NMR water proton relaxation in unheated and heated ultrahigh aqueous dilutions of histamine: Evidence for an air-dependent supramolecular organization of water

We measured 20-MHz R1 and R2 water proton NMR relaxation rates in ultrahigh dilutions (range 5.43.10(-8) M-5.43.10(-48) M) of histamine in water (Hist-W) and in saline (Hist-Sal), prepared by iterative centesimal dilutions under vigorous agitation in controlled atmospheric conditions. Water and saline were similarly and simultaneously treated, as controls. The samples were immediately sealed in the NMR tubes after preparation, and then code-labelled. Six independent series of preparations were performed, representing about 7000 blind measurements. R2 exhibited a very broad scatter of values in both native histamine dilutions and solvents. No variation in R1 and R2 was observed in the solvents submitted to the iterative dilution/agitation process. By contrast, histamine dilutions exhibited slightly higher R1 values than solvents at low dilution, followed by a slow progressive return to the values of the solvents at high dilution. Unexpectedly, histamine dilutions remained distinguishable from solvents up to ultrahigh levels of dilution (beyond 10(-20) in Hist-Sal). A significant increase in R2 with increased R2/R1 was observed in Hist-W. R1 and R2 were linearly correlated in solvents. but uncorrelated in histamine dilutions. After a 10-min heating/cooling cycle of the samples in their sealed NMR tubes (preventing any modification of the chemical composition and gas content), all of the relaxation variations observed as a function of dilution vanished, the R2/R1 ratio and the scatter of the R2 values dropped in all solutions and solvents, and the correlation between R1 and R2 reappeared in the Hist-W samples. All these results pointed to a more organized state of water in the unheated samples. more pronounced in histamine solutions than in solvents. dependent on the level of dilution. It was suggested that stable supra molecular structures, involving nanobubbles of atmospheric gases and highly ordered water around them, were generated during the vigorous mechanical agitation step of the preparation, and destroyed after heating. Histamine molecules might act as nucleation centres, amplifying the phenomenon which was thus detected at high dilution levels. (C) 2008 Elsevier B.V. All rights reserved.