Chitosan adsorption on the collagen tissue of the bovine pericardium from solutions in carbonic acid: Role of pressure

The degree of adsorption of chitosan on the collagen matrices of bovine pericardium upon deposition from solutions in the two-phase H₂O/CO₂ system was studied as a function of pressure.     

Electrochemically deposited palladium as a substrate for self-assembled monolayers

The vast majority of reports of self-assembled monolayers (SAMs) on metals focus on the use of gold. However, other metals, such as palladium, platinum, and silver offer advantages over gold as a substrate. In this work, palladium is electrochemically deposited from PdCl2 solutions on glassy carbon electrodes to form a substrate for alkanethiol SAMs. The conditions for deposition are optimized with respect to the electrolyte, pH, and electrochemical parameters. The palladium surfaces have been characterized by scanning electron microscopy (SEM) and the surface roughness has been estimated by chronocoulometry. SAMs of alkane thiols have been formed on the palladium surfaces, and their ability to suppress a Faradaic process is used as an indication for palladium coverage on the glassy carbon. The morphology of the Pd deposit as characterized by SEM and the blocking behavior of the SAM formed on deposited Pd delivers a consistent picture of the Pd surface. It has been clearly demonstrated that, via selection of experimental conditions for the electrochemical deposition, the morphology of the palladium surface and its ability to support SAMs can be controlled. The work will be applied to create a mixed monolayer of metals, which can subsequently be used to create a mixed SAM of a biocomponent and an alkanethiol for biosensing applications.     

Palladized aluminum as a novel substrate for electrosynthesis of polyaniline in sulfuric acid solutions

The electropolymerization of aniline on a palladized aluminum electrode (Pd/Al) by potentiodynamic as well as potentiostatic methods is described. The effect of the monomer concentration between 0.01 and 0.4 M on the polyaniline (PANI) formation and its growth on the Pd/Al electrode was investigated and a suitable concentration of 0.2 M is suggested. A similar study was carried out to investigate the effect of sulfuric acid concentration and 0.1 M sulfuric acid was chosen. A study on the influence of electropalladization time on the polymer formation and its growth suggested a convenient time of 40 s. The stability of the PANI film on the Pd/Al electrode was studied as function of the potential imposed on the electrode. For applied electrode potentials of 0.1–0.7 V, the first-order degradation rate constant, k, of PANI film varies between 1×10⁻⁶ and 2×10⁻⁵ s⁻¹, and a relatively low slope (i.e., 2.2) was obtained for the plot of log k versus E. The coatings were characterized by scanning electron microscopy (SEM), and cyclic voltammetric behavior of the PANI-deposited Pd/Al electrode is discussed. The electrocatalytic activity of the PANI-deposited Pd/Al electrode against para-benzoquinone/hydroquinone (Q/H₂Q) and redox systems were investigated and on the basis of of the corresponding cyclic voltammograms and the redox systems were identified as the reversible and quasi-reversible systems, respectively.     

Effect of pressure on the structure of composite chitosan films obtained from solutions in carbonic acid

The effect of pressure in solutions of chitosan in carbonic acid with the AgNO₃ precursor on the structure of cast nanocomposite films with silver nanoparticles has been studied for the first time. The size of silver nanoparticles can be controlled by varying pressure in carbonic acid.     

Cs(2) fixation by carbonic anhydrase model systems-a new substrate in the catalytic cycle

The conversion of CS(2) with common carbonic anhydrase model systems has been studied using Hartree-Fock and density-functional theory methods employing the 6-311+G basis set. The calculated geometries and energetical parameters for [L(3)ZnOH](+)/CS(2) model systems (L = NH(3), imidazole) are compared with those obtained previously for the CO(2) hydration. While the same reaction mechanism applies for both heterocumulenes, the hypothetical conversion of CS(2) to give [L(3)ZnSC(O)SH](+) is characterized by a higher barrier and is much more exothermic than the corresponding CO(2) reaction cascade. Due to the increased number of heteroatoms, additional intermediates and product structures (compared with those involved in the CO(2) conversion) must be taken into account and have been analyzed in detail. The smaller electrophilicity of CS(2) is the reason for the higher activation energies, while the significantly increased exothermicity is due to the strong zinc(II)/sulfur interaction. The reversibility and therefore the existence of a catalytic cycle which could allow comparable CS(2) transformations must be questioned. Nevertheless, an interesting field of stoichiometric zinc-mediated CS(2) transformations is conceivable.     

The ionization of carbonic acid in Na-Mg-Cl solutions at 25°C

The stoichiometric pK₂ ^* and pK₂ ^* for the ionization of carbonic acid has been determined from emf measurements in NaCl solutions with small amounts of MgCl₂ from I=0.5 to 6.0 molal at 25°C. Our results at low ionic strengths (I=0.7) are in agreement with the measurements of Dyrssen and Hansson and Pytkowicz and Hawley. Our results have been analyzed using the ion pairing model and Pitzer's specific interaction equations. From the values of pK₁ ^*, we have determined the Pitzer parameters ⁰[Mg (HCO₃)₂] = 0.0193 and ¹[Mg (HCO₃)₂] = 0.0193 which reproduces the pK₁ ^* results to ±0.01. The values of pK₂ ^* were used to determine ⁰(MgCO₃) = 2.833, ¹(MgCO₃) = -15.069, ²(MgCO₃) = -204.90 and C (MgCO₃)=–0.970 which reproduces the pK₂ ^* s to ±0.02. The pK₂ ^* results could be reproduced to the same precision with fewer parameters using the ion pairing model [pK(MgCO₃)=3.00 and log (MgCO₃)=0.0560 I].     

Ionization of carbonic acid in sodium chloride solutions at 25°C

The stoichiometric pK ₁ ^* and pK ₂ ^* for the ionization of carbonic acid has been determined from emf measurements in NaCl soluions to 6.0m at 25°C. Our results at low concentrations are in good agreement with the results of Harned and Bonner, of Dyrssen and Hansson and of Roy et al. The calculated values of pK ₁ ^* using Pitzer's equations agree with the measured values to ±0.01 pK units provided higher order terms are used. It was necessary to use a triplet interaction parameter () and higher order electrostatic terms (^E) to calculate reliable values of pK ₂ ^* (±0.03 pK units) over the entire concentration range. These results demonstrate the reliability of the Pitzer equations to estimate activity coefficients in concentrated salt solutions.     

Nonradiative energy transfer as a method for investigation of self-assembling nanostructures of lanthanide complexes in solutions

Works concerning the application of nonradiative transfer of electronic excitation energy to investigation into nanostructures of lanthanide complexes in aqueous solutions are surveyed. The effect of the formation of nanosized structures on the quenching of energy donors Ln(III) ions by acceptor ions in concentrated chloride solutions of structuring ions (Li(I), Ca(II)) was discussed. The columinescence phenomenon observed in aqueous solutions of lanthanide chelates was considered. It was shown that the enhancement of luminescence Eu(III) and Tb(III) complexes in water in the presence of excess β-diketones with an admixture of other Ln(III) ions, primarily Gd(III), (columinescence) is due to sensitization via energy transfer over triplet levels of the ligands in the nanostructures formed under these conditions and to the weakening of deactivation of excited luminescent ions by the formation of nanostructures. The influence of the solution preparation procedure on the formation of nanostructures of chelates with different lanthanide ions was revealed, which manifest itself as a variation in the enhancement and quenching of luminescence in the presence of ions from the cerium and yttrium subgroups. Possible applications of the columinescence phenomenon to chemical and medical analysis are briefly discussed.     

Dissolution of calcium bilirubinate disk as a model of a gallstone by mixed solutions of 1,3-dimethyl-2-imidazolidinone and ethylenediaminetetraacetic acid

Direct dissolution agents of calcium bilirubinate gallstones were prepared by dissolving chelating agents in aqueous solutions of sodium carbonate containing polar solvent. Dissolution experiments on a calcium bilirubinate disk as a model of a gallstone were performed using a static disk method.

From the amounts dissolved in an hour using dissolution agents with various composition, the most effective conditions for dissolving calcium bilirubinate were determined as follows: (1) the higher the pH of the dissolution agent, the more calcium bilirubinate was dissolved. Thus, pH 8.4 was chosen as the best pH condition within the range of harmless usage to the human body in vivo in limited amount; (2) a combination of ethylenediaminetetraacetic acid (EDTA) as chelating agent for calcium and 1,3-dimethyl-2-imidazolidinone (DMI) as polar solvent; (3) in the mixed system of EDTA and DMI, the most effective concentrations were about 4 wt.% EDTA and about 30 wt.% DMI.

The dissolution agent satisfying the above conditions gave a dissolved amount of about 70 mg dl⁻¹ in 1 h. This amount was considerably higher than those using DMI and EDTA independently. This suggests that dissolution is due to cooperation between EDTA and DMI.     

Micropatterning of cell-repellent polymer on a glass substrate for the highly resolved virus microarray

The development of a simple and easily accessible method to control cellular behavior under a spatially controlled surface is critical for fundamental studies in biotechnology. We fabricated a microarray of Spodoptera frugiperda 9 (Sf9) cells on a glass surface by microcontact printing cell-repellent polymeric molecules of poly(ethylene glycol)-branched-poly(methyl methacrylate) as a template for cell micropatterning. The polymer micropatterns enabled the stable confinement of Sf9 cells on the surface, resulting in the formation of a cell microarray. Subsequently, the patterned Sf9 cells were infected with recombinant baculovirus modified with green fluorescent protein (GFP) to form a virus microarray, and GFP expression in the virus microarray was verified with confocal fluorescence microscopy.     

Analysis of carbonic acid in water samples by ion-exclusion chromatography with pure water as eluent.

A simple, sensitive and rapid ion-exclusion chromatographic method for the simultaneous separation of carbonic acid and short chain organic acids (formic acid, acetic acid, and propionic acid) has been developed. A weakly acidic cation exchange resin column TSKgel OApak-A was used for the separation; pure water, owing to its lower background conductance, was employed as eluent in order to obtain high detection sensitivity. A good separation of these weak acids was achieved in 16 min. The linear range of the peak area calibration curve for carbonic acid was from 3.0 mg/L to 500 mg/L. The conductivity detection limit calculated at S/N = 3 was 0.084 mg/L for carbonic acid. The method developed in this work was successfully applied to the determination of carbonic acid in several environmental water samples without any pretreatment.     

Chitosan as a removing agent of beta-lactoglobulin from membrane models

Many chitosan biological activities depend on the interaction with biomembranes, but so far it has not been possible to obtain molecular-level evidence of chitosan action. In this article, we employ Langmuir phospholipid monolayers as cell membrane models and show that chitosan is able to remove beta-lactoglobulin (BLG) from negatively charged dimyristoyl phosphatidic acid (DMPA) and dipalmitoyl phosphatidyl glycerol (DPPG). This was shown with surface pressure isotherms and elasticity and PM-IRRAS measurements in the Langmuir monolayers, in addition to quartz crystal microbalance and fluorescence spectroscopy measurements for Langmuir-Blodgett (LB) films transferred onto solid substrates. Some specificity was noted in the removal action because chitosan was unable to remove BLG incorporated into neutral dipalmitoyl phosphatidyl choline (DPPC) and cholesterol monolayers and had no effect on horseradish peroxidase and urease interacting with DMPA. An obvious biological implication of these findings is to offer reasons that chitosan can remove BLG from lipophilic environments, as reported in the recent literature.     

Self-assembly of (perfluoroalkyl)alkanes on a substrate surface from solutions in supercritical carbon dioxide

Toroidal self-assembled structures of perfluorododecylnonadecane and perfluorotetradecyloctadecane have been deposited on mica and highly oriented pyrolytic graphite surfaces by exposure of the substrates to solutions of the (pefluoroalkyl)alkanes in supercritical carbon dioxide. Scanning force microscopy (SFM) images have displayed a high degree of regularity of these self-assembled nanoobjects regarding size, shape, and packing in a monolayer. Analysis of SFM images allowed us to estimate that each toroidal domain has an outer diameter of about 50 nm and consists of several thousands of molecules. We propose a simple model explaining the clustering of the molecules to objects with a finite size. The model based on the close-packing principles predicts formation of toroids, whose size is determined by the molecular geometry. Here, we consider the amphiphilic nature of the (perfluoroalkyl)alkane molecules in combination with incommensurable packing parameters of the alkyl- and the perfluoralkyl-segments to be a key factor for such a self-assembly.     

Ascorbic acid as a matrix modifier for determination of tin in concentrated boric acid solutions by electrothermal atomic-absorption spectrometry

It has been found that the atomic-absorption signal for tin is reduced in the presence of 5 micro1 of 0.05-0.30M boric acid at STPF-conditions. It has been proposed that the reason for the boron interferences is the formation of SnB(g) at the atomization stage. In the presence of palladium chloride the interferences from 0.2M boric acid are reduced by a factor of 1.3. The interferences are reduced most effectively when the sample is atomized from a polycrystalline graphite platform or in the presence of ascorbic acid. The interference of up to 0.2M boric acid can be suppressed and the area of the tin signal doubled. It is proposed that the observed phenomenon is connected with the bonding of boron as non-volatile B(4)C. Ascorbic acid is the most effective matrix modifier for the determination of different trace elements in boron compounds.     

Bisacylated diethylenetriamines as extractants for nonferrous metals from hydrochloric acid solutions

A series of bisacylated polyethylenepolyamines with linear and α-and α,α′-branched substituents were synthesized. The effects of the number of the nitrogen atoms in the polyethylenepolyamine fragment of the reagent and of the length and branching of its alkyl radicals on the extractant distribution between the organic and aqueous phases was studied. The performance characteristics of the extractants, such as the loss with the aqueous phase, hydrolytic stability, back extraction conditions for nonferrous metals, and Zn(II)/Fe(III) and Zn(II)/Cu(II) partition coefficients, were examined.