High‐Concentration Graphene Dispersions with Minimal Stabilizer: A Scaffold for Enzyme Immobilization for Glucose Oxidation

Modified acrylate polymers are able to effectively exfoliate and stabilize pristine graphene nanosheets in aqueous media. Starting with pre‐exfoliated graphite greatly promotes the exfoliation level. The graphene concentration is significantly increased up to 11 mg mL^?1 by vacuum evaporation of the solvent from the dispersions under ambient temperature. TEM shows that 75 % of the flakes have fewer than five layers with about 18 % of the flakes consisting of monolayers. Importantly, a successive centrifugation and redispersion strategy is developed to enable the formation of dispersions with exceptionally high graphene‐to‐stabilizer ratio. Characterization by high‐resolution transmission electron microscopy, X‐ray photoelectron spectroscopy, X‐ray diffraction, and Raman spectroscopy shows the flakes to be of high quality with very low levels of defects. These dispersions can act as a scaffold for the immobilization of enzymes applied, for example, in glucose oxidation. The electrochemical current density was significantly enhanced to be approximately six times higher than an electrode in the absence of graphene, thus showing potential applications in enzymatic biofuel cells.     

Advanced vapor recognition materials for selective and fast responsive surface acoustic wave sensors: A review

The necessity of selectively detecting various organic vapors is primitive not only with respect to regular environmental and industrial hazard monitoring, but also in detecting explosives to combat terrorism and for defense applications. Today, the huge arsenal of micro-sensors has revolutionized the traditional methods of analysis by, e.g. replacing expensive laboratory equipment, and has made the remote screening of atmospheric threats possible. Surface acoustic wave (SAW) sensors – based on piezoelectric crystal resonators – are extremely sensitive to even very small perturbations in the external atmosphere, because the energy associated with the acoustic waves is confined to the crystal surface. Combined with suitably designed molecular recognition materials SAW devices could develop into highly selective and fast responsive miniaturized sensors, which are capable of continuously monitoring a specific organic gas, preferably in the sub-ppm regime. For this purpose, different types of recognition layers ranging from nanostructured metal oxides and carbons to pristine or molecularly imprinted polymers and self-assembled monolayers have been applied in the past decade. We present a critical review of the recent developments in nano- and micro-engineered synthetic recognition materials predominantly used for SAW-based organic vapor sensors. Besides highlighting their potential to realize real-time vapor sensing, their limitations and future perspectives are also discussed.     

Metal‐based antibacterial and antifungal amino acid derived Schiff bases: their synthesis,characterization and in vitro biological activity

A new series of antibacterial and antifungal amino acid derived Schiff bases and their cobalt(II), copper(II), nickel(II) and zinc(II) metal complexes have been synthesized and characterized by their elemental analyses, molar conductances, magnetic moments, IR and electronic spectral measurements. The spectral data indicated the Schiff base ligands ( L ₁– L ₅) derived by condensation of salicylaldehyde with glycine, alanine, phenylalanine, methionine and cysteine, to act as tridentate towards divalent metal ions (cobalt, copper, nickel and zinc) via the azomethine‐N, deprotonated carboxyl group of the respective amino acid and deprotonated oxygen atom of salicylaldehyde by a stoichiometric reaction of M: L (1:2) to form complexes of the type K₂[M( L )₂] [where M = Co(II), Cu(II), Ni(II) and Zn(II)]. The magnetic moments and electronic spectral data suggested that all complexes have an octahedral geometry. Elemental analyses and NMR spectral data of the ligands and their Zn (II) complexes agree with their proposed structures. The synthesized ligands, along with their metal complexes, were screened for their in‐vitro antibacterial activity against four Gram‐negative (Escherichia coli, Shigella flexeneri, Pseudomonas aeruginosa and Salmonella typhi) and two Gram ‐ positive (Bacillus subtilis and Staphylococcus aureus) bacterial strains and for in‐vitro antifungal activity against Trichophyton longifusus, Candida albicans, Aspergillus flavus, Microsporum canis, Fusarium solani and Candida glaberata. The results of these studies show the metal complexes to be more antibacterial/antifungal against one or more species as compared with the uncomplexed Schiff base ligands. The brine shrimp bioassay was also carried out to study their in‐vitro cytotoxic properties. Only three compounds ( 2, 11 and 17 ) displayed potent cytotoxic activity as LD₅₀ = 8.196 × 10^?4, 7.315 × 10^?4 and 5.599 × 10^?4 M /ml respectively, against Artemia salina. Copyright © 2007 John Wiley & Sons, Ltd.     

Reactions of C2H with 1- and 2-butynes: an ab initio/RRKM study of the reaction mechanism and product branching ratios

Ab initio CCSD(T)/cc-pVTZ(CBS)//B3LYP/6-311G** calculations of the C(6)H(7) potential energy surface are combined with RRKM calculations of reaction rate constants and product branching ratios to investigate the mechanism and product distribution in the C(2)H + 1-butyne/2-butyne reactions. 2-Ethynyl-1,3-butadiene (C(6)H(6)) + H and ethynylallene (C(5)H(4)) + CH(3) are predicted to be the major products of the C(2)H + 1-butyne reaction. The reaction is initiated by barrierless ethynyl additions to the acetylenic C atoms in 1-butyne and the product branching ratios depend on collision energy and the direction of the initial C(2)H attack. The 2-ethynyl-1,3-butadiene + H products are favored by the central C(2)H addition to 1-butyne, whereas ethynylallene + CH(3) are preferred for the terminal C(2)H addition. A relatively minor product favored at higher collision energies is diacetylene + C(2)H(5). Three other acyclic C(6)H(6) isomers, including 1,3-hexadiene-5-yne, 3,4-hexadiene-1-yne, and 1,3-hexadiyne, can be formed as less important products, but the production of the cyclic C(6)H(6) species, fulvene, and dimethylenecyclobut-1-ene (DMCB), is predicted to be negligible. The qualitative disagreement with the recently measured experimental product distribution of C(6)H(6) isomers is attributed to a possible role of the secondary 2-ethynyl-1,3-butadiene + H reaction, which may generate fulvene as a significant product. Also, the photoionization energy curve assigned to DMCB in experiment may originate from vibrationally excited 2-ethynyl-1,3-butadiene molecules. For the C(2)H + 2-butyne reaction, the calculations predict the C(5)H(4) isomer methyldiacetylene + CH(3) to be the dominant product, whereas very minor products include the C(6)H(6) isomers 1,1-ethynylmethylallene and 2-ethynyl-1,3-butadiene.     

An Upper Bound for the Regularity of Ideals of Borel Type

We show that the regularity of monomial ideals of K[x ₁,…, x _n ] (K being a field), whose associated prime ideals are totally ordered by inclusion is upper bounded by a linear function in n.     

The kinetics of photostabilization of cyanocobalamin in liposomal preparations

Cyanocobalamin (B₁₂) is a photosensitive vitamin, and its photodegradation to hydroxocobalamin (B_12b) in liposomes has been investigated. The values of apparent first-order rate constants (k_obs) for the photodegradation of B₁₂ in liposomes (nine preparations) are in the range of (0.52-2.24) × 10^–3 min^–1, compared to 3.21 × 10^–3 min^–1 for B₁₂ in aqueous solution (pH 5.0). The entrapment efficiency of B₁₂ in liposomes is 26.4-38.8%. The values of k_obs show a linear relation with phosphatidylcholine (PC) content in liposomes, indicating the influence of PC in inhibiting the rate of photolysis of B₁₂. The value of the bimolecular rate constant for photochemical interaction of B₁₂ and PC is 0.32 M^–1 min^–1, indicating the stabilizing effect of PC on the photolysis of B₁₂. The ratio of B₁₂ stabilization in liposomal preparations is in the range 2-6 compared to that of the unentrapped vitamin The stabilization of B₁₂ is mediated by a photoinduced charge-transfer B₁₂-PC complex that leads to the reduction of B₁₂ to B_12r, which is then oxidized to B_12b that has low susceptibility to photolysis. The extent of stabilization of B₁₂ probably depends on the degree of interaction between the two compounds under the reaction conditions, indicated by the loss of B₁₂ fluorescence.     

Main fatty acid classes in vegetable oils by SB-ATR-Fourier transform infrared (FTIR) spectroscopy

The prospect of using single bounce attenuated total reflectance (SB-ATR)-Fourier transform infrared (FTIR) spectroscopy as a rapid quantitative tool to determine the main fatty acid groups present in different edible oils was investigated. Partial least squares (PLS) calibrations were developed using SB-ATR-FTIR spectra which were associated with fatty acid groups (saturated, trans, mono- and polyunsaturated) using quantitative data obtained by gas chromatography (GC). Good calibrations were obtained for all main four fat groups (saturated, mono, trans and polyunsaturated) with excellent precision. The coefficient of determination (R²), root mean square error of prediction (RMSEP) and bias for validation set were obtained as 0.999, 2.43 and 0.998 for saturated; 0.999, 1.850 and 0.003 for mono; 0.999, 0.625 and −0.001 for trans while for poly the values were 0.999, 1.170 and 0.003, respectively. The results of 13 validation samples for total saturated, mono, trans and polyunsaturated fats by FI-IR were found in the range of 8.16-55.16, 37.62-74.75, 0.20-18.16 and 1.36-62.35%, respectively. The present study shows that it may well be possible to expand the utility of SB-ATR-FTIR spectroscopy not only to provide isolated trans data, but also serve as a simple, rapid and quantitative means of categorizing the main groups present in the edible oils. The information obtained would be useful for meeting the new lipid nutritional labeling requirements.