Probe molecules ketones

Prins reaction, heteropolyacid catalysis, 41 156 Probe molecules, 42 119 acidic dissociation constant, 38 210 NMR solid acidity studies, 42 139-140 acylium ions, 42 139, 160 aldehydes, 42 162-163 alkyl carbenium ions, 42 154-157 allyl cation, 42 143-144 ammonia, 42 172-174 arenium ions, 42 150-154 carbonium ions, 42 157-160 chalcogenenonium ions, 42 161-162 cyclopentenyl cations, 42 140-143 indanyl cations, 42 144-147 ketones, 42 162,163-165 nitrogen-containing compounds, 42 165-170... 

As examples of probe molecules directly introduced onto solid acids, we consider ketones and aldehydes, amines and other nitrogen-containing compounds, phosphines, and molecules that form multiple hydrogen bonds. 

Oxidation of adamantanone as probe molecule with hydrogen peroxide was investigated in a liquid phase (1,4-dioxane, was used as a solvent) at the reaction temperature 90 °C. In a typical experiment 0.05 g of catalyst was added to a mixture of adamantanone (0.15 g), 1,4-dioxane (3 g) and hydrogen peroxide (0.15 g of 35 % solution in water), molar ratio ketone to hydrogen peroxide was 1.0 1.5. 

The entry/exit rate constants of ketones with SDS micelles was smdied by using either a micellar quencher such as y-methylvalerophenone or nitrite ion as an aqueous quencher (Table 17) [193,194]. Using a micellar quencher, the values of kp were determined by employing Eq. (27), which incorporates the fraction of micelles containing a probe molecule... 

The use of polar protic or nonprotic solvents for sample preparation (methanol, ethanol, acetonitrile, acetone) and even a nonpolar solvent as dioxane promotes hypsochromic shifts in the n n transition of benzophenone, while with solvents such as benzene, isooctane, or even dichloromethane, these bands are shifted to the red and exhibit some vibrational structure. These facts are a consequence of the different swelling capacities of these solvents toward the cellulose polymeric matrix [14,79b, 80]. The chain-chain interaction is replaced by the chain-solvent-chain interaction, allowing different probe molecules to penetrate within the matrix in different ways, or even the probe simply remains in the external cellulose surface for nonswelling solvents. In this case, increasing concentrations of the probe easily give rise to the formation of ketone microcrystals. Therefore, benzophenone could be used as a probe to evaluate the swelling capacity of several solvents regarding the cellulose matrix. 

All solvents and probe molecules were carefully dried, except the anhydrous ones. The resin and ketone were used as received the ester was synthesized and purified by double fiactional vacuum distillation. 

Based on steady-state and time-resolved emission studies, Scaiano and coworkers have concluded that silicalite (a pentasil zeolite) provides at least two types of sites for guest molecules [234-236], The triplet states of several arylalkyl ketones and diaryl ketones (benzophenone, xanthone, and benzil) have been used as probes. Phosphorescence from each molecule included in silicalite was observed. With the help of time-resolved diffuse reflectance spectroscopy, it has been possible to show that these triplet decays follow complex kinetics and extend over long periods of time. Experiments with benzophenone and arylalkyl ketones demonstrate that some sites are more easily accessed by the small quencher molecule oxygen. Also, diffuse reflectance studies in Na + -X showed that diphenylmethyl radicals in various sites decay over time periods differing by seven orders of magnitude (t varies between 20/is and 30 min) [237]. 

Another hydrazine derivative of fluorescein, 5-(((2-(Carbohydrazino)methyl)thio)-acetyl)-aminofluorescein, contains a longer spacer arm off its No. 5 carbon atom of its lower ring than fluorescein-5-thiosemicarbazide, described previously (Molecular Probes). The reagent can be used to react spontaneously with aldehyde- or ketone-containing molecules forming a hydrazone linkage (Fig. 209). It also can be used to label cytosine residues in DNA or RNA by use of the bisulfite activation procedure (Chapter 17, Section 2.1). The resulting fluorescent derivative exhibits a maximal excitation at 490 nm and a maximal luminescence emission peak at 516 nm when dissolved in buffer at pH 8. In the same buffered environment, the compound has an extinction coefficient of approximately 75,000 M-1cm 1 at 490 nm. 

BODIPY 530/550 C3 hydrazide is 4,4-difluoro-5,7-diphenyl-4-bora-3a,4a-diaza-s-indacene-3-propionyl hydrazide, a derivative of the basic BODIPY structure, which contains two phenyl rings off the No. 5 and 7 carbon atoms and a propionic acid hydrazide group on the No. 3 carbon atom (Molecular Probes). The hydrazide functional group reacts with aldehyde- or ketone-containing molecules to form hydrazone linkages (Fig. 229). The compound may be used to label glycoproteins or other carbohydrate-containing molecules after oxidation of their polysaccharide portions with sodium periodate to yield aldehyde residues. 

An exception to the straightforward correspondence between C shifts in zeolites (or other catalysts) and solution values occurs when the structure of the compound is significantly perturbed on the catalyst. The most common example is protonation equilibria on acidic catalysts. Indeed, there have been a number of reports of the use of protonation shifts of amines 151,521, phosphines (151, and phosphine oxides (531 as probes of catalyst acidity. Similar effects are (x ca-sionally encountered in in situ experiments when a basic molecule is formed as an intermediate or product. An interesting case is the conversion of acetone to hydrocarbons on zeolites, which may involve the intermediacy of diacetone alcohol, mesityl oxide, phorone, and isophorone—all ketones. The chemical shifts of the carbonyl carbons of all these species in acidic zeolites were found to be up to 10 ppm downfield of the corresponding values in reference compilations. Furthermore, although the chemical shifts of the olefinic carbons a to the carbonyl were in reasonable agreement with values for CDCI solutions, the resonances of the olefinic carbons p to the carbonyl were very broad and shifted 20-30 ppm downfield 54. ... 

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