Home About us Contact
|
Home About us Contact | ||
|
|
||
Subsequent Hydrolysis (subsequent + hydrolysis)
Selected AbstractsPorous Polymersomes with Encapsulated Gd-Labeled Dendrimers as Highly Efficient MRI Contrast AgentsADVANCED FUNCTIONAL MATERIALS, Issue 23 2009Zhiliang Cheng Abstract The use of nanovesicles with encapsulated Gd as magnetic resonance (MR) contrast agents has largely been ignored due to the detrimental effects of the slow water exchange rate through the vesicle bilayer on the relaxivity of encapsulated Gd. Here, the facile synthesis of a composite MR contrast platform is described; it consists of dendrimer conjugates encapsulated in porous polymersomes. These nanoparticles exhibit improved permeability to water flux and a large capacity to store chelated Gd within the aqueous lumen, resulting in enhanced longitudinal relaxivity. The porous polymersomes, ,130,nm in diameter, are produced through the aqueous assembly of the polymers, polyethylene oxide- b -polybutadiene (PBdEO), and polyethylene oxide- b -polycaprolactone (PEOCL). Subsequent hydrolysis of the caprolactone (CL) block resulted in a highly permeable outer membrane. To prevent the leakage of small Gd-chelate through the pores, Gd was conjugated to polyamidoamine (PAMAM) dendrimers via diethylenetriaminepentaacetic acid dianhydride (DTPA dianhydride) prior to encapsulation. As a result of the slower rotational correlation time of Gd-labeled dendrimers, the porous outer membrane of the nanovesicle, and the high Gd payload, these functional nanoparticles are found to exhibit a relaxivity (R1) of 292 109,mM,1,s,1 per particle. The polymersomes are also found to exhibit unique pharmacokinetics with a circulation half-life of >3.5,h and predominantly renal clearance. [source] Reactions of Polycyclic Ketones with Dimethoxycarbene; a Convenient Route for a ,One-Pot' Preparation of Some , -Hydroxycarboxylic Acid EstersHELVETICA CHIMICA ACTA, Issue 7 2007Jaros, aw Roma Abstract Polycyclic ,cage' ketones, such as pentacyclo[5.4.0.02,6.03,10.05,9]undecan-8-one (10), pentacyclo[5.4.0.02,6.03,10.05,9]undecane-8,11-dione (11), and adamantan-2-one (16) were treated with the nucleophilic dimethoxycarbene (DMC; 1), which was generated thermally from 2,5-dihydro-2,2-dimethoxy-5,5-dimethyl-1,3,4-oxadiazole (4a) in boiling toluene. In this ,one-pot' procedure, the , -hydroxycarboxylic acid ester 12 or a corresponding derivative 15 or 17 was obtained (Schemes,4,7). Additionally, ,cage' thione 21 was treated with DMC under the same conditions yielding dimethoxythiirane 22 (Scheme,8). Subsequent hydrolysis or desulfurization (followed by hydrolysis on silica gel) of 22 gave , -mercaptocarboxylate 25 and the corresponding desulfurized ester 24, respectively. In all cases, the addition of DMC occurred stereoselectively, and the addition from the exo -face is postulated to explain the structures of the isolated products. [source] Rapid assessment of in vivo cholinergic transmission by amperometric detection of changes in extracellular choline levelsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2004Vinay Parikh Abstract Conventional microdialysis methods for measuring acetylcholine (ACh) efflux do not provide sufficient temporal resolution to relate cholinergic transmission to individual stimuli or behavioral responses, or sufficient spatial resolution to investigate heterogeneities in such regulation within a brain region. In an effort to overcome these constraints, we investigated a ceramic-based microelectrode array designed to measure amperometrically rapid changes in extracellular choline as a marker for cholinergic transmission in the frontoparietal cortex of anesthetized rats. These microelectrodes exhibited detection limits of 300 nm for choline and selectivity (> 100 : 1) of choline over interferents such as ascorbic acid. Intracortical pressure ejections of choline (20 mm, 66,400 nL) and ACh (10 and 100 mm, 200 nL) dose-dependently increased choline-related signals that were cleared to background levels within 10 s. ACh, but not choline-induced signals, were significantly attenuated by co-ejection of the acetylcholinesterase inhibitor neostigmine (Neo; 100 mm). Pressure ejections of drugs known to increase cortical ACh efflux, potassium (KCl; 70 mm, 66, 200 nL) and scopolamine (Scop; 10 mm, 200 nL), also markedly increased extracellular choline signals, which again were inhibited by Neo. Scop-induced choline signals were also found to be tetrodotoxin-sensitive. Collectively, these findings suggest that drug-induced increases in current measured with these microelectrode arrays reflect the oxidation of choline that is neuronally derived from the release and subsequent hydrolysis of ACh. Choline signals assessed using enzyme-selective microelectrode arrays may represent a rapid, sensitive and spatially discrete measure of cholinergic transmission. [source] Hydrolytic Deallylation of N -Allyl Amides Catalyzed by PdII ComplexesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 30 2008Naoya Ohmura Abstract Hydrolytic deallylation of N -allyl amides to give amides and propanal can be achieved with PdII catalysts. The optimized catalyst consists of Pd(OCOCF3)2 and 1,3-bis(diphenylphosphanyl)propane (DPPP). Several kinds of open-chain N -allyl amides and N -allyl lactams undergo hydrolytic deallylation to give the corresponding amides and lactams in good to high yield. A mechanism which includes isomerization to enamides and subsequent hydrolysis is proposed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Synthesis of labeled galactosylhydroxylysineJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 3 2001Maciej Adamczyk Abstract A concise synthesis of isotopically labeled galactosylhydroxylysine (2) was achieved via glycosylation of labeled hydroxylysine derivative (3) with (+)-acetobromo-,-D-galactose (4) and subsequent hydrolysis in good overall yield. The hydroxylysine derivative (3) was prepared from (S)-(,)-methyl-2-[bis-(tert -butoxycarbonyl)amino]-5-oxopentanoate (4) with the introduction of label (13CD2) via a Wittig reaction using 13CD3PPh3I. Copyright © 2001 John Wiley & Sons, Ltd. [source] pH-Switchable Complexation between Double Hydrophilic Heteroarm Star Copolymers and a Cationic Block PolyelectrolyteMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 7 2008Zhishen Ge Abstract Double hydrophilic heteroarm star copolymers of poly(methacrylic acid) (PMAA) and poly(ethylene oxide) (PEO) were synthesized via atom-transfer radical polymerization (ATRP) using the "in-out" method. The synthesis consisted of three steps. Namely, ATRP was applied to the preparation of a star macroinitiator with PEO arms and a cross-linked core resulting from the polymerization of divinylbenzene (DVB) in the first step, chain extension with tert -butyl methacrylate (tBMA) under ATRP conditions, and subsequent hydrolysis of the tert -butyl groups afforded (PEO)n -PDVB-(PMAA)n heteroarm star copolymers with a cross-linked microgel core. This novel type of double hydrophilic heteroarm star copolymer can be considered as unimolecular micelles with hybrid coronas. The star copolymers exhibited pH-dependent solubility in water, being soluble at high pH and insoluble at low pH, due to the formation of hydrogen-bonded complexes between the PEO and PMAA arms. A mixed solution of the heteroarm star copolymer and a PEO- b -PQDMA diblock copolymer, where PQDMA is poly(2-(dimethylamino)ethyl methacrylate) fully quaternized with methyl iodide, remained stable in the whole pH range, and exhibited an intriguing pH-switchable complexation behavior accompanied with structural rearrangement. [source] Real-time detection of the morphological change in cellulose by a nanomechanical sensorBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2010Liming Zhao Abstract Up to now, experimental limitations have prevented researchers from achieving the molecular-level understanding for the initial steps of the enzymatic hydrolysis of cellulose, where cellulase breaks down the crystal structure on the surface region of cellulose and exposes cellulose chains for the subsequent hydrolysis by cellulase. Because one of these non-hydrolytic enzymatic steps could be the rate-limiting step for the entire enzymatic hydrolysis of crystalline cellulose by cellulase, being able to analyze and understand these steps is instrumental in uncovering novel leads for improving the efficiency of cellulase. In this communication, we report an innovative application of the microcantilever technique for a real-time assessment of the morphological change of cellulose induced by a treatment of sodium chloride. This sensitive nanomechanical approach to define changes in surface structure of cellulose has the potential to permit a real-time assessment of the effect of the non-hydrolytic activities of cellulase on cellulose and thereby to provide a comprehensive understanding of the initial steps of the enzymatic hydrolysis of cellulose. Biotechnol. Bioeng. 2010;107: 190,194. © 2010 Wiley Periodicals, Inc. [source] Influence of xylan on the enzymatic hydrolysis of steam-pretreated corn stover and hybrid poplarBIOTECHNOLOGY PROGRESS, Issue 2 2009Renata Bura Abstract The focus of this study was to alter the xylan content of corn stover and poplar using SO2 -catalyzed steam pretreatment to determine the effect on subsequent hydrolysis by commercial cellulase preparations supplemented with or without xylanases. Steam pretreated solids with xylan contents ranging from ,1 to 19% (w/w) were produced. Higher xylan contents and improved hemicellulose recoveries were obtained with solids pretreated at lower severities or without SO2 -addition prior to pretreatment. The pretreated solids with low xylan content (<4% (w/w)) were characterized by fast and complete cellulose to glucose conversion when utilizing cellulases. Commercial cellulases required xylanase supplementation for effective hydrolysis of pretreated substrates containing higher amounts of xylan. It was apparent that the xylan content influenced both the enzyme requirements for hydrolysis and the recovery of sugars during the pretreatment process. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] Modeling of Product Removal during Enzymatic Conversions by Using Affinity MoleculesBIOTECHNOLOGY PROGRESS, Issue 6 2007Daniël G. R. Halsema The feasibility of using magnetic particles for in-line product isolation during enzymatic conversion was studied. A comparison was made between a process based on magnetic particles and a conventional adsorption column. The enzymatic reaction was described by two consecutive first-order reactions (synthesis and subsequent hydrolysis), while the adsorption of substrate and product was described by multicomponent Langmuir isotherms. The yield as well as synthesis/hydrolysis ratio were calculated for various system characteristics. The results show that magnetic particles are very effective when the affinity with the particles is specific and for enzymatic conversions involving low ratios of the rate of synthesis versus the rate of hydrolysis. For slow conversions and for low specific affinity molecules column separations are more appropriate. [source] Collagens, stromal cell-derived factor-1, and basic fibroblast growth factor increase cancer cell invasiveness in a hyaluronan hydrogelCELL PROLIFERATION, Issue 2 2008L. David Objective: Beyond to control of cell migration, differentiation and proliferation, the extracellular matrix (ECM) also contributes to invasiveness of human cancers. As the roles of hyaluronan (HA) and collagens in this process are still controversial, we have investigated their involvement in cancer pathogenesis. Materials and methods: With this aim in view, we developed a three-dimensional matrix, as reticulate HA hydrogel alone or coated with different collagens, in which cells could invade and grow. Results: We show that cancer cells, which were non-invasive in a single HA hydrogel, acquired this capacity in the concomitant presence of type I or III collagens. Both types of ECM compound, HA and collagens, possess the capacity to stimulate production of metalloprotease-2, recognized otherwise as a factor for poor cancer prognosis. HA-provoked cellular invasiveness resulted from CD44-mediated increase in cytosolic [Ca2+] and its subsequent hydrolysis due to ADAM (a disintegrin and metalloprotease) proteolytic activity. Interestingly, this mechanism seemed to be absent in non-invasive cancer cell lines. Conclusion: Furthermore, using basic fibroblast growth factor and stromal cell-derived factor-1,, we also show that this three-dimensional reticulate matrix may be considered as a valuable model to study chemokinetic and chemotactic potentials of factors present in tumour stroma. [source] A Facile Synthesis of N -Aryl Substituted PiperidonesCHINESE JOURNAL OF CHEMISTRY, Issue 10 2009Qian Geng Abstract A general and efficient procedure for the synthesis of N -aryl-substituted 4-piperidones was developed. The two step syntheses proceeded with an overall yield of 60%-83% using L -proline as the ligand for the Cu(I)-catalyzed Ullmann amination followed by subsequent hydrolysis of resulting ketals. [source] | ||||||||||||||||