Probe molecules aldehydes

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. 

Indeed, radical probe studies have very decisively excluded the radical cyclization mechanism in at least one typical case. This experiment relies upon the circumstance that the cyclization of a carbon-centered radical to an aldehyde carbon group is known to occur at approximately the same rate as the exo-trig cyclization of such a radical to a carbon-carbon double bond. In a probe molecule designed to provide an opportunity for a hypothetical radical intermediate to add to either or both of these functionalities, no addition to the vinyl double bond was observed (Scheme 75). 

The ethylene diamine-dextran derivative may be used for the coupling of carboxylate-contain-ing molecules by the carbodiimide reaction, for the coupling of amine-reactive probes, or to modify further using heterobifunctional crosslinkers. The hydrazide-dextran derivative may be used to crosslink aldehyde-containing molecules, such as oxidized carbohydrates or glycoproteins. 

Purify the hydrazide-labeled oligo by gel filtration on desalting resin using 10 mM sodium phosphate, 0.15M NaCl, lOmM EDTA, pH 7.2. The probe now may be used to conjugate with an aldehyde-containing molecule. 

The mechanism of the aldol-Tishchenko reaction has been probed by determination of kinetics and isotope effects for formation of diol-monoester on reaction between the lithium enolate of p-(phenylsulfonyl)isobutyrophenone (LiSIBP) and two molecules of benzaldehyde. ". The results are consistent with the formation of an initial lithium aldolate (25) followed by reaction with a second aldehyde to form an acetal (26), and finally a rate-limiting intramolecular hydride transfer (Tishchenko... 

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. 

BODIPY 593/503 C3 hydrazide is 4,4-difluoro-l,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene-8-propionyl hydrazide (Molecular Probes). Unlike BODIPY 530/550 C3 hydrazide, this BODIPY derivative contains substituents that shift to lower wavelengths the spectral characteristics of its fluorescent properties. The molecule is highly reactive toward aldehyde-containing compounds, including glycoproteins that have been oxidized with sodium periodate to create the requisite groups (Fig. 230). 

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