Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation.

Atmospheric aerosols exert an important influence on climate through their effects on stratiform cloud albedo and lifetime and the invigoration of convective storms. Model calculations suggest that almost half of the global cloud condensation nuclei in the atmospheric boundary layer may originate from the nucleation of aerosols from trace condensable vapours, although the sensitivity of the number of cloud condensation nuclei to changes of nucleation rate may be small. Despite extensive research, fundamental questions remain about the nucleation rate of sulphuric acid particles and the mechanisms responsible, including the roles of galactic cosmic rays and other chemical species such as ammonia. Here we present the first results from the CLOUD experiment at CERN. We find that atmospherically relevant ammonia mixing ratios of 100 parts per trillion by volume, or less, increase the nucleation rate of sulphuric acid particles more than 100-1,000-fold. Time-resolved molecular measurements reveal that nucleation proceeds by a base-stabilization mechanism involving the stepwise accretion of ammonia molecules. Ions increase the nucleation rate by an additional factor of between two and more than ten at ground-level galactic-cosmic-ray intensities, provided that the nucleation rate lies below the limiting ion-pair production rate. We find that ion-induced binary nucleation of H(2)SO(4)-H(2)O can occur in the mid-troposphere but is negligible in the boundary layer. However, even with the large enhancements in rate due to ammonia and ions, atmospheric concentrations of ammonia and sulphuric acid are insufficient to account for observed boundary-layer nucleation.

Evidence for the role of organics in aerosol particle formation under atmospheric conditions.

New particle formation in the atmosphere is an important parameter in governing the radiative forcing of atmospheric aerosols. However, detailed nucleation mechanisms remain ambiguous, as laboratory data have so far not been successful in explaining atmospheric nucleation. We investigated the formation of new particles in a smog chamber simulating the photochemical formation of H(2)SO(4) and organic condensable species. Nucleation occurs at H(2)SO(4) concentrations similar to those found in the ambient atmosphere during nucleation events. The measured particle formation rates are proportional to the product of the concentrations of H(2)SO(4) and an organic molecule. This suggests that only one H(2)SO(4) molecule and one organic molecule are involved in the rate-limiting step of the observed nucleation process. Parameterizing this process in a global aerosol model results in substantially better agreement with ambient observations compared to control runs.

Synthesis of 2-amino-5-benzoyl-4-(2-furyl)thiazoles as adenosine A(2A) receptor antagonists.

The discovery and synthesis of a series of 2-amino-5-benzoyl-4-(2-furyl)thiazoles as adenosine A(2A) receptor antagonists from a small-molecule combinatorial library using a high-throughput radioligand-binding assay is described. Antagonists were further characterized in the A(2A) binding assay and an A(1) selectivity assay. Selected examples exhibited excellent affinity for A(2A) and good selectivity versus the A(1) receptor.

Sulfonamido-aryl ethers as bradykinin B1 receptor antagonists.

The synthesis and identification of sulfonamido-aryl ethers as potent bradykinin B1 receptor antagonists from a approximately 60,000 member encoded combinatorial library are reported. Two distinct series of compounds exhibiting different structure-activity relationships were identified in a bradykinin B1 whole-cell receptor-binding assay. Specific examples exhibit K(i) values of approximately 10nM.

Successful screening of large encoded combinatorial libraries leading to the discovery of novel p38 MAP kinase inhibitors.

Screening of more than 2 million compounds comprising 41 distinct encoded combinatorial libraries revealed a novel structural class of p38 mitogen-activated protein (MAP) kinase inhibitors. The methodology used for screening large encoded combinatorial libraries combined with the statistical interpretation of screening results is described. A strong preference for a particular triaminotriazine aniline amide was discovered based on biological activity observed in the screening campaign. Additional screening of a focused follow-up combinatorial library yielded data expanding the unique combinatorial SAR and emphasizing an extraordinary preference for this particular building block and structural class. The preference is further highlighted when the p38 inhibitor data set is compared to data obtained for a panel of other kinases.

The discovery of novel chemotypes of p38 kinase inhibitors.

In the late 1970s and the early 1980s the initial p38 chemotype, the triaryl imidazoles, was discovered as an off-target effect during the development of cyclooxygenase and 5-lipoxygenase inhibitors long before the identity of the p38 kinase was known. During the last 10 years a number of novel p38 chemotypes were discovered via high throughput screening. More recently, the first series of p38 inhibitors discovered by xray crystallographic and virtual screening was announced. Finally, throughout the life span of p38 drug discovery programs significant medicinal chemistry effort has continually been placed on the design of new inhibitors from known chemotypes using molecular modeling, protein crystallography, hybrid design and simply sound intuition. Indeed, the search for p38 kinase inhibitors offers an excellent historical perspective as to how technological changes that have taken place in the pharmaceutical industry over the last decade, have affected the ways in which new leads are discovered and advanced. It is the intent of this review to highlight the discoveries of novel p38 chemotypes, emphasizing where possible the key technologies used in the discoveries and the knowledge gained from each discovery.

5-Cyanopyrimidine derivatives as a novel class of potent, selective, and orally active inhibitors of p38alpha MAP kinase.

A novel class of 5-cyanopyrimidine-based inhibitors of p38alpha MAP kinase has been investigated. Analogues optimized through SAR iterations display low nanomolar enzymatic and cellular activity. The in vivo efficacy of this class of p38 inhibitors was demonstrated by 3a and 3b (>50% reduction in TNF levels when orally dosed at 5 mg/kg, 5 h prior to LPS administration in an acute murine model of inflammation). For 3a and 3b, the previously identified N-methoxybenzamide moiety (1) was replaced with N-(isoxazol-3-yl)benzamide, thereby providing increased metabolic stability. Cyanopyrimidine 3a demonstrated 100% oral bioavailability in mouse. High p38 kinase selectivity versus over 20 kinases was observed for analogue 3b. Direct hydrogen bonding of the cyano nitrogen of the 5-cyanopyrimidine core to the backbone NH of Met109 was confirmed by X-ray crystallographic analysis of 3a bound to p38alpha.

The discovery of orally active triaminotriazine aniline amides as inhibitors of p38 MAP kinase.

A new structural class of triaminotriazine aniline amides possessing potent p38 enzyme activity has been discovered. The initial hit (compound 1a) was identified through screening the Pharmacopeia ECLiPS compound collection. SAR modification led to the identification of a short acting triaminotriazine aniline methoxyamide (compound 1m) possessing in vitro and in vivo oral activity in animal models of acute and chronic inflammatory disease. An X-ray crystal structure of compound 1m in this class, cocrystallized with unactivated p38 alpha protein, indicates that these compounds bind to the ATP binding pocket and possess key H-bonding interactions within a deeper cleft. Hydrogen bonding between one of the triazine nitrogens and the backbone NH of the Met109 residue occurs through a water molecule. The methoxyamide NH and carbonyl oxygen are within H-bonding distance of Glu71 and Asp168.

A Chemosensor for Citrate in Beverages.

Competitive binding like that in immunoassays is the principle behind the chemosensor based on receptor 1, which was used to measure the concentration of citrate (2) in a series of common beverages. Citrate displaces the fluorescent colorimetric probe 5-carboxylfluorescein (3) from 1, and the process can be monitored by UV or fluorescence spectroscopy.

Determination of the aerosol yield of isoprene in the presence of an organic seed with carbon isotope analysis.

We examined a new method to determine the aerosol yield of precursors of secondary organic aerosols in the presence of organic seed particles. To distinguish between the oxidation products of the compound in question and the organic seed, the compound was labeled with stable isotopes and aerosol samples were analyzed by isotope ratio mass spectrometry (IRMS). 13C labeled isoprene was obtained from isoprene emitting plants that were exposed to (13)CO2. The aerosol yield of isoprene was determined from the 13C/12C ratio measured in the aerosol. Measurements at organic aerosol mass concentrations as low as 10 microg m(-3) were performed. Three different methods of aerosolsampling procedureswere evaluated: impactor, filter, and electrostatic deposition. The excess-% 13C measured by the three sampling methods agreed well. The aerosol yield of isoprene derived from these measurements showed a strong dependence on further oxidation of first-generation products and is within the range of reported yield values (1-5%) obtained so far from pure isoprene experiments.

Using proton transfer reaction mass spectrometry for online analysis of secondary organic aerosols.

Proton-transfer-reaction mass spectrometry (PTR-MS) is a useful tool in ambient trace gas analysis, especially for the analysis of oxygenated volatile organic compounds (OVOC). Many OVOCs are produced during photooxidation of volatile organic compounds and contribute to both the gas phase and secondary organic aerosols (SOA). The inlet system of the PTR-MS instrument was modified to allow also for the measurement of the particulate phase of an aerosol with a high time resolution. The new inlet consists mainly of a denuder to strip off the gas phase, and a heater (120/150 degrees C) to vaporize the aerosol particles. This inlet system was tested with pinonic acid particles generated with a nebulizer and SOA particles formed during the photooxidation of 1,3,5-trimethylbenzene and alpha-pinene with NO(x) in a smog chamber. The performance of this new technique is discussed and the partitioning coefficients for the oxidation products are estimated.

Combined determination of the chemical composition and of health effects of secondary organic aerosols: the POLYSOA project.

Epidemiological studies show a clear link between increased mortality and enhanced concentrations of ambient aerosols. The chemical and physical properties of aerosol particles causing these health effects remain unclear. A major fraction of the ambient aerosol particle mass is composed of secondary organic aerosol (SOA). Recent studies showed that a significant amount of SOA consists of high molecular weight compounds (oligomers), which are chemically not well characterized. Within the POLYSOA project a large variety of state-of-the-art analytical chemical methods were used to characterize the chemical composition of SOA particles with emphasis on the oligomeric mass fraction. Mass spectrometric results showed that SOA oligomers are highly oxidized compounds and that hydroperoxides are formed, which is consistent with NMR results. This high molecular weight fraction accounts for up to 23% of the total organic carbon in SOA particles. These well-characterized SOA particles were deposited on three lung cell culture systems (microdissected respiratory epithelia from porcine tracheae, the human bronchial epithelial cell line BEAS-2B, and porcine lung surface macrophages obtained by bronchoalveolar lavage) in a newly constructed particle deposition chamber with the goal to eventually identify particle components that are responsible for cell responses leading to adverse health effects. In addition, monolayers of the alveolar epithelial cell line A549 were used in an alveolar epithelial repair model. The lung cells were examined for morphological, biochemical, and physiological changes after exposure to SOA. Analyses of the lung cells after exposure to SOA are ongoing. First data give evidence for a moderate increase of necrotic cell death as measured by lactate dehydrogenase release and for effects on the alveolar epithelial wound repair mainly due to alterations of cell spreading and cell migration at the edge of the wound. Thus, these first results indicate that SOA, in concentrations comparable to environmental concentrations, may induce distinct effects in lung cells.

O/C and OM/OC ratios of primary, secondary, and ambient organic aerosols with high-resolution time-of-flight aerosol mass spectrometry.

A recently developed method to rapidly quantify the elemental composition of bulk organic aerosols (OA) using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) is improved and applied to ambient measurements. Atomic oxygen-to-carbon (O/C) ratios characterize the oxidation state of OA, and O/C from ambient urban OA ranges from 0.2 to 0.8 with a diurnal cycle that decreases with primary emissions and increases because of photochemical processing and secondary OA (SOA) production. Regional O/C approaches approximately 0.9. The hydrogen-to-carbon (H/C, 1.4--1.9) urban diurnal profile increases with primary OA (POA) as does the nitrogen-to-carbon (N/C, approximately 0.02). Ambient organic-mass-to-organic-carbon ratios (OM/OC) are directly quantified and correlate well with O/C (R2 = 0.997) for ambient OA because of low N/C. Ambient O/C and OM/OC have values consistent with those recently reported from other techniques. Positive matrix factorization applied to ambient OA identifies factors with distinct O/C and OM/OC trends. The highest O/C and OM/OC (1.0 and 2.5, respectively) are observed for aged ambient oxygenated OA, significantly exceeding values for traditional chamber SOA,while laboratory-produced primary biomass burning OA (BBOA) is similar to ambient BBOA, O/C of 0.3--0.4. Hydrocarbon-like OA (HOA), a surrogate for urban combustion POA, has the lowest O/C (0.06--0.10), similar to vehicle exhaust. An approximation for predicting O/C from unit mass resolution data is also presented.

Real-time measurement of oligomeric species in secondary organic aerosol with the aerosol time-of-flight mass spectrometer.

Real-time detection of oligomers in secondary organic aerosols has been carried out with an aerosol time-of-flight mass spectrometer sampling particles generated in a smog chamber. The photooxidation products of 1,3,5-trimethylbenzene and NOx were studied over a range of initial 1,3,5-trimethylbenzene concentrations (137-1180 ppb), while keeping the 1,3,5-trimethylbenzene to NOx ratio nearly constant. The photooxidation products of a mixture of alpha-pinene (initial concentration 191 ppb), 1,3,5-trimethylbenzene (60 ppb), and NOx were also investigated. In both systems, ions were observed in the single-particle mass spectra up to 750 Da; the species observed differed in the two systems. These high-mass ions occur with characteristic spacing of 14 and 16 Da, indicative of oligomeric species. The results obtained agree well with off-line (matrix-assisted) laser desorption/ionization mass spectrometry results. The real-time capabilities of the aerosol time-of-flight mass spectrometer make it possible to investigate the temporal development of the oligomers with 5-min time resolution and also demonstrate that there are certain ions within the oligomer population that occur in nearly all of the particles and with relatively high signal intensity, suggesting that these ions have higher stability or that the species are formed preferentially.

Discovery and characterization of triaminotriazine aniline amides as highly selective p38 kinase inhibitors.

The p38 mitogen-activated protein (MAP) kinases are a family of serine/threonine protein kinases that play important roles in cellular responses to inflammation and external stress. Inhibitors of the p38 MAP kinase have shown promise for potential treatment of inflammatory disorders such as rheumatoid arthritis, acute coronary syndrome, psoriasis, and Crohn's disease. We identified a novel class of p38 inhibitors via high-throughput screening. PS200981 [3-(4-(1,4-diazepan-1-yl)-6-(((1S,2R,5S)-6,6-dimethylbicyclo[3.1.1]heptan-2-yl)methylamino)-1,3,5-triazin-2-ylamino)-4-methylbenzamide], a representative compound identified from screening a collection of combinatorial libraries, amounting to 2.1 million compounds, inhibits p38alpha kinase and the lipopolysaccharide (LPS)-induced increase in tumor necrosis factor (TNF) alpha levels in cell media of human monocytes with IC50 values of 1 microM. The screening data revealed a preferred synthon, 3-amino-4-methyl benzamide, which is critical for the activity against p38. This synthon appeared almost exclusively in screening hits including PS200981, and slight variations of this synthon including 3-amino benzamide and 2-amino-4-methyl benzamide also contained in the library were inactive. PS200981 is equally potent against the alpha and beta forms of p38 but did not inhibit p38 gamma and is >25-fold selective versus a panel of other kinases. PS200981 inhibited the LPS-induced increase in TNFalpha levels when administered at 30 mg/kg to mice. Selectivity and in vivo activity of this class of p38 inhibitors was further demonstrated by PS166276 [(R)-3-(4-(isobutyl(methyl)-amino)-6-(pyrrolidin-3-ylamino)-1,3,5-triazin-2-ylamino)-4-methylbenzamide], a highly structurally related but more potent and less cytotoxic inhibitor, in several intracellular signaling assays, and in LPS-challenged mice. Overall, this novel class of p38 inhibitors is potent, active in vitro and in vivo, and is highly selective.

Effect of humic and fulvic acid concentrations and ionic strength on copper and lead binding.

We investigated the influence of humic and fulvic acid concentration (in the range of 1-1000 mg/L) on the binding of the two trace metals Cu(II) and Pb(II). The ability of the non-ideal competitive adsorption (NICA)-Donnan model to correctly predict Cu and Pb binding at low humic or fulvic acid concentration and lower ionic strength (0.01 M NaNO3), based on model parameters obtained from experiments conducted at high humic or fulvic acid concentrations (approximately 1000 mg/L) and higher ionic strength (0.1 M NaNO3), was tested. The binding of Cu and Pb to humic and fulvic acid in 0.01 M NaNO3 was determined over wide ranges in proton and metal ion activities using three different methods: ligand exchange-adsorptive differential pulse cathodic stripping voltammetry at low humic or fulvic acid concentrations (1-3 mg/L), differential pulse anodic stripping voltammetry at intermediate humic or fulvic acid concentrations (10-20 mg/L), and ion-selective electrodes at high humic or fulvic acid concentrations (approximately 1000 mg/L). The results demonstrate that binding isotherms for Cu and Pb can be measured at low humic or fulvic acid concentration using suitable voltammetric techniques. The binding isotherms for Cu and Pb to humic and fulvic acid obtained at constant pH values in the range of pH 4-8 are shown to be independent of humic and fulvic acid concentration. The NICA-Donnan model, calibrated for Cu and Pb binding using data measured at high humic and fulvic acid concentrations and an ionic strength of 0.1 M, accurately predicts Cu and Pb binding at low humic and fulvic acid concentrations and lower ionic strength (0.01 M). We conclude that NICA-Donnan parameters obtained by fitting experimental data measured with ion-selective electrodes at high humic or fulvic acid concentrations can be used for geochemical modeling of soils and aquatic environments with much lower concentrations of humic or fulvic acids.

Ion-pairing molecular recognition in water: aggregation at low concentrations that is entropy-driven.

Investigations into the thermodynamic parameters that characterize the binding of citrate to tris-guanidinium host 1 in water are reported. The parameters K(a), DeltaH degrees, DeltaS degrees, and DeltaG degrees for the binding event were quantified using isothermal titration calorimetry (ITC) techniques. The 1:1 binding stoichiometry was verified by a Job plot derived from NMR data, and the microcalorimetry data was collected for solutions of 1 and citrate ranging from 1 to 100 mM using phosphate buffer concentrations of 5 and 103 mM. At low buffer concentrations (low ionic strength) complexes with greater than 1:1 stoichiometries were observed by ITC, and K(1) was determined to range from 2.0 x 10(3) to 3.0 x 10(3) M(-1). At higher buffer concentrations (high ionic strength) the higher-order complexes were not detected, and K(1) was determined to be 409 M(-1). The 1:1 association of host 1 and citrate is characterized by a large favorable entropy component and negative enthalpy. However, the complexes with higher-order stoichiometry arise from desolvation processes that result from the association of polyions in aqueous media and is entirely entropy driven. This leads to an unusual observation: the dilution of one component of the host/guest complex leads to the formation of the higher-order complexes. The reason for this observation is discussed.

Thermodynamic analysis of receptors based on guanidinium/boronic acid groups for the complexation of carboxylates, alpha-hydroxycarboxylates, and diols: driving force for binding and cooperativity.

The thermodynamics of guanidinium and boronic acid interactions with carboxylates, alpha-hydroxycarboxylates, and diols were studied by determination of the binding constants of a variety of different guests to four different hosts (7-10). Each host contains a different combination of guanidinium groups and boronic acids. The guests included molecules with carboxylate and/or diol moieties, such as citrate, tartrate, and fructose, among others. The Gibbs free energies of binding were determined by UV/Vis absorption spectroscopy, by use of indicator displacement assays. The receptor based on three guanidinium groups (7) was selective for the tricarboxylate guest. The receptors that incorporated boronic acids (8-10) had higher affinities for guests that included alpha-hydroxycarboxylate and catechol moieties over guests containing only carboxylates or alkanediols. Isothermal titration calorimetry revealed the enthalpic and entropic contributions to the Gibbs free energies of binding. The binding of citrate and tartrate was investigated with hosts 7-10, for which all the binding events were exothermic, with positive entropy. Because of the selectivity of hosts 8-10, a simple boronic acid (14) was also investigated and determined to be selective for alpha-hydroxycarboxylates and catechols over amino acids and alkanediols. Further, the cooperativity of 8 and 9 in binding tartrate was also investigated, revealing little or no cooperativity with 8, but negative cooperativity with 9. A linear entropy/enthalpy compensation relationship for all the hosts 7-10, 14, and the carboxylate-/diol-containing guests was also obtained. This relationship indicates that increasing enthalpy of binding is offset by similar losses in entropy for molecular recognition involving guanidinium and boronic acid groups.