Here, we address the problem of stabilizing a new helicoid ferrocene. Of course, to obtain a helical complex, it is essential to design suitable organic ligands. The ligands should possess the correct symmetry to match the geometrical requirement of the metal center. We propose in silico a beautiful helix that consists of one polycyclic hydrocarbon composed of 10 fused cyclopentadiene rings bound on opposite sides of an iron atom. The nature of the metal-ligand interactions between Fe(2+) and the ligand was investigated with energy decomposition analysis. Our results provide strong evidence for the viability of the hitherto unknown helicoid ferrocene as a target for synthesis.

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A Quantitative Structure-Activity Relationship (QSAR) of coumarins by genetic algorithms employing physicochemical, topological, lipophilic and electronic descriptors was performed. We have used experimental antioxidant activities of specific coumarin derivatives against the DPPH· radical molecule. Molecular descriptors such as Randic Path/Walk, hydrophilic factor and chemical hardness were selected to propose a mathematical model. We obtained a linear correlation with R2 = 96.65 and Q LOO2 = 93.14 values. The evaluation of the predictive ability of the model was performed by applying the Q ASYM2, $\hat r^2 $ and Δr m2 methods. Fukui functions were calculated here for coumarin derivatives in order to delve into the mechanics by which they work as primary antioxidants. We also investigated xanthine oxidase inhibition with these coumarins by molecular docking. Our results show that hydrophobic, electrostatic and hydrogen bond interactions are crucial in the inhibition of xanthine oxidase by coumarins.

Recebido em 21/6/11; aceito em 5/9/11; publicado na web em 8/11/11 A USABILITY STUDY OF EDUCATIONAL MOLECULAR VISUALIZATION ON SMART PHONES. Chemistry students have difficulty understanding molecular structures and their functions. To aide their comprehension, molecular visualization software has been developed to run on smart phones, but in order to positively influence learning it must have a high degree of usability (usability measures how software is used in terms of efficiency, efficacy and satisfaction). This paper describes a usability study of molecular visualization software running on a smart phone, where chemistry students analyzed molecular models. Results showed very good usability and 95% of students wanted to use it in further classes.Keywords: molecular visualization; mobile computing; usability. INTRODUCCIÓNLos estudiantes de química generalmente tienen dificultad para comprender ciertos conceptos científicos de bioquímica y áreas afines, por ejemplo, las estructuras moleculares.1 Estudios empíricos llevados a cabo anteriormente 2 han mostrado que muchos estudiantes no comprenden fácilmente las representaciones microscópicas de moléculas debido a su escala y sus características físico-químicas abstractas. La dificultad en el aprendizaje se debe principalmente a que suceden los procesos a una escala muy diferente y diminuta y con una estructura tridimensional demasiado intrincada, por lo que su comprensión resulta difícil. Esto sucede a menudo con la comprensión de los enlaces moleculares.3 A pesar de que los alumnos de química, en los primeros años de estudio de licenciatura, aprenden a cómo representar en diferentes formatos las geometrías moleculares (proyecciones de Fisher, taquigráfica, etc.) aún se requiere que el alumno muestre ciertas facultades espaciales para construir y entender la disposición tridimensional de las estructuras moleculares. 4 Las herramientas didácticas tradicionales (por ejemplo, el pizarrón o los modelos moleculares de plástico) pueden servir para aprender ciertos conceptos generales sobre la estructura de las moléculas, pero tienen ciertas limitaciones para analizar y entender conceptos muy puntuales y precisos en la estructura y dinámica de las moléculas. Es por esto que para ayudar a su comprensión, los estudiantes deben apoyarse en información multisensorial, principalmente visual y táctil y dicha información debe mostrarse al estudiante de manera práctica y accesible. 5Una aplicación importante de la visualización molecular por computadora es en la enseñanza de las estructuras moleculares, de los elementos de simetría inherentes a las moléculas y algunas propiedades electrónicas que puedan visualizarse de acuerdo a algún código de colores, por ejemplo, densidad electrónica, el potencial electrostático, disposición de las fuerzas de van der Waals.6 Desde que se creó la WWW, los estudiantes de química pueden obtener de Internet infinidad de modelos moleculares en 3D, almacenados en formatos tales como VRML (Virtual Reality Modeling Language), el cual es un lenguaje...

The in vitro antioxidant activities of eight 3-carboxycoumarin derivatives were assayed by the quantitative 1,1-diphenyl-2-picrylhydrazil (DPPH•) radical scavenging activity method. 3-Acetyl-6-hydroxy-2H-1-benzopyran-2-one (C1) and ethyl 6-hydroxy-2-oxo-2H-1-benzopyran-3-carboxylate (C2) presented the best radical-scavenging activity. A quantitative structure-activity relationship (QSAR) study was performed and correlated with the experimental DPPH• scavenging data. We used structural, geometrical, topological and quantum-chemical descriptors selected with Genetic Algorithms in order to determine which of these parameters are responsible of the observed DPPH• radical scavenging activity. We constructed a back propagation neural network with the hydrophilic factor (Hy) descriptor to generate an adequate architecture of neurons for the system description. The mathematical model showed a multiple determination coefficient of 0.9196 and a root mean squared error of 0.0851. Our results shows that the presence of hydroxyl groups on the ring structure of 3-carboxy-coumarins are correlated with the observed DPPH• radical scavenging activity effects.

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This work presents a study of the structure of neutral and anionic copper cluster nonamers with density functional theory calculations. The structure optimization and frequency analysis were performed at the local density approximation (LDA) level of theory with the exchange correlation functional by Vosko, Wilk, and Nusair (VWN). Improved calculations for the structure stability were based on the generalized gradient approximation (GGA) where the exchange correlation functional of Perdew and Wang (PW) was used. For both neutral and anionic clusters, new isomers are found that are more stable than those already presented in the literature. Adiabatic and vertical electron affinities are calculated and compared with the experimental value reported for Cu9. The calculated values are in good agreement with the available experimental data. An analysis of the most relevant molecular orbitals (MOs) of the low-lying neutral and anionic copper cluster nonamers is reported, too.

Hyperjovinol-A ((2-methyl-1-(2,4,6-trihydroxy-3-(3-hydroxy-3,7-dimethyloct-6-enyl)phen yl)propan-1-one) is an acylated phloroglucinol isolated from Hypericum Jovis and exhibiting good antioxidant activity. The study investigates the compound’s antiradical ability on the basis of the electron-donor and electron-acceptor abilities of its conformers, deriving donor and acceptor indexes and mapping them in terms of donor-acceptor maps (DAM). The DAMs of vitamins C and E and of carotene astaxantine are used as comparison references. Calculations were performed at the DFT/BPW91/6-311+G(d,p) level, with optimizations on fully relaxed geometries to obtain the conformers of the neutral molecule in vacuo, and single point calculations to obtain the energies of the cationic and anionic species in vacuo and of the neutral, cationic, and anionic species in water, ethanol, and pentylethanoate. The calculations in solution utilized the polarizable continuum model (PCM). The results indicate that hyperjovinol-A may have better antiradical activity than vitamin C. This is in agreement with experimental results, showing that the antioxidant activity of hyperjovinol-A is comparable with that of the best drugs currently in clinical use. The activity is maintained in solution. The Fukui function f(·) was also calculated for all the conformers of hyperjovinol-A, to identify the regions of highest reactivity.