Isomers of the C84 fullerene: A theoretical consideration within energetic,structural, and topological approaches

Currently, there is no common conception on the stability and achievability of fullerene isomers under the arc-discharge synthesis conditions. Different approaches operate with energetic, structural, and topological parameters of the fullerene molecules to explain why some fullerene isomers are more preferable than the others. In the present work, we have selected the most appropriate approaches based on topological roundness, information entropy, nuclear volumes, and sphericities and compared their predictions with the relevant experimental data on the C₈₄ fullerene isomers (obeying the isolated pentagon rule) and density functional theory estimates of their stability. We have found that the molecules of most stable (and most abundant) C₈₄ isomers have the minimal extremal roundness, maximal sphericity, and largest volume and vice versa. In the case of the information entropy, no correlation is observed. Interestingly, the found correlation between the volume and the stability of the C₈₄ isomers is unexpectedly inverse, i.e. more stable C₈₄ isomers have larger inner cavities inside, though traditionally large volume is associated with instability of hollow framework molecules. We assume that the large volumes allows enhancing the sphericity of the fullerene cages as we found the last one favoring the stability and the unstable C₈₄ fullerene cages having low volumes are far from the spherical shape. We think that the results obtained may be extrapolated to other fullerene isomeric sets and contribute to the understanding the grounds of the interconnection in the triad “topology – structure – energy” underlying structural chemistry.     

Metallic Hydrogen

One of the great challenges in condensed matter physics has been to produce metallic hydrogen (MH) in the laboratory. There are two approaches: solid molecular hydrogen can be compressed to high density at extreme pressures of order 5–6 megabars. The transition to MH should take place at low temperatures and is expected to occur as a structural first-order phase transition with dissociation of molecules into atoms, rather than the closing of a gap. A second approach is to produce dense molecular hydrogen at pressures of order 1–2 megabars and heat the sample. With increasing temperature, it was predicted that molecular hydrogen first melts and then dissociates to atomic metallic liquid hydrogen as a first-order phase transition. We have observed this liquid–liquid phase transition to metallic hydrogen, also called the plasma phase transition. In low-temperature studies, we have pressurized HD to over 3 megabars and observed two new phases. Molecular hydrogen has been pressurized to 4.2 megabars. A new phase transition has been observed at 3.55 megabars, but it is not yet metallic.     

Financial performance, ISO 9000 standard and safe driving practices effects on accident rate in the U.S. motor carrier industry

The question this research address is if voluntary certification with ISO 9000 standards can reduce the number of accidents large trucks have. Certification might have a positive effect depending upon the actions a company takes as a result of being certified, for instance, a company may change driver training and maintenance and how it carries out corrective action. We identified 40 ISO 9002: 1994 certified U.S. trucking companies and compared their safety performance before and after ISO certification. We also compared them to a group of motor carriers that had similar characteristics but were not certified. The safety performance of the certified carriers was significantly better after certification than before, and it also was significantly better than that of non-certified carriers, findings that we believe can be useful to carriers, shippers and regulators who wish to better understand the value of certification.     

Co-pyrolysis of polymethyl methacrylate with brown coal and effect on monomer production

Pyrolysis capillary gas chromatography has been applied to the study of the co-pyrolysis of polymethyl methacrylate (PMMA) with Slovakian brown coal with the aim of finding pyrolysis conditions yielding a maximum amount of methyl methacrylate (MMA). Effects of pyrolysis temperature and PMMA-coal weight ratios were investigated. Capillary gas chromatography coupled with mass spectrometric detector (cGC-MS) was used for MMA identification. The highest yield of MMA in the pyrolysate was obtained at 750 °C. The optimal PMMA-coal weight ratio for maximum MMA production lies in the interval 0.5 mg PMMA and 0.6-0.8 mg brown coal with an MMA yield of 64%. Coal addition to the sample affects species recombination in gaseous phase, augments MMA production at higher temperatures and eliminates degradation products of PMMA and coal pyrolysis. Different conversion diagrams are characteristic for thermal degradation of single PMMA and in the mixture with coal. Detailed mechanism of synergetic effects arisen during co-pyrolysis are not yet known. It was also found that lower pyrolysis temperatures are more suitable to study degradation mechanism and kinetics while higher temperatures are more applicable for identification purposes. MMA decomposes completely at 900 °C.     

Granulocyte Colony-Stimulating Factor Restored Impaired Spermatogenesis and Fertility in an AML-Chemotherapy Mice Model

Leukemia and treatment of male patients with anticancer therapy (aggressive chemotherapy and/or radiotherapy) may lead to infertility or even permanent male sterility. Their mechanisms of spermatogenesis impairment and the decrease in male fertility are not yet clear. We showed that under acute myeloid leukemia (AML) conditions, alone and in combination with cytarabine (CYT), there was significant damage in the histology of seminiferous tubules, a significant increase in apoptotic cells of the seminiferous tubules, and a reduction in spermatogonial cells (SALL and PLZF) and in meiotic (CREM) and post-meiotic (ACROSIN) cells. In addition, we showed a significant impairment in sperm parameters and fertilization rates and offspring compared to control. Our results showed a significant decrease in the expression of glial cell line-derived neurotrophic factor (GDNF), macrophage colony-stimulating factor (MCSF) and stem cell factor (SCF) under AML conditions, but not under cytarabine treatment compared to control. In addition, our results showed a significant increase in the pro-inflammatory cytokine interleukin-1 (IL-1) alpha in whole testis homogenates in all treatment groups compared to the control. Increase in IL-1 beta level was shown under AML conditions. We identified for the first time the expression of GCSF receptor (GCSFR) in sperm cells. We showed that GCSF injection in combination with AML and cytarabine (AML + CYT + GCSF) extended the survival of mice for a week (from 6.5 weeks to 7.5 weeks) compared to (AML + CYT). Injection of GCSF to all treated groups (post hoc), showed a significant impact on mice testis weight, improved testis histology, decreased apoptosis and increased expression of pre-meiotic, meiotic and post- meiotic markers, improved sperm parameters, fertility capacity and number of offspring compared to the controls (without GCSF). GCSF significantly improved the spermatogonial niche expressed by increased the expression levels of testicular GDNF, SCF and MCSF growth factors in AML-treated mice and (AML + CYT)-treated mice compared to those groups without GCSF. Furthermore, GCSF decreased the expression levels of the pro-inflammatory cytokine IL-12, but increased the expression of IL-10 in the interstitial compartment compared to the relevant groups without GCSF. Our results show for the first time the capacity of post injection of GCSF into AML- and CYT-treated mice to improve the cellular and biomolecular mechanisms that lead to improve/restore spermatogenesis and male fertility. Thus, post injection of GCSF may assist in the development of future therapeutic strategies to preserve/restore male fertility in cancer patients, specifically in AML patients under chemotherapy treatments.     

Cure kinetics of bismaleimides as basis for polyimide-like inks for PolyJet™-3D-printing

Since polyimides are well known for their excellent chemical and thermal stability and outstanding mechanical properties there is increasing interest in developing polyimide-based inks to produce additively manufactured parts with properties superior to those of currently available materials. Usage of bismaleimides (BMI) as precursors allows polyimides to be fabricated via PolyJet™ printing (Stratasys Ltd., Rehovot, Israel). Characterization of the curing kinetics is a central part of process development, as fast curing initiated by UV light is desired. Here, a comprehensive study of thermal and UV curing of BMI oligomers with various molecular weights and chemical structures is presented. Fourier transform infrared spectroscopy serves as a tool for determining the curing degree. Furthermore, an estimation of the activation energy for thermal curing is performed. UV curing of the selected BMIs leads to highly crosslinked, thermoset polymers with excellent chemical resistance and thermal stability which are of great interest for PolyJet™ 3D printing. © 2018 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47244.     

The Role of Heteroatoms Leading to Hydrogen Bonds in View of Extended Chemical Stability of Organic Semiconductors

The major challenge in organic electronics concerns the stability of organic semiconductor materials which affects the operational lifetime of devices. Recent reports have shown that hydrogen‐bonded pigments of the indigoid family are air‐ and moisture resistant. The magenta pigment quinacridone, a hydrogen‐bonded molecule in the solid state with a pentacene like frame, is a perfect example for extraordinary chemical stability. Here, studies using in situ spectroscopic methods comparing quinacridone and pentacene are presented. A different spectral response of their radical cations is observed upon chemical doping. While in pentacene the barrier between doping and irreversible overoxidation is small, this stability toward overoxidation is increased by the heteroatomic structure, leading to hydrogen‐bonded quinacridone. This work provides insight into molecular design principles that may lead to next‐generation organic semiconductors with enhanced stability and performance.