Cornelis A. G. Haasnoot

The relationship between proton-proton NMR coupling constants and substituent electronegativities—I : An empirical generalization of the karplus equation

A new coupling constant-torsion angle relation for the three-bond 1H-1H spin-spin coupling constant is formulated. The relation includes a correction for the electronegativity of substituents. The correction term is written as a function of the electronegativity, the H-C-C-H torsion angle, and the orientation of each substituent relative to the coupled protons. A dataset consisting of 315 experimental coupling constants was used to derive six empirical parameters by means of an iterative least-squares minimization procedure. The precision of the proposed equation, expressed as the root-mean-square deviation (0.48 Hz), is superior to any hitherto reported. It is shown that separate treatment of CH2CH2, CH2CH and CHCH fragments even improves this precision. An application in the field of monosubstituted cyclohexanes is given.

The Quantitative Separation of Stacking and Self-Association Phenomena in a Dinucleoside Monophosphate by Means of NMR Concentration-Temperature Profiles: 6-N-(Dimethyl)Adenylyl- (3′,5′)-Uridine

The question whether short oligonucleotides are really suitable as models for longer regions in nucleic acids has been raised (1), but will not be answered until many careful systematic studies are carried out with experimental probes at atomic resolution using nuclear magnetic resonance (NMR), supplemented with thermodynamic information from independent techniques such as UV-hypochromism and circular dichroism (CD), and guided by information on geometrical details provided by X-ray methods.

Conformational Aspects of Hairpin Loops in DNA Oligonucleotides

Our studies (2–5) towards the structure, kinetics and thermodynamics of DNA hairpins formed in solution by the homologous, (partly-) selfcomplementary DNA fragments d (ATCCTATnTAGGAT), n=0-7, showed that the inherent stability of DNA hairpins is at its maximum when the loop of the hairpin comprises four or five nucleotides. This finding is at variance with earlier experiments (6) which indicated that in RNA hairpins loop lengths of six to seven residues are the most favourable.

Assignment of the 1H and 13C nuclear magnetic resonance spectra of norethisterone using two-dimensional nuclear magnetic resonance spectroscopy

The information obtained from 2D J-resolved and 2D spin-echo-correlated spectroscopy at 500 MHz allows the complete assignment of the 1H n.m.r. spectrum of norethisterone. In turn, the 1H n.m.r. assignment readily leads to the assignment of the 13C n.m.r. spectrum of this compound by means of a two-dimensional hetero-shift correlation experiment.

Discrimination of the two diastereoisomeric glycosides heterodendrin and epi-heterodendrin by the combined use of NOE and molecular mechanics

Abstract The two glycosides ( S )-heterodendrin and ( R )-epi-heterodendrin were synthesized in a novel, one-step enzymatic synthesis, and separated by means of column chromatography. The 1 H NMR spectra of the two diastereoisomers differ mainly in the chemical shift of H-2′ of the side chain. At first sight the 1 H NMR spectra do not allow a stereospecific assignment. It was found, however, that the NOE between the anomeric proton H-1 and H-2′ of the side chain is considerably larger in epi-heterodendrin than in heterodendrin, which indicates on a time-averaged basis a smaller distance between these two protons in epi-heterodendrin. This difference in conformational behaviour is correctly reproduced by molecular mechanics calculations, thereby offering a method for the discrimination of these two glycosides.