Electrostatic properties of L-alanine from x-ray diffraction at 23 K and ab initio calculations

Journal Article · Thu Jun 01 00:00:00 EDT 1989 · Journal of Physical Chemistry; (USA)

DOI:https://doi.org/10.1021/j100348a015· OSTI ID:6751468

Destro, R; Bianchi, R; Morosi, G ^[1]

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1. Universita di Milano (Italy)

Maps of the electrostatic potential of L-alnine have been derived from single-crystal X-ray diffraction data collected at 23 (1) K and interpreted with a multipole (pseudoatoms) formalism. In the crystal, minimia in the potential of virtually identical magnitudes are observed near both oxygen atoms, in spite of their different environments. For an isolated, zwitterionic molecule constructed by assembling the pseudoatoms, a single minimum of -500 (42) kJ mol{sup {minus}1} {vert bar} e {vert bar}{sup {minus}1} is obtained. Its position, which differs from those of the minima in the crystal, is at 1.15 {angstrom} from an oxygen atom-the one that forms two hydrogen bonds in the crystal structure- and along the line connecting, in the crystal, the oxygen and hydrogen atoms involved in the shortest hydrogen bond. Theoretical maps of the electrostatic potential, calculated by self-consistent field molecular orbital (SCF MO) ab initio methods with four different basis sets, have been compared with those derived from the experiment. In the region of the carboxylate group the best agreement is obtained with maps computed with the largest basis set here employed, of double-{zeta} plus polarization quality (6-31 G**). From various multipole models adopted to analyze the X-ray data, values of 12.7 (7)-13.1 (7) D are derived for {vert bar} {mu} {vert bar}, the magnitude of the molecular dipole moment of L-alanine in the solid state, to be compared with literature values, 12.3-17.0 D, of solution measurements. For an isolated molecule of the amino acid, the theoretical estimates of {vert bar} {mu} {vert bar} with our basis sets are in the range 12.0-12.9 D. Atomic electric field gradients (EFG) have also been derived from the results of the X-ray diffraction experiment, and the corresponding asymmetry parameters {eta} and quadrupole coupling constants (QCC) e{sup 2}qQ/h evaluated.

• OSTI ID: 6751468
• Journal Information: Journal of Physical Chemistry; (USA), Vol. 93:11; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
59 BASIC BIOLOGICAL SCIENCES
ALANINE-L
ELECTRODYNAMICS
CALCULATION METHODS
DATA ANALYSIS
EXPERIMENTAL DATA
MEASURING INSTRUMENTS
MEASURING METHODS
VERY LOW TEMPERATURE
X-RAY DIFFRACTION
ALANINE-ALPHA
ALANINES
AMINO ACIDS
CARBOXYLIC ACIDS
COHERENT SCATTERING
DATA
DIFFRACTION
INFORMATION
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
SCATTERING
400201* - Chemical & Physicochemical Properties
550200 - Biochemistry