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N-acetyl-l-glutamic acid, crystallizes in the orthorhombic space group P212121 with unit cell parameters a = 4.747(3), b = 12.852(7), c = 13.906(7) A, V = 848.5(8) A3, Z = 4, density (calculated) = 1.481 mg/m3, linear absorption coefficient 0.127 mm−1. The crystal structure determination was carried out with MoKα X-ray data measured with liquid nitrogen cooling at 100(2) K temperature. In the final refinement cycle the data/restraints/parameter ratios were 1,691/0/131; goodness-of-fit on F2 = 1.122. Final R indices for [I > 2sigma(I)] were R1 = 0.0430, wR2 = 0.0878 and R indices (all data) R1 = 0.0473, wR2 = 0.0894. The largest electron density difference peak and hole were 0.207 and −0.154 eA−3. Details of the molecular geometry are discussed and compared with a model DFT structure calculated using Gaussian 98. The low temperature X-ray structure of N-acetyl-l-glutamic acid, including absolute configuration, is described. Comparison with the DFT structure is also discussed. Molecular conformation of N-acetyl-l-glutamic acid: (a) drawn with MERCURY [22] and (b) surfaces drawn with VMD [26].

Experimental vibrational spectroscopic studies and density functional theory (DFT) calculations of the amino acid derivatives N-acetyl-L-Asp and N-acetyl-L-Glu have been undertaken. Raman and IR spectra have been measured in the solid state for both molecules. DFT simulations were conducted using the B3-LYP correlation functional and the cc-pVDZ basis set in order to determine their energy minimized/geometry optimized structures (based on a single isolated molecule in the gaseous state), and vibrational spectra were computed at the optimized geometry in each case. Normal coordinate calculations have provided vibrational assignments for fundamental modes, including their potential energy distributions. Significant differences are observed in the computed structures and in the vibrational spectra of N-acetyl-L-Asp and N-acetyl-L-Glu. The combination of experimental and calculated results provides an insight into the structural and vibrational spectroscopic properties of N-acetylated amino acid derivatives.

Experimental vibrational spectroscopic studies and density functional theory (DFT) calculations of the di-amino acid peptide derivatives alpha- and beta-N-acetyl-L-Asp-L-Glu have been undertaken. Raman and infrared spectra have been recorded for samples in the solid state. DFT simulations were conducted using the B3-LYP correlation functional and the cc-pVDZ basis set to determine energy minimized/geometry optimized structures (based on a single isolated molecule in the gaseous state). Normal coordinate calculations have provided vibrational assignments for fundamental modes, including their potential energy distributions. Significant differences are observed between alpha- and beta-N-acetyl-L-Asp-L-Glu both in the computed structures and in the vibrational spectra. The combination of experimental and calculated spectra provide an insight into the structural and vibrational spectroscopic properties of di-amino acid peptide derivatives.

Solid state IR and Raman as well as aqueous solution state Raman spectra are reported for the linear di-amino acid peptide L-aspartyl-L-glutamic acid (L-Asp-L-Glu); the solution state Raman spectrum has also been obtained for the N,O-deuterated derivative. SCF-DFT calculations at the B3-LYP/cc-pVDZ level established that the structure and vibrational spectra of L-Asp-L-Glu can be interpreted using a model of the peptide with ten hydrogen-bonded water molecules, in conjunction with the conductor-like polarizable continuum solvation method. The DFT calculations resulted in the computation of a stable zwitterionic structure, which displays trans-amide conformation. The vibrational spectra were computed at the optimised molecular geometry, enabling normal coordinate analysis, which yielded satisfactory agreement with the experimental IR and Raman data. Computed potential energy distributions of the normal modes provided detailed vibrational assignments.