Study of the structural and electronic properties of retinals and retinals linked to lysine through a protonated Schiff base

As transições eletrônicas que apresenta as energias mais baixas no retinal e em quatro retinais sintéticos foram analisadas em dois diferentes ambientes: no vácuo e ligados à proteína bacterioopsina por uma base de Schiff protonada, utilizando diversos métodos de química teórica. Os resultados aqui apresentados fornecem indicativos de que três estados eletrônicos estão envolvidos na formação da primeira banda de absorção dos aldeídos, enquanto que, no caso dos compostos ligados à proteína apenas dois estados estariam envolvidos. As análises discutidas neste trabalho também sugerem uma possível explicação para o envolvimento de dois estados eletrônicos excitados no processo de fotoisomerização do retinal ligado à bacterioopsina.Low-lying electronic transitions of retinal and of four synthetic retinals were analyzed in two different environments: in vacuum and linked to bacterioopsin through a protonated Schiff base, employing several methods of theoretical chemistry. The results here reported suggest that the first absorption band of the aldehydes involves three electronic states, while for the case of protein linked compounds, two states would be embraced. Our discussions also provided a possible explanation about the involvement of two electronic excited states in the photoisomerization process of retinal linked to bacterioopsin

Theoretical study of structural and electrical properties of self-assembled films of organic molecules

Compact models of ionized and nonionized Langmuir monolayers of stearic acid adsorbed on the water were simulated by means of atomistic molecular dynamics. The electrostatic, structural and dynamic properties of the molecules of models were studied throughout time evaluating the calculated trajectory. The structural analyses indicate a significant increase of the water density at the interface in comparison to the bulk aqueous phase. These results also showed that the water molecules near the interface orient hydrogen atoms toward to organic phase. The distribution of water molecules at interface neutralizes partially the charges of the polar group of stearic acid, reducing the contribution of this group of the electrostatic potential in the monolayer. The charge densities indicated two possible mechanisms of partial charges neutralization on the head of stearic acid. At low stearate concentrations, the water had the highest positive charge density contribution at the interface. However, the positive charge density is predominantly derived from monovalent ions of sodium at electrical double layer, for the monolayers with more than 30 % of the stearate in the organic phase. It was observed that water molecules at the interface have lower mobility than the bulk aqueous phase, especially those coordinating around the carbonyl group and the stearate of the organic phase.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Modelos de monocamadas de Langmuir compactas de ácido esteárico ionizados e não ionizado adsorvido sobre água, foram simulados por dinâmica molecular atomística. As propriedades eletrostática, estrutural e dinâmica das moléculas dos modelos foram estudadas ao longo do tempo avaliando as trajetórias calculadas. As análises estruturais indicam um aumento significativo da densidade de água na interface das monocamadas parcialmente ionizadas em comparação ao interior da fase aquosa, também observou-se que as águas na interface orientam os hidrogênios preferencialmente em direção à interface. A distribuição das moléculas de água na interface neutraliza parcialmente as cargas do grupo polar do ácido esteárico, provocando à redução da contribuição desse grupo no potencial eletrostático do monocamada. As análises das densidades de cargas, indicaram dois possíveis mecanismos de neutralização parcial das cargas na cabeça do ácido esteárico. Em baixas concentrações de estearato, as moléculas de água apresentaram a maior contribuição de densidade de carga positiva na interface. Contudo, a densidade de carga positiva é predominantemente proveniente dos íons monovalentes de sódio da dupla camada elétrica, para as monocamadas com mais de 30 % de estearato na fase orgânica. Observou-se ainda que as moléculas de água apresentam mobilidade relativamente menor na interface do que no seio da fase aquosa, em especial as que se coordenaram aos grupos carbonila e estearato da fase orgânica

Structural dependence of photochromism in MEH PPV solutions.

Submitted by Oliveira Flávia ([email protected]) on 2017-01-23T13:10:27Z No. of bitstreams: 1 ARTIGO_StructuralDependencePhotochromism.pdf: 343385 bytes, checksum: bc3d0842f699c61aea7006cb53de9d25 (MD5)Approved for entry into archive by Oliveira Flávia ([email protected]) on 2017-01-23T13:10:47Z (GMT) No. of bitstreams: 1 ARTIGO_StructuralDependencePhotochromism.pdf: 343385 bytes, checksum: bc3d0842f699c61aea7006cb53de9d25 (MD5)Made available in DSpace on 2017-02-01T13:23:26Z (GMT). No. of bitstreams: 1 ARTIGO_StructuralDependencePhotochromism.pdf: 343385 bytes, checksum: bc3d0842f699c61aea7006cb53de9d25 (MD5) Previous issue date: 201

Structural dependence of MEH-PPV chromism in solution.

The chromism observed in the MEH-PPV polymer in tetrahydrofuran (THF) solution is discussed as a function of the structural morphology of the backbone chains. To evaluate this phenomenon, we carried out simulations employing a hybrid methodology using molecular dynamics and quantum mechanical approaches. Our results support the hypothesis that the morphological order– disorder transition is related to the change from red to blue phase observed experimentally. The morphological disorder is associated with total or partial twisted arrangements in the polymer backbone, which induces an electronic conjugation length more confined to shorter segments. In addition, the main band of the MEH-PPV UV–Vis spectrum at the lower wavelength is related to the blue phase, in contrast to the red phase found for the more planar backbone chains

Anisotropic electron mobility in fluorene-PPV and fluorene-MEH-PPV.

Polyfluorene copolymers are attractive semiconductor materials, in particular for applications in the organic electronics field. They are versatile to be chemically modified and allow a tuning of the emission to cover the entire visible spectrum. A better understanding of the fundamental aspects of the nature of electronic structure and charge transport properties contribute to the improvement of optoelectronic properties of polymeric materials. Here, we provide a structure?property relationship for models of fluorene-PPV and fluorene-MEH-PPV copolymers, using molecular quantummechanics modelling. The anisotropy is discussed revisitingMulliken?s transitionmomenttheory. Accordingly, our results show that electron mobility occurs preferentially intrachain for both copolymers. Moreover, the interchain electron mobility has the most propensity to occur via ?-stacking interactions

Evaluation of the losartan solubility in the biowaiver context by shake-flask method and intrinsic dissolution.

This study aimed at evaluating the shake-flask use as a universal method to evaluate drug solubility in a biowaiver context as proposed by FDA, EMA and ANVISA. The solubility of losartan was determined in three buffers using the shake-flask method, intrinsic dissolution (ID) and Quantum Chemistry. Moreover, the evaluation of a losartan dissolution profile from coated tablets was conducted. The losartan low solubility in pH 1.2 and high solubility in pH 6.8 were observed using the shake-flask method. However, the solubility results using ID demonstrated its high solubility in pH 1.2 and 6.8. It was not possible to find conclusive results regarding the solubility of the drug in pH 4.5. The studies conducted by Quantum Chemistry provide molecular and electronic data that helped understand the losartan solvation in different pH values. Our experimental results defined that losartan can be classified as a low-solubility drug. In addition, this work shows that shake-flask cannot be a universal method of solubility studies in biowaiver context. Individual analysis will be necessary. The intrinsic dissolution should be considered as a complementary method

Polymorphic and quantum chemistry characterization of candesartan cilexetil : importance for the correct drug classification according to Biopharmaceutics Classification System.

The recommended method for the biopharmaceutical evaluation of drug solubility is the shake flask; however, there are discrepancies reported about the solubility of certain compounds measured with this method, one of them is candesartan cilexetil. The present work aimed to elucidate the solubility of candesartan cilexetil by associating others assays such as stability determination, polymorphic characterization and in silico calculations of intrinsic solubility, ionized species, and electronic structures using quantum chemistry descriptors (frontier molecular orbitals and Fukui functions). For the complete biopharmaceutical classification, we also reviewed the permeability data available. The polymorphic form used was previously identified as the form I of candesartan cilexetil. The solubility was evaluated in biorelevant media in the pH range of 1.2?6.8 at 37.0?C according to the stability previously assessed. The solubility of candesartan cilexetil is pH dependent and the dose/solubility ratios obtained demonstrated the low solubility of the prodrug. The in silico calculations supported the found results and evidenced the main groups involved in the solvation, benzimidazole, and tetrazol-biphenyl. The human absolute bioavailability reported demonstrates that candesartan cilexetil has low permeability and when associated with the low solubility allows to classify it as class 4 of the Biopharmaceutics Classification System

Synthesis and application of a new carboxylated cellulose derivative. Part III: Removal of auramine-O and safranin-T from mono- and bi-component spiked aqueous solutions

In the third part of this series of studies, the adsorption of the basic textile dyes auramine-O (AO) and safranin-T (ST) on a carboxylated cellulose derivative (CTA) were evaluated in mono- and bi-component spiked aqueous solutions. Adsorption studies were developed as a function of solution pH, contact time, and initial dye concentration. Adsorption kinetic data were modeled by monocomponent kinetic models of pseudo-first- (PFO), pseudo-second-order (PSO), intraparticle diffusion, and Boyd, while the competitive kinetic model of Corsel was used to model bicomponent kinetic data. Monocomponent adsorption equilibrium data were modeled by the Langmuir, Sips, Fowler-Guggenhein, Hill de-Boer, and Konda models, while the IAST and RAST models were used to model bicomponent equilibrium data. Monocomponent maximum adsorption capacities for AO and ST at pH 4.5 were 2.841 and 3.691 mmol g−1, and at pH 7.0 were 5.443 and 4.074 mmol g−1, respectively. Bicomponent maximum adsorption capacities for AO and ST at pH 7.0 were 1.230 and 3.728 mmol g−1. Adsorption enthalpy changes (ΔadsH) were obtained using isothermal titration calorimetry. The values of ΔadsH ranged from −18.83 to −5.60 kJ mol−1, suggesting that physisorption controlled the adsorption process. Desorption and re-adsorption of CTA was also evaluated