Adsorption Isotherm and Mechanism of Ca2+ Binding to Polyelectrolyte.

Polyelectrolytes, such as poly(acrylic acid) (PAA), can effectively mitigate CaCO3 scale formation. Despite their success as antiscalants, the underlying mechanism of binding of Ca2+ to polyelectrolyte chains remains unresolved. Through all-atom molecular dynamics simulations, we constructed an adsorption isotherm of Ca2+ binding to sodium polyacrylate (NaPAA) and investigated the associated binding mechanism. We find that the number of calcium ions adsorbed [Ca2+]ads to the polymer saturates at moderately high concentrations of free calcium ions [Ca2+]aq in the solution. This saturation value is intricately connected with the binding modes accessible to Ca2+ ions when they bind to the polyelectrolyte chain. We identify two dominant binding modes: the first involves binding to at most two carboxylate oxygens on a polyacrylate chain, and the second, termed the high binding mode, involves binding to four or more carboxylate oxygens. As the concentration of free calcium ions [Ca2+]aq increases from low to moderate levels, the polyelectrolyte chain undergoes a conformational transition from an extended coil to a hairpin-like structure, enhancing the accessibility to the high binding mode. At moderate concentrations of [Ca2+]aq, the high binding mode accounts for at least one-third of all binding events. The chain's conformational change and its consequent access to the high binding mode are found to increase the overall Ca2+ ion binding capacity of the polyelectrolyte chain.

Identification and quantification of polymeric impurity in block copolymer by one-dimensional and two-dimensional liquid chromatography coupled to high-resolution mass spectrometry and evaporative light scattering detector.

Identifying and quantifying polymeric impurities in a polymeric material is critical for understanding material quality and performance, but it remains a challenge requiring developing new characterization methods. In this work, a comprehensive two-dimensional liquid chromatography method with simultaneous evaporative light scattering and high-resolution mass spectrometry detection was developed to separate and identify a polymeric impurity in alkyl alcohol-initiated polyethylene oxide/polybutylene oxide diblock copolymer. Size exclusion chromatography was implemented in the first dimension, and gradient reversed-phase liquid chromatography using a large-pore C4 column was applied in the second dimension using an active solvent modulation valve as the interface to minimize the polymer breakthrough. The two-dimensional separation significantly reduced the complexity of the mass spectra data compared to the one-dimensional separation, and the combination of retention time and mass spectral interpretation led to the successful identification of the water-initiated triblock copolymer impurity. This identification was confirmed by comparison with the synthesized triblock copolymer reference material. A one-dimensional LC method with evaporative light scattering detection was employed to quantify the triblock impurity. The impurity level in three samples made with the different processes was determined to be in the range of 9-18 wt% using the triblock reference material as the standard.

Effect of Surfactant Concentration and Hydrophobicity on the Ordering of Water at a Silica Surface.

The performance of nonionic surfactants is mediated by the interfacial interactions at the solid-liquid interface. Here we applied sum frequency generation (SFG) vibrational spectroscopy to probe the molecular structure of the silica-nonionic surfactant solution interface in situ, supplemented by quartz crystal microbalance with dissipation monitoring (QCM-D) and molecular dynamics (MD) simulations. The combined studies elucidated the effects of nonionic surfactant solution concentration, surfactant composition, and rinsing on the silica-surfactant solution interfacial structure. The nonionic surfactants studied include ethylene-oxide (EO) and butylene oxide (BO) components with different ratios. It was found that the CH groups of the surfactants at the silica-surfactant solution interfaces are disordered, but the interfacial water molecules are ordered, generating strong SFG OH signals. Solutions with higher concentrations of surfactant lead to a slightly higher amount of adsorbed surfactant at the silica interface, resulting in more water molecules being ordered at the interface, or a higher ordering of water molecules at the interface, or both. MD simulation results indicated that the nonionic surface molecules preferentially adsorb onto silanol sites on silica. A surfactant with a higher EO/BO ratio leads to more water molecules being ordered and a higher degree of ordering of water molecules at the silica-surfactant solution interface, exhibiting stronger SFG OH signal, although less material is adsorbed according to the QCM-D data. A thin layer of surfactants remained on the silica surface after multiple water rinses. To the best of our knowledge, this is the first time the combined approaches of SFG, QCM-D and MD simulation techniques have been applied to study nonionic surfactants at the silica-solution interface, which enhances our understanding on the interfacial interactions between nonionic surfactants, water and silica. The knowledge obtained from this study can be helpful to design the optimal surfactant concentration and composition for future applications.

Insights into the behavior of ethylene oxide-1,2-epoxybutane diblock copolymers in water as a function of temperature and the presence of colloidal silica.

HYPOTHESIS: Nonionic surfactants have been widely used for many consumer products and industrial processes, and their applications often involve temperature-cycling across cloud point temperature (Tcloud). To explore the behavior of nonionic surfactants across Tcloud and when mixed with colloidal silica at a very dilute concentration around 0.1 wt%, a series of 1,2-epoxybutane-capped alcohol ethoxylates (BAEs) with various cloud points is used as a model system. EXPERIMENTS: BAEs with cloud points from 15 to 64 °C were successfully prepared by varying the lengths of 1,2-epoxybutane (BO) and ethylene oxide (EO) blocks and their phase behavior across Tcloud was studied using nuclear magnetic resonance spectroscopy (NMR), dynamic light scattering (DLS) and differential scanning calorimetry (DSC). FINDINGS: In the absence of silica, the NMR signals are not greatly affected by the cloud point transition, but both the water and surfactant exhibit a decrease in spin-spin relaxation time once the temperature reaches the Tcloud. In the presence of silica, the NMR spectra indicate significantly reduced mobility of the EO portion relative to the alkyl and BO segments. Furthermore, our results suggest that the BAE surfactants are not fractionally clouding out or precipitating with a portion of the compositional distribution during the cloud point transition.

Incidence of Naloxone Redosing in the Age of the New Opioid Epidemic.

STUDY OBJECTIVE: Naloxone, an opioid-antagonist deliverable by an intra-nasal route, has become widely available and utilized by law enforcement officers as well as basic life support (BLS) providers in the prehospital setting. This study aimed to determine the frequency of repeat naloxone dosing in suspected narcotic overdose (OD) patients and identify patient characteristics. METHODS: A retrospective chart review of patients over 17 years of age with suspected opioid overdose, treated with an initial intranasal (IN) dose of naloxone and subsequently managed by paramedics, was performed from April 2014 to June 2016. Demographic data was analyzed using descriptive statistics to identify those aspects of the history, physical exam findings. Results: A sample size of 2166 patients with suspected opioid OD received naloxone from first responders. No patients who achieved GCS 15 after treatment required redosing; 195 (9%) received two doses and 53 patients received three doses of naloxone by advanced life support. Patients were primarily male (75.4%), Caucasian (88.2%), with a mean age of 36.4 years. A total of 76.7% of patients were found in the home, 23.1% had a suspected mixed ingestion, and 27.2% had a previous OD. Two percent of all patients required a third dose of naloxone. CONCLUSION: In this prehospital study, we confirmed that intranasal naloxone is effective in reversing suspected opioid toxicity. Nine percent of patients required two or more doses of naloxone to achieve clinical reversal of suspected opioid toxicity. Two percent of patients received a third dose of naloxone.

Assessing the dysexecutive syndrome in dementia.

OBJECTIVE: We compared performance on tests of dysexecutive behaviour (DB) and executive function (EF) in patients with behavioural variant frontotemporal dementia (bvFTD), primary progressive aphasia (PPA) and corticobasal syndrome (CBS). METHODS: Patients diagnosed with bvFTD (n=124), PPA (n=34) and CBS (n=85) were recruited. EF was measured with the Delis-Kaplan Executive Function System (DKEFS: performance based), and DB was measured with the Frontal Systems Behavior Scale (FrSBe: caregiver-report based). Confirmatory factor analysis characterised the relationship between EF and DB, binary logistic regression evaluated the incremental diagnostic utility of the measures and neuroimaging data from 110 patients identified neural correlates. RESULTS: EF was lowest and DB was highest in bvFTD participants. EF and DB were distinct but related (r=-0.48). Measures correctly classified 89% of bvFTD from CBS patients and 93% of bvFTD from PPA patients-30% and 13% above base rates (59%, 80%), respectively. All modalities were useful in identifying CBS and PPA, whereas DB alone was useful for identifying bvFTD. EF was uniquely associated with caudal left dorsolateral prefrontal and lateral temporo-parietal cortices. DB was uniquely associated with the cingulate (R>L), right subcallosal and right anterior frontal cortex. EF and DB were associated with the rostral dorsolateral prefrontal cortex bilaterally. CONCLUSIONS: EF and DB measures displayed criterion and construct validity, had incremental utility at low DB levels (CBS and PPA) and were associated with overlapping and distinct neural correlates. EF and DB procedures can conjointly provide useful diagnostic and descriptive information in identifying and ruling out the dysexecutive syndrome.

Recurrent vision loss after endoscopic sinus surgery managed with palmar pressure.

A 41-year-old woman underwent endoscopic sinus surgery and 24 hours later, she developed acute orbital emphysema with marked vision loss. CT showed disruption of the inferior aspect of the medial wall of the orbit with fat herniation. She was immediately treated with the application of bedside palmar pressure to the globe with complete return of her vision without the need for a needle aspiration or orbital decompression. Weeks later, the patient experienced 2 more episodes of transient monocular visual loss that were again successfully treated with the same palmar pressure. Bedside digital decompression may be a potentially helpful method of restoring vision in cases of orbital emphysema with acute vision loss. We advise attempting this simple bedside procedure before committing the patient to a more invasive needle aspiration or surgical decompressive procedure.

Atherothrombosis in acute coronary syndromes: mechanisms, markers, and mediators of vulnerability.

We review the concept of atherothrombosis and the critically important role of inflammation in the development of acute coronary syndromes (ACS). Inflammation is now known to be a major driving force underlying the initiation of coronary plaques, their unstable progression, and eventual disruption, and it also contributes significantly to thrombotic complications that occur in ACS. In addition, we discuss the various local mediators and systemic markers that are involved in the inflammatory process, and review the concepts of 'vulnerable plaque,' 'vulnerable blood,' 'vulnerable myocardium,' and the 'vulnerable patient' who is at increased risk for ACS.