Retracted: Light-Induced Bistability in Iron(III) Spin-Transition Compounds of 5 X-Salicylaldehyde Thiosemicarbazone (X=H,Cl, Br)

The iron(III) spin-crossover compounds [Fe(Hthsa)(thsa)] ⋅ H₂O ( 1 ), [Fe(Hth5Clsa)(th5Clsa)₂] ⋅ H₂O ( 2 ), and [Fe(Hth5Brsa)(th5Brsa)₂] ⋅ H₂O ( 3 ) (H₂thsa=salicylaldehyde thiosemicarbazone, H₂th5Clsa=5-chlorosalicylaldehyde thiosemicarbazone, and H₂th5Brsa=5-bromosalicylaldehyde thiosemicarbazone) have been synthesized and their spin-transition properties investigated by magnetic susceptibility, Mössbauer spectroscopy, and differential scanning calorimetry measurements. The three compounds exhibit an abrupt spin transition with a thermal hysteresis effect. The more polarizable the substituent on the salicylaldehyde moiety, the more complete is the transition at room temperature with an increased degree of cooperativity. The molecular structures of 1 and 2 in the high-spin state are revealed. The occurrence of the light-induced excited-spin-state trapping phenomenon appears to be dependent on the substituent incorporated into the 5-position of the salicylaldehyde subunit. Whereas the compounds with an electron-withdrawing group (-Br or -Cl) exhibit light-induced trapped excited high-spin states with great longevity of metastability, the halogen-free compound does not, even though strong intermolecular interactions (such as hydrogen-bonding networks and π stacking) operate in the system. For compound 2 , the surface level of photoconversion is less than 35 %. In contrast, compound 3 displays full photoexcitation.     

Interface Structure between Immiscible Reactive Polymers under Transreaction: a Monte Carlo Simulation

Summary: The interface structure between two immiscible melts, a polycondensate polymer A (e.g., polycarbonate, polyester or polyamide) and a polymer B, was studied by means of Monte Carlo simulations using the bond fluctuation model. Polymer B contained a reactive end group (e.g., OH, NH₂ or COOH). Copolymers were generated in‐situ at the interfaces by transreactions (alcoholysis, aminolysis or acidolysis), composing of various length of block A, depending on the position of transreaction in the polycondensate chain A. The content of copolymer at the interface increased with the time, particular fast at the early stage. Fragments of polymers A were released with an end group, reactive to polymers A. This resulted in the proceeding of internal transreactions. An asymmetric interface structure was formed. The simulation also showed that copolymers generated by interfacial transreactions increased the compatibility of the two polymers and enhanced the adhesion strength at the interfaces.

     

Time-resolved fluorescence of the bacteriophage T4 capsid protein gp23

The time-resolved fluorescence properties of the bacteriophage T4 capsid protein gp23 are investigated. The structural characteristics of this protein are largely unknown and can be probed by recording time-resolved and decay-associated fluorescence spectra and intensity decay curves using a 200 ps-gated intensified CCD-camera. Spectral and decay data are recorded simultaneously, which makes data acquisition fast compared to time-correlated single-photon counting. A red-shift of the emission maximum within the first nanosecond of decay is observed, which can be explained by the different decay-associated spectra of fluorescence lifetimes of the protein in combination with dipolar relaxation. In addition, iodide quenching experiments are performed, to study the degree of exposure of the various tryptophan residues. A model for the origin of the observed lifetimes of 0.032 +/- 0.003, 0.39 +/- 0.06, 2.1 +/- 0.1 and 6.8 +/- 0.8 ns is presented: the 32 ps lifetime can be assigned to the emission of a buried tryptophan residue, the 0.4 and 2.1 ns lifetimes to two partly buried residues, and the 6.8 ns lifetime to a single tryptophan outside the bulk of the folded gp23.     

Ring-expansion polycondensation of 2-stanna-1,3-dioxepane (or 1,3-dioxepene) with dicarboxylic acid chlorides

2,2-Dibutyl-2-stanna-1,3-dioxepane 1 (or 1,3-dioxepene 2) were prepared from 1,4-butane (or 1,4-butene) diol and dibutyltin dimethoxide. They were polycondensed at 80°C in n-heptane with adipoyl-, suberoyl, sabacoyl chloride and with decane-1,10-dicarbonyl chloride. In the case of suberoyl chloride and 2,2-dibutyl-2-stanna-1,3-dioxepane reaction time, temperature and stoichiometry were varied to optimize both the molecular weight and the fraction of cyclic polyesters. With a slight excess of the dicarboxylic acid chlorides, only macrocyclic polyesters were obtained in all cases. The resulting cyclic polyesters were characterized by viscosity measurements, by ¹H and ¹³C NMR and by MALDI-TOF mass spectrometry.     

Infrared spectroscopy of gas-phase Cr+ coordination complexes: determination of binding sites and electronic states

Infrared spectra were recorded for a series of gas-phase Cr+ complexes using infrared multiphoton dissociation (IRMPD) in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. The functionalized aromatic ligands (acetophenone, anisole, aniline, and dimethyl aniline) offer a choice of either aromatic ring-pi or n-donor-base binding sites. Use of the FELIX free electron laser light source allowed convenient, rapid scanning of the chemically informative wavelength range from approximately 500 to 1800 cm(-1), which in many cases characterized the preferred site of metal binding, as well as the electronic spin state of the complex. Mono-complex ions, Cr+(ligand), for anisole, aniline, and dimethyl aniline and bis-complex ions, Cr+(ligand)(2), for anisole, aniline, and acetophenone were produced by ligand attachment to laser-desorbed Cr+ ions in the FT-ICR cell. The photodissociation yields plotted as a function of wavelength were interpreted as approximations to the infrared absorption spectra and were compared with computed spectra of different possible geometries and spin states. Clear-cut diagnostic features in the spectra of the acetophenone, anisole, and aniline complexes showed the sites of Cr+ attachment to be the carbonyl oxygen site for acetophenone (bis-complex) and the ring-pi site for anisole and aniline (both mono- and bis-complexes). The bis-complexes of aniline and anisole are low-spin (probably doublet) states, while the mono-complexes of these same ligands are high-spin (sextet) states. The dimethyl aniline complex gave a cluttered spectrum in poor agreement with calculations, which may reflect a mixture of binding-site isomers in this case.     

Hydrodynamic chromatography of polystyrene microparticles in micropillar array columns

We report on the possibility to perform HDC in micropillar array columns and the potential advantages of such a system. The HDC performance of a pillar array column with pillar diameter = 5 μm and an interpillar distance of 2.5 μm has been characterized using both a low MW tracer (FITC) and differently sized polystyrene bead samples (100, 200 and 500 nm). The reduced plate height curves that were obtained for the different investigated markers all overlapped very well, and attained a minimum value of about h_min = 0.3 (reduction based on the pillar diameter), corresponding to 1.6 μm in absolute value and giving good prospects for high efficiency separations. The obtained reduced retention time values were in fair agreement with that predicted by the Di Marzio and Guttman model for a flow between flat plates, using the minimal interpillar distance as characteristic interplate distance.     

Experimental study of the depth influence on the band broadening effect in a cyclo-olefin polymer column containing an array of ordered pillars

An experimental study of a micromachined non-porous pillar array column performance under non-retentive conditions is presented. The same pillar structure has been fabricated in cyclo-olefin polymer (COP) chips with three different depths via hot embossing and pressure-assisted thermal bonding. The influence of the depth on the band broadening along with the already known contribution arising from the top and bottom cover plates has been studied. The experimental results exhibit reduced plate heights as low as 0.2, which are in agreement with the previous experimental work. Moreover, the constant values of the reduced Van Deemter expression are also in accordance with the previous studies. A more exhaustive study of the C-term band broadening is also presented, showing that comparing the space between the pillars with different open tubular rectangular channels offers a good estimation of the C-term band broadening that is obtained experimentally. These experimental results, hence, confirm that micromachined pillar array columns fabricated in COP can achieve the same performance as the ones fabricated in silicon for the presently studied pillar channel design.     

XNBR/LDH nanocomposites: Effect of vulcanization and organic modifier on nanofiller dispersion and strain‐induced crystallization

In elastomer/organo clay nanocomposites, the morphological characteristics, and hence the mechanical properties, of the vulcanizates are strongly influenced by the organic modifier and the vulcanization process. When the elastomer itself undergoes strain‐induced crystallization, both the organic modifier and the dispersed filler particles could significantly influence the crystallization process. These phenomena are very common in case of natural rubber‐based vulcanizates. In this study, the similar effects have been demonstrated with carboxylated nitrile rubber (XNBR) and organically modified layered double hydroxide (O‐LDH)‐based nanocomposites. The effect of size of the organic modifier was obviously visible on the interlayer distance of O‐LDH and also on the morphological reorganization of the dispersed O‐LDH particles during vulcanization process. The strain‐induced crystallization of the XNBR was found to be strongly dependent on the morphological change that occurs during vulcanization process. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Thermodynamic property values of selected polycyclic aromatic hydrocarbons measured by differential scanning calorimetry

In this study, the use of differential scanning calorimetry (DSC) is demonstrated as a powerful technique that can provide accurate thermodynamic property values of environmental contaminants such as polycyclic aromatic hydrocarbons (PAHs). In total, 47 high purity PAH certified reference materials were selected and analysed by DSC. Their onset melting temperature, enthalpy of fusion and eutectic purity were calculated from the obtained melting endotherms. In addition, the entropy of fusion, which was calculated from the onset melting temperature and enthalpy of fusion, is presented. All measurements were evaluated in a metrologically rigorous manner, including measurement uncertainties.     

Development and validation of a differential scanning calorimetry purity determination method for polycyclic aromatic hydrocarbons

Based on a standard test method for purity by differential scanning calorimetry (DSC), ASTM E 928, a purity determination method for highly pure polycyclic aromatic hydrocarbons (PAHs) has been developed and validated. The robustness of the developed method was investigated by determining, under varying measurement conditions, the purity of two PAH certified reference materials (CRMs), benzo[c]phenanthrene and dibenzo[a,h]anthracene. The repeatability and intermediate precision of the developed method was determined by analysing the purity of benzo[c]phenanthrene and dibenzo[a,h]anthracene and PAH candidate CRMs indeno[1,2,3-c,d]pyrene, 6-methylchrysene and benzo[a]pyrene. The trueness of the method was studied using the same (candidate) CRMs and a series of 42 other PAH CRMs. For each of the five (candidate) CRMs, a full measurement uncertainty budget was developed. Also for PAH materials for which the DSC purity determination method has not been explicitly validated, the relative expanded measurement uncertainty was estimated.