Stereoselective recognition of an aziridine with a Co(III) complex: a potential transition-state analogue for catalytic epoxidation

Reversible and stereoselective coordination of 1-(R)-phenyl-2-(S)-methylaziridine to (S,S)L-Co(III) and (R,R)L-Co(III) (where L represents a salen ligand obtained from diamino cyclohexane and 2,4-di-tert-butyl salicylaldehyde) has been investigated. 1H NMR data indicate that the aziridine binds about three times more tightly to (S,S)L-Co(III) than to (R,R)L-Co(III). Crystal structures of two molecules of the aziridine coordinated to the Co(III) complexes have been determined. These structures together with molecular mechanics computation provide insight into the origin of stereoselective recognition of the aziridine to the Co(III) complexes.     

Homologous series of redox-active, dinuclear cations [M(2)(O(2)CCH(3))(2)(pynp)(2)](2+) (M = Mo, Ru, Rh) with the bridging ligand 2-(2-pyridyl)-1,8-naphthyridine (pynp)

A homologous series of dinuclear compounds with the bridging ligand 2-(2-pyridyl)-1,8-naphthyridine (pynp) has been prepared and characterized by X-ray crystallographic and spectroscopic methods. [Mo(2)(O(2)CCH(3))(2)(pynp)(2)][BF(4)](2) x 3CH(3)CN (1) crystallizes in the monoclinic space group P2(1)/c with a = 15.134(5) A, b = 14.301(6) A, c = 19.990(6) A, beta = 108.06(2) degrees, V = 4113(3) A(3), and Z = 4. [Ru(2)(O(2)CCH(3))(2)(pynp)(2)][PF(6)](2) x 2CH(3)OH (2) crystallizes in the monoclinic space group C2/c with a = 14.2228(7) A, b = 20.3204(9) A, c = 14.1022(7) A, beta = 95.144(1) degrees, V = 4059.3(3) A(3), and Z = 4. [Rh(2)(O(2)CCH(3))(2)(pynp)(2)][BF(4)](2) x C(7)H(8) (3) crystallizes in the monoclinic space group C2/c with a = 13.409(2) A, b = 21.670(3) A, c = 13.726(2) A, beta = 94.865(2) degrees, V = 3973.9(8) A(3), and Z = 4. A minor product, [Rh(2)(O(2)CCH(3))(2)(pynp)(2)(CH(3)CN)(2)][BF(4)][PF(6)] x 2CH(3)CN (4), was isolated from the mother liquor after crystals of 3 had been harvested; this compound crystallizes in the triclinic space group, P1 with a = 12.535(3) A, b = 13.116(3) A, c = 13.785(3) A, alpha = 82.52(3) degrees, beta = 77.70(3) degrees, gamma = 85.76(3) degrees, V = 2193.0(8) A(3), and Z = 2. Compounds 1-3 constitute a convenient series for probing the influence of the electronic configuration on the extent of mixing of the M-M orbitals with the pi system of the pynp ligand. Single point energy calculations performed on 1-3 at the B3LYP level of theory lend insight into the bonding in these compounds and allow for correlations to be made with electronic spectral data. Although purely qualitative in nature, the values for normalized change in orbital energies (NCOE) of the frontier orbitals before and after reduction are in agreement with the observed differences in reduction potentials as determined by cyclic voltammetry.     

Synthesis and Electrochemistry of Heterobimetallic Ruthenium/Platinum and Molybdenum/Platinum Complexes

As starting materials for heterobimetallic complexes, [RuCp(PPh(3))CO(PPh(2)H)]PF(6) and [RuCp(PPh(3))CO(eta(1)-dppm)]PF(6) were prepared from RuCp(PPh(3))(CO)Cl. In the course of preparing [RuCp(eta(2)-dppm)(eta(1)-dppm)]Cl from RuCp(Ph(3)P)(eta(1)-dppm)Cl, the new monomer RuCpCl(eta(1)-dppm)(2) was isolated. The uncommon coordination mode of the two monodentate bis(phosphines) was confirmed by X-ray crystallography [a = 11.490(1) ?, b = 14.869(2) ?, c = 15.447(2) ?, alpha = 84.63(1) degrees, beta = 70.55(1) degrees, gamma = 72.92(1) degrees, V = 2378.7(5) ?(3), d(calc) = 1.355 g cm(-)(3) (298 K), triclinic, P&onemacr;, Z = 2]. The dppm-bridged bimetallic complexes RuCp(PPh(3))Cl(&mgr;-dppm)PtCl(2), RuCpCl(&mgr;-dppm)(2)PtCl(2), and [RuCp(PPh(3))CO(&mgr;-dppm)PtCl(2)]PF(6) each exhibit electrochemistry consistent with varying degrees of metal-metal interaction. The cationic heterobimetallic complexes [Mo(CO)(3)(&mgr;-dppm)(2)Pt(H)]PF(6) and [MoCp(CO)(2)(&mgr;-PPh(2))(&mgr;-H)Pt(PPh(3))(MeCN)]PF(6) were prepared by chloride abstraction from the corresponding neutral bimetallic species and show electrochemical behavior similar to the analogous Ru/Pt complexes.     

Structure Determination of the Products from the Acid-Catalyzed Condensation of Indole with Acetone

Four of the previously reported compounds obtained from the acid-catalyzed condensation of indole with acetone are now assigned the following structures: cis-4,4a,9,9a-tetrahydro-2-(1H-indol-3-yl)-4,4-dimethyl-3H-carbazole (2a), 1,1',4,4'-tetrahydro-1,1,1',1'-tetramethyl-3,3'(2H,2'H)-spirobi[cyclopent[b]indole] (4), 4,4a-dihydro-2-(3-1H-indolyl)-4,4-dimethyl-3H-carbazol-4a-ol (7), and 5-(2-aminophenyl)-1,3,4,5-tetrahydro-1,1,4,4-tetramethylcyclopent[kl]acridine (8). The structure of the novel rearrangement product 8 was solved by an X-ray crystal structure determination. The two previously reported autoxidation products of 4 are now assigned the following structures: 1,3',4,4'-tetrahydro-1,1,4',4'-tetramethyl-cis-dispiro[cyclopent[b]indole-3(2H),2'(5'H)-furan-5',3"-[3H]-indol]-2"(1"H)-one (5) and 1,4-dihydro-1,1,5',5'-tetramethylspiro[cyclopent[b]indole-3(2H),3'(4'H)-1-benzazocine]-2'(1'H),6'(5'H)-dione (6).     

Metabolite profiling of licorice (Glycyrrhiza glabra) from different locations using comprehensive two-dimensional liquid chromatography coupled to diode array and tandem mass spectrometry detection

Profiling of the main metabolites from several licorice (Glycyrrhiza glabra) samples collected at different locations is carried out in this work by using comprehensive two-dimensional liquid chromatography (LC × LC) coupled to diode array (DAD) and mass spectrometry (MS) detectors. The optimized method was based on the application of a HILIC-based separation in the first dimension combined with fast RP-based second dimension separation. This set-up was shown to possess powerful separation capabilities allowing separating as much as 89 different metabolites in a single sample. Identification and grouping of metabolites according to their chemical class were achieved using the DAD, MS and MS/MS data. Triterpene saponins were the most abundant metabolites followed by glycosylated flavanones and chalcones, whereas glycyrrhizic acid, as expected, was confirmed as the main component in all the studied samples. LC × LC-DAD-MS/MS was able to resolve these complex licorice samples providing with specific metabolite profiles to the different licorice samples depending on their geographical origin. Namely, from 19 to 50 specific compounds were exclusively determined in the 2D-chromatograms from the different licorice samples depending on their geographical origin, which can be used as a typical pattern that could potentially be related to their geographical location and authentication.     

An advanced decision support system for European disaster management: the feature of the skills taxonomy

Central European Journal of Operations Research - Mankind has faced a huge increase in severe natural and man-made disasters worldwide in the last few years. Emergency responders on a strategic,...     

Cohn Path Algebras of Higher-Rank Graphs

In this article, we introduce Cohn path algebras of higher-rank graphs. We prove that for a higher-rank graph Λ, there exists a higher-rank graph T Λ such that the Cohn path algebra of Λ is isomorphic to the Kumjian-Pask algebra of T Λ. We then use this isomorphism and properties of Kumjian-Pask algebras to study Cohn path algebras. This includes proving a uniqueness theorem for Cohn path algebras.     

Designing Statistically Similar RVEs for 3D Dual Phase Steel Microstructures

This contribution presents a method for the construction of three-dimensional Statistically Similar Representative Volume Elements (SSRVEs) for dual phase steels (DP steels). From such kind of advanced high strength steels, enhanced material properties are observed, which originate in the interaction of the individual constituents of the material on the microscale. Our aim is to directly incorporate the microstructure in the material modeling, which can be accomplished by applying i. e. the FE² method. A RVE representing the real material is used in the microscopic boundary value problem, which is solved at each macroscopic integration point. Since such RVEs usually exhibit a high complexity due to the underlying real microstructure, high computational costs are a drawback of the approach. We replace this RVE with a SSRVE, which has a lower complexity but which is still able to represent the mechanical behavior of the RVE and thus of the real microstructure. Virtual experiments show the performance of the method. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Using Video‐Based Pedagogy in an Elementary Mathematics Methods Course

The study explored the impact of using video‐based pedagogy on preservice teachers' cognitions about teaching mathematics. The use of video‐based pedagogy was integrated into the course, Methods for Teaching Elementary School Mathematics. A variety of written and interview data were collected during the course and, in the following semester, during student teaching. Evidence from case studies of three preservice teachers indicates that they engaged in reflection and reconstruction of their beliefs about how children learn mathematics and moved from a more didactic perspective of teaching mathematics toward a student‐centered perspective. Such movement appears to have been influenced by the use of video‐based pedagogy.     

Lattices on Nonuniform Trees

Let X be a locally finite tree, and let G=Aut(X). Then G is a locally compact group. We show that if X has more than one end, and if G contains a discrete subgroup such that the quotient graph of groups \\X is infinite but has finite covolume, then G contains a nonuniform lattice, that is, a discrete subgroup such that \G is not compact, yet has a finite G-invariant measure.