Structural Studies on the Hydration of l-Glutamic Acid in Solution

Abstract

A combination of neutron diffraction augmented with isotopic substitution and computer modeling using empirical potential structure refinement has been used to extract detailed structural information for L-glutamic acid dissolved in 2 M NaOH solution. This work shows that the tetrahedral hydrogen bonding network in water is severely disrupted by the addition of glutamic acid and NaOH, with the number of water-water hydrogen bonds being reduced from 1.8 bonds per water molecule in pure water to 1.4 bonds per water molecule in the present solution. In the glutamic acid molecule, each carboxylate oxygen atom forms an average of three hydrogen bonds with the surrounding water solvent with one of these hydrogens being shared between the two oxygen atoms on each carboxylate group, while each amine hydrogen forms a single hydrogen bond with the surrounding water solvent. Additionally, the average conformation of the glutamic acid molecules in these solutions is extracted.

Structure and Hydration of l-Proline in Aqueous Solutions

“…Comparable orientations were also seen in the glutamic acid/ water system where again the hydrogen bond was split between the two oxygen atoms, although the number hydrogen bonds between water and the COO -are greater in glutamic acid. 24 This again supports the view that the hydration of carboxylate groups are similar among the amino acids; moreover the orientation of the hydration shell may also be similar among this group of biomolecules.…”

“…Interestingly, the coordination number about the carboxylate group is significantly lower than was observed for carboxylate groups in aqueous glutamate, where the coordination number of the g OHw (r) function is approximately three hydrogen bonds per oxygen atom. 24 There are several explanations for this difference between these two amino acids in solution. First, glutamate is a molecular ion in solution and carries a charge of -1 and as such causes a significant disruption to the bulk water network in solution as is the case with other ions in solution.…”

“…As was the case with the COO -function, the hydrogen bond donation from the NH 2 + group on proline to the water solvent is decreased when compared to measurements on glutamate where the amide hydrogens formed exactly 1.0 Hx‚‚‚Ow bonds per amine hydrogen. 24 Again, it should be emphasized that in addition to being a molecular ion glutamate was measured at a lower concentration, and it appears that, similar to carboxylatewater hydrogen bonds, amine-hydrogen bonds decrease with an increasing concentration of amino acid present in solution. Figure 10 shows the SDF for water molecules surrounding the amine group for the 1:10 proline water solution.…”

“…Interestingly, former studies on glutamate show a similar hydration of the carboxylate group in this distance range as that of the 1:20 concentration, implying that COOhydration is similar in structure among the amino acids, even though the coordination number itself varies, depending on the local charge distribution. 24 3. Orientational Correlation Functions.…”

A hybrid neutron diffraction and computer simulation study on the solvation of N-methylformamide in dimethylsulfoxide

“…The investigation was done using a hybrid experimentaltheoretical approach: neutron diffraction with isotopic substitution (NDIS) is used to obtain experimental data on the mixture structure and empirical potential structure refinement (EPSR) simulations with Monte Carlo method are used to detail that structure. NDIS can provide structural information concerning inter-molecular interaction at an unparalleled level of detail at the atomic length scale (0-12 Å) [37][38][39][40][41] and through the coupling of that methodology with EPSR simulations, it is possible to extract pair-wise atomic interactions between a particular molecule and the surrounding solvent. The technique is highly informative in the investigation of the structure of many hydrogen bonded liquids.…”