Hueder P. M. de Oliveira

pKa determinations of xanthene derivates in aqueous solutions by multivariate analysis applied to UV-Vis spectrophotometric data.

Xanthenes form to an important class of dyes which are widely used. Most of them present three acid-base groups: two phenolic sites and one carboxylic site. Therefore, the pKa determination and the attribution of each group to the corresponding pKa value is a very important feature. Attempts to obtain reliable pKa through the potentiometry titration and the electronic absorption spectrophotometry using the first and second orders derivative failed. Due to the close pKa values allied to strong UV-Vis spectral overlap, multivariate analysis, a powerful chemometric method, is applied in this work. The determination was performed for eosin Y, erythrosin B, and bengal rose B, and also for other synthesized derivatives such as 2-(3,6-dihydroxy-9-acridinyl) benzoic acid, 2,4,5,7-tetranitrofluorescein, eosin methyl ester, and erythrosin methyl ester in water. These last two compounds (esters) permitted to attribute the pKa of the phenolic group, which is not easily recognizable for some investigated dyes. Besides the pKa determination, the chemometry allowed for estimating the electronic spectrum of some prevalent protolytic species and the substituents effects evaluation.

Properties of Chlorophyll and Derivatives in Homogeneous and Microheterogeneous Systems

Chlorophyll (Mg-Chl) and its derivatives, zinc chlorophyll (Zn-Chl), copper chlorophyll (Cu-Chl), pheophytin (Pheo), pheophorbide (Pheid), and zinc chlorophyllide (Zn-Chld), were studied as to their acid-base equilibrium properties, hydrophobicity, stability, binding, and relative localization in neutral surfactant micellar systems. The stability order of metalochlorophyll (pH(M)) in acidic medium was found to be Cu-Chl > Zn-Chld > Zn-Chl > Mg-Chl. The apparent pK(a) for protonation of porphyrin ring nitrogens was around 1.0 for all derivatives. The pK(a) for protonation of carboxylate phorbide was 5.9 for Pheid and 2.4 for Zn-Chld. This difference was attributed to complexation of carboxylate with zinc. The hydrophobicity of chlorophyll in relation to the ability of partitioning the cell membrane lipid layer was estimated in the octanol/water biphasic system. Pheo, a more hydrophobic molecule, presented the highest partition coefficient (K(P)) in the organic phase, followed by Cu-Chl, Mg-Chl, Zn-Chl, Pheid, and Zn-Chld. The hydrophobic character was the key to relative drug location in the micellar systems. All studied derivatives interacted strongly with Tween 80 micellar systems, and particularly with P-123. For both surfactants, the order followed by binding constant (K(b)) was Zn-Chld > Pheo > Cu-Chl > Mg-Chl > Zn-Chl > Pheid, while binding constants estimated for the Chl containing the phytyl group correlated with K(P). Fluorescence quenching studies have shown that phorbides are located in a less hydrophobic region than the phytyl chain-containing derivatives, which are located preferentially in a deeper micellar microenvironment. Thus, the association of the chlorophylls with specific binding sites of micellar systems is strongly modulated by the presence of phytyl chains and metal coordinated to the porphyrinic ring.

Effects of Metal and the Phytyl Chain on Chlorophyll Derivatives: Physicochemical Evaluation for Photodynamic Inactivation of Microorganisms

Chlorophyll compounds and their derivatives containing metal or phytyl chain can be used as photosensitizer in photodynamic inactivation of microorganisms (PDI). So, the physicochemical properties and antimicrobial effect of chlorophyll derivatives were investigated: Mg‐chlorophyll (Mg‐Chl), Zn‐chlorophyll (Zn‐Chl), Zn‐chlorophyllide (Zn‐Chlde), Cu‐chlorophyll (Cu‐Chl), pheophytin (Pheo) and pheophorbide (Pheid). The photobleaching experiments showed photostability according to Cu‐Chl > Pheo ∼ Pheid ≫ Zn‐Chl ∼ Zn‐Chlde > Mg‐Chl. This order was discussed in terms of metal and the phytyl chain presences. Pheid and Zn‐Chl in aqueous Tween 80 solution exhibited highest singlet oxygen yield compared with the other derivatives. Chlorophyll derivatives (CD) with phytyl chain was limited by the self‐aggregation phenomenon at high concentrations, even in micellar systems (Tween 80 and P‐123). The antimicrobial effect of CD derivatives was investigated against Staphylococcus aureus, Escherichia coli, Candida albicans and Artemia salina. Pheid showed the best results against all organisms tested, Zn‐Chlde was an excellent bactericide in the dark and Cu‐Chl had no PDI effect. No correlation with CD uptake by microorganisms and darkness cytotoxicity was found. The physicochemical properties allied to bioassays results indicate that Mg‐Chl, Pheo, Zn‐Chl and Pheid are good candidates for PDI.

Dispositivos poliméricos eletroluminescentes

Here we present an overview of electroluminescent devices that use conjugated polymers as the active media. The principal components of the devices are described and we show some examples of conjugated polymers and copolymers usually employed in polymeric light emitting devices (PLED). Some aspects of the photo and electroluminescence properties as well as of the energy transfer processes are discussed. As an example, we present some of the photophysical properties of poly(fluorene)s, a class of conjugated polymers with blue emission.

Phenotiazinium Dyes as Photosensitizers (PS) in Photodynamic Therapy (PDT): Spectroscopic Properties and Photochemical Mechanisms

© 2012 Moreira et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Phenotiazinium Dyes as Photosensitizers (PS) in Photodynamic Therapy (PDT): Spectroscopic Properties and Photochemical Mechanisms

Influência de diferentes sistemas de solvente água-etanol sobre as propriedades físico-químicas e espectroscópicas dos compostos macrocíclicos feofitina e clorofila α

INFLUENCE OF DIFFERENT WATER-ETHANOL SOLVENT SYSTEMS ON THE SPECTROSCOPIC AND PHYSICO-CHEMICAL PROPERTIES OF THE MACROCYCLIC COMPOUNDS PHEOPHYTIN AND CHLOROPHYLL a. This work focus on the influence of solvent on the photophysical properties of chlorophyll a and pheophytin. Both compounds are related to the photosynthesis process and are considered prototypes of photosensitizers in Photodynamic Therapy. Fluorescence measurements were developed using water/ethanol mixtures at different compositions, since both solvents could be employed in biological applications. The spectroscopic properties of these compounds undergo profound changes depending on water content in the ethanol due to auto-aggregation processes. The major hydrophobicity and the lower dielectric constant of ethanol when compared with water precluded significantly the auto-aggregation process of these compounds.Keywords: chlorophyll a; pheophytin; aggregation.This work focus on the influence of solvent on the photophysical properties of chlorophyll α and pheophytin. Both compounds are related to the photosynthesis process and are considered prototypes of photosensitizers in Photodynamic Therapy. Fluorescence measurements were developed using water/ethanol mixtures at different compositions, since both solvents could be employed in biological applications. The spectroscopic properties of these compounds undergo profound changes depending on water content in the ethanol due to auto-aggregation processes. The major hydrophobicity and the lower dielectric constant of ethanol when compared with water precluded significantly the auto-aggregation process of these compounds.

Azure dyes as new photosensitizer prototypes to application in photodynamic therapy against Candida spp.

Infections caused by Candida albicans are of increasing concern, especially considering immunodepressed patients. The toxicity of most antifungal agents, the great number of cases with recidives, as well as the emergence of resistant samples has provoked the evaluation of new forms of therapy. In this context, the photodynamic therapy (PDT) presents auspicious antimicrobial properties, stimulating the development of trials employing several kinds of photosensitizers. In the present work, the application of different kind of Azure dyes as photosensitizer in PDT against C. albicans was evaluated through instrumental measurements of electronic spectroscopy. In fact, the values of optical density were a precise indicator of the growth inhibition of the microorganisms. Indeed, Azures are phenothiazinium derivatives that constitute a very relevant class of compounds with several biomedical applications, such as photoantimicrobial therapy against local bacterial infection, tuberculosis, trypanosomi- asis, malaria, Rickettsia, yeasts, viral infection n and cancer. Azure A, Azure B, Azure A thiocyanate, Azure B BF4 ,A zure A eosinate are the dyes tested against C. albicans. The results denoted completely distinct behaviors to the different types of Azure compound evaluated in this work. In fact, Azure A and Azure A eosinate presented significant results when irradiated with 56 J/cm 2 , since the growth inhibition of C. albicans reached approximately 60%. This Azure compounds have significant potential to be employed as photosensitizer (PS) in PDT, especially in cases of mucocutaneous candidosis. The spectroscopic evaluation was very effective to the detection of slight alterations in the growth of the microorganisms, denoting that this kind of analysis is an excellent alternative to determine growth inhibition of Candida albicans. The experimental data are discussed in details in agreement with recent results from literature.

Metallochlorophylls of magnesium, copper and zinc: evaluation of the influence of the first coordination sphere on their solvatochromism and aggregation properties

In this study the role of different metal centers (magnesium, zinc and copper) on the enhancement of the hydrophilic character of metallochlorophylls, was evaluated. The solvatochromism as well as the aggregation process for these compounds in water/ethanol mixtures at different volume ratios were evaluated using Fluorescence, and Resonant Light Scattering (RLS) measurements, aiming to characterize the behavior of these compounds. Independently on the studied metallochlorophyll, the presence of at least 60% of water results in a considerable increase in the fluorescence emission, probably a direct consequence of a lower aggregation of these compounds, which is confirmed by the results from RLS measurements. Additionally, the results suggest that magnesium and zinc chlorophyll should be promising phototherapeutic agents for Photodynamic Therapy.

Use of chitosan in the treatment of obesity: evaluation of interaction with vitamin B12.

Obesity is a serious health problem and its prevalence has increased over the years. Studies have assessed the polysaccharide chitosan as anti-obesity supplement due to its ability to absorb fats. However, this property may cause the interaction of chitosan with essential substances for the proper functioning of the body, such as vitamins. In this context, the purpose of the present study was to evaluate interactions of the chitosan with vitamin B2.These interactions were evaluated in the absence and the presence of acid aqueous solution of chitosan using fluorescence and ultraviolet–visible absorption measurements of vitamin B2.Results showed that the rigid microenvironment generated by chitosan solution modifies the photophysics properties of vitamin B2.Thus, chitosan is able to eliminate vitamin B2 and the present study aims to warn of excessive loss of vitamins or other nutrients by the body during prolonged treatment with chitosan.

Self-aggregation processes of 1,6-diphenyl-1,3,5-hexatriene in water/ethanol mixtures with high water percentages.

This work describes the behavior of 1,6-diphenyl-1,3,5-hexatriene (DPH) in ethanol/water mixtures. The dependence of DPH photophysical properties (absorption and fluorescence emission) on the water percentage in ethanol indicates that DPH undergoes self-aggregation processes in solvent conditions above a critical water content. Evidence such as an additional absorption band, Beers law deviation, kinetic behavior, and other experimental results obtained from temperature variation and surfactant addition demonstrated the presence of several types of DPH aggregates. Resonance light scattering measurements proved that the aggregate grew in water-rich media by a self-catalyzed process.