Chemoselective Reduction of Some Condensates derived from Chromone-3-carbaldehyde using Sm and Zn

Condensates 4–6 undergo reductive dimerization with Sm in THF containing aqueous NH₄Cl to produce 7–9, whereas with Zn under similar reaction condition 3–5 produce 10–12.     

Remarkable ESIPT induced NIR emission by a selective colorimetric dibenzimidazolo diimine sensor for acetate

A new dibenzimidazolo diimine sensor (DDS) has been designed and synthesized for selective detection of acetate ion. Significant naked eye recognized color change of DDS solution from light yellow to pink upon addition of only acetate ion is accompanied with near infra red (NIR) emission exploiting excited state intramolecular proton transfer (ESIPT).     

Synthesis of semitelechelic POSS‐polymethacrylate hybrids by thiol‐mediated controlled radical polymerization with unusual thermal behaviors

We have developed an efficient and versatile method for the synthesis of polyhedral oligomeric silsesquioxanes (POSS)‐polymethacrylate hybrids, such as POSS‐poly(methyl methacrylate) (POSS‐PMMA), POSS‐poly(ethyl methacrylate) (POSS‐PEMA), and POSS‐poly(benzyl methacrylate) (POSS‐PBzMA) of controllable molecular weights and low polydispersities by thiol‐mediated radical polymerization at elevated temperature (100 °C). By tuning the reactant concentrations and degree of polymerization of the grafted polymethacrylate chains, POSS content in these hybrid materials could be varied. MALDI‐TOF‐MS analysis of the hybrid molecule shows that the nanoscale POSS moiety is connected to the end of polymethacrylate chain through the sulfur atom bridge. These hybrid materials were further characterized using various techniques such as FTIR, XRD, NMR, TGA, and DSC. In all synthesized hybrids, the incorporation of POSS moiety at the end of polymethacrylate chain resulted in the decrease of glass transition temperature (T_g) compared to that of neat polymethacrylates of comparable molecular weights. Surprisingly, POSS‐PMMA hybrids only with relatively high POSS content (～ 10 and 16 wt %) showed physical aging behavior as reveled by DSC study. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1111–1123, 2008     

Quantitative chemical proteomics approach to identify post-translational modification-mediated protein-protein interactions

Post-translational modifications (PTMs) (e.g., acetylation, methylation, and phosphorylation) play crucial roles in regulating the diverse protein-protein interactions involved in essentially every cellular process. While significant progress has been made to detect PTMs, profiling protein-protein interactions mediated by these PTMs remains a challenge. Here, we report a method that combines a photo-cross-linking strategy with stable isotope labeling in cell culture (SILAC)-based quantitative mass spectrometry to identify PTM-dependent protein-protein interactions. To develop and apply this approach, we focused on trimethylated lysine-4 at the histone H3 N-terminus (H3K4Me(3)), a PTM linked to actively transcribed gene promoters. Our approach identified proteins previously known to recognize this modification and MORC3 as a new protein that binds H3M4Me(3). This study indicates that our cross-linking-assisted and SILAC-based protein identification (CLASPI) approach can be used to profile protein-protein interactions mediated by PTMs, such as lysine methylation.     

Evidence that monastrol is an allosteric inhibitor of the mitotic kinesin Eg5

Monastrol, a cell-permeable inhibitor of the kinesin Eg5, has been used to probe the dynamic organization of the mitotic spindle. The mechanism by which monastrol inhibits Eg5 function is unknown. We found that monastrol inhibits both the basal and the microtubule-stimulated ATPase activity of the Eg5 motor domain. Unlike many ATPase inhibitors, monastrol does not compete with ATP binding to Eg5. Monastrol appears to inhibit microtubule-stimulated ADP release from Eg5 but does not compete with microtubule binding, suggesting that monastrol binds a novel allosteric site in the motor domain. Finally, we established that (S)-monastrol, as compared to the (R)-enantiomer, is a more potent inhibitor of Eg5 activity in vitro and in vivo. Future structural studies should help in designing more potent Eg5 inhibitors for possible use as anticancer drugs and cell biological reagents.     

Synchronized oscillations on a Kuramoto ring and their entrainment under periodic driving

We consider a finite number of coupled oscillators on a ring as an adaptation of the Kuramoto model of populations of oscillators. The synchronized solutions are characterized by an integer m, the winding number, and a second integer l, with solutions of type (m, l = 0) being all stable. Following a number of recent works (see below) we indicate how the various solutions emerge as the coupling strength K is varied, presenting a perturbative expression for these for large K. The low K scenario is also briefly outlined, where the onset of synchronization by a tangent bifurcation is explained. The simplest situation involving three oscillators is described, where more than one tangent bifurcations are involved. Immediately before the tangent bifurcation leading to synchronization, the system exhibits the phenomenon of frequency- (or phase) splitting where more than one (usually two) phase clusters are involved. All the synchronized solutions are seen to be entrained by an external periodic driving, provided that the driving frequency is sufficiently close to the frequency of the synchronized population. A perturbative approach is outlined for the construction of the entrained solutions. Under a periodic driving with an appropriately limited detuning, there occurs entrainment of the phase-split solutions as well.