Zwitterions are the most stable form for neutral arginylglycine in gas phase: Clear theoretical evidence

2013 ◽  
Vol 1008 ◽  
pp. 96-102 ◽  
Author(s):  
Cuihong Wang ◽  
Zijing Lin ◽  
Ruiqin Zhang
Keyword(s):  
Gas Phase ◽  
Stable Form ◽  
Theoretical Evidence

Conformational polymorphism in a Schiff-base macrocyclic organic ligand: an experimental and theoretical study

2010 ◽  
Vol 66 (5) ◽  
pp. 527-543 ◽  
Author(s):  
Leonardo Lo Presti ◽  
Raffaella Soave ◽  
Mariangela Longhi ◽  
Emanuele Ortoleva
Keyword(s):  
Schiff Base ◽  
Solid State ◽  
Dft Calculations ◽  
Gas Phase ◽  
Phase Ii ◽  
Density Functional ◽  
Organic Ligand ◽  
Stable Phase ◽  
Stable Form ◽  
Molecular Conformations

Polymorphism in the highly flexible organic Schiff-base macrocycle ligand 3,6,9,17,20,23-hexa-azapentacyclo(23.3.1.111,15.02,6.016,20)triaconta-1(29),9,11,13,15(30),23,25,27-octaene (DIEN, C24H30N6) has been studied by single-crystal X-ray diffraction and both solid-state and gas-phase density functional theory (DFT) calculations. In the literature, only solvated structures of the title compound are known. Two new polymorphs and a new solvated form of DIEN, all obtained from the same solvent with different crystallization conditions, are presented for the first time. They all have P\bar 1 symmetry, with the macrocycle positioned on inversion centres. The two unsolvated polymorphic forms differ in the number of molecules in the asymmetric unit Z′, density and cohesive energy. Theoretical results confirm that the most stable form is (II°), with Z′ = 1.5. Two distinct molecular conformations have been found, named `endo' or `exo' according to the orientation of the imine N atoms, which can be directed towards the interior or the exterior of the macrocycle. The endo arrangement is ubiquitous in the solid state and is shared by two independent molecules which constitute an invariant supramolecular synthon in all the known crystal forms of DIEN. It is also the most stable arrangement in the gas phase. The exo form, on the other hand, appears only in phase (II°), which contains both the conformers. Similarities and differences among the occurring packing motifs, as well as solvent effects, are discussed with the aid of Hirshfeld surface fingerprint plots and correlated to the results of the energy analysis. A possible interconversion path in the gas phase between the endo and the exo conformers has been found by DFT calculations; it consists of a two-step mechanism with activation energies of the order of 30–40 kJ mol−1. These findings have been related to the empirical evidence that the most stable phase (II°) is also the last appearing one, in accordance with Ostwald's rule.

Experimental and theoretical evidence for the generation of a stable hydrazine dication in the gas phase

1987 ◽  
Vol 77 (2-3) ◽  
pp. R3-R6 ◽  
Author(s):  
Thomas Drewello ◽  
Carlito B. Lebrilla ◽  
Helmut Schwarz ◽  
Daniel Stahl
Keyword(s):  
Gas Phase ◽  
Theoretical Evidence

Complexation of Glycine by Atomic Metal Cations in the Gas Phase

2001 ◽  
Vol 7 (4-5) ◽  
pp. 303-311 ◽  
Author(s):  
Sophie Hoyau ◽  
Jean-Pierre Pélicier ◽  
Françoise Rogalewicz ◽  
Yannik Hoppilliard ◽  
Gilles Ohanessian
Keyword(s):  
Gas Phase ◽  
Metal Ion ◽  
Metal Cations ◽  
Carbonyl Oxygen ◽  
Stable Form ◽  
Neutral Form ◽  
Ion Attachment ◽  
Metal Properties ◽  
Doubly Charged

The interaction of glycine with 15 metal cations (M+ or M2+)in the gas phase has been studied by quantum chemical calculations. Three types of complexation have been considered: (i)chelation between nitrogen and the carbonyl oxygen, (ii)attachment to the carboxyl group of neutral glycine and (iii)attachment to the carboxylate group of zwitterionic glycine. It is found that the relative energies of these structures and, therefore, the nature of the lowest energy isomer, depend dramatically upon the metal ion. In several cases, metal ion attachment to glycine results in a switch from the neutral form (the most stable form of gaseous glycine)to the zwitterion (the most stable form of glycine in solution). This occurs with doubly-charged cations and, in some cases, with monocations. Several metal properties are invoked to explain these results: metal charge, size, electron affinity and polarizability. The role of metal–ion polarizability is illustrated by the computed geometries of M(CH3OH)2n+ complexes.

Estimation of Lattice Energies of Organic Molecular Crystals by Combination of Experimentally Determined and Quantum- Chemically Calculated Quantities: A New Value for the Lattice Energy of a-Glycine

1999 ◽  
Vol 54 (10-11) ◽  
pp. 611-616 ◽  
Author(s):  
Gerhard Raabe
Keyword(s):  
Total Energy ◽  
Ab Initio ◽  
Gas Phase ◽  
Molecular Crystals ◽  
Lattice Energy ◽  
Energy Difference ◽  
Crystalline Form ◽  
Stable Form ◽  
Organic Molecular Crystals ◽  
Ab Initio Theory

A new value for the lattice energy of a-glycine was determined by combination of the experimentally measured heat of sublimation taken from literature and the quantum-chemically calculated energy difference Etot,gp - Etot,cry, where Etot,gp is the total energy of the most stable form of the compound in the gas phase (carboxylic acid) and Etot,cry the total energy of the molecule as it occurs in its crystalline form (betaine). At the highest levels of ab initio theory employed in this study this energy difference is -(28±2) kcal/mol, indicating that older work overestimated this difference significantly. The reason for the overestimation of this energy difference was determined by means of additional ab initio calculations. The lattice energy of -(67±2)kcal/mol obtained using the new value for Etot,gp - Etot,cry is significantly more positive than an older value of -103 kcal/mol frequently cited in the literature.

Experimental and theoretical evidence for nonlinear coordination of sp-hybridized carbon atoms. The gas-phase structure of (trifluoroethylidyne)sulfur trifluoride, CF3C.tplbond.SF3

1987 ◽  
Vol 109 (13) ◽  
pp. 4009-4018 ◽  
Author(s):  
Dines Christen ◽  
Hans Georg Mack ◽  
Colin J. Marsden ◽  
Heinz Oberhammer ◽  
Gabriele Schatte ◽  
...  
Keyword(s):  
Gas Phase ◽  
Phase Structure ◽  
Theoretical Evidence ◽  
Gas Phase Structure

Theoretical Evidence for a Stable form of Cyclic Ozone, and its Chemical Consequences

1973 ◽  
Vol 51 (1) ◽  
pp. 139-146 ◽  
Author(s):  
James S. Wright
Keyword(s):  
Configuration Interaction ◽  
Pulse Radiolysis ◽  
Molecular Orbital Calculation ◽  
Low Energy ◽  
Basis Set ◽  
Slater Type Orbitals ◽  
Stable Form ◽  
Cyclic Form ◽  
Theoretical Evidence ◽  
Single Configuration

The total energy of the symmetrical, bent O3 molecule is studied as a function of internuclear angle and internuclear distance. The method used is an ab initio molecular orbital calculation with a minimum basis set of Slater-type orbitals, plus limited configuration interaction. Best single configuration energies show the existence of two stable minima: a cyclic (60°) structure and a bent (115°) structure. The cyclic structure is preferred by 48 kcal/mol, contrary to experiment (116° 48′) Configuration interaction results with two low lying orbitals show the cyclic form still preferred by 6 kcal/mol. A transition state for the bent-cyclic pathway lies 26 kcal/mol (or less) above the bent form. Based on these results, a possible low energy path via the cyclic form is proposed for the thermal decomposition of ozone. It is also proposed that cyclic ozone may have been observed in the pulse radiolysis of oxygen.

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