Conversion Reaction (conversion + reaction)

Distribution by Scientific Domains


Selected Abstracts


Conversion of Bioactive Borosilicate Glass to Multilayered Hydroxyapatite in Dilute Phosphate Solution

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2007
Yadong Li
The conversion of a bioactive borosilicate glass in aqueous phosphate solution was observed to produce vastly different reaction kinetics and hydroxyapatite (HA) microstructures, depending on whether the glass was reacted continuously or intermittently in the solution. Particles (150,300 ,m) of a borosilicate glass (designated H12) were reacted continuously or intermittently in 0.25M K2HPO4 solution with a starting pH value of 7.0 at 37°C. The conversion kinetics of the glass particles to HA were determined from weight loss measurements. Structural and compositional changes resulting from the conversion reaction were characterized using scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray analysis, and Fourier transform infrared spectroscopy. For conversion experiments carried out intermittently (12,24 h intervals, followed by drying), faster reaction kinetics and a unique multilayered microstructure, consisting of alternating layers of HA and an amorphous SiO2 -rich material with nearly uniform thickness (2,3 ,m), were observed. On the other hand, particles reacted continuously in the phosphate solution for the same total time converted more slowly and produced a single HA layer. The kinetics and mechanism of forming HA under the intermittent and continuous reaction conditions are described and compared with those for bioactive silicate and borate glasses studied in previous work. [source]


Psychogenic urinary dysfunction: A uro-neurological assessment,

NEUROUROLOGY AND URODYNAMICS, Issue 4 2007
Ryuji Sakakibara
Abstract Aims The diagnosis of psychogenic urinary dysfunction (PUD) is one of exclusion, particularly from urologic and neurologic causes, and is usually accompanied by more obvious psychologic/ psychiatric features. We here describe patients with PUD who were diagnosed in our uro- neurological laboratory. Materials and Methods We reviewed the digitized records of 2,300 urodynamic cases treated in the past 6 years to identify patients who fulfilled the diagnostic criteria of PUD. All 2,300 patients had completed a urinary questionnaire and undergone both electromyography (EMG)-cystometry and a detailed neurological examination. In addition, pressure-flow analysis, neurophysiology tests including sphincter EMG analysis, and MRI of the brain and spinal cord were performed as applicable. Results PUD was seen in 16 cases (0.7%): 6 men, 10 women, mean age 37 years. Lower urinary tract symptoms (LUTS) included overactive bladder (OAB) alone in 5, difficult urination alone in one, and both in 10. LUTS commonly occurred in particular situations, for example, OAB only while riding the train. Some patients showed extremely infrequent toileting. The urodynamic findings were normal except for increased bladder sensation (50%) for OAB and acontractile detrusor (31%) for difficulty. The final diagnosis was conversion reaction in six followed by anxiety in four. Conclusions PUD patients experienced the situational occurrence of OAB and/or difficult urination and, in some patients, extremely infrequent toileting. The main urodynamic abnormalities were increased bladder sensation and acontractile detrusor. However, even in cases suggestive of PUD, a non-PUD pathology behind the symptoms should be explored. Neurourol. Urodynam. 26:518,524, 2007. © 2007 Wiley-Liss, Inc. [source]


Structure of macrophomate synthase

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2004
Toyoyuki Ose
Macrophomate synthase (MPS) is an enzyme that catalyzes an extraordinarily complex conversion reaction, including two decarboxylations, two carbon,carbon bond formations and a dehydration, to form the benzoate analogue macrophomate from a 2-pyrone derivative and oxalacetate. Of these reactions, the two carbon,carbon bond formations are especially noteworthy because previous experiments have indicated that they proceed via a Diels,Alder reaction, one of the most widely used reactions in organic synthesis. The structural evidence that MPS catalyzes an intermolecular Diels,Alder reaction has been reported recently [Ose et al. (2003), Nature (London), 422, 185,189]. Interestingly, the tertiary structure as well as the quaternary structure of MPS are similar to those of 2-dehydro-3-deoxygalactarate (DDG) aldolase, a carbon,carbon bond-forming enzyme that catalyzes the reversible reaction of aldol condensation/cleavage. Here, the structure of MPS is described in detail and compared with that of DDG aldolase. Both enzymes have a (,/,)8 -barrel fold and are classified as belonging to the enolase superfamily based on their reaction strategy. The basic principles for carbon,carbon bond formation used by both MPS and DDG aldolase are the same with regard to trapping the enolate substrate and inducing subsequent reaction. The major differences in the active sites between these two enzymes are the recognition mechanisms of the second substrates, 2-pyrone and DDG, respectively. [source]


"Click Peptides",Chemical Biology-Oriented Synthesis of Alzheimer's Disease-Related Amyloid , Peptide (A,) Analogues Based on the "O- Acyl Isopeptide Method"

CHEMBIOCHEM, Issue 10 2006
Youhei Sohma
Abstract A clear understanding of the pathological mechanism of amyloid , peptide (A,) 1,42, a currently unexplained process, would be of great significance for the discovery of novel drug targets for Alzheimer's disease (AD) therapy. To date, though, the elucidation of these A,1,42 dynamic events has been a difficult issue because of uncontrolled polymerization, which also poses a significant obstacle in establishing experimental systems with which to clarify the pathological function of A,1,42. We have recently developed chemical biology-oriented pH- or phototriggered "click peptide" isoform precursors of A,1,42, based on the "O -acyl isopeptide method", in which a native amide bond at a hydroxyamino acid residue, such as Ser, is isomerized to an ester bond, the target peptide subsequently being generated by an O,N intramolecular acyl migration reaction. These click peptide precursors did not exhibit any self-assembling character under physiological conditions, thanks to the presence of the one single ester bond, and were able to undergo migration to give the target A,1,42 in a quick and easy, one-way (so-called "click")conversion reaction. The use of click peptides could be a useful strategy to investigate the biological functions of A,1,42 in AD through inducible activation of A,1,42 self-assembly. [source]


Secondary Synthesis of Two Cobalt Complexes by the Use of 5-Sulfosalicylate and 1,10-Phenanthroline and Their Crystal Structures

CHINESE JOURNAL OF CHEMISTRY, Issue 10 2005
Sai-Rong Fan
Abstract Cobalt(II) nitrate reacted with 1,10-phenanthroline (phen) and 5-sulfosalicylic acid (H3ssal) to yield the cobalt(II) complex [Co(phen)2(H2O)2](Hssal)·4H2O (1) and the reaction of 1 with copper acetate led to a novel complex [Co(phen)(H2O)4][Cu2(ssal)2(phen)2]·5H2O (2). These two complexes were cation-anion species and the cationic motif [Co(phen)2(H2O)2]2+of 1 could be converted to [Co(phen)(H2O)4]2+ in the formation process of new anion [Cu2(phen)2(ssal)2]2, of 2. In both complexes abundant hydrogen bonds construct different supramolecular architectures, thus the conversion reaction can provide a new path to create novel supramolecular network. [source]


Research on Advanced Materials for Li-ion Batteries

ADVANCED MATERIALS, Issue 45 2009
Hong Li
Abstract In order to address power and energy demands of mobile electronics and electric cars, Li-ion technology is urgently being optimized by using alternative materials. This article presents a review of our recent progress dedicated to the anode and cathode materials that have the potential to fulfil the crucial factors of cost, safety, lifetime, durability, power density, and energy density. Nanostructured inorganic compounds have been extensively investigated. Size effects revealed in the storage of lithium through micropores (hard carbon spheres), alloys (Si, SnSb), and conversion reactions (Cr2O3, MnO) are studied. The formation of nano/micro core,shell, dispersed composite, and surface pinning structures can improve their cycling performance. Surface coating on LiCoO2 and LiMn2O4 was found to be an effective way to enhance their thermal and chemical stability and the mechanisms are discussed. Theoretical simulations and experiments on LiFePO4 reveal that alkali metal ions and nitrogen doping into the LiFePO4 lattice are possible approaches to increase its electronic conductivity and does not block transport of lithium ion along the 1D channel. [source]