Role of Surface Molecular Architecture and Energetics of Hydrogen Bonding Sites in Adsorption of Polymers and Surfactants

Hydrogen bonding is generally thought to be an ubiquitous adsorption mechanism, which often foils selective adsorption schemes. Through investigation of hydrogen bonding energy and its dependence on surface molecular architecture, it may be possible to develop new methodologies to control the adsorption of surfactants and polymeric flocculants, depressants, and dispersants used in particulate processing industries. A model system using St?ber silica spheres and polyethylene oxide, a polymer known for its ability to form hydrogen bonds, was examined. The effect of two different surface treatments of the silica particles, calcination and rehydroxylation, upon the adsorption of two polymer molecular weights was studied. The adsorption behavior was then linked to the respective surface structures via characterization of the surfaces using FTIR, NMR, and Raman techniques. In this paper role of hydrogen bonding sites and surface architecture on adsorption is discussed. Copyright 2000 Academic Press.     

Preparation of a set of selectively protected disaccharides for modular synthesis of heparan sulfate fragments: toward the synthesis of several <Emphasis Type="Italic">O</Emphasis>-sulfonated [β-D-GlcUA-(1→4)-β-D-GlcNAc]OPr types

A concise method for a stereocontrolled synthesis of a set of selectively protected disaccharides is reported. Coupling of the donor 11 onto acceptors 23 and 24, promoted by trimethylsilyl triflate-N-iodosuccinimide (TMSOTf-NIS), generated the disaccharides 25 and 26. Under typical conditions, condensation of the fully protected donor 12 onto acceptors 23 and 24 produced the disaccharides 27 and 28. The building blocks 25–28 were prepared in moderate yields having exclusive β-stereoselectivity. A unique pattern of protecting groups distinguished clearly between positions to be sulfated and functional groups remaining as free hydroxyl groups. Acetyl and/or levulinoyl esters temporarily protected the positions to be sulfated, while benzyl ethers were used for permanent protection. The anomeric positions were protected as allyl ethers, whereas the 4′-positions were masked as p-methoxybenzyl (PMB) ethers. The orthogonality of the PMB and allyl groups can then be used for further elongation of the chain by recurrent deprotection and activation steps. The hydroxyl group, OH-6, of glucosamine moieties was protected as a TBDPS ether to avoid oxidation. A five-step deprotection/sulfonation sequence was applied to the disaccharide 27 to generate the corresponding sulfated [β-D-GlcUA-2-OSO₃Na-(1→4)-β-D-Glc pNAc]-(1→O-Pro) 34.     

An efficient procedure for the synthesis of coumarin derivatives using TiCl4 as catalyst under solvent-free conditions

The ability of titanium(IV) chloride as a catalyst to promote the Pechmann condensation reaction with a range of phenols and β-keto esters is described.The reaction was carried out by addition of TiCl₄ to a mixture of the phenol and the β-keto ester with thorough stirring in the absence of a solvent and represents an improvement on the classical Pechmann conditions. The yields of coumarins obtained via this novel protocol were significantly higher than those using the conventional method and the reaction duration was reduced to a few minutes or even a few seconds.     

Optical sensor for sulfur dioxide based on fluorescence quenching

A series of potential indicator dyes is evaluated for use in the development of optical sensors for measuring sulfur dioxide in gaseous samples. Rhodamine B isothiocyanate is selected on the basis of relative sensitivity to dynamic quenching by sulfur dioxide and oxygen. A solid-state fluorometer is described for monitoring the sulfur dioxide induced fluorescence quenching of sensing membranes composed of silicone and rhodamine B isothiocyanate. A modulated blue LED is coupled with the lock-in detection of a photodiode detector to provide high signal-to-noise ratios. The limit of detection is 0.114+/-0.009% for sulfur dioxide in a carrier stream of nitrogen gas. Selectivity measurements indicate no interference from several common gases (HCl, NH(3), NO, and CO(2)). Oxygen alters the sensor response when comparing signals for sulfur dioxide in 0, 20 and 100% oxygen environments.     

Atomic absorption spectrometric and potentiometric microdetermination of the nitro and nitroso groups in organic compounds

New simple, rapid, accurate, and selective methods are described for microdetermination of the nitro and nitroso groups in organic compounds. These are based on reduction with cadmium metal and 0.05 M HCl whereby 6 and 4 equivalents of the cadmium ions are released per nitro and nitroso groups, respectively. The cadmium ions are measured by atomic absorption spectrometry at 228.8 nm, potentiometrically by titration with EDTA using the cadmium ion selective electrode, and visually by EDTA titration using Eriochrome Black T indicator. Results with an average recovery of 98% and a mean standard deviation of 1.3% are obtainable and no interferences are caused by many nitrogen, oxygen, and sulfur functional groups.     

A simplified sampling technique for use with the Weisz ring oven: application to qualitative analysis of some gold and silver alloys

Up to 100 microg of sample can be collected from gold or silver alloys by rubbing the specimen with the ground hemispherical tip of a 4-mm Pyrex glass rod. Gold alloys are then dissolved in potassium cyanide solution containing hydrogen peroxide; silver alloys are exposed to vapours of nitric acid. Procedures for transfer, ring oven separation and identification of alloy constituents in the sample solutions are described.     

Thermal analysis of pharmaceutical compounds

Some sulphonamides are evaluated by means of thermal analysis. Use is made of their characteristic endothermic DTA peaks (melting peaks), where the area changes linearly with variations in the amount of sulphonamides. The method is suitable for the determination of 30–100 mg of sulphathiazole, sulphisomidine, sulphaguanidine, sulphacetamide sodium and sulphamethoxypyridazine with reasonable accuracy. As for sulphisoxazole, two peaks are used for its determination: an endothermic one to determine 30–100 mg, and an exothermic one to determine 6–30 mg.

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Zusammenfassung Einige Sulphonamide wurden durch thermische Analyse bestimmt, wobei von der linearen Abhängigkeit der Fläche der charakteristischen endothermen DTA-Peaks (Schmelzpeaks) von der Menge der Sulphonamide Gebrauch gemacht wurde. Mit der Methode können 30–100 mg Sulphathiazol, Sulphisoimidin, Sulphaguanidin, Natrium-Sulphacetamid und Sulphamethoxypyridazin mit ausreichender Genauigkeit bestimmt werden. Bei der Bestimmung von Sulphisooxazol wurde ein endothermer Peak für Mengen von 30–100 mg und ein exothermer für geringere Mengen von 6–30 mg herangezogen.

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. - ( ), . 30–100 , , , . , — 30 100 , — 6 30 .

     

Amperometric monitoring of lactate accumulation in rabbit ischemic myocardium

Fabrication and characterization of miniature, flexible, planar biosensors for monitoring l-lactate accumulation in an ischemic myocardium are described. Three configurations of Au-based electrodes were fabricated by a photolithographic technique on flexible polyimide Kapton((R)) foil. All sensors are based on an immobilized lactate oxidase with amperometric detection of the enzymatically produced hydrogen peroxide at a platinum-electroplated-gold base electrode polarized at 0.5 V versus Ag/AgCl. An inner electropolymeric layer is used to prevent electrode fouling and to reject the interference effects of easily oxidizable molecules. In addition, a diffusion controlling outer layer that greatly enhances the linear dynamic range of the sensor, is obtained by casting a polyurethane external film. The developed sensor was evaluated in vitro and proved to have high selectivity, good operational stability, good accuracy and precision (average recovery = 102.3 +/- 0.4% for control sera), fast response time (t(95) = 20 s) and high upper limit of the linear dynamic range (25-80 mM, with sensitivity of 1.7-0.4 nA mM(-1) respectively at PO(2) = 15 mmHg). Subsequently, the sensor was brought into direct contact with the surface of the rabbit papillary muscle and used for continuous quantitative monitoring of extracellular lactate accumulation during no-flow ischemia.     

Selective kinetic determination of pyridoxal-5'-phosphate with an ammonia gas-sensing electrode

The coenzyme pyridoxal-5'-phosphate (PLP) is deiermined by in situ measurement of the rate of ammonia production using a potentiometric gas-sensing membrane electrode. It is shown that the initial rate of ammonia liberation from L-tryptophan by action of tryptophanase apoenzyme and the coenzyme can be linearly related to PLP levels in the nanogram range with minimal interference from related compounds. Calibration data for the 1 × 10^-7–2.5 × 10^-6 M range for PLP yielded a least-squares equation of rate (mV min^-1) = (0.64 ± 0.01) C — 0.01 ± 0.02 with a standard error of 0.02 mV min^-1, where concentration, C, is expressed in units of 10^-7 mol l^-1.     

Challenges in validating the sterilisation dose for processed human amniotic membranes

Most of the tissue banks in the Asia Pacific region have been using ionising radiation at 25 kGy to sterilise human tissues for save clinical usage. Under tissue banking quality system, any dose employed for sterilisation has to be validated and the validation exercise has to be a part of quality document. Tissue grafts, unlike medical items, are not produced in large number per each processing batch and tissues relatively have a different microbial population. A Code of Practice established by the International Atomic Energy Agency (IAEA) in 2004 offers several validation methods using smaller number of samples compared to ISO 11137 (1995), which is meant for medical products. The methods emphasise on bioburden determination, followed by sterility test on samples after they were exposed to verification dose for attaining of sterility assurance level (SAL) of 10⁻¹. This paper describes our experience in using the IAEA Code of Practice in conducting the validation exercise for substantiating 25 kGy as sterilisation dose for both air-dried amnion and those preserved in 99% glycerol.