Fiber-based 1150-nm femtosecond laser source for the minimally invasive harmonic generation microscopy.

Harmonic generation microscopy (HGM) has become one unique tool of optical virtual biopsy for the diagnosis of cancer and the in vivo cytometry of leukocytes. Without labeling, HGM can reveal the submicron features of tissues and cells in vivo. For deep imaging depth and minimal invasiveness, people commonly adopt 1100- to 1300-nm femtosecond laser sources. However, those lasers are typically based on bulky oscillators whose performances are sensitive to environmental conditions. We demonstrate a fiber-based 1150-nm femtosecond laser source, with 6.5-nJ pulse energy, 86-fs pulse width, and 11.25-MHz pulse repetition rate. It was obtained by a bismuth borate or magnesium-doped periodically poled lithium niobate (MgO:PPLN) mediated frequency doubling of the 2300-nm solitons, generated from an excitation of 1550-nm femtosecond pulses on a large mode area photonic crystal fiber. Combined with a home-built laser scanned microscope and a tailor-made frame grabber, we achieve a pulse-per-pixel HGM imaging in vivo at a 30-Hz frame rate. This integrated solution has the potential to be developed as a stable HGM system for routine clinical use.

Synthesis and hydrolysis of a phenylalanyl adenylate pentacoordinated phosphorane.

Amino acid-nucleotide conjugates have important biological functions and therapeutic applications. For example, aminoacyl adenylates are key intermediates in aminoacyl tRNA synthetase reactions. They may also be involved in the prebiotic synthesis of polypeptides. Finally, various amino acid carbomethoxy aryl phosphoramidates of nucleotide prodrugs may be activated through a mechanism involving a pentacoordinated phosphorane intermediates. In order to understand better the chemistry of these compounds, a phenylalanyl adenylate pentacoodinated phosphorane has been synthesized in 72% yield and its decomposition in aqueous solution studied. Hydrolysis gave 2('),3(')-O-isopropylidene adenosine 5(')-monophosphate, 2('),3(')-O-isopropylidene adenosine, and phenylalanine. The results provide model chemistry for the enzymatic degradation mechanism of antiviral aryl amino acid phosphodiester amidates in cells, which leads to their activation.

Interaction of Colicin E(1) with Lipid Membranes.

In order to gain an insight into the mechanism of membrane insertion of the pore-forming protein colicin E(1) and the structure of its membrane-bound form, circular dichroism, fluorescence spectroscopy experiments were carried out. The results revealed the law of conformational changes by lipid membrane induction of the colicin E(1) molecule, and suggest that the lipid membranes with negative charges have a strong inducing action on colicin E(1) molecules. With the induction of membrane, the colicin E(1) molecules in different conformational states can all be recovered to the conformation of membrane insertion in native state. The induction intensity of different kinds of lipids on colicin E(1) was in the following order: DMPG>DMPE>DMPC. The binding of colicin E(1) with lipid vesicles was tight and the membrane-bound proteins were resistant to denaturation.