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61.
Ibon Alkorta José Elguero Hans‐Heinrich Limbach Ilja G. Shenderovich Tammo Winkler 《Magnetic resonance in chemistry : MRC》2009,47(7):585-592
In 1975 a large number of coupling constants were measured in 2‐fluorobenzamide labeled with 15N. Some of them were assigned to couplings through intramolecular N? H···F hydrogen bonds (HBs). These couplings change dramatically when CDCl3 is replaced by DMSO‐d6. In this theoretical paper we provide density functional theory (DFT) calculations that justify the existence of a weak HB in the absence of solvent, while solvents that act as HB acceptors break down the intramolecular hydrogen bond (IMHB) of 2‐fluorobenzamide. Atoms in molecules (AIM) analyses and Steiner‐Limbach plots were used to analyze the structure of the compounds. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
62.
Dr. Jose R. Magana Dr. Berta Gumí-Audenis Dr. Roderick P. Tas Levena Gascoigne Dr. Dylan L. Atkins Prof. Ilja K. Voets 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(66):15330-15336
Silica materials attract an increasing amount of interest in (fundamental) research, and find applications in, for example, sensing, catalysis, and drug delivery. As the properties of these (nano)materials not only depend on their chemistry but also their size, shape, and surface area, the controllable synthesis of silica is essential for tailoring the materials to specific applications. Advantageously, bioinspired routes for silica production are environmentally friendly and straightforward since the formation process is spontaneous and proceeds under mild conditions. These strategies mostly employ amine-bearing phosphorylated (bio)polymers. In this work, we expand this principle to supramolecular polymers based on the water-soluble cationic cyanine dye Pinacyanol acetate. Upon assembly in water, these dye molecules form large, polyaminated, supramolecular fibers. The surfaces of these fibers can be used as a scaffold for the condensation of silicic acid. Control over the ionic strength, dye concentration, and silicic acid saturation yielded silica fibers with a diameter of 25 nm and a single, 4 nm pore. Unexpectedly, other unusual superstructures, namely, nummulites and spherulites, are also observed depending on the ionic strength and dye concentration. Transmission and scanning electron microscopy (TEM and SEM) showed that these superstructures are formed by aligned silica fibers. Close examination of the dye scaffold prior silicification using small-angle X-ray scattering (SAXS), and UV/Vis spectroscopy revealed minor influence of the ionic strength and dye concentration on the morphology of the supramolecular scaffold. Total internal reflection fluorescence (TIRF) during silicification unraveled that if the reaction is kept under static conditions, only silica fibers are obtained. Experiments performed on the dye scaffold and silica superstructures evidenced that the marked structural diversity originates from the arrangement of silica/dye fibers. Under these mild conditions, external force fields can profoundly influence the morphology of the produced silica. 相似文献
63.
Czolkos I Hakonen B Orwar O Jesorka A 《Langmuir : the ACS journal of surfaces and colloids》2012,28(6):3200-3205
We describe a general photolithography-based process for the microfabrication of surface-supported Teflon AF structures. Teflon AF patterns primarily benefit from superior optical properties such as very low autofluorescence and a low refractive index. The process ensures that the Teflon AF patterns remain strongly hydrophobic in order to allow rapid lipid monolayer spreading and generates a characteristic edge morphology which assists directed cell growth along the structured surfaces. We provide application examples, demonstrating the well-controlled mixing of lipid films on Teflon AF structures and showing how the patterned surfaces can be used as biocompatible growth-directing substrates for cell culture. Chinese hamster ovary (CHO) cells develop in a guided fashion along the sides of the microstructures, selectively avoiding to grow over the patterned areas. 相似文献
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66.
Octanol-water partition coefficients are extraordinarily successful for correlating and predicting numerous processes of pharmacological and environmental importance. The amphiphilic nature of the 1-octanol molecules allows the octanol phase to mimic the complexities of many different environments ranging from biomembranes to soil. However, the structural details of the octanol phase and whether its structure is altered upon water saturation are not yet fully understood. Configurational-bias Monte Carlo simulations in the Gibbs ensemble demonstrate that a diverse spectrum of hydrogen-bonded aggregates exists in dry and wet 1-octanol, and that water saturation substantially alters the 1-octanol environment from predominantly linear aggregates in dry octanol to larger cylindrical micelles with water cores in wet octanol. These simulation results are able to reconcile the conflicting views (chain-like or water-centered aggregates vs spherical micelles) of the 1-octanol structure inferred from thermodynamic arguments, spectroscopic measurements, and diffraction experiments. Calculated partition constants quantify the influence of water saturation on the solubility characteristics of the dry and wet octanol phases. 相似文献
67.
A variation of the line integral method of Elber with self-avoiding walk has been implemented using a state of the art nonlinear constrained optimization procedure. The new implementation appears to be robust in finding approximate reaction paths for small and large systems. Exact transition states and intermediates for the resulting paths can easily be pinpointed with subsequent application of the conjugate peak refinement method [S. Fischer and M. Karplus, Chem. Phys. Lett. 194, 252 (1992)] and unconstrained minimization, respectively. Unlike previous implementations utilizing a penalty function approach, the present implementation generates an exact solution of the underlying problem. Most importantly, this formulation does not require an initial guess for the path, which makes it particularly useful for studying complex molecular rearrangements. The method has been applied to conformational rearrangements of the alanine dipeptide in the gas phase and in water, and folding of the beta hairpin of protein G in water. In the latter case a procedure was developed to systematically sample the potential energy surface underlying folding and reconstruct folding pathways within the nearest-neighbor hopping approximation. 相似文献
68.
Hofs B Voets IK de Keizer A Cohen Stuart MA 《Physical chemistry chemical physics : PCCP》2006,8(36):4242-4251
With light scattering titrations, we show that complex coacervate core micelles (C3Ms) form from a diblock copolymer with a polyelectrolyte block and either an oppositely charged polyelectrolyte, a diblock copolymer with an oppositely charged polyelectrolyte or a mixture of the two. The effect of added salt and pH on both types of C3Ms is investigated. The hydrodynamic radius of mixed C3Ms can be controlled by varying the percentage of oppositely charged polyelectrolyte or diblock copolymer. A simple core-shell model is used to interpret the results from light scattering, giving the same trends as the experiments for both the hydrodynamic radii and the relative scattering intensities. Temperature has only a small effect on the C3Ms. Isothermal titration calorimetry shows that the complexation is mainly driven by Coulombic attraction and by the entropy gain due to counterion release. 相似文献
69.
Féron FX Frissen I Boissinot J Guastavino C 《The Journal of the Acoustical Society of America》2010,128(6):3703-3714
Three experiments are reported, which investigated the auditory velocity thresholds beyond which listeners are no longer able to perceptually resolve a smooth circular trajectory. These thresholds were measured for band-limited noises, white noise, and harmonic sounds (HS), and in different acoustical environments. Experiments 1 and 2 were conducted in an acoustically dry laboratory. Observed thresholds varied as a function of stimulus type and spectral content. Thresholds for band-limited noises were unaffected by center frequency and equal to that of white noise. For HS, however, thresholds decreased as the fundamental frequency of the stimulus increased. The third experiment was a replication of the second in a reverberant concert hall, which produced qualitatively similar results except that thresholds were significantly higher than in the acoustically dry laboratory. 相似文献
70.
Darius Widera Ilja Mikenberg Margitta Elvers Christian Kaltschmidt Barbara Kaltschmidt 《BMC neuroscience》2006,7(1):64-18