Adsorption kinetics of carcinogens to DNA liquid crystalline gel beads

Adsorption behaviors of acridine orange (AO) and biphenyl (BP) to DNA liquid crystalline gel (LCG) beads in aqueous dispersing solution have been studied theoretically and experimentally. A theoretical consideration based on nonequilibrium thermodynamics predicted that the time course of the adsorption process is expressed with a scaled equation, and a scaled number of adsorbed carcinogen molecules ? is expressed with the square root of a scaled immersion time t, ? proportional, variant square root t at early stage, whereas it is expressed with a power law function 1 - ? proportional, variant (te - t)3/2 for ?0 > 1 and an exponential equation ?0 - ? proportional, variant e-t/alpha tau0 for ?0 > 1 at later stages of adsorption. Here, ?0 is the ratio of the initial number of carcinogen molecules in the dispersing solution to the number of the sites of adsorption of carcinogen molecules in the beads, te is the scaled equilibrium time of adsorption, tau0 is a time constant for adsorption, and alpha is a constant. Observed adsorption processes for AO were well expressed by the predicted ones, and the fitting parameters ?0 and tau0 increased with increasing cobalt chloride concentration CCo used for preparation of the beads, and both saturated above CCo > or = 400 mM for the adsorption of AO, whereas the adsorption processes for BP were expressed with the square root function. These results indicate that (1) the adsorption process at early stage is explained by diffusion-limited binding of the carcinogen molecules to DNA beads, and the time range of the early stage depends on the solubility (the solubility of AO in water is high whereas that of BP is low); and (2) the process at later stages depends on the balance of the numbers of adsorption sites and carcinogen molecules.     

Silaned glass beads for the preconcentration and spectrophotometric determination of cobalt with 2-(2-pyridylazo)-5-diethylaminophenol

Silaned glass beads are applied for the preconcentration and spectrophotometric determination of cobalt with 2-(2-pyridylazo)-5-diethylaminophenol (PADAP). Traces of cobalt are collected as the coloured PADAP complex on a column of the beads, and the complex is then eluted with a small volume of ethanol-hydrochloric acid mixture and the absorbance of the eluate is measured at 575 nm. The cobalt can easily be concentrated by a factor of 50-500 in this way, and 0.1-2 mug of cobalt in 100 ml of sample solution can be determined reproducibly. High concentrations of Fe(III), Cr(III), Pb, Zn, Cu(II), Mn(II), Cd, Al, Ca and Mg can be tolerated but Pd(II) interferes.     

Removal of Cobalt Ions from Aqueous Solution by Adsorption onto Cross-Linked Calcium Alginate Beads

The removal of cobalt ions from dilute aqueous solutions using cross linked calcium alginate beads as the adsorbent is reported in this article. The influence of various experimental parameters such as pH, initial metal ion concentration, contact time and solid to liquid ratio were studied. The adsorption data were applied to Langmuir and Freundlich isotherm equations and various static parameters were calculated. It was observed that the uptake of cobalt ions was found to increase with time and that maximum adsorption was obtained within the first 60 minutes of the process. These results indicate that the cross linked calcium alginate beads have potential for removing cobalt ions from industrial waste water.     

Physico-chemical properties of alginate gel beads

Alginate gel beads are used in many applications as matrices for release or immobilisation. Until now, the parameters (such as type and concentration of cation, ionic strength and pH) of the beads formation solution in which the Na-alginate solution was dropped were not deeply studied. Therefore, in this paper, the gel formation of alginate beads and their behavior in demineralized water has been investigated carefully. The results obtained in the present study about the gel formation showed that (1) the type and the concentration of the cation play a determinant role in the gel formation phenomenon giving beads of different volumes and characteristics; (2) the weight and volume losses occurring in the ‘syneresis’ are essentially by water elimination; (3) NaCl, which gives the ionic strength of the beads formation solution, plays two roles: a competitor with calcium and a screen in the electrostatic repulsion; and (4) finally, the pH controls the gel formation process as regulator in the dissociation of the alginate and in the complexation of the calcium cations. A study by weight change dynamic analysis was also carried out. The results showed that the transfer of a bead from its formation solution into demineralized water provokes a modification of its volume, weight and stability. These results are important to understand the behavior of beads in their utilization medium.     

Spatiotemporally controlled electrodeposition of magnetically driven micromachines based on the inverse opal architecture

We describe a double template-assisted electrodeposition of porous metal microstructures. The method combines two-dimensional photolithography and electrophoretic assembly of polystyrene beads, in order to confine the electrochemical growth of a porous magnetic cobalt–nickel alloy within well-defined microscale boundaries. Polystyrene beads are electrophoretically deposited onto a sulfonate derivatized gold substrate where a patterned photoresist layer (first template) is applied. The polystyrene beads trapped in the first template act as the second template, and cobalt–nickel alloy is electrochemically grown through the voids between the beads. After removal of both templates, magnetic microstructures with well-defined shapes and porosity are successfully obtained. Additionally, we demonstrate the capabilities of these magnetic microstructures as wireless cargo microtransporters by loading their pores with a stimulus-responsive hydrogel. Magnetic manipulation experiments are also demonstrated.     

Preparation of poly(N-normalpropyl- acrylamide) gel beads

 The gel beads of N-normal-propylacrylamide are prepared by the radical copolymerization of N-normalpropylacrylamide and N,N′-methylene-bis-acrylamide in water. The optimum reaction conditions to obtain the gel beads are revealed from the phase diagram of the reaction system together with the scanning electron microscopy of the reaction products. The scanning electron microscopy of the reaction products also indicates the formation of the spherical gel beads of sub-micron size ranging from 250 to 500 nm in diameter. The viscosity measurements of the suspension of the gel beads indicate that the concentration dependence of the viscosity of the suspension is well described by Einstein’s theory of the viscosity of colloidal particles. The intrinsic viscosity of the suspension of gel beads is then determined. The density of the gel beads, which was obtained from the intrinsic viscosity of the suspension, indicates that the gel beads are in the swollen state at a temperature of 20 ^°C. Received: 12 September 1997 Accepted: 17 December 1997     

Removal of some nitrophenol contaminants using alginate gel beads

Biopolymers such as alginates are commonly used to remove the cationic contaminants from wastewaters. The major component of the alginate is the alginic acid, a linear, binary heteropolymer of β-d-mannuronate and -l-guluronate residues. In this study the fundamental aspects in the preparation of alginate beads and the effects of salt, sodium alginate concentrations and two cationic surfactants (dodecyltrimethylammonium bromide, cetyltrimethylammonium bromide) on the domains of binding isotherms were investigated. The alginate cross-link complexes with metal ions can exist either as homogeneous clear solutions or precipitates or as spherical beads. The applicability of the calcium and calcium–iron alginate gel beads for removal of some nitrophenols from aqueous solutions was studied. The sorption and kinetic experiments were conducted under different values of pH, initial concentration of nitrophenols and the amount of alginate gel beads. The removal efficiency of contaminant increases with the increasing of the pH and the quantity of alginate beads and decreases with the increasing of initial contaminant concentration. The uptake of nitrophenols occurs rapidly in the first 12 h, followed by a slow process that takes about 72 h. According to the egg-box model of gelation mechanism the cavities formed in the alginate gel capture the cationic contaminants. The adsorption equilibrium data obtained for nitrophenols derivatives at various pH and initial solid sorbent amount were applied to the two classical models, i.e. Langmuir and Freundlich, and the isotherm parameters were calculated.     

The controlled release of a drug from biodegradable chitosan gel beads

Chitosan (CS) forms a gel in solutions with a pH above 12, and the gelation occurs at pH of about 9 in 10% amino acid solutions. In this paper, we investigated the enzymatic degradation and the drug release profile of this novel CS gel beads. The degradability of the CS gel beads was affected by the CS properties, e.g. the degree of deacetylation. The release of prednisolone (PS), as a model drug, from the CS gel beads was sustained significantly compared with the gel prepared with NaOH only. However, the release was not able to be sustained by the increment of NaOH concentration in the solution employed for the preparation of CS gel beads. We also investigated the control of drug release from CS gel beads by application of a complex formed between chondroitin sulfate (Cho) and CS. The release of PS from the CS gel beads treated with Cho was prolonged, and the release pattern was not affected by the treatment time. The time to 50% drug release was about 5 min with PS powder, about 200 min in CS gel beads with 10% glycine (Gly) (pH 9.0), and about 330 min in the CS gel beads with 10% Gly (pH 9.0) treated with Cho. Thus CS gel beads appear promising as a vehicle for sustained drug delivery, and the degradation of CS gel beads may be controlled by the degree of deacetylation of CS.     

Cobalt/silica gel system as a chemisorbent for oxygen

A study has been made of oxygen chemisorption and the phase composition of cobalt/silica gel samples containing from 1.1 to 7.7% Co by weight. Reduction in hydrogen leads to the formation of metallic cobalt with a crystal size of about 50 Å. The quantity of chemisorbed O₂ at 20°C increases in proportion to the increase of [Co]. The uptake of O₂ is essentially completed at 300°C with the formation of Co₃O₄. The high adsorption capacity for O₂ is preserved unchanged in repetitive reduction-oxidation cycles. The residual content of O₂ in the gas after passage through the layer of the cobalt/silica gel chemisorbent is 3·10^–6% by volume.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya, Khimicheskaya, No. 1, pp. 40–43, January, 1992.     

SYNTHESIS, CHARACTERIZATION AND CATALYTIC ACTIVITY OF N,N''''-BIS(3-ALLYL SALICYLIDENE)ETHYLENEDIAMINE COBALT(Ⅱ) SCHIFF BASE COMPLEX ANCHORED ON A NEW POLYMER SUPPORT

INTRODUCTIONAlthough homogeneous catalysts have higher selectivity and act under mild experimental conditions in variousreactions they have problems of separation and recovery from reaction products. Hence current research activitiesare aimed at developing catalysts of coordination compounds anchored on suitable supports[1,2]. This techniqueof immobilization of catalyst on an inert support increases the catalytic activity, selectivity, efficiency[3],operational flexibility and stability. …     

Immobilization of penicillin acylase in porous beads of polyacrylamide gel

A procedure is described for the immobilization of benzylpenicillin acylase from Escherichia coli within uniformly spherical, porous polyacrylamide gel beads. Aqueous solutions of the enzyme and sodium alginate and of acrylamide monomer, N,N'-methylene-bis-acrylamide, N,N,N,N'-tetramethylethylenediamine (TEMED) and sodium alginate are cooled separately, mixed, and dropped immediately into ice-cold, buffered calcium formate solution, pH 8.5, to give calcium alginate-coated beads. The beads are left for 30-60 min in the cold calcium formate solution for polyacrylamide gel formation. The beads are then treated with a solution of glutaraldehyde and the calcium alginate subsequently leached out with a solution of potassium phosphate. Modification of the native enzyme with glutaraldehyde results in a slight enhancement in the rate of hydrolysis of benzylpenicillin at pH 7.8 and 0.05M substrate concentration. The enzyme entrapped in porous polyacrylamide gel beads shows no measurable diffusional limitation in stirred reactors, catalyzing the hydrolysis of the substrate at a rate comparable to that of the glutaraldehyde-modified native enzyme. The immobilized enzyme preparation has been used in batch mode over 90 cycles without any apparent loss in hydrolytic activity.     

Preparation of filled temperature-sensitive poly(N-isopropylacrylamide) gel beads

Temperature-sensitive filled poly(N-isopropylacrylamide) (PNIPAAm) gel beads with diameters in the range of millimeters were prepared using the alginate technique. The polymerization and cross-linking reaction of NIPAAm in the presence of inorganic filling particles was performed in spherical networks of Ca-alginate forming interpenetrating networks (IPN). Thermo-sensitive gel beads could be obtained by washing these IPN with EDTA solution. The PNIPAAm gel beads were analyzed by optical methods to observe there swollen diameter in dependence on the temperature. The diameters of the swollen gel beads were in the range of 0.1 - 2 mm. The influence of the monomer to cross-linker ratio (MCR) and the filling materials (ferrofluid, BaTiO₃, TiO₂, and Ni,) were studied. The phase transition temperature (T_pt) was only weakly influenced by the MCR and the filling material remaining at around 34°C.     

SYNTHESIS, CHARACTERIZATION AND CATALYTIC ACTIVITY OF N,N''-BIS(3-ALLYL SALICYLIDENE)ETHYLENEDIAMINE COBALT(II) SCHIFF BASE COMPLEX ANCHORED ON A NEW POLYMER SUPPORT

A new chelating polymer support has been prepared by suspension copolymeriz a tion of synthesized N,N'-bis(3-allyl salicylidene)ethylenediamine monomer Schiff base (N,N'-BSEDA) with styrene (St) and divinylbenzene (DVB) using azobisisobutyronitrile (AIBN) as initiator in the presence of poly(vinyl alcohol). The content and complexation ability of monomer Schiff base (N,N'-BSEDA) for cobalt(II) ions in prepared crosslinked polymer beads have shown dependence on the amount of DVB used in reaction mixture. The amount of monomer Schiff base (N,N'-BSEDA) in crosslinked beads showed a substantial decreasing trend at high concentration of DVB in the reaction mixture (＞ 1.5 mol dm-3), hence the efficiency of complexation (EC%) and cobalt(II) ion loading (EL%) of polymer beads showed a decreasing trend. The structure of monomer Schiff base (N,N'-BSEDA) and its cobalt(II) complex on polymer support was elucidated by IR, UV and magnetic measurements. The catalytic activity of polymer bound cobalt(Ⅱ) Schiff base complex was evaluated by analyzing kinetic data of decomposition of hydrogen peroxide in the presence of either supported cobalt (II) complex or free cobalt(II) complex. The activation energy for the decomposition of hydrogen peroxide by polymer supported cobalt(II)complex was found to be low (33.37 kJ mol-l) in comparison with unsupported cobalt(II) complex (56.35 kJ mol-1). On the basis of experimental observations, reaction steps are proposed and a suitable rate expression derived.     

Simple semiquantitative determination of trace metal ions by use of reagent gel columns-I: determination of mercury with dithizone gel

Mercury(II) at the sub-ppm level was determined by using a column packed with gel beads containing dithizone stabilized as the zinc complex. The beads turned from pink to green when the acidified sample solution was passed through the column. If the solution contained mercury (II), the colour of the gel beads turned to orange owing to the formation of mercury dithizonate. The length of the coloured zone was proportional to the amount of mercury in the sample. With 0.01% dithizone gel, as little as 0.1 ppm of mercury(II) could be determined in a 20-ml sample at a flow-rate of 1 ml/min.     

Cobalt-extraction studies on dithiocarbamate grafted on silica gel surface

Extraction of cobalt(II) ion from aqueous solution was studied using silica gel grafted with dithiocarbamate ligand (Si–dtc), which was prepared by reacting silica gel with γ-aminopropyltriethoxysilane followed by alkaline carbon disulfide. ²⁹Si MAS NMR, IR spectra were taken to establish the grafting of dithiocarbamate ligand on silica gel. This modified surface contains 0.37 mmol g⁻¹ of the ligand sites available for the extraction of cobalt. The sorbent extracts cobalt only when the pH of the aqueous phase is above 7 and the extraction process does not follow ideal ion-exchange mechanism. The electronic absorption spectra of cobalt present in the sorbent phase suggested the oxidation of Co(II) to Co(III). Kinetic data were fitted to surface complexation model and the rate constant (k_s) for such model was found to vary from 1.5×10⁻³ to 5.82×10⁻³ l mg⁻¹ min⁻¹ depending on the initial concentration of cobalt. An estimate of enthalpy and entropy changes accompanying the extraction was obtained by temperature variation method. The increase in the overall entropy of the system seems to favour the extraction of cobalt by Si–dtc.     

Analytical applications of organic reagents in hydrophobic gel media-II Selective preconcentration of mercury(II) with dithizone or thiothenoyltrifluoroacetone gel

Mercury(II) at the sub-ppm level is selectively trapped on a column packed with cross-linked polystyrene gel beads soaked with zinc dithizonate or thiothenoyltrifluoroacetone. Mercury trapped on the beads can be back-extracted into the aqueous phase with a hydrogen halide solution. Mercury in sea water at ppm or ppM level has been successfully preconcentrated by this procedure.     

Preparation and drug retention of biodegradable chitosan gel beads.

Chitosan (CS) gel beads containing drug could be prepared in amino acid solutions of pH about 9, despite the requirement for a pH above 12 for gelation in water. This phenomenon was observed not only in amino acid solutions but also in solutions of compounds having amino groups. A solute concentration of more than 10% was required for preparation of gel beads at pH 9. Gelation of the CS beads required about 25 to 40 min, depending on the species of amino acid. Lidocaine hydrochloride (LC) as a model drug was retained in the beads to about 20 to 35% of the theoretical total amount, despite being a water-soluble drug. The release of LC from the CS gel beads was prolonged. The release pattern was not affected by the species of amino acid or CS, or the preparation time.     

Characteristics and antioxidant activity of catechin-loaded calcium pectinate gel beads prepared by internal gelation

Catechin-loaded calcium pectinate gel beads prepared by internal gelation were characterized for their catechin entrapment efficiency and release behavior. The entrapment efficiency was higher when the beads were prepared with a lower catechin-to-pectin ratio, shorter gelling time, higher pectin concentration, and lower acetic acid concentration. The entrapment efficiency was much higher under all tested conditions, when the beads were prepared by internal gelation instead of external gelation. The catechin release was slower for the beads prepared with lower catechin-to-pectin ratio, longer gelling time, and higher concentrations of pectin and acetic acid in both simulated gastric and intestinal fluids. Antioxidant power of catechin was effectively maintained in alkaline simulated intestinal fluid when catechin was entrapped within the beads, compared to cases where it was not entrapped, indicating that the beads can protect catechin molecules from the alkaline environment and release them in a sustained fashion.     

Adsorption of mercury(II) on macroreticular styrene-divinylbenzene copolymer beads

The adsorption characteristics of mercury(II) on several kinds of styrene-divinylbenzene copolymer beads having different surface properties were studied. It was found that the polymer beads selectively adsorbed mercury(II) from solutions over a wide range of pH with high efficiency. The amount of mercury(II) adsorbed increased with increase in specific surface area of the polymer beads and the adsorption behaviour was found to be of the Langmuir type. The presence of chloride strongly reduced the adsorption, but this interference was not observed with nitrate, sulphate, perchlorate, cadmium(II), cobalt(II), copper(II), nickel(II), silver(I) and zinc(II). More than 95% of the mercury(II) adsorbed on a column of polymer beads could be recovered with dilute hydrochloric acid.     

SYNTHESIS, CHARACTERIZATION AND CATALYTIC ACTIVITY OF N,N'-BIS(3-ALLYL SALICYLIDENE)ETHYLENEDIAMINE COBALT SCHIFF BASE COMPLEX ANCHORED ON A NEW POLYMER SUPPORT

 A new chelating polymer support has been prepared by suspension copolymerization of synthesized N,N'-bis(3-allyl salicylidene)ethylenediamine monomer Schiff base (N,N'-BSEDA) with styrene (St) and divinylbenzene (DVB) using azobisisobutyronitrile (AIBN) as initiator in the presence of poly(vinyl alcohol). The content and complexation ability of monomer Schiff base (N,N'-BSEDA) for cobalt(Ⅱ) ions in prepared crosslinked polymer beads have shown dependence on the amount of DVB used in reaction mixture. The amount of monomer Schiff base (N,N '-BSEDA) in crosslinked beads showed a substantial decreasing trend at high concentration of DVB in the reaction mixture (> 1.5 mol dm^-3), hence the efficiency of complexation (EC%) and cobaltⅡion loading (EL%) of polymer beads showed a decreasing trend. The structure of monomer Schiff base (N,N'-BSEDA) and its cobalt(Ⅱ)complex on polymer support was elucidated by IR, UV and magnetic measurements. The catalytic activity of polymer bound cobalt(Ⅱ)Schiff base complex was evaluated by analyzing kinetic data of decomposition of hydrogen peroxide in the presence of either supported cobalt(Ⅱ)complex or free cobalt(Ⅱ)complex. The activation energy for the decomposition of hydrogen peroxide by polymer supported cobalt complex was found to be low (33.37 kJ mol^-1) in comparison with unsupported cobalt(Ⅱ)complex (56.35 kJ mol^-1). On the basis of experimental observations, reaction steps are proposed and a suitable rate expression derived.