Effect of variable power levels on the yield of total aerosol mass and formation of aldehydes in e-cigarette aerosols.

The study objective was to determine the effect of variable power applied to the atomizer of refillable tank based e-cigarette (EC) devices. Five different devices were evaluated, each at four power levels. Aerosol yield results are reported for each set of 25 EC puffs, as mass/puff, and normalized for the power applied to the coil, in mass/watt. The range of aerosol produced on a per puff basis ranged from 1.5 to 28 mg, and, normalized for power applied to the coil, ranged from 0.27 to 1.1 mg/watt. Aerosol samples were also analyzed for the production of formaldehyde, acetaldehyde, and acrolein, as DNPH derivatives, at each power level. When reported on mass basis, three of the devices showed an increase in total aldehyde yield with increasing power applied to the coil, while two of the devices showed the opposite trend. The mass of formaldehyde, acetaldehyde, and acrolein produced per gram of total aerosol produced ranged from 0.01 to 7.3 mg/g, 0.006 to 5.8 mg/g, and <0.003 to 0.78 mg/g, respectively. These results were used to estimate daily exposure to formaldehyde, acetaldehyde, and acrolein from EC aerosols from specific devices, and were compared to estimated exposure from consumption of cigarettes, to occupational and workplace limits, and to previously reported results from other researchers.

Absorption, circular dichroism, and photoluminescence in perylene diimide bichromophores: polarization-dependent H- and J-aggregate behavior.

Using a single-mode Holstein Hamiltonian with through-space excitonic couplings evaluated quantum mechanically, the absorption, circular dichroism, and photoluminescence spectral line shapes of a chiral perylene diimide dimer complex were accurately reproduced. In general, a dimer consisting of two chromophores related through a C(2) rotation is neither a J- nor an H-aggregate because oscillator strength is divided between the top and bottom of the exciton band. The division gives rise to the two Davydov components per vibronic band in the absorption spectrum. Nevertheless, it is shown that the vibronic structure of the absorption component polarized in the same direction as the lower (upper) Davydov component is identical to what one would obtain from an ideal J- (H-) aggregate. Emission generally contains both polarization components, but the component polarized in the same direction as the lower (upper) Davydov component behaves similarly to the emission from an ideal J- (H-) aggregate. The basic photophysical behavior also applies to molecular crystals containing two molecules per unit cell in which the interactions between inequivalent molecules dominate over interactions between equivalent molecules.

Comparison of intra- and intermolecular proton transfer in human carbonic anhydrase II.

The catalysis of the hydration of CO2 by human carbonic anhydrase II (HCA II) includes the transfer of a proton from zinc-bound water to histidine 64 utilizing a network of intervening hydrogen-bonded water molecules, then the proton is transferred to buffer in solution. We used stopped-flow spectrophotometry and 18O exchange between CO2 and water measured by mass spectrometry to compare catalytic constants dependent on proton transfer in HCA II and in the mutant H64A HCA II containing the replacement His64-->Ala. Maximal velocities and oxygen-18 exchange catalyzed by H64A HCA II showed that nearly all of the proton transfer with this mutant proceeded through the imidazole buffer. The following parameters were very similar or identical in catalysis by H64A HCA II compared with catalysis by wild-type HCA II both in the presence of large concentrations of imidazole (100 mM): the maximal rate of initial velocity and of exchange of 18O between CO2 and water, solvent hydrogen isotope effects on the maximal velocity, and the dependence of these isotope effects on the atom fraction of deuterium in solvent water. These results indicate that the proton transfer involving the zinc-bound water in catalysis is not significantly affected by the difference between the mobility of the free imidazole buffer and the side chain of His 64. Moreover, data for both the wild-type and mutant enzymes are consistent with proton transfer through intervening hydrogen-bonded water bridges in the active sites. These features of the proton transfer are discussed in terms of a model in which the first proton transfer from the zinc-bound water to an adjacent water is rate limiting.