Interaction of cationic water-soluble meso-tetrakis(4-N-methylpyridiniumyl)porphyrin (TMPyP) with ionic and nonionic micelles: aggregation and binding

The equilibrium of meso-tetrakis(4-N-methylpyridiniumyl)porphyrin (TMPyP) in aqueous solution in the presence of surfactants was studied by optical spectroscopic techniques and SAXS (small angle X-ray scattering). Anionic SDS (sodium dodecyl sulfate), zwitterionic HPS (N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate) and nonionic TRITON X-100 (t-octyl-phenoxypolyethoxyethanol), surfactants were used. TMPyP is characterized by a protonation equilibrium with a pK(a) around 1.0, associated with the diacid-free base transition, and a second pK(a) around 12.0 related with the transition between the free base and the monoanion form. Three independent species were observed for TMPyP at pH 6.0 as a function of SDS concentration: free TMPyP, TMPyP-SDS aggregates and porphyrin monomer bound to micelles. For HPS and TRITON X-100, the equilibrium of TMPyP as a function of pH is quite similar to that obtained in pure aqueous solution: no aggregation was observed, suggesting that electrostatic contribution is the major factor in the interaction between TMPyP and surfactants. SAXS data analysis demonstrated a prolate ellipsoidal shape for SDS micelles; no significant changes in shape and size were observed for SDS-TMPyP co-micelles. Moreover, the ionization coefficient, alpha, decreases with the increase of the porphyrin concentration, suggesting the ""screening"" of the anionic charge of SDS by the cationic porphyrin. These results are consistent with optical absorption, fluorescence and RLS (resonance light scattering) spectroscopies data, allowing to conclude that neutral surfactants present a smaller interaction with the cationic porphyrin as compared with an ionic surfactant. Therefore, the interaction of TMPyP with the ionic and nonionic surfactants is predominantly due to the electrostatic contribution. Copyright (c) 2008 Society of Porphyrins & Phthalocyanines.

Graphene modification with gold nanoparticles using the gas aggregation technique

Gold nanoparticles (Au-NPs) were deposited on single layer graphene (SLG) and few layers graphene (FLG) by applying the gas aggregation technique, previously adapted to a 4-gun commercial magnetron sputtering system. The samples were supported on SiO2 (280 nm)/Si substrates, and the influence of the applied DC power and deposition times on the nanoparticle-graphene system was investigated by Confocal Raman Microscopy. Analysis of the G and 2D bands of the Raman spectra shows that the integrated intensity ratio (I-2D/I-G) was higher for SLG than for FLG. For the samples produced using a sputtering power of 30W, the intensity (peak height) of the G and 2D bands increased with the deposition time, whereas for those produced applying 60W the peak heights of the G and 2D bands decreased with the deposition time. This behaviour was ascribed to the formation of larger Au-NPs aggregates in the last case. A significant increase of the Full Width Half Maximum (FWHM) of the G band for SLG and FLG was also observed as a function of the DC power and deposition time. Surprisingly, the fine details of the Raman spectra revealed an unintentional doping of SLG and FLG accompanying the increase of size and aggregation of the Au-NPs. (C) 2011 Elsevier B.V. All rights reserved.

SPATIAL PATTERN OF FOUR FOREST COMMUNITIES BY RIPLEY'S K FUNCTION IN SAO PAULO STATE

Investigating tree's spatial patterns according to their size classes and according to their more abundant species can provide evidences about the structure of the vegetal community, since the spatial pattern is a key question for forestry ecology studies. The tree spatial organization patterns on the environment depend on several ecological processes and on the specific characteristics of each environment, so that the best understanding of this frame provides important elements for the knowledge on forestry formation. This paper aimed to study tree spatial patterns, according to the diameter classes and from four most abundant species in different forests, in order to provide evidences regarding to the ecology of each vegetal community. The spatial pattern description in each forestry formation was developed using Ripley's K function. The studied forestry formations were: Ombrophilous Forest, Cerradao, Seasonal Forest and Restinga Forest. In this work, a 10.24 ha plot was installed in each forestry formation, and every tree, with a circumference at breast height (CBH) larger than 15 cm were measured, georeferenced and identified. The obtained data highlights the aggregated character in tropical forests, as observed in every studied forest. The 'Cerraddo' and 'Restinga' forest trees showed close aggregate patterns. In the Ombrophilous forest, for all distance scales, the aggregate pattern was meaningful. In the seasonal forest, a random tendency was observed, although a meaningful aggregation was observed in all short distances. The spatial pattern by diameter classes was generally aggregated for trees smaller than 10 cm of diameter and between 10 and 20 cm and random for the others, proving the existence of a tendency which in young trees is more aggregated than in old ones. The spatial pattern of the dominant species is always strongly similar to the general pattern of each forestry formation. The differences between the spatial patterns of two or three coincident species, among the forestry formations, indicate that its pattern is influenced by each different environment. This stands out the importance of its self-ecology and of its ecological processes, intrinsic of each community that can explain the observed patterns.