Lixin Zang

Comparison study on the influence of the central metal ions in palladium(II)- and gadolinium(III)-porphyrins for phosphorescence-based oxygen sensing

The luminescence and oxygen sensing properties of a series of palladium(II)- and gadolinium(III)-porphyrins were evaluated and compared. Spectral analysis indicates that absorption and luminescence of Gd-porphyrins are red-shifted compared to those of Pd-porphyrins. This demonstrates that the energy levels of excited states in Gd-porphyrins are lower than those in the corresponding Pd-porphyrins. Phosphorescence quantum yield of Pd-hematoporphyrin monomethyl ether (HMME) was about 3-fold higher than that of Gd-HMME due to the decreased non-radiative decay rate of triplet states in Pd-HMME, which was confirmed by the longer phosphorescence lifetime of Pd-HMME. This is attributed to the higher first excited triplet state (T1) in Pd-HMME as compared to that of Gd-HMME. However, the phosphorescence intensity and lifetime responses of Gd-HMME to oxygen were larger than those of Pd-HMME. To understand this difference, oxygen quenching constants (kq) of Gd- and Pd-HMME were evaluated and were found to be 4972.9 and 26.4 s−1, respectively. The huge difference in kq between the two species is responsible for their disparate oxygen responses. We suggest that the greater kq of Gd-HMME results from the better energy matching between its T1 (12 658–14 006 cm−1) and the second excited state (13 123 cm−1) of oxygen, which was demonstrated by the higher singlet oxygen quantum yield of Gd-HMME. The same phenomena (spectral red-shifts, lower phosphorescence quantum yields, shorter lifetimes, and larger oxygen responses) were also observed upon substituting Pd(II) by Gd(III) in other porphyrins studied in this work.

Photophysical properties of sinoporphyrin sodium and explanation of its high photo-activity

Sinoporphyrin sodium (DVDMS) is a novel photosensitizer with high photodynamic therapy (PDT) effect. Reasons for its high photo-activity were investigated according to the study of photophysical characteristics of DVDMS. Extinction coefficients (e) of DVDMS at 405 nm and 630 nm are 4.36 × 105 and 1.84 × 104 M−1.cm−1; fluorescence quantum yield (ΦF) is 0.026; quantum yield of lowest triplet state formation is 0.94 and singlet oxygen quantum yield (ΦΔ) is 0.92. Although ΦΔ of DVDMS is only 10% higher than that of Photofrin®; (0.83), the extinction coefficient of DVDMS at 630 nm is 10-fold greater than that of Photofrin®;. This leads to its higher singlet oxygen generation efficiency (eΦΔ). The higher eΦΔ of DVDMS can result in an effective reduction of dosage (1/10 of Photofrin®;) reaching the same cytotoxic effect as Photofrin®;. Even though ΦF is approximately equal to that of Photofrin®;, brightness (eΦF) of DVDMS is 10-fold greater than that of Photofrin®; because of the 10-fold greater extinction coeff...

The effect of imidazole on the enhancement of gadolinium-porphyrin phosphorescence at room temperature

A mechanism for the enhanced room-temperature phosphorescence (RTP) of gadolinium-coordinated hematoporphyrin monomethyl ether (Gd-HMME) in the presence of imidazole and free gadolinium ions (Gd3+) is revealed. Imidazole, the molten solvent used in the synthesis of Gd-HMME, was effective in enhancing the Gd-HMME RTP. In the presence of imidazole, further enhancement of the Gd-HMME RTP was observed upon adding Gd3+. Overall, a 40-fold enhancement of Gd-HMME RTP intensity was achieved by adding both imidazole and Gd3+. In addition, there was an increase in the RTP lifetime. Through spectroscopic analysis, we deduced that a protective medium is formed by the imidazole and the degree of this protection is further increased by Gd3+. The protective medium enhances the Gd-HMME RTP by partially inhibiting energy transfer from the lowest triplet state of Gd-HMME to oxygen. This was demonstrated by the presence of lower levels of singlet oxygen in the Gd-HMME solution after the addition of imidazole. These results indicate that imidazole could have potential application as an RTP enhancer or triplet state protector.

Application of fluorescence spectroscopy and imaging in the detection of a photosensitizer in photodynamic therapy

Photodynamic therapy (PDT) is currently an advanced optical technology in medical applications. However, the application of PDT is limited by the detection of photosensitizers. This work focuses on the application of fluorescence spectroscopy and imaging in the detection of an effective photosenzitizer, hematoporphyrin monomethyl ether (HMME). Optical properties of HMME were measured and analyzed based on its absorption and fluorescence spectra. The production mechanism of its fluorescence emission was analyzed. The detection device for HMME based on fluorescence spectroscopy was designed. Ratiometric method was applied to eliminate the influence of intensity change of excitation sources, fluctuates of excitation sources and photo detectors, and background emissions. The detection limit of this device is 6 μg/L, and it was successfully applied to the diagnosis of the metabolism of HMME in the esophageal cancer cells. To overcome the limitation of the point measurement using fluorescence spectroscopy, a two-dimensional (2D) fluorescence imaging system was established. The algorithm of the 2D fluorescence imaging system is deduced according to the fluorescence ratiometric method using bandpass filters. The method of multiple pixel point addition (MPPA) was used to eliminate fluctuates of signals. Using the method of MPPA, SNR was improved by about 30 times. The detection limit of this imaging system is 1.9 μg/L. Our systems can be used in the detection of porphyrins to improve the PDT effect.

Note: Measuring instrument of singlet oxygen quantum yield in photodynamic effects

Using diphenylisobenzofuran (C20H14O) as a singlet oxygen (1O2) reporter, a comparison method, which can be used to measure the singlet oxygen quantum yield (ΦΔ) of the photosensitizer quantitatively, is presented in this paper. Based on this method, an automatic measuring instrument of singlet oxygen quantum yield is developed. The singlet oxygen quantum yield of the photosensitizer hermimether and aloe-emodin is measured. It is found that the measuring results are identical to the existing ones, which verifies the validity of the measuring instrument.

Studying the origin of fluorescence emissions of neodymium porphyrin based on the analysis of energy level structure

This paper studies the origin of fluorescence emissions of metalloporphyrins. The absorption spectrum of neodymium-coordinated hematoporphyrin monomethyl ether (Nd-HMME) was found to have four Q bands, which is different from the accepted knowledge (two Q bands). The absorbance of Nd-HMME was comparable to the corresponding absorbance of HMME at wavelengths of 538 nm and 572 nm, but the absorbance of Nd-HMME at wavelengths of 502 nm and 622 nm was approximately 1/30 of that at 572 nm. The doping of Nd3+ enhanced the symmetry of HMME, and led to changes in energy level properties. Moreover, Nd-HMME still exhibited two fluorescence peaks at 624 nm and 686 nm, similar to HMME, which can be explained by the observation of a weak absorption peak of Nd-HMME at 622 nm.