Insight into the acidic behavior of oxazolidin-2-one,its thione and selone analogs through computational techniques

Deprotonation thermochemistry of Oxazolidin-2-one (OXA), Oxazolidine-2-thione (OXA-S), and Oxazolidine-2-selone (OXA-Se) has been studied in order to find the most acidic site and relative acidities of these heterocyclics at various sites. The deprotonation enthalpies at MP2/6-311++G**//MP2/6-31+G* and B3LYP/6-31+G* levels, while the free energies for deprotonation process and pKa values at B3LYP/6-31+G* level both in gas and aqueous phase (using PCM continuum model) of the anions of the three heterocyclics have been computed at 298 K. Calculated aqueous phase pKa values of OXA vary by ~6–7 units from the experimental aqueous phase pKa values of OXA and its derivatives. The deprotonation at the nitrogen is favored in OXA over the carbon atoms in contrast to the OXA-S and OXA-Se where in the deprotonation at the carbon attached to the nitrogen is most preferred. Deprotonation at this carbon induces an important C–O bond rupture in OXA-S and OXA-Se promoting an energetically favored ring-opening process. The finding offers a rare case when C–H acidity is able to dominate over the N–H acidity. In order to explain the relative stabilities, relative acidities and deprotonation enthalpies various characteristics of these molecules as well as their anions such as molecular electrostatic potential surface (MEP), frontier molecular orbital (FMO) features, chemical hardness, softness have been governed. The three dimensional MEP maps and HOMO–LUMO orbitals encompassing these molecules yield a reliable relative stability and reactivity (in terms of acidity) map displaying the most probable regions for deprotonation. The differential distribution of the electrostatic potential over the neutral and anionic species of OXA, OXA-S, and OXA-Se molecules is authentically reflected by HOMO–LUMO orbitals and NBO charge distribution analysis. The lone pair occupancies, second order delocalization energies for orbital interactions and the distribution of atomic charges over the entire molecular framework as obtained from natural bond orbital (NBO) analysis are found to faithfully replicate the predictions from the MEP maps and HOMO–LUMO band gaps in respect of explaining the relative stabilities and acidities in most of the cases. Good linear correlations have been obtained between HOMO–LUMO gap and pKa values in the aqueous phase for OXA and OXA-S molecules.     

Fluorogenic ratiometric dipodal optode containing imine-amide linkages: Exploiting subtle thorium (IV) ion sensing

The (13E,19E)-N1′,N3′-bis[4-(diethylamino)-2-hydroxybenzylidene]malonohydrazide (L) has been developed for the detection of Th⁴⁺ ions using dual channel signalling system. The UV–vis absorbance and fluorescence spectroscopic data revealed the formation of L–Th⁴⁺ complex in 1:1 equilibrium. The density functional theory (DFT) also confirms the optimum binding cavity for the recognition of metal ion. The binding constant computed from different mathematical models for an assembly of L–Th⁴⁺. The detection limit of L for Th⁴⁺ recognition is to a concentration down to 0.1 μM (0.023 μg g⁻¹). The present sensing system is also successfully applied for the detection of Th⁴⁺ ion present in soil near nuclear atomic plants.     

Isolation,Purification, and Characterization of Antimicrobial Compound 6-[1,2-dimethyl-6-(2-methyl-allyloxy)-hexyl]-3-(2-methoxy-phenyl)-chromen-4-one from Penicillium sp. HT-28

A fungal culture (Penicillium sp., HT-28), isolated from soil has been evaluated for its bioactivity, which showed broad spectrum antimicrobial activity and was effective against methicillin-resistant Staphylococcus aureus (MRSA) also. Statistical optimization of the medium by response surface methodology (RSM) enhanced the antimicrobial activity up to 1.8-fold. Column chromatography was used to isolate the active compound (A), which was characterized to be 6-[1,2-dimethyl-6-(2-methyl-allyloxy)-hexyl]-3-(2-methoxy-phenyl)-chromen-4-one by various spectroscopic techniques such as infrared (IR), ¹H and ¹³C nuclear magnetic resonance (NMR) spectra, and mass spectroscopy. Minimum inhibitory concentration (MIC) of the active compound (A) ranged from 0.5 to 15 μg/mL. Viable cell count studies of the active compound (A) showed S. aureus, Escherichia coli, Staphylococcus epidermidis, and Salmonella typhimurium 1 to be the most sensitive. The compound retained its bioactivity after treating it at 100 °C for 1 h. Furthermore, the compound (A) when tested for its biosafety was found neither to be cytotoxic nor mutagenic. The study demonstrated that an apparently novel compound isolated from Penicillium sp. (HT-28) seems to be a stable and potent antimicrobial.     

Synthesis,Characterization, and Surface Properties of Cationic Gemini Surfactants

New pyridinium gemini surfactants have been synthesized by esterification of renewable fatty acids with mercaptoethanol furnishing respective esters (mercaptomethyl decanoate, mercaptomethyl dodecanoate, mercaptomethyl tetradecanoate, mercaptomethyl hexadecanoate) followed by their subsequent treatment with 4-dimethyl amino pyridine resulting in the formation of title gemini surfactants: 1-(5-(decanoyloxy)-2-hydroxypentyl)-4-((5-(decanoyloxy)-2-hydroxypentyl)dimethyl ammonio)pyridin-1-ium chloride (9), 1-(5-(dodecanoyloxy)-2-hydroxypentyl)-4-((5-(dodecanoyloxy)-2-hydroxypentyl)dimethyl ammonio)pyridin-1-ium chloride (10), 1-(5-(tetradecanoyloxy)-2-hydroxypentyl)-4-((5-(tetradecanoyloxy)-2-hydroxypentyl)dimethyl ammonio)pyridin-1-ium chloride (11), and 1-(5-(hexadecanoyloxy)-2-hydroxypentyl)-4-((5-(hexadecanoyloxy)-2-hydroxypentyl)dimethyl ammonio)pyridin-1-ium chloride (12). Their identifications are based on infrared, ¹H NMR, ¹³C NMR, distortionless enhanced polarization transfer, co-relational spectroscopy (COSY), and mass spectral studies. Their surface active properties are also evaluated on the basis of surface tension and conductivity measurements. Thermal stability of these long chain cationic gemini surfactants have been measured by thermal gravimetric analysis under nitrogen atmosphere.     

Thiacalix[4]arene based fluorescent probe for sensing and imaging of Fe3+ ions

A thiacalix[4]arene based fluorescent chemosensor 3 in the cone conformation has been synthesized and its recognition behaviour is evaluated toward various metal ions in mixed aqueous media. The chemosensor 3 showed high selectivity towards Fe(3+) ions by fluorescence quenching of excimer emission. Further, evaluation of the 3·Fe(3+) complex prepared in situ demonstrated great promise for the detection of the Fe(3+) ion in the presence of amino acids, blood serum and bovine serum albumin (BSA) solution. The compound 3 has suitable permeability into the PC3 cells and can be utilized as a Fe(3+) selective sensor in living cells (PC3 cells).     

Synthesis and biological evaluation of the osteoblast proliferating cyclic peptides dianthins G and H

The first synthesis and osteoblast proliferative activity of the naturally occurring cyclic peptides dianthins G and H is described. The greater potency of naturally occurring dianthin G over dianthin H at physiological concentrations mirrored the osteoblast proliferative activity observed for synthetic dianthins G and H. Six alanine-scan analogues of the more potent dianthin G were also synthesised and osteoblast assays revealed that four of the six residues can be further modified for improved activity. We also confirmed by variable temperature ¹H NMR spectroscopic analysis that the sets of major and minor signals observed for dianthins G and H in DMSO-d₆ are in fact due to cis–trans rotational isomers of the proline ring.     

Organocatalytic asymmetric Friedel–Crafts reaction of 1-naphthols with isatins: an enantioselective synthesis of 3-aryl-3-hydroxy-2-oxindoles

An organocatalytic enantioselective Friedel–Crafts reaction of 1-naphthols with isatins has been developed employing bifunctional thiourea–tertiary amine organocatalysts. A variety of isatin derivatives react well with 1-naphthols in the presence of Cinchona derived thiourea 1a to provide biologically important chiral 3-aryl-3-hydroxy-2-oxindoles (3a–zg) in good yield (70–84%) and moderate to good enantioselectivity (37–83%).     

Elucidating the intermolecular hydrogen bonding interaction of proline with amides—quantum chemical calculations

Structural Chemistry - The hydrogen-bonded complexes formed between proline and amides have been investigated completely by the use of computational methods such as Atoms In Molecules (AIM),...