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Described here is a titanocene‐catalyzed reaction for the synthesis of acetals and hemiaminals from benzylic ethers and benzylic amines, respectively, with pendant epoxides. The reaction proceeds by catalysis in single‐electron steps. The oxidative addition comprises an epoxide opening. An H‐atom transfer, to generate a benzylic radical, serves as a radical translocation step, and an organometallic oxygen rebound as a reductive elimination. The reaction mechanism was studied by high‐level dispersion corrected hybrid functional DFT with implicit solvation. The low‐energy conformational space was searched by the efficient CREST program. The stereoselectivity was deduced from the lowest lying benzylic radical structures and their conformations are controlled by hyperconjugative interactions and steric interactions between the titanocene catalyst and the aryl groups of the substrate. An interesting mechanistic aspect is that the oxidation of the benzylic center occurs under reducing conditions., Oxidations with reducing agents? Fact and not fiction in a reaction featuring titanocene(III) catalysis, H‐atom transfer, and an organometallic oxygen rebound. Acetals and hemiaminals can be readily prepared from benzylic ethers and amines, respectively, under mild reaction conditions and in high yields. The structures of the radical intermediates were elucidated by the CREST program.

Yeast amino acid transporters of the APC superfamily are responsible for the proton motive force‐driven uptake of amino acids into the cell, which for most secondary transporters is a reversible process. The l‐lysine proton symporter Lyp1 of Saccharomyces cerevisiae is special in that the Michaelis constant from out‐to‐in transport ( Kmout→in ) is much lower than Kmin→out , which allows accumulation of l‐lysine to submolar concentration. It has been proposed that high intracellular lysine is part of the antioxidant mechanism of the cell. The molecular basis for the unique kinetic properties of Lyp1 is unknown. We compared the sequence of Lyp1 with APC para‐ and orthologues and find structural features that set Lyp1 apart, including differences in extracellular loop regions. We screened the extracellular loops by alanine mutagenesis and determined Lyp1 localization and activity and find positions that affect either the localization or activity of Lyp1. Half of the affected mutants are located in the extension of extracellular loop 3 or in a predicted α‐helix in extracellular loop 4. Our data indicate that extracellular loops not only connect the transmembrane helices but also serve functionally important roles., We performed alanine‐scanning mutagenesis of the extracellular loops of the yeast lysine transporter Lyp1. We find positions that affect either the localization or activity of Lyp1. Half of the affected mutants are located in the extension of extracellular loop 3 or in a predicted α‐helix in extracellular loop 4. We conclude that extracellular loops of amino acid transporters of the APC superfamily serve functionally important roles.

We present a combined electrochemical, kinetic, and synthetic study with a novel and easily accessible class of titanocene catalysts for catalysis in single-electron steps. The tailoring of the electronic properties of our Cp2 TiX-catalysts that are prepared in situ from readily available Cp2 TiX2 is achieved by varying the anionic ligand X. Of the complexes investigated, Cp2 TiOMs proved to be either equal or substantially superior to the best catalysts developed earlier. The kinetic and thermodynamic properties pertinent to catalysis have been determined. They allow a mechanistic understanding of the subtle interplay of properties required for an efficient oxidative addition and reduction. Therefore, our study highlights that efficient catalysts do not require the elaborate covalent modification of the cyclopentadienyl ligands.

Although calcium (Ca) precipitation may play a pathogenic role in atherosclerosis, information on temporal patterns of microcalcifications in human coronary arteries, their relation to expression of calcification-regulating proteins, and colocalization with iron (Fe) and zinc (Zn) is scarce. Human coronary arteries were analyzed post mortem with a proton microprobe for element concentrations and stained (immuno)histochemically for morphological and calcification-regulating proteins. Microcalcifications were occasionally observed in preatheroma type I atherosclerotic intimal lesions. Their abundance increased in type II, III, and IV lesions. Moreover, their appearance preceded increased expression of calcification-regulating proteins, such as osteocalcin and bone morphogenetic protein-2. In contrast, their presence coincided with increased expression of uncarboxylated matrix Gla protein (MGP), whereas the content of carboxylated MGP was increased in type DI and IV lesions, indicating delayed posttranslational conversion of biologically inactive into active MGP. Ca/phosphorus ratios of the microcalcifications varied from 1.6 to 3.0, including amorphous Ca phosphates. Approximately 75% of microcalcifications colocalized with the accumulation of Fe and Zn. We conclude that Ca microprecipitation occurs in the early stages of atherosclerosis, inferring a pathogenic role in the sequel of events, resulting in overt atherosclerotic lesions. Microcalcifications may be caused by local events triggering the precipitation of Ca rather than by increased expression of calcification-regulating proteins. The high degree of colocalization with Fe and Zn suggests a mutual relationship between these trace elements and early deposition of Ca salts. (Ant J Pathol 2011, 178:2879-2887; DOI: 10.1016/j.ajpath.2011.02.004)

Summary Evidence is accumulating that calcium-rich microdeposits in the vascular wall might play a crucial role in the onset and progression of atherosclerosis. Here we investigated an atherosclerotic lesion of the carotid artery in an established murine model, i.e. the apolipoprotein E-deficient (APOE ) ⁄ ) ) mouse to identify (i) the presence of microcalcifications, if any, (ii) the elemental composition of microcalcifications with special reference to calcium ⁄ phosphorus mass ratio and (iii) co-localization of increased concentrations of iron and zinc with microcalcifications. Atherosclerosis was induced by a flow-divider placed around the carotid artery resulting in low and high shear-stress regions. Element composition was assessed with a proton microprobe. Microcalcifications, predominantly present in the thickened intima of the low shear-stress region, were surrounded by areas with normal calcium levels, indicating that calcium-precipitation is a local event. The diameter of intimal microcalcifications varied from 6 to 70 lm. Calcium ⁄ phosphorus ratios of microcalcifications varied from 0.3 to 4.8, mainly corresponding to the ratio of amorphous calciumphosphate. Increased iron and zinc concentrations commonly co-localized with microcalcifications. Our findings indicate that the atherosclerotic process in the murine carotid artery is associated with locally accumulated calcium, iron and zinc. The calcium-rich deposits resemble amorphous calcium phosphate rather than pure hydroxyapatite. We propose that the APOE ) ⁄ ) mouse, in which atherosclerosis was evoked by a flow-divider, offers a useful model to investigate the pathophysiological significance of accumulation of elements such as calcium, iron and zinc.

Human coronary arteries in both early and advanced stages of atherosclerosis were studied for understanding the nature of Ca deposits in terms of their Ca/P mass ratio with the use of Eindhoven nuclear microprobe. The ratios observed differed appreciably from that of hydroxyapatite (2.15), which is commonly referred to as the Ca component in arteries affected by atherosclerosis. Very small granular calcified structures were found in an early stage. Broadly, two types of calcified structures were observed: the Ca/P ratio corresponding to the advanced stage (3.18) was found higher compared to those for the early stage (1.46–1.77). It has been argued that besides phosphates, the large Ca/P ratio corresponding to intense calcification may be due to a Ca deposit with a different anion (oxalate, hydroxide or even carbonate), while, the lower ratios may be due to an additional inorganic phosphate. The distribution of S/P ratios was used to account for enhanced deposition of lipid materials in the affected area at the expense of proteins.

The current paradigm reads that calcifications characterize the advanced and complex lesions in the atherosclerotic process. To explore the possibility that coronary artery wall calcifications already commence at an early stage of atherosclerosis, a combination of proton beam techniques with a (sub-) micrometer resolution, i.e., micro-proton induced X-ray emission, backward and forward scattering spectroscopy, was applied on human coronary arteries with lesions preceding overt atheromas. The detection limits of phosphorus and calcium in each separate pixel, 0.88*0.88 microm2 in size, were approximately 150 and 80 microg/g dry weight, respectively. Calcium distributions of entire coronary artery cross section were obtained, and calcifications were demonstrated at a preatheroma stage of the atherosclerotic process. The size of the microcalcifications varied between 1 and 10 microm. The composition of the microcalcifications was deduced from the calcium-to-phosphorus ratio. In order to quantify this ratio, the thickness of the specific X-ray absorber used for PIXE had to be accurately determined. Also, thick target PIXE calculations were performed and the method was validated. The calcium-to-phosphorus ratios of the microcalcifications were assessed with good accuracy and varied from 1.62 to 2.79, which corresponds with amorphous calcium phosphate.

Principal component analysis was applied to identify normal and pathological structures using combinations of levels of phosphorus, sulphur, chlorine, potassium and calcium in early stages of atherosclerotic coronary arteries. An inverse correlation was found between the combination of Ca–P, and that of S–Cl–K. This finding points towards the presence of smaller calcified deposits in an early phase of atherosclerosis in the human coronary artery. A possible location of cholesterol or some other carbon-based materials could also be identified. Further, a histogram method proved to be useful for characterising calcified structures of Ca/P mass ratio lower than that of hydroxyapatite. An empirical formula of (1− n )Ca 3 (PO 4 ) 2 · n A m (PO 4 ) is suggested to explain composition of these calcified structures.

Large Plexiglas columns were used to evaluate the changes in the forms and amounts of nitrogen in the bottom waters and sediments of three freshwater lakes during stratified (anoxic) and turnover (aerated) conditions. Sampling ports and permanently placed black Pt electrodes were installed so that water and sediment phases could be monitored. Sediment lZh declined rapidly to -150 to -250 mV and remained at this level irrespective of the oxygen concentration in the overlying water. During anoxic conditions, NHa-N was released to the water at a relatively constant rate. Aeration affected rapid nitrification. Nitrate in the overlying water decreased with time, possibly due to diffusion into the highly reduced sediment and subsequent denitrification. Lake sediments can significantly affect the nutrient concentrations of the overlying waters (Foess and Feng 1971). One factor that affects the transformation and exchange of nutrients at the sediment-water interface is the redox potential of the sediment-water system (Mortimer 1941, 1942; Hutchinson 1957; Gorham 1958; Gorham and Swaine 1965; Lee 1970a). The potential measured with an inert clcctrodc (Eh) is often used as a qualitative measure of redox conditions in natural systems even though it defies quantitative interpretation due to the complexity of these systems. Whitficld ( 1969), Bohn ( 1968, 1971), Morris and Stumm ( 1967) and Garrels and Christ (1965) have reviewed the problems and limitations of measurement and interpretation of the Eh status of natural systems. Some of these stem from the performance of the inert metal electrodes while others are associated with the complexity of natural systems. Natural systems are inherently dynamic and thus no true equilibrium potential can be measured l Supported by the College of Agricultural and Life Sciences, University of Wisconsin and by Environmental Protection Agency Grant 16010 EHR, K. L. Chen assisted with laboratory analyses. 2 Present address : Soils Department, University of Florida, Gainesville 32601. 3 Present address: Department of Soil Science, University of the Philippines, Los Banos Units, College, Laguna, The Philippines. ( Whi tficld 1969 ) , although steady states may be approximated. Also microenvironments bearing no relationship to the total environment may be measured, while in some instances highly reversible redox reactions having no general significance to the chemistry of the environment may be responsible for the Eh level (Whitfield 1969). Despite these limitations, Eh values measured with inert metal electrodes may be utilized as a qualitative measure of the intensity of redox conditions in the environment (Whitfield 1969; van DcrWeijden et al. 1970; Bohn 1971). Most of the redox reactions in soils and aquatic environs are biologically mediated. Under aerobic conditions molecular oxygen serves as the electron acceptor in microbial metabolism while the electron donor is organic C for heterotrophs or reduced inorganic compounds for autotrophs. Eh is relatively insensitive to dissolved oxygen and remains nearly constant down to values of 0.1% saturation (Greenwood 1962). When dissolved oxygen is depleted, alternate electron acceptors are utilized. This stage generally corresponds to an Eh of +300 to +350 mV (Turner and Patrick 1968) and involves, initially, facultative microorganisms. Several redox systems may bc operating in these first stages of anaerobic respiration. However, it is generally bclicvcd that, if present, NOs is the first electron acceptor following depletion of LIMNOLOGY AND OCEANOGRAPHY 908 NOVEMBER 1973, V. 18(6) ?7 L 1;fl. ANlJ NllllUbLN ’ I-m ---““‘T TRANSFORMATIONS dissolved oxygen. Nitrate stabilizes the Eh at about +200 to +lOO mV (Redman and Patrick 1965; Bell 1969; Bailey and Beauchamp 1971). Manganese and Fe follow NO3 as electron acceptors. Reduction of SO.*“to S2occurs after Fe reduction and begins at about 0 to -150 mV (Parr 1969) ; this is the start of the second stage of anaerobic digestion and involves obligate anaerobes. Below -150 mV, H+ and CO2 are reduced forming Ha and CHZi. The H2 system appears to be the terminal system in reduced soils (Ponnamperuma et al. 1966 ) . The nitrogen budget of a lake may bc significantly affected by the Eh status of the sediments and the scdimcnt-water interface. Sediment organic nitrogen can act as a source of inorganic nitrogen to the lake water through ammonification. Byrncs et al. (1972) have shown that sediment NH4 (interstitial and exchangeable) rapidly reaches equilibrium with the overlying water and that much of the NH4 mineralizcd from decaying organic matter in the sediment is soon returned to the overlying water. If the lake water contained oxygen it is likely that the NH4 would be rapidly converted to NO3 as it moved out of the anaerobic sediment ( Chen et al. 1972b), particularly in alkaline lakes where the pH is favorable for nitrification. This might then actually result in a loss of nitrogen from the lake as some of this NO3 would likely diffuse back into the anaerobic scdimcnt and bc denitrified (Chen et al. 1972c; Mortimcr 1941). It is not known how much of the NO3 might diffuse into the sediment but the fate of that which does can bc postulated from the work of Chen et al. ( 1972a), in which nitrate ( 15N labeled) added to Wisconsin lake sediment samples disappeared within 4 days: 37 s of the added NO3 was immobilized and 63% was denitrified and lost from the system, It was also shown that the newly immobilized nitrogen was subject to rapid mineralization. Detailed discussion of nitrogen transformations in the aquatic environment can bc found in Kecney ( 1973) and Brezo

Coconut water (CW) was obtained from matured nuts and used as culture medium for rhizobial isolates C11, C4 from Centrosema pubescens; L15, L5 from Leucaena leucocephala; M5, M4 from Vigna radiata (mungbean); P7, P3 from Arachis hypogaea (peanut) and S38, S13 from Glycine max (soybean). Growth responses of these isolates in CW media, yeast extract mannitol broth (YEMB) and basal medium (BM) were determined after 4 days incubation at 30°C. The CW media were: aseptically collected CW (aseptic CW), original pH 5.4, aseptic CW, adjusted pH 7; sterilized CW (121°C at 15 psi for 18 min), pH 5.4, sterilized CW, pH 7.0; CW + NH4C1 (50 mg/ 100 ml), pH 5.2; and CW + K2HP04 (100 mg/100 ml), pH 6.0. Growth responses were rated according to optical density at 420 nm as follows: >1.0 = 4; 0.7 to 0.9 = 3; 0.4 to 0.6 = 2; 0.1 to 0.3 = 1