Controlling the structure and photophysics of fluorophore dimers using multiple cucurbit[8]uril clampings

A modular strategy has been employed to develop a new class of fluorescent molecules, which generates discrete, dimeric stacked fluorophores upon complexation with multiple cucurbit[8]uril macrocycles. The multiple constraints result in a “static” complex (remaining as a single entity for more than 30 ms) and facilitate fluorophore coupling in the ground state, showing a significant bathochromic shift in absorption and emission. This modular design is surprisingly applicable and flexible and has been validated through an investigation of nine different fluorophore cores ranging in size, shape, and geometric variation of their clamping modules. All fluorescent dimers evaluated can be photo-excited to atypical excimer-like states with elongated excited lifetimes (up to 37 ns) and substantially high quantum yields (up to 1). This strategy offers a straightforward preparation of discrete fluorophore dimers, providing promising model systems with explicitly stable dimeric structures and tunable photophysical features, which can be utilized to study various intermolecular processes.

Dimerisation of a wide range of fluorophores through multiple CB[8] clampings leads to constrained intracomplex motion and distinct photophysical properties.     

Phosphorylation of RAF Kinase Dimers Drives Conformational Changes that Facilitate Transactivation

RAF kinases are key players in the MAPK signaling pathway and are important targets for personalized cancer therapy. RAF dimerization is part of the physiological activation mechanism, together with phosphorylation, and is known to convey resistance to RAF inhibitors. Herein, molecular dynamics simulations are used to show that phosphorylation of a key N‐terminal acidic (NtA) motif facilitates RAF dimerization by introducing several interprotomer salt bridges between the αC‐helix and charged residues upstream of the NtA motif. Additionally, we show that the R‐spine of RAF interacts with a conserved Trp residue in the vicinity of the NtA motif, connecting the active sites of two protomers and thereby modulating the cooperative interactions in the RAF dimer. Our findings provide a first structure‐based mechanism for the auto‐transactivation of RAF and could be generally applicable to other kinases, opening new pathways for overcoming dimerization‐related drug resistance.     

On the inter‐instrument and inter‐laboratory transferability of a tandem mass spectral reference library: 1. Results of an Austrian multicenter study

The inter‐instrument and inter‐laboratory transferability of a tandem mass spectral reference library originally built on a quadrupole‐quadrupole‐time‐of‐flight instrument was examined. The library consisted of 3759 MS/MS spectra collected from 402 reference compounds applying several different collision‐energy values for fragmentation. In the course of the multicenter study, 22 test compounds were sent to three different laboratories, where 418 tandem mass spectra were acquired using four different instruments from two manufacturers. The study covered the following types of tandem mass spectrometers: quadrupole‐quadrupole‐time‐of‐flight, quadrupole‐quadrupole‐linear ion trap, quadrupole‐quadrupole‐quadrupole, and linear ion trap‐Fourier transform ion cyclotron resonance mass spectrometer. In each participating laboratory, optimized instrumental parameters were gathered solely from routinely applied workflows. No standardization procedure was applied to increase the inter‐instrument comparability of MS/MS spectra. The acquired tandem mass spectra were matched against the established reference library using a sophisticated matching algorithm, which is presented in detail in a companion paper. Correct answers, meaning that the correct compound was retrieved as top hit, were obtained in 98.1% of cases. For the remaining 1.9% of spectra, the correct compound was matched at second rank. The observed high percentage of correct assignments clearly suggests that the developed mass spectral library search approach is to a large extent platform independent. Copyright © 2009 John Wiley & Sons, Ltd.     

Pyridine- and phosphonate-containing ligands for stable Ln complexation. Extremely fast water exchange on the Gd(III) chelates

Two novel ligands containing pyridine units and phosphonate pendant arms, with ethane-1,2-diamine (L2) or cyclohexane-1,2-diamine (L3) backbones, have been synthesized for Ln complexation. The hydration numbers obtained from luminescence lifetime measurements in aqueous solutions of the Eu(III) and Tb(III) complexes are q = 0.6 (EuL2), 0.7 (TbL2), 0.8 (EuL3), and 0.4 (TbL3). To further assess the hydration equilibrium, we have performed a variable-temperature and -pressure UV-vis spectrophotometric study on the Eu(III) complexes. The reaction enthalpy, entropy, and volume for the hydration equilibrium EuL <--> EuL(H2O) were calculated to be DeltaH degrees = -(11.6 +/- 2) kJ mol(-1), DeltaS degrees = -(34.2 +/- 5) J mol(-1) K(-1), and = 1.8 +/- 0.3 for EuL2 and DeltaH degrees = -(13.5 +/- 1) kJ mol(-1), DeltaS degrees = -(41 +/- 4) J mol(-1) K(-1), and = 1.7 +/- 0.3 for EuL3, respectively. We have carried out variable-temperature 17O NMR and nuclear magnetic relaxation dispersion (NMRD) measurements on the GdL2(H2O)q and GdL3(H2O)q systems. Given the presence of phosphonate groups in the ligand backbone, a second-sphere relaxation mechanism has been included for the analysis of the longitudinal (17)O and (1)H NMR relaxation rates. The water exchange rate on GdL2(H2O)q, = (7.0 +/- 0.8) x 10(8) s(-1), is extremely high and comparable to that on the Gd(III) aqua ion, while it is slightly reduced for GdL3(H2O)q, = (1.5 +/- 0.1) x 10(8) s(-1). This fast exchange can be rationalized in terms of a very flexible inner coordination sphere, which is slightly rigidified for L3 by the introduction of the cyclohexyl group on the amine backbone. The water exchange proceeds via a dissociative interchange mechanism, evidenced by the positive activation volumes obtained from variable-pressure 17O NMR for both GdL2(H2O)q and GdL3(H2O)q (DeltaV = +8.3 +/- 1.0 and 8.7 +/- 1.0 cm(3) mol(-1), respectively).     

Quantification of Conversion Degree and Monomer Elution from Dental Composite Using HPLC and Micro-Raman Spectroscopy

The purpose of the study was to analyze the correlation between the quantity of eluted monomers from dental resin-based composite using reverse-phase HPLC and the degree of conversion (DC) using micro-Raman spectroscopy, and to evaluate the influence of the energy of polymerization delivered on the composite material and the applied resin layer thickness on these properties. There was direct proportion in degree of conversion and inverse proportion in monomer elution when the energy of light polymerization was increased from 20 to 40 J cm^?2; however, further increase in energy density did not influence significantly the DC and the elution of monomers. Investigating the depth of cure significant differences could be measured both in DC and the elution of monomers. 1 mm layer increment up to 3 mm from the top led to 10 % decrease in DC and 30–35 % increase in monomer elution. Further increase in depth from 3 to 4 mm caused 30 % drop in DC and 55 % increase in the amount of leached monomers. The overall result of the findings indicates that direct correlation exists between DC of composite and the elution of unreacted monomers.     

A porous silicon immunoassay platform for fluorometric determination of α-synuclein in human cerebrospinal fluid

Levels of total and/or oligomeric α-synuclein may be used as a biomarker tool to aid in the diagnosis and development of new disease-modifying therapies. We report here on a porous silicon antibody microarray for the fluorimetric determination of cerebrospinal fluid levels of total α-synuclein, a protein involved the pathology of Parkinson’s disease. The surface of porous silicon has a 3-dimensional macro- and nanoporous structure, and this offers a large binding capacity for capturing probe molecules. Porous silicon also warrants efficient immobilization of antibodies by surface adsorption, and does not require chemical immobilization. The platform requires 10 μL of cerebrospinal fluid, and each test requires 4 h for assay only (including immobilization of capturing antibody). The limit of detection is 35 pg mL^?1 of α-synuclein in cerebrospinal fluid, and the dynamic analytical range extends from 0.01 to 100 ng·mL^?1.

不同类型表面活性剂对纳米SiO2流体粘度的影响

系统地研究了不同类型的表面活性剂对低浓度纳米SiO2流体粘度的影响规律,并在此基础上深入探讨了不同碳链长度的阳离子和非离子表面活性剂对纳米SiO2流体粘度的影响。结果表明,阴离子表面活性剂十二烷基苯磺酸钠(SDBS)对纳米流体粘度的影响较小,其相对粘度值维持在1.23左右;而阳离子表面活性剂十四烷基三甲基溴化铵(TTAB)、十六烷基三甲基溴化铵(CTAB)、十八烷基三甲基溴化铵(OTAB)、十六烷基氯化吡啶(CPC)、非离子表面活性剂OP-8、OP-10和两性离子表面活性剂DXS14、DXS18对纳米流体粘度的变化影响较大,其最大相对粘度值分别能达到3.42、1.82和8.87。同时也发现,阳离子表面活性剂碳链越长,纳米流体最高粘度值越大,且纳米流体最高粘度所对应的表面活性剂浓度均在其临界胶束浓度值附近。     

Photonic crystals obtained by soap-free emulsion terpolymerization

This paper presents the use of soap-free emulsion terpolymerization to obtainphotonic crystals (PCs). Monodisperse latexes resulted from the polymerization of styrene (ST) with 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AA) at different compositions defined as system A, B and C respectively. The water solubility of the macroradicals determined different nucleation mechanisms in all three cases. The micellar nucleation mechanism was more predominant for generating system A, whereas the homogeneous nucleation was specific for system C. For system B, both nucleation mechanisms werepossible with the same probability. The latexes and the resulted PCs were characterized by optical microscopy (OM), dynamic light scattering (DLS), gel permeation chromatography (GPC) and UV-VIS spectroscopy.