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PubMed2005

Locally Addressable Electrochemical Patterning Technique (LAEPT) applied to poly(L-lysine)-graft-poly(ethylene glycol) adlayers on titanium and silicon oxide surfaces.

The protein-resistant polycationic graft polymer, poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG), was uniformly adsorbed onto a homogenous titanium surface and subsequently subjected to a direct current (dc) voltage. Under the influence of an ascending cathodic and anodic potential, there was a steady and gradual loss of PLL-g-PEG from the conductive titanium surface while no desorption was observed on the insulating silicon oxide substrates. We have implemented this difference in the electrochemical response of PLL-g-PEG on conductive titanium and insulating silicon oxide regions as a biosensing platform for the controlled surface functionalization of the titanium areas while maintaining a protein-resistant background on the silicon oxide regions. A silicon-based substrate was micropatterned into alternating stripes of conductive titanium and insulating silicon oxide with subsequent PLL-g-PEG adsorption onto its surfaces. The surface modified substrate was then subjected to +1800 mV (referenced to the silver electrode). It was observed that the potentiostatic action removed the PLL-g-PEG from the titanium stripes without inducing any polyelectrolyte loss from the silicon oxide regions. Time-of-flight secondary ions mass spectroscopy and fluorescence microscopy qualitatively confirmed the PLL-g-PEG retention on the silicon oxide stripes and its absence on the titanium region. This method, known as "Locally Addressable Electrochemical Patterning Technique" (LAEPT), offers great prospects for biomedical and biosensing applications. In an attempt to elucidate the desorption mechanism of PLL-g-PEG in the presence of an electric field on titanium surface, we have conducted electrochemical impedance spectroscopy experiments on bare titanium substrates. The results showed that electrochemical transformations occurred within the titanium oxide layer; its impedance and polarization resistance were found to decrease steadily upon both cathodic and anodic polarization resulting in the polyelectrolyte desorption from the titanium surface.

Biosensing Techniques↗
PubMed2006

Role of cranberry juice on molecular-scale surface characteristics and adhesion behavior of Escherichia coli.

Cranberry juice has long been believed to benefit the prevention and treatment of urinary tract infections (UTIs). As the first step in the development of infection, bacterial adhesion is of great research interest, yet few studies have addressed molecular level adhesion in this context. P-fimbriated Escherichia coli play a major role in the development of a serious type of UTI, acute pyelonephritis. Experiments were conducted to investigate the molecular-scale effects of cranberry juice on two E. coli strains: HB101, which has no fimbriae, and the mutant HB101pDC1 which expresses P-fimbriae. Atomic force microscopy (AFM) was used to investigate both bacterial surface characteristics and adhesion forces between a probe surface (silicon nitride) and the bacteria, providing a direct evaluation of bacterial adhesion and interaction forces. Cranberry juice affected bacterial surface polymer and adhesion behavior after a short exposure period (<3 h). Cranberry juice affected the P-fimbriated bacteria by decreasing the adhesion forces between the bacterium and tip and by altering the conformation of the surface macromolecules on E. coli HB101pDC1. The equilibrium length of polymer (P-fimbriae) on this bacterium decreased from approximately 148 to approximately 48 nm upon being exposed to cranberry juice. Highly acidic conditions were not necessary for the prevention of bacterial adhesion, since neutralization of cranberry juice solutions to pH = 7.0 allowed us to observe differences in adhesion between the E. coli strains. Our results demonstrate molecular-level changes in the surfaces of P-fimbriated E. coli upon exposure to neutralized cranberry juice.

Bacterial Adhesion↗
PubMed2006

Catalytic asymmetric mannich-type reactions activated by ZnF2 chiral diamine in aqueous media.

Catalytic asymmetric Mannich-type reactions of an alpha-hydrazono ester with silicon enolates in aqueous media have been developed by using ZnF2 and chiral diamines as catalysts. In these reactions, both Zn2+ and a fluoride anion were necessary to achieve high yields and enantioselectivities, suggesting a double activation mechanism, in which Zn2+ activates the alpha-hydrazono ester and the fluoride anion simultaneously activates the silicon enolate. When chiral diamine ligands bearing methoxy-substituted aromatic rings were employed, the reactions in aqueous THF were markedly accelerated. Furthermore, the use of these diamines facilitated the asymmetric Mannich-type reactions in water without any organic cosolvents. It is noteworthy that either syn or anti adducts were stereospecifically obtained from (E)- or (Z)-silicon enolates, respectively. Interestingly, these reactions proceeded smoothly only in the presence of water. On the basis of several experimental results, it can be concluded that the reaction mechanism is likely to be a fluoride-catalyzed one, in which the ZnF2 chiral diamine complex is regenerated from the Me3SiF formed during the reaction.

Catalysis↗
PubMed2006

(14)N NMR and two-dimensional suspension (1)H and (13)C HRMAS NMR spectroscopy of ionic liquids immobilized on silica.

A variety of popular ionic liquids have been synthesized and characterized, including by optimized (14)N NMR spectroscopy of the neat and dissolved ionic liquids. Ionic liquids incorporating Si(OEt)(3) groups have been immobilized on silica in a well-defined manner with the imidazolium moiety remaining intact. This has been proved by optimized one- and two-dimensional (1)H and (13)C HRMAS NMR spectroscopy of the materials suspended in suitable solvents.

Ions↗
PubMed2007

Catalysis of a peptidic micellar assembly covalently immobilized within mesoporous silica channels: importance of amphiphilic spatial design.

A mesostructured silica/organic composite 1-MS, constructed from a rodlike micelle of amino acid amphiphile 1 that has a condensable head group and that can be used as a template, was found to be able to catalyze the acetalization of cyclohexanone, in ethanol at 25 degrees C (50% in 12 h), whereas no reaction took place with unfunctionalized mesoporous silica. In sharp contrast, hydrolytic removal of the C16 alkyl tail of immobilized 1 resulted in the complete disappearance of the catalytic activity, which suggests the importance of a hydrophobic inner domain for the admission of cyclohexanone. Unsupported peptide amphiphile 2, under identical conditions to those above, was inefficient for acetalization regardless of the absence (2% in 24 h) or presence of mesoporous silica (7% in 24 h). Reference composite 2-MS, which is a noncovalently immobilized peptidic micelle, was virtually inactive (1% in 24 h). These observations indicate the importance of covalent immobilization of the peptidic rod micelle for catalysis. Mesostructured silicate 3-MS hybridized with a nonpeptidic, ammonium ion amphiphile (3) showed a certain catalytic activity, but the yield (12% in 24 h) of the acetal was much lower than that achieved by using 1-MS as the catalyst. Amorphous silica with immobilized 1 on its surface was much less active than 1-MS for acetalization (5% in 24 h).

Acetals↗
PubMed1998

A new technique for stripping of polyimide coating from fused-silica capillaries.

A novel method for the manufacture of detection windows in polyimide-coated fused-silica capillary columns is described. Concentrated fuming nitric acid at room temperature is utilized for stripping of the coating from a defined section of the capillary. The technique is particularly suitable for columns that have a heat sensitive coating on the inner wall or for columns that contain an immobilized hydrogel sieving-matrix. A column holder for the simultaneous preparation of detection windows in an array of more than 100 capillaries is also reported.

Electrophoresis, Capillary↗
PubMedDate not supplied

Morphology of gastric microcirculation in cirrhosis.

Morphologic alterations in the gastric microcirculation in cirrhosis were investigated following infusion of a silicone rubber compound into vessels of the excised stomach which was then cleared with methyl salicylate. In cirrhosis, arteriovenous anastomoses 15 to 50 micron in diameter were present in 5 of 10 patients; spiral arterioles were less than one-tenth as numerous as in stomachs from noncirrhotic patients. The arterioles mainly had a straight pattern and precapillaries, capillaries, and submucosal and subserosal veins were dilated in cirrhotics (p less than 0.05). The number of arteriovenous anastomoses was unrelated to the degree of vascular dilatation and the number of spiral arterioles. These morphological alterations are consistent with decreased arteriovenous flow resistance in the stomach of cirrhotic patients.

Adult↗
PubMedDate not supplied

Three-dimensional view of the vascular structure of the lower esophagus in clinical portal hypertension.

The venous anatomy of the lower esophagus and upper stomach was studied in nine patients with portal hypertension and in five without, following infusion of a silicon rubber compound into vessels of the excised organs within whole tissues made transparent with methyl salicylate. Four venous channels were identified in normal tissues: intraepithelial, subepithelial superficial, deep submucosal and adventitial veins. In portal hypertensive patients, giant esophageal varices formed 2 to 3 cm above the esophagogastric junction fused with numerous superficial and deep submucosal veins. Gastric varices were present in the submucosa where the left gastric venous branch penetrated the gastric wall 2 cm below the esophagogastric junction. The lower esophageal varices were classified into two types of vascular structure: palisading type in five and bar type in four. The palisading type had dilated intraepithelial channels and numerous small superficial collateral veins extending in a longitudinal arrangement. The bar type had triply dilated subepithelial superficial veins and deep submucosal veins which eroded the epithelium, and the gastric varices were present in the latter type. Our study provides evidence of the three-dimensional vascular structure of the lower esophageal varices without the necessity for tissue dissection.

Aged↗
PubMed1984

Pharmacokinetics of compound 58-112, a potential skeletal muscle relaxant, in man.

The pharmacokinetics of 4-[(3-methoxyphenyl)methyl] -2,2,6,6-tetramethyl-1-oxa-4-aza-2,6-disilacyclohexane (Sandoz compound 58-112), a new chemical entity with a unique myotonolytic effect, was studied in 12 healthy male volunteers who received an oral dose of 50 or 100 mg of the 14C-labeled drug. Serial blood and breath samples and complete urine and feces were collected for 120 hours after dosing. All samples were analyzed for total radioactivity while the blood and urine were also assayed for unchanged compound 58-112. Measurable blood radioactivity levels were observed at 0.5 hour, and peak concentrations were attained at 1 to 2 hours after dosing. The absorption of the radioactive doses was complete and appeared linear in the 50-100 mg range, as indicated by blood 14C levels that were proportional to the dose. The 50- and 100-mg doses also resulted in virtually identical excretion patterns, with 95 per cent of the administered radioactivity recovered within 9 hours, almost exclusively in the urine. However, the disproportionately higher blood concentrations of unchanged compound 58-112 after the 100-mg dose could suggest saturable presystemic metabolism in the liver. Simultaneous fitting of all data in the 100-mg dose study to a pharmacokinetic model showed that unchanged compound 58-112 was distributed into a central and a peripheral compartment and was eliminated entirely by metabolism, the distribution and elimination half-lives being 0.5 and 3.9 hours, respectively. The metabolite(s) was distributed into one homogeneous space, and its elimination half-life was 0.1 hour, with a renal:fecal clearance ratio of approximately 96:4.

Adult↗
PubMed2002

Interactions of 3T3 fibroblasts and endothelial cells with defined pore features.

The colonization of biodegradable polymer scaffolds with cell populations has been established as the foundation for the engineering of a number of tissues, including cartilage, liver, and bone. Within these scaffolds, the cells encounter a porous environment in which they must migrate across the convoluted polymer surface to generate a homogenous cell distribution. Predicting the interactions between cells and pores is important if scaffold characteristics are to be optimized. Therefore, we investigated the behavior of two model cell types over a range of defined pore features. These pore features range from 5 to 90 microm in diameter and have been fabricated by photolithographic techniques. Quantitatively, the behavior of the cells is dependent on three factors: 1) percentage cell coverage of the surface; 2) pore size; and 3) cell type. Fibroblast cells displayed a co-operative pattern of cell spreading in which pores with diameters greater than the cell dimensions were bridged by groups of cells using their neighbors as supports. Endothelial cells were unable to use neighbors as support structures and failed to bridge pores greater than the cell diameter.

3T3 Cells↗