Diacyl analysis

Instrumental methods of peroxide analysis feature polarography, which is used to detn hydroperoxides, peroxyesters and diacyl peroxides as well as dicyclohexyl peroxydicarbonate in polystyrene. Other techniques include infrared (800 to 900cm 1) chemiluminescent analysis for kinetic studies, and chromatography for the identification and separation of peroxides in complex mixts (Refs 5,6, 7,14,15,16,17, 20 21)... 

Liquid and paper chromatographies as well as mass spectrometry (MS) are used for the identification and analysis of hydroperoxides [60]. Nuclear magnetic resonance (NMR) spectroscopy is used for identification of diacyl peroxides. 

The dependence of relative rates in radical addition reactions on the nucleophilicity of the attacking radical has also been demonstrated by Minisci and coworkers (Table 7)17. The evaluation of relative rate constants was in this case based on the product analysis in reactions, in which substituted alkyl radicals were first generated by oxidative decomposition of diacyl peroxides, then added to a mixture of two alkenes, one of them the diene. The final products were obtained by oxidation of the intermediate allyl radicals to cations which were trapped with methanol. The data for the acrylonitrile-butadiene... 

Diacyl peroxides are, however, also electron transfer oxidants, which according to a theoretical analysis should possess standard potentials, °[(ArCOO)2/RCOO RCOO ) of around 0.6 V in water, provided that the electron transfer process is of the dissociative type (50) (Eberson, 1982c). Such a value brings thermal ET steps involving DBPO within reach for redox-active organic molecules, as for example suggested by the so-called CIEEL mechanism of chemiluminescence (Schuster, 1982). 

McBride and co-workers have studied extensively the reactions of such free-radical precursors as azoalkanes and diacyl peroxides (246). By employing a variety of techniques, including X-ray structure analysis, electron paramagnetic resonance (EPR), and product studies, and comparing reactions in the crystal and in fluid and rigid solvents, they have been able to obtain extremely detailed pictures of the solid-state processes. We will describe here some of the types of lattice control they have elucidated, and the mechanisms that they suggest limit the efficacy of topochemical control. 

Because the accuracy of the data for three of the diacyl peroxides is in question, we will attempt to derive enthalpies of formation for them from the reverse of equations 15 and 16. The enthalpy of reaction 15 for dibenzoyl peroxide, using enthalpy of formation values of unquestioned accurac)f, is —400.8 kJmor. This is the same as the ca —398 kJmol for the hquid non-aromatic diacyl peroxides discussed above. Using the solid phase enthalpy of reaction for dibenzoyl peroxide and the appropriate carboxylic acid enthalpies of formation, the calculated enthalpies of formation of bis(o-toluyl) peroxide and bis(p-toluyl) peroxide are —432.2 and —457.6 kJ moU, respectively. From the foregoing analysis, it would seem that the measured enthalpy of formation is accurate for the bis(p-toluyl) peroxide but is not for its isomer. The analysis for dicinnamoyl peroxide is complicated by there being two enthalpies of formation for frawi-cinnamic acid that differ by ca 12 kJmoU. One is from our archival source (—336.9 12 kJmoU ) and the other is a newer measurement (—325.3 kJmol ). The calculated enthalpies of formation of dicinnamoyl peroxide are thus —273.0 and —249.8 kJmoU. Both of these results are ca 80-100 kJmol less negative than the reported enthalpy of formation. 

DET see Density functional theory Diabetes, Upid peroxides, 613 Diacetylene peroxides, thermal analysis, 715 Diacyl peroxides... 

The phosphoric acid esters of diacyl glycerides, phospholipids, are important constituents of cellular membranes. Lecithins (phosphatidyl cholines) from egg white or soybeans are often added to foods as emulsifying agents or to modify flow characteristics and viscosity. Phospholipids have very low vapor pressures and decompose at elevated temperatures. The strategy for analysis involves preliminary isolation of the class, for example by TLC, followed by enzymatic hydrolysis, derivatization of the hydrolysis products, and then GC of the volatile derivatives. A number of phospholipases are known which are highly specific for particular positions on phospholipids. Phospholipase A2, usually isolated from snake venom, selectively hydrolyzes the 2-acyl ester linkage. The positions of attack for phospholipases A, C, and D are summarized on Figure 9.7 (24). Appropriate use of phospholipases followed by GC can thus be used to determine the composition of phospholipids. 

Li AH, Moro S, Melman N, Ji XD, Jacobson KA (1998) Structure-activity relationships and molecular modelling of 3, 5-diacyl-2, 4-dialkylpyridine derivatives as selective A, adenosine receptor antagonists. J Med Chem 41 3186-3201 Li AH, Moro S, Forsyth N, Melman N, Ji XD, Jacobson KA (1999) Synthesis, CoMFA analysis, and receptor docking of 3, 5-diacyl-2, 4-dialkylpyridine derivatives as selective A3 adenosine receptor antagonists. J Med Chem 42 706-721... 

The l,4-diacyl-3-acylamino-5-phenyl-4,5-dihydro-1H-1,2,4-triazole (99) was generated by the ring-closure of a guanidinylhydrazone with acetic anhydride in ca. 80% yield. The structure of the triazole was confirmed by spectroscopy and x-ray analysis [95M733], The N-benzyl triazoline (100) was prepared by reaction of N-benzylidinebenzylamine with a hydrazonyl halide with K,CO, in benzene, followed by 2 eq of Et,N for 1 h, in 75% yield [95ZOB308]. 

Treatment of aromatic carboxaldehyde (diaminomethylene)hydrazones (105) with hot acetic anhydride or benzoyl chloride affords l,4-diacyl-3-acylamino-5-ary 1-4,5-dihydro- 1H-1,2,4-traizoles (106) in 75-95% yields. In contrast, when the 4-pyridine analog of 105 was employed, the unusual hemianimal triazole derivative (107) was obtained. The structures of the novel compounds were determined by spectral methods and in several cases by x-ray structural analysis. Mechanistic considerations are discussed [95M733]. The oxazole-1,2,4-triazole (108) was prepared by cyclization of the corresponding oxazolecarbonyl-thiosemicarbazide with bicarbonate, alkylation at the sulfur and oxidation to the sulfoxide with MCPBA [95JHC1235]. 

At the present time there is no satisfactory route to isolation of diacyl-, alkylacyl-, or alkenylacylcholine phosphoglycerides as individual components— for example, only the diacyl type or the alkylacyl form, and so on. In general, a differential analytical approach must be invoked and this will be discussed later. However, since diacylphosphatidylcholine has been discussed, proof of structure of ether-linked choline phosphoglycerides as individual species will be described as well as some of their structural features. Later, as the big picture emerges, the route to analysis of a naturally occurring mixture will be examined. 

Exactly the same methodology as applied to analysis of diacylphosphatidyl-choline can be used here. Thin-layer chromatography using several different types of adsorbents will show that usually the alkylacyl derivative will comigrate with the diacyl—as well as the alkenylacyl—phosphatidylcholine counterparts. 

The monoacylated derivative (6"-0-butyrate) was detected as the major product by H PLC analysis for all enzymatic reactions, while a diacylated derivative was also detected and confirmed by MS analysis [17]. As it can be seen in Table 9.3, higher regioselectivity of the process was observed in [bmim]BF4 than in [bmim]PF,5, while the selectivity was even lower in acetone. The lower regioselectivity of the enzymatic acylation of polyhydroxylated compounds in [bmim]PF,5 as well as in the organic solvent could be related to the lower solubility of unmodified phenolic substrates in these media, compared to that of their monoacylated derivatives [5, 16, 17]. On the other hand, the enhanced solubility of phenoHc substrates in [bmim]BF4 could explain the increased regioselectivity observed in this ionic liquid. 

Abbreviations used EMSA, electrophoretic mobility shift analysis IMPase 1, inositol monophosphatase 1 inositol synthase, A/vo-inositol 3-phosphate synthase NCBI, National Center for Biotechnology Information PCR, polymerase chain reaction Rb, retinoblastoma protein tss, transcriptional start site IP3, Inositol trisphosphate DAG, diacyl glycerol FISH, fluorescent in situ hybridization. 

Estimates of the probability of escape of radical pairs in conventional solvents have been made by product analysis of the decomposition of diacyl peroxides. For example, Braun et al. [22] estimated that 60 to 80% of the methyl radicals produced in the thermolysis of acetyl peroxide escape geminate cage recombination. However, Guillet and Gilmer [25] showed that for longer chain and Cjj radicals the probability was much lower, ranging from 5% at 760C to 16% at 262<>C (Table VI). 

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