th  - 1988 - 51st ENC Conference

-- 150 I ISOTOPE DETECTED NOE EXPERIMENTS ON 13C LABELED tRNAPhe: William
H. Gmeiner*and C. Dale Poulter, Department of Chemistry, University
of Utah, Salt Lake City, UT 84112
Isotope directed and isotope detected nuclear Overhauser effect experiments are
performed on tRNA^ ne from E. coli in which all the adenine residues were labeled at
position 8 with ±jC. The experiments are used to establish the presence of the
unusual Hoogsteen type base-pair in the solution structure of the molecule. A
relaxation p~file of the lab~edlsite is presented in which the effect of two
quadrupolar --N spins on the -C- H spin system is analyzed. The rel~ation effect
on the imino proton of uridine in adenosine-uridine base-pairs by the--C label is
used to measure the relative populations of Watson-Crick and Hoogsteen base-pairs in
a chloroform soluble model system.
- - isi
I
Inversion Recovery Cross Polarization (IRCP) techniques are used to probe the
structures of morphologlcally different polyethylenes. Crystalline and amorphous
components were resolved by their different cross polarization (CP) rates which were
discriminated by an IRCP pulse sequence. At least two major magnetically distinct
environments were detected in each sample. The arystalllne-amorphous interfaclal
domains were also detected in some samples. The cross polarization time, TCH, of
each phase was compared among these morphologically different samples and can be
interpreted in terms of structural details.
The effect on TCH by varying magic angle spinning speed and spln-lock power
were also studied. The chemical shift anlsotropy (CSA) of each component and the
degree of crystalllnlty of these semicrystalllne polymers were also discussed in the
study.
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