General Method to Increase Carboxylic Acid Content on Nanodiamonds

Carboxylic acid is a commonly utilized functional group for covalent surface conjugation of carbon nanoparticles that is typically generated by acid oxidation. However, acid oxidation generates additional oxygen containing groups, including epoxides, ketones, aldehydes, lactones, and alcohols. We present a method to specifically enrich the carboxylic acid content on fluorescent nanodiamond (FND) surfaces. Lithium aluminum hydride is used to reduce oxygen containing surface groups to alcohols. The alcohols are then converted to carboxylic acids through a rhodium (II) acetate catalyzed carbene insertion reaction with tert–butyl diazoacetate and subsequent ester cleavage with trifluoroacetic acid. This carboxylic acid enrichment process significantly enhanced nanodiamond homogeneity and improved the efficiency of functionalizing the FND surface. Biotin functionalized fluorescent nanodiamonds were demonstrated to be robust and stable single-molecule fluorescence and optical trapping probes.     

Dewetting of glassy polymer films

Dynamics and morphology of hole growth in a film of power hardening viscoplastic solid [ yield stress approximately (strain-rate)(n)] is investigated. At short times the growth is exponential and depends on the initial hole size. At long times, for n>1 / 3, the growth is again exponential but with a different exponent. However, for n<1 / 3 the hole growth slows and the hole radius approaches an asymptotic value at long times. The rim shape is highly asymmetric, the height of which has a power law dependence on the hole radius (exponent close to unity for 0.25相似文献   

Electric-quadrupole interaction at 181Ta in f.c.t. ZrHi1.97

Time-differential perturbed γ-ray angular correlation experiments have been carried out on ¹⁸¹Ta impurities in ?-phase zirconium hydride over the temperature range from 20 to 588 K. A static, slightly asymmetric electric quadripole interaction is found at all temperatures. The static nature of the pattern indicates the absence of significant hydrogen diffusion at these temperatures on the time scale of the experiment (0.1 μsec). The temperature dependence of the static quadrupole frequency is given by the relation v_q(t) = 130[1 ? (1.9 × 10^?5)T^1.5] MHz.     

169Tm Mössbaüer spectroscopy and crystal field calculations in TmNi3 and TmCo3 intermetallics

The values of the magnetic moments and the electric field gradient in TmNi₃ and TmCo₃ are obtained from ¹⁶⁹Tm Mössbauer spectroscopy. These values are compared to those from crystal field model based on point charge calculations for these intermetallics.     

Investigations into the role of ion pairing in reactions of heteroatom-substituted cyclic oxocarbenium ions

[reaction: see text] The O-to-C rearrangement of vinyl acetals is used to demonstrate that tight ion pairing is not involved in the stereoselective nucleophilic addition reactions of alkoxy-substituted cyclic oxocarbenium ions.     

Meniscus instability in a thin elastic film

A new kind of meniscus instability leading to the formation of stationary fingers with a well-defined spacing has been observed in experiments with elastomeric films confined between a plane rigid glass and a thin curved glass plate. The wavelength of the instability increases linearly with the thickness of the confined film, but it is remarkably insensitive to the compliance and the energetics of the system. However, lateral amplitude (length) of the fingers depends on the compliance of the system and on the radius of curvature of the glass plate. A simple linear stability analysis is used to explain the underlying physics and the key observed features of the instability.     

Extraction of uranium(VI) by tri iso-amyl phosphate (TiAP) in ionic liquids

Batch extraction of uranium(VI) from uranyl nitrate solutions using TiAP in ionic liquids ([BMIM]PF₆ and [HMIM]PF₆) is studied. Effects of acidity, TiAP concentration in ionic liquid and temperature on distribution coefficient are studied. Results show that distribution coefficient increases with an increase in acidity and reduces with an increase in the alkyl chain length of the cation of the ionic liquid. Extraction of uranium(VI) by TiAP-[HMIM]PF₆ system is found to involve two molecules of the extractant per metal ion and extraction is found to change from being exothermic to endothermic as the percentage of the extractant is increased.     

Asymmetric oxidation of sulfides catalyzed by (R)-6,6'-dibromo-BINOL derived titanium complex

Abstract

An efficient asymmetric oxidation of sulfides was achieved using (R)-6,6'-dibromo-BINOL as chiral ligand in combination with Ti(OⁱPr)₄ using 70% aqueous tertiary butyl hydroperoxide as oxidant. The resulting sulfoxides had high enantiopurities and good yields. A range of aryl alkyl and aryl benzyl sulfides were oxidized to the corresponding sulfoxides with 78–95% ee in 72–80% yields.