Why do the heavy-atom analogues of acetylene E2H2 (E = Si-Pb) exhibit unusual structures?

DFT calculations at BP86/QZ4P have been carried out for different structures of E(2)H(2) (E = C, Si, Ge, Sn, Pb) with the goal to explain the unusual equilibrium geometries of the heavier group 14 homologues where E = Si-Pb. The global energy minima of the latter molecules have a nonplanar doubly bridged structure A followed by the singly bridged planar form B, the vinylidene-type structure C, and the trans-bent isomer D1. The energetically high-lying trans-bent structure D2 possessing an electron sextet at E and the linear form HEEH, which are not minima on the PES, have also been studied. The unusual structures of E(2)H(2) (E = Si-Pb) are explained with the interactions between the EH moieties in the (X(2)Pi) electronic ground state which differ from C(2)H(2), which is bound through interactions between CH in the a(4)Sigma(-) excited state. Bonding between two (X(2)Pi) fragments of the heavier EH hydrides is favored over the bonding in the a(4)Sigma(-) excited state because the X(2)Pi --> a(4)Sigma(-) excitation energy of EH (E = Si-Pb) is significantly higher than for CH. The doubly bridged structure A of E(2)H(2) has three bonding orbital contributions: one sigma bond and two E-H donor-acceptor bonds. The singly bridged isomer B also has three bonding orbital contributions: one pi bond, one E-H donor-acceptor bond, and one lone-pair donor-acceptor bond. The trans-bent form D1 has one pi bond and two lone-pair donor-acceptor bonds, while D2 has only one sigma bond. The strength of the stabilizing orbital contributions has been estimated with an energy decomposition analysis, which also gives the bonding contributions of the quasi-classical electrostatic interactions.     

Suitable reference genes for relative quantification of miRNA expression in prostate cancer

Real time quantitative PCR (qPCR) is the method of choice for miRNA expression studies. For relative quantification of miRNAs, normalization to proper reference genes is mandatory. Currently, no validated reference genes for miRNA qPCR in prostate cancer are available. In this study, the expression of four putative reference genes (hsa-miR-16, hsa-miR-130b, RNU6-2, SNORD7) was examined with regard to their use as normalizer. After SNORD7 was already shown an inappropriate reference gene in preliminary experiments using total RNA pools, we studied the expression of the putative reference genes in tissue and normal adjacent tissue sample pairs from 76 men with untreated prostate carcinoma collected after radical prostatectomy. hsa-miR-130b and RNU6-2 showed no significantly different expression between the matched malignant and non-malignant tissue samples, whereas hsa-miR-16 was significantly underexpressed in malignant tissue. Softwares geNorm and Normfinder predicted hsa- miR-130b and the geometric mean of hsa-miR-130b and RNU6-2 as the most stable reference genes. Normalization of the four miRNAs hsa-miR-96, hsa- miR-125b, hsa-miR-205, and hsa-miR-375, which were previously shown to be regulated, shows that normalization to hsa-mir-16 can lead to biased results. We recommend using hsa-miR-130b or the geometric mean of hsa-miR-130b and small RNA RNU6-2 for normalization in miRNA expression studies of prostate cancer.     

Packed to the Rafters: Filling up C60 with Rare Gas Atoms

How many rare gas atoms can be placed into a fullerene cage until the pressure becomes large enough to break the C₆₀ framework? The answer given by density functional and ab initio computations is surprising and underlines the high stability of this unique carbon structure.     

Teaching students with mathematics disabilities to solve multiplication and division word problems: the role of schema-based instruction

ZDM – Mathematics Education - Mathematical knowledge involving whole number multiplication and division is integral to understanding multiplicative structures such as ratios, slope, rate of...     

TEM observations of rhombohedral and monoclinic domains in LaCoO3-based ceramics

Twin structures in rhombohedrally distorted polycrystalline LaCoO₃, La_0.8Ca_0.2CoO_3-δ and La_0.5Sr_0.5Co_0.5Fe_0.5O_3-δ have been studied by transmission electron microscopy. Normal {100} and {110} twinning was predominant in LaCoO₃ and La_0.8Ca_0.2CoO_3-δ. In addition, ferroelastic domains with a one-dimensional superstructure corresponding to a tripling of the pseudocubic lattice parameter, a _c, were found in some grains. The monoclinic superstructure vanished over time and was sensitive to external mechanical stress. In La_0.5Sr_0.5Co_0.5Fe_0.5O_3-δ no normal twinning was observed, but domains with a one-dimensional superstructure of two times a _c were observed. The superstructures have been interpreted as atomic scale twinning, which reduce the crystal symmetry from rhombohedral to monoclinic.     

Die Beanspruchung einfacher Ringe und zweiteiliger Ringverbände unter Innendruck und deren günstigste Bemessung

Ohne Zusammenfassung     

Theoretical Studies of Inorganic Compounds. 27 Quantum Chemical Investigations of Transition Metal Nitrido Complexes with a TM‐N‐E Linkage (E = Main Group Element)

It is reported about quantum chemical DFT calculations of various transition metal (TM) nitrido complexes which contain a TM‐N‐E linkage. The goal is to elucidate the nature of the TM‐N‐E bonding situation with modern quantum chemical tools. Five comparative investigations have been carried out. (a) Comparison of the N‐donor ability in the nitrido complexes Cl₃W‐N‐ECl_n where ECl_n = NaCl, MgCl₂, AlCl₃. (b) Comparative analysis of the bonding situation in Cl₄W‐N‐X where X = Na, MgCl, AlCl₂, SiCl₃, PCl₂, SCl, Cl. (c) Comparison of the structure and bonding in Cl₅W‐NPH₃, Cl₅W‐OPH₃⁺, Cl₄W‐(NPH₃)(OPH₃)⁺. (d) Comparative analysis of the bonding situation in Cl₅Ta‐OPH₃, Cl₅W‐NPH₃, Cl₅Re‐CPH₃. (e) Energy decomposition analysis of the bonding of the isolobal ligands NPH₃ and Cp with WCl₅.