Fast grain boundary: A FORTRAN-77 program for calculating the effects of retrograde interdiffusion of stable isotopes

Exchange of stable isotopes between coexisting minerals is recognized widely as an important factor in the interpretation of stable isotope geochemistry of plutonic and high-grade metamorphic rocks. Where retrogression has occurred without major recrystallization events, the rate limiting step for stable isotope exchange will be diffusion. The mathematics of diffusion are well known for many problems, but no analytical solution, including that for closure temperature, adequately describes the complex and highly variable controls of rate and mass balance that will dominate many diffusion processes in rocks. We have implemented a model describing diffusional exchange for rocks in which grain boundary diffusion is sufficiently rapid that a representative volume of rock (typically millimeter to centimeter) is able to have mutual equilibration of all grain boundaries for the time scale of cooling. This Fast Grain Boundary model explicitly links intracrystalline diffusion rates and abundances of all minerals in a rock, and allows study of the impact of rock type on stable isotope thermometry, retrogression, and zonation.The FORTRAN-77 program for the Fast Grain Boundary model presented here can be used with a personal computer to solve typical problems in minutes. Input includes the grain size(s), model abundance(s), diffusion coefficient, and fractionation factor for each constituent mineral, and a cooling rate for the rock. Output includes the diffusion profile and integrated (bulk) composition of every mineral in a rock, as well as the apparent temperatures that would be observed by applying bulk-mineral stable isotope thermometry to such a rock.     

Monitoring ligand modulation of protein-protein interactions by mass spectrometry: estrogen receptor alpha-SRC1

Many drugs and chemicals exert their biological effect by modulating protein-protein interactions. In vitro approaches to characterize these mechanisms are often based on indirect measurements (e.g., fluorescence). Here, we used mass spectrometry (MS) to directly monitor the effect of small-molecule ligands on the binding of a coactivator peptide (SRC1) by the human estrogen receptor alpha ligand binding domain (hERalpha LBD). Nanoelectrospray mass spectrometry (nanoESI-MS) and high-mass matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) combined with chemical cross-linking were employed to follow these processes. The chemical cross-linking protocol used prior to high-mass MALDI analysis allows detection of intact noncovalent complexes. The binding of intact hERalpha LBD homodimer with two coactivator peptides was detected with nanoESI-MS and high-mass MALDI-MS only in the presence of an agonist ligand. Furthermore, high-mass MALDI-MS revealed an increase of the homodimer abundance after incubating the receptor with a ligand, independent of the ligand character (i.e., agonist, antagonist). The binding characteristics of the compounds tested by MS correlate very well with their biological activity reported by cell-based assays. High-mass MALDI appears to be an efficient and simple tool for directly monitoring ligand regulation mechanisms involved in protein-protein interactions. Furthermore, the combination of both MS methods allows identifying and characterizing endocrine-disrupting compounds or new drug compounds in an efficient way.     

Secondary ion mass spectrometry of vapor-liquid-solid grown, Au-catalyzed, Si wires

Knowledge of the catalyst concentration within vapor-liquid-solid (VLS) grown semiconductor wires is needed in order to assess potential limits to electrical and optical device performance imposed by the VLS growth mechanism. We report herein the use of secondary ion mass spectrometry to characterize the Au catalyst concentration within individual, VLS-grown, Si wires. For Si wires grown by chemical vapor deposition from SiCl 4 at 1000 degrees C, an upper limit on the bulk Au concentration was observed to be 1.7 x 10(16) atoms/cm(3), similar to the thermodynamic equilibrium concentration at the growth temperature. However, a higher concentration of Au was observed on the sidewalls of the wires.     

The potential of collagenase as a new therapy for separation of human retained placenta: hydrolytic potency on human, equine and bovine placentae

The purpose of this study was to determine to what degree bacterial collagenase may digest human placentae compared to equine and bovine placentae. Placenta samples from human, equine and bovine were incubated with bacterial collagenase solution at various concentrations. The degree of hydrolysis and collagen breakdown was measured by the release of total proteins and hydroxyproline into the incubation media. Also, whole placentae were injected via umbilical cord arteries with collagenase solution (200 U/ml, 200 ml total volume in human and 1000 ml in equine) and hydrolysis determined chemically and subjectively. Human and equine placental collagens were the most sensitive to collagenase digestion. Overall mean collagenase activity determined by the release of hydroxyproline from human placenta was 1.6 times and in equine placenta three times greater than in bovine placenta, while the breakdown of non-collagenous proteins remained negligible. When injected into whole placenta, the collagenase digested placentae evenly within 6-12 h. At 24 h, placentae were liquefied, although, umbilical blood vessels resisted collagenase digestion. Bacterial collagenase was highly effective in breaking down human placenta collagen. Intraplacental injections of collagenase via umbilical cord arteries may help to detach retained placenta in women as it does in mares and cows.     

Amphetamine lowers brain stimulation reward (BSR) threshold in alcohol-preferring (P) and non-preferring (NP) rats: Regulation by D? and D? receptors in the nucleus accumbens.

Differences in the mesolimbic dopamine (DA) pathway that regulates alcohol preference may also increase sensitivity to the reinforcing effects of other drugs of abuse. In the present study, the curve-shift (rate-frequency) paradigm was used to quantify the interaction of amphetamine with the rewarding effects of lateral hypothalamic brain stimulation reward (BSR) in alcohol-preferring (P) and -nonpreferring (NP) rats. The role of D? and D? DA receptors of the nucleus accumbens (NAcc) in mediating the reward-potentiating effects of amphetamine was also determined. Animals were tested with randomly administered amphetamine (0.25, 0.75, 1.25 mg/kg ip), DA-receptor antagonists (SCH 23390 [2.0 μg, 5.0 μg]; eticlopride [2.0 μg, 5.0 μg]), or a combination of the 2 (SCH 23390 [2.0 μg, 5.0 μg] + 0.75 mg/kg amphetamine; eticlopride [2.0 μg, 5.0 μg] + 0.75 mg/kg amphetamine). Amphetamine produced comparable dose-related leftward shifts in the rate-frequency function for both P and NP rats, with a greater than 60% reduction observed in BSR threshold. On intervening days, baseline threshold was unaltered between tests and similar between rat lines. Unilateral infusion in the NAcc of either the D? or D? receptor antagonist produced rightward shifts in the rate-frequency function of amphetamine, completely reversing-attenuating its reward-enhancing effects. The results demonstrate that amphetamine produces similar threshold-lowering effects in both P and NP rats and that the reward-potentiating effects of amphetamine do not correlate with alcohol preference under the conditions of the present study. (PsycINFO Database Record (c) 2010 APA, all rights reserved)