A novel single frequency stabilized Fabry-Perot laser diode at 1590 nm for gas sensing

A novel single frequency stabilized Fabry-Perot (SFP) laser diode with an emission wavelength of lambda = 1590 nm for H2S gas sensing is reported. Sculpting of the multi-mode spectral distribution of a FP laser to achieve single frequency emission is carried out using post growth photolitographic processing of the device. The resulting longitudinal-mode controlled FP laser has a stabilized single frequency emission with a side mode suppression ratio (SMSR) of 40 dB. The application of this device to spectroscopic based H2S sensing is demonstrated by targeting absorption lines in the wavelength range 1588 < or = lambda < or = 1591 nm. Using wavelength modulation spectroscopy (WMS), a low detection limit of 120 ppm x m x Hz(-1/2) was estimated while targeting the absorption line at 1590.08 nm. These initial results demonstrate the potential of the stabilized FP laser diode at this wavelength as a tunable, single frequency source for spectroscopic based gas sensing.     

Infrared spectra and isomerization of CHNO species in rare gas matrices

Infrared and uv absorption spectra of the CHNO isomers in rare gas matrices and their photolysis products by ultraviolet light were studied. The most efficient processes occurring in the matrix involve isomerization between the CHNO species. The NCO free radical is the only fragment appearing in the ir spectrum. The diatomic fragments CN, NH, and OH are also observable in the uv spectrum of photolyzed samples.     

Energetics of oxaspirocycle prototypes: 1,7-dioxaspiro[5.5]undecane and 1,7,9-trioxadispiro[5.1.5.3]hexadecane

The relative gas-phase energetics of several low-lying isomers of 1,7-dioxaspiro[5.5]undecane and 1,7,9-trioxadispiro[5.1.5.3]hexadecane have been calculated with second-order Mller-Plesset perturbation theory and basis sets as large as aug-cc-pVQZ. Relative energies in THF, dichloromethane, acetone, and DMSO have been estimated with corrections from polarized continuum model calculations at the B3LYP/6-311+G(d) level. In the most stable conformation of 1,7-dioxaspiro[5.5]undecane, both rings adopt chair conformations, and both oxygens are axially disposed (2A). It is more than 2 kcal mol(-1) more stable than all the other conformers. In agreement with previous work, the "twist-boat" trans isomer (3A) is the most stable isomer of 1,7,9-trioxadispiro[5.1.5.3]hexadecane. However, in contrast to this earlier study, an "all-chair" conformation (3B) is found to be the most stable cis isomer of 1,7,9-trioxadispiro[5.1.5.3]hexadecane (E approximately 0.5 kcal mol(-1) in acetone and DMSO). Gauge-independent atomic orbital computations at the B3LYP/6-311+G(d) level indicate that this is the only cis isomer with (13)C NMR chemical shifts that are qualitatively consistent with the experimental spectra.     

A constrained interval approach to the generalized distance geometry problem

This paper presents a new approach to the generalized distance geometry problem, based on a model that uses constraint interval arithmetic. In addition to theoretical results, we give some computational experiments that illustrate the better performance of the proposed approach, compared to others from the literature.     

Rotational analyses of the A1Π-X1Σ+ and the a3Π-X1Σ+ systems of AlBr

The absorption spectrum of the A¹Π-X¹Σ⁺ system and the emission spectrum of the a³Π-X¹Σ⁺ system of AlBr have been examined at higher resolution than previously used. The present study has produced a significantly improved set of molecular constants for these excited states of AlBr. All data have been fitted in a self-consistent manner for an optimum set of constants. The broadening of features in the A-X system has been attributed to type c⁺ predissociation in the A¹Π state. Also, a comparison is made between the emission and absorption spectra of the A-X system.     

Radiative Transitions of Singlet Oxygen: New Tools, New Techniques and New Interpretations

The near-IR phosphorescence of singlet delta oxygen, O₂(a¹Δg), has provided a wealth of information since it was first observed in solution-phase systems. The techniques employed and the quality of the data obtained have unproved significantly over the years that, in turn, presently makes it possible to address a wide variety of problems using both steady-state and time-resolved measurements. The development of spectroscopic methods to monitor other transitions in oxygen, specifically those that involve the singlet sigma state, O₂(b¹σ_g⁺), and the incorporation of high-level computational methods provides access to an even broader range of fundamental issues. The expertise presently available to monitor radiative transitions in oxygen, coupled with the current understanding of the effect of solvent on these transitions as achieved through state-of-the-art theoretical modeling makes it possible to consider the next step forward: the incorporation of spatial resolution and the construction of the singlet oxygen microscope.     

Lithium Ephedrinate Mediated Aldol Reaction of Arylacetonitriles: Thermodynamic Control of Enantioselectivity

Deracemization , the conversion of a racemic mixture into an enantiomerically enriched material, is achieved with the retro-aldol reaction of rac- 1 in the presence of lithium (−)-ephedrinate [Eq. (1)]. Remarkably, two stereogenic centers are simultaneously deracemized. This reaction shows that efficient thermodynamic control of the enantioselectivity of aldol reactions is possible     

Effect of surface nanotopography on immunoaffinity cell capture in microfluidic devices

Immunoaffinity microfluidic devices have recently become a popular choice to isolate specific cells for many applications. To increase cell capture efficiency, several groups have employed capture beds with nanotopography. However, no systematic study has been performed to quantitatively correlate surface nanopatterns with immunoaffinity cell immobilization. In this work, we controlled substrate topography by depositing close-packed arrays of silica nanobeads with uniform diameters ranging from 100 to 1150 nm onto flat glass. These surfaces were functionalized with a specific antibody and assembled as the base in microfluidic channels, which were then used to capture CD4+ T cells under continuous flow. It is observed that capture efficiency generally increases with nanoparticle size under low flow rate. At higher flow rates, cell capture efficiency becomes increasingly complex; it initially increases with the bead size then gradually decreases. Surprisingly, capture yield plummets atop depositions of some particle diameters. These dips likely stem from dynamic interactions between nanostructures on the substrate and cell membrane as indicated by roughness-insensitive cell capture after glutaraldehyde fixing. This systematic study of surface nanotopography and cell capture efficiency will help optimize the physical properties of microfluidic capture beds for cell isolation from biological fluids.     

Novel heterotricyclic systems: 2,6-dioxa- and 2-oxa-6-thia-10-azatricyclo-[5.2.1.04,10] deeanes; 2,6-dioxa-11-azatricyclo[5.3.1.04,11] undecane; and 9,13-dioxa-14-azatetracyclo[6.5.1.02,7.011,14]tetradeca-2,4,6-triene

The acid-catalyzed condensation of 2-amino-1,3-propanediols and 1,4-diketones under water-azeotroping conditions has led to the first synthesis of the new tent-like, essentially strain-free heterotricyclic system, 2,6-dioxa-10-azatricyclo[5.2.1.0^4,10]decane. Over thirty new compounds containing this system are reported. In cases where the aminodiol is unsubstituted or bears a phenyl substituent a mixture of the tricycle and the isomeric pyrrole resulted. These observations indicate alternative pathways in the Knorr-Paal condensation which lead to one, or the other, or both of these products. A scheme postulating common intermediates is presented. Examples of three additional, related, novel heteropolycyclic systems synthesized in analogous fashion are also reported.