Biological coupling constants

The conformation of nonsulfated L-idosyluronic acid residues is a controversial issue, especially on account of a possible role of the 2-O-sulfo substituent in determining the relative orientation of biologically relevant groups. However, the interproton coupling-constants observed for (nonsulfated) methyl a-D-idopyranosiduronic acid131 and dermatan sulfate350 are essentially the same as those of the sulfated L-iduronate resi-... 

The spin-spin coupling constants [2-4] of the enkephalins in solution can be interpreted in terms of folded conformations resembling that of morphine in the placement of the residues which appear important for biological activity. X-ray crystallography and theoretical calculations (4-9) have also shown that methionine and leucine enkephalin adopt conformations similar to those concluded from NMR studies. Hence it would appear that opioid peptides can topographically resemble the opiates by assuming preferred, folded, conformations. However, earlier studies from this laboratory (TO) have shown that NMR data can be interpreted in terms of a conformationally flexible structure for methionine enkephalin. 

Q and 3Q correlations can be utilized in combination with highest efficiency. In some cases more than one spectrum of each is worthwhile to acquire because cross peak intensity is an explicit function of all coupling constants involved [6, 27, 28]. Coherences of higher order than 3Q exhibit significantly reduced sensitivity. Also, few spin systems in biologically relevant molecules allow sufficient communication between multiple spins to allow observation of higher order spin systems. 

Fluorine is a very important atom both for the biological applications of fluorinated heterocycles [175, 176] and for 19F chemical shifts and the large coupling constants with 19F [177], We have already discussed the case of fluoroindazoles, 44-46) [51] and we have published a paper reporting MP2/6-311G calculations of all C-fluoropyrazoles 191-197. The order of stability of monofluoropyrazoles is 3-F (191)... 

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