Effects amino acid complexes

Another hypothesis was provided by Mikio Shimitso (1982) on the basis of studies of steric effects in molecular models. It had been noted years previously that the fourth nucleotide at the 3 end of the tRNA molecules (referred to as the discrimination base) might have a recognition function. In the case of certain amino acids (i.e., their tRNA-amino acid complexes) this base pair, in combination with the anticodon of the tRNA molecule, can select the amino acid corresponding to the tRNA species in question this is done on the basis of the stereochemical properties of the molecule. Since the anticodon of a tRNA molecule and the fourth nucleotide of the acceptor stem are far apart in space, two tRNA molecules must complex in a head-to-tail manner. The pocket thus formed can then fit specifically to the corresponding amino acid. 

Many of the results reported are of a dubious nature. For example, Perkins (219, 222) assumed that complexes of the type ML2 were formed and quoted log /32 values between 9.8 and 14.2. Not only was the possible formation of a simple complex of the type ML excluded (not to mention any other complexes), but the effects of hydrolysis (which, to be fair, were poorly understood at the time) were completely ignored. The high stability of amino acid complexes was put in doubt in successive publications (220, 229, 232, 233). It has even been suggested, on the basis of Raman spectra, that the amino group does not coordinate to the beryllium atom (232). Unfortunately the opposite conclusion was reached on the basis of IR measurements, namely that only the amino group was coordinated (234). 

Emetine and dehydroemetine are natural alkaloid obtained from Cephaelis ipecacuanha and synthetic analog respectively. They are effective against tissue trophozoites of . histolytica. It has no effect on cysts but effective in amoebic liver abscess also. It acts by inhibiting protein synthesis by arresting intraribosome translocation of tRNA-amino acid complex. Dehydroemetine is less toxic than emetine and very effective drug for tissue amoebiasis. It is more rapidly eliminated from the body than emetine. 

The complexes of amino acids with copper are formed according to the general reaction shown in Equation 7.14 [47]. The formation constants for the copper-amino acid complexes are generally greater than that for copper ammonia complex [48]. Therefore, it is anticipated that amino acids should be more effective than ammonia in assisting the dissolution of oxidized copper during CMP. 

Amino-acid Complexes. A small, but reproducible, stereoselective effect has been observed in both the free energy and enthalpy changes associated with formation of [Ni(L,L-methioninate)2]. The meso-complex [Ni(o-Met)(L-Met)] is more stable in AH than the optically active NiL2 by 1.0 (0.1) kJ mol" L The stereoselectivity is attributed to terdentate co-ordination and so supports weak co-ordination of the thioether group. Formation constants of nickel(ii) and copper(ii) with N -benzyl-L-histidine and N N -dibenzyl-L-histidine and of the ternary complexes with d- and L-histidine have been measured. Stabilization of ternary complexes is small but significant stereoselectivity is found with ternary nickel complexes, when the meso configuration is preferred in each case with copper, stereoselectivity is small or absent. The i.r. spectra of tra s-[Ni(Gly)2(H20)2] and its 0-, N-, 1- C-, and 2- C-labelled... 

Additivity of Circular Dichroism of d—d Transitions The Vicinal Effect in a Homologous Series of Triethylenetetraaminecobalt(IH) Amino Acid Complexes... 

The compounds studied are the substituted triethylenetetra-aminecobalt(III) amino acid complexes depicted in Figure 1. Formally the A Bj chromophore will be the triethylenetetraamine-cobalt(III) glycinato moiety (compounds 1 and 7, identified in Figure 1) (with an associated configurational effect) and the optically active (Bj) chromophores will be represented by the various R2 substituents at the a-carbon of the chelated glycine... 

Although additivity in a tetraaminecobalt(III) amino acid complexes has been previously demonstrated (6 16), the current work has demonstrated a high additivity in a carefully chosen system. However, treatment of these results has not taken into account the charge transfer bands which, being of proper symmetry, must have some nontrivial effect on the dj-d transitions. The relevance of the steric contribution to the deviations from perfect additivity will be discussed in a forthcoming publication. 

Copper complexes of amino acids have also been found to be effective in preventing and reducing the severity of Shay ulcers [267, 268]. As data in Table 6.17 show, the copper complex of glycine was the most effective of all of the amino-acid complexes studied and it was essentially as effective as Propantheline in reducing ulcer number as well as ulcer severity [267]. 

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. 

The ORD spectra of several L-a-amino acid complexes with Cr(III) (Tsangaris, 1970) show strong negative Cotton effects in the 536-508-nm range (d-d transition). The only exception is the hydroxyproline complex, which gives rise to a positive Cotton effect. Additional Cotton effects are observed in the 598-584-nm range and in the neighborhood of 400 nm. All complexes have two absorption bands at 572-530 and 412-399 nm. The CD spectral characteristics of a number of amino acid complexes of Cr(III) have also been described (Oki, 1977 Oki and Takahashi, 1977). 

The effects of intermolecular interaction which are characteristic of different crystal lattices of amino acid complexes can be avoided by comparing the spectra of aqueous solutions (see also, Nakamoto, 1963). 

Yasui et al found that the CD curve in the first band region for a series of typical optically active amino acid complex ions of the type [Co(NH3)4(aa)] (aa = amino acid anion) were of the same form as reported for the vicinal effect of optically active amino acids in complex ions of the type [Co(en)2(aa)] (Fig. 1). Cyclic amino acids and some others gave different types of CD curves. The CD curves for vicinal effects are also of the same type for some isomers of [Co trien(aa)] complex ions, vide infra. The combination of such an effect with the configurational contribution can account for the appearance of one or two CD peaks in the first band region for complex ions of the [Co(en)2aa] type without assuming a change in frequency interval for the two transitions. 

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