Synthesis and electrochemical reaction with lithium of mesoporous iron oxalate nanoribbons

Mesoporous FeC 2O 4 was prepared by dehydration of bulk monoclinic- and micellar orthorhombic FeC 2O 4.2H 2O precursors at 200 degrees C. The micellar material shows nanoribbon shaped particles, which are preserved after dehydration. These solids are used as high-capacity lithium storage materials with improved rate performance. The mesoporous nanoribbons exhibit higher capacities close to 700 mA h/g after 50 cycles at 2C (C = 1 Li h (-1) mol (-1)) rate between 0 and 2 V.     

Changes in dynamics of SRE-RNA on binding to the VTS1p-SAM domain studied by 13C NMR relaxation

RNA recognition by proteins is often accompanied by significant changes in RNA dynamics in addition to conformational changes. However, there are very few studies which characterize the changes in molecular motions in RNA on protein binding. We present a quantitative (13)C NMR relaxation study of the changes in RNA dynamics in the pico-nanosecond time scale and micro-millisecond time scale resulting from interaction of the stem-loop SRE-RNA with the VTS1p-SAM domain. (13)C relaxation rates of the protonated carbons of the nucleotide base and anomeric carbons have been analyzed by employing the model-free formalism, for a fully (13)C/(15)N-labeled sample of the SRE-RNA in the free and protein-bound forms. In the free RNA, the nature of molecular motions are found to be distinctly different in the stem and the loop region. On binding to the protein, the nature of motions becomes more homogeneous throughout the RNA, with many residues showing increased flexibility at the aromatic carbon sites, while the anomeric carbon sites become more rigid. Surprisingly, we also observe indications of a slow collective motion of the RNA in the binding pocket of the protein. The observation of increased motions on binding is interesting in the context of growing evidence that binding does not always lead to motional restrictions and the resulting entropy gain could favor the free energy of association.     

Gadolinium chelate coated gold nanoparticles as contrast agents for both X-ray computed tomography and magnetic resonance imaging

Functionalized gold nanoparticles were applied as contrast agents for both in vivo X-ray and magnetic resonance imaging. These particles were obtained by encapsulating gold cores within a multilayered organic shell which is composed of gadolinium chelates bound to each other through disulfide bonds. The contrast enhancement in MRI stems from the presence of gadolinium ions which are entrapped in the organic shell, whereas the gold core provides a strong X-ray absorption. This study revealed that these particles suited for dual modality imaging freely circulate in the blood vessels without undesirable accumulation in the lungs, spleen, and liver.     

Effect of temperature on the chromatographic retention of ionizable compounds. III. Modeling retention of pharmaceuticals as a function of eluent pH and column temperature in RPLC

We propose a general simple equation for accurately predicting the retention factors of ionizable compounds upon simultaneous changes in mobile phase pH and column temperature at a given hydroorganic solvent composition. Only four independent experiments provide the input data: retention factors measured in two pH buffered mobile phases at extreme acidic and basic pH values (e. g., at least +/- 2 pH units far from the analyte pK(a)) and at two column temperatures. The equations, derived from the basic thermodynamics of the acid-base equilibria, additionally require the knowledge of the solute pK(a )and enthalpies of acid-base dissociation of both the solute and the buffer components in the hydroorganic solvent mixture. The performance of the predictive model is corroborated with the comparison between theoretical and experimental retention factors of several weak acids and bases of important pharmacological activity, in mobile phases containing different buffer solutions prepared in 25% w/w ACN in water and at several temperatures.     

An understanding of the electrophilic/nucleophilic behavior of electro-deficient 2,3-disubstituted 1,3-butadienes in polar diels-alder reactions. A density functional theory study

The electrophilic/nucleophilic behavior of dimethyl 2,3-dimethylenesuccinate 1, an electron-deficient 2,3-disubstituted 1,3-butadiene, in polar Diels-Alder reactions has been studied using DFT methods at the B3LYP/6-31G(d) level of theory. The electronic nature of bonding of the transition structures involved in the cycloaddition reactions of the diene 1 toward the nucleophilically activated dienophile 6 and the strong electrophilically activated dienophile 7 has been carefully examined within the natural bond orbital (NBO) and the topological analysis of the electron localization function (ELF) frameworks. Additionally, a study of the global electrophilicity pattern of the reagents at the ground state was performed. This evidence allows us to rationalize the participation of electron-deficient 2-susbtituted and 2,3-disubstituted 1,3-butadienes as nucleophiles in polar Diels-Alder reactions.     

Effect of polyethyleneimine ion on the sorption of a reactive dye onto Leacril fabric: electrokinetic properties and surface free energy of the system

Data are presented on the kinetics, electrokinetics, and surface free energy in the process of adsorption of polyethyleneimine (PEI) as a pretreatment of Leacril, later dyed with the reactive dye Remazol Brilliant Blue R (RBBR). The electrokinetic potential of Leacril is negative, due probably to the presence of sulfonate and sulfate end-group onto Leacril fibers. The zeta potential of Leacril decreases in absolute value as a function of NaCl concentration in solution, probably because of compression of the electrical double layer. The zeta potential of Leacril as a function of the concentration of PEI in solution increases because of the adsorption of PEI ions through chemical reaction between the sulfonate end-groups of Leacril and the amine groups of PEI. The adsorption kinetics shows that an increase in the concentration of PEI, brings about an increase in the amount of RBBR adsorbed onto the fiber. This may be an indication of the chemical reaction between the reactive groups of the polyelectrolyte and dye molecules. The behavior of the surface free energy of the systems involved confirms these conclusions.     

Suzuki-Miyaura cross-coupling reactions of aryl tellurides with potassium aryltrifluoroborate salts

[reaction: see text] Palladium(0)-catalyzed cross-coupling between potassium aryltrifluoroborate salts and aryl tellurides proceeds readily to afford the desired biaryls in good to excellent yield. The reaction seems to be unaffected by the presence of electron-withdrawing or electron-donating substituents in both the potassium aryltrifluoroborate salts and aryl tellurides partners. Biaryls containing a variety of functional groups can be prepared. A chemoselectivity study was also carried out using aryl tellurides bearing halogen atoms in the same compound. In addition, this new version of the Suzuki-Miyaura cross-coupling reaction was monitored by electrospray ionization mass spectrometry where some reaction intermediates were detected and analyzed.     

A new isoreticular class of metal-organic-frameworks with the MIL-88 topology

We report here a new family of isoreticular MOFs, comprising three larger analogues of the nanoporous metallocarboxylate MIL-88; these solids were synthesized using a controlled SBU approach and the three crystal structures were solved using an original simulation-assisted structure determination method in direct space.     

Versatile coordination chemistry towards multifunctional carbon nanotube nanohybrids

Dispersible single-walled carbon nanotubes grafted with poly(4-vinylpyridine), SWNT-PVP, were tested in coordination assays with zinc tetraphenylporphyrin (ZnP). Kinetic and spectroscopic evidence corroborates the successful formation of a SWNT-PVPZnP nanohybrid. Within this SWNT-PVPZnP nanohybrid, static electron-transfer quenching (2.0+/-0.1) x 10(9) s(-1) converts the photoexcited-ZnP chromophore into a radical-ion-pair state with a microsecond lifetime, namely one-electron oxidized-ZnP and reduced-SWNT.     

Formaldehyde Formation on Vanadium Oxide Surfaces V2O3(0001) and V2O5(001): How does the Stable Methoxy Intermediate Form?

Hydroxy‐mediated methoxy formation or stabilization is probably an important process in many methanol adsorption systems. Hydrogen atoms originating from the scission of the methanol O? H bond react with the substrate and form water. This process may result 1) in the production of additional surface defects as reactive centers for methoxy formation and 2) in the stabilization of methoxy groups by suppression of methanol formation.