Stimuli-responsive surfaces using polyampholyte polymer brushes prepared via atom transfer radical polymerization

The synthesis of AB diblock copolymer polyampholyte polymer brushes of the type Si/SiO2//poly(acrylic acid-b-vinyl pyridine) prepared using atom transfer radical polymerization is reported. Both 2- and 4-vinyl pyridine have been used. The diblock polyampholyte polymer brushes demonstrate stimuli-responsive behavior with respect to pH, showing both polyelectrolyte and polyampholyte effects. Furthermore, we have quaternized the 4-vinyl pyridine segments to form a mixed weak/strong, or annealed/quenched, polyelectrolyte system. The quaternized polymer brush exhibits different pH-responsive behavior, with decreasing film thickness being observed with increasing pH.     

Exact Stratified Linear Rank Tests for Ordered Categorical and Binary Data

Abstract

We present an efficient algorithm for generating exact permutational distributions for linear rank statistics defined on stratified 2 × c contingency tables. The algorithm can compute exact p values and confidence intervals for a rich class of nonparametric problems. These include exact p values for stratified two-population Wilcoxon, Logrank, and Van der Waerden tests, exact p values for stratified tests of trend across several binomial populations, exact p values for stratified permutation tests with arbitrary scores, and exact confidence intervals for odds ratios embedded in stratified 2 × c tables. The algorithm uses network-based recursions to generate stratum-specific distributions and then combines them into an overall permutation distribution by convolution. Where only the tail area of a permutation distribution is desired, additional efficiency gains are achieved by backward induction and branch-and-bound processing of the network. The algorithm is especially efficient for highly imbalanced categorical data, a situation where the asymptotic theory is unreliable. The backward induction component of the algorithm can also be used to evaluate the conditional maximum likelihood, and its higher order derivatives, for the logistic regression model with grouped data. We illustrate the techniques with an analysis of two data sets: The leukemia data on survivors of the Hiroshima atomic bomb and data from an animal toxicology experiment provided by the U.S. Food and Drug Administration.     

MP-NeRF: A massively parallel method for accelerating protein structure reconstruction from internal coordinates

The conversion of proteins between internal and cartesian coordinates is a limiting step in many pipelines, such as molecular dynamics simulations and machine learning models. This conversion is typically carried out by sequential or parallel applications of the Natural extension of Reference Frame (NeRF) algorithm. This work proposes a massively parallel NeRF implementation which, depending on the polymer length, achieves speedups between 400 and 1200× over the previous state-of-the-art. It accomplishes this by dividing the conversion into three main phases: parallel composition of the monomer backbone, assembly of backbone subunits, and parallel elongation of sidechains; and by batching these computations into a minimal number of efficient matrix operations. Special emphasis is placed on reusability and ease of use. We open source the code (available at https://github.com/EleutherAI/mp_nerf ) and provide a corresponding python package.     

Improving protein secondary structure prediction: the evolutionary optimized classification algorithms

Structural Chemistry - Determining protein structures plays an important role in the field of drug design. Currently, the machine learning methods including artificial neural network (ANN) and...     

Hybrid Interface Based on Carboxymethyl Cellulose/N-Doped Porous Reduced Graphene Oxide for On-Demand Electrochemical Release of Imatinib

Russian Journal of Electrochemistry - The modern drug delivery research strives to utilize novel materials and fabrication technologies for the preparation of robust drug delivery systems to combat...     

Electrocatalytic Application of Girard's Reagent T to Simultaneous Determination of Furaldehydes in Pharmaceutical and Food Matrices by Highly Sensitive Voltammetric Methods

Sensitive and precise voltammetric methods for the determination of trace amounts of furaldehydes, mainly as furfural (F) and 5‐hydroxymethyl‐2‐furaldehyde (HMF), in foods, pharmaceutical and other matrices is described. Determination of total furaldehyde at <μg g^?1 levels in alkaline buffered aqueous media was individually investigated. By the use of ordinary SWV and adsorptive square wave stripping voltammetry (Ad‐SWSV), the detection limits for determination of F and HMF found to be 400 and 10 ng g^?1, respectively. At a 1.0 μg g^?1 level of furfural in sample, the relative standard deviation (n=4) was 2.79%. The application of Ad‐SWSV to the determination of F and HMF, after their in situ derivatization with trimethylaminoacetohydrazide chloride (Girard's reagent T) at a static mercury drop electrode (SMDE) in NH₃‐NH₄Cl buffer of pH 9.5, resulted in a limit of detection of 10 ng g^?1 for the resolved peaks of HMF and F. The results obtained by the proposed method for the real samples were compared with the corresponding results from UV‐spectrophotometry and HPLC experiments in various matrices.     

Structural evolution of environmentally responsive cationic liposome-DNA complexes with a reducible lipid linker

Environmentally responsive materials (i.e., materials that respond to changes in their environment with a change in their properties or structure) are attracting increasing amounts of interest. We recently designed and synthesized a series of cleavable multivalent lipids (CMVLn, with n = 2-5 being the number of positive headgroup charges at full protonation) with a disulfide bond in the linker between their cationic headgroup and hydrophobic tails. The self-assembled complexes of the CMVLs and DNA are a prototypical environmentally responsive material, undergoing extensive structural rearrangement when exposed to reducing agents. We investigated the structural evolution of CMVL-DNA complexes at varied complex composition, temperature, and incubation time using small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). A related lipid with a stable linker, TMVL4, was used as a control. In a nonreducing environment, CMVL-DNA complexes form the lamellar (L(α)(C)) phase, with DNA rods sandwiched between lipid bilayers. However, new self-assembled phases form when the disulfide linker is cleaved by dithiothreitol or the biologically relevant reducing agent glutathione. The released DNA and cleaved CMVL headgroups form a loosely organized phase, giving rise to a characteristic broad SAXS correlation profile. CMVLs with high headgroup charge also form condensed DNA bundles. Intriguingly, the cleaved hydrophobic tails of the CMVLs reassemble into tilted chain-ordered L(β') phases upon incubation at physiological temperature (37 °C), as indicated by characteristic WAXS peaks. X-ray scattering further reveals that two of the three phases (L(βF), L(βL), and L(βI)) constituting the L(β') phase coexist in these samples. The described system may have applications in lipid-based nanotechnologies.     

On equivalencies between design-based and regression-based variance estimators for randomized experiments

This paper demonstrates that the randomization-based “Neyman” and constant-effects estimators for the variance of estimated average treatment effects are equivalent to a variant of the White “heteroskedasticity-robust” estimator and the homoskedastic ordinary least squares (OLS) estimator, respectively.     

Linear and nonlinear optical properties of a macrocyclic trichromophore bundle with parallel-aligned dipole moments

A macrocyclic trichromophore bundle 1 with parallel-aligned dipole moments has been synthesized to study the influence of aggregation and orientation of a nonlinear optical (NLO) chromophore on its optical properties. The linear and nonlinear optical properties of 1 and a single chromophore standard 2 have been studied by UV-vis absorption, fluorescence, solvatochromic spectrometry, and hyper-Rayleigh scattering (HRS). Reduced first-order hyperpolarizability beta, hypsochromic shift, enhanced solvatochromic shifts, and fluorescence quenching for individual chromophores were observed when 1 was compared with 2. Analysis of the data showed that the transition dipole moment changes only slightly when the chromophores are parallel aligned in the bundle architecture. However, the apparent hyperpolarizability of the individual chromophores decreased significantly by about 20%. The reduction in beta for the individual chromophores in 1 is largely due to the hypsochromic shift, i.e., excitation energy increase of the interband (charge-transfer) energy gap and the reduced difference between the ground-state and excited-state dipole moments. The hypsochromic shift and fluorescence quenching are consistent with exciton theory. Possible reasons for the enhanced solvatochromic shift are discussed.