Total synthesis of malyngamide M and isomalyngamide M

The stereoselective synthesis of malyngamide M (1) was accomplished in nine steps from o-cresol in 12% overall yield. The key steps involved the Wittig reaction of an α-NHBoc aryl ketone 4 for the introduction of vinyl chloride functionality, an amidation of lyngbic acid 3 with a secondary amine 2 for the framework of target molecule, and an isomerization of a (Z)-vinyl chloride to the (E)-configuration using benzophenone as a photosensitizer. The isomalyngamide M (Z-1) was also synthesized.     

Zintl-Verbindungen mit Gold: M3AuSn4 mit M = K,Rb, Cs und M3AuPb4 mit M = Rb,Cs

Zintl-Compounds with Gold: M₃AuSn₄ with M = K, Rb, Cs and M₃AuPb₄ with M = Rb, Cs Silver coloured, brittle single crystals of the compounds M₃AuSn₄ with M = K, Rb, Cs and M₃AuPb₄ with M = Rb, Cs were synthesized by reactions of alkali metal azides (MN₃) with gold sponge and tin (lead) powder at T = 923 K. The structures of the isotypic compounds (space group Pmmn, Z = 2) were determined from X-ray single-crystal diffractometry data (see ‘‘Inhaltsübersicht”︁”︁). The Zintl-compounds M₃AuE(14)₄ with E(14) = Sn, Pb contain [AuE(14)₄]-chains with P₄-analogous E(14)₄-tetrahedra which are connected by μ₂-bridging gold atoms.     

FeMo cofactor of nitrogenase: a density functional study of states M(N), M(OX), M(R), and M(I).

The M(N) S = (3)/(2) resting state of the FeMo cofactor of nitrogenase has been proposed to have metal-ion valencies of either Mo(4+)6Fe(2+)Fe(3+) (derived from metal hyperfine interactions) or Mo(4+)4Fe(2+)3Fe(3+) (from M?ssbauer isomer shifts). Spin-polarized broken-symmetry (BS) density functional theory (DFT) calculations have been undertaken to determine which oxidation level best represents the M(N) state and to provide a framework for understanding its energetics and spectroscopy. For the Mo(4+)6Fe(2+)Fe(3+) oxidation state, the spin coupling pattern for several spin state alignments compatible with S = (3)/(2) were generated and assessed by energy and geometric criteria. The most likely BS spin state is composed of a Mo3Fe cluster with spin S(a) = 2 antiferromagnetically coupled to a 4Fe' cluster with spin S(b) = (7)/(2). This state has a low DFT energy for the isolated FeMoco cluster and the lowest energy when the interaction with the protein and solvent environment is included. This spin state also displays calculated metal hyperfine and M?ssbauer isomer shifts compatible with experiment, and optimized geometries that are in excellent agreement with the protein X-ray data. Our best model for the actual spin-coupled state within FeMoco alters this BS state by a slight canting of spins and is analogous in several respects to that found in the 8Fe P-cluster in the same protein. The spin-up and spin-down components of the LUMO contain atomic contributions from Mo(4+) and the homocitrate and from the central prismane Fe sites and muS(2) atoms, respectively. This qualitative picture of the accepting orbitals for M(N) is consistent with observations from M?ssbauer spectra of the one-electron reduced states. Similar calculations for the Mo(4+)4Fe(2+)3Fe(3+) oxidation state yield results that are in poorer agreement with experiment. Using the Mo(4+)6Fe(2+)Fe(3+) oxidation level as the most plausible resting state, the geometric, electronic and energetic properties of the one-electron redox transition to the oxidized state, M(OX), catalytically observed M(R) and radiolytically reduced M(I) states have also been explored.     

Synthesis of Isodehydroilludin M

Isodehydroilludin M was synthesized from carbonyl ylid 1,3-dipolar cycloaddition product that was further elaborated with an unusual PCC-mediated double oxidation reaction.     

Relativistic-consistent electron densities of the coinage metal clusters M2, M4, M4(2-), and M4Na2 (M = Cu, Ag, Au): a QTAIM study

We employ second-order M?ller-Plesset perturbation theory level in combination with recently developed pseudopotential-based correlation consistent basis sets to obtain accurate relativistic-consistent electron densities for small coinage metal clusters. Using calculated electron densities, we employ Bader's quantum theory of atoms in molecules (QTAIM) to gain insights into the nature of metal-metal bonding in the clusters M(2), M(4), M(4)(2-), and M(4)Na(2) (M = Cu, Ag, Au). For the simplest case of the metal dimer, M(2), we correlate the strength of the metal-metal bond with the value of the electron density at the bond critical point, the total energy density at the bond critical point, the sharing (delocalization) index, and the values of the two principle negative curvatures. We then consider changes to the metal-metal bonding and charge density distribution upon the addition of two metal atoms to form the metal tetramer, M(4), and then followed by the addition of an electron pair to form M(4)(2-) and finally followed by the addition of two alkali metal (sodium) ions to form M(4)Na(2). Using topological properties of the electron density, we present evidence for the existence of σ-aromaticity in Au(4)(2-). We also report the existence of two non-nuclear attractors in the molecular graph of Cu(4)(2-) and large negative charge accumulation in the nonbonded Cu basins of this cluster.     

Total synthesis of the aglycone of the 8-methyl benzonaphthopyrone antibiotics,gilvocarcin M,virenomycin M,and albacarcin M

A short, convergent synthesis of the aglycone 5a of the 8-methyl benzonaphthopyrone antibiotics is described which utilizes as a key step a Suzuki biaryl coupling.     

Ti-48Al-2M~1-2M~2(M~1=Nb,V;M~2=Mn,Cr,V)合金电子结构

用紧束缚能带计算方法(EHT)研究了标题多元合金的能带及电子结构。发现少量的多种元素在γ-TiAl中掺杂,对合金中电荷分布的影响,具有单种元素掺杂的叠加性;选择适当的合金元素就能达到多种掺杂的性能互补。多种元素掺杂能更有效地使成键电子云趋势于球形化,Peierls力均称为化,有利于增加γ-TiAl合金的塑性和变形性。     

Collisional energy transfer in the reactions I + NO + M → INO + M and I + NO2 + M → INO2 + M

The low-pressure recombination rate constants of the reactions I + NO + M → INO + M (with 14 different M) and I + NO₂ + M → INO₂ + M (with 26 different M) have been measured at 330°K by laser flash photolysis. The collision efficiencies β_c are analyzed and compared with other thermal activation systems. Whereas β_c increases in one reaction with an increasing number of atoms in M, practically no such effect is found when, for the same M, different reactions with varying complexities of the reacting molecules are considered.