How close can you get? Studies of ultrafast light-induced processes in ruthenium-[60] fullerene dyads with short pyrazolino and pyrrolidino links

Two pyrazoline- and one pyrrolidine-bridged Ru(II)bipyridine-[60]fullerene dyads have been prepared and studied by ultrafast time-resolved spectroscopy. A silver-assisted synthesis route, in which Ag(I) removes the chlorides from the precursor complex Ru(bpy) 2Cl 2 facilitates successful coordination of the [60]fullerene-substituted third ligand. Upon light excitation of the ruthenium moiety, the emission was strongly quenched by the fullerene. The main quenching mechanism is an exceptionally fast direct energy transfer ( k obs > 1 x 10 (12) s (-1) in the pyrazoline-bridged dyads), resulting in population of the lowest excited triplet state of fullerene. No evidence for electron transfer was found, despite the extraordinarily short donor-acceptor distance that could kinetically favor that process. The observations have implications on the ongoing development of devices built from Ru-polypyridyl complexes and nanostructured carbon, such as C 60 or nanotubes.     

Multifunctional Antioxidants: Regenerable Radical‐Trapping and Hydroperoxide‐Decomposing Ebselenols

Regenerable, multifunctional ebselenol antioxidants were prepared that could quench peroxyl radicals more efficiently than α‐tocopherol. These compounds act as better mimics of the glutathione peroxidase enzymes than ebselen. Production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in human mononuclear cells was considerably decreased upon exposure to the organoselenium compounds. At a concentration of 25 μm , the ebselenol derivatives showed minimal toxicity in pre‐osteoblast MC3T3 cells.     

Correlated theoretical, spectroscopic and X-ray crystallographic studies of a non-covalent molecularly imprinted polymerisation system

The correlation of the recognition properties of a molecularly imprinted polymer (MIP) with the recognition events in pre-polymerisation mixtures is of central importance to our understanding of the molecular imprinting technique. Using the NSAID naproxen as a model template, we have applied parallel theoretical (molecular dynamics) and practical ((1)H-NMR, X-ray crystallography, HPLC, radioligand binding) methods to examine the nature of template-functional monomer complexation. An effective imprint is achieved, despite the presence of only one site on the template which provides for the formation of effective electrostatic interactions with the functional monomer used, 4-vinylpyridine. This is attributed to the creation of a well-defined receptor site for the acidic terminus of the molecule and complementary van der Waals interactions, as described in preliminary simulations of the pre-polymerisation system, and as confirmed for the resultant MIP by HPLC data. Qualitative agreement is also observed between simulation and proton NMR data examining monomer self-association in the presence and absence of the template. On the basis of the data obtained, the role of a cross-linker appears to be more significant for this system than previously anticipated.     

Thermodynamic characterization of the adsorption of selected chiral compounds on immobilized amyloglucosidase in liquid chromatography

Immobilized amyloglucosidase was used as a chiral stationary phase (CSP). First, the retention and enantioselectivity of several model chiral amines and acids were investigated. We found that this CSP was unable to separate the enantiomers of acids, though all selected amines could be resolved. The adsorption of (R)- and (S)-propranolol and its influence on column temperature and 2-propanol content in the eluent were then studied in detail, using a three-step methodology. The adsorption was first evaluated using Scatchard plots; thereafter, the adsorption was characterized in detail by calculating the adsorption energy distribution. With this model-independent information, a better judgment could be made of the possible adsorption models selected in the last step, the model fitting to the data. In the case examined, the bi-Langmuir model (containing nonselective and enantioselective sites) describes the system well. The retention of (R)- and (S)-propranolol at low temperatures increases with the content of 2-propanol in the eluent, due to the increased saturation capacity of the enantioselective sites. The retention is an enthalpy-driven process at both types of sites, whereas the enantioseparation is due to differences between the entropy changes of the two enantiomers at the enantioselective sites. The enthalpy of adsorption at the nonselective sites is almost identical at the two concentrations of 2-propanol in the eluent. Enantioselective adsorption, on the other hand, is more exothermic at higher modifier content (20%). Thus, at high temperatures the retention decreases with increasing modifier content, whereas the opposite (unusual) trend is the case at low temperatures.     

Anomalous Rotational Resonance Spectra in Magic-Angle Spinning NMR

Magic-angle spinning NMR spectra of samples containing dilute spin-1/2 pairs display broadenings or splittings when a rotational resonance condition is satisfied, meaning that a small integer multiple of the spinning frequency matches the difference in the two isotropic shift frequencies. We show experimental rotational resonance NMR spectra of a 13C2-labeled retinal which are in qualitative disagreement with existing theory. We propose an explanation of these anomalous rotational spectra involving residual heteronuclear couplings between the 13C nuclei and the neighboring 1H nuclei. These couplings strongly influence the rotational resonance 13C spectrum, despite the presence of a strong radiofrequency decoupling field at the 1H Larmor frequency. We model the residual heteronuclear couplings by differential transverse relaxation of the 13C single-quantum coherences. We present a superoperator theory of the phenomenon and describe a numerical algorithm for rapid Liouville space simulations in periodic systems. Good agreement with experimental results is obtained by using a biexponential transverse relaxation model for each spin site.     

Mass spectrometric analysis of ceramide composition in mono-, di-, tri-, and tetraglycosylceramides from mouse kidney: an experimental model for uropathogenic Escherichia coli.

Many bacteria have been shown to bind to the carbohydrate part of glycosphingolipids, but also the lipid moieties of receptor-active glycolipids are of importance. To investigate the chemistry of the ceramides of kidney glycolipids to which the uropathogenic Escherichia coli bind, different mass spectrometric techniques were utilized. First, a mixture of glycolipids isolated from man and mice kidney was separated by thin-layer chromatography (TLC) and scanned by direct desorption from the plate by fast atom bombardment mass spectrometry (TLC/FAB-MS). Second, the glycolipids were purified by preparative TLC and analyzed by negative-ion FAB-MS. After methylation, further analyses were made with positive-ion FAB-MS, positive-ion electron ionization (EI)-MS, high-temperature capillary gas chromatography (GC/EI-MS) and positive-ion matrix-assisted laser desorption/ionization (MALDI)-MS. The ceramide compositions of the four glycolipids were determined using all these MS techniques and the reliability of the different methods for this type of analyses is discussed. Comparison of the mouse kidney glycolipids with the corresponding glycolipids from human kidney showed the same degree of hydroxylation of ceramides among mono- and disaccharide glycolipids, but a significantly higher degree of hydroxylation among mouse kidney glycolipids with three and four sugar residues. This result might be of relevance for the binding of P-fimbriated E. coli to the urinary tract tissues.     

Use of immobilized amyloglucosidase as chiral selector in chromatography. Control of enantioselective retention and resolution in liquid chromatography

Summary Several mobile phase parameters were investigated for controlling enantioselective retention and resolution on a chiral stationary phase made in-house. The chiral selector was the enzyme amyloglucosidase, which was immobilized onto a silica support via reductive amination. The influences of the mobile phase pH, concentration and type of uncharged organic modifier, ionic strength and column temperature on enantios-electivity were studied. The analysis time for resolving enantiomers could be adjusted with only a minor decrease in enantioselectivity by using a high ionic strength mobile phase buffer. This indicated a retention mechanism involving ion-exchange interactions. It was further confirmed by the decreasing enantioselectivity of amines when using a mobile phase pH below the isoelectric point of the native protein. Interesting effects were observed when the organic modifier concentration was increased and also when the column temperature was raised. Both retention and enantioselectivity increased with increasing concentration of 2-propanol in the mobile phase. Examples are given where both enantioselectivity and retention increased with increasing column temperature. Thermodynamic studies were performed to calculate the entropy and enthalpy constants. The results showed that, depending on mobile phase composition, the enantioselective retention may be caused by differences in entropy or enthalpy.     

Cryo-TEM Snapshots of Ferritin Adsorbed on Small Zeolite Crystals

The adsorption of macromolecules on zeolite crystal surfaces has been investigated by cryo transmission electron microscopy (TEM) of frozen hydrates. It was determined that ferritin shows different adsorption behavior on NaY (TEM image on the right) and USY zeolites (TEM image on the left).     

Dynamics in prediction of life-time of environmental adaptable polymers

Environmentally adaptable polymers are materials with well-defined life times made by tailoring the synthesis and creating a molecular architecture with precise functionality and morphology. Synthesis of such materials develops initiators/catalysts systems and enzymatic polymerisation while processing need to be adopted to the labile repeating units. The secondary structure of the environmentally adaptable polymers is susceptible to traditional processing introducing e.g. changes in the atomic positions of oxygen of poly(3-hydroxy-co-3-hydroxyvalerate). (Bio-) degradation of these materials is complex and difficult to predict. Modelling test-environments require an understanding of the many biological processes possible in nature. Many biodegradations require e.g. the co-operation of more than one microbial specium, which sometimes render standard biodegradation tests inadequate. The nonabsolute specificity of enzymes are probably responsible for the transformation of many of the novel molecules created in recent times, but it is wishful thinking to expect that every new compound has an enzyme able to catalyse its alteration.