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The kinetics and the mechanism of the reaction of 4-hydroxy-2-pentanone (4H2P) with Cl atom were investigated using quantum theoretical calculations. Density functional theory, CBS-QB3, and G3B3 methods are used to explore the reaction pathways. Rice–Ramsperger–Kassel–Marcus theory is employed to obtain rate constants of the reaction at atmospheric pressure and the temperature range 278–400 K. This study provides the first theoretical and kinetic determination of Cl rate constant for reactions with 4H2P over a large temperature range. The obtained rate constant 1.47 × 10–10 cm3 molecule–1 s–1 at 298 K is in reasonable agreement with those obtained for C4–C5 hydroxyketones both theoretically and experimentally. The results regarding the structure–reactivity relationship and the atmospheric implications are discussed. [ABSTRACT FROM AUTHOR]

We synthesize and characterize stimulus-responsive nanocomposites consisting of poly( N-isopropylacrylamide) (PNIPAM) with controlled loadings of anisotropic plate-like silver nanoprisms. These composites show strong, reversible switching of their optical extinction and scattering properties in response to temperature cycling. We use UV-vis-NIR spectroscopy and dynamic light scattering to characterize the hybrids and show that the loading density of the silver nanoprisms in the polymer and the size of the nanoprisms are both factors that can be used to tailor the optical response of the composites, extending the range of colors beyond that previously reported with PNIPAM/plasmonic nanoparticle composites. These PNIPAM/silver nanoprism hybrids exhibit thermochromic shifts that are 5-10 times larger than those typically reported for similar structures of PNIPAM composites with silver nanoparticles of a comparable range of loading density. In addition, we show that these composites can exhibit very large ratiometric changes in scattering in the NIR, which could open applications for related materials in thermal management and NIR labeling and taggants.

An operationally simple cascade protocol has been developed for the construction of 1,2- and 1,3-dithiole derivatives from α-enolic dithioesters. 1,2-Dithioles are achieved by the reaction of dithioesters with elemental sulfur in the presence of InCl 3 under solvent-free conditions. 1,3-Dithioles have been constructed via DABCO mediated self-coupling of dithioesters in open air enabling the formation of two new C-S bonds and one ring in a single operation in contiguous fashion. The reactions proceeded smoothly affording the desired sulfur-rich heterocycles in good to excellent yields, exhibiting gram-scale ability and broad functional group tolerance utilizing easy to handle cheap and easily available reagents. The probable mechanisms for the formation of 1,2- and 1,3-dithioles from α-enolic dithioesters have been suggested.

We use dynamic force spectroscopy to study the melting properties of azobenzene-modified double-stranded DNA (azo-dsDNA) in both the shearing and unzipping geometries. By fitting the rupture force vs loading rate data with a Friddle-Noy-De Yoreo model, we extract the location of the barrier (x t ), the equilibrium force for the bond/transducer system (F eq ), and the dissociation rate of dsDNA (k off 0 ). We find that the k off 0 of azo-dsDNA increases after UV illumination (365 nm) in both the shearing and unzipping geometries. Notably, we find that k off 0 of azo-dsDNA in the unzipping geometry is 5-7 orders of magnitude larger than that in the shearing geometry, a result that helps explain the dependence of k off 0 on the azobenzene photoswitch position during shearing experiments. We also extract the difference of free energy (ΔG bu ) between binding and unbinding states of azo-dsDNA with F eq and the system spring constant (k c ). Our results provide important insights into the dynamic melting properties of azo-dsDNA and a new route for designing applications for reconfigurable sensors, stimulus-response materials, and nanoscale energy harvesting schemes based on photoswitch-modified biomolecules such as DNA.

Protein aggregation leading to various nanoscale assemblies is under scrutiny due to its implications in a broad range of human diseases. In the present study, we have used ovalbumin, a model non-inhibitory serpin, to elucidate the molecular events involved in amyloid assembly using a diverse array of spectroscopic and imaging tools such as fluorescence, laser Raman, circular dichroism spectroscopy, and atomic force microscopy (AFM). The AFM images revealed a progressive morphological transition from spherical oligomers to nanoscopic annular pores that further served as templates for higher-order supramolecular assembly into larger amyloid pores. Raman spectroscopic investigations illuminated in-depth molecular details into the secondary structural changes of the protein during amyloid assembly and pore formation. Additionally, Raman measurements indicated the presence of antiparallel β-sheets in the amyloid core. Overall, our studies revealed that the protein conformational switch in the context of the oligomers triggers the hierarchical assembly into nanoscopic amyloid pores. Our results will have broad implications in the structural characterization of amyloid pores derived from a variety of disease-related proteins.

An efficient and experimentally rapid protocol for the synthesis of hitherto unreported 2,3-dicarboalkoxy-4-aroyl/heteroaroyl/alkanoyl thiophenes has been developed via 1-2 (C-S) and 3-4 (C-C) bond connections promoted by 4-dimethylaminopyridine (DMAP). Optimally, the reaction takes only 3-5 min when β-oxodithioester and dialkyl acetylenedicarboxylate are stirred in DCM at room temperature in the presence of DMAP. This method allows a clean and general synthesis of previously inaccessible and synthetically demanding thiophenes containing the ferrocenyl group. The speed, experimental ease, and high yields of this process are improvements over existing methods to access this important substructure.

A highly efficient one-pot three-component regioselective synthesis of 4-aryl-3-aroyl-2-methylsulfanyl-4,6,7,8-tetrahydrothiochromen-5-ones has been developed by annulation of β-oxodithioesters with aldehydes and cyclic 1,3-diketones under solvent-free conditions promoted by P(2)O(5). No cocatalyst or activator is needed in this protocol. The merit of this process is highlighted by its high efficiency of producing three new bonds and a stereocenter in one operation., (© 2011 American Chemical Society)

An efficient and highly convergent route to dihydropyrimidinones (DHPMs) and hitherto unreported dihydropyridopyrimidinones has been developed by one-pot, three-component cyclocondensation of aromatic aldehydes, β-oxodithioesters, and urea/6-amino-1,3-dimethyluracil in the presence of recyclable SiO2-H2SO4. On the other hand, salicylaldehyde, β-oxodithioester, and urea reacted under similar conditions to afford the 3-aroyl/heteroaroyl-2H-chromen-2-thiones in high yields instead of Biginelli product. The attractive feature of this approach is the synthesis of three important bioactive heterocyclic frameworks from the same β-oxodithioester under the similar reaction conditions, making this new strategy highly useful in diversity-oriented synthesis (DOS).