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In previous papers, we highlighted the role of ammonium sulfate in increasing peptide fragmentation by in-source decay (ISD). The current work systematically investigated effects of matrix assisted laser desorption ionization (MALDI) extraction delay, peptide amino acid composition, matrix, and ammonium sulfate concentration on peptide ISD fragmentation. The data confirmed that ammonium sulfate increased peptides signal-to-noise ratio as well as their in-source fragmentation, resulting in complete sequence coverage regardless of the amino acid composition. This method is easy, inexpensive, and generates the peptides sequence instantly. 10.1021/ac901518a

Aqueous evaporation and condensation kinetics are poorly understood, and uncertainties in their rates affect predictions of cloud behavior and therefore climate. We measured the cooling rate of 3 M ammonium sulfate droplets undergoing free evaporation via Raman thermometry. Analysis of the measurements yields a value of 0.58 [+ or -] 0.05 for the evaporation coefficient, identical to that previously determined for pure water. These results imply that subsaturated aqueous ammonium sulfate, which is the most abundant inorganic component of atmospheric aerosol, does not affect the vapor-liquid exchange mechanism for cloud droplets, despite reducing the saturation vapor pressure of water significantly. aerosol | clouds | aqueous | inorganic www.pnas.org/cgi/doi/10.1073/pnas.0907988106

Vibrational broad bandwidth sum frequency generation spectroscopy was used to investigate the organization of 1-butanol and 1-hexanol at their air-liquid interface of aqueous, aqueous ammonium bisulfate and sulfuric acid solutions. It was found that at aqueous, ammonium bisulfate and at most sulfuric acid solution surfaces, butanol molecules organize in all-trans conformations indicating that butanol self-aggregates while hexanol chains were disordered at the surface of their respective solutions.

The crystallization of aqueous ammonium sulfate droplets containing soot and kalolinite and crystallization of aqueous ammonium sulfate droplets without solid material is investigated using optical microscopy. Under experimental conditions, the results showed that the crystallization relative humidity of aqueous ammonium sulfate particles was not influenced by soot.

The classical homogeneous nucleation theory is used to calculate the efflorescence relative humidity (ERH) of airborne ammonium sulfate particles with a wide size range at room temperature. The Kelvin effect is theoretically verified to substantially affect the ERH of ammonium sulfate particles small than 30 nm, while the aerosol size is the dominant factor affecting the efflorescent behavior of ammonium sulfate particles larger than 50 nm.

The attempted synthesis of the 2-acetamido and 2-amino derivatives of salacinol, a naturally occurring glycosidase inhibitor is described. Reaction of the protected acetamidothioarabinitol gave the corresponding sulfonium sulfate, which underwent ring opening to give an acyclic amido sulfate.

An investigation is conducted of the kinetics of reactive uptake of [[N.sub.2][O.sub.5]] on submicron aerosol particles containing humic acid and ammonium sulfate as a function of relative humidity and aerosol composition using a laminar flow reactor coupled with a differential mobility analyzer (DMA) to characterize the aerosol. The concentration of liquid water in the aerosol droplets was calculated using the aerosol inorganic model and a new combined FTIR-DMA system.

The measurement of the light scattering intensity and homogeneous ice nucleation temperatures from water droplets containing 0-33 wt percent ammonium sulfate is discussed. The ammonium sulfate freezing temperature data set with water activity of less than 0.98 is found to be consistent with a curve deviating in activity shift by about 5 percent from the best-fit ice nucleation temperature versus water activity curve.

The organic/electrolyte interactions of ammonium sulfate, nitrate and sodium chloride with substances containing carboxylic acids (COOH) and hydroxyl (OH) functional groups are examined. A liquid-liquid phase separation in the 1,2-hexanediol/water system is induced by all salts.

In this study, S. cerevisiae crude membrane fractions were prepared using the acid-labile detergent RapiGest from cells grown under rich and minimal media conditions using [sup.14]N and [sup.15]N ammonium sulfate as the sole nitrogen source. Four independent MudPIT analyses of 1:1 mixtures of sample were prepared and analyzed via quantitative multidimensional protein identification technology on a two-dimensional ion trap mass spectrometer. Using the method described in this study, low-abundance integral membrane proteins with up to 14 transmembrane domains were identified and their protein expression determined when sufficient spectrum counting and ion chromatogram information was generated. We demonstrate that spectrum counting and mass spectrometry derived ion chromatograms strongly correlate for determining quantitative changes in protein expression. Spectrum counting proved more reproducible and has a wider dynamic range contributing to the deviation of the two quantitative approaches from a perfect positive correlation.

Aerosol flow tube infrared spectroscopy (AFT-IR) was used to study the ice freezing of aqueous ammonium sulfate particles containing hematite or corundum mineral dust cores. The results demonstrate the important role of mineral dust as initiators of cirrus cloud formation by heterogeneous nucleation.

Optical microscopy and differential scanning calorimetry are used to investigate heterogeneous freezing of aqueous particles with the morphology of solid inclusions of crystallized ammonium sulphate, ice and letovicite. Results revealed that the surface area and surface microstructure of crystalline solids present in aqueous aerosols could significantly change the heterogeneous freezing temperature and critical ice saturations.

Observations on single internally mixed ammonium sulfate/calcium carbonate microparticles are reported. Deliquescence and efflorescence relative humidities for the mixed system are reported.

Ammonium sulfate fractionation and divalent cation precipitation were applied to purify major contractile proteins from relaxed actomyosin extracted from molluscan catch muscle myofibrils, as a supramolecular complex composed of twitchin (TW), myosin (MY), and myorod (MR). The phosphorylation of twitchin by PKA-like kinase and the phosphorylation of myosin and myorod by myosin-associated kinase were found to play crucial role in the development of the catch state.

The synthesis of new fluorinated lithium and ammonium sulfonimides by using the corresponding sulfonyl fluorides is described. The intermediates oxonium sulfonimides are neutralized and the obtained sulfonimides are shown to be potential electrolytes for lithium batteries or fuel cells.

The results of the study of the extinction spectra, measured in an aerosol flow tube (AFT) is used to discover a new and highly improved set of complex indices of refraction for crystalline ammonium sulfate [(N[H.sub.4]).sub.2]S[O.sub.4] at different temperatures. The new indices of refraction can be very effectively used for remote-sensing and laboratory studies of ammonium sulfate, however their differences cannot be observed by using atmospheric remote sensing measurements.

The deliquescence and crystallization of ammonium sulfate particles internally mixed with water-soluble organic species having a range of chemical and physical properties is investigated. It is estimated that organics on average are only a minor perturbation on the deliquescence relative humidity (DRH) of the pure inorganic particles, whereas the organics on average may decrease the crystallization relative humidity (CRH) of pure inorganic particles.