Conductance measurements of some electrolytes in N,N-dimethyformamide and its binary mixtures witth other organic solvents—II

Equivalent conductances of Bu₄NBPh₄, Bu₄NNO₃, Bu₄NI,KClO₄, Kl, NaI, NaBPh₄, Ph₄PCl, LiCl, AgNO₃ and CuClO₄. 4AN have been measured at 25°C in binary mixtures of N,N-dimethylformamide (DMF) containing 1 mol % of 1, 1, 3, 3-tetramethylurea (TMU), dimethylsulphoxide (DMSO) and hexamethylphosphotriamide (HMPT). Such measurements for LiCl, NaI, KClO₄ and CuClO₄. 4AN have also been carried out in DMF and in binary mixtures of DMF containing 1 mol % pyridine (Py), α-picoline (α-Pic), β-picoline (β-Pic), γ-picoline (γ-Pic) and acetonitrile (AN). The conductance data in all the cases have been analyzed by the Shedlovsky equation. Limiting ion conductances have been obtained by the method of Fuoss et al. The actual solvated radii of ions, evaluated using limiting ion conductances show that Ag⁺ and Cu₊ have strong preferential solvation by all solvents which have been used to prepare the binary mixtures with DMF and the preferential solvation for both Ag⁺ and Cu⁺ with HMPT, DMSO and TMU is relatively stronger than with AN and is practically of similar magnitude as with the organic bases.     

PROTEIN-PHYTATE INTERACTIONS IN SOYBEANS. II. MECHANISM OF PROTEIN-PHYTATE BINDING AS AFFECTED BY CALCIUM

Phytate and bovine serum albumin were used in a model system to investigate the mechanism of their binding. Ultrafiltration studies using response surface design showed the association of protein and phytic acid to be highly pH dependent. Under acid conditions, the protein formed an insoluble complex with phytic acid. At pH 3.0, a binding constant of 2.3 times 10⁵ was obtained and it was calculated that there are 78 binding sites of the total 93 basic amino acid residues potentially available. This low pH complex was not disrupted at high temperatures but the presence of calcium ions caused dissolution of the precipitate. Calcium produced different effects at higher pH (> 6). Soluble protein-calcium-phytic acid complexes were formed which were less stable to heat and dissociated above pH 10 at high ionic strength. Since this interaction occurred only in the presence of calcium, a salt linkage is implicated in which divalent cations simultaneously bind to the protein and phytic acid in the form of a soluble complex. It is proposed that either the addition of divalent cations at low pH or sequestering agents at high pH would best effect the removal of phytate from soy products by ultrafiltration.     

The critical role of water in spider silk and its consequence for protein mechanics

Due to its remarkable mechanical and biological properties, there is considerable interest in understanding, and replicating, spider silk's stress-processing mechanisms and structure-function relationships. Here, we investigate the role of water in the nanoscale mechanics of the different regions in the spider silk fibre, and their relative contributions to stress processing. We propose that the inner core region, rich in spidroin II, retains water due to its inherent disorder, thereby providing a mechanism to dissipate energy as it breaks a sacrificial amide-water bond and gains order under strain, forming a stronger amide-amide bond. The spidroin I-rich outer core is more ordered under ambient conditions and is inherently stiffer and stronger, yet does not on its own provide high toughness. The markedly different interactions of the two proteins with water, and their distribution across the fibre, produce a stiffness differential and provide a balance between stiffness, strength and toughness under ambient conditions. Under wet conditions, this balance is destroyed as the stiff outer core material reverts to the behaviour of the inner core.     

Flow-injection amperometric glucose biosensors based on graphene/Nafion hybrid electrodes

In this research, we demonstrated the fabrication of flow-injection amperometric glucose biosensors based on RGO/Nafion hybrids. The nanohybridization of the reduced graphene oxide (RGO) by Nafion provided the fast electron transfer (ET) for the sensitive amperometric biosensor platforms. The ET rate (k_s) and the charge transfer resistance (R_CT) of GOx-RGO/Nafion hybrids were evaluated to verify the accelerated ET. Moreover, hybrid biosensors revealed a quasi-reversible and surface controlled process, as confirmed by the low peak-to-peak (ΔE_p) and linear relations between I_p and scan rate (ν). Hybrid biosensors showed the fast response time of ∼3 s, the sensitivity of 3.8 μA mM⁻¹ cm⁻², the limit of detection of 170 μM, and the linear detection range of 2–20 mM for the flow-injection amperometric detection of glucose. Furthermore, interference effect of oxidizable species such as ascorbic acid (AA) and uric acid (UA) on the performance of hybrid biosensors was prevented at the operating potential of −0.20 V even under the flow injection mode. Therefore, the fast, sensitive, and stable amperometric responses of hybrid biosensors in the flow injection system make it highly suitable for automatically monitoring glucose.     

Electrochemical and ellipsometric study of the oxide films formed on copper in borax solution: Part I: Effect of oxygen

The formation and reduction of passive layers on copper in weakly alkaline solutions saturated with N2 and O2 were studied. Voltammetric and ellipsometric techniques were employed to examine the structural characteristics of the layers formed in the –0.32 to 0.75 V vs RHE potential region. Optical measurements at open circuit potentials (Eoc) were also made to simulate operational conditions. The passive layer consists of a duplex structure: an outer hydrated copper oxide film and an inner dehydrated film. This inner layer is composed of Cu2O with a surface excess of Cu(ii) ions. The growth rate of the oxide layers at controlled potentials is higher in O2 saturated solution. The corrosion resistance of copper depends on the presence of O2 in the electrolyte, on the stirring rate and on the Eoc value.     

Chemo-enzymatic synthesis of amino acid-based surfactants

The application of lipases to the synthesis of amino acid-based surfactants was investigated. Low yields (2–9%) were obtained in the acylation of free amino acids, such as l-serine and l-lysine, as well as their ethyl esters and amides with fatty acids, owing in part to low miscibility of the reactants. When the N-carbobenzyloxy (Cbz)-l-amino acids were used in an effort to improve miscibility of the amino acid derivatives with the acyl donor, a dramatic improvement was observed for N-Cbz-l-serine (92% yield) but not for N _α-Cbz- or N _ζ-Cbz-l-lysine (7 and 2% yield, respectively). As an alternative, and efficient synthesis of N _ζ-acyl-l-lysines was developed, based on the regiospecific chemical acylation of copper(II) lysinate. In pursuit of a general route to amino acid-fatty acid surfactants, the utility of a polyol linker was investigated. Thus, the glycerol ester of N _α′ N _ζ-di-Cbz-l-lysine was prepared and evaluated as a substrate for acylation. As expected, this and other glycer-1-yl esters of N-protected amino acids were excellent substrates for lipase-catalyzed acylation. Their reaction with myristic acid in the presence of Novozyme resulted in the regioselective acylation of the primary hydroxyl group of the glycerol moiety to afford the corresponding 1-O-(N-Cbz-l-aminoacyl)-3-O-myris-toylglycerols with conversions of 50–90%. These were readily deprotected to give a range of 1-O-(aminoacyl)-3-O-myristoyl-glycerols with overall yields of 27–71%.     

Prunella vulgaris Suppresses HG-Induced Vascular Inflammation via Nrf2/HO-1/eNOS Activation

Vascular inflammation is an important factor which can promote diabetic complications. In this study, the inhibitory effects of aqueous extract from Prunella vulgaris (APV) on high glucose (HG)-induced expression of cell adhesion molecules in human umbilical vein endothelial cells (HUVEC) are reported. APV decreased HG-induced expression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin. APV also dose-dependently inhibited HG-induced adhesion of HL-60 monocytic cells. APV suppressed p65 NF-κB activation in HG-treated cells. APV significantly inhibited the formation of intracellular reactive oxygen species (ROS). HG-stimulated HUVEC secreted gelatinases, however, APV inhibited it. APV induced Akt phosphorylation as well as activation of heme oxygenase-1 (HO-1), eNOS, and nuclear factor E2-related factor 2 (Nrf2), which may protect vascular inflammation caused by HG. In conclusion, APV exerts anti-inflammatory effect via inhibition of ROS/NF-κB pathway by inducing HO-1 and eNOS expression mediated by Nrf2, thereby suggesting that Prunella vulgaris may be a possible therapeutic approach to the inhibition of diabetic vascular diseases.     

Micro-Analysis of ＂Sulfate Salt Weathering Distress on Concrete＂：Ⅱ.Concrete

运用环境扫描电镜、能谱仪和X射线衍射等微观分析手段研究了稳定环境中,半浸泡混凝土试件在硫酸钠和硫酸镁溶液中的劣化破坏特征,以及混凝土碳化对＂混凝土硫酸盐结晶破坏＂的影响。结果表明：粗骨料界面过渡区生成的大量钙矾石和石膏等晶体是引起混凝土试件劣化的原因;在碳化混凝土内发现了硫酸钠结晶破坏现象。