Hydrogen bonding carbonyl group with water

The applications of PM-IRRAS also include fatty acids, phospholipids, and protein conformations. Desbat and co-workers reported on the variation of the dissociation of a Langmuir monolayer of arachidic acid at the air-water interface as a function of the subphase pH and for several cations (Cd2+, Ca2 +, Mg2 +, and Na+) with the help of the PM-IRRAS method [92]. Fig. 14 shows the PM-IRRAS spectra of Langmuir monolayer of deuterated arachidic acid in the presence of CdCb as a function of the subphase pH. At low subphase pH (pH = 3.5), the spectrum only presents absorption bands related to the acid form, i.e., the C = O stretching vibration (v(C = O)) and the OH bending (<5(0-H)) located at 1720 and 1270 cm respectively. The frequency position of the v(C = O) is characteristic of a hydrogen-bonded carbonyl group. As the subphase pH is increased, the arachidic acid is progressively deprotonated to... 

The carbonyl group is strongly polar, and it can form hydrogen bonds with hydrogen-bond donors such as water, alcohols, and amines. Aldehydes and ketones containing up to four carbon atoms are miscible with water. Both acetone and acetaldehyde are miscible with water. Acetone, often used in nail polish remover, is a common solvent with low toxicity. 

Fig. 20.6 The interaction between HlV-protease and its polyprotein substrate involves a pair of hydrogen bonds (via a buried water molecuie) from substrate carbonyls of Gly 27 and Gly 27 a pair of hydrogen bonds (via a buried water molecule) from substrate C=0 groups to main-chain groups of lieu 50 and lieu 50 and nonplar interactions with hydrophobic residues lining the pockets that accommodate side chains R and R. In the transition state the carboxyi of the central (scissile) bond forms a tetrahedral hydroxy intermediate which interacts with the carboxyl groups of Asp 25 and Asp 25. ...

---