Solvation Enhances the Distinction Between Carboxylated Armchair and Zigzag Single-Wall Carbon Nanotubes (SWNT-COOH)

The effect of various solvents on the structures and properties of carboxylated SWNTs has been explored using the Same Level Different Basis Set approach (SLDB), where B3LYP functional of density functional theory (DFT) was applied. Armchair (4,4) and zigzag (8,0) and (9,0) tubes were considered as the test bed. In order to simulate varying concentration of –COOH groups, one to five acids groups were placed at one end of these tubes. These samples were placed in different solvents (namely, CS2, THF and water) with varying polarity and results were compared with gas-phase properties. Similar to the gas-phase, zigzag tubes also exhibit both regular (r-COOH, v(C=O) above 1700 cm-1) and low-frequency (lf-COOH, v(C=O) below 1700 cm-1) acid groups. Characteristics of r-COOH group are not affected much in solvents, but lf-COOH of the zigzag tube is the one that makes these tubes distinguishable from its armchair cousin. Stability and charge distribution of SWNT-COOH strongly depend on the number of acid groups in different solvents which may help controlling further functionalization. Vibrational analyses reveal certain features in the 1400-1600 cm-1 range that are characteristic of lf-COOH in different solvents, which may help in the assignment of experimental spectra of oxidized SWNT in solvents

Hydrogen bond and the resonance effect on the formamide-water complexes

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)The interaction of formamide and the two transition states of its amide group rotation with one, two, or three water molecules was studied in vacuum. Great differences between the electronic structure of formamide in its most stable form and the electronic structure of the transition states were noticed. Intermolecular interactions were intense, especially in the cases where the solvent interacted with the amide and the carbonyl groups simultaneously. In the transition states, the interaction between the lone pair of nitrogen and the water molecule becomes important. With the aid of the natural bond orbitals, natural resonance theory, and electron localization function (ELF) analyses an increase in the resonance of planar formamide with the addition of successive water molecules was observed. Such observation suggests that the hydrogen bonds in the formamidewater complexes may have some covalent character. These results are also supported by the quantitative ELF analyses. (C) 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012112514011420Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)FAPESCConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Isatin-Schiff base copper(II) complexes-A DFT study of the metal-ligand bonding situation

Herein, we report results of calculations based on density functional theory (BP86/TZVP) of a set of isatin-Schiff base copper(II) and related complexes, 1-12, that have shown significant pro-apoptotic activity toward diverse tumor cells. The interaction of the copper(II) cation with different ligands has been investigated at the same level of theory. The strength and character of the Cu(II)-L bonding was characterized by metal-ligand bond lengths, vibrational frequencies, binding energies, ligand deformation energies, and natural population analysis. The metal-ligand bonding situation was also characterized by using two complementary topological approaches, the quantum theory of atoms-in-molecules (QTAIM) and the electron localization function (ELF). The calculated electronic g-tensor and hyperfine coupling constants present significant agreement with the EPR experimental data. The calculated parameters pointed to complex 10 as the most stable among the isatin-Schiff base copper(II) species, in good agreement with experimental data that indicate this complex as the most reactive in the series. (C) 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012FAPESP (Processo Tematico)FAPESP (Processo Tematico) [05/60596-8]FAPESP [2007/04379-3, 2006/06035-7]FAPESPFAPESC (UFSC)FAPESC (UFSC) [17.413/2009]Fundacao de Amparo a Pesquisa do Estado de Sao PauloFundacao de Amparo a Pesquisa do Estado de Sao PauloConselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq, INCT Processos Redox em Biomedicina, Redoxoma)Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq, INCT Processos Redox em Biomedicina, Redoxoma

Probing the potential of ureasil-poly(ethylene oxide) as a glyphosate scavenger in aqueous milieu: Force-field parameterization and MD simulations

The intensive use of glyphosate in conventional agriculture and its high solubility in water have led to contamination of aqueous systems worldwide. The removal of organic pollutants from water by hybrid materials like ureasil-poly(ethylene oxide) U-PEO800 is gaining attention due to its efficiency, robustness, and matrix regeneration possibilities, leading to successive applications. A new application for the U-PEO800 polymer as a glyphosate scavenger in aqueous medium is proposed and investigated theoretically by molecular dynamics (MD) simulations, providing new insights into the sorption process. The quality of MD simulations is highly dependent on the nature of the applied force field. For that reason, it is reported here, for the first time, the parameterization of the U-PEO800 polymer fragment containing Si atoms. The parameterization procedure, containing bonded terms compatible with GAFF for the U-PEO800 fragment, has employed rigorous ab initio methods. The behavior of U-PEO800 in water was then investigated by MD simulations using the new parameters obtained, and the aggregation process between polymer molecules has been observed. The polymer was able to interact with the pesticide, even under different pH conditions. When the pesticide and polymer have neutral chains, the interaction is mostly through hydrogen bonds between the PEO monomer unit and the pesticide hydrogen bond donor groups. On the other hand, when considering the structures at different pHs, the electrostatic component of the interaction is predominant, since the polymer has a total charge +4 e and the pesticide was evaluated with net charges -1 and -2 e. Our findings reveal that U-PEO800 proved to be a very promising sorbent for glyphosate. This journal isThe authors are grateful to funding agencies CAPES, CNPq, and FAPESP (2011/07623-8). Research carried out with the support of UNIFRAN and GH computational resources. GFC and RLTP thank CNPq for research fellowships (grants 311132/2020-0 and 313648/2018-2)

Hydrogen bond and the resonance effect on the formamide-water complexes

The interaction of formamide and the two transition states of its amide group rotation with one, two, or three water molecules was studied in vacuum. Great differences between the electronic structure of formamide in its most stable form and the electronic structure of the transition states were noticed. Intermolecular interactions were intense, especially in the cases where the solvent interacted with the amide and the carbonyl groups simultaneously. In the transition states, the interaction between the lone pair of nitrogen and the water molecule becomes important. With the aid of the natural bond orbitals, natural resonance theory, and electron localization function (ELF) analyses an increase in the resonance of planar formamide with the addition of successive water molecules was observed. Such observation suggests that the hydrogen bonds in the formamidewater complexes may have some covalent character. These results are also supported by the quantitative ELF analyses. (C) 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012CNPqCNPq [481560/2010-6, 17413/2009-0, 310731/2009-7]FAPESP [2008/02677-0, 2006/06035-7]FAPESPCAPES/PROAPCAPES/PROAP [56/07-3]FAPESCFAPES

Bond analysis in dihalogen–halide and dihalogen– dimethylchalcogenide systems

The bonding in mixed chalcogen/halogen three- body systems of general formula XI···Y (X = Cl, Br, I; Y = I–, EMe2; E = S, Se, Te) is theoretically examined by using different methodologies, namely: charge-displacement (CD) analysis, which quantifies the electronic flux throughout the whole ad- duct; the energy decomposition analysis combined with natural orbital for chemical valence (EDA-NOCV) method; and zeroth order symmetry adapted perturbation theory (SAPT0), where the latter two methods decompose the contributions of the interaction energy between XI and Y into physically meaningful terms. In the solid state, the distribution of the relative elonga- tions of the two bonds (δXI and δIY) in the three-body systems examined here can be rationalized in terms of only one com- mon equation derived from the bond-valence model. According to CD and EDA-NOCV, the charge transfer between the two fragments does not depend on the exact nature of the atoms involved, but only on the values of δXI and δIY, with a variability of 0.05 e, and on the total charge of the system. On the other hand, using the SAPT0 method and computing the polariza- tion-free value of the charge transfer between the two frag- ments, the results are the same for all of the systems with the same δXI and δIY, irrespectively not only of the nature of the atoms, but also of the total charge of the system (anionic and neutral)

Platinum nanoparticles embledded in layer-by-layer films from SnO2/polyallylamine for ethanol electrooxidation

Self-assembled films from SnO2 and polyallylamine (PAH) were deposited on gold via ionic attraction by the layer-by-layer(LbL) method. The modified electrodes were immersed into a H2PtCl6 solution, a current of 100 mu A was applied, and different electrodeposition times were used. The SnO2/PAH layers served as templates to yield metallic platinum with different particle sizes. The scanning tunnel microscopy images show that the particle size increases as a function of electrodeposition time. The potentiodynamic profile of the electrodes changes as a function of the electrodeposition time in 0.5 mol L-1 H2SO4, at a sweeping rate of 50mVs(-1). Oxygen-like species are formed at less positive potentials for the Pt-SnO2/PAH film in the case of the smallest platinum particles. Electrochemical impedance spectroscopy measurements in acid medium at 0.7 V show that the charge transfer resistance normalized by the exposed platinum area is 750 times greater for platinum electrode (300 k Omega cm(2)) compared with the Pt-SnO2/PAH film with 1 min of electrodeposition (0.4 k Omega cm(2)). According to the Langmuir-Hinshelwood bifunctional mechanism, the high degree of coverage with oxygen-like species on the platinum nanoparticles is responsible for the electrocatalytic activity of the Pt-SnO2/PAH concerning ethanol electrooxidation. With these features, this Pt-SnO2/PAH film may be grown on a proton exchange membrane (PEM) in direct ethanol fuel cells (DEFC). (c) 2008 Elsevier B.V. All rights reserved.CNPq/PIBIC[07.1.800.59.5]FAPESP[2006/06035-7]FAPESP[05/00106-7]CNPq[555436/2006-3]CNPq[550581/2005-7]IMMP/MC

Pt/TiO(2)/poly(vinyl sulfonic acid) Layer-by-Layer Films for Methanol Electrocatalytic Oxidation

One major challenge for the widespread application of direct methanol fuel cells (DMFCs) is to decrease the amount of platinum used in the electrodes, which has motivated a search for novel electrodes containing platinum nanoparticles. In this study, platinum nanoparticles were electrodeposited on layer-by-layer (LbL) films from TiO(2) and poly(vinyl sulfonic) (PVS), by immersing the films into a H(2)PtCl(6) solution and applying a 100 mu A current during different electrode position times. Scanning tunnel microscopy (STM) and atomic force microscopy (AFM) images showed increased platinum particle size and electrode roughness for increasing electrodeposition times. The potentiodynamic profile of the electrodes indicated that oxygen-like species in 0.5 mol L(-1) H(2)SO(4) were formed at less positive potentials for the smallest platinum particles. Electrochemical impedance spectroscopy measurements confirmed the high reactivity for the water dissociation and the large amount of oxygen-like species adsorbed on the smallest platinum nanoparticles. This high oxophilicity of the smallest nanoparticles was responsible for the electrocatalytic activity of Pt-TiO(2)/PVS systems for methanol electrooxidation, according to the Langmuir-Hinshelwood bifunctional mechanism. Significantly, the approach used here combining platinum electrodeposition and LbL matrices allows one to both control the particle size and optimize methanol electrooxidation, being therefore promising for producing membrane-electrode assemblies of DMFCs.FAPESP[2006/06035-7]FAPESP[05/00106-7]CNPq[555436/2006-3]CNPq[550581/2005-7]CNPq[301149/2006-2]IMMP/MC

Quest for Insight into Ultrashort C–H···π Proximities in Molecular “Iron Maidens”

Molecular iron maidens are a strained type of cyclophane in which a methine hydrogen, by the action of the bridges, is placed closer to the center of an aromatic ring. Such constrained molecular frameworks are in fact a noteworthy synthetic challenge. The present study provides a comprehensible theoretical analysis that elucidates unique structural and energetic aspects of this class of molecules, evaluating, in the light of quantum chemistry, both the influence of the aromatic moiety, from π-basic to π-acid, and the nature of the heteroatoms located at the bridges. Our results not only propose the shortest intramolecular centered C–H···π distance to date, which is supported by calculated ¹H chemical shifts, but also shed light on the main factors that rationalize and justify such proximity. QTAIM, NBO, and NCI analyses allow us prematurely to conclude that the ultrashort C–H···π distance is sustained by an interplay between a large stabilizing electrostatic component with a non-negligible covalent character. However, the energetics involving such strained molecular scaffolds, addressed by means of isodesmic reactions, revealed that the C–H···π proximity is modulated mainly by the capacity of the bridges to support the strain imposed by the whole structure, hence compressing the C–H bond against the π-system

Anion Recognition by Organometallic Calixarenes: Analysis from Relativistic DFT Calculations

The physical nature of the noncovalent interactions involved in anion recognition was investigated in the context of metalated calix[4]­arene hosts, employing Kohn–Sham molecular orbital (KS-MO) theory, in conjunction with a canonical energy decomposition analysis, at the dispersion-corrected DFT level of theory. Computed data evidence that the most stable host–guest bonding occurs in ruthenium complexed hosts, followed by technetium and molybdenum metalated macrocyclic receptors. Furthermore, the guest’s steric fit in the host scaffold is a selective and crucial criterion to the anion recognition. Our analyses reveal that coordinated charged metals provide a larger electrostatic stabilization to anion recognition, shifting the calixarenes cavity toward an electron deficient acidic character. This study contributes to the design and development of new organometallic macrocyclic hosts with increased anion recognition specificity