Affinity Chromatography of Mushroom Tyrosinase

Abstract

The purification by column chromatography of a phenol-oxidizing enzyme, mushroom tyrosinase, was investigated using solid phase adsorbents designed to have specific affinity for the enzyme. Sepharose 4B, aminophenyl-bearing porous glass, and p-aminobenzylcellulose were chemically modified to introduce phenolic, catecholic, or benzoic groups on the polymer surface. The resulting preparations were tested for their effectiveness in separating tyrosinase from an impure protein mixture. The phenolic and benzoic polymers displayed no specific affinity for tyrosinase. Aminophenyl glass, with or without an attached phenolic group, adsorbed appreciable quantities of protein nonspecif-ically, thus complicating studies of its tyrosinase affinity properties. Dopamine, a dihydroxyphenyl derivative, was bound to Sepharose and was found to be effective in retaining tyrosinase at pH 5.5; elution of the enzyme by washing at pH 8.8 resulted in its purification by a factor of 10 to 14. Enzymatic oxidation of the adsorbent limited the number of purification cycles which could be carried out on a single column.     

Predicting the Outcome of Photocyclisation Reactions: A Joint Experimental and Computational Investigation

Photochemical oxidative cyclodehydrogenation reactions are a versatile class of aromatic ring‐forming reactions. They are tolerant to functional group substitution and heteroatom inclusion, so can be used to form a diverse range of extended polyaromatic systems by fusing existing ring substituents. However, despite their undoubted synthetic utility, there are no existing models—computational or heuristic—that predict the outcome of photocyclisation reactions across all possible classes of reactants. This can be traced back to the fact that “negative” results are rarely published in the synthetic literature and the lack of a general conceptual framework for understanding how photoexcitation affects reactivity. In this work, we address both of these issues. We present experimental data for a series of aromatically substituted pyrroles and indoles, and show that quantifying induced atomic forces upon photoexcitation provides a powerful predictive model for determining whether a given reactant will photoplanarise and hence proceed to photocyclised product under appropriate reaction conditions. The propensity of a molecule to photoplanarise is related to localised changes in charge distribution around the putative forming ring upon photoexcitation. This is promoted by asymmetry in molecular structures and/or charge distributions, inclusion of heteroatoms and ethylene bridging and well‐separated or isolated photocyclisation sites.     

Understanding Why Scholars Hold Different Views on the Influences of Video Games on Public Health

Despite decades of research, no scholarly consensus has been achieved regarding the potential impact of video games on youth aggression or other public health concerns. In recent years, hypotheses have been raised that scholarly opinions on video games may resemble past moral panics, with attitudes reflective of generational conflicts. These hypotheses are tested in a sample of 175 criminologists, psychologists, and media scholars, examining both overall negative attitudes about video games and perceived linkages with youth assaults specifically. Results reflected continued lack of scholarly consensus on the issue of video game influences with only 15.3% of scholars endorsing the view that violent video games contribute to youth assaults. As hypothesized, older scholars endorsed more negative views of video games generally, although this appeared to be related to experience with games rather than age per se. Scholars with more negative attitudes toward youth themselves were also more negative about games. Criminologists and media scholars were more skeptical of violent video games contributing to youth assaults than were psychologists. These results are discussed in relation to Moral Panic Theory.     

Nickel-catalyzed intramolecular C–H arylation using aryl pivalates as electrophiles

This paper describes a method for nickel catalyzed intramolecular C–H arylation using aryl pivalates as electrophiles. The transformation is efficient for the synthesis of diverse electronically and sterically differentiated dibenzofurans. Additionally, the method could be expanded toward the synthesis of carbazoles. Preliminary mechanistic studies of the transformation are also described.     

An Investigation of 1:1 Adducts of Gallium Trihalides with Triarylphosphines by Solid‐State 69/71Ga and 31P NMR Spectroscopy

Several 1:1 adducts of gallium trihalides with triarylphosphines, X₃Ga(PR₃) (X=Cl, Br, and I; PR₃=triarylphosphine ligand), were investigated by using solid‐state ^69/71Ga and ³¹P NMR spectroscopy at different magnetic‐field strengths. The ^69/71Ga nuclear quadrupolar coupling parameters, as well as the gallium and phosphorus magnetic shielding tensors, were determined. The magnitude of the ⁷¹Ga quadrupolar coupling constants (C_Q(⁷¹Ga)) range from approximately 0.9 to 11.0 MHz . The spans of the gallium magnetic shielding tensors for these complexes, δ₁₁?δ₃₃, range from approximately 30 to 380 ppm; those determined for phosphorus range from 10 to 40 ppm. For any given phosphine ligand, the gallium nuclei are most shielded for X=I and least shielded for X=Cl, a trend previously observed for In^III–phosphine complexes. This experimental trend, attributed to spin‐orbit effects of the halogen ligands, is reproduced by DFT calculations. The signs of C_Q(^69/71Ga) for some of the adducts were determined from the analysis of the ³¹P NMR spectra acquired with magic angle spinning (MAS). The ¹J(^69/71Ga,³¹P) and ΔJ(^69/71Ga, ³¹P) values, as well as their signs, were also determined; values of ¹J(⁷¹Ga,³¹P) range from approximately 380 to 1590 Hz. Values of ¹J(^69/71Ga,³¹P) and ΔJ(^69/71Ga,³¹P) calculated by using DFT have comparable magnitudes and generally reproduce experimental trends. Both the Fermi‐contact and spin‐dipolar Fermi‐contact mechanisms make important contributions to the ¹J(^69/71Ga,³¹P) tensors. The ³¹P NMR spectra of several adducts in solution, obtained as a function of temperature, are contrasted with those obtained in the solid state. Finally, to complement the analysis of NMR spectra for these adducts, single‐crystal X‐ray diffraction data for Br₃Ga[P(p‐Anis)₃] and I₃Ga[P(p‐Anis)₃] were obtained.     

Divergent and Overlapping Roles for Selected Phytochemicals in the Regulation of Pathological Cardiac Hypertrophy

Plant-based foods, like fruits, vegetables, whole grains, legumes, nuts, seeds and other foodstuffs, have been deemed as heart healthy. The chemicals within these plant-based foods, i.e., phytochemicals, are credited with protecting the heart. However, the mechanistic actions of phytochemicals, which prevent clinical endpoints, such as pathological cardiac hypertrophy, are still being elucidated. We sought to characterize the overlapping and divergent mechanisms by which 18 selected phytochemicals prevent phenylephrine- and phorbol 12-myristate 13-acetate-mediated cardiomyocyte enlargement. Of the tested 18 compounds, six attenuated PE- and PMA-mediated enlargement of neonatal rat ventricular myocytes. Cell viability assays showed that apigenin, baicalein, berberine hydrochloride, emodin, luteolin and quercetin dihydrate did not reduce cell size through cytotoxicity. Four of the six phytochemicals, apigenin, baicalein, berberine hydrochloride and emodin, robustly inhibited stress-induced hypertrophy and were analyzed further against intracellular signaling and genome-wide changes in mRNA expression. The four phytochemicals differentially regulated mitogen-activated protein kinases and protein kinase D. RNA-sequencing further showed divergence in gene regulation, while pathway analysis demonstrated overlap in the regulation of inflammatory pathways. Combined, this study provided a comprehensive analysis of cardioprotective phytochemicals. These data highlight two defining observations: (1) that these compounds predominantly target divergent gene pathways within cardiac myocytes and (2) that regulation of overlapping signaling and gene pathways may be of particular importance for the anti-hypertrophic actions of these phytochemicals. Despite these new findings, future works investigating rodent models of heart failure are still needed to understand the roles for these compounds in the heart.     

Investigation of N‐Heterocyclic Carbene‐Supported Group 12 Triflates as Pre‐catalysts for Hydrosilylation/Borylation

N‐Heterocyclic carbene (NHC) complexes of Cd and Hg triflates (OTf) were prepared and their attempted conversion into rare cadmium and mercury hydrides was explored. In contrast to zinc, which forms stable [ZnH]⁺ complexes with NHCs, the heavier Cd and Hg congeners could not be formed; the increased instability of Cd‐H and Hg‐H units was rationalized with the aid of computations. It was also discovered that the dimeric adduct [IPr?Cd(μ‐OTf)₂]₂ (IPr=[(HCNDipp)₂C:]; Dipp=2,6‐iPr₂C₆H₃) is an active precatalyst for the hydrosilylation and hydroborylation of hindered aldehydes and ketones. The related zinc congener was inactive as a catalyst highlighting a distinct advantage of using heavy Group 12 metals to promote catalytic hydrosilylation/borylation.     

Dalitz analysis of D0-->K(0)(S)pi(+)pi(-)

In e(+)e(-) collisions using the CLEO detector, we have studied the decay of the D0 to the final state K(0)(S)pi(+)pi(-) with the initial flavor of the D0 tagged by the decay D(*+)-->D0pi(+). We use the Dalitz technique to measure the resonant substructure in this final state and clearly observe ten different contributions by fitting for their amplitudes and relative phases. We observe a K(*)(892)(+)pi(-) component which arises from doubly Cabibbo suppressed decays or D0-D0; mixing.     

Improved measurement of Vub with inclusive semileptonic B decays

We report a new measurement of the Cabibbo-Kobayashi-Maskawa parameter Vub made with a sample of 9.7 x 10(6) BB- events collected with the CLEO II detector. Using heavy quark theory, we combine the observed yield of leptons from semileptonic B decay in the end-point momentum interval 2.2-2.6 GeV/c with recent CLEO II data on B-->X(s)gamma to find Vub = (4.08+/-0.34+/-0.44+/-0.16+/-0.24)x10(-3), where the first two uncertainties are experimental and the last two are from theory.