scholarly journals Theoretical Study of HOCl-Catalyzed Keto–Enol Tautomerization of β-Cyclopentanedione in an Explicit Water Environment

2013 ◽  
Vol 117 (35) ◽  
pp. 8437-8448 ◽  
Author(s):  
Cassian D’Cunha ◽  
Alexander N. Morozov ◽  
David C. Chatfield
Keyword(s):  
Theoretical Study ◽  
Water Environment ◽  
Explicit Water

Theoretical reconsideration on the hydrogen bonding and coordination interactions of chlorophyll a in aqueous solution

2011 ◽  
Vol 15 (03) ◽  
pp. 202-210 ◽  
Author(s):  
Ji-Feng Liu
Keyword(s):  
Hydrogen Bonding ◽  
Absorption Band ◽  
Water Molecule ◽  
Chlorophyll A ◽  
Absorption Spectra ◽  
Density Functional ◽  
Theoretical Study ◽  
Absorption Bands ◽  
Hydrogen Bonding Interactions ◽  
Explicit Water

In the present work, explicit water molecule and solvent-field effects on the absorption spectrum of chlorophyll a have been studied using time-dependent density functional theory (TDDFT) method. Calculated results show that the one complex and two water coordinated complexes formed by concerted coordination and hydrogen-bonding interactions would be the most preferable conformations of chlorophyll a in aqueous surroundings. Moreover, four obvious absorption bands are assigned by comparing the theoretically simulated absorption spectra with the experimental ones. The theoretical study shows that the explicit water molecule interactions slightly influence the first absorption band. However, the water coordination and hydrogen-bonding interactions can significantly affect the second absorption band which has a strong red-shift. The solvent-field effect due to the polarity of water on absorptions in Q-bands is relatively smaller than that on absorptions in B-bands. As a consequence, our theoretical study on the absorption spectra in the 350–400 nm region presents that the absorption strength in this region was influenced by the explicit coordination and hydrogen bonding interactions from water molecules, significantly.

scholarly journals Understanding the Exceptional Properties of Nitroacetamides in Water: A Computational Model Including the Solvent

Molecules ◽  
2018 ◽  
Vol 23 (12) ◽  
pp. 3308 ◽  
Author(s):  
Giovanni La Penna ◽  
Fabrizio Machetti
Keyword(s):  
Proton Transfer ◽  
Density Functional ◽  
Water Environment ◽  
Average Energy ◽  
Thermal Fluctuations ◽  
Energy Difference ◽  
Tautomeric Forms ◽  
Geminal Proton ◽  
Solvent Molecules ◽  
Explicit Water

Proton transfer in water involving C–H bonds is a challenge and nitro compounds have been studied for many years as good examples. The effect of substituents on acidity of protons geminal to the nitro group is exploited here with new p K a measurements and electronic structure models, the latter including explicit water environment. Substituents with the amide moiety display an exceptional combination of acidity and solubility in water. In order to find a rationale for the unexpected p K a changes in the (ZZ ′ )NCO- substituents, we measured and modeled the p K a with Z=Z ′ =H and Z=Z ′ =methyl. The dominant contribution to the observed p K a can be understood with advanced computational experiments, where the geminal proton is smoothly moved to the solvent bath. These models, mostly based on density-functional theory (DFT), include the explicit solvent (water) and statistical thermal fluctuations. As a first approximation, the change of p K a can be correlated with the average energy difference between the two tautomeric forms (aci and nitro, respectively). The contribution of the solvent molecules interacting with the solute to the proton transfer mechanism is made evident.

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