Magdalena Prokopowicz

Utilization of standards generated in the process of thermal decomposition chemically modified silica gel for a single point calibration of a GC/FID system

The utilization of a multicomponent gaseous standard mixture, containing CO and CO(2) and obtained by thermal decomposition of a so-called immobilized compound, for a single point calibration of a GC/FID system are described. The generation of such a mixture takes place as a result of thermal decomposition of a sample of chemically modified silica gel placed in a heated chamber of thermal desorber coupled with the device being calibrated via a catalytic methanizer. The mean amount of the analyte librated from unit mass of the gel was 0.71 mg g(-1) (RSD = 3%) for carbon monoxide and 0.86 mg g(-1) (RSD = 3%) for carbon dioxide.

Synthesis of sol-gel mesoporous silica materials providing a slow release of doxorubicin

Samples of mesoporous base-catalysed silica xerogel materials made by the sol-gel process were impregnated with an anticancer drug—doxorubicin, followed by different times of ageing at room temperature. The effect of ageing time on the physical and structural properties as well as sorption–desorption of the drug was investigated. The obtained results suggest an inverse relationship with a solid density and surface area increasing as the pore size and volume decrease during ageing time. These results also revealed the effect of ageing time on the efficiency of sorption–desorption of the drug. An increase in ageing time results in an increase of the efficiency of drug sorption and a decrease in the rate of drug release.

Synthesis and application of doxorubicin-loaded silica gels as solid materials for spectral analysis

A new approach to synthesis and the possibility of application of solid gel matrices containing the target analyte, a cancer drug-doxorubicin for the calibration of UV-vis spectrometers is presented. The doxorubicin-loaded gels were prepared by the acid-catalyzed sol-gel pre-doping method. The efficiency of doxorubicin encapsulation in gels by the sol-gel process was 100+/-1.2% (w/w). The amount of doxorubicin encapsulated per unit mass of the gel (1g) was found to be independent of the mass of the gel taken for analysis, which demonstrates the homogeneity of encapsulation of the drug in the gel matrix. The gelation process of doxorubicin in the sol was found to be both repeatable (R.S.D.=11.2% for n=80, confidence level P=95%) and reproducible (largest value of R.S.D.=4.8% for n=27, P=95%). The prepared doxorubicin-loaded gel matrices are characterized primarily by their lack of toxicity as compared to the toxic free form of doxorubicin as well as by high stability over a long-time span.

Thermal decomposition of immobilized compounds for the generation of gaseous standard mixtures containing ammonia and amines

The thermal decomposition of phthalamic acid derivatives chemically bonded to the surface of silica gel was examined and utilized for the generation of single-component gaseous standard mixtures of ammonia, methylamine, diethylamine and triethylamine. The conditions of the thermal decomposition (temperature, time, diluent gas flow rate) were optimized to ensure complete liberation and rapid elution of the compounds from the bed of modified silica gel. The total amounts of these four compounds that can be released from unit mass of the modified silica gel are in the range of several mg.

Synthesis and characterization of modified silica gel as an intermediate in the generation of gaseous standard mixtures

SummaryA possibility of extending analytical applications of chemically modified silica gels is described. This involves their utilization for the generation of gaseous standard mixtures consisting of methyl chloride as the analyte and nitrogen as a carrier gas to be used for the calibration of the GC-FID system. N-methylmorpholine was chemically bonded to the propylsilylated surface of silica gel forming chloride of an appropriate immobilized compound which, under certain conditions, undergoes thermal decomposition yielding a single, volatile component (methyl chloride). Such a method of generating specific amounts of a standard substance can be used both for a single point calibration and for checking the accuracy of an analytical instrument in a relatively wide measurement range. It was found that 3.40±0.081 mg of methyl chloride can be generated per 1 g of the modified gel.

Silica-Polyethylene Glycol Matrix Synthesis by Sol-Gel Method and Evaluation for Diclofenac Diethyloammonium Release

Modified silica-polyethylene glycol xerogels were prepared by the sol-gel method to explore the possibilities of using these polymers as drug delivery systems. The synthesis was performed at room temperature and under atmospheric pressure using tetraethylorthosilicate (TEOS) as a precursor, low-molecular polyethylene-glycol (600) as a modifier, and acetic acid as a catalyst. The composition in a mole ratio of the initial sols corresponds to TEOS:H2O:EtOH:CH3COOH:PEG = 1:4:6:0.005:0.147. Diclofenac diethyloammonium was used as a model drug and encapsulated in predoping sol-gel process. After 5 days of gelation time of matrices at room temperature two different forms of xerogels were obtained: monolithic form of pellet and cracked, irregular-shaped of particles. The rate of release from the both forms of xerogels was controlled by the rate of diffusion of the drug through the pores. The dissolution testing for the loaded irregular-shaped xerogels showed an initial burst release followed by sustained release. The degradation of the PEG/silica xerogels followed a zero-order kinetics.

The Effect of PEG Concentration on the Release Rate of Cisplatin from PEG-Modified Silica Xerogels

Cisplatin—an antineoplastic medicine—was incorporated into a polyethylene glycol (PEG)-modified silica xerogels received by the sol-gel method. The influence of PEG concentration and drying temperature on the release of cisplatin was studied. From our results we may state that addition of PEG (MW 600) and drying of silica xerogels at 80 °C augmented the release of cisplatin. The release of cisplatin from the matrices grows with the increase of PEG volume in xerogel (up to 74–97% within 7 days), whereas application of thermal drying resulted in both increased speed and amount of the drug released up to 91–97% within 2 days.

Utilization of a sol–gel method for encapsulation of doxorubicin

The sol-gel pre-doping method was used to encapsulate doxorubicin in silica gels and optimum conditions of preparation of drug-loaded gel were established, ensuring both reproducible and effective results of quantitative encapsulation of doxorubicin and its gradual but complete release. Doxorubicin was encapsulated in polysiloxane polymers using the method based on sol-gel encapsulation without a catalyst, with an acid catalyst (HCl) and a base catalyst (NH3). The time of gelation of the gel loaded with doxorubicin, encapsulation efficiency of the drug and the degree of release of the drug from the gel are all affected by the kind of catalyst (acidic or basic) or its absence at the gel preparation stage, and the temperature of the gelation process. The time of sol gelation when using the NH3 or HCl catalyst was 9 days at 21°C, 2 days at 30°C and 1.5 days at 37°C, while for the gel prepared without a catalyst it was 90 days at 21°C, 75 days at 30°C and 70 days at 37°C. The efficiency of doxorubicin encapsulation was 99.5 ± 0.5% (w/w) for acid-catalyzed gel, 98.9 ± 1.01% (w/w) for base-catalyzed gel and 86.4 ± 11.6% (w/w) for non-catalyzed gel. A 100% (w/w) release of doxorubicin by diffusion through pores was found only in the case of base-catalyzed gel after a 140-h incubation time. For acid-catalyzed gel and non-catalyzed gel, the total amounts of released doxorubicin after 140 h of incubation were 3-5% (w/w) and 9-11% (w/w), respectively. The stability of doxorubicin encapsulated in the three kinds of gel matrices was found to be improved compared to the stability of a free form of the drug in solution.

Thermal decomposition of silica based surface compounds as a source of volatile standards. A new approach to the generation of gaseous calibration mixtures

A new approach to the preparation of standard gaseous mixtures based on thermal decomposition of surface compounds, has been reviewed. The method is used to prepare standard mixtures containing volatile analytes such as thiols, isothiocyanates, carbon monoxide, carbon dioxide, ammonia, amines, ethylene and methyl chloride. The method enables the preparation of the standard immediately before a calibration step. It is specially useful for the generation of standard mixtures containing volatile, malodorous, unstable and toxic compounds.

The measurement of conformational stability of proteins adsorbed on siloxanes.

The paper investigates the conformational stability of bovine serum albumin (BSA) and fibrinogen during 24-h incubation in turn with a linear silicone polymer (polydimethylsiloxane (PDMS)), with linear silicone oligomers (hexamethyldisiloxane and octamethyltrisiloxane) and with cyclic silicone oligomers (octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5)). Ten-fold and 100-fold excesses of siloxanes with respect to the proteins were used. Using fluorescence spectroscopy of tryptophan located in the domain of proteins and fluorescence of 8-anilino-1-naphthalenesulfonic acid (1,8-ANS), which interacts with hydrophobic domains of proteins, changes in the tertiary structure of the protein were recorded. The results demonstrated that BSA does not change its native form during 24-h incubation with siloxanes. In contrast, the tertiary structure of fibrinogen was found to be altered by both short-chain linear siloxanes: (hexamethyldisiloxane and octamethyltrisiloxane) and long-chain PDMS. The changes can be observed only at a 100-fold excess of siloxanes with respect to the protein. No conformational changes in fibrinogen exposed to cyclic siloxanes were observed.