The citrate reduction method of synthesis of gold nanoparticles (AuNP) is standardized with the assistance of instruments like spectrophotometer and TEM. A correlation has been developed between the particle diameter ...The citrate reduction method of synthesis of gold nanoparticles (AuNP) is standardized with the assistance of instruments like spectrophotometer and TEM. A correlation has been developed between the particle diameter and the fractional concentration of the reductant. This enables one to assess the diameter of the AuNP to be synthesized, in advance, from the composition of the reaction mixture and the diameter of the synthesized particles can be confirmed simply from spectrophotometry. Further, it has been demonstrated that the synthesized AuNPs serve as excellent acceptors for a super-efficient energy transfer (ET) from the donor coumarin 153, leading to a quenching of fluorescence of the latter. The Stern-Volmer constants determined from the fluorescence lifetimes are in the range 107 - 109 mol-1·dm3 and are orders of magnitude higher than the normal photochemical quenching processes. The energy transfer efficiency increases radically with an increase in the size of the metal nanoparticle. The highly efficient energy transfer and the variation of the efficiency of the ET process with a variation of the particle size is ascribed to a large enhancement in the extinction coefficient and an increase in the spectral overlap between the plasmon absorption band of AuNPs and the fluorescence spectrum of C153 with an increase in the size of the nanoparticles. The impact of the work remains in providing a demonstration of a super quenching effect of the AuNPs and projects that they can be exploited for developing biosensors with high degree of sensitivity, if tagged to the biomacromolecules.展开更多
Investigating the impact of microhydration on the excited-states and electronic excitation properties of biomolecules has remained one of the important yet challenging aspects of science because of the complexity of d...Investigating the impact of microhydration on the excited-states and electronic excitation properties of biomolecules has remained one of the important yet challenging aspects of science because of the complexity of developing models. However, with the advent of computational chemistry methods such as TD-DFT, many useful insights about the electronic excitation energy and excited-state nature of biomolecules can be explored. Accordingly, in our study, we have incorporated the TD-DFT/wB97XD/cc-pVTZ method to study the excited state properties of N-acetyl phenylalanine amide (NAPA-A(H<sub>2</sub>O) <sub>n</sub>) (n = 1 to 4) clusters from ground to the tenth lowest gaseous singlet excited state. We found that the C=O bond length gradually increases both in N-terminal amide and C-terminal amide after the sequential addition of water molecules because of intermolecular H-bonding and this intermolecular H-bonding becomes weaker after the sequential addition of H<sub>2</sub>O molecules. The UV absorption maxima of NAPA-A (H<sub>2</sub>O)<sub>n</sub> (n = 1 - 4) clusters consisted of two peaks that are S<sub>5</sub>←S<sub>0</sub> (1<sup>st</sup> absorption) and S<sub>6</sub>←S<sub>0</sub> (2<sup>nd</sup> absorption) excitations. The first absorption maxima were blue-shifted with the increase in oscillator strength. This means that strong H-bonds reduce the charge transfer and make clusters more rigid. On the other hand, the second absorption maxima were red-shifted with the decrease in oscillator strength. In the ECD spectra, the negative bands indicate the presence of an amide bond and L-configuration of micro hydrated NAPA-A clusters. Finally, our calculated absorption and fluorescence energy confirm that all the NAPA-A (H<sub>2</sub>O) <sub>n</sub> (n = 0 - 4) clusters revert to the ground state from the fluorescent state by emitting around 5.490 eV of light.展开更多
文摘The citrate reduction method of synthesis of gold nanoparticles (AuNP) is standardized with the assistance of instruments like spectrophotometer and TEM. A correlation has been developed between the particle diameter and the fractional concentration of the reductant. This enables one to assess the diameter of the AuNP to be synthesized, in advance, from the composition of the reaction mixture and the diameter of the synthesized particles can be confirmed simply from spectrophotometry. Further, it has been demonstrated that the synthesized AuNPs serve as excellent acceptors for a super-efficient energy transfer (ET) from the donor coumarin 153, leading to a quenching of fluorescence of the latter. The Stern-Volmer constants determined from the fluorescence lifetimes are in the range 107 - 109 mol-1·dm3 and are orders of magnitude higher than the normal photochemical quenching processes. The energy transfer efficiency increases radically with an increase in the size of the metal nanoparticle. The highly efficient energy transfer and the variation of the efficiency of the ET process with a variation of the particle size is ascribed to a large enhancement in the extinction coefficient and an increase in the spectral overlap between the plasmon absorption band of AuNPs and the fluorescence spectrum of C153 with an increase in the size of the nanoparticles. The impact of the work remains in providing a demonstration of a super quenching effect of the AuNPs and projects that they can be exploited for developing biosensors with high degree of sensitivity, if tagged to the biomacromolecules.
文摘Investigating the impact of microhydration on the excited-states and electronic excitation properties of biomolecules has remained one of the important yet challenging aspects of science because of the complexity of developing models. However, with the advent of computational chemistry methods such as TD-DFT, many useful insights about the electronic excitation energy and excited-state nature of biomolecules can be explored. Accordingly, in our study, we have incorporated the TD-DFT/wB97XD/cc-pVTZ method to study the excited state properties of N-acetyl phenylalanine amide (NAPA-A(H<sub>2</sub>O) <sub>n</sub>) (n = 1 to 4) clusters from ground to the tenth lowest gaseous singlet excited state. We found that the C=O bond length gradually increases both in N-terminal amide and C-terminal amide after the sequential addition of water molecules because of intermolecular H-bonding and this intermolecular H-bonding becomes weaker after the sequential addition of H<sub>2</sub>O molecules. The UV absorption maxima of NAPA-A (H<sub>2</sub>O)<sub>n</sub> (n = 1 - 4) clusters consisted of two peaks that are S<sub>5</sub>←S<sub>0</sub> (1<sup>st</sup> absorption) and S<sub>6</sub>←S<sub>0</sub> (2<sup>nd</sup> absorption) excitations. The first absorption maxima were blue-shifted with the increase in oscillator strength. This means that strong H-bonds reduce the charge transfer and make clusters more rigid. On the other hand, the second absorption maxima were red-shifted with the decrease in oscillator strength. In the ECD spectra, the negative bands indicate the presence of an amide bond and L-configuration of micro hydrated NAPA-A clusters. Finally, our calculated absorption and fluorescence energy confirm that all the NAPA-A (H<sub>2</sub>O) <sub>n</sub> (n = 0 - 4) clusters revert to the ground state from the fluorescent state by emitting around 5.490 eV of light.
