Technetium nitrido complexes with amine and thiolate ligands: structural characterizations of nitridobis(1,1,2,2-tetramethylguanidine)bis(2,3,5,6-tetramethylbenzenethiolato)technetium, a complex with coordinatively bound 1,1,2,2-tetramethylguanidine

Abstract

facile accretion.34 Cd(II) complexes with yEC peptides longer than = 4 are predicted to be less effective in nucleating CdS crystallite formation perhaps by virtue of enhanced stability of Cd-cysteinyl thiolate clusters. The importance of sulfide in metal detoxification is highlighted by the isolation of sulfide-deficient S. pombe mutants that exhibit cadmium hypersensitivity.15The increased stability of S. pombe CdS crystallites does not imply that 5. pombe is more resistant to cadmium salts than C.glabrata. The yeast C. glabrata is highly resistant to toxicity of cadmium salts. Formation of CdS crystallites is only one cellular detoxification mechanism in this organism. The other mechanisms have not been elucidated.The crystallites exhibit properties analogous to those of semiconductor clusters. The yeast CdS particles are quantum crystallites that luminesce and mediate electron transfer to methyl viologen. The latter two properties are attributed to the localization of excited electrons on the surface of the particles.31 Luminescence in synthetic CdS semiconductor clusters is attributed to the recombination of a photogenerated electron and an existing hole.28 The electronic state of the electron is not apparent in the absorption spectrum.28 Luminescence correlates with particle size and is influenced by surface adsorbed cations. Cations are known (34) Dameron, C. T.; Winge, D. R. J. Biol. Chem., in press.to quenched the luminescence of synthetic colloidal CdS.30 The effect is attributed to electron scavenging at the surface of the particles. Electrons are also scavenged by methyl viologen at the surface. Under anaerobic conditions, the reduced dye is stable against facile oxidation, but a significant back-reaction occurs that is attributed to reoxidation of the dye by trapped holes (h+) in the particle.30 The presence of hole scavengers has been shown to inhibit this route of oxidation in some but not all studies.35•36 Crystallites formed in vitro with yEC peptides exhibit corresponding excited electronic state properties.The effectiveness of 7EC peptides in stabilizing discrete sizes of CdS crystallites either in vivo or in vitro may enable the peptides to be used as a matrix for other types of mineralization where discrete particle size is desired. As metal-sulfide clusters are used as photosensitizing and catalytic agents,30•37 discrete sizes of these quantum particles may yield more predictable properties. Presently, synthetic semiconductor clusters are typically coated with nonspecific organic polymers, leading to a wide spectrum of particle sizes.

Amidine and guanidine complexes of manganese and molybdenum. Crystal structures of (η-cyclopentadienyl)(N,N′-diphenylguanidino)- and (η-cyclopentadienyl)(N,N′,N ″-triphenylguanidino)-dicarbonylmolybdenum(II)

“…The first complexes of transition metals (Co, Cu, Zn, Pd and Ni) with 1,1,3,3tetramethylguanidine (tmg) were reported long ago 5 and the monodentate two-electron co-ordination of tmg through the imine nitrogen atom was postulated on the basis of the IR spectra. Such co-ordination was later confirmed by X-ray diffraction studies in the complexes of Tc with tmg 4 and of Pt with HN᎐ ᎐ C(NEt 2 ) 2 . 6 Of the substituted guanidines, cyanoguanidine recently became popular as a ligand, capable of terminal, bridging and chelating co-ordination.…”

“…We suppose that the guanidine ligands are co-ordinated via the imino nitrogen atom, as has been observed earlier. 4,6 The stereochemical configurations of 5 and 6 were assigned on the basis of the intensities and pattern of the ν(CO) stretching frequencies (see Table 1) and there was no evidence for isomerisation of the fac into the mer isomer of 6, as occurs for bulkier ligands such as triphenylphosphine. 16 The ν(CN) stretching frequencies of the guanidine ligands remain virtually the same as those for the free guanidines and their complexes with other Lewis acids.…”

“…amidine derivatives with an amino-substituent RЈ, seem even more promising, being stronger electron donors than amidines 3 and apparently possessing all the co-ordination possibilities of the latter plus another potential co-ordination centre in the form of the third nitrogen atom. On the other hand, it was supposed 4 that electron delocalisation over the N 3 C moiety should actually impair the co-ordinating ability of the nitrogen atoms by making their lone pairs more diffuse. The first complexes of transition metals (Co, Cu, Zn, Pd and Ni) with 1,1,3,3tetramethylguanidine (tmg) were reported long ago 5 and the monodentate two-electron co-ordination of tmg through the imine nitrogen atom was postulated on the basis of the IR spectra.…”

Contribution of electrospray mass spectrometry for the characterization, design, and development of nitrido technetium and rhenium heterocomplexes as potential radiopharmaceuticals

“…The characterization of radioactive technetium compounds by mass spectrometry (mainly via fast atom bombardment-FABMS or field desorption-FDMS techniques) has been the subject of very few investigation in the past (de Vries et al, 1990;Kronauge et al, 1991) probably because of radiation safety restrictions to prevent contamination. However, the use of more recent, soft and sensitive ESI-MS techniques allow the use of micromoles of radioactive material, thereby achieving unambiguous molecular identification without contamination of the mass apparatus and without producing radioactive wastes.…”

Synthesis and Characterization of Bis(β-diketonato)nitridotechnetium(V) Complexes

“…Starting materials for this purpose are frequently the readily accessible nitrido complexes AsPh4[TcNCl4] with C4 symmetry of the TcNCl^ anion or TcNCl2(PPh3)2 with a planar-pyramidal geometry at the technetium atom and a trans arrangement of the phosphine ligands. Examples are: reactions of the Solution of TcNClJ with dithiooxalate (dto), 2,3,5,6-tetramethylbenzenethiolate (tmbt) in the presence of pyridine, maleonitriledithiolate (mnt) or 8-quinolinethiol to yield [TcN(dto)2]^~ [3], TcN(tmbt)2(py)2 [4], [TcN(mnt)2]^- [5] or [TcN-(C9H6NS)2] [6], respectively; reactions of TCNCI2-(PPh3)2 with ethylenediamine (en), diaminedithiol (L) of the type HSCR2CH2NR'CH2CH2NR'CH2-CR2SH (R = Me or Et), or 1,4,8,11-tetraazacyclotetradecane (cyclam) to yield [TcN(en)2Cl] [7], [TcN(L)] [8] or [TcN(cyclam)Cl]+ [9], respectively. Further the reaction of TCOCI4 with dto, tmbt mnt, 8-quinolinol, en, diaminedithiol (L), or cyclam has been reported to give [TcO(dto)2]" [3], TcO(tmbt)3(py) [10], [TcO(mnt)2]- [11], [TcO(C9H6NO)2Cl] [12], [Tc02(en)2]^ [13], [TcO(L)]+ [8], or [Tc02(cyclam)] + [14], respectively.…”