Multiple Hydrogen-Bonding Interactions of Uric Acid/9-Methyluric Acid with Melamine Identified by Infrared Spectroscopy

Abstract

Hydrogen-bonded complexes of uric acid/9-methyluric acid (UA/9MUA) with melamine (MEL) are prepared by the combined technique of laser desorption and supersonic-jet expansion, and their stable structures are investigated by infrared spectroscopy and theoretical calculations. It is shown that the 1:1 complex formed between UA and MEL is of nonplanar type, in which the two chromophore planes are significantly folded and thus allow for triple hydrogen-bonding interactions. An anomalously broad IR band is observed in the low-frequency range 2500-2800 cm(-1), which is taken as evidence for the formation of a strong hydrogen bond between one of the NH sites of UA and MEL. In the case of 9MUA, in which hydrogen bonding to the N9H site of UA is blocked by the methyl group, two planar pairs formed of 9MUA and MEL are found to coexist. The nature of the multiple hydrogen-bonding interactions in these complexes is discussed based on the natural bond orbital analysis and compared with those of the guanine-cytosine base pair. The results are expected to provide important information on the structural characterization of urinary stones developed in infants after ingesting MEL-contaminated formula.

Nanoarchitectured Nitrogen-Doped Graphene/Carbon Nanotube as High Performance Electrodes for Solid State Supercapacitors, Capacitive Deionization, Li-Ion Battery, and Metal-Free Bifunctional Electrocatalysis

“…In the spectra of GO/UA/oCNT, the presence of uric acid was observed due to its strong signal toward the IR region, which did not appear with the GO/CNT mixture. Small shifts toward the left of CO stretching (1658 cm –1 ) and N–O stretching (1585 cm –1 ) could be observed in GO/UA/oCNT from the CO stretching (1664 cm –1 ) and N–O stretching (1589 cm –1 ) of uric acid, indicating the formation of hydrogen bonding …”

“…Small shifts toward the left of CO stretching (1658 cm −1 ) and N−O stretching (1585 cm −1 ) could be observed in GO/UA/oCNT from the CO stretching (1664 cm −1 ) and N−O stretching (1589 cm −1 ) of uric acid, indicating the formation of hydrogen bonding. 45 The morphology and structure of the obtained composite after pyrolysis were characterized by SEM and TEM. The SEM images of N-Gr/CNT revealed the intercalated CNT networks inside the graphene layers (Figure 3a and Figure S1).…”

Hydrogen-bonding interactions of uric acid complexes with water/melamine by mid-infrared spectroscopy

“…5 In both UA-MEL structures, the other two H-bonds, COÁ Á ÁHN(amino) and NHÁ Á ÁN(amino) are calculated to be much weaker than the middle H-bond, as can be seen in Fig. This large red-shift is explained to occur by the formation of a robust H-bond between the hydrogen atom of the NH site (N3H or N9H) of UA and nitrogen atom of the MEL ring (NHÁ Á ÁN).…”

“…Multiple H-bonding interactions of UA with MEL (Chart 1) were also studied 5 in relation to the serious food safety incident in which urinary stones are accumulated in infants after ingesting a melamine (MEL)-contaminated formula. [6][7][8] Analysis of urinary stones by high-performance liquid chromatographymass spectrometry (HPLC-MS) showed that most stones were composed of UA and MEL at a molar ratio of 1 : 1 to 2 : 1.…”

Understanding of Structure and Thermodynamics of Melamine Association in Aqueous Solution from a Unified Theoretical and Experimental Approach

“…27−32 In 2007, an elastic hydrogel was prepared from the sonication of rigid small complementary molecules such as melamine and uric acid. 33 Later Asami et al 34 in 2014 and Saigusa et al 35 in 2015 reported separately about the exact mechanism of formation of urinary stones by the hydrogen bonded 1:1 complex between melamine and uric acid by using different spectroscopic methods. The kidney stone is a serious threat, caused mainly by the aggregation and deposition of melamine in kidneys in human beings and animals.…”