An experimental and computational approach to pH‐dependent self‐aggregation of poly(2‐isopropyl‐2‐oxazoline)

Besides temperature, self‐aggregation of poly(2‐isopropyl‐2‐oxazoline) (PIPOX) can also be triggered via pH in aqueous solution (25 °C, pH > 5). Lowest energy structures and interaction energies of PIPOX with H₃O⁺, OH^?, and H₂O were calculated by DFT methods showed that, in addition to their ability to protonate PIPOX, H₃O⁺ ions had strong interaction with both water and PIPOX in acidic conditions. H₃O⁺ ions acted as compatibilizer between PIPOX and water and increased the solubility of PIPOX. OH^? ions were found to have stronger interaction with water compared to PIPOX resulting in desorption of water molecules from PIPOX phase and decreased solubility, leading to enhanced hydrophobic interactions among isopropyl groups of PIPOX and formation of aggregates at high pH. Results concerning the effect of end‐groups on aggregate size were in good agreement with statistical mechanics calculations. Moreover, the effect of polymer concentration on the aggregate size was examined. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 210–221     

Structural studies and cytotoxic activity of a new dinuclear coordination compound of palladium(II)–2,2′:6′,2″‐terpyridine with rigid dianionic 1,2,4‐triazole‐3‐sulfonate linker

A new dinuclear coordination compound of palladium(II), [Pd₂(terpy)₂(μ‐tas‐N¹,N⁴)]SO₄?11H₂O ( 1 ), was synthesized by tethering a doubly deprotonated 1,2,4‐triazole‐3‐sulfonate (tas) linker generated in situ via oxidation of 1,2,4‐triazole‐3‐thione (tat) under the synthetic conditions. X‐ray diffraction analysis reveals that tat molecules adopt the thione form in the solid state, and are combined in infinite chains by symmetrically related classical intermolecular hydrogen bonds N1─H1???S1, N3─H3???N2 to give rise to R₂²(7) pattern in one‐dimensional chains along the b‐axis propagating along the a‐axis. Further short contacts through lone pairs of N2???S1 on the rings between the adjacent chains along the a‐axis lead to a two‐dimensional network structure. Compound 1 was characterized using infrared, ¹H NMR and UV–visible spectroscopies, electrospray ionization mass spectrometry and X‐ray crystallography. The crystal structure determination of 1 reveals that the Pd(II) ions are coordinated with four nitrogen atoms: three from terpy and one from tas acting as an end‐to‐end (μ‐1,4) bridging ligand. The Pd(II) ions in 1 adopt a distorted square planar geometry. The anti‐growth effect of 1 was tested on colorectal cancer (HCT‐15), non‐small‐cell lung cancer (A549), prostate cancer (PC‐3) and cervical cancer (HeLa) cell lines using sulforhodamine B viability assay. The cytotoxic effect was further confirmed using adenosine triphosphate viability assay. Compound 1 shows a promising cytotoxic activity in the diverse cancer cell models in vitro (p <0.0001).     

Computation of thermal fracture parameters for orthotropic functionally graded materials using Jk-integral

This article introduces a computational method based on the J_k-integral for mixed-mode fracture analysis of orthotropic functionally graded materials (FGMs) that are subjected to thermal stresses. The generalized definition of the J_k-integral is recast into a domain independent form composed of line and area integrals by utilizing the constitutive relations of plane orthotropic thermoelasticity. Implementation of the domain independent J_k-integral is realized through a numerical procedure developed by means of the finite element method. The outlined computational approach enables the evaluation of the modes I and II stress intensity factors, the energy release rate, and the T-stress. The developed technique is validated numerically by considering two different problems, the first of which is the problem of an embedded crack in an orthotropic FGM layer subjected to steady-state thermal stresses; and the second one is that of periodic cracks under transient thermal loading. Comparisons of the mixed-mode stress intensity factors evaluated by the J_k-integral based method to those calculated through the displacement correlation technique (DCT) and to those available in the literature point out that, the proposed form of the J_k-integral possesses the required domain independence and leads to numerical results of high accuracy. Further results are presented to illustrate the influences of the geometric and material constants on the thermal fracture parameters.     

Kinetic Analysis of Multi Enzyme Systems: A Case Study of the Closed System of Creatine Kinase, Hexokinase and Glucose 6-Phosphate Dehydrogenase

This paper describes a general methodology to handle closed multi enzyme systems using mixture of symbolic (which depends on the Gröbner Basis technique) and numerical computation methods. The applicability of the proposed method has been examined for the closed three-enzyme system of rabbit heart creatine kinase (EC 2.7.3.2), yeast hexokinase (EC 2.7.1.1) and human erythrocyte glucose 6-phosphate dehydrogenase (EC 1.1.1.49) using experimental data.     

A simple theory of 40 K superconductivity in MgB2: first-principles calculations of Tc, its dependence on boron mass and pressure

We have studied the superconducting properties of MgB₂ from first-principles under isotropic, uniaxial, and biaxial compressions. We find that the in-plane boron phonons near the zone-center are very anharmonic and strongly coupled to the planar B σ bands near the Fermi level. This mode is found to be the key to quantitatively explain the observed high T_c, the total isotope effect and the pressure dependence of T_c. We propose that a stringent test on the hole and phonon based theories of the superconductivity in MgB₂ would be a measurement of the biaxial ab-compression dependence of T_c.     

Biological distribution of iodo-allyl gabapentin and iodo-gabapentin

Gabapentin (GBP) is an anticonvulsant and is widely used in the treatment of epilepsy. In this study, GBP and an allyl derivative of GBP were radioiodinated with ¹³¹I using the iodogen method; then their radiopharmaceutical potential in rats and rabbits was investigated. The radiochemical purity of ¹³¹I-GBP and its derivatives was determined by RTLC. The labeling yield was 95±2%. Biological evaluation was performed in normal rats and rabbits. Labeled compounds were intravenously injected into two rabbits via the ear vein after anesthetizing. The dynamic and static scintigrams were obtained using a gamma camera at different time. Then the labeled compounds were administered intravenously into the rats. The distribution was studied by counting the radioactivity in the removed organs. The results of biodistribution in the rats showed the clearance of ¹³¹I-ALGBP was faster than ¹³¹I-GBP. On the other hand, the uptake of ¹³¹I-ALGBP in the brain was higher than ¹³¹I-GBP at 60 minutes.     

Antimicrobial activities and absorption properties of disazo dyes containing imidazole and pyrazole moieties

The newly synthesized thirteen disazo dyes containing imidazole and pyrazole cycles (3a-3m) were carried out by diazotization reaction of 5-amino-4-arylazo-3-methyl-1H-pyrazoles (2a-2m) and coupling reaction with 1-methyl imidazole. Structures of synthesized azo dyes were characterized by UV–Vis, FT-IR, ¹H-NMR, elemental analysis and their solvatochromic properties were studied in DMSO, DMF, methanol, acetic acid and chloroform. In addition, the antimicrobial activities of dyes against twelve pathogenic bacteria were examined in detail and all dyes showed antimicrobial activity against different bacterial strains.     

Stacking effects on local structure in RNA: changes in the structure of tandem GA pairs when flanking GC pairs are replaced by isoG-isoC pairs

The Watson-Crick-like isoG-isoC (iGiC) pair, with the amino and carbonyl groups transposed relative to the Watson-Crick GC pair, provides an expanded alphabet for understanding interactions that shape nucleic acid structure. Here, thermodynamic stabilities of tandem GA pairs flanked by iGiC pairs are reported along with the NMR structures of the RNA self-complementary duplexes (GCiGGAiCGCA)2 and (GGiCGAiGCCA)2. A sheared GA pairing forms in (GCiGGAiCGCA)2, and an imino GA pairing forms in (GGiCGAiGCCA)2. The structures contrast with the formation of tandem imino and sheared GA pairs flanked by GC pairs in the RNA self-complementary duplexes (GCGGACGC)2 and (GGCGAGCC)2, respectively. In both iGiC duplexes, Watson-Crick-like hydrogen bonds are formed between iG and iC, and iGiC substitutions result in less favorable loop stability. The results provide benchmarks for testing computations of molecular interactions that shape RNA three-dimensional structure.