Liezheng Deng

Improved method for measuring absolute O2(a1Δg) concentration by O2(a1Δg→X3Σg−) IR radiation

We describe an improved technique for measuring the absolute O-2(a(1)Delta) concentration via the quantitative determination of IR radiation from O-2(a(1)Delta(g)-->X(3)Sigma(g)(-)) transition. An exact geometrical optical model was first established, in which the influence of reflection and refraction on the radiation characteristics of a luminous volume source was given full consideration, making possible the accurate calculation of the coupling efficiency between the volume source and a receiving area. Then, an IR radiation receiving apparatus (IRRRA) was constructed and its responsivity (mV/W) to the power of IR radiation calibrated by a tungsten standard lamp. An optical detection system was, in turn, built according to the optical model with fine alignment between the IRRRA and an optical cell. We then demonstrate the procedure to obtain the absolute concentration of O-2(a(1)Delta) flowing through the optical cell from a jet singlet oxygen generator from the signal of the IRRRA, the optical cell volume, and the coupling efficiency between the cell and the IRRRA. Moreover, to verify the accuracy of this method, the absolute O-2(a(1)Delta) concentration was compared to that measured by an established isothermal calorimetry method. Based on the comparison of the O-2(a(1)Delta) concentrations determined by the two methods, the Einstein A-coefficient was estimated as (2.70+/-0.84)x10(-4) s(-1), which agrees with Badgers value of 2.58x10(-4), Spaleks of 2.24x10(-4), Newmans of 2.19x10(-4), and Millers of 2.3x10(-4) within the uncertainty of the experimental techniques. The method advanced in this article is worthwhile for the measurement of absolute O-2(a(1)Delta) concentration in a chemical oxygen iodine laser or a singlet oxygen generator. It can also provide a general technique for the measurement of absolute concentrations of long-lifetime luminous species other than O-2(a(1)Delta)

Singlet oxygen phosphorescence lifetime imaging based on a fluorescence lifetime imaging microscope.

The feasibility of singlet oxygen phosphorescence (SOP) lifetime imaging microscope was studied on a modified fluorescence lifetime imaging microscope (FLIM). SOP results from the infrared radiative transition of O2(a(1)Δg → X(3)Σg(-)) and O2(a(1)Δg) was produced in a C60 powder sample via photosensitization process. To capture the very weak SOP signal, a dichroic mirror was placed between the objective and tube lens of the FLIM and used to divide the luminescence returning from the sample into two beams: the reflected SOP beam and the transmitted photoluminescence of C60 (C60-PL) beam. The C60-PL beam entered the scanner of the FLIM and followed the normal optical path of the FLIM, while the SOP steered clear of the scanner and directly entered a finely designed SOP detection channel. Confocal C60-PL images and nonconfocal SOP images were then simultaneously obtained by using laser-scanning mode. Experimental results show that (1) under laser-scanning mode, the obstacle to confocal SOP imaging is the infrared-incompatible scanner, which can be solved by using an infrared-compatible scanner. Confocal SOP imaging is also expected to be realized under stage-scanning mode when the laser beam is parked and meanwhile a pinhole is added into the SOP detection channel. (2) A great challenge to SOP imaging is its extraordinarily long imaging time, and selecting only a few interesting points from fluorescence images to measure their SOP time-dependent traces may be a correct compromise.

An irradiation density dependent energy relaxation in plant photosystem II antenna assembly

Plant photosystem II (PSII) is a multicomponent pigment-protein complex that harvests sunlight via pigments photoexcitation, and converts light energy into chemical energy. Against high light induced photodamage, excess light absorption of antenna pigments triggers the operation of photoprotection mechanism in plant PSII. Non-photochemical energy relaxation as a major photoprotection way is essentially correlated to the excess light absorption. Here we investigate the energy relaxation of plant PSII complexes with varying incident light density, by performing steady-state and transient chlorophyll fluorescence measurements of the grana membranes (called as BBY), functional moiety PSII reaction center and isolated light-harvesting complex LHCII under excess light irradiation. Based on the chlorophyll fluorescence decays of these samples, it is found that an irradiation density dependent energy relaxation occurs in the LHCII assemblies, especially in the antenna assembly of PSII supercomplexes in grana membrane, when irradiation increases to somewhat higher density levels. Correspondingly, the average chlorophyll fluorescence lifetime of the highly isolated BBY fragments gradually decreases from ~1680 to ~1360 ps with increasing the irradiation density from 6.1×10(9) to 5.5×10(10) photon cm(-2) pulse(-1). Analysis of the relation of fluorescence decay change to the aggregation extent of LHCIIs suggests that a dense arrangement of trimeric LHCIIs is likely the structural base for the occurrence of this irradiation density dependent energy relaxation. Once altering the irradiation density, this energy relaxation is quickly reversible, implying that it may play an important role in photoprotection of plant PSII.

Experimental and Theoretical Study of Centrifugal Flow Singlet Oxygen Generator

We designed and realized a novel centrifugal flow Singlet oxygen generator (CFSOG) that was originally proposed by Emanuel [Proc. SPIE 5448 (2004) 233]. In this device, singlet oxygen O(2)((1)Delta) is generated by the reaction of gaseous Cl(2) with aqueous basic hydrogen peroxide (BHP) that flows rapidly along an arc-shaped concave to form a rotating liquid layer. so that the nascent O(2)((1)Delta) generated in the liquid phase will be separated from it quickly to suppress the collision quenching loss of O(2)((1)Delta) with the help of the enormous centrifugal force produced by the rotating fluid. Our preliminary experiment shows that, because the specific reactive Surface area of this novel singlet oxygen generator (SOG) is much lamer than that of the jet-type SOG normally used in current chemical oxygen-iodine laser (COIL). enhanced performance of O(2)((1)Delta) yield similar to 60%. O(2)((1)Delta) partial pressure similar to 31 Torr, and an extremely high chlorine utilization within 96-98% have been realized.

Production of singlet oxygen by the reaction of non-basic hydrogen peroxide with chlorine gas

Non-basic hydrogen peroxide was found to be very easy to react with Cl(2) to produce singlet oxygen O(2)(a(1)Δ(g)) (i.e. the molecular oxygen in its first electronic excited state) when an H(+) absorbent such as C(5)H(5)N, CH(3)COONH(4), HCOONH(4) or NH(4)F was added into H(2)O(2) aqueous solution, and the long concealed fact that molecular H(2)O(2) can react with Cl(2) to produce O(2)(a(1)Δ(g)) was then uncovered. It is only when an H(+) absorbent has provided a stronger base than H(2)O to absorb the H(+) produced during the reaction that O(2)(a(1)Δ(g)) can be produced.

O2(1Δ) Yield Measurement by Raman Spectroscopy With Elimination of Chlorine Fluorescence Interference

Deleterious chlorine fluorescence was found to occur at the same frequency as the Raman scattering of O2(1Δ) and O2(3Σ), seriously affecting the O2(1Δ) yield measurement in the reaction of chlorine with basic hydrogen peroxide by use of the Raman spectroscopy technique. To solve this problem we have taken advantage of the fact that Raman radiation is always strongly polarized while fluorescence is essentially non-polarized in a gaseous medium. When chlorine utilization of a singlet oxygen generator is 88%, O2(1Δ) yield reaches (42.4±7.4)% with the effect of chlorine fluorescence completely eliminated.