Size exclusion chromatography with dual-beam refractive index gradient detection of polystyrene samples

Non-aqueous size exclusion chromatography (SEC) of polystyrenes (as model analytes) is examined using the microscale molar mass sensor (μ-MMS) for detection. The μ-MMS is combined with SEC to demonstrate this simultaneously universal and molar mass selective detection method for polymer characterization. The μ-MMS is based on measuring the refractive index gradient (RIG) at two positions (upstream and downstream) within a T-shaped microfluidic channel. The RIG is produced from a sample stream (eluting analytes in the mobile phase) merging with a mobile phase stream (mobile phase only). The magnitude of the RIG is measured as a probe beam deflection angle and is related to analyte diffusion coefficient, the time allowed for analyte diffusion from the sample stream toward the mobile phase stream, and the bulk phase analyte refractive index difference relative to the mobile phase. Thus, two deflection angles are measured simultaneously, the upstream angle and the downstream angle. An angle ratio is calculated by dividing the downstream angle by the upstream angle. The μ-MMS was found to extend the useful molar mass calibration range of the SEC system (nominally limited by the total exclusion and total permeation regions from ∼100,000 g/mol to ∼800 g/mol), to a range of 3,114,000-162 g/mol. The injected concentration LOD (based on 3 s statistics) was 2 ppm for the upstream detection position. The point-by-point time-dependent ratio, termed a ‘ratiogram’, is demonstrated for resolved and overlapped peaks. Within detector band broadening produces some anomalies in the ratiogram shapes, but with highly overlapped distributions of peaks this problem is diminished. Ratiogram plots are converted to molar mass as a function of time, demonstrating the utility of SEC/μ-MMS to examine a complex polymer mixture.     

Numerical Properties of Shifted Tridiagonal LU Factorizations

In this paper, we consider shifted tridiagonal matrices. We prove that the standard algorithm to compute the LU factorization in this situation is mixed forward-backward stable and, therefore, componentwise forward stable. Moreover, we give a formula to compute the corresponding condition number in O(n) flops. This research has been partially supported by Dirección General de Investigación (Ministerio de Ciencia y Tecnología) of Spain through grants BFM2003-06335-C03-02 and MTM2006-06671 as well as by the Postdoctoral Fellowship EX2004-0658 provided by Ministerio de Educación y Ciencia of Spain.     

Simultaneous Aromatic–Beryllium Bonds and Aromatic–Anion Interactions: Naphthalene and Pyrene as Models of Fullerenes,Carbon Single‐Walled Nanotubes,and Graphene

The possibility of forming stable BeR₂:ArH:Y^? (R=H, F, Cl; ArH=naphthalene, pyrene; Y=Cl, Br) ternary complexes in which the beryllium compounds and anions are located on the opposite sides of an extended aromatic system is explored by means of MP2/aug‐cc‐pVDZ ab initio calculations. Comparison of the electron‐density distribution of these ternary complexes with the corresponding BeR₂:ArH and ArH:Y^? binary complexes reveals the existence of significant cooperativity between the two noncovalent interactions in the triads. The energetic effects of this cooperativity are quantified by evaluation of the three‐body interaction energy Δ³E in the framework of the many‐body interaction‐energy (MBIE) approach. Although an essential component of the interaction energies is electrostatic and is well reflected in the changes in the molecular electrostatic potential of the aromatic system on complexation, strong polarization effects, in particular for the BeR₂:ArH interactions, also play a significant role. The charge transfers associated with these polarization effects are responsible for significant distortion of both the BeR₂ and the aromatic moieties. The former are systematically bent in all the complexes, and the latter are curved to a degree that depends on the nature of the R substituents of the BeR₂ subunit.     

Material properties of matrix lipids determine the conformation and intermolecular reactivity of diacetylenic phosphatidylcholine in the lipid bilayer

Photopolymerizable phospholipid DC(8,9)PC (1,2-bis-(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine) exhibits unique assembly characteristics in the lipid bilayer. Because of the presence of the diacetylene groups, DC(8,9)PC undergoes polymerization upon UV (254 nm) exposure and assumes chromogenic properties. DC(8,9)PC photopolymerization in gel-phase matrix lipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monitored by UV-vis absorption spectroscopy occurred within 2 min after UV treatment, whereas no spectral shifts were observed when DC(8,9)PC was incorporated into liquid-phase matrix 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). Liquid chromatography-tandem mass spectrometry analysis showed a decrease in the amount of DC(8,9)PC monomer in both DPPC and POPC environments without any change in the matrix lipids in UV-treated samples. Molecular dynamics (MD) simulations of DPPC/DC(8,9)PC and POPC/DC(8,9)PC bilayers indicate that the DC(8,9)PC molecules adjust to the thickness of the matrix lipid bilayer. Furthermore, the motions of DC(8,9)PC in the gel-phase bilayer are more restricted than in the fluid bilayer. The restricted motional flexibility of DC(8,9)PC (in the gel phase) enables the reactive diacetylenes in individual molecules to align and undergo polymerization, whereas the unrestricted motions in the fluid bilayer restrict polymerization because of the lack of appropriate alignment of the DC(8,9)PC fatty acyl chains. Fluorescence microscopy data indicates the homogeneous distribution of lipid probe 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-lissamine rhodamine B sulfonyl ammonium salt (N-Rh-PE) in POPC/DC(8,9)PC monolayers but domain formation in DPPC/DC(8,9)PC monolayers. These results show that the DC(8,9)PC molecules cluster and assume the preferred conformation in the gel-phase matrix for the UV-triggered polymerization reaction.     

Microwave promoted Suzuki reactions between aroyl chlorides and boronic acids catalyzed by heterogeneous and homogeneous phosphine-free palladium catalysts

Suzuki cross-coupling reactions between arylboronic acids and aroyl chlorides with phosphine-free palladium catalysis under microwave irradiation were performed to obtainment of aromatic ketones in good yields within short times. Heterogeneous and homogeneous catalysts were studied as well as their influence in the reaction selectivity relative to homocoupling of the boronic acids.     

Tunable multi-function broadband splitter with optical bistability based on surface plasmon

A tunable multi-function broadband splitter consisted of a silver film, Kerr medium and a silver grating sandwiched between linear dielectrics waveguides is proposed and numerically investigated. This splitter can realize the functions of the beam splitter, the polarization splitter and wavelength beam splitter. This surface plasmon based device provides a unique approach for polarization sensitive manipulation of light in an integrated circuit and will be essential for future classical and quantum information processes.     

Magnetic,Spectroscopic and Thermal Study of [Cu(NO3)(PyTz)2](NO3). A Copper(II) Complex Containing Thiazine Derivative Ligand

The copper(II) complex [Cu(NO₃)(PyTz)₂](NO₃) has been previously characterized means X‐ray powder diffraction and now studied by IR spectroscopy, UV‐Vis‐NIR diffuse reflectance, magnetic susceptibility measurement, electronic spin resonance (ESR) and thermal analysis. The results are correlated with a distorted square pyramidal coordination around copper(II) ion rather than the cis‐distorted octahedral stereochemistry of a CuN₄OO′ chromophore in good concordance with their structure. Likewise, in order to indicate towards what square pyramidal isomer the complex is distorted, the method proposed by Carugo and Bisi has been applied to the structural data of [Cu(NO₃)(PyTz)₂](NO₃). It is deduced that there is a large distortion from the trigonal bipyramid geometry, close to a square pyramid geometry, being produced almost exclusively through the B route of the Berry mechanism.     

A compilation of wavelengths and energy levels for the spectrum of neutral rubidium (Rb I)

We are presenting a complete list of wavelengths for all classified lines of Rb I. The data are based mainly on the observations and analysis of this spectrum by many authors. The tabulated data include 615 observed lines in the spectral range 103-, classified as transitions among 22 even-parity and 414 odd-parity levels. Vacuum wavelengths are given for all the lines, and wavelengths in air are also included for the region above . We also present the results of the doppler-free two-photon absorption spectrum for the transition n2S←52S and n2D←52S of atomic rubidium.