The ability of relatively stable Cr(V) and Cr(IV) complexes with 2-hydroxycarboxylato ligands [2-ethyl-2-hydroxybutanoate(2-) = ehba; (1R,3R,4R,5R)-1,3,4,5-tetrahydroxycyclohexanecarboxylate(2-) = quinate = qa] to induce single-strand breaks in plasmid DNA has been studied under a wide range of reaction conditions. The Cr(V) complex, Na[CrVO(ehba)2], causes substantial DNA cleavage at pH 4.0-8.0 [[Cr(V)]0 = 0.010-0.75 mM, phosphate buffer, and 37 degrees C]. The DNA cleavage is inhibited by the presence of excess ligand, by exclusion of O2, or by addition of organic compounds, such as alcohols, carboxylic acids, or DMSO, but it is not affected by traces of catalytic metals [Fe(III) or Cu(II)] or by addition of catalase. The Cr(IV)-qa complexes, unlike the Cr(V) complexes, are able to cleave DNA in the presence of the ligand in a large excess [[Cr(IV)]0 = 0.50 mM, [qa] = 20-100 mM, pH 3.5-6.0, and 37 degrees C]. This is the first direct evidence for DNA cleavage induced by well-characterized Cr(IV) complexes. The proposed mechanism for DNA cleavage includes the following: (i) partial aquation of the bis-chelated Cr(V) and -(IV) complexes with the formation of reactive monochelated forms, (ii) binding of the Cr(V) and -(IV) monochelates to the phosphate backbone of DNA, (iii) one- or two-electron oxidations at the deoxyribose moieties of DNA by Cr(V) and -(IV), and (iv) cleavage of the resulting DNA radicals or cations with or without participation of O2. The patterns of DNA damage by Cr(V) and -(IV) can include strand breaks, generation of abasic sites, and the formation of Cr(III)-DNA complexes.

Amino acid anions (AAO Ϫ ) chelated to cobalt() in [(en) 2 Co(AAO)](O 3 SCF 3 ) 2 (AA = Gly, Sar, Ala and Glu) were selectively oxidized to their imine derivatives by a new general procedure utilizing PBr 3 and N-bromosuccinimide in dmf. The new iminoacetato complexes, Λand ∆-[(en) 2 Co(O 2 CCH᎐ ᎐ NH)](O 3 SCF 3 ) 2 , constitute chiral glycine equivalents which can serve as synthons for stereoselective α-amino acid synthesis. In alkaline EtOH, quantitative addition of CH 2 (COMe) 2 , CH 2 (CO 2 Et) 2 or MeCOCH 2 CO 2 Et to the imine of the iminoacetate ligand initially produced both diastereomers of the product α-amino acid cobalt() complexes. However, subsequent crystallizationinduced asymmetric transformations in the heterogeneous reaction mixtures led to better than 90% excess of a single diastereomer after five days, and the diastereopure product triflate salts were obtained after recrystallization. Both enantiomers of isotopically substituted (3-13 C, 98%)aspartic acid were produced by facile synthesis from ∆-[(en) 2 Co(O 2 CCH᎐ ᎐ NH)](O 3 SCF 3 ) 2 and diethyl (2-13 C)malonate. The new N-methyliminoacetato complex, rac-[(en) 2 Co(O 2 CCH᎐ ᎐ NMe)](O 3 SCF 3 ) 2 , also yielded to imine addition reactions providing a route to the α-N-methylamino acid subclass. The molecular structures of the new imine complexes, Λ-(ϩ) 578 -[(en) 2 Co(O 2 CCH᎐ ᎐ NH)]Br 2 ؒH 2 O and rac-[(en) 2 Co(O 2 CCH᎐ ᎐ NMe)]S 2 O 6 ؒ1.5H 2 O, and the diethyl carboxy-aspartate addition product, (ΛS,∆R)-[(en) 2 Co{O 2 CCH(CH(CO 2 Et) 2 )NH 2 }](ClO 4 ) 2 , were determined by X-ray crystallography.

The H+- and Cl--assisted dissociation kinetics and the stabilities of the complexes [Hg(sar)]2+ and [Hg((NH2)2-sar)]2+ (sar = 3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane and (NH2)2-sar = 1,8-diamino-sar) were determined. The Hg2+ dissociation rates depend on both the proton and the chloride ion concentrations. H+ competes with the metal ion for dissociated amine groups, and Cl- competes with the amine for vacant coordination sites. The rate laws are complicated. For the [Hg(sar)]2+ system (0.1 ≤ [H+] ≤ 1.0 M, 0.01 ≤ [Cl-] ≤ 1.0 M, I = 2.0 M (NaO3SCF3), 25.0 °C) the observed rate law is v - Hg 2+ = (a + b[Cl-])[H+][Hg(sar)2+]/(1 + c[Cl-]), with a = 35(3) M-1 s-1, b = 2.9(4) × 103 M-2 s-1, and c = 33(5) M-1. For the [Hg((NH3)2-sar)]4+ system (0.001 ≤ [H+] ≤ 1.0 M, 0.01 ≤ [Cl-] ≤ 1.0 M, I = 1.0 M (LiClO4), 25.0 °C) the observed rate law is v - Hg 2+ = (a + b[H+] + c[H+]2)[Cl-][Hg((NH3)2-sar)4+])/((1 + d[Cl-])(1 + e[H+])), with a = 0.056(6) M-1 s-1, b = 8(3) M-2 s-1, c = 5(3) M-3 s-1, d = 1.3(4) M-1, and e = 1.1(5) × 102 M-1. Intimate mechanisms for the dissociation reactions are proposed. Using iodide ion or sar ligand as competing ligands and the reported values for the stabilities of HgI3 -and HgI4 2- the stability constants at 25.0 °C were determined for [Hg(sar)]2+ (1028.1(1) M-1), [Hg(sar)I]+ (1029.1(1) M-2), [Hg((NH2)2-sar)I]+ (1028.5(1) M-2), and [Hg(cyclam)I]+ (1030.8(1) M-2) (cyclam = 1,4,8,11-tetraazacyclotetradecane) with [OH-] = 0.1 M, I = 0.5 M (NaClO4) and for [Hg((NH2)2-sar)]2+ (1026.4(3) M-1) with [OD-] = 0.1 M, I = 0.1 M (NaOD).