Marjatta Louhi-Kultanen

Physicochemical stability of high indomethacin payload ordered mesoporous silica MCM-41 and SBA-15 microparticles

Stability of high indomethacin (IMC) content formulations based on ordered mesoporous silica MCM-41 and SBA-15 materials was studied before and after a 3 month storage in stressed conditions (30°C/56% RH). Overall, the physical stability of the samples was found satisfactory after the storage. However, some issues with the chemical stability were noted, especially with the MCM-41 based samples. The stability issues were evident from the decreased HPLC loading degrees of the drug after stressing as well as from the observed extra peaks in the HPLC chromatograms of the drug in the stressed samples. Drug release from the mesoporous formulations before stressing was rapid at pH 1.2 in comparison to bulk crystalline IMC. The release profiles also remained similar after stressing. Even faster and close to complete IMC release was achieved when the pH was raised from 1.2 to 6.8. To our knowledge, this is the first report of chemical stability issues of drugs in mesoporous silica drug formulations. The present results encourage further study of the factors affecting the chemical stability of drugs in mesoporous silica MCM-41 and SBA-15 formulations in order to realize their potential in oral drug delivery.

Oxidation of aqueous pharmaceuticals by pulsed corona discharge

Oxidation of aromatic compounds of phenolic (paracetamol, β-oestradiol and salicylic acid) and carboxylic (indomethacin and ibuprofen) structure used in pharmaceutics was studied. Aqueous solutions were treated with pulsed corona discharge (PCD) as a means for advanced oxidation. Pulse repetition frequency, delivered energy dose and oxidation media were the main parameters studied for their influence on the process energy efficiency. The PCD treatment appeared to be effective in oxidation of the target compounds: complete degradation of pollutant together with partial mineralization was achieved at moderate energy consumption; oxidation proceeds faster in alkaline media. Low-molecular carboxylic acids were identified as ultimate oxidation by-products formed in the reaction.

Effect of mixing on enzymatic hydrolysis of cardboard waste: Saccharification yield and subsequent separation of the solid residue using a pressure filter

Cellulosic wastes, from sources such as low-quality cardboard and paper, are regarded as potential feedstocks for bioethanol production. One pathway from these cellulosic materials to ethanol is saccharification (hydrolysis) followed by fermentation. Saccharification is commonly performed using enzymes that are able to cleave the cellulosic structure to smaller units, preferably to glucose monomers. During the hydrolysis, mixing conditions have a considerable impact on the performance of the enzymes. Thus mixing conditions in the hydrolysis tank can also influence the downstream operations and, consequently, the overall economy of the bioethanol process. In this experimental study, four types of impeller, at different hydrolysis conditions were used. The effect of mixing on the glucose yield and on the filtration characteristics of the hydrolysate was evaluated. It was shown that not only the sugar yield depended on the mixing conditions: the effect on the solid-liquid separation step was even more significant.

Application of CFD simulation to suspension crystallization—factors affecting size-dependent classification

Abstract A size-dependent classification function, which is a parameter used to characterise crystallization in imperfectly mixed suspensions, was simulated using CFD. The CFX4.2 program was employed to simulate the local particle-size distribution in a multifluid flow using the k−e turbulence model with respect to interface transfer between the particles and the solution. The problem was studied three dimensionally. A sliding grid technique was used to simulate the transient flow in the mixing tank. The size-dependent classification was calculated based on the local particle-size distribution. The factors that affect the classification function are discussed.

Fluorescence Properties Reinforced by Proton Transfer in the Salt 2,6-Diaminopyridinium Dihydrogen Phosphate

Luminescent materials have many interesting applications, but it remains difficult to control the luminescence of organic materials and in particular to retain the same luminescence in solution and in the solid state, a property of interest for various imaging applications. In the present work, the fluorescent properties of the salt of 2,6-diaminopyridinium with dihydrogen phosphate have been explored. As a result of proton transfer from phosphoric acid to the pyridine nitrogen and the stabilizing effect of the two primary amines at the positions ortho to the pyridine nitrogen, the band gap between the HOMO and the LUMO is considerably diminished in comparison with that in 2,6-diaminopyridine. This is confirmed by a red shift in its absorption spectrum. Because protonation is retained in aqueous solution, the dissolved 2,6-diaminopyridinium dihydrogen phosphate salt retains a similar fluorescent spectrum as in the solid state. The crystals have been studied by single-crystal X-ray diffraction; FTIR, Raman, UV-vis-NIR, and luminescence spectroscopy; HOMO-LUMO calculations using DFT; and thermal analysis. The compound provides an example of a supramolecular motif that controls the crystal structure and the luminescence properties. In addition, the crystal exhibits negligible thermal expansion over a temperature interval of 150 °C. In short, 2,6-diaminopyridinium dihydrogen phosphate is an interesting compound for the design of luminescent devices.

Oxidation of Aqueous Paracetamol by Pulsed Corona Discharge

Oxidation of paracetamol in aqueous solution was studied by using pulsed corona discharge as a means for advanced oxidation. Pulse repetition frequency, the delivered energy dose, and oxidation media were the main parameters evaluated. The pulsed corona discharge treatment appeared to be effective in oxidation of paracetamol: complete degradation of target pollutant together with partial mineralization was achieved at moderate energy consumption; oxidation proceeds faster in alkaline media, the fastest oxidation rate was observed in oxygen-enriched air. Low-molecular carboxylic acids were identified as the products formed in the reaction.

Crystallization kinetics of potassium sulfate in an MSMPR stirred crystallizer

Abstract Experimental work on a potassium sulfate-water system was carried out using ten and fifty liter crystallizers. Different impeller velocities and suspension densities were used. The crystal size distribution was determined over the range from 0.1 μm to the largest crystals, which have been produced in the crystallizers, by the combination of Coulter LS-130 light scattering laser and by Vidas image analyzer results. Experimental evidence from continuous crystallizers frequently shows, at least for small crystals, deviation from the McCabe ΔL law. In this case, the estimation of kinetics of both nucleation and growth rate becomes more complicated. In this work the crystal size distribution was determined experimentally. The relation between growth rate and particle size is investigated. The methods of estimation of kinetics for industrial use are discussed. The experimental data of population density distribution was fitted directly by the three-parameter model presented by Mydlarz and Jones for a steady state MSMPR crystallizer. Then the relation between growth rate and particle size was calculated by the corresponding three-parameter growth rate model. The relation between growth rate and particle size shows that the apparent crystal growth rate increases linearly with the crystal size when the crystal size is smaller than about 10 μm, is strongly size-dependent when the crystal size is between 10–700 μm, and is size-independent when the crystal size is greater than 700 μm. A mechanism of growth rate dispersion is suggested.

Activity Coefficients of Potassium Dihydrogen Phosphate in Aqueous Solutions at 25°C and in Aqueous Mixtures of Urea and this Electrolyte in the Temperature Range 20–35°C

Abstract Simple two-parameter Hückel and Pitzer equations were determined for the calculation of the activity and osmotic coefficients of aqueous solutions of potassium dihydrogen phosphate at 25°C up to a molality of the saturated solution (= 1.83 mol kg−1). The isopiestic data measured by Stokes (1945) were used in the parameter estimations. The resulting parameter values were tested with all thermodynamic data found in the literature for this electrolyte at this temperature. In these tests it was observed, that the Hückel equation applies to the data within experimental error up to a molality of 1.0 mol kg−1, and the Pitzer equation applies well to the data in the molality range 1.0–1.83 mol kg−1 but not very well in dilute solutions. Therefore, also a three-parameter Pitzer equation was determined that applies to all data. The activity and osmotic coefficients calculated by these three models were compared to the values suggested by Robinson and Stokes (1959) and to those calculated by the equations of Hamer and Wu (1972) and of Pitzer and Mayorga (1973) for this electrolyte. Solubility measurements of KH2PO4 at 20, 25, 30 and 35°C were made in aqueous urea solutions, and the molality of urea varied in these measurements from 0 to 2.5 mol kg−1. The thermodynamics of these studies were analyzed by using the Pitzer formalism. It was observed that only one interaction parameter between urea molecules and ions (this parameter is linearly dependent on the temperature) was needed to describe almost completely the new solubility data.

Pulsed corona discharge oxidation of aqueous lignin: decomposition and aldehydes formation

Lignin is the mass waste product of pulp and paper industry mostly incinerated for energy recovery. Lignin is, however, a substantial source of raw material for derivatives currently produced in costly wet oxidation processes. The pulsed corona discharge (PCD) for the first time was applied to lignin oxidation aiming a cost-effective environmentally friendly lignin removal and transformation to aldehydes. The experimental research into treatment of coniferous kraft lignin aqueous solutions was undertaken to establish the dependence of lignin oxidation and aldehyde formation on the discharge parameters, initial concentration of lignin and gas phase composition. The rate and the energy efficiency of lignin oxidation increased with increasing oxygen concentration reaching up to 82 g kW−1 h−1 in 89% vol. oxygen. Oxidation energy efficiency in PCD treatment exceeds the one for conventional ozonation by the factor of two under the experimental conditions. Oxidation at low oxygen concentrations showed a tendency of the increasing aldehydes and glyoxylic acid formation yield.

Thermodynamics and kinetics of KDP crystal growth from binary and ternary solutions

The influence of solution thermodynamics and surface kinetics on the growth of single potassium dihydrogen phosphate (KDP) crystals from aqueous solutions in the presence of relatively high concentrations of organic compounds have been studied. Urea, 1-propanol and ethanol were used as the organic compounds. It was shown that the mean activity coefficient of the KDP species in the studied ternary system was successively derived based on the Pitzer activity equations and that the growth processes at different organic compound systems were described using the resulting activity-based driving force. The growth rates of single KDP crystals were measured in pure aqueous and water-organics solutions as functions of supersaturation, the velocity of the solution over a single crystal and the concentration of organics. The results reveal that, in pure solutions, the growth kinetics follows the Burton–Cabrera–Frank (BCF) surface diffusion mechanism and, at a relatively low solution velocity, the growth is controlled by both diffusion and the surface integration mechanism according to the two-step model. In the studied range of organics concentrations, the influence of urea on the growth rate is less important, while that of alcohols is significant. This evidence was explained by the chemical nature of urea and alcohol molecules for adsorption on the growth surface.