The stereochemistry of the hydroboration rearrangement.

Hydroboration of 1,2-dimethylcyclopentene with BH₃·THF affords a product in which boron migrates $\text{stereospecifically}$ at low temperature into the cyclopentane ring. At higher temperatures subsequent (non-stereospecific) isomerisation occurs via a competing reaction mechanism.     

A Markov model for relaxation and exchange in NMR spectroscopy

A two-state Markov noise process for lattice fluctuations and chemical exchange dynamics is used to derive a stochastic Liouville equation describing the evolution of the spin-density operator in nuclear magnetic resonance spectroscopy. Relaxation through lattice fluctuations and chemical exchange processes is incorporated into the theory at the same fundamental level, and the results are valid for all time scales provided that lattice fluctuations are much faster than chemical exchange kinetics. Time-scale separation emerges as an essential feature from the lowest-order perturbation expansion of the average resolvent in the Laplace domain.     

Investigation of the ceriumIV oxidation of poly(vinyl alcohol)

Initiation of ceric ion-induced grafting from poly(vinyl alcohol) (PVOH) was studied by examining the formation and lifetime of colored complexes between cerium^IV and (1) a commercial PVOH, (2) a diol-free PVOH, and (3) several model 1,2-diols. UV/visible spectroscopy was employed using a wavelength of 520 nm. Results showed that the 1,2-diols, which are an inherent defect in PVOH, are the sites most reactive toward ceric ion. The observed rate constant for the reaction was found to increase with decreasing [Ce^IV] until the maximum rate was reached at which time reaction took place exclusively with 1,2-diols. The activation energy for oxidation of commercial PVOH at the maximum rate was 15.4 kcal/mol while that for diol-free PVOH was 22.4 kcal/mol. The 1,2-diols of PVOH displayed a high equilibrium constant for complexation with ceric ion, compared to the model 2,3-butanediol. It was suggested that the PVOH chain segments bring about crowding of the diol group, and this leads to a higher equilibrium constant for complexation. The lowest energy conformation of a PVOH chain segment containing a 1,2-diol linkage was calculated using the CHEMLAB-II molecular design program, and the 1,2-diol was predicted to be at the center of a sharp bend in the chain brought about by its presence.     

Using a non-invasive stable isotope tracer to measure the absorption of water in humans

The development of solutions that prevent dehydration or promote adequate re-hydration play a vital role in preventing fatigue during exercise, however, the methods commonly used to assess the hydration ability of such solutions are invasive and often assess the components of absorption separately. This paper describes using a non-invasive deuterium tracer technique that assesses gastric emptying and intestinal absorption simultaneously to evaluate the uptake of water during rest and exercise. The kinetics of absorption are further examined by mathematical modelling of the data generated. For the rest group, 0.05 g/kg of body weight of deuterium, contained in gelatine capsules, was ingested with ordinary tap water and saliva samples were collected every 5 min for one hour while the subject remained seated. The deuterium was administered as above for the exercise group but sample collection was during one hour of exercise on a treadmill at 55% of the subject's maximum heart rate. The enrichment data for each subject were mathematically modelled and the parameters obtained were compared across groups using an independent samples t-test. Compared with the rest condition, the exercise group showed delayed absorption of water as indicated by significant differences for the modelling parameters t2, t1/2, maximum absorption rate and solution absorption amount at t1. Labelling with a deuterium tracer is a good measure of the relative rate ingested fluids are absorbed by the body. Mathematical modelling of the data generates rates of maximum absorption and allows calculation of the percentage of the solution that is absorbed at any given time during the testing period.     

Novel alkyl-modified anionic siloxanes as pseudostationary phases for electrokinetic chromatography. III. Performance in organic-modified buffers

Anionic water-soluble siloxanes modified with different amounts of alkyl chains have been used as pseudostationary phases in electrokinetic chromatography. Ionic siloxane polymers with attached alkyl chains of C8 and C12 and having different alkyl chain densities have been employed previously to achieve selective and efficient separations with a range of electrophoretic mobilities and methylene selectivities. In this study, the performance of three alkyl-modified siloxanes is examined in different organic-modified buffers and at differing amounts of organic modifier. The organic modifiers used are acetonitrile and methanol. The siloxanes are stable in these organic solvents and show good mobility and good methylene selectivities even at high concentration of organic solvent. Siloxanes have also been used to separate a mixture of 14 polynuclear aromatic hydrocarbons in an acetonitrile-modified buffer.