Circular dichroism spectra of amino acid complexes. III. Copper(II) compounds

1970 ◽  
Vol 23 (11) ◽  
pp. 2237 ◽  
Author(s):  
CJ Hawkins ◽  
CL Wong

The solution circular dichroism spectra of the 1 : 1 and 1 : 2 copper(II) complexes of a series of �-amino acids are reported for the region 12500-25000 cm-1. These spectra and spectra of the isolated 1 : 2 complexes dispersed in KBr disks have been interpreted as arising from three Cotton effects with a -,+,- sign pattern for the L configuration, except for the L-proline spectra, which were analysed in terms of a +,-,+ pattern. A tentative assignment is made for these Cotton effects, and the relative contributions of vicinal and conformational effects to the rotational strength are discussed.

1970 ◽  
Vol 23 (9) ◽  
pp. 1735 ◽  
Author(s):  
CJ Hawkins ◽  
PJ Lawson

The circular dichroism spectra of a series of optically active (α-aminocarboxylato)tetraamminecobalt(111) complexes have been measured in aqueous solution, and in the presence of salts of polarizable anions. The observed spectra in the visible region have been analysed to determine the signs of the Cotton effects of the three components of the 1A1g ↔ 1T1g cobalt(111) transition. For L-amino acids, the transition with A2g(D4h) parentage is negative, and the two transitions with Eg(D4h) parentage have opposite signs. Published circular dichroism spectra of complexes of the type [Co(en)2(L-am)]2+ were similarly interpreted in terms of a perturbed tetragonal chromophore, and it was shown that the vicinal effect of the L-amino acids imposed the same signs onto the component transitions as for the tetraammines and for a similar series of pentaamminecobalt(111) complexes.


1979 ◽  
Vol 57 (1) ◽  
pp. 62-66 ◽  
Author(s):  
E. A. Sullivan

A number of Pd(II) and Pt(II) complexes of amino acids and dipeptides have been isolated and characterized. The solution and solid-state circular dichroism of the amino acid complexes show a fairly consistent pattern, which is opposite to that shown by the dipeptide complexes. Some of the problems associated with the interpretation of the spectra in terms of spectroscopic assignment and structural features are discussed.


1971 ◽  
Vol 24 (11) ◽  
pp. 2275 ◽  
Author(s):  
CJ Hawkins ◽  
GA Lawrance

The preparations of a series of optically active complexes with the general formula Co(NH3)5(OCOCH(X)CH3)2+ are reported for X = NH3+, OH, F, Cl, Br, C2H5, and C6H5. The circular dichroism spectra of the complexes have been measured in aqueous solution, in the presence of salts of polarizable anions, and in KBr disks. The spectra have been analysed in terms of three Cotton effects under the 1A1g → 1T1g cubic absorption band and found to be consistent with a +, -, - sign pattern for the L- isomer, corresponding to the two components of the 1A1g → 1Eg (D4h) and to the 1A1g → A2g (D4h) transition, respectively.


1978 ◽  
Vol 31 (11) ◽  
pp. 2399 ◽  
Author(s):  
CJ Hawkins ◽  
GA Lawrance ◽  
JA Palmer

The circular dichroism spectra are reported for tetraamminecobalt(III) complexes with the chiral amino alcohols 2-aminopropan-1-ol, 2- aminobutan-1-ol, 1-aminopropan-2-ol, 2-amino-1-phenyl-ethanol, ψ- ephedrine and ephedrine with the alcohol groups protonated (OH) and deprotonated (O-). The solvent dependence of the chemical shifts of the NH protons was investigated to determine the effects of stereoselective solvation on the circular dichroism, but, in contrast to some other related systems, the chemical shift difference between the two NH2 protons was relatively insensitive to solvent. Consistent with this, the circular dichroism spectra of the tetraphenylborate salts of the deprotonated complexes were found not to be markedly dependent on solvent. Tetraammine-{(-)-ψ-ephedrine)cobalt(III) and tetraammine{(-)- ephedrine}cobalt(III) were found to have the same signs of Cotton effects for the various d-d transitions, whereas bis{(-)-ψ- ephedrine}copper(II) and bis{(-)-ephedrine}copper(II) had opposite signs. This has been explained in terms of different conformer populations in the cobalt(III) and copper(II) systems.


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