A rigid, monolithic but still scannable cavity ring-down spectroscopy cell.

A novel cell for continuous wave cavity ring-down spectroscopy (cw-CRDS) is described and tested. The cell is monolithic and maintains a rigid alignment of the two cavity mirrors. Two high-resolution and high-force piezoelectric transducers are used to sweep the length of the cell by elastic deformation of the 2.86 cm outer diameter stainless steel tube that makes up the body of the cell. The cavity length is scanned more than 1/2 wavelength of the near-IR light used, which ensures that at least one TEM(00) mode of the cavity will pass through resonance with the laser. This allows the use of a frequency-locked-laser cw-CRDS technique, which increases the precision of the measurements compared to the alternative of sweeping the laser more than one free spectral range of the cavity. The performance of the cell is demonstrated by using it to detect the absorption spectrum of methane (CH(4)) at the wavenumber regions of around 6051.8-6057.7 cm(-1).

Spectroscopic and kinetic properties of HO(2) radicals and the enhancement of the HO(2) self reaction by CH(3)OH and H(2)O.

The line center absorption cross sections and the rate constants for self-reaction of hydroperoxy radicals (HO(2)) have been examined in the temperature range of 253-323 K using pulsed laser photolysis combined with tunable diode laser absorption in the near-IR region. The transition probed was in the 2nu(1) OH overtone transition at 1506.43 nm. The temperature dependence of the rate constant (k) for the HO(2) + HO(2) reaction was measured relative to the recommended value at 296 K, giving k = (3.95 +/- 0.45) x 10(-13) x exp[(439 +/- 39)/T] cm(3) molecule(-1) s(-1) at a total pressure of 30 Torr (N(2) + O(2)). After normalizing our determination and previous studies at low pressure, we recommend k = (2.45 +/- 0.50) x 10(-13) x exp[(565 +/- 130)/T] cm(3) molecule(-1) s(-1) (0 < P < 30 Torr, 95% confidence limits). The observed rate coefficient, k(obs), increases linearly with CH(3)OH concentration, and the enhancement coefficient (k'), defined by k(obs) = k + k'[CH(3)OH], is found to be (3.90 +/- 1.87) x 10(-35) x exp[(3849 +/- 135)/T] cm(6) molecule(-2) s(-1) at 30 Torr. The analogous water vapor enhancement coefficient (k'') is (1.16 +/- 0.58) x 10(-36) x exp[(4614 +/- 145)/T] cm(6) molecule(-2) s(-1). The pressure-broadened HO(2) absorption cross section is independent of temperature in the range studied. The line center absorption cross sections at 1506.43 nm, after correction for instrumental broadening, are (4.3 +/- 1.1) x 10(-19), (2.8 +/- 0.7) x 10(-19), and (2.0 +/- 0.5) x 10(-19) cm(2)/molecule at total pressures of 0, 30, and 60 Torr, respectively (95% confidence limits).

[Effect of herba schizonepetae volatile oil (STO) on activity of 5-lipoxygenase in rat thoracic cavity leukocytes].

OBJECTIVE: To investigate the effect of herba schizonepetae volatile oil (STO) on the activity of 5-lipoxygenase (5-LO), so as to elucidate its mechanisms of anti-inflammatory action which is related to the arachidonic acid (AA) metabolism. METHOD: Thoracic cavity leukocytes from the pleurisy model rat induced by injecting 1%-carrageenan into the pleural cavity were collected. Then 0. 4 mL cell suspension including 2 x 10(7) cells per millilitre were used as the reaction system in vitro. STO in different concentrations (final concentration 0.011, 0.022, 0.043, 0.087, 0.179, 0.255, 0.364 g x L(-1)), zileuton (final concentration 0.625 x 10(-3) g x L(-1)), and DMSO in the same volume were added into the reaction tube respectively. The reaction tubes were incubated at 37 degrees C for 20 min and CaCl2 (final concentration 2 mmol x L(-1)), MgCl2 (final concentration 0.5 mmol x L(-1)), exogenous AA (final concentration 200 micromol x L(-1)) and A23187 (final concentration 5 micromol x L(-1)) were added in turns during this period. The reaction tubes were mixed and continuously incubated at 37 degrees C for 30 min. After terminating reaction by adding methanol, the metabolites of 5-LO, leukotriene B4 (LTB4) and 5-hydroxy-6, 8, 11, 14-eicosatetraenoic acid (5-HETE), were extracted, separated and detected by means of RP-HPLC. RESULT: Compared with control group, STO significantly inhibited the biosynthesis of LTB4 and 5-HETE at final concentration between 0. 022 g x L(-1) and 0.364 g x L(-1) (P < 0.05 or 0.001) in dose dependence manner, and its IC50 value was 0.124 g x L(-1) and 0.142 g x L(-1) for LTB4 and 5-HETE, respectively. CONCLUSION: STO can inhibited the activity of 5-LO, which is an important enzyme of AA metabolism, in rat thoracic cavity leukocytes in a dose-dependent manner in vitro. It is suggested that the mechanism of anti-inflammatory action of STO is related to its inhibiting the activity of 5-LO and decreasing the level of major inflammatory mediators LTB4.

Photolysis of 4-oxo-2-pentenal in the 190-460 nm region.

We have studied the gas-phase photolysis of 4-oxo-2-pentenal by laser photolysis combined with cavity ring-down spectroscopy. Absorption cross sections of cis- and trans-4-oxo-2-pentenal have been measured in the 190-460 nm region. The product channel following 193, 248, 308, and 351 nm photolysis of 4-oxo-2-pentenal was investigated. The HCO radical is a photodissociation product of 4-oxo-2-pentenal only at 193 and 248 nm. The HCO quantum yields from the photolysis of a mainly trans-4-oxo-2-pentenal sample are 0.13 +/- 0.02 and 0.014 +/- 0.003 at 193 and 248 nm, where errors quoted (1sigma) represent experimental scatter. The HCO quantum yields from the photolysis of a mainly cis-4-oxo-2-pentenal sample are 0.078 +/- 0.012 and 0.018 +/- 0.007 at 193 and 248 nm, where errors quoted (1sigma) represent experimental scatter. The end-products from 193, 248, 308, and 351 nm photolysis of 4-oxo-2-pentenal (the 4-oxo-2-pentenal sample had a tran/cis ratio of 1.062:1) have been determined by FTIR. Ethane, methyl vinyl ketone, and 5-methyl-3H-furan-2-one have been observed, suggesting the occurrence of 4-oxo-2-pentenal photolysis pathways such as CH(3)COCH=CHCHO + hnu --> CH(3) + COCH=CHCHO, CH(3)COCH=CHCHO + hnu --> CH(3)COCH=CH(2) + CO, and CH(3)COCH=CHCHO + hnu --> 5-methyl-3H-furan-2-one. The estimated yields for the CH(3) + COCH=CHCHO channel are about 25%, 33%, 31%, and 23% at 193, 248, 308, and 351 nm, respectively. The absolute uncertainties in the determination of CH(3) + COCH=CHCHO yields are within 55% at 193 nm, and 65% at 248, 308, and 351 nm. The estimated yields for the CH(3)COCH=CH(2) + CO channel are about 25%, 23%, 40%, and 33% at 193, 248, 308, and 351 nm, respectively. The absolute uncertainties in the determination of CH(3)COCH=CH(2) yields are within 80% at 193 and 248 nm and 65% at 308 and 351 nm. The estimated yields for the 5-methyl-3H-furan-2-one channel are about 1.2%, 2.1%, 5.3%, and 5.5% at 193, 248, 308, and 351 nm, respectively. The absolute uncertainties in the determination of 5-methyl-3H-furan-2-one yields are about 23%, 86%, 40%, and 46% at 193, 248, 308, and 351 nm. Results from our investigation indicate that photolysis is a dominant removal pathway for 4-oxo-2-pentenal degradation in the atmosphere.