High-yield immobilization of a puromycin analogue for the solid support synthesis of aminoacyl-tRNA fragments

[reaction: see text] An efficient procedure for the immobilization of 3'-deoxy-3'-(O-methyltyrosyl)aminoadenosine was developed. A poly(ethylene glycol)-derived diacid linker/spacer was attached to aminomethyl polystyrene. Coupling of the 2'-hydroxy instead of the 2'-O-succinylated ribonucleoside resulted in high immobilization yields (over 80%) and allowed for the recovery of valuable unreacted material. This specific procedure should be applicable to other ribonucleosides containing a bulky modification at the 3'-position and can be used for the stepwise construction of 3'-aminoacyl- or 3'-peptidyl-RNA conjugates.     

Design of new bidentate ligands constructed of two Hoechst 33258 units for discrimination of the length of two A3T3 binding motifs

[structure: see text] The aim of this study is to develop bidentate minor-groove binders that bind the double binding motifs cooperatively. The new bidentate ligands (1) have been designed by connecting two Hoechst 33258 units with a polyether linker for cooperative binding with two remote A3T3 sites of DNA. The linker is introduced to the benzimidazole ring so that it is located at the convex side of the Hoechst unit. DNA binding affinity of the ligands was evaluated by measuring surface plasmon resonance (SPR), circular dichroism, and fluorescence spectra. Interestingly, the bidentate ligands (1) did not show affinity to DNA1 with a single A3T3 motif but showed selective affinity to DNA2 with two A3T3 motifs. The Long Bis-H (1L) having a long polyether linker showed specific binding to DNA2(6) with two A3T3 motifs separated by six nonbinding base pairs. The Long Bis-H (1L) has also shown specific binding to the three-way junction DNA4 with two A3T3 motifs. This study has demonstrated that DNA with double binding motifs can be selectively recognized by the newly designed bidentate ligands.     

Chiral distortion in a Mn(IV)(salen)(N3)2 derived from Jacobsen's catalyst as a possible conformation model for its enantioselective reactions

The Mn (IV)(salen)(N 3) 2 complex ( 3) from Jacobsen's catalyst is synthesized, and the X-ray crystal structures of 3 as well as the starting Mn (III)(salen)(N 3)(CH 3OH) complex ( 2) are determined in order to investigate the conformation of the high-valent Mn (IV)(salen) molecule in comparison with that of Mn (III)(salen). The asymmetric unit of the crystal of 3 contains four complexes, all of which adopt a nonplanar stepped conformation effectively distorted by the chirality of the diimine bridge. The asymmetric unit of 2 also contains four complexes. Two of them show a stepped conformation of a lesser degree, but the other two adopt a bowl-shaped conformation. Comparison of the structural parameters shows that the Mn center in 3 is coordinated from both sides by two external axial N 3 ligands with significantly shorter bond lengths, which could induce greater preference for the stepped conformation in 3. The CH 3CN solution of 3 shows circular dichroism with a significantly strong band at 275 nm as compared to 2, suggesting that 3 may adopt a more chirally distorted conformation also in solution. The circular dichroism spectrum of 3 is slightly altered with isodichroic points from 298 to 253 K and shows no further change at temperatures lower than 253 K, suggesting that the solution of 3 contains an equilibrium between two conformers, where a low-energy conformer with more chiral distortion is predominantly favored even at room temperature. Complexes 2 and 3 are thoroughly characterized using various techniques including cyclic voltammetry, magnetic susceptibility, UV-vis, electron paramagnetic resonance, (1)H NMR, infrared spectroscopy, and electrospray ionization mass spectrometry.     

Chemical bonding in phosphane and amine complexes of main group elements and transition metals

The geometries and bond dissociation energies of the main group complexes X3B-NX3, X3B-PX3, X3Al-NX3, and X3Al-PX3 (X = H, Me, Cl) and the transition metal complexes (CO)5M-NX3 and (CO)5M-PX3 (M = Cr, Mo, W) have been calculated using gradient-corrected density functional theory at the BP86/TZ2P level. The nature of the donor-acceptor bonds was investigated with an energy decomposition analysis. It is found that the bond dissociation energy is not a good measure for the intrinsic strength of Lewis acidity and basicity because the preparation energies of the fragments may significantly change the trend of the bond strength. The interaction energies between the frozen fragments of the borane complexes are in most cases larger than the interaction energies of the alane complexes. The bond dissociation energy of the alane complexes is sometimes higher than that of the borane analogues because the energy for distorting the planar equilibrium geometry of BX3 to the pyramidal from in the complexes is higher than for AlX3. Inspection of the three energy terms, DeltaE(Pauli), DeltaE(orb), and DeltaE(elstat), shows that all three of them must be considered to understand the trends of the Lewis acid and base strength. The orbital term of the donor-acceptor bonds with the Lewis bases NCl3 and PCl3 have a higher pi character than the bonds of EH3 and EMe3, but NCl3 and PCl3 are weaker Lewis bases because the lone-pair orbital at the donor atoms N and P has a high percent s character. The calculated DeltaE(int) values suggest that the trends of the intrinsic Lewis bases' strengths in the main-group complexes with BX3 and AlX3 are NMe3 > NH3 > NCl3 and PMe3 > PH3 > PCl3. The transition metal complexes exhibit a somewhat different order with NH3 > NMe3 > NCl3 and PMe3 > PH3 > PCl3. The slightly weaker bonding of NMe3 than that of NH3 comes from stronger Pauli repulsion. The bond length does not always correlate with the bond dissociation energy, nor does it always correlate with the intrinsic interaction energy.     

Characterization of Lewis acid sites on the (100) surface of beta-AlF3: Ab initio calculations of NH3 adsorption

The current study employs hybrid-exchange density functional theory to show that the Lewis base, NH(3), binds to the beta-AlF(3) (100) surface with a binding energy (BE) of up to -1.96 eV per molecule. This is characteristic of a strong Lewis acid. The binding of NH(3) to the surface is predominately due to electrostatic interactions. There is only a small charge transfer from the NH(3) molecule to the surface. The BE as a function of coverage is computed and used to develop a lattice Monte Carlo model which is used to predict the temperature programed desorption (TPD) spectrum. Comparison with experimental TPD studies of NH(3) from beta-AlF(3) strongly suggests that these structural models and binding mechanisms are good approximations to those that occur on real AlF(3) surfaces.     

Second hyperpolarizability of phenalenyl radical system involving acetylene π-conjugated bridge

The static second hyperpolarizability (γ) of a singlet diradical system involving phenalenyl radicals linked with acetylene π-conjugated bridge, BPLE, is investigated as well as reference closed-shell systems, BPRY1 and BPRY2, by the hybrid density functional theory method. The γ value of BPLE with intermediate diradical character is shown to be about four times as large as that of BPRY1 with similar π-conjugation length and to be about twice as large as that of BPRY2 with longer π-conjugation length. This feature is in agreement with our prediction that the molecules with intermediate diradical characters enhance γ values compared to the closed-shell molecules.     

硅氮负离子引发六甲基环三硅氧烷开环聚合的动力学研究

以二甲基亚砜(DMSO)或四氢呋喃(THF)作为促进剂,六苯基环三硅氮烷三锂盐(P3NLi)可以引发六甲基环三硅氧烷(D3)进行开环聚合,通过29Si-NMR谱的硅峰面积比例确定了不同反应时间D3的转化率,经过计算得到聚合反应对THF、DMSO、D3、P3NLi的反应级数,并给出了对应的动力学方程.     

Rapid simultaneous assay of serum estrone, estradiol, and estriol in pregnant women using methyl ether acetate derivatives by capillary gas chromatography and electron-impact mass spectrometry

A simple gas chromatographic--mass spectrometric method capable of measuring estrone, estradiol, and estriol simultaneously with a sensitivity close to that of radioimmunoassay has been developed. The estrogens in serum were extracted with diethyl ether, and internal standards (3-O-C2H3-estrone, 3-O-C2H3-estradiol, and 3-O-C2H3-estriol) were added, followed by converting to methyl ether compounds with an extractive alkylation procedure. The methyl ethers were then acetylated. Analyses were performed using a SP-2250 capillary column gas chromatograph coupled with an electron-impact mass spectrometer. The estrogen methyl ether acetate derivatives were more stable chemically and gave less fragmentation upon electron impact than the conventional trimethylsilyl derivatives. The use of selected ion monitoring of molecular ions and that of the corresponding internal standards (M + 3) provides a sensitivity down to 10 pg for estrone and estradiol and to 200 pg for estriol. The time required for the preparation of multiple samples is within 4 hours.     

纳米/微米碳酸钙的结构表征和热分解行为

采用棕榈酸对纳米碳酸钙进行有机表面改性, 运用SEM﹑TEM、XRD、FTIR 及TG-DTG 对表面改性前后的纳米碳酸钙进行表征, 并与微米碳酸钙的微晶结构及热分解特性进行比较. FTIR 分析结果确证了棕榈酸与纳米碳酸钙表面是以化学键合和物理吸附方式相结合, 粒子表面存在羧基等有机官能团的红外吸收特征. 对比研究发现, 碳酸钙微晶纳米化后, 其红外V3特征吸收峰出现约35 cm-1 的蓝移现象, 并且明显窄化. 初步解释了纳米碳酸钙红外吸收峰蓝移的原因, 认为尺寸效应和晶体场效应是影响纳米碳酸钙红外光谱特征的主要因素. 微晶结构的变化使得纳米碳酸钙的热分解反应表现出反常特性, 热分解温度较微米碳酸钙下降了40.6 ℃.     

Amplified quenching of a conjugated polyelectrolyte by cyanine dyes

The conjugated polyelectrolyte PPESO3 features a poly(phenylene ethynylene) backbone substituted with anionic 3-sulfonatopropyloxy groups. PPESO3 is quenched very efficiently (KSV > 10(6) M(-1)) by cationic energy transfer quenchers in an amplified quenching process. In the present investigation, steady-state and picosecond time-resolved fluorescence spectroscopy are used to examine amplified quenching of PPESO3 by a series of cyanine dyes via singlet-singlet energy transfer. The goal of this work is to understand the mechanism of amplified quenching and to characterize important parameters that govern the amplification process. Steady-state fluorescence quenching of PPESO3 by three cationic oxacarbocyanine dyes in methanol solution shows that the quenching efficiency does not correlate with the Forster radius computed from spectral overlap of the PPESO3 fluorescence with the cyanines' absorption. The quenching efficiency is controlled by the stability of the polymer-dye association complex. When quenching studies are carried out in water where PPESO3 is aggregated, changes observed in the absorption and fluorescence spectra of 1,1',3,3,3',3'-hexamethylindotricarbocyanine iodide (HMIDC) indicate that the polymer templates the formation of a J-aggregate of the dye. The fluorescence dynamics in the PPESO3/HMIDC system were probed by time-resolved upconversion and the results show that PPESO3 to HMIDC energy transfer occurs on two distinctive time scales. At low HMIDC concentration, the dynamics are dominated by an energy transfer pathway with a time scale faster than 4 ps. With increasing HMIDC concentration, an energy pathway with a time scale of 0.1-1 ns is active. The prompt pathway (tau < 4 ps) is attributed to quenching of delocalized PPESO3 excitons created near the HMIDC association site, whereas the slow phase is attributed to intra- and interchain exciton diffusion to the HMIDC.     

An optimised small-molecule stabiliser of the 14-3-3-PMA2 protein-protein interaction

Modulation of protein-protein interactions (PPIs) is a highly demanding, but also a very promising approach in chemical biology and targeted drug discovery. In contrast to inhibiting PPIs with small, chemically tractable molecules, stabilisation of these interactions can only be achieved with complex natural products, like rapamycin, FK506, taxol, forskolin, brefeldin and fusicoccin. Fusicoccin stabilises the activatory complex of the plant H(+)-ATPase PMA2 and 14-3-3 proteins. Recently, we have shown that the stabilising effect of fusicoccin could be mimicked by a trisubstituted pyrrolinone (pyrrolidone1, 1). Here, we report the synthesis, functional activity and crystal structure of derivatives of 1 that stabilise the 14-3-3-PMA2 complex. With a limited compound collection three modifications that are important for activity enhancement could be determined: 1) conversion of the pyrrolinone scaffold into a pyrazole, 2) introduction of a tetrazole moiety to the phenyl ring that contacts PMA2, and 3) addition of a bromine to the phenyl ring that exclusively contacts the 14-3-3 protein. The crystal structure of a pyrazole derivative of 1 in complex with 14-3-3 and PMA2 revealed that the more rigid core of this molecule positions the stabiliser deeper into the rim of the interface, enlarging especially the contact surface to PMA2. Combination of the aforementioned features gave rise to a molecule (37) that displays a threefold increase in stabilising the 14-3-3-PMA2 complex over 1. Compound 37 and the other active derivatives show no effect on two other important 14-3-3 protein-protein interactions, that is, with CRaf and p53. This is the first study that describes the successful optimisation of a PPI stabiliser identified by screening.     

Energy flow and fragmentation dynamics of n,n-dimethylisopropylamine

The energy flow and fragmentation dynamics of N,N-dimethylisopropylamine (DMIPA) upon excitation to the 3p Rydberg states has been investigated with use of time-resolved photoelectron and mass spectrometry. The 3p states are short-lived, with a lifetime of 701 +/- 45 fs. From the time dependence of the photoelectron spectra, we infer that the primary reaction channel leads to the 3s level, which itself decays to the ground state with a decay time of 87.9 +/- 10.2 ps. The mass spectrum reveals fragmentation with cleavage at the alpha C-C bond, indicating that the energy deposited in vibrations during the internal conversion from 3p to 3s exceeds the bond energy. A thorough examination of the binding energies and temporal dynamics of the Rydberg states, as well as a comparison to the related fragmentation of N,N-dimethyl-2-butanamine (DM2BA), suggests that the fragments are formed on the ion surfaces, i.e., after ionization and on a time scale much slower than the fluorescence decay from 3s to the ground state.     

Drawing out the structural information of the first layer of hydrated ions: ATR-FTIR spectroscopic studies on aqueous NH4NO3, NaNO3, and Mg(NO3)2 solutions

ATR-FTIR technique was used to obtain the difference spectra of aqueous NH4NO3 NaNO3, and Mg(NO3)2 solutions, with NO3- concentrations ranging from 0 to 4.00 mol dm(-3). The water monomers weakly hydrogen bonded with NO3- ions showed a positive peak near at 3565 cm(-1) for both Mg(NO3)2 and NH4NO3 solutions. The positive peak was shift to approximately 3543 cm(-1) for NaNO3 solutions due to the total contributions of the hydrated NO3- (approximately 3565 cm(-1)) and the hydrated Na+ (approximately 3440 cm(-1)). Compared with perchlorate solutions, the positive peak of nitrate solutions has a red shift of about 20 cm(-1) and the peak area is about half of that of perchlorate solutions with the same concentrations, indicating that the hydrogen bonding between NO3- and water monomers is relative stronger than that between ClO4- and water monomers, and NO3- has a strict requirement on the orientation of water molecules when hydrogen bonded with water monomers due to its planar structure. The ab initio calculations were used to understand the splitting of the nu3 band and hydration effect on the infrared activation of the nu1. The absorbance of nu3b, nu1 and nu2 bands, dependent on the type of cations, was observed to departed from Beer low with increasing concentrations, which is considered as the results of the interactions between cations and nitrate ions.     

Nanoparticles comprising a mixed monolayer for specific bindings with biomolecules

This work presents a strategy of using mixed monolayer protected nanoparticles for specific interactions with target biological molecules. The mixed monolayer is composed of a shielding component and a capture component. The shielding component utilizes ethylene glycol oligomers to prevent nonspecific binding with biomolecules. The capture component is chosen to specifically interact with the target of interest, such as a protein molecule. Such a concept was demonstrated by two synthetic systems. The first one is gold nanoparticles protected by a mixed monolayer of tri(ethylene glycol) thiol (EG(3)-SH) and tiopronin (Tp), which was prepared by a one-step synthesis. Surface chemical composition studies using (1)H NMR spectroscopy revealed that the reactivity of EG(3)-SH is 3 times as high as that of Tp in the nanoparticle formation. Gel electrophoresis analysis identified a critical ratio of (EG(3)-S-)/Tp on the nanoparticle surface above which no nonspecific binding occurred. By further derivatizing Tp into a biotin group, we synthesized Au(-S-EG(3))(n)/Tp-biotin particles that bind specifically to streptavidin with negligible nonspecific binding. The second system is gold nanoparticles protected by a mixed monolayer of EG(3)-SH and glutathione (GSH). By controlling the feeding ratio of EG(3)-SH and GSH, we made Au(-S-EG(3))(n)/GSH particles that bind specifically to gultathione-S-transferase (GST) with negligible nonspecific binding.     

Low-bandgap donor-acceptor conjugated polymer sensitizers for dye-sensitized solar cells

A set of two donor-acceptor type conjugated polymers with carboxylic acid side groups have been synthesized and utilized as active materials for dye-sensitized solar cells (DSSCs). The polymers feature a π-conjugated backbone consisting of an electron-poor 2,1,3-benzothiadiazole (BTD, acceptor) unit, alternating with either a thiophene-fluorene-thiophene triad (2a) or a terthiophene (3a) segment as the donor. The donor-acceptor polymers absorb broadly throughout the visible region, with terthiophene-BTD polymer 3a exhibiting an absorption onset at approximately 625 nm corresponding to a ～1.9 eV bandgap. The polymers adsorb onto the surface of nanostructured TiO(2) due to interaction of the polar carboxylic acid units with the metal oxide surface. The resulting films absorb visible light strongly, and their spectra approximately mirror the polymers' solution absorption. Interestingly, a series of samples of 3a with different molecular weight (M(n)) adsorb to TiO(2) to an extent that varies inversely with M(n). DSSCs that utilize the donor-acceptor polymers as sensitizers were tested using an I(-)/I(3)(-) electrolyte. Importantly, for the set of polymer sensitizers 3a with varying M(n), the DSSC efficiency varies inversely with M(n), a result that reflects the difference in adsorption efficiency observed in the film absorption experiments. The best DSSC cell tested is based on a sample of 3a with M(n) ～ 4000, and it exhibits a ～65% peak IPCE with J(sc) ～12.6 mA cm(-2) under AM1.5 illumination and an overall power conversion efficiency of ～3%.     

苯甲醛缩氨基硫脲对CH_3COO~-和H_2PO_4~-的识别作用

设计合成了受体分子苯甲醛缩氨基硫脲,利用紫外-可见吸收光谱考察了在DMSO中对ClO3-,H2PO4-及CH3COO-的选择性识别作用,当加入H2PO4-或CH3COO-时,溶液颜色立刻由无色转变为黄色,而加入ClO3-阴离子则无变化,从而实现对此2种离子的裸眼检测。通过计算可知,由于阴离子碱性各异,受体分子对2种阴离子的识别作用呈现出有规律的变化,即CH3COO-H2PO4-;且主客体间形成1∶1的配合物。质子溶剂效应实验进一步证明了受体分子与阴离子之间以氢键作用方式相结合。     

新型含卤噻唑类酰腙化合物的合成及其与小牛胸腺DNA的相互作用

以2-氨基噻唑-4-甲酸乙酯和水合肼为原料,制得2-氨基噻唑-4-甲酰肼(2); 2与卤代(F, Cl, Br)对苯甲醛反应,合成了3种新型的含卤噻唑类酰腙化合物［C₁₁H₉N₄OSF(3a), C₁₁H₉N₄OSCl(3b)和C₁₁H₉N₄OSBr(3c)］,其结构和性能经元素分析,XRD和TG-DTG表征。结果表明：3a和3c属于三斜晶系,Pī空间群;3b属于单斜晶系,P2(1)/c空间群。3a~3c的热稳定性均较好,最大热分解过程的表观活化能均大于100 kJ·mol^-1。采用UV-Vis研究了3a~3c与小牛胸腺DNA(CT-DNA)的相互作用。结果表明：3a~3c与CT-DNA均以插入方式相互作用。     

Mass-spectrometric monitoring of the thermally induced decomposition of trimethylgallium,tris(<Emphasis Type="Italic">tert</Emphasis>-butyl)gallium,and triethylantimony at low pressure conditions

The thermal decomposition of trimethylgallium (GaMe(3)), tris(tert-butyl)gallium (Ga(t)Bu(3)) and triethylantimony (SbEt(3)) was investigated in a tubular hot-wall reactor coupled with a molecular-beam sampling mass spectrometer, and decomposition mechanisms were proposed. The obtained results confirm the predominance of the surface reactions and reveal that the radical decomposition path of Ga(t)Bu(3) and SbEt(3), responsible for the formation of butane and ethane respectively, is restricted to a narrow temperature range in contrast to the molecular route that is responsible for the formation of the corresponding alkenes. GaMe(3) decomposes above 480 degrees C, forming essentially methane and also ethane to a lesser extent, whereas Ga(t)Bu(3) decomposes starting 260 degrees C to form predominantly i-butane and i-butene as major species. The decomposition of SbEt(3) starts at 400 degrees C and forms n-butane, ethane, and ethene. The selectivity to n-butane increases with the thermolysis temperature. The resulting activation energies of the relevant decomposition paths show good agreement with those among them that have been measured before by temperature-programmed desorption techniques.     

Preparation of liposomes containing Ceramide 3 and their membrane characteristics

Liposomes composed of Ceramide 3, [2S,3S,4R-2-stearoylamide-1,3,4-octadecanetriol], and L-alpha-dipalmitoylphosphatidylcholine (DPPC) were prepared by varying the amount of Ceramide 3, and the effects of Ceramide 3 on the liposome formation, particle size, dispersibility, microviscosity and phase transition temperature were examined by means of a microscopy, a dynamic light scattering method, a fluorescence polarization method, a differential scanning calorimetry (DSC) and so on. All the DPPC was able to contribute to the formation of liposomes up to 0.130 mol fraction of Ceramide 3. The particle size of liposomes was almost unaffected by the addition of Ceramide 3. The dispersibility of liposomes containing Ceramide 3 was maintained for at least 15 days. The microviscosity of liposomal bilayer membranes in the liquid crystalline state was increased with increasing the mole fraction of Ceramide 3, while that in the gel state was independent of the mole fraction of Ceramide 3. The phase transition temperature from gel to liquid crystalline states of DPPC bilayer membranes was shifted upwards with the addition of Ceramide 3, indicating a cooperative interaction between DPPC and Ceramide 3 molecules. However, a sharp DSC peak became broad and split at higher mole fractions of Ceramide 3, suggesting a phase separation in the mixed DPPC/Ceramide 3 liposomal bilayer membranes. These phenomena were suggested to be related to the previously observed fact for the mixed DPPC/Ceramide 3 monolayers that Ceramide 3 interacts with DPPC in the liquid-expanded phase with consequent phase separation accompanied with domain formation.     

Structure and oxidation state of silica-supported manganese oxide catalysts and reactivity for acetone oxidation with ozone

Silica-supported manganese oxide catalysts with loadings of 3, 10, 15, and 20 wt % (as MnO2) were characterized with use of X-ray absorption spectroscopy and X-ray diffraction (XRD). The edge positions in the X-ray absorption spectra indicated that the oxidation state for the manganese decreased with increasing metal oxide loading from a value close to that of Mn2O3 (+3) to a value close to that of Mn3O4 (+2(2)/3). The XRD was consistent with these results as the diffractograms for the supported catalysts of higher manganese oxide loading matched those of a Mn3O4 reference. The reactivity of the silica-supported manganese oxide catalysts in acetone oxidation with ozone as an oxidant was studied over the temperature range of 300 to 600 K. Both oxygen and ozone produced mainly CO2 as the product of oxidation, but in the case of ozone the reaction temperature and activation energy were significantly reduced. The effect of metal oxide loading was investigated, and the activity for acetone oxidation was greater for a 10 wt % MnOx/SiO2 catalyst sample compared to a 3 wt % MnOx/SiO2 sample.