Temperature-Transferable Coarse-Grained Model for Poly(propylene oxide) to Study Thermo-Responsive Behavior of Triblock Copolymers.

Thermo-responsive behavior of ethylene oxide (EO)-propylene oxide (PO) copolymers makes them suitable for many potential applications. Reproducing the origins of the tunable properties of EO-PO copolymers using coarse-grained (CG) models such as the MARTINI force field is critically important for building a better understanding of their behavior. In the present work, we have investigated the effects of coarse-graining on the water-polymer interaction across a temperature range. We compared the performance of different all-atom force fields to find the most appropriate one for the purpose of PO block parameterization in the MARTINI platform. We parameterized a CG temperature-dependent PO model based on the reproduction of the atomistic free energy of transfer of propylene oxide trimer from octane to water over a range of temperatures (20-60 °C) and compared the atomistic bond and angle distributions. Then, we used the model to study the effects of EO/PO ratio, molecular weight, and concentration on the thermo-responsive behavior of EO-PO copolymers in water. The results show an excellent agreement with experiments in different areas. Our temperature-dependent model reproduces (1) micellar phase above critical micelle temperature (CMT) and unimer phase below CMT for different Pluronics (a class of EO-PO triblock copolymers) spanning many EO/PO ratios and molecular weights; (2) spherical-to-rodlike micellar shape transition for Pluronics with 60 wt % of PO content or more; (3) diffusion coefficients for Pluronics with high PO content (P104 Pluronic with a PO mass of 3500 g mol-1) across a broad range of temperatures; and (4) micelle core size and micelle diameter similar to experimental results. Overall, our model improves the temperature sensitivity of EO-PO copolymers of existing models significantly, particularly for copolymers that are dominated by PO agents.

Prevalence of oral ulcers and its association with addictions in rural population of western Uttar Pradesh and eastern Rajasthan.

BACKGROUND: Head and neck cancer in Indian perspective predominantly relates to tobacco use. The present study explores the prevalence of oral ulcers and its association with addictions among the population of Uttar Pradesh and Rajasthan, India. METHODOLOGY: The screening method in early detection of head and neck cancer is broadly symptom based. 1399 subjects from Uttar Pradesh and Rajasthan were screened by trained personnel between April and June 2015. RESULTS: Study findings showed, mouth ulcers and trismus were common symptoms and tobacco chewing and smoking were common addictions. There were statistically significant associations among the symptoms and addictions as well as predominance in rural populations. The majority of smokers (27.1%) belonged to age ≥55 years whereas the tobacco chewers (29.2%) and alcohol abusers (45.8%) in the age group 25-34 years. Also the risk of developing mouth ulcers and trismus in this area are approximately 35 (MRR: 35.7, 95% CI: 15.5-81.9) and nearly eight (MRR: 7.7, 95% CI: 2.2-26.6) times higher respectively in males. However, joint use of smoked and smokeless tobacco increases nearly three times more risk of either mouth ulcers or trismus. CONCLUSION: Male individuals are more exposed to certain addictions such as tobacco (smoked and smokeless) and alcohol. The prevalence of oral ulcers is primarily associated with the addictions. Therefore, these persons are more at risk of further developing head neck cancer. A large level community screening and awareness are required especially among the rural population of India.

Finite size effects on aluminum/Teflon reaction channels under combustive environment: a Rice-Ramsperger-Kassel-Marcus and transition state theory study of fluorination.

The effect of particle size on combustion efficiency is an important factor in combustion research. Gas-phase aluminum clusters in oxidizing environment constitute a relatively simple and extensively studied system. In an attempt to underscore the correlation between electronic structure, finite size effect, and reactivity in small aluminum clusters, reactions between aluminum, [Al(13)](-) cluster, and Teflon decomposition fragments were studied using theoretical calculations at the density functional theoretical level. The unimolecular rate constants calculated using transition state and Rice-Ramsperger-Kassel-Marcus theory show that reactions with COF and CF(2) species with aluminum are faster than those involving CF(3) and COF(2). The results show that the kinetic barriers along different exothermic reaction channels correlate with the trends in HOMO(R)-HOMO(TS) (HOMO denotes highest occupied molecular orbital) energy gap and related shifts of the HOMO levels of reactants. Overall reactions involving carbonyl fluoride species (COF and COF(2)) lead to CO elimination and fluorination of the Al cluster. The CF(3)/CF(2) fragments lead to stable multicenter Al-C bond formation on the fluorinated Al cluster surface. Temperature-, energy-, and pressure-dependent rate constants are provided for extrapolating the expected reaction kinetics to conditions similar to known combustion reactions.

Theoretical study of elementary steps in the reactions between aluminum and teflon fragments under combustive environments.

Gas-phase reactions between aluminum particles and Teflon fragments were studied to develop a fundamental understanding of the decomposition reactions and combustion processes of the Al-Teflon composites. The reactions were investigated theoretically using ab initio calculations at the MP2/aug-cc-pVDZ level, with the final thermokinetic data obtained with coupled cluster theory (CCSD(T)/aug-cc-pVTZ). Among reactions under oxygen-lean conditions, CF(3) + Al --> CF(2) + AlF channel is the fastest, followed by the CF(2) + Al --> CF + AlF and CF + Al --> C + AlF channels. Under oxygen-rich conditions, reactions of COF with aluminum are probed to be faster than those involving COF(2) species. Reaction path multiplicity has been considered. Our results show that multiplicity plays a very important role in determining the reaction order, that is first order or addition-elimination reactions of Al with CF(3) are predicted to be faster than those proceeding through direct abstraction or second order. In addition, the present kinetic model suggests that CF(3) + Al --> CF(2) + AlF with m = 1 and COF + Al --> CO + AlF channels are very competitive under the same thermal conditions. The computed enthalpies of reaction are systematically compared with the available literature. The predicted kinetic model and its time constants (tau) are in good qualitative agreement with experimental observations of the reactions between Al nanoparticles and Teflon for the 500-1200 K temperature range.

Cigarette smoke extract induces changes in growth and gene expression of Saccharomyces cerevisiae.

The response of Saccharomyces cerevisiae cells to an aqueous extract of cigarette smoke was studied. Exposure to cigarette smoke extract inhibits yeast growth and results in global changes in gene expression spanning many functional classes of genes. Genes involved in response to oxidative stress are upregulated after a brief exposure to cigarette smoke extract. The effects of cigarette smoke extract on yeast growth can be reversed by treatment with anti-oxidants. Mutants lacking superoxide dismutase gene were hypersensitive to cigarette smoke exposure. YAP1 is a central transcriptional regulator of oxidative stress in yeast. YAP1 dependent expression of beta-galactosidase was enhanced following exposure to cigarette smoke. The overall agreement between our observations and the recently reported effects of cigarette smoke on gene expression in rodent and human cells suggests that yeast can be used as a model system in toxicogenomics studies for monitoring toxic agents and studying the cellular and molecular consequences of exposure to potentially toxic agents.

Activation of S phase checkpoint by cigarette smoke extract in Schizosaccharomyces pombe.

Cigarette smoke has long been recognized as a major environmental pollutant that can cause significant damage to the cellular macromolecules. Although much is known about the types of damage, little is known about the cellular responses to the stress caused by cigarette smoke. We have used the fission yeast Schizosaccharomyces pombe to elucidate the overall cellular responses towards cigarette smoke. Here, we demonstrate that fission yeast cells exposed to aqueous extract of cigarette smoke exhibit cell cycle arrest and cell death in a dose-dependent manner. Cigarette smoke treatment also results in accumulation of reactive oxygen species, unusual nuclear morphology and altered cellular structure. Our data further establish activation of the S phase checkpoint in cigarette smoke-exposed Sz. pombe cells. The checkpoint proteins Rad3, Rad26, Rad17, Rad1, Hus1 and Cds1 play key roles in this process, as evidenced by cell survival and biochemical analysis, although another checkpoint protein, Rad9, seems to be less required. Our results also suggest involvement of the stress-activated protein kinase Spc1/Sty1 and the bZIP transcription factors Atf1 and Pap1 in the cellular response towards cigarette smoke extract. These findings indicate activation of the critical S phase checkpoint and cell cycle arrest in Sz. pombe following CSE assault.