Determination of the stability constants of mercury(II) complexes of mixed donor macrobicyclic encapsulating ligands

The reactions of mercury(II) with the mixed donor encapsulating ligands 3,6,16-trithia-6,11,19-triazabicyclo[6.6.6]icosane (AMN(3)S(3)sar) and 1-amino-8-methyl-6,19-dithia-3,10,13,16-tetraazabicyclo[6.6.6]icosane (AMN(4)S(2)sar) have been studied. NMR ligand-ligand competition experiments with the ligands 1,4,8,11-tetraazaeyclotetradecane ([14]aneN(4)), 1-thia-4,7,10-triazacyclododecane ([12]aneN(3)S) and ethylenediaminetetraacetic acid (EDTA) with AMN(3)S(3)sar and Hg(II) indicated that [14]aneN(4) would be an appropriate competing ligand for the, determination of the Hg(II) stability constant. Calculations indicated the ratio of concentrations of AMN3S3sar, [14]aneN(4) and Hg(II) required for the determination of the stability constant ranged from 1:1:1 to 1:5:1. Refinement of the titration curves yielded log(10)K[Hg(AMN(3)S(3)sar)](2+) = 17.7. A similar competition titration resulted in the determination of the stability constant for the AMN(4)S(2)sar system as log(10)K[Hg(AMN(4)S(2)sar)](2+) = 19.5. The observed binding constants for the mixed N/S donor systems and the hexaaza analogues sar (3,6,10,13,16,19-hexaazabicyclo [6.6.6]icosane) and diamsar (1,8-diamino-3,6,10,13,16,19 -hexazabicyclo [6.6.6] icosane (log(10)K-[Hg(diamsar)](2+) = 26.4; log(10)K[Hg(sar)](2+) = 28.1) differ by approximately ten orders of magnitude. The difference is ascribed not to a cryptate effect but to a mismatch in the Hg-N and Hg-S bond lengths in the N/S systems.

Removal of a cysteine ligand from rubredoxin: assembly of Fe2S2 and Fe(S-Cys)(3)(OH) centres

The electron transfer protein rubredoxin from Clostridium pasteurianum contains an Fe(S-Cys)(4) active site. Mutant proteins C9G, C9A, C42G and C42A, in which cysteine ligands are replaced by non-ligating Gly or Ala residues, have been expressed in Escherichia coli. The C42A protein expresses with a (Fe2S2)-S-III cluster in place. In contrast, the other proteins are isolated in colourless forms, although a (Fe2S2)-S-III cluster may be assembled in the C42G protein via incubation with Fe-III and sulfide. The four mutant proteins were isolated as stable mononuclear Hg-II forms which were converted to unstable mononuclear Fe-III preparations that contain both holo and apo protein. The Fe-III systems were characterized by metal analysis and mass spectrometry and by electronic, electron paramagnetic resonance, X-ray absorption and resonance Raman spectroscopies. The dominant Fe-III form in the C9A preparation is a Fe(S-Cys)(3)(OH) centre, similar to that observed previously in the C6S mutant protein. Related centres are present in the proteins NifU and IscU responsible for assembly and repair of iron-sulfur clusters in both prokaryotic and eukaryotic cells. In addition to Fe(S-Cys)(3)(OH) centres, the C9G, C42G and C42A preparations contain a second four-coordinate Fe-III form in which a ligand appears to be supplied by the protein chain. Electronic supplementary material to this paper can be obtained by using the Springer Link server located at http://dx.doi.org/10.1007/s00775-0020355-1.

Modulation of cytochrome P450 monooxygenase by cadmium chloride in the mouse liver: Involvement of transcription factor Nrf2.

Modulation of the cytochrome P450 (CYP) monooxygenase system and haem oxygenase by cadmium was investigated in male, adult DBA/2J mice treated with a single dose (16 Amol/kg body weight, i.p.) of cadmium chloride (CdCl2), at various time points. Total CYP content of liver microsomes decreased significantly (P < 0.05) at 12, 18, and 24 hours (22%, 47%, and 56%, respectively) after treatment. In contrast, progressive increases of hepatic coumarin 7-hydroxylase (COH) activity (indicative of CYP2A5 activity) were observed at 8 hrs (2-fold), 12 hrs (3-fold), and 7-fold at 18 and 24 hrs. Simultaneously, haem oxygenase activity increased significantly at 4 hours and continued to increase progressively to more than 50-fold compared to control. Liver CYP2A5 mRNA levels increased maximally 12 hours after treatment and decreased to almost half 6 hours later, while western blot analysis showed 2- and 3- fold increase in CYP2A5 apoprotein at 12 and 24 hours. The CYP2A5 mRNA levels in the liver increased after Cd treatment in Nrf2 +/+ but not in Nrf2 / mouse. This study demonstrates that hepatic haem oxygenase and CYP2A5 are upregulated by cadmium. The upregulation of haem oxygenase precedes that of CYP2A5. The strong upregulation of the CYP2A5 both at mRNA and enzyme activity levels, with a simultaneous decrease in the total CYP concentration suggest an unusual mode of regulation of CYP2A5 in response to cadmium exposure, amongst the CYP enzymes. The observed increase in the mRNA but not in protein levels after maximal induction may suggest involvement of post-transcriptional mechanisms in the regulation. Upregulation of CYP2A5 by cadmium in the Nrf2 +/+ mice but not in the Nrf2 / mice indicates a role for this transcription factor in the regulation.

The relationship between prepulse inhibition and perceived intensity of the blink-eliciting stimulus: Stimulus intensity and lead interval effects

The hypothesis that prepulse inhibition of the blink reflex reflects a transient process that protects preattentive processing of the prepulse was investigated. Participants were presented with pairs of blink-eliciting noises, with some noises preceded by a prepulse, and were asked to rate the intensity of the second noise relative to the first. Inhibition of blink amplitude was greater for a 110 dB(A) noise than for a 95 dB(A) noise with a 120 ms lead interval, whereas there was no difference with a 30 ms lead interval. The reduction in perceived intensity was greater for the 110 dB(A) noise than for the 95 dB(A) noise with the 120 ms lead interval, but not with the 30 ms lead interval. The parallel results support an association between prepulse inhibition and perceived intensity. However, the prepulse did not reduce intensity ratings relative to control trials in some conditions, suggesting that prepulse inhibition is not always associated with an attenuation of the impact of the blink-eliciting stimulus.

High speed versus conventional grinding in high removal rate machining of alumina and alumina-titania

High removal rate (up to 16.6 mm(3)/s per mm) grinding of alumina and alumina-titania was investigated with respect to material removal and basic grinding parameters using a resin-bond 160 mu m grit diamond wheel at the speeds of 40 and 160 m/s, respectively. The results show that the material removal for the single-phase polycrystalline alumina and the two-phase alumina-titania composite revealed identical mechanisms of microfracture and grain dislodgement under the grinding conditioned selected. There were no distinct differences in surface roughness and morphology for both materials ground at either conventional or high speed. An increase in material removal rate did not necessarily worsen the surface toughness for the two materials at both speeds. Also the grinding forces for the two ceramics demonstrated similar characteristics at any grinding speeds and specific removal rates. Both normal and tangential grinding forces and their force ratios at the high speed were lower than those at the conventional speed, regardless of removal rates. An increase in specific removal rate caused more rapid increases in normal and tangential forces obtained at the conventional grinding speed than those at the high speed. Furthermore, it is found that the high speed grinding at all the removal rates exerted a great amount of coolant-induced normal forces in grinding zone, which were 4-6 times higher than the pure normal grinding forces. (c) 2004 Elsevier Ltd. All rights reserved.

Thermal analysis, nuclear magnetic resonance spectroscopy, and impedance spectroscopy of N,N-dimethyl-pyrrolidinium iodide: An ionic solid exhibiting rotator phases

N,N-dimethyl-pyrrolidinium iodide has been investigated using differential scanning calorimetry, nuclear magnetic resonance (NMR) spectroscopy, second moment calculations, and impedance spectroscopy. This pyrrolidinium salt exhibits two solid-solid phase transitions, one at 373 K having an entropy change, Delta S, of 38 J mol(-1) K-1 and one at 478 K having Delta S of 5.7 J mol(-1) K-1. The second moment calculations relate the lower temperature transition to a homogenization of the sample in terms of the mobility of the cations, while the high temperature phase transition is within the temperature region of isotropic tumbling of the cations. At higher temperatures a further decrease in the H-1 NMR linewidth is observed which is suggested to be due to diffusion of the cations. (C) 2005 American Institute of Physics.

LiI-doped N,N-dimethyl-pyrrolidinium iodide, an archetypal rotator-phase ionic conductor

N,N-Dimethyl-pyrrolidinium iodide, and the effect of doping with LiI, has been investigated using DSC, NMR, and impedance spectroscopy. It was found that the addition of a small amount of LiI enhances the ionic conductivity by LIP to 3 orders of magnitude for this ionic solid. Furthermore, a slight decrease in phase transition onset temperatures, as well as the appearance of a superimposed narrow line in the H-1 NMR spectra with dopant, suggest that the LiI facilitates the mobility of the matrix material, possibly by the introduction of vacancies within the lattice. Li-7 NMR line width measurements reveal a narrow Li line width, decreasing in width and increasing in intensity with temperature, indicating mobile Li ions.

Experiments and modelling of phenanthrene biodegradation in the aqueous phase by a mixed culture

Pollution by polycyclic aromatic hydrocarbons(PAHs) is widespread due to unsuitable disposal of industrial waste. They are mostly defined as priority pollutants by environmental protection authorities worldwide. Phenanthrene, a typical PAH, was selected as the target in this paper. The PAH-degrading mixed culture, named ZM, was collected from a petroleum contaminated river bed. This culture was injected into phenanthrene solutions at different concentrations to quantify the biodegradation process. Results show near-complete removal of phenanthrene in three days of biodegradation if the initial phenanthrene concentration is low. When the initial concentration is high, the removal rate is increased but 20%-40% of the phenanthrene remains at the end of the experiment. The biomass shows a peak on the third day due to the combined effects of microbial growth and decay. Another peak is evident for cases with a high initial concentration, possibly due to production of an intermediate metabolite. The pH generally decreased during biodegradation because of the production of organic acid. Two phenomenological models were designed to simulate the phenanthrene biodegradation and biomass growth. A relatively simple model that does not consider the intermediate metabolite and its inhibition of phenanthrene biodegradation cannot fit the observed data. A modified Monod model that considered an intermediate metabolite (organic acid) and its inhibiting reversal effect reasonably depicts the experimental results.