Manganese detection in marine sediments: anodic vs. cathodic stripping voltammetry

Three different electroanalytical techniques for the detection of manganese in marine sediments are evaluated. The anodic stripping voltammetry of manganese at an in situ bismuth-film-modified boron-doped diamond electrode and cathodic stripping voltammetry at a carbon paste electrode are shown to lack the required sensitivity and reproducibility whereas cathodic stripping voltammetry at a bare boron-doped diamond electrode is shown to be reliable and selective with a limit of detection, from applying a 60 s accumulation period of 7.4 × 10⁻⁷ M and a sensitivity of 0.24 A M⁻¹. The method was used to evaluate the manganese content of marine sediments taken from Šibenik, Croatia.     

Supersonically cooled hydronium ions in a slit-jet discharge: high-resolution infrared spectroscopy and tunneling dynamics of HD2O+

Jet-cooled high-resolution infrared spectra of partially deuterated hydronium ion (HD2O+) in the O-H stretch region (nu3 band) are obtained for the first time, exploiting the high ion densities, long absorption path lengths, and concentration modulation capabilities of the slit-jet discharge spectrometer. Least-squares analysis with a Watson asymmetric top Hamiltonian yields rovibrational constants and provides high level tests of ab initio molecular structure predictions. Transitions out of both the lower (nu3(+)<--0(+)) and the upper (nu3(-)<--0(-)) tunneling levels, as well as transitions across the tunneling gap (nu3(-)<--0(+)) are observed. The nu3(-)<--0(+) transitions in HD2O+ acquire oscillator strength by loss of D(3h) symmetry, and permit both ground-state-[27.0318(72) cm(-1)] and excited-state-[17.7612(54) cm(-1)]-tunneling splittings to be determined to spectroscopic precision from a single rovibrational band. The splittings and band origins calculated with recent high level ab initio six-dimensional potential surface predictions for H3O+ and isotopomers [X. C. Huang, S. Carter, and J. M. Bowman, J. Chem. Phys. 118, 5431 (2003); T. Rajamaki, A. Miani, and L. Halonen, J. Chem. Phys. 118, 10929 (2003)] are in very good agreement with the current experimental results.     

Asymmetric Synthesis Using Sulfinimines (N-Sulfinyl Imines)

Abstract

Sulfinimine-derived polyfunctionalized chiral building blocks, often prepared in one pot, provide efficient access, with a minimum of chemical manipulation, to enantiopure, multifunctional amine derivatives including piperidines and pyrrolidines.     

A simplified device for protein identification by microcapillary gradient liquid chromatography-tandem mass spectrometry

A simplified device and procedure have been developed for microcapillary gradient liquid chromatography-tandem mass spectrometry (LC-MS/MS). This procedure has proved useful in identifying low level quantities of proteins from sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) gel bands. Microelectrospray needles are packed with reversed-phase resin and function both as a high performance liquid chromatography (HPLC) column and a nanospray mass spectrometer tip when interfaced between an HPLC and ion trap mass spectrometer. Variable submicroliter flow rates are generated by flow splitting between the microelectrospray capillary and an HPLC system. A manual injector is used to inject a protein digest mixture that binds to the column and is then washed at a high flow rate (2 microL/min post split). Gradient elution of bound peptides was initiated by the injection of a filled loop of 70% v/v methanol (5 microL) concomitant with a reduction of flow rate (0.1 microL/min post split). This forms a diffusion-dependent gradient of variable length (typically 15-30 min in length) depending upon the final flow rate. Chromatographic separations of a standard solution digest demonstrate that this diffusion-dependent gradient provides reasonable separations such that multiple peptide identifications by MS/MS can be obtained. Application of this methodology to the analysis of several in-gel-digested gel-separated proteins is presented to demonstrate its utility.     

Thermosensitive graphene nanocomposites formed using pyrene‐terminal polymers made by RAFT polymerization

Thermosensitive graphene‐polymer composites have been prepared by attaching poly(N‐isopropylacrylamide) (PNIPAAm) onto the basal plane of graphene sheets via π‐π stacking. Pyrene‐terminated PNIPAAm was synthesized using reversible addition fragmentation chain transfer (RAFT) polymerization via a pyrene‐functional RAFT agent. Aqueous solutions of the graphene‐polymer composites were stable and thermosensitive. The lower critical solution temperature (LCST) of pyrene‐terminated PNIPAAm was measured to be 33 °C. When the pyrene‐functional polymer was attached to graphene the resultant composites were also thermosensitive in aqueous solutions exhibiting a reversible suspension behavior at 24 °C. Atomic force microscopy (AFM) analysis revealed that the thickness of a graphene‐PNIPAAm (M_n: 10,000 and PDI: 1.1) sheet was ～5.0 nm. The surface coverage of polymer chains on the graphene basal plane was calculated to be 7.2 × 10^?11 mol cm^?2. The graphene‐PNIPAAm composite material was successfully characterized using X‐ray photoelectron spectroscopy (XPS), attenuated total reflection infrared (ATR‐IR) spectroscopy, and thermogravimetric analysis (TGA). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 425–433, 2010     

Ecionines A and B, two new cytotoxic pyridoacridine alkaloids from the Australian marine sponge, Ecionemia geodides

Chemical investigations of the Australian marine sponge Ecionemia geodides resulted in the isolation of two new pyridoacridine alkaloids, ecionines A (1) and B (2), along with the previously isolated marine natural products, biemnadin (3) and meridine (4). Compounds 1 and 2 both contain an imine moiety, which is rare for the pyridoacridine structure class. The chemical structures of 1 and 2 were determined by extensive 1D and 2D NMR and MS data analyses. All compounds were tested against a panel of human bladder cancer cell lines, the increasingly metastatic TSU-Pr1 series (TSU-Pr1, TSU-Pr1-B1 and TSU-Pr1-B2) and the superficial bladder cancer cell line 5637. Ecionine A (1) displayed cytotoxicity against all cell lines, with IC₅₀ values ranging from 3 to 7 μM. This is the first report of chemistry from the sponge genus Ecionemia.     

Monte Carlo Model of Stricture Formation in Photodynamic Therapy of Normal Pig Esophagus

Photodynamic therapy (PDT) is FDA-approved for use in patients with Barrett's esophagus using porfimer sodium (2 mg per kg) and a recommended light dose of 130 J cm⁻¹ for high grade dysplasia. Despite uniform drug and light doses, the clinical outcome of PDT is variable. A significant number of PDT cases result in esophageal strictures, a side effect related to excessive energy absorption. The purpose of this project was to model esophageal stricture formation with a Monte Carlo simulation. An original multilayer Monte Carlo computer simulation was developed for esophageal PDT. Optical absorption and scattering coefficients were derived for mucosal and muscle layers of normal porcine esophagus. Porfimer sodium was added to each layer by increasing the absorption coefficient by the appropriate amount. A threshold-absorbed light dose was assumed to be required for stricture formation and ablation. The simulation predicted irreversible damage to the mucosa with a 160 J cm⁻¹ light dose and damage to the muscle layer with an additional 160 J cm⁻¹ light dose for a tissue porfimer sodium content of 3.5 mg kg⁻¹. The simulation accurately modeled photodynamic stricture formation in normal pig in vivo esophageal tissue. This preliminary work suggests that the absorbed light threshold for stricture formation may be between 2 and 4 J per gram of tissue.     

Synthesis of Calcium(II) Amidinate Precursors for Atomic Layer Deposition through a Redox Reaction between Calcium and Amidines

We have prepared two new Ca^II amidinates, which comprise a new class of ALD precursors. The syntheses proceed by a direct reaction between Ca metal and the amidine ligands in the presence of ammonia. Bis(N,N′‐diisopropylformamidinato)calcium(II) ( 1 ) and bis(N,N′‐diisopropylacetamidinato)calcium(II) ( 2 ) adopt dimeric structures in solution and in the solid state. X‐ray crystallography revealed asymmetry in one of the bridging ligands to afford the structure [(η²‐L)Ca(μ‐η²:η²‐L)(μ‐η²:η¹‐L)Ca(η²‐L)]. These amidinate complexes showed unprecedentedly high volatility as compared to the widely employed and commercially available Ca^II precursor, [Ca₃(tmhd)₆]. In CaS ALD with 1 and H₂S, the ALD window was approximately two times wider and lower in temperature by about 150 °C than previously reported with [Ca₃(tmhd)₆] and H₂S. Complexes 1 and 2 , with their excellent volatility and thermal stability (up to at least 350 °C), are the first homoleptic Ca^II amidinates suitable for use as ALD precursors.     

Platform Synthetic Lectins for Divalent Carbohydrate Recognition in Water

Biomimetic carbohydrate receptors (“synthetic lectins”) have potential as agents for biological research and medicine. However, although effective strategies are available for “all‐equatorial” carbohydrates (glucose, etc.), the recognition of other types of saccharide under natural (aqueous) conditions is less well developed. Herein we report a new approach based on a pyrene platform with polar arches extending from aryl substituents. The receptors are compatible with axially substituted carbohydrates, and also feature two identical binding sites, thus mimicking the multivalency observed for natural lectins. A variant with negative charges forms 1:2 host/guest complexes with aminosugars, with K₁>3000 m ^?1 for axially substituted mannosamine, whereas a positively charged version binds the important α‐sialyl unit with K₁≈1300 m ^?1.