Hydrogen bonding Part 20. Infrared study of the high temperature β-form of choline chloride

Infrared spectral studies of β-choline chloride at 95°C clearly demonstrate the presence of O---H … Cl hydrogen bonding. This observation contradicts an earlier conclusion, based on X-ray structural studies, that such hydrogen bonding could not occur in this high-temperature form of choline chloride. A moderate reinterpretation of the X-ray data may reconcile these contradictory conclusions. Unlike -choline chloride, β-choline chloride does not show C---H … Cl hydrogen bonding. It is possible that loss of C---H … Cl hydrogen bonding is a factor in the marked difference in radiation sensitivity of the - and β-forms.     

Laser-induced breakdown spectroscopy analysis of minerals: Carbonates and silicates

Laser-induced breakdown spectroscopy (LIBS) provides an alternative chemical analytical technique that obviates the issues of sample preparation and sample destruction common to most laboratory-based analytical methods. This contribution explores the capability of LIBS analysis to identify carbonate and silicate minerals rapidly and accurately. Fifty-two mineral samples (18 carbonates, 9 pyroxenes and pyroxenoids, 6 amphiboles, 8 phyllosilicates, and 11 feldspars) were analyzed by LIBS. Two composite broadband spectra (averages of 10 shots each) were calculated for each sample to produce two databases each containing the composite LIBS spectra for the same 52 mineral samples. By using correlation coefficients resulting from the regression of the intensities of pairs of LIBS spectra, all 52 minerals were correctly identified in the database. If the LIBS spectra of each sample were compared to a database containing the other 51 minerals, 65% were identified as a mineral of similar composition from the same mineral family. The remaining minerals were misidentified for two reasons: 1) the mineral had high concentrations of an element not present in the database; and 2) the mineral was identified as a mineral with similar elemental composition from a different family. For instance, the Ca–Mg carbonate dolomite was misidentified as the Ca–Mg silicate diopside. This pilot study suggests that LIBS has promise in mineral identification and in situ analysis of minerals that record geological processes.     

Insulin binding and glucose transport in the R3230AC mammary adenocarcinoma.

Cells dissociated from the R3230AC mammary adenocarcinoma from intact and diabetic rats were examined for insulin binding and glucose transport. The Kd for insulin binding, approximately 10(--10) M, was similar in all tumors studied. However, the apparent number of receptor sites per cell increased in cells from diabetic rats. Kinetic analysis of 3-0-methyl glucose (3-OMG) entry showed both diffusional and passive carrier characteristics. Insulin (4 X 10(--9) M) in vitro did not affect diffusional entry, whereas the hormone altered the passive carrier system, as reflected by an increase in Km and Vmax. Insulin decreased initial velocity of glucose transport at 4--6 mM glucose levels but increased initial velocity of glucose transport at 20 mM glucose. An explanation of the role of insulin on tumor growth in vivo from effects on glucose transport in vitro is proposed.     

Methanol transport in PMMA: The effect of mechanical deformation

The effect of cold work on the transport of liquid methanol in crosslinked PMMA disks has been determined at temperatures from 35–56°C. Deformed samples absorb at fast rates with kinetics that approach those of Fickian diffusion. Undeformed samples sorb at lower rates and the kinetics tend toward those of Case II transport. Shape recovery accompanied swelling in deformed samples. Samples saturated with methanol were desorbed in cyclohexanol. Resorption of desorbed samples showed fast rates for both deformed and undeformed samples and matched those of the absorption cycle in deformed samples. An analogy is made between the microstructure due to cold work and due to swelling.     

Enhancement of phosphoprotein analysis using a fluorescent affinity tag and mass spectrometry

A fluorescent affinity tag (FAT) was synthesized and was utilized to selectively modify phosphorylated serine and threonine residues via beta-elimination and Michael addition chemistries in a 'one-step' reaction. This labeling technique was used for covalent modification of both phosphoproteins and phosphopeptides, allowing identification of these molecular species by fluorescence imaging after solution- or gel-based separation methods. In addition to the strong fluorescence of the rhodamine tag, a commercially available antibody can be used to enrich low-abundance post-labeled phosphopeptides present in complex mixtures. Application of this methodology to phosphorylation-site mapping has been evaluated for a phosphoprotein standard, bovine beta-casein. Initial results demonstrated low femtomole detection limits after fluorescence image analysis of FAT-labeled proteins or peptides.     

Induced radioactivity of LDEF materials and structural components

We present an overview of the Long Duration Exposure Facility (LDEF) induced activation measurements. The LDEF, which was gravity-gradient stabilized, was exposed to the low Earth orbit (LEO) radiation environment over a 5.8 year period. Retrieved activation samples and structural components from the spacecraft were analyzed with low and ultra-low background HPGe gamma spectrometry at several national facilities. This allowed a very sensitive measurement of long-lived radionuclides produced by proton- and neutron-induced reactions in the time-dependent, non-isotropic LEO environment. A summary of major findings from this study is given that consists of directionally dependent activation, depth profiles, thermal neutron activation, and surface beryllium-7 deposition from the upper atmosphere. We also describe a database of these measurements that has been prepared for use in testing radiation environmental models and spacecraft design.