Hydroboration with pyridine borane at room temperature

Treatment of pyridine borane (Py.BH3) with iodine, bromine, or strong acids affords activated Py.BH2X complexes that are capable of hydroborating alkenes at room temperature. Evidence is presented for an unusual hydroboration mechanism involving leaving group displacement. In contrast to THF.BH3, hydroboration with Py.BH2I selectively affords the monoadducts. The crude hydroboration products are converted into synthetically useful potassium alkyltrifluoroborate salts upon treatment with methanolic KHF2.     

An effective method for the discrimination of motional anisotropy and chemical exchange

Analysis of the ratio of transverse and longitudinal relaxation rates (R2/R1) is an approach commonly used for estimation of overall correlation time and identification of chemical exchange in biological macromolecules. However, this analysis fails to distinguish between chemical exchange and motional anisotropy. We describe a simple method for identifying chemical exchange and motional anisotropy using the product, R1R2. In the slow tumbling regime, the R1R2 product results in a constant value that is independent of overall correlation time and motional anisotropy. This analysis provides a simple method for rapidly estimating and dissociating the effects of motional anisotropy and chemical exchange in NMR heteronuclear spin relaxation data. We demonstrate the utility of the method with 15N relaxation data collected on the proteins E. coli ribonuclease H and the trimeric E. coli membrane associated lipoprotein lpp.