle [55.11 (11) and 48.50 (10)°] with the adjacent benzene ring. In the crystal, the bis(anil) molecules form an inversion dimer by a pair of weak C—H...O interactions. The dimers arrange in a one-dimensional column along the b axis via another C—H...O interaction and a π–π stacking interaction between the hydroxynaphthalene ring system with a centroid–centroid distance of 3.6562 (16) Å. The solvent 1,2-dichlorobenzene molecules are located between the dimers and bind neighbouring columns by weak C—H...Cl interactions. Theoretical prediction of potential biological activities was performed, which suggested that the title anil compound can exhibit histone deacetylase SIRT2, histone deacetylase class III and histone deacetylase SIRT1 activities, and will act as inhibitor to aspulvinone dimethylallyltransferase, dehydro-L-gulonate decarboxylase and glutathione thiolesterase.

Controlling the stereochemistry in 2-oxo-aldehyde-derived Ugi adducts through the cinchona alkaloid-promoted electrophilic fluorination

In this report, we introduce a new strategy for controlling the stereochemistry in Ugi adducts. Instead of controlling stereochemistry directly during the Ugi reaction we have attempted to stereodefine the chiral center at the peptidyl position through the post-Ugi functionalization. In order to achieve this, we chose to study 2-oxo-aldehyde-derived Ugi adducts many of which partially or fully exist in the enol form that lacks the aforementioned chiral center. This in turn led to their increased nucleophilicity as compared to the standard Ugi adducts. As such, the stereocenter at the peptidyl position could be installed and stereodefined through the reaction with a suitable electrophile. Towards this end, we were able to deploy an asymmetric cinchona alkaloid-promoted electrophilic fluorination producing enantioenriched post-Ugi adducts fluorinated at the peptidyl position.

Protonation, Tautomerism, and Base Pairing of the Antiviral Favipiravir (T-705)

Favipiravir (T-705) is an antiviral medication used to treat influenza. T-705 is also currently being trialled as a repurposed COVID-19 treatment. To help accelerate these efforts, this study provides important solution-phase properties of T-705 determined via computational chemistry. Density functional theory (DFT) calculations combined with the SMD continuum solvation model demonstrate that T-705 prefers the aromatic enol form in solution over the ketone tautomer. Deprotonation constants for the conjugate acids of T-705 (pKas) are then evaluated, by combining the DFT/SMD calculations with accurate G4 gas-phase basicities. These calculations indicate that T-705 is a weak base that should not significantly protonate at physiological pH. The preferential site for protonation is at the ring nitrogen ortho to the alcohol functional group (pKa ~ 7.4), followed by protonation of the oxygen on the amide side-chain at more acidic conditions (pKa ~ -9.8). Significantly, protonation of the ring nitrogen produces an acid that can deprotonate to the enol form (pKa ~ -5.1), providing a pathway for their interconversion. Finally, base-pairing of the active ribose-bound form of T-705 to cytidine and uridine is also examined. These calculations indicate that both base pairs have large binding free energies of around 4 – 5 kcal/mol, supporting previous findings that T-705 can bind with both nucleobases, leading to mis-incorporation of these pairs into viral RNA.<br>

Protonation, Tautomerism, and Base Pairing of the Antiviral Favipiravir (T-705)

Favipiravir (T-705) is an antiviral medication used to treat influenza. T-705 is also currently being trialled as a repurposed COVID-19 treatment. To help accelerate these efforts, this study provides important solution-phase properties of T-705 determined via computational chemistry. Density functional theory (DFT) calculations combined with the SMD continuum solvation model demonstrate that T-705 prefers the aromatic enol form in solution over the ketone tautomer. Deprotonation constants for the conjugate acids of T-705 (pKas) are then evaluated, by combining the DFT/SMD calculations with accurate G4 gas-phase basicities. These calculations indicate that T-705 is a weak base that should not significantly protonate at physiological pH. The preferential site for protonation is at the ring nitrogen ortho to the alcohol functional group (pKa ~ 7.4), followed by protonation of the oxygen on the amide side-chain at more acidic conditions (pKa ~ -9.8). Significantly, protonation of the ring nitrogen produces an acid that can deprotonate to the enol form (pKa ~ -5.1), providing a pathway for their interconversion. Finally, base-pairing of the active ribose-bound form of T-705 to cytidine and uridine is also examined. These calculations indicate that both base pairs have large binding free energies of around 4 – 5 kcal/mol, supporting previous findings that T-705 can bind with both nucleobases, leading to mis-incorporation of these pairs into viral RNA.<br>

Protonation, Tautomerism, and Base Pairing of the Antiviral Favipiravir (T-705)

Favipiravir (T-705) is an antiviral medication used to treat influenza. T-705 is also currently being trialled as a repurposed COVID-19 treatment. To help accelerate these efforts, this study provides important solution-phase properties of T-705 determined via computational chemistry. Density functional theory (DFT) calculations combined with the SMD continuum solvation model demonstrate that T-705 prefers the aromatic enol form in solution over the ketone tautomer. Deprotonation constants for the conjugate acids of T-705 (pKas) are then evaluated, by combining the DFT/SMD calculations with accurate G4 gas-phase basicities. These calculations indicate that T-705 will preferentially protonate the ring nitrogen ortho to the alcohol functional group (pKa ~ 7.4), along with protonation of the oxygen on the amide side-chain at more acidic conditions (pKa ~ 9.8). No other protomers are expected to be important. Significantly, protonation of the ring nitrogen produces an acid that can deprotonate to the enol form (pKa ~ 5.1), providing a pathway for their facile interconversion. Finally, base-pairing of the active ribose-bound form of T-705 to cytidine and uridine is also examined. These calculations indicate that both base pairs have large binding free energies of around 7 – 8 kcal/mol, supporting previous findings that T-705 can bind with both nucleobases, leading to mis-incorporation of these pairs into viral RNA.<br>

Favipiravir Tautomerism: A Short Theoretical Report

There is no experimental data about the tautomerism of Favipiravir (T-705). Therefore its tautomeric state was predicted by using density functional theory in gas phase and in solution (toluene, acetonitrile and water). The solvent effect was described by means of the Polarizable Continuum Model. The results have shown that the enol form is strongly dominating in both gas phase and solution. In order to validate the theoretical predictions, 2-hydroxy pyridine and 2-hydroxy pyrazine were also included in the set of studied compounds. The available experimental data for their tautomerism are in very good agreement with the theoretical predictions, which validate the conclusions made for T-705.