Structures of N2-acetyl-DL-alaninamide and N2-acetyl-DL-leucinamide

Puliti, R.; Mattia, Carlo Andrea; Barone, G.; Giancola, Concetta

doi:10.1107/s010827019100063x

Cited by 8 publications

(6 citation statements)

References 1 publication

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“…To calculate the molecular structure factors, the x-ray crystal structure of NALA (28) calculate the molecular structure factor using a total of 589 conformations from 10,491 occurrences of a leucine sidechain in the data base. A comparison between the molecular structure factor and the experimental data is shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

Direct evidence for modified solvent structure within the hydration shell of a hydrophobic amino acid.

Pertsemlidis

Saxena

Soper

et al. 1996

Proc. Natl. Acad. Sci. U.S.A.

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Neutron scattering experiments are used to determine scattering profiles for aqueous solutions of hydrophobic and hydrophilic amino acid analogs. Solutions of hydrophobic solutes show a shift in the main diffraction peak to smaller angle as compared with pure water, whereas solutions of hydrophilic solutes do not. The same difference for solutions of hydrophobic and hydrophilic side chains is also predicted by molecular dynamics simulations. The neutron scattering curves of aqueous solutions of hydrophobic amino acids at room temperature are qualitatively similar to differences between the liquid molecular structure functions measured for ambient and supercooled water. The nonpolar solute-induced expansion of water structure reported here is also complementary to recent neutron experiments where compression of aqueous solvent structure has been observed at high salt concentration.Interest in the structural organization of the solvent within the hydration shell of amino acid side chains arises partly from questions related to the thermodynamic and structural explanations of the hydrophobic interaction between nonpolar side chains. Much thermodynamic evidence is conventionally interpreted as indicating a differently organized structure of the water that is in contact with a nonpolar solute as compared with the pure liquid (1, 2). As one example, there is a significant increase in heat capacity when proteins are unfolded or when hydrophobic compounds are dissolved in water, and this change in heat capacity is a linear function of the area of the hydrophobic surfaces (3, 4). The large and positive heat capacity change is normally attributed to the extra heat needed to "melt" the ordered water structure near hydrophobic groups exposed to water. As a second example, departures from ideality in the observed freezing-point depression of aqueous solutions of amino acids support the picture that there are significant structural changes within the hydration shell of amino acid side chains (5). Once again, the observed effect (in this case, nonideality) is a linear function of the exposed surface area.The relationship between water structure and the hydrophobic effect has also been the subject of a number of theoretical studies (6, 7) and computer simulations (8-13) on a number of model side chain solutes. Structural analyses of the simulation data indicate that water retains its hydrogenbonded network by "straddling" the surface of the nonpolar group with three of its four tetrahedral hydrogen bonds, with the fourth bond pointing away from the hydrophobic surface. Neutron scattering experiments have provided confirmation of this view, where water molecules are observed to lie roughly tangential to the surface of the nonpolar solute (14, 15). Further experimental evidence for a hydrogen-bonded hydration shell around hydrophobic groups is found in the x-ray crystal structures of clathrate compounds (16). In these solid, crystalline hydrates, water molecules are organized completely into hydrogen-bonded polygons that ...

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Section: Resultsmentioning

confidence: 99%

Direct evidence for modified solvent structure within the hydration shell of a hydrophobic amino acid.

Pertsemlidis

Saxena

Soper

et al. 1996

Proc. Natl. Acad. Sci. U.S.A.

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“…The molecules in this study were chosen to reflect a reasonable amount of diversity in primary and secondary structures and at the same time small enough in size to be computationally tractable. The molecular structures shown in Figure were taken directly from the crystal structures listed without further refinement. − Two sets of ab initio calculations were carried out on most of the molecules studied in this work. The first set of calculations consisted of the molecules in isolation (that is without the hydrogen bonding), and the second set of calculations consisted of the molecule surrounded by its complete set of hydrogen bonding partners taken directly from the crystallographic coordinates.…”

Section: Methodsmentioning

confidence: 99%

Orientation of Amide-Nitrogen-15 Chemical Shift Tensors in Peptides: A Quantum Chemical Study

2001

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Knowledge of the orientation of the nitrogen-15 chemical shift anisotropy (CSA) tensor is critical for a variety of experiments that provide information on protein structure and dynamics in the solid and solution states. Unfortunately, the methods available for determining the orientation of the CSA tensor experimentally have inherent limitations. Rotation studies of a single crystal provide complete information but are tedious and limited in applicability. Solid-state NMR studies on powder samples can be applied to a greater range of samples but suffer from ambiguities in the results obtained. Density functional gauge-including-atomic-orbitals (GIAO) calculations of the orientations of (15)N CSA tensors in peptides are presented here as an independent source of confirmation for these studies. A comparison of the calculated (15)N CSA orientations with the available experimental values from single-crystal and powder studies shows excellent agreement after a partial, constrained optimization of some of the crystal structures used in the calculation. The results from this study suggest that the orientation as well as the magnitudes of (15)N CSA tensors may vary from molecule to molecule. The calculated alpha(N) angle varies from 0 degrees to 24 degrees with the majority in the 10 degrees to 20 degrees range and the beta(N) angle varies from 17 degrees to 24 degrees in good agreement with most of the solid-state NMR experimental results. Hydrogen bonding is shown to have negligible effect on the orientation of (15)N CSA tensor in accordance with recent theoretical predictions. Furthermore, it is demonstrated that the orientation of the (15)N CSA can be calculated accurately with much smaller basis sets than is needed to calculate the chemical shift, suggesting that the routine application of ab initio calculations to the determination of (15)N CSA tensor orientations in large biomolecules might be possible.

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“…The D-monomers were synthesized at the Department of Chemistry, University 'Federico II' of Naples [6] and the racemic mixtures were prepared by cocrystallization from equimolar mixtures of the two enantiomers in chloroform (D,L-NAAA) and ethanol-ethyl ether (D, L-NALA), respectively. No optical activity was detected after redissolution of small racemic crystals.…”

Section: Methodsmentioning

confidence: 99%

Enthalpies and entropies of fusion of some substituted dipeptides

Barone

Giancola

Lilley³

et al. 1992

Journal of Thermal Analysis

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Enthalpies and temperatures of fusion or transition for four substituted dipeptides (Nacetylamides of glycyl-L-alanine (NAGAA), L-alanyl-L-alanine (NAA~A), L-prolyl-glyeine (NAPGA) and L-leucyl-L-proline monohydrate (NALPA.H20)) were determined by differential scanning calorimetry and the entropies of fusion derived. The results obtained have been compared with those of the corresponding substituted aminoaeids and some of their racemic crystalline mixtures. The enthalpies and entropies of fusion of some substituted aminoacids have been redetermined. The results are discussed in comparison with crystal structural data, which has been reported in the literature or determined recently by some of the authors. Rationalization of the fusion parameters was attempted mainly on the basis of the number of intramoleeular hydrogen bonds and the packing densities in the crystals.

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Structures of N2-acetyl-DL-alaninamide and N2-acetyl-DL-leucinamide

Cited by 8 publications

References 1 publication

Direct evidence for modified solvent structure within the hydration shell of a hydrophobic amino acid.

Direct evidence for modified solvent structure within the hydration shell of a hydrophobic amino acid.

Orientation of Amide-Nitrogen-15 Chemical Shift Tensors in Peptides: A Quantum Chemical Study

Enthalpies and entropies of fusion of some substituted dipeptides

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