Dual Binding of an Antibody and a Small Molecule Increases the Stability of TERRA G‐Quadruplex

In investigating the binding interactions between the human telomeric RNA (TERRA) G‐quadruplex (GQ) and its ligands, it was found that the small molecule carboxypyridostatin (cPDS) and the GQ‐selective antibody BG4 simultaneously bind the TERRA GQ. We previously showed that the overall binding affinity of BG4 for RNA GQs is not significantly affected in the presence of cPDS. However, single‐molecule mechanical unfolding experiments revealed a population (48 %) with substantially increased mechanical and thermodynamic stability. Force‐jump kinetic investigations suggested competitive binding of cPDS and BG4 to the TERRA GQ. Following this, the two bound ligands slowly rearrange, thereby leading to the minor population with increased stability. Given the relevance of G‐quadruplexes in the regulation of biological processes, we anticipate that the unprecedented conformational rearrangement observed in the TERRA‐GQ–ligand complex may inspire new strategies for the selective stabilization of G‐quadruplexes in cells.     

Nonlinear atomic response to intense ultrashort x rays

The nonlinear absorption mechanisms of neon atoms to intense, femtosecond kilovolt x rays are investigated. The production of Ne(9+) is observed at x-ray frequencies below the Ne(8+), 1s(2) absorption edge and demonstrates a clear quadratic dependence on fluence. Theoretical analysis shows that the production is a combination of the two-photon ionization of Ne(8+) ground state and a high-order sequential process involving single-photon production and ionization of transient excited states on a time scale faster than the Auger decay. We find that the nonlinear direct two-photon ionization cross section is orders of magnitude higher than expected from previous calculations.     

Design of zero dispersive double clad fiber for high efficiency operation of two color light

A double clad solid silica fiber is newly designed for applications which need the high efficiency operation of two colors of light. Ultrashort pulses with a central wavelength of 800?nm are delivered by the core of the double clad fiber which can realize the transmission of the optical pulses with a net chromatic dispersion of zero. This is achieved by integrating the double clad fiber with a pair of long period gratings, which allows optical pulses to propagate in a higher order mode (LP₀₂) in the middle of the fiber as well as in a fundamental mode (LP₀₁) at the beginning and end of the fiber. The index profile of the double clad fiber is engineered so that the higher order mode has high anomalous dispersion that can be used to compensate for normal dispersion of the fundamental mode. By controlling the lengths of the fiber where pulses are in a fundamental and in a higher order modes, the fiber with total zero dispersion can be realized. The double clad fiber can collect 100?% of visible light within the numerical aperture of 0.21 with a loss of the optical pulses less than 1?%. The design of this fiber is essential for applications including fiber-optic nonlinear imaging for compactness, robustness, and low optical power loss in dispersion compensation.