Journal of Theoretical and Computational Chemistry

Using molecular dynamics simulation method, the effects of external electric fields of 900MHz and 2450 frequencies on $\alpha \beta$-tubulin dimer stabilized by paclitaxel, have been modeled. Due to this purpose, two systems, (A) $\alpha \beta$-tubulin dimer and (B) $\alpha \beta$-tubulin dimer stabilized by paclitaxel, were exposed to an external electric field of 0.01V/nm with frequency values of 900MHz and 2450MHz. It was found that application of these fields, which are in the range of cell phone and microwave frequencies, increased the flexibility of each system. Since paclitaxel, as chemotherapy drug, is used to increase the rigidity of dimer, application of such fields may disturb the effect of paclitaxel on the dimer. Consequently, negative side effects on the chemotherapy process may be observed.

The glass transition temperature $(T_g)$ is the most important parameter of an amorphous polymer. A quantitative structure-property relationship (QSPR) was developed for $T_g$s of 82 polyacrylates, by applying stepwise multiple linear regression (MLR) analysis. Molecular descriptors used to describe polymer structures were, for the first time, calculated from the motion units of polymer backbones, which are chain segments with 20 carbons in length (10 repeating units). After internal validation with leave-one-out (LOO) method, external validation was carried out to test the stability of the MLR model of $T_g$s. Compared to the models already published in the literature, the MLR model in this paper was accurate and acceptable, although our model was based on bigger data sets. The feasibility of calculating molecular descriptors from the motion units of polymer backbones for developing $T_g$ models of polyacrylates has been demonstrated.

The reaction mechanisms between 2, 4-Diisocyanatotolune (2, 4-TDI) and cellulose have been investigated using the density functional theory at the B3LYP/6-31$+$G (d, p) level. The calculations show that the direct addition of 2, 4-TDI and cellulose possesses an unrealistically high barrier of 32–34kcal$\cdot$mol${}^{-1}$. With a neighboring $\beta$-d-glucose serving as a proton transporter by forming a flexible six-membered ring transition state, the energy barrier of the reaction is significantly reduced to 16–18 kcal$\cdot$mol${}^{-1}$, which is in a good accordance with the experimental activation energy of 13.9–16.7kcal$\cdot$mol${}^{-1}$. It is indicated that the reaction between 2, 4-TDI and cellulose is auto-catalyzed with a neighboring $\beta$-d-glucose acting as a reactive catalyst.

The photodissociation of water on rutile (110) is studied from first principles. Using an embedded cluster approach, the motion of one hydrogen atom with a fixed OH group served as a model system. The ground and an electronically excited state are calculated on a CASSCF level of theory, explicitly accounting for the multi-reference character of the wave function during bond breaking. The dynamics is simulated by solving the time-dependent Schrödinger equation for a wave packet moving on the electronic potential energy surface. Photodissociation probabilities of water are calculated for hydrogen, deuterium and tritium, thereby revealing significant isotope effects.

The full vibrational spectra especially those high-lying vibrational energies in the dissociation region of the electronic state ${\text{A}}^2{\mathrm{\Pi }}_u$ of ${\text{N}}_2^{+}$, the $X^2{\mathrm{\Pi }}_g$ state of ${\text{F}}_2^{+}$, the ${\text{A}}^2{\mathrm{\Pi }}_u$ and $X^2{\mathrm{\Pi }}_g$ states of ${\text{O}}_2^{+}$ are obtained using the variational algebraic method (VAM). Then, an analytical potential energy function (APEF) with adjustable parameter $\lambda$ for each electronic state is determined by the 4-terms variational algebraic energy consistent method (VAECM(4)) based on the VAM vibrational energies. The full vibrational energies, the vibrational spectroscopic constants, the force constants $f_n$, and the expansion coefficients $a_n$ of the potential are tabulated. Compared with experimental and other calculated results, accurate APEFs, vibrational energy levels and spectroscopic parameters are obtained with the VAECM(4) for the four electronic states of diatomic ions. The results show that the VAECM(4) method also applies to diatomic ion systems.

The hydrogen bonding interactions between letrozole (Let) anticancer drug and three copolymers of methacrylic acid-trimethylolpropane trimethacrylate (M1–M3 as molecular imprinted polymers) were studied using density functional theory (DFT) at both B3LYP and B3PW91 levels. The binding energies were corrected for the basis set superposition error (BSSE) and zero-point vibrational energies (ZPVE) so that the most negative $\mathrm{\Delta }{E}_{\mathrm{\text{binding}}}$ were measured for compounds 7 and 8 formed between M1 copolymer and endocyclic N1 and N2 atoms of drug, respectively. Also, among complexes 13–15 in which two copolymers were contributed in the formation of O–H$\dots$N bonds with the drug, compound 13 (containing two M1 copolymers) showed the highest $\mathrm{\Delta }{E}_{\mathrm{\text{binding}}}$ value. The interactions of all copolymers with drug were exergonic (spontaneous interaction) and exothermic. The QTAIM data supported the covalent character of the C–N, C–H, N–N, C–O, O–H and O–H$\dots$N bonds, the intermediate nature of C$\equiv$N and C$=$O bonds while the electrostatic character of C–H$\dots$O, HC$\dots$HC and CH$\dots$N interactions. According to the $\mathrm{\Delta }{E}_{\mathrm{\text{binding}}}$, $\mathrm{\Delta }{G}_{\mathrm{\text{interaction}}}$ and $\mathrm{\Delta }{H}_{\mathrm{\text{interaction}}}$ values, it was suggested that t complexes 7 and 8 (among two particles systems) as well as complex 13 (among three particles systems) can be the most promising drug delivery systems.

Density functional theory and generalized gradient approximation using a Hubbard-like term was employed to study tin dioxide material containing an oxygen vacancy as an intrinsic defect and being codoped simultaneously with Fe and Ni atoms. Results on atomic displacements, electronic and magnetic features are obtained and discussed for different configurations taking into consideration relative impurity–impurity as well as impurity–vacancy positions. It appears that Fe atom addition to the system enlarges considerably a local magnetic moment due to the strong magnetic coupling between the Fe 3d and O 2p states for the $\beta$ spin subsystem.

The FTIR, UV–Vis and NMR spectra of 4-(2-hydroxy-3-morpholin-4-yl-propoxy)-chromen-2-one (4-HMPC) have been recorded and analyzed. The optimized geometry and harmonic vibrational frequencies of 4-HMPC were obtained by the Hartree–Fock (HF) and density functional theory (DFT) using B3LYP functional with 6-311$++$G basis set. The ¹H and ${}^{13}$C NMR chemical shifts were calculated by the GIAO method in chloroform. The absorption spectra of 4-HMPC were computed in ethanol and water solutions using TD-B3LYP/6-311$++$G(d,p) approach. The correlation of theoretical and experimental results provides a detailed description of the structural and physicochemical properties of the molecule. The results obtained from the studies of HOMO and LUMO were used to calculate the conceptual-DFT-based global reactivity descriptors such as electronic chemical potential, electronegativity, chemical hardness, global softness and electrophilicity index of the compound.

In the present study, microsolvation and interaction of the CH${}^{+}$ cation with He${}_{n=1-11}$ clusters are investigated by means of ab initio calculations at MP2/aug-cc-pVTZ and QCISD/aug-cc-pVTZ levels. Stabilization energies of the studied complexes including basis set superposition error (BSSE) and zero point energy (ZPE) corrections are in the range of $-1.8$kJ/mol and $-11.6$kJ/mol. A good linear correlation is found between the stabilization energy and stretching frequency shift ($\mathrm{\Delta }\nu$) in the studied complexes. According to energy decomposition analysis, it is found that polarization effects are the major source of the attraction in these complexes.