Química orgânica experimental: integração de teoria, experimento e análise

A new approach for teaching in basic experimental organic chemistry is presented. Experimental work goes on parallel to theoretical lectures leading to an immediate application of theoretical concepts transmitted therein. One day/week is dedicated exclusively to the organic laboratory. Reactions are proposed as problems to be solved; the student has to deduce the structure of the product on the basis of his observations, the analytical data and his mechanistical knowledge. 70 different experiments, divided in 7 thematical chapters, are presented. All experiments require the analysis and discussion of 1H and 13C NMR, IR and UV spectra. Additional questions about each reaction have to be answered by the student in his written report. Laboratory safety is garanteed by the exclusion or substitution of hazardous and toxic reagents. Microscale preparations are adopted in most cases to lower the cost of materials and the amount of waste. Recycling of many reaction products as starting materials in other experiments reduces the need for commercial reagents and allows the execution of longer reaction sequences. Only unexpensive standard laboratory equipment and simple glassware are required. All experiments include instructions for the save treatment or disposal of chemical waste.

Determinação espectrofotométrica por injeção em fluxo de vitamina B6 (piridoxina) em formulações farmacêuticas

A flow injection (FI) spectrophotometric procedure is proposed for the determination of vitamin B6 (pyridoxine hydrochloride) in pharmaceutical preparations. Powdered samples containing from 2.5 to 4.5 mg, were previously dissolved in 0.1 mol L-1 phosphate buffer solution (pH 7.0) and a volume of 500 muL was injected directly into a carrier stream consisting of this same phosphate buffer solution, flowing at 4.4 mL min-1. The stable blue indophenol dye produced in the oxidation of pyridoxine hydrochloride by potassium hexacyanoferrate(III) and N,N-diethyl-p-phenylenediamine solution was directly measured at 684 nm. Vitamin B6 was determined in five pharmaceutical preparations in the 0.5 to 6.0 mg L-1 concentration range (calibration graph: A= -0.00499 + 0.11963 C; r= 0.9991, where A is the absorbance and C is the vitamin B6 concentration in mg L-1), with a detection limit of 0.02 mg L-1 (3 Sblank/slope). The recovery of this vitamin from three samples ranged from 97.5 to 103.3 %. The analytical frequency was 62 h-1 and r.s.d. were less than 2% for solutions containing 1.0 and 3.0 mg L-1 vitamin B6 (n= 10). The results obtained for the determination of vitamin B6 in commercial formulations were in good agreement with those obtained by a spectrophotometric procedure (r=0.9997) and also with the label values (r= 0.9998).

Determinação espectrofotométrica de vitamina B2 (riboflavina) em formulações farmacêuticas empregando sistema de análises por injeção em fluxo

A flow injection spectrophotometric procedure exploiting merging zones is proposed for determining vitamin B2 (riboflavin) in pharmaceutical preparations. The determination is based on the red-colored complex formation between vitamin B2 and silver(I) which was measured at 520 nm. Vitamin B2 was determined in four pharmaceutical preparations in the 1.0 to 50.0 mg L-1 concentration range, with a detection limit of 0.5 mg L-1. The recovery from three samples ranged from 98.0 to 104.0 %. The analytical frequency was 42 h-1 and r.s.d. were lower than 1% for solutions containing 10.0, 30.0 and 50.0 mg L-1 vitamin B2 (n= 10). The results obtained in commercial formulations using the FIA procedure were in good agreement with those obtained by using a conventional fluorimetric procedure (r=0.9998) and also with the label values (r= 0.9997).

Lipossomas: a bala mágica acertou?

Efficient drug delivery systems are as important as drug themselves. A powerful drug unable to reach the target cell is useless in practice. Ehrlich's Magic Bullet was the first carrier system to be proposed. The evolution in this domain has been quite slow as the natural mechanisms of mammals against foreign products are hard to overcome. However, lipid-based systems (liposomes and related vesicles) have attained reasonable success. The basic preparations and structural features of liposomes and related vesicles as well as their applications are addressed from the chemist's and biochemist's point of view.

Design and production of protein nanostructures for biomolecular detection

Particulate nanostructures are increasingly used for analytical purposes. Such particles are often generated by chemical synthesis from non-renewable raw materials. Generation of uniform nanoscale particles is challenging and particle surfaces must be modified to make the particles biocompatible and water-soluble. Usually nanoparticles are functionalized with binding molecules (e.g., antibodies or their fragments) and a label substance (if needed). Overall, producing nanoparticles for use in bioaffinity assays is a multistep process requiring several manufacturing and purification steps. This study describes a biological method of generating functionalized protein-based nanoparticles with specific binding activity on the particle surface and label activity inside the particles. Traditional chemical bioconjugation of the particle and specific binding molecules is replaced with genetic fusion of the binding molecule gene and particle backbone gene. The entity of the particle shell and binding moieties are synthesized from generic raw materials by bacteria, and fermentation is combined with a simple purification method based on inclusion bodies. The label activity is introduced during the purification. The process results in particles that are ready-to-use as reagents in bioaffinity. Apoferritin was used as particle body and the system was demonstrated using three different binding moieties: a small protein, a peptide and a single chain Fv antibody fragment that represents a complex protein including disulfide bridge.If needed, Eu3+ was used as label substance. The results showed that production system resulted in pure protein preparations, and the particles were of homogeneous size when visualized with transmission electron microscopy. Passively introduced label was stably associated with the particles, and binding molecules genetically fused to the particle specifically bound target molecules. Functionality of the particles in bioaffinity assays were successfully demonstrated with two types of assays; as labels and in particle-enhanced agglutination assay. This biological production procedure features many advantages that make the process especially suited for applications that have frequent and recurring requirements for homogeneous functional particles. The production process of ready, functional and watersoluble particles follows principles of “green chemistry”, is upscalable, fast and cost-effective.

Síntese do isobutileno e seu emprego em reações de esterificação: propostas de aulas práticas de química orgânica para a graduação

An experiment for the synthesis of isobutylene from tert-butanol dehydratation using oxalic acid as catalyst, followed by preparations of tert-butyl benzoate and tert-butyl cinnamate is described. The synthesis are simple, requiring two periods of 4 hours and are suitable for undergraduate organic chemistry experimental courses.

Antimoniais empregados no tratamento da leishmaniose: estado da arte

Antimony preparations are the drugs of choice for the treatment of leishmaniasis over 90 years, a disease that currently affects 12 million people worldwide. Its introduction was based on 19th century concepts of therapeutic effects of metal salts as arsenicals and other metals, most of them abandoned due to toxic effects or better drugs. In the last three decades, there was a great improvement in the knowledge of cell biology and immunology of those infections, but chemotherapy has not been improved in the same strength. The structure and mechanism of action of the two pentavalent antimonial drugs of choice, meglumine antimoniate and sodium stibogluconate, are not well known and the contamination of those pharmaceutical by toxic contaminants have been verified.

Extração de esteróides em frutos de Ottonia martiana Miq., Piperaceae, com gás liqüefeito

A new extraction method for sterols was tested in fruits of Ottonia martiana Miq., a shrub belonging to the family Piperaceae, popularly known as "anestésica" due to the use of its roots and aerial parts, in alcoholic preparations, in treatment of odontological problems. For this purpose, a portable extraction equipment was developed, to operate with liquified gases, which showed to be practical, fast and effective, besides being economical and ecological. In the chromatographic analysis of the extracts obtained in this equipment, it was demonstrated the presence of two sterols, isomers of b-sitosterol and stigmasterol.

Validação de metodologia analítica para doseamento de soluções de lapachol por CLAE

Lapachol is a naphthoquinone found in several species of the Bignoniaceae family possessing mainly anticancer activity. The present work consists of the development and validation of analytical methodology for lapachol and its preparations. The results here obtained show that lapachol has a low quantification limit, that the analytical methodology is accurate, reproducible, robust and linear over the concentration range 0.5-100 µg/mL of lapachol.

Stability-indicating methods for quantitative determination of zidovudine and stavudine in capsules

Zidovudine (AZT) and stavudine (D4T) are nucleoside reverse transcriptase inhibitors extensively used in human immunodeficiency virus (HIV) infected patients. In order to evaluate the quality of these drugs, two stability indicating HPLC methods were developed. The validated methods were applied in quantitative determination of AZT, D4T and their induced degradation products in capsule preparations. The stability studies were conducted at controlled temperature and relative humidity conditions based on the International Conference on Harmonization stability studies protocol for Zone IV areas. Easy sample preparation and low-cost make these methods especially useful for quality control and stability studies of AZT and D4T in drug products.

Determinação turbidimétrica de metilbrometo de homatropina em formulações farmacêuticas empregando um sistema de análise por injeção em fluxo

A flow injection turbidimetric procedure exploiting merging zones is proposed for determining homatropine methylbromide (HMB) in pharmaceutical preparations. The determination is based on the precipitation reaction of homatropine methylbromide with AgNO3 solution to form a precipitate, which was measured at 410 nm. The analytical curve was linear in the HMB concentration range from 8.0x10-4 to 1.7x10-3 mol L-1, with a detection limit of 9.5x10-5 mol L-1. The recoveries ranged from 94.9 to 104 %, the sampling frequency was 75 h-1 and relative standard deviations were smaller than 2.0 % for solutions containing 1.2x10-3 and 1.5x10-3 mol L-1 HMB (n=10). The results obtained for commercial formulations using the FIA procedure were in good agreement with those obtained by using a comparative method (r= 0.9983).

Analytical methods for vancomycin determination in biological fluids and in pharmaceuticals

Vancomycin is a glycopeptide antibiotic employed in the treatment of infections caused by certain methicillin-resistant staphylococci. It is indicated also for patients allergic to penicillin or when there is no response to penicillins or cephalosporins. The adequate vancomycin concentration levels in blood serum lies between 5 and 10 mg/L. Higher values are toxic, causing mainly nephrotoxicity and ototoxicity. Various analytical methods are described in the literature: spectrophotometric, immunologic, biologic and chromatographic methods. This paper reviews the main analytical methods for vancomycin determination in biological fluids and in pharmaceutical preparations.

Performance characteristics of bioassay UV-spectrophotometry and high perfomance liquid chromatographic determination of gatifloxacin in tablets

The microbiological bioassay, UV-spectrophotometry and HPLC methods for assaying gatifloxacin in tablets were compared. Validation parameters such as linearity, precision, accuracy, limit of detection and limit of quantitation were determined. Beer's law was obeyed in the ranges 4.0-14.0 μg/mL for HPLC and UV-spectrophotometric method, and 4.0-16.0 μg/mL for bioassay. All methods were reliable within acceptable limits for antibiotic pharmaceutical preparations being accurate, precise and reproducible. The bioassay and HPLC are more specific than UV-spectrophotometric analysis. The application of each method as a routine analysis should be investigated considering cost, simplicity, equipment, solvents, speed, and application to large or small workloads.

Quantitative determination of acetaminophen, phenylephrine and carbinoxamine in tablets by high-performance liquid chromatography

An alternative methodology for analysis of acetaminophen (Ace), phenylephrine (Phe) and carbinoxamine (Car) in tablets by ion-pair reversed phase high performance liquid chromatography was validated. The pharmaceutical preparations were analyzed by using a C18 column (5 μm, 300 mm, 3.9 mm) and mobile phase consisting of 60% methanol and 40% potassium monobasic phosphate aqueous solution (62.46 mmol L-1) added with 1 mL phosphoric acid, 0.50 mL triethylamine and 0.25 g sodium lauryl sulfate. Isocratic analysis was performed under direct UV detection at 220 nm for Phe and Car and at 300 nm for Ace within 5 min.

Determinação espectrofotométrica de hexametilenotetramina (HMT) em medicamentos, utilizando ácido cromotrópico e forno de micro-ondas

This paper proposes a methodology for spectrophotometric determination of hexamethylenetetramine (HMT) by using chromotropic acid in a phosphoric acid media employing a domestic microwave oven as a source of heating. The reddish-purple soluble product is quantitatively formed after 30 s of irradiation and obeys the Beer´s law in the range between 0.1-1.2 mg L-1 HMT (r = 0.99925). The method was applied successfully in commercial pharmaceutical preparations containing dyes in their composition. The results showed that the method proposed is feasible for simplicity, speed, low cost, precision and accuracy when compared with United States Pharmacopeia official method.