Ni-catalyzed carbon–carbon bonds cleavage of mixed polyolefin plastics waste

The inert carbon–carbon(C–C) bonds cleavage is a main bottleneck in the chemical upcycling of recalcitrant polyolefin plastics waste. Here we develop an efficient strategy to catalyze the complete cleavage of C–C bonds in mixed polyolefin plastics over non-noble metal catalysts under mild conditions. The nickelbased catalyst involving Ni₂Al₃ phase enables the direct transformation of mixed polyolefin plastics into natural gas, and the gas carbon yield reaches up to 89.6%. R...     

Secondary structure analysis of peptides with relevance to iron–sulfur cluster nesting

Peptides coordinated to iron–sulfur clusters, referred to as maquettes, represent a synthetic strategy for constructing biomimetic models of iron–sulfur metalloproteins. These maquettes have been successfully employed as building blocks of engineered heme-containing proteins with electron-transfer functionality; however, they have yet to be explored in reactivity studies. The concept of iron–sulfur nesting in peptides is a leading hypothesis in Origins-of-Life research as a plausible path to bridge the discontinuity between prebiotic chemical transformations and extant enzyme catalysis. Based on past biomimetic and biochemical research, we put forward a mechanism of maquette reconstitution that guides our development of computational tools and methodologies. In this study, we examined a key feature of the first stage of maquette formation, which is the secondary structure of aqueous peptide models using molecular dynamics simulations based on the AMBER99SB empirical force field. We compared and contrasted S…S distances, [2Fe-2S] and [4Fe-4S] nests, and peptide conformations via Ramachandran plots for dissolved Cys and Gly amino acids, the CGGCGGC 7-mer, and the GGCGGGCGGCGGW 16-mer peptide. Analytical tools were developed for following the evolution of secondary structural features related to [Fe-S] cluster nesting along 100 ns trajectories. Simulations demonstrated the omnipresence of peptide nests for preformed [2Fe-2S] clusters; however, [4Fe-4S] cluster nests were observed only for the 16-mer peptide with lifetimes of a few nanoseconds. The origin of the [4Fe-4S] nest and its stability was linked to a “kinked-ribbon” peptide conformation. Our computational approach lays the foundation for transitioning into subsequent stages of maquette reconstitution, those being the formation of iron ion/iron–sulfur coordinated peptides. © 2018 Wiley Periodicals, Inc.     

Discovery of β-Dihydroagarofuran-Type Sesquiterpenoids from the Leaves of Tripterygium wilfordii with Neuroprotective Activities

Nine undescribed dihydro-β-agarofuran sesquiterpenoid derivatives(1—9),along with a known analogue(10),were obtained from the leaves of Tripterygium wilfordii.Their gross structures were determined via extensive spectroscopic data,and the absolute configurations were elucidated by means of single-crystal X-ray diffraction analysis and electron circular dichroism(ECD)techniques,which include ECD exciton chirality,octant rule of saturated cyclohexanone and comparison between the experimental and calculated ECD spectra.All the isolated compounds were tested for their neuroprotective activities against H2O2-induced cell injury in human neuroblastoma SH-SY5Y cells.Compounds 5 and 6 improved cell viability by 16.15%and 15.12%compared with the H2O2 treated group at 25μmol·L^-1,respectively.     

μLC coupled to ICP–SFMS with post-column isotope dilution analysis of sulfur for absolute protein quantification

Absolute protein quantification has become an important challenge in modern bioanalytical chemistry. Among several approaches based on mass spectrometric techniques, inductively coupled plasma (ICP) as ionisation source provides element-selective and sensitive detection of heteroatoms, and thus, a potentially emerging tool in protein analysis. In this work we applied coupling of capillary liquid chromatography (μLC) and inductively coupled plasma-sector field mass spectrometry (ICP–SFMS) to the separation and determination of standard proteins. For quantification purposes, post-column isotope dilution of sulfur was applied and optimised for this type of hyphenated technique. Provided that the protein sequence is known (number of sulfur-containing amino acids, i.e. cysteines and methionines) the protein amount can then be directly calculated from the determined sulfur content in a certain protein fraction. In order to prove the reliability of the presented method, two different certified reference materials were analysed: CRM 393 (human apolipoprotein A-I) and CRM 486 (α-fetoprotein). For CRM 393 excellent agreement (37.0 ± 1.4 μmol L⁻¹) was obtained with the certificate (37.7 ± 1.8 μmol L⁻¹). However, the recovery rate for α-fetoprotein in CRM 486 was found to be about 60% indicating incomplete elution of the protein during the chromatographic separation.     

Synthesis and structural characterization of iron–sulfur complexes with hydrophilic nitrogen–phosphorus ligands

Reaction of the parent complex (μ-PDT)Fe₂-(CO)₆ (A) (PDT = 1,3-SCH₂CH₂CH₂S^2?) with the bidentate N/P ligand [(Ph₂P)₂N(C₆H₄Cl-p)] in the presence of Me₃NO as decarbonylating agent produced an unexpected iron–sulfur complex [(μ-PDT)Fe₂(CO)₅{PPh₂(NHC₆H₄Cl-1,4)}] (1). Extending this chemistry further, two similar complexes [(μ-PDT)Fe₂(CO)₅{PPh₂(NHC₆H₄NO₂-1,4)}] (2) and [(μ-PDT)Fe₂(CO)₅{PPh₂(NHC₆H₄CO₂Et-1,4)}] (3) could be prepared from the simple substitution reactions of the precursor A with the monodentate N/P ligands Ph₂P(NHC₆H₄NO₂-1,4) and Ph₂P(NHC₆H₄CO₂Et-1,4), respectively. These new complexes, which can be considered as active site models of [FeFe] hydrogenases, have been characterized by elemental analysis, FTIR, and NMR (¹H, ¹³C, ³¹P) spectroscopies, as well as by X-ray crystallography for complex 1.     

An integrated approach to improve the performance of lean–electrolyte lithium–sulfur batteries

While the sulfur conversion reaction kinetics in Li–S batteries is nowadays improved by the use of appropriate electrocatalysts,it remains a challenge for the batteries to perform well under the lean electrolyte condition where polysulfide shuttle,electrode passivation and the loss of electrolyte due to side reactions,are aggravated.These challenges are addressed in this study by the tandem use of a polysulfide conversion catalyst and a redox–targeting mediator in a gel sulfur cathode.Specifical...     

A novel modified sulfur cathode to facilitate the adsorption and conversion of polysulfides in lithium–sulfur batteries

Journal of Solid State Electrochemistry - Physical confinement through particular nanostructures is inadequate to avoid the shuttle effect in the lithium–sulfur batteries. Electrocatalysts...     

Chalcogenation of 1,3-dichloropropene with elemental chalcogens in the system hydrazine hydrate–base

Sulfur reacts with 1,3-dichloropropene in the system hydrazine hydrate–KOH to form bis(1-chloroprop-1-en-3-yl) sulfide, and in the system hydrazine hydrate–monoethanolamine, bis(1-chloroprop-1-en- 3-yl) disulfide. The reaction of tellurium in the system hydrazine hydrate–KOH leads to diallyl telluride, the product of nucleophilic substitution of the allylic chlorine atom and reductive cleavage of the С_sp2–Cl bond. The reaction of selenium with 1,3-dichloropropene gives a complex mixture of products. At excess KOH (Se: KOH = 1: 5) bis(1-chloroprop-1-en-3-yl) selenide was isolated.     

Nickel foam as interlayer to improve the performance of lithium–sulfur battery

In this report, a porous, electronically conductive nickel foam foil (NFF), which is rolled for smooth surface, is introduced as an interlayer placed between the sulfur electrode and the separator to suppress the loss of active material and self-discharge behavior in lithium–sulfur (Li–S) systems. The electrodes are characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge–discharge test. The cell with the rolled NFF interlayer shows superior performance in terms of capacity utilization, reversibility, and enhanced rate capability. It exhibits reversible discharge capacity of 604 mAh g^?1 after 80 cycles at 0.2 C, which is much higher than that of pristine sulfur without NFF (424 mAh g^?1). The improvement on electrochemical performance is attributed to the 3D architecture of nickel foam foil as lithium–sulfur batteries interlayer, which can provide a good conductive network with structural stability and the porous architecture accommodating the migrating polysulfide to reduce the shuttling phenomenon during the charge–discharge processes.     

Evaluation of cerium–zirconium mixed oxides for separation of 125Sb from radioactive liquid waste

Journal of Radioanalytical and Nuclear Chemistry - Low level radioactive liquid waste (LLW) contains various radioisotopes like 125Sb, 106Ru, 99Tc and traces of 137Cs, 134Cs, 90Sr. Chemical...     

Rh(I)-catalyzed asymmetric 1,2-additions of arylboronic acids to isatins with chiral sulfur–alkene hybrid ligands

A rhodium-catalyzed asymmetric 1,2-addition of arylboronic acids to isatins with chiral sulfur–alkene hybrid ligands was achieved, and a variety of 3-aryl-3-hydroxy-2-oxindoles were obtained in moderate to good yields with up to 85% ee and a biologically active compound was synthesized with this strategy.     

Ion exchange removal of cesium from Hanford tank waste supernates with SuperLig® 644 resin

SuperLig^Ò 644 ion exchange resin is currently being evaluated for cesium (¹³⁷Cs) removal from radioactive Hanford tank waste supernates as part of the River Protection Project. Testing was performed with actual Hanford tank wastes of widely different compositions using two identical ion exchange columns connected in series each containing approximately 5.5-6.5 ml of SuperLig 644 resin. The ion exchange columns utilized the same resin material that was eluted between the column tests. This was done to demonstrate the performance of the SuperLig 644 resin for cesium removal from waste samples of different compositions, determine the loading and elution profiles, and to validate design assumptions for full-scale column performances. Decontaminated product solutions generated at the same operating temperature and constant residence times (bed volumes per hour) exhibited the same chemical compositions as their feed samples. The compositions of eluate solutions were generally as expected with the exception of uranium and total organic carbon, which where concentrated by the resin. Development of a pretreatment method for the SuperLig 644 resin has been critical to successful column operation with different waste solutions.     

Discovery of a Chiral DNA-Targeted Platinum–Acridine Agent with Potent Enantioselective Anticancer Activity

A structure–activity relationship study was performed for a set of rigidified platinum–acridine anticancer agents containing linkers derived from chiral pyrrolidine and piperidine scaffolds. Screening a library of microscale reactions and selected resynthesized compounds in non-small-cell lung cancer (NSCLC) cells showed that cytotoxicities varied by more than three orders of magnitude. A potent hit compound was discovered containing a (R)-N-(piperidin-3-yl) linker ( P2-6R ), which killed NCI-H460 and A549 lung cancer cells 100 times more effectively than the S enantiomer ( P2-6S ). P2-6R accumulated in A549 cells significantly faster and produced 50-fold higher DNA adduct levels than P2-6S . Ligand similarity analysis suggests that only module 6R may be compatible with strainless monofunctional intercalative binding. NCI-60 screening and COMPARE analysis highlights the spectrum of activity and potential utility of P2-6R for treating NSCLC and other solid tumors.     

Deoxygenation of coordinated oxaphosphiranes: a new route to pc double-bond systems

Phosphaalkenes: Deoxygenation of oxaphosphirane complexes 1 and 2 by using Ti(III) complexes gave mixtures of E/Z phosphaalkene complexes 3?a,?b and 4?a,?b. Theoretical calculations of deoxygenation pathways of 1 revealed that the final products are obtained via intermediate 5 providing the final products by reaction with a second [TiCpCl(2) ] unit and C?O bond cleavage.     

Synthesis of new biocarrier–nucleotide systems for cellular delivery in bacterial auxotrophic strains

In search for a delivery approach for thymidine monophosphate (TMP) in bacterial cells, we have synthesized a series of conjugates of TMP with biotin having an oxymethyleneoxy ester, a carboxy ester, and different carboxamide linkers between the carboxyl group of biotin and the 3′-OH group of TMP. The synthetic strategy starts from 5′-O-(dibenzylphosphate)-thymidine having the linkers already connected at the 3′-position. Likewise, kanamycin A was linked at the 3′-position of TMP using a carbamoyl or thioethyl carbamoyl group. None of the conjugates were able to sustain growth of a ΔthyA, ΔphoA Escherichia coli strain.     

Stoichiometry of Zn(II)–heparin–glycine complex,determined using data from elemental and thermal analysis

Russian Journal of Physical Chemistry A - Ternary polymer Zn(II)–heparin–glycine complex with the composition {Na3[ZnHepGly]·H2O} n , where Hep4− is the monomer chain of a...     

Organocatalytic asymmetric vinylogous 1,4-addition of α,α-Dicyanoolefins to chalcones under a bio-based reaction media: Discovery of new Michael adducts with antiplasmodial activity

The organocatalysed asymmetric vinylogous Michael addition of α,α-dicyanoolefins to α,β-unsaturated aldehydes and ketones have been reported in the last decade, however, chalcones have been poorly explored. Moreover, a considerable part of the publications in this theme still employs undesirable solvents, such as toluene and THF, with concerns related to health and environmental safety. We report herein the use of a bifunctional catalyst derived from a Cinchona alkaloid to perform the enantio- and diastereoselective Michael addition of α,α-dicyanoolefins to chalcones using 2-MeTHF as solvent. The Michael adducts were obtained in moderate to good yields and were evaluated for their antiplasmodial and cytotoxic activity.