[Determination of pathological margin of hypopharyngeal cancer by terahertz time-domain spectroscopy system]

Objective:To investigate the accuracy of the terahertz system in differentiating hypopharyngeal cancer from normal tissue and its role in determining the pathological incised margin of hypopharyngeal cancer. Method:The transplantation model of hypopharyngeal cancer in 5-week-old male BALB/c nude mice were established by subcutaneous injection. The obtained transplanted tumor specimens were pathologically diagnosed to determine the extent of tumor tissue. Tumor tissue, normal tissue and paracellular tissue of transplantation tumor were scanned by terahertz time-domain spectroscopy. The differential spectral data were obtained through the detection of frozen tissue sections and paraffin tissue sections, respectively. The results were compared by t-test. Result:The tarahertz absorption coefficient of tumor tissues was higher than that of normal tissues, and the difference was statistically significant when the detection frequency was greater than 0.48 THz in frozen sections（P<0.05）. In the paraffin sections, the difference was statistically significant within the effective spectrum range of 0.2-1.6 THz（P<0.01）. The difference of refractive index between tumor tissue and normal tissue was significant in specimens treated in two ways（P<0.01）. The absorption coefficient of adjacent tissue felt between that of normal tissue and tumor tissue. Conclusion:Terahertz technology can distinguish tumor tissues and normal tissues accurately, and can detect the spectral changes in adjacent tissues sensitively. Therefore, terahertz technology may become another tool for the judgment of pathologic margin.

How intermolecular interactions influence electronic absorption spectra: insights from the molecular packing of uracil in condensed phases

Intermolecular interactions in terms of molecular packing are crucial for the investigation of the absorption spectra of uracil in different environments.

Dynamics of the excited-state hydrogen transfer in a (dG)·(dC) homopolymer: intrinsic photostability of DNA

The intrinsic photostability of nucleic acids is intimately related to evolution of life, while its understanding at the molecular and electronic levels remains a challenge for modern science. Among the different decay pathways proposed in the last two decades, the excited-state hydrogen transfer between guanine-cytosine base pairs has been identified as an efficient non-reactive channel to dissipate the excess of energy provided by light absorption. The present work studies the dynamics of such phenomena taking place in a (dG)·(dC) B-DNA homopolymer in water solution using state-of-the-art molecular modelling and simulation methods. A dynamic effect that boosts the photostability of the inter-strand hydrogen atom transfers, inherent to the Watson-Crick base pairing, is unveiled and ascribed to the energy released during the proton transfer step. Our results also reveal a novel mechanism of DNA decay named four proton transfer (FPT), in which two protons of two adjacent G-C base pairs are transferred to form a biradical zwitterionic intermediate. Decay of the latter intermediate to the ground state triggers the transfer of the protons back to the guanine molecules recovering the Watson-Crick structure of the tetramer. This FPT process is activated by the close interaction of a nearby Na+ counterion with the oxygen atoms of the guanine nucleobases and hence represents a photostable channel operative in natural nucleic acids.