Reaction Kinetics of the Benzylation of Adenine in DMSO: Regio-Selectivity Guided by Entropy.

The factors governing the regio-selectivity of the alkylation of adenine have been of interest for many years due to the biological importance of adenine derivatives, however, no reaction kinetic studies have been conducted. Herein, we report the rate constants and activation parameters of the benzylation of adenine under basic conditions in DMSO in the absence and presence of 15-crown-5 ether using real-time H NMR spectroscopy. The reaction is second-order for the formation of the N9- and N3-benzyladenine products, with a regio-selectivity factor 2.

Uncovering thermally activated purple-to-blue luminescence in Co-modified MgAl-layered double hydroxide.

Thermally activated blue-to-purple luminescence of Co-modified nano-sandrose MgAl-layered double hydroxides (LDHs) is concentration dependent, occurring only for MgCoAl-LDH with a molar metal cation concentration of 15% Co. Temperature sweep luminescence spectroscopy between 83 K and 298 K shows that the luminescence is strongest at room temperature, increasing with an activation energy of 1 kJ mol between these temperatures. The luminescence occurs in a broad, but fine-structured band below the conduction band (CB) edge at 3.

Preserving Cultural Diversity in Rural Africa Using Renewable Energy.

Ninety percent of the large interior, rural part of Africa is not an abundant user of fossil fuels and is not connected to an electricity grid. This limits habitability and leads to significant migration to larger cities in attempts to improve economic and social welfare, which happens at the cost of its rich cultural diversity by inevitable adaption and mixing of societies. A direct transition from a firewood to an off-grid renewable electricity age can mitigate this detrimental development.

What Is Heat? Can Heat Capacities Be Negative?

In the absence of work, the exchange of heat of a sample of matter corresponds to the change of its internal energy, given by the kinetic energy of random translational motion of all its constituent atoms or molecules relative to the center of mass of the sample, plus the excitation of quantum states, such as vibration and rotation, and the energy of electrons in excess to their ground state. If the sample of matter is equilibrated it is described by Boltzmann's statistical thermodynamics and characterized by a temperature . Monotonic motion such as that of the stars of an expanding universe is work against gravity and represents the exchange of kinetic and potential energy, as described by the virial theorem, but not an exchange of heat.

Towards a Molecular Understanding of Cation-Anion Interactions and Self-aggregation of Adeninate Salts in DMSO by NMR and UV Spectroscopy and Crystallography.

Rare anionic forms of nucleic acids play a significant biological role and lead to spontaneous mutations and replication and translational errors. There is a lack of information surrounding the stability and reactivity of these forms. Ion pairs of mono-sodium and -potassium salts of adenine exist in DMSO solution with possible cation coordination sites at the N1, N7 and N9 atoms of the purine ring.

Superatom chemistry: promising properties of near-spherical noble metal clusters.

Properties of near-spherical metal clusters are best understood on the basis of the concept of conventional atoms. Their conduction electrons occupy cluster orbitals that remind of hydrogen-like orbitals since they have the same angular dependence. When populated with electrons, maxima in their ionization potentials and minima in electron affinities reveal the closing of shells in the same sense as for noble gases.

In command of non-equilibrium.

The second law of thermodynamics is well known for determining the direction of spontaneous processes in the laboratory, life and the universe. It is therefore often called the arrow of time. Less often discussed but just as important is the effect of kinetic barriers which intercept equilibration and preserve highly ordered, high energy non-equilibrium states.

Understanding catalysis.

The large majority of chemical compounds underwent at least one catalytic step during synthesis. While it is common knowledge that catalysts enhance reaction rates by lowering the activation energy it is often obscure how catalysts achieve this. This tutorial review explains some fundamental principles of catalysis and how the mechanisms are studied.

Platinum-hydrogen vibrations and low energy electronic excitations of 13-atom Pt nanoclusters.

Two Pt-H vibrational bands at 1679 cm(-1) and 1392 cm(-1) observed with 13-atom Pt clusters supported in LTL zeolite by Fourier Transform Infrared (FTIR) spectroscopy confirms that H atoms bridge two Pt atoms across the edges of the metal cluster. An additional broad absorption band centred near 2200 cm(-1) which exhibits some substructure is assigned to low energy electronic excitations across the HOMO-LUMO gap of the developing band structure of the nanocluster.

Anomalous diamagnetic susceptibility in 13-atom platinum nanocluster superatoms.

We are used to being able to predict diamagnetic susceptibilities χD to a good approximation in atomic increments since there is normally little dependence on the chemical environment. Surprisingly, we find from SQUID magnetization measurements that the χD per Pt atom of zeolite-supported Pt13 nanoclusters exceeds that of Pt(2+) ions by a factor of 37-50. The observation verifies an earlier theoretical prediction.

Hydrogen storage by physisorption on dodecahydro-closo-dodecaboranes.

Hydrogen physisorption on dodecahydro-closo-dodecaborane units is studied using ab initio quantum chemical calculations based on Møller-Plesset perturbation theory. After adding zero-point energy corrections, the adsorption energy due to the charge-quadrupole and the charge-induced dipole interaction is somewhat larger than the more common dispersion interaction with spacer molecules in molecular framework compounds. Furthermore, the energy landscape on the surface of the near-spherical B12H12(2-) permits considerable residual dynamics with corresponding configurational entropy that releases partly the requirements on the magnitude of the adsorption energy.

Maximum hydrogen chemisorption on KL zeolite supported Pt clusters.

Platinum clusters supported on KL zeolites were characterized by EPR, HRTEM, and EXAFS. Two kinds of hydrogen chemisorption experiments both result in a saturation value of 2.9 hydrogen atoms per platinum atom, significantly more than that reported so far.

Application of a contact mode AFM for spatially resolved electrochemical impedance spectroscopy measurements of a Nafion membrane electrode assembly.

A Nafion fuel cell membrane is investigated by means of electrochemical atomic force microscopy in different gas atmospheres. From chronoamperometric experiments with a point contact electrode spatially resolved electrochemical impedance spectra are obtained from which information about electrode processes and proton transport in the membrane is derived. In the first part the oxygen reduction reaction is investigated.

Reversible transient hydrogen storage in a fuel cell-supercapacitor hybrid device.

A new concept is investigated for hydrogen storage in a supercapacitor based on large-surface-area carbon material (Black Pearls 2000). Protons and electrons of hydrogen are separated on a fuel cell-type electrode and then stored separately in the electrical double layer, the electrons on the carbon and the protons in the aqueous electrolyte of the supercapacitor electrode. The merit of this concept is that it works spontaneously and reversibly near ambient pressure and temperature.

Impedance Spectroscopic Investigation of Proton Conductivity in Nafion Using Transient Electrochemical Atomic Force Microscopy (AFM).

Spatially resolved impedance spectroscopy of a Nafion polyelectrolyte membrane is performed employing a conductive and Pt-coated tip of an atomic force microscope as a point-like contact and electrode. The experiment is conducted by perturbing the system by a rectangular voltage step and measuring the incurred current, followed by Fourier transformation and plotting the impedance against the frequency in a conventional Bode diagram. To test the potential and limitations of this novel method, we present a feasibility study using an identical hydrogen atmosphere at a well-defined relative humidity on both sides of the membrane.

Spin trapping of hydroxyl radicals on Cu/HY zeolites suspended in aqueous solution.

Hydroxyl radical intermediates are trapped in calcined Cu/HY zeolites in the presence of oxygen and water. This suggests that hydrogen peroxide is formed in situ from oxygen. Brønsted acids enhance the formation of the radicals.

Adsorption of oxygen on copper in Cu/HZSM5 zeolites.

The present study focuses on the characterization of the active sites for oxygen adsorption in both copper-free and copper-containing HZSM5 zeolites. FTIR, EPR, EXAFS and UV-Vis measurements offer insight into the initial state of the catalyst before oxygen adsorption. Both liquid and solid state ion exchanged samples contain a certain amount of Cu(ii) and Cu(i) ions in the alpha3, alpha4 and gamma6 position, their population ratio depending on the ion exchange temperature.

Adsorption of dioxygen to copper in CuHY zeolite.

The adsorption of dioxygen to copper in CuHY zeolites has been studied by means of FTIR spectroscopy and model calculations at the quantum mechanical/molecular mechanics (QM/MM) level. Different Si/Al ratios, substitution patterns and adsorption sites within the cavities of the zeolite lead to a large number of different isomers to be studied. In addition, these parameters control the end-on vs.

EPR spectroscopic investigation of radical-induced degradation of partially fluorinated aromatic model compounds for fuel cell membranes.

EPR spectroscopic investigations of reactions between monomeric model compounds representing typical structural moieties of poly(aryl) ionomers and photochemically generated hydroxyl radicals are reported. Deoxygenated solutions of the model compounds (in a water/methanol mixture) containing hydrogen peroxide at defined pH values were exposed to UV light in the flow cell within the cavity of an EPR spectrometer. Spectra were analyzed by computer simulation and the formed radicals were assigned by comparing their g-factors and hyperfine coupling constants (hfccs) with those from the literature and from density functional theory (DFT) calculations.

Nitrogen oxide reaction with six-atom silver clusters supported on LTA zeolite.

Silver containing catalysts were prepared by aqueous ion exchange of Ag(+) against Na(+) in an LTA zeolite. A well-defined paramagnetic cluster consisting of six equivalent silver nuclei was obtained after oxidation and hydrogen reduction. Continuous wave EPR demonstrates that the reduced Ag(6)(+) clusters are isolated and all silver atoms are close to equivalent.

Using polarized muons as ultrasensitive spin labels in free radical chemistry.

In a chemical sense, the positive muon is a light proton. It is obtained at the ports of accelerators in beams with a spin polarization of 100%, which makes it a highly sensitive probe of matter. The muonium atom is a light hydrogen isotope, nine times lighter than H, with a muon as its nucleus.

Platinum species in the pores of NaX, NaY and NaA zeolites studied using EPR, XAS and FTIR spectroscopies.

The results of X-band EPR, X-ray absorption and Fourier transform infrared spectroscopy on Pt(NH(3))(4)(2+) exchanged NaX, NaY and NaA zeolites reveal after oxygen calcination at 573 K that diamagnetic Pt(2+) is not the only product. Calcination provides Pt(3+) cations, but depending on the heating rate, the decomposition of amino groups during calcination also produces hydrogen that reduces Pt(3+) to Pt(2+) and Pt(+). NaX (Si/Al = 1.

Cloning and characterization of a new laccase from Bacillus licheniformis catalyzing dimerization of phenolic acids.

A new laccase gene (cotA) was cloned from Bacillus licheniformis and expressed in Escherichia coli. The recombinant protein CotA was purified and showed spectroscopic properties, typical for blue multi-copper oxidases. The enzyme has a molecular weight of approximately 65 kDa and demonstrates activity towards canonical laccase substrates 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), syringaldazine (SGZ) and 2,6-dimethoxyphenol (2,6-DMP).