Kinetics of phenol oxidation by peroxidase

Studies of the kinetic behavior of horseradish peroxidase (HRP) at pH 8 and at room temperature indicate that the reaction of phenol with H₂O₂ catalyzed by HRP exhibits normal Michaelis-Menten saturation kinetics. An irreversible reaction mechanism for the steady-state kinetics of HRP, which is consistent with the experimental data, is considered. The second-order rate constants for the reactions of HRP with H₂O₂ and compound II with phenol are 4.14 × 10⁵ M^-1s^-1 and 5.54 × 10⁴M^-1s^-1, respectively.     

Trimethylsilyl fluorosulfonyldifluoroacetate (TFDA): a new, highly efficient difluorocarbene reagent

TFDA is readily prepared from the reaction of fluorosulfonyldifluoroacetic acid with trimethylsilyl chloride, and it is a very effective and efficient source of difluorocarbene for use in addition reactions to alkenes of a broad scope of reactivities. Acid-sensitive substrates may require an additional purification step involving treatment of the distilled TFDA with sufficient Et₃N to remove the acid impurity. Other trialkylsilyl fluorosulfonyldifluoroacetates can also be prepared, and they have been found to have reactivities similar to TFDA. The triethyl derivative, TEFDA is more convenient to prepare in a pure state and has similar reactivity to TFDA. Thus, it may prove to be a superior reagent.     

Detection of nisin expression by Lactococcus lactis using two susceptible bacteria to associate the effects of nisin with EDTA

Nisin, a bacteriocin produced during the exponential growth phase of Lactococcus lactis ATCC 11454, inhibits the growth of a broad range of Grampositive bacteria. Gram-negative bacteria can also be inhibited by nisin with EDTA. In this study, nisin production was assayed by the agar diffusion method using Lactobacillus sake ATCC 15521 and a recombinant Escherichia coli DH5-α expressing the recombinant green fluorescent protein as the nisin-susceptible test organisms. The titers of nisin expressed and released in culture media were quantified and expressed in arbitrary units (AU/mL of medium) and converted to standard nisin concentration (Nisaplin^®, 25 mg of pure nisin with an activity of 1×10⁶ AU/mL). The expression and release of nisin by L. lactis in skimmed milk (9.09% total solids) with Man Rugosa Shepeer-Bacto Lactobacilli broth (1∶1) was monitored in a 5 L New Brunswick fermentor. Combining EDTA with nisin increased the bactericidal effect of nisin on the bacteria examined. The presence of EDTA was necessary to inhibit E. coli growth with nisin. L. sake was shown to be a good indicator for the evaluation of nisin release in the culture media, including with the addition of EDTA.     

Method optimization by solid-phase microextraction in combination with gas chromatography with mass spectrometry for analysis of beer volatile fraction

A simple and sensitive method for the analysis of beer volatile compounds was optimised using headspace solid-phase microextraction (SPME) and gas chromatography with mass detection. Headspace SPME using a 75 microm Carboxen-polydimethylsiloxane (CAR-PDMS) fiber provided effective sample enrichment and enabled extraction of a wide variety of compounds. The reproducibility depended on the compounds, with a mean value of 1.4% for alcohols, 3.3% for ethers, 6.7% for aldehydes, 3.4% for acids, 1.7% for aromatic compounds, 2.4% for esters, 7.4% for hydrocarbons, 1.8% for alicyclic compounds, and 3.4% for heterocyclic compounds. The optimised methodology can be used to compare volatile profile from different types of beers and eventually to study the evolution of a particular beer during aging.     

A two-step,single pot procedure for the synthesis of substituted dihydropyrazolo-pyrimidines

In this study, we report a two-step, one pot tandem microwave-assisted reaction of 3-formylchromones with aminopyrazoles followed by a tin-free radical addition. A library of alkyl substituted dihydropyrazolopyrimidines was prepared using this new process.     

Oxidation of UO2(s) in aqueous solution

In this review the kinetics and mechanism of oxidative dissolution of UO₂(s), mainly under conditions of relevance for the safety assessment of a deep geological repository for spent nuclear fuel, are discussed. Rate constants for the elementary processes involved (oxidation of UO₂ and dissolution of oxidized UO₂) are used to calculate the rates of oxidative UO₂(s) dissolution under various conditions (type of oxidant, oxidant concentration and HCO₃ ⁻/CO₃ ²⁻ concentration) for which experimental data are also available. The calculated rates are compared to the corresponding experimental values under the assumption that the experimental numbers reflect the steady-state conditions of the system. The agreement between the calculated rates and the corresponding experimental ones is very good, in particular for the higher rates. In general, the calculated rates are somewhat higher than the experimental numbers. This can be due partly to the use of initial concentrations rather than steady-state concentrations in the calculations. The kinetic data are also used to quantitatively discuss the dynamics of spent nuclear fuel dissolution under deep geological repository conditions.      

Spectacular induced-fit process for guest binding by a calix[6]arene Zn(II) funnel complex

The host properties of a calix[6]arene cone capped by a Zn(II) tris-imidazole core at the small rim and decorated by three NH(2) substituents at the large rim are described and compared to the hexa-tBu parent complex. It is shown that the replacement of three bulky tBu substituents by three hydrophilic and small NH(2) groups has three major impacts: the receptor is now soluble in aqueous media, it accepts large guests such as dimethyldopamine and, most interestingly, undergoes a spectacular induced-fit behavior for guest binding.     

Reactivity of a two heteroatom stabilized anionic chromium (0) carbene complex towards a mono- and a disubstituted alkyne: New synthesis of γ-aminobutenolides and formation of a novel oligomer chromium (0) complex

The reaction of the chromium anionic carbene complex 1 towards diphenylacetylene and phenylacetylene is reported. In the former case the synthesis of γ-functionalized butenolides results after demetallation of the chromium complex 2 and the latter leads to the formation of a novel oligomer chromium complex 5. These complexes were characterized by mass spectrometry, IR and ¹H and ¹³C NMR spectroscopies and their structures were confirmed by single-crystal X-ray analysis.     

Managing contribution and capital market risk in a funded public defined benefit plan: Impact of CVaR cost constraints

Using a Monte Carlo framework, we analyze the risks and rewards of moving from an unfunded defined benefit pension system to a funded plan for German civil servants, allowing for alternative strategic contribution and investment patterns. In the process we integrate a Conditional Value at Risk (CVaR) restriction on overall plan costs into the pension manager’s objective of controlling contribution rate volatility. After estimating the contribution rate that would fully fund future benefit promises for current and prospective employees, we identify the optimal contribution and investment strategy that minimizes contribution rate volatility while restricting worst-case plan costs. Finally, we analyze the time path of expected and worst-case contribution rates to assess the chances of reduced contribution rates for current and future generations. Our results show that moving toward a funded public pension system can be beneficial for both civil servants and taxpayers.