Recebido em 11/7/01; aceito em 10/12/01 PHOTODYNAMIC THERAPY: PHARMACOLOGICAL ASPECTS, APPLICATIONS AND NEWS FROM MEDICATIONS DEVELOPMENT. Photodynamic Therapy (PDT) is a clinical procedure, which utilize a photosensitive compound and light. This is a new modality of treatment for cancer, aged related macular degenerescence (AMD), psoriasis, arthritis, arterial restenosis, etc which exhibits efficiency, less traumatic effects, low recovery time and few co-lateral effects. The first officially approved drug for PDT by the Food and Drug Administration (EUA) is Photofrin â , which is applied for cancer. A new generation drug for PDT, Visudyne â was recently approved to treat AMD; its photoactive compound is BPDMA, a benzoporphyrin mono-acid derivative (chlorin-type molecule). A concise history, technical information and some drugs for PDT are reported.Keywords: photodynamic therapy; visudyne; tumor. INTRODUÇÃOTumor, sinônimo de neoplasma ou blastoma, é o crescimento anormal de tecidos. Células doentes, com um distúrbio genético, passam a se reproduzir mais rapidamente do que as células normais levando à formação do tumor, podendo este ser benigno ou maligno. Quando o crescimento do tumor é muito acelerado, desorganizado e com tendência a se alastrar a outros órgãos, geralmente é maligno. Câncer é a designação genérica de qualquer tumor maligno; a palavra câncer é derivada do latim e significa caranguejo. O nome é decorrente da facilidade com que este crustáceo tem de se aderir firmemente em qualquer lugar, assim como o tumor se adere a um local do corpo humano em que se desenvolve 1,2 . Os tipos mais comuns de câncer são os de pele, mama feminina, próstata, pulmão e estômago sendo que os últimos quatro são letais e compõem a segunda maior causa de mortes por doenças no Brasil 3 . Entre os citados, o câncer de pele é o de maior incidência no país, porém, com exceção do câncer melanoma, é a variedade de menor letalidade 3 . Diante dos graves efeitos colaterais e da eficiência limitada das terapias tradicionais (cirurgia, quimioterapia e radioterapia) outras alternativas estão sendo constantemente propostas na área de oncologia (cancerologia). Dentre estas destaca-se a terapia fotodinâmica (TFD), uma modalidade relativamente nova no tratamento de câncer. Apesar de boa parte do uso da TFD ser centrada nesta doença, outras moléstias tais como degeneração macular da retina, psoríase, artrite reumatóide sistêmica, restenosis, micoses fungóides, infestações bacterianas, verrugas, arteriosclerose, AIDS, etc têm como característica comum um crescimento anormal de tecidos igualmente ao câncer [4][5][6] . Assim a TFD está sendo usada e investigada em nível mundial no tratamento dessas e outras doenças correlatas na origem.A combinação droga mais luz forma a base da TFD. Um composto fotossensível é introduzido no paciente e se acumula preferencialmente em células que se reproduzem rapidamente. Essas são posteriormente irradiadas, via laser através de um cateter de fibra óptica, junto ao tecido doente. A luz (tipicamente 600 a 8...
Benzoporphyrins, chlorin‐type compounds, are efficient new drugs in photodynamic therapy. In this work, some aspects of the benzoporphyrin‐1,3‐diene dimethyl ester (DiesterB) aggregation were investigated in water–organic solvent mixtures, using visible spectrophotometry. The effects of solvent mixtures, water with acetonitrile, dioxane, methanol and ethanol, were compared taking the calculated aggregation equilibrium constant (K) and the aggregation number. The K dependence on temperature, DiesterB concentration and water content suggest that, in water with acetonitrile, the predominant species is a dimer, whereas in dioxane, methanol and ethanol systems, there are multiple equilibria, with a pre‐equilibrium between the monomer and dimer (small amount), followed by trimer formation. Not only the solvent polarity but also the nature of the organic solvent are important for the aggregation process, driving the aggregate size and the magnitude of the equilibrium constant. Copyright © 2004 John Wiley & Sons, Ltd.
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.
Recebido em 9/5/01; aceito em 22/1/02 MOLAR MASS DETERMINATION BY CRYOSCOPY: TERT-BUTYL ALCOHOL, AN EXTREMELY APPROPRIATE SOLVENT. We intend to divulge an easy experiment that permits the determination of molar masses of various compounds by cryoscopy. The major advantage of this is the use of the tert-butyl alcohol as a solvent, which requires simple apparatus and easy procedures. The melting point of this alcohol is around 25 o C, which makes it easy to freeze and then melt the solutions. This 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 frequently taught in undergraduate courses.Keywords: tert-butyl alcohol; cryoscopy; molar mass determination. INTRODUÇÃOColigar, do latim colligare, significa unir, ligar, juntar, juntar para um fim comum. As denominadas propriedades coligativas referem-se a quatro propriedades físicas características de soluções diluídas (abaixamento crioscópico, pressão osmótica, elevação do ponto de ebulição e abaixamento da pressão de vapor), cujos comportamentos são correlacionados e unidos pelo fato de dependerem do número de partículas de soluto presente (independente de sua natureza química) em uma dada quantidade de determinado solvente. Todas têm em comum o fato do potencial químico do solvente no estado líquido ser diminuído na presença de um soluto (solução no estado líquido), de tal forma que o equilíbrio com a fase vapor (para solutos não-voláteis) ou com a fase sólida seja estabelecido em temperaturas diferentes, a uma dada pressão, ou a pressões diferentes a uma dada temperatura. Uma discussão simples, mas bem didática, desses fenômenos é encontrada em Atkins 1 e Levine 2 . O abaixamento crioscópico, DT f , do solvente ocorre porque o seu potencial químico na solução é menor que o do líquido puro, enquanto que o da fase sólida (se ela for constituída somente do solvente puro) permanece o mesmo. Então, para restaurar o equilí-brio entre as duas fases (solução e sólida) do solvente, a temperatura deve ser diminuída 2 . Quando essa temperatura for atingida teremos a igualdade entre os potenciais químicos das duas fases (solução e sólida) do solvente:O lado esquerdo da equação 1 representa o potencial químico do solvente (A) na solução e o direito, o do sólido puro, sendo que o asterisco indica as espécies puras e a A , a atividade do solvente na solução. A diferença de potenciais químicos que aparece nessa equação (entre o líquido e o sólido), como se refere às espécies puras, identifica-se com a energia de Gibbs de fusão do solvente.A partir dessa equação (que supõe que somente o solvente congela a partir da solução), supondo que o abaixamento crioscópico (DT f ) seja bem menor que a temperatura de fusão do solvente puro, o que permite usar a aproximação de que...
Two SAABA [3‐ and 4‐(ω‐sulphoalkylamino)benzoic acid] derivatives, 3‐(3‐sulphopropylamino)benzoic acid and 3‐(4‐sulphobutylamino)benzoic acid, were studied by a potentiometric method to determine two macroscopic constants (K a 2 and K a 3) for each derivative. The combination of these values with 13C NMR spectroscopic titration data was used to determine their tautomeric (KT) microscopic constants at 25.0 °C and ionic strength 1.00 mol dm−3 (KCl). From these results, it was possible to estimate the other microscopic constants and consequently the Hammett substituent constants (σm) for two m‐aminoalkylsulphonates and the electronic effects of two alkylsulphonate substituents separately. For the m‐aminoalkylsulphonate substituents the σm values are −0.12 for m‐aminopropylsulphonate and −0.27 for m‐aminobutylsulphonate, and therefore the electron‐donating effect prevails when three methylene units are present. On the other hand, in alkylsulphonate substituents, this effect prevails only for four methylene units. Copyright © 2002 John Wiley & Sons, Ltd.
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