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Die ein-, zwei- und vier-kernigen Titelkomplexe (I) bis (IV) sind aus einfachen Eisensalzen zuganglich.

The bischelate monoanion (Fe((SCH2)2C6H4)2)1_ contains an unconstrained, near-tetrahedral Fe(III)-S4 coordination unit (similar to the Fe-SU coordination unit occurring in rubredoxin proteins) and exhibits the Fe(III)/Fe(II) redox couple. Mossbauer parameters at 77 K are isomer shift S = 0.13 mm/s (relative to iron metal) and electric quadrupole splitting AZIQ = 0.57 mm/s. Application of an external magnetic field parallel to the direction of observa­ tion at 4.2 K induces a saturation magnetic hyperfine field of — 380 kOe. Upon reduction to the dianion (Fe((SCH2)2C6H.t)2)2- the isomer shift changes to S = 0.61 mm/s and the quadrupole splitting at 4.2 K to A£Q = 3.34 mm/s. From the temperature dependence of AEQ for 1.4 K < T < 295 K we infer the splitting of the ground orbital doublet, e(dz2, dX2-yi), to be A s 900 cm-1. External magnetic fields up to 80 kOe reveal the sign of Vzz to be negative indicating that the ground orbital has dz% symmetry and induce a magnetic hyperfine interaction of negative sign. For H0 = 60 kOe, Hm = — 128 kOe. |HM | increases with increasing H0, showing that saturation has not been reached up to Ho = 80 kOe, and implying a zero field splitting of several cm -1 of the electronic ground state. These results as well as magnetic moment measurements for the unconstrained model compounds are comparable to measurements in oxidized and reduced rubredoxin and imply that an « entatic state » description of rubredoxin is not valid.

Die ein-, zwei- und vier-kernigen Titelkomplexe (I) bis (IV) sind aus einfachen Eisensalzen zuganglich.

To complete the set of synthetic analogs of the three recognized types of active sites in iron-sulfur redox proteins, the compound (Et4N)[Fe((SCH2)2C6H4)2], derived from o-xylyl-alpha,alpha'-dithiol, has been prepared and its structure has been determined by x-ray diffraction. The bischelate anion contains a near-tetrahedral Fe(III)-S4 coordination unit with small rhombic distortions and all Fe-S bond distances in the range 2.252-2.279 A. Its electronic properties have been partially characterized by measurement of electronic absorption, paramagnetic resonance, Mössbauer spectra, and magnetic susceptibility. The analog, as the protein, exhibits the Fe(III)/Fe(II) redox couple. These results substantiate designation of [Fe((SCH2)2C6H4)2]- as a synthetic analog of the Fe(III)(S-Cys)4 center in oxidized rubredoxin proteins. Comparison of the analog structure with that of the Clostridium pasteurianum rubredoxin active site shows that the former is substantially less distorted from idealized tetrahedral symmetry, and is considered to represent an essentially unconstrained structural model of the latter. Provided the grossly distorted tetrahedral stereochemistry of the protein site persists through final structural refinement, the analog-protein structural comparison supports an entatic state description of oxidized rubredoxin.

Biologically active phorbol ester derivatives displace [3H]phorbol-12, 13-dibutyrate from thioglycollate-elicited mouse peritoneal macrophages in a time-, temperature-, and concentration-dependent manner. Scatchard analysis revealed an apparent Kd of 54.1 nM and 8.0 X 10(5) sites/cell, indicating that these macrophages possess saturable, high-affinity phorbol ester-binding sites. These derivatives also act as chemoattractants for the macrophage at equivalent concentrations. A notable exception to this pattern is phorbol-12,13-diacetate. Phorbol-12,13-diacetate inhibits specific binding of [3H]phorbol-12,13-dibutyrate (concentration required for a 50% inhibition of the maximum specific binding of [3H]phorbol-12,13-dibutyrate, 2.6 microM) and chemotaxis to phorbol-12-myristate, 13-acetate (concentration required for a 50% inhibition of the maximum chemotactic response, 0.39 microM) while exhibiting no activity as a chemoattractant at concentrations up to 10(-5) M. The data indicate that phorbol-12,13-diacetate may be an antagonist for receptor-mediated chemotaxis to phorbol-12-myristate, 13-acetate in the macrophage.