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61.
Nienhaus K Nar H Heilker R Wiedenmann J Nienhaus GU 《Journal of the American Chemical Society》2008,130(38):12578-12579
An important class of red fluorescent proteins (RFPs) feature a 2-iminomethyl-5-(4-hydroxybenzylidene)imidazolinone chromophore. Among these proteins, eqFP611 has the chromophore in a coplanar trans orientation, whereas the cis isomer is preferred by other RFPs such as DsRed and its variants. In the photoactivatable protein asFP595, the chromophore can even be switched from the nonfluorescent trans to the fluorescent cis state by light. By using X-ray crystallography, we have determined the structure of dimeric eqFP611 at high resolution (up to 1.1 A). In the far-red emitting eqFP611 variant d2RFP630, which carries an additional Asn143Ser mutation, the chromophore resides predominantly (approximately 80%) in the cis isomeric state, and in RFP639, which has Asn143Ser and Ser158Cys mutations, the chromophore is found completely in the cis form. The pronounced red shift of excitation and emission maxima of RFP639 can thus unambiguously be assigned to trans-cis isomerization of the chromophore. Among RFPs, eqFP611 is thus unique because its chromophore is highly fluorescent in both the cis and trans isomeric forms. 相似文献
62.
Stokes–Einstein (SE) and Stokes–Einstein–Debye (SED) relations in the neat ionic liquid (IL) [C2mim][NTf2] and IL/chloroform mixtures are studied by means of molecular dynamics (MD) simulations. For this purpose, we simulate the translational diffusion coefficients of the cations and anions, the rotational correlation times of the C(2)? H bond in the cation C2mim+, and the viscosities of the whole system. We find that the SE and SED relations are not valid for the pure ionic liquid, nor for IL/chloroform mixtures down to the miscibility gap (at 50 wt % IL). The deviations from both relations could be related to dynamical heterogeneities described by the non‐Gaussian parameter α(t). If α(t) is close to zero, at a concentration of 1 wt % IL in chloroform, both relations become valid. Then, the effective radii and volumes calculated from the SE and SED equations can be related to the structures found in the MD simulations, such as aggregates of ion pairs. Overall, similarities are observed between the dynamical properties of supercooled water and those of ionic liquids. 相似文献
63.
64.
The existence of electrophoretic mobility at high electrolyte concentrations defines a remarkable peculiarity in the electrosurface characteristics of soft particles. According to Ohshima [H. Ohshima, Colloids Surf. 103 (1995) 249], this effect is caused by the electroosmotic flow within the soft particle shell. An explanation supporting Ohshima's conclusion can be derived from classic electrokinetic theories. Based on the Henry theory [D.C. Henry, Proc. R. Soc. London Ser. A 133 (1931) 106], we demonstrate that the electrophoretic mobility of soft particles does not disappear at decinormal concentration. 相似文献
65.
Thermophysical properties and material modelling of acrylic bone cements used in vertebroplasty 总被引:1,自引:0,他引:1
Sebastian Kolmeder Alexander Lion Ralf Landgraf Jörn Ihlemann 《Journal of Thermal Analysis and Calorimetry》2011,105(2):705-718
The stabilization of osteoporotic vertebrae with acrylic bone cement, called vertebroplasty, is a common procedure in modern
surgery. However, the thermomechanical-chemically coupled material behaviour of curing bone cements makes the application
even for experienced surgeons difficult and can lead to potential complications like heat necrosis, leaking bone cement, embolisms
and postoperative load shifting. In order to reduce these potential complications, to minimize the risks and to better understand
the occurring effects, the thermophysical properties of a commercial acrylic bone cement were investigated in detail using
differential scanning calorimetry, volumetric dilatometry and temperature controlled rheometry. More specifically, the reaction
kinetics, the specific heat, the thermal conductivity, the thermal expansion, the chemical shrinkage as well as the mechanical
behaviour was studied during the reaction process of the bone cement. Furthermore, the explored material behaviour is described
by a customized material model that takes into account all observed effects. With the aid of this model the inhomogeneous
chemical, thermal and mechanical states that appear during the application and curing of acrylic bone cements, can be studied
by finite element treatment. 相似文献
66.
Lu Z Moss RA Warmuth R Krogh-Jespersen K 《The journal of physical chemistry. A》2011,115(47):13799-13803
Laser flash photolysis of fluorophenyldiazirine incarcerated in hemicarcerand 2 affords incarcerated fluorophenylcarbene [2⊙3], which forms a metastable, innermolecular π-complex with aryl moieties of 2. This carbene complex can be observed spectroscopically. Extensive computational studies provide insights into the structure, spectroscopy, energetics, and kinetics of the 2⊙3 carbene complex. 相似文献
67.
The ligand field molecular mechanics method has been extended to treat η(6)-arene ligands coordinated to a ruthenium(II) centre by employing a dummy atom located at the centroid of the arene ring and distributing the forces on the dummy to the arene carbon atoms. Angular overlap model parameters based on orbital energies derived from Kohn-Sham density functional theory (KS-DFT) calculations show that, relative to the Ru-dummy vector, the arene behaves as a very strong π donor and weak σ donor. Based on KS-DFT geometries, partial atomic charges and potential energy scans for a series of homoleptic and half sandwich complexes spanning arene, am(m)ine, imine, pyridyl, hydride and chloride ligands, a new LFMM force field has been developed which accurately reproduces the KS-DFT data. This FF was validated against 47 half-sandwich complexes obtained from the Cambridge Structural Database which, after minor corrections to account for the systematic errors between our chosen functional (BP86) and the experimental structures, yields a 'structurally tuned' FF where 93% of the Ru-L contacts are reproduced to 0.05 ? or better and all bar two bond lengths are within 0.1 ? of experiment. Over half the systems have non-hydrogen-atom rmsds of less than 0.5 ?. Larger differences are usually due to rotation of the arene moiety which is shown by ligand field molecular dynamics (LFMD) simulations to be an inherently low-energy process. Comparisons between LFMD and Car-Parrinello MD for [Ru(p-cymene)(ethylenediamine)Cl](+)show that LFMD is equally accurate but much faster enabling modelling of dynamic properties which occur on a timescale beyond the scope of CPMD. 相似文献
68.
Bieler M Heilker R Köppen H Schneider G 《Journal of chemical information and modeling》2011,51(8):1897-1905
Computer-based chemogenomics approaches compare macromolecular drug targets based on their amino acid sequences or derived properties, by similarity of their ligands, or according to ligand-target interaction models. Here we present ARTS (Assay Related Target Similarity) as a quantitative index that estimates target similarity directly from measured affinities of a set of probe compounds. This approach reduces the risk of deducing artificial target relationships from mutually inactive compounds. ARTS implements a scoring scheme that matches intertarget similarity based on dose-response measurements. While all experimentally derived target similarities have a tendency to be data set-dependent, we demonstrate that ARTS depends less on the used data set than the commonly used Pearson correlation or Tanimoto index. 相似文献
69.
Alexey P. Kostikov Joshua Chin Björn Wängler Klaus Jurkschat Ralf Schirrmacher 《Journal of fluorine chemistry》2011,132(1):27-6205
18F-labeled compounds play a major role in the development of new in vivo imaging agents for Positron Emission Tomography (PET), a non invasive imaging modality depicting the biodistribution of radioactive compounds in humans. Recently we reported a new method for the introduction of fluorine-18 into a range of organic molecules exploiting the very fast 18F-19F isotope exchange of fluorosilanes (termed SiFA compounds). Here, we wish to report the labeling of the first charged SiFA molecule N-(4-(di-tert-butylfluorosilyl)benzyl)-2-hydroxy-N,N-dimethylethylammonium bromide (SiFAN+Br−) serving as a lead compound in the development of SiFA-based prosthetic groups of reduced lipophilicity for biomolecule labeling. Mild conditions for synthesis of [18F]SiFAN+Br− and an easy purification procedure using simple C-18 solid phase cartridge have been developed yielding the [18F]SiFAN+Br− in radiochemical yields of 34% (non-decay corrected) within 40 min. A series of kinetic experiments were performed that show high isotopic exchange rate constants. Low activation energy (15.7 kcal/mol) and a large preexponential factor (7.9 × 1013 M−1 s−1) were calculated for the isotopic exchange reaction from a corresponding Arrhenius plot. For comparison, the 18F-fluorination of ethyleneglycol-di-p-tosylate via the formation of a carbon-18F bond showed a 1.3 kcal/mol higher activation energy and a much lower preexponential factor of 2.9 × 109 M−1 s−1. Moderate hydrophilicity (log D = 0.44), stability in aqueous media at pH up to 7.4 and a high specific activity of [18F]SiFAN+Br− (SA = 20.4 GBq/μmol, 0.55 Ci/μmol) make this charged SiFA compound useful for the development of novel SiFA-based 18F-labeling synthons. 相似文献
70.