Scielo RSS <![CDATA[Journal of the Chilean Chemical Society]]> vol. 55 num. 4 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>CELLULOSE SULFURIC ACID AS A NEW, BIODEGRADABLE AND ENVIRONMENTALLY FRIENDLY BIO-POLYMER FOR SYNTHESIS OF 4,4'-(ARYLMETHYLENE)BIS(3-METHYL-1-PHENYL-1H-PYRAZOL-5-OLS)</b>]]> The one-pot multicomponent synthesis of 4,4'-arylmethylene-bis(3-methyl-1-phenyl-1H-pyrazol-5-ol) was performed effectively by tandem Knoevenagel-Michael reaction of aryl aldehydes and 5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one in the presence of a catalytic amount of cellulose sulfuric acid as an environmentally friendly biopolymer-based solid acid catalyst at reflux conditions. All of obtained compounds were characterized by FT IR, ¹H and 13C NMR. This new methodology is of interest due to minimizing the cost operational hazards and environmental pollution, high yields, short reaction time, cost effective and simple work-up. <![CDATA[<b>REMOVAL OF METAL IONS FROM AQUEOUS SOLUTIONS USING CROSSLINKED POLYETHYLENE -GTMFJ-POLYSTYRENE SULFONIC ACID ADSORBENT PREPARED BY RADIATION GRAFTING</b>]]> Crosslinked polyethylene-graft-polystyrene sulfonic acid (PE-g-PSSA) adsorbent prepared by simultaneous radiation induced grafting of styrene/divinyl benzene (DVB) mixture onto low density polyethylene (PE) film followed by sulfonation was investigated for the adsorption of Co(II), Cu(II), Ni(II), Pb(II) and Ag(I) ions from aqueous solutions on batch process basis. The effects of treatment parameters such as contact time, initial metal ion concentration, pH and temperature of the solution, on the adsorption capacity of the membrane were studied. The adsorption capacity of metal ions were found to be strongly dependent on the initial metal ion concentration and pH of adsorption medium and increased in the order of Ni(II)>Co(II)>Cu(II)>Pb(II)>Ag(I). Langmuir isotherm model was found to be more fitting to the adsorption equilibrium data of all metal ions than Freundlich isotherm model. The adsorption kinetics of all tested metal ions was found to follow the pseudo-first order kinetic model. The membrane showed an interesting stability represented by five repeated adsorption/desorption cycles of heavy metal ions without any significant loss in its adsorption capacity. It can be suggested that crosslinked PE-g-PSSA membrane obtained in this work can be effectively used for the adsorption of heavy metal ions from aqueous solutions and the preference order is Ni(II)> Co(II)>Cu(II)>Pb(II)> Ag(I). <![CDATA[<b>ENANTIOSELECTIVE ADDITION OF DIETHYL ZINC TO BENZALDEHYDE CATALYZED BY TI(IV) AND GLUCOSE DERIVATIVES</b>]]> D-Glucose derivatives 1,2:5,6-di-O-isopropyline-a-D-glucofuranose (1) and 1,2-O-isopropyline-a-D-glucofuranose (2) with Ti(IV) are chiral catalysts in the addition of diethylzinc to benzaldehyde. The Ti(IV)-carbohydrate catalytic system is optimal with excess Ti(IV) and substoichiometric carbohydrate and 2 is the more active chiral catalyst probably because this derivative acts as a bidentate ligand in the proposed reaction. The arrangement of OH groups is crucial in determining the configuration of the alcohol product. <![CDATA[<b>LIQUID - LIQUID EXTRACTION OF CERIUM(IV) FROM SALICYLATE MEDIA USING N-7V-OCTYLANILINE IN XYLENE AS AN EXTRACTANT</b>]]> Extraction behaviour of Ce(IV) from salicylate medium has been studied with the using N-n-octylaniline in xylene as an extractant. Cerium(IV) was completely recovered from the organic phase using 2.0 M hydrochloric acid and determined spectrophotometrically as complex with Arsenazo III. The influence of equilibrium pH, extractant concentration, stripping agents, equilibration time, nature of diluents, and diverse ions on the extraction of Ce(IV) was investigated. The stoichiometry of the extracted species was determined on the basis of slope analysis. The separation of Ce(IV) was carried out from some associated metals like U(VI), Th(IV), La(III), Y(III), Zr(IV), Nb(V), Gd(III) and Nd(III). The method presented is simple, reproducible, rapid and has been successfully applied for the determination of Ce(IV) in synthetic mixture, semiconductor films and monazite sand. <![CDATA[<b>EFFECTS OF HUMIC AND OXALIC ACID IN WOOD BIODEGRADATION BY <i>Gloeophyllum trabeum</i></b>]]> To degrade wood, brown rot fungi (BRF) have developed a mechanism based on low molar mass iron reducing compounds that promote Fenton reaction. These compounds, also solubilise Fe(III), in conjunction with oxalic acid, making it available for reaction. It have been postulated that the humic acids participates on wood biodegradation by BRF, acting in a similar way that the fungal compounds. In this work this effect and its interaction with oxalic acid were evaluated. The effect of humic acid and oxalic acid on the biodegradation of radiata pine chips by the BRF Gloeophyllum trabeum was evaluated using a two level factorial design. Absence or concentrations of 5 g/L and 0.05 M for humic acid and oxalic acid respectively, were evaluated; temperature (25°C) and initial pH (5.0) were kept constant. The responses were mass loss, holocellulose content and viscosity, measured after 30 days of biodegradation. The effects of the variables were determined using standardized coefficients of the polynomial equation, which were obtained through a multiple linear regression. All experiments were performed in quadruplicate and the obtained model was validated through an ANOVA test with a confidence interval of 95%. Oxalic acid was the factor that has a greater effect on these variables; it was able to extract metals from wood and to inhibit biodegradation when used without further treatment of humic acid. Humic acid impregnation increases the metal content in wood, but did not stimulate the wood biodegradation. <![CDATA[<b>POLYPROPYLENE/CLAY NANOCOMPOSITES</b>: <b>SYNTHESIS AND CHARACTERIZATION</b>]]> Polypropylene nanocomposites were synthesized by using the method of mixing in the molten state. Nanocomposites were obtained in twin-screw co-rotating extruders and the nanocomposites were prepared with percentage of nanoclay (C2) from 5 wt-%, with and without compatibilizer agent (PP-g-MA). The thermal (DSC, TGA), morphology (XRD, TEM), and dynamical mechanical (DMA) properties of the nanocomposites were characterized. All nanocomposites prepared are in intercalated state as corroborated by XRD and TEM. The Tm and Xc were not affected by the presence of clay, PP-g-MA, or processing support. The incorporation of clay and compatibilizer agent increases the thermal stability and heat deflection temperature (HDT). <![CDATA[<b>PREPARATION AND CHARACTERIZATION OF PEROVSKITE OXIDES BY POLYMERIZATION-COMBUSTION</b>]]> This paper describes the preparation of La075Sr0 25Cr02Fe08O3 perovskite oxide, using a polymerization-combustion route, to obtain materials for potential applications like electrodes in solid oxide fuel cells (SOFC). For such purpose, initially the solid precursor was characterized by FT-IR spectroscopy and thermal analysis (TGA-DTA), showing the obtention of polymeric citrate precursors. The thermal analysis (TGA-DTA), X-ray diffraction (XRD) and scanning electronic microscopy (SEM), provides information about the formation of a perovskite phase, while the texture, relief and roughness found are characteristic of the method of synthesis used. The size of crystallites, calculated using the Scherrer calculator software and transmission electron microscopy (TEM), confirmed the presence of nanometric crystallites (< 41.0 nm), whereas the chemical composition and crystallographic structure, indicating a high correlation with respect to proposed system, which was confirmed by X-ray fluorescence (XRF), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). Finally the electrical characterization by impedance spectroscopy (IS), determined the capacitance and resistance of the system in order to provide information related to the concentration of charge carriers and the diffusion rate of ions in the material a high conductivity values, related to semiconductor behavior for potential applications. <![CDATA[<b>STRESS DEGRADATION STUDIES OF RAMIPRIL BY A VALIDATED STABILITY-INDICATING LIQUID CHROMATOGRAPHIC METHOD</b>]]> Ramipril is an angiotensin-converting enzyme inhibitor which has chemical structure susceptible to degradation, therefore in this work forced degradation studies of ramipril were carried out by a developed and validated stability-indicating liquid chromatographic method. Stress testing was performed on drug substance under hydrolysis (0.1 N HCl, water and 0.1 N NaOH), oxidation (3% H2O2), heat (70°C) and photolysis (UV and VIS radiation). The drug was degraded under acidic, neutral, alkaline, oxidation and thermal stress conditions but it was stable under photolysis. Chromatographic separation of ramipril from its degradation products was achieved on a RP-18 column, using a mobile phase consisting of methanol - tetrahydrofuran - phosphate buffer (pH 2.4; 0.01M) (55:5:40, v/v/v) at a flow rate of 1.0 mL min-1 and UV detection at 215 nm. The assay was linear for ramipril concentrations of 50-300 ug/mL. The developed method was stability indicating, specific, accurate and precise for ramipril determination. This method was used to quantify ramipril in tablets. The results showed that the method described here is suitable for quantitative determination and the stability study of ramipril. <![CDATA[<strong>DEVELOPMENT AND VALIDATION OF A GC-NPD/micro-ECD METHOD USING DUAL COLUMN FOR THE DETERMINATION OF BENZODIAZEPINE IN HUMAN WHOLE BLOOD AND PLASMA</strong>]]> Four benzodiazepines flunitrazepam, nitrazepam, clonazepam, and alprazolam, have been analyzed from biological matrices by dual column gas chromatography using a nitrogen-phosphorus detector (NPD) and a micro-electron capture detector (m-ECD). The recoveries of the four benzodiazepines spiked into human whole blood and plasma were 88.8 - 97.9 and 90.7 - 97.5%, respectively. The regression equations for the four benzodiazepines showed excellent linearity. The detection limits (LODs) were 0.14 - 0.95 ng/mL for whole blood and 0.13 - 0.93 ng/mL for plasma. The method is simple and sensitive for the determination of benzodiazepines in human whole blood and plasma, and may be useful in forensic science practice. <![CDATA[<b>REACTION OF ALKYL GALLATES WITH DIPHENYL PICRYLHYDRACYL RADICALS IN SDS MICELLES</b>]]> Diphenylpicrylhydracyl is a stable free radical that readily reacts with phenol groups. In the present work we have measured the reaction of DPPH with three alkyl gallates of different hydrophobicity: methyl gallate, propyl gallate, and octyl gallate. Experiments were carried out in acetate buffer (pH 5.0) in presence of several SDS concentrations. At surfactant concentrations higher than 20 mM, the gallates are almost totally associated to the micellar pseudophase. Under these conditions the rate of the reaction becomes almost independent of the length of the alkyl group. This indicates that the average localization of the gallate reactive group is almost independent of the solute hydrophobicity. <![CDATA[<b>DEVELOPMENT AND VALIDATION OF LIQUID CHROMATOGRAPHIC METHOD FOR THE SIMULTANEOUS ESTIMATION OF EZETIMIBE AND LOVASTATIN IN HUMAN PLASMA</b>]]> In the present study conditions were optimized for the development and validation of a simple, sensitive and isocratic reverse phase high performance liquid chromatographic method for the simultaneous determination of ezetimibe and lovastatin in human plasma using gemfibrozil as internal standard. After a single step extraction with acetonitrile, satisfactory elution of both the analytes along with internal standard was achieved on a Merck C-18 column using a mixture of 0.1 M ammonium acetate pH 5.0 and acetonitrile in the ratio of (28:72, v/v) at a flow rate of 1.5 ml/min. The detection was carried out at a wavelength of 240 nm using a photodiode array detector. The method was linear in the concentration range of 0.2-25 |xg/ml for ezetimibe and 0.4-50 |xg/ml for lovastatin. The extraction recovery of analytes was greater than 85 % and within day and between day precision was also satisfactory. The method was validated by performing its linearity, recovery, precision, LOD/LOQ values and stability of solutions. The total eluting time for the analysis is less than twelve minutes. As the plasma peaks did not interfere with the peaks of analytes so the method can be used for the determination of ezetimibe and lovastatin in human plasma and may possibly be for the pharmacokinetic study. <![CDATA[<b>EFFECT OF LIQUID SPATIAL VELOCITY ON M<sub>D</sub> [M<sub>D</sub> = Mn, Fe, Co, Ni, Cu AND Zn]//Mo SYNERGISM IN THE HYDRODESULPHURIZATION REACTION</b>]]> A study is made of Mn//Mo, Fe//Mo, Co//Mo, Ni//Mo, Cu//Mo or Zn//Mo stacked beds systems, separated by g-Al2O3, in the gas-oil hydrodesulphurization reaction, under experimental conditions similar to those industry. The synergism between these beds is clearly detected, and occurs in the absence of mixed phases. The results show that the promotion effect of the pairs in stacked beds, caused by the spillover hydrogen increases when the liquid spatial velocity decreases. <![CDATA[<b>CYANIDE DETERMINATION WITH A MODIFIED NINHYDRIN REAGENT USING N-ACETYL CYSTEINE IN THE PRESENCE OF HEAVY METAL IONS</b>]]> Sensitive and selective, but fast and simple assays of cyanide ion in waste and natural waters, as well as in biological samples are required in case of accidental pollution with such species. Cyanide reaction with ninhydrin has been recommended for instant detection of small traces of cyanide (detection limit 1.5 ng ml-1). However, the oxidizers and heavy metal ions, such as Hg, Cu, Ag may interfere with the determinations. Therefore, we report here cyanide determination with ninhydrin and its usage in monitoring polluted water with heavy metals. The effect of heavy metals and SH-compounds were studied in order to increase the method range of use. N-acetyl cysteine proved to be a selective reagent for protection of cyanide detection and determination against the interference of heavy metal ions. <![CDATA[<b>SURFACE-ENHANCED RAMAN SCATTERING</b>: <b>METAL NANOSTRUCTURES COATED WITH LANGMUIR-BLODGETT FILMS</b>]]> This review deals with surface-enhancved Raman scattering (SERS) employing Langmuir-Blodgett (LB) films, which serve as model systems for developing theoretical and experimental studies to elucidate the SERS effect. In addition, LB films have be used as integral parts of molecular architectures for SERS-active substrates. On the other hand, SERS and surface-enhaced resonant Raman scattering (SERRS) have allowed various properties of LB films to be investigated, especially those associated with molecular-level interactions. In the paper, emphasis is placed on single molecule detection (SMD), where the target molecule is diluted on an LB matrix of spectral silent material (low Raman cross section). The perspectives and challenges for combining SERS and LB films are also discussed. <![CDATA[<b>SYNTHESIS, CHARACTERIZATION AND PRELIMINARY CATALYTIC PROPERTIES OF NEW COPPER (I)</b> <b>COMPLEXE [Cu (pyrazolyl)<sub>2</sub>]X TYPE</b>]]> The preparation of tetracoordinated copper (I) complexes with the pyrazolyl heterocyclic nitrogen ligand is reported. The new complexes of [Cu(pyrazolyl)2] X type with X = chloride, bromine, and iodine were characterized by spectroscopic and electrochemical techniques. The results obtained show that the heterocyclic nitrogen ligand is bonded in a bidentate fashion to form monometallic complexes. Exploratory homogeneous catalysis experiments of the water-gas shift reaction (WGSR) have been accomplished by the use of copper complexes in 80 % aqueous 4-picoline solutions. For such systems, formation of H2 y CO2 was observed in the initial gas samples. <![CDATA[<b>SYNTHESIS, CHARACTERIZATION AND ANTIBACTERIAL EVALUATION OF FEW 2, 3-SUBSTITUTED QUINOXALINES</b>]]> The quinoxaline derivatives (i-v) were synthesized through cyclization-oxidation of a- bromo carbonyl compounds with o-phenyl diamines (7a and 10a) and further coupling at 6-position via Suzuki reaction using PdCl2 (dppf).DCM, ter. BuNH2, Na2CO3 in IPA, H2O refluxed for 16 h. As the results of antibacterial screening tests done by paper disc method, quinoxaline derivatives (i) and (v) revealed significant inhibition zone on Bacillus spericus and quinoxaline derivatives (iii) and (v) on Escherichia coli cultures. <![CDATA[<b>A PRELIMINARY STUDY OF THE DISTRIBUTION AND MOBILITY OF MERCURY IN WATER AND SEDIMENTS FROM THE SAN JUAN RIVER WATERSHED, NUEVO LEON MEXICO</b>]]> Monitoring of distribution and fractionation of mercury (Hg) from within the San Juan River Basin that provides water for the Metropolitan Area of Monterrey, Mexico (MAM), was performed. The purpose of this work was to characterize the risk of Hg exposure to human populations that reside in communities nearby the area. Total Hg was quantified from water and surface sediments (0-10 cm) collected from 11 locations during the summer season of 2006. The analysis of Hg was carried out by Cold Vapor Atomic Absorption Spectroscopy (CVAAS). Simultaneously, some relevant physical and chemical parameters were analyzed in water samples and correlated to Hg concentrations to trace the fate of Hg in the watershed. In the river water samples, Hg levels were in the range from 0.17 to 1.14 |ig/L. The mean concentration level of Hg in sediment samples was 0.405±0.074 mg/Kg and showed a uniform Hg distribution along the San Juan River Basin, conversely, the fractionation studies showed that chemical speciation plays an important role in stability and low mobility. <![CDATA[<b>PREPARATION OF NEW OPTICALLY ACTIVE AND THERMALLY STABLE POLY(AMIDE-IMIDE) CONTAINING BICYCLO SEGMENT AND ETHER GROUP IN THE MAIN CHAIN BY DIRECT POLYCONDENSATION IN TWO DIFFERENT MEDIA</b>]]> A new series of optically active and thermally stable poly(amide-imide)s (PAIs) with good inherent viscosities based on bicyclo diacids and etheric diamine in the main chain were synthesized from the direct polycondensation reaction of AW'-(bicyclo[2,2,2]oct-7-ene-tetracarboxylic)-bis-L-amino acids 3a-g with 1,2-Bis[4-aminophenoxy]ethane 7 by direct polycondensatios with two different media such as direct polycondensation in a medium consisting of N-methyl-2-pyrrolidone (NMP)/triphenyl phosphite (TPP)/calcium chloride (CaCl2)/pyridine (Py) and direct polycondensation in a tosyl chloride (TsCl)/pyridine (Py)/N,N-dimethylformamide (DMF) system. Also 3a-g were synthesized by the condensation reaction of bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride 1 with two equimolars of various amino acids such as L-alanine 2a, L-valine 2b, L-leucine 2c, L-isoleucine 2d, L-phenylalanine 2e, L-2-aminobutyric acid 2f and L-histidine 2g in an acetic acid solution. The polymerization reactions produced a series of thermally stable and optically active organosoluble PAIs. The resulting polymers were fully characterized by means of FT-IR and ¹H-NMR spectroscopy, elemental analyses, inherent viscosity, specific rotation, solubility tests and differential scanning calorimeter (DSC). Also thermal properties of the PAIs 8a-g were investigated using thermal gravimetric analysis (TGA) and derivative of thermaogravimetric (DTG) analysis. <![CDATA[<b>STUDIES ON GRAFT COPOLYMERIZATION OF 2-HYDROXYETHYLMETHACRYLATE ONTO KAPPA-CARRAGEENAN INITIATED BY CERIC AMMONIUM NITRATE</b>]]> The polysaccharide, kappa-carrageenan (kC), has been chemically modified by graft copolymerization of 2-hydroxyethylmethacrylate (HEMA) in an aqueous medium using ceric ammonium nitrate (CAN) as an initiator under argon atmosphere. A plausible reaction mechanism of grafting has been suggested. Evidence of grafting was obtained by comparison of FTIR spectra of kC and homopolymer-free kC-g-poly(HEMA) as well as solubility characteristics and gravimetric analysis of the products. The optimum reaction conditions affording maximum grafting ratio and add-on value have been determined. The grafting parameters have been found to increase with increasing in kC, CAN, and HEMA concentrations as well as polymerization time and temperature, up to a certain value, but these parameters decrease on further increasing in reaction conditions. <![CDATA[<b>THEORETICAL STUDY OF THE S<sup>2</sup>-P INTERACTION BETWEEN TL(I) AND OLEFINIC SYSTEMS ON HYPOTHETICAL [TL(c<sub>2</sub>H<sub>4</sub>)<sub>2</sub>]+ And [TL(c<sub>2</sub>H<sub>2</sub>)<sub>n</sub>]+ (N = 2,3) COMPLEXES</b>]]> The attraction between [C2HJ2 and [C2HJ23 and Tl(I) in the hypothetical [Tl(C2H4)2]+ and [Tl(C2H2)n]+ (n = 2,3) complexes was studied using ab initio methods. It was found that the changes around the equilibrium C-Tl distance and in the interaction energies are sensitive to the electron correlation potential. We evaluated these effects using several levels of theory, including HF, MP2, MP4 and CCSD(T). The equilibrium C-Tl distances in the complexes are in the range of 294 pm to 338 pm. The interaction energy differences obtained at the equilibrium distance range from 55 to 110 kJ/mol at the different levels used. These results indicate that the complexes formed are in the category of van der Waals systems. Also, these results indicated that the interaction between olefinic systems and Tl(I) are a real minimum on the potential energy surfaces. <![CDATA[<b>CONVERSION OF METHANOL TO FORMALDEHYDE ON TiO<sub>2</sub> SUPPORTED Ag NANOPARTICLES</b>]]> TiO2 supported Ag nanoparticles with metal loading ranging from 2.0 to 12.0 wt.% have been prepared by reduction of a silver precursor with formic acid under mild conditions. XPS showed that silver remains in a reduced state and TEM has demonstrated that the procedure was effective to produce silver nanoparticles. Only small changes in the metal particle size from 2.0-3.4 nm occurs when the Ag content increases from 2.0 to 12.0 wt.%. O2 TPD has revealed the presence of different types of adsorbed oxygen species being the one assigned to the active specie called Ob which one displayed the highest proportion in the catalysts with higher metal loading. Catalytic activity in the conversion of methanol to formaldehyde showed that those samples with metal loading higher than 7.0 wt% displays higher yields compared to the unsupported silver catalyst. <![CDATA[<b>SYNTHESIS AND SPECTRAL ANALYSIS OF AN ARRAY OF NOVEL 4-(4-MORPHOLINOPHENYL)-6-ARYL-PYRIMIDIN-2-AMINES</b>]]> An array of newly synthesized novel 4-(4-morpholinophenyl)-6-arylpyrimidin-2-amines (20-28) are synthesized from the respective (E)-1-4-morpholinophenyl)-3-aryl-prop-2-en-1-ones (11-19) by the treatment of guanidine nitrate in refluxing ethanol catalyzed by lithium hydroxide and characterized by melting point, elemental analysis, MS, FT-IR, one-dimensional NMR (¹H & 13C) spectroscopic data. <![CDATA[<b>SIMULTANEOUS DETERMINATION OF PHENYLEPHRINE HYDROCHLORIDE AND TROPICAMIDE IN OPHTHALMIC DOSAGE FORM WITH THREE RAPID DERIVATIVE SPECTROPHOTOMETRIC METHODS</b>]]> Three spectrophotometric methods have been developed for simultaneous estimation of Phenylephrine hydrochloride (PHE) and Tropicamide (TPC) in their combined dosage form. Method-I: zero-crossing derivative spectrophotometry involves amplitudes measurement of the first derivative spectra of the binary mixture at 284.0nm for PHE and 241.2nm for TPC. Method-II: dual wavelength,which uses the difference in absorbance at 260.8 nm and 268.2 nm for estimation of PHE and 245.4nm and 271.8nm for TPC. Method III: Ratio spectra derivative spectrophotometry, in which division of the absorption spectrum of the binary mixture by a standard spectrum of one of the components and then calculating first derivative amplitudes at 270.8nm for PHE and 240.8nm for TPC . The calibration graph follows Beer's law in the range of 25-125 mg/ml for PHE and 4-20 mg/ml for TPC for all the three methods. The accuracy and precision of the methods were validated statistically. <![CDATA[<b>STRUCTURAL STUDY OF A NEW 1-(2-THIENYL)-3-(3-METHYL-2-THIENYL)-PROPENONE, IN SITU RADIATION-INDUCED DIMERIZATION PRODUCTS</b>]]> The new conjugated system ("chalcone kind") reported herein, 1-(2-thienyl)-3-(3-methyl-2-thienyl)-propenone, C12H10OS2 presents a monomeric molecular structure, and it most interesting aspects are to be found in it intermolecular interactions, of varied type (C-H-O, C-H---7C, n-n) and strength. Some anomalies detected in the refinement process, however, provided evidence that an unexpected in-situ, radiation-induced dimerization reaction had taken place during data collection, with the starting and final products coexisting in a topotactic fashion. This effect is depended of structural packing; that is not all this kind of conjugated system presents this effect. The main factor is the distance between the double bonds of neighboring monomers (about 3 A). <![CDATA[<b>UTILIZATION OF ACRYLAMIDE AND NATURAL POLYSACCHARIDE BASED POLYMERIC NETWORKS IN PH CONTROLLED RELEASE OF 5-AMINO SALICYLIC ACID</b>]]> In this paper, psyllium (Psy) and acrylamide (AAm) based superabsorbent, synthesized using potassium persulphate (KPS) as an initiator and hexamethylene tetramine (HTMA) as a crosslinker, has been investigated for its swelling behaviour in distilled water as a function of time, temperature and pH. The hydrogel has further been applied for controlled delivery of 5-amino salicylic acid (5-ASA) under different pH conditions at 37 oc. It has been found to show Fickian type mechanism as the drug release showed diffusion coefficient less than 0.50 for all the pH conditions.The gel characteristic constant has been found to show 6.9 x 10², 20.61 X 10² and 33.4 x 10² values for pH 4.0, 7.0 and 9.2, respectively. The initial diffusion coefficient has been found to show greater values than late diffusion coefficient confirming greater release at the early stages of the drug release than that in the late stages. <![CDATA[<b>Erratum</b>]]> In this paper, psyllium (Psy) and acrylamide (AAm) based superabsorbent, synthesized using potassium persulphate (KPS) as an initiator and hexamethylene tetramine (HTMA) as a crosslinker, has been investigated for its swelling behaviour in distilled water as a function of time, temperature and pH. The hydrogel has further been applied for controlled delivery of 5-amino salicylic acid (5-ASA) under different pH conditions at 37 oc. It has been found to show Fickian type mechanism as the drug release showed diffusion coefficient less than 0.50 for all the pH conditions.The gel characteristic constant has been found to show 6.9 x 10², 20.61 X 10² and 33.4 x 10² values for pH 4.0, 7.0 and 9.2, respectively. The initial diffusion coefficient has been found to show greater values than late diffusion coefficient confirming greater release at the early stages of the drug release than that in the late stages.