In Situ IRRAS Studies of Molecular Recognition of Barbituric Acid Lipids to Melamine at the Air–Water Interface

Abstract

Recognition and detection of melamine are of very significance in food industries. Molecular recognitions of barbituric acid lipids to melamine at the air-water interface have been investigated in detail using in situ infrared reflection absorption spectroscopy (IRRAS). Hydrogen bonding patterns and molecular orientations of the molecular recognitions have been revealed. Prior to molecular recognition, the barbituric acid moieties in the monolayers were hydrogen bonded with a flat-on fashion at the air-water interface, and the alkyl chains were preferentially oriented with their CCC planes perpendicular to the water surface. After molecular recognition, the NH(2) stretching bands of recognized melamine were clearly observed at the air-water interface as well as primary characteristic bands, the barbituric acid moieties underwent a change in orientation with non-hydrogen bonded C4═O bonds almost perpendicular to the water surface and C2═O and C6═O bonds involved in hydrogen bonds with melamine, and the alkyl chains were preferentially oriented with their CCC planes parallel to the water surface. The monolayers of barbituric acid lipids exhibited excellent selectivity for melamine over nucleosides.

Chemical and Biological Sensing Using Diatom Photonic Crystal Biosilica With In-Situ Growth Plasmonic Nanoparticles

“…The intake of melamine can lead to kidney disease and even death in infants [43], [44]. Thus, the sensitive and accurate detection of melamine is of the utmost importance for food safety.…”

Comparing C2=O and C2=S Barbiturates: Different Hydrogen-Bonding Patterns of Thiobarbiturates in Solution and the Solid State

“…It was reported [ 27 , 28 , 29 ] that barbiturates can form Langmuir films on a water subphase; however, there is no report regarding their thio-analogues. Thus, a Langmuir film of either B and TB was generated by spreading the compound solutions on the water subphase, evaporating the solvent, and compressing the films by moving the barriers of the Langmuir trough.…”

“…They can bind specifically and strongly towards artificial receptors like the Hamilton Wedge [ 17 , 18 , 19 ], triazines [ 20 ], and diaminopyridines [ 21 ], display self-association [ 22 , 23 , 24 ], and generate transient H-bonds networks in barbiturate-bearing polymers [ 25 , 26 ], despite their comparatively low association constant in nonpolar solvents of only 23.6 M −1 (allobarbital) [ 22 ]. When attaching them onto (macro-)molecules, unique dynamic properties via their distinctive H-bonding in functional materials can be achieved, such as in monolayers [ 27 , 28 , 29 ], in coordination complexes [ 30 , 31 ], in 3D printing [ 32 ], or as self-healing-polymers [ 25 , 26 , 32 , 33 , 34 ] in self-assembled materials [ 35 , 36 ].…”

A Fluorescence-Based Chemical Sensor for Detection of Melamine in Aqueous Solutions

“…The sensor consisted of a carbazole fluorophore brandishing two barbituric acid units that are conjugated to the fluorophore through a carbon-carbon double bond. The barbiturate groups provide a binding cleft for melamine with complementary hydrogen bonding motifs that bind a molecule of melamine from two sides, as depicted in Scheme 1 [16][17][18]. We hypothesized that the binding of melamine by the barbiturates through six hydrogen bonds alters the electronic distribution within the molecule and the carbazole fluorophore, leading to observable and measurable changes in the emission profile of CB that reflect the concentration of melamine in the solution.…”