Methacrylate monolithic stationary phases for gradient elution separations in microfluidic devices

Methacrylate monolithic stationary phases were produced in fused-silica chips by UV initiation. Poly(butyl methacrylate-co-ethylene dimethacrylate) (BMA) and poly(lauryl methacrylate-co-ethylene dimethacrylate) (LMA) monoliths containing 30, 35 and 40% monomers were evaluated for the separation of peptides under gradient conditions. The peak capacity was used as an objective tool for the evaluation of the separation performance. LMA monoliths of the highest density gave the highest peak capacities (≈40) in gradients of 15 min and all LMA monoliths gave higher peak capacities than the BMA monoliths with the same percentage of monomers. Increasing the gradient duration to 30 min did not increase the peak capacity significantly. However, running fast (5 min) gradients provides moderate peak capacities (≈20) in a short time. Due to the system dead volume of 1 μL and the low bed volume of the chip, early eluting peptides migrated over a significant part of the column during the dwell time under isocratic conditions. It was shown that this could explain an increased band broadening on the monolithic stationary phase materials used. The effect is stronger with BMA monoliths, which partly explains the inferior performance of this material with respect to peak capacity. The configuration of the connections on the chip appeared to be critical when fast analyses were performed at pressures above 20 bar.     

Photoelectron imaging spectroscopy of nitroethane anions

We present low-energy velocity map photoelectron imaging results for bare and Ar solvated nitroethane anions. We report an improved value for the adiabatic electron affinity of nitroethane of (191 ± 6) meV which is used to obtain a C-NO(2) bond dissociation energy of (0.589 ± 0.019) eV in nitroethane anion. We assign a weak feature at (27 ± 5) meV electron binding energy to the dipole-bound anion state of nitroethane. Photoelectron angular distributions exhibit increasing anisotropy with increasing kinetic energies. The main contributions to the photoelectron spectrum of nitroethane anion can be assigned to the vibrational modes of the nitro group. Transitions involving torsional motion around the CN bond axis lead to strong spectral congestion. Interpretation of the photoelectron spectrum is assisted by ab initio calculations and Franck-Condon simulations.     

Structural dynamics and energy flow in Rydberg-excited clusters of N,N-dimethylisopropylamine

In molecular beams, the tertiary amine N,N-dimethylisopropyl amine can form molecular clusters that are evident in photoelectron and mass spectra obtained upon resonant multiphoton ionization via the 3p and 3s Rydberg states. By delaying the ionization pulse from the excitation pulse we follow, in time, the ultrafast energy relaxation dynamics of the 3p to 3s internal conversion and the ensuing cluster evaporation, proton transfer, and structural dynamics. While evaporation of the cluster occurs in the 3s Rydberg state, proton transfer dominates on the ion surface. The mass-spectrum shows protonated species that arise from a proton transfer from the alpha-carbon of the neutral parent molecule to the N-atom of its ionized partner in the dimer. DFT calculations support the proton transfer mechanism between tightly bonded cluster components. The photoelectron spectrum shows broad peaks, ascribed to molecular clusters, which have an instantaneous shift of about 0.5 eV toward lower binding energies. That shift is attributed to the charge redistribution associated with the induced dipoles in surrounding cluster molecules. A time-dependent shift that decreases the Rydberg electron binding energy by a further 0.4 eV arises from the structural reorganization of the cluster solvent molecules as they react to the sudden creation of a charge.     

9-H-9-Borafluorene dimethyl sulfide adduct: a product of a unique ring-contraction reaction and a useful hydroboration reagent

The dimethyl sulfide adduct 2(DMS) is a crystalline storage form of the unstable hydroboration reagent 9-H-9-borafluorene (2); 2(DMS) is available by the addition of DMS to either in situ generated [2](2) or 1,2-(2,2'-biphenylylene)diborane(6) (7).     

Cooperative spin transition in a lipid layer like system

A novel iron(II) mononuclear spin transition complex [FeL(py)(2)] displays an abrupt spin transition around 225 K accompanied by a very wide thermal hysteresis loop (～50 K) that spreads out over 100 K. Crystal structure analysis in both low-spin and high-spin states reveals a lipid layer-like arrangement of the complex molecules and provides insights into the spin switching mechanism.     

Controlling phase formation in solids: rational synthesis of phase separated Co@Fe2O3 heteroparticles and CoFe2O4 nanoparticles

A wet chemical approach from organometallic reactants allowed the targeted synthesis of Co@Fe(2)O(3) heterodimer and CoFe(2)O(4) ferrite nanoparticles. They display magnetic properties that are useful for magnetic MRI detection.     

Phytochemical and cytotoxic investigations of Curcuma mangga rhizomes

Investigations on the cytotoxic effects of the crude methanol and fractionated extracts (hexane, ethyl acetate) C. mangga against six human cancer cell lines, namely the hormone-dependent breast cell line (MCF-7), nasopharyngeal epidermoid cell line (KB), lung cell line (A549), cervical cell line (Ca Ski), colon cell lines (HCT 116 and HT-29), and one non-cancer human fibroblast cell line (MRC-5) were conducted using an in-vitro neutral red cytotoxicity assay. The crude methanol and fractionated extracts (hexane and ethyl acetate) displayed good cytotoxic effects against MCF-7, KB, A549, Ca Ski and HT-29 cell lines, but exerted no damage on the MRC-5 line. Chemical investigation from the hexane and ethyl acetate fractions resulted in the isolation of seven pure compounds, namely (E)-labda-8(17),12-dien-15,16-dial (1), (E)-15,16-bisnor-labda-8(17),11-dien-13-on (2), zerumin A (3), β-sitosterol, curcumin, demethoxycurcumin and bis-demethoxycurcumin. Compounds 1 and 3 exhibited high cytotoxic effects against all six selected cancer cell lines, while compounds 2 showed no anti-proliferative activity on the tested cell lines. Compound 1 also demonstrated strong cytotoxicity against the normal cell line MRC-5. This paper reports for the first time the cytotoxic activities of C. mangga extracts on KB, A549, Ca Ski, HT-29 and MRC-5, and the occurrence of compound 2 and 3 in C. mangga.     

Unexpected electron transfer in cryptochrome identified by time-resolved EPR spectroscopy

Subtle differences in the local sequence and conformation of amino acids can result in diversity and specificity in electron transfer (ET) in proteins, despite structural conservation of the redox partners. For individual ET steps, distance is not necessarily the decisive parameter; orientation and solvent accessibility of the ET partners, and thus the stabilization of the charge-separated states, contribute substantially.