Carboxy group, detection

This method is more efficient in the resolution of cis and trans conformational isomers of fatty acids than the usually used GC methods with packed columns, and there are no problems with derivatization of short-chain fatty acids or heat-labile polyunsaturates. Another advantage over GC methods is that the separated fatty acids are not destroyed during their detection, which enables further analysis to be performed. The trans isomers are generally eluted after the corresponding cis isomers. Positioning of the double bonds in the proximity of the carboxy group of an acid usually leads to a shift in the direction of the methyl end of the carbon chain. 

In another report published near the same time, this group demonstrated the electrochemical detection of electroactive enantiomers, d- and L-3,4-dihydroxypheny-lalanine (DOPA) and (R)- and (.S )-A, A /-dimcthylfcrroccnylcthylamine (FcN) in imprinted sol-gel-derived thin films.68 To improve response times, the imprinted films were made to be very thin, — 70 nm, which is about 3 to 10 times thinner than typical sol-gel-derived films. The functional monomer used to imprint DOPA was PTMOS (Fig. 20.2) because it was expected to exhibit tt-tt and hydrophobicity interactions. For the ferrocene derivative, both PTMOS (Fig. 20.2) and carboxyethylsila-netriol sodium salt (CTES) were used for hydrophobicity and tt-tt interactions and electrostatic interactions between the amine and carboxy groups, respectively.68... 

High-resolution molecular mass analysis provides the molecular formula CnH2iO of acanthifolin, which corresponds to seven double bond equivalents. The proton broadband decoupled NMR spectrum (Fig. 6a) displays all 17 carbon atoms of the molecule, including a carboxy group (5c = 170.5) and four additional C atoms in the sp range of chemical shifts (5c = 145.8, 138.1, 119.8 and 116.2), indicating two CC double bonds. Only three of all seven double bonds of the molecule are detected by NMR. To conclude, acanthifolin incorporates a tetracyclic ring system... 

Insertion of carboxy groups between C2 and C3 of the molecules in mixtures of even shorter n-alkanes, hexadecane and octadecane, does allow a new hexatic B liquid crystalline phase to form [52]. Thus, between 10 and 75 wt% of methyl stearate (H(CH2)i7C02CH3) in methyl palmitate (H(CH2)i5C02CH3), an phase whose birefringent pattern is indistinguishable from that of BS can be detected. From X-ray diffraction measurements, the layer spacing of a 1 1 mixture in its phase, 25.7 A, is 2.5 A longer than that found in the lower temperature (and more densely packed) solid phase. 

Using and H n.m.r. spectroscopy, approximately 3% of the norcaradiene tautomer with the carboxy group in the exo-position was detected in equilibrium with... 

The IR spectra are useful for detecting functional groups of Aristolochia alkaloids. Aristolochic acids show two characteristic bands at 1550 and 1350 cm due to the absorption of nitro group, and the carboxy OH group appears at 3000-2500 cm as a broad continuous absorption. Hydroxy derivatives of aristolochic acids or aristolactams show OH and NH absorptions at 3300-3500 and 3200-3400 cm The carboxy or lactam carbonyl is present at 1690 cm i. In general, the aromatic ring system shows stretches at 1625-1575 and 1525-1475 cm 1 as usual, and observation of the 900-700 cm region is often used for analysis of substitution type in aromatic derivatives 28). 

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