The use of aqueous normal‐phase chromatography is explored as a possible format for the analysis of the forensically significant compounds ethyl glucuronide and ethyl sulfate. Standard solutions of the two compounds are used to verify the retention capabilities of two stationary phases (diamond hydride and undecanoic acid). These results are then compared to data obtained on hair extracts to determine if any matrix effects exist with respect to both retention and peak shape. The undecanoic stationary phase is used for the establishment of calibration curves for quantitative analysis. These curves are utilized to determine the concentration of ethyl glucuronide in several hair samples tested. 相似文献
A simple, “click” synthetic approach to a new type of hybrid phosph(III)azane/NHC system is described. The presence of the phosphazane P2N2 ring unit, with P atoms flanking the NCN fragment and with this ring perpendicular to the binding site of the NHC, provides unique opportunities for modifying the electronic and steric character of these carbenes. 相似文献
Rectangular arrays of pyramidal recesses coated by silver film are investigated by means of polarization‐resolved nonlinear microscopy at 900 nm fundamental wavelength, demonstrating strong dependence of the dipole‐allowed SHG upon the lattice parameters. The plasmonic band gap causes nearly complete SHG suppression in arrays of 650 nm periodicity, whereas a sharp resonance at 550 nm periodicity is observed due to excitation of band edge Bloch states at fundamental frequency, accompanied by symmetry‐constrained interactions with similar modes at the second‐harmonic frequency. Additionally, coupling with modes at the bottom side of the silver film may lead to extraordinary optical transmission, opening a channel for SHG from the highly nonlinear GaAs substrate. Changing the lattice geometry enables SHG intensity modulation over three orders of magnitude, while the effective nonlinear anisotropy can be continuously switched between the two lattice directions, reaching values as high as ±0.96.
Construction of receptors with binding sites of specific size, shape, and functional groups is important to both chemistry and biology. Covalent imprinting of a photocleavable template within surface–core doubly cross‐linked micelles yielded carboxylic acid‐containing hydrophobic pockets within the water‐soluble molecularly imprinted nanoparticles. The functionalized binding pockets were characterized by their binding of amine‐ and acid‐functionalized guests under different pH values. The nanoparticles, on average, contained one binding site per particle and displayed highly selective binding among structural analogues. The binding sites could be modified further by covalent chemistry to modulate their binding properties. 相似文献
Here we demonstrate that neat reactions of amphoteric azoles with more basic azoles give a family of finely tunable, nonstoichiometric liquids which are useful for N‐donor coordination chemistry. Reacting 4,5‐dicyanoimidazole (4,5‐DCNIm) with 1‐methylimidazole (1‐mim) gives new compounds with composition‐dependent speciation. Two crystalline compounds, a 1:1 protic salt, [H(1‐mim)][4,5‐DCNIm], and a 1:2 salt co‐crystal, [H(1‐mim)][4,5‐DCNIm]?4,5‐DCNIm, were isolated and structurally characterized, while differential scanning calorimetry revealed both suppression of crystallization and the presence of neutral and anionic species in the melt. Reactions of Cu(NO3)2?2.5 H2O, CuO, and ZnO with the neat 2:1 1‐mim/4,5‐DCNIm melt resulted in the isolation of entirely N‐donor ligated complexes of the formula M(4,5‐DCNIm)2(1‐mim)4 (M=Cu, Zn). 相似文献
Native mass spectrometry (MS) with electrospray ionization (ESI) has evolved as an invaluable tool for the characterization of intact native proteins and non-covalently bound protein complexes. Here we report the structural characterization by high resolution native top-down MS of human thrombin and its complex with the Bock thrombin binding aptamer (TBA), a 15-nucleotide DNA with high specificity and affinity for thrombin. Accurate mass measurements revealed that the predominant form of native human α-thrombin contains a glycosylation mass of 2205 Da, corresponding to a sialylated symmetric biantennary oligosaccharide structure without fucosylation. Native MS showed that thrombin and TBA predominantly form a 1:1 complex under near physiological conditions (pH 6.8, 200 mM NH4OAc), but the binding stoichiometry is influenced by the solution ionic strength. In 20 mM ammonium acetate solution, up to two TBAs were bound to thrombin, whereas increasing the solution ionic strength destabilized the thrombin–TBA complex and 1 M NH4OAc nearly completely dissociated the complex. This observation is consistent with the mediation of thrombin-aptamer binding through electrostatic interactions and it is further consistent with the human thrombin structure that contains two anion binding sites on the surface. Electron capture dissociation (ECD) top-down MS of the thrombin–TBA complex performed with a high resolution 15 Tesla Fourier transform ion cyclotron resonance (FTICR) mass spectrometer showed the primary binding site to be at exosite I located near the N-terminal sequence of the heavy chain, consistent with crystallographic data. High resolution native top-down MS is complementary to traditional structural biology methods for structurally characterizing native proteins and protein–DNA complexes.
Polycaprolactone (PCL) is widely used in biomedical applications as electrospun fibers or porous foams. As PCL is synthetic polymer, many researchers have explored blends of PCL–gelatin to combine mechanical and bioactive properties of individual components. High pressure carbon dioxide (CO2) has been studied to foam and impregnate many biocompatible polymers. In case of PCL–gelatin blends, certain compositions can be swelled reversibly under high pressure CO2 without permanent deformation. This allows successful impregnation of PCL–gelatin blends under CO2. This study summarizes effect of different treatments adopted during impregnation process including high pressure CO2 on several blend compositions of PCL–gelatin blends. Stress relaxation, polymer melting and dissolution were observed during several treatments which affects porosity and scaffold structure significantly. Results summarized in this study will aid in optimum selection of PCL–gelatin blend composition for biomedical applications. Furthermore, CO2 solubility in polymers is restricted due to thermodynamic limitations but can be altered in the presence of a co-solvent to produce better foams. PCL can be foamed using supercritical CO2. However, CO2 foaming of PCL–gelatin blend becomes challenging to simultaneous swelling of PCL and compression of gelatin providing blend structural stability. This study has demonstrated ability of supercritical CO2 to foam PCL–gelatin blends in presence of water to create porous structure. These foams were subjected post-fabrication crosslinking and supercritical CO2 without losing porosity of foams. Thus, creating a strategy to use environmentally benign processes to fabricate, crosslink and impregnate porous scaffolds for biomedical applications. 相似文献