A comparative study of thermal radiation model in Chinese solar greenhouse.

The performance of three widely used thermal radiation models, the P-1 model, the surface-to-surface (S2S) model and the Discrete-Ordinates (DO) model, were evaluated for simulation temperature in Chinses solar greenhouse. The thermal radiation models were evaluated by comparing the numerical results with experimental data at representative points in the CSG. For indoor rear wall, the indoor soil and indoor air, the models showed good agreement between the experimental data and the simulated results correspond to P1, S2S and DO respectively. This work provides information for simulate greenhouse temperature and use specific radiation models for the most suitable thermal environment for crop growth.

Ultrafast Förster resonance energy transfer between tyrosine and tryptophan: potential contributions to protein-water dynamics measurements.

Ultrafast Förster Resonance Energy Transfer (FRET) between Tyrosine (Tyr, Y) and Tryptophan (Trp, W) in the model peptides Trp-(Pro)n-Tyr (WPnY) has been investigated using a femtosecond up-conversion spectrophotofluorometer. The ultrafast energy transfer process (<100 ps) in short peptides (WY, WPY and WP2Y) has been resolved. In fact, this FRET rate is found to be mixed with the rates of solvent relaxation (SR), ultrafast population decay (QSSQ) and other lifetime components. To further dissect and analyze the FRET, a spectral working model is constructed, and the contribution of a FRET lifetime is separated by reconciling the shapes of decay associated spectra (DAS). Surprisingly, FRET efficiency did not decrease monotonically with the growth of the peptide chain (as expected) but increased first and then decreased. The highest FRET efficiency occurred in peptide WPY. The kinetic results have been accompanied with molecular dynamics simulations that reconcile and explain this strange phenomenon: due to the strong interaction between amino acids, the distance between the donor and receptor in peptide WPY is actually closest, resulting in the fastest FRET. In addition, the FRET lifetimes (τcal) were estimated within the molecular dynamics simulations, and they were consistent with the lifetimes (τexp) separated out by the experimental measurements and the DAS working model. This benchmark study has implications for both previous and future studies of protein ultrafast dynamics. The approach taken can be generalized for the study of proximate tyrosine and tryptophan in proteins and it suggests spectral strategies for extracting mixed rates in other complex FRET problems.

Excited State Dynamics of Methylated Guanosine Derivatives Revealed by Femtosecond Time-resolved Spectroscopy.

Methylated DNA/RNA nucleobases are important epigenetic marks in living species and play an important role for targeted therapies. Moreover, methylation could bring significant changes to the photo-stability of nucleic acid, leading these sites become mutational hotspots for disease such as skin cancer. While a number of studies have demonstrated the relationship between excited state dynamics and the biological function of methylated cytosine in DNA, investigations aimed at unraveling the excited state dynamics of methylated guanosine in RNA have been largely overlooked. In this work, influence of methylation on the excited state dynamics of guanosine is studied by using femtosecond time-resolved spectroscopy. Our results suggest that the effect of methyl substitution on the photophysical properties of guanosine is position sensitive. N1-methylguanosine shows very similar excited state dynamics as that in guanosine, while almost one order of magnitude longer lifetime of the La state is observed in N2, N2-dimethylguanosine. Notably, N7-methylation can lead to a new minimum on the La state and the excited state lifetime is two orders of magnitude longer than that of guanosine. These findings not only help understanding excited state dynamics of methylated guanosines, but also lay the foundation for further studying DNA/RNA strands incorporated with these bases.

Ultrafast Fluorescence Spectroscopy via Upconversion and Its Applications in Biophysics.

In this review, the experimental set-up and functional characteristics of single-wavelength and broad-band femtosecond upconversion spectrophotofluorometers developed in our laboratory are described. We discuss applications of this technique to biophysical problems, such as ultrafast fluorescence quenching and solvation dynamics of tryptophan, peptides, proteins, reduced nicotinamide adenine dinucleotide (NADH), and nucleic acids. In the tryptophan dynamics field, especially for proteins, two types of solvation dynamics on different time scales have been well explored: ~1 ps for bulk water, and tens of picoseconds for "biological water", a term that combines effects of water and macromolecule dynamics. In addition, some proteins also show quasi-static self-quenching (QSSQ) phenomena. Interestingly, in our more recent work, we also find that similar mixtures of quenching and solvation dynamics occur for the metabolic cofactor NADH. In this review, we add a brief overview of the emerging development of fluorescent RNA aptamers and their potential application to live cell imaging, while noting how ultrafast measurement may speed their optimization.

Dehydrogenase Binding Sites Abolish the "Dark" Fraction of NADH: Implication for Metabolic Sensing via FLIM.

The fluorescence of dinucleotide NADH has been exploited for decades to determine the redox state of cells and tissues in vivo and in vitro. Particularly, nanosecond (ns) fluorescence lifetime imaging microscopy (FLIM) of NADH (in free vs bound forms) has recently offered a label-free readout of mitochondrial function and allowed the different "pools" of NADH to be distinguished in living cells. In this study, the ultrafast fluorescence dynamics of NADH-dehydrogenase (MDH/LDH) complexes have been investigated by using both a femtosecond (fs) upconversion spectrophotofluorometer and a picosecond (ps) time-correlated single photon counting (TCSPC) apparatus. With these enhanced time-resolved tools, a few-picosecond decay process with a signatory spectrum was indeed found for bound NADH, and it can best be ascribed to the solvent relaxation originating in "bulk water". However, it is quite unlike our previously discovered ultrafast "dark" component (∼26 ps) that is prominent in free NADH (Chemical Physics Letters 2019, 726, 18-21). For these two critical protein-bound NADH exemplars, the decay transients lack the ultrafast quenching that creates the "dark" subpopulation of free NADH. Therefore, we infer that the apparent ratio of free to bound NADH recovered by ordinary (>50 ps) FLIM methods may be low, since the "dark" molecule subpopulation (lifetime too short for conventional FLIM), which effectively hides about a quarter of free molecules, is not present in the dehydrogenase-bound state.