We consider the Galerkin finite element method for non-self-adjoint boundary value problems on Bakhvalov's grids. Using the Galerkin projections method the convergence of a sequence of computational grids with an unknown boundary of the boundary layer has been proved. Numerical examples are presented.
A model of double porosity in the case of an anisotropic fractured porous medium is considered (Dmitriev, Maksimov; 2007). The function of the exchange flow between fractures and porous blocks, which depends on the direction of a flow, is investigated. The flow function is based on the difference between pressure gradients. This feature enables one to take into account anisotropic filtering properties in a more general form. The results of the numerical solution of the model two-dimensional problem are presented. The computational algorithm is based on the finite element spatial approximation and the explicit-implicit temporal approximation.
The iterative product, that is, the triangular skew-symmetric method (PTSM) is used to solve linear algebraic equation systems obtained by approximation of a central-difference scheme of the first boundary value problem of convection-diffusion-reaction and standard grid ordering. Sufficient conditions of a non-negative definiteness of the matrix resulting from this approximation have been obtained for a non-stationary sign of the reaction coefficient. This feature ensures the convergence of a sufficiently wide class of iterative methods, in particular, the PTSM. In the test problems, the compliance of the theory with computational experiments is verified, and comparison of the PTSM and the SSOR is made.
P. Singh1, M.K. Kadalbajoo2, K. Sharma3 1Thapar University, Patiala, India 2Indian Institute of Technology, Kanpur, India 3South Asian University, New Delhi, India
Keywords: модель с утечками «интегрировать-и-сработать», уравнение переноса, конечно-объемная аппроксимация, шум Леви, Leaky integrate-and-fire model, transport equation, finite volume approximation, Lèvy noise
We investigate a numerical analysis of a leaky integrate-and-fire model with Lèvy noise. We consider a neuron model in which the probability density function of a neuron in some potential at any time is modeled by a transport equation. Lèvy noise is included due to jumps by excitatory and inhibitory impulses. Due to these jumps the resulting equation is a transport equation containing two integrals in the right-hand side (jumps). We design, implement, and analyze numerical methods of finite volume type. Some numerical examples are also included.
The Tikhonov finite-dimensional approximation was applied to an integral equation of the first kind. This allowed us to use the variation regularization method of choosing the regularization parameter residuals from the principle of reducing the problem to a system of linear algebraic equations. The estimate of accuracy of the approximate solution with allowance for the error of the finite-dimensional problem approximation has been obtained. The use of this approach is illustrated on an example of solving an inverse boundary value problem for the heat conductivity equation.
Igor Semyonovich Shreifel, Ivan Nikolaevich Eliseev
Don State Technical University, Rostov region, the Russian Federation 346500, Shevchenko st., 147, Shakhty, Rostov region, Russia
Keywords: итерационный процесс, итерационная последовательность, трудность задания, уровень подготовки студента, дихотомическая матрица ответов, iterative process, an iterative sequence, difficulty of test questions, level of training students, dichotomous response matrix
In this paper, we study the iterative process of the joint numerical assessment of levels of training students and difficulties in tasks of diagnostic tools using the dichotomous response matrix A of N x M size, with allowance for the contribution of tasks of different difficulty to the assessments obtained. It is shown that not for any matrix A there exist infinite iterative sequences, and in the case of their existence, they do not always converge. A wide range of sufficient conditions for their convergence have been obtained, which are based on the following: 1) matrix A contains at least three different columns; 2) if one places the columns of A in non-decreasing order of column sums, then for any position of the vertical dividing line between the columns there exists a row, which has, at least, one unity to the left of the line, and at least one zero to the right of the line. It is established that the response matrix A obtained as a result of testing reliability satisfies these two conditions. The properties of such matrices have been studied. In particular, the equivalence of the above conditions of primitiveness of the square matrix B of order M with the entries bij ∑ N ell 1 (1- ali ) alj has been proved. Using the matrix analysis we have proved that the primitiveness of the matrix B ensures the convergence of iterative sequences, as well as independence of their limits of the choice of the initial approximation. We have estimated the rate of convergence of these sequences and found their limits.
A review is given for
the state of the art and future development of the geothermal
power engineering. Different diagrams of GeoPP are shown for different levels
of geofluid temperature. A special focus is made on challenges for
petrothermal power production. The huge amount of heat from petrothermal
resources can be harnessed through creating geothermal circulation systems
within the dry rocks. Estimates for system lifetime and heat production
capacity of circulation systems are given for different flow rates of
coolant.
The results of study of evaporation of water droplets
and NaCl salt solution from
a solid substrate made of anodized aluminum are presented in this paper.
The experiment provides the parameters describing the droplet
profile: contact spot diameter, contact angle, and droplet
height. The specific rate of evaporation was calculated from
the experimental data. The water droplets or brine droplets with
concentration up to 9.1 % demonstrate evaporation with the pinning mode for the contact
line. When the salt concentration in the brine is taken up
to 16.7 %, the droplet spreading mode was observed. Two stages
of droplet evaporation are distinguished as a function of phase transition
rate.
Results of numerical
simulation of heat and mass transfer in a laminar flow of three-component
gas at adiabatic evaporation of binary solutions from a flat plate are
presented. The studies were carried out for the perfect solution
of ethanol/methanol and zeotrope solutions of water/acetone, benzene/acetone,
and ethanol/acetone. The liquid-vapor equilibrium
is described by the Raoult law for the ideal solution and
Carlson–Colburn model for real solutions. The effect of gas temperature and liquid composition
on the heat and diffusion flows, and temperature of vapor-gas mixture
at the interface is analyzed. The formula for calculating
the temperature of the evaporation surface for the binary liquid
mixtures using the similarity of heat and mass transfer was proposed. Data
of numerical simulations are in a good agreement with the results of
calculations based on the proposed dependence for all examined liquid
mixtures in the considered range of temperatures and pressures.
The aim of this study is
to investigate the effect of mass flow rate on film cooling effectiveness
and heat transfer over a gas turbine rotor blade with three staggered rows
of shower-head holes which are inclined at 30° to the spanwise direction,
and are normal to the streamwise direction on the blade. To improve
film cooling effectiveness, the standard cylindrical
holes, located on the leading edge region, are replaced with
the converging slot holes (console). The ANSYS CFX has been
used for this computational simulation.
The turbulence is approximated by a k-e model. Detailed film effectiveness distributions
are presented for different mass flow rate. The numerical results are
compared with experimental data.
Results of an
experimental study of the excitation of high-intensity disturbances by a weak
external shock wave in laminar boundary layer on flat-plate models with sharp
and blunted leading edges at М = 2.5 are reported. The field of disturbances produced by a 2D sticker
in turbulent boundary layer on the wall of wind-tunnel test section in the free
stream is shown to have the form of an
N-wave. It is found that, on the blunted plate, the intensity of pulsations
produced by weak external shock waves in boundary layer several times exceeds
the intensity of pulsations produced in boundary layer on the model with a
sharp leading edge.
A possible influence of the deflection of control surfaces on the aerodynamics of an axisymmetric slender configuration at supersonic flow speeds is considered. A classical configuration consisting from the fuselage in the form of a body of revolution and having cross frontal fins and six-blade trailing stabilizers is considered as the investigation object. The physical flow pattern at the deflection of horizontal fin consoles is investigated and the estimates are obtained for the influence of this deflection on both the characteristics of elements (the body and stabilizers) as well as on the integral aerodynamic characteristics of the entire configuration. Numerical computations of the flow have been done at the freestream Mach number М = 3 in the range of attack angles α = 0-10° and the angles of the control surfaces deflection δcs = ±5° on the basis of the averaged Navier-Stokes equations and the SST k-ω turbulence model.
The numerical model of
momentumless turbulent wake in a horizontally homogeneous shear flow of
linearly stratified medium has been constructed. Based on this model,
the investigation of the wake dynamics has been performed. The obtained data demonstrate
the transformation of the zone of turbulent perturbations and
internal waves generated by the wake under the action of shear flow,
which leads to the deceleration of turbulence decay at large time values
after the body passage.
This article presents an investigation on heat transfer enhancement in a round tube inserted with a helically twisted tape. The effects of a helically twisted tape with alternate axis (HTT-A) on heat transfer, friction factor, and thermal performance factor behaviours are reported for the turbulent regime. HTT-A geometries are tape pitch to tube diameter, P/D = 1.0, 1.5, and 2.0; alternate length to pitch length, l/P = 1.0, 1.5, and 2.0; twisted length to tape width, y/W = 3.0; and tape width to tube diameter, w/D
= 0.2. The experiment has been performed by varying the volumetric air flow rate in order to adjust Reynolds number ranging from 6 000 to 20 000. The wall of the testing tube is uniformly heated as a constant heat flux while the tests are covered with thermal insulations to reduce heat loss to surroundings. Thermal performance is evaluated by comparing the present experimental results with the results of the modified HTT-A and also those obtained from previous study (conventional helically twisted tape, HTT). The thermal performance of tested tube with HTT-A is evaluated to obtain the degree of heat transfer enhancement and friction factor induced by HTT-A with respect to the plain tube under the same test conditions. Evenly, it is interesting to observe that the tube with HTT-A consistently possesses higher heat transfer and thermal performance factor than those with the HTT around 14.1% and 1.9%, respectively. The HTT-A with the smaller pitch ratio and adjacent twist length provides higher heat transfer rate and friction factor than the one with larger pitch ratio and alternate length as a result of a larger contact surface area, stronger swirl intensity and, thus, better fluid mixing near the tube wall. In the range determined, the tubes with the largest pitch ratio (P/D
= 2.0) and smallest alternate length (l/P = 1.0) give the highest thermal performance factor
at around 1.35. In
addition, the empirical correlations of the Nusselt number, friction
factor, and thermal performance factor are also described.
The analysis and evaluation of the forces acting on
the particle in a linear shear flow of power-law fluid (PLF) in the presence of the wall were performed. Using the
results of a series of computations for a model problem with a spherical particle near a flat wall in the Reynolds number range of 0-200 and the distance to the wall from 0 to 20
particle diameters, the correlation formulas for calculating the coefficients
of drag force and lift force were obtained. Special attention was paid to the
behavior of the forces acting on the particle approaching the wall.
The paper presents an investigation of the influence of thermophoresis on MHD mixed convective heat and mass transfer of a viscous, incompressible and electrically conducting fluid along a vertical flat plate with radiation effects. The plate is permeable and embedded in a porous medium. To describe the deviation from the Darcy model the Forchheimer flow model is used. The Rosseland approximation is used to describe the radiative heat flux in the energy equation. The governing partial differential equations are transformed into a system of ordinary differential equations using similarity transformation. The nonlinear ordinary differential equations are linearized by using quasi-linearization technique and then solved numerically by using implicit finite difference scheme. The numerical results are analyzed for the effects of various physical parameters such as magnetic parameter Ha, mixed convection parameter Rad/Ped, Reynolds number Red, radiation parameter R, thermophoretic parameter τ, Prandtl number Pr, and
Schmidt number Sc. The heat transfer coefficient is also tabulated for
different values of physical parameters.
The thermal state of
a translucent selectively absorbing medium was studied by the methods
of numerical simulation at different values of the optical properties of
boundaries and heat transfer from the left surface in approximation of
one-phase Stefan problem. The temperature fields and densities of
resultant radiation fluxes as well as the thermal state of the left
boundary and dynamics of layer reduction in the melting process were
analyzed. The processes of phase transition in a flat layer of
selective and gray absorbing media and emitting media were compared, and their
fundamental differences were shown.
Plasma technology was developed to create
protective-decorative coatings on the wood surfaces. Experimental investigation on applying the protective
coating using the low-temperature plasma energy as well as studies of the distribution of
temperature fields over the section of the treated workpiece have
been carried out, and the calculated results have been compared with
the experimental data.
The computational experiments using the “Overfire Air” (OFA) technology at the coal dust torch combustion in the combustor of the BKZ-160 boiler of the heat power plant No. 2 in Almaty have been conducted. The results show a possibility of reaching a reduction of the emission of noxious nitrogen oxides NOx and minimizing the energy losses. The results
of numerical experiments on the influence of the additional air supply on
the main characteristics of heat and mass transfer are presented. A
comparison with the base regime of the solid fuel combustion when there is no
supply of the additional air (OFA = 0 %) has been made.
The speed of sound in liquid
and gaseous refrigerant R-407C
was measured by the method of ultrasonic interferometer in the temperature
range from 293 to 373 K and pressure from 0.05 to 0.5 to 3.7 MPa. The experimental uncertainties of the temperature,
pressure, and speed of sound measurements were estimated to be within ±20 mK, ±4 kPa, and ±(0.1–0.3) %, respectively. The obtained results are
compared with the calculated speed of sound from the fundamental state equation for the Helmholtz free
energy.
The effect of parameters of the multi-ring
Couette system with counter rotating coaxial cylinders on the process
of thermal energy release in a viscous liquid filling this system is
considered with regard to the problem of determining the possibility
of creating the high-performance wind heat generator.
The multi-cylinder rotor design allows directly conversion of the mechanical
power of a device consisting of two “rotor” wind turbines with
a common axis normal to the air flow into the thermal energy in
a wide range of rotational speed of the cylinders. Experimental
results on the measurement of thermal power released in the pilot
heat generator at different relative angular speeds of cylinder rotation are
presented.
A
formula for evaluating the gas-flow exergy at heat supply/removal without
concretization of the process and the way in which the dissipation of
kinetic energy proceeds is reported.
January
28, 2016 is the 100th anniversary of the birth of the outstanding researcher in
the field of power engineering, thermophysics and thermodynamics, great
scientist and brilliant organizer Academician Ivan I. Novikov (15(28) January
1916-30 May 2014). Results of his fundamental research
are widely known in our country and abroad at the level of discoveries and
inventions.
T. I. Madzhidov1, A. V. Bodrov2, T. R. Gimadiev1,3, R. I. Nugmanov1, I. S. Antipin1, A. A. Varnek1,3 1Kazan Federal University, Russia 2Kazan State Medical University, Russia 3University of Strasburg, France
Keywords: bimolecular elimination, reaction rate constant, condensed graph of a reaction, cheminformatics, reaction descriptors, solvent descriptors
By means of a structural representation of the chemical reactivity as a condensed graph a model predicting rate constants of the bimolecular elimination reaction is derived for the first time. The model developed enables the prediction of rate constants of reactions proceeding in different solvents or water-organic mixtures at different temperatures. It demonstrates a good predictive performance: a mean square deviation of predicted values from experimental ones is less than 0.7 logarithmic units. An outlier analysis shows that prediction errors are mainly due to the imperfection of the training data containing unique reactions. The model is available for users at arsole.u-strasbg.fr.
S. Mandal1, G. Das2 1Centre of Advanced Study and Department of Chemistry, North-Eastern Hill University, Shillong, 793022, Meghalaya, India 2Faculty of Chemistry, Central Institute of Technology, Kokrajhar (B.T.A.D.), 783370, Assam, India guna_das78@yahoo.co.in
Keywords: ab initio calculations, selenomethionine conformers, vibrational frequency, HOMO-LUMO energy gap, intramolecular H bonds
Selenium containing amino acids are known to play numerous key biological roles in various life-supporting processes. In the current theoretical investigation DFT(B3LYP) and MP2 methods are used to study the gas phase conformers of the selenomethionine molecule in view of their relative stabilities, theoretically predicted harmonic frequencies, HOMO-LUMO energy gaps, rotational constants, and dipole moments. The number and type of intramolecular H-bond interactions existing in the selenomethionine conformers, which play key roles in determining the energy of the conformers, are also analyzed. The predicted geometries as well as the relative stabilities of the conformers suggest that the structural aspects and energies of the conformers may depend on the level of theory and the size of the basis set used. A comparison of the vibrational frequencies furnished in this study with the previous experimental and theoretical results obtained at MP2/6-31++G( d , p ) and B3LYP/6-311++G( d , p ) levels promotes the interpretation of the vibrational spectroscopy data on biologically relevant molecules.
A. Shelke1, N. N. Karade1, P. Kr. Dutta2, S. P. Bahekar3, H. S. Chandak3 1Department of Chemistry, Rashtrasant Tukadoji Maharaj Nagpur University, Nagpur, Maharashtra, India nnkarade@gmail.com 2Department of Chemical Sciences, Indian Institute of Science, Education and Research (USER) Kolkata, Mohan-pur, India 3Department of Chemistry, G. S. Science, Arts and Commerce College, Khamgaon, India chemants@gmail.com
Keywords: thiazolo[3, 2-a]pyrimidine, single crystal X-ray diffraction (SCXRD), DFT calculation, Hirshfeld surface analysis
The structural characterization of fused thiazolopyrimidine 1 (C24H24N2O4S) is performed using the single crystal X-ray study, the DFT calculation, and the Hirshfeld surface analysis. The molecular packing of the crystal is mainly stabilized by C-H…O and C-H…p interactions. A DFT calculated HOMO-LUMO energy gap of 3.90 eV indicates a high kinetic stability of the compound. The 3D Hirshfeld surfaces and the associated 2D fingerprint plots are investigated for short contact interactions. The relative contribution of different interactions to the Hirshfeld surface indicates that the H…H, C…H, and O…H contacts account for about 83.4% of the total Hirshfeld surface area.
S. A. Beyramabadi, A. Morsali, M. Pordel, H. Chegini, M. Khashi, I. Ahmadi, M. Poorzaki
Department of Chemistry, Mashhad Branch, Islamic Azad University, Mashhad, Iran beiramabadi@yahoo.com. beiramabadi6285@mshdiau.ac.ir
Keywords: DFT, PCM, intramolecular proton transfer, AIM analysis, tautomerization
The titled imidazo compound can exist as three tautomers: OH, CH, and NH forms. Firstly, the OH tautomer is produced, which can be tautomerized to the CH and NH tautomers via the intramolecular-proton transfer. Herein, employing density functional theory and handling the solvent effects with the PCM model, the structural parameters, energy behavior, and also tautomerization mechanism of the tautomers are investigated. Based on the DFT results and the obtained-AIM parameters, the CH tautomer is considered to be the most stable one. Also, the CH tautomer is a kinetically and thermodynamically controlled product in tautomerization of the OH tautomer in a methanol solution.
P. Wu1,2 1Department of Chemistry, Dezhou College, Shandong, P. R. China Pingwu.dzu@gmail.com 2Key Laboratory of Coordination Chemistry and Functional Materials at Universities of Shandong
Keywords: azomethine ylide, B3LYP/6-311++G(d,p), formaldehyde, glycine
The mechanism to generate azomethine ylide from formaldehyde and glycine is systematically investigated. The density functional theory at the B3LYP/6-311++G(d,p) level is employed for both geometry optimization and single point energy calculation. Our results indicate that two possible pathways can lead to the generation of the carbinolamine intermediate with a favorable step-wise pathway. However, as for the step to form azomethine ylide, a concerted elimination of water and carbon dioxide is preferred. This calculation result is totally different from the widely accepted revised Rizzi mechanism.
J. Tong, J. Chang, L. Li, M. Bai
College of Chemistry and Chemical Engineering, Shaanxi University of Science & Technology, Xian, P.R. China jianbotong@aliyun.com
Keywords: peptide drugs, 3D-HoVAIF, QSAR, MLR, r
By applying a three-dimensional holographic vector of the atomic interaction field (3D-HoVAIF) to express the structure of three classical peptide drugs, quantitative structure activity relationship (QSAR) models are built by the multiple linear regression. The accuracy of the proposed model is illustrated using (cross-validation) and r 2 (test set validation). Moreover, the r m2 metrics is used to further refine the predictive ability of the developed QSAR models. The results show that 3D-HoVAIF, due to the high predictive ability, offers a useful alternative to the costly and time-consuming experiments determining the bioactivity of peptide drugs.
Y.Gulseven Sıdır, İ. Sıdır, F. Demiray 1Bitlis Eren University, Faculty of Arts and Sciences, Department of Physics, Bitlis, Turkey ygsidir@bitliseren.edu.tr. yadigar.gulseven@gmail.com 2Abant Izzet Baysal University, Vocational Higher School, Mudurnu, Bolu, Turkey
Keywords: heptachlor, density of states, hyperpolarizability, NBO analysis, DFT, ESP
In this work, the molecular geometry of heptachlor is investigated using ab initio HF, DFT, LDA, and GGA methods. The natural bond orbital (NBO) analysis is performed at the B3LYP/6-311++G(d,p) level of theory. The first order hyperpolarizability btotal, the mean polarizability Da, the anisotropy of the polarizability Da, and the dipole moment m, are calculated by B3LYP/6-311++G(d,p) and HF/6-311++G(d,p) methods. The first order hyperpolarizability (btotal) is calculated based on the finite field approach. UV spectral parameters along with HOMO, LUMO energies for heptachlor are determined in vacuum and the solvent phase using HF, DFT, and TD-DFT/B3LYP methods implemented with the 6-311++G(d,p) basis set. Atomic charges and electron density of heptachlor in vacuum and ethanol are calculated using DFT/B3LYP and TD-DFT/B3LYP methods and the 6-311++G(d,p) basis set. In addition, after the frontier molecular orbitals (FMOs), the molecular electrostatic potential (MEP), the electrostatic potential (ESP), the electron density (ED), and the solvent accessible surface of heptachlor are visualized as a results of the B3LYP/6-311++G(d,p) calculation. Densities of states (DOS), the external electric field (EF) effect on the HOMO-LUMO gap, and the dipole moment are investigated by LDA and GGA methods.
M. Samadizadeh1, S. S. Gorgani2 1Department of Chemistry, Faculty of Basic Science, Central Tehran Branch, Islamic Azad University, Tehran, Iran 2Young Researches and Elite Club, Central Tehran Branch, Islamic Azad University, Tehran, Iran sarasoleimani240@yahoo.com
Keywords: molecular scissors, photoisomerization, DFT, azobenzene, stilbene, open-close motion
DFT calculations are employed to investigate the effects of the addition of a photoisomerizable stilbene unit to Aida's molecular scissors on relative energies, dipole moments, and kinetic stability according to HOMO-LUMO energy gaps and amplitude of the open-close motion of blade moieties. The most obvious finding emerging from this study is the coming into existence of a new pair of molecular scissors operated by two photoswitchable units. Based on photoisomerization of azobenzene and stilbene units, four conformations appear for these new molecular scissors: cis-cis, cis-trans, trans-cis, and trans-trans. The HOMO-LUMO energy gaps promise that all isomers are kinetically stable. The other important finding is that in these new molecular scissors the dihedral angle between the two blade moieties can be controlled and measured through the open-close motion and the blade parts can adopt two middle states in addition to open-close forms.
Z. Sadeghian
Department of Chemistry, Faculty of Science, Imam Khomeini International University, Qazvin, Iran sadeghianzahra421@yahoo.com
Keywords: 2,3-bis(furan-2-yl)pyrazino[2,3-f][1, 10]phenanthroline, density functional theory, theoretical calculations, LanL2DZ level, B3LYP level
This paper reports the optimized geometrical parameters of the stationary point for 2,3-bis(furan-2-yl)pyrazino[2,3-f][1,10]phenanthroline. The calculations are performed using the density functional theory (DFT) method at the B3LYP/ LanL2DZ level. Bond lengths and bond angles are determined for the compound and the amount of bond hybridization is calculated according to the natural bond orbital theory (NBO). The energy of frontier orbitals (HOMO and LUMO) are computed. In addition, the calculated data are accurately compared with the experimental results. This comparison shows that our theoretical data are in reasonable agreement with the experimental values.
A. H. Moussa1, M. Shalaby1, H. Talaat1, S.El-Wallid Sedik2, M.T. El-Din Kamal2 1Physics Department, Faculty of Science, Ain Shams University, Cairo, Egypt 2Theoretical Physics Department, National Research Center, Dokki, Giza, Egypt esedik@gmail.com
Keywords: reaction dynamics, potential surface, normal modes, Cl + CH → HCl + CH reaction
A time dependent quantum-mechanical QM study is performed on the Cl + CH4 → HCl + CH3 reaction, using a pseudotriatomic ab initio based surface. Probabilities present some clear peaks versus t, which we assign to transition state resonances where the light H atom oscillates between heavy Cl and CH3 groups. For ground-state reactants, the reactivity is of quantum origin. The reaction occurs through an abstraction mechanism, following both direct and an indirect mechanisms. The calculations show the participation of a short-lived collision complex in the microscopic reaction mechanism. This theoretical result and other oscillating properties found here could, however, be related to the existence of resonance for the production of HCl, as suggested by experimentalists.
Y. Umar1, J. Tijani2 1Department of Chemical and Process Engineering Technology, Jubail Industrial College, Jubail Industrial City, Saudi Arabia umar_y@jic.edu.sa 2Department of General Studies, Jubail Industrial College, Jubail Industrial City, Saudi Arabia
Keywords: density functional theory, rotational barrier, vibrational wavenumber, conformational preference, infrared spectra, geometry optimization, solvent effect, formylfuran, furan carbaxaldehyde, polarizable continuum model
The torsional potentials, molecular structures, conformational stability, and vibrational wavenumbers for the rotational isomers of 2-formylfuran and 3-formylfuran are computed using the density functional theory (B3LYP) method with the 6-31+G* basis set. All structures are fully optimized and the optimized geometries, rotational constants, dipole moments, and energies are presented. From the computations, both 2-formylfuran and 3-formylfuran are predicted to exist predominantly in trans conformation with a cis-trans rotational barrier of 11.19 kcal/mol and 8.10 kcal/mol, respectively. The vibrational wavenumbers and the corresponding vibrational assignments of the molecules in the Cs symmetry are examined and the infrared spectra of the molecules are simulated using the wavenumbers and the corresponding intensities obtained from the computations. The effect of solvents on the conformational stability of all the molecules in nine different solvents (heptane, chloroform, tetrahydrofuran, dichloroethane, acetone, ethanol, methanol, dimethylsulfoxide, and water) is investigated. The integral equation formalism in the polarizable continuum model (IEF-PCM) is used for all solution phase computations.
Q. Z. Liu1,2, Y. Wang1,2, L. Qiu1,2, T. F. Wang1,2, S. N. Luo1,2, H. L. Yuan2, J.G. Lin2 1School of Chemical and Material Engineering, Jiangnan University, Wuxi, P. R. China qiuling@jsinm.org 2Key Laboratory of Nuclear Medicine, Ministry of Health & Jiangsu Key Laboratory of Molecular Nuclear Medicine, Jiangsu Institute of Nuclear Medicine, Wuxi, P. R. China linjianguo@jsinm.org
Keywords: zoledronic acid, different conformations, spectroscopic properties, thermodynamic properties, electronic characteristics
The structure, spectroscopic, thermodynamic, and electronic properties of zoledronic acid (ZL,1-hydroxy-2-(1H-imidazol-1-yl)ethane-1,1-diyldiphosphonic acid), typical third-generation nitrogen-containing bisphosphonates (N-BPs), have been investigated systematically. Six conformations are taken into account, including three unprotonated and three protonated structures. They are optimized by four different density functional theory (DFT) methods combined with four different basis sets to evaluate their performance in predicting the structural and spectral features of ZL. Thermodynamic properties are calculated based on the harmonic vibrational analysis, including the standard heat capacity (Cp,m0), entropy (Sm0), and enthalpy (Hm0). The 1H and 13C NMR chemical shifts are calculated using the GIAO method and compared with the experimental data. Molecular electrostatic potential (MEP) and frontier molecular orbital (FMO) analyses are also performed to study the electronic characteristics of the title compound.
S. Chandrasekaran1, I. V. Muthu1, V. Enoch1,2 1Department of Chemistry, Karunya University, Coimbatore, Tamil Nadu, India drisraelenoch@gmail.com 2Department of Nanosciences and Technology, Karunya University, Coimbatore, Tamil Nadu, India
Keywords: host-guest complex, morin, b-cyclodextrin, C-hexylpyrogallol[4]arene, fluorescence spectroscopy
The study of the host-guest association of Morin hydrate (MO) with b-cyclodextrin (b-CD) and C-hexylpyrogllol[4]arene (C-HPA) is reported in this paper. The iInclusion complexation of MO is studied by ultraviolet-visible, steady-state fluorescence, time-resolved fluorescence, 1H nuclear magnetic resonance (NMR), and two dimentional rotating-frame nuclear overhauser effect correlation (2D ROESY) spectroscopic techniques. The stoichiometry and the binding constant for the MO-b-CD complex are derived from the linearity of the Benesi-Hildebrand equation. The binding constant for the MO-C-HPA complex is calculated from the nonlinear curve fitting of fluorescence intensities. The effects of the acid strength on the absorption and fluorescence spectra of MO are studied in the absence and the presence of b-CD/C-HPA host molecules. The pKa values of the ground and the excited states are reported.
S. K. Amini
Chemistry and Chemical Engineering Research Center of Iran, Tehran, Iran amini_s@ccerci.ac.ir
Keywords: configuration, NMR, computational, fischerin, ab initio
The unassigned configurations of a toxic metabolite to mammals extracted from Neosartorya fischeri (fischerin) in C19, C20, C21, and C22 are assigned as R, R, R, and S, respectively. In this assignment, the extensive ab initio calculations followed by chemical shift computations are performed. Computed chemical shifts are correlated to experimental ones in order to find the correct configuration shown here.
The titled molecule 4-[3-(2,5-dimethylphenyl)-3-methylcyclobutyl]-N-methylthiazol-2-amine (C17H22N2S) is synthesized and characterized by 1H NMR, 13C NMR, IR, and X-ray single crystal determination. The compound crystallizes in the monoclinic space group P 21/ c with a = 6.3972(4) Å, b = 9.4988(6) Å, c = 26.016(2) Å and β = 93.496(7)°. In addition to the molecular geometry from the X-ray determination, vibrational frequencies and gauge, including the atomic orbital (GIAO), 1H and 13C NMR chemical shift values of the titled compound in the ground state are calculated using the density functional (B3LYP) method with 6-31G( d ), 6-31++G(d,p) and 6-311+G(2d,p) basis sets. The calculated results show that the optimized geometries can well reproduce the crystal structure. Moreover, the theoretical vibrational frequencies and chemical shift values show good agreement with the experimental values. The predicted nonlinear optical properties of the titled compound are greater than those of urea. DFT calculations of the molecular electrostatic potentials and frontier molecular orbitals of the titled compound are carried out at the B3LYP/6-31G(d) level of theory.
A pyridine-diimine compound N,N'-[pyridine-2,6-diyldi( E )methylylidene]bis(4-chloroaniline) is synthesised by a Schiff base condensation of 2,6-diformylpyridine with 4-chloroaniline in methanol and characterised by spectroscopic and analytical techniques. The molecular structure of the compound is determined by the single crystal X-ray diffraction study. The compound crystallizes in the monoclinic crystal system, I 2/ c space group with unit cell parameters a = 7.0843(12) Å, b = 6.1909(11) Å, c = 36.262(6) Å, β = 91.576(3)°, V = 1589.8(5) Å3 and Z = 4. There is an intermolecular hydrogen bonding in the molecule resulting in a 1D hydrogen bonding chain and these hydrogen bonding chains are linked by Cl…HC(aromatic) interactions forming a 2D network. Crystal packing of the compound is determined by Cl…HC and p-p interactions. In the fluorescence emission spectra in CH3CN, DMF, DMSO and EtOH, the compound shows only one emission maximum.
G. S. Khaibullina1, V. V. Kuznetsov1,2, E. S. Meshcheriakova3, T. V. Tyumkina3, L. M. Khalilov3 1Ufa State Petroleum Technological University, Russia 2Ufa State Aviation Technical University, Russia 3Institute of Petroleum Chemistry and Catalysis, Russian Academy of Sciences, Ufa, Russia
Keywords: 2-метил-1,3,2-диоксаборинан, координационная связь В-N. пиридиновый комплекс, молекулярная структура, конформер, 2-methyl-1,3,2-dioxaborinane, B-N coordination bond, pyridine complex, molecular structure, conformer
The molecular structure of 2-methyl-5-nitro-5-bromo-1,3,2-dioxaborinane and its complex with pyridine is determined by single crystal X-ray diffraction. The structure of the synthesized compounds in the solution is also confirmed by the NMR spectroscopy data, and the conformational preference of their molecules is confirmed by the calculations using hybrid density functional theory.
