Pi Character Research Articles

The elusive diiodosulphanes and diiodoselenanes

Diiodosulphanes (S n I2, where 1 ≤ n ≤ 6) are scarcely studied. There are indirect evidences of the existence of diiodoselenanes (Se n X2) such as RMN or UV–vis spectroscopy. The geometry of these compounds was stated at different theory levels: DFT (M06-2X-D3, PBE0) and MP2. Certain S–S and Se–Se bonds have bond orders higher than 1, and the bond among the S or Se atoms has some pi character. These compounds are involved in many reactions in equilibrium. The thermochemistry of these reactions was studied using DFT, MP2, MP4(SDTQ) and, in some cases, with CCSD(T) or CCSD(TQ) methods. For reactions such as S m I2 + S n I2 → S m +n I2 + I2, the used methods stated that ΔH is around −25 to −50 kJ/mol when the length of the S–S chain increases. In these reactions, the equilibrium is displaced towards the formation of products. Instead, when the reactants are diiodoselenanes, ΔH goes from −4 to −23 kJ/mol. Finally, the electronic spectra of these compounds were described using TDDFT methods. The results for diiodosulphanes matched with the experimental data, which allowed for the assignment of the different transitions. The electronic spectra for diiodoselenanes, which are unknown for the moment, were estimated.

Приближенное решение задачи о квадратуре круга

It is known that squaring the circle (the problem consisting in construction of a square with the same area as a given circle), together with duplication of cube and angle trisection, is one of the most famous unsolv able problems of constructive geometry for construction with compass and straightedge. The solution of squaring the circle problem is reduced to the straightening of the circle, that is, to the construction of a segment equal in length to the circle, and its insolvability is connected with the pi character transcendence. In this paper, the limiting case of one of Christian Huygens theorems, which establishes an estimate for length of circumference of a circle through perimeters of regular polygons inscribed in circle and circumscribed about it, is proved. On this basis has been proposed and justified an approximate method for squaring the circle problem solving, which allows consistently construct arbitrarily exact solutions of the problem. We will approximate an arc of a circle whose radius is a multiple of the given circle’s radius, with the help of a segment which is parallel to a shrinking it chord, and then will increase or decrease this segment in the required number of times, so that the resulting segment’s length would be approximately equal to half of the given circle’s circumference. The approximation accuracy will be the higher the smaller arc of the circle we will consider. But possibilities of real tools are limited, and not suitable for both too small and too large drawing scales. In order to cope with this problem, an algorithm for scaled approximation has been proposed, in which it is sufficient to increase (or reduce) the drawing fragment, so that all the time sta y within the sheet of the same size. Perhaps this approach will be useful for other constructions, including the exact ones, where it is necessary to come to very large or vice versa very small drawings’ dimensions.

AN ANALYSIS OF TRANSLATION TECHNIQUES AND QUALITY IN TERMS OF ACCURACY, ACCEPTABILITY AND READBILITY OF PI'S EXPRESSIVE SPEECH ACT IN THE FILM ENTITLED LIFE OF PI

<p>This research was conducted to analysis the translation techniques and quality of types on expressive speech acts exploited by Pi, the main character in the film “Life of PI”. The research used the Pragmatics approach with speech act as the field of study. It was a descriptive qualitative research and it employed purposive sampling as the sampling technique. The data in this research were the types of expressive speech acts. From the result of data analysis, there are four types of expressive speech acts employed by Pi character in the film “Life of PI”, they are thanking, apologizing, blaming and praising. From the analysis, the first finding of the research shows that the total data of research are 24 data. There are four expressive, thanking expressive speech act 7 data, apologizing speech act 10 data, blaming 3 data, and praising 4 data. The second finding of the research shows that there are two techniques employed by the translator in translating expressive speech act in the film “Life of Pi”. They are literal translation 19 data and explicit translation 5 data. The third finding dealing with the quality of translation, the translation of expressive speech act in the subtitle film “Life of Pi” belongs to accurate and acceptable and readable translation. For the accuracy of the translation, from 24 data, 19 data are accurately translated, 5 data are less accurately translated. For the acceptability of the translation, from 24 data, 21 data are acceptably translated, 3 data are less acceptably translated. For the readability, all the 24 data are readable.</p>

On cardinal invariants of space of finite subsets


 In article some cardinal invariants of the space of finite subsets are examined. We obtained that such cardinal invariants us density and network weight, character and pi–character, pi–weight and weight coincide for any (A,B)–topology (Proposition 1). Also we obtained estimates of space of the finite subset of Lindelioft number and Suslin’s number (Theorem 2). Also is proved that for the space of finite subsets pseudo character is countable than and if than it’s diagonal number is countable for any (A,B)–topology (Proposition 4). Characterization when space of finite subsets has countable character is given (Proposition 5).

Particle-hole symmetry breaking in the pseudogap state ofPb0.55Bi1.5Sr1.6La0.4CuO6+δ: A quantum chemical perspective

Two Bi2201 model systems are employed to demonstrate how, beside the Cu-O \sigma-band, a second band of purely O2p\pi character can be made to cross the Fermi level owing to its sensitivity to the local crystal field. This result is employed to explain the particle-hole symmetry breaking across the pseudo-gap recently reported by Shen and co-workers, see M. Hashimoto et al., Nature Physics 6, (2010) 414. Support for a two-bands-on-a-checkerboard candidate mechanism for High-Tc superconductivity is claimed.

DFT Mechanistic Study on Diene Metathesis Catalyzed by Ru‐Based Grubbs–Hoveyda‐Type Carbenes: The Key Role of π‐Electron Density Delocalization in the Hoveyda Ligand

The catalytic activity and catalyst recovery of two heterogenized ruthenium-based precatalysts (H and NO(2)(4)) in diene ring-closing metathesis have been studied by means of density functional calculations at the B3LYP level of theory. For comparison and rationalization of the key factors that lead to higher activities and higher catalyst recoveries, four other Grubbs-Hoveyda complexes have also been investigated. The full catalytic cycle (catalyst formation, propagation, and precatalyst regeneration) has been considered. DFT calculations suggest that either for the homogeneous and heterogenized systems the activity of the catalysts mainly depends on the ability of the precursor to generate the propagating carbene. This ability does not correlate with the traditionally identified key factor, the Ru...O interaction strength. In contrast, precatalysts with lower alkoxy-dissociation energy barriers and lower stabilities compared with the propagating carbene also present larger C1-C2 bond length (i.e., lower pi character of the C-C bond that exists between the metal-carbene (Ru=C) and the phenyl ring of the Hoveyda ligand). Catalyst recovery, regardless of whether a release-return mechanism occurs or not, is also mainly determined by the pi delocalization. Therefore, future Grubbs-Hoveyda-type catalyst development should be based on fine-tuning the pi-electron density of the phenyl moiety, with the subsequent effect on the metalloaromaticity of the ruthenafurane ring, rather than considering the modification of the Ru...O interaction.

Conformational Dependence of σ‐Electron Delocalization in Linear Chains: Permethylated Oligosilanes

The effects of sigma-electron delocalization on optical properties of saturated linear chains of permethylated oligosilanes are strongly conformation dependent. We analyze the origin of the conformational dependence of the energies of molecular orbitals and of electronic excitations in simple intuitively understandable terms by using a first-order approximation to the Hückel version of the "Ladder C" model. The analysis is supported by comparison with results of numerical calculations from time-dependent density functional theory, which agree well with experiment. To facilitate the comparison, a simple procedure has been developed that defines the overall and local fractional sigma and pi characters of a backbone molecular orbital and a fractional overall and local sigma sigma* and sigma pi* characters of an excited state for any conformation of a linear chain.

Electronic Structure and Magnetic Properties of Potassium Ozonide KO3

The electronic structure and magnetic properties of potassium ozonide, KO(3), have been investigated by means of periodic spin polarized Hartree-Fock and Density Functional Theory based approaches. These calculations show that KO(3) is a strongly ionic compound with paramagnetic O(3)(-) centers. The most reliable results, provided by the B3LYP hybrid approach, suggest that the system behaves as a magnetic insulator with a gap of approximately 3.0 eV, and with the states around the insulating gap arising mainly from the pi orbitals of the O(3)(-) units while the participation of potassium orbitals in the bands around the band gap is practically negligible. The calculations suggest that, because of the pi character of the magnetic orbitals, the magnetic structure for KO(3) has a significant one-dimensional character, with antiferromagnetically coupled chains along the c axis and a much weaker antiferromagnetic coupling between neighboring chains. This behavior is consistent with available experimental susceptibility data.

A variable temperature spectroscopic study on Paracoccus pantotrophus pseudoazurin: Protein constraints on the blue Cu site

The blue or Type 1 (T1) copper site of Paracoccuspantotrophus pseudoazurin exhibits significant absorption intensity in both the 450 and 600 nm regions. These are sigma and pi S(Cys) to Cu(2+) charge transfer (CT) transitions. The temperature dependent absorption, EPR, and resonance Raman (rR) vibrations enhanced by these bands indicate that a single species is present at all temperatures. This contrasts the temperature dependent behavior of the T1 center in nitrite reductase [S. Ghosh, X. Xie, A. Dey, Y. Sun, C. Scholes, E. Solomon, Proc. Natl. Acad. Sci. 106 (2009) 4969-4974] which has a thioether ligand that is unconstrained by the protein. The lack of temperature dependence in the T1 site in pseudoazurin indicates the presence of a protein constraint similar to the blue Cu site in plastocyanin where the thioether ligand is constrained at 2.8 A. However, plastocyanin exhibits only pi CT. This spectral difference between pseudoazurin and plastocyanin reflects a coupled distortion of the site where the axial thioether in pseudoazurin is also constrained, but at a shorter Cu-S(Met) bond length. This leads to an increase in the Cu(2+)-S(Cys) bond length, and the site undergoes a partial tetragonal distortion in pseudoazurin. Thus, its ground state wavefunction has both sigma and pi character in the Cu(2+)-S(Cys) bond.

Photoluminescence of 1-D Copper(I) Cyanide Chains: A Theoretical Description

Solid copper(I) cyanide occurs as extended one-dimensional chains with interesting photophysical properties. To explain the observed luminescence spectroscopy of CuCN, we report a series of computational studies using short bare and potassium-capped [Cu(n)(CN)(n+1)] (-) (n = 1, 2, 3, 4, 5, and 7) chains as CuCN models. On the basis of TD-DFT calculations of these model chains, the excitation transitions in the UV spectrum are assigned as Laporte-allowed pi-pi transitions from MOs with Cu 3d(pi) and CN pi character to empty MOs with Cu 4p and CN pi* character. Transitions between the HOMO (3d(z)) and LUMO (Cu 4p and CN pi*) are symmetry forbidden and are not assigned to the bands in the excitation spectrum. The emission spectrum is assumed to arise from transitions between the lowest triplet excited state and the ground-state singlet. The lowest energy triplet for the model networks has a bent structure due to distortions to remove the degeneracies in the partially occupied MOs of the linear triplet. The S(0)-T gap for the bent triplet chains is consistent with the emission wavelength for bulk CuCN.

Vibrational Kondo Effect in Pure Organic Charge-Transfer Assemblies

A Kondo resonance has been observed using a scanning tunneling microscope on a single molecular layer of a purely organic charge-transfer salt grown on a metal surface. Analysis of the Kondo anomaly reveals that the electron acceptor of the film possesses a spin-1/2 ground state due to the localization of an unpaired electron in the conjugated lowest unoccupied molecular orbital. Because of the pi character of this molecular state the unpaired electron is strongly coupled to molecular vibrations, leading to the split of the Kondo resonance in vibrational sidebands.

Time dependent density functional theory study of the near-edge x-ray absorption fine structure of benzene in gas phase and on metal surfaces

The near-edge x-ray absorption fine structure of benzene in the gas phase and adsorbed on the Au(111) and Pt(111) surfaces is studied with time dependent density functional theory. Excitation energies computed with hybrid exchange-correlation functionals are too low compared to experiment. However, after applying a constant shift the spectra are in good agreement with experiment. For benzene on the Au(111) surface, two bands arising from excitation to the e(2u)(pi(*)) and b(2g)(pi(*)) orbitals of benzene are observed for photon incidence parallel to the surface. On Pt(111) surface, a broader band arises from excitation to benzene orbitals that are mixed with the surface and have both sigma(*)(Pt-C) and pi(*) characters.

Electric Field Effects on Aromatic and Aliphatic Hydrocarbons: A Density-Functional Study

The influence of a uniform static external electric field on some aliphatic and aromatic molecular species is studied within the density functional theory (DFT) employing the 6-311++G(2d,2p) basis set with B3LYP exchange-correlation prescription. The electric field perturbs the molecular geometry but drastically alters the dipole moments and engenders, to a varying degree, the molecular vibrational Stark effect, i.e., shifts in the infrared (IR) vibrational frequencies accompanied by spectral intensity redistribution. For polar molecules, significant negative ("red") and positive ("blue") frequency shifts are observed for field orientations both parallel and antiparallel to their permanent dipole moments. Further, a selective reordering of frontier orbitals is observed to be brought about by moderately intense fields. In particular, molecules having a lowest unoccupied molecular orbital (LUMO) with predominant pi character possess a threshold field beyond which energy gap between the highest occupied molecular orbital (HOMO) and LUMO diminishes rapidly. A time-dependent (TD) DFT analysis reveals that an increase in the applied field strength by and large increases the excitation energies corresponding to significant electronic transitions among frontier MOs with a concomitant decrease in their oscillator strengths.

Homo- and Heteroleptic Complexes of Four-Membered Group 13 Metal(I) N-Heterocyclic Carbene Analogues with Group 10 Metal(0) Fragments

A series of complexes between recently developed four-membered group 13 metal(I) heterocycles and group 10 metal(0) fragments have been prepared and structurally characterized. One prepared complex, [Pt{Ga[N(Ar)]2CNCy2}3] (Ar = C6H3Pri2-2,6; Cy = cyclohexyl), possesses the shortest Pt-Ga bonds yet reported, the covalent components of which are suggested by theoretical studies to have significant pi character.

Theoretical Insight into the Spectroscopy and Photochemistry of Isoalloxazine, the Flavin Core Ring

The electronic singlet-singlet and singlet-triplet electronic transitions of the isoalloxazine ring of the flavin core are studied using second-order perturbation theory within the framework of the CASPT2//CASSCF protocol. The main features of the absorption spectrum are computed at 3.09, 4.28, 4.69, 5.00, and 5.37 eV. The lowest singlet (S1) and triplet (T1) excited states are found to be both of pi character with a singlet-triplet splitting of 0.57 eV. On the basis of the analysis of the computed spin-orbit couplings and the potential energy hypersurfaces built for the relevant excited states, the intrinsic mechanism for photoinduced population of T1 is discussed. Upon light absorption, evolution of the lowest singlet excited state along the relaxation pathway leads ultimately to the population of the lowest triplet state, which is mediated by a singlet-triplet crossing with a state of npi* type. Subsequently a radiationless decay toward T1 through a conical intersection takes place. The intersystem crossing mechanism and the internal conversion processes documented here provide a plausible route to access the lowest triplet state, which has a key role in the photochemistry of the flavin core ring and is mainly responsible for the reactivity of the system.

The Transfer of Tin and Germanium Atoms from N‐Heterocyclic Stannylenes and Germylenes to Diazadienes

New N-heterocyclic stannylenes and germylenes were synthesized by transamination of E[N(SiMe3)2] (E = Ge, Sn) with alpha-amino-aldimines or ethylidene-1,2-diamines and were characterized by spectroscopic methods and in the case of the germylene 10 g by X-ray diffraction. The reactions of several germylenes and stannylenes with diazadienes were studied by using dynamic NMR and computational methods. Experimental and theoretical studies confirmed that metathesis with exchange of the Group 14 atom is feasible for both stannylenes and germylenes, with exchange rates being generally higher for stannylenes. The metathesis of the diazadiene 3 b and the stannylene 1 b follows second-order kinetics and exhibits a sizeable negative entropy of activation. The transfer reaction is inhibited by bulky substituents in both reactants and surprisingly coincides with a suppression of the fragmentation of the stannylene into tin and diazadiene. A connection between oxidative addition and ring fragmentation was also observed in the reaction of 1 f with sulfur. Density functional theory (DFT) calculations suggest that all metathesis reactions proceed via transient spirocyclic [1+4] cycloaddition products, the formation of which is generally endothermic and endergonic. The spirostannanes display a distorted Psi-tbp geometry at the tin atom and their cycloreversion requires low or nearly negligible activation energies; spirogermanes exhibit distorted tetrahedral central atoms and sizeable energy barriers with respect to the same reaction. Complementary studies of cycloadditions of diazadienes to triplet germylenes or stannylenes indicate that these reactions are exothermic. The lowest triplet state in the carbene homologues results from promotion of an electron from an n(N) orbital with pi character rather than the n(C)-sigma orbital as in carbenes, and singlet-triplet excitation energies decrease from carbon to tin. Spirostannanes exhibit a triplet ground-state multiplicity that implies that the energy hypersurfaces for the reactions of singlet and triplet stannylenes with diazadienes intersect; for germylenes, the singlet hypersurface is always lower in energy. A reaction mechanism explaining the different thermal stabilities of N-heterocyclic germylenes and stannylenes, and the coincidence between ring metathesis and thermal decomposition of the latter, is proposed based on the different separation of the singlet and triplet energy hypersurfaces.

Genotypic Variation of the Ability of Root to Penetrate Hard Soil Layers among Japanese Wheat Cultivars

The hard soil in the field is a major constraint for the cereal production because it mechanically restricts the root expansion and water absorption. The ability of root to penetrate into the hard soil is an important factor affecting yield stability of wheat (Triticum aestivum L.) under hard soil and drought conditions. We investigated the variation in the penetrating ability of roots (PA) among Japanese wheat cultivars and its relationship with other shoot and root characters to acquire basic information to develop the cultivars with a higher PA. The evaluation was conducted by the two experiments using the two groups of cultivars: 1) 43 Hokkaido cultivars in the first experiment, 2) 38 Honsyu, including Shikoku and Kyusyu, cultivars in the second experiment. In each experiment, one seedling of each cultivar was grown in a pot with a disc made of paraffin and Vaseline mixture (PV) as a substitute for the hard soil layer. The number of roots penetrating through the PV disc per plant (NRP), the number of seminal and crown roots reached the PV disc per plant (NRR) and the penetration index (PI = NRP/NRR) of each cultivar were evaluated as the traits related to PA. NRP significantly varied with the cultivar from 4.0 to 29.7 and 3.0 to 22.0 in the first and second experiments, respectively. NRP were significantly correlated with NRR (r=0.644** in the first and r=0.477** in the second experiment) and PI (r=0.863** in the first and r=0.811** in the second experiment), but the relationships between NRR and PI were not significant (r=0.260 in the first and r=0.190 in the second experiment). NRR was significantly correlated with the degree of winter growth habit (requirement of vernalization), root dry weight (DW) above the PV disc, the number of stems and leaf DW in each population. Correlations between PI and other characters were low or not significant. These results indicate that a large genotypic variation exists among Japanese wheat cultivars in NRP, and that PI is a suitable indicator of PA. Cultivars with a high PA detected in this study will be useful genetic resources of wheat to improve the yield stability under drought and hard soil conditions.

Empty Level Structure and Dissociative Electron Attachment Cross Section in (Bromoalkyl)benzenes

The gas-phase electron transmission (ET) and dissociative electron attachment (DEA) spectra are reported for the series of (bromoalkyl)benzenes C6H5(CH2)nBr (n = 0-3), where the bromine atom is directly bonded to a benzene ring or separated from it by 1-3 CH2 groups, and the dihalo derivative 1-Br-4-Cl-benzene. The relative DEA cross sections (essentially due to the Br- fragment) are reported, and the absolute cross sections are also evaluated. HF/6-31G and B3LYP/6-31G* calculations are employed to evaluate the virtual orbital energies (VOEs) for the optimized geometries of the neutral state molecules. The pi* VOEs, scaled with empirical equations, satisfactorily reproduce the corresponding experimental vertical electron attachment energies (VAEs). According to the calculated localization properties, the LUMO (as well as the singly occupied MO of the lowest lying anion state) of C6H5(CH2)3Br is largely localized on both the benzene ring and the C-Br bond, despite only a small pi*/sigma*C-Br interaction and in contrast to the chlorine analogue where the LUMO is predicted to possess essentially ring pi character. This would imply a less important role of intramolecular electron transfer in the bromo derivative for production of the halogen negative fragment through dissociation of the first resonant state. The VAEs calculated as the anion/neutral energy difference with the 6-31+G* basis set which includes diffuse functions are relatively close to the experimental values but do not parallel their sequence. In addition the SOMO of some compounds is not described as a valence MO with large pi* character but as a diffuse sigma* MO.

On the Representation of Molecular Quadrupole Moments in Terms of Atomic Moments

The magnitude and algebraic sign of the molecular quadrupole moments of the homonuclear diatomic molecules N2, O2, F2, P2, S2 and Cl2 are analyzed by expressing them as a sum of the quadrupole moments of the free atoms and an induced molecular quadrupole due to bond formation. This induced molecular quadrupole is further analyzed in terms of in situ atomic dipole and quadrupole moments constructed following the electron partitioning method suggested by Hirshfeld. These in situ moments are interpreted in terms of the sigma and pi character of the chemical bonds and are compared with those predicted by the DMA method of Stone (The Theory of Intermolecular Forces; Clarendon: Oxford, 1996).

Ligand-to-Diimine/Metal-to-Diimine Charge-Transfer Excited States of [Re(NCS)(CO)3(α-diimine)] (α-diimine = 2,2‘-bipyridine, di-iPr-N,N-1,4-diazabutadiene). A Spectroscopic and Computational Study

Two new complexes fac-[Re(NCS)(CO)3(N,N)] (N,N = 2,2'-bipyridine (bpy), di-iPr-N,N-1,4-diazabutadiene (iPr-DAB)) were synthesized and their molecular structures determined by X-ray diffraction. UV-vis absorption, resonance Raman, emission, and picosecond time-resolved IR spectra were measured experimentally and calculated with TD-DFT. A good agreement between experimental and calculated ground- and excited-state spectra is obtained, but only if the solvent (MeCN) is included into calculations and excited state structures are fully optimized at the TD-DFT level. The lowest excited states of the bpy and iPr-DAB complexes are assigned by TD-DFT as 3aA' by comparison of calculated and experimental IR spectra. Excited-state lifetimes of 23 ns and ca. 625 ps were determined for the bpy and DAB complex, respectively, in a fluid solution at room temperature. Biexponential emission decay (1.3, 2.7 micros) observed for [Re(NCS)(CO)3(bpy)] in a 77 K glass indicates the presence of two unequilibrated emissive states. Low-lying electronic transitions and excited states of both complexes have a mixed NCS --> N,N ligand-to-ligand and Re --> N,N metal-to-ligand charge-transfer character (LLCT/MLCT). It originates in mixing between Re d(pi) and NCS pi characters in high-lying occupied MOs. Experimentally, the LLCT/MLCT mixing in the lowest excited state is manifested by shifting the nu(CO) and nu(NC) IR bands to higher and lower wavenumbers, respectively, upon excitation. Resonant enhancement of both nu(CO) and nu(NC) Raman bands indicates that the same LLCT/MLCT character mixing occurs in the lowest allowed electronic transition.