Biomedical subjects

Bernd Ondruschka

Publications and source records attributed to Bernd Ondruschka.

8 recordsLinked to original sources

PubMed2005

Roles of hydrophobicity and volatility of organic substrates on sonolytic kinetics in aqueous solutions.

The aquasonolytic rate constants of cyclic C6H(X), aliphatic C6H(X), thioethers, thiophenes, and N-heterocyclic compounds show over a 90-fold variation under identical conditions of ultrasonic irradiations. Henry's Law constant of the substrate has a substantial effect on the aquasonolytic rate; a higher Henry's Law constant leads to a aquasonolytic rate constant, which indicating the transfer process of organic substrate between bulk liquid and cavitational bubbles is essential for aquasonolysis. The aquasonolytic rate constants, however, dramatically show an irregular variation with increasing vapor pressure among various substrates. Although the volatility of substrate has been widely regarded as a basic factor influencing aquasonolysis, it seems that vapor pressure of substrate is not a determining one that accounts for the difference of aquasonolytic rate constants. In contrast, the hydrophobic parameters of volatile substrate such as water solubility and octanol-water partition coefficient have shown obvious correlation with the aquasonolytic rate constant for the model compounds; a higher hydrophobicity of volatile substrate results in a higher aquasonolytic rate constant. It could be concluded that the transfer process from bulk liquid to cavitational bubbles and the aquasonolytic kinetics of organic substrate are jointly controlled by the hydrophobicity and volatility; therein the hydrophobicity dominates the transfer process and the aquasonolysis of volatile substrate.

Journal Article↗

PubMed2005

Aquasonolysis of thioethers.

The aquasonolytical rate constants and products of diethyl sulfide, diallyl sulfide, dipropyl sulfide, dibutyl sulfide, diethyl disulfide, and dipropyl disulfide have been investigated. The sonolysis for model compounds in aqueous solutions follows the pseudo-first-order kinetics. Disulfides are more rapidly sonicated than sulfides. Neither vapour pressure nor thermostability of thioethers can obviously affect their aquasonolytical rates. Higher Henry's Law constant and hydrophobicity of substrate result in a higher aquasonolytical rate constant. Furthermore, the aquasonolytical rate constant decreases as the initial concentration of dipropyl sulfide increases. CS2, COS, thiols, thiirane, lower sulfides, butenyne, and butadiene are detected as principal very volatile products during ultrasonic irradiations. Thiophene, benzene, 1,5-hexadiene, and cyclopentadiene are additionally obtained during the aquasonolysis of diallyl sulfide. Furthermore, trisulfides, trithiolane, and other cyclic thiolanes as volatile products are observed. These results demonstrate that thioethers undergo thermal decomposition during their aquasonolyses. The transfer process of volatile thioethers between cavitation bubbles and bulk liquid remarkably affect the aquasonolysis, and the hydrophobicity of substrate dominates the transfer process.

Journal Article↗

PubMed2005

Ultrasonic cleavage of thioethers.

The rates of DPPH (diphenylpicrylhydrazyl) trapping and the sonolytical products obtained during the sonolysis of thioethers at normal and low temperature are reported. CS2, lower sulfides, thiophene, and sulfurized species are the common products during the ultrasonic irradiations. Hydrocarbons are also obtained during the sonolysis of diallyl sulfide, diethyl disulfide, and dipropyl disulfide. Furthermore, aldehydes are obtained as oxidized species; SO2 is found at 208 K. The principal sonochemical process appears to be the cleavage of C-S or S-S bond with secondary combinations and rearrangements. DPPH has been used to probe the sonolytical potential of thioethers. The results show a good correlation between the rates of DPPH trapping and the vapor pressures of thioethers. In conclusion, a lower vapor pressure results in a higher sonolytical rate. The sonochemical behaviors of thioethers have strong qualitative similarities to the pyrolysis.

Journal Article↗

PubMed2005

Sonochemical reaction of selected cyclic C6Hx hydrocarbons in organic solvents.

The rates and products of the sonochemical reactions of benzene, 1,4-cyclohexadiene, 1,3-cyclohexadiene, cyclohexene, and cyclohexane in selected organic solvents have been investigated. The sonochemical reactions of these educts in the investigated organic solvents follow first-order kinetics. Generally, they are sonicated more rapidly in polar than in non-polar solvent; higher volatility of the solute results in faster sonolysis in the organic solvents. However, the sonication of cyclohexane in n-decane and the sonication of benzene in n-propanol are exceptional cases. Since cyclohexane exhibits a much higher lipophilicity and benzene a much higher hydrophilicity than other educts, it might be more difficult to transfer either educt from the bulk liquid into the cavitation bubbles. In tetrachloroethylene, the reactivity of the tested educts with in situ generated chlorine as well as chlorine-containing radical intermediates can accelerate the rate of sonochemical reactions under the employed conditions. In n-propanol and n-decane, the pyrolysis during the collapse of the cavitation bubbles is the only reaction pathway of sonolysis. In tetrachloroethylene, the pyrolysis during the collapse of the cavitation bubbles and the free radical reaction in the bulk liquid may occur simultaneously. Except for the products generated from sonolysis, products formed from chlorine transformations (substitution or addition reactions) are detected. Benzene is hardly decomposed in tetrachloroethylene. However, when FeCl3 is added into the reaction system, benzene is sonoconverted rapidly, and the product chlorobenzene was detected. In organic solvents, the sonoreaction rates and the sonoproducts are dependent on the physicochemical properties of the solvents used, as well as the volatility, the polarity and the reactivity of educts.

Hydrocarbons, Cyclic↗

PubMed2005

Benzene formation during aquasonolysis of selected cyclic C6Hx hydrocarbons.

Yield and selectivity of benzene produced from aquasonolysis of the selected cyclic C6Hx hydrocarbons, i.e., 1,4-cyclohexadiene, 1,3-cyclohexadiene, cyclohexene, cyclohexane, and methylcyclopentane, have been investigated in this work. Benzene cannot be detected during the aquasonolysis of cyclohexane and methylcyclopentane. The order of yield and selectivity of benzene was as follows: 1,4-cyclohexadiene>>1,3-cyclohexadiene>>cyclohexene. The initial concentrations of substrates can affect the yield of benzene. During the aquasonolysis of 1,3-cyclohexadiene and cyclohexene, other C6 species except benzene were also found. It was suggested that benzene could directly be generated by formal dehydrogenation of cyclic C6Hx hydrocarbons.

Benzene↗

PubMed2004

Aquasonolysis of thiophene and its derivatives.

The rate constants and products of the aquasonolysis of thiophene, tetrahydrothiophene, 2-methylthiophene, 2,5-dimethylthiophene, and 2-ethylthiophene have been investigated. The sonolysis of the selected compounds in aqueous solution follows pseudo-first-order kinetics. The aquasonolytical rate constants correlate very well with the water solubility and Henry's Law constants of thiophenes. Surprisingly, vapour pressures and heats of formation of thiophenes have little effect on their aquasonolytical rates. The pseudo-first-order rate constant for the decay of thiophene decreases as its initial concentration increases. These results indicate that the transfer process of organic solutes between cavitation bubbles and the bulk liquid can strongly affect the aquasonolysis. Furthermore, carbon disulfide, diacetylene, and dimers can be detected as common products during ultrasonic irradiations. Hence, the predominant pathway of the aquasonolysis of thiophenes is the pyrolysis during the collapse of cavities.

Sonication↗

PubMed2004

Aquasonolysis of selected cyclic C(6)H(x) hydrocarbons.

Aquasonolysis rates and products of selected cyclic C(6)H(x) hydrocarbons, benzene, 1,3-cyclohexadiene, 1,4-cyclohexadiene, cyclohexene, cyclohexane, and methylcyclopentane have been investigated. The sonolysis of selected compounds in aqueous solution follows first-order kinetics, and the aquasonolysis rate correlated well with the water solubility. The degradation rate decreased with the increase of initial concentration. The effect of initial concentration on the degradation of cyclohexene was more significant than that of benzene. The transfer process of organic solutes between cavitation bubbles and the bulk liquid affects the rates and products of their aquasonolysis.

Journal Article↗

PubMed2003

Tools for microwave-assisted parallel syntheses and combinatorial chemistry.

A protocol for transferring conventional reactions to the microwave field explores the effectiveness of parallel syntheses and combination approaches. Applicability to the reaction systems combiCHEM, multiPREP, MMR8 and HPR is defined. Model reactions have been performed in laboratory equipment. Emphasis is placed on similar reaction conditions in the individual vessels and the repeatability of results. Outcomes include esterifications and multi-center reactions exhibiting a great potential for combinatorial chemistry.

Acyclic Monoterpenes↗