Irregular Hydrogen-bond Interactions In Organic Acid Hydration

Organic acids are water-soluble organic compounds containing carboxylic groups,which often exist in the form of solution.Their special biological activities play an important role in eliminating inflammation and maintaining health in the human body,such as bacteriostasis,gallbladder benefit,anti-inflammation,hypoglycemia,anti-oxidation and regulation body immunity.Organic acids mostly participate in life and health modulation in the form of aqueous solution.However,people have not clear understanding of the hydration effect,solute-solvent interaction,ion injection evolution of water hydrogen bond network,etc.In the process of dissolving organic acid solutes in water,the organic acid solution can be regarded as the formation of ionic electric field due to the dissociation of organic acid groups in water and the amount of charge,which induces the orderly arrangement of neighboring water molecules to form a hydration shell,while the water molecules outside the shell still maintain their original volume phase characteristics.Therefore,based on the bond relaxation theory and the coupled hydrogen bond model,this paper applies Lagrangian mechanics to explore the evolution of short-range force field and potential field of hydrogen bond induced by organic acid groups represented by carboxylic acid.The main results of this paper are summarized as follows:(1)Based on the synergistic relationship between the Lagrange equation and the various physical parameters of hydrogen bond relaxation in liquid water,and the vibration frequencies of the high and low frequency phonons of hydrogen bond in acetic acid solution at each concentration obtained by Raman spectroscopy,the variation of hydrogen bond length,force constant and bond energy with the concentration was obtained.The results show that the organic acid molecules in the solution polarize adjacent water molecules to form a hydration shell,which induces hydrogen bond relaxation,redshifts of low-frequency phonons and blue-shifts of high-frequency phonons,and the amplitude of frequency shift increases as the concentration increases.(2)The effect of molecular types of organic acids on hydrogen bond relaxation in three typical organic acid solutions of methyl/ethyl/propionic acid was investigated.With the increase of methyl groups in organic acid molecules,the low frequency phonons in hydrogen bond undergo red shift and the high frequency phonons blue shift.Non-bond stretches and weakens,while covalent bond shortens and strengthens.The non-bond force constant decreases while the covalent force constant increases.This indicates that the increase of methyl groups enhances the polarization ability of organic acid molecules.(3)Hydrogen bond relaxation behavior in the solution of glycine and its alkyl derivatives was studied.The results show that glycine and its alkyl derivatives are the same organic acids as methyl/ethyl/propionic acid and have polarizing effect on water molecules.However,glycine-based organic acids have new nitrogen atoms and more hydrogen protons compared to methyl/ethyl/propionic acid,so there are more hydrogen bonds and anti-hydrogen bonds formed,and the polarization effect is stronger.(4)In combination with Lagrangian method and Raman spectroscope measurement,short-range potential field maps of hydrogen bonds of acetic acid,methyl/ethyl/propionic acid and glycine with its alkyl derivatives in varying concentrations were constructed.The results show that increasing the concentration and increasing the number of alkyl groups in the organic acid have the same effect on the hydrogen bonds in the original aqueous solution,and the relaxation effect of the hydrogen bond in the original aqueous solution is intensified.The O:H stretches and weakens,and the bond energy is reduced.At the same time,O-O Coulomb repulsion modulated H—O covalent bond shortener and strengthener,and the evolution range of the hydrogen bond bond length and potential energy is significantly reduced.