Field NMR Spectrometers Research Articles

Isolation and identification by 2D NMR of two new complex saponins fromMichrosechium helleri

Two complex saponins, amole F and G, were characterized and their spectra were assigned using only 1D and 2D 1H and NMR methods. Amole F and G have seven and six monosaccharides, respectively, linked to the triterpene aglycone bayogenin. In addition to standard 2D methods, a series of TOCSY spectra with different mixing times and a high-resolution coupled HSQC spectrum were particularly useful for assigning the monosaccharide units. It is concluded that saponins of this complexity are approaching the limit of structural complexity that can be solved by NMR alone, although the limit might be pushed further by access to ultra-high field NMR spectrometers. © 1998 John Wiley & Sons, Ltd.

Study of Nb/sub 3/Sn superconducting joints for very high magnetic field NMR spectrometers

A new, simple method for making Nb/sub 3/Sn-Nb/sub 3/Sn superconducting joints is described in this paper. Joints with resistance 5/spl times/10/sup -13/ /spl Omega/, which is good enough for NMR spectrometers, have been fabricated, using a simple and reproductive procedure. An in situ joint test system and joint test results are presented. >

A New Weak Field Double Resonance NMR Spectrometer

Abstract Weak field NMR and double resonance spectrometers are mostly homemade. In this work, some electronic units of such a spectrometer operating at 1.437 mT were designed and realized by includ­ing new integrated circuits: an audio generator, digital sweep generator, digital additional field and delay unit, Quartz generator, NMR detector(Q-meter), AF-narrowband amplifier, phase shifter and phase sensitive detector.

Structure determination of altemicidin by nmr spectroscopic analysis

Recently various pulse experiments using the high field NMR spectrometer are available to study structures of only truly small amounts of natural products. In the course of our research on the screening of new antibiotics, we isolated altemicidin which showed anti-brine shrimp activity. The relative structure of altemicidin was determined by NMR spectroscopic analysis which included 1H, 13C, 1H- 1H, HMQC and HMBC spectra.

Structure verification of some chlorinated p-cymenes by high field NMR and IR spectroscopies

Seven chlorinated p-cymenes were synthesized by the chlorination of p-cymene and the alkylation of chlorinated toluenes. 2,6-Dichloro-p-cymene was made by the Sandmeyer reaction from 2-amino-6-chloro-p-cymene and 2,3,5-trichloro-p-cymene was synthesized by the chlorination from 3,5-dichloro-p-cymene. The chlorinated compounds were purified by preparative gas chromatography. The coupled 13C NMR spectra of (1) p-cymene, (2) 2-chloro-, (4) 2,3-dichloro-, (8) 2,3,6-trichloro-, and (10) 2,3,5,6-tetrachloro-p-cymenes were recorded by a high field NMR spectrometer and the IR spectra of nine chlorinated p-cymenes were recorded.

Ultrahigh resolution in proton NMR spectra at 500 MHz: two-bond intrinsic chlorine and silicon isotope effects

Heavy-atom isotope effects on NMR /sup 1/H chemical shifts have been reported in a few cases but only for second-row elements. The authors now show that /sup 37/Cl//sup 35/Cl isotope effects on the /sup 1/H chemical shifts in chlorinated methanes are about +0.2 ppb (ca. 0.1 Hz at 500 MHz) and that the /sup 29/Si//sup 28/Si isotope effect on the /sup 1/H chemical shift in tetramethylsilane (TMS) is +0.06 +/- 0.01 ppb. It is likely that previously unreported splittings arising from heavy-atom isotope effects will be observable in the /sup 1/H NMR spectra of other organic compounds, given the excellent resolution of modern high field NMR spectrometers.

Quenching in coupled adiabatic coils

The prediction of the effects of a quench on stress and temperature is an important aspect of the design of superconducting magnets. Of particular interest, and the exclusive topic of this study, is the prediction of the effects of quenching in coupled adiabatic coils, such as the multi-section windings of a high field NMR spectrometer magnet. The predictive methods used here are based on the measurement of the time of propagation of quench between turns. From this measurement an approximate algorithum for the propagation time is used in a code which solves the linear differential equations for the coil currents and calculates the movement of normal zone boundaries and hence the associated winding resistance.

Autocorrelated 13c‐13c double quantum coherence two‐dimensional nmr spectroscopy: Utilization of a modified version of the technique as an adjunct in the total assignment of the 1h‐ and 13c‐nmr spectra of the mutagen phenanthro[3,4‐b]thiophene

AbstractDevelopment of successively higher field nmr spectrometers has facilitated the study of increasingly more complex molecules, although smaller molecules such as phenanthro[3,4‐b]thiophene still offer very substantial assignment problems because of the highly congested nature of their 1H‐ and 13C‐nmr spectra. Assignments of such spectra, if they are to be unequivocal, frequently require the utilization of two‐dimensional nmr spectroscopic techniques. Total assignments of the 1H‐ and 13C‐nmr spectra of phenanthro[3,4‐b]thiophene are reported. Assignments were based on a conventional high resolution 500 MHz 1H‐nmr spectrum, autocorrelated two‐dimensional 1H‐nmr spectra (COSY), two‐dimensional 1H‐13C chemical shift correlation spectra and a modified version of autocorrelated 13C‐13C double quantum coherence two‐dimensional nmr spectroscopy. From NOE measurements, a separation of 1.99 Å between H1 and H11 was computed, suggesting that phenanthro[3,4‐b]thiophene has a pronounced helical conformation in solution.