Detecting structure, dynamics, and chemical reactions at the single-molecule level represents the ultimate degree of sensitivity for sensing and imaging. There is a tremendous need to develop new molecular systems and methodology for single-molecule-based sensing. This work presents for the first time the single-molecule spectroscopy of a new molecular probe which uses an intramolecular electron transfer mechanism to detect binding, local structure, and interfacial processes. Moreover, we show how information about the interaction of these probes with their environment is obtained from an analysis of the intensity, duration and time-varying behavior of the single-molecule fluorescence.

The transport kinetics of the positively charged triphenylmethane dye, malachite green (MG(+)), across liposome bilayers effects the transport of monovalent inorganic cations when ionophores are present in the membrane. Three different types of ionophores characterized by different transport mechanisms have been studied. The ionophores are gramicidin A (gA) (a channel former), valinomycin (VAL) (a lipophilic cyclopeptide that encloses an alkali ion), and carbonyl cyanide-m-chlorophenylhydrazone (CCCP) (a weak acid that functions as a protonophore). The effects of these ionophores on the kinetics and extent of MG(+) crossing into the liposome, investigated using the interface selective second harmonic generation method, were found to be markedly different.

The effect of charge on the rotational dynamics of the molecular probe coumarin 314 (C314) at air/water interfaces covered with the negatively charged surfactant sodium dodecyl sulfate (SDS) was investigated using femtosecond time-resolved second harmonic spectroscopy. The out-of-plane orientational time constant at the highest SDS surface coverage of 100 Å 2 per molecule is 383 ( 9 ps. The rotational dynamics is slower than at the air/water interface where the out-of-plane reorientational time constant is 336 ( 6 ps. At the air/water interface the rotational dynamics is over three times slower than the bulk orientational diffusion time of 100 ps. The relatively small effect of the surfactant charge density on the C314 rotation time constant is surprising, considering the marked dependence of the C314 orientation, spectra, and surfactant phase diagram on surfactant density.

Context.-Elevated free hemoglobin (Hb) and bilirubinemia complicate extracorporeal membrane oxygenation and could affect unfractionated heparin (UH) therapy monitoring by anti-Xa assay and activated partial thromboplastin time (aPTT).Objectives.-To compare in vitro response of anti-Xa and aPTT assays to UH in samples with artificial hyperbilirubinemia and hyperhemoglobinemia and to estimate if this interference is also observed in vivo in pediatric extracorporeal membrane oxygenation.Design.-Measurement of aPTT and anti-Xa activity in plasma spiked with UH and increased concentration of free Hb and/or conjugated bilirubin. All samples with antiXa activity, antithrombin, free Hb, and bilirubin determination and infused dose of UH from inpatients on extracorporeal membrane oxygenation were extracted from the clinical patient database and analyzed.Results.-Each increment of free Hb by 100 mg/dL significantly shortened aPTT, whereas an increment of bilirubin by 6 mg/dL caused significant prolongation of aPTT and stepwise increase of free Hb and/or bilirubin in plasma decreased anti-Xa activity by 0.03 to 0.05 IU/mL. Extracorporeal membrane oxygenation samples with free Hb 50 mg/dL or greater had significantly lower anti-Xa activity compared with normal ones: 0.33 (0.25-0.42) versus 0.4 (0.31-0.48) IU/mL (P ¼ .01), despite the identical UH infusion and similar antithrombin activity. Moderate increase of free Hb by 59 mg/dL was associated with absolute decrease of anti-Xa activity by 0.07 IU/mL.Conclusions.-Activated partial thromboplastin time and anti-Xa assay are affected by elevated level of free Hb and/or bilirubin in the presence of UH, and lower antiXa activity is noted in extracorporeal membrane oxygenation patients with elevated free Hb. Severe hemolysis and/or hyperbilirubinemia could compromise UH monitoring based on these assays.

Bariatric surgery has emerged as the most durably effective treatment of type 2 diabetes (DM). However, the mechanisms governing improvement in glucose homeostasis have yet to be fully elucidated. In this review we discuss the various types of surgical interventions and the multitude of factors that potentially mediate the effects on glycemia, such as altered delivery of nutrients to the distal ileum, duodenal exclusion, gut hormone changes, bile acid reabsorption, and amino acid metabolism. Accumulating evidence that some of these changes seem to be independent of weight loss questions the rationale of using body mass index as the major indication for surgery in diabetic patients. Understanding the complex mechanisms and interactions underlying improved glycemic control could lead to novel therapeutic targets and would also allow for greater individualization of therapy and optimization of surgical outcomes.

Improvement in type 2 diabetes after Roux-en-Y gastric bypass (RYGB) has been attributed partly to weight loss, but mechanisms beyond weight loss remain unclear. We performed an ancillary study to the Diabetes Surgery Study to assess changes in incretins, insulin sensitivity, and secretion 1 year after randomization to lifestyle modification and intensive medical management (LS/IMM) alone (n = 34) or in conjunction with RYGB (n = 34). The RYGB group lost more weight and had greater improvement in HbA1c. Fasting glucose was lower after RYGB than after LS/IMM, although the glucose area under the curve decreased comparably for both groups. Insulin sensitivity increased in both groups. Insulin secretion was unchanged after LS/IMM but decreased after RYGB, except for a rapid increase during the first 30 min after meal ingestion. Glucagon-like peptide 1 (GLP-1) was substantially increased after RYGB, while gastric inhibitory polypeptide and glucagon decreased. Lower HbA1c was most strongly correlated with the percentage of weight loss for both groups. At baseline, a greater C-peptide index and 90-min postprandial C-peptide level were predictive of lower HbA1c at 1 year after RYGB. β-Cell glucose sensitivity, which improved only after RYGB, and improved disposition index were associated with lower HbA1c in both groups, independent of weight loss. Weight loss and preserved β-cell function both predominantly determine the greatest glycemic benefit after RYGB.

Despite our best efforts at adequate anticoagulation with unfractionated heparin, neonates showed persistent increase in coagulation activation on extracorporeal membrane oxygenation. Fibrinolysis activation may contribute to bleeding in patients older than 30 days. Different anticoagulation protocols should be individualized based on age.

The in-plane rotational dynamics of the molecular probe coumarin 314 (C314) at the negatively charged surfactant sodium dodecyl sulfate (SDS)/aqueous interface was measured using femtosecond time-resolved second-harmonic spectroscopy. The in-plane orientational time constant at an SDS surface coverage of 100 Å 2 per SDS molecule is 348 ( 12 ps, which is comparable to the out-of-plane reorientational time of 383 ( 9 ps at the same SDS density. At 100 Å 2 , the SDS surfactant forms a homogeneous monolayer because it is in the liquid-condensed region of the surface pressure phase diagram. The rotation dynamics is slower than at the neat air/water interface, where the in-plane orientational time constant is 304 ( 8 ps and the out-ofplane reorientational time constant is 336 ( 6 ps. For purposes of comparison, we found that the orientational relaxation time of C314 in bulk water is 262 ( 10 ps. There is clear evidence for strong C314-SDS interfacial interactions based on the significant dependence of equilibrium properties on the SDS density. For example, large changes are seen in the C314 interfacial molecular orientation, marked changes in the SHG surface spectra, and changes in the surfactant phase diagram. Unlike these equilibrium properties, neither the inplane nor the out-of-plane rotations are strongly affected by interfacial SDS. The relative insensitivity of interfacial molecular rotations to the presence of anionic surfactants has implications to molecular rotations at biological cell/membrane aqueous interfaces, most of which contain anionic phospholipids.