Amino-acid complexes

Amino-acid Complexes. X-Ray crystal structures have been reported for many cobalt(m) amino-acid complexes. Potassium dinitrobis(P-alaninato)cobaltate(m) has octahedral co-ordination about the cobalt, trans nitro-groups, and a trans arrangement of amino N- and carboxylato O-donors from the bidentate P-alaninates.371 In Ca[Co(aspar-tate)2] there are two isomeric ions the cis(N)trans Os) (64) and cis(lSl)trans 06) (65), 

Prelesnik, Lj. Manojlovic-Muir, and K. W. Muir, Acta Cryst., 1974, B30, 229. 

Four of the six possible isomers of [Co(acac)(iV-methyl-S-alaninato)2] have been separated by chromatography, and identified as AtransN, AtransN, AcisN, and Acis-N—Ct, the AcisN—C2 and AcisN—Cx were not isolated.379 In the [Co(acac)-(S-aminoacidate)2] systems, six isomers have been separated for S-alanine, and five for S-valine,380 the AcisN—C2 being obtained in very small yield for S-alanine and being absent in the S-valine system, probably due to steric effects. 

Hidaka and Y. Shimura, Proceedings 16th International Coordination Chemistry Conference, Dublin, 1974. 

Okamoto, J. Hidaka, and Y. Shimura, Bull. Chem. Soc. Japan, 1973,46, 3134. 

Amino-acul complexes. frans-(0,X)-[CoX(aminoacidato)(dien)]Y (X == CN, NO2, or Cl Y = Br, Cl, or ClO aminoacid === Gly, a-aminobutyric acid, L-Ala. L-Val, L-Thr, or L-Pro) complexes have been isolated. The cyano-complexes were shown to exist in the new conformational isomeric endo- and cxo-forms. This refers to the position of the hydrogen atom bonded to the central N of dien w ith respect to the cyanide group. The tetramine ligands 1,3-diaminopropane, 3,7-diaza-l,9-nonanediamine (2,3,2-tet), and 4,7-diaza-1.10-decanediamine (2,2,3-tet) exhibit marked topological specificity in the complexes [Co(tetramine)(aa)] (aa = Gly. Ala, Val. or Sar). Thus a-[Co-(3,2,3-tet)aa] and P2-[Co(2,3,2-tet)aa] appear to be formed exclusively under the synthetic conditions employed. 

Three isomers of Na[Co (L-apa)2] have been prepared as a mixture from Co(OH)3 and apaH (apaH = L-aspartic acid) in the presence of NaOH. The brick-red, violet, and blue-violet optical isomers were separated by chromatography, the first having fra/is-N, the second cis-N-fra/is-0, the third oi.s-N- 

Jursik and B. Hajek, Coll. Czech. Chem. Comm.. 1971, 36, 3362. 

X-Ray studies on Na[(-)5 g-Co(ox)(aa)2],2H20 [aa = trans-iV-methyl-(S)-alaninate] confirm the RS configuration of the aa ligands and show the absolute configuration of the anion to be A. Fractional crystallization and column chromatography on D-lactose has been used to separate diastereoisomers of [Co(acac)2(L-Phe)] and [Co(acac)2(L-Val)]. The method was, however, unsuccessful for the corresponding L-Ala complex.  

Bedetti, W. B. Ceipidor, V. Carunchio, and M. Tomassetti, J. Inorg. Nuclear Chem., 1976, 38, 1391. M. Wataba, S. Kerwaai, and S. Yoshikawa, Bull. Chem. Soc. Japan, 1976, 49, 1845. 

The yellow compound potassium (-l-)tris-(L-cysteine-sulphinato(2 —)-SN)-cobalt(iii) is very easily prepared by a rapid stereoselective synthesis from L-cysteine, and has proved a very good resolving agent for tripositive cations. The anions [Co(L-Pro-iV-prop)2] , [Co(L-Pro-iV-ac)(ida)], [Co- 

Bagger, K. Gibson, and C. S. Sorensen, Acta Chem. Scand., 1972, 26, 2503. 

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Copper III) is known in complex oxides and fluorides and in amino-acid complexes. 

Similar ligand-ligand interactions have been reported for a large number of ternary -amino acid complexes, built up of two different amino acid.s. A compilation of 72 examples is presented in reference 39. The extra stabilisation due to ligand-ligand interactions in these complexes depends on the character of the amino-acid side chains and amounts to 0.34 - 0.57 kJ/mole for combinations of aromatic and aliphatic side chains and 0.11 - 6.3 kJ/mole when arene - arene interactions are possible. ... 

Table 3.5. G, 711 and 7S for the binding of 3.8c to different copper(II)-amino acid complexes in water at 25 C at pH 5-6.

Metal template reactions, 1, 416, 433 equilibrium kinetic, 1, 434 thermodynamic, 1, 434 Metal tolerance amino acid complexes, 2, 964 plants, 2, 963 Metal toxicity... 

Uchegbu and coworkers have studied the complexation and delivery of DNA using a unique poly(amino acid)-based polymer vesicle. A polymer of either poly (L-lysine) or poly(L-omithine) was functionalized with methoxy-poly(ethylene glycol) (mPEG) and hydrophobic palmitic acid chains to synthesize an amphiphilic triblock of either mPEG-6-poly(L-lysine)-6-palmitoyl or mPEG-Z>-poly(L-omithine)-6-palmitoyl. Vesicles formed from these polymers were complexed with DNA and showed improved transfection in vitro over poly(amino acid) complexed with DNA or DNA alone [82]. 

With the death of the bean, cellular structure is lost, allowing the mixing of water-soluble components that normally would not come into contact with each other. The complex chemistry that occurs during fermentation is not fully understood, but certain cocoa enzymes such as glycosidase, protease, and polyphenol oxidase are active. In general, proteins are hydrolyzed to smaller proteins and amino acids, complex glycosides are split, polyphenols are partially transformed, sugars are hydrolyzed, volatile acids are formed, and purine alkaloids diffuse into the bean shell. The chemical composition of both unfermented and fermented cocoa beans is compared in Table 1. 

There are a number of important N/O bidentate ligands including the chelate stabilized ketone and aldehyde complexes, and amino acid complexes. 

The amino acid complexes [TcNCl(L)(PPh3)] (HL=L-cysteine, L-cysteine ethyl ester, cysteamine) have been prepared from [TcNC PPlfj ] or ASPI14 [TcNCU]/PPh3 [88]. The crystal structure of the L-cysteine ethyl ester complex 21 shows a Tc=N bond length of 1.605(3) A and the Tc atom displaced by 0.594(1) A above the square basal plane [88]. Other structurally characterized examples are the square pyramidal 22 with ONSP coordination and Tc=N 1.611(3) A [81], and 23 with NSPC1 coordination and Tc=N 1.615(7) A [89],... 

Strange and Dark demonstrated the presence of a hexosamine containing peptide in the spore coats of B. megaterium and B. subtilis. The breakdown of an insoluble peptide complex might well be one of the first steps of the germination process. It was believed that the release of the hexosamine-amino acid complex was the result of the action of lysozyme present in the spores. 

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. 

Amino acid is one of the most important biological ligands. Researches on the coordination of metal-amino acid complexes will help us better understand the complicated behavior of the active site in a metal enzyme. Up to now many Ln-amino acid complexes [50] and 1 1 or 1 2 transition metal-amino acid complexes [51] with the structural motifs of mononuclear entity or chain have been synthesized. Recently, a series of polynuclear lanthanide clusters with amino acid as a ligand were reported (most of them display a Ln404-cubane structural motif) [52]. It is also well known that amino acids are useful ligands for the construction of polynuclear copper clusters [53-56], Several studies on polynuclear transition metal clusters with amino acids as ligands, such as [C03] [57,58], [Co2Pt2] [59], [Zn6] [60], and [Fe ] [61] were also reported. 

The versatile binding modes of the Cu2+ ion with coordination number from four to six due to Jahn-Teller distortion is one of the important reasons for the diverse structures of the Cu-Ln amino acid complexes. In contrast, other transition metal ions prefer the octahedral mode. For the divalent ions Co2+, Ni2+, and Zn2+, only two distinct structures were observed one is a heptanuclear octahedral [LnM6] cluster compound, and the other is also heptanuclear but with a trigonal-prismatic structure. 

Ashby and Craig72 reported that MeSn3+ and small amounts of Me2Sn2+ are also produced when a baker s yeast (Saccharomyces cerevisiae) is incubated with tin(II) compounds including tin(II) oxalate, tin(II) sulfide and various tin amino acid complexes. Tin(II) chloride and tin(II) amino acid complexes were methylated by methyl-cobalamin, under conditions of chloride ion concentrations and pH relevant to the natural environment73. The main identified product of all reactions was monomethyltin. 

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). 

Crystal structures are available for many (N)4Co-amino acid complexes (Table I). Many of the diastereomers (AS, AS) in the bis-en series have been resolved using classic crystallization (usually via bromocamphor sulfonate, arsenyl-, or antimonyl-tartrate salts) or ion exchange methods (Table II). Reversed-phase ion-pair HPLC, using aryl phosphate or aryl/alkyl sulfonate ion pairing reagents in MeOH/ H20 eluent, has allowed diastereomer separations to be carried out on analytical amounts (28) (Table II). 

In practice iodide salts of the amino acid complexes are used, as I is lost as Mel under conditions of excess alkylating agent. 

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