Incorporation of D-glucosamine alkyi glucopyranosides into the bilayer of small unilamellar vesicles of egg phosphatidyl choline

Alkyl 2-acetamido-2-deoxy-β-d-glucopyranosides were incorporated into the phospholipid bilayer of small unilamellar vesicles. Depending on the lengths of the alkyl aglycone group (C₈–C₁₄), the carbohydrate was either found in the form of micelles (C₈) or was effectively incorporated in the bilayer (C₁₄). The use of radiolabelled lipids and/or carbohydrates enabled the quantitative determination of the amounts of lipid and carbohydrate recovered into the vesicles. An enzymatic assay has been carried out to evaluate the outer and inner distribution of the carbohydrate moieties on the liposomes.     

大单室CdTe量子点脂质体的制备及其体内代谢途径

在水相中用谷胱甘肽(Glutathione,GSH)为稳定剂合成了量子产率为61%、发射峰为601.2nm的CdTe-GSH量子点,然后用大豆卵磷脂为膜,通过减压蒸发法合成了粒径在1.5μm左右大小的大单室CdTe量子点脂质体(GUVs-CdTe).GUVs-CdTe对量子点的包封率比其他量子点脂质体显著提高,可达86.3%.由静脉注射到小白鼠体内后,各组织切片的荧光显微照片表明GUVs-CdTe不能通过血脑屏障和气血屏障,主要被网状内皮系统去除,在脾脏和肝脏呈弥漫状分布,这和大单室脂质体静脉注射体内后的代谢完全一致.     

Stabilization of small unilamellar DMPC-liposomes by uncharged polymers

 Polymer-free and polymer-bearing small unilamellar (SUV) liposomes from dimyristoyl-phosphatidylcholine (DMPC) were prepared under standardized conditions. Polymer-bearing liposomes were formed by incorporating an uncharged polymer [hydrolyzed poly(vinyl alcohol) (PVA), poly(vinyl alcohol-co-vinylacetal) (PVA-Al), poly(vinyl alcohol-co-vinyl propional) (PVA-Prol) poly(vinyl alcohol-co-vinyl butiral) (PVA-Bul) copolymer or poly(vinyl pyrrolidone) (PVP)] into the membrane bilayer of vesicles. The kinetic (long-term) stability of the liposome dispersions stored in distilled water, in physiological NaCl solution and at various pH values, respectively, were studied. The physical stability of vesicles was tested by measuring the size and the zeta potential of liposomes by means of a Malvern Zetasizer 4 apparatus. It was shown that most of these polymers are effective steric stabilizers for the DMPC-liposomes. Among the polymers, the PVA-Bul and PVA-Prol copolymers and the PVP of high molecular mass exhibited the most efficient stabilizing effect at each pH studied, indicating that the formation of a relatively thick polymer layer around the lipid bilayers ensures an enhanced and prolonged physical stability of liposomes. Also, the butiral or propional side chain in the PVA-based copolymers presumably promotes the anchoring of macromolecules to the vesicles. Using these macromolecules, the colloidal interactions between vesicles can be modified and so the physical stability of liposomes and the kinetic stability of liposome dispersions can also be controlled. Received: 20 May 1997 Accepted: 03 September 1997     

Formation and properties of HCO-10 vesicles

 The characteristics of poly(oxyethylene) hydrogenated caster oil ether (HCO-10) vesicles were studied for the standpoints of encapsulation efficiency, stability, solubilization and permeability or barrier efficiency. The vesicles of 5% HCO-10 had 6.24% of calcein-entrapment efficiency and 240 nm of mean diameter. The stability of HCO-10 vesicle suspensions was dependent on their concentrations. In the vesicle suspensions of 10% HCO-10 or more, both the size of the vesicles and the fluidity of the suspensions obviously varied with incubation time, indicating that a flocculation occurred; whereas, the vesicle suspension of 5% HCO-10 was relatively stable. The solubilization process of HCO-10 vesicles by SDS was similar to that of EggPC liposomes. The rate constants for permeation of Cl ion and calcein were 2.46×10^-3 s^-1 and 5.79×10^-5 s^-1, respectively, suggesting that HCO-10 vesicles possessed some barrier potential for Cl ion and calcein although they were smaller than those of liposomes. Furthermore, the efflux of the solute such as calcein from HCO-10 vesicles was maximum at 37 °C, where the vesicle membrane was presumably destabilized by dehydration of EOs in HCO-10 molecules. Received: 7 May 1996 Accepted: 3 September 1996     

Enzymatic hydrolysis of poly(D, L-lactide) spread monolayers by cutinase

 The enzymatic hydrolysis of a model poly(D,L-lactide) by cutinase was studied by using a barostat surface balance. A theoretical approach based on the adaptation of the Michaelis–Menten scheme at the interface and a process of random fragmentation of the macromolecules was developed. The role of the interfacial organisation of the reaction products was discussed. Hydrolysis rate constant values and the specific activity were estimated and compared with those obtained for the hydrolysis of lipid monolayers. The process of fragmentation of the interfacial polymer structures was visualised by using AFM imaging. Received: 19 August 1996 Accepted: 13 December 1996     

3D Reconstruction of Rough Surfaces by SEM Stereo Imaging

 The paper describes the current state of a multidisciplinary research project which aims to apply advanced stereovision methods to the 3D reconstruction of rough surfaces using scanning electron microscopy (SEM) imaging. SEM stereo imaging compares very favourably to atomic force microscopy (AFM) in a medium range corresponding to elevations less than 10 μm and scanned size less than 100 μm. But the interest of the stereoscopic method is that it enables to characterise wider fields with higher elevations.     

Activation and inhibition of lipoprotein lipase in mixed monolayers of medium or long chain-triglycerides and phospholipids

 We evaluated the activation and inhibition effects of phosphatidylcholine (PC) and sphingomyelin (SM) on lipoprotein lipase (LPL) for medium or long chain-triglycerides (TG) in monolayers at the air/water interface. Monolayers of medium chain-TG, being in an expanded state at a surface pressure of 15 mN/m, showed low susceptibility to LPL in the subphase. Adding 50 mole% of PC or SM into these monolayers reduced the partial molecular area of the TG and enhanced the LPL activity. Monolayers of long chain-TG, being in a condensed state, showed high susceptibility of LPL either with or without PC. SM added to the long chain-TG monolayers, however, inhibited the LPL action. We investigated the interaction between TG and phospholipid on the basis of the collapse pressure-measurements of mixed monolayers. For medium chain-TG monolayers, PC and SM gave similar collapse pressure-composition profiles. Contrary to this, SM gave a markedly higher collapse pressure of long chain-TG than PC: SM stabilized the monolayer state of long chain-TG. These results suggested that I) orientation of the acyl chains of TG molecule in a monolayer is crucial for the LPL activity, and that II) strong interaction between SM and long chain-TG retards the substrate-transfer from the mixed monolayer to the catalytic pocket of LPL. Received: 6 March 1996 Accepted: 19 July 1996     

Computational insight into the effect of C(19) substituents on [1,7]-hydrogen shift in previtamin D

 B3LYP calculations in conjunction with natural bond orbital population analysis have been performed for a previtamin D model and corresponding transition structures for the [1,7]-hydrogen migration. In addition the 19,19-difluoro, 19-methoxy and 19-fluoro substituted analogs were investigated. The calculated activation barriers decrease in the following order: CHF₂>CH₃>CH₂OCH₃ (24.8, 23.5 and 20.1 kcal/mol). This is in qualitative agreement with experiments. It has been suggested that a decrease of the barrier by a 19-methoxy substituent and its increase by a 19,19-difluoro substituent are phenomena of different origin. In the case of 19-methoxy substitution, the effect is due to the charge redistribution in the triene system and the decrease of the C(19)–H bond energy. The effect of two fluorine substituents at C-19 on the activation barrier is suggested to originate from the combination and balance of several factors: electrostatic repulsion between the negative fluorine atom and the π-electron cloud over the conjugated system, an increase of the HOMO–LUMO gap, and geminal difluoro substitution affecting C–F and C–C bond energies. Received: 17 May 2002 / Accepted: 11 September 2002 / Published online: 14 February 2003     

Validity of the Kelvin equation in estimation of small pore size by nitrogen adsorption

 We have investigated a practical lower limit of a pore-size estimation by the nitrogen desorption isotherms at 77 K using the Kelvin equation. Changes in pore size of porous silica glasses before and after the monolayer preadsorption of n-propylalcohol were estimated by measuring the nitrogen adsorption and desorption isotherms. These changes should correspond to the thickness of monolayer of adsorbed n-propylalcohol. The thickness of monolayers obtained for the samples whose pore sizes are below ca. 2 nm were underestimated, when the Kelvin equation was applied to the nitrogen desorption isotherms using the values of surface tension and molar volume of bulk liquid nitrogen at 77 K. Below ca. 2 nm pore radius a careful application of the Kelvin equation is required to estimate a pore size. These results suggest that a change in the physical properties of liquid nitrogen in such a small pore occurs. It is supposed that the interaction between the solid surface and adsorbate molecules causes the changes in the surface tension and density of liquid nitrogen in such a narrow pore. Received: 21 March 1997 Accepted: 18 July 1997     

Structural and catalytic aspects of cutinase in w/o microemulsions

 Structural and catalytic properties of cutinase were studied in bis(2-ethylhexyl) sodium sulfo-succinate (AOT)-isooctane microemulsion systems. The effect of the water content of the microemulsions on the cutinase activity on an esterification reaction of lauric acid with pentanol showed that cutinase followed a bell-shaped profile presenting a maximum at w _o=9, with w _o=[H₂O]/[AOT]. Kinetic studies allowed the determi-nation of the apparent parameters K _m and V _max. Electron paramagnetic resonance (EPR) spectroscopy studies of active site labeled cutinase in microemulsions with varying w _o values showed that in all microemulsions, the mobility of the label is higher than in the aqueous solution. Furthermore, it was found that the maximum of the enzyme activity did not correspond to a reduced active site mobility. Up to w _o=9 there was an increase of both activity and active site mobility. As the water content of the system became higher, the mobility of the bound spin label further increased whereas the enzymatic activity dropped considerably. Received: 20 December 1996 Accepted: 24 February 1997     

Growth process of polymer aggregates formed by perfluorooctyltriethoxysilane. Time-resolved near-IR and two-dimensional near-IR correlation studies

The polymerization of 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane in ethanol, catalyzed by 0.5, 1.0 and 2.0 M HCl·H₂O, has been examined using time-resolved near-IR (NIR) and 2D NIR correlation techniques. The time-resolved NIR results have demonstrated that the growth of polymeric aggregates prior to the phase separation proceeds in a two-step process, which depends upon the HCl concentration. Furthermore, it has been found that the 2D NIR correlation data provide direct information on the sequence of the intricate reaction steps and interaction of participating components through hydrogen bonding in the growth process. Received: 25 July 2001 Accepted: 16 October 2001     

Investigation on the basic hydrolysis of crystal violet in mixed reverse micelles formed with AOT and nonionic surfactants

 The kinetics and thermodynamics of the basic hydrolysis of crystal violet (CV) in mixed reverse micelles formed with anionic surfactant AOT and nonionic surfactants have been investigated. It was found that the mixed reverse micelles had inhibitory effects on CV hydrolysis compared with the normal aqueous solution, and the equilibrium constant K of the reaction in mixed reverse micellar systems is smaller than that in pure water. The influence of water content and surfactant composition in reverse micelles on the second-order rate constant k ₁ of the positive reaction, on the first-order rate constant k _-1 of the reverse reaction, as well as on the equilibrium constant K of the reaction has been studied, and the results obtained were interpreted in terms of the nature of surfactants and the properties of microenvironment where the reaction took place. Received: 24 October 1997 Accepted: 18 March 1998     

Relaxation modulus in the fitting of polycarbonate and poly(vinyl chloride) viscoelastic polymers by a fractional Maxwell model

 The stress relaxation of two different polymers under a constant strain has been studied and approached by using a fractional Maxwell model in which the stress appears as a noninteger-order derivative of the strain. To obtain an accurate approximation of the experimental data for the model, two noninteger values for the derivative order are required. These values are related to two relaxation types. For short times, the derivative order is smaller and near zero, which indicates behavior close to the ideal elastic solid. For long times the derivative order is higher, showing more plastic behavior. In this work some classic models are revised and the fractional Maxwell model is used to fit the experimental data. Finally, the complex fractional modulus, the two derivative orders, and the relaxation times for samples of polycarbonate and poly(vinyl chloride) are obtained. Received: 16 June 2001 Accepted: 19 October 2001     

Recent advances in quantum mechanical/molecular mechanical calculations of enzyme catalysis: hydrogen tunnelling in liver alcohol dehydrogenase and inhibition of elastase by α-ketoheterocycles

 Hybrid quantum mechanical (QM)/molecular mechanical (MM) calculations are used to study two aspects of enzyme catalysis, Kinetic isotope effects associated with the hydride ion transfer step in the reduction of benzyl alcohol by liver alcohol dehydrogenase are studied by employing variational transition-state theory and optimised multidimensional tunnelling. With the smaller QM region, described at the Hartree–Fock ab initio level, together with a parameterised zinc atom charge, good agreement with experiment is obtained. A comparison is made with the proton transfer in methylamine dehydrogenase. The origin of the large range in pharmacological activity shown by a series of α-ketoheterocycle inhibitors of the serine protease, elastase, is investigated by both force field and QM/MM calculations. Both models point to two different inhibition mechanisms being operative. Initial QM/MM calculations suggest that these are binding, and reaction to form a tetrahedral intermediate, the latter process occurring for only the more potent set of inhibitors. Recieved 3 October 2001 / Accepted: 6 September 2002 / Published online: 31 January 2003 Contribution to the Proceedings of the Symposium on Combined QM/MM Methods at the 222nd National Meeting of the American Chemical Society, 2001 Correspondence to: I. H. Hillier Acknowledgements. We thank EPSRC and BBSRC for support of the research and D.G. Truhlar for the use of the POLYRATE code.     

Determination of Amoxycillin and Clavulanic Acid in Some Pharmaceutical Preparations by Derivative Spectrophotometry

 Derivative spectrophotometry was applied for the simultaneous determination of amoxycillin and clavulanic acid in pharmaceutical preparations: “Augmentin” inj. and tablets and “Amoksiklav” drops and tablets, in solutions after hydrolysis with sodium hydroxide. As the absorption spectra overlap strongly (amoxycillin λ_max = 247 nm and 290 nm, clavulanic acid λ_max = 258 nm) the first and the second derivative spectrophotometric procedure was elaborated for their determination. Amoxycillin was determined at λ = 257.9 nm (1-st derivative spectra) or λ = 273 nm (2-nd derivative) while clavulanic acid at λ = 280.3 nm (1-st derivative) or λ = 285 nm (2-nd derivative spectra). The Beer’s law is obeyed in the range of 0.004–0.04 mg/ml for amoxycillin and 0.002–0.02 mg/ml for clavulanic acid. Received December 6, 1999. Revision August 1, 2000.     

Microbial and Enzymatic Synthesis of Optically Pure D- and L-3-Trimethylsilyl-alanine by Deracemization of D,L-5-Trimethylsilyl-methyl-hydantion

Summary.  The sterospecificities of hydantoinases and N-carbamoyl amino acid amidohydrolases (N-carbamoylases) from different microbial sources were investigated for the stereoselective syntheses of the unnatural silicon-containing amino acids D- and L-3-trimethylsilyl-alanine (3) from the respective racemic hydantoin D,L-1. In a preparative biotransformation, whole resting cells of Agrobacterium sp. IP I 671, immobilized in a Ca-alginate matrix, were used for the synthesis of amino acid D-3 in 88% yield and 95% enantiomeric excess. Since the purified D-N-carbamoylase from Agrobacterium sp. IP I 671 was shown to be 100%D-selective, the enantiomeric purity of 95% of D-3 arising from the transformation with the immobilized cells must be explained by the participation of a further, L-selective N-carbamoylase or, which is more likely, by racemization of the final hydrolysis product by the action of an amino acid racemase. Isolated hydantoinases from Bacillus thermoglucosidasius, Thermus sp., Arthrobacter aurescens DSM 3745, and Arthrobacter crystallopoietes DSM 20117 turned out to be stereospecific for the conversion of the D-form of hydantoin D,L-1. The enantiomerically pure L-form of 3 was also prepared. It was synthesized from racemic N-carbamoyl amino acid D,L-2 by enantiomer-specific hydrolysis of the L-form in presence of L-N-carbamoylase from Arthrobacter aurescens DSM 3747. Received December 20, 1999. Accepted January 7, 2000     

Preparation by hydrolysis of aerosols and properties of Cr, Mn and Co doped alumina spherical particles

 A method for the preparation of chromium-doped (pink), manganese-doped (brown) and cobalt-doped (blue) alumina pigments consisting of spherical particles of broad size distribution (<5 μm) is reported. The procedure, based on the room-temperature hydrolysis of aerosols generated from a mixture of aluminum sec-butoxide and a solution of the corresponding metal nitrates in sec-butanol, yields amor-phous solids. The temperature of calcination and the composition of the so produced powders were varied to investigate their effects on the color properties of the pigments, which were also characterized in terms of their composition, crystalline structure and electrokinetic behavior. Received: 15 April 1997 Accepted: 25 June 1997     

A pilot experiment of joint assessments by accreditation and certification bodies in clinical laboratories

When the quality system of the health care organization is certified and the laboratory accredited, two different types of assessments are also performed. To reduce the extra work caused by these different assessments the Finnish Accreditation Service FINAS and SFS-Certification have made a pilot experiment in combining the assessments. Joint assessments have been a positive experience to the laboratory as well as to the assessing bodies, and we find this operating model worth developing.     

Investigation of the interactions in emulsions stabilized by a polymeric surfactant and its mixtures with an anionic surfactant

 The interaction of a nonionic polymeric surfactant with an anionic surfactant at the oil–water interface has been studied by its effects on the droplet size, stability and rheology of emulsions. Oil-in-water (o/w) emulsions were prepared using isoparaffinic oil and mixtures of a nonionic polymeric surfactant with an anionic surfactant. The macro-molecular surfactant was a graft copolymer with a backbone of polymethyl methacrylate and grafted polyethylene oxide (a graft copolymer with PEO chains of MW=750). The anionic surfactant was sodium dodecyl sulfate (SDS). The stabiliza-tion of the emulsion droplets was found to be different when using one or the other surfactant. The mechanism of stabilization of emulsion droplets by the macro-molecular surfactant is of the steric type while the stabilization by anionic surfactant is of the electrostatic repulsion type. Emulsions stabilized with mixtures present both types of stabilization. Other effects on the preparation and stabilization of emulsions were found to be dependent on properties associated with the surfactant molecular weight such as the Marangoni effect and Gibbs elasticity. The initial droplet size of the emulsions showed a synergistic effect of the surfactant combination, showing a minimum for the mixtures compared to the pure components. Emulsion stability also shows a synergistic interaction of both surfactants. Rheological measurements allow for the estimation of the interparticle interaction when measured as a function of volume fraction. Most of the effects observed can be attributed to the differences in interfacial tension and droplet radius produced by both surfactants and their mixtures. The elastic moduli are well explained on the basis of droplet deformation. Ionic versus steric stabilization produce little difference in the observed rheology, the only important differences observed concerned the extent of the linear viscoelasticity region. Received: 22 November 1996 Accepted: 24 March 1997     

Estimation of kinetic rate constants by turbidity and nephelometry techniques in a homocoagulation process with different model colloids

 In this work turbidimetric and nephelometric techniques have been used to study the homocoagulation of aqueous dispersions of uniform spherical particles of surfactant-free latexes. Cationic and anionic latexes of similar particle sizes (361 and 370 nm) and different surface charge densities (+16.4 and −3.6 μC/cm²) were used throughout. The kinetic constants which control the aggregation processes when the electrical repulsion disappears were estimated by both techniques at different particle concentration and wavelength in order to establish the experimental conditions which provided reliable and similar values for the coagulation rate constant. Both experimental techniques (turbidity and nephelometry) and two ways of fitting the data have been used with both latexes. For the first method, the initial slope of turbidity or total scattered intensity versus time curves were used to calculate the kinetic constants. In the second method, the whole turbidity or total scattered intensity versus time curves were fitted and the kinetic constants calculated. An unambiguous experimental value for the doublet rate constant in diffusion conditions is obtained by turbidity and nephelometry techniques. By nephelometry both data treatments have permitted a distinction between the doublet rate constant and the global rate constant in diffusion conditions. Received: 2 June 1997 Accepted: 14 August 1997