Calculation of the geometry, absorption spectrum, and first hyperpolarizability of 4,5-dicyanoimidazole derivatives in solution. A multiscale ASEC-FEG study.

We investigate the effects of solvents on the geometry, absorption spectrum, and first hyperpolarizability of six push-pull molecules, each containing a 4,5-dicyanoimidazole group as an electron acceptor and a N,N-dimethylamino group as an electron donor, with systematically extended π-conjugated systems. Geometry optimizations in dichloromethane, methanol, water, and formamide under normal thermodynamic conditions were performed using the average solvent electrostatic configuration-free energy gradient method, which employs a discrete solvent model. The conformational structure of molecules is moderately affected by the environment, with the π-conjugated system becoming more planar in protic solvents. Solvent effects on the first hyperpolarizability result in marked increases that are in line with the red shifts of the absorption spectrum. The hyperpolarizability of smaller molecules within the set may be significantly influenced by the effects of geometry relaxation in highly polar protic solvents. The results illustrate the role of hydrogen bonds in the structure and electronic properties of push-pull molecules in protic environments. For smaller molecules, hydrogen bonds significantly contribute to enhancing the hyperpolarizability, but the effect of these specific interactions becomes less significant with the length of the π-conjugated system.

Understanding Nonlinear Optical Phenomena in N-Pyrimidinyl Stilbazolium Crystals via a Self-Consistent Electrostatic Embedding - DFT Approach.

Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) have been used to investigate the nonlinear optical (NLO) properties of phenolic N-pyrimidinyl stilbazolium cationic chromophore in its corresponding noncentrosymmetric crystals. Such a cationic chromophore, the OPR (4-(4-hydroxystyryl)-1-(pyrimidin-2-yl)pyridinium), consists of a strong electron donor, the 4-hydroxyphenyl group, and a strong electron acceptor, the N-pyrimidinylpyridinium group based on two electron-withdrawing groups. The in-crystal NLO properties were determined by applying a supermolecule approach in combination with an iterative electrostatic scheme, in which the surrounding molecules of a unit cell are represented by point charges. With CAM-B3LYP, our absolute estimates for the largest diagonal component of the second-order nonlinear susceptibility tensor of OPR-based crystals range from 64.00 to 80.34 pm/V in the static regime and from 162.09 to 175.52 pm/V at 1907 nm. These values are significant when compared to those of benchmark stilbazolium-based crystals. Furthermore, the third-order susceptibility, which is related to the nonlinear optical process of the intensity-dependent refractive index, is also significant compared to the results for other organic crystals, such as chalcone derivatives. With TD-CAM-B3LYP, the two-state model effectively explains the similarity in the first hyperpolarizability values in the crystalline phase. This similarity arises from the combination of the oscillator strength and the charge transfer of the crucial transition. Therefore, phenolic organic salt crystals show great promise for various nonlinear optical applications.

Theoretical investigation on the linear and nonlinear optical properties of DAPSH crystal.

The linear polarizability, first and second hyperpolarizabilities of the asymmetric unit of DAPSH crystal are studied and compared with available experimental results. The polarization effects are included using an iterative polarization procedure, which ensures the convergence of the dipole moment of DAPSH embedded within a polarization field generated by the surrounding asymmetric units whose atomic sites are considered as point charges. We estimate macroscopic susceptibilities from the results of the polarized asymmetric units in the unit cell, considering the significant contribution of the electrostatic interactions in crystal packing. The results show that the influence of the polarization effects leads to a marked decrease of the first hyperpolarizability, compared with the respective isolated counterpart, which improves the concordance with the experiment. There is a minor influence of polarization effects on the second hyperpolarizability but our estimated result for the third-order susceptibility, related to the NLO process of the intensity dependent refractive index, is significant as compared with the results for other organic crystals, such as chalcone-derivatives. In addition, supermolecule calculations are conducted for explicit dimers in presence of the electrostatic embedding to illustrate the role played by the electrostatic interactions in the hyperpolarizabilities of the DAPSH crystal.

Applicability of DFT functionals for evaluating the first hyperpolarizability of phenol blue in solution.

The first electronic hyperpolarizability (ß) of phenol blue (PB) in several solvents in a wide range of dielectric constants is investigated using the density functional theory (DFT). The reliability of various exchange-correlation functionals is assessed by a comparison to reference Møller-Plesset second-order perturbation theory (MP2) calculations. The equilibrium geometry of PB in each solvent is obtained by using the average solvent electrostatic configuration/free energy gradient method, which performs optimizations on the free energy hyper-surface by employing iteratively the sequential quantum mechanics/molecular mechanics methodology. The dependence of ß on the bond length alternation (BLA) coordinate is rationalized by means of the two-level model. Within the employed exchange-correlation functionals, the LC-BLYP functional shows the best performance for describing the static and dynamic MP2 results of ß, which increases as the BLA diminishes, reaching a maximum in an intermediate value of BLA. The results also illustrate the role played by the difference between the ground- and excited-state dipole moments (Δµ) in determining the hyperpolarizability behavior in solution. Particularly, in the aqueous solution case, Δµ goes to around zero when BLA is near zero, leading to an abrupt decline in the ß value. The DFT results of this study, therefore, indicate a clear relationship between the first hyperpolarizability and the BLA coordinate for the PB in solution, in agreement with experiment.

Assessing the structure and first hyperpolarizability of Li@B10H14 in solution: a sequential QM/MM study using the ASEC-FEG method.

The structure and electronic properties of the lithium decahydroborate (Li@B10H14) complex in chloroform and water in normal thermodynamic conditions have been investigated using sequential QM/MM calculations by means of the average solvent electrostatic configuration (ASEC) and the Free Energy Gradient (FEG) methods. To obtain the structure of the Li@B10H14 complex in each of the solvents considered, we have performed geometry optimizations in solution using the ASEC-FEG method. The results show, for the first time with a realistic model of the molecular environment, that this alkali-metal-borane cluster is stable in chloroform but unstable in water. We have also explored the role of the electronic polarization of the solute due to solvent in the static first hyperpolarizability. The results show that, despite the reduction due to the effect of electrostatic polarization in chloroform, the Li@B10H14 complex still exhibits a large electronic first hyperpolarizability, with potential for application as a second-order nonlinear optical (NLO) material. In water, in contrast, the contribution of the excess electron for NLO responses is significantly affected by the electrostatic polarization effects. Therefore our results reveal that the influence of the environment must be considered in the design of new stable NLO materials.

Electronic and Vibrational Hyperpolarizabilities of Lithium Substituted (Aza)benzenes and (Aza)naphthalenes.

In this article we report results for the electronic and vibrational hyperpolarizabilities of ten molecules: Li@benzene, Li@pyridine, Li@pyrimidine, and Li@pyrazine; Li@naphthalene, Li@quinoline, Li@isoquinoline, Li@cinnolin, Li@quinazoline, and Li@quinoxaline. An electron correlation study shows that second-order many-body perturbation theory and density functional theory with CAM-B3LYP and M05-2X functionals give results for the electronic hyperpolarizabilities in good agreement with coupled cluster with single and doubles reference values. Static and dynamic vibrational corrections were computed through the perturbation theoretical method of Bishop and Kirtman and using a variational approach. In general, we obtained notable discrepancies between the results obtained by the two methods for the pure vibrational corrections because of the deficiency of the perturbation method to properly treat low-frequency normal modes present in the investigated systems. However, both methods give results similar to the zero-point vibrational average corrections.

Confirming the relationship between first hyperpolarizability and the bond length alternation coordinate for merocyanine dyes.

We investigated the first electronic hyperpolarizability of a typical merocyanine dye in several solvents in a wide range of dielectric constants. The equilibrium geometry of the molecule was obtained in each solvent by employing an optimization technique allied to atomistic simulations. The results confirm, for the first time with a realistic model of the molecular environment, the relationship between the first electronic hyperpolarizability (ß) and the bond length alternation (BLA) coordinate, with a maximum value of ß for intermediate positive BLA and a vanishing ß when the BLA goes to zero.

Electronic and vibrational second hyperpolarizabilities of (MgO)n clusters.

In this work, we report results for the static second hyperpolarizability of magnesium oxide clusters including electronic and vibrational contributions. The comparison between second-order Møller-Plesset (MP2) perturbation theory and coupled cluster results to the electronic contribution points out that MP2 is a suitable method to compute this property. When computed at the MP2 level, the electronic contribution per atom converges to approximately 5000 a.u. Vibrational corrections were computed at the MP2 level through the perturbation theoretical method of Bishop and Kirtman. Results obtained showed that the term [α2]0,0 represents around 20% of the electronic counterpart while the term [µß]0,0 is comparable to it. Modes that contribute significantly to [α2]0,0 are those in which all or part of the bond lengths simultaneously increase and decrease, leading to large polarizability derivatives. In turn, modes that provide relevant contributions to [µß]0,0 are those in which oxygen anions move in opposite directions to the magnesium cations yielding large derivatives of the dipole moment and first hyperpolarizability.

Vibrational corrections to the second hyperpolarizabilities of Al(n)P(n) clusters.

In this work, we report results of vibrational corrections to the second hyperpolarizabilities of Al2P2, Al3P3, Al4P4, Al6P6, and Al9P9 clusters. The vibrational corrections were calculated through the perturbation theoretic method of Bishop and Kirtman and also using a variational methodology at the second order Møller-Plesset perturbation theory level with the aug-cc-pVDZ basis set. Results show that the vibrational corrections are important, accounting for more than half of the corresponding electronic second hyperpolarizabilities at the static limit. Comparisons between results obtained through both methods show very good agreements for the terms [α(2)] and [µß] but significant differences for the term [µ(2)α]. Dynamic vibrational corrections to the second hyperpolarizabilities related to the dc-second harmonic generation, intensity dependent refractive index, and dc-Kerr nonlinear optical processes are also reported.

Vibrational corrections to the first hyperpolarizability of the lithium salt of pyridazine Li-H3C4N2.

In this work we report results of vibrational corrections to the polarizability and first hyperpolarizability of the lithium salt of pyridazine Li-H3C4N2 obtained at the second-order Mo̸ller-Plesset theory level with the aug-cc-pVDZ basis set. The calculations were carried out by means of the perturbation theoretical method of Bishop and Kirtman and also using a variational approach proposed here. The results obtained show that at the static limit, the pure vibrational corrections for the polarizability and first hyperpolarizability have the same order of magnitude of the corresponding electronic contributions. Comparisons between the results obtained through the two methods show that the perturbation theoretical method is not suitable to treat the system studied, while the variational methodology presented seems to be an alternative approach to treat anharmonic systems.

Dynamic (hyper)polarizabilities of the sulphur dioxide molecule: coupled cluster calculations including vibrational corrections.

In this work we report results for dynamical (hyper)polarizabilities of the sulphur dioxide molecule with inclusion of vibrational corrections. The electronic contributions were computed analytically at the single and double coupled cluster level through response theories for the frequencies 0, 0.0239, 0.0428, 0.0656, 0.0720, and 0.0886 hartree. Contributions of the connected triple excitations to the dynamic electronic properties were also estimated through the multiplicative correction scheme. Vibrational corrections were calculated by means of the perturbation theoretical method. The results obtained show that the zero point vibrational correction is very small for all properties studied while the pure vibrational correction is relevant for the dc-Pockels effect, intensity dependent refractive index, and dc-Kerr effect. For these nonlinear optical processes, the pure vibrational corrections represent approximately 75%, 13%, and 6% of the corresponding electronic contributions for the higher frequencies quoted. The results presented for the polarizability are in good agreement with experimental values available in the literature. For the hyperpolarizabilities we have not obtained experimental results with precision sufficient for comparison.

Dynamic (hyper)polarizabilities of the ozone molecule: coupled cluster calculations including vibrational corrections.

In this work, we present results for dynamical (hyper)polarizabilities of the ozone molecule with inclusion of vibrational corrections. Electronic contributions for dynamic properties were computed analytically at the single and double coupled cluster level through response theories for the frequencies 0, 0.0239, 0.0428, and 0.0656 hartree. In the static limit, the electronic contributions were also computed at the single and double coupled cluster with perturbative correction of connected triple excitations level by means of the finite-field method. It was found that the inclusion of connected triple excitations is important, especially for a reliable description of the hyperpolarizabilities. Vibrational corrections were calculated by means of the perturbation theoretical method. The zero-point vibrational average correction was found to be relevant only for the linear polarizability, representing approximately 8% of the corresponding electronic contribution. Results also showed that the pure vibrational correction is relevant for the dc-Pockels effect, dc-second harmonic generation, intensity dependent refractive index, and dc-Kerr effect nonlinear optical processes. The double-harmonic approximation is in general suitable to compute this correction, the anharmonicity being small for the dc-Kerr effect and negligible for the other processes.

Hyperpolarizabilities of the methanol molecule: A CCSD calculation including vibrational corrections.

In this work we present the results for hyperpolarizabilities of the methanol molecule including vibrational corrections and electron correlation effects at the CCSD level. Comparisons to random phase approximation results previously reported show that the electron correlation is in general important for both electronic contribution and vibrational corrections. The role played by the anharmonicities on the calculations of the vibrational corrections has also been analyzed and the obtained results indicate that the anharmonic terms are important for the dc-Pockels and dc-Kerr effects. For the other nonlinear optical properties studied the double-harmonic approximation is found to be suitable. Comparison to available experimental result in gas phase for the dc-second harmonic generation second hyperpolarizability shows a very good agreement with the electronic contribution calculated here while our total value is 14% larger than the experimental value.

Vibrational effects on the dynamic electric properties of hydrogen peroxide.

In this work we present a method based on the perturbation theoretic approach of Bishop and co-workers [J. Chem. Phys. 95, 2646 (1991); 97, 5255 (1992); 108, 10013 (1998)] to calculate the effect of torsional motion on the polarizability and hyperpolarizabilities of hydrogen peroxide. The frequency dependence has been evaluated using the time-dependent Hartree-Fock method. The results obtained show that the zero-point vibrational averaging contributions are small compared to the corresponding electronic contributions. In the static limit the pure vibrational contributions are very large, specially for beta and gamma. These contributions are significant for the hyperpolarizabilities even in the visible region, except for the second harmonic generation and third harmonic generation processes.

Histological and histochemical changes of the intestinal mucosa at the urothelial-enteric anastomotic site.

OBJECTIVE: The incorporation of bowel segments for urinary tract reconstruction may induce intestinal mucosal changes with the development of metabolic, nutritional, gastrointestinal and carcinogenic complications. The early histological and histochemical changes of the intestinal mucosa in contact with the feces-urine mixture, are evaluated in the present study. MATERIALS AND METHODS: Twelve rats (operated group) were submitted to a vesico-colonic anastomosis, and 10 rats (control group) underwent a sham operation (the colon was opened and immediately sutured). On the operated group, the left colon was divided into 3 equal portions and the middle segment was used for the bladder-colonic anastomosis. After 20 weeks, the animals were sacrificed and the entire left colon in each group, as well as the bladder and the vesico-colonic anastomosis in the operated group, was removed. The proximal, middle (anastomotic site in the operated group and sutured portion in the control group) and distal colon were used for histological and histochemical studies. RESULTS: Metaplasia, chronic inflammatory process and fibrosis were significantly greater at the anastomotic site compared to the middle segment of the control group. There were no differences in both groups in terms of dysplasia, atrophy and hypertrophy either on the proximal, middle or anastomotic area and distal portion of the left colon. All animals in the operated group showed a reduced presence of sulfomucin and an increase in the sialomucin content. CONCLUSION: The histological changes observed in this study may suggest a precancerous phenomenon.

Histological and histochemical changes of the intestinal mucosa at the urothelial-enteric anastomotic site

OBJECTIVE: The incorporation of bowel segments for urinary tract reconstruction may induce intestinal mucosal changes with the development of metabolic, nutritional, gastrointestinal and carcinogenic complications. The early histological and histochemical changes of the intestinal mucosa in contact with the feces-urine mixture, are evaluated in the present study. MATERIALS AND METHODS: Twelve rats (operated group) were submitted to a vesico-colonic anastomosis, and 10 rats (control group) underwent a sham operation (the colon was opened and immediately sutured). On the operated group, the left colon was divided into 3 equal portions and the middle segment was used for the bladder-colonic anastomosis. After 20 weeks, the animals were sacrificed and the entire left colon in each group, as well as the bladder and the vesico-colonic anastomosis in the operated group, was removed. The proximal, middle (anastomotic site in the operated group and sutured portion in the control group) and distal colon were used for histological and histochemical studies. RESULTS: Metaplasia, chronic inflammatory process and fibrosis were significantly greater at the anastomotic site compared to the middle segment of the control group. There were no differences in both groups in terms of dysplasia, atrophy and hypertrophy either on the proximal, middle or anastomotic area and distal portion of the left colon. All animals in the operated group showed a reduced presence of sulfomucin and an increase in the sialomucin content. CONCLUSION: The histological changes observed in this study may suggest a precancerous phenomenon.

Atualizaçäo em fístulas uretrovaginais e vesicovaginais / Up-to-date in urethrovaginal and vesicovaginal fistulas

Os autores realizam uma revisao da literatura sobre a epidemiologia, etiologia, classificaçao, clínica, diagnóstico e tratamento das fístulas uretrovaginais e vesicovaginais. Concluem que condutas como a correçao precoce da fístula, a nao-ressecçao do trajeto fistuloso e a interposiçao de tecidos nas fístulas complexas sao fatores importantes no tratamento destas patologias e conseqüente melhora na qualidade de vida das pacientes.