Femtosecond X-ray absorption spectroscopy of pyrazine at the nitrogen K-edge: on the validity of the Lorentzian limit

We calculate the femtosecond X-ray absorption spectrum of pyrazine at the nitrogen K-edge including the wavepacket dynamics in both the valence and core-excited state manifolds. We do not invoke the widely used short-time (or Lorentzian) approximation which neglects the nuclear dynamics after the X-ray probe excitation. Instead, we calculate the X-ray-induced polarization in the time-domain where the optical pump as well as X-ray probe pulses are explicitly described. While the non-adiabatic population transfer following the optical excitation is well reproduced in the Lorentzian limit the transient X-ray absorption spectra obtained under this approximation lack some vibronic features, even when considering the short core-hole lifetime of nitrogen. We further demonstrate the effect of an increasingly longer pulse on the observed photo-triggered wavepacket dynamics which are blurred to the point that the X-ray probe response becomes effectively time-independent.

Sources of Polycyclic Aromatic Hydrocarbons in South China Sea Short Core Sediments Off Southern Part Terengganu, Malaysia and Multivariate Statistics Approaches

Sediment cores from the southern South China Sea off the Terengganu coast were analyzed for polycyclic aromatic hydrocarbons (PAH s) and perylene. The concentrations of total 17 PAH (TPAHs) and perylene varied between 5.45-27.7 ng/g and 0.51-7.77 ng/g, respectively. Analyses of variance showed significant differences between the stations, but not in sub-bottom depths at the 0.05 level. The PAH cross plots showed a predominance of pyrogenic over petrogenic PAH s. Principal component analysis (PCA) showed clustered PAH s that are correlated with total organic carbon (TOC), indicating the importance of surface runoff via fluvial transport for contributing these PAH s to the coastal environment of the study area. Overall, the concentrations of PAH s in the study area are considered to be in the low range, not exceeding the 100 ng/g mark.

O-linked mucin-type glycosylation regulates the transcriptional programme downstream of EGFR

Aberrant mucin type O-linked glycosylation is a common occurrence in cancer where the upregulation of sialyltransferases is often seen leading to early termination of O-glycan chains. Mucin type O-linked glycosylation is not limited to mucins and occurs on many cell surface glycoproteins including EGFR, where the number of sites can be limited. Upon EGF ligation, EGFR induces a signalling cascade and may also translocate to the nucleus where it directly regulates gene transcription, a process modulated by Galectin-3 and MUC1 in some cancers. Here we show that upon EGF binding, breast cancer cells carrying different O-glycans respond by transcribing different gene expression signatures. MMP10, the principal gene upregulated when cells carrying sialylated core 1 glycans were stimulated with EGF, is also upregulated in ER positive breast carcinoma reported to express high levels of ST3Gal1 and hence mainly core 1 sialylated O-glycans. In contrast, isogenic cells engineered to carry core 2 glycans upregulate CX3CL1 and FGFBP1 and these genes are upregulated in ER negative breast carcinomas, also known to express longer core 2 O-glycans. Changes in O-glycosylation did not significantly alter signal transduction downstream of EGFR in core 1 or core 2 O-glycan expressing cells. However, striking changes were observed in the formation of an EGFR/galectin-3/MUC1/β-catenin complex at the cell surface that is present in cells carrying short core 1-based O-glycans but absent in core 2 carrying cells.

O-linked mucin-type glycosylation regulates the transcriptional programme downstream of EGFR in breast cancer

ABSTRACTAberrant mucin type O-linked glycosylation is a common occurrence in cancer. This type of O-linked glycosylation is not limited to mucins but can occur on many cell surface glycoproteins where only a small number of sites may be present. Upon EGF ligation, EGFR induces a signaling cascade but can also translocate to the nucleus where it can directly regulate gene transcription. Here we show that upon EGF binding, human breast cancer cells carrying different O-linked glycans respond by transcribing different gene expression signatures. This is not a result of changes in signal transduction but due to the differential nuclear translocation of EGFR in the two glyco-phenotypes. This is regulated by the formation of an EGFR/galectin-3/MUC1/β-catenin complex at the cell surface that is present in cells carrying short core-1-based O-glycans characteristic of tumour cells but absent in core-2-carrying cells.