The Structure of Neutral Proline

Abstract

An intramolecular hydrogen bond of the type OH⋅⋅⋅N is present in both conformers of proline (see picture) that were observed in the gas phase using laser‐ablation molecular‐beam Fourier‐transform microwave spectroscopy.

Importance of Entropy in the Conformational Equilibrium of Phenylalanine: A Matrix-Isolation Infrared Spectroscopy and Density Functional Theory Study

“…27,28 Most of these studies also reported theoretical calculations at various levels of theory. [5][6][7][8][9][10][11][12][13]15,17,[19][20][21][22][23][24][25][26][27][28] In general, the gas-phase results are qualitatively consistent with the matrix-isolation data, despite van der Waals forces appearing in the solid matrix between the sample and inner gas molecules. The most stable structures of aliphatic amino acids have been found to be stabilized by a bifurcated H-bond linking the carboxylic oxygen atom and the hydrogen atoms of the amino group.…”

“…In proteins, amino acids occur as residues of neutral L-R forms, whereas the zwitterionic structures are found in the crystalline state and in solution. [1][2][3] Amino acids adopt their neutral form also in the gas phase [4][5][6][7][8][9][10][11][12][13] and in low-temperature inert matrixes. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] Therefore, the structures of these compounds have been extensively studied in both these media.…”

“…[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] Therefore, the structures of these compounds have been extensively studied in both these media. A number of aliphatic amino acids as well as some of their derivatives have been investigated experimentally up to date: glycine, 4,5,[14][15][16][17][18] sarcosine (N-methylglycine), 19 N,N-dimethylglycine, 20 alanine, 6,[21][22][23] valine, 7,24 proline 8,25,26 and serine. 27,28 Most of these studies also reported theoretical calculations at various levels of theory.…”

“…However, existence of other conformers has been proven experimentally for all molecules studied hitherto. [4][5][6][7][8][9][10][11][12][13][15][16][17][18][21][22][23][24][25][26][27][28] The conformational distribution of amino acids depends strongly on the experimental conditions, because they have low conformational interconversion barriers. Low barriers have been predicted theoretically for glycine and alanine (for alanine, as low as 129 cm -1 and less than 35 cm -1 for the internal rotations around C-N and C-C(dO) bonds, respectively).…”

Interaction of Proline with Cu+and Cu2+Ions in the Gas PhaseGab Yong Lee*Department of Life Chemistry, Catholic University of Daegu, Gyeongsan 712‐702, Korea(Received March 3, 2009)INTRODUCTIONCopper ions are the most important transitionmetals involved in several biological processes ofliving systems, including oxidation, dioxygentransport, and charge transfer.1 The study of interactionsbetween the metal ion and amino acids hasattracted considerable attention from experimental2-6and

“…25 Therefore, extensive structural studies have been performed on amino acids in their natural solid state. However, amino acids have a zwitterionic structure in their solid state.…”