Effect of intramolecular crosslinker properties on the mechanochemical fragmentation of covalently folded polymers

The mechanochemical stability of polymers in solution is enhanced if the chains are covalently folded. Under shear forces, the additional bonds absorb mechanical energy and inhibit unfolding, and as a result, slow down fragmentation. However, not all crosslinkers are equal in terms of their properties (length, strength, etc.). In order to understand the role of these added bonds in the polymers' stability under mechanical stress, a thorough study compares the rate of mechanochemistry on single-chain polymer nanoparticles which have been folded with crosslinkers with different lengths, strengths, positioning, and valencies. The usage of bonds with different mechanical strengths in the crosslinkers was found to be the most powerful way to change the mechanochemical fragmentation rate. In addition, positioning and valency also play significant role in the mechanical stabilization mechanism. © 2020 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2020 © 2020 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2020 , 58, 692–703     

Aerosol retrievals from channel-1 and -2 AVHRR radiances: Long-term trends updated and revisited

The nominal Global Aerosol Climatology Project (GACP) record of aerosol optical thickness (AOT) and Ångström exponent (AE) over the oceans is extended by 6 months to cover the period from August 1981 through December 2005. The most recent 4-year segment reveals no significant short-term tendencies in globally and hemispherically averaged AOTs and AEs. This finding is consistent with contemporaneous MODIS and MISR results and the accumulating evidence of a gradual transition from global brightening to global dimming. We also analyze the retrieval implications of allowing the imaginary part of the aerosols refractive index Im(m) to change over the duration of the GACP record. Our sensitivity study shows that increasing Im(m) from 0.003 during the 4-year pre-Pinatubo period up to 0.007 during the most recent 4-year segment of GACP data eliminates the previously identified long-term decreasing AOT trend. Should this long-term trend in Im(m) be real then it would cause the global absorption AOT over the oceans to more than double and the global single-scattering albedo to decrease from ～0.95 to ～0.88. Such changes could make tropospheric aerosols significant contributors to the recent surface temperature increase.     

Convexity preserving C 0 splines

Linear conditions for a C ⁰ spline to be convex are developed and used to create some convexity preserving interpolation and approximation methods.     

Inverse electron demand hetero-Diels–Alder reaction in preparing 1,4-benzodioxin from o-quinone and enamine

A process for synthesizing 1,4-benzodioxin, through oxidation of a phenol to an o-quinone followed by treatment with an enamine, has been developed. Adduct stereochemistry is found to be retained via this one-pot reaction. The method uses hypervalent iodine reagent under mild conditions and is compatible with a wide scope of phenols and enamines.     

Combined prostate diffusion tensor imaging and dynamic contrast enhanced MRI at 3T — quantitative correlation with biopsy

The purpose of this work was to compare diagnostic accuracy of Diffusion Tensor Imaging (DTI), dynamic contrast-enhanced magnetic resonance imaging (DCE MRI) and their combination in diagnosing prostate cancer. Twenty-five patients with clinical suspicion of prostate cancer underwent MRI, prior to transrectal ultrasound-guided biopsies. MRI data were correlated to biopsy results. Logistic regression models were constructed for the DTI parameters, DCE MRI parameters, and their combination. The areas under the receiver operator characteristic curves (AUC) were compared between the models. The nonparametric Wilcoxon signed rank test was used for statistical analysis. The sensitivity and specificity values were respectively 81% (74–87%) and 85% (79–90%) for DTI and 63% (55–70%) and 90% (85–94%) for DCE. The combination “DTI or DCE MRI” had 100% (97–100%) sensitivity and 77% (69–83%) specificity, while “DTI and DCE MRI” had 44% (37–52%) sensitivity and 98% (94–100%) specificity. The AUC for DTI+DCE parameters was significantly higher than that for either DTI (0.96 vs. 0.92, P=.0143) or DCE MRI parameters (0.96 vs. 0.87, P=.00187) alone. In conclusion, the combination of DTI and DCE MRI has significantly better accuracy in prostate cancer diagnosis than either technique alone.     

Long-Wave Asymptotics of Lamb Waves

The six-dimensional complex formalism is used to obtain equations for determining long-wave asymptotics of symmetric fundamental modes of Lamb waves in an anisotropic layer. Analytic expressions are obtained for long-wave asymptotics of phase velocities of Lamb waves propagating in an isotropic layer.     

Profiling primaquine metabolites in primary human hepatocytes using UHPLC‐QTOF‐MS with 13C stable isotope labeling

Therapeutic efficiency and hemolytic toxicity of primaquine (PQ), the only drug available for radical cure of relapsing vivax malaria are believed to be mediated by its metabolites. However, identification of these metabolites has remained a major challenge apparently due to low quantities and their reactive nature. Drug candidates labeled with stable isotopes afford convenient tools for tracking drug‐derived metabolites in complex matrices by liquid chromatography‐tandem mass spectrometry (LC‐MS‐MS) and filtering for masses with twin peaks attributable to the label. This study was undertaken to identify metabolites of PQ from an in vitro incubation of a 1:1 w/w mixture of ¹³C₆‐PQ/PQ with primary human hepatocytes. Acquity ultra‐performance LC (UHPLC) was integrated with QTOF‐MS to combine the efficiency of separation with high sensitivity, selectivity of detection and accurate mass determination. UHPLC retention time, twin mass peaks with difference of 6 (originating from ¹³C₆‐PQ/PQ), and MS‐MS fragmentation pattern were used for phenotyping. Besides carboxy‐PQ (cPQ), formed by oxidative deamination of PQ to an aldehyde and subsequent oxidation, several other metabolites were identified: including PQ alcohol, predictably generated by oxidative deamination of PQ to an aldehyde and subsequent reduction, its acetate and the alcohol's glucuronide conjugate. Trace amounts of quinone‐imine metabolites of PQ and cPQ were also detected which may be generated by hydroxylation of the PQ/cPQ quinoline ring at the 5‐position and subsequent oxidation. These findings shed additional light on the human hepatic metabolism of PQ, and the method can be applied for identification of reactive PQ metabolites generated in vivo in preclinical and clinical studies. Copyright © 2013 John Wiley & Sons, Ltd.     

Halogenation of 2-Hydroxynicotinic Acid

A convenient method to prepare 5-halo-2-hydroxy-nicotinic acid is described.     

Comparison of impurities in charcoal sorbents found by neutron activation analysis

Neutron activation of gas samples in a reactor often requires a medium to retain sufficient amounts of the gas for analysis. Charcoal is commonly used to adsorb gas and hold it for activation; however, the amount of activated sodium in the charcoal after irradiation swamps most signals of interest. Neutron activation analysis was performed on several commonly available charcoal samples in an effort to determine the activation background. The results for several elements, including the dominant sodium element, are reported. It was found that ECN charcoal had the lowest elemental background, containing sodium at 2.65 ± 0.05 ppm, as well as trace levels of copper and tungsten.