Dutta S.,Optical Science and Technology Center |
Li Y.-L.,Optical Science and Technology Center |
Rock W.,Optical Science and Technology Center |
Houtman J.C.D.,University of Iowa |
And 2 more authors.
Journal of Physical Chemistry B
Functionally relevant femtosecond to picosecond dynamics in enzyme active sites can be difficult to measure because of a lack of spectroscopic probes that can be located in the active site without altering the behavior of the enzyme. We have developed a new NAD+ analog 3-Picolyl Azide Adenine Dinucleotide (PAAD+), which has the potential to be a general spectroscopic probe for NAD-dependent enzymes. This analog is stable and binds in the active site of a typical NAD-dependent enzyme formate dehydrogenase (FDH) with characteristics similar to those of natural NAD+. It has an isolated infrared transition with high molar absorptivity that makes it suitable for observing enzyme dynamics using 2D IR spectroscopy. 2D IR experiments show that in aqueous solution, the analog undergoes complete spectral diffusion within hundreds of femtoseconds consistent with the water hydrogen bonding dynamics that would be expected. When bound to FDH in a binary complex, it shows picosecond fluctuations and a large static offset, consistent with previous studies of the binary complexes of this enzyme. These results show that PAAD+ is an excellent probe of local dynamics and that it should be a general tool for probing the dynamics of a wide range of NAD-dependent enzymes. © 2011 American Chemical Society. Source
Koerperick E.J.,Optical Science and Technology Center |
Norton D.T.,University of Iowa |
Olesberg J.T.,University of Iowa |
Olson B.V.,University of Iowa |
And 2 more authors.
IEEE Journal of Quantum Electronics
Superlattice InAs/GaSb light-emitting diodes with peak emission wavelength of 8.6 μ and output power approaching 190 μ W at 77 K from a 120 × 120 μ m 2 mesa are demonstrated. Output power in excess of 600 μ W dollar; was demonstrated from a 520 × 520 μ m 2; mesa at 1 A drive current and 50% duty cycle. Devices were grown by molecular beam epitaxy on lightly n-doped GaSb substrates and employed a 16-stage cascaded active region configuration to improve current efficiency and increase optical output. Emitting regions were coupled by semi-metallic tunnel junctions consisting of a p-GaSb layer and a thickness-graded InAs/GaSb superlattice stack. © 2010 IEEE. Source