Infrared spectroscopic study of natural hydrotalcites carrboydite and hydrohonessite

Infrared spectroscopy has proven most useful for the study of anions in the interlayer of natural hydrotalcites. A suite of naturally occurring hydrotalcites including carrboydite, hydrohonessite, reevesite, motukoreaite and takovite were analysed. Variation in the hydroxyl stretching region was observed and the band profile is a continuum of states resulting from the OH stretching of the hydroxyl and water units. Infrared spectroscopy identifies some isomorphic substitution of sulphate for carbonate through an anion exchange mechanism for the minerals carrboydite and hydrohonessite. The infrared spectra of the CO3 and SO4 stretching region of takovite is complex because of band overlap. For this mineral some sulphate has replaced the carbonate in the structure. In the spectra of takovites, a band is observed at 1346 cm(-1) and is attributed to the carbonate anion hydrogen bonded to water in the interlayer. Infrared spectroscopy has proven most useful for the study of the interlayer structure of these natural hydrotalcites.     

Simultaneous determination of triclosan,triclocarban, and transformation products of triclocarban in aqueous samples using solid‐phase micro‐extraction‐HPLC‐MS/MS

The presence of triclosan and triclocarban, two endocrine‐disrupting chemicals and antimicrobial agents, and transformation products of triclocarban, 1,3‐di(phenyl)urea, 1,3‐bis(4‐chlorophenyl)urea and 1,3‐bis(3,4‐dichlorophenyl)urea, in tap water, treated household drinking water, bottled water, and river water samples were investigated using solid‐phase micro‐extraction coupled with‐HPLC‐MS/MS, a rapid, green, and sensitive method. Factors influencing the quantity of the analytes extracted onto the solid‐phase micro‐extraction fiber, such as addition of salt, sample pH, extraction time, desorption time, and sample volume, were optimized using solid‐phase micro‐extraction‐HPLC‐MS/MS. The results showed that the method gave satisfactory sensitivities and precisions for analyzing sub‐part‐per‐trillion levels of triclosan, triclocarban, and transformation products of triclocarban in samples collected locally. The recoveries of analytes ranged from 97 to 107% for deionized water samples, and 99 to 110% for river water samples, and limits of detection were in the range of 0.32–3.44 and 0.38–4.67 ng/L for deionized water and river water samples, respectively. On average, the daily consumption of triclosan and triclocarban by an adult by consuming 2 liters of different types of drinking water were estimated to be in the range of 6.13–425 ng/day as a result of the concentrations of triclosan and triclocarban measured in this study.     

Rapid separation of beryllium and lanthanide derivatives by capillary gas chromatography

Previous studies describe derivatization of metal ions followed by analysis using gas chromatography, usually on packed columns. In many of these studies, stable and volatile derivatives were formed using fluorinated β‐diketonate reagents. This paper extends previous work by investigating separations of the derivatives on small‐diameter capillary gas chromatography columns and exploring on‐fiber, solid‐phase microextraction derivatization techniques for beryllium. The β‐diketonate used for these studies was 1,1,1,2,2,6,6,7,7,7‐decafluoro‐3,5‐heptanedione. Derivatization of lanthanides also required addition of a neutral donor, dibutyl sulfoxide, in addition to 1,1,1,2,2,6,6,7,7,7‐decafluoro‐3,5‐heptanedione. Unoptimized separations on a 100‐μm i.d. capillary column proved capable of rapid separations (within 15 min) of lanthanide derivatives that are adjacent to one another in the periodic table. Full‐scan mass spectra were obtained from derivatives containing 5 ng of each lanthanide. Studies also developed a simple on‐fiber solid‐phase microextraction derivatization of beryllium. Beryllium could be analyzed in the presence of other alkali earth elements (Ba(II) and Sr(II)) without interference. Extension of the general approach was demonstrated for several additional elements (i.e. Cu(II), Cr(III), and Ga(III)).     

The Deligne–Mumford compactification of the real multiplication locus and Teichmüller curves in genus 3

In the moduli space M \mathcal{M} _g of genus-g Riemann surfaces, consider the locus RM_O \mathcal{R}{\mathcal{M}_{\mathcal{O}}} of Riemann surfaces whose Jacobians have real multiplication by the order O \mathcal{O} in a totally real number field F of degree g. If g = 3, we compute the closure of RM_O \mathcal{R}{\mathcal{M}_{\mathcal{O}}} in the Deligne–Mumford compactification of M \mathcal{M} _g and the closure of the locus of eigenforms over RM_O \mathcal{R}{\mathcal{M}_{\mathcal{O}}} in the Deligne–Mumford compactification of the moduli space of holomorphic 1-forms. For higher genera, we give strong necessary conditions for a stable curve to be in the boundary of RM_O \mathcal{R}{\mathcal{M}_{\mathcal{O}}} . Boundary strata of RM_O \mathcal{R}{\mathcal{M}_{\mathcal{O}}} are parameterized by configurations of elements of the field F satisfying a strong geometry of numbers type restriction.     

Strong-field ionization and coulomb explosion of chlorine weakly bound to small water clusters

Clusters exhibit an enhancement in ionization rates under intense, ultrafast laser pulses compared to their molecular/atomic counterparts. Studies of ionization enhancement of weakly bound molecules to clusters have not been previously characterized and quantified. We demonstrate that weakly bound ClO to (H(2)O)(n) (n = 1-12) clusters and weakly bound HCl to (H(2)O)(n) (n = 1-12) clusters produce high atomic charge states of chlorine via Coulomb explosion. Density functional theory (DFT) was used to qualitatively compare the interaction energy of ClO with respect to the number of water molecules as well as HCl with respect to the number of water molecules. The chlorine ion signal intensity for each atomic charge state was observed to be dependent on the molecule-cluster bond strength. The observed ionization enhancement was quantified using semiclassical tunneling theory, and it was found that the Cl(3+-5+) and O(2+) charge states are enhanced in ionization. Possible mechanisms of ionization enhancement are explored for weakly bound chlorine species.     

Efficient simultaneous reverse Monte Carlo modeling of pair-distribution functions and extended x-ray-absorption fine structure spectra of crystalline disordered materials

An efficient implementation of simultaneous reverse Monte Carlo (RMC) modeling of pair distribution function (PDF) and EXAFS spectra is reported. This implementation is an extension of the technique established by Krayzman et al. [J. Appl. Cryst. 42, 867 (2009)] in the sense that it enables simultaneous real-space fitting of x-ray PDF with accurate treatment of Q-dependence of the scattering cross-sections and EXAFS with multiple photoelectron scattering included. The extension also allows for atom swaps during EXAFS fits thereby enabling modeling the effects of chemical disorder, such as migrating atoms and vacancies. Significant acceleration of EXAFS computation is achieved via discretization of effective path lengths and subsequent reduction of operation counts. The validity and accuracy of the approach is illustrated on small atomic clusters and on 5500-9000 atom models of bcc-Fe and α-Fe(2)O(3). The accuracy gains of combined simultaneous EXAFS and PDF fits are pointed out against PDF-only and EXAFS-only RMC fits. Our modeling approach may be widely used in PDF and EXAFS based investigations of disordered materials.     

Advanced Characterization of Propylene-Based Copolymers and Olefin Block Copolymers

Summary: The newly developed interactive separation of polyolefins by high temperature liquid chromatography (HTLC) provides new information about the chemical composition distribution of polyolefin elastomers. The technique has the advantage of being quantitative in its separation, and has high resolution for the separation of polyolefins by their chemical composition without influence by cocrystallization. Chemical composition distributions can be determined for individual polymers and blends which contain the full range of comonomer typically present in polyethylene and poylypropylene homopolymers, semi-crystalline copolymers, and amorphous copolymers. HTLC analysis in combination with the other fractionation techniques, such as DSC, TREF, NMR, and xylene fractionation, can be used to estimate the amount of olefin block copolymer present in a block composite produced by chain shuttling catalysis.     

Biocompatible Crosslinked Nanofibers of Poly(Vinyl Alcohol)/Carboxymethyl‐Kappa‐Carrageenan Produced by a Green Process

This study presents a new type of biocompatible nanofiber based on poly(vinyl alcohol) (PVA) and carboxymethyl‐kappa‐carrageenan (CMKC) blends, produced with no generation of hazardous waste. The nanofibers are produced by electrospinning using PVA:CMKC blends with ratios of 1:0, 1:0.25, 1:0.4, 1:0.5, and 1:0.75 (w/w PVA:CMKC) in aqueous solution, followed by thermal crosslinking. The diameter of the fibers is in the nanometer scale and below 300 nm. Fourier transform infrared spectroscopy shows the presence of the carboxyl and sulfate groups in all the fibers with CMKC. The nanofibers from water‐soluble polymers are stabilized by thermal crosslinking. The incorporation of CMKC improves cytocompatibility, biodegradability, cell growth, and cell adhesion, compared to PVA nanofibers. Furthermore, the incorporation of CMKC modulates phenotype of human adipose‐derived stem cells (ADSCs). PVA/CMKC nanofibers enhance ADSC response to osteogenic differentiation signals and are therefore good candidates for application in tissue engineering to support stem cells.     

Response of the jalpaite membrane copper(II) ion-selective electrode in marine waters

The response of the Orion 94-29 Cu^II ion-selective electrode (ISE) [employing a jalpaite membrane] in seawater has been related to levels of free Cu^II yielding results for the Derwent River and San Diego Bay that are 2 to 3 orders of magnitude higher than those for the Pacific Ocean. Response data for the electrode in acidified seawater at pH 2 are internally consistent with total Cu^II levels determined using differential pulse anodic stripping voltammetry (DPASV) and graphite furnace atomic absorption spectrometry (GFAAS). It has been found that, even in acidified seawater, the organic ligands influence the response of the electrode, and this effect can be compensated successfully by either analyzing UV-photooxidized seawater and/or using a standard addition technique. The assigned ISE results for total Cu^II in acidified seawater fall within ± (0.1–0.5) pCu unit of values determined using GFAAS. Electrode drift in seawater can be minimized by using a polished electrode that has been conditioned in seawater for 24 h. The improved response rate of a conditioned ISE minimizes electrode soaking times and sample contamination through membrane corrosion.