Conversion of azomethine moiety to carboxamido group at cobalt(III) center in model complexes of Co-containing nitrile hydratase

The Co(III) complex of the Schiff base ligand N-2-mercaptophenyl-2'-pyridylmethyl-enimine (PyASH), namely, [Co(PyAS)(2)]Cl (1), has been synthesized via an improved method and its structure has been determined by X-ray crystallography. The two deprotonated ligands are arranged in mer configuration around the Co(III) center and the overall coordination geometry is octahedral. The coordinated azomethine function in 1 is rapidly converted into carboxamido group upon reaction with OH(-). The product is the bis carboxamido complex (Et(4)N)[Co(PyPepS)(2)] (2), reported by us previously. Reaction of H(2)O(2) with 1 in DMF affords [Co(PyASO(2))(PyPepSO(2))] (3), a species with mixed imine and carboxamido-N donor centers as well as S-bound sulfinates. Further reaction with H(2)O(2) in the presence of NaClO(4) converts 3 into the previously reported bis carboxamido/sulfinato complex Na[Co(PyPepSO(2))(2)] (4). The reaction conditions for the various transformation reactions for complexes 1-4 and the structure of 3 are also reported. The mechanism of the -CH=NR + [O] --> -C(=O)NHR transformation has been discussed. The reactions reported here provide convenient alternate routes for the syntheses of Co(III) complexes with coordinated carboxamide, thiolate, and/or sulfinate donors as models for the Co-site in the Co-containing nitrile hydratase(s).

Co(III) complexes with coordinated carboxamido nitrogens and thiolato sulfurs as models for Co-containing nitrile hydratase and their conversion to the corresponding sulfinato species

Recent spectroscopic data suggest that the Co(III) site in Co-containing nitrile hydratase is ligated to carboxamido nitrogens and thiolato sulfurs and most possibly one or more of the bound thiolates exist as sulfenato and/or sulfinato groups. The absence of any Co(III) complex with such coordination makes it quite difficult to predict the reactivity of this kind of Co(III) site. In this paper, the Co(III) complexes of two designed ligands PyPepSH2 (1) and PyPepRSH2 (2) have been reported. The two complexes, namely, (Et4N)[Co(PyPepS)2] (3) and Na[Co(PyPepRS)2] (4) are the first examples of Co(III) complexes with carboxamido nitrogens and thiolato sulfurs as donors. The average Co(III)-Namido and Co(III)-S distances in these complexes lie in the range 1.90-1.92 and 2.22-2.24 A, respectively. Reaction of H2O2 with both complexes readily affords Na[Co(PyPepSO2)2] (5) and Na[Co(PyPepRSO2)2] (6), species in which the thiolato sulfurs are converted to sulfinato (SO2) groups. Such conversion also occurs when solutions of 3 and 4 are exposed to dioxygen in the presence of activated charcoal. These reactions are clean and the S --> SO2 transformation does not introduce significant changes in the metric parameters of these complexes. The reactivity of 3 and 4 indicates that the bound Cys-sulfurs around the biological Co(III) site could be oxidized to sulfinato groups.

Production and interpretation of perspective drawings by blind and sighted people

In three experiments the production and interpretation of perspective drawings by blind and sighted subjects were examined. Blindfolded sighted, early-blind, and late-blind subjects first attempted to produce raised-line drawings of a surface at a number of angles-0 degree (panel horizontal), -22.5 degrees, -45 degrees, -67.5 degrees, and -90 degrees (vertical). Congenitally blind subjects did not show foreshortening in their naive raised-line drawings. However, the congenitally blind subjects were able to understand aspects of perspective, and performed as well as the blindfolded sighted and late-blind subjects in a subsequent multiple-choice task. Subjects in the multiple-choice task were required to match tangible perspective drawings to a slanted board. Although the three groups performed alike, both groups of blind subjects performed better than blindfolded sighted controls on judgments involving drawings of the vertical panel in the second experiment. In a final experiment, in which vision and touch were compared, sighted subjects were required to adjust the angle of the panel to match foreshortened, perspective drawings. This experiment yielded significantly better performance with vision than with touch, but only for drawings of the board at the vertical orientation. The results suggested that congenitally blind people may benefit from haptic exposure to raised-line configurations representing geometric perspective.

Tactual picture identification by blind and sighted people: effects of providing categorical information

Four experiments examined the influence of categorical information and visual experience on the identification of tangible pictures, produced with a raised-line drawing kit. In Experiment 1, prior categorical information aided to accuracy and speed of picture identification. In a second experiment, categorical information helped subjects when given after the examination of each picture, but before any attempt at identification. The benefits of categorical information were also obtained in another group of subjects, when the superordinate categories were named at the start of the experiment. In a third experiment, a multiple-choice picture recognition task was used to eliminate the difficulty of naming from the picture-identification task. The multiple-choice data showed higher accuracy and shorter latencies when compared with identification tasks. A fourth experiment evaluated picture identification in blindfolded sighted, early, and late blind participants. Congenitally blind subjects showed lower performance than did the other groups, despite the availability of prior categorical information. The data were consistent with theories that assume that visual imagery aids tactual perception in naming raised line drawings. It was proposed that part of the difficulty in identification of raised line pictures may derive from problems in locating picture categories or names, and not merely in perception of the patterns.