On the Role of Structural Zinc in Bis(Cysteinyl) Protein Sequences

Zinc(ii) and cadmium(ii) complexes of N-terminally free peptides containing two separate cysteinyl binding sites

The novel synthesized cysteine peptides form stable zinc(ii) and cadmium(ii) complexes; the specific sequence makes possible metal induced amide deprotonation.

Organic-sulfur-zinc hybrid nanoparticle for optical applications synthesized via polycondensation of trithiol and Zn(OAc)2

Organic-sulfur-zinc hybrid materials were prepared via polycondensation of Zn(OAc)2 and trithiols bearing various alkyl groups. A soluble nanoparticle could be obtained by the polycondensation using a trithiol bearing octadecyl moieties. The good dispersing ability as nano-scaled particles was confirmed by dynamic light scattering and atomic force microscopy analyses. This hybrid nanoparticle was miscible with poly(methyl methacrylate) and served as a refractive additive to increase refractive indexes. The calculated refractive index value for the nanoparticle was 1.58.

Tripodal pseudopeptides with three histidine or cysteine donors: synthesis and zinc complexation

Peptide coupling of benzene-1,3,5-carboxylic acid with 3 equiv of histidine ethyl ester or cysteine ethyl ester has yielded the tripodal pseudopeptide ligands THB and H(3)TCB. Likewise, the combination of tris(carboxyethyl)nitromethane with 3 equiv of cysteine ethyl ester gave the tripod H(3)TCM. With zinc salts, the pseudopeptides form the insoluble compounds (THB)(2)Zn(5)Cl(10), Zn(3)(TCB)(2), and Zn(3)(TCM)(2) which are likely to be coordination polymers. Solution studies of THB with potentiometric methods have identified the complex species [(THB)(2)Zn](2+), [(THB)Zn-OH(2)](2+), and [(THB)Zn-OH](+). The pK(a) of the zinc-bound water molecule is 6.2, making the (THB)Zn complex a viable model of carbonic anhydrase.

Chiral ferrocene amines derived from amino acids and peptides: synthesis, solution and X-ray crystal structures and electrochemical investigations

For the recognition of all but the simplest naturally occurring molecules, electrochemical sensors based on ferrocene will certainly require chiral centers. To advance the necessary chemistry, this work describes the synthesis and properties of ferrocene derivatives of enantiomerically pure amino acids, peptides, and other chiral amines. Ferrocene aldehyde is condensed with amino acid esters to yield the corresponding Schiff bases 2, which are reduced by NaBH4 in methanol to the ferrocene methyl amino acids 3. An X-ray single-crystal analysis was carried out on the phenylalanine derivative 3a (monoclinic space group P2(1), a = 10.301(1) A, b = 9.647(1) A, c = 18.479(2) A, beta = 102.98(2) degrees, Z = 4). Further peptide chemistry at the C terminus proceeds smoothly as demonstrated by the synthesis of the ferrocene labeled dipeptide Fc-CH2-Phe-Gly-OCH3 5 (Fc = ferrocenyl ((eta-C5H4)Fe(eta-C5H5))). We also report the synthesis of the C,N-bis-ferrocene labeled tripeptide Phe-Ala-Leu and its electrochemical characterization. Starting from the enantiomerically pure ferrocene derivative 9, which was synthesized from ferrocene aldehyde and L-1-amino-ethylbenzene, two diastereomers 10 were obtained by peptide coupling with N-Boc protected D- and L-alanine. There was, however, only very little diastereomeric induction if 0.5 equiv of a racemic mixture of alanine were used. This suggests that amino acid activation rather than coupling is the rate-determining step. A combination of NOESY (nuclear Overhauser effect spectroscopy) spectra and molecular modeling furnished detailed insights into the solution structures of 3, 9, and 10 and was used to rationalize their different reactivity.

Alcohol and Aldehyde Adducts of Zinc Thiolates: Structural Modeling of Alcoholdehydrogenase

Bis(pentafluorothiophenolato)zinc (1) and bis(2,4,6-triisopropylthiophenolato)zinc (2) can be combined with nitrogen-containing derivatives of benzyl alcohol and benzaldehyde to form (N,O-chelate) zinc thiolates. 2-Pyridylmethanol as well as 2-quinolylmethanol (HetMeOH) yield [(HetMeO)Zn(SR)](4) (3, 4) having a cyclo-Zn(4)(&mgr;-O)(4) backbone and only terminal SR. Likewise, thiolate 1 and 2-(dimethylamino)benzyl alcohol form zwitterionic [(dimethylammoniobenzylato)Zn(SR)(2)](2) (5) with bridging alkoxide and terminal thiolate. In contrast, 6-picolylmethanol (PicMeOH) and thiolate 1 result in [(PicMeOH)Zn(SC(6)F(5))(2)] (6) containing zinc in a tetrahedral ZnNS(2)O, environment. Simple aromatic aldehydes form polymeric complexes [(RCHO)Zn(SC(6)F(5))(2)] (7: R = p-tolyl, 8: R = mesityl) with a [Zn-S](infinity) backbone. Chelating aldehydes (CA) yield mononuclear complexes with tetrahedral ZnNS(2)O coordination [(CA)Zn(SC(6)F(5))(2)] (9, CA = pyridine-2-carbaldehyde; 10, CA = 6-methylpyridine-2-carbaldehyde; 11, CA = 6-methoxypyridine-2-carbaldehyde; 12, CA = quinoline-2-carbaldehyde; 13, CA = 2-(dimethylamino)benzaldehyde). In contrast, N-methylimidazole-2-carbaldehyde (ImA) is coordinated twice in tetrahedral [(ImA)(2)Zn(SC(6)F(5))(2)] (14) lacking any Zn-O interactions. Pyridine-2,6-dicarbaldehyde (PDA) forms trigonal bipyramidal [(PDA)Zn(SC(6)F(5))(2)] (15) with ZnNO(2)S(2) ligation. The structures of 3, 4, 6, 8, 10, 11, 13, and 14 were determined crystallographically, and the structures of 5 and 15 were deduced from those of the corresponding ZnBr(2) complexes. The ZnNS(2)O coordination pattern observed for the enzyme has been reproduced to a very good approximation. In complexes 6 and 10, which are almost superimposable, it is realized for both the corresponding alcohol and aldehyde.