Structure of an F430 variant from archaea associated with anaerobic oxidation of methane

Microbial mats collected at cold methane seeps in the Black Sea carry out anaerobic oxidation of methane (AOM) to carbon dioxide using sulfate as the electron acceptor. These mats, which predominantly consist of sulfate-reducing bacteria and archaea of the ANME-1 and ANME-2 type, contain large amounts of proteins very similar to methyl-coenzyme M reductase from methanogenic archaea. Mass spectrometry of mat samples revealed the presence of two nickel-containing cofactors in comparable amounts, one with the same mass as coenzyme F430 from methanogens (m/z = 905) and one with a mass that is 46 Da higher (m/z = 951). The two cofactors were isolated and purified, and their constitution and absolute configuration were determined. The cofactor with m/z = 905 was proven to be identical to coenzyme F430 from methanogens. For the m/z = 951 species, high resolution ICP-MS pointed to F430 + CH2S as the molecular formula, and LA-ICP-SF MS finally confirmed the presence of one sulfur atom per nickel. Esterification gave two stereoisomeric pentamethyl esters with m/z = 1021, which could be purified by reverse phase HPLC and were subjected to comprehensive NMR analysis, allowing determination of their constitution and configuration as (17(2)S)-17(2)-methylthio-F430 pentamethyl ester and (17(2)R)-17(2)-methylthio-F430 pentamethyl ester. The corresponding diastereoisomeric pentaacids could also be separated by HPLC and were correlated to the esters via mild hydrolysis of the latter. Equilibration of the pentaacids under acid catalysis showed that the (17(2)S) isomer is the naturally occurring albeit thermodynamically less stable one. The more stable (17(2)R) isomer (80% at equilibrium) is an isolation artifact generated under the acidic conditions necessary for the isolation of the cofactors from the calcium carbonate-encrusted mats.     

An improved method for de novo sequencing of arginine-containing, Nalpha-tris(2,4,6-trimethoxyphenyl)phosphonium-acetylated peptides

An improved method for de novo sequencing of arginine-containing peptides modified with succinimidyloxycarbonylmethyl tris(2,4,6-trimethoxyphenyl)phosphonium bromide (TMPP-Ac-OSu) is reported. A tagging reagent, TMPP-Ac-OSu, was introduced to improve the sequence analysis of peptides owing to the simplified fragmentation pattern. However, peptides containing arginine residues did not fragment efficiently even after TMPP-Ac modification at their N-termini. This report describes how fragmentation efficiency of TMPP-Ac-modified arginine-containing peptides was significantly improved by modifying the guanidino group on the side chain of arginine with acetylacetone.     

Characterization of the Fe site in iron-sulfur cluster-free hydrogenase (Hmd) and of a model compound via nuclear resonance vibrational spectroscopy (NRVS)

We have used (57)Fe nuclear resonance vibrational spectroscopy (NRVS) to study the iron site in the iron-sulfur cluster-free hydrogenase Hmd from the methanogenic archaeon Methanothermobacter marburgensis. The spectra have been interpreted by comparison with a cis-(CO)2-ligated Fe model compound, Fe(S2C2H4)(CO)2(PMe3)2, as well as by normal mode simulations of plausible active site structures. For this model complex, normal mode analyses both from an optimized Urey-Bradley force field and from complementary density functional theory (DFT) calculations produced consistent results. For Hmd, previous IR spectroscopic studies found strong CO stretching modes at 1944 and 2011 cm(-1), interpreted as evidence for cis-Fe(CO)2 ligation. The NRVS data provide further insight into the dynamics of the Fe site, revealing Fe-CO stretch and Fe-CO bend modes at 494, 562, 590, and 648 cm(-1), consistent with the proposed cis-Fe(CO)2 ligation. The NRVS also reveals a band assigned to Fe-S stretching motion at approximately 311 cm(-1) and another reproducible feature at approximately 380 cm(-1). The (57)Fe partial vibrational densities of states (PVDOS) for Hmd can be reasonably well simulated by a normal mode analysis based on a Urey-Bradley force field for a five-coordinate cis-(CO)2-ligated Fe site with additional cysteine, water, and pyridone cofactor ligands. A "truncated" model without a water ligand can also be used to match the NRVS data. A final interpretation of the Hmd NRVS data, including DFT analysis, awaits a three-dimensional structure for the active site.     

A Two-on-One Linear Pursuit–Evasion Game with Bounded Controls

A linearized engagement with two pursuers versus a single evader is considered, in which the adversaries’ controls are bounded and have first-order dynamics and the pursuers’ intercept times are equal. Wishing to formulate the engagement as a zero-sum differential game, a suitable cost function is proposed and validated, and the resulting optimization problem and its solution are presented. Construction and analysis of the game space is shown, and the players’ closed-form optimal controls are derived for the case of two “strong” pursuers. The results are compared to those of a 1-on-1 engagement with a “strong” pursuer, and it is shown that the addition of a second pursuer enlarges the capture zone and introduces a new singular zone to the game space, in which the pursuers can guarantee equal misses, regardless of the evader’s actions. Additionally, it is concluded that in the regular zones the closed-form optimal pursuit strategies are unchanged compared to two 1-on-1 engagements, whereas the optimal evasion strategy is more complex. Several simulations are performed, illustrating the adversaries’ behavior in different regions of the game space.     

A third type of hydrogenase catalyzing H2 activation

The activation of molecular hydrogen is of interest both from a chemical and biological viewpoint. The covalent bond of H(2) is strong (436 kJ mol(-1)). Its cleavage is catalyzed by metals or metal complexes in chemical hydrogenation reactions and by metalloenzymes named hydrogenases in microorganisms. Until recently only two types of hydrogenases are known, the [FeFe[-hydrogenases and [NiFe[-hydrogenases. Both types, which are phylogenetically unrelated, harbor in their active site a dinuclear metal center with intrinsic CO and cyanide ligands and contain iron-sulfur clusters for electron transport as revealed by their crystal structures. Fifteen years ago a third type of phylogenetically unrelated hydrogenase was discovered, which has a mononuclear iron active site and is devoid of iron-sulfur clusters. It was initially referred to as "metal free" hydrogenase, but was later renamed iron-sulfur cluster-free hydrogenase or [Fe[-hydrogenase. In this review, we introduce first the [FeFe[-hydrogenases and [NiFe[-hydrogenases, and then focus on the structure and function of the iron-sulfur cluster-free hydrogenase (Hmd) and show that this enzyme contains an iron-containing cofactor. The low-spin iron is complexed by two intrinsic CO-, one sulfur- and one or two N/O ligands and has one open coordination site, which is proposed to be the location of H(2) binding.     

Recent progress in asymmetric Biginelli reaction

The Biginelli reaction, which involves the interaction of ethyl acetoacetate, urea, and an appropriate aryl aldehyde, was first discovered by Pietro Biginelli about 120 years ago. The Biginelli products (3,4-dihydropyrimidin-2(1 $H$ )-ones) are interesting materials due to their significant pharmacological and structural profiles. In the last decades, the asymmetric synthesis as a powerful tool has an effective impact on the Biginelli products and has increased their potencies and applications as drugs. Having the importance of this subject in mind, in this review we wish to present the recent rapid progress of asymmetric Biginelli reaction.     

The synergistic chaperoning operation in a Bi-chaperone system consisting of alpha-crystallin and beta-casein: bovine pancreatic insulin as the target protein

While chaperone activity of alpha-crystallin (α-Crs) is important in maintaining lens transparency that of beta-casein (β-CN) is vital to prevent the development of corpora amylacea (accumulation of amyloid deposits in mammary glands). These two chaperone proteins are amphiphilic, each contains distinct polar and non-polar regions in the structure. While polar domain of α-Crs is highly electropositive, the counterpart domain in β-CN is strongly electronegative. In this study a Bi-chaperone system consisting of α-Crs and β-CN with different molar ratios were used to prevent the chemical-induced insulin aggregation spectroscopically. As shown, α-Crs and β-CN in the Bi-chaperone system exhibit synergistic chaperoning operation which strongly depends to the specific ratio of the chaperone components. The results of both fluorescence study and native gel electrophoresis confirmed the non-covalent interactions between α-Crs and β-CN. Consequently the synergistic activity can be explained with the possible electrostatic interactions between their polar/charged domains which bring them in close proximity, allowing their synergistic chaperoning operation in the Bi-chaperone system.     

Synthesis of Pr<Superscript>3+</Superscript> doped or Tb<Superscript>3+</Superscript>–Mg codoped CaSnO<Subscript>3</Subscript> perovskite phosphor by the polymerized complex method

Pr³⁺ doped or Tb³⁺–Mg codoped CaSnO₃ phosphor powder with perovskite structure was synthesized by the polymerized complex method. Powder samples crystallized into the perovskite phase at approximately 600 °C, which is 400 °C lower than the crystallization temperature for the solid-state reaction method. Uniform-sized powders with average particle sizes of 1–2 μm were obtained after heat treatment at 1,400 °C. Although the samples heat-treated at 600 °C did not exhibit photoluminescence, white photoluminescence of Pr³⁺ doped CaSnO₃ or green photoluminescence of Tb³⁺–Mg codoped CaSnO₃ was observed from the sample heat-treated above 800 °C. The intensity of the photoluminescence increased with increase of the heat-treatment temperature and reached a maximum for heat treatment at 1,400 °C. The maximum photoluminescence intensity for the samples prepared by the polymerized complex method was larger than those prepared by solid-state reaction method, which is probably due to the homogeneous mixing of the doped rare earth ions.     

H_5PW(10)V_2O_(40)催化高效环保合成14-芳基-14H-二苯并[a,j]氧杂蒽(英文)

A rapid and efficient procedure for the preparation of various aryl-14H-dibenzo[a,j]xanthenes was reported.The method developed produced excellent yields via one-pot condensation of β-naphthol with various aryl-aldehydes in the presence of Keggin vanadium substituted heteropolyacid,H5PW10V2O40,as catalyst under solvent free conditions.The present methodology therefore offered several advantages but not limited to excellent yields(82%-98%),short reaction times(30-50 min),mild reaction conditions,simple work-up,as well as the utilization of cheap and environmentally benign catalyst in the absence of organic solvents.     

Non-resonant Triple-α Reaction Rate at Low Temperature

The triple α reaction rate in stars is quite important in many astrophysical scenarios including the stellar evolution and carbon synthesis in stars. Recently the non-resonant triple α reaction rate has been reevaluated using a calculation with the continuum-discretized coupled-channels (CDCC) method, which dramatically increased the rate at low temperature compared to the widely-used NACRE compilation. Since the enhancement influences strongly on astrophysical model simulations, we have planned an experiment for drawing conclusion on the non-resonant triple α reaction rate at low temperature by measuring the three-α continuum state in ¹²C. We report the present situation of the experiment.