Retention of nisin activity at elevated pH in an organic acid complex and gold nanoparticle composite

Biocompatible organic acids and citrate-stabilized gold nanoparticles were interacted with nisin to generate robust antimicrobial agents, which display archetypical nisin activity even at elevated pH.     

Theoretical analysis of photoinduced H-atom elimination in thiophenol

The photoinduced hydrogen elimination reaction in thiophenol via the conical intersections of the dissociative (1)πσ? excited state with the bound (1)ππ? excited state and the electronic ground state has been investigated with ab initio electronic-structure calculations and time-dependent quantum wave-packet calculations. A screening of the coupling constants of the symmetry-allowed coupling modes at the (1)ππ?-(1)πσ? and (1)πσ?-S(0) conical intersection shows that the SH torsional mode is by far the most important coupling mode at both conical intersections. A model including three intersecting potential-energy surfaces (S(0), (1)ππ?, (1)πσ?) and two nuclear degrees of freedom (SH stretch and SH torsion) has been constructed on the basis of ab initio complete-active-space self-consistent field and multireference second-order perturbation theory calculations. The nonadiabatic quantum wave-packet dynamics initiated by optical excitation of the (1)ππ? and (1)πσ? states has been explored for this three-state two-coordinate model. The photodissociation dynamics is characterized in terms of snapshots of time-dependent wave packets, time-dependent electronic population probabilities, and the branching ratio of the (2)σ/(2)π electronic states of the thiophenoxyl radical. The dependence of the timescale of the photodissociation process and the branching ratio on the initial excitation of the SH stretching and SH torsional vibrations has been analyzed. It is shown that the node structure, which is imposed on the nuclear wave packets by the initial vibrational preparation as well as by the transitions through the conical intersections, has a profound effect on the photodissociation dynamics. The effect of additional weak coupling modes of CC twist (ν(16a)) and ring-distortion (ν(16b)) character has been investigated with three-dimensional and four-dimensional time-dependent wave-packet calculations, and has been found to be minor.     

Simple and one-pot protocol for synthesis of indene-spiro-oxindoles involving tandem Prins and Friedel-Crafts reactions

[reaction: see text] A simple and one-pot protocol for the synthesis of indene-spiro-oxindole derivatives via TiCl4-mediated reaction between 1,1-diarylethylenes and isatin derivatives involving construction of two carbon-carbon bonds through tandem Prins and intramolecular Friedel-Crafts (PFC) reactions has been described. A plausible mechanism for this transformation is also presented.     

Conformationally rigid aromatic amino acids as potential building blocks for abiotic foldamers

This communication describes the development of conformationally constrained unnatural aromatic amino acids, constructed on rigid backbone wherein the carboxyl and amino groups project in two dimensions (planes) on the aromatic framework. Such a feature offers the possibility of design and development of conformationally ordered synthetic oligomers with intriguing structural architectures distinct from those classically observed. Furthermore, such amino acids will have the potential to extend the conformational space available for foldamer design with diverse backbone conformation and structural architectures.     

Differentiation of electrophilic and ambiphilic carbenes

Comparative selectivities toward alkenes of CH₃CCl, CCl₂, and CH₃OCCl establish the former two carbenes as electrophiles; the latter is an ambiphile.     

Magnetic nanoparticle‐tethered Schiff base–palladium(II): Highly active and reusable heterogeneous catalyst for Suzuki–Miyaura cross‐coupling and reduction of nitroarenes in aqueous medium at room temperature

As a continuation of our efforts to develop new heterogeneous nanomagnetic catalysts for greener reactions, we identified a Schiff base–palladium(II) complex anchored on magnetic nanoparticles (SB‐Pd@MNPs) as a highly active nanomagnetic catalyst for Suzuki–Miyaura cross‐coupling reactions between phenylboronic acid and aryl halides and for the reduction of nitroarenes using sodium borohydride in an aqueous medium at room temperature. The SB‐Pd@MNPs nanomagnetic catalyst shows notable advantages such as simplicity of operation, excellent yields, short reaction times, heterogeneous nature, easy magnetic work up and recyclability. Characterization of the synthesized SB‐Pd@MNPs nanomagnetic catalyst was performed with various physicochemical methods such as attenuated total reflectance infrared spectroscopy, UV–visible spectroscopy, inductively coupled plasma atomic emission spectroscopy, energy‐dispersive X‐ray spectroscopy, field‐emission scanning electron microscopy, transmission electron microscopy, powder X‐ray powder diffraction, thermogravimetric analysis and Brunauer–Emmett–Teller surface area analysis.     

Spectral,electrochemical and computational investigations on the host–guest interaction of Coumarin-460 with <Emphasis Type="Italic">p</Emphasis>-sulfonatocalix[4]arene

The supramolecular host–guest investigation of Coumarin 460 (C460), a salient coumarin family dye molecule is studied with a noteworthy host molecule, p-sulfonatocalix[4]arene (p-SC4). The investigation is carried out by both experimental and theoretical approach. The binding affinity of C460 with p-SC4 is experimentally studied using absorption, emission, excited state lifetime and Cyclic Voltammetry methods. The binding constant is around 10³ M^??1, which shows potent binding. The binding stoichiometry is 1:1. The binding orientations and binding energies are studied using computational simulations. The mode of binding is also established using NMR spectral techniques.     

Electrochemical and photocatalytic investigation of nickel oxide for energy storage and wastewater treatment

Nickel oxide (NiO) was synthesized via a one-step facile method. X-ray diffraction analysis confirmed the face-centered cubic structure of NiO. The bonding nature and surface purity were confirmed via Fourier-transform infrared spectroscopy. NiO revealed partial spherical morphology with less particle aggregation. The optical bandgap of NiO was found to be 3.75 eV. Cyclic voltammetry revealed well-defined oxidation and reduction peaks for NiO. The charge–discharge curve exhibited specific capacitance of 184.6 F/g at current density of 0.3 A/g. NiO electrode exhibited longer cyclic stability of 93 % up to 1500 cycles. In addition, NiO + H₂O₂ revealed efficient photocatalytic degradation of methylene blue (organic pollutant) under visible-light irradiation with degradation efficiency of ~88 %. These results confirm that nanosized NiO is more suitable for dual application.

     

Calcium Alginate Bead-mediated Enhancement of the Selective Recovery of a Lead Novel Antifungal Bacillomycin Variant

In the pursuit of new antifungal compounds, five coproduced lipopeptide variants (AF₁ to AF₅) from wild-type Bacillus subtilis RLID 12.1 were identified in our previous study. Out of five, AF₄ was identified as a novel lead molecule belonging to the bacillomycin family showing less cytotoxicity at its respective minimum inhibitory concentrations (MIC) evaluated against 81 strains of Candida and Cryptococcus species (including clinical isolates); besides this, AF₄ purified in the present study exhibited encouraging MIC values against 10 clinical mycelial fungi. Aiming for a selective production augmentation of AF₄ lipopeptide variant, a new fermentation media comprising malt extract (1.01%), dextrose (0.55%), peptone (1.79%), MnSO₄ (2 mM), and NaCl (0.5%) was formulated. Maximum production of 954.8?±?10.8 mg/L was achieved with 44% selectivity at 30 °C compared to unoptimized conditions (186.4?±?6.1 mg/L). Use of calcium alginate beads in the formulated media during the onset of lipopeptide production resulted in an augmentation in the selectivity of the most efficacious AF₄ variant to about 72% presumably due to attenuation of other coproduced lipopeptide variants AF₁ and AF₂. Difference in yield of lipopeptides varied with bead size, bead preparation ratios, and sodium alginate concentrations. Use of Ca-alginate beads in the upstream production process of the lead AF₄ variant may be considered as a novel strategy to address the potential challenge that may arise during the scale-up and downstream processing steps. Another significant finding derived from the study is that the proportion of bacillomycin variants of B. subtilis RLID 12.1 could be controlled by temperature and metal ions under static and shaking conditions.