ToF-SIMS investigation of octadecylphosphonic acid monolayers on a mica substrate

In this paper, time-of-flight secondary ion mass spectrometry (ToF-SIMS) under static conditions was used to investigate self-assembled monolayers (SAMs) of octadecylphosphonic acid (OPA) formed on freshly cleaved muscovite mica substrates. The coverage of OPA on mica ranged from 20 to 100%, with a film thickness of 1.7+/-0.2 nm, which was determined by atomic force microscopy (AFM) imaging. The relative intensity of the specific secondary ion species associated with the OPA and with the exposed mica substrate exhibited good correlation with surface coverage. An excellent correlation was also observed (R2=0.98) between the relative SIMS [OPA-H]- intensity and the surface carbon concentration (OPA C 1s, in atomic %) from XPS at the prescribed surface coverage. The observation of positive and negative OPA molecular attachment of secondary ions involving the substrate species is discussed in terms of the chemical affinity of the OPA phosphonate headgroup for the cleaved mica surface as well as the sampling depth. In addition, the OPA molecular attachment species formed with the potassium ions on the cleaved mica substrate dominated the positive secondary ion mass spectrum in the high-mass range. A temperature-dependent, ToF-SIMS study employing in situ heating of a 100% coverage OPA monolayer revealed that the molecules begin to diffuse above approximately 80 degrees C, resulting in a decrease in the relative secondary ion yield of the OPA-specific secondary ions. This observation is hypothesized to be due to a decrease in the effective coverage of the substrate by the OPA molecules, which in turn could be due to the formation of multilayers upon heating in an effort to minimize the energy of the system. The interesting behavior of the novel OPA dimer species as a function of temperature is also reported. It was observed that the relative intensity of OPA and the mica-specific secondary ion peak intensities to that of Si (mica substrate) provides an effective means to estimate the change in coverage at elevated temperatures.     

Antibodies with broad specificity to azaspiracids by use of synthetic haptens

The development of general, sensitive, portable, and quantitative assays for the azaspiracid (AZA) class of marine toxins is urgently needed. Use of a synthetic hapten containing rings F-I of AZA to generate antibodies that cross-react with the AZAs via their common C28-C40 domain and use of these antibodies in ELISA and immunoaffinity columns are reported. This approach has many advantages over using intact azaspiracids (AZAs) derived from environmental samples or total synthesis as haptens for antibody development. A derivative of the levorotatory C28-C40 azaspiracid domain (1) was synthesized efficiently using a one-pot Staudinger reduction/intramolecular aza-Wittig reaction-imine capture sequence to form the H-I ring spiroaminal and a double intramolecluar hetero-Michael addition to assemble the F-G ring ketal. Conjugation of the hapten 1 to cBSA and immunization in sheep generated antibodies that recognized and bound to ovalbumin-conjugated 1 in the absence of AZA1. This binding was inhibited by 1 in a concentration-dependent manner. A mixture of AZA1, AZA2, AZA3, and AZA6 caused a degree of inhibition of antibody binding consistent with its total AZA content, rather than just its content of AZA1. This result suggests that the antibodies also have a similar affinity for AZA2, AZA3, and AZA6 as they do for AZA1 and that such antibodies are suitable for analysis of AZAs in shellfish samples.     

Synthesis and reactivity of N@C60O

The endohedral fullerene epoxide N@C60O was synthesised, isolated by High Performance Liquid Chromatography (HPLC), and characterised by Electron Spin Resonance (ESR). This nitrogen radical displays predominantly axial symmetry characteristics as expected for a monoadduct, evidenced by a zero-field splitting D parameter of 6.6 MHz and an E parameter of 0.5 MHz in powder at 77 K. Photo- and thermally-activated silencing of the nitrogen radical were observed, the latter showing the evolution of a new spin signal during heating at 100 degrees C. We suggest that loss of nitrogen spin is due to coupling with a radical formed by opening of the epoxide ring. This implies that the reaction of C60O with C60 in the solid state proceeds via a radical, rather than ionic, intermediate.     

Fullerene-acene chemistry: diastereoselective synthesis of a cis,cis-tris[60]fullerene adduct of 6,8,15,17-tetraphenylheptacene

[structure: see text]. A one-pot, diastereoselective synthesis of a cis,cis-tris[60]fullerene adduct of 6,8,15,17-tetraphenylheptacene has been demonstrated starting from [60]fullerene and 5,7,9,14,16,18-hexahydro-6,8,15,17-tetraphenylheptacene.     

Removal of interference in the differential pulse polarographic determination of progestogens in some combined low-dosage oral contraceptives

Previously published differential pulse methods for the determination of certain progestogens (laevonorgestrel and norethisterone) are not applicable to combined low-dosage oral contraceptives because interference from excipients in the tablets completely eliminates the polarographic response. An ultrafiltration device allows rapid prior extraction of the interfering substances before the polarographic determination in 50% ($\text{v}\text{v}$) methanol—phosphate buffer (pH 6.0). Recoveries of 100 ± 1% were obtained by the recommended method, and data for a range of formulations are in excellent agreement with expected values. Electrode characteristics of the progestogens and interfering substances are reported, based on studies employing cyclic voltammetry at a hanging mercury drop electrode, a.c. polarography and normal pulse polarography. Competitive adsorption processes seem to occur when the progestogen and excipients are simultaneously present.     

The CF bond as a tool in the conformational control of amides

The conformation of 2-fluoro-N-(2-fluoroethyl)-propionamide 4 in the solid state indicates the influence of both a β-fluorine-amide gauche effect and an α-fluoroamide effect. The structure reveals the influence of two recently observed stereoelectronic effects associated with the CF bond, which has resulted in the successful prediction of the solid state conformation of amide 4. A gauche relationship (−69.9°) was observed for atoms N(1)C(4)C(5)F and a syn planar (2.0°) relationship was observed for N(1)C(3)C(2)F. The paper demonstrates the predictive power of using the CF bond as a tool in influencing the conformation of amides and peptides.     

Solid state and theoretical evaluation of β-fluoroethyl esters indicate a fluorine-ester gauche effect

Single crystal X-ray diffraction studies and a theoretical analysis indicate a preferred conformation for O-β-fluoroethyl esters, where the CF and CO(CO) bonds are gauche rather than anti to each other. The OCCF dihedral angles for three compounds and five independent structures indicate a range of only 63.4-69.6°. Evaluation of a rotational energy profile around this bond in a model system (β-fluoroethyl acetate) predicted a similar dihedral angle and the gauche conformation to be the minimum on the rotational energy profile. High level ab initio calculations measured the gauche conformer to be 0.95 kcal mol⁻¹ lower in energy than the anti conformer and application of a solvation model further increased this differential to 1.6 kcal mol⁻¹, consistent with a previous solution state (NMR) evaluation of this system.     

The interaction of vinyl acetate and allyl acetate with chloro-bridged platinum(II) complexes [Pt2Cl4(PR3)2]: Crystal structure of cis-[PtCl2(PMe2Ph2)(CH2=CHOCOCH3)]

Five complexes of type cis-[PtCl₂(PR₃)Q] (PR₃ =PMe₃, PMe₂Ph, PEt₃; Q = CH₂ CHOCOCH₃ or CH₂=CHCH₂OCOCH₃) have been prepared. The crystal structure of cis-[PtCl₂[PME₂Ph)(CH₂=CHOCOCH₃)] is described. Crystals of cis-[PtCl₂(PME₂Ph)(CH₂-CHOCOCH₃)] are triclinic, with a 8.441(4), b 13.660(5), c 7.697(3) Å, a 101.61(3)°, β 111.85(3)° γ 95.22(3)°, pP1, Z = 2. The structure was determined from 2011 reflections I σ 3σ (I) and refined to R = 0.037. The CH₃COO grouping is syn to the cis-PMe₂Ph ligand, with bond lengths of PtCl (trans to P) 2.367(3), PtCl (trans to olefin) 2.314(3), PtP 2.264(2), and PtC of 2.147(12) and 2.168(11) Å. The complexes cis-[PtCl₂- (PR₃)Q] were studied by variable temperature ¹H and ³¹P NMR spectroscopy. Spectra of the vinyl acetate complexes were temperature dependent as a result of rotation about the platinum—olefin bond. The rotation was “frozen out” at ca. 240 K; for cis-[PtCl₂(PME₂Ph)(CH₂=CHOCOCH₃] ΔG≠ (rotation) 15.0 ± 0.2 kcal mol^-1. NMR parameters for the rotamers are reported. NMR studies of the interaction between chloro-bridged complexes of type [Pt₂Cl₂(PR₃)₂] (PR₃ = P-N-Pr₃ or PMe₂Ph) and vinyl acetate shows that even at low temperatures (213 K) equilibrium favours the bridged complex and the proportion of trans-[PtCl₂(PR₃)CH₂=CHOCOCH₃)] is very small e.g. 2%. The allyl acetate complexes cis-[PtCl₂(PR₃)(CH₂₌CHCH₂OCOCH₃)] showed only one rotamer over the range 333–213 K. Reversible dissociation of cis-[PtCl₂(PMe₂Ph)- (CH₂=CHCH₂OCOCH₃)] to [Pt₂Cl₄(PMe₂Ph)₂] + allyl acetate was studied at ambient temperature. At low temperatures e.g. 213–190 K addition of allyl acetate to a CDCl₃ solution of [Pt₂Cl₂(P-n-Pr₃)₂] reversibly gave some olefin complex trans-[PtCl₂(P-n-Pr₃)(CH₂=CHCH₂OCOCH₃)] and some O-bonded complex trans-[PtCl₂(P-n-Pr₃)(CH₂=CHCH₂OCOCH₃)].