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ABSTRACT: La presencia de depósitos minerales es muy común en microorganismos, plantas hongos y mamíferos. Estos organismos son, por lo tanto, un modelo natural excelente para estudiar la relación entre las principales partes que los componen, es decir la fase biopolímérica y la mineral. La importancia de este tipo de estudios se relaciona directamente con la nanotecnología, una rama científica relativamente reciente, encargada de estudiar los fenómenos químicos, físicos, además de los fisicoquímicos a escalas menores a los 500 nm. Cuando el sistema de estudio tiene importancia biológica, posee estructuras biológicamente activas, o procede de un sistema biológico, se llama entonces bionanotecnología, este es el caso del estudio de la biomineralización en las algas diatomeas. Esta línea de investigación tiene alta relevancia por la dificultad de producir micro- y nanoestructuras altamente controladas de dióxido de silicio o sílice (SiO2), un tipo de vidrio, que tiene potencialmente aplicaciones tecnológicas en libración de drogas, celdas solares y materiales cerámicos de alto rendimiento.
Los factores que afectan la geometría, las propiedades mecánicas y fisicoquímicas en estas estructuras son muy pobremente comprendidos, por lo cual este tipo de estudios son de suma importancia. Si se logra entender las interacciones y los procesos de formación en estos sistemas que producen vidrio en entes biológicos, como las algas diatomeas, podremos acercarnos racionalmente a la síntesis de nuevos y sofisticados materiales nanoestructurados, con aplicaciones en una gran gama de áreas que van desde la nanotecnología (semiconductores híbridos) hasta la biología y biomedicina (biomateriales y estructuras liberadoras de drogas). En el presente trabajo se hace un esbozo “ascendente” (bottom-up) de la síntesis de “biosilice” en diatomeas donde se enfatiza la importancia de éste fenómeno en la nanotecnología.
Palabras clave. Biosílice, biominerales, biopolímero, vesícula de depósito de sílice (SDV).
La Granja. 07/2013; 17(July):?.
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ABSTRACT: Biosilica from diatoms is formed at ambient conditions under the control of biological and physicochemical processes. The changes in growth and biosilica formation through uptake of different concentrations of Cd2+ by the diatom Nitzschia palea (Kützing) W. Smith was investigated, correlating Cd2+ effects to changes in the biosilica nanostructure and the relative content of the encapsulated biomolecules. Diatom growth rates at different Cd2+ concentrations (as 1, 2, 3, 4, and 5 × 10−1 mg L−1 CdCl2) were studied in order to determine the concentrations at which sublethal effects were visible, allowing the harvest of sufficient diatom cells for further experiments. We found a clear correlation between the Cd2+ concentrations and both the nanostructure of the biosilica and content of encapsulated peptides. Cd2+ induced biosilica deformation was assessed by scanning electron microscopy and attenuated total reflectance-Fourier Transformed Infrared Spectroscopy (FTIR), revealing that micromorphological changes in frustule features (striae, costae, pores) and nanostructural modifications (structure of the silica and conformation of the encapsulated peptides) occurred at applied Cd2+ concentrations of 2 and 3 × 10−1 mg L−1. In particular the FTIR contribution of peptides decreased at elevated Cd2+ concentrations, whereas shifts in wave number of several relevant organic bonds as C = O stretching (1765 cm−1) and possibly hydrated sulfate (1160, 1110 and 980 cm−1) were assigned. Additional analysis of the amide I band showed a relative increase in β-sheet structure (1680–1620 cm−1) when Cd2+ concentration increased. Cadmium uptake clearly affected the molecular ordering of the biosilica in Nitzschia palea, most probably by interfering in biological or physicochemical processes involved in diatom biosilicification.
Phycological Research 07/2012; 60(3):229-240. · 1.54 Impact Factor
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ABSTRACT: Nanostructure derivatives of fullerene C(60) are used in emerging applications of composite matrices, including protective and decorative coating, superadsorbent material, thin films, and lightweight high-strength fiber-reinforced materials, etc. In this study, quantum chemical calculations and experimental studies were performed to analyze the derivatives of diamine-fullerene prepared by the gas-phase solvent-free functionalization technique. In particular, the aliphatic 1,8-diamino-octane and the aromatic 1,5-diaminonaphthalene, which are diamines volatile in vacuum, were studied. We addressed two alternative mechanisms of the amination reaction via polyaddition and cross-linking of C(60) with diamines, using the pure GGA BLYP, PW91, and PBE functionals; further validation calculations were performed using the semiempirical dispersion GGA B97-D functional which contains parameters that have been specially adjusted by a more realistic view on dispersion contributions. In addition, we looked for experimental evidence for the covalent functionalization by using laser desorption/ionization time-of-flight mass spectrometry, thermogravimetric analysis, and atomic force microscopy.
The Journal of Physical Chemistry A 02/2012; 116(6):1663-76. · 2.95 Impact Factor
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The Canadian Journal of Chemical Engineering 01/2012; · 0.75 Impact Factor
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ABSTRACT: Short pristine multi-walled carbon nanotubes (MWNTs) were functionalized with a series of long-chain (including polymeric) aliphatic amines, namely octadecylamine (ODA), 1,8-diaminooctane (DO), polyethylene glycol diamine (PEGDA) and polyethylenimine (PEI), via two "green" approaches: (1) gas-phase functionalization (for volatile ODA and DO) and (2) direct heating in the melt (for polymeric PEGDA and PEI). Both of them consist in one-step reaction between MWNTs and amine without the use of organic solvents. The nanostructures obtained were characterized by using infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. It was observed that both solvent-free methods were efficient in the nanotube functionalization, and the nanostructures of variable solubility and morphology were obtained depending on the amines attached. ODA, PEGDA and PEI-functionalized MWNTs were found to be soluble in propanol, meanwhile the MWNTs-PEGDA and MWNTs-PEI were soluble in water as well. The attachment of 1,8-diaminooctane onto MWNTs resulted in cross-linked stable nanostructure.
Journal of Nanoscience and Nanotechnology 06/2011; 11(6):5546-54. · 1.56 Impact Factor
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ABSTRACT: The gas-phase treatment with 1,5-diaminonaphthalene (DAN) is proposed as an efficient way of chemical functionalization of fullerene C60 thin films in order to modify their electronic properties; a temperature of 190 degrees C and reaction time of 4 h were found to be optimal reaction conditions. Two amino groups of DAN add on two neighboring C60 cages, thus producing cross-links in the fullerene phase. The resulting oligomeric and/or polymeric products exhibit a lower solubility in toluene as compared to pristine C60 films. The functionalized films exhibit lower surface roughness, as found by atomic force microscopy. Raman spectra keep, with some decrease in intensity, the most important features of C60 upon functionalization. The infrared band intensities corresponding to pristine fullerene decrease even stronger, where a number of new absorption bands appear not only due to DAN moieties, but also due to the covalently derivatized C60 cages. The diamine molecules are able to penetrate throughout the entire fullerene phase to provide an efficient and uniform functionalization. As a result, the DAN-functionalized films exhibit higher conductivity as compared to that of pristine films not only along the surface layer, but also through the entire phase of C60, by one and four orders of magnitude, respectively.
Journal of Nanoscience and Nanotechnology 06/2011; 11(6):5569-73. · 1.56 Impact Factor
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ABSTRACT: We performed density functional theory (DFT) calculations of noncovalently bonded 1:1 complex of meso-tetraphenylporphine H2TPP with fullerene C60. The functionals used were PW91, PBE and BLYP of general gradient approximation (GGA), as well as PWC and VWN of local density approximation (LDA) as implemented in the DMol3 module of Materials Studio package from Accelrys. The computed geometries were compared to the experimental X-ray diffraction data obtained elsewhere for rhombohedral and monoclinic H2TPP + C60 crystalline complexes. If the correlation coefficient between the calculated and experimental data is applied, the covalent bond lengths and angles within H2TPP unit are best reproduced by BLYP functional, whereas PWC and VWN are least precise. On the other hand, PWC and VWN are the best functionals in reproducing the separations between H2TPP and C60 found from X-ray diffraction analysis: the LDA-calculated N(H2TPP) ... C(C60) distances are of about 2.9-3.0 angstroms, whereas the corresponding experimental values are of ca. 3.0-3.1 angstroms. Next are PW91 and PBE functionals, giving N(H2TPP) ... C(C60) distances of ca. 3.5-3.6 angstroms. BLYP produced the separations of around 4.0-4.1 angstroms, which are inconsistent with both X-ray data and the results produced other functionals. We also analyzed functional-dependent variations in formation energies, electrostatic potential, HOMO, LUMO and charge transfer. We concluded that of DFT functionals incorporated into DMol3 module and tested in this study, PWC and VWN are the most adequate ones, and BLYP is the least recommended one for the studies of noncovalent interactions of porphyrins with carbon nanoclusters.
Journal of Nanoscience and Nanotechnology 06/2011; 11(6):5519-25. · 1.56 Impact Factor
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ABSTRACT: The self-assembly of porphyrins into highly organized functional arrays supported on appropriate solid substrates is an area of research with multiple potential applications in the "bottom-up" approach to manufacturing. In order to analyze the self-assembly of meso-tetraphenylporphine (H2TPP) on the surfaces of highly oriented pyrolytic graphite (HOPG) and single-walled carbon nanotubes (SWNTs), we performed molecular mechanics modeling (by MM+ force field) and scanning tunneling microscopy (STM) imaging. Molecular modeling predicted an energetic preference of the H2TPP molecules to adsorb in monolayers on the surfaces of graphite and SWNT sidewall, rather than their stacking or separation. On graphite, the most favorable arrays were predicted to be ribbons composed of interacting parallel chains of H2TPP molecules. On the SWNT sidewall, the energetic preference pointed toward the formation of parallel and interacting long-period helixes, resulting in an almost full coverage of the SWNT surface. These preferable arrays on both carbon materials assure the interaction of every porphyrin unit with as many neighbors as possible, thus lowering the potential energy of the adsorption complexes. STM imaging results are in good agreement with molecular modeling predictions. The formation of self-assembled ribbons was a frequently observed phenomenon on the HOPG surface, while on the SWNT surface a full coverage of the exposed portion of the sidewalls was observed, suggesting the formation of interacting long-period helixes. A preferential adsorption of H2TPP molecules near graphite topographic defects was also observed.
Journal of Nanoscience and Nanotechnology 06/2011; 11(6):5457-68. · 1.56 Impact Factor
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ABSTRACT: Human serum albumin (HSA) is the most abundant protein in blood plasma showing a remarkable ability to bind a broad range of hydrophobic substrates. We employed scanning tunneling microscopy and atomic force microscopy to characterize the morphology of HSA aggregates on highly-ordered pyrolytic graphite (HOPG) and single-walled carbon nanotubes (SWNTs). The morphologies found for albumin aggregates on HOPG are quite different from the ones observed on SWNTs. On HOPG, HSA forms aggregates of roughly 10-20 molecules; single protein molecules were observed as well. In the case of SWNTs, nanotubes were partially or totally covered with HSA, exhibiting four general types of aggregation: (i) SWNT sidewalls contain single molecules of albumin which are away from each other at distances longer than the HSA molecular size; (ii) SWNTs are completely covered with HSA, which forms a thin and relatively homogeneous layer; (iii) SWNTs have a complete layer of HSA with additional accumulation of protein at separate sites; and (iv) several SWNTs totally covered with albumin assemble into a bundle-like structure common for bare nanotubes. These observations are interpreted in terms of stronger interactions of HSA with nanotube sidewalls than with flat graphite surface.
Journal of Nanoscience and Nanotechnology 06/2011; 11(6):5491-8. · 1.56 Impact Factor
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ABSTRACT: We analyzed theoretically the behavior of simple homopeptides (up to decapeptides, starting with the parent amino acid) derived from glycine and L-alanine, arranged into α helix and β sheet, when interacting non-covalently with fullerene C60. The main goal was to study how the increase of peptide chain length influences the geometry and formation energy of peptide +C60 complex. We employed a series of computational techniques, including two DFT functionals (BLYP GGA and VWN LDA implemented in the DMol3 module of Materials Studio) and two force fields (AMBER and MM+ available in the HyperChem package). Of the two DFT functionals tested, BLYP in a number of cases produced positive energies of the complex formation, as well as strongly overestimated intermolecular separations (sometimes exceeding 4 Å). VWN calculations produced reasonable and consistent values for the closest intermolecular contacts between amino acids/peptides and fullerene, along with likely overestimated absolute values of (all negative) binding energies; therefore, the VWN data are preferable to be taken as a reference to compare with the results obtained with other computation techniques. Of the two force fields used, AMBER produced stronger interactions (even stronger than those obtained by VWN DFT) in terms of binding energies and complexation-induced conformational changes in peptide molecules. On the other hand, the results of MM+ calculations are in much closer agreement with the data obtained by VWN DFT. The general trend in which all the calculation techniques employed coincide is a remarkable rigidity of α; helix peptides and a considerable flexibility of their β sheet counterparts, when interacting with C60 molecule. The degree of conformational changes observed in β sheet peptides depends on the parent amino acid, length of peptide, and computational method used.
Journal of Computational and Theoretical Nanoscience 01/2011; 8(2):243-252. · 0.91 Impact Factor
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ABSTRACT: We report on DFT calculations of noncovalent porphyrin-pyridine-fullerene triad ZnTPP·Py·C60 (ZnTPP = zinc(II) complex of meso-tetraphenylporphine; Py = pyridine), using PW91, PBE and BLYP functionals of general gradient approximation (GGA), as well as PWC and VWN functionals of local density approximation (LDA) implemented in the DMol3 module of Materials Studio. The optimized geometries were compared to the corresponding experimental parameters obtained previously by X-ray diffraction study of ZnTPP·BPy·C60 complex (BPy = bipyridyl). If the correlation coefficient between the calculated and experimental X-ray geometric parameters is used, all DFT functionals tested show a very similar performance for the covalent/coordination bond lengths and angles within ZnTPP·Py unit. If the root mean square error is applied, BLYP is the best functional for calculating bond angles and worst for calculating bond lengths, and vice versa for LDA functionals. The separation between ZnTPP and fullerene units, expressed as N(ZnTPP)…C(C60 and Zn…C(C60 distances, was best reproduced using PWC and VWN LDA functionals (slightly shortened by 0.1-0.2 Å). PW91 and PBE GGA functionals overestimated the experimental N(ZnTPP)…C(C60 and Zn…C(C60 distances by roughly 0.4 Å. The worst results were obtained by BLYP, which produced totally unrealistic separations. Taken together with positive formation energy obtained with BLYP (which implies repulsive interaction), the results obtained suggest that PWC and VWN are the most appropriate, whereas BLYP is the least recommendable functional of DMol3 for the studies of noncovalent interactions of porphyrins with fullerenes and carbon nanotubes.
Journal of Computational and Theoretical Nanoscience 10/2010; 7(11):2322-2330. · 0.91 Impact Factor
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ABSTRACT: We performed DFT calculations of noncovalent 1:2 complex of meso-tetraphenylporphine H2TPP with fullerene C60, using PW91, PBE and BLYP functionals of general gradient approximation (GGA), as well as PWC and VWN functionals of local density approximation (LDA) implemented in the DMol3 module of Materials Studio. The computed geometries were compared to the experimental ones obtained previously by X-ray analysis of rhombohedral and monoclinic H2TPP+C60 crystalline complexes. The covalent bond lengths and angles within H2TPP are best reproduced by BLYP; PWC and VWN are least precise. LDA functionals better perform for dihedral angles. PWC and VWN are the best functionals in reproducing the experimental separations between H2TPP and C60: the LDA-calculated N(H2TPP)…C(C60) distances are of about 2.9-3.0 Å, whereas the experimental values are 3.0-3.1 Å. Next are PW91 and PBE functionals, giving N(H2TPP)…C(C60) distances of ca. 3.4-3.6 Å. BLYP produced the separations of around 4.7 Å, which are inconsistent with both X-ray data and the results obtained with other functionals. Of DFT methods incorporated into DMol3 module and tested in this study, PWC and VWN functionals were concluded to be most adequate, and BLYP to be least recommended to study noncovalent interactions of porphyrins with carbon nanoclusters (fullerenes and carbon nanotubes).
Journal of Computational and Theoretical Nanoscience 09/2010; 7(10):1996-2003. · 0.91 Impact Factor
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ABSTRACT: We performed DFT calculations of noncovalently bonded complexes (or dyads) of metal-free meso-tetraphenylporphine H2TPP and its complexes Co(II)TPP and Ni(II)TPP with fullerene C60, using PW91, PBE and BLYP functionals of general gradient approximation (GGA), as well as PWC and VWN functionals of local density approximation (LDA) implemented in the DMol3 module of Materials Studio package, in conjunction with the DNP basis set. The results obtained are analyzed in order to estimate how realistic they are, what differences and similarities they have. We found that none of five functionals tested matches well enough the experimentally observed separations between porphyrin and fullerene units; the experimental separations turn to be in between those calculated by PW91 and PBE GGA and those obtained by PWC and VWN LDA. BLYP produces totally unrealistic values for all the dyads, reaching almost 5 Å in the case of NiTPP + C60. Laser desorption/ionization time-of-flight (LDI-TOF) mass spectrometry of mechanical porphyrin/fullerene mixtures was employed to roughly estimate relative stability of the porphyrin-C60 dyads. In the case of H2TPP + C60 and NiTPP + C60 we observed much weaker complexation (estimated as the dyad peak intensity attributed to the intensity of porphyrin peak) as compared to the case of CoTPP + C60. Apparently, the closed-shell systems behave similarly to each other and different to the paramagnetic Co complex, which matches better the formation energies found from LDA calculations.
Journal of Computational and Theoretical Nanoscience 05/2010; 7(6):1095-1103. · 0.91 Impact Factor
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ABSTRACT: The adsorptions of several molecules of NO2 (considering their spin-states) on an elongated fullerene [i.e., a very short (8, 0) closed-cap single-walled carbon nanotube] were examined by computing their binding energies through spin-unrestricted density functional theory methods. While NO2 (2A1) is weakly adsorbed (binding energies of ca. 0.07 eV), the 4A2 spin-state leads to form the most energy-favored complex. As a result of the new attachments, transitions from metallic to semiconducting states were observed. These results show, on one hand, dependence on the selection of a suitable nanotube model (e.g., closed caps) and, on the other hand, the importance for accounting different spin-states for studying interactions with paramagnetic molecules.
Journal of Computational and Theoretical Nanoscience 01/2010; 7(2):408-413. · 0.91 Impact Factor
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ABSTRACT: The goal of the present paper was to study the behavior of commercially available pristine multi-walled carbon nanotubes (MWNTs) under microwave irradiation (exposures up to 200 s) in vacuum, by means of several experimental techniques. An intense glow and heating of the nanotube samples were observed. Raman spectra, scanning electron microscopy (SEM) and scanning tunneling microscopy (STM) images of the processed nanotubes did not show considerable changes as compared to those for pristine MWNTs. Closer structural investigation by means of conventional and high-resolution transmission electron microscopy (TEM and HRTEM, respectively) revealed an increase in the occurrence of open nanotube ends, whereas the sidewalls remained generally unchanged. The possibility of increase in the number of entry ports for gases was verified by employing temperature programmed desorption experiments with mass spectrometric detection (TPD-MS) with pristine and microwave-irradiated MWNTs exposed to atmosphere. The overall adsorption capacity did not change, whereas the rate of adsorption increased roughly by twice for the nanotubes irradiated for 200 s as compared to pristine MWNTs, which is consistent with selective opening of the nanotube ends.
Journal of Nanoscience and Nanotechnology 01/2010; 10(1):448-55. · 1.56 Impact Factor
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ABSTRACT: A rational approach to the design and preparation of new nanohybrids and nanoassemblies based on porphyrins and low-dimensional carbon materials (0-D fullerenes, 1-D carbon nanotubes and 2-D graphite) is impossible without understanding the forces governing interactions between the components. Here, as in many other areas of modern science and technology, the role of theoretical methods cannot be overestimated. At the same time, the electronic structure calculations on the nanohybrids composed of low-dimensional carbon materials and porphyrins are a challenging task due to the large system sizes and imperfections of the available theoretical approaches. In ther present review, the non-covalent interactions between porphyrins and low-dimensional carbon materials are discussed. Theoretical results obtained in this area using the methods of density functional theory (DFT) and molecular mechanics, with special emphasis on DFT, are reviewed and compared with relevant experimental data, when available (X-ray crystal structure for porphyrin-fullerene dyads, and scanning tunneling microscopy images for carbon nanotubes and graphite).
Journal of Computational and Theoretical Nanoscience 06/2009; 6(7):1383-1411. · 0.91 Impact Factor
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ABSTRACT: The solvent-free polymerization of epsilon-caprolactam on 1,8-diaminooctane-functionalized multi-walled carbon nanotubes (DA-MWNTs) is proposed as a simple and ecologically friendly approach to the preparation of carbon nanotubes/nylon 6 hybrid materials. The main goal of the present study was to find a minimum temperature resulting in an efficient epsilon-caprolactam polymerization, along with the optimization of the weight ratio of DA-MWNTs to epsilon-caprolactam and reaction time. The effect of temperature was studied in the range of 170 degrees C to 210 degrees C. After the reaction at 170 degrees C, the nanotubes functionalized contained a large amount of unreacted monomer along with ca. 14% of polyamide. Increasing the reaction temperature dramatically reduced the content of epsilon-caprolactam impurity and increased the nylon 6 content to ca. 20%. The reaction time tested was 1, 2, 4, 6 and 8 h. Exposures at less than 4 h were insufficient, where the infrared spectral bands of nylon 6 were barely seen. The reaction time of 6 h was found to be optimal since a more prolonged heating for 8 h did not provide an evident further increase in polyamide content. The effect of stoichiometry was studied by varying the weight ratio of DA-MWNTs to epsilon-caprolactam from 1:0.1 to 1:1. The ratios 1:0.1 and 1:0.2 were too high, since they did not provide the amount of epsilon-caprolactam necessary to form the composites with at least 20% content of nylon 6. Starting with the ratio of 1:0.3, the infrared band intensities qualitatively stabilized and did not show dramatic variations. The use of reagent ratios of 1:0.3 to 1:0.7 might be especially appropriate for preparing the composites targeted to biomedical applications, whereas higher weight ratios are expected to increase the content of undesirable monomer impurities.
Journal of Nanoscience and Nanotechnology 06/2009; 9(5):3313-9. · 1.56 Impact Factor
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ABSTRACT: By means of density functional theory calculations at the PW91/DN theoretical level, we performed a systematic analysis of possible nucleophilic addition sites of one to six methylamine molecules onto fullerene C60. Particular questions we addressed, using the formation energy as a thermodynamic criterion of reactivity, were whether the 6,6 C=C bonds of pyracylene units remain always the preferential addition sites at every amination step, and whether the carbon atoms with larger pyramidalization angles θp play a relevant role for the addition regioselectivity. By comparing the energies of formation of different isomeric products, we found that the most favorable additions are observed on the 6,6 C=C bonds, and never on the 5,6 junctions. Furthermore, a preferable polyaddition pattern is the one where -NHCH3 and -H addends form an aligned chain, with the carbon atoms to which they are attached alternating in a zigzag order. As a whole, no direct correlation between the pyramidalization angle θp and reactivity was found. An analysis of the plots of formation energy versus the initial (before addition) 6,6 bond length showed that the preferential additions are those onto relatively short C=C bonds of about 1.380-1.390 Å long, but not on the shortest bonds of ca. 1.370 to 1.375 Å. The latter cases are associated with a considerable steric hindrance due to the addition of three methylamine units to one hexagon of C60, as well as with the smallest values of pyramidalization angles at the site of the third CH3NH2 addition.
Journal of Computational and Theoretical Nanoscience 12/2008; 6(1):73-79. · 0.91 Impact Factor
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ABSTRACT: To attempt theoretical predictions of the regioselectivity pattern in molecules with multiple reactive sites, the energies of formation of all possible isomers are usually considered. This means that the computing becomes highly demanding if high theoretical levels are used. The study objective was to predict the regioselectivity in the reaction of hydrogen addition onto azahydro[60]fullerene C 59H n+1 N ( n = 0-4) systems using a new reactivity indicator termed general-purpose reactivity indicator, Xi Delta N<or=0,alpha (kappa), proposed by Anderson et al. ( J. Chem. Theory Comput. 2007, 3, 358). Because Xi Delta N<or=0,alpha (kappa) combines the information from the electrostatic potential and the Fukui function, this indicator is a two-parameter model that depends on the atomic charges and Fukui values calculated. We used the gradient-corrected BLYP and BOP functionals to approximate the electronic density of the systems, and these densities were employed to determinate the parameters. In terms of regioselectivity, the preferential addition sites at every hydrogenation step on C 59H n+1 N ( n = 0-4) shows that 1,4-adducts are more stable than 1,2-adducts. However, we show that the multiple additions are only feasible up to a C 59H 5N (tetraddition) product. Consequently, the application of this indicator not only helps to avoid systematic computational studies by comparing energies of formation in several isomersmany of which are not currently supported by experimental resultsbut also provides an insight of how the pattern of addition is achieved. Comparisons with traditional indicators show that the application of Xi Delta N<or=0,alpha (kappa) performs much better for predicting reactivity in the aza[60]fullerene derivatives studied.
The Journal of Physical Chemistry A 09/2008; 112(35):8154-63. · 2.95 Impact Factor
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ABSTRACT: We report on the preparation of fullerene C60 thin films chemically cross-linked with octane-1,8-dithiol, which are capable of binding gold nanoparticles. The formation of a polymer was directly proved by means of laser desorption/ionization time-of-flight mass spectra, in which we observed the cleavage of fullerene-dithiol polymer at different bonds. Fourier-transform infrared, Raman and UV-visible spectra of the functionalized films exhibited notorious changes due to the formation of new covalent bonds between C60 molecules and bifunctional thiol. We further demonstrated that the dithiol-functionalized fullerene can be employed as a support for stable and homogeneous deposition of gold nanoparticles. Their average size is about 5 nm according to high-resolution transmission electron microscopy observations, and up to 20 nm, as found from scanning tunneling microscopy images. The proposed binding mechanism is through a strong coordination attachment between Au nanoclusters and sulfur donor atoms of the functionalized fullerene, as supported by density functional theory calculations.
Journal of Nanoscience and Nanotechnology 07/2008; 8(8):3828-3837. · 1.56 Impact Factor
