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.     

A chelating resin containing bis(2-benzimidazolylmethyl)amine: synthesis and metal-ion uptake properties suitable for analytical application

A new stable chelating resin was synthesized by incorporating the bis(2-benzimidazolyl methyl)amine into Merrifield polymer through CN covalent bond and characterized by elemental analysis, IR and thermal study. The sorption capacity of the newly formed resin for Ag(I), Cu(II), Fe(III), Hg(II) and Pb(II) as a function of pH have been studied. The resin exhibits no affinity for alkali or alkaline earth metals. In column operation it has been observed that Ag(I) in trace quantities can be separated from different complex matrices and Hg(II) can be removed from the river water spiked with Hg(II) at usual pH of natural waters.     

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.     

Zero-Sum Stochastic Games with Partial Information and Average Payoff

We consider a discrete time partially observable zero-sum stochastic game with average payoff criterion. We study the game using an equivalent completely observable game. We show that the game has a value and also we present a pair of optimal strategies for both the players.     

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.     

A C Symmetric Nitrate Complex with a Thiophene-Based Tripodal Receptor

A thiophene-based tripodal receptor has been synthesized and its complexes with nitrate and iodide have determined by single-crystal X-ray analysis. In the nitrate complex, one nitrate is encapsulated in a selective orientation forming a C(3) symmetric complex, which is bonded to three protonated secondary amines with six NH···O bonds. The anion is coordinated in a plane perpendicular to the principal rotation axis passing through the tertiary nitrogen of the receptor and the nitrogen of the encapsulated nitrate. High-level DFT calculations support the crystallographic results demonstrating that an adduct with trigonal binding of three oxygen atoms is more stable than that of one oxygen atom of the encapsulate nitrate. On the other hand, in the structure of the iodide complex, all three iodides lie outside the cavity. (1)H NMR titration studies indicate that the receptor forms a 1:1 complex with nitrate with a binding constant of K = 315 M(-1) in chloroform, showing a moderate selectivity over halides and perchlorate.     

Synthesis,characterization, thermal and luminescent properties of thiophenol-functionalized platinum(II) bis(acetylide) complexes

Transition Metal Chemistry - Two thiophenol-functionalized trans-platinum(II) bis(acetylide) complexes, having one thiophenol moiety in each alkenyl backbone with general formula...