Reaction Rate

The utilization of ultrasound radiation in the Baylis–Hillman reaction with several aldehydes (aromatics and aliphatics) and different α,β-unsaturated reactants is described. For all aldehydes tested, the utilization of ultrasound sources augmented the reaction rate and the chemical yields. The use of ultrasound with two different catalysts (tri-n-butylphosphine and 1,4-diazabicyclo[2.2.2]octane [DABCO]) was also investigated. It was clearly demonstrated that DABCO is much more effective for catalyzing a Baylis–Hillman reaction under the influence of ultrasound than is tri-n-butylphosphine. No effect on reaction rate was observed when the concentration of DABCO was increased.The scope of the utilization of ultrasound radiation in the Baylis–Hillman reaction with several aldehydes (substituted aromatics and aliphatics) is described. For all aldehydes tested, the use of ultrasound sources augmented the reaction rate and the chemical yields. Ultrasound radiation is also compatible with...

HIV-1 integrase is responsible for one of the key steps of the viral replication, integration of the viral cDNA into the host cell genome. Integration inhibition leads to complete block of the virus replication. In this study inhibition of integration by dimeric bisbenzimidazoles DBBI(7) with heptamethylene and DBBI(8) with tri(ethylene glycol) spacers was examined, and it was learned out that IC50 for DBBI(7) was about 0.03 microM, and IC50 for DBBI(8) was about 10 microM. By using cross-linking assays, it was shown that both compounds impeded a proper disposition of DNA-substrate at the active centre of integrase. Dissociation constants for complexes between either DBBI and DNA-substrate of integrase were determined. Calculated Kd values were 270 nM and 140 nM for complexes formed by DBBI(7) and DBBI(8), respectively. Therefore, inhibition of integration does not directly result from the binding of DBBIs with DNA. The dependence of initial rates of enzymatic reaction on the DNA-substrate concentration in presence of different concentrations of inhibitors was found, and inhibition constants were determined. All the data obtained allow us to suppose that the different inhibition activity of DBBI(7) and DBBI(8) results from the different mechanism of their binding: DBBI(7) is a competitive inhibitor of integrase whereas DBBI(8) is assumed to show a more complex mechanism of inhibition.

Hydrochlorous acid bleaches c-phycocyanin visible absorbance with a second-order rate constant (pH 7.4) of 1.3x10(3) M(-1) s(-1). In excess of protein, ca. 0.16 bilin moieties are disrupted by each reacted HOCl molecule. This indicates that the main reaction takes place at the apoprotein level, with a total rate constant (in monomeric units concentration) of 2.5x10(4) M(-1) s(-1). This rate constant is too low to provide protection to other biomolecules under physiological conditions. The reported antiinflammatory properties of phycocyanin are not then related to the removal of HOCl. On the other hand, the rather slow reaction rate with HOCI could be beneficial to its role as antiinflammatory agent since it will allow the protein to maintain its integrity at the inflammation locus.

Metal dispersion and support effects on Fischer-Tropsch synthesis rate and selectivity were studied at conditions that favor the information of C 5 + hydrocarbons (> 80% selectivity). On Ru, these effects are minor for the supports (SiO 2 , Al 2 O 3 , TiO 2 ) and the dispersion range ...

The kinetic consequences of resonance tunnelling processes that may occur in chemical reactions are investigated in terms of a multi-centered unsymmetrical Eckart potential barrier. This potential function does not only simulate the possible existence of intermediate wells in the effective potential energy cut along the reaction path, but also is amenable to analytic solutions. The reaction rate as well as its dependence on temperature, reduced mass,Q-value, activation energy and barrier diffuseness are evaluated for successively increasing the number of barrier stages. Comparisons between results due to single and multi-humped potential energy barriers are made and discussed.

Information about the times of thermal breakthrough and subsequent rates of thermal drawdown in enhanced geothermal systems (EGS) is necessary for reservoir management, designing fracture stimulation and well drilling programs, and forecasting economic return. Thermal breakthrough in heterogeneous porous media can be estimated using conservative tracers and assumptions about heat transfer rates; however, tracers that undergo temperature-dependent changes can provide more detailed information about the thermal profile along the flow path through the reservoir. To be effectively applied, the thermal reaction rates of such temperature sensitive traces must be well characterized for the range of conditions that exist in geothermal systems. Reactive tracers proposed in the literature include benzoic and

Cyanide is a highly toxic anion and ingestion exposure can be fatal. Cyanide can be removed from water systems using Zn-Al-OAc hydrotalcite (OAc-=acetate) as an ion exchanger. A synthesis of Zn-Al-OAc hydrotalcite has been performed and it was used as an anion exchanger to reduce the concentration of cyanide in the form of [Fe(CN)6]4-. Zn-Al-OAc hydrotalcite was prepared using a stoichiometric method followed by hydrothermal treatment. The chemical composition of Zn-Al-OAc hydrotalcite was found to be Zn0.73Al0.27(OH)2(OAc)0.27.0.95H2O. The anion exchange reaction of OAc- by [Fe(CN)6]4- was fit to yield a second order reaction rate constant of k = 0.215 M-1s-1 with R2=0.996. The anion exchange capacity (AEC) was found to be 219 meq [Fe(CN)6]4-/100 g hydrotalcite. It was found that Zn-Al-Fe(CN)6 hydrotalcite could not be regenerated by OAc-.

The degradation of title dyes with ferrioxalate and H2O2 couple has been investigated spectrophotometrically. In the absence of either one of the oxidizing agents no degradation occurred. The reaction rate was proportional to moderate concentrations of the dye and H2O2. At high concentration of the dye and H2O2 the reaction rate decreased. With regard to the concentration of the ferrioxalate

The ability of peroxidases and laccases enzymes to treat organic pollutants is reviewed. Enzymatic methods generally have low energy requirements, are easy to control, can operate over a wide range of conditions and have a minimal environmental impact. Peroxidases and laccases have broad substrate specificities and can catalyze the oxidation of a wide range of toxic organic compounds. The results show that an enzymatic oxidation can diminish the toxicity of some polycyclic aromatic hydrocarbons (PAHs), phenols, organophosphorus pesticides and azo dyes in laboratory and some field conditions. Due to the hydrophobicity and low aqueous solubility of these substrates, reactions are usually performed in the presence of organic solvents. However, it was detected that organic solvents can provoke enzyme denaturation, unfavorable substrate partition, inhibition or stabilization of enzyme–substrate complexes, depending on the enzyme, substrate and organic solvent used. Strategies to overcome these problems are proposed. Additionally, the low stability of heme-containing peroxidases to hydrogen peroxide, the low reaction rates of laccases, the mediators toxicity, the limited availability and high costs of these enzymes are other limitations detected for commercial applications. Due to field reaction conditions are more complex than laboratory conditions efforts have to be made to achieve the cheap overproduction of these biocatalysts in heterologous hosts and also their modification by chemical means or protein engineering to obtain more robust and active enzymes.

The stability of the contraceptive steroid, Nestorone (16-methylene-17 alpha-acetoxy-19-nor-pregn-4-ene-3,20-dione) in the solid state and in aqueous solutions, was investigated using reverse-phase high-performance liquid chromatography. In the solid state, whether as a powder or when it is incorporated into Silastic implants, the steroid does not undergo detectable degradation even under severe experimental conditions. In solution, the drug undergoes slow degradation that is dependent on temperature and pH of the medium. The decomposition is defined by first-order mechanism. As expected, the reaction rate increases with increasing storage temperature. The linearity of the Arrhenius plot indicates that there is no change in the reaction mechanism within the temperature range studied. In alkaline media, the drug degrades at a faster rate through hydrolytic rather than an oxidative mechanism. The major hydrolytic degradation product, 16-methylene-17 alpha-hydroxy-19-nor-pregn-4-ene-3,...