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At least 613 records · Page 34Linked to original sources
PubMed2000

Role of the transition metal in metallaborane chemistry. Reactivity of (Cp*ReH2)2B4H4 with BH3.thf, CO, and Co2(CO)8.

The reaction of Cp*ReCl4, [Cp*ReCl3]2, or [Cp*ReCl2]2 (Cp* = eta 5-C5Me5) with LiBH4 leads to the formation of 7-skeletal-electron-pair (7-sep) (Cp*ReH2)2(B2H3)2 (1) together with Cp*ReH6. Compound 1 is metastable and eliminates H2 at room temperature to generate 6-sep (Cp*ReH2)2B4H4 (2). The reaction of 2 with BH3.thf produces 7-sep (Cp*Re)2B7H7, a hypoelectronic cluster characterized previously. Heating of 2 with 1 atm of CO leads to 6-sep (Cp*ReCO)(Cp*ReH2)B4H4 (3). Both 2 and 3 have the same bicapped Re2B2 tetrahedral cluster core structure. Monitoring the reaction of 2 with CO at room temperature by NMR reveals the formation of a 7-sep, metastable intermediate, (Cp*ReCO)(Cp*ReH2)(B2H3)2 (4), which converts to 3 on heating. An X-ray structure determination reveals two isomeric forms (4-cis and 4-trans) in the crystallographic asymmetric unit which differ in geometry relative to the disposition of the metal ancillary ligands with respect to the Re-Re bond. The presence of these isomers in solution is corroborated by the solution NMR data and the infrared spectrum. In both isomers, the metallaborane core consists of fused B2Re2 tetrahedra sharing the Re2 fragment. On the basis of similarities in electron count and spectroscopic data, 1 also possesses the same bitetrahedral structure. The reaction of 2 with CO2(CO)8 results in the formal replacement of the four rhenium hydrides with a 4-electron CO2(CO)5 fragment, thereby closing the open face in 2 to produce the 6-sep hypoelectronic cluster (Cp*Re)2CO2(CO)5B4H4 (5). These reaction outcomes are compared and contrasted with those previously observed for 5-sep (Cp*Cr2)2B4H8.

Journal Article↗
PubMed2005

Calpain activation in apoptosis of ventral spinal cord 4.1 (VSC4.1) motoneurons exposed to glutamate: calpain inhibition provides functional neuroprotection.

Glutamate toxicity has been implicated in cell death in neurodegenerative diseases and injuries. Glutamate-induced Ca2+ influx may mediate activation of calpain, a Ca2+-dependent cysteine protease, which in turn may degrade key cytoskeletal proteins. We investigated glutamate-mediated apoptosis of VSC4.1 motoneurons and functional neuroprotection by calpain inhibition. Exposure of VSC4.1 cells to 10 microM glutamate for 24 hr caused significant increases in intracellular free [Ca2+], as determined by fura-2 assay. Pretreatment of cells with 10 or 25 microM calpeptin (a cell-permeable calpain-specific inhibitor) for 1 hr prevented glutamate-induced Ca2+ influx. Western blot analyses showed an increase in Bax:Bcl-2 ratio, release of cytochrome c from mitochondria, and calpain and caspase-3 activities during apoptosis. Cell morphology, as evaluated by Wright staining, indicated predominantly apoptotic features following glutamate exposure. ApopTag assay further substantiated apoptotic features morphologically as well as biochemically. Our data showed that calpeptin mainly prevented calpain-mediated proteolysis and apoptosis and maintained whole-cell membrane potential, indicating functional neuroprotection. The results imply that calpeptin may serve as a therapeutic agent for preventing motoneuron degeneration, which occurs in amyotrophic lateral sclerosis and spinal cord injury. In this investigation, we also examined glutamate receptor subtypes involved in the initiation of apoptosis in VSC4.1 cells following exposure to glutamate. Our results indicated that the N-methyl-D-aspartate (NMDA) receptors contributed more than alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) receptors to glutamate-mediated Ca2+ influx and cell death mechanism. Inhibition of the activities of both NMDA and AMPA receptors protected VSC4.1 cells from glutamate toxicity and preserved whole-cell membrane potential.

Animals↗
PubMed1992

Regeneration in Salaria pavo (Blenniidae, Teleostei). Histogenesis of the regenerating pectoral fin suggests different mechanisms for morphogenesis and structural maintenance.

The pectoral fin of blennies is differentiated into a dorsal field and a ventral hook field. A histogenetic analysis of the regenerating pectoral fin was related to two questions. First, are histological specializations of the hook field responsible for the impairment of the regenerative capacity of pectoral fins of blennies? Second, can analysis of the temporal sequence of histogenetic events be used to make testable predictions about the tissue interactions required to re-establish the adult pattern? Regeneration of pectoral fins was examined in Salaria pavo (Blenniidae, Teleostei). Approximately 80% of the length of the fin rays was amputated. Fin ray stumps were evaluated 7, 14, 24, 48 and 72 h after amputation, regenerates 4, 5, and 6 days after amputation and at length of about 30%, 50% and 60% regeneration of the original fin length. The regeneration process is subdivided into four stages: wound healing, blastema formation, fin ray formation and distal outgrowth and differentiation of hook characters. Analysis of the early events of regeneration, wound healing, blastema formation and distal outgrowth, yielded no profound differences from those of conventional fins in general. Impairment of regenerative capacity becomes manifested before histological differentiation of hook characters, and it is thus unlikely that their presence is the proximate cause of heteromorphic regeneration. The sequence in which the anatomical specializations characteristic of fin hooks (lepidotrichal cord, cuticle, fin web regression) appear was variable. Detailed analysis of older regenerates revealed a more regular pattern. In the first phase the characters appear to be largely independently organized, while they become locally correlated later. It is concluded that the anatomical differentiation passes through two stages, initiation of anatomical differentiation, and then mutual adjustment of character expression leading to spatially correlated expression of the lepidotrichal cord, the cuticle and the fin web regression.

Animals↗
PubMed2003

Evaluation of doses in radiotherapy using solid-state composites based on natural colourless topaz.

The thermoluminescent properties of composites containing powdered topaz embedded in Teflon or glass were studied and compared with the corresponding properties of the well known TLD-100 commercial dosimeters. Relative sensitivity, TL fading, reproducibility of the sample preparation process, and possibility of re-utilisation of the dosimeters were investigated. Measurements of absorbed doses in simulated radiotherapy treatments were also taken. The irradiations were performed using gamma rays from a 60Co source in the dose range from 1cGy to 2Gy. The dosimeters were installed in badges and attached inside acrylic plates of various thicknesses in the radiation fields. The dose profiles obtained with this procedure are very similar to the ones obtained with equivalent tissues. It is concluded that these composites of natural colourless topaz crystals can be efficiently used as TL dosimeters.

Aluminum Silicates↗
PubMed2006

Structural and kinetic analyses of the H121A mutant of cholesterol oxidase.

Cholesterol oxidase is a monomeric flavoenzyme that catalyses the oxidation of cholesterol to cholest-5-en-3-one followed by isomerization to cholest-4-en-3-one. The enzyme from Brevibacterium sterolicum contains the FAD cofactor covalently bound to His121. It was previously demonstrated that the H121A substitution results in a approximately 100 mV decrease in the midpoint redox potential and a approximately 40-fold decrease in turnover number compared to wild-type enzyme [Motteran, Pilone, Molla, Ghisla and Pollegioni (2001) Journal of Biological Chemistry 276, 18024-18030]. A detailed kinetic analysis of the H121A mutant enzyme shows that the decrease in turnover number is largely due to a corresponding decrease in the rate constant of flavin reduction, whilst the re-oxidation reaction is only marginally altered and the isomerization reaction is not affected by the substitution and precedes product dissociation. The X-ray structure of the mutant protein, determined to 1.7 A resolution (1 A identical with 0.1 nm), reveals only minor changes in the overall fold of the protein, namely: two loops have slight movements and a tryptophan residue changes conformation by a rotation of 180 degrees about chi1 compared to the native enzyme. Comparison of the isoalloxazine ring moiety of the FAD cofactor between the structures of the native and mutant proteins shows a change from a non-planar to a planar geometry (resulting in a more tetrahedral-like geometry for N5). This change is proposed to be a major factor contributing to the observed alteration in redox potential. Since a similar distortion of the flavin has not been observed in other covalent flavoproteins, it is proposed to represent a specific mode to facilitate flavin reduction in covalent cholesterol oxidase.

Amino Acid Substitution↗
PubMed1984

Beta- and gamma-dose measurements of the Godiva IV critical assembly.

To aid in the re-evaluation of an exposure that occurred in 1963, information was required on the response of film badges to the beta- and gamma-ray doses from a critical assembly. Of particular interest was the beta spectra from the assembly. The techniques used and the results obtained in this study are of interest to health physicists at facilities where exposures to betas occur. The dose rates from the Los Alamos National Laboratory Godiva IV Critical Assembly were measured at numerous distances from the assembly four and 12 days following a burst. Information was obtained on the beta-particle spectra using absorption curve studies. The beta/gamma dose-rate ratio as a function of distance from the assembly was determined. Shielding provided by various metals, gloves and clothing was measured. The beta- and gamma-ray doses measured were compared with a film packet used in the past at the Nevada Test Site with two types of current TLD personnel badges. Measurements made with a commercial thin-window ion chamber instrument are compared with the dose rates obtained using other dosimeters.

Electrons↗
PubMed2004

Facial characterization of infants with cleft lip and palate using a three-dimensional capture technique.

OBJECTIVE: To characterize the soft tissue features of infants with unilateral cleft lip (UCL) and unilateral complete cleft lip and palate (UCLP) prior to primary surgery and compare with noncleft controls. DESIGN: Prospective controlled capture of the facial morphology of infants using a noninvasive three-dimensional stereophotogrammetry method. PARTICIPANTS: 23 children with presurgical cleft: 11 UCL (M = 6, F = 5); 12 UCLP (M = 9, F = 3), and 21 noncleft controls (M = 7, F = 14) were imaged at approximately 3 months of age (range 10 to 16 weeks). MAIN OUTCOME MEASURE: Accurate, repeatable quantification of facial soft tissues in infants with clefts prior to surgery. RESULTS: Significant differences (p <.05) were found between the UCLP group and UCL and control groups in anatomical and soft nose width, cleft-side alar wing length, and nasal tip horizontal displacement. Both cleft groups were significantly different from controls and from each other in cleft-side nostril dimensions, alar wing angulation, columella angle, and alar base to corner of mouth dimension; alar base width; and soft tissue defect in nose and the lip and philtrum length bordering the cleft. Significant differences between clefts and controls were identified in the nostril and philtrum on the noncleft side. CONCLUSIONS: The use of children with UCL as controls for UCLP studies is inappropriate. This technique overcame the limitations of direct measurement of infant faces to aid the surgeon in the planning and subsequent re-evaluation of surgical rationale.

Analysis of Variance↗
PubMed2002

[Acute respiratory failure due to Gemcitabine-induced pulmonary toxicity].

Gemcitabine is a therapeutic agent that has been recently employed in the treatment of various cancers. Pulmonary toxicity has rarely been described. We report a case of a patient treated with Gemcitabine who developed acute respiratory symptoms related to a hypersensitivity pneumonia. Despite a severe clinical and radiological presentation, the outcome was favorable with corticosteroid treatment. In the event of respiratory symptoms in patients receiving Gemcitabine further investigations (chest X-ray, thorax CT-scan, bronchoalveolar lavage) are indicated. In view of the severity of pulmonary toxicity that can be caused by Gemcitabine, re-introduction of treatment is not recommended. We compare our case with other published cases of Gemcitabine-induced pulmonary toxicity.

Acute Disease↗
PubMed1991

[A case of pneumothorax which was operated with the axillary longitudinal small incision].

A pneumothorax usually occurs in young men. From the cosmetic point of view, the size of the skin incision should be considered to be minimal if surgery is applied for young pneumothorax patients. We reported a case of pneumothorax which was operated with a small longitudinal axillary skin incision, the size of which was 3.5 cm long. The patient was a 18-year-old high school student. He was admitted to our hospital with the diagnosis of spontaneous pneumothorax. His chest X-ray showed a moderate collapse of his left lung and bullae in his left apex. Tube drainage was performed and the collapsed lung re-expanded completely. Chest CT scan demonstrated that he had bullae in the apex of his left lung. No other lesions were found in the other part of both lungs. Surgery was indicated socially. Bullectomy was successfully performed with a small (3.5 cm) longitudinal axillary skin incision. We recommend this skin incision for young patients with pneumothorax if the chest CT scan confirms that the bullae or blebs are localized to the apex of superior segment of the lower lobe.

Adolescent↗
PubMed2005

Two-potential electrochemical probe for study of DNA immobilization.

A two-potential electrochemical method is applied to study DNA immobilization, by the simultaneous characterization of capture probe DNA self-assembled monolayers and hybridized target DNA molecules on a given gold electrode surface. Capture probe and target DNA strands are labeled with ferrocenes composed of differing chemical environments, to permit their simultaneous, yet independent signaling at different formal potentials, so that their respective signals may be de-convoluted and assessed for relative surface concentration. Some special attributes of the nondestructive two-potential electrochemical probe described herein include surface sensitivity, chemical and orientation specificity, and the ability to provide a real-time, in situ probe that does not need any wash steps for stringency. This electrochemical probe is applied to study the kinetics, surface architecture, coverage, and orientation of DNA during its immobilization on gold. On the basis of our results primarily from this electrochemical probe, and validated by N(1s) core-level X-ray photoelectron spectra, we judge significant DNA deposition within 5 min of incubation in the deposition solutions, with the capture probe DNA anchored predominantly via the thiol end, even at low coverages. Surface coverage for DNA immobilization plateaus within 30 min of incubation time to approximately 2 x 10(13) molecules/cm(2) and the immobilization kinetics as determined from this electrochemical method are consistent with surface re-organization as the rate-determining step.

DNA↗
PubMed2001

X-Ray study on an artificial mung bean inhibitor complex with bovine beta-trypsin in neat cyclohexane.

The active trypsin inhibiting component, SPC1, was obtained during the synthesis of a 22-residue peptide with three disulfide bridges according to the mimic mung bean Bowman-Birk type inhibitor. The K(i) value of SPC1 is 1.2x10(-7) M. In order to determine the topological structure of SPC1, X-ray diffraction studies were carried out on the complex of SPC1 with bovine beta-trypsin. Only the binding loop of SPC1 resolved at 2.2 A resolution due to conformational flexibility of the other residues [1]. The amino acid sequence was re-determined and electrospray mass spectroscopy was also performed to ensure that no cleaving occurred on SPC1 and the primary sequence of SPC1 is correct. Because the protein is more rigid in nonaqueous medium as has been proved by others [2], we treated the complex of SPC1 with neat cyclohexane and then subjected it to X-ray diffraction analysis, and the result showed that all the 22 residues of SPC1 were located in the electron density map. So the topological structure of SPC1 has been determined, suggesting that crystal treatment with cyclohexane may be used as a method to determine the conformation of the disordered regions in protein crystal structures.

Amino Acid Sequence↗