Chemically Modified Human Immunoglobulin G: Hydrophobicity and Surface Activity at Air/Solution Interface

Covalent modification of human IgG by fatty acid esters (C8 and C16) of N-hydroxysuccinimide was carried out. Surface hydrophobicity measurements, using the fluorescent probe 8-anilino-1-naphthalenesulfonate, indicate an increase in the surface protein hydrophobicity with an increase in the number and in the length of the attached alkyl chains. The modified IgGs decrease surface tension at the air/solution interface more effectively than the native protein. The values of the molecular cross-sectional areas (DeltaA) estimated from the kinetic data are in the range of 100-300 ?2 and reflect the size of protein segments at the interface during the adsorption process. About 40-50% increase in the DeltaA was observed upon attachment of the C8 groups to the native IgG. The lengthening of the bound alkyl chain from C8 to C16 results in a further increase in this value. The influence of the overall IgG hydrophobicity and the length of the attached alkyl chain on the dimensions of the mobile protein segment at the surface are discussed. Copyright 1999 Academic Press.     

Synthesis of copper nanoparticles catalyzed by pre-formed silver nanoparticles

Synthesis of well dispersed copper nanoparticles was achieved by reduction of copper nitrate in aqueous solution using hydrazine monohydrate as a reducer in the presence of preformed silver nanoparticles as catalysts. It has been demonstrated that addition of silver nanoparticles to the reaction mixture leads to formation of aqueous dispersion of copper nanoparticles and also results in a drastic reduction in reaction time compared to procedures reported in the literature. The absorption spectrum of the dispersions, HR-TEM and STEM images and XRD pattern indicate the formation of copper nanoparticles with particle size in the range of 5–50 nm.     

Ring stain effect at room temperature in silver nanoparticles yields high electrical conductivity

We demonstrate that metallic rings formed spontaneously at room temperature via evaporation of aqueous drops containing silver nanoparticles (20-30 nm in diameter) exhibit high electrical conductivity (up to 15% of that for bulk silver). The mechanism underlying this self-assembly phenomena is the "ring stain effect", where self-pinning is combined with capillary flow to form a ring consisting of close-packed metallic nanoparticles along the perimeter of a drying droplet. Our macroscopic and microscopic (applying conductive atomic force microscopy) transport measurements show that the conductivity of the ring, which has a metallic brightness, is orders of magnitude larger than that of corresponding aggregates developed without the ring formation, where high conductivity is known to appear only after annealing at high temperature.     

Adsorption of Hydrophobized Glucose Oxidase at Solution/Air Interface

The modification of glucose oxidase by palmitic acid ester ofN-hydroxysuccinimide leads to the formation of a new hydrophobized enzyme with five covalently bound C₁₆groups. Such a modification was shown not to alter noticeably the native structure of the enzyme. The modified glucose oxidase displays enhanced surface activity at the water/air interface in comparison with the native enzyme. The maximum reduction of surface tension at all concentrations studied was higher for the modified glucose oxidase than for the native one. The modified enzyme also displayed a much steeper rise of the surface potential with time and a much more rapid attainment of the saturation plateau than the unmodified enzyme.     

Native and modified glucose oxidase in reversed micelles

The enzymatic activity of the native and modified glucose oxidase (GOx) from Aspergillus niger in the system of reversed micelles of Aerosol OT in octane was investigated. Two forms of the modified enzyme were studied: a hydrophobized form obtained by the attachment of palmitic chains to lysine amino groups by the reaction with palmitic acid ester of N-hydroxysuccinimide and a glycosylated (hydrophilized) form obtained by the attachment of the cellobiose moieties. The native glucose oxidase and its derivatives, while incorporated into micelles in a surfactant concentration range from 0.05 to 0.3 M, display an enzymatic activity, which is comparable with the activity in aqueous solution. The dependence of the enzymatic activity on hydration degree of surfactant (the molar ratio of water to surfactant, W₀) does not indicate the formation of qualitatively new associated forms of the enzyme subunits inside the micelles. The apparent size of Aerosol OT micelles obtained by dynamic light scattering gradually increases from 10±3 nm at low W₀ up to 25±5 nm at high W₀. Incorporation of the native and hydrophobized glucose oxidase into micelles does not affect their mean size. Kinetic analysis shows that the enzyme specificity is about an order of magnitude greater in the system of reversed micelles as compared with aqueous solution.     

Stabilization of silicon nanoparticles by carbenes

Sodium reduction of a mixture of tetrabromosilane with imidazole ionic liquids in organic solvents gives dispersions of silicon nanoparticles stabilized by carbene ligands. It was shown that the size of silicon nanoclusters depends on the size of substituents at nitrogen atoms of 1,3-dialkylimidazol-2-ylidenes.     

Sulfur stable isotope distribution of polysulfide anions in an (NH4)2Sn aqueous solution

Methylation of polysulfides [(NH4)2Sn)] by reaction with CF3SO3CH3 followed by separation of the produced dimethylpolysulfides by liquid chromatography and subsequent highly accurate stable isotope analysis by a continuous-flow isotope ratio mass spectrometer shows that polysulfide anions in an aqueous solution exchange isotopes with the other sulfur species in the system. It demonstrates for the first time that polysulfide anions are 34S-enriched in equilibrium relative to total sulfur as a function of their sulfur chain length.     

Quantification of free and metal-complexed cyanide by tetrathionate derivatization

A sensitive and robust method for detection of free and metal-complexed cyanide in solutions is described. The method does not require a distillation step and is applicable for both low ionic strength and sea-water samples. The method is based on the reaction of cyanide with potassium tetrathionate followed by high-performance liquid chromatography (HPLC) separation and UV detection of formed thiocyanate. The detection limit of the method is 250?nmol?L^?1 cyanide (6.5?µg?L^?1 CN^?) without a pre-concentration step. Storage for three days does not significantly change the results. The sum of free and weak metal-complexed cyanide can be measured by tetrathionate derivatization at a pH of 10. The sum of free, weak metal-complexed cyanide, iron(II) and iron(III)-complexed cyanides may be measured by tetrathionate derivatization at pH 4.4. Derivatization requires heating to 90°C for 20?min at pH?=?10 and for 12 h at pH?=?4.4. Weighted mean recoveries for free, iron(II), iron(III), nickel(II), silver(I), Cd(II) and Zn(II) complexed cyanide were in the range of 87 to 112% and weighted standard deviations were in the range of 1.7 to 10.0%. The method is not applicable for cyanide complexes of gold and cobalt. We illustrate an application of cyanide quantification using pore-waters from the Delaware Great Marsh.     

Regulation of acid phosphatase in reverse micellar system by lipids additives: structural aspects

Reverse micelles system is suggested as a direct tool to study the influence of membrane matrix composition on the activity and structure of membrane-associated enzymes with the use of acid phosphatase (AP) as an example. In reverse micelles the functioning of the monomeric and dimeric forms of AP could be separately observed by variation of the size of the micelles. We found that including the lipids into the micellar system can dramatically affect the enzyme functioning even at low lipid content (2% w/w), and this effect depends on the lipid nature. Structural studies using CD spectroscopy and DLS methods have shown that the influence of lipid composition on the enzyme properties might be caused by the interaction of lipids with the enzyme as well as by the influence of lipids on structure and properties of the micellar matrix.     

Monolayer Parameters of Gelatin Chemically Modified with N-Hydroxysuccinimide Ester of Caprylic Acid

The behavior of gelatin chemically modified with N-hydroxysuccinimide ester of caprylic acid at the aqueous (NH₄)₂SO₄ solution–air interface is studied. The compression isotherms of gelatin monolayers whose pattern is dependent on the degree of gelatin modification are obtained. It is established that the area corresponding to the beginning of isotherm rise, two-dimensional pressure of completely compressed monolayer, and the modulus of monolayer surface elasticity increase with the degree of gelatin hydrophobization. The surface (adsorption) activity of gelatin with the modification degree of 85% is approximately threefold higher than for the initial gelatin.