Reply to the comment of Chudnovsky&Garanin on "Spin relaxation in Mn12-acetate"

Reply to the comment of E.M. Chudnovsky and D.A. Garanin on Europhys. Lett. 46, 692 (1999).Comment: 2 pages, Latex (europhys.sty

Berry-phase blockade in single-molecule magnets

We formulate the problem of electron transport through a single-molecule magnet (SMM) in the Coulomb blockade regime taking into account topological interference effects for the tunneling of the large spin of a SMM. The interference originates from spin Berry phases associated with different tunneling paths. We show that in the case of incoherent spin states it is essential to place the SMM between oppositely spin-polarized source and drain leads in order to detect the spin tunneling in the stationary current, which exhibits topological zeros as a function of the transverse magnetic field.Comment: 4 pages, Revtex 4, 4 EPS figure

Spin relaxation in Mn12-acetate

We present a comprehensive derivation of the magnetization relaxation in a Mn12-acetate crystal based on thermally assisted spin tunneling induced by quartic anisotropy and weak transverse magnetic fields. The overall relaxation rate as function of the magnetic field is calculated and shown to agree well with data including all resonance peaks. The Lorentzian shape of the resonances is also in good agreement with recent data. A generalized master equation including resonances is derived and solved exactly. It is shown that many transition paths with comparable weight exist that contribute to the relaxation process. Previously unknown spin-phonon coupling constants are calculated explicitly.Comment: 4 pages,4 EPS figures,LaTeX(europhys.sty);final version accepted for EP

Synthesis and Metabolism of Drugs by Means of Enzyme-Catalysed Reactions

The usefulness of enzyme catalysed-reactions is exemplified by recent results from research at Roche.Sequences of enzyme reactions, well organised in metabolic pathways of selected microorganisms, lead to secondary metabolites with innovative chemical structures. An example is the pancreas-lipase inhibitor lipstatin produced by Streptomyces toxytricini. Hydrogenation of lipstatin yields tetrahydrolipstatin, the active substance of the anti-obesity drug Xenical™. The biosynthetic pathway has been elucidated and an improved fermentation process for the production of lipstatin has been developed.Intermediates of the primary metabolism can be valuable building blocks for the chemical synthesis of drugs. Examples are quinic acid and shikimic acid, which are both suitable starting materials for the synthesis of the neuraminidase inhibitor GS 4104. Metabolic engineering of Escherichia coli with the goal to overproduce these two substances is briefly described.Microorganisms or enzymes derived thereof are used in drug synthesis to catalyse single, highly specific reaction steps (biotransformations). Three examples yielding chiral precursors of a protein-kinase inhibitor, a collagenase inhibitor, and an antifungal compound are discussed.Recombinant Escherichia coli strains expressing human drug-metabolising enzymes are suited to mimic drug metabolism and to produce intermediates of human drug metabolism. The desired hydroxylated drug derivatives could be obtained after incubation of drug substances with strains coexpressing one specific human cytochrome P450 isozyme together with human reductase

Toxic effects of estradiol E2 on development in the European tree frog (Hyla arborea)

Estrogenic hormones are a major environmental threat to aquatic wildlife. Here we report chronic toxic effects of exposure to the naturally excreted estrogen, 17β-estradiol (E2), on the larval and subadult development of the European tree frog (Hyla arborea), by an experimental setting and long-term monitoring. In addition to the documented impact on sexual development and mating behavior, the general toxicity of human-released estrogens may contribute to global amphibian declines

Thyroid hormones, blood plasma metabolites and haematological parameters in relationship to milk yield in dairy cows

To study their relationship to milk yield, the concentrations, in jugular venous blood, of thyroxine iodine (T4I), thyroxine (T4), 3,5,3'-tri-iodothyronine (T3), glucose, non-esterified fatty acids (NEFA), triglycerides, phospholipids, cholesterol, total protein, albumin, urea, haemoglobin and packed cell volume (PCV) have been measured in 36 cows (Simmental, Swiss Brown, Holstein and Simmental × Holstein) of different ages during a full lactation, pregnancy, dry period, parturition and 150 days of the ensuing lactation. Thyroid hormones and triglycerides were negatively, and total protein, globulin, cholesterol and phospholipids were positively, correlated with uncorrected or corrected milk yield during several periods of lactation, whereas glucose, NEFA, albumin, urea, haemoglobin and packed cell volume were not correlated with milk yield. The 10 animals with the highest milk yield (18·9 to 23·5 kg/day) exhibited significantly lower values of T4I, T4, T3 and glucose, significantly higher levels of total protein and globulin and tended to have higher levels of NEFA than the 10 cows with the lowest milk yield (10·9 to 14·3 kg/day) throughout or during certain periods of lactation, whereas concentrations of triglycerides, phospholipids, cholesterol, albumin, haemoglobin and PCV did not differ. Changes in T4I, T4, T3, glucose and total protein during lactation were also influenced by age, presumably associated with an increase in milk production with age. T3 was consistently lowest and cholesterol and phospholipids, during later stages of lactation, were highest in Holsteins, which had the highest milk yields of all breeds. Changes of blood parameters were mainly caused by shifts in energy and protein metabolism in association with level of milk productio

Investigating masking effects of age trends on the correlations among tree ring proxies

Age-related trends are present in tree-ring widths (TRW), but their presence in tree rings isotope is debated. It is unclear how cambial age influences the relationships between TRW and isotopes. Tree-ring isotopes of alpine larch and cembran-pine trees showed only trends in the juvenile period (>100 years), which might mask the inter-relations between tree-ring proxies during cambial age. This work tries to unmask the age-trend influences by examining the correlations in TRW-stable isotopes with and without age-trend correction. The non-detrended and linear-detrended values of TRW, of δD and δ18O showed significant correlations for ages up to 100 years, but not afterward. However, the correlation values, after spline or first-difference time-series detrending, were not age-related. Thus, detrending methods affect the correlations in the juvenile phase and may affect climate-related interpretations. The correlations between TRW and δ13C were not age-related, while those among the isotopes were significant throughout the ages. The correlation between δ13C and δD was the exception, as it became significant only after age > 100 years, suggesting a different use of reserves in the juvenile phase. In conclusion, the relationships among the tree-ring parameters are stable in all the different detrend scenarios after the juvenile phase, and they can be used together in multi-proxy paleoclimatic studies. The data of the juvenile phase can be used after spline-detrending or first-difference time-series calculation, depending on the purpose of the analysis to remove age-related trends. The work also provides clues on the possible causes of juvenile age trends

Temperature-dependent spin gap and singlet ground state in BaCuSi2O6

Bulk magnetic measurements and inelastic neutron scattering were used to investigate the spin-singlet ground state and magnetic gap excitations in BaCuSi2O6, a quasi-2-dimensional antiferromagnet with a bilayer structure. The results are well described by a model based on weakly interacting antiferromagnetic dimers. A strongly temperature-dependent dispersion in the gap modes was found. We suggest that the observed excitations are analogous to magneto-excitons in light rare-earth compounds, but are an intrinsic property of a simple Heisenberg Hamiltonian for the S=1/2 magnetic bilayer.Comment: 10 pages, 4 figures, REVTeX and PS for text, PS for figures direct download: http://papillon.phy.bnl.gov/preprints/bacusio.htm

Tim54p connects inner membrane assembly and proteolytic pathways in the mitochondrion

Tim54p, a component of the inner membrane TIM22 complex, does not directly mediate the import of inner membrane substrates but is required for assembly/stability of the 300-kD TIM22 complex. In addition, Δtim54 yeast exhibit a petite-negative phenotype (also observed in yeast harboring mutations in the F1Fo ATPase, the ADP/ATP carrier, mitochondrial morphology components, or the i–AAA protease, Yme1p). Interestingly, other import mutants in our strain background are not petite-negative. We report that Tim54p is not involved in maintenance of mitochondrial DNA or mitochondrial morphology. Rather, Tim54p mediates assembly of an active Yme1p complex, after Yme1p is imported via the TIM23 pathway. Defective Yme1p assembly is likely the major contributing factor for the petite-negativity in strains lacking functional Tim54p. Thus, Tim54p has two independent functions: scaffolding/stability for the TIM22 membrane complex and assembly of Yme1p into a proteolytically active complex. As such, Tim54p links protein import, assembly, and turnover pathways in the mitochondrion

Feedback Effect on Landau-Zener-Stueckelberg Transitions in Magnetic Systems

We examine the effect of the dynamics of the internal magnetic field on the staircase magnetization curves observed in large-spin molecular magnets. We show that the size of the magnetization steps depends sensitively on the intermolecular interactions, even if these are very small compared to the intra-molecular couplings.Comment: 4 pages, 3 Postscript figures; paper reorganized, conclusions modifie