The validation of molecular interaction among dimer chitosan with urea and creatinine using density functional theory: In application for hemodyalisis membrane.

The formation of chitosan dimer and its interaction with urea and creatinine have been investigated at the density functional theory (DFT) level (B3LYP-D3/6-31++G**) to study the transport phenomena in hemodialysis membrane. The interaction energy of chitosan-creatinine and chitosan-urea complexes are in range -4 kcal/mol < interaction energy <-20 kcal/mol which were classified in medium hydrogen bond interaction. The chemical reactivity parameter proved that creatinine was more electrophilic and easier to bind chitosan than urea. The energy gap of HOMO-LUMO of chitosan-creatinine complex was lower than chitosan-urea complex that indicating chitosan-creatinine complex was more reactive and easier to transport electron than chitosan-urea complex. Moreover, the natural bond orbital (NBO) analysis showed a high contribution of hydrogen bond between chitosan-creatinine and chitosan-urea. The chitosan-creatinine interaction has a stronger hydrogen bond than chitosan-urea through the interaction O18-H34....N56 with stabilizing energy = -13 kcal/mol. The quantum theory atom in molecule (QTAIM) also supported NBO data. All data presented that creatinine can make hydrogen bond interaction stronger with chitosan than urea, that indicated creatinine easier to transport in the chitosan membrane than urea during hemodialysis process.

A first principles study of fluorescence quenching in rhodamine B dimers: how can quenching occur in dimeric species?

Rhodamine B (RhB) is widely used in chemistry and biology due to its high fluorescence quantum yield. In high concentrations, the quantum yield of fluorescence decreases considerably which is attributed to the formation of RhB dimers. In the present work, a possible mechanism of fluorescence quenching in RhB dimers is investigated with the use of time-dependent density functional theory (TD-DFT). The excited states of monomeric and dimeric RhB species have been studied both in the gas phase and in solution with the use of the TD-BLYP/6-311G* method. Results of the calculations suggest that quenching can occur via an internal conversion to the charge-transfer singlet excited states, which can be followed by an intersystem crossing with the charge-transfer triplet states. A possibility to reduce the loss of the fluorescence quantum yield is discussed.