Reactions of ketones with coordinated nitriles on β-diketonato ruthenium complexes leading to formation of compounds with new carbon-carbon bonds

The reactions of [Ru(acac)₂(CH₃CN)₂] with four ketones (acetone, ethyl methyl ketone, acetylacetone and monochloroacetone), and the reactions of [Ru(acac)₂(C₆H₅CN)₂] with two ketones (acetone and ethyl methyl ketone) yielded six novel compounds of β-ketiminato ruthenium complexes: [Ru(acac)₂(mhmk)], [Ru(acac)₂(ehmk)], [Ru(acac)₂(mAmk)], [Ru(acac)₂(mClmk)], Ru(acac)₂(mhbk)], and [Ru(acac)₂(ehbk)] (mhmk = 4-iminopentane-2-one mono anion, ehmk = 5-iminohexane-3-one mono anion, mAmk = 3-(1-iminoethyl)-2,4-pentanedione mono anion, mClmk = 3-chloro-4-imino-pentane-2-one mono anion, mhbk = 1-phenyl-1-iminobutane-3-one mono anion, ehbk = 1-phenyl-1-iminopentane-3-one mono anion). All the new complexes have been characterized by elemental analyses, ¹H NMR, MS and electronic spectral data. Crystal and molecular structures for the six β-ketimine complexes have been solved by single crystal X-ray diffraction studies. A mechanism involving the attack of ketones on the coordinated nitrile has been proposed. The electrochemical redox behavior of the β-ketimine complexes has been elucidated.     

Turnover of ubiquinone-0 at the acceptor side of photosynthetic reaction center

The steady-state operation of photosynthetic reaction center from Rhodobacter sphaeroides was investigated by measuring the rate of cytochrome photo-oxidation under intensive continuous illumination (808 nm, 5 W cm(-2)). The native quinone UQ(10) in Q(B) binding site of the reaction center was substituted by tailless UQ(0) and the binding parameters and the turnover rate of the UQ(0) was studied to test the recently discovered light-intensity dependent acceptor side effect (Gerencsér and Maróti 2006). The binding parameters of UQ(0) (k (on) = 2.1 x 10(5) M(-1) s(-1) and k (off) = 100 s(-1)) were characteristic to the RC exposed to high light-intensity. The dissociation constant (K (D) = 480 muM) determined under high light intensity is 2-3 times larger than that determined from flash-experiments. The light-intensity dependent acceleration of cytochrome turnover measured on reaction center of inhibited proton binding was independent of the type of the quinone and was sensitive only to the size ("pressure") of the quinone pool. The dissociation constants of different types of semiquinones show similarly high (several orders of magnitude) increase in the modified conformation of the Q(B) binding pocket due to high intensity of illumination. This result indicates the exclusive role of the quinone headgroup in the binding of semiquinone to different conformations of the protein.     

Alanine-dependent reactions of 5'-deoxypyridoxal in water

The non-enzymatic reaction of 5′-deoxypyridoxal (DPL) with l-alanine in water at 25 °C was investigated. DPL reacts with alanine to form an imine, which then undergoes deprotonation at the α-amino carbon of alanine to form a resonance delocalized DPL-stabilized carbanion. At early reaction times the only detectable products are pyruvate and the dimeric species formed by addition of the α-pyridine stabilized carbanion to DPL. No Claisen-type products of addition of the α-amino carbanion to DPL, as was previously reported to form from the reaction between DPL and glycine [K. Toth, T.L. Amyes, J.P. Richard, J.P.G. Malthouse, M.E. Nı´Beilliu, J. Am. Chem. Soc. 126 (2004) 10538–10539], are observed. The electrophile reacts instead at the α-pyridyl carbon. This dimer is in chemical equilibrium with reactants. At longer reaction times about 50% of DPL is converted to 5′-deoxypyridoxamine, the thermodynamically favored product of formal transamination of DPL.     

应用分子轨道方法分析生物体系NO与氧自由基反应特性

用分子轨道对称生规则阐明生物体系ＮＯ与Ｏ＾－２、ＮＯ２、ＯＨ、ＬＯＯ反应动力主其生物学意义。从分子轨道,电子结构,化学键的稳定性,诱导效应以及极化与反极化作用,阐明ＯＮＯＯＨ的极不稳定性。用量子化学ＭＯ理论建立ＮＯＮＯＯ＾－、ＯＮＯＯＨ键合模型,从理论和实验事实证证模型的唯一合理性。提出了ＯＮＯＯＨ存在特殊共轭大π停顿同它们的π分子轨道能级顺序和示意图,从而能很好解释ＯＮＯＯ＾－和ＯＮＯＯＨ的氧化     

Near infrared spectroscopy compared to liquid chromatography coupled to mass spectrometry and capillary electrophoresis as a detection tool for peptide reaction monitoring

Peptide interaction is normally monitored by liquid chromatography (LC), liquid chromatography coupled to mass spectrometry (LC-MS), mass spectrometric (MS) methods such as MALDI-TOF/MS or capillary electrophoresis (CE). These analytical techniques need to apply either high pressure or high voltages, which can cause cleavage of newly formed bondages. Therefore, near infrared reflectance spectroscopy (NIRS) is presented as a rapid alternative to monitor the interaction of glutathione and oxytocin, simulating physiological conditions. Thereby, glutathione can act as a nucleophile with oxytocin forming four new conjugates via a disulphide bondage. Liquid chromatography coupled to UV (LC-UV) and mass spectrometry via an electrospray ionisation interface (LC-ESI-MS) resulted in a 82% and a 78% degradation of oxytocin at pH 3 and a 5% and a 7% degradation at pH 6.5. Capillary electrophoresis employing UV-detection (CE-UV) showed a 44% degradation of oxytocin. LC and CE in addition to the NIRS are found to be authentic tools for quantitative analysis. Nevertheless, NIRS proved to be highly suitable for the detection of newly formed conjugates after separating them on a thin layer chromatography (TLC) plate. The recorded fingerprint in the near infrared region allows for a selective distinct qualitative identification of conjugates without the need for expensive instrumentation such as quadrupole or MALDI-TOF mass spectrometers. The performance of the established NIRS method is compared to LC and CE; its advantages are discussed in detail.     

Motor-mediated Cortical versus Astral Microtubule Organization in Lipid-monolayered Droplets

The correct spatial organization of microtubules is of crucial importance for determining the internal architecture of eukaryotic cells. Microtubules are arranged in space by a multitude of biochemical activities and by spatial constraints imposed by the cell boundary. The principles underlying the establishment of distinct intracellular architectures are only poorly understood. Here, we studied the effect of spatial confinement on the self-organization of purified motors and microtubules that are encapsulated in lipid-monolayered droplets in oil, varying in diameter from 5–100 μm, which covers the size range of typical cell bodies. We found that droplet size alone had a major organizing influence. The presence of a microtubule-crosslinking motor protein decreased the number of accessible types of microtubule organizations. Depending on the degree of spatial confinement, the presence of the motor caused either the formation of a cortical array of bent microtubule bundles or the generation of single microtubule asters in the droplets. These are two of the most prominent forms of microtubule arrangements in plant and metazoan cells. Our results provide insights into the combined organizing influence of spatial constraints and cross-linking motor activities determining distinct microtubule architectures in a minimal biomimetic system. In the future, this simple lipid-monolayered droplet system characterized here can be expanded readily to include further biochemical activities or used as the starting point for the investigation of motor-mediated microtubule organization inside liposomes surrounded by a deformable lipid bilayer.     

Computational studies on imidazole heme conformations

Abstract Density functional theory computations of heme with ionized propionic acid groups, axially coordinated with two imidazoles, were performed for different mutual orientations of the imidazole planes. Environmental influences from water or protein were considered with a continuum dielectric medium by solving the Poisson equation. In vacuum, optimized geometries yielded imidazole–heme conformations where the NH groups of imidazoles are oriented toward the heme propionic groups in agreement with data from crystal structures of heme proteins. Conformational free-energy dependencies of the mutual orientation of axially ligated imidazoles calculated in protein (=10) and water (=80) environments confirmed the vacuum results, albeit the energy difference between the preferred and the 180° opposite orientations of the imidazole ligand decreased from 3.84 kcal/mol in vacuum to 2.35 and 2.40 kcal/mol in protein and water, respectively. Two main factors determine the imidazole orientation: (1) the direct intramolecular electrostatic interactions of propionic groups with the polar NH groups of imidazole and (2) the electrostatic interaction of the total dipole moment of the imidazole–heme complex with the reaction field. In vacuum, only the first type of interaction is present, while in a dielectric medium the latter effect becomes competitive at high dielectric constant, resulting in a decrease of the orientational preference. Interestingly, the orientational preference of the imidazole axially ligated to heme becomes even more pronounced, if the negatively charged propionates are neutralized by counter charges that mimic salt bridges or protonation of the propionates.Electronic Supplementary Material Supplementary material is available for this article at .     

Mechanistic study of the intramolecular conversion of maltose to trehalose by Thermus caldophilus GK24 trehalose synthase

This paper questions what types of molecular transformation are involved in the conversion of maltose to trehalose by trehalose synthase from Thermus caldophilus GK24. The reverse reaction pathway has been examined with the aid of alpha,alpha-(2,4,6,6',2',4',6",6"'-(2)H(8))trehalose (1). The mass data of the isolated reaction products clearly indicate that deuterated glucose is confined only to substrate molecules, and thus the reversible enzymatic conversion of trehalose into maltose proceeds through an intramolecular pathway.     

One-dimensional daisyworld: spatial interactions and pattern formation

The zero-dimensional daisyworld model of Watson and Lovelock (1983) demonstrates that life can unconsciously regulate a global environment. Here that model is extended to one dimension, incorporating a distribution of incoming solar radiation and diffusion of heat consistent with a spherical planet. Global regulatory properties of the original model are retained. The daisy populations are initially restricted to hospitable regions of the surface but exert both global and local feedback to increase this habitable area, eventually colonizing the whole surface. The introduction of heat diffusion destabilizes the coexistence equilibrium of the two daisy types. In response, a striped pattern consisting of blocks of all black or all white daisies emerges. There are two mechanisms behind this pattern formation. Both are connected to the stability of the system and an overview of the mathematics involved is presented. Numerical experiments show that this pattern is globally determined. Perturbations in one region have an impact over the whole surface but the regulatory properties of the system are not compromised by transient perturbations. The relevance of these results to the Earth and the wider climate modelling field is discussed.     

Methodology for detecting trace amounts of microchimeric DNA from peripheral murine white blood cells by real-time PCR

Real-time PCR methodology can successfully quantitate microchimeric cell populations at a concentration of 100 microchimeric cells/100,000 host cells; however, it has not been successful in quantitating DNA from trace numbers of microchimeric white blood cells which we reported are present in murine peripheral blood at a concentration as low as 2/100,000 host cells. We report methodology using primers for a portion of the H2-k^b murine histocompatibility sequence, specific for the C57BL/6J mouse. When these primers were used in the presence of 11,000 μM primer, a 20-fold increase in the median manufacturer’s recommended concentration, the assay could be optimized to detect 34 pg of C57BL/6J DNA in a background of 2.5 μg of carrier BALB/cJ DNA (1/100,000). These conditions resulted in a detection limit half as sensitive as that found when no carrier DNA was present. Published: April 7, 2003