Comments on the primary and scatter dose-spread kernels used for convolution methods

The basic primary and scatter dose-spread kernels used for convolution methods are usually produced by Monte Carlo simulations with the interaction point forced to the center of a large water phantom. However, it is still not clear whether such Monte Carlo based kernels allow accurate dose calculations with a wide range of field sizes and depths, especially in thorax phantoms. Using the differential primary and scatter concept, this paper proposes another type of basic kernel, with which perfectly accurate primary and scatter absorbed dose calculations can be performed under conditions that the beam is parallel, the incident beam intensity is uniform within and zero outside the field, and the primary beam attenuation coefficient along raylines is not a function of depth and off-axis distance.     

Synthesis, structure, and physical properties of 1,11-o-benzeno[2]orthocyclo[2](1,2)tropyliophane

The title compound (2) has been synthesized, the structure and the physical properties of which are investigated by X-ray, spectroscopic analyses, and MO calculations. There exists charge transfer (CT) interaction between the tropylium ion and the facing phenyl ring. From the pK_R⁺ value of 2, it can be clear that the cation 2 is stabilized by the CT interaction. In spite of the presence of bond weakening σ-π orbital mixing, the cation 2 withstands retro[4+4]type bond cleavage, which is quite interesting when compared to a facile cleavage for the congener with anthracene photodimer type structure.     

Polymerization of tetraallyl ammonium chloride

The radical polymerization of tetraallyl ammonium chloride (TAAC) was carried out in water using azo-initiator as compared to that of diallyl dimethyl ammonium chloride (DADMAC); the rate of polymerization was quite low for TAAC, around one-third of DADMAC. Kinetic discussion revealed the importance of degradative chain transfer in the polymerization of TAAC. The cyclopolymerizability of TAAC was estimated kinetically as the ability of 5-membered monocyclic radical to form a bicyclic ring, giving the cyclization constant of 21 mol/L at [M] = 2 mol/L. Gelation occurred at around 20% conversion.     

Studies of the polymerization of diallyl compounds. XXVII. Copolymerization of diallyl tartrate with several vinyl monomers

The radical copolymerization of diallyl tartrate (DATa) (M₁) with diallyl succinate (DASu), diallyl phthalate (DAP), allyl benzoate (ABz), vinyl acetate (VAc), or styrene (St) was investigated in order to disclose in more detail the characteristic hydroxyl group's effect observed in the homopolymerization of DATa. In the copolymerization with DASu or DAP as a typical diallyldicarboxylate, the dependence of the rate of copolymerization on monomer composition was different for different copolymerization systems and unusual values larger than unity for the product of monomer reactivity ratios, r₁r₂, were obtained. In the copolymerization with ABz or VAc (M₂), the r₁ and r₂ values were estimated to be 1.50 and 0.64 for the DATa/ABz system and 0.76 and 2.34 for the DATa/VAc system, respectively; the product r₁r₂ for the latter copolymerization system was found again to be larger than unity. In the copolymerization with St, the largest effect due to DATa monomer of high polarity was observed. Solvent effects were tentatively examined to improve the copolymerizability of DATa. These results are discussed in terms of hydrogen-bonding ability of DATa.     

Hair analysis of nicotine and cotinine for evaluating tobacco smoke exposure by liquid chromatography-mass spectrometry

A simple liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) method for the determination of nicotine and cotinine in human hair was established. In the procedure, a hair sample (10 mg) was washed with dichloromethane and digested in 2.5 M sodium hydroxide. The digest was extracted with dichloromethane and then 25 mM hydrochloric acid in methanol was added to the extract, to prevent loss of analytes. The solution was evaporated and redissolved in the mobile phase, methanol/10 mM ammonium acetate (30/70, v/v). A 20 microL aliquot of redissolved solution was subjected to analysis. Nicotine and cotinine in human hair were quantified by using deuterated analytes as internal standards. The quantification limits were 8 microg/L for nicotine and 0.9 microg/L for cotinine. The proposed method was applied to measure the concentrations of nicotine and cotinine in hair of smokers and non-smokers to evaluate their self-reported smoking and exposure to environmental tobacco smoke. In both cases, the method provided good selectivity, accuracy and precision.     

Application of samarium diiodide (SmI2)-induced reduction of gamma-acetoxy-alpha,beta-enoates with alpha-specific kinetic electrophilic trapping for the synthesis of amino acid derivatives

Gamma-acetoxy-alpha,beta-enoates were easily reduced by samarium diiodide (SmI2) in THF to generate samarium dienolates which were kinetically trapped with ease at their alpha-positions by electrophiles (proton, aldehydes or ketones) to yield (E)-alkene dipeptide isosteres or gamma-amino acid derivatives in high chemical yields.     

SmI2-mediated reduction of gamma,gamma-difluoro-alpha,beta-enoates with application to the synthesis of functionalized (Z)-fluoroalkene-type dipeptide isosteres

A samarium diiodide (SmI(2))-mediated reduction of gamma,gamma-difluoro-alpha,beta-enoates (15, 29, and 34) was successfully applied to the synthesis of (Z)-fluoroalkene dipeptide isosteres (23, 30, and 35), which have served as potential dipeptide mimetics. Reduction of the gamma,gamma-difluoro-alpha,beta-enoates by SmI(2) proceeded via successive two-electron transfers to form dienolate species which upon kinetically controlled trapping with t-BuOH yielded Xaa-Gly-type fluoroalkene isosteres exemplified by 23, 30, and 35. Replacement of the t-BuOH kinetic trapping agent with aldehydes or ketones provided access to alpha-substituted fluoroalkene isosteres (43 and 45) through aldol reactions of Sm-dienolates with the carbonyl compounds. Of particular note, the use of the SmI(2)-HCHO reagent system with chiral enoate 34 provided D-Phe-psi[(Z)-CF[double bond]CH]-D/L-Ser isosteres (45), which could be converted to enantiomerically pure isosteres (49-52) that bore a variety of side chain functionalities at the alpha-position. This was achieved by a sequence of manipulations consisting of beta-lactone formation followed by chromatographic separation and ring-opening with soft nucleophiles. Included in the present work is the first utilization of a Rh-catalyzed Reformatsky reaction of chiral imines for the stereoselective preparation of alpha,alpha-difluoro-beta-amino acid derivatives (28 and 33). The appropriate choice of reagents (carbonyl compounds for kinetic trapping or ring-opening nucleophiles and imines for Reformatsky reactions) allows the presented methodology to yield various fluoroalkene isosteres possessing a wide range of side chain functionalities.     

Surface derivatization of poly(p-phenylene terephthalamide) fiber designed for novel separation and extraction media

The surface derivatization of poly(p-phenylene terephthalamide) fiber was studied. The obtained surface-derivatized filaments were packed into a fused-silica capillary to evaluate its surface characteristics by using GC. As the stationary phase for GC the surface-derivatized fibers showed higher retention for alkanes and alkylbenzenes than that with the untreated Kevlar fiber. The improvements on the retention power and the peak shape were observed on the benzyl-modified fibrous stationary phase. The derivatized fibrous materials were also evaluated as the extraction medium in fiber-in-tube SPE, and the effect of the surface modification on the extraction power was compared to the parent fiber. The results indicated that the modified fiber possessed a higher extraction power than the untreated fiber. Based on the facts, the successful modification of the fiber surface was estimated.     

Studies of the polymerization of diallyl compounds. XXVI. Enhanced polymerizability by the hydroxyl group in the polymerization of diallyl hydroxydicarboxylates

In order to elucidate the effect of the hydroxyl group on the polymerization of diallyl hydroxydicarboxylates, we investigated in detail the radical polymerizations of diallyl succinate (DASu), diallyl malate (DAMa), and diallyl tartrate (DATa), each of which have similar structure differing only in the number of hydroxyl groups present. The rate of polymerization (R_p) was quite enhanced in the order DASu < DAMa < DATa, in accord with the increase in the number of hydroxyl groups within a monomer unit. The enhanced ability of the allylic monomer radical to reinitiate chain growth was also in the same order, as was clear from the dependence of R_p on the initiator concentration. The dependence of the residual unsaturation of the polymer on the monomer concentration in the polymerizations of DAMa and DATa was abnormal in terms of cyclopolymerization. These results are discussed in connection with the formation of the intermolecular hydrogen bond through the hydroxyl groups.     

Fluorimetric assay for measuring Dns-His-Lys-Arg-His-Lys cleaving enzyme using high-performance liquid chromatography

A rapid and sensitive assay for the determination of Dns-His-Lys-Arg-His-Lys cleaving enzyme activity is reported. This assay is based on fluorimetric detection of a dansylated dipeptide, 5-dimethylaminonaphthalene-1-sulfonyl-His-Lys, enzymatically formed from the substrate 5-dimethylaminonaphthalene-1-sulfonyl-His-Lys-Arg-His-d-Lys, after separation by high-performance liquid chromatography (HPLC) using a C-18 reversed-phase column by isocratic elution. This assay is sensitive enough to measure 5-dimethylaminonaphthalene-1-sulfonyl-His-Lys at concentrations as low as 7 pmol, and yields highly reproducible results and requires less than 9.0 min per sample for separation and quantitation. The optimum pH for Dns-His-Lys-Arg-His-Lys cleaving enzyme activity was 7.5-8.0. The Michaelis constant (K_m) and the maximum velocity (V_max) values were 33.3 μM and 47.07 pmol/(μg h), respectively with the use of enzyme extract obtained from bovine pituitary. By using this assay, axonal transport of this enzyme activity was observed 48 h after double ligations of rat sciatic nerves. The high sensitivity and selectivity of this assay would be useful for clarification of the physiological role of this enzyme.