'H NMR spectra at 300 and 400 MHz have been recorded for the thyroid hormones thyroxine (T4) and triiodothyronine (T3) over a range of temperatures from 175 to 298 K in MeOH-d, . Above 200 K the aromatic region of the NMR spectrum of T4 consists of two peaks, one for the H-2',H-6' protons and one for H-2,H-6. As the temperature is lowered each of these resonances first broadens and then splits into two peaks of equal intensity at low temperature. This is consistent with dowed exchange between two equally populated conformers. Similar behaviour is noted for T3, although in this case the spectrum is complicated by the presence of spin-spin splitting. Consideration of coalescence temperatures and a line-shape analysis yielded activation barriers in the range 35-38 kJ mol-'. It is concluded that the observed spectral changes are due to dynamic interconversion between proximal and distal forms of the hormones, and that the interconversion takes place by cooperative rotations around the bonds between each phenyl ring and the linking oxygen atom.
The sterol fraction of the internal lipids of wool has been separated by HPLC into two major components, cholesterol and its precursor, desmosterol (cholesta-5,24-dien- 3β-ol). The total of extractable sterols varied significantly between the six samples examined, representing wool from different breeds of sheep and from different climatic zones. However, the ratio of desmosterol to cholesterol remained relatively constant.
.Proton magnetic resonance spectra of a wide variety of substituted 2-nitro-
and 2,4-dinitro-diphenylamines and related compounds reveal that long-range
coupling occurs between the NH proton and the 5-proton of the nitrophenyl ring in
non-polar or weakly polar solvents. However, in the case of the 2,4-dinitrodiphenyl-
amines, this coupling is absent in highly polar solvents, except when the non-nitrated
ring carries powerful electron-donating substituents, e.g. methoxyl or dimethylamino,
ortho or para (but not meta) to the NH group. An examination of these phenomena
leads to the conclusion that such long-range coupling provides evidence that
intramolecular hydrogen bonding occurs between the NH and the 2-nitro groups.
N-Benzyl-2,4-dinitroaniline also exhibited similar long-range coupling but, in
dimethyl sulphoxide solut'ion, this coupling was temperature-dependent. The
chemical shift data of the ortho-nitrodiphenylamines suggest that they adopt a
non-planar skew conformation in solution.
A six-bond H-F coupling was observed between the fluorine atom and the
6-proton of 2'-fluoro-2,4-dinitrodiphenylamine.
Several fibre–reactive basic (polymethine) dyes containing the N–chloroacetyl group have been prepared. They had better washing fastness on wool than their non–reactive analogues.
Exhaustion figures were obtained in the usual way (colorimetrically) for all the dyes in Table 1 at the following pH: 2. 5, 3. 6, 4. 7, 5. 8, 6. 9 and 8. 4. However, these results were not in accord with visual assessments of the depths and it appears likely that some decomposition of the dyes takes place, in the presence of wool, particularly at higher pH values.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.