Luminescence Enhancement based Sensing of L‐Cysteine by Doped Quantum Dots

The interaction of a presynthesized orange emitting Mn²⁺‐doped ZnS quantum dots (QDs) with L‐Cysteine (L?Cys) led to enhance emission intensity (at 596 nm) and quantum yield (QY). Importantly, the Mn²⁺‐doped ZnS QDs exhibited high sensitivity towards L?Cys, with a limit of detection of 0.4±0.02 μM (in the linear range of 3.3–13.3 μM) and high selectivity in presence of interfering amino acids and metal ions. The association constant of L?Cys was determined to be 0.36×10⁵ M^?1. The amplified passivation of the surface of Mn²⁺‐doped ZnS QDs following the incorporation and binding of L?Cys is accounted for the enhancement in their luminescence features. Moreover, the luminescence enhancement‐based detection will bring newer dimension towards sensing application.     

Degradation of Na amylose xanthate in dilute caustic soda solution during ripening

Na amylose xanthate was prepared from potato starch by xanthation of amylose in dilute NaOH solution. Pure xanthate was then isolated and viscometric and turbidimetric studies on its ripening characteristics were carried out for a period of about 200 hrs. Prolonged ripening in air degraded the amylose chain without formation of gel. To study the nature of ripening more precisely, it was carried out in an identical way under N₂ and followed both viscometrically and turbidimetrically. The refractive-index increment (dn/dc) of the xanthate solutions during ripening under both air and nitrogen was continuously measured so as to avoid any possible error in computing correct molecular weights during ripening. Light-scattering molecular weights (M?_w) thus computed during the course of degradation of Na amylose xanthate extending for about 200 hr under both air and nitrogen were found to obey a first-order rate equation, In (M₀/M_t) = Kt where M_o is the initial molecular weight, M_t the molecular weight at time t of ripening, and K the rate constant of the degradation process.     

m-Aminobenzoic acid inserted β-turn in acyclic tripeptides: a peptidomimetic design

X-ray diffraction studies show that peptides Boc-Leu-Aib-m-ABA-OMe (I) (Aib, α-aminoisobutyric acid; m-ABA, meta-aminobenzoic acid) and Boc-Phe-Aib-m-ABA-OMe (II) adopt a type-II β-turn conformation, solely stabilized by co-operative steric interactions amongst the amino acid residues. This type of β-turn without any intramolecular hydrogen bonding is generally referred to as an open turn. Although there are some examples of constrained cyclic peptides in which o-substituted benzenes have been inserted to mimic the turn region of the neurotrophin, a nerve growth factor, peptides I and II present novel two examples where m-aminobenzoic acid has been incorporated in the β-turn of acyclic tripeptides. The result also demonstrates the first crystallographic evidence of a β-turn structure containing an inserted m-aminobenzoic acid, which can be considered as a rigid γ-aminobutyric acid with an all-trans extended configuration.     

Size-dependent interaction of gold nanoparticles with transport protein: A spectroscopic study

Gold nanoparticles of different sizes have been synthesized using sodium citrate as a reducing agent for tetrachloroauric (III) acid. The formed gold nanoparticles have been characterized by the UV-visible and transmission electron microscopy (TEM) measurements. The different sized gold nanoparticles have been used to study the interaction with model transport protein, bovine serum albumin (BSA). Experimental results reveal that BSA molecules adsorbed on the metallic surfaces, suffer strong quenching of their fluorescence and the rate of quenching efficiency is different for different particle size. The analysis of the quenching results has been performed in terms of the Stern-Volmer equation. The mechanism of quenching of fluorescence has been explained. The extent of adsorption of BSA on the gold nanoparticles has been estimated.     

Polyelectrolyte Configuration of Low Molecular Weight Sodium Amylose Xanthate in Aqueous and Salt Solutions

The polyelectrolyte chain configuration of low molecular weight sodium amylose xanthate (NaAX) in aqueous and salt solutions has been studied by viscometry and light scattering. The viscometric results in aqueous solution have been found to be in accordance with the Fuoss's modified equation. The intrinsic viscosities of NaAX in salt solutions from 0.00125 to 0.25 M NaCl have been determined and the expansion factor a at each ionic strength has been determined. The dependence of a on ionic strength has been studied according to the theories of Hermans and Overbeek, Flory, etc. But though qualitative agreement between experimental and theoretical results has been found, quantitative agreement was far from expectations. The frictional coefficient per monomer unit | has been calculated from the relationship of Kirkwood and Riseman. The NaAX macromolecule has been found to have the polydispersed random coil chain configuration in 0.25 M NaCl. Some macromolecular configurational parameters such as effective bond length b, Kuhn-Kuhn equivalent chain length A_m, and steric factor α has been determined.     

Solvent-Dependent Nanostructures Based on Active π-Aggregation Induced Emission Enhancement of New Carbazole Derivatives of Triphenylacrylonitrile

In the present study, the carbazole and 2,3,3-triphenylacrylonitrile (TPAN) nanostructures (2-CTPAN and 2,2′-CTPAN) have been designed and synthesized by Pd-catalyzed Sonogashira cross-coupling reaction. CTPAN exhibit aggregation-induced emission enhancement (AIEE) behavior in water with high fluorescence quantum yield. Both the compounds show tunable self-assembly in water as well as in N,N-dimethylformamide (DMF) by extended π–π stacking interactions. CTPAN can be self-assembled into spherical particles in water and the structures of these self-assemblies have been investigated using X-ray diffraction. Interestingly, 2-CTPAN and 2,2′-CTPAN form organogels with a critical gelation concentration (CGC) of 11 and 15 mg mL⁻¹, respectively, in DMF and exhibit acicular and rod shaped morphology, respectively. The single-crystal structure of 2-CTPAN shows that the intermolecular C−H⋅⋅⋅π interactions lock the molecular conformation into a staircase-shaped supramolecular assembly. These AIEE active compounds reveal high water dispersibility, strong yellow fluorescence with high quantum yield, promising photostability and excellent biocompatibility, which make them potential bioimaging agents.     

Biological Efficacy of Compounds from Stingless Honey and Sting Honey against Two Pathogenic Bacteria: An In Vitro and In Silico Study

Honey inhibits bacterial growth due to the high sugar concentration, hydrogen peroxide generation, and proteinaceous compounds present in it. In this study, the antibacterial activity of stingless and sting honey against foodborne pathogenic bacteria isolated from spoiled milk samples was examined. The isolated bacterial strains were confirmed as Bacillus cereus and Listeria monocytogenes through morphological, biochemical, and 16 s RNA analysis. Physiochemical characterizations of the honey samples revealed that both of the honey samples had an acidic pH, low water content, moderate reducing sugar content, and higher proline content. Through the disc diffusion method, the antibacterial activities of the samples were assayed and better results were observed for the 50 mg/disc honey. Both stingless and sting honey showed the most positive efficacy against Bacillus cereus. Therefore, an in silico study was conducted against this bacterium with some common compounds of honey. From several retrieved constituents of stingless and sting honey, 2,4-dihydroxy-2,5-dimethyl 3(2H)-furan-3-one (furan) and 4H-pyran-4-one,2,3-dihydro of both samples and beta.-D-glucopyranose from the stingless revealed high ligand-protein binding efficiencies for the target protein (6d5z, hemolysin II). The root-mean-square deviation, solvent-accessible surface area, the radius of gyration, root-mean-square fluctuations, and hydrogen bonds were used to ensure the binding stability of the docked complexes in the atomistic simulation and confirmed their stability. The combined effort of wet and dry lab-based work support, to some extent, that the antimicrobial properties of honey have great potential for application in medicine as well as in the food industries.     

Eco-friendly synthesis of 2-aryl-1-arylmethyl-1H-benzimidazoles using alumina-sulfuric acid as a heterogeneous reusable catalyst

A cost-effective and eco-friendly synthesis of 2-aryl-1-arylmethyl-1H-benzimidazoles has been developed through the condensation of different aldehydes with o-phenylenediamine using alumina-sulfuric acid as a recyclable heterogeneous solid acid catalyst. Morphological properties of the catalyst have been investigated. Effect of different solvents and comparison of alumina-sulfuric acid with different acid catalysts have also been studied. A plausible mechanistic pathway has been proposed on the basis of the isotope labelling experiments where catalytic behaviour of alumina-sulfuric acid has been explained.     

Silica sulfuric acid: an efficient reusable heterogeneous solid support for the synthesis of 3H,3′H-spiro[benzofuran-2,1′isobenzofuran]-3,3′-diones under solvent-free condition

A highly efficient protocol for the library synthesis of biologically important 3H,3′H-spiro[benzofuran-2,1′isobenzofuran]-3,3′-diones has been developed by employing silica sulfuric acid (SSA) as solid acid support under solvent-free condition. The dual characteristics of SSA, as an activating agent as well as oxidizing agent, have been well exposed in these syntheses. The intrinsic advantages of the methodology are the use of solvent-free reaction condition without using any toxic reagents or metal catalyst, operational simplicity, recyclability of the solid support, good availability of the starting materials, and excellent yields which make the method attractive, economic, and ‘benign by design’.