Lipid nanotube formation from streptavidin-membrane binding

A novel transformation of giant lipid vesicles to produce nanotubular structures was observed upon the binding of streptavidin to biotinylated membranes. Unlike membrane budding and tubulation processes caused by proteins involved with endocytosis and vesicle fusion, streptavidin is known to crystallize at near the isoelectric point (pI 5 to 6) into planar sheets against biotinylated films. We have found, however, that at neutral pH membranes of low bending rigidity (<10kT), such as 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), spontaneously produce tubular structures with widths ranging from micrometers to below the diffraction limit (<250 nm) and lengths spanning up to hundreds of micrometers. The nanotubes were typically held taut between surface-bound vesicles suggesting high membrane tension, yet the lipid nanotubes exhibited a fluidic nature that enabled the transport of entrained vesicles. Confocal microscopy confirmed the uniform coating of streptavidin over the vesicles and nanotubes. Giant vesicles composed of lipid membranes of higher bending energy exhibited only aggregation in the presence of streptavidin. Routes toward the development of these highly curved membrane structures are discussed in terms of general protein-membrane interactions.     

低温加氢催化剂的设计: 理论与实践

简要总结了我们在C=C及C=O双键低温加氢双金属催化剂方面的最新研究成果. 首先, 我们以环己烯加氢为探针反应, 证明了平行使用多种研究手段的重要性, 包括单晶表面的基础研究与DFT计算, 多晶表面的合成与表征, 负载型催化剂的制备与性能测试等. 其次, 总结了双金属催化剂在其他加氢反应, 如丙烯醛C=O双键的选择性加氢, 苯的低温加氢, 以及乙炔的选择性加氢等反应中的应用. 最后, 讨论了利用金属碳化物代替贵金属Pt以减少双金属催化剂中Pt用量的可能性.     

Ion chemistry of 1H-1,2,3-triazole. 2. Photoelectron spectrum of the iminodiazomethyl anion and collision induced dissociation of the 1,2,3-triazolide ion

The 363.8 nm photoelectron spectrum of the iminodiazomethyl anion has been measured. The anion is synthesized through the reaction of the hydroxide ion (HO-) with 1 H-1,2,3-triazole in helium buffer gas in a flowing afterglow ion source. The observed spectrum exhibits well-resolved vibronic structure of the iminodiazomethyl radical. Electronic structure calculations have been performed at the B3LYP/6-311++G(d,p) level of theory to study the molecular structure of the ion. Equilibrium geometries of four possible conformers of the iminodiazomethyl anion have been obtained from the calculations. Spectral simulations have been performed on the basis of the calculated geometries and normal modes of these conformationally isomeric ions and the corresponding radicals. The spectral analysis suggests that the ions of two conformations are primarily formed in the aforementioned reaction. The relative abundance of the two conformers substantially deviates from the thermal equilibrium populations, and it reflects the potential energy surfaces relevant to conformational isomerization processes. The electron affinities of the ( ZE)- and ( EE)-iminodiazomethyl radicals have been determined to be 2.484 +/- 0.007 and 2.460 +/- 0.007 eV, respectively. The energetics of the iminodiazomethyl anion is compared with that of the most stable structural isomer, the 1,2,3-triazolide ion. Collision-induced dissociation of the 1,2,3-triazolide ion has also been studied in flowing afterglow-selected ion flow tube experiments. Facile fragmentation generating a product ion of m/ z 40 has been observed. DFT calculations suggest that fragmentation of the 1,2,3-triazolide ion to the cyanomethyl anion and N2 is exothermic. The stability of the ion is discussed in comparison with other azolide ions with different numbers of N atoms in the five-membered ring.     

Fluorescent probe: complexation of Fe3+ with the myo-inositol 1,2,3-trisphosphate motif

Natural myo-inositol phosphate antioxidants containing the 1,2,3-trisphosphate motif bind Fe(3+) in the unstable penta-axial conformation.     

Nickel(II), copper(II), and cobalt(II) solid-state structures formed through hydrogen bonding with ditopic heteroscorpionate ligands

New complexes of nickel(II), copper(II), and cobalt(II) derived from bidentate coordinating heteroscorpionate ligands, (4-carboxyphenyl)bis(3,5-dimethylpyrazolyl)methane, (L4c) and (3-carboxyphenyl)bis(3,5-dimethylpyrazolyl)methane, (L3c) have been synthesized and characterized by X-ray diffraction, IR, elemental analysis and UV-vis spectroscopy. By adjusting the reaction conditions the coordination modes of the ligands can be controlled. Solid-state interactions utilizing the strong hydrogen bonding capabilities of protonated and uncoordinated carboxylate groups can be the result of these changed reaction conditions. Finally the different orientation of the carboxylate groups in the ligands L3c and L4c also affect the overall coordination modes and the nature of the solid-state interactions in these systems.     

Characterizing the distribution of nonylphenol ethoxylate surfactants in water-based pressure-sensitive adhesive films using atomic-force and confocal Raman microscopy

Surfactant distributions in model pressure-sensitive adhesive (PSA) films were investigated using atomic force microscopy (AFM) and confocal Raman microscopy (CRM). The PSAs are water-based acrylics synthesized with n-butyl acrylate, vinyl acetate, and methacrylic acid and two commercially available surfactants, disodium (nonylphenoxypolyethoxy)ethyl sulfosuccinate (anionic) and nonylphenoxypoly(ethyleneoxy) ethanol (nonionic). The ratio of these surfactants was varied, while the total surfactant content was held constant. AFM images demonstrate the tendency of anionic surfactant to accumulate at the film surfaces and retard latex particle coalescence. CRM, which was introduced here as a means of providing quantitative depth profiling of surfactant concentration in latex adhesive films, confirms that the anionic surfactant tends to migrate to the film interfaces. This is consistent with its greater water solubility, which causes it to be transported by convective flow during the film coalescence process. The behavior of the nonionic surfactant is consistent with its greater compatibility with the polymer, showing little enrichment at film interfaces and little lateral variability in concentration measurements made via CRM. Surfactant distributions near film interfaces determined via CRM are well fit by an exponential decay model, in which concentrations drop from their highs at interfaces to plateau values in the film bulk. It was observed that decay constants are larger at the film-air interface compared with those obtained at the film-substrate side indicating differences in the mechanism involved. In general, it is shown here that CRM acts as a powerful compliment to AFM in characterizing the distribution of surfactant species in PSA film formation.     

Preparation of aryloxetanes and arylazetidines by use of an alkyl-aryl suzuki coupling

The oxetan-3-yl and azetidin-3-yl substituents have previously been identified as privileged motifs within medicinal chemistry. An efficient approach to installing these two modules into aromatic systems, using a nickel-mediated alkyl-aryl Suzuki coupling, is presented.     

Simple and rapid extraction, separation, and detection of alkaloids in beverages

Implementation of an uncomplicated SPE process for the rapid extraction and preconcentration of the alkaloids, colchicine, strychnine, aconitine, and nicotine, from water, apple juice, and nonfat milk samples is presented. When coupled to analysis via micellar EKC (MEKC), the total analysis time per sample was less than 15 min for the water and juice samples and less than 20 min for the milk. The SPE process allowed for anywhere from a three to a fourteen-fold improvement in the LOD for each alkaloid when compared to detecting the alkaloids in a nontreated water sample matrix. Following SPE, the LODs for colchicine, strychnine, and nicotine were sufficient to meet levels from 150 to 5000 times more dilute than the LD(50) for a 50 kg individual drinking 12 oz of a contaminated beverage. Aconitine, on the other hand, was detected at approximately the LD(50) level. The percent recoveries for the SPE ranged from 37% to as high as 99%. Nicotine attained the highest recovery efficiencies, followed by colchicine, and finally, aconitine and strychnine, which were nearly identical. The greatest recovery efficiencies were achieved from apple juice and water, whereas nonfat milk yielded the lowest.     

Early transition metal complexes bearing a C-capped tris(phenolate) ligand incorporating a pendant imine arm: synthesis, structure, and ethylene polymerization behavior

The ligand 3-[2,2'-methylenebis(4,6-di- tert-butylphenol)-5- tert-butylsalicylidene-(2,6-diisopropyl)phenylimine] (L(1)H 3) was reacted with MCl 4 (M = Ti, Zr) or MCl 5 (M = Nb, Ta) to give complexes of the type [MCl 2(L(1)H 2) 2] (M = Ti (1); Zr (2)), [NbCl 3( L (1)H)] (3), or [TaCl 4(L(1)H 2)] (4), respectively. Single crystal X-ray diffraction of 1- 4 revealed common "iminium" species resulting in zwitterionic complexes. Reaction of [V(N p-tol)(O n-Pr) 3] with L (1)H3 afforded [{(VN p-tol)(L(1)H)} 2(mu-O n-Pr)2] (5), and a second complex [(VO) 2(mu-O)(L(3)H) 2] (6)(L(3)H being derived from 3-[2,2'-methylenebis(4,6-di-tert-butylphenol)-5-tert-butylsalicylidene- p-tolylimine]). The condensation reaction between 3-[2,2'-methylenebis(4,6-di-tert-butylphenol)-5-tert-butyl-2-hydroxybenzaldehyde] (L(0)H 3) and o-phenylenediamine (1,2-diaminobenzene) afforded two products: a pseudo-16-membered hydrogen bonded macrocyclic structure {1,2-bis-3-[2,2'-methylenebis(4,6-di-tert-butylphenol)-5-tert-butylsalicylidene-benzyldiimine]} (L(5)H6), or the benzimidazolyl bearing ligand (L(6)H 3). The reaction of L (5)H6 or L(6)H 3 with [VO(O n-Pr) 3] under varying conditions produced the complexes [(VO)(L(5)H 4)] (7), [(VO) 2(L(5)H)] (8), or [VO(L(6)H 2) 2] (9). L (0)H 3 was reacted with a number of anilines to give the proligands {3-[2,2'-methylenebis(4,6-di- tert-butylphenol)-5-tert-butylsalicylidene-R-imine]}, where R = NC 6H 5 (L(2)H3), NC 6H 4-Me (L(3)H 3), and NC 6H 2-Me 3 (L(4)H 3). Reactions of these ligands with [VO(O n-Pr) 3] formed bischelating complexes of the form [(VO)(L(2-4)H 2)2] (10, 11, and 12, respectively). The reaction of L (1)H 3 with trimethylaluminum led to a bis-aluminum complex {(AlMe 2)[AlMe(NCMe)] L (1)} (13). The ability of complexes 1-12 to polymerize ethylene in the presence of an organoaluminum cocatalyst was investigated. Procatalysts 1 and 2 were found to produce negligible activities in the presence of dimethylaluminum chloride (DMAC) and the reactivator ethyltrichloroacetate (ETA), whereas 3 and 4 were found to be completely inactive for polymerization using a variety of different organoaluminum cocatalysts. Using the combination of DMAC and ETA, complexes 5-12 were found to be highly active catalysts; in all cases, the polymer formed was of high molecular weight linear polyethylene.     

In situ formation of heterobimetallic salen complexes containing titanium and/or vanadium ions

A combination of high-resolution electrospray mass spectrometry and (1)H NMR spectroscopy has been used to prove that when a mixture of [(salen)TiO]2 complexes containing two different salen ligands (salen and salen') is formed, an equilibrium is established between the homodimers and the heterodimer [(salen)TiO2Ti(salen')]. Depending upon the structure and stereochemistry of the two salen ligands, the equilibrium may favor either the homodimers or the heterodimer. Extension of this process to mixtures of titanium(salen) complexes [(salen)TiO]2 and vanadium (V)(salen') complexes [(salen')VO] (+)Cl (-) allowed the in situ formation of the heterobimetallic complex [(salen)TiO2V(salen')] (+)X (-) to be confirmed for all combinations of salen ligands studied except when the salen ligand attached to titanium contained highly electron-withdrawing nitro-groups. The rate of equilibration between heterobimetallic complexes is faster than that between two titanium complexes as determined by line broadening in the (1)H NMR spectra. These structural results explain the strong rate-inhibiting effect of vanadium (V)(salen) complexes in asymmetric cyanohydrin synthesis catalyzed by [(salen)TiO]2 complexes. It has also been demonstrated for the first time that the titanium and vanadium complexes can undergo exchange of salen ligands and that this is catalyzed by protic solvents. However, the ligand exchange is relatively slow (occurring on a time scale of days at room temperature) and so does not complicate studies aimed at using heterobimetallic titanium and vanadium salen complexes as asymmetric catalysts. Attempts to obtain a crystal structure of a heterobimetallic salen complex led instead to the isolation of a trinuclear titanium(salen) complex, the formation of which is also consistent with the catalytic results obtained previously.