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101.
Highly-charged droplets, as formed by an electrospray process, are known to undergo asymmetric fission to form smaller droplets. We have observed a chemical and physical separation phenomenon that occurs in the droplet break-up process and is related to a compound's surface activity in solution. Two experimental approaches demonstrated that the smaller satellite droplets and the progeny droplets generated by the spray formation and asymmetric fission processes to be surfactant-enriched. These smaller droplets were also effectively separated from the larger primary and residual droplets because of their smaller inertia and high surface charge density, and a region attributed to the initially formed smaller satellite droplets was found to be strikingly confined in a narrow periphery region of the electrospray. The phenomenon may have utility for chemical separations and have significant implications for the sensitivity and selectivity of electrospray ionization-mass spectrometry. 相似文献
102.
Smith RA Verlet JR Boleat ED Stavros VG Fielding HH 《Faraday discussions》2000,(115):63-70; discussion 79-102
Rydberg electron wavepackets have been studied in molecular NO for a variety of rotational states of the ion core. Predominantly radial motion of the electron wavepacket is observed which is similar to that previously reported in atomic systems. Interference effects similar to those observed in unperturbed Rydberg series are evident and third and fourth order partial revivals are identified. Most interestingly, when the classical period of electronic motion is close to the classical period of rotation of the molecular ion, the molecular dynamics dominates the electronic dynamics. 相似文献
103.
The adsorption, desorption, and clustering behavior of H2O on Pt111 has been investigated by specular He scattering. The data show that water adsorbed on a clean Pt111 surface undergoes a structural transition from a random distribution to clustered islands near 60 K. The initial helium scattering cross sections as a function of temperature are found to be insensitive to the incident H2O flux over a range of 0.005 monolayers (ML)/s-0.55 ML/s indicating that the clustering process is more complex than simple surface diffusion. The coarsening process of an initially random distribution of water deposited at 25 K is found to occur over a broad temperature range, 60相似文献
104.
Watanabe M Sue K Adschiri T Inomata H Smith RL Arai K 《Chemical communications (Cambridge, England)》2001,(21):2270-2271
In supercritical water the rate of methanol oxidation was controlled by ionic behavior as follows: the oxidation rate of methanol decreased with increasing proton and hydroxide ion concentration, possibly due to stabilization of the reactant, while that of CO was suppressed by added protons and enhanced by added hydroxide ions. 相似文献
105.
An effective total synthesis of (-)-callystatin A (1), member of the leptomycin family of antibiotics, has been achieved. The synthesis features Evans extended aldol methodology to construct the northern polypropionate subunit and two separate Julia olefinations to assemble the conjugated dienes. The total synthesis proceeded in 2.3% overall yield with the longest linear sequence of 15 steps. 相似文献
106.
Tris(2-aminoethyl)amine derivatives with appended urea and sulfonamide groups are shown to facilitate the translocation of fluorescent phospholipid probes and endogenous phosphatidylserine across vesicle and erythrocyte cell membranes. The synthetic translocases appear to operate by binding to the phospholipid head groups and forming lipophilic supramolecular complexes which diffuse through the non-polar interior of the bilayer membrane. 相似文献
107.
Spikmans V Lane SJ Leavens B Manz A Smith NW 《Rapid communications in mass spectrometry : RCM》2002,16(14):1377-1388
A system is presented that demonstrates the principle of on-line and on-chip post-column derivatisation reactions in micro-high-performance liquid chromatography (micro-HPLC) hyphenated to electrospray time-of-flight mass spectrometry (ESI-TOFMS). In this micro-HPLC-chip-MS set-up, the analytes are separated using gradient micro-HPLC and subsequently derivatised on-chip and detected. One of the major limitations of MS detection is its dependency on the degree of ionisation, which is widely variable and compound-specific. Optimising and controlling the degree of ionisation in a simple manner would allow MS detection to be truly generic. One way of achieving this is by pre-ionisation of analytes using simple derivatisation procedures that are both rapid and quantitative. Performing this in situ on the system described here overcomes issues of sample handling and efficiency losses when time-consuming "bench chemistry" is necessary prior to analysis. The power of the system is demonstrated by the separation of primary and secondary amines, which are subsequently derivatised with a positively charged phosphonium complex and detected in an enhanced manner. Typically, molecular cations (M(+)) are detected showing that the ionisation process is dominated by the phosphonium species, leading to more constant ionisation for a variety of compounds. In addition, stable isotopically labelled ((12)C/(13)C)-phosphonium reagent is used for the reactions, allowing for inherent signal/noise (S/N) improvement and automated data processing using cluster analysis. A similar reaction scheme is used for the derivatisation of ketones and aldehydes, also demonstrating dramatic increases in sensitivity, especially with increasing temperature. Minimal loss in chromatographic fidelity in terms of retention times is observed by the introduction of the micromixer chip into the system. Optimal flow rates in micro-HPLC and ESI-MS are compatible with flow rates for the chip as well as a multitude of in-line optical detectors including UV and fluorescence. In addition, the micromixer chip can be positioned pre-column if preferred. The system is robust, easily fully automated and applicable to a wide variety of reactions. The system has a major advantage in its simple robust connection to the "normal scale" outside world. 相似文献
108.
D. L. Schmidt H. B. Smith M. Yoshimine M. J. Hatch 《Journal of polymer science. Part A, Polymer chemistry》1972,10(10):2951-2966
A new class of zwitterionic monomers were prepared in which the positive and negative sites are cyclic sulfonium and phenolate. Thermal polymerization occurs by phenolic anionic attack upon the aliphatic carbon α to the sulfonium sulfur. Polymerization proceeds with ring opening and net loss of charge to form nonionic polymers. The monomeric zwitterions are generally hydrated, crystalline solids that are soluble in water or alcohol. Chlorination of the aromatic portion of the molecule yields nonhydrated species. The polymerizations of 1-(4-hydroxy-3-methylphenyl)tetrahydrothiophenium hydroxide inner salt (dihydrate) and 1-(3,5-dichloro-4-hydroxyphenyl)tetrahydrothiophenium hydroxide inner salt were studied. The latter monomer gave a polymer with M?n of 46,000 when a nucleophile was present as an initiator. The physical properties of this polymer were determined. Cyclization appears to be the main mechanism of termination in the polymerization of zwitterions. 相似文献
109.
An easy method of approximating the electron density of a molecule by expressing it as a sum of squares of atomic orbitals is described. The coefficients are determined by minimizing the error in the electric field. The optimal population analysis is an integration of this optimized density over the orbitals belonging to one atom. The Mulliken population analysis can be interpreted as the integral of a Mulliken density that is a similar expression with fixed coefficients. The two densities are compared in détail using calculations on the water molecule and, more briefly, HF, LiH, BH, and C2H4. The error in the densities is identified and examined. The optimal population analysis is strongly recommended as a practical improvement to the Mulliken populations. 相似文献
110.
We have partially purified active delta and epsilon subunits of the E. coli membrane-bound Mg2+-ATPase (ECF1). Treating purified ECF1 with 50% pyridine precipitates the major subunits (alpha, beta, and gamma) of the enzyme, but the two minor subunits (delta and epsilon), which are present in relatively small amounts, remain in solution. The delta and epsilon subunits were then resolved from one another by anion exchange chromatography. The partially purified epsilon strongly inhibits the hydrolytic activity of ECF1. The epsilon fraction inhibits both the highly purified five-subunit ATPase and the enzyme deficient in the delta subunit. The latter result indicates that the delta subunit is not required for inhibition by epsilon. By contrast, two-subunit enzyme, consisting chiefly of the alpha and beta subunits, was insensitive to the ATPase inhibitor, suggesting that the gamma subunit may be required for inhibition by epsilon. The partially purified delta subunit restored the capacity of ATPase deficient in delta to recombine with ATPase-depleted membranes and to reconstitute ATP-dependent transhydrogenase. Previously we reported (Biochem, Biophys. Res. Commun. 62:764 [1975]) that a fraction containing both the delta and epsilon subunits of ECF1 restored the capacity of ATPase missing delta to recombine with depleted membranes and to function as a coupling factor in oxidative phosphorylation and for the energized transhydrogenase. These reconstitution experiments using isolated subunits provide rather substantial evidence that the delta subunit is essential for attaching the ATPase to the membrane and that the epsilon subunit has a regulatory function as an inhibitor of the ATPase activity of ECF1. 相似文献