A combined experimental and density functional theory study on the complexation ability of 15-crown-5 with Li+, Na+, K+, and NH4 + cations

The complexation processes among Li⁺, Na⁺, K⁺, and NH₄ ⁺ cations with the macrocyclic ligand, 15-crown-5 (15C5) have been studied in acetonitrile–methanol binary mixtures at different temperatures using conductometric method. The stability constants of the resulting 1:1 complexes were calculated from the computer fitting of the molar conductance–mole ratio data at various temperatures. The values of thermodynamic parameters ( $ \Updelta H_{\text{c}}^{^\circ } $ and $ \Updelta S_{\text{c}}^{^\circ } $ ) for the formation of the complexes were obtained from temperature dependence of the stability constants of complexes using van’t Hoff plots. In addition, a theoretical study has been carried out using density functional theory to obtain the stability of the complexes and the geometrical structure of the 15C5 and its complexes with Li⁺, Na⁺, K⁺ and NH₄ ⁺ cations in the gas phase. We compared the experimental data with those obtained by quantum chemistry calculations to investigate the effect of the solvent on complexation process.     

2-Isoxazolidineethanols: an NMR study of the effect of intramolecular H-bonding on the population of nitrogen invertomers and inversion process

A series of (betaR,5R)- and (betaR,5S)-2,5-disubstituted isoxazolidines: 5-(substituent)-beta-phenyl-2-isoxazolidineethanols, have been prepared by asymmetric nitrone cycloaddition reactions and their NMR spectra recorded over a wide range of temperatures. The spectra at low temperatures indicate the presence of the (betaR,5S) diasteromer almost exclusively as a single invertomer having trans disposition of the substituents at N(2) and C(5), while the (betaR,5R) diasteromer remained as a mixture of two interconverting invertomers in deuterated chloroform. The effect of H-bonding - intramolecular in CDCl(3) and intermolecular in CD(3)OD - on the population ratio of the invertomers and nitrogen inversion process has been investigated. The nitrogen inversion barriers are determined using complete line-shape analysis, and their dependence on solvent is discussed. Due to steric factor the trans-invertomers are found to be more stable than their cis counterparts.     

Textural and adsorption characteristics of carbon xerogel adsorbents for removal of Cu (II) ions from aqueous solution

Resorcinol–formaldehyde (RF) carbon xerogels were synthesized using different resorcinol/sodium carbonate catalyst molar ratios (R/C = 50, 200, 500 and 1000) and heat treatment temperatures (HTT = 500, 600 and 700) under no external gas flow. The carbon adsorbents were extensively characterized by CHO content, FTIR, TEM and nitrogen adsorption isotherm at 77 K. The effect of R/C, HTT and oxygen content on the development of porosity within carbons was studied. Also, the adsorption capacity of these adsorbents was investigated by the removal of copper (II) ions from aqueous solution using single bottle test. The produced carbon xerogels exhibit a micro-mesopore character, but with different extents depending on the mechanism of porosity generation in relation to R/C, HTT and oxygen functional groups. Results show that the optimum conditions to obtain porous carbon xerogels were the highest R/C = 500–1000 in combination with carbonization preferably at 600 or 700 °C. Single bottle removal of Cu (II) ions indicated the developed carbons with appreciable capacity (q_u = 32–130 mg/g) which are controlled by the surface area and surface chemical nature (acidic O-functional groups). Finally, the present investigation provides a new, nanoporous type of porous carbon adsorbents with high adsorption capacity for removal of heavy metals from wastewater media.     

Spectral and thermal studies of divalent transition metal complexes with indole-2-carboxylic acid and 4-substituted hydrazinethiocarbamide

Ternary complexes of Co(II), Ni(II) and Cu(II) with indole-2-carboxylic acid (A) and 4-substituted hydrazinethiocarbamide (L) [4-phenylhydrazinethiocarbamide (L1), 4-benzylhydrazinethiocarbamide (L2) and 4-(2-propenyl)hydrazinethiocarbamide (L3)] were prepared. The structures of the complexes were proposed by molar conductance, electronic, IR, 1H NMR, mass spectra as well as thermogravimetric (TG) studies. An octahedral structure is suggested for Co(II), Ni(II) and Cu(II) ternary complexes.     

Biosynthesis of Silver Chloride Nanoparticles by Rhizospheric Bacteria and Their Antibacterial Activity against Phytopathogenic Bacterium Ralstonia solanacearum

Ralstonia solanacearum is the most destructive pathogen, causing bacterial wilt disease of eggplant. The present study aimed to develop green synthesis and characterization of silver chloride nanoparticles (AgCl-NPs) by using a native bacterial strain and subsequent evaluation of their antibacterial activity against R. solanacearum. Here, a total of 10 bacterial strains were selected for the biosynthesis of AgCl-NPs. Among them, the highest yield occurred in the synthesis of AgCl-NPs using a cell-free aqueous filtrate of strain IMA13. Ultrastructural observation revealed that the AgCl-NPs were spherical and oval with smooth surfaces and 5–35 nm sizes. XRD analysis studies revealed that these particles contained face-centered cubic crystallites of metallic Ag and AgCl. Moreover, FTIR analysis showed the presence of capping proteins, carbohydrates, lipids, and lipopeptide compounds and crystalline structure of AgCl-NPs. On the basis of phylogenetic analysis using a combination of six gene sequences (16S, gyrA, rpoB, purH, polC, and groEL), we identified strain IMA13 as Bacillus mojavensis. Three kinds of lipopeptide compounds, namely, bacillomycin D, iturin, and fengycin, forming cell-free supernatant produced by strain IAM13, were identified by MALDI-TOF mass spectrometry. Biogenic AgCl-NPs showed substantial antibacterial activity against R. solanacearum at a concentration of 20 µg/mL⁻¹. Motility assays showed that the AgCl-NPs significantly inhibited the swarming and swimming motility (61.4 and 55.8%) against R. solanacearum. Moreover, SEM and TEM analysis showed that direct interaction of AgCl-NPs with bacterial cells caused rupture of cell wall and cytoplasmic membranes, as well as leakage of nucleic acid materials, which ultimately resulted in the death of R. solanacearum. Overall, these findings will help in developing a promising nanopesticide against phytopathogen plant disease management.     

The Biodiversity of the Genus Dictyota: Phytochemical and Pharmacological Natural Products Prospectives

Although a broad variety of classes of bioactive compounds have already been isolated from seaweeds of the genus Dictyota, most different species are still chemically and biologically unexplored. Dictyota species are well-known brown seaweeds belonging to the Dictyotaceae (Phaeophyta). The phytochemical composition within the genus Dictyota has recently received considerable interest, and a vast array of components, including diterpenes, sesquiterepenes, sterols, amino acids, as well as saturated and polyunsaturated fatty acids, have been characterized. The contribution of these valued metabolites to the biological potential, which includes anti-proliferative, anti-microbial, antiviral, antioxidant, anti-inflammatory, and anti-hyperpigmentation activities, of the genus Dictyota has also been explored. Therefore, this is the most comprehensive review, focusing on the published literature relevant to the chemically and pharmacologically diverse biopharmaceuticals isolated from different species of the genus Dictyota during the period from 1976 to now.     

Does Urea Preferentially Interact with Amide Moieties or Nonpolar Sidechains? A Question Answered Through a Judicious Selection of Model Systems

The transfer model suggests that urea unfolds proteins mainly by increasing the solubility of the amide backbone, probably through urea-induced increase in hydrogen bonding. Other studies suggest that urea addition increases the magnitude of solvent-solute van der Waals interactions, which increases the solubility of nonpolar sidechains. More recent analyses hypothesize that urea has a similar effect in increasing the solubility of backbone and sidechain groups. In this work, we compare the effects of urea addition on the solvation of amides and alkyl groups. At first, we study the effects of urea addition upon solvent hydrogen bonding acidity and basicity through the perturbation in the fluorescence spectrum of probes 1-AN and 1-DMAN. Our results demonstrate that the solvent's hydrogen bonding properties are minimally affected by urea addition. Subsequently, we show that urea addition does not perturb the intra-molecular hydrogen bonding in salicylic acid significantly. Finally, we investigate how urea preferentially interacts with amide and alkyl groups moieties in water by comparing the effects of urea addition upon the solubility of acetaminophen and 4-tertbutylphenol. We show that urea affects amide and t-butyl solubility (lowers the transfer free energy of both amide (backbone) and alkyl (sidechain) groups) in a similar fashion. In other words, preferential interaction of urea with both moieties contributes to protein denaturation.