Ruth Records

Optically active amines—V : Comparison of the optical rotatory dispersion and circular dichroism curves of the N-salicylidene derivatives of some open-chain α- and β-arylalkylamines

Abstract The circular dichroism (CD) curves of the N-salicylidene derivatives of some open-chain α- and β-arylalkylamines and of α,β-diphenylethylamine in ethanol, dioxan, and isooctane were measured from 450 to about 240 mμ. In comparison with similar optical rotatory dispersion (ORD) measurements reported earlier, reliable observations to shorter wavelengths with greater resolution of the individual Cotton effects were possible. Cotton effects near 315 and 255 mμ are assigned to π-π* transitions of the intramolecularly hydrogen-bonded salicylidenimino moiety, and for the α-arylalkylamine derivatives, an additional Cotton effect near 280 mμ is assigned to the π-π* transition of the aromatic ring of the parent amines. The present measurements are in agreement with the conclusion drawn earlier that there is present in these derivatives an inherently dissymmetric chromophore, arising from the interaction of the π-electrons of the aryl group and the salicylidenimino moiety. However, only some of the changes in the CD curves which occur with changes in temperature could be interpreted with the simple conformational model used earlier to indicate the steric requirements for a rotationally significant interaction of the aryl and the salicylidenimino groups.

Partial reduction of aquomethemoglobin on a sephadex G-25 column as detected by magnetic circular dichroism spectroscopy and revised extinction coefficients for aquomethemoglobin

In a typical preparation of aquomethemoglobin, oxyhemoglobin is oxidized with potassium ferricyanide, and the resultant mixture of methemoglobin and potassium ferro- and ferricyanides is separated on a Sephadex G-25 column. We find that about 1% of the heme is reduced on the column and is eluted with the methemoglobin. Magnetic circular dichroism spectra show that the reduced species is oxyhemoglobin. Magnetic circular dichroism is more sensitive than is absorption spectroscopy to small amounts of oxyhemoglobin in such solutions; we can detect its presence at the 0.1% level. A redetermination of the extinction coefficients for methemoglobin gives a value of 0.80 for the absorbance ratio A570A630 at pH 6. This value lies clearly outside the currently accepted range of 0.83 to 0.87.

Magnetic circular dichroism spectroscopy: Convenient quantitative determination of uroporphyrin and coproporphyrin in urine samples

Abstract Magnetic circular dichroism provides a convenient, sensitive, and accurate method to determine the concentration of uroporphyrin (I) and coproporphyrin (II) in urine specimens. The acidified sample is measured directly, and the recorded spectrum is analyzed by a least-squares fitting procedure using the spectra of the pure components as fitting functions. The lowest detection limit is 10 μg/liter of total porphyrins, the accuracy is about 5%, and the minimum sample volume required is 1 ml. The possibility of determining small amounts of myoglobin in serum was also investigated. Conversion to the hemochrome results in the occurrence of a very intense MCD band at 555 nm, thus permitting the detection of myoglobin levels as low as 0.1–0.2 μg/ml.

Magnetic circular dichroism analysis of the ihp effect on spin equilibria in human ferric hemoglobins

Magnetic circular dichroism (MCD) spectroscopy has been to explore the connection between optical spectra and the high spin population of several hemoglobins under various conditions. It is found that the effectiveness of IHP in inducing spectral changes can be markedly affected by solvent. For example, the IHP-induced spectral changes in the visible region for nitritomethemoglobin-A in mixed buffer solvent systems (glycerol or polyethylene glycol (PEG), mw 190-210) are more than double those observed in aqueous buffers. We estimate that IHP induces a mix of R/T forms in bis-tris phosphate buffers, for NO-2metHb that is only about 50%. While PEG and glycerol both lead to enhanced IHP-induced spectral differences, they behave differently in two aspects. PEG shifts the visible MCD and absorption spectra of F-metHb-A, supposedly already biased towards the T form by ligand, in the same direction that IHP does. PEG also maximizes the spin state changes with IHP for three R from hemoglobins and N-3metHb-A, and so appears to stabilize the T form in all cases. Glycerol does not. In addition, the apparent binding constant for NO-2 to H2OmetHb-A differs between these two solvents. Comparison of the data from several hemoglobins leads to the conclusion that the changes in spin state distributions induced by IHP correlate well with quaternary structure for a given hemoglobin. An analogous correlation amongst various proteins between initial spin state distribution (IHP) absent) and quaternary structure is not found.