Electrostatic Screening of Charged Defects in Monolayer MoS2.

Defects in monolayer transition-metal dichalcogenides (TMDCs) may lead to unintentional doping, charge-carrier trapping, and nonradiative recombination. These effects impair electronic and optoelectronic technologies. Here we show that charged defects in MoS2 monolayers can be effectively screened when they are in contact with an ionic liquid (IL), leading to an increase in photoluminescence (PL) yield by up to two orders of magnitude. The extent of this PL enhancement by the IL correlates with the brightness of each pretreated sample. We propose the existence of two classes of nonradiative recombination centers in monolayer MoS2: (i) charged defects that relate to unintentional doping and may be electrostatically screened by ILs and (ii) neutral defects that remain unaffected by the presence of ILs.

Lack of interference of icodextrin on creatinine measurements.

Glucose has been reported to interfere in the analysis of creatinine by the Jaffe method. The potential interference of icodextrin and its primary metabolites (maltose, maltotriose, maltotetraose) on creatinine measurements has not previously been addressed. We evaluated the potential interference of icodextrin and its metabolites at various concentrations using both the Jaffe and Creatinine Plus methods. Interference was determined in samples containing 0.6-20 mg/dL creatinine in saline solution or in plasma (n = 6), and in dialysate samples (n = 6) spiked with icodextrin, maltose, maltotriose, and maltotetraose at concentrations up to twofold the level found in plasma and dialysate from patients treated using icodextrin. Results confirm that no interference occurs when using either the colorimetric Jaffe method or the enzymatic Creatinine Plus method at levels up to 65 g/L icodextrin, 2 g/L maltose, 2 g/L maltotriose, and 1 g/L maltotetraose, levels representing worst-case clinical concentrations. In addition, our results confirm that comparable values can be obtained using either the Jaffe or the Creatinine Plus method for the analysis of creatinine in uremic plasma and in dialysate samples.

Quantitation of dextran 70 in peritoneal dialysate from patients administered 7.5% polyglucose.

A method using gel permeation chromatography was evaluated for the quantitation of dextran 70 in dialysate samples containing polyglucose. Dialysate samples containing dextran 70 and polyglucose were pretreated using the enzyme alpha-amylase to selectively hydrolyze the alpha(1-4)-linked polyglucose, while leaving the alpha(1-6)-linked dextran 70 intact. Following sample deproteinization with trichloroacetic acid, dextran 70 was quantitated using gel permeation chromatography with refractive index detection. This method was evaluated for accuracy, precision, specificity, linearity, range, and analyte stability. Adequate method linearity with a correlation of >0.999 was established over the range of dextran 70 concentration from 1 to 0.025 mg/ml. Method precision was approximately 2% R.S.D. and accuracy (% recovery) was approximately 98-100% in the typical sample concentration range (1-0.5 mg/ml). This method was applied to the determination of intraperitoneal fluid kinetics in continuous ambulatory peritoneal dialysis (CAPD) patients administered daily night-time intraperitoneal exchanges with either 7.5% polyglucose or 4.25% dextrose. Dextran 70 was added to the dialysis solutions to yield an initial concentration of 1 mg/ml. Dialysate samples were collected at various times over a 10-h dwell-time and assayed for dextran 70. Intraperitoneal volume profiles based on dextran 70 concentrations and drain volumes were then calculated for each dialysis solution.

Maltose and isomaltose in uremic plasma following icodextrin administration.

The presence of mixed disaccharides (maltose and isomaltose) in plasma from uremic patients has been previously investigated using gel-permeation chromatography. However, this method is unable to separate maltose (linked alpha-1-4) from isomaltose (linked alpha-1-6). We describe an alternative method using high-performance anion-exchange chromatography with pulsed amperometric detection (HPAE-PAD) for the direct determination of maltose and isomaltose in uremic plasma. We measured maltose and isomaltose using HPAE-PAD in 6 normal subjects and in 15 uremic patients before and after once-daily icodextrin administration for at least 4 weeks. Both maltose and isomaltose were below limits of detection (< 1.0 mg/L) in plasma from normal controls. Patients with end-stage renal disease treated by continuous ambulatory peritoneal dialysis had elevated levels of isomaltose (23.6 +/- 8.3 mg/L) but low levels of maltose (< 3.0 mg/L). Treatment with icodextrin resulted in elevated plasma levels of maltose (range: 500-1600 mg/L), while levels of isomaltose declined to 9.8 +/- 5.2 mg/L (P < 0.0001 vs. baseline levels). We conclude that isomaltose (not maltose) is the primary disaccharide isomer that is elevated in the plasma of uremic patients, whereas maltose is the primary disaccharide isomer that is elevated following icodextrin administration. Furthermore, icodextrin administration results in an apparent reduction of isomaltose. Additional investigation will be required to address the mechanism for the reduction of isomaltose in patients treated by icodextrin.

Direct determination of polyglucose metabolites in plasma using anion-exchange chromatography with pulsed amperometric detection.

High-performance anion-exchange chromatography with pulsed amperometric detection (HPAE-PAD) was evaluated for the quantitation of polyglucose metabolites (DP2-DP7) in human plasma. The method was investigated for accuracy, precision, specificity, linearity, range and analyte stability. Samples were prepared by dilution into the standard range (0.1-10 microg/ml) followed by deproteinization using a 30,000 molecular mass cut-off filtration device. The limit of detection was 0.05 microg/ml for all metabolites. Method precision for DP2-DP7 varied from approximately 2% R.S.D. in the upper range to approximately 15% R.S.D. at the limit of quantitation. Samples were stable following one or two freeze-thaw cycles and, after preparation, they could be refrigerated for up to 72 h. Application of this method to clinical plasma samples from continuous ambulatory peritoneal dialysis (CAPD) patients administered one daily night-time intraperitoneal exchange of 2 l of 7.5% polyglucose solution for four weeks indicated that plasma levels of DP2, DP3 and DP4 increased from baseline levels of <0.01 g/l to steady-state levels of 1.2+/-0.3, 1.2+/-0.3 and 0.4+/-0.1 g/l (mean+/-S.D.), respectively. These steady state plasma levels for DP2 and DP3 are comparable to previously reported levels in patients administered daily overnight 7.5% polyglucose dialysis solution.

The effect of blood contact and reuse on the transport properties of high-flux dialysis membranes.

The effect of blood contact and reprocessing using bleach on the convective transport of both neutral and positively charged dextrans was determined for cellulose triacetate (CT), polyacrylonitrile (PAN), and polysulfone (PS) dialyzers (Fresenius USA, F60B, Concord, CA). For neutral dextrans, blood contact reduced the convective permeability, determined by differences in the sieving coefficient profile for both the PAN and PS, but not for CT dialyzers. Reprocessing of the dialyzers with bleach (up to 15 reuses) did not affect the convective transport of dextrans through CT or PAN, but did enhance the permeability of the blood contacted PS dialyzers. However, sieving coefficients for the blood contacted and reprocessed PS (F60B) dialyzers were significantly lower than those for the other dialyzers studied, approaching zero for dextrans larger than 18 k molecular weight. Sieving coefficients for positively charged, diethylaminoethyl (DEAE) dextrans were a function not only of solute size, but also of the membrane's capacity for adsorption of charged molecules. The majority of smaller, filtered DEAE dextrans adsorbed to the PAN membrane. Adsorption of DEAE dextrans to PAN was not observed for larger dextrans, or for DEAE dextrans of any size with CT, despite the lower permeability of both membranes for DEAE dextran compared to that for neutral dextrans.

Nosocomial pneumonia in intubated patients given sucralfate as compared with antacids or histamine type 2 blockers. The role of gastric colonization.

Gram-negative nosocomial pneumonia may result from retrograde colonization of the pharynx from the stomach, and this may be more likely when the gastric pH is relatively high. We studied the rate of nosocomial pneumonia among 130 patients given mechanical ventilation in an intensive care unit who were receiving as prophylaxis for stress ulcer either sucralfate (n = 61), which does not raise gastric pH, or conventional treatment with antacids, histamine type 2 (H2) blockers, or both (n = 69). At the time of randomization to treatment, the two groups were similar in age, underlying diseases, and severity of acute illness. Patients in the sucralfate group had a higher proportion of gastric aspirates with a pH less than or equal to 4 (P less than 0.001) and significantly lower concentrations of gram-negative bacilli (P less than 0.05) in gastric aspirates, pharyngeal swabs, and tracheal aspirates than did patients in the antacid-H2-blocker group. The rate of pneumonia was twice as high in the antacid-H2 group as in the sucralfate group (95 percent confidence interval, 0.89 to 4.58; P = 0.11). Gram-negative bacilli were isolated more frequently from the tracheal aspirates of patients with pneumonia who were receiving antacids or H2 blockers. Mortality rates were 1.6 times higher in the antacid-H2 group than in the sucralfate group (95 percent confidence interval, 0.99 to 2.50; P = 0.07). Although our results fell just short of statistical significance when they were analyzed according to intention to treat, they suggest that agents that elevate gastric pH increase the risk of nosocomial pneumonia in patients receiving ventilation by favoring gastric colonization with gram-negative bacilli. We conclude that in patients receiving mechanical ventilation, the use of a prophylactic agent against stress-ulcer bleeding that preserves the natural gastric acid barrier against bacterial overgrowth may be preferable to antacids and H2 blockers.