Density functional theory (DFT) calculations have been performed to develop a systematic structural analysis of Au 13 L 8 3+ , where L = SCH 3 , SeCH 3 , SCH 2 OCH 3 and S(CH 2) 2 NH 2 , in order to examine the influence of different ligands. Binding energy calculations indicate that the gold core is more stabilized by the ligand in the following sequence S(CH 2) 2 NH 2 > SCH 2 OCH 3 > SeCH 3 > SCH 3. Natural bond orbital (NBO) analysis describes the interaction between the gold and the ligands, showing that the strongest electron donation occurs from a lone pair orbital on the sulfur and selenium atoms to the antibonding acceptor σ * (Au−S) and σ * (Au−Se) orbitals, respectively. The NBO analysis allowed to understand the origin of enhanced stability of the [Au 13 (S(CH 2) 2 NH 2) 8 ] 3+. Time-dependent DFT (TDDFT) calculations have been performed to simulate the optical absorption spectra of Au 13 L 8 3+ in gas phase and under the effect of solvents with different polarities. The absorption spectrum of [Au 13 (S(CH 2) 2 NH 2) 8 ] 3+ shows a spectral profile that differs considerably from the others in gas phase and which is strongly affected by the solvent.
The luminescence of skim milk samples with distinct protein content doped with rhodamine B was investigated. The samples were excited by a nanosecond laser tuned at 532 nm, and the emission was characterized as a random laser. Its features were analyzed as a function of the protein aggregate content. The results showed a linear correlation between the random laser peak intensity and the protein content. This paper proposes a rapid detection photonic method to evaluate the protein content in skim milk based on the intensity of the random laser emission.
A method to evaluate the content of protein in skim milk was proposed, based on the correlation of random laser emission intensity from a solution rhodamine B and skim milk, and its protein content.
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