The direct α-vinylation of carbonyl compounds to form a quaternary stereocenter is a challenging transformation. It was discovered that δ-oxocarboxylic acids can serve as masked vinyl compounds and be unveiled by palladium-catalyzed decarbonylative dehydration. The carboxylic acids are readily available through enantioselective acrylate addition or asymmetric allylic alkylation. A variety of α-vinyl quaternary carbonyl compounds are obtained in good yields, and an application in the first enantioselective total synthesis of (-)-aspewentins A, B, and C is demonstrated.
Vinyl chloride monomer (VCM) is widely used in the production of polyvinyl chloride (PVC) plastics. VCM is recognized as a confirmed human and animal carcinogenic compound. Recent studies have reported poor health of plastic workers, even having exposure at concentrations below the permissible limit to VCM. There has not been any study regarding exposed workers to VCM in Iran. Similarly, no information exists as to the biological monitoring of such workers. The main purpose of this study was to conduct a thorough occupational and biological monitoring of Iranian plastic workers exposed to VCM.A total of 100 workers from two plastic manufacturing plants (A and B) in Tehran along with 25 unexposed workers as controls were studied. The personal monitoring of all nonsmoking workers exposed to VCM at two plastic manufacturing plants (A and B) was performed in the morning shift (8 a.m. to 4 p.m.) according to the National Institute For Occupational Safety And Health method no. 1007.Biological monitoring of workers was carried out through collection of exhaled breath of all exposed and control workers in Tedlar bags and with a subsequent analysis using gas chromatography-flame ionization detector.Not only the mean occupational exposure of workers to VCM at plant A was higher than the respective threshold limit value but also the statistical significance was higher than workers at plant B. Similarly, VCM concentration in exhaled breath of workers at plant A was also statistically significantly higher than at plant B. Correlation of occupational exposure of all workers to vinyl chloride with its concentration in exhaled breath was statistically significant.This is the first study on biological monitoring for exposed plastic workers to VCM using exhaled breath. On the basis of the results in this study, a novel method of biological monitoring of plastic workers was proposed.
This full report details the development of the iron-catalyzed conversion of olefins to radicals and their subsequent use in the construction of C-C bonds. Optimization of a reductive diene cyclization led to the development of an intermolecular cross-coupling of electronically differentiated donor and acceptor olefins. Although the substitution on the donor olefins was initially limited to alkyl and aryl groups, additional efforts culminated in the expansion of the scope of the substitution to various heteroatom-based functionality, providing a unified olefin reactivity. A vinyl sulfone acceptor olefin was developed, which allowed for the efficient synthesis of sulfone adducts that could be used as branch points for further diversification. Moreover, this reactivity was extended into an olefin-based Minisci reaction to functionalize heterocyclic scaffolds. Finally, mechanistic studies resulted in a more thorough understanding of the reaction, giving rise to the development of a more efficient second-generation set of olefin cross-coupling conditions.
A series of end-functionalized poly(9,9'-di-n-octylfluorene vinylene)s (EF-PFVs) with different end groups were obtained by 1) synthesizing EF-PFV with vinyl end groups by acyclic diene metathesis (ADMET) polymerization with a molybdenum catalyst and termination with an aldehyde and 2) subsequent olefin metathesis of the vinyl group with the molybdenum catalyst followed by Wittig-type coupling with another aldehyde. The exclusive formation of EF-PFVs containing a vinyl end group by the ADMET polymerization was confirmed by grafting PEG, and by the synthesis of amphiphilic triblock copolymers by combining atom transfer radical polymerization from the PFV chain end with PEG grafting through a click reaction. Various EF-PFVs with different end groups, such as C6 F5 , pyridyl, ferrocenyl, and terthiophene, have thus been prepared. Their fluorescence spectra (e.g., intensities, emission wavelengths) were influenced by the end groups and the length of the conjugation.
Stimuli-sensitive hydrogels changing their volumes and shapes in response to various stimulations have potential applications in multiple fields. However, these hydrogels have not yet been commercialized due to some problems that need to be overcome. One of the most significant problems is that conventional stimuli-sensitive hydrogels are usually brittle. Here we prepare extremely stretchable thermosensitive hydrogels with good toughness by using polyrotaxane derivatives composed of α-cyclodextrin and polyethylene glycol as cross-linkers and introducing ionic groups into the polymer network. The ionic groups help the polyrotaxane cross-linkers to become well extended in the polymer network. The resulting hydrogels are surprisingly stretchable and tough because the cross-linked α-cyclodextrin molecules can move along the polyethylene glycol chains. In addition, the polyrotaxane cross-linkers can be used with a variety of vinyl monomers; the mechanical properties of the wide variety of polymer gels can be improved by using these cross-linkers.
Reactive: Se-phenyl prop-2-eneselenoate (phenyl selenoacrylate) 2, readily prepared from acryloyl chloride, is a very reactive dienophile in Diels-Alder reactions, and more reactive than acrylates. Its cycloadducts 3 with many dienes 1 can be easily reduced to the hydrocarbons 4 under radical conditions. This process works even in cases where there is an adjacent group that can be easily eliminated, e.g., an allylic ether.
The concentrations and fluxes of airborne phthalates were measured from five types of polyvinyl chloride (PVC) consumer products (vinyl flooring, wallcovering, child’s toy, yoga mat, and edge protector) using a small chamber (impinger) system. Airborne phthalates released from each of those PVC samples were collected using sorbent (Tenax TA) tubes at three temperature control intervals (0, 3, and 6 h) under varying temperature conditions (25, 40, and 90 °C). A total of 11 phthalate compounds were quantified in the five PVC products examined in this study. To facilitate the comparison of phthalate emissions among PVC samples, their flux values were defined for total phthalates by summing the average fluxes of all 11 phthalates generated during the control period of 6 h. The highest flux values were seen in the edge protector sample at all temperatures (0.40 (25 °C), 9.65 (40 °C), and 75.7 μg m-2 h-1 (90 °C)) of which emission was dominated by dibutyl isophthalate. In contrast, the lowest fluxes were found in wallcovering (0.01 (25 °C) and 0.05 μg m-2 h-1 (40 °C)) and child’s toy (0.23 μg m-2 h-1 (90 °C)) at each temperature level. The information regarding phthalate composition and emission patterns varied dynamically with type of PVC sample, controlled temperature, and duration of control.
A new effective surface poly(1-vinyl-2-pyrrolidone) (PVP) grafted layer protected selective etching strategy has been used for preparing vinyl functionalized porous silica nanospheres (V-PSNSs). The main reaction mechanism was relied on the vinyl groups distributed on the surface of outer vinyl silica nanospheres (V-SiO2) which can be polymerized with another vinyl monomer, such as 1-vinyl-2-pyrrolidone (VP), in the presence of initiator. It was observed from the research results that only grafting PVP on the surface of outer vinyl silica nanospheres (V-SiO2) can V-PSNSs be obtained, because grafting PVP was able to protect outer V-SiO2 from being etched prior to inner pure silica (sSiO2). In addition, effect of the amounts of sSiO2@V-SiO2 as another monomer substrate on the formation of PVP grafted sSiO2@V-SiO2 (sSiO2@V-SiO2/PVP) was discussed. The results showed that the less of the sSiO2@V-SiO2 amounts, the thinner of the PVP grafted layer on the surface of sSiO2@V-SiO2, the poorer protection ability of the surface. In the present study, V-PSNSs with 29 m2g-1 of BET surface areas and 0.1 cm3g-1 pore volumes were successfully synthesized by grafting 0.3 g of VP on the surface of 0.3 g of sSiO2@V-SiO2 and subsequent etching.
Composites of polyvinyl chloride (PVC) with 2% calcium carbonate, 2% diethyl phthalate, 2% paraffin wax and 2% lead sulfate and different contents of antimony trioxide (Sb2O3) prepared by melting and irradiated with gamma-ray have been considered. Assessment of the mechanical and thermal properties of the unirradiated and irradiated FPVC were completed utilizing elasticity (TS), Elongation at break (Eb) and TGA measurements. TS and thermal stability of FPVC displayed advanced improvement after addition of additives and this approach highlighted the efficiency of those ingredients on PVC. The compounding of FPVC with Sb2O3in various extents was examined by FTIR, X-ray diffraction and SEM methods. It is obviously that the presence of Sb2O3begins impacting oxidative degradation leading to decrease in mechanical properties up to 10%. Moreover, slightly increase in the thermal stability of composites by exposure to ionizing radiation is apparently due to cross-linking of FPVC chains.
Although many putative heme transporters have been discovered, it has been challenging to prove that these proteins are directly involved with heme trafficking in vivo and to identify their heme binding domains. The prokaryotic pathways for cytochrome c biogenesis, Systems I and II, transport heme from inside the cell to outside for stereochemical attachment to cytochrome c, making them excellent models to study heme trafficking. System I is composed of eight integral membrane proteins (CcmA-H) and is proposed to transport heme via CcmC to an external “WWD” domain for presentation to the membrane-tethered heme chaperone, CcmE. Herein, we develop a new cysteine/heme crosslinking approach to trap and map endogenous heme in CcmC (WWD domain) and CcmE (defining “2-vinyl” and “4-vinyl” pockets for heme). Crosslinking occurs when either of the two vinyl groups of heme localize near a thiol of an engineered cysteine residue. Double crosslinking, whereby both vinyls crosslink to two engineered cysteines facilitated a more detailed structural mapping of the heme binding sites, including stereospecificity. Using heme crosslinking results, heme ligand identification, and genomic coevolution data, we model the structure of the CcmCDE complex, including the WWD heme binding domain. We conclude CcmC trafficks heme via its WWD domain and propose the structural basis for stereochemical attachment of heme.