Understanding barium sulfate precipitation onto stainless steel

This paper investigates the influence of barium sulfate scaling and scaling inhibitors on the electrochemical behaviour of stainless steel. The results of a synchrotron radiation grazing incidence X-ray diffraction (SR-GIXRD) and electrochemical impedance spectroscopy (EIS) study on stainless steel shows that different scaling inhibitors interact uniquely with the substrate when barium sulfate is precipitated on the electrode surface. The main effect of the substrate in the presence of inhibitor is a tendency to form smaller barium sulfate particles. The SR-GIXRD patterns obtained in the presence of the two inhibitors were different to each other and to the control, with the carboxylate showing greater amounts of barite solids precipitated together with iron(III) and (II) sulfate, while the phosphonate showed low amounts of barite solid were precipitated. The presence of iron sulfates on the electrode surface as detected by SR-GIXRD, in the case of NTA, suggests that scaling inhibitors are not always benign, and can promote the dissolution of iron species from the substrate.     

Crystal and molecular structure of augustamine

The crystal and molecular structure of augustamine (1), C₁₇H₁₉NO₄ an amaryllidaceae alkaloid of the tazettine group has been determined by direct methods from single crystal x-ray diffractometer data and refined by full-matrix least squares. The alkaloid (1) crystallizes in the space group P2₁2₁2₁, with cell parameters: a = 7.833(8) b = 11.08(2) å, c = 16.69(6) Å, Z = 4, D_c = 1.381 g/cm^–3, R = 7.6% for 1115 observed reflections. The molecule, having a hexacyclic ring system, is very rigid with the ring B in a chair conformation. Molecular mechanics calculations have been made using MM3(2000) force field.     

Spectroscopy of the A(1B2)-X(1A1) transition of jet-cooled fluorobenzene: laser-induced fluorescence, dispersed fluorescence, and pathological Fermi resonances

A detailed study of the S1((1)B2)-S0((1)A1) electronic transition of jet-cooled fluorobenzene has been carried out using laser-induced fluorescence and dispersed fluorescence (DF) spectroscopies. Analysis of over 40 single vibronic level DF spectra resulted in the assignment of 16 fundamental frequencies in the excited electronic state. Progressions in totally symmetric modes, particularly in the ring-breathing mode nu9, feature in both types of fluorescence spectrum. There is also significant activity in non-totally-symmetric modes, with activity in Franck-Condon (FC)-allowed overtones, FC-forbidden combinations induced by Duschinsky mixing, and symmetry-forbidden transitions induced by the same Herzberg-Teller vibronic coupling mechanism that induces the benzene S1-S0 transition. Fermi resonances (FRs) are extensive throughout the spectrum, especially in the important FC-active a1 modes. A consequence of these extensive FRs is that several important previous assignments are shown to be incorrect and have been reassigned here. Ab initio and density functional theory calculations have also been performed to support the experimental assignments.     

Synthesis of the Bicyclic Lactone Core of Leonuketal,Enabled by a Telescoped Diels–Alder Reaction Sequence

The Diels–Alder cycloaddition reaction has become established as a fundamental approach for the preparation of complex natural products; however, successful application of the intermolecular Diels–Alder cycloaddition reaction to the synthesis of particularly congested scaffolds remains surprisingly problematic. Inspired by the terpenoid spiroketal natural product leonuketal, a challenging telescoped reaction sequence has been realized to access the core [2.2.2]‐bicyclic lactone ring system and its [3.2.1] isomer. Our four‐step, protecting‐group‐free process required detailed investigation to circumvent the problems of adduct fragmentation and intermediate instability. Successful solution of these practical issues, along with unambiguous structural determination of the target structures, provide useful insights that will facilitate future applications of the Diels–Alder cycloaddition reaction to challenging, highly congested molecular scaffolds and ongoing synthetic efforts towards this natural product.     

Controlled microfluidic encapsulation of cells, proteins, and microbeads in lipid vesicles

Cells have been encapsulated inside lipid vesicles by using a new microfluidic lipid vesicle formulation technique. Lipid vesicles are formulated within minutes without using toxic lipid solvents. The encapsulation efficiency inside the vesicles is controlled by the microfluidic flows. Green fluorescent proteins (GFP), carcinoma cells, and bead encapsulated vesicles have mean diameters of 27.2 mum, 62.4 mum, and 55.9 mum, respectively. The variations of vesicle sizes are approximately 20% for the GFP and cell encapsulated vesicles and approximately 10% for the bead encapsulated vesicles.     

Alkylation of inorganic oxo compounds and insights on preventing DNA damage

Metabolism of food- and tobacco-borne procarcinogens results in the exposure of DNA to toxic alkylating agents. These assaults can bring about DNA alkylation damage, mutations, and cancer. Dietary inorganic compounds such as selenium and vanadium are known to prevent cancer, possibly by reacting directly with alkylating agents, thereby preventing DNA damage. To understand potential interactions between oxo species and alkylating toxins, we reacted a series of alkylating agents with varied classes of oxo compounds (i.e., vanadates, selenate, phosphate, sulfate, acetate, nitrate, and nitrite). A new organic-soluble selenate, [(C6H5)4P]3(O3SeOCH2OSeO3)(HSeO4), was synthesized and characterized for these studies. Vanadates were found to convert ethylating agents into ethanol, whereas other anions formed esters upon alkylation. General trends show that oxo anions of the greatest charge density were the most reactive. These studies suggest that the design of new compounds for cancer prevention should incorporate reactive oxo groups with high anionic charge density.     

PbTe colloidal nanocrystals: synthesis, characterization, and multiple exciton generation

We report an alternative synthesis and the first optical characterization of colloidal PbTe nanocrystals (NCs). We have synthesized spherical PbTe NCs having a size distribution as low as 7%, ranging in diameter from 2.6 to 8.3 nm, with first exciton transitions tuned from 1009 to 2054 nm. The syntheses of colloidal cubic-like PbSe and PbTe NCs using a PbO "one-pot" approach are also reported. The photoluminescence quantum yield of PbTe spherical NCs was measured to be as high as 52 +/- 2%. We also report the first known observation of efficient multiple exciton generation (MEG) from single photons absorbed in PbTe NCs. Finally, we report calculated longitudinal and transverse Bohr radii for PbS, PbSe, and PbTe NCs to account for electronic band anisotropy. This is followed by a comparison of the differences in the electronic band structure and optical properties of these lead salts.     

Reactive carbon-chain molecules: synthesis of 1-diazo-2,4-pentadiyne and spectroscopic characterization of triplet pentadiynylidene (H-C[triple bond]C-:C-C[triple bond]C-H)

1-Diazo-2,4-pentadiyne (6a), along with both monodeuterio isotopomers 6b and 6c, has been synthesized via a route that proceeds through diacetylene, 2,4-pentadiynal, and 2,4-pentadiynal tosylhydrazone. Photolysis of diazo compounds 6a-c (lambda > 444 nm; Ar or N2, 10 K) generates triplet carbenes HC5H (1) and HC5D (1-d), which have been characterized by IR, EPR, and UV/vis spectroscopy. Although many resonance structures contribute to the resonance hybrid for this highly unsaturated carbon-chain molecule, experiment and theory reveal that the structure is best depicted in terms of the dominant resonance contributor of penta-1,4-diyn-3-ylidene (diethynylcarbene, H-C[triple bond]C-:C-C[triple bond]C-H). Theory predicts an axially symmetric (D(infinity h)) structure and a triplet electronic ground state for 1 (CCSD(T)/ANO). Experimental IR frequencies and isotope shifts are in good agreement with computed values. The triplet EPR spectrum of 1 (absolute value(D/hc) = 0.6157 cm(-1), absolute value(E/hc) = 0.0006 cm(-1)) is consistent with an axially symmetric structure, and the Curie law behavior confirms that the triplet state is the ground state. The electronic absorption spectrum of 1 exhibits a weak transition near 400 nm with extensive vibronic coupling. Chemical trapping of triplet HC5H (1) in an O2-doped matrix affords the carbonyl oxide 16 derived exclusively from attack at the central carbon.     

Homogeneous chemiluminescent assays for free choline in human plasma and whole blood

Choline was oxidized in the presence of choline oxidase and the hydrogen peroxide generated was detected using a chemiluminescent acridinium-9-carboxamide. The dose response for choline (0-150 μM) was established in buffer and was validated for the quantification of choline in human plasma and whole blood. This homogeneous assay was performed in a 96-well microplate format and required minimal sample volume (4 μL) and short analysis time (<5 s per well). The new assay(s) correlated well (R > 0.98, plasma; R > 0.97, whole blood) with LC-MS/MS.