The new N(2)S(alkylthiolate) ligand 2-methyl-1-[methyl-(2-pyridin-2-ylethyl)amino]propane-2-thiolate, PATH (1), has been prepared and reacted with zinc(II) and cobalt(II) to give the monomeric complexes [(PATH)ZnBr] (2), [(PATH)ZnNCS] (3), [(PATH)CoBr] (4), and [(PATH)CoNCS] (5). The molecular structures of 4 and 5 have been determined by X-ray diffraction. Each complex displays a distorted tetrahedral geometry at the metal center, with the PATH ligand providing the N(2)S(alkylthiolate) donors. These complexes are close structural mimics of the active site of metalloproteins with a His(2)Cys-M(II) site such as that found in peptide deformylase. Complexes 4 and 5 are the first examples of crystallographically characterized Co(II) complexes with an N(2)SL (L not equal N,S) donor set. Only one diastereomer for 2-5 is observed in the solid state, and simple molecular mechanics (Chem3D) calculations suggest this isomer is stable because of a favorable ligand conformation. NMR studies in the case of Zn(II) and UV-vis studies in the case of Co(II) provide strong evidence that their solid-state structures are retained in solution. Cyclic voltammetry reveals processes for both the Co(II/I) (4, - 1.51 V; 5, - 1.49 V) and Co(III/II) (4, + 0.9 V; 5, + 0.9 V) couples. The UV-vis data for the cobalt complexes are consistent with a monomeric, four-coordinate geometry regardless of the nature of the solvent (i.e., donating (MeOH, CH(3)CN) vs nondonating (CH(2)Cl(2))) and are compared with other cobalt complexes as well as cobalt-substituted His(2)Cys metalloproteins (peptide deformylase and blue-copper proteins). In addition, reaction of the bromide complexes 2 and 4 with hydroxide anion leads to the formation of 1:1 hydroxide:M(II) complexes which have been characterized in situ by (1)H NMR and UV-vis spectroscopy, respectively.

Reactions of alkaline earth metal chlorides with 2-aminobenzoic acid (2-abaH) have been investigated. The treatment of MCl2.nH2O (M = Mg, Ca, Sr or Ba) with 2-abaH in a 1:2 ratio in a MeOH/H2O/NH3 mixture leads to the formation of anthranilate complexes [Mg(2-aba)2] (1), [Ca(2-aba)2(OH2)3]infinity (2), [[Sr(2-aba)2(OH2)2].H2O)]infinity (3), and [Ba(2-aba)2(OH2)]infinity (4) respectively. Alternatively, these products can also be obtained starting from the corresponding metal acetates. Anthranilate complexes 1-4 have been characterized with the aid of elemental analysis, pH measurements, thermal analysis, and infrared, ultraviolet, and NMR (1H and 13C) spectroscopic studies. All the products are found to be thermally very stable and do not melt on heating to 250 degrees C. Thermal studies of complexes 2-4, however, indicate the loss of coordinated and lattice water molecules below 200 degrees C. In the case of the magnesium complex, the analytical and thermogravimetric studies indicate the absence of any coordinated or uncoordinated water molecules. Further, the solid-state structures of metal anthranilates 2-4 have been established by single-crystal X-ray diffraction studies. While the calcium ions in 2 are heptacoordinated, the strontium and barium ions in 3 and 4 reveal a coordination number of 9 apart from an additional weak metal-metal interaction along the polymeric chains. The carboxylate groups show different chelating and bridging modes of coordination behavior in the three complexes. Interestingly, apart from the carboxylate functionality, the amino group also binds to the metal centers in the case of strontium and barium complexes 3 and 4. However, the coordination sphere of 2 contains only O donors. All three compounds form polymeric networks in the solid state with the aid of different coordinating capabilities of the carboxylate anions and O-H...O and N-H...O hydrogen bonding interactions.

No abstract

A combination of experimental and theoretical studies on (N,S(thiolate))M II -formate complexes (M = Fe, Zn) suggests a rationale for the metal ion dependence of peptide deformylase.Based on active site structure (tetrahedral (His 2 Cys)M II (OH n )), conserved sequence motifs, and function (hydrolysis), peptide deformylase (PDF) belongs to the mononuclear zinc(II) enzyme family. 1 However, recent evidence shows bacterial PDF to be the first example of an iron(II) metallopeptidase, which hydrolyzes the formyl bond of the N-terminus of newly synthesized polypeptides. [2][3][4] Intriguingly, the Zn II form of bacterial PDF is dramatically less active than the Fe II form, although their native structures are identical. [4][5][6] The mechanism of this enzyme and an explanation of the metal-ion dependence are under investigation. PDF is also a target for new antibiotic agents, and therefore knowledge regarding its mechanism is of practical significance. 7 We are involved in the synthesis of Zn II and Fe II model complexes of PDF to gain a better understanding of the mechanism and unusual metal dependence of this enzyme.Previously we reported the synthesis of (PATH)Zn II (O 2 CH), a model complex of the putative (formate)Zn II -PDF intermediate. 8 Analysis of the bonding mode in this complex showed that the formate was coordinated in an anisobidentate fashion. It was suggested that this bonding mode, as opposed to a purely monodentate interaction, might slow down the displacement of formate by water in the final step of the catalytic cycle, and account for the low reactivity of Zn-PDF. Following this argument, it was expected that the analogous (formate)Fe II -PDF would exhibit a monodentate bonding mode.Recently, high-resolution X-ray structures of (formate)M II -PDF (M = Zn, Fe) from Chan and coworkers have revealed bonding motifs in contrast to our prediction; monodentate coordination was observed in the case of Zn II and bidentate coordination was seen for Fe II The synthesis of 1 is shown in Scheme 1. Addition of (Py 2 S − )Na + to ferrous formate in MeOH gives a cloudy, yellow solution which turns clear over 18 h. Removal of the solvent under vacuum gives an orange solid which can be partly redissolved in toluene. Crystals of 1 were grown from Et 2 O/toluene, and an ORTEP diagram of 1 is shown in Figure 1. The iron center is in a five-coordinate geometry with the formate ligand occupying the axial position opposite the N(amine) donor. The N(pyridyl)-Fe II and S-Fe II distances (Table 1) are in the normal range. The N(amine)-Fe II distance of 2.366(4) Å is long, but is quite close to the related complexes (Py 2 S)Fe II X (X = Br, N(amine)-Fe II = 2.387(1) Å; X = Cl (2.352(2) Å). 10 There is no obvious reason for the elongation of this bond in these complexes, and theoretical calculations show that another isomer of 1 with a more conventional Fe II -N(amine) distance should be accessible (vide infra). Interestingly, the formate ligand is clearly monodentate with Fe-O(2) = 4.12 Å, and is in fact bound in ...