Experimental and computational studies of crystal violet removal from aqueous solution using sulfonated graphene oxide.

Positively charged contaminants can be strongly attracted by sulfanilic acid-functionalized graphene oxide. Here, sulfonated graphene oxide (GO-SO3H) was synthesized and characterized for cationic crystal violet (CV) adsorption. We further studied the effect of pH, initial concentration, and temperature on CV uptake. The highest CV uptake occurred at pH 8. A kinetic study was also carried out by applying the pseudo-first-order and pseudo-second-order models. The pseudo-second-order's adsorption capacity (qe) value was much closer to the experimental qe (qeexp:0.13, qecal:0.12) than the pseudo-first-order model (qeexp:0.13, qecal:0.05). The adsorption performance was accomplished rapidly since the adsorption equilibrium was closely obtained within 30 min. Furthermore, the adsorption capacity was significantly increased from 42.85 to 79.23%. The maximum adsorption capacities of GO-SO3H where 97.65, 202.5, and 196.2 mg·g-1 for CV removal at 298, 308, and 328 K, respectively. The Langmuir and Freundlich adsorption isotherms were applied to the experimental data. The data fit well into Langmuir and Freundlich except at 298 K, where only Langmuir isotherm was most suitable. Thermodynamic studies established that the adsorption was spontaneous and endothermic. The adsorption mechanism was revealed by combining experimental and computational methods. These findings suggest that GO-SO3H is a highly adsorbent for removing harmful cationic dye from aqueous media.

A DFT study of the adsorption of O2 and [Fe(H2O)2(OH)3] on the (001) and (112) surfaces of chalcopyrite.

The oxidation of chalcopyrite, CuFeS2, is still not well understood and relevant in the context of the hydrometallurgical extraction of copper. Herein, we used DFT calculations within the periodic boundary conditions formalism to study the adsorption of O2 and [Fe(H2O)2(OH)3] molecules on the (001) and (112) surfaces of CuFeS2. The O2 molecule adsorbs strongly by a dissociative pathway at sulfur atoms on the (001) surface with an adsorption energy of - 76.5 kcal mol-1. The surface is chemically modified forming SO2 groups, in which the S-O bond length is calculated to be 1.47 and 1.54 Å. PDOS and Löwdin charges analyses indicate the oxidation of the sulfur atoms on the surface. We tested different adsorption modes of [Fe(H2O)2(OH)3], and a bidantade coordination with the Oads-Fesur and Feads-Ssur bond lengths of 2.02 and 2.47 Å is the most favorable with an adsorption energy of - 18.8 kcal mol-1 on the (001) surface. Adsorptions of each species are also observed on the (112) surface, but they are weaker than those observed on the (001) surface.

Growing Mechanism of Polysulfides and Elemental Sulfur Formation: Implications to Hindered Chalcopyrite Dissolution.

Metal-deficient polysulfides have been argued for a long time to be responsible for the low kinetics of chalcopyrite leaching to extract copper. It has been shown that chalcopyrite surfaces are the source of sulfur that is oxidized to form polysulfides and elemental sulfur. Electronic structure calculations were performed for HxSnx-2 (x = 0, 1, 2 and n = 1...20), aiming to understand the effect of the pH on the growing chains and the formation of elemental sulfur. The estimated pKa1 of the H2Sn polysulfides converges from 4.2 (n = 3) to 3.4 (n ≥ 8), and the estimated pKa2 converges from 7.6 (n = 3) to 4.1 (n ≥ 8). The initial steps of the formation of polysulfide chains are more favored for protonated species. The elemental sulfur formation due to the decomposition of polysulfides to form smaller chains is mostly favored for protonated species with n smaller than 12. For larger chains, the decomposition is thermodynamically favored for polysulfides with any degree of protonation. The consequences of these results to the understanding of the mechanism of the chalcopyrite leaching process are discussed with the focus on the pH effect and the formation of elemental sulfur.

Accurate SCC-DFTB Parametrization for Bulk Water.

The SCC-DFTB repulsion parameters based on the material science set (matsci) were redesigned to describe the structure and dynamic properties of bulk liquid water. The iterative Boltzman inversion (IBI) approach was applied by simultaneously correcting the O-H and O-O SCC-DFTB repulsion energy contribution to develop the new water-matsci and water-matsci-UFF set of parameters. The water-matsci parameters provide O-O and O-H radial distribution functions in excellent agreement with available state-of-the-art experimental data. The parametrization is applied to compute binding energies of a set of water clusters with 2-10 molecules and compared to other DFTB parameters and reference data. The self-diffusion coefficients of ambient and supercooled (254 K) water have been estimated and compared to other SCC-DFTB calculated values and experiment. The performance of the new parameters for describing the density of ambient water and reactions involving water dissociation into H3O+ and OH-, the self-diffusion coefficient, and neutralization energy were investigated. Finally, we show that the new parametrization can be reliably applied to adsorption of water on the mineral pyrite by combining the new water-matsci parameters with the available matsci set of parameters for pyrite. This opens opportunities for investigating materials and phenomena of increasing complexity involving water.

Peroxoniobium inhibits leukemia cell growth.

A new class of polyoxoniobate complex has been synthesized and characterized as a novel anticancer agent for photodynamic therapy. The complex inhibits the growth of chronic myelogenous leukemia cells with an IC50 value of 30 µM, in the dark. However, upon exposure to light (365 nm) there is a fivefold increase in the cytotoxic activity. Light radiation activate the complex with the formation of radical species capable of interacting with DNA according to our experimental and theoretical data.

Structural, Electronic, and Thermodynamic Properties of the T and B Phases of Niobia: First-Principle Calculations.

Different polymorphs of Nb2O5 can be obtained depending on the pressure and temperature of calcination leading to different catalytic properties. Two polymorphs of niobia, T-Nb2O5 and B-Nb2O5, have been investigated by means of density functional/plane waves method. The equation of state predicted that B-Nb2O5 phase is more stable than the T-Nb2O5 at low temperature; however at high pressure both phases are stable. These results are in good agreement with the available experimental data. The calculated cohesive energies of 6.63 and 6.59 eV·atom-1 for the B-Nb2O5 and T-Nb2O5, respectively, also corroborate this conclusion, and it can be compared to the experimental value of 9.56 eV atom-1 estimated for the most thermodynamically stable phase. The topological analyses based on quantum theory of atoms in molecules (QTAIM) and electron localization function (ELF) were applied and reveal bonds with large ionic character for both phases. The B-Nb2O5 presented larger stiffness than T-Nb2O5, and the oxygen sites in the T-Nb2O5 are more compressible. The density of states comparison for both structures indicates that B-Nb2O5 has lower concentration of acid sites compared to T-Nb2O5. This result is consistent with the experimental observations that the concentration of Lewis acid sites decreases with the temperature.

First-principles calculations and electron density topological analysis of covellite (CuS).

Covellite (CuS) is an important mineral sulfide that can be used in many technological applications. It has a simple formula but a complex structure consisting of alternating layers of planar CuS3 triangles and CuS4 tetrahedrons with S-S bonds. Accurate first-principles calculations are performed for covellite structure (CuS), aiming to provide insights about its structural, mechanical and electronic properties and to unveil the nature of its chemical bonding. DFT and DFT+U methods have been used and showed to be sensitive to the correlation treatment (U value). Although it is not possible to extract a universal value of the U, this study indicates that U = 5 eV is an adequate value. The electronic structure analysis shows a significant metallic character due to p(S)-d(Cu) orbital interactions up to Fermi level. The projected density of states indicates that most of the contribution comes from the atomic orbitals in the [001] plane of the covellite, explaining the conductivity anisotropy observed experimentally. Topological analysis of the electron density was performed by means of quantum theory of atoms in molecules (QTAIM). Two different topological charges in Cu and S were calculated, confirming an ionic model with mix-charges. This mineral presents ionic degree of ∼ 32%. On the basis of the QTAIM analysis, the covalent character of S-S bond is confirmed, and the favored cleavage of CuS at the [001] surface might be at the Cu-S bond. The S atoms occupy most of the cell volume, and their contributions dominate the crystal compressibility: κ(S) ≈ κ(CuS).

Benzocaine complexation with p-sulfonic acid calix[n]arene: experimental ((1) H-NMR) and theoretical approaches.

The aim of this work was to study the interaction between the local anesthetic benzocaine and p-sulfonic acid calix[n]arenes using NMR and theoretical calculations and to assess the effects of complexation on cytotoxicity of benzocaine. The architectures of the complexes were proposed according to (1) H NMR data (Job plot, binding constants, and ROESY) indicating details on the insertion of benzocaine in the cavity of the calix[n]arenes. The proposed inclusion compounds were optimized using the PM3 semiempirical method, and the electronic plus nuclear repulsion energy contributions were performed at the DFT level using the PBE exchange/correlation functional and the 6-311G(d) basis set. The remarkable agreement between experimental and theoretical approaches adds support to their use in the structural characterization of the inclusion complexes. In vitro cytotoxic tests showed that complexation intensifies the intrinsic toxicity of benzocaine, possibly by increasing the water solubility of the anesthetic and favoring its partitioning inside of biomembranes.

Dermatitis de Jacquet en los niños después de la cirugía de la enfermedad de Hirschsprung: comunicación de un caso / Jacquet dermatitis in children after surgery for Hirschsprung's disease: a case report

La enfermedad de Hirschsprung o megacolon congénito es una anomalía rara, caracterizada por la ausencia de las células ganglionares del intestino. Esto genera una falla en su relajación distal, que impide la eliminación de la materia fecal y causa una obstrucción inmediata después del nacimiento. El tratamiento es eminentemente quirúrgico y a las semanas de la reanastomosis coloanal los pacientes presentan diarrea. Por su parte, la dermatitis de Jacquet es una forma infrecuente de la dermatitis del pañal por irritante primario, provocada por el contacto prolongado de la piel de esta región con la orina o heces acuosas. Comunicamos el caso de un niño con enfermedad de Hirschsprung que, luego de la intervención quirúrgica, presentó una dermatitis de Jacquet asociada a diarrea grave...

Hirschsprung´s disease, also known as congenital aganglionic megacolon, is a rare anomaly, marked by the absence of ganglionic cells of the large intestine, resulting in failure of its distal looseness, blocking evacuation and causing obstruction right after birth. The treatment is mainly surgical and weeks after coloanal reanastomosis, these patients develop diarrhea. Jacquet dermatitis is an unusual presentation of irritant diaper dermatitis, caused by prolonged contact of the skin of this region with urine and/or watery diarrhea. We report a case of a child with Hirschsprung´s disease that, after surgical treatment, presented Jacquet dermatitis as an outcome of severe diarrhea...

Chemical speciation of metal complexes from chemical shift calculations: the interaction of 2-amino-N-hydroxypropanamide with V(V) in aqueous solution.

The chemical speciation of 2-amino-N-hydroxypropanamide (ß-alaninohydroxamic acid, HL) and vanadium (V) in aqueous solution has been investigated through calculations of the thermodynamic properties and the (51)V nuclear magnetic resonance (NMR) chemical shifts of the species formed at equilibrium. The results have been compared directly with the experimental (51)V NMR data. The (51)V NMR chemical shifts have been calculated by using a density functional theory (DFT) approach accounting for relativistic corrections and solvent effects. All tautomers of the 1:1 and 1:2 VO2(+)/ß-ala complexes with different degrees of protonation have been calculated and thermodynamic and structural properties are presented for the most stable species. The system is better modeled as tautomeric equilibria, and species lying down in the range of 10 kcal·mol(-1) cannot be neglected at the BP/TZ2P/COSMO approach. In fact, the metal complex speciation in aqueous solution should not be investigated based solely on the thermodynamic analysis, but together with spectroscopic calculations such as NMR.

Imogolite-like nanotubes: structure, stability, electronic and mechanical properties of the phosphorous and arsenic derivatives.

Imogolite is a single-walled aluminosilicate nanotube (NT) found in nature that can be easily synthesized, as well as its analogue aluminogermanate NT. Based on geometrical assumptions and pKa values, species such as H3PO4, H3PO3, H3AsO3, H3AsO4 could also be candidates to form imogolite-like structures. In the present work, we provide insights about the stability, electronic, structural and mechanical properties of possible imogolite like NTs by means of self-consistent charge density-functional tight-binding method (SCC-DFTB). Similarly to aluminogermanate, where the tetrahedral silicate groups are replaced by germanate, in this work tetrahedral silicate groups are substituted by phosphate, phosphite, arsenate and arsenite units in the imogolite structure. Detailed analysis is focused on structural properties, strain energy, band gap and Mulliken charges distribution. The calculated strain energy curves for all studied zigzag imogolite-like NTs present well-defined minima, which change as a consequence of composition variation. Moreover, the strain energy curves of armchair imogolite-like NTs also present minima, although in all cases less stable than zigzags by at least 2.2 meV per atom. The insulating NT behaviour changes after internal modification from silicate to phosphate, phosphite, arsenate and arsenite, as well as the charge distribution inside and outside the nanotubes.

Structural, mechanical and electronic properties of nano-fibriform silica and its organic functionalization by dimethyl silane: a SCC-DFTB approach.

Self-consistent-charge density-functional tight-binding (SCC-DFTB) approximated method was employed to investigate the structural, mechanical and electronic properties of the zigzag and armchair nano-fibriform silica (SNTs) and their outer surface organic modified derivatives (MSNTs) with internal radii in the range of 8 to 36 Å. The strain energy curves showed that the nanotubes structures are energetically more stable compared to the respective sheet structures. External hydroxyl dihedral angles in silica nanotubes have small influence, about 0.5 meV.atom(-1), in the strain energy curve tendency of those materials favoring the zigzag chirality. The chemical modification of outer surface of SNTs by dimethyl silane group affects their relative stability favoring the armchair chirality in approximately 2 meV.atom(-1). MSNTs have axial elastic constants, Young's moduli, determined at the harmonic approximation, around 100 GPa smaller than the respective SNTs. The Young's moduli of zigzag and armchair SNTs are in the range of 150-195 GPa and 232-260 GPa, respectively. And for the zigzag and armchair MSNTs these values are in the range of 77-89 and 110-140 GPa, respectively. The SNTs and MSNTs were characterized as insulators with band gaps around 8-10 eV.

Dynamical discrete/continuum linear response shells theory of solvation: convergence test for NH4+ and OH- ions in water solution using DFT and DFTB methods.

A new dynamical discrete/continuum solvation model was tested for NH(4)(+) and OH(-) ions in water solvent. The method is similar to continuum solvation models in a sense that the linear response approximation is used. However, different from pure continuum models, explicit solvent molecules are included in the inner shell, which allows adequate treatment of specific solute-solvent interactions present in the first solvation shell, the main drawback of continuum models. Molecular dynamics calculations coupled with SCC-DFTB method are used to generate the configurations of the solute in a box with 64 water molecules, while the interaction energies are calculated at the DFT level. We have tested the convergence of the method using a variable number of explicit water molecules and it was found that even a small number of waters (as low as 14) are able to produce converged values. Our results also point out that the Born model, often used for long-range correction, is not reliable and our method should be applied for more accurate calculations.

Uncaria tomentosa in the treatment of the herpes labialis: randomized double-blind trial / Uncaria tomentosa no tratamento de herpes labial: estudo duplo-cego randomizado

Introduction: the lesions caused by herpes simplex are common and have symptoms affecting the quality of life of affected people. Objective: this study aims to assess the safety efficacy of cream with Uncaria tomentosa (cat?s claw), for topical treatment of the herpes labialis. Methods: a clinical investigation was undertaken by means of controlled, randomized, double-blinded protocol in humans. According to the regulatory procedures, 74 patients were selected based on inclusion/exclusion criteria previously submitted to the Local Ethical Committee (no 144/02) whenever herpes labialis lesion appeared. Following, those selected through medical evaluation received either the test (Uncaria) or the reference (Acyclovir) drug. Results: fifty-four episodes of herpes labialis lesions ecloded in 31 volunteers. After their clinical assessment, one showed 4 episodes, two had 3 episodes and six had 2 infections. Hence, 27 patients received the reference drug while 27 applied the Uncaria cream four times a day. Overall, there were not significant differences between either responses. Although, the Uncaria group showed lower scores on the first two days of treatment (p < 0,005; t = 0,028), on day 3, it was even to Acyclovir. Conclusion:the assessment of clinical efficacy of either treatment demonstrated that both drugs were safe as no adverse reactions were reported. Futher, there was no difference (p > 0,05) in the overall period infections as well as in the inflammatory process or crost formation. Regarding the severity of inflammatory reaction, the clinical efficacy of Uncaria tomentosa was significantly better than acyclovir. Rather than the being antiviral drug, the Uncaria tomentosa may act as an anti-inflammatory agent and this would possibly represent an advantage of not inducing viral resistance for long use.

Introdução: as lesões causadas por herpes simples são comuns e apresentam sintomatologia que altera a qualidade de vida das pessoas acometidas. Objetivo: este estudo visa avaliar a eficácia da segurança de creme com Uncaria tomentosa (unha-de-gato) para o tratamento tópico de herpes labial. Métodos: a pesquisa clínica foi realizada por meio de protocolo controlado, randomizado e duplo-cego. De acordo com os procedimentos de regulamentação, 74pacientes foram selecionados com base em critérios de inclusão e exclusão previamente submetidos à Comissão de Ética Local (no 144/02), sempre a lesão de herpes labial apareceu. Em seguida, os selecionados através de avaliação médica receberam o produto-teste (Uncaria) ou o de referência (aciclovir).Resultados: cinquenta e quatro episódios de lesões de herpes labial eclodiram em 31 voluntários. Após a avaliação clínica, um apresentou quatro episódios, dois tiveram três episódios e seis tinham duas infecções. Assim, 27 pacientes receberam a droga de referência, enquanto 27 aplicaram o creme Uncaria quatro vezes por dia. Em geral, não houve diferença significativa entre as respostas. Contudo, o grupo de Uncaria apresentou escores inferiores nos dois primeiros dias de tratamento (p < 0,005 t = 0,028), depois do dia 3, foi similar ao aciclovir. Conclusão: a avaliação da eficácia clínica dos tratamentosdemonstraram que ambas as drogas foram seguras, bem como não foram notificadas reações adversas. Além disso, não houve diferença significativa (p 0,05) no período total de infecções, bem como no processo inflamatório ou na formação de crosta. Quanto à gravidade da reação inflamatória, a eficácia clínica da Uncaria tomentosa foi significativamente melhor do que o aciclovir. Em vez de a droga ser antiviral, a Uncaria tomentosa pode atuar como um agente anti-inflamatório e isso, possivelmente, representa uma vantagem de não induzir resistência viral para uso por muito tempo.

Dermatoscopy in the diagnosis of tinea nigra.

Tinea nigra is an asymptomatic superficial fungal infection caused by Phaeoannelomyces werneckii, generally affecting the skin of the palms and characterized by deeply pigmented macular non-scaly patches. These lesions are quite characteristic. However, they can be misdiagnosed as a malignant melanoma or a junctional melanocytic nevus and unnecessary biopsies may be performed. Thus, dermoscopy is a fast, useful, clinical adjunctive tool in differentiating tinea nigra from melanocytic lesion.

Antioxidant activity of (+)-bergenin: a phytoconstituent isolated from the bark of Sacoglottis uchi Huber (Humireaceae).

(+)-Bergenin (1) was isolated from Sacoglottis uchi, a species of vegetable found in the Amazon region and popularly used for the treatment of several hepatic problems. The structure of 1 was fully characterized using IR, GC-MS and NMR (1D and 2D) analyses. This phytoconstituent has been used as an oriental folk medicine for the treatment of many diseases and shows antihepatotoxic properties. Tests with beta-carotene, DPPH and a heterogeneous Fenton system were carried out, confirming the antioxidant activity of 1. Theoretical calculations were performed to investigate the formation of the radical derivatives of 1 using *H, *OH, *CH(3), and *CCl(3) as initiator radicals. DFT thermodynamic calculations showed that the methoxyl group (O-6-CH(3)) is the most favorable site for radical attack. Frontier molecular orbital analysis showed that nucleophilic radical attack is favored on the aromatic ring of 1 where the LUMO is localized, with antibonding character with respect to the O-6-CH(3) bond. The possibilities of attack at other sites on 1 were investigated in detail in order to understand the regiospecificity of this reaction.

Study of angiotensin-(1-7) vasoactive peptide and its beta-cyclodextrin inclusion complexes: complete sequence-specific NMR assignments and structural studies.

We report the complete sequence-specific hydrogen NMR assignments of vasoactive peptide angiotensin-(1-7) (Ang-(1-7)). Assignments of the majority of the resonances were accomplished by COSY, TOCSY, and ROESY peak coordinates at 400MHz and 600MHz. Long-side-chain amino acid spin system identification was facilitated by long-range coherence transfer experiments (TOCSY). Problems with overlapped resonance signals were solved by analysis of heteronuclear 2D experiments (HSQC and HMBC). Nuclear Overhauser effects (NOE) results were used to probe peptide conformation. We show that the inclusion of the angiotensin-(1-7) tyrosine residue is favored in inclusion complexes with beta-cyclodextrin. QM/MM simulations at the DFTB/UFF level confirm the experimental NMR findings and provide detailed structural information on these compounds in aqueous solution.

Raman spectroscopy and DFT calculations of As(III) complexation with a cysteine-rich biomaterial.

Arsenite adsorption onto a protein-rich biomass and, more specifically, the chemical groups involved in the uptake were investigated using Raman spectroscopy and DFT calculations. The study was based on spectroscopic analyses of raw and arsenic-loaded biomass as well as standard samples of amino acids and arsenic salts. The predominant secondary structure of the protein was identified as the beta-sheet type, with some contribution from alpha-helix structures. The participation of sulphydryl groups from cystine/cysteine molecules during the adsorption of arsenite was demonstrated. Only the gauche-gauche-gauche (g-g-g) conformation type of the disulfide bonds was involved in arsenic complexation. The formation of a pyramidal trigonal As(HCys)(3) complex was modeled according to the density functional theory (DFT). The agreement of the DFT harmonic frequencies with the RAMAN spectra of the As(HCys)(3) complex demonstrated the relevant features of the cysteine-rich biomaterial regarding arsenic uptake as well as of the mechanism involved in the As(III)/biomass interaction at a molecular level. The results also illustrate that Raman spectroscopy can be successfully applied to investigate the mechanism of metal adsorption onto amorphous biomaterials.

Structure and dynamics of beta-cyclodextrin in aqueous solution at the density-functional tight binding level.

Structure and dynamics of beta-cyclodextrin (beta-CyD), a prototype host for inclusion compounds of biological interest, is investigated by means of density-functional based tight-binding molecular dynamics (MD) simulations. The computational protocol is benchmarked against available experimental data and first-principles calculations. Solvent-solute interactions, including the diffusion into and dwell time of the solvent in the cavity of beta-CyD, are studied with a hybrid QM/MM method. Comparison of MD simulations of beta-CyD in the gas phase and in water shows that the solvent reduces the flexibility of the structure framework, while the terminal hydroxyl groups become more flexible and are embedded in a network of hydrogen bonds. Our 160 ps MD simulations, provide enough sampling to discuss the dynamics of the water inside the cavity. The dwell time of the encapsulated water molecule has a wide distribution with a peak at 70 fs. Surprisingly, despite only the 17% difference between the "top" and "bottom" opening area of the beta-CyD cone, 64% of the water molecules enter the cavity through the slightly bigger "bottom" aperture.