Enhancement of Palladium-Porphyrin Room Temperature Phosphorescence by Alkaline Earth Metal in Deoxycholate Aggregates Solution

Room temperature phosphorescence (RTP) of three palladium (Pd)-phorphyrins in air-saturated solution of sodium deoxycholate (NaDC) aggregates was measured. RTP of Pd-mesotetrakis (4-carboxyphenyl) porphyrin (Pd-TCPP) was obviously enhanced in NaDC-aggregates mediated by alkaline earth metal (AEM). Under the same experimental conditions, Ca2+, Ba2+ and Mg2+ induced 200, 90 and 24 times greater enhancement in RTP of Pd-TCPP, respectively. It is ascribed to form the complex of NaDC-aggregate/AEM/Pd-TCPP in the system. The positively charged AEM has a strong capability of coordination with negatively charged carboxyl groups of NaDC and Pd-TCPP. The phosphor Pd-TCPP is confined in rigid NaDC-aggregates/AEM system by the coordination which decreases the probability of collision of phosphor with quenchers such as dissolved oxygen molecules and prolongs the lifetime of the phosphor on the triplet state. Long excited-state lifetimes resulted in great enhancement of Pd-TCPP phosphorescence. Observations by optical microscope showed that specific fan-like structures of NaDC were formed under the influence of AEM. Surface tension measurements supported a close interaction between Ca2+ ions and anion aggregates of NaDC with 1: 1 stoichiometric ratio. Due to its outstanding RTP behavior in NaDC-aggregates induced by Ca2+, Pd-TCPP was used as a RTP probe to detect bovine serum albumin (BSA). A broad linear range from 1.0 x 10(-9) to 9.0 x 10(-7) g mL(-1) was obtained. Detection limit is 2.6 x 10(-11) g mL(-1), the relative standard deviation (n = 6) is 2.3% for 2.0 x 10(-9) g mL(-1) BSA.