Abrupt change reflected by the van Hove singularity in the optical spectra of CaMn2P2.

The trigonal CaAl2Si2-type structure CaMn2P2has been reported undergoing an exotic first order phase transition at the critical temperatureTN=69.5K. In this paper, we present the optical spectra for theab-plane of CaMn2P2single crystal from 300 K to 10 K for the first time. In the real part of the optical conductivity spectraσ1(ω), a direct gap could be determined at all temperatures without any Drude term visible, i.e., the sample goes through the first order phase transition from one insulator state to the other insulator state. At higher energy, an asymmetric sharp interband transition peak appears in allσ1(ω) spectra, which indicates a divergence of the joint density of states. This sharp peak could be well described by the two dimensional van Hove singularity function. In particular, this peak is very sensitive to the first order phase transition, especially the peak positionEtwhose the most prominent blue shift occurs only when the first order transition happens. Our data and analysis reveal that the first order phase transition leads to a weak partial re-normalization of the band structure. Our study will be useful in further investigations about the mechanism of the first order phase transition in the insulator.

Effects of pheophorbide a-mediated photodynamic therapy on proliferation and metastasis of human prostate cancer cells.

OBJECTIVE: To observe the effects of pheophorbide a-mediated photodynamic therapy (Pa-PDT) on the in vitro proliferation, apoptosis, invasion and metastasis of human prostate cancer PC-3 cells and to investigate its possible mechanism. MATERIALS AND METHODS: Pa-PDT in gradient concentrations (0 µM, 0.25 µM, 0.5 µM, 1 µM, 2 µM, and 4 µM) were used to act on PC-3 cells; the cell proliferation in each group was detected via methyl thiazolyl tetrazolium (MTT) assay and clone formation assay, and the cell apoptosis was detected via Hochst33258 staining and Annexin V/propidium iodide (PI) double labeling. Moreover, the effects of Pa-PDT on invasion and proliferation of PC-3 cells were observed via wound healing assay and transwell chamber assay. Finally, the expressions of apoptosis-related proteins, epithelial-mesenchymal transition (EMT)-related proteins and matrix metalloproteinases (MMPs) in each group were detected after treatment by Western blotting. RESULTS: MTT and clone formation assays showed that Pa-PDT could inhibit the proliferation of PC-3 cells in a dose-dependent manner. The results of apoptosis assay revealed that Pa-PDT could significantly promote the apoptosis of PC-3 cells, obviously up-regulate the expressions of pro-apoptotic proteins, such as B-cell lymphoma-2-associated X protein (BAX), Caspase-3 and poly adenosine diphosphate-ribose polymerase (PARP), and inhibit the expression of Bcl-2. Besides, the wound healing assay and Transwell chamber assay showed that Pa-PDT could inhibit the invasion and metastasis capacities of PC-3 cells, whose relevant mechanisms were related to the fact that Pa-PDT inhibited the EMT process and down-regulated the expressions of MMPs in PC-3 cells. CONCLUSIONS: Pa-PDT can inhibit the proliferation and promote the apoptosis of PC-3 cells. Moreover, it can also inhibit the invasion and metastasis capacities of PC-3 cells via inhibiting the EMT process and down-regulating the expressions of MMPs.