Global energy minimization of alanine dipeptide via barrier function methods

This paper presents an interior point method to determine the minimum energy conformation of alanine dipeptide. The CHARMM energy function is minimized over the internal coordinates of the atoms involved. A barrier function algorithm to determine the minimum energy conformation of peptides is proposed. Lennard-Jones 6-12 potential which is used to model the van der Waals interactions in the CHARMM energy equation is used as the barrier function for this algorithm. The results of applying the algorithm for the alanine dipeptide structure as a function of varying number of dihedral angles are reported, and they are compared with that obtained from genetic algorithm approach. In addition, the results for polyalanine structures are also reported.     

Theoretical realization of cluster-assembled hydrogen storage materials based on terminated carbon atomic chains

The capacity of carbon atomic chains with different terminations for hydrogen storage is studied using first-principles density functional theory calculations. Unlike the physisorption of H(2) on the H-terminated chain, we show that two Li (Na) atoms each capping one end of the odd- or even-numbered carbon chain can hold ten H(2) molecules with optimal binding energies for room temperature storage. The hybridization of the Li 2p states with the H(2)σ orbitals contributes to the H(2) adsorption. However, the binding mechanism of the H(2) molecules on Na arises only from the polarization interaction between the charged Na atom and the H(2). Interestingly, additional H(2) molecules can be bound to the carbon atoms at the chain ends due to the charge transfer between Li 2s2p (Na 3s) and C 2p states. More importantly, dimerization of these isolated metal-capped chains does not affect the hydrogen binding energy significantly. In addition, a single chain can be stabilized effectively by the C(60) fullerenes termination. With a hydrogen uptake of ～10 wt.% on Li-coated C(60)-C(n)-C(60) (n = 5, 8), the Li(12)C(60)-C(n)-Li(12)C(60) complex, keeping the number of adsorbed H(2) molecules per Li and stabilizing the dispersion of individual Li atoms, can serve as better building blocks of polymers than the (Li(12)C(60))(2) dimer. These findings suggest a new route to design cluster-assembled hydrogen storage materials based on terminated sp carbon chains.     

A Dual Colorimetric and Fluorometric Sensor for Lead Ion Based on Conjugated Polydiacetylenes

A PDA based sensor, derived from a di‐(2‐picolyl) amine (DPA) substituted diacetylene monomer, displayed a selective colorimetric change and a large fluorescence enhancement in the presence of lead ions. The lead selective PDA‐based chemosensor enabled easy detection of the presence of lead in 100% aqueous solution by the naked‐eye.

     

Non-chromatographic determination of ultratraces of V(V) and V(IV) based on a double column solid phase extraction flow injection system coupled to electrothermal atomic absorption spectrometry

In this work, a non-chromatographic procedure for the on-line determination of ultratraces of V(V) and V(IV) is presented. The method involves a solid phase extraction-flow injection system coupled to electrothermal atomic absorption spectrometry (SPE-FI-ETAAS). The system holds two microcolumns (MC) set in parallel and filled with lab-made mesoporous silica functionalized with 3-aminopropyltriethoxy silane (APS) and mesoporous silica MCM-41, respectively. The pre-concentration of V(V) is performed by sorption onto the first MC (C1) filled with APS at pH 3, whilst that of V(IV) is performed by sorption onto the second column (C2) filled with mesoporous silica MCM-41 at pH 5. Aqueous samples containing both analytes are loaded and, after pre-concentration (pre-concentration factor PCF = 10, sorption flow rate = 1 mL min⁻¹, sorption time = 10 min), they are eluted in separate vessels with hydroxylammonium chloride (HC) 0.1 mol L⁻¹ in HCl 0.5 mol L⁻¹ (elution volume = 1 mL, elution flow rate = 0.5 mL min⁻¹). Afterwards, both analytes are determined through ETAAS with graphite furnace. Under optimized conditions, the main analytical figures of merit for V(V) and V(IV) are, respectively: detection limits (3 s): 0.5 and 0.6 μg L⁻¹, linear range: 2-100 μg L⁻¹ (both analytes), sensitivity: 0.015 and 0.013 μg⁻¹ L and sample throughput: 6 h⁻¹ (both analytes). Recoveries of both species were assayed in different water samples. Validation was performed through certified reference materials for ultratraces of total vanadium in river water.     

Bicontinuous Nanoporous Frameworks: Caged Longevity for Enzymes

The preparation of bicontinuous nanoporous covalent frameworks, which are promising for caging active enzymes, is demonstrated. The frameworks have three‐ dimensionally continuous, hydrophilic pores with widths varying between 5 and 30 nm. Enzymes were infiltrated into the bicontinuous pore by applying a pressured enzyme solution. The new materials and methods allowed the amount of caged proteins to be controlled precisely. The resulting enzyme‐loaded framework films could be recycled many times with nearly no loss of catalytic activity. Entropic trapping of proteins by a bicontinuous pore with the right size distribution is an unprecedented strategy toward facile in vitro utilization of biocatalysts.     

Target-oriented multifunctional organocatalysis for enantioselective synthesis of bicyclo[3.3.1]nona-2,6-dien-9-ones. A formal asymmetric synthesis of huperzine A

A target-oriented highly enantioselective multifunctional organocatalytic approach has been developed to construct the bicycle-[3.3.1]nona-2,6-dien-9-one core of (?)-huperzine A for the first time, with up to 95% ee in the gram-scale procedure. The newly established methodology is also eligible to synthesize a variety of bicyclo[3.3.1]nona-2,6-dien-9-ones in high enantiopurities, and thus is useful for the future development of novel huperzine A analogs with medicinal interests.     

Development of an impregnated reagent and automation of solid-phase analytical derivatization for carbonyls: proof of principle

This study undertakes reduction of scale and automation of a solid-phase analytical derivatization of carbonyls with 2,4-dinitrophenylhyrazine on a styrene-divinylbenzene resin (XAD-2). Three processes are tested. In the batch process, an aqueous phase consisting of 50 microL of sample and 150 microL of reagent solution is contacted with 6 mg XAD-2 by shaking. An impregnated reagent consisting of 2,4-dinitrophenylhydrazine hydrochloride (DNPH) deposited on XAD-2 enables two additional processes. In-vial derivatization with an impregnated reagent requires shaking 50 microL of sample with 6 mg of the impregnated reagent and reduced the reaction time from 10 to 5 min. The third process involves packing impregnated reagent a mini-column and flowing 50 microL of sample through under positive pressure supplied by a Harvard Pump. This reduces sample preparation time to 1 min. Studies are conducted with worst-case model analytes: butanone, 2-pentanone, and malonyldialdehyde. The carbonyl of the two ketones is hindered, and, thus, these two compounds react very slowly with DNPH in aqueous solution. Malonyldialdehyde is highly water soluble, and it does not react in aqueous phase but also would not sorb onto XAD-2 for reaction. Nevertheless, derivatization/extraction of all model compounds any of the three procedures result in reproducible and high yields.     

Analysis of the variations in IL-28RA gene and their association with allergic rhinitis

IL-28RA is one of the important candidate genes for complex trait of genetic diseases, but there is no published information of the genetic variation in this gene. We scanned the seven exons and their boundary introns sequence of IL-28RA including the promoter regions to analyze genetic variation sites, and identified eighteen single nucleotide polymorphisms (SNPs) and two variation sites. We chose seven SNPs (g.-1193 A>C, g.-30 C>T, g.17654 C>T, g.27798 A>G, g.31265 C>T, g.31911 C>T and g.32349 G>A) of them for large sample size genotyping, and assessed the association of genotype and allele frequencies of these SNPs between allergic rhinitis patients and non-allergic rhinitis controls. We also compared the genotype frequencies between Korean controls and Han Chinese control or Korean Chinese control. We investigated the frequencies of haplotype constructed by these SNPs between allergic rhinitis patients and non-allergic rhinitis controls. Our results suggested that the g.32349 G>A polymorphism of IL-28RA might be associated with susceptibility to allergic rhinitis (P=0.032), but seems to have no relationship with serum total IgE levels. The haplotype frequencies by these SNPs also show significant association between controls and allergic rhinitis patients.