Equilrium, kinetic and mechanistic studies for thcoordination of
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some amino acids "'AA'1
glycine, alanine, .a:ncl histidine, to Cr (Ill)
center of trans .[Cr(ox}2(B.2 0hr {TJ'} cornplein monderarely acidic
range ofpH=4.8-6-.7 ( p =Q.4M NaN03) are reported. The equili rium
c.onsta:nts at 25°C .were found logKequ.=4.95J ,5.206and5.128for glycine, alap.ine, md histidine, ligation. reactions respectively.. The substitution reaction is kinetically involve rwo parallel complex reactions, each inch,tdes there difierent e_onsecutive steps of different
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species of Ct(III). The reactant, Ti, branches through byrolysis into, doubly charged anion, conjugated se of trans[Cr(ox)22(H0)0Hr2
whlch inleracts with (AAH) to from outer-sphere complex, that is followed by interchange reaction of one molecule H20 with one end of AA- ron from an active intermediate species of trans [Cr(Qx)2(AA)OHT3 which cbanges to final product ; c.is [Cr(ox}1(AA)J?. While the remai ning part of reactant interacts also
with zwitter i:on (AAH) on other side to form another outer-sphere
.complex which also undergaes interchange reaction of one molecule
H10 wHh AA- ion to ive two· active intennediates species, trans and cis-[Cr(ox)2(AA)H2 or, whlch later convert tp the same prod·uct .; cisÂ
fCr(ox)z(AA)]2-. TI1e interchange rate co.nstant of trans [Cr(ox)2(AA)OH] formation relatively appears much larger than (A H*=8.8kc 1/n1ol) that of ds[Cr(.oxh AA)H:z Ot formation
( l\ H*·=14.0Kca l/mol), wbile the latter rate constant'is oeaily (5-10)
time l(!I'ger than that oftrans-{Cr(ox)2(AA)H20t fennatlon