X‐ray Absorption Near‐Edge Structure and Nuclear Magnetic Resonance Study of the Lithium–Sulfur Battery and its Components

Understanding the mechanism(s) of polysulfide formation and knowledge about the interactions of sulfur and polysulfides with a host matrix and electrolyte are essential for the development of long‐cycle‐life lithium–sulfur (Li–S) batteries. To achieve this goal, new analytical tools need to be developed. Herein, sulfur K‐edge X‐ray absorption near‐edge structure (XANES) and ^6,7Li magic‐angle spinning (MAS) NMR studies on a Li–S battery and its sulfur components are reported. The characterization of different stoichiometric mixtures of sulfur and lithium compounds (polysulfides), synthesized through a chemical route with all‐sulfur‐based components in the Li–S battery (sulfur and electrolyte), enables the understanding of changes in the batteries measured in postmortem mode and in operando mode. A detailed XANES analysis is performed on different battery components (cathode composite and separator). The relative amounts of each sulfur compound in the cathode and separator are determined precisely, according to the linear combination fit of the XANES spectra, by using reference compounds. Complementary information about the lithium species within the cathode are obtained by using ⁷Li MAS NMR spectroscopy. The setup for the in operando XANES measurements can be viewed as a valuable analytical tool that can aid the understanding of the sulfur environment in Li–S batteries.     

A new pentacyclic pyrylium fluorescent probe that responds to pH imbalance during apoptosis

Efficient fluorophores with easy synthetic routes and fast responses are of great importance in clinical diagnostics. Herein, we report a new, rigid pentacyclic pyrylium fluorophore, PS-OMe, synthesised in a single step by a modified Vilsmeier–Haack reaction. Insights into the reaction mechanism facilitated a new reaction protocol for the efficient synthesis of PS-OMe which upon demethylation resulted in a “turn-on” pH sensor, PS-OH. This new fluorescent probe has been successfully used to monitor intracellular acidification at physiological pH. From the fluorescence image analysis, we were able to quantify the intracellular dynamic pH change during apoptosis. This new pH probe is a potential chemical tool for screening, drug discovery and dose determination in cancer therapy.

A modified Vilsmeier–Haack reaction resulted in the synthesis of a pyrylium based turn-on fluorescent pH probe. The probe can monitor minute acidification and dynamic pH variation in cells during apoptosis with therapeutic chemo drugs.     

Separation of chelating agents as copper complexes by capillary zone electrophoresis using quaternary ammonium bromides as additives in N-methylformamide

This study presents the use of quaternary ammonium bromides as additives in N-methylformamide (NMF) for the separation and quantification of chelating agents as copper complexes by capillary zone electrophoresis (CZE). The new quaternary ammonium bromides were synthesized in our laboratory and used for the first time for CZE applications performed in NMF media. The methods were developed and optimized for determination of six chelating agents (trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (CDTA), diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA), N-(2-hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid (HEDTA), nitrilotriacetic acid (NTA) and triethylenetetraaminehexaacetic acid (TTHA)) as copper complexes. Among the tested electrolyte additives in NMF media (pH_app 10.2) dimethyldioctylammonium bromide (DMDOAB), dimethyldinonylammonium bromide (DMDNAB) and dimethyldidecylammonium bromide (DMDDAB), at a concentration of 20 mmol L⁻¹ improved the separation of the copper complexes. The optimized methods require only 12 min for one analysis, and the detection limits for copper complexes of DMDNAB, the best-performing additive, were ≤24 μmol L⁻¹. Relative standard deviations (R.S.D.) for migration times were ≤2.5, ≤2.1, ≤3.1% and for peak areas, ≤3.1, ≤3.0, ≤3.2% for DMDOAB, DMDNAB and DMDDAB used as additives, respectively. All three methods were successfully applied to the analysis of natural and wastewater samples. No matrix effects from these samples were observed. The interaction between quaternary ammonium bromides and copper complexes is discussed.     

Flow cytometry-based evaluation and enrichment of multiwalled carbon nanotube dispersions

The uniform aqueous dispersion of carbon nanotubes (CNTs) is a vital but challenging task required for their utilization in most technologies. We propose and demonstrate a technique based on forward- and side-scatter analysis on a flow cytometer to characterize the components in a dispersion of multiwalled CNTs (MWCNTs). The method simultaneously distinguishes various MWCNT components such as short and long CNTs, nanotube bundles, and particulates. It also detects the emergence of new CNT populations as a result of centrifugation. We use this method, together with classical methods such as UV and Raman spectroscopy, to observe and study the multistep MWCNT dispersion process in various surfactants (Pluronic, Triton X-100, sodium dodecyl sulfate, and cetyl trimethylammonium bromide). On the basis of the distinct scatter patterns obtained, we confirm and elaborate the surfactant-assisted unzipping mechanism of MWCNT dispersion. We also show that the ultrasonic energy spent after MWCNT unbundling and unwinding can be minimized and the process optimized for each surfactant by correct end point detection through scatter analysis. The ability to enrich nanotube population in dispersion by using the sorting mode of a flow cytometer is confirmed by electron microscopy and Raman spectroscopy. This method can thus be used for observing and enriching MWCNT components and as a complementary technique to UV spectroscopy for studying and optimizing MWCNT dispersion in surfactants.     

Electron Spin Resonance and Ground State Wave Functions of Vanadyl Ion in LiNaSO<Subscript>4</Subscript>

Electron spin resonance (ESR) of VO²⁺ doped into LiNaSO₄ has been studied at 300 K on an X-band spectrometer. The ESR powder spectra have been analyzed and spin Hamiltonian parameters have been evaluated. Using the crystal-field approach, a theoretical estimate of the ground state wave functions of VO²⁺ in LiMSO₄ (M = Na, K) has been made from the ESR data. The dipolar hyperfine coupling constant P and Fermi contact parameter K have also been estimated.     

Thermal and X‐ray powder diffraction studies of aliphatic polyester dendrimers

The syntheses and thermal and X‐ray powder diffraction analyses of three sets of aliphatic polyester dendrimers based on 2,2‐bis(hydroxymethyl)propionic acid as a repeating unit and 2,2‐dimethyl‐1,3‐propanediol, 1,5‐pentanediol, and 1,1,1‐tris(hydroxymethyl)ethane as core molecules are reported. These dendritic polyesters were prepared in high yields with the divergent method. The thermal properties of these biodendrimers were evaluated with thermogravimetric analysis and differential scanning calorimetry. The thermal decomposition of the compounds occurred around 250 °C for the hydroxyl‐ended dendrimers and around 150 °C for the acetonide‐protected dendrimers. In addition, the crystallinity of the lower generation dendrimers was evaluated with X‐ray powder diffraction. The highest crystallinity and the highest melting points were observed for the first‐generation dendritic compounds. The higher generation dendrimers showed weaker melting transitions during the first heating scan. Only the glass‐transition temperatures were observed in subsequent heating scans. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5574–5586, 2004     

Self-assembly properties of bile acid derivatives of l-cysteine,l-valine and l-serine alkyl esters

Comprehensive self-assembly studies for nine bile acid amides of amino acid esters are reported. The number of the hydroxyl groups attached to the steroidal skeleton and the character of the amino acid ester moiety were used as variables when examining the self-assembly properties of the compounds. Two of the compounds were shown to undergo self-assembly leading to organogelation. In addition, preliminary self-assembly studies in aqueous mixtures of polar organic solvents were conducted. Microscopic methods (optical microscopy and scanning electron microscopy) were utilised in order to gain a deeper insight into the self-assembled structures. Furthermore, single-crystal X-ray structures for three of the compounds were solved.     

Alkylchlorotins grafted to cross-linked polystyrene beads by a -(CH2)n- spacer (n=4, 6, 11): selective, clean and recyclable catalysts for transesterification reactions

Insoluble polystyrene grafted compounds of the type (P-H)(1-t){P-(CH2)n SnBu(p)Cl(3-p)}(t), (P-H)(1-t){P-(CH2)n SnBuO}(t) and (P-H)(1-t)[{P-(CH2)n SnBuCl}2O](t/2), in which (P-H) is a cross-linked polystyrene; n=4, 6, and 11; p=0 and 1; and t the degree of functionalisation, were synthesised from Amberlite XE-305, a polystyrene cross-linked with divinylbenzene. The compounds were characterised by using elemental analysis, and IR, Raman, solid-state 117Sn NMR, and 1H and 119Sn high-resolution MAS NMR spectroscopy. The influence of the spacer length and the tin functionality on the catalytic activity of these compounds, as well as their recycling ability, was assessed in the transesterification reaction of ethyl acetate with various alcohols. These studies showed significant differences in the activity of the catalysts interpreted in terms of changes in the mobility of the catalytic centres. Some of the supported catalysts could be recycled at least seven times without noticeable loss of activity. The residual tin content in the reaction products was found to be as low as 3 ppm.     

The advantageous way of getting the lowest uncertainty values of elemental concentration by INAA

Analysts in a NAA accredited laboratory bear full responsibility for the report on the material they investigated. The document has to contain the most accurate values that can be, as confidence to further use of the material on the market. To this end, analysts are expected to use the standardization method providing the lowest element concentration uncertainty and carefully quantify every factor that may contribute to the validity of the results. The question is which method is the most advantageous one from this perspective and in what conditions. This paper presents a comparison between results of the elemental analysis of a CRM sample by INAA, as obtained through two standardization methods and three calculations variants applied to the same experimental data. The results were discussed in terms of uncertainty and of the E _n statistical criterion recommended for inter-comparison exercises. The influence of the nuclear reaction and decay data was studied in several cases.     

A Review of Recent Progress in Solid State Fabrication of Composites and Functionally Graded Systems Via Friction Stir Processing

Friction stir processing (FSP) is a rapidly emerging newer solid-state technique for composite fabrication. It involves surface modification which in turn enables successful adaptation of surface properties through plastic deformations in solid state. During initial years of FSP inception, it was primarily employed in development of metal matrix composites of light metal alloys like aluminum. However, recently, it has gained an alluring role in fabrication of composites of various nonferrous and ferrous metal alloys as well as of polymers. In addition to composite fabrication, FSP has evolved as a revolutionary technique in developing functionally graded systems/surfaces (FGS) of metal matrix. This article covers all aspects of FSP in which reinforcement particles are embedded in the base matrix to develop composites and FGS. It presents a critical review on domains of recent developments, effects of different types of reinforcement particles and properties enhancement of composites, and FGS fabrication. In addition to this, various issues, challenges, and future work that demand attention are systematically addressed.