Simulating the relaxation dynamics of microwave-driven zeolites

We have performed equilibrium and nonequilibrium molecular dynamics simulations to study how microwave (MW)-heated zeolite systems relax to thermal equilibrium. We have simulated the relaxation of both ionic and dipolar phases in FAU-type zeolites, finding biexponential relaxation in all cases studied. Fast-decay times were uniformly below 1 ps, while slow-decay times were found to be as long as 14 ps. Fast-decay times increase with an increase in the initial temperature difference between MW-heated ions/dipoles and the equilibrium system. Slow-decay times were found to be relatively insensitive to the details of the MW-heated nonequilibrium state. Velocity, force, and orientational correlation functions, calculated at equilibrium to explore the natural dynamics of energy transfer, decay well before 1 ps and show little evidence of biexponential decay. In contrast, kinetic energy correlation functions show strong biexponential behavior with slow-decay times as long as 14 ps. We suggest a two-step mechanism involving initial, efficient energy transfer mediated by strongly anharmonic zeolite-guest forces, followed by a slower process mediated by weakly anharmonic couplings among normal modes of the zeolite framework. In addition to elucidating relaxation from MW-heated states, we expect that these studies will shed light on energy transfer in other contexts, such as adsorption and reaction in zeolites, which often involve significant heat release.     

The effect of hydration/dehydration on the AC electrical conductivity of H4PVMo11O40 and some of its cesium salts used as catalysts

Changes in AC electrical conductance G of vanadium substituted 12-molybdophosphoric acid and of its (mono)-acid and neutral cesium salts were studied. Depending on the environment, the electrical conductivity is a combination of protonic and electronic conduction, the protonic one dominating at low temperature.     

On-chip cell lysis by local hydroxide generation

We present a novel method for on-chip cell lysis based on local hydroxide electro-generation. Hydroxide ions porate the cell membrane, leading to cell lysis. After lysis occurs, hydrogen ions, also generated on chip, react with excess hydroxide, creating a neutral pH lysate and eliminating the need for a wash step. Three different cell types are shown to be effectively lysed by this method: red blood cells, HeLa (human tumor line) and Chinese Hamster Ovary (CHO) cell lines. The release of cytoplasmic molecules from HeLa and CHO cells is demonstrated by monitoring the escape of a membrane impermeant dye from the cytoplasm. In the vicinity of the cathode, the hydroxide concentration is predicted by finite element simulations and shown to fit the lysis rates at different distances from the generating cathode. For flow-through experiments, a second device integrating a mechanical filter with hydroxide generation is fabricated and tested. The purpose of the filter is to trap whole cells and only allow lysate to pass through. The flow rate dependence of hydroxide concentration at the lysis filter is modeled and lysis efficiency is experimentally determined to be proportional to the hydroxide concentration for flow rates from 15 to 30 microl min(-1).     

Separation and Identification of Piperine and Chavicine in Black Pepper by TLC and GC–MS

JPC – Journal of Planar Chromatography – Modern TLC -     

Chiral 1,2,5-triphenylphospholanium tetrafluoroborate as ligand precursor in Rh-catalyzed asymmetric hydrogenation of methyl (Z)-2-acetamidocinnamate

(S,S)-1,2,5-Triphenylphospholanium tetrafluoroborate salt 2 was conveniently used as chiral ligand precursor in rhodium-catalyzed asymmetric hydrogenation of methyl (Z)-2-acetamidocinnamate. ³¹P NMR showed the existence of a solvent-dependent equilibrium between the salt and the free phosphine.     

Reduction of alkyl and vinyl sulfonates using the CuCl2·2H2O-Li-DTBB(cat.) system

The reduction of a series of alkyl mesylates, dimesylates and triflates to the corresponding hydrocarbons was efficiently performed using a reducing system composed of CuCl₂·2H₂O, an excess of lithium sand and a catalytic amount (5 mol%) of 4,4′-di-tert-butylbiphenyl (DTBB), in tetrahydrofuran at room temperature. The process was also applied to enol and dienol triflates affording alkenes and dienes, respectively. The use of the deuterated copper salt CuCl₂·2D₂O allowed the simple preparation of the corresponding deuterated products.     

Polymer–silica hybrids obtained by microemulsion polymerization

The styrene (St), butyl acrylate (BuA), and methyl methacrylate (MMA) polymerization in microemulsion in the presence of sodium dodecylsulfate is studied. This process is conducted in the presence of some comonomers having groups that can participate in sol–gel processes: 3(trimethyloxysilyl) propyl methacrylate (MPTS), triethoxy vinylsilane (VTES), and a comonomer with a sulfate group, styrene sodium sulfonate (StSO₃Na). It has been observed that stabile latexes are obtained by radical polymerization at pH = 7, followed by a sol–gel process in the presence of ammonia. Latex particles sizes and zeta potential grow with MTPS concentration and in StSO₃Na presence. VTES effect depends on its reactivity in St, MMA, and BuA copolymerization. Glass transition temperature and thermal decomposing temperature are influences by functional comonomer concentration and chemical structure. The Fourier transform infrared spectrum and inorganic residue growth after organic part thermal decomposition shows the presence of silica in obtained latexes.     

Photoexcitation and relaxation dynamics of catecholato-iron(III) spin-crossover complexes.

The photophysical properties of the ferric catecholate spin-crossover compounds [(TPA)Fe(R-Cat)]X (TPA=tris(2-pyridylmethyl)amine; X=PF(6) (-), BPh(4) (-); R-Cat=catecholate dianion substituted by R=NO(2), Cl, or H) are investigated in the solid state. The catecholate-to-iron(III) charge-transfer bands are sensitive both to the spin state of the metal ion and the charge-transfer interactions associated with the different catecholate substituents. Vibronic progressions are identified in the near-infrared (NIR) absorption of the low-spin species. Evidence for a low-temperature photoexcitation process is provided. The relaxation dynamics between 10 and 100 K indicate a pure tunneling process below approximately 40 K, and a thermally activated region at higher temperatures. The relaxation rate constants in the tunneling regime at low temperature, k(HL)(T-->0), vary in the range from 0.58 to 8.84 s(-1). These values are in qualitative agreement with the inverse energy-gap law and with structural parameters. A comparison with ferrous spin-crossover complexes shows that the high-spin to low-spin relaxation is generally faster for ferric complexes, owing to the smaller bond length changes for the latter. However, in the present case the corresponding rate constants are smaller than expected based on the single configurational coordinate model. This is attributed to the combined influence of the electronic configuration and the molecular geometry.     

Di- and tri-organotin(IV) diphenyldithiophosphinates

Di- and tri-organotin(IV) diphenyldithiophosphinates, R₂Sn(S₂PPh₂)₂ (R = Me, n-Bu, Bz, Ph) and R₃SnS₂PPh₂ (R = Me, Cy, Bz, Ph) were prepared by reaction of the corresponding organotin chlorides or oxides with diphenyldithiophosphinic acid or its ammonium salt. All the compounds were characterized by IR and ¹H NMR spectra. For R₂Sn(S₂PPh₂)₂ (R = Me, Ph) and Ph₃SnS₂PPh₂ mass spectra and tin-119m Mössbauer spectra were also recorded. Monodentate bonding of the dithiophosphinic ligand and tetrahedral structures are proposed for the triorganotin derivatives, while in diorganotin compounds there appears to be distorted octahedral geometry around tin, with anisobidentate dithiophosphonic ligands.