Four New Compounds from Sinacalia tangutica

Four new compounds, 9α‐hydroxy‐1β‐methoxycaryolanol ( 1 ), stigmast‐5‐ene‐7α,22α‐diol‐3β‐tetradecanoate ( 2 ), 7‐O‐(6′‐acetoxy‐β‐D ‐glucopyranosyl)coumarin ( 3 ), and 8‐O‐(6′‐acetoxy‐β‐D ‐glucopyranosyl)‐7‐hydroxycoumarin ( 4 ), together with ten known compounds, were isolated from the aerial parts of Sinacalia tangutica. The structures of the new compounds were established by means of extensive spectroscopic analyses (1D‐ and 2D‐NMR, EI‐MS, HR‐ESI‐MS, as well as IR and UV) and by comparison of their spectroscopic data with those of structurally related compounds reported in the literature.     

Efficient immobilization and patterning of live bacterial cells

A monolayer of live bacterial cells has been patterned onto substrates through the interaction between CFA/I fimbriae and the corresponding antibody. Patterns of live bacteria have been prepared with cellular resolution on silicon and gold substrates for Salmonella enterica serovar Typhimurium as a model with high specificity and efficiency. The immobilized cells are capable of dividing in growth medium to form a self-sustaining bacterial monolayer on the patterned areas. Interestingly, the immobilized cells can alter their orientation on the substrate, from lying-down to standing-up, as a response to the cell density increase during incubation. This method was successfully used to sort a targeted bacterial species from a mixed culture within 2 h.     

Multidomain protein solves the folding problem by multifunnel combined landscape: theoretical investigation of a y-family DNA polymerase

Approximately three-fourths of eukaryotic proteins are composed of multiple independently folded domains. However, much of our understanding is based on single domain proteins or isolated domains whose studies directly lead to well-known energy landscape theory in which proteins fold by navigating through a funneled energy landscape toward native structure ensembles. The degrees of freedom for proteins with multiple domains are many orders of magnitude larger than that for single domain proteins. Now, the question arises: How do the multidomain proteins solve the "protein folding problem"? Here, we specifically address this issue by exploring the structure folding relationship of Sulfolobus solfataricus DNA polymerase IV (DPO4), a prototype Y-family DNA polymerase which contains a polymerase core consisting of a palm (P domain), a finger (F domain), and a thumb domain (T domain) in addition to a little finger domain (LF domain). The theoretical results are in good agreement with the experimental data and lead to several theoretical predictions. Finally, we propose that for rapid folding into well-defined conformations which carry out the biological functions, four-domain DPO4 employs a divide-and-conquer strategy, that is, combining multiple individual folding funnels into a single funnel (domains fold independently and then coalesce). In this way, the degrees of freedom for multidomain proteins are polynomial rather than exponential, and the conformational search process can be reduced effectively from a large to a smaller time scale.     

Sorption of Am(Ⅲ) on Na-bentonite:Effect of pH,ionic strength,temperature and humic acid

Sorption of Am(Ⅲ) on Na-bentonite as a function of contact time,pH,ionic strength,humic acid(HA) and temperature was investigated under ambient conditions.The results showed that the sorption was strongly dependent on pH and ionic strength. Am(Ⅲ) sorption can be described well by pseudo-second-order model.The presence of HA takes a positive effect at low pH;but a negative influence under high pH range.Enthalpy,entropy and Gibbs free energy(i.e.,△H~0,△S~0 and△G~0) calculated from sorption isotherms suggested that sorption process of Am(Ⅲ) was spontaneous and endothermic.     

Dendritic structures of poly(ethylene glycol) on silicon nitride and gold surfaces

A hydrophilic silicon nitride surface was grafted with poly(ethylene glycol) monomethyl ether (average formula weight of 5000 Da) in a one-step protocol. The domains of stable dendritic structures of self-assembled monolayer islands on a silicon nitride surface were observed with atomic force microscopy. The moduli of elasticity of these dendritic structures in air and in KCl aqueous solution were compared. The value of the Young's modulus of these structures is reduced by more than 3 orders of magnitude, from approximately 12 GPa measured in air to approximately 5 MPa in KCl solution. This dramatic reduction in elasticity was attributed to the swelling of the dendritic structures in aqueous solution, which was verified by the increased film thickness. These dendritic structures were not stable in the aqueous environment and could be removed by soaking in water for 22 h because of the hydrolysis of the silicate bonds. This fact was confirmed by the reduction of the C1s signal in the X-ray photoelectron spectroscopy experiments. These morphologies are not unique to silicon nitride substrate; similar features were also observed for thiolated poly(ethylene glycol) monomethyl ether molecules absorbed on a gold surface.     

A bacteria-immunity system with delayed quorum sensing

Considering the mechanism of quorum sensing, we formulate a bacteria-immunity model to describe the competition between bacteria and immune cells on the basis of Zhang’s model (see Zhang et al. 2008, to appear, for more details). A distributed delay is introduced to characterize the time in which bacteria receive signal molecules and then combat with immune cells. We analyze the stability of the equilibrium points and discuss the existence of Hopf bifurcation near the positive equilibrium point. Finally, numerical simulation is carried out to illustrate our qualitative results.     

Construction of Multi-ribozyme Expression System and Its Characterization of Cleavage on the MDR1/MRP1 Double Target Substrate in vitro

To improve catalytic activity of ribozyme on its substrate,the multi-ribozyme expression system was designed and constructed from 20 cis-acting hammerhead ribozymes undergoing self-cleavage with 10 trans-acting hammerhead ribozymes inserted altematively regularly and the plasmid of pGEM-MDRI/MRPI used to transcribe the M DRI/MRPI(196/210) substrate containing double target sites was also constructed by DNA recombination.Endonuclease digestion analysis and DNA sequencing indicate all the recombinant plasmids were correct.The cleavage activities were evaluated for the multi-ribozyme expression system on the MDR1/MRP1 substrate in the cell free system.The results demonstrate that the cis-acting hammerhead ribozymes in the multi-ribozyme expression system were able to cleave themselves and the 72 nt of 196Rz and the 71 nt of 210Rz trans-acting hammerhead ribozymes were liberated effectively,and the trans-acting hammerhead ribozymes released were able to act on the MDR1/MRP1 double target RNA substrate and cleave the target RNA at specific sites effectively.The multiribozyme expression system of the [Coat'A196Rz/Coat'B210Rz]5 is more significantly superior to that of the [Coat'A 196Rz/Coat'B210Rz]1 in cleavage of RNA substrate.The fractions cleaved by [Coat'A196Rz/Coat'B210Rz]5 on the MDR1/MRP1 substrate for 8 h at observed temperatures showed no marked difference.The studies of Mg2+ on cleavage efficiency indicate that cleavage reaction is dependent on Mg2+ ions concentration.The plot of Ig(kobs) vs.Igc(Mg2+) displays a linear relationship between 2.5 mmol/L and 20 mmol/L Mg2..It suggests that Mg2+ ions play a crucial role in multi-ribozyme cleavage on the substrate.     

Surface energy as a barrier to creasing of elastomer films: an elastic analogy to classical nucleation

In a soft elastic film compressed on a stiff substrate, creases nucleate at preexisting defects and grow across the surface of the film like channels. Both nucleation and growth are resisted by the surface energy, which we demonstrate by studying creases for elastomers immersed in several environments-air, water, and an aqueous surfactant solution. Measurement of the position where crease channeling is arrested on a gradient thickness film provides a uniquely characterized strain that quantitatively reveals the influence of surface energy, unlike the strain for nucleation, which is highly variable due to the sensitivity to defects. We find that these experimental data agree well with the prediction of a scaling analysis.     

Design,synthesis, and antilung adenocarcinoma activity research of novel paeonol Schiff base derivatives containing a 1,2,3-triazole moiety

A new series of paeonol Schiff base derivatives containing a 1,2,3-triazole moiety were synthesized using the copper(I) catalyzed azide-alkynecycloaddition (CuAAC) reaction and evaluated for their cytotoxicity in vitro against human cervical carcinoma HeLa cells, human lung cancer A549 cells, and human liver cancer HepG2 cells. Unfortunately, all the tested compounds showed poor activities toward the human cervical carcinoma HeLa cells and human liver cancer HepG2 cells. However, compounds (E)-2-(1-(((1-[2-fluorophenyl]-1H-1,2,3-triazol-4-yl)methyl)imino)ethyl)-5-methoxyphenol ( 4c ) and (E)-2-(1-(((1-[3- chlorophenyl]-1H-1,2,3-triazol-4-yl)methyl)imino)ethyl)-5-methoxyphenol ( 4i ) exhibited inhibitory activities toward human lung cancer A549 cells (IC₅₀ = 45.1 μM for 4c and 78.9 μM for 4i ) compared with that of paeonol, which indicated that such paeonol Schiff base derivatives containing a 1,2,3-triazole moiety could be further modified to obtain good cytotoxicity in vitro against human lung cancer A549 cells.