Hyperconjugation versus back bonding in AH3−nXn species (A = Si and Ge; X = F,Cl and Br; and n = 1, 2 and 3)

In this research two competing phenomena, back bonding and hyperconjugation, have been investigated based on Natural Bond Orbital (NBO) and Atoms in Molecules (AIM) analyses for radical AH_3?nX_n species, where A = Si and Ge, and n = 1, 2 and 3. It is demonstrated in this article that both above phenomena will be occurred significantly, while back bonding is the only event in analogous compounds with carbon and hyperconjugation is rather negligible. It was also found that only one back bonding with the help of keyword $CHOOSE in NBO analysis can be found in this type of compounds with reasonable structure, while it can be sometimes detected in AH_3?nX_n without using keyword $CHOOSE. It is also shown that there is always an increase in bond length in comparison with reference molecules in mentioned species due to existing hyperconjugation, while if the central atom is carbon, we have always a decrease of bond length due to only having back bonding. Additionally, from AIM point of view, the delocalization indices for α-spin (majority spin) is more than β-spin (minority spin) in radical species for molecules without back bonding, while the situation in our compounds is quite reverse, which can be attributed to the π back bonding in the β-spin electrons.     

Developmental changes of poly(ADP-ribose) polymerase expression in Sarcophaga peregrina

To elucidate the physiological role of poly(ADP-ribose) polymerase (PARP), we studied the levels of PARP mRNA and protein during the developmental stages of Sarcophaga peregrina. PARP mRNA expression changed remarkably throughout the developmental stages. The level of PARP mRNA (the molecular ratio of PARP mRNA to the total RNA) was highest in unfertilized eggs and that of PARP protein (the molecular ratio of PARP protein to the total protein of the crude extract) was high in unfertilized and fertilized eggs and in 1st instar larvae. During the embryogenesis period, the levels of PARP mRNA and protein gradually decreased. The levels of PARP mRNA during larval and pupal periods became less than about 5% of that in unfertilized eggs. After the emergence of adult flies, the levels of PARP mRNA and protein increased both in female and male flies. PARP activity normalized with the total amount of protein in the crude extract changed in parallel to the level of PARP protein throughout the developmental stages. The biological significance of the drastic change of mRNA and protein levels of PARP still remains to be clarified.     

Electron Density Analysis of Hyperconjugation

Hyperconjugation is analyzed through the electron density of orbitals responsible for hyperconjugative interactions, which cannot be detected by means of conventional electron‐density‐based calculations. This interaction is detected through the π electron density topology, by excluding σ electron density from the total. As the presence of the hyperconjugation phenomenon in carbocation systems is well understood, several carbocations are benchmarked, and the results show that the positive carbon atom establishes a hyperconjugative critical point with the adjacent methyl group(s). Also, π localization and delocalization indices are employed to support the conclusions made by the topological analysis.     

Decomposition of deformation density into orbital components

In this research, deformation density matrix has been introduced as matrix representation of the density difference between the complex and fragments. The deformation density matrix is then diagonalized to obtain the magnitude of displaced charges as eigenvalues. Correspondingly, the eigenvectors reveal the spaces responsible for reorganization of the electrons because of the complex formation. The formalism has been applied on some CO₂ planar clusters, and the results showed that how the deformation density can be successfully separated into in‐plane and out‐of‐plane contributions. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Block deformation analysis: Density matrix blocks as intramolecular deformation density

Block deformation analysis as deformation density of atomic orbitals is introduced to analyze intramolecular interactions. In this respect, density matrix blocks in terms of natural atomic orbitals are employed to find interacting and noninteracting multicenter subsystem and extract the corresponding deformation density. Eigenanalysis of this deformation density is performed to result eigenvalues and eigenorbitals as displaced charge due to the intramolecular interaction and orbital space responsible for charge reorganization, respectively, that possesses advantages of other methods, simultaneously. It is applied to several small molecules, different types of carbon allotropes including zero-, one-, and two-dimensional nanostructures, and challenging systems such as ortho-hydrogen atoms in planar biphenyl. Results highly correlate with delocalization and Wiberg bond indices and show that eigenvalues of block deformation analysis deserved to be considered as bonding index.     

Poly(ADP-ribose) polymerase-1 gene in human tumor cell lines: Its expression and structural alteration

Poly(ADP-ribose) polymerase-1 (Parp-1) is involved in DNA repair and cell-death induction after DNA damage. Parp-1^−/− mice show higher susceptibility to the carcinogenic effects of nitrosamine and azoxymethane. To elucidate the role of alterations of the PARP-1 gene in human carcinogenesis, we examined the expression level of PARP-1 gene in various human tumor cell lines. The presence of gross rearrangement of PARP-1 gene in these cell lines was also examined by Southern blot hybridization analysis. The expression levels of PARP-1 gene in several cell lines, including T-cell leukemia cell lines (Molt-4 and CCRF-CEM), colon cancer cell line (WiDr), and gastric cancer cell lines (KATOIII, OKAJIMA, and MKN45) was substantially lower than in other cancer cell lines. Among the 85 analyzed cell lines, structural alteration of PARP-1 gene was detected in a gastric cancer cell line, MKN28. A low level of PARP-1 expression in human cancer could potentially influence cancer cell growth, differentiation and cancer development by affecting genomic instability, as well as the response of tumors to chemo- and radiotherapy.     

Molecular Modeling of Human CCR2 Receptor within POPC Lipid Bilayer

Structural Chemistry - Chemokine receptor 2 (CCR2), a G-protein coupled receptor (GPCR), is a critical target for several inflammatory and autoimmune diseases. The main restriction on designing...     

The Eigenvalues of a Class of Elliptic Differential Operators

Consider $\left(M,g\right)$ as an $n$-dimensional compact Riemannian manifold. In this paper we are going to study a class of elliptic differential operators which appears naturally in the study of hypersurfaces with constant mean curvature and also the study of variation theory for $1$-area functional.     

A Tunable Er3+-Doped Fiber Laser by Use of an Integrated Optics Mach-Zehnder Interferometer

Wavelength tunability of an Er³⁺-doped fiber laser is reported by the use of an integrated optics Mach-Zehnder interferometer driven electro-optically. A pump laser threshold of 5 mW and a continuous tunable band from 1530 nm to 1554 nm are achieved with a drive voltage varying between 0 to +7 volts. An evaluation of the design and improvements are given based on the experimental and theoretical analysis.     

Micrometer-sized graphitic balls produced together with single-wall carbon nanohorns

We present in this report a new type of particles with micrometer-order sizes, which we called giant graphitic balls (GG balls). The GG balls are produced by CO2 laser ablation of graphite together with single-wall carbon nanohorns. They have graphitic structures whose layers tend to align parallel with the GG-ball surfaces, resulting in polygonal-like arrangements. Comparing the GG-ball structure with that of the previously reported polygonal graphite-particles, the growth mechanism of the GG ball is discussed briefly.