Direct mass measurements of short-lived A=2Z-1 nuclides (63)Ge, (65)As, (67)Se, and (71)Kr and their impact on nucleosynthesis in the rp process.

Mass excesses of short-lived A=2Z-1 nuclei (63)Ge, (65)As, (67)Se, and (71)Kr have been directly measured to be -46,921(37), -46,937(85), -46,580(67), and -46,320(141) keV, respectively. The deduced proton separation energy of -90(85) keV for (65)As shows that this nucleus is only slightly proton unbound. X-ray burst model calculations with the new mass excess of (65)As suggest that the majority of the reaction flow passes through (64)Ge via proton capture, indicating that (64)Ge is not a significant rp-process waiting point.

Unique selectivity of perfluorinated stationary phases with 2,2,2-trifluoroethanol as organic mobile phase modifier.

The selectivity of Luna C18 Xterra C18 and Fluophase (perfluorinated C6) stationary phases has been investigated with aqueous acetonitrile, methanol and 2,2,2-trifluoroethanol mobile phases using linear solvation equations. The gradient retention times of a set of 60 compounds with known molecular descriptors have been determined. Linear solvation equations have been set up to describe the relationship between the gradient retention times and the molecular properties. The selectivity of the stationary phase/mobile phase systems was characterised by the regression coefficients of the molecular descriptors. The perfluorinated stationary phase showed very different selectivity using 2,2,2-trifluoroethanol (TFE) as co-solvent. Compounds with H-bond donor functionality were retained much less than in the other investigated high-performance liquid chromatography (HPLC) systems. This unique selectivity can be explained by the stronger adsorption of trifluoroethanol on the perfluorinated stationary phase surface, than on the hydrocarbon surface. It suggests the importance of the adsorbed organic modifiers in the separation mechanism during reversed-phase HPLC.

Rapid-gradient HPLC method for measuring drug interactions with immobilized artificial membrane: comparison with other lipophilicity measures.

A fast-gradient high-performance liquid chromatographic (HPLC) method has been suggested to characterize the interactions of drugs with an immobilized artificial membrane (IAM). With a set of standards, the gradient retention times can be converted to Chromatographic Hydrophobicity Index values referring to IAM chromatography (CHI(IAM)) that approximates an acetonitrile concentration with which the equal distribution of compound can be achieved between the mobile phase and IAM. The CHI(IAM) values are more suitable for interlaboratory comparison and for high throughput screening of new molecular entities than the log k(IAM) values (isocratic retention factor on IAM). The fast-gradient method has been validated against the isocratic log k(IAM) values using the linear free energy relationship solvation equations based on the data from 48 compounds. The compound set was selected to provide a wide range and the least cross-correlation between the molecular descriptors in the solvation equation: (2) where SP is a solute property (e.g., logarithm of partition coefficients, reversed-phase (RP)-HPLC retention parameters, such as log k, log k(w), etc.) and the explanatory variables are solute descriptors as follows: R(2) is an excess molar refraction that can be obtained from the measured refractive index of a compound, pi(2)(H) is the solute dipolarity/polarizability, summation operatoralpha(2)(H) and summation operatorbeta(2)(0) are the solute overall or effective hydrogen-bond acidity and basicity, respectively, and V(x) is the McGowan characteristic volume (in cm(3)/100 mol) that can be calculated for any solute simply from molecular structure using a table of atomic constants. It was found that the relative constants of the solvation equation were very similar for the CHI(IAM) and for the log k(IAM). The IAM lipophilicity scale was quite similar to the octanol/water lipophilicity scale for neutral compounds. The effect of charge on the interaction with IAM was studied by varying the mobile phase pH.

Characterizing the selectivity of stationary phases and organic modifiers in reversed-phase high-performance liquid chromatographic systems by a general solvation equation using gradient elution.

Retention data for a set of 69 compounds using rapid gradient elution are obtained on a wide range of reversed-phase stationary phases and organic modifiers. The chromatographic stationary phases studied are Inertsil (IN)-ODS, pentafluorophenyl, fluoro-octyl, n-propylcyano, Polymer (PLRP-S 100), and hexylphenyl. The organic solvent modifiers are 2,2,2-trifluoroethanol (TFE); 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP); isopropanol; methanol (MeOH); acetonitrile (AcN); tetrahydrofuran; 1,4-dioxane; N,N-dimethylformamide; and mixed solvents of dimethylsulfoxide (DMSO) with AcN and DMSO with MeOH (1:1). A total of 25 chromatographic systems are analyzed using a solvation equation. In general, most of the systems give reasonable statistics. The selectivity of the reversed phase-high-performance liquid chromatographic (HPLC) systems with respect to the solute's dipolarity-polarity, hydrogen-bond acidity, and basicity are reflected in correspondingly large coefficients in the solvation equation. We wanted to find the most orthogonal HPLC systems, showing the highest possible selectivity difference in order to derive molecular descriptors using the gradient retention times of a compound. We selected eight chromatographic systems that have a large range of coefficients of interest (s, a, and b) similar to those found in water-solvent partitions used previously to derive molecular descriptors. The systems selected are IN-ODS phases with AcN, MeOH, TFE, and HFIP as mobile phase, PLRP-S 100 phase with AcN, propylcyano phase with AcN and MeOH, and fluorooctyl phase with TFE. Using the retention data obtained for a compound in the selected chromatographic systems, we can estimate the molecular descriptors with the faster and simpler gradient elution method.

Effects of intravenous L-dopa on P300 and regional cerebral blood flow in parkinsonism.

The P300 and regional cerebral blood flow were measured before and after intravenous injection of L-dopa in 10 patients with idiopathic Parkinson's disease and 10 patients with vascular parkinsonism. The P300 was measured with an evoked potential recorder using an oddball paradigm and the regional cerebral blood flow was measured using the stable xenon computed tomography method. The P300 latency was significantly longer and the regional cerebral blood flow in the cerebral cortex and basal ganglia was significantly lower in the Parkinson's disease group and the vascular parkinsonism group than in the age-matched healthy control group. The intravenous injection of L-dopa improved these abnormalities significantly in the Parkinson's disease group but did not improve these abnormalities in the vascular parkinsonism group. Cognitive function is considered to be impaired in Parkinson's disease and vascular parkinsonism and L-dopa is considered to improve it in Parkinson's disease.

Selective vapor sorption by polymers and cavitands on acoustic wave sensors: is this molecular recognition?

Selectivity patterns for the sorption of organic vapors from the gas phase into cavitand monolayers on acoustic wave sensors are very similar to those seen for sorption of the same vapors by amorphous polymers, demonstrating that the vapor/cavitand selectivity patterns are determined primarily by solubility interactions. The amorphous polymers serve as controls demonstrating that the three-dimensional structure of a cavitand layer is not primarily responsible for the selectivity observed. Binding and selectivity in the examples cited are governed primarily by general dispersion interactions and not by specific oriented interactions that could lead to molecular recognition.

Magnetic stimulation of peripheral nerves. Comparison of magnetic stimulation with electrical stimulation.

We measured total peripheral motor conduction time by two different methods, magnetic stimulation and electrical stimulation, to reveal which is better in determining actual peripheral motor conduction time. In the upper extremities, the difference between magnetic stimulation and electrical stimulation was within a mean time of 1.39 +/- 0.8 msec, while that in the lower extremities was 2.3 +/- 1.1 msec. In any 4 extremities, total peripheral motor conduction time obtained by magnetic stimulation was significantly shorter than that measured by electrical stimulation employing conventional F-wave response. We conclude that stimulus sites 8.8 +/- 5.1 cm distal to spinal motoneurons in the upper extremities, and 10.5 +/- 5.3 cm distal in the lower extremities were stimulated by magnetic stimulation of the peripheral nerves. Electrical stimulation employing conventional F-wave measurement is superior to magnetic stimulation for actual total peripheral nerve conduction study.