@article {456, title = {N-14 Squid Nqr of L-Ala-L-His and of Serine}, journal = {Zeitschrift Fur Naturforschung Section a-a Journal of Physical Sciences}, volume = {49}, year = {1994}, note = {Z Naturforsch AQh740Times Cited:2Cited References Count:15}, month = {Dec}, pages = {1188-1192}, abstract = {N-14 nuclear quadrupole resonance spectroscopy, detected with a Superconducting Quantum Interference Device, makes possible the study of nitrogen environments in amino acids and small peptides. The present experiments characterize: 1) the effects of intermolecular interactions upon the amino nitrogen of serine upon cocrystallization of the stereoisomers in a range of concentrations; 2) the changes of the amino and imidazole nitrogen environments brought about by combining L-Alanine and L-Histidine into the dipeptide L-Ala-L-His.}, keywords = {n-14}, isbn = {0932-0784}, url = {://WOS:A1994QH74000013}, author = {Wernerzwanziger, U. and Ziegeweid, M. and Black, B. and Pines, A.} } @article {455, title = {SQUID-NQR of N-14}, journal = {NQI Newsletter}, volume = {3}, year = {1994}, pages = {24-25}, author = {Ziegeweid, M. and Werner, U. and Black, B. and Pines, A.} } @article {483, title = {Squid-Nmr Study of Methyl Quantum Tunneling in a Series of Carboxylic-Acids}, journal = {Chemical Physics Letters}, volume = {201}, year = {1993}, note = {Chem Phys LettKf754Times Cited:12Cited References Count:23}, month = {Jan 8}, pages = {550-554}, abstract = {

Quantum tunneling frequencies of methyl groups at low temperature can be measured directly by low-field nuclear magnetic resonance (NMR) using our dc-SQUID (superconducting quantum interference device) spectrometer. From NMR spectra recorded in magnetic fields below 20 mT, tunneling frequencies between 140 and 250 kHz were measured for a homologous series of carboxylic acids at 4.2 K. For solids with equivalent crystal structures, we observe an exponential correlation between the tunneling frequency and the enthalpy of fusion; from this correlation we obtain information about the contribution of intermolecular interactions to the energy barrier for methyl rotation.

}, keywords = {nuclear}, isbn = {0009-2614}, doi = {Doi 10.1016/0009-2614(93)85115-5}, url = {://WOS:A1993KF75400026}, author = {Black, B. and Majer, G. and Pines, A.} } @article {471, title = {Squid-Nqr of N-14 in Amino-Acids and Small Peptides}, journal = {Chemical Physics Letters}, volume = {209}, year = {1993}, note = {Chem Phys LettLh246Times Cited:7Cited References Count:13}, month = {Jun 25}, pages = {17-21}, abstract = {

We present a technique for the study of nuclear quadrupole resonance of N-14 interacting with low electric field gradients as found, for example, in amino acids. A superconducting quantum interference device (SQUID) is used to detect directly small NMR signals via cross relaxation of the N-14 polarization to adjacent proton spins, eliminating the need for field cycling. When one nitrogen quadrupolar transition matches the proton Zeeman splitting, the remaining two quadrupolar transitions can be observed by sweeping a saturating rf field through resonance. In addition, signal enhancement by simultaneous excitation of two nitro n resonances helps to identify connected transitions.

}, keywords = {resonance}, isbn = {0009-2614}, doi = {Doi 10.1016/0009-2614(93)87194-8}, url = {://WOS:A1993LH24600003}, author = {Werner, U. and Black, B. and Ziegeweid, M. and Pines, A.} }