Alanine, cobalt complex

NO2C2H5, Glycine cobalt complex, 25 135 cobalt complexes, 23 75, 92 N02CjH,7, Alanine cobalt complex, 25 137... 

O2IOSC7HS, Osmium, dicarbonyI(Ti -cycIo-pentadienyI)iodo-, 25 191 02lOsC,2H,s, Osmium, dicarbonyliodo(Ti -pentamethylcyclopentadienyl)-, 25 191 O2NC2HS, Glycine cobalt complex, 25 135 02NC3Ht, Alanine cobalt complex, 25 137 02N4P2QH,2, 1 W,5W-[1, 4,2,3]Diazadiphos-phoIo[2,3-b][l,4,2,3]diazadiphosphoIe-2,6-(3W,7W)-dione, 1,3,5,7-tetrame-thyl-, 24 122... 

Little is known about the direct oxidation of amino acid derivatives. Although an a-acetoxy derivative can be prepared from hippuric acid by treatment with lead tetraacetate (99) this reaction is not applicable to N-phthaloyl- or N-benzyloxycarbonyl-glycine. Anodic oxidation of acetamidomalonic acid monoester in alcohol yielded the ot-alkoxy-a-acetamino acetic acid, while in acetic acid the corresponding oc-acetoxy compound was obtained (186). The oxidation of optically active N-salicylidene-alanine cobalt (III) complexes has been studied as a model reaction for enzymatic deamination of a-amino acids, and found to yield the corresponding diastereomeric a-hydroxy alanine complexes (118). 

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),... 

A novel light-reversible redox system has been discovered381 with glycylglycine it is summarized in Scheme 7. Preparations of mixed cobalt(m) complexes of macrocycles and amino-acids, trans-[Co [ 14]aneN4 (amino-acid)2]3 + and trans-[Co Me4-[14]tetraeneN4](amino-acid)2]3+, have been reported using glycine, S-alanine, S-phenylalanine, and S-leucine.382... 

An interesting result, which may have some bearing on the effect of replacing native metals in enzymes with other metals, has been reported by Nakon et al.260 They found that the co-ordination sites of 3-[(ethoxycarbonyl ethyl)thio]-L-alanine (SCMC), and 3-[(2-aminoethyl)thio]-L-alanine in binding to bivalent zinc, copper, cobalt, and nickel are dependent on both pH and metal. The copper complex of SCMC has the structure (10), while the zinc complex has structure (11). Similar effects are seen on changing pH. 

The X-ray method was first applied (52) to a chelated inorganic molecule4) in the case of the most accessible product of the reaction of aqueous L(+)alanine with cobalt(III) hydroxide, the violet crystalline, a(+)-[Co(L-ala)s]. The absolute configuration of L(+)alanine is known and could be projected only on to the configuration shown. The configuration of the whole complex (IV) was thus established as D. 

Pasternack and co-workers have reported a series of detailed temperature-jump studies on mixed ligand complexes involved in the copper(ll) + bipyridine + glycine system [142], the copper(ll) + bipyridine + ethylene-diamine, of-alanine, and j3-alanine systems, and the cobalt(ll) + bipyridine + glycine system [143]. 

The stereochemistry of cobalt(III) complexes with 0,N,0-terdentate ligands of the linear type was studied by Okamoto et al. In a [Co(0,N,0-terdentate)2]-type complex four isomers,/ac-/rans(N), mer-trans(ti), A-c/ (N) and A-cis(N), are shown in Fig. 3.7. When L-alanine-N-monoacetic acid (L-H2alama) participates in coordination, the nitrogen donor atom of the L-alama is optically rtivated, and hence three isomers, RR, RS, and SS, are possible for each of the above rrans(N) and cis(N) forms. 

The experimentally determined (S)/(R)-ratio of 18/82 was compared with the relative stabilities of the two diastereomeric products ([Co((S),(S)-ppm)((R)-ala)] / [Co((S),(S)-ppm)((S)-ala)] ), calculated by strain-energy minimization. The reported strain energies, based on a single conformer for each of the two diastereomeric products (identical to the crystal structure of the complex with coordinated (R)-alanine [328]), are in good agreement with the experimentally determined data (23/77 versus 18/82). A full conformational analysis led to a ratio of 30/70 when only conformational flexibility is allowed, or 33/67 when other isomers were also included in the analysis [294]. The assumption in the original report was that the enantio-selectivity is based on the relative energies of the diastereomeric forms of the cobalt(III) products [327]. Fortunately, a qualitatively similar result is expected if the stereoselectivity is controlled by the deprotonated intermediates. However, a quantitatively accurate prediction of the product ratio is not expected in this case. 

Metal ions can bind amino and carboxylate groups (vide supra), so are well-adapted to amino acid recognition. The cobalt(II) complex 33 (racemic) reacts with DL-alanine to give diastereomeric products 34 and 35 in 2 1 ratio. A controlling influence is the tendency of the carboxylates to locate trans to each other. Interestingly, 35 is converted almost exclusively to 34 upon treatment with... 

Interference from Ring-closure.—In 1966, Kustin, Pasternack, and Weinstock published a paper entitled Steric effects in fast metal complex substitution reactions , in which they reported a temperature-jump study involving the nickel(ii) and cobalt(ii) complexes with a- and jS-alanine. With a-alanine, the substitution at cobalt was significantly faster than at nickel, but with the jS-isomer, whereas the Ni + substitution rate was approximately the same as before, substitution at Co + was significantly slower. The rate constants shown in Table 4 were obtained for the 1 1... 

Arakawa, R., Kobayashi, M., Ama,T. (2000) Chiral recognition in association between antimony potassium tartrate and bis(L-alaninate)ethylenediamine cobalt(III) complexes using electrospray ionization mass spectrometry. /. Am. Soc. Mass Spectrom., 11, 804-808. 

The kinetics of stereoselective deuteration of malonate hydrogens in bis(malonato)-cobalt(III) complexes [Co(mal)2L2] containing L2 = en, pn, N,N -Me2en, phen, c/5 -(NH3)2, or c/5-(py)2 have been monitored. Both acid and base hydrolysis are observed, and there is a reversal of stereoselectivity with solution pH. There are some kinetic differences between the amine ligands on the one hand and py and phen on the other, as competition for OD" between malonate and amine is possible, between malonate and py or phen not. The rate law for deuteration of a hydrogens in a-aminocarboxylato complexes of cobalt(III) containing various combinations of glycine, sarcosine, or alanine with ammonia, ethylenediamine, or diaminopropane is simple second order. 

The rate constants for the reaction of [Ni(nta)(H20)a] with various ligands in their neutral and protonated forms have been reported, as has that for the formation of the bis-complex of nickel(n) with the purine base theophylline. Rate constants have also been reported for the formation of bis-complexes of cobalt(n), nickel(n), and copper(n) with L-proline, L-hydroxypyroline, glycyl-L-leucine, , L-Ieucylglycine, a-alanine, jS-alanine, iminodiacetic acid, iminodipropionic acid, and aspartic acid. ... 

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