The interference of HEPES buffer during amperometric detection of ATP in clinical applications

HEPES-based biological buffer is subject to photooxidation upon exposure to fluorescent illumination. Thereby hydrogen peroxide is generated, which interferes with amperometric oxidoreductase-based biosensors for glucose or adenosine triphosphate (ATP). These biosensors operate at an oxidation potential above 500 mV vs. the standard calomel electrode (SCE) and involve hydrogen peroxide as the electroactive molecule detected at the electrode surface. False-positive detection of ATP was observed in HEPES buffer utilizing an amperometric microbiosensor based on the co-immobilization of glucose oxidase and hexokinase for detection of ATP in biological specimens. Electrochemical, mass spectrometric, ³¹P NMR, and ¹H NMR studies indicate that complexation of ATP and HEPES induced by the presence of Ca²⁺ in HEPES buffer decreases the photooxidation of HEPES. Consequently, the hydrogen peroxide background concentration is reduced, thereby leading to erroneous ATP detection at the dual-enzyme microbiosensor, which determines an increase in ATP via a reduced hydrogen peroxide signal.     

Elucidation by computer simulations of the CUS regeneration mechanism during HDS over MoS<Subscript>2</Subscript> in combination with <Superscript>35</Superscript>S experiments

The first part of this paper is a short review of the ³⁵S radioactive tracer methods developed in recent years. Then, the experimental results obtained so far on Mo/Al₂O₃ catalysts are compared with computer simulation results recently claimed in order to elucidate the coordinatively unsaturated site (CUS) creation/replenishment/ regeneration mechanism over MoS₂ crystallites. The computer simulations allowed us to pre-select thermodynamically acceptable mechanisms among a set of suggested ones. Then, by comparison of the calculated activation energies with the ³⁵S experiments results we could further validate the most probable mechanism. This mechanism involved the dissociative adsorption of an H₂ molecule on the metallic edge of a MoS₂ crystallite surface with further creation of a CUS by release of one H₂S molecule in the gas phase. Both laboratory and computer simulated experiments permitted to calculate the activation energy for the H2S liberation reaction. In both cases, this energy was about 10- 12 kcal/mol, confirming the accuracy of the proposed mechanism. Moreover, the calculated activation energy of the rate-limiting step for the creation of one CUS by the proposed mechanism was about 23 kcal/mol, which was also in good agreement with the experimental activation energy of the dibenzothiophene (DBT) hydrodesulphurisation (HDS) reaction (typically about 20- 22 kcal/mol). This correlation indicated that the DBT HDS reaction rate might be intrinsically governed by the CUS formation/replenishment process, i.e. that the vacancy formation process is a crucial parameter in the global HDS reaction mechanism. Nevertheless, in the case of the 4,6-dimethyl DBT (4,6-DMDBT) HDS reaction, the experimental activation energy is higher (approx. 30 kcal/mol), confirming that external parameters induced by the 4,6-DMDBT-specific properties themselves are likely to play an important role in the reaction process, in addition to the ones intrinsic to the catalytic phase.     

Phase transitions of an ionic liquid self-assembled monolayer on Au

The properties of a surface modified with an ionic liquid self-assembled monolayer (IL-SAM) can be tuned by simply changing the deposition temperature. Mid-IR, SERS, and molecular modelling demonstrated that 1-(12-mercaptododecyl)-3-methylimidazolium bromide (MDMIBr) exhibited a crystalline monolayer for deposition temperatures below 25 °C. Above 25 °C, the aliphatic chain collapsed into a disordered conformation. At 40 °C, another phase transition occurs due to the imidazolium group tilting parallel to the surface. Consequently, the wettability of IL-SAM was tuned over a broad range of contact angle (from 20° to nearly 40°) by varying the deposition temperature. Permeation of redox mediators to a Au electrode coated with MDMIBr strongly depends on the net charge of the redox mediator. Electron transfer was excellent for neutral and negatively charged redox mediators on electrodes coated with IL-SAM regardless of deposition temperature.     

Photoconduction in [Fe(Htrz)2(trz)](BF4)·H2O nanocrystals

Sub-micron-sized [Fe(Htrz)(2)(trz)](BF(4))·H(2)O nanoparticles that exhibit a spin crossover transition are positioned between Au electrodes with sub-100 nm separation. After voltage poling, samples exhibit unexpected large conductivity, with photoconductance and photovoltaic behavior.     

Synthesis of Isobrassilexin,a Biologically Active Isomer of Brassilexin,a Cruciferac Phytoalexin

The synthesis of isobrassilexin 2, a hitherto non natural indoloisothiazole is reported (two steps, 43% yield). This substance, an isomer of brassilexin 1 has shown important biological properties in vitro.     

Predicting variability in the dynamic failure strength of brittle materials considering pre-existing flaws

We perform two-dimensional dynamic fracture simulations of a specimen in biaxial tension, incorporating various distributions of pre-existing microcracks. The simulations consider the spatial distribution of flaws while modeling the discrete failure processes of crack interactions and coalescence, and predict the macroscopic variability in failure strength. The model quantitatively predicts the effect (on the dynamic failure strength) of different shapes of the flaw size distribution function, the random spatial distribution of flaws, and the random local resistance to crack growth (i.e. strength) associated with each flaw. The effect of changing material volumes on the variability in failure strengths is also examined in relation to the flaw size distribution. The effect of loading rate on the variability in failure strengths is presented in a form that will enable improved constitutive modeling using non-local formulations at the continuum scale.     

Molecular orbitals and photoelectron spectra of some titanium(IV) organometallic compounds

The photoelectron spectra of some titanium(IV) organometallic compounds are reported, and the data and the bonding in the compounds are discussed with the aid of extended CNDO/2 calculations.     

Palladium and nickel-catalyzed reaction of grignard reagents with trichloroethylene. A simple synthesis of 1,1-dichloroalkenes.

The palladium (or nickel) catalyzed reaction of Grignard reagents with trichloroethylene affords 1,1-dichloroalkenes in good yield under mild conditions.     

How to use a very simple microcomputing system for a dynamical conformational analysis of versatile molecules. The case of some anticancer inorganic ring systems

A very simple use of a suitable microcomputing system allows discrimination of a set of X-ray structures of anticancer drugs which (i) are the “natural” preferred conformations and (ii) are the direct relationships logically linking these conformations together. Such an approach appears the main interest for a deep understanding of the relative antitumour activities of drugs, whatever the target may be.