IMS–MS and IMS–IMS Investigation of the Structure and Stability of Dimethylamine-Sulfuric Acid Nanoclusters

Recent studies of new particle formation events in the atmosphere suggest that nanoclusters (i.e, the species formed during the early stages of particle growth which are composed of 10¹–10³ molecules) may consist of amines and sulfuric acid. The physicochemical properties of sub-10 nm amine-sulfuric acid clusters are hence of interest. In this work, we measure the density, thermostability, and extent of water uptake of <8.5 nm effective diameter dimethylamine-sulfuric (DMAS) nanoclusters in the gas phase, produced via positive electrospray ionization. Specifically, we employ three systems to investigate DMAS properties: ion mobility spectrometry (IMS, with a parallel-plate differential mobility analyzer) is coupled with mass spectrometry to measure masses and collision cross sections for <100 kDa positively charged nanoclusters, two differential mobility analyzers in series (IMS–IMS) are used to examine thermostability, and finally a differential mobility analyzer coupled to an atmospheric pressure drift tube ion mobility spectrometer (also IMS–IMS) is used for water uptake measurements. IMS–MS measurements reveal that dry DMAS nanoclusters have densities of ∼1567 kg/m³ near 300 K, independent of the ratio of dimethylamine to sulfuric acid originally present in the electrospray solution. IMS–IMS thermostability studies reveal that partial pressures of DMAS nanoclusters are dependent upon the electrospray solution concentration ratio, <i>R</i> = [H₂SO₄]/[(CH₃)₂NH]. Extrapolating measurements, we estimate that dry DMAS nanoclusters have surface vapor pressures of order 10^–4 Pa near 300 K, with the surface vapor pressure increasing with increasing values of <i>R</i> through most of the probed concentration range. This suggests that nanocluster surface vapor pressures are substantially enhanced by capillarity effects (the Kelvin effect). Meanwhile, IMS–IMS water uptake measurements show clearly that DMAS nanoclusters uptake water at relative humidities beyond 10% near 300 K, and that larger clusters uptake water to a larger extent. In total, our results suggest that dry DMAS nanoclusters (in the 5–8.5 nm size range in diameter) would not be stable under ambient conditions; however, DMAS nanoclusters would likely be hydrated in the ambient (in some cases above 20% water by mass), which could serve to reduce surface vapor pressures and stabilize them from dissociation

Tuning Mobility Separation Factors of Chemical Warfare Agent Degradation Products via Selective Ion-Neutral Clustering

Combining experimental data with computational modeling, we illustrate the capacity of selective gas-phase interactions using neutral gas vapors to yield an additional dimension of gas-phase ion mobility separation. Not only are the mobility shifts as a function of neutral gas vapor concentration reproducible, but also the selective alteration of mobility separation factors is closely linked to existing chemical functional groups. Such information may prove advantageous in elucidating chemical class and resolving interferences. Using a set of chemical warfare agent simulants with nominally the same reduced mobility values as a test case, we illustrate the ability of the drift-gas doping approach to achieve separation of these analytes. In nitrogen, protonated forms of dimethyl methyl phosphonate (DMMP) and methyl phosphonic acid (MPA) exhibit the reduced mobility values of 1.99 ± 0.01 cm² V^–1s^–1 at 175 °C. However, when the counter current drift gas of the system is doped with 2-propanol at 20 μL/h, full baseline resolution of the two species is possible. By varying the concentration of the neutral modifier, the separation factor of the respective clusters can be adjusted. For the two species examined and at a 2-propanol flow rate of 160 μL/h, MPA demonstrated the greatest shift in mobility (1.58 cm²V^–1s^–1) compared the DMMP monomer (1.63 cm²V^–1s^–1). Meanwhile, the DMMP dimer experienced no change in mobility (1.45 cm²V^–1s^–1). The enhancement of separation factors appears to be brought about by the differential clustering of neutral modifiers onto different ions and can be explained by a model which considers the transient binding of a single 2-propanol molecule during mobility measurements. Furthermore, the application of the binding models not only provides a thermodynamic foundation for the results obtained but also creates a predictive tool toward a quantitative approach

X-ray Data collection and refinement statistics.

a<p>The values in parentheses refer to statistics in the highest shell.</p>b<p>Rmerge = |Ii−<i>|/|Ii| where Ii is the intensity of the ith measurement, and <i>is the mean intensity for that reflection.</i></i></p><i><i>c<p>Rwork = Σh|Fo(h)−Fc(h)|/ΣhFo(h), where Fo and Fc are the observed and calculated structure factor amplitudes, respectively.</p>d<p>Rfree was calculated with 10% of the reflections in the test set.</p>e<p>Categories were defined by MolProbity.</p></i></i

Chemiluminescence Reaction Kinetics-Resolved Multianalyte Immunoassay Strategy Using a Bispecific Monoclonal Antibody as the Unique Recognition Reagent

The multianalyte immunoassay (MIA) has attracted increasing attention due to its high sample throughput, short assay time, low sample consumption, and reduced overall cost. However, up to now, the reported MIA methods commonly require multiple antibodies since each antibody can recognize only one antigen. Herein, a novel bispecific monoclonal antibody (BsMcAb) that could bind methyl parathion and imidacloprid simultaneously was produced by a hybrid hybridomas strategy. A chemiluminescence (CL) reaction kinetics-resolved strategy was designed for MIA of methyl parathion and imidacloprid using the BsMcAb as the unique recognition reagent. Horseradish peroxidase (HRP) and alkaline phosphatase (ALP) were adopted as the signal probes to tag the haptens of the two pesticides due to their very different CL kinetic characteristics. After competitive immunoreactions, the HRP-tagged methyl parathion hapten and the ALP-tagged imidacloprid hapten were simultaneously bound to the BsMcAb since there were two different antigen-binding sites in it. Then, two CL reactions were simultaneously triggered by adding the CL coreactants, and the signals for methyl parathion and imidacloprid detections were collected at 0.6 and 1000 s, respectively. The linear ranges for methyl parathion and imidacloprid were both 1.0–500 ng/mL, with detection limits of 0.33 ng/mL (S/N = 3). The proposed method was successfully used to detect pesticides spiked in <i>ginseng</i> and <i>American ginseng</i> with acceptable recoveries of 80–118%. This proof-of-principle work demonstrated the feasibility of MIA using only one antibody

Human Cbx3 chromodomain binds to methylated histone H1K26 and G9aK185.

<p>ITC data for Cbx3 chromodomain binding to (A) H1K26 peptides (residues 18–29) and (B) G9aK185 peptides (residues 179–190). Lower panel show fit to a one-site binding model to the binding isotherms.</p

Comparison of three structures of Cbx3 chromodomain binding to methylated histone H3, H1 and G9a peptides.

<p>(A) Superposition of human Cbx3 chromodomain in complex with methylated histone H1 peptide (yellow), histone H3 peptide (orange), G9a peptide (cyan), Cbx3 chromodomains are colored as magenta, gray and green, respectively. (B) Superposition of histone H1 peptide (yellow), histone H3 peptide (orange). (C) Structure of Cbx3-H3K9me3 complex (magenta) was superposed to one protomer of the tetramer of Cbx3-G9aK185me3 complex (green) formed in one asymmetric unit. (D) The α helix (residues 70 to 79) of the chromodomain in the structure of Cbx3-G9aK185me3 complex (green) shifts 4.9 Å away from its counterpart in the structures of Cbx3-H3K9me3 (magenta).</p

Peptide binding specificity of human Cbx3 chromodomain.

*<p>N/B: No binding was detected.</p

Structure basis for Cbx3 binding to methylated histone H1K26 and G9aK185 peptide.

<p>(A and C) Electrostatic surface depiction of human Cbx3-histone H1K26me2, and Cbx3-G9aK185me3 complex. Peptide substrates are shown in a stick mode. Surfaces with positive electrostatic potential are blue, and negative potential are red. The side chain of residue H1A24 (G9aA183) inserts into the small hydrophobic pocket formed by Phe48 and Leu49 of human Cbx3. The size of the pocket is only sufficient to accommodate a methyl group but not other residue side chains. (B and D) Binding of histone H1 peptide and G9a peptide in the binding groove of Cbx3 chromodomain, respectively. Hydrogen-bonds are shown as dashed lines. Yellow: histone H1 peptide; Gray: Cbx3 chromodomain in Cbx3-histone H1K26me2 complex. Cyan: G9a peptide; Green: Cbx3 chromodomain in Cbx3-G9aK185me3 complex.</p

Intestinal barrier dysfunction in SII mice.

<p>(A) The tight junctions observed with TEM in SII-Reb mice at day 5 and SII-Sal mice at day 5 and at day 10 were significantly damaged. The wider intervals (green arrowheads) between the intestinal epithelial cells were indicated. (B-C) The mRNA expressions of Zo-1 (B) and Occludin (C) in the small intestine of the 4 groups were shown (n = 6, *<i>P</i> < 0.05 when compared with Con-Reb and Con-Sal groups; ^&<i>P</i> < 0.05 when compared with SII-Sal, Con-Reb, and Con-Sal groups). (D-F) Protein abundances of Zo-1 (E) and Occludin (F) were indicated by Western blotting (n = 6, *<i>P</i> < 0.05 when compared with Con-Reb and Con-Sal groups; ^&<i>P</i> < 0.05 when compared with SII-Sal, Con-Reb, and Con-Sal groups). (G) Serum levels of D-LAC in mice of the four groups were shown (n = 6, *<i>P</i> < 0.05 when compared with Con-Reb and Con-Sal groups).</p

Highly Specific Bacteriophage-Affinity Strategy for Rapid Separation and Sensitive Detection of Viable Pseudomonas aeruginosa

A virulent bacteriophage highly specific to Pseudomonas aeruginosa (P. aeruginosa) was isolated from hospital sewage using a lambda bacteriophage isolation protocol. The bacteriophage, named as PAP1, was used to functionalize tosyl-activated magnetic beads to establish a bacteriophage-affinity strategy for separation and detection of viable P. aeruginosa. Recognition of the target bacteria by tail fibers and baseplate of the bacteriophage led to capture of P. aeruginosa onto the magnetic beads. After a replication cycle of about 100 min, the progenies lysed the target bacteria and released the intracellular adenosine triphosphate. Subsequently, firefly luciferase-adenosine triphosphate bioluminescence system was used to quantitate the amount of P. aeruginosa. This bacteriophage-affinity strategy for viable P. aeruginosa detection showed a linear range of 6.0 × 10² to 3.0 × 10⁵ CFU mL^–1, with a detection limit of 2.0 × 10² CFU mL^–1. The whole process for separation and detection could be completed after bacteria capture, bacteriophage replication, and bacteria lysis within 2 h. Since the isolated bacteriophage recognized the target bacteria with very high specificity, the proposed strategy did not show any signal response to all of the tested interfering bacteria. Furthermore, it excluded the interference from inactivated P. aeruginosa because the bacteriophage could replicate only in viable cells. The proposed strategy had been applied for detection of P. aeruginosa in glucose injection, human urine, and rat plasma. In the further work, this facile bacteriophage-affinity strategy could be extended for detection of other pathogens by utilizing virulent bacteriophage specific to other targets