MonodentateN coordination of 1aza4oxo1,3butadienes [R1NC(R2)C(R3)O] to platinum(II). X-ray structure of trans-[PtCl2(PEt3){σ-N-(t-BuNCHC(Me)O)}]

Reaction of dimeric trans-[PtCl₂(PR₃)]₂ with 1-aza-4-oxo-1,3-butadienes [R¹NC(R²)C(R³)O, R³ = Me, Ph, OMe, NEt₂] in a 1:2 molar ratio results in almost quantitative formation of mononuclear complexes trans·[PtCl₂(PR₃){σ-N-(R¹NC(R²)C(R³)O)}]. The ligands are bonded in the monodentate σ-N bonding mode to the platinum(II) centre. This has been established by an X-ray structure determination of trans-[PtCl₂(PEt₃){σ-N-(t-BuNCHC(Me)O)}]. Crystals of the latter compound are orthorhombic with space group Pc2₁n; cell constants are a = 14.712(3), b = 15.053(2), c = 9.025(5) Å, Z= 4 and R_w = 0.056 for 3281 reflections. The 1aza4oxol,3butadiene (α-iminoketone for R³ is alkyl or aryl) has the E-configuration about the imine bond (CN 1.34(4) Å), with a C(5)C(6) distance of 1.44(5) Å and a NC(5)/ C(6)O torsion angle of 89(4)°. As a result of this ligand conformation, the acetyl hydrogen atoms are positioned (on average) into the neighbourhood of the Pt-atom above the Pt-coordination plane. Infrared and NMR (¹H, ¹³C, ³¹p) data show that these structural features are also predominant in solution.     

Nucleophilic addition and various species formed in the Cu(II)NCO−3(5)-methylpyrazole system

From the Cu(II)NCO⁻3(5)-methylpyrazole (mpz) system two compounds Cu(NCO)₂(mpz)₂ and four compounds Cu(mpz·NCO)₂ were isolated. The latter compounds contain carbamoylmethylpyrazolate anions as chelate ligands and are coligand isomers of the cyanate compounds. According to the results of indirect structural methods, the Cu(NCO)₂(mpz)₂ complexes have pseudooctahedral structures and differ in their polyhedron distortions. The Cu(mpz·NCO)₂ complexes show tetragonally distorted six or five coordinate structures, possibly differing also by the methyl group position on the pyrazole ring.     

Reactions of thiols and selenols with the FeMoS cluster [Fe(MoS4)2]3−

The known complex [Et₄N]₃[Fe(MoS₄)₂] has been shown by EPR and visible spectral studies to react with both thiophenol and selenophenol. The reaction results in a change in the characteristic S=3/2 EPR spectrum of this species from a complex rhombic pattern to one of a very simple axial appearance. Although this effect is similar to that observed for reaction of these species with the iron- molybdenum cofactor of nitrogenase, a moiety known to consist of a FeMoS cluster species, the large excesses of reagents and the long reaction times required for complete formation of product indicate that these reactions are of questionable direct relevance to the biological system. The reaction corresponding to the EPR spectral change from rhombic to axial in the [Fe(MoS₄)₂]³⁻/PhSeH system has also been partially characterized by product isolation which indicates that attack by selenol of the two terminal MoS₂ moieties in the starting material has occurred.     

STM of freeze-dried and PtIrC-coated bacteriophage T4 polyheads

STM imaging was carried out on the outer surface of bacteriophage T4 type III polyheads, after freeze-drying and coating with a thin conducting film. By taking advantage of the high resolution power of the STM especially in the z-direction (i.e., perpendicular to the support), an apparent surface topography of only about 1 nm height was resolved. The average capsomere morphology was determined by correlation averaging. Because of the high signal-to-noise ratio of the tunneling data, only a few unit cells were needed to reveal a stable average. Both the topology as well as the absolute height of the polyheads have been reproduced in several experiments. The influence of the tip geometry on the STM topographs is discussed.     

Fabrication and biocompatibility of a porous bioglass ceramic in a Na2OCaOSiO2P2O5 system

A porous bioglass ceramic was prepared from a finely pulverized bioglass powder mixed with particles of two sizes (5 and 500 μm) of 30% by weight with the foaming agent polyethylene glycol 4000 (HO (C₂H₄O) nH). The batch composition of the bioglass was Na₂O 12%, CaO 28%, SiO₂ 50% and P₂O₅ 10% by weight. The specimens, formed by pressing, were sintered in a high temperature furnace. In this study we are concerned with the preparation and microstructure of the material and its performance in biological tests. The microstructure and crystalline phases of the material were investigated by differential thermal analysis, X-ray diffraction analysis, transmission electron microscopy and scanning electron microscopy. In a biomedical examination, it was shown that the porous material was compatible with animal tissues. The microstructure of the implant indicated that newly grown bone interlocked well with the glass ceramic and that macropores and micropores were distributed uniformly in the material, which provided channels for bone ingrowth and improved the microscopic bioresorption.     

Synthesis,characterization and study of the PtPt interaction in cis-[(aa)(bb)FCrNCPt(CN)3] (aa,bb=bidentate amine)

Two new dinuclear μ-cyano complexes, cis-[(en)(tn)FCrNCPt(CN)₃] and cis-[(chxn)(tn)FCrNCPt(CN)₃] en=ethylenediamine, tn=1,3-diaminepropane and chxn=1,2-cyclohexanediamine) have been obtained by solid state heating of the trans[Cr(aa)(bb)F(H₂O)][Pt(CN)₄] salts. These complexes have been characterized by chemical analysis, electronic and IR spectra. The dinuclear complexes show strong PtPt interaction both in the solid state and in solution. The association constant of the oligomers formed has been calculated and correlated with the size of the amine ligands. An orbital explanation is proposed to account for the enhancement of the PtPt interaction in the dinuclear complexes relative to the complex salts.     

Concentration of 3-Methylindole (3MI) and distribution of radioactivity from 14C3MI in goat tissues associated with acute pulmonary edema

3-Methylindole (3MI) can cause acute pulmonary edema in goats. Because of known lipophilic properties and direct effects on biological membranes, the concentration of 3MI and distribution of radioactivity from ¹⁴C3MI in tissues was investigated during development of 3MI-induced APE. Goats were given a 2 hr jugular infusion of 3MI containing ¹⁴C3MI using propylene glycol as the vehicle. Groups of 3 goats were killed at 0, .5, 2 and 4 hr and 2 goats were killed at 8 and 24 hr. Plasma, lung, liver, kidney and other selected tissues were collected. 3MI was rapidly cleared from blood plasma and tissues after infusion, and 81% of the radioactivity was excreted in the urine by 24 hr. Maximum concentrations of unmetabolized 3MI in the tissues ranged from 2.6 to 15 μg 3MI/g, including 7.5 μg 3MI/g in the lung. The ratios of equivalent radioactivity to unmetabolized 3MI indicated rapid metabolism and the presence of metabolites in all tissues studied. The lung contained the highest proportion of metabolites with ratios of radioactivity to unmetabolized 3MI of about 50, 10, 250, 150 and 80 at 0.5, 2, 4, 8 and 24 hr. The data demonstrate that 3MI does not selectively concentrate in the lung and that the concentrations are lower than those usually associated with direct membrane damage. They also indicate that 3MI is rapidly metabolized and that metabolites are present in tissues, especially the lung. These results suggest that direct effects of 3MI on biological membranes are not primarily responsible for lung injury in goats.     

Mössbauer studies of ferrihemequinidine complexes

The system ferriprotoporphyrin IX-(+)-quinidine (FPQd) was investigated by Mössbauer spectroscopy at both 4.1 and 90 K. FPQd complexes were prepared by interaction of 10⁻² to 10⁻³ M aqueous solutions of the components at pH 11–12 and 26 °C. Previous investigations of analogous complexes showed characteristic and unusually large circular dichroism bands near 400 nm at alkaline pH values. The present Mössbauer data obtained for FP either in the presence or absence of Qd at both pH 11–12 and 9 indicate identical isomeric shifts in all cases. Both free and complexed FP iron is in a high-spin state. The temperature dependence of the FPQd complex indicates slow spin-spin relaxation at 90 K and fast relaxation at 4.1 K. Qd appears to increase the iron-iron distance of FP in the complexes with references to FP alone, in agreement with previous suggestions on the structure of the complex.     

Phototautomerism of the GC base pair of DNA

Electronic spectra and ground and excited state electronic structures of normal G and rare tautomeric G1z.sbnd;C1 base pairs as well as of the individual rare tautomeric bases (purines and pyrimidines) have been studied using the VE-PPP molecular orbital method. The nature and consequences of the lowest energy purine-localized and purine to pyrimidine charge transfer type π?π1 singlet excitations of the base pairs have been investigated. The results indicate that in these excited states, particularly in the charge transfer excited state, the probability for the GC base pair to change over to G1C1 would be larger than in the ground state. The likeliness of the relevance of results obtained experimentally by other workers from the study of a model system to the GC base pair is discussed.     

NaK-dependent conformation change of proteins of excitable membranes

The K⁺, Na⁺ and Ca²⁺ form of excitable membranes of rat brain were investigated by infrared, ORD and CD spectroscopy. It is shown that with the K⁺ form the conformatio of relatively large parts of the membrane proteins occurs as an antiparallel β structure. No β structure is found with the Na⁺ and Ca²⁺ form. In the presence of these ions the proteins are largely helical. This suggests that during the action potential, membrane proteins change their conformation depending on the cations shifted.     

CO2 donation by malate and aspartate reduces photorespiration in Panicum milioides,A C3C4 intermediate species

Oxygen inhibition of leaf slice photosynthesis in Panicum milioides increased from 20% to 30% at 21% O₂ in the presence of maleate, a phosphoenolpyruvate carboxylase inhibitor. The increased O₂ sensitivity was completely reversed by the addition of malate and aspartate, the stable products of the phosphoenolpyruvate carboxylase reaction. The C₄ acids, malate and aspartate, also reduced O₂ inhibition of photosynthesis by isolated bundle sheath strands, but not mesophyll protoplasts. Similarly, only bundle sheath strands exhibited an active C₄ acid-dependent O₂ evolution. Compartmentation of C₄ cycle enzymes, with pyruvate, Pi dikinase in the mesophyll and NAD-malic enzyme in the bundle sheath, was demonstrated. It is concluded that reduced photorespiration in P. milioides is due to a limited potential for C₄ photosynthesis permitting an increase in pCO₂ at the site of bundle sheath ribulosebisphosphate carboxylase.