Ab initio and DFT conformational study on N-nitrosodiethylamine, (C2H5)2N-N=O

Ab initio (MP2) and DFT (B3LYP) calculations, using the cc-pVTZ and aug-cc-pVTZ basis sets, have been performed to characterize some stationary points on the ground state potential energy surface of the title molecules. Several properties as, for instance, relative energies, the barriers for NO rotation around the NN bond, NBO charges on O and amino N atoms, as well as the dipole moments, have been calculated and analyzed in the light of the structures found. Both computational levels here employed yield three minima, in which the C₂NNO frame is ‘planar’ or ‘quasi-planar’. Important correlations between NBO charges and geometric parameters, as well as between some structural features and dipole moments are also discussed. A total of 17 structures have been found for the (C₂H₅)₂N-N=O molecule. Two ranges of values have been obtained for the dipole moment, with the largest values occurring for the structures in which the nitrogen lone pair is parallel to the NO group π system. For instance, these two ranges are from ~4.1 to 4.5 D, and from ~1.6 to 2.1 D, at the MP2/cc-pVTZ level. These ranges are consistent with a larger and a smaller contribution of a dipolar resonance structure, respectively. As the method or basis set changes the values of the dipole moments change by at most ~0.23 D.     

A combined spectroscopic and TDDFT investigation of the solute‐solvent interactions of two coumarin derivatives

The UV/Vis absorption and fluorescence characteristics of 3‐cyano‐7‐hydroxycoumarin [ CHC ] and 7‐amino‐4‐methyl‐3‐coumarinylacetic acid [ AMCA‐H ] were studied at room temperature in several neat solvents and binary solvent mixtures of 1,4‐dioxane/acetonitrile. The effects of solvent on the spectral properties are analyzed using single and multi‐parameter solvent polarity scales. Both general solute/solvent interactions and hydrogen bond interactions are operative in these systems. The solvation of CHC and AMCA‐H dyes in 1,4‐dioxane/acetonitrile solvent mixtures has been studied. The solutes CHC and AMCA‐H are preferentially solvated by acetonitrile and a synergistic effect is observed for both molecules in dioxane/acetonitrile solvent mixtures. In addition, using the solvatochromic method the ground‐ and the excited‐state dipole moments of both the dyes were calculated. The ground‐ and excited‐state dipole moments, absorption and emission maxima and HOMO–LUMO gap were also estimated theoretically using B3LYP/6–311+ G (d,p) level of theory in the gaseous phase, dioxane and acetonitrile solvents. Furthermore, changes in dipole moment values were also calculated using the variation of Stokes shift with the molecular–microscopic empirical solvent polarity parameter ( ). The observed excited‐state dipole moments are larger than their ground‐state counterparts, indicating a substantial redistribution of the electron densities in a more dipolar excited state for both coumarins investigated.     

Investigations on spectra and orientation of dipole moments of uracil and thymine by electrochromism

The direction of the ground stale dipole moment with respect to the transition moment to the lowest excited singlet state as well as the dipole moment in this excited state could be determined from the influence of an electric field on the light absorption of uracil and thymine in solution. By making use of results on the orientation of the transition moment in the molecular framework, the orientation of the ground-and excited-state dipole moments can also be fixed and compared with theoretical predictions. The agreement is fair. The measurements show that in both compounds a weak band is hidden under the longest-wavelength absorption band.     

Molecular Mechanics: The Conjugate Nitro Group Parameters in the MM2 Force Field

The conjugated nitro group has been included in the π system calculation within the MM2 force field. New parameters have been estimated by a statistical process from X-ray molecular structures recorded in the C.S.D.S. Comparison of the corresponding results with those given by the MM2(91) force field parameters show a clear improvement for dihedral and bond angles. For N-O and C-N bond lengths a slight global improvement is also observed. A closer examination of the results for the latter bond shows that sometimes MM2(91) gives better results for six membered ring nitro compounds. By contrast the parameters proposed here are more adapted to five membered ring derivatives. The derived linear relations permit the study of molecules over a wider range of π indices. The introduction of a correction factor to the calculated molecular π dipole moment in conjunction with a necessary reestimation of some σ-bond dipole moments also leads to improved total molecular dipole moments.     

Molecular Mechanics: The Conjugate Nitro Group Parameters in the MM2 Force Field

The conjugated nitro group has been included in the π system calculation within the MM2 force field. New parameters have been estimated by a statistical process from X-ray molecular structures recorded in the C.S.D.S. Comparison of the corresponding results with those given by the MM2(91) force field parameters show a clear improvement for dihedral and bond angles. For N-O and C-N bond lengths a slight global improvement is also observed. A closer examination of the results for the latter bond shows that sometimes MM2(91) gives better results for six membered ring nitro compounds. By contrast the parameters proposed here are more adapted to five membered ring derivatives. The derived linear relations permit the study of molecules over a wider range of π indices. The introduction of a correction factor to the calculated molecular π dipole moment in conjunction with a necessary reestimation of some σ-bond dipole moments also leads to improved total molecular dipole moments.     

Electric dipole theory and thermodynamics of actomyosin molecular motor in muscle contraction

Movements in muscles are generated by the myosins which interact with the actin filaments. In this paper we present an electric theory to describe how the chemical energy is first stored in electrostatic form in the myosin system and how it is then released and transformed into work. Due to the longitudinal polarized molecular structure with the negative phosphate group tail, the ATP molecule possesses a large electric dipole moment (p(0)), which makes it an ideal energy source for the electric dipole motor of the actomyosin system. The myosin head contains a large number of strongly restrained water molecules, which makes the ATP-driven electric dipole motor possible. The strongly restrained water molecules can store the chemical energy released by ATP binding and hydrolysis processes in the electric form due to their myosin structure fixed electric dipole moments (p(i)). The decrease in the electric energy is transformed into mechanical work by the rotational movement of the myosin head, which follows from the interaction of the dipoles p(i) with the potential field V(0) of ATP and with the potential field Psi of the actin. The electrical meaning of the hydrolysis reaction is to reduce the dipole moment p(0)-the remaining dipole moment of the adenosine diphosphate (ADP) is appropriately smaller to return the low negative value of the electric energy nearly back to its initial value, enabling the removal of ADP from the myosin head so that the cycling process can be repeated. We derive for the electric energy of the myosin system a general equation, which contains the potential field V(0) with the dipole moment p(0), the dipole moments p(i) and the potential field psi. Using the previously published experimental data for the electric dipole of ATP (p(0) congruent with 230 debye) and for the amount of strongly restrained water molecules (N congruent with 720) in the myosin subfragment (S1), we show that the Gibbs free energy changes of the ATP binding and hydrolysis reaction steps can be converted into the form of electric energy. The mechanical action between myosin and actin is investigated by the principle of virtual work. An electric torque always appears, i.e. a moment of electric forces between dipoles p(0) and p(i)(/M/ > or = 16 pN nm) that causes the myosin head to function like a scissors-shaped electric dipole motor. The theory as a whole is illustrated by several numerical examples and the results are compared with experimental results.     

Dielectrophoresis of macromolecules

Dilute solutions of rigid helical macromolecules with permanent dipole moments have been studied with dielectrophoresis. The polymers used were poly-γ-benzyl-L -glutmate and poly-n-butyl isocyanate, both fractions of average molecular weight 120,000. In this phenomenon dipolar molecules migrate in an inhomogeneous electric field towards the region of maximum field strength. The field gradient is produced by a 10-μm diameter Pt wire serving as the inner electrode of a cell, and a 2.5-mm diameter cylinder as the outer electrode. An equilibrium exponential concentration gradient is achieved within a few wire radii of the inner electrode in a matter of minutes, making both kinetic and equilibrium measurements feasible. The concentration gradient is monitored by measuring the change in capacitance ΔC of the cell from its value for a uniform solute concentration. The time dependences of ΔC for the build-up of the concentration gradient towards the equilibrium value, and the decay to a uniform concentration after the field is removed have been calculated, using a frictional coefficient and a Boltzmann factor, β₁, as the sole adjustable parameters. For low voltages (β₁ small), the measured build-up and decay are completely symmetrical, in agreement with theory, and yield the same frictional coefficient. For larger β₁, the build-up is faster, reflecting a reduced frictional coefficient due to partial alignment of the long axes of the polymers in the direction of migration. In either case, the decay determines a diffusion constant of randomly aligned molecules, identical to classical diffusion measurement. The value of ΔC at equilibrium, for β₁ small, determines μ²F², where μ is the dipole moment and F is the internal field at the polymer. Combined with a classical dielectric constant measurement, which gives μ²F, both μ and F may be determined, independent of assumptions about cavity shapes. Dielectrophoresis works in alternating as well as constant fields, provided the dipolar orientation can follow the field reversals. The dispersion of dielectrophoresis with frequency is a sensitive measure of the molecular-weight distribution of a given sample.     

Rapid energy exchange of enzymes with solvent water by dipolar interaction

One important problem for the function of proteins, especially enzymes, concerns the exchange of energy with the surrounding medium. In this paper, we study the interaction of vibrational degrees of freedom with the fluctuating water dipole moments. The rates of activation or deactivation attain a maximum at slow frequency vibrations near the water dispersion frequencies, i.e. in the gigahertz region. For medium proteins with molecular weights of ~10⁴ a.m.u., the rates are estimated to be of the order of magnitude of $\text{k}{}_{\mathrm{B}}\text{T}\text{h}$, the frequency factor of the transition state theory. We discuss the connection between energy exchange and reaction rates and show that a rapid energy exchange is at least a necessary condition for enzymatic catalysis.     

Kerr effect of charged dipolar macromolecules without condensed counterions in conducting solution.

The theoretical treatment of the Kerr constant of rigid, dipolar, conducting ellipsoidal macromolecules of O'Konski and Krause (1970. J. Phys. Chem. 74:3243) has been extended to very low ionic strength solutions for charged macromolecules. The O'Konski and Krause theoretical treatment postulated a surface conductivity directly on the surface of each macromolecule. For charged macromolecules, this surface conductivity was generally assumed to be caused by movement of condensed counterions on the macromolecules. In the present work, it has been assumed that, at very low ionic strength, the average counterion is at the Debye characteristic distance from the surface of each charged macromolecule and contributes to surface conductivity at that distance, with no additional surface conductivity on the true surface of the macromolecule. Essentially, these considerations change the calculated interaction energy of the macromolecule with an externally applied electric field via a change in both the internal field components and in the reaction field of the macromolecular dipole. The new interaction energy is used to calculate the orientation distribution function of the macromolecules in solution and this distribution function can, in principle, be used to calculate the steady state electric linear or circular dichroism, electric light scattering, anisotropy of conductivity, etc., using the appropriate theoretical treatment for each of these quantities.     

Shear Viscosity of Model Mixtures by Nonequilibrium Molecular Dynamics III. Effect of Quadrupolar Interactions

Abstract

We present new results for thermodynamic properties and viscosities of pure quadrupolar fluids, a pure dipolar quadrupolar fluid, nonquadrupolar/quadrupolar mixtures, and quadrupolar/quadrupolar mixtures. It is evident that, the addition of quadrupolar interactions to the pure Ar and the addition of quadrupolar interactions to the pure dipolar Ar, leads to higher viscosities as was observed in the addition of dipolar interactions to the pure Ar [Lee and Cummings, J. Chem. Phys., 105, 2044 (1996)]. The total energies and the mixture densities show a linear dependence for both nonquadrupolar Ar/quadrupolar Kr (case B) and quadrupolar Ar/quadrupolar Kr (case C), and the linearity of case C is better than that of case B. This is not consistent with the idea that in the cases of the dipolar mixtures, dipolar/dipolar and nondipolar/nondipolar mixture are likely to be more ideal than nondipolar/dipolar mixtures. This is mainly due to the weaker interaction of quadrupole-quadrupole than that of dipoledipole.     

Effects of microwave irradiation on triglyceride transesterification: Experimental and theoretical studies

An improved reaction rate of biodiesel fuel formation was observed under microwave irradiation. Such irradiation is effective for not only heating during the reaction but also preheating. The advantages observed in this study suggest that a continuous process, that is, the introduction of reactant preheated by microwave irradiation into reactor will be feasible. The reasons for the improved reaction rate are explained through the use of optimized structures, dipole moments, IR spectra and activation energies obtained using molecular orbital calculations. Planar triolein formed by microwave irradiation has higher reactivity, a lower dipole moment, a lower activation energy and stronger vibration around the carboxyl carbon, and is more reactive than triolein with a higher dipole moment.     

Magnetic Fields in Earth-like Exoplanets and Implications for Habitability around M-dwarfs

We present estimations of dipolar magnetic moments for terrestrial exoplanets using the Olson & Christiansen (EPS Lett 250:561–571, 2006) scaling law and assuming their interior structure is similar to Earth. We find that the dipolar moment of fast rotating planets (where the Coriolis force dominates convection in the core), may amount up to ~80 times the magnetic moment of Earth, M _⊕ , for at least part of the planets’ lifetime. For slow rotating planets (where the force of inertia dominates), the dipolar magnetic moment only reaches up to ~1.5 M _⊕ . Applying our calculations to confirmed rocky exoplanets, we find that CoRoT-7b, Kepler-10b and 55 Cnc e can sustain dynamos up to ~18, 15 and 13 M _⊕ , respectively. Our results also indicate that the magnetic moment of rocky exoplanets not only depends on rotation rate, but also on their formation history, thermal state, age, composition, and the geometry of the field. These results apply to all rocky planets, but have important implications for the particular case of planets in the Habitable Zone of M-dwarfs.     

An electrostatic model of a membrane ion pump

The model is based upon an ion channel with an electric dipolar structure. With simplifying assumptions it is possible to calculate that a typical channel, 1 nm in diameter and 5 nm long, could contain at most two or three univalent cations at a time. The channel ion binding sites have an effective affinity for ions from the fluid bathing the negative end of the channel, several orders of magnitude higher than their affinity for ions from the fluid bathing the positive end of the channel. The approach of an external, positively charged body to the negative end of the channel, is sufficient to convert the two- or three-channel ion sites with high affinity for ions from the fluid bathing this end into very low affinity sites for the same ions that now have access only to the fluid bathing the other end of the channel. The change in affinity and fluid access requires no molecular or electrical change in the channel structure other than the passive superposition of the electrostatic potential of the dipolar channel and that of the charged body. An oscillating electric field externally applied to an electric dipolar channel is shown to result in the unidirectional pumping of cations in the direction of the channel dipole even against large adverse ion concentration gradients. The energy required must be supplied by the sources of the electric field. By using two such channels in close proximity, one selective for K+ ions with its dipole moment pointing into a cell and the other selective for Na+ ions with its dipole moment pointing out from the cell, it is possible to construct a model pump with calculated properties that simulate many of those measured for Na+-K+-ATPase, with both physiological and artificial ionic concentrations.     

Electro-optic scattering studies on deoxyribonucleic acid

Measurements have been made of the intensity of light scattered from aqueous solutions of calf thymus DNA with and without the application of electric fields. For fields approaching 150 V/cm and frequencies below 2.5 KHz, changes (ΔI) of up to 10% in the residual scattered intensity were observed. In agreement with previous dielectric and electric birefringence measurements, a low frequency dispersion of ΔI was observed, from which a rotary diffusion constant (D) of 1200 s^?1 was determined. Interpreting the electric field data in terms of the classical dipolar orientation theory led to values of 2.4 × 10^?25 cm (7.4 × 10^?14 esu) and 4.3 × 10^?25 cm (13 × 10^?14 esu) for the permanent dipole moment and the anisotropy of the electric polarisabilities respectively. Furthermore the permanent dipole moment was along the major molecular axis and the particles orientated in the field as rigid entities. The zero field data indicated a molecular shape which was not rodlike but corresponded to the Kratky-Porod “stiffness” parameter of x = 24 for the wormlike coil model. Although curved, the molecules appeared to orientate in low-intensity electric fields as rigid, but not rodlike molecules. The implications of this on recent discrepancies in D determined by two or more dynamic relaxation methods is briefly discussed.     

Polarized fluorescent emission from probes near dielectric interfaces

The electromagnetic field surrounding and emitted by a dipolar molecular probe very near to a dielectric interface is the sum of the real dipole field and the field of the image dipole induced inside the dielectric interface. The total charge distribution, made up of the real and image dipoles in close proximity to each other, approximates a quadrupole distribution and emits a light intensity pattern similar to that of an oscillating electric quadrupole. The electromagnetic field emitted by this system contains information that can be directly related to the spatial and orientational distributions of the dipole near the interface. Experimental methods are discussed that utilize this system for determining the spatial and orientational distribution of fluorescent probes in biological material.     

Effects of solvent polarity on the absorption and fluorescence spectra of chlorogenic acid and caffeic acid compounds: determination of the dipole moments

The effects of solvent polarity on absorption and fluorescence spectra of biologically active compounds (chlorogenic acid (CGA) and caffeic acids (CA)) have been investigated. In both spectra pronounced solvatochromic effects were observed with shift of emission peaks larger than the corresponding UV‐vis electronic absorption spectra. From solvatochromic theory the ground and excited‐state dipole moments were determined experimentally and theoretically. The differences between the excited and ground state dipole moment determined by Bakhshiev, Kawski–Chamma–Viallet and Reichardt equations are quite similar. The ground and excited‐state dipole moments were determined by theoretical quantum chemical calculation using density function theory (DFT) method (Gaussian 09) and were also similar to the experimental results. The HOMO‐LUMO energy band gaps for CGA and CFA were calculated and found to be 4.1119 and 1.8732 eV respectively. The results also indicated the CGA molecule is more stable than that of CFA. It was also observed that in both compounds the excited state possesses a higher dipole moment than that of the ground state. This confirms that the excited state of the hydroxycinnamic compounds is more polarized than that of the ground state and therefore is more sensitive to the solvent. Copyright © 2015 John Wiley & Sons, Ltd.     

Ab initio and dielectric studies of succinic acid and maleic acid in 1,4-dioxane

In a continuing effort to understand the hydrogen bond through the study of dielectric and computational conformal studies of dilute solutions, succinic acid and maleic acid are studied in solutions of 1,4-dioxane solvent. Dielectric studies give an account of the net dipole moment of the system under study, which is then compared with the values obtained from conformal analysis. The dielectric measurements were made at 303 K at a frequency of 9.83 GHz using a X-band microwave test bench in order to determine the relaxation times and the dipole moments. The static dielectric permittivity and the high frequency dielectric permittivity were measured using a LCR meter and an Abbe's refractometer, respectively. The results are inspected in comparison with the dipole moment results of ab initio calculations of some of the conformers in gas phase and in liquid phase. Gaussian-03 software package with 6–31G(d) basis set optimisation was used for this purpose. Onsager's reaction field model is used to study the solvation of the dicarboxylic acids in 1,4-dioxane. The results are interpreted in terms of the intermolecular and intramolecular hydrogen bond interactions in the dilute systems.     

Probing the effect of electric field in 9,10-dimethoxy-2,6-bis(2-p-tolylethynyl)anthracene molecular nanowire using quantum chemical and charge density analysis

The effect of electric field (EF) in a newly designed molecular nanowire 9,10-dimethoxy-2,6-bis(2-p-tolylethynyl)anthracene has been analysed theoretically from the structural and electronic charge transport properties using quantum chemical and charge density calculations. The applied EF (0–0.36 VÅ^? 1) alters the molecular conformation, charge density distribution, electrostatic properties and the electronic energy levels of the molecule. Furthermore, the applied EF decreases the highest occupied molecular orbital–lowest unoccupied molecular orbital gap significantly from 1.775 to 0.258 eV and it also induces polarisation in the molecule, which leads to increase the dipole moment of the molecule. The electrostatic potential for various levels of applied EF reveals the charge-accumulated regions of the molecule. The I–V characteristics of the molecule have been studied against various applied fields using Landauer formalism.     

Dielectric study of the urea denaturation of delipidated and relipidated bovine serum albumin

Dielectric relaxation and viscosity measurements were performed on delipidated and relipidated samples of bovine serum albumin (BSA) at urea concentrations between O and 6M. By the combined interpretation of these two hydrodynamic methods the characterization of conformational changes of the molecule during urea denaturation is possible. The denaturation of delipidated BSA results from two mechanisms. The first one is a slow, time-dependent elongation of the molecule; the second one is a rapid swelling which becomes most pronounced at urea concentrations higher than 4M. For relipidated albumin, the slow elongation mechanism occurs but the presence of fatty acids protects the protein aganist molecular swelling. In both cases these conformational changes are accompanied by an increased disymmetry of charge repartition and a concomitant increase of the dipole moment. From these results it follows that lipidated albumin (as occurs under physiological conditions) is less sensitive to denaturation than delipidated albumin.     

Ab initio calculations of molecular properties of low–lying electronic states of 2–cyclopenten–1–one – link with biological activity

Geometries, vibrational frequencies, vertical and adiabatic excitation energies, dipole moments and dipole polarizabilities of the ground and the three lowest electronic excited states, S(1)(n, π (*)), T(1)(n, π (*)), and T(2)(π, π (*)) of the 2-cyclopenten-1-one molecule (2CP) were calculated at the CCSD and CCSD(T) levels of approximation. Our results indicate that two triplets T(1)(n, π (*)) and T(2)(π, π (*)) are lying very close each to other, while the singlet S(1)(n, π (*)) is well above them. There are dramatic changes in dipole moments for (n, π (*)) excited states in respect to the ground state. On the other hand the T(2)(π, π (*)) state has a similar dipole moment as the ground state. These changes can be interpreted within the MO picture using electrostatic potential maps and changes in model IR spectra. Our CCSD(T) dipole moment data for the ground state and almost isoenergetic triplets T(1)(n, π (*)) and T(2)(π, π (*)) are 1.469?a.u., 0.551?a.u., and 1.124?a.u., respectively. Dipole polarizabilities of investigated excited states are much less affected by electron excitations than dipole moments. These are the first dipole moment and polarizability data of 2CP in the literature. The changes of molecular properties upon excitation to S(1)(n, π (*)) and T(1)(n, π (*)) correlate with the experimental data on the biological activity of 2CP related to the α, β-unsaturated carbonyl group.