Optical manipulation of particle ensembles in air

We demonstrate that airborne light-absorbing particles can be photophoretically trapped and moved inside an optical lattice formed by multiple-beam interference. This technique allows simultaneous three-dimensional manipulation of multiple micro-objects in gases.     

GC-MS analysis of aroma of Medemia argun (mama-n-khanen or mama-n-xanin), an ancient Egyptian fruit palm

The fruits of the edible and medicinal Egyptian palm, Medemia argun, were collected from Aswan in Egypt and the essential oil (EO) from fruits and headspace (HS) of the seeds and fleshy mesocarps were analyzed by GC and GC-MS. Results obtained by GC-MS analysis indicated a high variability in the oil and in the headspace from seeds and mesocarps. Sesquiterpene derivatives were the main group of volatiles in the EO from fruits and in the HS from seeds (45.0 and 64.0%, respectively), while oxygenated hydrocarbon derivatives were the main constituents in the HS obtained from fleshy mesocarps (96.5%). The different chemical composition of the headspace obtained from the seeds and mesocarps of M. argun can be correlated with the different roles that the different constituents play in the prevention of dehydration of the fruits in the desert region from where the plant was collected.     

Model potentials in studies of atomic electron density distribution

In density functional theory (DFT ), a many-electron problem for the electron density in atoms may be reduced, according to the Kohn-Sham scheme, to a one-electron problem. In the present work, a variational model is proposed which leads, within some assumptions, to the set of equations describing the change of the electron density ρ and energy ϵ during the ionization process. It is shown that the one-electron density contributions are not necessarily spherically symmetric, but assume the symmetry which depends upon the symmetry of the positive field. A few nonspherically symmetric potentials are studied in the present article. The nonlinear differential equation for density r is formulated and solved for Coulombic, Fues-Kratzer, and Hartmann potentials. The solutions and some particular examples are presented. © 1996 John Wiley & Sons, Inc.     

From Colloidal Dispersions of Zeolite Monolayers to Effective Solid Catalysts in Transformations of Bulky Organic Molecules: Role of Freeze-Drying and Dialysis

We investigated the properties and catalytic activity of zeolites with MWW topology obtained by unprecedented liquid exfoliation of the MCM-56 zeolite into solutions of monolayers and isolation/reassembly of the dispersed layers by various methods, with optional purification by dialysis or ammonium exchange. The layers were recovered by flocculation with alcohol or ammonium nitrate and freeze-drying. Flocculation alone, even with ammonium nitrate, did not ensure removal of residual sodium cations resulting in catalysts with low activity. Dialysis of the solutions with dispersed monolayers proved to be efficient in removing sodium cations and preserving microporosity. The monolayers were also isolated as solids by freeze-drying. The highest BET area and pore volume obtained with the freeze-dried sample confirmed lyophilization efficiency in preserving layer structure. The applied test reaction, Friedel–Crafts alkylation of mesitylene, showed high benzyl alcohol conversion due to increased concentration of accessible acid centers caused by the presence of secondary mesoporosity. The applied treatments did not change the acid strength of the external acid sites, which are the most important ones for converting bulky organic molecules. Zeolite acidity was not degraded in the course of exfoliation into monolayers, showing the potential of such colloid dispersions for the formation of active catalysts.     

A binuclear tantalum(III) complex with a bridging carboxylato ligand

Ta₂Cl₆(SMe₂)₃ reacts with one equivalent of C₄H₉CO₂Li to give a complex with a bridging carboxylate ligand, Ta₂Cl₅(O₂CC₄H₉)(SMe₂)(THF)₂. The product was isolated in two crystalline forms, 1 and 2, from a THF/hexane and benzene/hexane solvent mixture, respectively. The following are the unit cell parameters, for 1: monoclinic (P2₁/n), a = 10.537(5) Å, b = 22.015(4) Å, c = 11.663(4) Å, β = 107.80(3)°, V = 2576(3) ų, and Z = 4; for 2: monoclinic (P2₁/c), a = 15.584(4) Å, b = 15.647(4) Å, c = 11.275(3) Å, β = 106.04(5)°, V = 2642(3) ų and Z = 4. The complex is a dimer with a distorted octahedra-sharing-an-edge geometry. The TaTa distances in 1 and 2 were 2.766(1) Å and 2.779(1) Å, respectively, which is somewhat longer than in previously reported Nb(III) and Ta(III) dinuclear compounds. Diamagnetism of the complex is shown by NMR. Fenske—Hall calculations, which correctly predict an electronic transition at about 16,000 cm^?1, indicate a double TaTa bond. The observed elongation of the metalmetal bond is attributed mainly to steric crowding. The complex is the first proven low-valent Ta species with a coordinated carboxylate ion.     

Distance distributions recovered from steady-state fluorescence measurements on thirteen donor-acceptor pairs with different Förster distances

The end-to-end distance distribution of a flexible molecule was recovered from steady-state fluorescence energy transfer measurements using the method suggested by Cantor and Pechukas (Proc. Natl. Acad. Sci. USA 68, 2099–2101, 1971). In this method, the Förster distance (R ₀) is varied by attaching different donor-acceptor (D-A) pairs to the flexible linker of interest. Distance distributions are then recovered from energy transfer efficiency measurements on the set of D-A pairs with differentR ₀ values. Thirteen D-A pair compounds were synthesized withR ₀ values ranging from 6 to 32 Å. Each compound contained a tryptamine donor linked by an alkyl chain (10 carbons) to 1 of 13 acceptors. Using these compounds, we have experimentally confirmed the Cantor and Pechukas method for recovering distance distributions. The measured transfer efficiencies, as a function ofR ₀, were fit to the transfer efficiencies predicted for both Gaussian and skewed Gaussian distance distributions. The data support the existence of a skewed Gaussian distribution, and we believe that this is the first experimental observation of an asymmetric distribution for a flexible molecule using fluorescence resonance energy transfer measurements. Finally, the experimentally recovered distance distribution was found to be in good agreement with the distribution predicted from the rotational isomeric state model of Flory (Statistical Mechanics of Chain Molecules, John Wiley & Sons, New York, 1969, Chaps. 1, 3, and 5) but not with the predicted distribution for a freely rotating or freely jointed chain.     

A Convenient Synthesis of 2-Phenylglycerol

1,3-Dihydroxyacetone dimer is treated with trimethylsilyl chloride and triethylamine in dichloromethane to provide monomeric ketone having both of its alcohols protected as their di-TMS ethers. The latter is added to phenylmagnesium bromide in ether at -78°C. Work-up by treatment with aqueous ammonium chloride followed by 2 N HCl provides 2-phenylglycerol in 70% yield     

A Convenient Synthesis of the Orthogonally-Protected Benzodiazepine-2,5-Dione Scaffold

We have identified the benzodiazepine-2,5-dione 4 as a convenient, orthogonally-protected template, suitable for parallel solid-phase chemistry. Scaffold 4 offers superior stability, compared to other, analogous benzodiazepine-2,5-diones, such as A. We describe a gram-scale synthesis of 4 in six steps and in 25% yield.     

From gene to HSQC in under five hours: high-throughput NMR proteomics

A simple, rapid, in vitro cell-free protein expression system, Expressway NMR, is introduced and used to express the small ubiquitin-related modifier protein SUMO-1. This 12 kDa molecule is challenging for NMR as it has limited solubility and requires relatively high salt (200 mM) for stability in solution. Starting with the gene, the cell-free system, and milligram amounts of nitrogen-15 isotopically enriched amino acids, sufficient protein is produced in 4 h to obtain a high-resolution 2D HSQC spectrum of the protein in 40 min. This time would be closer to 10 min with the aid of a higher sensitivity salt-tolerant cryogenic NMR probe. With all protein purification steps included, and aggressive data processing using the filter diagonalization method (FDM), it is but 6 h from gene to heteronuclear single quantum coherence (HSQC). As the cell-free system is nearly background-free, it is also possible to work with the crude reaction mixture, in which case only a total of 5 h is required. Sample stability over time, whether crude extract or purified, was notable, with no significant change in the 15N-1H HSQC spectrum over 6 months at 4 degrees C (300 muM, pH 6.1, capped NMR tube). The combination of a turnkey, high-yield, protease-free in vitro protein expression system, an optimized sensitivity-enhanced HSQC pulse sequence, and FDM processing makes this scheme an attractive first step to rapidly assess the suitability of proteins for complete solution structure determination.