Molecular dynamics simulation of cross-linked urea-formaldehyde polymers for self-healing nanocomposites: prediction of mechanical properties and glass transition temperature

Urea-formaldehyde polymers, which are utilized in the adhesives industry, have recently been shown to be suitable materials for synthesizing micro/nanocapsules for use in self-healing (nano)composites. In this study, molecular dynamics was employed to simulate the process in which urea and formaldehyde are cross-linked via methylene and ether cross linkers, and to study the structure and mechanical/thermal properties of simulated poly(urea-formaldehyde)s (PUFs). The elastic stiffness constants of the simulated materials were calculated using the constant-strain (static) method. A temperature cycle was applied to the cross-linked PUFs, and the glass transition behavior of each material was investigated through the mean squared displacement (MSD) and temperature evolution of the energy and the specific volume of the polymer. The simulation results confirmed that there was considerable improvement in the properties of the poly(UF) materials upon cross linking. The radial distribution function was also used to study the local structures of the polymers, and this revealed that increasing the temperature and cross linking density results in a significant drop in hydrogen bonding intensity in the cross-linked PUF systems.     

Spatial distribution and diversity of commercial demersal fish species in the shelf waters of the Caspian Sea

The Caspian Sea (CS) is a unique ecosystem known for its several fish species, especially sturgeons. To exhaustively manage the fish stocks of this ecosystem, detailed knowledge of species composition, abundance, distribution, and the habitat traits of the living organisms is necessary. This study analyzed the diversity, spatial, and seasonal distribution of commercial demersal fish species, and examined the relationships between community structure and environmental variability in Iranian shelf waters of the CS. For this purpose, seasonally fish sampling took place between 2009 and 2011 with a bottom trawl. Among 11 fish species captured, Chelon spp., Rutilus kutum, and Vimba vimba showed the highest abundances (i.e. 88.49%, 10.67%, and 0.69%, respectively). Univariate and multivariate analyses showed differences in commercial fish assemblages (abundance and species richness) according to seasons and regions. Distance-based Linear Model (DisTLM) showed that eight environmental variables display significant linear relationships with the fauna resemblance matrix (p < .05). Based on AIC criteria, the combination of silt&clay, TOM, longitude, depth, bottom, and surface temperature used to build the parsimonious DisTLM model explain 67.03% of the total variability. The results revealed a biogeographical and temporal gradient from the west to the east and summer to winter, in terms of commercial demersal fish assemblages and species diversity, as a consequence of different geomorphological, bottom substratum conditions and benthic communities.     

Dinoflagellate Endosymbiont of the Soft Coral Stichodactyla haddoni Saville-Kent Collected from the Coast of Hormuz Island,Strait of Hormuz

Russian Journal of Marine Biology - An endosymbiotic dinoflagellate isolated from the soft coral Stichodactyla haddoni from the coast of Hormuz Island, Strait of Hormuz, Persian Gulf, has been...     

Therapeutic effects of medicinal plants and their constituents on lung cancer,in vitro,in vivo and clinical evidence

The most common type of cancer in the world is lung cancer. Traditional treatments have an important role in cancer therapy. In the present review, the most recent findings on the effects of medicinal plants and their constituents or natural products (NP) in treating lung cancer are discussed. Empirical studies until the end of March 2022 were searched using the appropriate keywords through the databases PubMed, Science Direct and Scopus. The extracts and essential oils tested were all shown to effect lung cancer by several mechanisms including decreased tumour weight and volume, cell viability and modulation of cytokine. Some plant constituents increased expression of apoptotic proteins, the proportion of cells in the G2/M phase and subG0/G1 phase, and Cyt c levels. Also, natural products (NP) activate apoptotic pathways in lung cancer cell including p-JNK, Akt/mTOR, PI3/ AKT\ and Bax, Bcl2, but suppressed AXL phosphorylation. Plant-derived substances altered the cell morphology, reduced cell migration and metastasis, oxidative marker production, p-eIF2α and GRP78, IgG, IgM levels and reduced leukocyte counts, LDH, GGT, 5′NT and carcinoembryonic antigen (CEA). Therefore, medicinal plant extracts and their constituents could have promising therapeutic value for lung cancer, especially if used in combination with ordinary anti-cancer drugs.     

The effect of cross linking density on the mechanical properties and structure of the epoxy polymers: molecular dynamics simulation

Recently, great attention has been focused on using epoxy polymers in different fields such as aerospace, automotive, biotechnology, and electronics, owing to their superior properties. In this study, the classical molecular dynamics (MD) was used to simulate the cross linking of diglycidyl ether of bisphenol-A (DGEBA) with diethylenetriamine (DETA) curing agent, and to study the behavior of resulted epoxy polymer with different conversion rates. The constant-strain (static) approach was then applied to calculate the mechanical properties (Bulk, shear and Young’s moduli, elastic stiffness constants, and Poisson’s ratio) of the uncured and cross-linked systems. Estimated material properties were found to be in good agreement with experimental observations. Moreover, the dependency of mechanical properties on the cross linking density was investigated and revealed improvements in the mechanical properties with increasing the cross linking density. The radial distribution function (RDF) was also used to study the evolution of local structures of the simulated systems as a function of cross linking density.     

Alzheimer's disease: the beta amyloid protein A4 is also present in the cortical white matter

Amyloid deposits constituted with the beta amyloid protein A4 (beta PA4) have been recently immunodetected in skin and intestine wall of Alzheimer's patients. These findings support the hypothesis of an extraneuronal origin of the beta PA4. Until now, these amyloid deposits had not been observed in the white matter of Alzheimer's brains. Using an antiserum against the 1-10 N Ter subsequence of the beta PA4, we immunodetected amyloid deposits in white matter sections of Alzheimer's brains, pretreated with periodic acid. The immunolabelled amyloid substance was associated with capillaries. These original findings are in good agreement with the vascular origin of the beta PA4.