Narrowband and tunable ring optical parametric oscillator with a volume Bragg grating

We demonstrate a tunable nanosecond optical parametric oscillator with a narrowed signal spectrum. This was done by use of a volume Bragg grating based retroreflector, which makes the tuning simple and yields a compact design. Using periodically poled KTiOPO4 as the nonlinear medium, we generated 0.42 mJ of signal energy at 760 nm with a tuning range of 5 nm(2.6 THz) and a bandwidth of 0.25 nm(130 GHz) when the oscillator was pumped at 532 nm with 1.3 mJ of energy.     

Efficient skew-angle cladding-pumped tunable narrow-linewidth Yb-doped fiber laser

A skew-angle cladding-pumped tunable Yb-doped fiber laser is presented. The laser was tunable over more than 30 nm, from 1022 to 1055 nm, by employing a volume Bragg grating in a retroreflector configuration as one of the cavity delimiters. Output powers in excess of 4.3 W were recorded with a spectral bandwidth of 5 GHz and an M(2) value below 1.3 over the whole tuning range.     

Theoretical evidence for C-F bond activation by a fluoro-calix[4]pyrrole-tert-amine macrocycle

Density functional theory as well as highly correlated ab initio molecular orbital theory was used to explore the possibility of activating C-F bonds in fluoroalkanes by organic macrocycles. The results indicate that the reaction between fluoro-calix [4]pyrrole-tert-amine and CH3F via a Menshutkin displacement mechanism is highly favorable and competitive from a thermochemical point of view with the very efficient C-Cl activation by a simple macrocyclic amine recently reported in the literature (Stanger, L. J.; Noll, B. C.; Gonzalez, C.; Marquez, M.; Smith, B. D. J. Am. Chem. Soc. 2005, 127, 4184).     

Micellar induced regioselectivity in the two-step consecutive reaction of SO3(2-) with Br-(CH2CH2)n-Br (n=2-5)

High field (800 MHz) (1)H NMR was used to monitor the two-step consecutive reaction of excess SO(3)(2-) with symmetrical bifunctional alpha,omega-dibromoalkanes with butane (DBB), hexane (DBH), octane (DBO), and decane (DBD) chains in CTAB micelles at 25 degrees C. The first-order rate constant for the first substitution step for DBB and DBH is about 5 times faster than for the second, but the kinetics for DBO and DBD were not cleanly first-order. After 40 min, the solution contained about 80% of the intermediate bromoalkanesulfonate from DBB and DBH and the remainder is alkanedisulfonate and unreacted starting material. The same reactions were carried out in homogeneous MeOH/D(2)O solutions at 50 degrees C. The rate constants for all four alpha,omega-dibromoalkanes were first-order throughout the time course of the reaction and the same within +/-10%. However, because micellar solutions are organized on the nanoscale and bring together lipophilic and hydrophilic reactants into a small reaction volume at the micellar interface, they speed this substitution reaction considerably compared to reaction in MeOH/D(2)O. The CTAB micelles also induce a significant regioselectivity in product formation by speeding the first step of the consecutive reaction more than the second. The results are consistent with the bromoalkanesulfonate intermediates having a radial orientation within the micelles with the -CH(2)SO(3)(-) group in the interfacial region and the -CH(2)Br group directed into the micellar core such that the concentration of -CH(2)Br groups in the reactive zone, i.e., the micellar interface, is significantly reduced. These results provide the first example of self-assembled surfactant system altering the relative rates of the reaction steps of a consecutive reaction and, in doing so, enhancing monosubstitution of a symmetrically disubstituted species.     

Structural effects in the analysis of supported lipid bilayers by time-of-flight secondary ion mass spectrometry

We contribute to the rapidly emerging interest in the application of time-of-flight secondary ion mass spectrometry (TOF-SIMS) for chemical analysis of biological materials by presenting a careful TOF-SIMS investigation of structurally different SiO2-supported phospholipid assemblies. Freeze-dried supported 1-oleoyl-2-palmitoyl-sn-glycero-3-phosphocholine (POPC) bilayers, Langmuir-Blodgett POPC monolayers, and disordered thick POPC films were investigated. Compared with the two latter structures, the supported bilayer showed a strong (5-10 times) enhancement in the yield of both the molecular and the dimer ion peaks of POPC, suggesting that the molecular peak may be used as a sensitive indicator for changes in the membrane structure and, in particular, an indicator for the presence of bilayer structures in, e.g., cell and tissue samples. The detection efficiency and the useful lateral resolution indicate that a lateral resolution of around 100 nm can be obtained on all structures by imaging the phosphocholine ion at 184 u using Bi3+ primary ions. For the chemically specific molecular peak at 760 u, the measured detection efficiencies correspond to a useful lateral resolution of around 2 microm for the bilayer structure. The results are discussed in relation to recent dynamic SIMS (nano-SIMS) analysis of freeze-dried supported lipid bilayers, displaying similar or higher lateral resolution, but which in contrast to TOF-SIMS requires isotopic labeling of the analyzed lipids.     

Electromembrane extraction of peptides--fundamental studies on the supported liquid membrane

A large screening of different components in the supported liquid membrane (SLM) in electromembrane extraction (EME) was performed to test the extraction efficiency on eight model peptides. Electromembrane extraction from a 500 μL acidified aqueous sample containing the model peptides in the concentration 10 μg/mL was used. Extraction time was 5 min with an electric potential of 10 V and 900 rpm agitation of the sample vial. The samples were extracted through a hollow fiber-based SLM with different compositions of organic solvents and carriers. A small volume of acidified acceptor solution (25 μL) was after extraction analyzed directly, or with some dilution, on CE or HPLC. This article has identified mono- or di-substituted phosphate groups as the prominent group of carrier molecules needed to obtain acceptable recoveries. For the organic solvents, primary alcohols and ketones have shown promise regarding recovery and reproducibility, with some differences in selectivity. A new composition of the SLM, namely 2-octanone and tridecyl phosphate (90:10 w/w) has proved to give higher extraction recoveries and lower standard deviation than SLMs previously reported in the literature.     

Injection molded nanofluidic chips: fabrication method and functional tests using single-molecule DNA experiments

We demonstrate that fabrication of well-defined nanofluidic systems can be greatly simplified by injection molding of thermoplastic polymers. Chips featuring nanochannel arrays, microchannels and integrated interconnects are produced in a single processing step by injection molding. The resulting open channel structures are subsequently sealed by facile plasma-enhanced thermal bonding of a polymer film. This fast, inexpensive and industry-compatible method thus provides a single-use all-polymer platform for nanofluidic lab-on-a-chip applications. Its applicability for nanofluidics is demonstrated by DNA stretching experiments performed on individual double-stranded DNA molecules confined in the injection molded nanochannels. The obtained results are consistent with measurements performed in costly state-of-the-art silica nanochannels, for both straight and tapered channel geometries.     

Reactions between Grignard reagents and heterocyclic N-oxides: stereoselective synthesis of substituted pyridines, piperidines, and piperazines

In this perspective we discuss the recent developments of stereoselective synthesis of substituted pyridines, piperidines, and piperazines from cheap and commercially readily available starting materials. Pyridine N-oxides and pyrazine N-oxides are reacted with alkyl, aryl, alkynyl and vinyl Grignard reagents to give a diverse set of heterocycles in high yields. Optically active substituted piperazines are obtained by an asymmetric reaction from pyrazine N-oxides using sparteine as chiral ligand. In addition, a stereoselective synthesis of dienal-oximes from the reaction between pyridine N-oxides and Grignard reagents is presented, which results in a useful intermediate for the synthesis of a diverse set of compounds.     

Columnar self-assembly and alignment of planar carbenium ions in Langmuir-Blodgett films

Structural and optical properties of multilayer Langmuir-Blodgett (LB) films of two amphiphilic carbenium salts 2-didecylamino-6,10-bis(dimethylamino)-4,8,12-trioxatriangulenium hexafluorophosphate (ATOTA-1) and 2,6-bis(decylmethylamino)-10-dimethylamino-4,8,12-trioxatriangulenium hexafluorophosphate (ATOTA-2) are described. The LB films were prepared on lipophilic glass by standard vertical dipping. Grazing incidence X-ray diffraction (GIXD) measurements show that the planar organic cores, in spite of their positive charge, form closely packed columns with a repeating distance of ～3.45 ?. Specular X-ray reflectivity (SXR) reveals the LB multilayers to consist of Y-type bilayers with thickness 31 ? for ATOTA-1 and 41 ? for ATOTA-2. This significant difference is ascribed to the different packing motifs of the alkyl chains in the two LB films. GIXD and polarized UV-vis absorption and emission spectroscopy show that the columnar aggregates in the LB films are oriented along the dipping direction. This alignment is attributed to shear effects during LB transfer. The main absorption band of the LB films is blue-shifted compared to that in solution, while the fluorescence is red-shifted by more than 100 nm. These findings suggest the presence of H-aggregates in agreement with the cofacial packing derived from the X-ray measurements. Polarized absorption spectroscopy with variable angle of incidence was used to resolve two perpendicular optical transitions in the visible range, one at 460 nm polarized perpendicular to the columnar direction, in the plane of the film, and one at 420 nm polarized along the film normal.