THE EFFECTS OF NEAR-UV RADIATION ON HUMAN LENS β-CRYSTALLINS: PROTEIN STRUCTURAL CHANGES and THE PRODUCTION OF O2_ and H2O2

beta-Crystallins (beta 1-, beta 2- and beta 3-crystallin) comprise nearly half the protein of the human lens. The effect of near-UV radiation, which is one of the possible risk factors in cataract formation, on the beta-crystallins is investigated in this study. Protein intersubunit crosslinking, change in charge of the protein subunits to more acidic species and changes in protein tertiary structure (conformation) by 300 nm irradiation are reported. The fluorescence yield of protein tryptophan residues decreases by 300 nm irradiation. There is an increase in nontryptophan fluorescence (lambda cx 340 nm, lambda cm 400-600 nm), and in protein absorption at 340 nm, due to the formation of tryptophan photooxidation products. Both tryptophan and its oxidation products can be photoexcited by 300 nm irradiation and the latter are known to be good photosensitizers. The results provide evidence for the generation of H2O2 in the irradiated human beta-crystallin solutions by the Type I photosensitizing action of the chromophores absorbing at 300 nm. The H2O2 is generated via the intermediate production of O2 anion; the latter spontaneously dismutates to H2O2, presumably via O2- protein interactions. The amount of H2O2 generated per absorbed photon is compared for various solutions of beta 1-, beta 2- and beta 3-crystallins from human lenses of different age.     

Biogenetically inspired approach to the Strychnos alkaloids. Concise syntheses of (+/-)-akuammicine and (+/-)-strychnine

A linear synthesis of the indole alkaloid (+/-)-akuammicine (2) was completed by a novel sequence of reactions requiring only 10 steps from commercially available starting materials. The approach features a tandem vinylogous Mannich addition and an intramolecular hetero Diels-Alder reaction to rapidly assemble the pentacyclic heteroyohimboid derivative 8 from the readily available hydrocarboline 6. Oxidation of the E ring of 8 gave the lactone 9 that was converted into deformylgeissoschizine (11). The subsequent elaboration of 11 into 2 was effected by a biomimetically patterned transformation that involved sequential oxidation and base-induced skeletal reorganization. A variation of these tactics was then applied to the synthesis of the C(18) hydroxylated akuammicine derivative 36. Because 36 had previously been converted into strychnine (1) in four steps, its preparation constitutes a concise, formal synthesis of this complex alkaloid.     

Validation of the CALUX bioassay for the screening of PCDD/Fs and dioxin-like PCBs in retail fish

The chemical-activated luciferase expression (CALUX) assay is a reporter gene assay that detects dioxin-like compounds based on their ability to activate the aryl hydrocarbon receptor (AhR) and thus expression of the reporter gene. In this paper, the CALUX assay was examined for its application in the screening of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dioxin-like PCBs) in retail fish. The sample extracts were cleaned up on a sulfuric acid-silica gel column followed by an activated carbon column, and the AhR activity of the separated PCDD/F and dioxin-like PCB fractions was determined using the assay. The quantitative limit for 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) was 0.98 pg ml(-1) (0.19 pg assay(-1) in the standard curve, corresponding to 0.16 pg g(-1) of CALUX-based toxic equivalency (2,3,7,8-TCDD equivalents) in the tested sample. Recovery tests in which dioxins were added to fish samples resulted in acceptable recoveries (77-117%). The CALUX assay performed well in the analysis of dioxins in fish samples and a comparative study revealed a strong correlation between the CALUX assay and high-resolution gas chromatography-high-resolution mass spectrometry analysis for the determination of PCDD/Fs (r = 0.89) and dioxin-like PCBs (r = 0.91) in retail fish (n = 22). These data revealed that the CALUX assay would be a useful screening method for PCDD/Fs and dioxin-like PCBs in retail fish.     

Et3SiH + KOtBu provide multiple reactive intermediates that compete in the reactions and rearrangements of benzylnitriles and indolenines

The combination of potassium tert-butoxide and triethylsilane is unusual because it generates multiple different types of reactive intermediates simultaneously that provide access to (i) silyl radical reactions, (ii) hydrogen atom transfer reactions to closed shell molecules and to radicals, (iii) electron transfer reductions and (iv) hydride ion chemistry, giving scope for unprecedented outcomes. Until now, reactions with this reagent pair have generally been explained by reference to one of the intermediates, but we now highlight the interplay and competition between them.

The combination of potassium tert-butoxide and triethylsilane provides simultaneous access to multiple reactive intermediates, radicals, H-atom donors, hydride donors and electron donors, giving scope for unprecedented reaction outcomes.     

Chromatographic and mass spectral studies on isobaric and isomeric substances related to 3,4-methylenedioxymethamphetamine

A series of isobaric and isomeric molecules related to 3,4methylenedioxymethamphetamine (3,4-MDMA) are prepared and evaluated as potential mass spectral equivalents to this controlled substance. These compounds have the potential to produce a mass spectrum equivalent to 3,4-MDMA, thus making mass spectrometry a nonconclusive method for confirming the identity of any one of the substances. The various isomeric forms of the methoxymethylphenethylamines and the methoxymethcathinones have mass spectra essentially equivalent to 3,4-MDMA, but the ethoxy substituted phenethylamines show a unique fragment at m/z 107. Gas chromatographic separation on nonpolar stationary phases successfully resolved these compounds from 3,4-MDMA, however only a limited set of side chain regioisomers and ring substitution patterns are evaluated in this initial study.     

Molecular motion and interactions in aqueous carbohydrate solutions. I. Dielectric-relaxation studies

Dielectric-relaxation studies in the frequency range 200 kHz to 35 GHz are reported for a range of sugars (from mono- to trisaccharides) in aqueous solution. The complex dielectric spectra were analyzed using a weighted least-squares minimization method to resolve the various component relaxations, and the implications of the analyses in terms of the molecular dynamics of solute and solvent and the interactions between solute and solvent are discussed. For the highest concentration studied (ca. 2M), it was found that the most significant analysis required three discrete relaxation processes, whereas lower concentration samples could usually be satisfactorily fitted with two. Irrespective of any uncertainty in model selection, a number of conclusions regarding the solute-solvent interactions can be made, and it is shown how final quantification of the extents of hydration can be made using the input of information from other techniques.     

General perspectives on model construction and evaluation for stochastic estimation,with application to a blunt trailing edge wake

The technique of stochastic estimation is examined as a specific application of linear least squares modelling. Factors that are relevant to the objectives of estimation in fluids, such as the number of sensors, the use of multiple time lags, and the strength of linear correlations, are discussed in the context of a general regression formulation. We consolidate the established findings of several research fields in order to outline clearly the potential pitfalls and reasonable performance expectations of these empirical strategies. Experimental measurements of velocity and fluctuating pressure in the wake of a blunt trailing edge body are used for quantitative illustration of key considerations for model construction and performance evaluation. It is emphasized that estimator accuracy is influenced strongly by the physical relationships among the measured variables, in addition to their correlation with the estimated variable. The evaluation of several performance metrics on an independent test set provides valuable information for the selection of a suitably complex model. In particular, “variance inflation” is interpreted as an indicator of the potential amplification of noise by a stochastic estimator.     

Allyl sulfides and α‐substituted acrylates as addition–fragmentation chain transfer agents for methacrylate polymer networks

The rapid and uncontrolled nature of network formation from di(meth)acrylate monomers produces high shrinkage stress and results in polymers with oftentimes brittle mechanical properties. Methods for regulating polymerization and network formation are sought. One option is the use of addition–fragmentation chain transfer (AFCT) agents, which are well known to control molecular weight and molecular weight distribution of monofunctional (meth)acrylates. A series of novel and previously described AFCT reagents were synthesized and screened with laser flash photolysis to determine reactivity. Well‐performing AFCT reagents were then tested in polymerizations with monofunctional and difunctional methacrylates. With monofunctional monomers, the molecular weight and polydispersity of the resultant linear polymers tend to decrease with the addition of AFCT agent. In copolymerization with dimethacrylate monomers, the AFCT agents were found to substantially lower and sharpen the glass transition. Sharpness of the glass transition is here indicative of a more regular and homogenous network. After coupling of the instruments, photorheology was performed simultaneously with real‐time IR to show an increase in monomer conversion at the time of gelation, which appears to have a positive effect on reducing shrinkage stress. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 394–406