A Facile Method for the Separation of Methionine Sulfoxide Diastereomers,Structural Assignment,and DFT Analysis

Methionine (Met) oxidation is an important biological redox node, with hundreds if not thousands of protein targets. The process yields methionine oxide (MetO). It renders the sulfur chiral, producing two distinct, diastereomerically related products. Despite the biological significance of Met oxidation, a reliable protocol to separate the resultant MetO diastereomers is currently lacking. This hampers our ability to make peptides and proteins that contain stereochemically defined MetO to then study their structural and functional properties. We have developed a facile method that uses supercritical CO₂ chromatography and allows obtaining both diastereomers in purities exceeding 99 %. ¹H NMR spectra were correlated with X-ray structural information. The stereochemical interconversion barrier at sulfur was calculated as 45.2 kcal mol⁻¹, highlighting the remarkable stereochemical stability of MetO sulfur chirality. Our protocol should open the road to synthesis and study of a wide variety of stereochemically defined MetO-containing proteins and peptides.     

Production and characterization of elastomeric cardiac tissue-like patches for Myocardial Tissue Engineering

Cardiovascular disease remains the leading cause of death. Damaged heart muscle is the etiology of heart failure. Heart failure is the most frequent cause of hospital and emergency room admissions. As a differentiated organ, current therapeutics and techniques can not repair or replace the damaged myocardial tissue. Myocardial tissue engineering is one of the promising treatment modalities for repairing damaged heart tissue in patients with heart failure. In this work, random Polylactic acid (PLA), Polylactic acid/Polyethylene glycol (PLA/PEG) and random and aligned Polylactic acid/Polyethylene glycol/Collagen (PLA/PEG/COL) nanofiber patches were successfully produced by the electrospinning technique. In vitro cytotoxic test (MTT), morphological (SEM), molecular interactions between the components (FT-IR), thermal analysis (DSC), tensile strength and physical analysis were carried out after production. The resulting nanofiber patches exhibited beadless and smooth structures. When the fiber diameters were examined, it was observed that the collagen doped random nanofiber patches had the lowest fiber diameter value (755 nm). Mechanical characterization results showed that aligned nanofiber patches had maximum tensile strength (5.90 MPa) values compared to PLA, PLA/PEG, and PLA/PEG/COL (random). In vitro degradation test reported that aligned patch had the highest degradation ratio. The produced patches displayed good alignment with tissue on cardiomyocyte cell morphology studies. In conclusion, newly produced patches have noticeable potential as a tissue-like cardiac patch for regeneration efforts after myocardial infarction.     

非Hermitian正定线性方程组的外推的HSS迭代方法

为了高效地求解大型稀疏非Hermitian正定线性方程组，在白中治、Golub和Ng提出的Hermitian和反Hermitian分裂（HSS）迭代法的基础上，通过引入新的参数并结合迭代法的松弛技术，对HSS迭代方法进行加速，提出了一种新的外推的HSS迭代方法（EHSS），并研究了该方法的收敛性.数值例子表明：通过参数值的选择，新方法比HSS方法具有更快的收敛速度和更少的迭代次数，选择了合适的参数值后，可以提高HSS方法的收敛效率.     

A BLOW-UP RESULT FOR A CLASS DOUBLY NONLINEAR PARABOLIC EQUATIONS WITH VARIABLE-EXPONENT NONLINEARITIES

This paper deals with the following doubly nonlinear parabolic equations(u + |u|~(r(x)-2)u)t-div(|?u|~(m(x)-2)?u) = |u|~(p(x)-2)u, where the exponents of nonlinearity r(x), m(x) and p(x) are given functions. Under some appropriate assumptions on the exponents of nonlinearity, and with certain initial data, a blow-up result is established with positive initial energy.     

Tensor products of n-complete algebras

If A and B are n- and m-representation finite k-algebras, then their tensor product $\mathrm{\Lambda }=A{?}_{k}B$ is not in general $(n+m)$-representation finite. However, we prove that if A and B are acyclic and satisfy the weaker assumption of n- and m-completeness, then Λ is $(n+m)$-complete. This mirrors the fact that taking higher Auslander algebra does not preserve d-representation finiteness in general, but it does preserve d-completeness. As a corollary, we get the necessary condition for Λ to be $(n+m)$-representation finite which was found by Herschend and Iyama by using a certain twisted fractionally Calabi–Yau property.     

Sonication enhances the stability of MnO2 nanoparticles on silk film template for enzyme mimic application

We have developed an in-situ method using sonication (3 mm probe sonicator, 30 W, 20 kHz) and auto-reduction (control) to study the mechanism of the formation of manganese dioxide (MnO₂) on a solid template (silk film), and its resulting enzymatic activity on tetramethylbenzidine (TMB) substrate. The fabrication of the silk film was first optimized for stability (no degradation) and optical transparency. A factorial approach was used to assess the effect of sonication time and the initial concentration of potassium permanganate (KMnO₄). The result indicated a significant correlation with a fraction of KMnO₄ consumed and MnO₂ formation. Further, we found that the optimal process conditions to obtain a stable silk film with highly catalytic MnO₂ nanoparticles (NPs) was 30 min of sonication in the presence of 0.5 mM of KMnO₄ at a temperature of 20–24 °C. Under the optimal condition, we monitored in-situ the formation of MnO₂ on the silk film, and after thorough rinsing, the in-situ catalysis of 0.8 mM of TMB substrate. For control, we used the auto-reduction of KMnO₄ onto the silk film after about 16 h. The result from single-wavelength analysis confirmed the different kinetics rates for the formation of MnO₂ via sonication and auto-reduction. The result from the multivariate component analysis indicated a three components route for sonication and auto-reduction to form MnO₂-Silk. Overall, we found that the smaller size, more mono-dispersed, and deeper buried MnO₂ NPs in silk film prepared by sonication, conferred a higher catalytic activity and stability to the hybrid material.