An efficient cluster elongation method in density functional theory and its application to poly‐hydrogen‐bonding molecules

1994 ◽  
Vol 101 (12) ◽  
pp. 10808-10823 ◽  
Author(s):  
Yuriko Aoki ◽  
Sándor Suhai ◽  
Akira Imamura
Keyword(s):  
Density Functional Theory ◽  
Hydrogen Bonding ◽  
Density Functional ◽  
Functional Theory ◽  
Elongation Method

scholarly journals Structure and vibrational spectroscopy of methanesulfonic acid

2018 ◽  
Vol 5 (12) ◽  
pp. 181363 ◽  
Author(s):  
Lisha Zhong ◽  
Stewart F. Parker
Keyword(s):  
Density Functional Theory ◽  
Hydrogen Bonding ◽  
Vibrational Spectroscopy ◽  
Density Functional ◽  
Inelastic Neutron Scattering ◽  
Linear Chain ◽  
Methanesulfonic Acid ◽  
Chain Structure ◽  
Trifluoromethanesulfonic Acid ◽  
Functional Theory

In this work, we have used a combination of vibrational spectroscopy (infrared, Raman and inelastic neutron scattering) and periodic density functional theory to investigate the structure of methanesulfonic acid (MSA) in the liquid and solid states. The spectra clearly show that the hydrogen bonding is much stronger in the solid than the liquid state. The structure of MSA is not known; however, mineral acids typically adopt a chain structure in condensed phases. A periodic density functional theory (CASTEP) calculation based on the linear chain structure found in the closely related molecule trifluoromethanesulfonic acid gave good agreement between the observed and calculated spectra, particularly with regard to the methyl and sulfonate groups. The model accounts for the large widths of the asymmetric S-O stretch modes; however, the external mode region is not well described. Together, these observations suggest that the basic model of four molecules in the primitive unit cell, linked by hydrogen bonding into chains, is correct, but that MSA crystallizes in a different space group than that of trifluoromethanesulfonic acid.

pH-related fluorescence quenching mechanism of pterin derivatives and the effects of 6-site substituents

2018 ◽  
Vol 96 (4) ◽  
pp. 404-410
Author(s):  
Lei Liu ◽  
Bingqing Sun
Keyword(s):  
Density Functional Theory ◽  
Hydrogen Bonding ◽  
Fluorescence Quenching ◽  
Density Functional ◽  
Relaxation Processes ◽  
Quenching Mechanism ◽  
Functional Theory ◽  
Td Dft ◽  
Fluorescence Quenching Mechanism ◽  
Acidic Conditions

2-Amino-4-hydroxypteridine (pterin) and its derivatives serve as photooxidants and exhibit strong fluorescence. When they interact with hydrogen acceptors such as acetate and phosphate, their fluorescences are significantly quenched in acidic conditions (pH 4.9–5.5) but are retained in basic conditions (pH 10.0–10.5). This pH-related fluorescence quenching mechanism of pterin and its derivatives are fully investigated by using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). Pterin and its derivatives are demonstrated to show favorable excited-state proton transfer (ESPT) abilities in acidic conditions that induce the experimentally observed fluorescence quenching. In contrast, the ESPT processes are found to be retarded due to the lack of strong hydrogen-bonding interactions in basic environments, which sustain their fluorescence. Interestingly, these ESPT processes are found to show different site specificities depending on the 6-site substituents. The introduction of electron-donating substituent activates the N1 site, making it the preferred ESPT site. By contrast, the introduction of an electron-withdrawing substituent activates the N5 site, making it the favorable ESPT site. The substitutions of different functional groups are found to affect the locations of acidic centers during the excitation and relaxation processes. This further affects the hydrogen-bonding patterns and ultimately brings site specificity to the ESPT process.

Sign in / Sign up

Export Citation Format

Share Document