Sporulenes, heptaprenyl metabolites from Bacillus subtilis spores

Sporulene, a C 35-terpenoid hydrocarbon with an unusual pentacyclic structure, is produced by Bacillus subtilis during sporulation.     

The evolution of model catalytic systems; studies of structure, bonding and dynamics from single crystal metal surfaces to nanoparticles, and from low pressure (<10(-3) Torr) to high pressure (>10(-3) Torr) to liquid interfaces

The material and pressure gap has been a long standing challenge in the field of heterogeneous catalysis and have transformed surface science and biointerfacial research. In heterogeneous catalysis, the material gap refers to the discontinuity between well-characterized model systems and industrially relevant catalysts. Single crystal metal surfaces have been useful model systems to elucidate the role of surface defects and the mobility of reaction intermediates in catalytic reactivity and selectivity. As nanoscience advances, we have developed nanoparticle catalysts with lithographic techniques and colloidal syntheses. Nanoparticle catalysts on oxide supports allow us to investigate several important ingredients of heterogeneous catalysis such as the metal-oxide interface and the influence of noble metal particle size and surface structure on catalytic selectivity. Monodispersed nanoparticle and nanowire arrays were fabricated for use as model catalysts by lithographic techniques. Platinum and rhodium nanoparticles in the 1-10 nm range were synthesized in colloidal solutions in the presence of polymer capping agents. The most catalytically active systems are employed at high pressure or at solid-liquid interfaces. In order to study the high pressure and liquid interfaces on the molecular level, experimental techniques with which we bridged the pressure gap in catalysis have been developed. These techniques include the ultrahigh vacuum system equipped with high pressure reaction cell, high pressure Sum Frequency Generation (SFG) vibration spectroscopy, High Pressure Scanning Tunneling Microscopy (HP-STM), and High Pressure X-ray Photoemission Spectroscopy (HP-XPS), and Quartz Crystal Microbalance (QCM). In this article, we overview the development of experimental techniques and evolution of the model systems for the research of heterogeneous catalysis and biointerfacial studies that can shed light on the long-standing issues of materials and pressure gaps.     

Selective formation of diblock copolymers using radical trap‐assisted atom transfer radical coupling

Polystyrene (PSt) radicals and poly(methyl acrylate) (PMA) radicals, derived from their monobrominated precursors prepared by atom transfer radical polymerization (ATRP), were formed in the presence of the radical trap 2‐methyl‐2‐nitrosopropane (MNP), selectively forming PSt‐PMA diblock copolymers with an alkoxyamine at the junction between the block segments. This radical trap‐assisted, atom transfer radical coupling (RTA‐ATRC) was performed in a single pot at low temperature (35 °C), while analogous traditional ATRC reactions at this temperature, which lacked the radical trap, resulted in no observed coupling and the PStBr and PMABr precursors were simply recovered. Selective formation of the diblock under RTA‐ATRC conditions is consistent with the PStBr and PMABr having substantially different K_ATRP values, with PSt radicals initially being formed and trapped by the MNP and the PMA radicals being trapped by the in situ‐formed nitroxide end‐capped PSt. The midchain alkoxyamine functionality was confirmed by thermolysis of the diblock copolymer, resulting in recovery of the PSt segment and degradation of the PMA block at the relatively high temperatures (125 °C) required for thermal cleavage. A PSt‐PMA diblock formed by chain extenstion ATRP using PStBr as the macroinitiator (thus lacking the alkoxyamine between the PSt‐PMA segements) was inert to thermolysis. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3619–3626     

Synthesis, Structural Characterization and Crystal Structure of Selenium Bearing 3-(Phenylseleno) Propylammonium Acetate Salt and its Cleavage on Reaction with Mercury(II) and Tin(IV) Salts

Abstract  

3-(Phenylseleno) propylammonium acetate, C₉H₁₄NSe⁺ C₂H₃O₂ ^–, L ¹ , the first example of a selenium bearing acetate salt has been synthesized and characterized by spectroscopic, NMR, DSC and single crystal X-ray crystallographic techniques. L ¹ crystallizes with one cation–anion pair in the asymmetric unit. Reactions of L ¹ with four different metal salts revealed four new selenium bearing compounds (1–4) whose identities are characterized by spectroscopic and NMR techniques. The crystal structure of Compound 1, [C₉H₁₄NSe]₂⁺ [ClO₄]₂^–, whose crystal structure has been confirmed. It crystallizes with two independent cation–anion pairs in the asymmetric unit. Both L ¹ and Compound 1 display strong N–H···O hydrogen bond intermolecular interactions which help stabilize crystal packing in the unit cell.     

Synthesis,characterization and crystal structures of dinuclear macrocyclic Schiff base copper(I) complexes bearing different bridges

Utilizing a new 20-membered macrocyclic Schiff base ligand with two coordination sites formed from the [2+2] condensation of 1,3-diaminopropane and benzene-1,3-dicarboxaldehyde in the presence of CuX (X = Cl⁻, Br⁻, I⁻) salts, air-stable dicopper(I) complexes were synthesized in acetonitrile, intramolecularly linked via two halide groups, and characterized by different physico-chemical techniques. The single crystal X-ray diffraction technique indicates these complexes consist of two N₂X₂ donor sets that have distorted tetrahedral coordination environments around the copper(I) ions. In these halogen-bridged binuclear Cu₂LX₂ systems the Cu?Cu separation can be controlled, as this distance is reduced on increasing the halide size and hence the X?X repulsion, with the rigidity of the macrocycle playing a significant role.     

Nickel(II) complexes of 5-phenyl and 5-furan-1,3,4-oxadiazole-2-thiones containing ethylenediamine: synthesis,spectral and X-ray characterization

The products obtained by the reactions of Ni(OAc)₂·4H₂O with Hpot (Hpot = 5-phenyl-1,3,4-oxadiazole-2-thione) and [K(H₂fchc)] (potassium N′-(furan-2-carbonyl) hydrazine carbodithioate), on treatment with excess of ethylenediamine (en), gave mixed ligand complexes [Ni(pot)₂(en)₂] (1) and [Ni(fot)₂(en)₂] (2) (fot = 5-furan-(1,3,4)-oxadiazole-2-thione). These complexes have been characterized with the aid of elemental analyses, IR, magnetic susceptibility and single crystal X-ray studies. In both complexes, the heterocyclic ligand coordinates through oxadiazole nitrogen, and the ligand exists as the thione form. The complexes 1 and 2 have distorted octahedral geometries around the centrosymmetric Ni(II) center with trans oxadiazole ligands. Both complexes show extended hydrogen bonding to give a supramolecular framework.     

Modulation of fluorescence emission of 1-(2-pyridyl) pyrazole derived Schiff base ligands by exploiting their metal ion sensitive binding modes

Dioxomolybdenum(VI) complexes [MoO₂(B¹)H₂O] (1), [MoO₂(B²)EtOH] (2), [MoO₂(B³)EtOH] (3) and [MoO₂(B⁴)EtOH] (4) were synthesized using the Schiff base ligands H₂B¹(previously reported), H₂B², H₂B³ and H₂B⁴, respectively. These ligands were prepared by condensation of 1-(2-pyridyl) 5-methyl 3-pyrazole carbohydrazide with salicylaldehyde, o-hydroxy acetophenone, 5-bromo salicylaldehyde and 5-nitro salicylaldehyde respectively. Due to the presence of a substituted 1-(2-pyridyl) pyrazole unit, ligands H₂B¹, H₂B² and H₂B³ exhibit fluorescent emissions, and the most intense emission was obtained for H₂B³. H₂B⁴ is incapable of showing fluorescence emission. As the ligands are capable of using different binding modes, according to the demands of the guest metal ions, their emission properties also change accordingly. The dioxomolybdenum(VI) complex of the ligand H₂B¹, i.e. complex 1, shows quenched emission compared to H₂B¹. Again when Cu²⁺, Co²⁺ or Ni²⁺ ions are added to a solution of 1, in each case a new complex of Cu²⁺ Co²⁺ or Ni²⁺ is formed in solution and further quenching was observed. However, with Zn²⁺ input to a solution of 1, fluorescence recovery was observed up to the level of the free ligand. The copper(II) complex of H₂B¹ (complex 5), produced by adding equivalent amount of Cu²⁺ salt to a solution of 1, was isolated and characterized. One of the dioxomolybdenum(VI) complexes, 3, when subjected to an oxo-transfer reaction with PPh₃ produces complex [MoO(B³)CH₃CN] (6). Complex 6 shows reduced fluorescence emissions compared to 3 in the solid phase. These observations open up the possibilities for these ligands to work as fluorescent signaling system with different metal ion inputs. All the complexes are characterized by elemental analyses, electronic spectra, IR, ¹H NMR, magnetic measurements, EPR and by cyclic voltammetry. Complexes 1 and 5, as well as the ligands H₂B² and H₂B³, have been crystallographically characterized.     

New Methodologies for Fracture Detection of Automotive Steels in Tight Radius Bending: Application to the VDA 238–100 V-Bend Test

Background

The VDA 238–100 tight radius V-bend test can be used to efficiently characterize the bendability and fracture limits of sheet metals in severe plane strain bending. Material performance in plane strain bending is critical for the selection of advanced high strength steels for energy absorbing structural components.

Objective

The detection of failure based upon a reduction in the punch force can lead to erroneous predictions of failure for ductile or thin gage alloys in the VDA 238–100 test. New failure criteria were proposed and evaluated across a range of automotive steels.

Methods

Four detection methods in the V-bend test were evaluated based upon the load drop, bending moment, novel stress metric and the strain rate for seven steels with strength levels from 270 to 1500 MPa. The appropriate failure threshold was identified from visual inspection of the surface during bending.

Results

The vertical punch force will decrease as a consequence of the mechanics in the V-bend test at intermediate bend angles even without fracture. The novel stress-based metric accounts for sheet thinning and could successfully identify “false positives” and punch lift-off when considering the strain-rate evolution.

Conclusions

Failure detection using the VDA load threshold method may significantly under-report the bend performance of alloys with intermediate-to-high bendability or thin gauges. The proposed stress-based metric can reliably detect fracture for bend angles in excess of 160° and be readily calculated using the existing data. The VDA load threshold for failure can work well for materials that exhibit significant cracking.