Radiation-induced grafting of hexafluoroacetone to polyethylene

Although hexafluoroacetone is not polymerized by ionizing radiation, it is shown that γ-irradiation of hexafluoroacetone dissolved in polyethylene films produces a graft with a G value of 500 and, therefore, a kinetic chain length of 200. The effects of dose rate (0.021–3.55 Mrad/hr), temperature (21–53°C), and pressure (1.5–6.2 atm) on the graft rates have been measured. Also the effect of temperature (21–53°C) on the postirradiation grafting reaction and on the physical properties of the grafted films have been investigated. Together with solubility, diffusivity, infrared, and EPR data, the results lead to the following mechanism: The first step represents production of secondary alkyl radicals in the polyethylene by irradiation of the polymer–monomer system. The second step involves the linkage of the monomer to the radical site to form the alkoxy radical. Since it cannot add to another monomer unit, this radical abstracts a hydrogen atom from an adjacent polyethylene chain in the third step. Radical R· can then continue the kinetic chain. Radical combination and radical–impurity reactions terminate the chain. The graft may be unique in that it is the only one we have found in which a pendant group containing only one monomer unit is attached by a chain reaction. At dose rates up to 0.215 Mrad/hr, the grafting was linear with time and proportional to the 0.73 power of the dose rate at 21°C and to the 0.81 power at 53°C. The reaction is insensitive to increases in dose rate above 0.215 Mrad/hr where diffusivity measurements show the reaction to be diffusion-controlled. The rate of reaction increased 10% when the temperature was increased from 21 to 53°C. While there was significant postirradiation grafting reaction at 21°C, there was none at 53°C. The results do not fit the equations of reaction-controlled steady-state graft-polymerization kinetics. The deviations arise from an observed increase in monomer solubility in the film with increasing graft combined with low diffusivity of the monomer in polyethylene, and the presence of a radical-scavenging impurity which terminates the kinetic chain with the appearance of a relatively stable radical. EPR data suggests that the impurity is a trace of oxygen which may be produced radiolytically.     

Cyclization of methyl 6,7-epoxycitronellate to methylcyclopentane derivatives : Alkoxide induced conversion of γ-lactones to γ,δ-unsaturated acids

The reaction of sodium hydride or potassium t-butoxide with methyl epoxycitronellate (1) in dimethylformamide affords a mixture of cis,cis-puleganolide (2) and cis,trans-puleganolide (3) in high yield. When the cyclization is conducted at 110°, the isomeric 2-isopropenyl-5-methylcyclopentanecarboxylic acids (8a–d) become the major products. It is demonstrated that γ-lactones undergo alkoxide-induced elimination to afford γ,δ-unsaturated acids.     

Accelerated exchange in polyelectrolyte multilayers by "catalytic" polyvalent ion pairing

Self-exchange of isotopically labeled polycarboxylic acid within a polyelectrolyte multilayer proceeds to completion and is reversible. Similar exchange with poly(styrene sulfonate), which forms nonlabile polyelectrolyte complexes, is slow and irreversible but is facilitated by polyvalent ion pairing interventions of a third polyelectrolyte. This is an example of accelerated kinetics in "sticky" synthetic systems associated by nonspecific polyvalent interactions.     

Estimation of urinary diamines and polyamines by thin-layer chromatography

The dansylated derivatives of ammonia, 1.3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, spermidine, histamine, and spermine were separated by one ascending development in chloroform—triethylamine (5:1) on a 250-μm silica gel 60 plate. Putrescine, cadaverine, spermidine, and spermine in human urine were quantitated by a direct scan of the fluorescent intensity of the spots corresponding to these compounds. Higher amounts of spermidine and spermine were found in the urines of cancer patients compared to the values of these substances in normal urine.     

Functionalization of substituted 2-(1H)pyridones. II. Synthetic pathways to c-6 modified 3-cyano- and 3-carboxy-2-(1H)pyridones from a common precursor

Starting from readily available 1,2-dihydro-6-methyl-2-oxo-3-pyridinecarbonitrile, 1, viable synthetic pathways to a number of C-6 functionalized 1,2-dihydro-2-oxo-3-pyridinecarbonitriles and corresponding acids are presented. Through the utilization of dianion chemistry, the C-6 methyl substituent is selectively functionalized to three different oxidation levels.     

Simple high-performance liquid chromatographic method for the concurrent determination of the amine metabolites vanillylmandelic acid, 3-methoxy-4-hydroxyphenylglycol, 5-hydroxyindoleacetic acid, dihydroxyphenylacetic acid and homovanillic acid in urine using electrochemical detection

A simple method for the concurrent analysis of the noradrenaline metabolites vanillylmandelic acid and 3-methoxy-4-hydroxyphenylglycol, the dopamine metabolites dihydroxyphenylacetic acid and homovanillic acid, and the serotonin metabolite 5-hydroxyindoleacetic acid in human urine is described. Following organic extraction of the metabolites from acidified urine, they are separated by single-step gradient elution high-performance liquid chromatography on a reversed-phase column. Detection and quantification are achieved with an electrochemical detector using a carbon-paste electrode; samples can be injected at 40-min intervals. Optimisation of analytical parameters is described, and examples of the application of the method in the fields of clinical chemistry and clinical neuroscience are given. This provides a convenient method for the concurrent study of the metabolism of three major biogenic amines, and is readily adaptable for studies on cerebrospinal fluid and brain tissue.     

Mass-spectrometric studies on alkylated 6-thiopurines

6-Thiopurine and its N- or C-alkyl derivatives all form an [M – 1]-ion upon fragmentation. In the 7-alkyl derivatives, this ion represents the major component of the spectrum. This is ascribed to formation of a five-membered thiazoline-like ring. Similar ring formation stabilises the [M – 1]-ion in the 7-methyl derivatives of hypoxanthine, adenine and 6-selenopurine.     

Methyl displacements from cyclopentadienyl ring planes in sterically crowded (C5Me5)3M complexes

The displacements of the methyl substituents away from the metal and out of the cyclopentadienyl ring plane are compared in sterically crowded (C(5)Me(5))(3)M complexes vs sterically normal f-element complexes in an attempt to evaluate the utility of this parameter in predicting unusual (C(5)Me(5))(1-) ring reactivity. The out-of-plane displacements of 16 sterically crowded tris(cyclopentadienyl) complexes of general formula (C(5)Me(5))(3)M, (C(5)Me(4)R)(3)M (R = Et, (i)Pr, (t)()Bu, SiMe(3)), (C(5)Me(5))(3)MX (X = anion), and (C(5)Me(5))(3)ML (L = neutral ligand) are compared with [(C(5)Me(5))(2)U](2)(C(6)H(6)), (C(5)Me(5))(2)Sm(PC(4)H(2)(t)Bu(2)), and 33 representative examples of f-element bis(cyclopentadienyl) complexes with normal cyclopentadienyl behavior and coordination numbers ranging from 6 to 10. In general, the methyl displacement values of sterically crowded complexes overlap with those in the other complexes, which demonstrates that the basis of the structural distortions is complex. However, if the most extreme out-of-plane displacement in each of the sterically crowded complexes is examined vs the analogous maximum out-of-plane displacement in less crowded systems, there appears to be a basis for predicting cyclopentadienyl reactivity.     

Critical micelle concentrations for alkyltrimethylammonium bromides in water from 25 to 160°C

Critical micelle concentrations were determined by conductance measurements for decyl-, dodecyl-, tetradecyl- and hexadecyltrimethylammonium bromide in water at 25, 60, 95, 130, and 160°C. The results are discussed in terms of the equilibrium model and the nonlinear Poisson-Boltzmann model for micelle formation. The free energies of transferring a methylene group from water to the oil-like interior of the micelle are found to be –781 at 25°C, –796 at 60°C, –819 at 95°C, –815 at 130°C, and –787 at 160°C cal-mol^–1.     

Dual analyte flow injection fluorescence immunoassays using thiophilic gel reactors and synchronous scanning detection

Heterogeneous fluorescence immunoassays have been automated using flow injection manifolds incorporating thiophilic gel solid phase reactors to separate antibody-bound and unbound analyte molecules. Antibody elution is achieved by changes in ionic strength, thus allowing the use of pH sensitive fluorescent labels. This facilitates the development of dual analyte systems, in which two competitive immunoassays with separate labels are monitored in parallel. Detection of the fluorophores by high speed synchronous fluorescence scanning while the flow is briefly stopped utilises either one synchronous interval which detects both fluorophores, or two separate scans at different wavelength intervals, one for each fluorophore. Simultaneous analyses of serum albumin and transferrin exemplify these novel approaches. Spectroscopic interferences are very small, analyte recoveries are close to 100%, with a relative standard deviation of 5-6% and a sampling rate of 20 h-1.