Copper Cotton effect

Cotton Effect in Copper-Proline Complexes in the Visible Region 169... 

The absorption and rotatory dispersion of the complexes of ovotransferrin and serum transferrin with Mn3+ and Cu2+ were compared to those of the ferric complexes (Fig. 5 and Fig. 9). The Mn3+ complexes absorbed maximally at 429 mp and gave rise to positive Cotton effects closely similar in both transferrins. The Cu2+ complexes absorbed maximally at 436 mp but this absorption, in contrast to those of the Fe3+ and Mn 3+ complexes, was not optically active. It was concluded that copper does... 

Comparisons of the iron and copper complexes of the transferrins (128, 129) showed that the iron transferrin had a negative Cotton effect at the absorption maximum of the iron complex while the copper complex showed no such relationship. They concluded that the copper did not form an asymmetric center in the metal complexes, whereas the iron did form an asymmetric center. 

Copper salts, effect on conformation of sugars, 37 Cotton effect, 127... 

XAES) shows that CuLj chelates (LH = glutamine or asparagine) have distorted octahedral structures. The oxidative decarboxylation product of Gly-Gly-L-His and Cu(OH)2 is four-co-ordinate and square planar decarboxylation occurs at C-5 with deprotonation at C-4 to give a C==C system. Amine adducts of bis(ben-zoyl-/5-alaninato)copper(ii) have been isolated and characterized. Equilibrium constants have been reported for copper(ii) complexes of histidylhistidine from pH-titration data. " Qualitative analysis of the Cotton effect of d-d transitions of copper(ii) complexes with optically active acids has been obtained. ... 

Visible and near-ultraviolet CD spectra were recorded for this blue plant protein, which was shown by EPR to contain two bivalent copper atoms in equivalent sites. The Cotton effects observed indicated asymmetry of the copper chromophoric site (108). 

The positive CD Cotton effect at 260 nm and the negative Cotton effect at 274 nm may be at least partly attributed to amino-acid residues. The side-chain residues of L-cystine, L-phenylalanine. L-tyrosine or L-tryptophan cause Cotton effects at 250—310 nm (101). However, copper complexes of simple amino acids show CD extremes at 245— 290 nm. Therefore, some contribution to the 260 nm band of erythro-... 

Earlier structural studies of carbohydrates by CD involved introduction of suitable chromophores into the sugar molecule thereby affording derivatives which exibit Cotton effects. These include, among others, xanthates (4-8) or azides (9). Later it was found that some metal ions (10), i.e. copper (11,13), vanadate (14), chromium (15), molybdate (16-22), nickel (23) or cobalt (24,25) ions form complexes with carbohydrates, which show appreciable Cotton effects. 

Yasui et al. (1965 Yasui, 1965) studied the CD spectra of copper-amino acid complexes in more detail and showed that copper complexes with l-amino acids in water exhibit four Cotton effects in the region of the d-d absorption band positive at 830 and 730 nm and negative at 635 and 565 nm. The CD curves of the complexes of proline, hydroxyproline, and histidine are considerably different from those of other amino acid complexes for which the main CD band at ca. 630 nm shows the opposite positive Cotton effect. It was suggested that the vicinal effect of the asymmetric a-carbon atom is stronger than that of the asymmetric j -carbon atom (L-threonine and L-allothreonine) and thus determines the sign of the Cotton effects. 

Cotton constructed an apparatus to measure optical rotations and CD over a range of wavelengths. He established Cotton effects for potassium chromium tartrate and potassium copper tartrate solutions. These were the first ORD and CD studies of coordination compounds, but the complexes were not isolated. For a long period there was little activity in ORD or CD studies of complexes. Kuhn (13) was interested in metal complexes in connection with his ideas about the theory of optical activity (14), J. P. Mathieu (15,16) presented combined studies of ORD, CD, and absorption spectra of many complexes of Co, Cr, Pt, Rh, and Ir during the 1930s. After his work there was no activity in CD studies of complexes for many years. 

Tendering Effects. CeUulosic materials dyed with sulfur black have been known to suffer degradation by acid tendering when stored under moist warm conditions. This effect may result from the Hberation of small quantities of sulfuric acid which occurs when some of the polysulfide links of the sulfur dye are mptured. A buffer, such as sodium acetate, or a dilute alkaH in the final rinse, especially after oxidation in acidic conditions, may prevent this occurrence. Copper salts should never be used with sulfur black dyes because they cataly2e sulfuric acid generation. Few instances of tendering with sulfur dyes other than black occur and the problem is largely confined to cotton. 

The use of bisethylenediamine copper (II) hydroxide solutions to effect solution of cotton has been practiced for many years and is still industrially practiced on a small scale as a method of regeneration of cotton. Copper-amine solutions were utilized for this study for a number of reasons including a. as noted above, an abundance of prior knowledge exists concerning the technique b. it allows fairly good solution of the cotton c. it was found, early in our work, to allow the execution of the types of modification desired and d. it is easily handled and can be utilized on the gram as well as ton scale. Further purity of modified material, i.e. effectiveness of removal of unreacted, etc. material is easily followed through analysis of the copper present in the modified material. 

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