Bacterial EPS are heteropolysaccharides containing different functional groups in their backbone including amino, sulfate, phosphate, and hydroxyl substituents as well as N-acetylamino sugars and hemiacetal
ends; all of these functional groups are great candidates in the reduction, complexation, and stabilization of metal nanoparticles during their synthesis.
On the other hand, almost all of the carbohydrates that exist in nature are glycosidic compounds as a result of dehydrative condensation of hemiacetal
The slight increase in gelatinization temperatures also confirm our observation of higher peak viscosity of [oxAYBS.sup.*] than nAYBS in the viscoAmylograph, reasons of which was attributed to probable formation of crosslinks by hemiacetals
that may be formed by low levels of oxidants.
, and ethyl acetate formation from ethanol is as follows:
The P450-dependent hydroxylation of the methoxy group yields an intermediate corresponding to the hemiacetal
of formaldehyde that can cyclize to form a methylenedioxy bridge via an ionic mechanism involving the methylene oxonium ion intermediate.
The primary products from the methanolysis of CS and DS were presumed to be uronic or iduronic acid-N-acetylhexosamine dimers, methylated at both the carboxylic acid and terminal hemiacetal
In aqueous solution, they occur as an equilibrium of four related molecular structures; namely the fiavylium cation, quinoidal base, hemiacetal
and chalcone forms.
However, by the treatment of 15 with Yb[(OTf).sub.3] in methanol and reflux of the reaction mixture for 6h, 17 (17% yield) and 18 (32% yield) were obtained, probably via a hemiacetal
intermediate (3-hydroxy-3,5,7,3', 4'-pentamethoxyflavane) 16 (Scheme 4).
In the particular case of alcohols and acids, it seems to be likely that formation of esters by esterification of alcohols and acids (or by transesterification of two esters), addition reactions of alcohols to aldehydes or ketones to form hemiacetals
or acetals, oxidation of alcohols, etc.
And the study we cited from the New England Journal of Medicine raised a red flag about the formaldehyde-containing hemiacetals
formed when some e-cig flavoring substances are vaped.
The two sets of [sup.1]H NMR chemical shift values for the methylene group C-26 (3.95, 3.62 and 4.06, 4.53) suggested that the saponin was actually a mixture of the 25R and 25S epimeric hemiacetals
. Both approaches, comparison of the [sup.1]H NMR chemical shift values with data from the same kind of saponins recorded under the same conditions (Farid et al.