Noboru Hioka - Profile on Academia.edu (original) (raw)
Papers by Noboru Hioka
Characterization of chlorophyll derivatives in micelles of polymeric surfactants aiming photodynamic applications
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2017
The spectrophotometric properties of chlorophylls' derivatives (Chls) formulated in the P... more The spectrophotometric properties of chlorophylls' derivatives (Chls) formulated in the Pluronics® F-127 and P-123 were evaluated and the results have shown that the Chls were efficiently solubilized in these drug delivery systems as monomers. The relative location of the Chls in the Pluronics® was estimated from the Stokes shift and micropolarity of the micellar environment. Chls with phytyl chain were located in the micellar core, where the micropolarity is similar to ethanol, while phorbides' derivatives (without phytyl chain) were located in the outer shell of the micelle, i.e., more polar environment. In addition, the thermal stability of the micellar formulations was evaluated through electronic absorption, fluorescence emission and resonance light scattering with lowering the temperature. The Chls promote the stability of the micelles at temperatures below the Critical Micellar Temperature (CMT) of these surfactants. For F-127 formulations, the water molecules drive through inside the nano-structure at temperatures below the CMT, which increased the polarity of this microenvironment and directly affected the spectrophotometric properties of the Chls with phytyl chain. The properties of the micellar microenvironment of P-123, with more hydrophobic core due to the small PEO/PPO fraction, were less affected by lowering the temperature than for F-127. These results enable us to better understand the Chls behavior in micellar copolymers and allowed us to design new drug delivery system that maintains the photosensitizer's properties for photodynamic applications.
Chemical determination of singlet oxygen from photosensitizers illuminated with LED: New calculation methodology considering the influence of photobleaching
Abstract The singlet oxygen (1 O 2) is one of the reactive species responsible for the destructio... more Abstract The singlet oxygen (1 O 2) is one of the reactive species responsible for the destruction of target cells in Photodynamic Therapy (PDT). However, the quantification of 1 O 2 yields (?? ??) involves lifetime measurements with very expensive equipment. An ...
Xanthenes form to an important class of dyes which are widely used. Most of them present three ac... more 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 pK a determination and the attribution of each group to the corresponding pK a value is a very important feature. Attempts to obtain reliable pK a through the potentiometry titration and the electronic absorption spectrophotometry using the first and second orders derivative failed. Due to the close pK a 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 pK a of the phenolic group, which is not easily recognizable for some investigated dyes. Besides the pK a determination, the chemometry allowed for estimating the electronic spectrum of some prevalent protolytic species and the substituents effects evaluation.
Anais da Academia Brasileira de Ciências, 2013
The development of drugs for photodynamic therapy (PDT) is an important area of research due to t... more The development of drugs for photodynamic therapy (PDT) is an important area of research due to their growing use in medical applications. Therefore, it is important to develop new bioassay methods for PDT photosensitizers that are inexpensive, easy to handle and highly sensitive to environmental conditions. Xanthene dyes (fluorescein, rose bengal B, erythrosine B and eosin Y) with LED light sources were investigated using Artemia salina as a bioindicator of photodynamic activity. In this study, three factors were investigated: (i) photosensitizers concentration, (ii) the LED irradiation time and (iii) the waiting time between the addition of the photosensitizers and the beginning of the irradiation. To analyze the photo-killing of A. salina, it was employed a 2³ full factorial design. The death of A. salina was related to dye structure and the interaction between the irradiation time and the photosensitizers concentration. About 60% of crustaceans death was obtained using rose beng...
Photochemistry and Photobiology, 2003
This study investigates the potential of Pluronics for the formulation of tetrapyrrole-based phot... more This study investigates the potential of Pluronics for the formulation of tetrapyrrole-based photosensitizers, with a particular focus on B-ring benzoporphyrin derivatives. The B-ring derivatives have a high tendency to aggregate in aqueous solutions, and this poses a significant formulation problem. Pluronics are ABA-type triblock copolymers composed of a central hydrophobic polypropylene oxide section with two hydrophilic polyethylene oxide sections of equal length at either end. Out of a range of different commercially available block copolymers studied, it was found that the longer the hydrophobic block, the better the stabilization of tetrapyrrolic drugs in monomeric form in aqueous suspensions. Of these the best performance was observed in the micelle-forming Pluronic P123. Micelle size determination by laser light scattering confirmed that particle size in stable Pluronic formulations was around 20 nm. Pluronics such as L122 formed emulsions spontaneously without the need for emulsion stabilizers; emulsions were highly stable at ambient temperatures over several days and also highly effective as potential drug delivery agents. {Posted on the website on 18 December 2002.
Quimica Nova, 2002
solvent has a high cryoscopic constant and is miscible with both polar and non-polar compounds. T... more solvent has a high cryoscopic constant and is miscible with both polar and non-polar compounds. The molar masses of acetone, water, chloroform, dichloro-methane, ethanol, hexane, carbon tetrachloride and toluene were determined. The results were good except for water. Even though there are reliable techniques of molar mass determination nowadays, this method is still frequent ly taught in undergraduate courses.
Quimica Nova, 2006
Recebido em 31/1/05; aceito em 12/8/05; publicado na web em 14/3/06 THE pK a OF ACID-BASE INDICAT... more Recebido em 31/1/05; aceito em 12/8/05; publicado na web em 14/3/06 THE pK a OF ACID-BASE INDICATORS AND THE INFLUENCE OF COLLOIDAL SYSTEMS. An experiment is proposed that can be included in undergraduate courses of chemistry. The subject is the acidity of organic compounds, which are employed as pH indicators, particularly in acid-base titrations. The indicators used are methyl orange, bromophenol blue and bromocresol green in aqueous medium. The influence of colloidal systems on the equilibrium is evaluated by the pK a . The colloids employed are surfactants like sodium dodecyl sulfate, cetyl-trimethylammonium bromide and a polymeric non-ionic F127 (pluronics). The effect of stabilization promoted by the system on the acidic or basic structureof the indicator establishes the action mechanism of the colloid on the pK a values.
Journal of Molecular Liquids, 2000
The parallel (k║) and perpendicular (k┴) absorption coefficients are determined along the entire ... more The parallel (k║) and perpendicular (k┴) absorption coefficients are determined along the entire range of a calamitic nematic phase (NC) and near the NC - reentrant isotropic (IRE) and NC - isotropic (I) phase transitions. We have made these measurements in a lyotropic mixture of potassium laurate, decanol and D2O in the spectral range from 400 to 700nm using a
Influences of experimental parameters on the stability of a benzoporphyrin drug in water/ethanol mixtures: a statistical approach investigation
Journal of Porphyrins and Phthalocyanines, 2005
WSPC Journals Online,WorldSciNet.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2011
Xanthenes form to an important class of dyes which are widely used. Most of them present three ac... more 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 pK a determination and the attribution of each group to the corresponding pK a value is a very important feature. Attempts to obtain reliable pK a through the potentiometry titration and the electronic absorption spectrophotometry using the first and second orders derivative failed. Due to the close pK a 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 pK a of the phenolic group, which is not easily recognizable for some investigated dyes. Besides the pK a determination, the chemometry allowed for estimating the electronic spectrum of some prevalent protolytic species and the substituents effects evaluation.
Química Nova, 2010
Recebido em 12/12/08; aceito em 24/7/09; publicado na web em 8/1/10 INFLUENCE OF DIFFERENT WATER-... more Recebido em 12/12/08; aceito em 24/7/09; publicado na web em 8/1/10 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 autoaggregation processes. The major hydrophobicity and the lower dielectric constant of ethanol when compared with water precluded significantly the auto-aggregation process of these compounds.
Journal of Physical Chemistry A - J PHYS CHEM A, 2004
The kinetics of the aggregation process of DiesterB, a homologous coproduct generated in Vertepor... more The kinetics of the aggregation process of DiesterB, a homologous coproduct generated in Verteporfin synthesis (the drug used in the medication Visudyne applied in photodynamic therapy), was investigated by visible spectrophotometry in several aqueous organic solvents (dimethyl sulfoxide (DMSO), acetonitrile, dioxane, methanol, and ethanol). The monomeric form of DiesterB is stable in pure organic solvents, showing a characteristic peak at 690 nm. In water-rich medium, an aggregation process is induced, giving rise to a new band in the 720-740 nm region. In aqueous DMSO and acetonitrile solvents this process is very fast and leads to the formation of dimers, while in dioxane-, methanol-, and ethanol-water mixtures the absorption intensities show a sigmoidal time profile, suggesting a slow initial reaction (lag phase) followed by a rapid aggregation (log phase), characteristic of autocatalyzed reactions. The proposed final species in these solvents is a trimer as the main aggregate (supported by resonance light scattering and small-angle X-ray scattering experiments). The experimental absorbance values, taken at monomer or aggregate peaks during the reaction, were fitted using a nonconventional treatment proposed by Pasternack. This model allows evaluating two rate constants, due to a first (k 0 , noncatalytic) and a second (k c , catalytic) step, as well as a parameter (m), related to the size and amount of the catalyst nucleus. Although the model was originally applied to large porphyrin arrays growing on templates, an excellent accordance was obtained between its formalism and our kinetic experimental data. The global mechanism seems to start with a dimeric nucleus formation (lag phase), which acts, despite its small amount, as a catalytic center driving to trimers (log phase). The effects caused by water content and DiesterB concentration on the kinetic results support the proposed multistep equilibrium. The absence of isosbestic points during the process reinforces the presence of more than one step. The most unusual feature is the effect of the temperature on the rate constants. As the temperature is raised, the constants increase up to a maximum, and decrease for higher temperatures. The effect is more pronounced for k c than for the k 0 rate constant. The model proposed states that at high temperatures the equilibrium is shifted toward monomers, reducing the catalyst nucleus formation and resulting in an overall reaction velocity decrease.
The Journal of Physical Chemistry B, 2011
Terapia fotodinâmica: aspectos farmacológicos, aplicações e avanços recentes no desenvolvimento de medicamentos
Química Nova, 2002
Química Nova, 2010
Recebido em 30/10/08; aceito em 30/7/09; publicado na web em 11/1/10 DETERMINATION OF THE ENTHALP... more Recebido em 30/10/08; aceito em 30/7/09; publicado na web em 11/1/10 DETERMINATION OF THE ENTHALPY OF VAPORIZATION OF LIQUID COMPOUNDS BY THE SMITH MENZIES (ISOTENISCOPE) METHOD. This article proposes an experimental procedure to determine the enthalpy (and entropy) of vaporization of organic liquid compounds, by the Smith-Menzies (isoteniscope) method. The values of vapor pressure at different temperatures were obtained and D v H (and D v S) were graphically determined, using the Clausius-Clapeyron equation. The results for diethyl-ether, propanone, ethanol and n-hexane are in very good agreement with those from literature. A historical and thermodynamic discussion on equations that correlates vapor pressures and temperature precedes the experimental proposition.
Química Nova, 2006
Recebido em 24/5/05; aceito em 5/10/05; publicado na web em 31/3/06 A SIMPLE APPARATUS TO FOLLOW ... more Recebido em 24/5/05; aceito em 5/10/05; publicado na web em 31/3/06 A SIMPLE APPARATUS TO FOLLOW RAPID REACTIONS: A LOW-COST STOPPED-FLOW. The modern stopped-flow reaction analyzer has shown high efficiency and flexibility, which provides outstanding sample economy with a dead-time of less than 1 ms. However the cost of the equipment imposes a serious restriction to many Brazilian scientists and teachers. In this work we describe the construction of a low-cost stopped-flow system coupled to a UV-Vis spectrophotometer. The performance of the system was checked by monitoring the kinetics of two reactions: the fading of phenolphthalein in aqueous alkaline solution and the chlorophyll a demetallation in acid medium. The apparatus showed reasonable efficiency with a dead-time of 0.3 to 0.5 s. The very good results obtained in these two illustrative processes show that the system is satisfactory for determining rate constants with mean reaction times ranging from seconds to minutes.
Photodiagnosis and Photodynamic Therapy, 2012
Photodynamic therapy studies have shown promising results for inactivation of microorganisms rela... more Photodynamic therapy studies have shown promising results for inactivation of microorganisms related to dental caries. A large number of studies have used a variety of protocols, but few studies have analyzed photosensitizers and light source properties to obtain the best PDT dose response for dental caries. This study aims to discuss the photosensitizers and light source properties employed in PDT studies of dental caries. Three questions were formulated to discuss these aspects. The first involves the photosensitizer properties and their performance against Gram positive and Gram negative bacteria. The second discusses the use of light sources in accordance with the dye maximum absorbance to obtain optimal results. The third looks at the relevance of photosensitizer concentration, the possible formation of self-aggregates, and light source effectiveness. This review demonstrated that some groups of photosensitizers may be more effective against either Gram positive or negative bacteria, that the light source must be appropriate for dye maximum absorbance, and that some photosensitizers may have their absorbance modified with their concentration. For the best results of PDT against the main cariogenic bacteria (Streptococcus mutans), a variety of aspects should be taken into account, and among the analyzed photosensitizer, erythrosin seems to be the most appropriate since it acts against this Gram positive bacteria, has a hydrophilic tendency and even at low concentrations may have photodynamic effects. Considering erythrosin, the most appropriate light source should have a maximum emission intensity at a wavelength close to 530 nm, which may be achieved with low cost LEDs.
Journal of the Brazilian Chemical Society, 2010
O espectro de absorção de DPH, em concentração fixa, não varia com o teor de água em solvente org... more O espectro de absorção de DPH, em concentração fixa, não varia com o teor de água em solvente orgânico. Tem-se a banda de monômeros igual àquela em etanol puro. A absorção não muda até o limite de 54 e 46% de água em etanol e DMSO, respectivamente, para [DPH] = 5,0 × 10 -6 mol L -1 a 30 °C. Entretanto, em misturas com água muito abaixo desses conteúdos críticos, observou-se um decaimento intenso de fluorescência enquanto a absorção manteve-se constante. Propõese que moléculas de água atuam como supressores dos estados excitados e a constante de supressão de Stern-Volmer através de intensidade relativas, resultou em 7,4 × 10 -2 (água/etanol) e 2,6 × 10 -2 L mol -1 (água/DMSO). Os tempos de vida do DPH na ausência e presença do supressor forneceram constantes de 7,1 × 10 -2 L mol -1 em água/etanol, indicando supressão dinâmica. Em investigações de ambientes com esta sonda, este processo deve ser considerado tendo em vista o risco de erros de interpretação.
Reactions of 1,?-bis(2-bromopyridinium)alkanes with hydroxide ion in aqueous solutions
Journal of Physical Organic Chemistry, 1998
ABSTRACT
Reactions of 1,-bis(2-bromopyridinium)alkanes with azide ions: charge effect and intermediates
Journal of Physical Organic Chemistry, 1999
ABSTRACT
Characterization of chlorophyll derivatives in micelles of polymeric surfactants aiming photodynamic applications
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2017
The spectrophotometric properties of chlorophylls' derivatives (Chls) formulated in the P... more The spectrophotometric properties of chlorophylls' derivatives (Chls) formulated in the Pluronics® F-127 and P-123 were evaluated and the results have shown that the Chls were efficiently solubilized in these drug delivery systems as monomers. The relative location of the Chls in the Pluronics® was estimated from the Stokes shift and micropolarity of the micellar environment. Chls with phytyl chain were located in the micellar core, where the micropolarity is similar to ethanol, while phorbides' derivatives (without phytyl chain) were located in the outer shell of the micelle, i.e., more polar environment. In addition, the thermal stability of the micellar formulations was evaluated through electronic absorption, fluorescence emission and resonance light scattering with lowering the temperature. The Chls promote the stability of the micelles at temperatures below the Critical Micellar Temperature (CMT) of these surfactants. For F-127 formulations, the water molecules drive through inside the nano-structure at temperatures below the CMT, which increased the polarity of this microenvironment and directly affected the spectrophotometric properties of the Chls with phytyl chain. The properties of the micellar microenvironment of P-123, with more hydrophobic core due to the small PEO/PPO fraction, were less affected by lowering the temperature than for F-127. These results enable us to better understand the Chls behavior in micellar copolymers and allowed us to design new drug delivery system that maintains the photosensitizer's properties for photodynamic applications.
Chemical determination of singlet oxygen from photosensitizers illuminated with LED: New calculation methodology considering the influence of photobleaching
Abstract The singlet oxygen (1 O 2) is one of the reactive species responsible for the destructio... more Abstract The singlet oxygen (1 O 2) is one of the reactive species responsible for the destruction of target cells in Photodynamic Therapy (PDT). However, the quantification of 1 O 2 yields (?? ??) involves lifetime measurements with very expensive equipment. An ...
Xanthenes form to an important class of dyes which are widely used. Most of them present three ac... more 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 pK a determination and the attribution of each group to the corresponding pK a value is a very important feature. Attempts to obtain reliable pK a through the potentiometry titration and the electronic absorption spectrophotometry using the first and second orders derivative failed. Due to the close pK a 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 pK a of the phenolic group, which is not easily recognizable for some investigated dyes. Besides the pK a determination, the chemometry allowed for estimating the electronic spectrum of some prevalent protolytic species and the substituents effects evaluation.
Anais da Academia Brasileira de Ciências, 2013
The development of drugs for photodynamic therapy (PDT) is an important area of research due to t... more The development of drugs for photodynamic therapy (PDT) is an important area of research due to their growing use in medical applications. Therefore, it is important to develop new bioassay methods for PDT photosensitizers that are inexpensive, easy to handle and highly sensitive to environmental conditions. Xanthene dyes (fluorescein, rose bengal B, erythrosine B and eosin Y) with LED light sources were investigated using Artemia salina as a bioindicator of photodynamic activity. In this study, three factors were investigated: (i) photosensitizers concentration, (ii) the LED irradiation time and (iii) the waiting time between the addition of the photosensitizers and the beginning of the irradiation. To analyze the photo-killing of A. salina, it was employed a 2³ full factorial design. The death of A. salina was related to dye structure and the interaction between the irradiation time and the photosensitizers concentration. About 60% of crustaceans death was obtained using rose beng...
Photochemistry and Photobiology, 2003
This study investigates the potential of Pluronics for the formulation of tetrapyrrole-based phot... more This study investigates the potential of Pluronics for the formulation of tetrapyrrole-based photosensitizers, with a particular focus on B-ring benzoporphyrin derivatives. The B-ring derivatives have a high tendency to aggregate in aqueous solutions, and this poses a significant formulation problem. Pluronics are ABA-type triblock copolymers composed of a central hydrophobic polypropylene oxide section with two hydrophilic polyethylene oxide sections of equal length at either end. Out of a range of different commercially available block copolymers studied, it was found that the longer the hydrophobic block, the better the stabilization of tetrapyrrolic drugs in monomeric form in aqueous suspensions. Of these the best performance was observed in the micelle-forming Pluronic P123. Micelle size determination by laser light scattering confirmed that particle size in stable Pluronic formulations was around 20 nm. Pluronics such as L122 formed emulsions spontaneously without the need for emulsion stabilizers; emulsions were highly stable at ambient temperatures over several days and also highly effective as potential drug delivery agents. {Posted on the website on 18 December 2002.
Quimica Nova, 2002
solvent has a high cryoscopic constant and is miscible with both polar and non-polar compounds. T... more solvent has a high cryoscopic constant and is miscible with both polar and non-polar compounds. The molar masses of acetone, water, chloroform, dichloro-methane, ethanol, hexane, carbon tetrachloride and toluene were determined. The results were good except for water. Even though there are reliable techniques of molar mass determination nowadays, this method is still frequent ly taught in undergraduate courses.
Quimica Nova, 2006
Recebido em 31/1/05; aceito em 12/8/05; publicado na web em 14/3/06 THE pK a OF ACID-BASE INDICAT... more Recebido em 31/1/05; aceito em 12/8/05; publicado na web em 14/3/06 THE pK a OF ACID-BASE INDICATORS AND THE INFLUENCE OF COLLOIDAL SYSTEMS. An experiment is proposed that can be included in undergraduate courses of chemistry. The subject is the acidity of organic compounds, which are employed as pH indicators, particularly in acid-base titrations. The indicators used are methyl orange, bromophenol blue and bromocresol green in aqueous medium. The influence of colloidal systems on the equilibrium is evaluated by the pK a . The colloids employed are surfactants like sodium dodecyl sulfate, cetyl-trimethylammonium bromide and a polymeric non-ionic F127 (pluronics). The effect of stabilization promoted by the system on the acidic or basic structureof the indicator establishes the action mechanism of the colloid on the pK a values.
Journal of Molecular Liquids, 2000
The parallel (k║) and perpendicular (k┴) absorption coefficients are determined along the entire ... more The parallel (k║) and perpendicular (k┴) absorption coefficients are determined along the entire range of a calamitic nematic phase (NC) and near the NC - reentrant isotropic (IRE) and NC - isotropic (I) phase transitions. We have made these measurements in a lyotropic mixture of potassium laurate, decanol and D2O in the spectral range from 400 to 700nm using a
Influences of experimental parameters on the stability of a benzoporphyrin drug in water/ethanol mixtures: a statistical approach investigation
Journal of Porphyrins and Phthalocyanines, 2005
WSPC Journals Online,WorldSciNet.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2011
Xanthenes form to an important class of dyes which are widely used. Most of them present three ac... more 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 pK a determination and the attribution of each group to the corresponding pK a value is a very important feature. Attempts to obtain reliable pK a through the potentiometry titration and the electronic absorption spectrophotometry using the first and second orders derivative failed. Due to the close pK a 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 pK a of the phenolic group, which is not easily recognizable for some investigated dyes. Besides the pK a determination, the chemometry allowed for estimating the electronic spectrum of some prevalent protolytic species and the substituents effects evaluation.
Química Nova, 2010
Recebido em 12/12/08; aceito em 24/7/09; publicado na web em 8/1/10 INFLUENCE OF DIFFERENT WATER-... more Recebido em 12/12/08; aceito em 24/7/09; publicado na web em 8/1/10 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 autoaggregation processes. The major hydrophobicity and the lower dielectric constant of ethanol when compared with water precluded significantly the auto-aggregation process of these compounds.
Journal of Physical Chemistry A - J PHYS CHEM A, 2004
The kinetics of the aggregation process of DiesterB, a homologous coproduct generated in Vertepor... more The kinetics of the aggregation process of DiesterB, a homologous coproduct generated in Verteporfin synthesis (the drug used in the medication Visudyne applied in photodynamic therapy), was investigated by visible spectrophotometry in several aqueous organic solvents (dimethyl sulfoxide (DMSO), acetonitrile, dioxane, methanol, and ethanol). The monomeric form of DiesterB is stable in pure organic solvents, showing a characteristic peak at 690 nm. In water-rich medium, an aggregation process is induced, giving rise to a new band in the 720-740 nm region. In aqueous DMSO and acetonitrile solvents this process is very fast and leads to the formation of dimers, while in dioxane-, methanol-, and ethanol-water mixtures the absorption intensities show a sigmoidal time profile, suggesting a slow initial reaction (lag phase) followed by a rapid aggregation (log phase), characteristic of autocatalyzed reactions. The proposed final species in these solvents is a trimer as the main aggregate (supported by resonance light scattering and small-angle X-ray scattering experiments). The experimental absorbance values, taken at monomer or aggregate peaks during the reaction, were fitted using a nonconventional treatment proposed by Pasternack. This model allows evaluating two rate constants, due to a first (k 0 , noncatalytic) and a second (k c , catalytic) step, as well as a parameter (m), related to the size and amount of the catalyst nucleus. Although the model was originally applied to large porphyrin arrays growing on templates, an excellent accordance was obtained between its formalism and our kinetic experimental data. The global mechanism seems to start with a dimeric nucleus formation (lag phase), which acts, despite its small amount, as a catalytic center driving to trimers (log phase). The effects caused by water content and DiesterB concentration on the kinetic results support the proposed multistep equilibrium. The absence of isosbestic points during the process reinforces the presence of more than one step. The most unusual feature is the effect of the temperature on the rate constants. As the temperature is raised, the constants increase up to a maximum, and decrease for higher temperatures. The effect is more pronounced for k c than for the k 0 rate constant. The model proposed states that at high temperatures the equilibrium is shifted toward monomers, reducing the catalyst nucleus formation and resulting in an overall reaction velocity decrease.
The Journal of Physical Chemistry B, 2011
Terapia fotodinâmica: aspectos farmacológicos, aplicações e avanços recentes no desenvolvimento de medicamentos
Química Nova, 2002
Química Nova, 2010
Recebido em 30/10/08; aceito em 30/7/09; publicado na web em 11/1/10 DETERMINATION OF THE ENTHALP... more Recebido em 30/10/08; aceito em 30/7/09; publicado na web em 11/1/10 DETERMINATION OF THE ENTHALPY OF VAPORIZATION OF LIQUID COMPOUNDS BY THE SMITH MENZIES (ISOTENISCOPE) METHOD. This article proposes an experimental procedure to determine the enthalpy (and entropy) of vaporization of organic liquid compounds, by the Smith-Menzies (isoteniscope) method. The values of vapor pressure at different temperatures were obtained and D v H (and D v S) were graphically determined, using the Clausius-Clapeyron equation. The results for diethyl-ether, propanone, ethanol and n-hexane are in very good agreement with those from literature. A historical and thermodynamic discussion on equations that correlates vapor pressures and temperature precedes the experimental proposition.
Química Nova, 2006
Recebido em 24/5/05; aceito em 5/10/05; publicado na web em 31/3/06 A SIMPLE APPARATUS TO FOLLOW ... more Recebido em 24/5/05; aceito em 5/10/05; publicado na web em 31/3/06 A SIMPLE APPARATUS TO FOLLOW RAPID REACTIONS: A LOW-COST STOPPED-FLOW. The modern stopped-flow reaction analyzer has shown high efficiency and flexibility, which provides outstanding sample economy with a dead-time of less than 1 ms. However the cost of the equipment imposes a serious restriction to many Brazilian scientists and teachers. In this work we describe the construction of a low-cost stopped-flow system coupled to a UV-Vis spectrophotometer. The performance of the system was checked by monitoring the kinetics of two reactions: the fading of phenolphthalein in aqueous alkaline solution and the chlorophyll a demetallation in acid medium. The apparatus showed reasonable efficiency with a dead-time of 0.3 to 0.5 s. The very good results obtained in these two illustrative processes show that the system is satisfactory for determining rate constants with mean reaction times ranging from seconds to minutes.
Photodiagnosis and Photodynamic Therapy, 2012
Photodynamic therapy studies have shown promising results for inactivation of microorganisms rela... more Photodynamic therapy studies have shown promising results for inactivation of microorganisms related to dental caries. A large number of studies have used a variety of protocols, but few studies have analyzed photosensitizers and light source properties to obtain the best PDT dose response for dental caries. This study aims to discuss the photosensitizers and light source properties employed in PDT studies of dental caries. Three questions were formulated to discuss these aspects. The first involves the photosensitizer properties and their performance against Gram positive and Gram negative bacteria. The second discusses the use of light sources in accordance with the dye maximum absorbance to obtain optimal results. The third looks at the relevance of photosensitizer concentration, the possible formation of self-aggregates, and light source effectiveness. This review demonstrated that some groups of photosensitizers may be more effective against either Gram positive or negative bacteria, that the light source must be appropriate for dye maximum absorbance, and that some photosensitizers may have their absorbance modified with their concentration. For the best results of PDT against the main cariogenic bacteria (Streptococcus mutans), a variety of aspects should be taken into account, and among the analyzed photosensitizer, erythrosin seems to be the most appropriate since it acts against this Gram positive bacteria, has a hydrophilic tendency and even at low concentrations may have photodynamic effects. Considering erythrosin, the most appropriate light source should have a maximum emission intensity at a wavelength close to 530 nm, which may be achieved with low cost LEDs.
Journal of the Brazilian Chemical Society, 2010
O espectro de absorção de DPH, em concentração fixa, não varia com o teor de água em solvente org... more O espectro de absorção de DPH, em concentração fixa, não varia com o teor de água em solvente orgânico. Tem-se a banda de monômeros igual àquela em etanol puro. A absorção não muda até o limite de 54 e 46% de água em etanol e DMSO, respectivamente, para [DPH] = 5,0 × 10 -6 mol L -1 a 30 °C. Entretanto, em misturas com água muito abaixo desses conteúdos críticos, observou-se um decaimento intenso de fluorescência enquanto a absorção manteve-se constante. Propõese que moléculas de água atuam como supressores dos estados excitados e a constante de supressão de Stern-Volmer através de intensidade relativas, resultou em 7,4 × 10 -2 (água/etanol) e 2,6 × 10 -2 L mol -1 (água/DMSO). Os tempos de vida do DPH na ausência e presença do supressor forneceram constantes de 7,1 × 10 -2 L mol -1 em água/etanol, indicando supressão dinâmica. Em investigações de ambientes com esta sonda, este processo deve ser considerado tendo em vista o risco de erros de interpretação.
Reactions of 1,?-bis(2-bromopyridinium)alkanes with hydroxide ion in aqueous solutions
Journal of Physical Organic Chemistry, 1998
ABSTRACT
Reactions of 1,-bis(2-bromopyridinium)alkanes with azide ions: charge effect and intermediates
Journal of Physical Organic Chemistry, 1999
ABSTRACT