Size-dependent tunneling and optical spectroscopy of CdSe quantum rods

Photoluminescence excitation spectroscopy and scanning-tunneling spectroscopy are used to study the electronic states in CdSe quantum rods that manifest a transition from a zero-dimensional to a one-dimensional quantum-confined structure. Both optical and tunneling spectra show that the level structure depends primarily on the diameter of the rod and not its length. With increasing diameter, the band gap and the excited state level spacings shift to the red. The level structure was assigned using a multiband effective-mass model, showing a similar dependence on rod dimensions.     

Determination of plasma lactic acid concentration and specific activity using high-performance liquid chromatography.

Assessment of lactate metabolism is of particular interest during exercise and in disease states such as diabetes, shock, and absorptive abnormalities of short-chain fatty acids by the colon. We describe an analytical method that introduces radio-active tracers and high-performance liquid chromatography (HPLC) to simultaneously analyze concentrations and specific activities (SAs) of plasma lactate. The HPLC conditions included separation on a reversed-phase column (octadecylsilane) and an isocratic buffer (30% acetonitrile in water). [3H]Acetate served as an internal standard. Lactate and acetate were extracted from plasma samples with diethyl ether following a pH adjustment to less than 1.0 and back-extracted into a hydrophilic phase with sodium carbonate (2 mM, pH greater than 10.0). Lactate is detected in the ultraviolet range (242 and 320 nm) by derivatization with alpha-bromoacetophenone. Control plasma samples were studied after an overnight fast for precision and analytical recovery. Calibration curves were linear in the range 0.18-6.0 mM (r = 0.92). The precision was 3% and the analytical recovery was 87%. The detection limit of the method was 36 pmol. Determination of lactate metabolism was performed in a patient with chronic congestive heart failure who was administered primed-continuous L-[U-14C]lactate (10 microCi bolus and 0.3 microCi/min continuously) during a 60-min rest period. Mean arterial lactate concentration and SA were 1.69 +/- 0.2 mM and 253.8 +/- 22 dpm/mumol, respectively. Systemic lactate turnover was 25.65 mumol/kg per min. Lactic acid systemic turnover, organ uptake and release rates can be accurately determined by isocratic HPLC.     

Radiation-induced dechlorination of carbon tetrachloride in cyclohexane Solutions. The kinetics of liquid-phase reactions of trichloromethyl radicals

The kinetics of the gamma-radiation induced free-radical chain reaction in solutions of carbon tetrachloride in cyclohexane (RH) has been investigated in the temperature range of 303–383°K. Trichloromethyl radicals were produced by the reaction of radiolytically generated cyclohexyl radicals with carbon tetrachloride. The kinetics of the following reactions were investigated: The following rate expression was obtained: The error limits are the standard deviation from the least mean square Arrhenius plots. Effects of phase on the kinetics of reactions (3) and (4) are considered.     

Further results on integral generalized inverses of integral matrices

This paper further investigates integral generalized inverses of integral matrices.     

A facile synthesis of α-chloroboronic esters via the base induced reaction of α,α-dichloromethyl methyl ether with hindered borinic esters

Treatment of hindered borinic esters, R₂ BOR′; with an equimolar quantity of α,α-dichloromethyl methyl ether and lithium triethylcarboxide yields the α-chloroboronic esters, R₂ CHClB(OCH₃)OR′, in excellent yields. In cases where the steric requirements of R are not sufficient, the steric requirements of R′ can be increased to achieve the synthesis.     

Microheterogeneity in crosslinked polysiloxanes

Previously reported studies on crosslinked castable poly(dimethylsiloxanes) have been extended. A series of dimethylsiloxane difumarates were copolymerized with styrene, and some of their rheological properties were determined. Investigation of these and previously prepared polymers has shown that segregation on a microscale can take place in two-component crosslinked systems with relatively short network chains. This may occur even if one of the components is a nonpolymeric species involved in crosslinking. Microheterogeneity was observed in systems made up of prepolymer chains of a single type, when these were short enough to expose a specific structure of the crosslinking site. It seems that microheterogeneity can be expected in crosslinked polymers when the size of the crosslinking site is significant in comparison with the network chain length and when its cohesive energy density differs considerably from that of the main network chains. Additional factors affecting microphase separation include the existence of physical interactions between chemical groups, steric positioning of interacting groups during the process of crosslinking, and physical effects of the degree of crosslinking leading to local differences in the density of the system.     

Light‐Responsive Biomaterials: Development and Applications

Novel biomaterials are beneficial to the growing fields of drug delivery, cell biology, micro‐devices, and tissue engineering. With recent advances in chemistry and materials science, light is becoming an attractive option as a method to control biomaterial behavior and properties. In this Feature Article, we explore some of the early and recent advances in the design of light‐responsive biomaterials. Particular attention is paid to macromolecular assemblies for drug delivery, multi‐component surface patterning for advanced cell assays, and polymer networks that undergo chemical or shape changes upon light exposure. We conclude with some remarks about future directions of the field.