Analysis of selected pesticides and alkylphenols in human cord blood by gas chromatograph-mass spectrometer

A total of seven pesticides and eight alkylphenols were monitored using this method for the determination of their trace levels in human cord blood. The pesticides are lindane, diazinon, α-endosulfan, β-endosulfan, endosulfan sulfate, chlorpyrifos and endrin; while the alkylphenols are 4-n-butylphenol, 4-n-pentylphenol, 4-n-hexylphenol, 4-t-octylphenol, 4-n-heptylphenol, nonylphenol, 4-n-octylphenol and bisphenol A. The pesticides and alkylphenols in the cord blood samples were extracted with solid phase extraction IST C18 cartridges and analyzed by selected ion monitoring mode using quadrapole detector in Shimadzu QP-5000 gas chromatograph-mass spectrometer. Trace levels of pesticide and alkylphenols in the range of non-detectable to 15.17 ng ml⁻¹, were detected in the human cord blood samples. This technique of monitoring the levels of endocrine-disruptors in blood samples is consistent, reliable and cost effective while reducing wastage of time and solvents.     

Polyoma T (tumor) antigen species in abortively and stably transformed cells.

Stable neoplastic transformation of cells by polyoma virus requires the particpation of two viral genes, designated ts-a and hr-t. The effects of mutations in these two genes on the patterns of T-antigen synthesis during productive infection have been previously described: ts-a mutants are affected in the "large" (100K) nuclear T antigen, and hr-t mutants are affected in the "middle" (36K, 56K, 63K) and "small" (22K) T antigens. The latter are associated predominantly with the plasma membrane (56K) and cytosol fractions, respectively. Here we examine the expression of the various forms of polyoma T antigen in nonproductive infection (abortive transformation) as well as in stably transformed cell lines of different species. The results on abortive transformation are essentially the same as those described above for productive infection. In stably transformed cells, the middle and small T antigens are seen to various extents. The large T antigen, however, is often absent or present below the level of detection. Clones lacking the large T antigen are found most often among mouse transformants, but are also seen among rat transformants. Retention of the 100K species in transformed cells therefore appears to be, at least in part, an inverse function of the level of permissivity of the host toward productive viral infection. These findings indicate that the induction of the transformed phenotype in both abortively and stably transformed cells generally does not require the large T antigen, but rather the products of the hr-t gene.     

Magic-angle spinning solid-state NMR spectroscopy of the beta1 immunoglobulin binding domain of protein G (GB1): 15N and 13C chemical shift assignments and conformational analysis

Magic-angle spinning solid-state NMR (SSNMR) studies of the beta1 immunoglobulin binding domain of protein G (GB1) are presented. Chemical shift correlation spectra at 11.7 T (500 MHz 1H frequency) were employed to identify signals specific to each amino acid residue type and to establish backbone connectivities. High sensitivity and resolution facilitated the detection and assignment of every 15N and 13C site, including the N-terminal (M1) 15NH3, the C-terminal (E56) 13C', and side-chain resonances from residues exhibiting fast-limit conformational exchange near room temperature. The assigned spectra lend novel insight into the structure and dynamics of microcrystalline GB1. Secondary isotropic chemical shifts report on conformation, enabling a detailed comparison of the microcrystalline state with the conformation of single crystals and the protein in solution; the consistency of backbone conformation in these three preparations is the best among proteins studied so far. Signal intensities and line widths vary as a function of amino acid position and temperature. High-resolution spectra are observed near room temperature (280 K) and at <180 K, whereas resolution and sensitivity greatly degrade substantially near 210 K; the magnitude of this effect is greatest among the side chains of residues at the intermolecular interface of the microcrystal lattice, which we attribute to intermediate-rate translational diffusion of solvent molecules near the glass transition. These features of GB1 will enable its use as an excellent model protein not only for SSNMR methods development but also for fundamental studies of protein thermodynamics in the solid state.     

Vapor Pressure and Solid Phases of Methanol below Its Triple Point Temperature

We present an experimental work devoted to study of the thermodynamical properties of solid methanol. We combine Fourier transform infrared spectroscopy (FTIR) and mass spectrometry (MS) to measure, for the first time, the vapor pressure of various methanol solid phases and determine their Clausius-Clapeyron equations. We perform our experiments between T = 130 K and the triple point temperature T(t) = 175.61 K. When methanol is condensed from its vapor below T(t), we observe three different solid phases depending on temperature. A condensation at T = 130 K forms a metastable phase with an enthalpy of sublimation deltaH(metastable-vapor) = 42.9 +/- 0.5 kJ.mol(-1). Upon heating, this phase transforms itself at T approximately 145 K to the alpha-phase that has an enthalpy of sublimation deltaH(alpha-vapor) = 46.9 +/- 0.2 kJ.mol(-1). Cooling the alpha-phase does not lead back to the metastable phase, whereas heating this alpha-phase leads to the beta-phase occurrence at T(alpha-beta) = 157.36 K. This latter one is stable until T(t) and has an enthalpy of sublimation deltaH(beta-vapor) = 44.2 +/- 0.5 kJ.mol(-1).     

Clar valence bond representation of pi-bonding in carbon nanotubes

The application of the Clar aromatic sextet valence bond (VB) model to extended, defect-free single-walled carbon nanotubes (CNTs) with roll-up vectors (m, n) provides a real space model of their electronic structure. If m - n = 3k, where k is an integer, then all pi-electrons can be represented by aromatic sextets, and the CNT is fully benzenoid; the converse is also true. Since m - n = 3k is known to be a necessary criterion for conductivity in CNTs, only fully benzenoid CNTs are metallic, and only potentially metallic CNTs are fully benzenoid. This behavior contrasts with that of planar polycyclic aromatic hydrocarbons, in which the fully benzenoid structures are known to have large HOMO-LUMO gaps. For CNTs that are not fully benzenoid, e.g., m - n = 3k + l, where l = 1 or 2 and k is an integer, a seam of double bonds wraps about an otherwise benzenoid CNT at the chiral angle - 60 degrees or the chiral angle, respectively. Nucleus-independent chemical shift calculations on hydrogen-terminated CNT segments support this, and show that the magnetic manifestation of aromatic sextets is not due to electron correlation. The resonance hybrid of the Clar VB structures corresponds to patterns occasionally observed in scanning tunneling microscopy images of CNTs.     

Synthesis of macrocycles via cobalt-mediated [2 + 2 + 2] cycloadditions

We investigated the formation of macrocycles from alpha,omega-diynes in cobalt-mediated co-cyclotrimerization reactions. Long-chain alpha,omega-diynes underwent metal-mediated [2 + 2 + 2] cycloadditions with nitriles, cyanamides, or isocyanates in the presence of CpCo(CO)2 (Cp = cyclopentadienide) to yield pyridine-containing macrocycles, i.e., meta- and para-pyridinophanes, such as 5m/5p, 35m/35p, and 41m/41p. The regioselectivity of these reactions was affected by the length and type of linker unit between the alkyne groups, as well as by certain stereoelectronic factors. An analogous alpha,omega-cyano-alkyne, 28, combined with an alkyne to yield two isomeric meta-pyridinophanes, such as 5m and 29m, and an ortho cycloadduct (benzannulation product), such as 29o. We developed a reaction protocol for these cobalt-based [2 + 2 + 2] cycloadditions that involves markedly improved conditions such that this process offers a convenient, flexible synthetic approach to macrocyclic pyridine-containing compounds. For example, diyne 6 reacted with p-tolunitrile in 1,4-dioxane to give 7p and 7m (7:1 ratio) in 87% yield at a moderate temperature of ca. 100 degrees C in 24 h without photoirradiation or syringe-pump addition. Isocyanates were also effective reactants, as exemplified by the formation of 44p almost exclusively (44p:44m > 50:1) in 64% yield from diyne 8 and 2-phenylethylisocyanate. By using this improved protocol we were able to co-cyclotrimerize long-chain alpha,omega-diynes with alkynes in certain cases to demonstrate a successful macrocyclic variant of the Vollhardt reaction. For instance, diyne 6 reacted with dipropylacetylene to give paracyclophane 57p and benzannulene 57o (2:1 ratio) in 29% yield.     

Protein-reactive natural products

Researchers in the post-genome era are confronted with the daunting task of assigning structure and function to tens of thousands of encoded proteins. To realize this goal, new technologies are emerging for the analysis of protein function on a global scale, such as activity-based protein profiling (ABPP), which aims to develop active site-directed chemical probes for enzyme analysis in whole proteomes. For the pursuit of such chemical proteomic technologies, it is helpful to derive inspiration from protein-reactive natural products. Natural products use a remarkably diverse set of mechanisms to covalently modify enzymes from distinct mechanistic classes, thus providing a wellspring of chemical concepts that can be exploited for the design of active-site-directed proteomic probes. Herein, we highlight several examples of protein-reactive natural products and illustrate how their mechanisms of action have influenced and continue to shape the progression of chemical proteomic technologies like ABPP.     

Artificial metalloenzymes: The powerful alliance between protein scaffolds and organometallic catalysts

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Self-selection in olefin cross-metathesis: the effect of remote functionality

Olefin cross-metathesis (CM) is potentially an attractive method for generating dynamic combinatorial libraries (DCLs). In order for the CM reaction to be useful for DCL production, the course of the reaction and product distribution must be relatively insensitive to functionality remote from the reacting centers. We report on the CM of a series of allyl- and homoallylamides that are strongly dependent on remote functionality. This includes an unusual example of a cis-selective CM. [Reaction: see text]     

Further reactions of some bis(vinylidene)diruthenium complexes

Whereas {Ru(dppm)Cp*}₂(μ-CCCC) (2) is the only product formed by deprotonation of [{Ru(dppm)Cp*}₂{μ(CCHCHC)}]⁺ with dbu, a mixture of 2 with Ru{CCCHCH(PPh₂)₂[RuCp*]}(dppm)Cp* (3) and {Cp*Ru(PPh₂CHCCH-)}₂ (4) is obtained with KOBu^t. A similar reaction with [{Ru(dppm)Cp*}₂{μ(CCMeCMeC)}]⁺ (5) gave Ru{CCCMeCH(PPh₂)₂[RuCp*]}(dppm)Cp* (6). X-ray structures of 4, 5 and 6 confirm the presence of the 1-ruthena-2,4-diphosphabicyclo[1.1.1]pentane moiety, which is likely formed by an intramolecular attack of the deprotonated dppm ligand on C(1) of the vinylidene ligand. Protonation of {Ru(dppe)Cp*}₂(μ-CCCC) (8-Ru) regenerates its precursor [{Ru(dppe)Cp*}₂{μ(CCHCHC)}]²⁺ (7-Ru). Ready oxidation of the bis(vinylidene) complex affords the cationic carbonyl [Ru(CO)(dppe)Cp*]PF₆ (9) (X-ray structure).