RNA-mediated synthesis of palladium nanoparticles on Au surfaces

RNA catalysts for the shape-controlled synthesis of Pd particles from the precursor complex trisdibenzylideneacetone dipalladium ([Pd2(DBA)3] were recently discovered in our laboratory (J. Am. Chem. Soc. 2005, 127, 17814-17818). In the work described here, RNA codes for hexagonal Pd platelets and Pd cubes were covalently immobilized on gold surfaces and evaluated for their activity toward particle synthesis. When coupled to gold via oligoethylene glycol linkers, both RNA sequences were able to catalyze the formation of Pd particles with the same shape control previously observed in solution. For low surface coverages, the average distance between RNA molecules on the surface was estimated at ca. 300 nm, yet large (e.g., dimensions of hundreds of nanometers) Pd hexagons and cubes still formed. This surprising result suggests that a single RNA molecule may be sufficient for nucleating and controlling the shapes of these particles. Finally, the use of surface-bound RNA as a tool for directing the orthogonal synthesis of materials on surfaces was demonstrated. Patterning the RNA code for Pd hexagons next to the code for Pd cubes, followed by incubation in a solution containing [Pd2(DBA)3], resulted in the spontaneous formation of spatially distinct spots of hexagonal and cubic particles.     

Dipolar control of monolayer morphology: spontaneous SAM patterning

A strategy for controlling relative placements of molecules within multicomponent monolayers at the solution-HOPG interface is demonstrated. The monolayers assemble from complementary pairs of 1,5-bis-alkyldiether-anthracenes bearing self-repelling side chains. Each diether side chain suffers repulsive dipolar interactions if it adsorbs next to an identical side chain in the morphology normally assumed by 1,5-bis-substituted-anthracene monolayers. Complementary side-chain pairs experience attractive dipolar interactions when adsorbed as neighbors in the normal morphology monolayer. The repulsive and attractive forces spontaneously drive formation of a patterned monolayer at the solution-HOPG interface. Each molecule adsorbs in its own row, sandwiched between two rows of the complementary anthracene. These studies demonstrate the viability of using weak dipolar interactions to control molecular placement and monolayer morphology and to pattern multicomponent monolayers.     

Complexation, structure, and superoxide dismutase activity of the imidazolate-bridged dinuclear copper moiety with beta-cyclodextrin and its guanidinium-containing derivative

An imidazolate-bridged homodinuclear complex, {[Cu(L)(H2O)]2(im)}(ClO4)3 (1), assembled with beta-cyclodextrin (betaCD) and its guanidinium-containing derivative (betaGCD), and thus a helical inclusion complex, {[Cu(L)(H2O)(betaCD)]2(im)}(ClO4)3 (2), were successfully isolated and structurally characterized. Structural analysis showed that each Cu(II) ion has a distorted square pyramidal N4Ow coordination sphere and forms a chiral chain through hydrogen-bonding and hydrophobic interactions. The UV-vis data showed that such a chain can provide the imidazolate bridge additional stability and results in the dissociation equilibrium taking place at the physiological pH. The obtained IC50 value for 2 (0.23 muM) showed a high superoxide dismutase (SOD) activity, which corresponds to a highly stable imidazolate bridge. Interestingly, the guanidinium-containing 1/betaGCD system showed higher SOD activity (IC50 = 0.16 muM), which is enhanced at least by 30% in comparison with that of guanidinium-lacking 2. This result supports that the positive guanidinium plays a role in the catalytic mechanism of Cu,Zn-SOD by ensuring that superoxide enters and peroxide leaves rapidly from the coordination sphere of the copper ion.     

Chemical and biological evaluation on scopadulane-type diterpenoids from Scoparia dulcis of Vietnamese origin

From the aerial parts of Scoparia dulcis L. (Scrophulariaceae) grown in Vietnam, four scopadulane-type diterpenoids (4-7), of which 7 is new and was given the trivial name scopadulcic acid C, together with nine known compounds were isolated. Their structures were elucidated by spectroscopic analyses. The absolute configurations of 4-7 were ascertained by applying the modified Mosher's method to iso-dulcinol (6). The isolation of the lignans nirtetralin and niranthin for the first time from S. dulcis is also of chemotaxonomic interest. The cytotoxic activity in KB cells, inhibitory effect on LPS/IFNgamma-induced NO production, inhibition of multidrug resistance (MDR), and antibacterial and antifungal activities of the scopadulane-type diterpenoids 4-7 were examined in this study.     

Identification of unstable metabolites of Lonafarnib using liquid chromatography-quadrupole time-of-flight mass spectrometry, stable isotope incorporation and ion source temperature alteration

Structural characterization of unstable metabolites and other drug-derived entities poses a serious challenge to the analytical chemist using instrumentation such as LC-MS and LC-MS/MS, and may lead to inaccurate identification of metabolite structures. The task of structural elucidation becomes even more difficult when an analyte is unstable in the ion source of the mass spectrometer. However, a judicious selection of the experimental conditions and the advanced features of new generation mass spectrometers can often overcome these difficulties. We describe here the identification of three drug-derived peaks (A, B and C) that were detected from a Schering-Plough developmental compound (Lonafarnib) following incubation with cDNA-expressed human CYP3A4. Definitive characterization was achieved using (1) accurate mass measurement, (2) stable isotope incorporation, (3) reduced ion source temperature, (4) alkali ion attachment and (5) MS/MS fragmentation studies. The protonated ions of compounds A and B fragmented almost completely in the source, yielding ions of the same mass-to-charge ratio (m/z) as that of protonated C (CH+). Fortunately, the presence of Na+ and K+ adducts of A and B provided information crucial to distinguishing AH+ and BH+ from their fragment ions. Metabolite A was shown to be an unstable hydroxylated metabolite of Lonafarnib. The metabolite C was shown to be a dehydrogenated metabolite of Lonafarnib (Lonafarnib-2H), unstable in the presence of protic solvents. Finally, B was artifactually formed most likely from C by the solvolytic addition of methanol during sample preparation. MS/MS fragmentation experiments assisted in identifying the site of metabolism in A and chemical modification in B. A and C readily interconvert through hydration/dehydration, and B and C through addition/elimination of methanol present in the sample-processing solvents. Finally, NMR experiments were performed to confirm the structures of A and C.     

Study on spectroscopic characterization of Pd porphyrin and its interaction with ctDNA

The fluorescence and solid substrate room temperature phosphorescence (SS-RTP) properties of Pd(II) meso-tetrakis (4-N-methyl-pyridiniumyl) porphyrin (Pd(II)TMPyP) were studied. The factors influencing the SS-RTP emission, such as filter type, inorganic salt sort, drying temperature, pre-drying time and drying time were investigated in detail. Strong SS-RTP signal can be induced on the slow speed filter paper in the presence of the external inorganic salt, Ca(NO₃)₂, with the maximum excitation and emission wavelengths at 421 nm and 675 nm, respectively. The interaction between calf thymus DNA (ctDNA) and Pd(II)TMPyP was investigated at pH 7.2 using SS-RTP, fluorescence and UV-vis spectroscopy. The SS-RTP intensity of Pd(II)TMPyP was enhanced efficiently with the increasing amount of ctDNA. This phenomenon demonstrates that the intercalated porphyrin is shielded by ctDNA to avoid collision quenching. This result was supported by SS-RTP lifetime measurement, SS-RTP anion quenching experiment and fluorescence polarization measurement. Furthermore, with the addition of ctDNA, the UV-vis spectra of Pd(II)TMPyP shows apparent hypochromicity (40%) at the Soret maximum of 417 nm and a red shift of Δλ = 15 nm, also indicating that Pd(II)TMPyP intercalates into ctDNA bases. The binding constant of Pd(II)TMPyP to ctDNA was calculated to be 4.41 × 10⁵ L/mol based on the derivative McGhee-von Hippel plots.     

Suzuki coupling at the periphery of diruthenium coordination and organometallic compounds

A series of diruthenium compounds, Ru2(DArF)3(L")Cl (2), where the auxiliary ligand DArF is DmAniF or D(3,5-Cl2Ph)F and L" is one of the diarylformamidinate ligands containing at least one biphenyl, were prepared from Suzuki reactions between Ru2(DArF)3(L')Cl (1), where L' is (4-I-Ph)NC(H)NPh (N-(4-iodophenyl)-N'-phenylformamidinate) or D(4-I-Ph)F (N,N'-di(4-iodophenyl)formamidinate), and ArB(OH)2 (Ar = Ph and 4-CH3C(O)Ph) in satisfactory yields. Alkynylation of the type 2 compounds with LiCCPh yielded the alkynyl derivatives Ru2(DArF)3(L")(CCPh) (3). Alternatively, type 3 compounds can be prepared from the Suzuki coupling reaction between Ru2(DArF)3(L')(C2Ph) and ArB(OH)2. A structural comparison between the type 1 and 2 compounds revealed minimal changes in the coordination sphere of Ru2 core. Cyclic voltammograms of Suzuki derivatives resemble those of the parent compounds, indicating the retention of the electrophore characteristic of diruthenium species upon peripheral modification.     

Alternating Poly(Pt‐salphen)‐(p‐phenyleneethynylene) as Phosphorescent Conjugated Linear‐Rod and Coilable Sensory Materials

Phosphorescent conjugated polymers consisting of alternating p‐phenylene‐ethynylene and ‘para‐’ or ‘meta‐type’ Pt(II)‐salphen luminophore units have been synthesized. Side‐arms bearing different substituents (n‐alkoxy and acetylated‐sugar) have afforded contrasting emission properties that are attributed to the polymer conformation, extent of π‐stacking interactions and differences in chemical structure. Intriguing selectivity in luminescent sensing of metal ions has been observed.

     

A Stabilized Finite Element Method for Non-Stationary Conduction-Convection Problems

This paper is concerned with a stabilized finite element method based on two local Gauss integrations for the two-dimensional non-stationary conduction-convection equations by using the lowest equal-order pairs of finite elements. This method only offsets the discrete pressure space by the residual of the simple and symmetry term at element level in order to circumvent the inf-sup condition. The stability of the discrete scheme is derived under some regularity assumptions. Optimal error estimates are obtained by applying the standard Galerkin techniques. Finally, the numerical illustrations agree completely with the theoretical expectations.     

多相材料结构拓扑优化: 体积约束还是质量约束?

针对拓扑优化设计中多年沿用的体积约束作为控制材料用量的思路, 研究了采用质量约束开展多相材料结构拓扑优化的新方法, 提出了相应的质量约束结构优化问题模型和材料插值模型. 通过研究广义SIMP模型和对等混合模型两类多相材料属性插值方法, 发现广义SIMP插值模型导致质量约束具有复杂的非线性特征, 给优化问题的全局寻优和数值求解带来困难;采用的线性对等混合材料插值策略保证质量约束函数具有线性和变量可分离特征, 为拓扑设计问题的数值求解, 特别是凸规划寻优提供了极大便利. 算例表明多相材料插值策略和结构优化模型的正确性和有效性; 优化设计结果的比较说明了使用质量约束相对于体积约束的合理性和必要性, 阐述了质量约束在解决结构轻量化布局设计问题的有效性以及所带来的显著收益.