One homogeneous catalysis limitation is catalyst reuse. Thus two-phase systems are an alternative... more One homogeneous catalysis limitation is catalyst reuse. Thus two-phase systems are an alternative to this problem. There is great interest in using water-soluble complexes in biphasic catalysis [13]. In our laboratory we have prepared the water-soluble RuCl(g5-C5H5)(TPPMS)2 [4] ...
Page 1. Electrochemical Behaviour of 5 nm Undoped Diamond Nanoparticles Katherine B. Holt*, Daren... more Page 1. Electrochemical Behaviour of 5 nm Undoped Diamond Nanoparticles Katherine B. Holt*, Daren J. Caruana, Christoph Ziegler, Jianbing Zang, Enrique Millan-Barrios Department of Chemistry, University College London, 20, Gordon St., London WC1H 0AJ, UK ...
Swelling studies of an acrylamide/maleic acid/methylene-bis-acrylamidebased hydrogel prepared by ... more Swelling studies of an acrylamide/maleic acid/methylene-bis-acrylamidebased hydrogel prepared by free radical polymerization (weight ratio of 90/10/3) are presented. Water penetration mechanism was studied by using two classical definitions, i.e., Crank (F C = w t /w eq ) and Karadag (F K = (w t -w o )/w o ), of the water fraction into the hydrogel (F). An anomalous water penetration mechanism (0.5<n<1.0) was obtained by employing both definitions and Buckley equation (F = kt n ); however, using the combined Peppas and Sahlin equation (F = k 1 t 1/2 + k 2 t) pointing out that swelling occurs in two stages: at first controlled by diffusion and relaxation contributions and then defined mainly by the diffusion contribution. Hydrogel was also studied as a system for the adsorption of cationic dye Safranin. Results show that this system perfectly fit to a Langmuir isotherm and the dye adsorption process stops when coverage of all active sites on the hydrogel has been achieved. Interestingly, adsorption process does not seem to be affected even though the hydrogel concurrently suffers the well known collapse phenomenon.
The present review is focused on the diverse approaches employing chitin and/or chitosan as eithe... more The present review is focused on the diverse approaches employing chitin and/or chitosan as either active or passive components which have been employed to pesticide control in environmental protection and water purification. In some cases, ideas are presented in order to contribute to the solution of particular problems associated with this topic. The first section is dedicated to introduce the most important basic elements in the work as for example classification of the pesticides (according to their toxicological effects, chemical similarities and type of plague to control), description of the chitin and chitosan and some general applications of these biomaterials on removal of pollutants. Second section briefly analyzes some strategies employed in order to minimize the effects of the indiscriminate application of pesticide, through previous actions, as controlled release and protected dosing system. Third part is dedicated to discuss the diverse action modes which chitin or chi...
Electroanalytical studies on a polyaniline modified glassy carbon electrode is reported. Kegging ... more Electroanalytical studies on a polyaniline modified glassy carbon electrode is reported. Kegging type heteropolyanion (H6[PMo9V3O40]) was incorporated into the polymeric matrix by applying a potential pulse program, An uniform, adhered and electroactive film was obtained by electropolymerisation of 1.5 x10-3 M aniline in 0.5 M sulfuric acid. AA oxidation was studied on the modified glassy electrode and a 3 to 30 mM linear response was obtained for AA determination by differential pulse voltammetry technique, detection limit of 2.4 mM and quantification limit of 8 mM was achieved by using the modified electrode. These results allow us to propose the use of this modified electrode in the determination of drug level AA.
SYNTHESIS OF POLYESTER-URETHANE BASED ON METILENBIS-4-PHENYLISOCIANATE AND 1,4-CICLOHEXANEDIOL AB... more SYNTHESIS OF POLYESTER-URETHANE BASED ON METILENBIS-4-PHENYLISOCIANATE AND 1,4-CICLOHEXANEDIOL ABSTRACT: . This synthesis of polyester-diol was carried out aiming to prepare polyester-urethane. The polyesters are based on 1,4- cyclohexanediol and the acids: adipic, succinic, ftalic and isoftalic. Bulk polyesterification was used to prepare each polyester using 0.0903 mol of 1,4-cyclohexanediol and 0.0861 mol of acid. The synthesis of the polyester-uretane was
... Polymer Bu I leti n 0 Springer-Verlag 2002 New results on the polymerisation of the itaconic ... more ... Polymer Bu I leti n 0 Springer-Verlag 2002 New results on the polymerisation of the itaconic acid in aqueous medium Cristobal Lhrez V (m), Freddy Canelon, Enrique Millhn, G. Perdomo and Issa Katime&#x27;*&#x27; ... 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. Marvel C, Shepherd T (1959) J. Org. ...
An electrochemical study of ascorbic acid (AA) determination on a modified glassy carbón (GC) ele... more An electrochemical study of ascorbic acid (AA) determination on a modified glassy carbón (GC) electrode is reported. GC has been modified by using polyaniline (PANI) and H4PMo11VO40 (HPA). PANI was deposited on GV by repetitive cycling (60 scans) at -0.2 to 0.8V vs Ag/AgCl of a 50 mM aniline solution by employing 0.1M sulfuric acid as electrolyte solution. HPA was incorporated to the polymeric matrix by using a potential program. Scanning electron microscopy showed a porous and uniform morphology for PANI and PANI/PDA films, although PANI/PDA film showed a compacted structure.Differential pulse voltammetry (DPV) was used to quantify AA on a sulfate pH 2.04 buffer solution. We have found higher stability and better definition of the AA oxidation wave. Analytical analysis of the simple calibration curve for AA on the modified electrodes showed better response for the PANI electrode rather than PANI/PDA electrode. Analysis of AA on the PANI modify electrode showed a linear response at ...
Enzymatic depolymerization of chitosan (acetylation degree and average viscosimetric molecular we... more Enzymatic depolymerization of chitosan (acetylation degree and average viscosimetric molecular weight (M ) of 0,85 and 310 kDa, respectively) was studied using commercial bromelain. Decrease of the average viscosimetric polymerization degree (X ) was followed in a buffer solution of acetic acid (0,3 M)/sodium acetate (0,2 M) at 25 ºC. Under these experimental conditions it is possible to relate the instantaneous intrinsic viscosity [η ] with M through the Mark-Houwink-Sakurada equation. Equations of Sano, which allow to compute values of intrinsic viscosity with a single measurement of relative and/or specific viscosity, was employed to obtain instantaneous values of [η ], which were also obtained for comparative purpose through an iterative process using Huggins equation. Initial velocity of depolymerization (v ) was obtained from different concentration of chitosan solutions and a fixed bromelain concentration. Michaelis-Menten constant (k ) and maximum velocity (V ) Mm were obtai...
Summary Polycomplexes of poly(itaconic acid) have been synthesized in the presence of small amo... more Summary Polycomplexes of poly(itaconic acid) have been synthesized in the presence of small amounts of chitosan (eq. NH2/eq. COOH between 0 and 1.31%). We have studied the effect on the yield and polydispersity of the final materials when increasing quantities of chitosan are employed. Under the reported experimental conditions, we have found that chitosan is quantitatively incorporated into the new
Swelling studies of an acrylamide/maleic acid/methylene-bis-acrylamidebased hydrogel prepared by ... more Swelling studies of an acrylamide/maleic acid/methylene-bis-acrylamidebased hydrogel prepared by free radical polymerization (weight ratio of 90/10/3) are presented. Water penetration mechanism was studied by using two classical definitions, i.e., Crank (F C = w t /w eq ) and Karadag (F K = (w t -w o )/w o ), of the water fraction into the hydrogel (F). An anomalous water penetration mechanism (0.5<n<1.0) was obtained by employing both definitions and Buckley equation (F = kt n ); however, using the combined Peppas and Sahlin equation (F = k 1 t 1/2 + k 2 t) pointing out that swelling occurs in two stages: at first controlled by diffusion and relaxation contributions and then defined mainly by the diffusion contribution. Hydrogel was also studied as a system for the adsorption of cationic dye Safranin. Results show that this system perfectly fit to a Langmuir isotherm and the dye adsorption process stops when coverage of all active sites on the hydrogel has been achieved. Interestingly, adsorption process does not seem to be affected even though the hydrogel concurrently suffers the well known collapse phenomenon.
Two salts of the biopolymer chitosan were prepared in aqueous medium by employing an excess of HC... more Two salts of the biopolymer chitosan were prepared in aqueous medium by employing an excess of HCl or HNO 3 in order to ensure neutralization of all NH 2 -chitosan groups. Chitosan salts were extensively dialyzed in dionised water and dried at 40 ºC until film formation. The films were characterized by thermogravimetry, FTIR and conductimetric tritration. QH + Cl − and QH + NO 3 − salts were viscosimetrically evaluated in free acid aqueous solutions in the presence of NaCl to control ionic strength of the medium. Unexpected high intrinsic viscosity values were obtained at low ionic strength when QH + NO 3 − salt were evaluated.
Conductimetric studies of chitosan in aqueous medium Cristóbal Lárez Velásquez1 ( ), Joel Sánchez... more Conductimetric studies of chitosan in aqueous medium Cristóbal Lárez Velásquez1 ( ), Joel Sánchez Albornoz1, Jorge Uzcátegui Nava2, Enrique Millán Barrios3, Hanzel Lárez Velásquez4 ... Venezuela 4Núcleo Universitario Rafael Rangel, Departamento de Matemáticas. ...
One homogeneous catalysis limitation is catalyst reuse. Thus two-phase systems are an alternative... more One homogeneous catalysis limitation is catalyst reuse. Thus two-phase systems are an alternative to this problem. There is great interest in using water-soluble complexes in biphasic catalysis [13]. In our laboratory we have prepared the water-soluble RuCl(g5-C5H5)(TPPMS)2 [4] ...
Page 1. Electrochemical Behaviour of 5 nm Undoped Diamond Nanoparticles Katherine B. Holt*, Daren... more Page 1. Electrochemical Behaviour of 5 nm Undoped Diamond Nanoparticles Katherine B. Holt*, Daren J. Caruana, Christoph Ziegler, Jianbing Zang, Enrique Millan-Barrios Department of Chemistry, University College London, 20, Gordon St., London WC1H 0AJ, UK ...
Swelling studies of an acrylamide/maleic acid/methylene-bis-acrylamidebased hydrogel prepared by ... more Swelling studies of an acrylamide/maleic acid/methylene-bis-acrylamidebased hydrogel prepared by free radical polymerization (weight ratio of 90/10/3) are presented. Water penetration mechanism was studied by using two classical definitions, i.e., Crank (F C = w t /w eq ) and Karadag (F K = (w t -w o )/w o ), of the water fraction into the hydrogel (F). An anomalous water penetration mechanism (0.5<n<1.0) was obtained by employing both definitions and Buckley equation (F = kt n ); however, using the combined Peppas and Sahlin equation (F = k 1 t 1/2 + k 2 t) pointing out that swelling occurs in two stages: at first controlled by diffusion and relaxation contributions and then defined mainly by the diffusion contribution. Hydrogel was also studied as a system for the adsorption of cationic dye Safranin. Results show that this system perfectly fit to a Langmuir isotherm and the dye adsorption process stops when coverage of all active sites on the hydrogel has been achieved. Interestingly, adsorption process does not seem to be affected even though the hydrogel concurrently suffers the well known collapse phenomenon.
The present review is focused on the diverse approaches employing chitin and/or chitosan as eithe... more The present review is focused on the diverse approaches employing chitin and/or chitosan as either active or passive components which have been employed to pesticide control in environmental protection and water purification. In some cases, ideas are presented in order to contribute to the solution of particular problems associated with this topic. The first section is dedicated to introduce the most important basic elements in the work as for example classification of the pesticides (according to their toxicological effects, chemical similarities and type of plague to control), description of the chitin and chitosan and some general applications of these biomaterials on removal of pollutants. Second section briefly analyzes some strategies employed in order to minimize the effects of the indiscriminate application of pesticide, through previous actions, as controlled release and protected dosing system. Third part is dedicated to discuss the diverse action modes which chitin or chi...
Electroanalytical studies on a polyaniline modified glassy carbon electrode is reported. Kegging ... more Electroanalytical studies on a polyaniline modified glassy carbon electrode is reported. Kegging type heteropolyanion (H6[PMo9V3O40]) was incorporated into the polymeric matrix by applying a potential pulse program, An uniform, adhered and electroactive film was obtained by electropolymerisation of 1.5 x10-3 M aniline in 0.5 M sulfuric acid. AA oxidation was studied on the modified glassy electrode and a 3 to 30 mM linear response was obtained for AA determination by differential pulse voltammetry technique, detection limit of 2.4 mM and quantification limit of 8 mM was achieved by using the modified electrode. These results allow us to propose the use of this modified electrode in the determination of drug level AA.
SYNTHESIS OF POLYESTER-URETHANE BASED ON METILENBIS-4-PHENYLISOCIANATE AND 1,4-CICLOHEXANEDIOL AB... more SYNTHESIS OF POLYESTER-URETHANE BASED ON METILENBIS-4-PHENYLISOCIANATE AND 1,4-CICLOHEXANEDIOL ABSTRACT: . This synthesis of polyester-diol was carried out aiming to prepare polyester-urethane. The polyesters are based on 1,4- cyclohexanediol and the acids: adipic, succinic, ftalic and isoftalic. Bulk polyesterification was used to prepare each polyester using 0.0903 mol of 1,4-cyclohexanediol and 0.0861 mol of acid. The synthesis of the polyester-uretane was
... Polymer Bu I leti n 0 Springer-Verlag 2002 New results on the polymerisation of the itaconic ... more ... Polymer Bu I leti n 0 Springer-Verlag 2002 New results on the polymerisation of the itaconic acid in aqueous medium Cristobal Lhrez V (m), Freddy Canelon, Enrique Millhn, G. Perdomo and Issa Katime&#x27;*&#x27; ... 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. Marvel C, Shepherd T (1959) J. Org. ...
An electrochemical study of ascorbic acid (AA) determination on a modified glassy carbón (GC) ele... more An electrochemical study of ascorbic acid (AA) determination on a modified glassy carbón (GC) electrode is reported. GC has been modified by using polyaniline (PANI) and H4PMo11VO40 (HPA). PANI was deposited on GV by repetitive cycling (60 scans) at -0.2 to 0.8V vs Ag/AgCl of a 50 mM aniline solution by employing 0.1M sulfuric acid as electrolyte solution. HPA was incorporated to the polymeric matrix by using a potential program. Scanning electron microscopy showed a porous and uniform morphology for PANI and PANI/PDA films, although PANI/PDA film showed a compacted structure.Differential pulse voltammetry (DPV) was used to quantify AA on a sulfate pH 2.04 buffer solution. We have found higher stability and better definition of the AA oxidation wave. Analytical analysis of the simple calibration curve for AA on the modified electrodes showed better response for the PANI electrode rather than PANI/PDA electrode. Analysis of AA on the PANI modify electrode showed a linear response at ...
Enzymatic depolymerization of chitosan (acetylation degree and average viscosimetric molecular we... more Enzymatic depolymerization of chitosan (acetylation degree and average viscosimetric molecular weight (M ) of 0,85 and 310 kDa, respectively) was studied using commercial bromelain. Decrease of the average viscosimetric polymerization degree (X ) was followed in a buffer solution of acetic acid (0,3 M)/sodium acetate (0,2 M) at 25 ºC. Under these experimental conditions it is possible to relate the instantaneous intrinsic viscosity [η ] with M through the Mark-Houwink-Sakurada equation. Equations of Sano, which allow to compute values of intrinsic viscosity with a single measurement of relative and/or specific viscosity, was employed to obtain instantaneous values of [η ], which were also obtained for comparative purpose through an iterative process using Huggins equation. Initial velocity of depolymerization (v ) was obtained from different concentration of chitosan solutions and a fixed bromelain concentration. Michaelis-Menten constant (k ) and maximum velocity (V ) Mm were obtai...
Summary Polycomplexes of poly(itaconic acid) have been synthesized in the presence of small amo... more Summary Polycomplexes of poly(itaconic acid) have been synthesized in the presence of small amounts of chitosan (eq. NH2/eq. COOH between 0 and 1.31%). We have studied the effect on the yield and polydispersity of the final materials when increasing quantities of chitosan are employed. Under the reported experimental conditions, we have found that chitosan is quantitatively incorporated into the new
Swelling studies of an acrylamide/maleic acid/methylene-bis-acrylamidebased hydrogel prepared by ... more Swelling studies of an acrylamide/maleic acid/methylene-bis-acrylamidebased hydrogel prepared by free radical polymerization (weight ratio of 90/10/3) are presented. Water penetration mechanism was studied by using two classical definitions, i.e., Crank (F C = w t /w eq ) and Karadag (F K = (w t -w o )/w o ), of the water fraction into the hydrogel (F). An anomalous water penetration mechanism (0.5<n<1.0) was obtained by employing both definitions and Buckley equation (F = kt n ); however, using the combined Peppas and Sahlin equation (F = k 1 t 1/2 + k 2 t) pointing out that swelling occurs in two stages: at first controlled by diffusion and relaxation contributions and then defined mainly by the diffusion contribution. Hydrogel was also studied as a system for the adsorption of cationic dye Safranin. Results show that this system perfectly fit to a Langmuir isotherm and the dye adsorption process stops when coverage of all active sites on the hydrogel has been achieved. Interestingly, adsorption process does not seem to be affected even though the hydrogel concurrently suffers the well known collapse phenomenon.
Two salts of the biopolymer chitosan were prepared in aqueous medium by employing an excess of HC... more Two salts of the biopolymer chitosan were prepared in aqueous medium by employing an excess of HCl or HNO 3 in order to ensure neutralization of all NH 2 -chitosan groups. Chitosan salts were extensively dialyzed in dionised water and dried at 40 ºC until film formation. The films were characterized by thermogravimetry, FTIR and conductimetric tritration. QH + Cl − and QH + NO 3 − salts were viscosimetrically evaluated in free acid aqueous solutions in the presence of NaCl to control ionic strength of the medium. Unexpected high intrinsic viscosity values were obtained at low ionic strength when QH + NO 3 − salt were evaluated.
Conductimetric studies of chitosan in aqueous medium Cristóbal Lárez Velásquez1 ( ), Joel Sánchez... more Conductimetric studies of chitosan in aqueous medium Cristóbal Lárez Velásquez1 ( ), Joel Sánchez Albornoz1, Jorge Uzcátegui Nava2, Enrique Millán Barrios3, Hanzel Lárez Velásquez4 ... Venezuela 4Núcleo Universitario Rafael Rangel, Departamento de Matemáticas. ...
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