A Kinetic Study of the ortho-Claisen Rearrangement1

A pyrene-tagged ruthenium carbene 8 was synthesized and immobilized on single-walled carbon nanotubes (SWNTs) via π−π stacking. These π−π interactions were greatly affected by the reaction temperature and the solvent polarity, thus, offering a new reversible immobilization model that can be controlled by reaction temperature in polar solvents, such as acetone. SWNTs-supported ruthenium carbene 8 is a robust and recyclable catalyst system. Six to seven cycles were achieved for ring-closing metathesis of selected substrates. Importantly, after the complete loss of activity, the SWNTs can be easily recycled by washing with tetrahydrofuran. The recycled SWNTs can then be reloaded with 8. The reusability of the catalyst supported on recycled SWNTs is comparable with that supported on fresh SWNTs.

Controlled Reversible Immobilization of Ru Carbene on Single-Walled Carbon Nanotubes: A New Strategy for Green Catalytic Systems Based on a Solvent Effect on π−π Interaction

The cytotoxicities of a series of simple phenols as well as estrogenic phenols such as octyl and nonyl phenols, Bisphenol A, diethylstilbestrol, estradiol, estriol, equilin and equilenin were studied in a fast growing murine leukemia cell line. The use of calculated homolytic bond dissociation energies (BDE) as the electronic parameter led to the development of a Quantitative Structure–Activity Relationship model with superior results; one which established the importance of relatively low BDE values in enhancing toxicity to rapidly multiplying cells. The correlation equation that emerged is as follows: log 1/C = –0.19BDE + 0.21 log P + 3.11. It suggests that toxicity is closely related to mostly homolytic cleavage of the phenolic O–H bond and overall hydrophobicity of the phenol.

On the toxicity of phenols to fast growing cells. A QSAR model for a radical-based toxicity

Biofilm-forming bacteria present formidable challenges across diverse settings, and there is a need for new antimicrobial agents that are both environmentally acceptable and relatively potent against microorganisms in the biofilm state. The antimicrobial activity of three naturally occurring, low molecular weight, phenols, and their derivatives were evaluated against planktonic and biofilm Staphylococcus epidermidis and Pseudomonas aeruginosa. The structure activity relationships of eugenol, thymol, carvacrol, and their corresponding 2- and 4-allyl, 2-methallyl, and 2- and 4-n-propyl derivatives were evaluated. Allyl derivatives showed a consistent increased potency with both killing and inhibiting planktonic cells but they exhibited a decrease in potency against biofilms. This result underscores the importance of using biofilm assays to develop structure-activity relationships when the end target is biofilm.

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Richard F. Miller

Papers

The Introduction of Isobutyl Groups into Phenols, Cresols and Homologous Compounds