Four-color fluorescence correlation spectroscopy realized in a grating-based detection platform

We have developed a filterless multicolor detection unit for fluorescence correlation spectroscopy (FCS). This grating-based setup is continuously tunable for multicolor separation and is thus a powerful alternative to the classical cascade of dichroic mirrors and filters. Our tailored platform allows for accommodation of up to 15 detection channels covering the entire visible spectral range. As a proof of principle, we successfully demonstrate simultaneous FCS of four distinct fluorescent quantum dot species being mixed in aqueous solution. Grating-based detection allows for spectral high-resolution FCS in a stable and compact setup and is a feasible tool for quantitative investigation of complexbiomolecular dynamics on a single molecule level.     

Experimental confirmation of the Alhassid-Whelan arc of regularity

Evidence is presented to show that a group of nuclei, spanning a range of structures, corresponds to a previously proposed isolated region of regular behavior between vibrational and rotational structures that was never before observed empirically. Nuclei predicted to show such regular spectra correspond to Hamiltonian parameters that lie amidst those giving more chaotic spectra. We identify a key observable that has a one-to-one correspondence to this arc of regularity and which therefore provides both an empirical signature for it and a clue to its underlying nature.     

High-pressure selectivity studies--a simple route to a homochiral wistarin precursor

The cycloaddition of spirobutenolide 3 to the homochiral cyclopentadiene 1 at 6.5 kbar leads exclusively to cycloadduct 5. Subsequent Diels-Alder or Michael additions again favour the cyclohexenone double bond; this perfect chemo- regio- and face selectivity was employed for a short and efficient approach to the wistarin framework.     

Synthesis of diblock methylcellulose derivatives with regioselective functionalization patterns

This article describes a new synthesis strategy to prepare diblock copolymers as model compounds for industrially produced cellulose ethers exemplified with methylcellulose (MC). To elucidate a key structure for thermoreversible gelation of MC, five regioselectively methylated celluloses 1 – 5 (236, 23, 26, 3, and 6 MC), five corresponding methyl‐β‐D‐glucopyranosyl‐(1→4)‐cellulosides 6 – 10 , and five equiv methyl‐β‐D‐glucopyranosyl‐(1→4)‐β‐D‐glucopyranosyl‐(1→4)‐cellulosides 11 – 15 were synthesized for the first time via combination of the glycosyl trichloroacetimidate method and the acid‐catalyzed methanolysis method. The structure of compounds 1 – 15 was confirmed by means of NMR spectroscopy and MALDI‐TOF MS. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Broyden's method in Hilbert space

Broyden's method is formulated for the solution of nonlinear operator equations in Hilbert spaces. The algorithm is proven to be well defined and a linear rate of convergence is shown. Under an additional assumption on the initial approximation for the derivative we prove the superlinear rate of convergence.     

Homogeneous methylation of wood pulp cellulose dissolved in LiOH/urea/H2O

Spruce sulphite cellulose (number average degree of polymerization 620) dissolved in an aqueous solution of 8% (w/w) LiOH*H₂O and 12% (w/w) urea was methylated with dimethyl sulphate (DMS). By varying the reaction temperature between 22 and 50 °C, the molar ratio between 9 and 15 mol DMS per mol anhydroglucose unit, and the reaction time from 4 to 24 h, methyl cellulose (MC) with degree of substitution (DS) values in the range of 1.07 and 1.59 was prepared. The chemical structure of MC was analysed by FTIR and ¹H NMR spectroscopy. The turbidity (given in nephelometric turbidity units, NTU) of the aqueous solution of MC reached an optimum of 10 NTU for a product obtained with 12 mol DMS/mol AGU at 50 °C. GPC measurements revealed polymer degradation to a certain extent. The intrinsic viscosity and the Huggins constant k of the MC samples increased with increasing DS value. The MC samples possess k values higher than 0.8, indicating association of the polymer chain. The zero-shear viscosity decreased with increase of both temperature and the amount of methylation agent due to the depolymerization. During the heating/cooling cycle (20-90 °C) of the aqueous solutions of MC, it was observed that samples synthesized at 22 °C with DS values lower than 1.3 did not undergo phase separation in aqueous solution. Phase separation hysteresis with a precipitation temperature up to 80 °C was obtained for aqueous solutions of MC with DS values between 1.07 and 1.66 synthesized at higher temperatures. The functionalization pattern determined by GLC of the corresponding partially methylated glucitol acetates is close to randomness and comparable with those of commercial MC samples.     

Xylan‐Based Nanoparticles: Prodrugs for Ibuprofen Release

Esterification of xylan with ibuprofen via activiation of the carboxylic acid with N,N′‐carbonyldiimidazole (CDI) yields products of high drug loadings. Subsequent sulfation of xylan ibuprofen esters using the gentle agent SO₃/DMF was successfully carried out in order to modify hydrophobicity of the xylan esters. The structure of the novel xylan esters was evaluated by means of NMR spectroscopy. The resulting xylan derivatives self assemble into spherical nanoparticles with mean diameters ranging from 162 to 472 nm. Preliminary stability measurements indicate that hydrolytic stability decreases with increase in degree of substitution of sulfate groups. Thus, a new concept toward improved drug delivery from polysaccharide‐based nanoparticles can be established here.