Selective detection of single-enantiomer spectrum of chiral molecules aligned in the polypeptide liquid crystalline solvent: Transition selective one-dimensional H-1-H-1 COSY

One-dimensional (1D) proton NMR spectra of enantiomers are generally undecipherable in chiral orienting poly-gamma-benzyl-L-glutamate (PBLG)/CDCl3 solvent. This arises due to large number of couplings, in addition to superposition of spectra from both the enantiomers, severely hindering the H-1 detection. On the other hand in the present study the benefit is derived front the presence of several couplings among the entire network of interacting protons. Transition selective 1D H-1-H-1 correlation experiment (1D-COSY) which utilizes the Coupling assisted transfer of magnetization not only for unraveling the overlap but also for the selective detection of enantiopure spectrum is reported. The experiment is simple, easy to implement and provides accurate eanantiomeric excess in addition to the determination of the proton-proton couplings of an enantiomer within a short experimental time (few minutes). (C) 2009 Elsevier Inc. All rights reserved.

Application of z-COSY experiment and its variant for accurate chiral discrimination by H-1 NMR

We report the application of z-COSY experiment and a band selected version of it by employing a selective 90 degrees pulse entitled BASE-z-COSY for precise chiral discrimination, quantification of enantiomeric excess and the analyses of the H-1 NMR spectra of chiral molecules aligned in the chiral liquid crystalline solvent poly-gamma-benzyl-L-glutamate (PBLG). We have demonstrated their applicability for obtaining very high resolution in the H-1 NMR spectra of small organic molecules. It is well known that the commonly employed z-COSY experiment disentangles the spectral complexity, provides pure phase spectra with high resolution, aids in the complete spectral analyses, in addition to yielding information on relative signs of the Couplings. The BASE-z-COSY experiment possesses all these properties, permits the measure of enantiomeric excess, in addition to large saving of instrument time.

Antibodies specific for 1-methylguanosine as a probe of tRNA conformation

Antibodies specific for 1-methylguanosine (m1G) were produced by immunization of rabbits with a bovine serum albumin conjugate of m1G. Antibodies specificity was determined by measuring the inhibition of binding of 3H-m1G trialcohol by various nucleosides or related derivatives. The relative affinities of the unpurified antibodies for various nucleosides showed that m1G trialcohol had an 8-fold higher affinity than m1G; further, guanosine and 2'-O-methylguanosine had at least a 500-fold lower affinity than m1G. The antibodies were purified on m1G-AH-Sepharose column and subsequently immobilized to Sepharose. Immobilized m1G antibodies quantitatively and exclusively retained m1G-containing oligonucleotides derived from ribonuclease A digests of 32P-labeled phage T4 tRNAPro. On the other hand, intact 32P-labeled T4 tRNAPro or its precursor RNA(s) did not bind to the same column. These findings indicate that at least a portion of m1G adjacent to the 3' end of the anticodon in intact T4 tRNAPro is not accessible for antibody binding.