Václav Lochař

Mechanism of selective oxidation of methanol over stannic oxide-molybdenum oxide catalyst

The mechanism of the selective oxidation of methanol on Sn-Mo oxide catalyst with molar ratio Mo/(Mo + Sn) = 0.3 is investigated. The interaction of methanol and its oxidation products (i.e. formaldehyde and methyl formate) is studied by FT-IR spectroscopy. The data are interpreted on the basis of a reaction mechanism which contains 10 elementary steps. The behaviors of the surface species (methoxy, formate and dioxymethylene groups) are compared with those monitored on other systems and the catalyst requirements for the title reaction are discussed.

Formulation and dissolution kinetics study of hydrophilic matrix tablets with tramadol hydrochloride and different co-processed dry binders

The aim of this study is to present the possibility of using of co-processed dry binders for formulation of matrix tablets with drug controlled release. Hydrophilic matrix tablets with tramadol hydrochloride, hypromellose and different co-processed dry binders were prepared by direct compression method. Hypromelloses Methocel™ K4M Premium CR or Methocel™ K100M Premium CR were used as controlled release agents and Prosolv® SMCC 90 or Disintequik™ MCC 25 were used as co-processed dry binders. Homogeneity of the tablets was evaluated using scanning electron microscopy and energy dispersive X-ray microanalysis. The release of tramadol hydrochloride from prepared formulations was studied by dissolution test method. The dissolution profiles obtained were evaluated by non-linear regression analysis, release rate constants and other kinetic parameters were determined. It was found that matrix tablets based on Prosolv® SMCC 90 and Methocel™ Premium CR cannot control the tramadol release effectively for >12h and tablets containing Disintequik™ MCC 25 and Methocel™ Premium CR >8h.

Compressibility of tableting materials and properties of tablets with glyceryl behenate

Abstract The paper studies the compressibility of directly compressible tableting materials with dry binders, spray-dried lactose and microcrystalline cellulose, and glyceryl dibehenate at various concentrations. Compressibility was evaluated by means of the energy profile of compression and tensile strength of tablets. Release rate of the active ingredient, salicylic acid, from the tablets was also examined. In the case of microcrystalline cellulose, a higher concentration of glyceryl dibehenate increased the strength of tablets, while this did not occur in the case of spray-dried lactose. Increasing concentration of glyceryl dibehenate prolonged the release of salicylic acid; however, no statistically significant difference was found compared to the type of the dry binder used

A Study of Tablets with a Co-Processed Dry Binder Containing Hypromellose and Α-Lactose Monohydrate

The paper examines the co-processed dry binder RetaLac from the aspect of its compressibility and dissolution of the active ingredient from tablets. RetaLac contains α-lactose monohydrate and hypromellose in the identical proportion. The same parameters are tested in the corresponding physical mixtures of Flowlac100 and various types of hypromellose (Metolose 100SR, Metolose 4000SR, Metolose 100000SR) and compared with the substance RetaLac. Compressibility is evaluated by means of the energy profile of compression and tensile strength of tablets. The values of the total energy of compression and plasticity were higher in the substance RetaLac than in the physical mixtures of lactose and various types of hypromellose; tablet strength, on the contrary, was lower. Dissolution profile of the active ingredient from tablets with RetaLac corresponded to the dissolution profile of tablets from a physical mixture of Flowlac 100 and Metolose 4000SR.

Why is the hydrolytic activity of acetylcholinesterase pH dependent? Kinetic study of acetylcholine and acetylthiocholine hydrolysis catalyzed by acetylcholinesterase from electric eel

Abstract The dependence of the activity of acetylcholinesterase from electric eel at a pH value range of 4.8–9.8 (phosphate buffer), regarding acetylcholine and acetylthiocholine hydrolysis, was determined at 25 °C, ionic strength of 0.11 M, and initial substrate concentration of 4 mM. At a pH range of 4.8–9.8, the dependences A(pH) form a sigmoid increasing curve with the maximum catalytic activity at a pH range 8–9.5. For acetylcholine hydrolysis, the kinetic reason for such an increase in A consists mainly of an increase in the rate constant k2 (Michaelis-Menten) model with increasing pH of the reaction mixture. For acetylthiocholine hydrolysis, the kinetic explication of the determined dependence A(pH) is more complicated.

Comparative evaluation of the use of dry binders in a physical mixture or as a coprocessed dry binder in matrix tablets with extended drug release

Abstract This paper evaluates and compares the properties of directly compressible tabletting materials and matrix tablets containing a combination of α-lactose monohydrate and microcrystalline cellulose in the 3:1 ratio in a physical mixture and in a coprocessed dry binder. Tested parameters include flow properties, compressibility, compactibility and the rate of drug release from tablets. Compressibility is evaluated by means of the energy profile of the compression process. Compactibility is evaluated by means of the tensile strength of the tablets. Dissolution testing is done using the rotating basket method. Dissolution profiles are evaluated by non-linear regression analysis. Total energy of compression and plasticity values were higher in tabletting materials with the coprocessed dry binder. Increasing additions of polyvinyl alcohol decreased the values of total energy of compression, plasticity, tensile strength of tablets and drug release rate. Dissolution behaviour of tablets, which contained the physical mixture or coprocessed dry binder and the same amount of polyvinyl alcohol, was comparable.