CdSe/CdS quantum dots (QDs) capped with L-cysteine can provide an effective platform for the interactions with bovine serum albumin (BSA). In this study, absorption and fluorescence (FL) spectroscopy were used to study the binding reactions of QDs with BSA, respectively. The binding constant (≈10(4) M(-1)) from FL quenching method matches well with that determined from the absorption spectral changes. The modified Stern-Volmer quenching constant (5.23 × 10(4), 5.22 × 10(4), and 4.90 × 10(4) M(-1)) and the binding sites (≈1) at different temperatures (304 K, 309 K, and 314 K) and corresponding thermodynamic parameters were calculated (∆G < 0, ∆H < 0, and ∆S < 0). The results show the quenching constant is inversely correlated with temperature. It indicates the quenching mechanism is the static quenching in nature rather than dynamic quenching. The negative values of free energy (∆G < 0) suggest that the binding process is spontaneous, ∆H < 0 and ∆S < 0 suggest that the binding of QDs to BSA is enthalpy-driven. The enthalpy and entropy changes for the formation of ground state complex depend on the capping agent of QDs and the protein types. Furthermore, the reaction forces were discussed between QDs and BSA, and the results show hydrogen bonds and van der Waals interactions play a major role in the binding reaction.
Positron annihilation lifetime spectra are measured in uniaxially drawn polyethylene (PE) at room temperature as function of deformation ϵ from 0 to 190%. The positron annihilation parameters are very sensitive to the microstructural changes of PE during the drawing process. In the elastic stage (ϵ = 0 to 20%), the amount and size of voids in amorphous regions and the size of defects in crystalline regions increase drastically with increasing deformation and reach a maximum at the yield point. In the strain softening stage (ϵ = to 40%), the fractional free volume f is nearly constant. When ϵ < 40%, i.e. in the plastic stage, the fractional free volume f continuously decreases, which shows that the degree of crystallinity increases owing to the orientation of chains and strain‐induced crystallization. continuously decreases, which shows that the degree of crystallinity increases owing to the orientation of chains and strain‐induced crystallization.
The time‐dependent variation in ortho‐positronium (o‐Ps) intensity I3 has been investigated during long‐term positron lifetime measurements in polymers. It has been found that I3 in polar polymers, e.g. poly(ether urethane), almost keeps constant, while in nonpolar polymers, high‐density polyethylene and polypropylene, I3 decreases as a function of positron source exposure time. The formation of Ps‐inhibiting species induced by the positron source radiation might give rise to the decrease of the o‐Ps intensity I3.
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