5 research outputs found
L-Asparagine crystals with wide gap semiconductor features : optical absorption measurements and density functional theory computations
Results of optical absorption measurements are presented together with calculated structural, electronic, and optical properties for the anhydrous monoclinic L-asparagine crystal. Density functional theory (DFT) within the generalized gradient approximation (GGA) including dispersion effects (TS, Grimme) was employed to perform the calculations. The optical absorption measurements revealed that the anhydrous monoclinic L-asparagine crystal is a wide band gap material with 4.95 eV main gap energy. DFT-GGA+TS simulations, on the other hand, produced structural parameters in very good agreement with X-ray data. The lattice parameter differences a, b, c between theory and experiment were as small as 0.020, 0.051, and 0.022 Ă
, respectively. The calculated band gap energy is smaller than the experimental data by about 15%, with a 4.23 eV indirect band gap corresponding to Zâ and ZâÎČ transitions. Three other indirect band gaps of 4.30 eV, 4.32 eV, and 4.36 eV are assigned to α3â , α1â , and α2â transitions, respectively. -sol computations, on the other hand, predict a main band gap of 5.00 eV, just 50 meV above the experimental value. Electronic wavefunctions mainly originating from O 2pâcarboxyl, C 2pâside chain, and C 2pâcarboxyl orbitals contribute most significantly to the highest valence and lowest conduction energy bands, respectively. By varying the lattice parameters from their converged equilibrium values, we show that the unit cell is less stiff along the b direction than for the a and c directions. Effective mass calculations suggest that hole transport behavior is more anisotropic than electron transport, but the mass values allow for some charge mobility except along a direction perpendicular to the molecular layers of L-asparagine which form the crystal, so anhydrous monoclinic L-asparagine crystals could behave as wide gap semiconductors. Finally, the calculations point to a high degree
Research Activity of the Complex Inorganic inhibitors trans-2-enoyl reductase
CoordenaĂĂo de AperfeiĂoamento de Pessoal de NĂvel SuperiorA tuberculose tem sido uma das principais causas de morte no Mundo. Infelizmente, nĂo existem ainda novas drogas disponĂveis, o que tem desestimulado a investigaĂĂo neste campo. Neste trabalho, preparou-se novos metalo-compostos baseado no sistema Na3[Fe(CN)5L].H2O, sendo L = oxadiazois, hidrazonas ou derivados, que sĂo drogas estudas no tratamento para tuberculose. Esses compostos foram sintetizados e totalmente caracterizados por tĂcnicas espectroscĂpicas e eletroquĂmicas. Em relaĂĂo Ă espectroscopia eletrĂnica, foi mostrada a intensidade relativa das interaĂĂes de retrodoaĂĂo - π entre os compostos utilizando a forĂa do oscilador. Este resultado foi reforĂado por outras tĂcnicas espectroscĂpicas, tal como espectroscopia na regiĂo do infravermelho, onde uma mudanĂa no estiramento CN- (cianeto) para mais altas frequĂncias indica maior interaĂĂo de retrodoaĂĂo - π (Fe(II) L). AlĂm disso, resultados de RMN e eletroquĂmicos reforĂa a coordenaĂĂo do ligante ao centro metĂlico. Os resultados de RMN mostraram que estes compostos foram igualmente coordenados atravĂs do Ătomo de nitrogĂnio do anel piridinico, ao mesmo tempo a voltametria cĂclica mostrou que o ferro foi estabilizado na sua forma reduzida (2+). Foram realizados cĂlculos teĂricos para avaliar a distribuiĂĂo de carga desses compostos e tambĂm correlacionou com as interaĂĂes de retrodoaĂĂo - π. A relevĂncia deste estudo reside na constataĂĂo de que vĂrios inibidores interagem de forma direta com a enzima alvo. Estes compostos foram preparados com o objetivo de inibir a enzima InhA, que Ă responsĂvel pela a biossĂntese da parede celular da micobacteria, conhecendo o efeito da distribuiĂĂo de carga do complexo na inibiĂĂo da enzima podemos fornecer informaĂĂes adicionais para desenhar uma melhor droga. Este resultado foi importante para estabelecer um mapa de reatividade. Estudos bioquĂmicos foram realizados para avaliar a inibiĂĂo da enzima enoil redutase (InhA) tipo selvagem e mutante (S94A). Os complexos derivados de oxadiazois foram muito eficientes na inibiĂĂo da enzima selvagem, incluindo a enzima resistente Ăs drogas convencionais. Testes de toxicidade mostraram que estes compostos apresentaram baixa toxicidade. Um interessante mapa de reatividade foi apresentado, onde foi correlacionado a distribuiĂĂo de carga e o potencial eletroquĂmico do metal para investigar a eficiĂncia de inibiĂĂo. Isso pode levar a uma melhor concepĂĂo racional de outras metalodrogas anti-tuberculose.Tuberculosis has been one of the major causes of death in the World. Unfortunately, there is still a lack of new drugs available, which has stimulated research in this field. Here, it was prepared a spectrum of new metallo-compounds based on Na3[Fe(CN)5L].H2O, where L is hydrazones or oxadiazols derivatives, which are metallodrug candidates for tuberculosis treatment. These compounds were fully characterized by spectroscopic and electrochemical techniques. Regarding to the electronic spectroscopy, it was showed the relative intensity of the π-backbonding effect among these compounds using the oscillator strength. This result was further supported by other techniques such as infrared spectroscopy, where a shift on the CN- (cyanide) stretching to higher frequency indicates stronger backbonding Fe(II) to L. Additionally, NMR and electrochemical results reinforced the back-bonding effect previously assigned in these compounds. NMR results showed these compounds were also coordinated through the nitrogen atom of the pyridine ring, while cyclic voltammetry showed the iron was made more stable in the reduced form (2+). Theoretical calculations were done to evaluate the charge distribution of these compounds and also correlate them with the backbonding effect. The relevance of this study lies on the observation that several inhibitors interact with the proteic target through intermolecular forces. These compounds were prepared aiming to inhibit the InhA enzyme, which is responsible for the biosynthesis of the mycobacterial cell-wall, by knowing the effect of charge distribution on enzyme inhibition it provides extra information to design better drugs. This result was important to draw a reactivity map. Biochemical investigations were carried out to evaluate the inhibition of the wild-type and mutant of the enzyme enoyl reductase (InhA). The complexes of oxadiazol derivatives were very efficient enzyme inhibitor, including toward strains resistant to conventional drugs. Toxicity tests showed these compounds presented low toxicity. An interesting map of reactivity was drawn, where charge distribution and electrochemical potential were correlated to the efficiency to inhibit InhA. This can lead to a better rational design of other anti-tuberculosis metallodrugs
L-Asparagine crystals with wide gap semiconductor features : optical absorption measurements and density functional theory computations
Results of optical absorption measurements are presented together with calculated structural, electronic, and optical properties for the anhydrous monoclinic L-asparagine crystal. Density functional theory (DFT) within the generalized gradient approximation (GGA) including dispersion effects (TS, Grimme) was employed to perform the calculations. The optical absorption measurements revealed that the anhydrous monoclinic L-asparagine crystal is a wide band gap material with 4.95 eV main gap energy. DFT-GGA+TS simulations, on the other hand, produced structural parameters in very good agreement with X-ray data. The lattice parameter differences a, b, c between theory and experiment were as small as 0.020, 0.051, and 0.022 Ă
, respectively. The calculated band gap energy is smaller than the experimental data by about 15%, with a 4.23 eV indirect band gap corresponding to Zâ and ZâÎČ transitions. Three other indirect band gaps of 4.30 eV, 4.32 eV, and 4.36 eV are assigned to α3â , α1â , and α2â transitions, respectively. -sol computations, on the other hand, predict a main band gap of 5.00 eV, just 50 meV above the experimental value. Electronic wavefunctions mainly originating from O 2pâcarboxyl, C 2pâside chain, and C 2pâcarboxyl orbitals contribute most significantly to the highest valence and lowest conduction energy bands, respectively. By varying the lattice parameters from their converged equilibrium values, we show that the unit cell is less stiff along the b direction than for the a and c directions. Effective mass calculations suggest that hole transport behavior is more anisotropic than electron transport, but the mass values allow for some charge mobility except along a direction perpendicular to the molecular layers of L-asparagine which form the crystal, so anhydrous monoclinic L-asparagine crystals could behave as wide gap semiconductors. Finally, the calculations point to a high degree