Isotope Effects and Temperature Dependences in the Action of the Glucose Dehydrogenase of the Mesophilic Bacterium Bacillus megaterium

This is the peer reviewed version of the following article: Anandarajah K., Schowen K. B. and Schowen R. L. (2013), Isotope effects and temperature dependences in the action of the glucose dehydrogenase of the mesophilic bacterium Bacillus megaterium, Journal of Physical Organic Chemistry. doi: 10.1002/poc.3166, which has been published in final form at http://doi.org/10.1002/poc.3166. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.The glucose dehydrogenase of the mesophilic bacterium Bacillus megaterium (optimal growth around 35 °C) exhibits non-linear Eyring temperature dependences from 25 to 55 °C in its catalysis of the oxidation by hydride-transfer to NAD+ of the β-anomers of 1-h-D-glucose and 1-d-D-glucose (rate constant kcat/KMβ). A break around 300K separates a high-T region from a low-T region. In the high-T region, isotopic enthalpies of activation within a considerable experimental error are equal to zero. In the low-T region, the enthalpies of activation are roughly equal for the isotopic substrates but are different from zero. An alternative treatment with Eyring plots taken as effectively linear produces enthalpies of activation having the unusual feature of being larger for the H-substrate (26 kJ/mol) than for the D-substrate (21 kJ/mol). Compensation of the enthalpic effect by a more positive entropy for the H-substrate then reproduces the isotope effects. For oxidation by NADP+ of the same pair of isotopic glucose substrates, catalysis by the glucose dehydrogenase of Thermoplasma acidophilum, a thermophilic archaeon, leads to temperature dependences characterized by a high-T region and a low-T region separated by a gentle thermal transition (K. Anandarajah, K.B. Schowen, and R.L. Schowen, Z. phys. Chem. 2008, 222, 1333–1347). Tentative approaches to a mechanistic interpretation of both cases rely on models featuring configurational searches of the enzyme for tunneling states, followed by hydrogen-transfer tunneling, although explanations can be constructed also on the basis of simple transition-state stabilization without tunnelling

Inverse scattering approach to multiwavelength Fabry-Pérot laser design

A class of multiwavelength Fabry-Pérot lasers is introduced where the spectrum is tailored through a patterning of the cavity effective index. The cavity geometry is obtained using an inverse scattering approach and can be designed such that the spacing of discrete Fabry-Pérot lasing modes is limited only by the bandwidth of the inverted gain medium. A specific two-color semiconductor laser with a mode spacing in the THz region is designed, and measurements are presented demonstrating the simultaneous oscillation of the two wavelengths. The nonperiodic effective index profile of the particular two-color device considered is shown to be related to a Moiré or superstructure grating

Optical Properties of Superconducting Nanowire Single-Photon Detectors

We measured the optical absorptance of superconducting nanowire single photon detectors. We found that 200-nm-pitch, 50%-fill-factor devices had an average absorptance of 21% for normally-incident front-illumination of 1.55-um-wavelength light polarized parallel to the nanowires, and only 10% for perpendicularly-polarized light. We also measured devices with lower fill-factors and narrower wires that were five times more sensitive to parallel-polarized photons than perpendicular-polarized photons. We developed a numerical model that predicts the absorptance of our structures. We also used our measurements, coupled with measurements of device detection efficiencies, to determine the probability of photon detection after an absorption event. We found that, remarkably, absorbed parallel-polarized photons were more likely to result in detection events than perpendicular-polarized photons, and we present a hypothesis that qualitatively explains this result. Finally, we also determined the enhancement of device detection efficiency and absorptance due to the inclusion of an integrated optical cavity over a range of wavelengths (700-1700 nm) on a number of devices, and found good agreement with our numerical model.Comment: will appear in optics express with minor revision

Increased bit rate direct modulation AMO-OFDM transmission by optical injection using monolithically integrated lasers

Experimental and simulation work, presented in this letter, demonstrates for the first time how the monolithic integration of two single-mode lasers in a master-slave configuration, can substantially increase the achievable bit rate of a direct modulation adaptively modulated optical orthogonal frequency-division multiplexing (AMO-OFDM) system. The Levin-Campello algorithm is applied to select the OFDM bit and power loading scheme used for each system configuration. Improvement in terms of data throughput due to injection is measured for several transmission distances with the improvement in performance presented in terms of error vector magnitude per OFDM subcarrier

Compensation of nonlinearity in a fiber-optic transmission system using frequency-degenerate phase conjugation through counter-propagating dual pump FWM in a semiconductor optical amplifier

We present a scheme of frequency-degenerate mid-span spectral inversion (MSSI) for nonlinearity compensation in fiber-optic transmission systems. The spectral inversion is obtained by using counter-propagating dual pump four-wave mixing in a semiconductor optical amplifier (SOA). Frequency-degeneracy between signal and conjugate is achieved by keeping two pump frequencies symmetrical about the signal frequency. We simulate the performance of MSSI for nonlinearity compensation by scrutinizing the improvement of the Q-factor of a 200 Gbps QPSK signal transmitted over a standard single mode fiber, as a function of launch power for different span lengths and number of spans. We demonstrate a 7.5 dB improvement in the input power dynamic range and an almost 83% increase in the transmission length for optimum MSSI parameters of −2 dBm pump power and 400 mA SOA current

Off-axis cavity-enhanced absorption spectroscopy of 14NH3 in air using a gain-switched frequency comb at 1.514 μm

A custom-designed gain-switched frequency comb (GSFC) source was passively coupled to a medium finesse (F ≈ 522) cavity in off-axis configuration for the detection of ammonia (14NH3) in static dry air. The absorption of ammonia was detected in the near infrared spectral region between 6604 and 6607 cm−1 using a Fourier transform detection scheme. More than 30 lines of the GSFC output (free spectral range 2.5 GHz) overlapped with the strongest ro-vibrational ammonia absorption features in that spectral region. With the cavity in off-axis configuration, an NH3 detection limit of ∼3.7 ppmv in 20 s was accomplished in a laboratory environment. The experimental performance of the prototype spectrometer was characterized; advantages, drawbacks and the potential for future applications are discusse

Integrated dual optical frequency comb source

A monolithically integrated dual-channel optical frequency comb source is demonstrated in this paper. Three lasers are integrated on a single chip using a regrowth-free fabrication process in a master-slave-slave configuration. The master laser’s power is split equally using a 1x2 multimode interference coupler and injection locks the two slave lasers. The slave lasers are gain-switched to produce dual optical frequency combs at 4.1 GHz and 5 GHz. To the best of our knowledge, this is the first demonstration of a dual optical frequency comb source with all light sources monolithically integrated in a photonic integrated circuit (PIC)