Syntheses, structural studies, and magnetic properties of divalent Cu and Co selenites with organic constituents

Six new divalent metal selenites have been synthesized by hydro-/solvothermal methods which leads to the incorporation of the organic template as a cation or a ligand. The structure of [H(2)pip][Cu(SeO(3))(2)] (1) (pip=piperazine) features 1D anionic chains of [Cu(SeO(3))(2)](2-) which are cross-linked by the template cations through hydrogen bonds into a 2D layer. In [Cu(C(3)H(4)N(2))(SeO(3))] (2) the organic template is coordinated to the copper(II) ion of the inorganic Cu(SeO(3)) layer. The isostructural compounds [H(2)en][M(HSeO(3))(2)Cl(2)] (en=ethylenediamine; M=Cu (3), Co (4)) contain layers of [MCl(2)(HSeO(3))(2)](2-) units (M=Cu, Co), which are cross-linked by the template cations via hydrogen bonds into a 3D network. The structure of [H(2)en][Cu(2)(SeO(3))(2)(HSeO(3))](2)H(2)O (5), consists of a pillared layered architecture in which the Cu(SeO(3)) layers are further interconnected by bridging hydrogen selenite groups (the pillar). The compound [H(2)pip][Cu(2)(Se(2)O(5))(3)] (6), which crystallizes as a 3D open framework represents the first organically templated metal diselenite. These new compounds are thermally stable up to at least 170 degrees C. All of the compounds exhibit fairly strong antiferromagnetic interactions. More interestingly, compounds 3 and 4 behave as a weak ferromagnets below the critical temperatures of T(c)=12 and 8 K, respectively, and both of them exhibit spin-flop phase transitions around 800+/-100 Oe.     

Anion-pi interactions as controlling elements in self-assembly reactions of Ag(I) complexes with pi-acidic aromatic rings

Reactions of 3,6-bis(2'-pyridyl)-1,2,4,5-tetrazine (bptz) and 3,6-bis(2'-pyridyl)-1,2-pyridazine (bppn) with the AgX salts (X = [PF6]-, [AsF6]-, [SbF6]-, and [BF4]-) afford complexes of different structural motifs depending on the pi-acidity of the ligand central ring and the outer-sphere anion. The bptz reactions lead to the polymeric [[Ag(bptz)][PF6]]infinity (1) and the dinuclear compounds [Ag2(bptz)2(CH3CN)2][PF6]2 (2) and [Ag2(bptz)2(CH3CN)2][AsF6]2 (3), as well as the propeller-type species [Ag2(bptz)3][AsF6]2 (4) and [Ag2(bptz)3][SbF6]2 (5a and 5b). Reactions of bppn with AgX produce the grid-type structures [Ag4(bppn)4][X]4 (6-9), regardless of the anion present. In 6-9, pi-pi stacking interactions are maximized, whereas multiple and shorter (therefore stronger) anion-pi interactions between the anions and the tetrazine rings are established in 1-5b. These differences reflect the more electron-rich character of the bppn pyridazine ring as compared to the bptz tetrazine ring. The evidence gleaned from the solid-state structures was corroborated by density functional theory calculations. In the electrostatic potential maps of the free ligands, a higher positive charge is present in the bptz as compared to the bppn central ring. Furthermore, the electrostatic potential maps of 3, 4, and 5b indicate an electron density transfer from the anions to the pi-acidic rings. Conversely, upon addition of the [AsF6]- ions to the cation of 7, there is negligible change in the electron density of the central pyridazine ring, which supports the presence of weaker anion-pi interactions in the bppn as compared to the bptz complexes. From the systems studied herein, it is concluded that anion-pi interactions play an important role in the outcome of self-assembly reactions.     

Crystal Structure of the Radical-Cation Salt (<Emphasis Type="Italic">o</Emphasis>-Me<Subscript>2</Subscript>TTF)I<Subscript>3</Subscript> with Close Intermolecular Sulfur Contacts

Abstract  The synthesis and crystal structure of the organic radical-cation salt (o-Me₂TTF)I₃ is described. The salt crystallizes in the monoclinic space group P2 ₁ /n with a = 10.927(2) ?, b = 11.904(2) ?, c = 12.660(2) ?, β = 115.174(5)°. The bond length of the central C=C bond in o-Me₂TTF is 1.401(1) ?, indicating an approximate oxidation state of +1 for the o-Me₂TTF radical cation. Graphical Abstract  The X-ray crystallographic structure of the radical cation salt (o-Me₂TTF)I₃ has been determined and its structural properties and synthetic preparation are discussed.      

Selectivity, directionality, and promiscuity in peptide processing from a Bacillus sp. Al Hakam cyclodehydratase

The thiazole/oxazole-modified microcins (TOMMs) represent a burgeoning class of ribosomal natural products decorated with thiazoles and (methyl)oxazoles originating from cysteines, serines, and threonines. The ribosomal nature of TOMMs allows for the generation of derivative products from mutations in the amino acid sequence of the precursor peptide, which ultimately manifest in differing structures and, sometimes, biological functions. Employing a TOMM system for the purpose of creating new structures and functions via combinatorial biosynthesis requires processing machinery that can tolerate highly variable substrates. In this study, TOMM enzymatic promiscuity was assessed using a currently uncharacterized cluster in Bacillus sp. Al Hakam. As determined by Fourier transform tandem mass spectrometry (FT-MS/MS), azole rings were formed in both a regio- and chemoselective fashion. Cognate and noncognate precursor peptides were modified in an overall C- to N-terminal directionality, which to date is unique among characterized ribosomal natural products. Studies focused on the inherent promiscuity of the biosynthetic machinery elucidated a modest bias for glycine at the preceding (-1) position and a remarkable flexibility in the following (+1) position, even allowing for the incorporation of charged amino acids and bisheterocyclization. Two unnatural substrates were utilized as the conclusive test of substrate flexibility, of which both were processed in a predictable fashion. A greater understanding of substrate processing and enzymatic tolerance toward unnatural substrates will prove beneficial when designing combinatorial libraries to screen for artificial TOMMs that exhibit desired activities.     

Oil in Louisiana's estuarine environments: A development model

Coastal erosion, accelerated by sea level rise, and subsidence are major Louisiana issues. With current sea-level-rise projections, coupled with the state's eroding barrier islands and coastal wetlands, the region's estuarine environments are in jeopardy of being lost, redefined, or permanently altered. As the coast erodes, Louisiana is endangered of losing valuable wetland's habitat. In addition, if the barrier islands disappear, the region's wetland-oriented oil and gas wells and associated infrastructure will be at risk to open Gulf conditions. If this should occur, each well, pipeline, and storage battery represents a potential environmental catastrophe.     

Controlled Fabrication of Cd-Bi Nanoparticles via Sonochemical Method

IntroductionMetal or alloy nanoparticles,because of their con-spicuous physicochemical properties,have been widelyapplied to various fields such as electronics,catalysis,magnetism,and corrosion-resistant materialsfields[1—4].It has been estimated that the particle sizeand the properties of nanoparticles depend strongly onthe specific method of fabrication and the applied ex-periment conditions,which makes the controlled syn-thesis of nanomaterials become an increasingly activeand important ar…     

素理想完全分裂的一个判别法则

本文给出了数域K内一个素理想在K的有限次正规扩域L内完全分裂的一个判别法则。     

Highly anisotropic orbitally dependent superexchange in cyano-bridged clusters containing Mn(III) and Mn(II) ions.

We study the orbitally dependent magnetic exchange in cyanide-based clusters as a source of the barrier for reversal magnetization. We consider the Mn(III)-CN-Mn(II) dimer and linear Mn(II)-NC-Mn(III)-CN-Mn(II) trimer containing octahedrally coordinated Mn(III) and Mn(II) ions with special emphasis on the magnetic manifestations of the orbital degeneracy of the Mn(III) ion. The kinetic exchange mechanism involves the electron transfer from the single occupied t(2) orbitals of the Mn(II) ion [6A1(t2(3)e2) ground state] to the singly occupied t(2) orbitals of the Mn(III) ion [3T1(t2(4)) ground state] resulting in the charge-transfer 5T2(t2(2)e2)Mn(III) - 2T2(t2(5))Mn(II) state of the pair. The deduced effective exchange Hamiltonian that takes into account orbital degeneracy leads to an essentially non-Heisenberg energy pattern. The energy levels are shown to be dependent on both spin and orbital quantum numbers, thus providing direct information about the magnetic anisotropy of the system. Along with the magnetic exchange, the model includes an axial component of the crystal field and spin-orbit coupling operating within the ground 3T1(t2(4)) cubic term of the Mn(III) ion. We have shown that under certain conditions both named interactions lead to the occurrence of the barrier for the reversal of magnetization, which significantly increases when passing from the dimer to the trimer. This provides a possible way for raising the magnetic barrier in the family of cyano-bridged manganese clusters.