The results indicate that the ointment gained access to the eye, causing the postoperative complications described. These cases highlight the importance of appropriate wound construction and integrity, as well as the risks of tight eye patching following placement of ointment.
Despite the tremendous sensitivity and lower sample requirements for nanospray vs. conventional electrospray, metallized nanospray emitters have suffered from one of two problems: low mechanical stability (leading to emitter failure) or lengthy, tedious production methods. Here, we describe a simple alternative to metallized tips using polyaniline (PANI), a synthetic polymer well known for its high conductivity, anticorrosion properties, antistatic properties, and mechanical stability. A simple method for coating borosilicate emitters (1.2 mm o.d.) pulled to fine tapers (4 +/- 1 microm) with water-soluble and xylene-soluble dispersions of conductive polyaniline (which allows for electrical contact at the emitter outlet) is described. The polyaniline-coated emitters show high durability and are resistant to electrical discharge, likely because of the thick (yet optically transparent) coatings; a single emitter can be used over a period of days for multiple samples with no visible indication of the destruction of the polyaniline coating. The optical transparency of the coating also allows the user to visualize the sample plug loaded into the emitter. Examples of nanospray using coatings of the water-soluble and xylene-soluble polyaniline dispersions are given. A comparison of PANI-coated and gold-coated nanospray emitters to conventional electrospray ionization (ESI) show that PANI-coated emitters provide similar enhanced sensitivity that gold-coated emitters exhibit vs. conventional ESI.
We report on the tail-tail cyclization and unfolding kinetics of poly(dimethylsiloxane) that is end-labeled with pyrene (Py-PDMS-Py) when it is dissolved at low concentration in liquid toluene (a good solvent) as a function of added CO 2 (0-204 bar). The pyrene excimer emission provides information on the PDMS tail-tail cyclization and unfolding kinetics and the conformation of the polymer chains. Under the aforementioned conditions, the Py-PDMS-Py excimer emission is entirely intramolecular in nature; there is no evidence for any inter-or intramolecular ground-state preassociation of the pyrene residues. However, the pyrene excimer-to-monomer intensity ratio (E/M) increases by ∼5-fold as we increase the CO 2 pressure from 0 to 70 bar. E/M begins to decrease gradually as the CO 2 pressure is increased above 70 bar. Timeresolved fluorescence spectroscopy reveals three important points. First, the rate of Py-PDMS-Py tail-tail unfolding (k unfolding ) is essentially independent of added CO 2 . Second, the rate that describes the intramolecular Py-PDMS-Py tail-tail cyclization (k cyclization ) increases 5-6-fold between 0 and ∼90 bar CO 2 . Above ∼90 bar CO 2 , k cyclization decreases with increasing CO 2 pressure. Finally, the apparent excited-state equilibrium constant (K* ) k cyclization /k unfolding ) increases with added CO 2 up to ∼90 bar and then decreases above 90 bar. The independence of k unfolding on adding CO 2 suggests that this rate coefficient reports on a local process that is not influenced to any significant extent by chain conformation or the viscosity of the medium. The large change in K* argues that the addition of CO 2 affects the PDMS chain cyclization probability which is a manifestation of changes in chain conformation brought on by the addition of CO 2 . Together these results show that the addition of CO 2 to liquid toluene (up to ∼90 bar) results in a systematic decrease in the mean free distance between the pyrene-labeled PDMS termini. This change in the mean free tail-tail distance is consistent with an excluded volume argument which is in line with Monte Carlo simulations and small-angle neutron scattering experiments. Above ∼90 bar CO 2, the mean free distance between the pyrene-labeled termini begins to increase. This arises from an increase in the solvent quality with increasing CO 2 density.
Rate constants for the hydrolysis of L-proline methyl ester to form proline and methanol in D(2)O buffered at neutral pD and 25 degrees C and the deuterium enrichment of the proline product determined by electrospray ionization mass spectrometry are reported. The data give k(DO) = 5.3 +/- 0.5 M(-1) s(-1) as the second-order rate constant for carbon deprotonation of N-protonated proline methyl ester by deuterioxide ion in D(2)O at 25 degrees C and I = 1.0 (KCl). The data provide good estimates of carbon acidities of pK(a) = 21 for N-protonated proline methyl ester and pK(a) = 29 for proline zwitterion in water and of the second-order rate constant k(HO) = 4.5 x 10(-5) M(-1) s(-1) for carbon deprotonation of proline zwitterion by hydroxide ion at 25 degrees C. There is no detectable acceleration of the deprotonation of N-protonated proline methyl ester by the Brønsted base 3-quinuclidinone in water, and it is not clear that such Brønsted catalysis would make a significant contribution to the rate acceleration for deprotonation of bound proline at proline racemase. A comparison of the first-order rate constants k(HO)[HO(-)] = 4.5 x 10(-11) s(-1) for deprotonation of free proline zwitterion in water at pH 8 and k(cat) = 2600 s(-1) for deprotonation of proline bound to the active site of proline racemase at pH 8 shows that the enzymatic rate acceleration for proline racemase is ca. 10(13)-fold. This corresponds to a 19 kcal/mol stabilization of the transition state for deprotonation of the enzyme-bound carbon acid substrate by interaction with the protein catalyst. It is suggested that (1) much of the rate acceleration of the enzymatic over the nonenzymatic reaction in water may result from transfer of the substrate proline zwitterion from the polar solvent water to a nonpolar enzyme active site and (2) the use of thiol anions rather than oxygen anions as Brønsted bases at this putative nonpolar enzyme active site may be favored, because of the smaller energetic price for desolvation of thiol anions than for desolvation of the more strongly solvated oxygen anions.
In this study we compare on-line gel permeation chromatography (GPC) electrospray ionization (ESI) time-of-flight (TOF) mass spectrometry (MS) to automated GPC matrix assisted laser desorption ionization (MALDI) TOF MS for poly (dimethylsiloxane) (PDMS) analysis. Average mass values for a hydroxyl-terminated PDMS (OH-PDMS) sample were obtained and compared to traditional GPC that was calibrated with narrow polystyrene standards, by direct ESI and MALDI MS analysis, by a summation of mass spectra of all GPC fractions, and also by the recalibration method determined by both mass spectrometric methods. Quantitatively, the difference noted here between these hyphenated techniques is that GPC-ESI-TOF MS effectively reports the low-mass oligomers and underestimates the high-mass oligomers, while GPC-MALDI-TOF MS effectively reports the high-mass oligomers and underestimates the low-mass oligomers. In the GPC-ESI-TOF MS experiments, ion current suppression was observed in the high molecular weight region. The suppression effect was confirmed by repeatable sample runs and by injecting different PDMS samples. Higher chromatographic resolution was observed for GPC-ESI-TOF MS compared to GPC-MALDI-TOF MS. In fact, truly mono-disperse oligomers were observed in the low molecular weight range from GPC-ESI MS experiments. (J
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