Adsorption behavior of DODAB/DPPC vesicles on silica

The interaction between composite dipalmitoylphosphatidylcholine (DPPC)/dioctadecyldimethylammonium bromide (DODAB) bilayer vesicles in the gel state and silica is investigated over the 0-20% DODAB range from determination of adsorption curves, silica sedimentation, particle sizing and zeta-potentials. At 1 mg/mL silica, 0% DODAB, pH 6.3, over the 0-150 mM NaCl range of ionic strengths, high affinity adsorption curves were barely affected by ionic strength and all of them exhibited limiting adsorption values above the level expected for single bilayer deposition. At 1 mg/mL silica, 2% DODAB, pH 6.3 and 1 mM NaCl, high affinity adsorption curves fortuitously presented limiting adsorption indicative of one bilayer deposition on each silica particle. At %DODAB<2% or %DODAB>2%, limiting adsorption was above and below the level expected for bilayer deposition, respectively. Increasing %DODAB in the vesicle composition negatively modulated the limiting adsorption on silica despite the increasing surface charge on vesicles and electrostatic attraction between vesicles and particles. The results point out the difficulty of closed vesicle disruption (required for bilayer deposition from vesicles) when the bilayer is tightly packed in the rigid gel state and might be of interest for analytical applications of immobilized vesicles on silica.     

Cu(I) catalysed cyclopropanation of olefins: Stereoselectivity studies with Arylid-Box and Isbut-Box ligands

In our quest to find new ligands for highly stereoselective reactions, we tested a variety of chiral non-racemic pseudo-C₂ symmetric bis-oxazolines derived from malonic acid containing an arylidene bridge unit (and appropriately termed Arylid-Box) in the catalytic asymmetric cyclopropanation (CAP) reaction of styrene and ethyl diazoacetate using between only 1-2 mol% of a Cu(I) pre-catalyst. Some very good e.e.s (up to 86%), were obtained. It was possible to isolate 10a′-[Cu(CH₃CN)₄]PF₆ which existed as a bench stable solid that proved to be more efficient than the catalyst prepared in situ. Cu(I) pre-catalysts were used for the first time in the CAP reaction with the Isbut-Box ligands 13a and 13b and, although, the e.e.s were better for ligand 13a using these pre-catalysts, in the case of ligand 11b this was not the case. Spectroscopic studies (UV-Vis and ¹H NMR) were carried out to gain an insight into the nature of the catalytic species at work so that the conditions could be optimised giving better results. Some theoretical studies were conducted to try to explain the better enantioselectivities obtained using Evans’ tert-Box-Cu(I) complex over our complex.     

Fusion-fission of light nuclear systems

Considerable interest has been devoted to fusion reactions between light heavy ions specially between weakly bound ones, due to the anomalous decrease of the fusion cross sections when compared to the total reaction cross section in the energy region around the barrier [1–4]. While the exact nature of the process responsible for the fusion cross section limitation at barrier energies is still unclear, this study shows an inhibition of the yield as the system mass decreases, resulting from the progressive increase of the barrier height and decrease of the effective barrier radius [3]. Furthermore, extensive efforts have been made recently in the study of energy-damped binary yields from light heavy-ion collisions [2,4]. Based on the substantial amount of data accumulated so far, it is now generally accepted and supported by the transition state model [4], that the observed yields arise mostly from a fusion-fission process. Data on complete fusion, fusion-fission and ‘elastic fission’ for the ⁹Be, ^10,11B+^10,11B; ^16,17,18O + ^10,11B; ¹⁹F+¹²C; ^6,7Li+⁹Be, ¹²C reactions among others, are presented. For the loosely bound nuclei it was found that the severe fusion cross section limitation is due to a low survival probability of the weakly bound nuclei until the instant of the collision [1].     

新型二硫杂环戊烯硫酮化合物的合成及其对谷氨酸诱导损伤HT22细胞的保护作用

在保留ADT-OH的3H-1,2-二硫杂环戊烯-3-硫酮结构的基础上,用芳乙烯基替换4-羟基苯环,设计并合成了6个二硫杂环戊烯硫酮化合物（L₁~L₆,其中L₂, L₃, L₅和L₆为新化合物）,其结构经¹H NMR, ¹³C NMR和HR-MS(ESI)表征。采用MTT法研究了L₁~L₆对谷氨酸诱导损伤的海马神经元HT22细胞的影响。药理初筛结果表明:给药浓度为10~100 μmol·L^-1时,L₁, L₂, L₄和L₆均能提高受损HT22细胞的存活率(P<0.01);给药浓度为1 μmol·L^-1时,L₃和L₅均可提高损伤HT22细胞的存活率(P<0.01)。     

胭脂鱼消化道黏膜上皮扫描电镜观察

应用扫描电镜观察了胭脂鱼食管、胃、前肠、中肠和后肠黏膜上皮表面细微结构。发现消化道黏膜皱褶形态差异显著,胃黏膜上皮细胞表面有微绒毛,分布密集,但在部分区域有成簇的壁细胞,呈柱状;肠黏膜上皮表面的微绒毛似苔藓状覆盖在细胞的表面,扫描电镜观察发现前肠上皮细胞分泌孔较多,微绒毛密集且高度参差不齐;中肠上皮细胞分泌孔明显减少,微绒毛比前肠密且平整;后肠分泌孔孔径变小,数量最少,且微绒毛较稀疏,表面最平滑,细胞呈梭形环绕,形成杯状结构。亚成体鱼与幼鱼的消化道黏膜上皮结构相似,但其分泌孔孔径和分泌孔密度有差异,亚成体鱼的分泌孔孔径和分泌孔密度更大,说明亚成体鱼消化能力强于幼鱼。 更多还原     

共面对称条件下Mg原子(e,2e)反应的三重微分截面的计算

采用修正的扭曲波玻恩近似(DWBA)方法,本文计算了共面对称几何条件下电子碰撞Mg(3s2) 原子(e,2e)反应的三重微分截面.理论方法通过引入Gamow因子来表示(e,2e)反应的后碰撞相互作用(PCI).将计算结果与实验结果及标准DWBA计算结果进行了比较,发现PCI效应起着重要的作用.     

1-苯并噻唑基-吡唑啉类荧光化合物的合成及其荧光光谱

合成了几种苯并噻唑基 -吡唑啉类化合物 ,经红外吸收光谱和荧光发射光谱测定 ,此类化合物具有一定的荧光性 ,其荧光强度的大小与衍生物中不同的取代基有关。     

Micellization study and adsorption properties of an ionic surfactant synthesized from hydrogenated cardanol in air–water and in air–brine interfaces

A sulfonate (2,4-sodium dissulfonate-5-n-pentadecylphenol) was synthesized from hydrogenated cardanol and the micellization study was carried out using temperature and electrolyte concentration as variables. The adsorption parameters were obtained using surface tension data by the Frumkin adsorption model and the Simplex Nelder–Mead method. Values of critical micelle concentration (cmc) and surface excess (Γ) were obtained in three different temperatures (303 K, 313 K, and 323 K) and two electrolyte concentrations (NaCl solution—0.1 M and 0.25 M). It was verified that cmc decreased with increasing electrolyte concentration and temperature. The Gibbs free energy showed that the micellization process was spontaneous for all studied systems and temperatures, and also that the presence of several CH₂ groups was significant for micelle formation.     

Hooker’s ‘lapachol peroxide’ revisited

The structure of ‘lapachol peroxide’ was published by Hooker in 1936; however, we recently discovered a mistake in the originally proposed structure; the correct structure, according to X-ray spectroscopy, is given here.     

The effect of the sixth sulfur ligand in the catalytic mechanism of periplasmic nitrate reductase

The catalytic mechanism of nitrate reduction by periplasmic nitrate reductases has been investigated using theoretical and computational means. We have found that the nitrate molecule binds to the active site with the Mo ion in the +6 oxidation state. Electron transfer to the active site occurs only in the proton‐electron transfer stage, where the Mo^V species plays an important role in catalysis. The presence of the sulfur atom in the molybdenum coordination sphere creates a pseudo‐dithiolene ligand that protects it from any direct attack from the solvent. Upon the nitrate binding there is a conformational rearrangement of this ring that allows the direct contact of the nitrate with Mo^VI ion. This rearrangement is stabilized by the conserved methionines Met141 and Met308. The reduction of nitrate into nitrite occurs in the second step of the mechanism where the two dimethyl‐dithiolene ligands have a key role in spreading the excess of negative charge near the Mo atom to make it available for the chemical reaction. The reaction involves the oxidation of the sulfur atoms and not of the molybdenum as previously suggested. The mechanism involves a molybdenum and sulfur‐based redox chemistry instead of the currently accepted redox chemistry based only on the Mo ion. The second part of the mechanism involves two protonation steps that are promoted by the presence of Mo^V species. Mo^VI intermediates might also be present in this stage depending on the availability of protons and electrons. Once the water molecule is generated only the Mo^VI species allow water molecule dissociation, and, the concomitant enzymatic turnover. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009