The Distal Effect of N-Electron-withdrawing Groups on the Stability of Peptide Carbon Radicals

2011 ◽  
Vol 64 (4) ◽  
pp. 403 ◽  
Author(s):  
Junming Ho ◽  
Michelle L. Coote ◽  
Christopher J. Easton
Keyword(s):  
Hydrogen Bonding ◽  
Ab Initio ◽  
Radical Formation ◽  
Ab Initio Methods ◽  
Amide Nitrogen ◽  
Amide Carbonyl ◽  
Carbon Radicals ◽  
The Stability ◽  
High Level ◽  
Calculated Activation

The effect of electron-withdrawing substituents, hydrogen bonding and protonation at amide nitrogen on the stability of radicals formed by loss of either a distal C–H adjacent to the amide carbonyl or one proximal to the amide nitrogen for a series of acetamides and diketopiperazines has been studied via high-level ab initio methods. These studies show that the effect is to destabilize the radicals formed by abstraction of the proximal hydrogens, typically by 10–20 kJ mol–1, and stabilize the distal radicals typically by 5–10 kJ mol–1, but only if the distal radicals are polarized by another dative substituent. The different radical stabilities are not directly mirrored in calculated activation energies or experimental rates of radical formation in bromination reactions, because there is significant charge development in these reaction transition states.

scholarly journals Photophysical properties of pyrrolocytosine, a cytosine fluorescent base analogue

2016 ◽  
Vol 18 (30) ◽  
pp. 20189-20198 ◽  
Author(s):  
Quynh L. Nguyen ◽  
Vincent A. Spata ◽  
Spiridoula Matsika
Keyword(s):  
Hydrogen Bonding ◽  
Ab Initio ◽  
Photophysical Properties ◽  
Fluorescence Properties ◽  
Water Molecules ◽  
Pi Stacking ◽  
High Level

The fluorescence properties of pyrrolocytosine, a cytosine analogue, are investigated using high level ab initio methods, and they are found to be affected by hydrogen bonding to water molecules, as well as by pi-stacking with guanine.

scholarly journals Amines are likely to enhance neutral and ion-induced sulfuric acid-water nucleation in the atmosphere more effectively than ammonia

2008 ◽  
Vol 8 (14) ◽  
pp. 4095-4103 ◽  
Author(s):  
T. Kurtén ◽  
V. Loukonen ◽  
H. Vehkamäki ◽  
M. Kulmala
Keyword(s):  
Sensitivity Analysis ◽  
Sulfuric Acid ◽  
Ab Initio ◽  
Acid Water ◽  
Ab Initio Methods ◽  
Free Energies ◽  
Ionic Clusters ◽  
The Difference ◽  
High Level ◽  
Formation Thermodynamics

Abstract. We have studied the structure and formation thermodynamics of dimer clusters containing H2SO4 or HSO4− together with ammonia and seven different amines possibly present in the atmosphere, using the high-level ab initio methods RI-MP2 and RI-CC2. As expected from e.g. proton affinity data, the binding of all studied amine-H2SO4 complexes is significantly stronger than that of NH3•H2SO4, while most amine-HSO4− complexes are only somewhat more strongly bound than NH3•HSO4−. Further calculations on larger cluster structures containing dimethylamine or ammonia together with two H2SO4 molecules or one H2SO4 molecule and one HSO4− ion demonstrate that amines, unlike ammonia, significantly assist the growth of not only neutral but also ionic clusters along the H2SO4 co-ordinate. A sensitivity analysis indicates that the difference in complexation free energies for amine- and ammonia-containing clusters is large enough to overcome the mass-balance effect caused by the fact that the concentration of amines in the atmosphere is probably 2 or 3 orders of magnitude lower than that of ammonia. This implies that amines might be more important than ammonia in enhancing neutral and especially ion-induced sulfuric acid-water nucleation in the atmosphere.

The stability of biradicaloid versus closed-shell [E(μ-XR)]2 (E = P, As; X = N, P, As) rings. Does aromaticity play a role?

2016 ◽  
Vol 18 (17) ◽  
pp. 11879-11884 ◽  
Author(s):  
Rafael Grande-Aztatzi ◽  
Jose M. Mercero ◽  
Jesus M. Ugalde
Keyword(s):  
Ab Initio ◽  
Closed Shell ◽  
The Stability ◽  
High Level

High-level CASSCF calculations, supplemented with MCQDPT ab initio calculations, demonstrate that the [E(μ-XH)]2 (E = P, As; X = N, P, As) compounds possess one planar and one butterfly-like isomers.

On the stability of NCNO and its dissociation into CN and NO radicals as treated by ab initio methods

1977 ◽  
Vol 24 (3) ◽  
pp. 355-366 ◽  
Author(s):  
Cecilia Björkman ◽  
Helge Johansen ◽  
Børge Bak ◽  
Björn Roos
Keyword(s):  
Ab Initio ◽  
Ab Initio Methods ◽  
The Stability
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