Chemical Paradigm vs. Biological Paradigm in the Biological Clock Controversy

Examples of biological rhythmicity mounted in the first half of the twentieth century, but the nature of biological rhythms – whether they were direct responses to rhythmic environmental stimuli or generated internally by biological clocks or oscillators – remained sharply disputed. When Frank A. Brown Jr. observed precise twenty-four-hour rhythms in the colour changes of fiddler crabs that were isolated from changes in environmental lighting that could synchronise them with the daily cycle, he rejected the internal clock as an explanation, owing to his belief that such a biological mechanism must operate chemically and consequently run faster at higher temperatures (Van’t Hoff’s rule), which was not borne out by his experiments. Colin Pittendrigh was committed to the idea that the rhythms were generated by unknown, temperature-compensated mechanisms, without offering any explanation for how this might be accomplished. At the core of their dispute, which was aired publicly from 1954 until Brown’s death in 1983, was a difference in belief: Brown’s fundamental reductionism, which required biological processes to conform to the laws of chemistry, vs. Pittendrigh’s trust in the power of evolution to select for such a temperature compensated biological clock, for which no plausible chemical model then existed.     

Solid state thermochemical decomposition of neat 1,3,5,5-tetranitrohexahydropyrimidine (DNNC) and its DNNC-d6 perdeuterio-labeled analogue

The solid state thermochemical decomposition kinetics and activation energy of neat 1,3,5,5-tetranitrohexahydropyrimidine (DNNC) and its DNNC-d₆ deuterium labeled analogue were obtained by isothermal differential scanning calorimetry (IDSC) at 142, 145, and 148 °C. Global rate constants and kinetic deuterium isotope effect (KDIE) data from the exothermic decomposition process suggest that homolytic CH bond rupture, in one or both types of chemically non-equivalent methylene (CH₂) groups of the DNNC ring structure, constitutes the exothermic rate-controlling step. A DNNC-d₆ energy of activation equal to 115 kJ/mol was determined for this initial autocatalytic exothermic energy release from which a 106 kJ/mol activation energy was calculated for unlabeled DNNC. This exothermic autocatalytic decomposition process follows an extended endothermic induction period for DNNC which shows a higher 128 kJ/mol activation energy during which a catalytic initiating species may form by a rate-controlling step different from CH bond rupture.     

A Movel Neighboring Group Participation in the solvolysis of α-3,4-Epoxycarane with a Carboxylic Acid

The racent interest in the conformational and configurational relationships in the carane serises¹ prompts us to report an abnrnality observed in the solvelysis of (m%+)-3,4-epoxycarane, xs1, with a sodium acetate buffered solution of glaacial acetic acid.²     

A piezoelectric detector for organophosphorus pesticides in the air

The concentration-time data obtained in kinetic analyses may be easily and conveniently interpreted by multiparametric curve-fitting. A new technique of kinetic analysis, in which the overall extent of reaction is monitored by following the variation with time of the difference between the temperature of a reaction mixture and that of a reference solution, is described. Both these techniques are illustrated with-data obtained in oximations of mixtures of propanal-and cyclohexanone. The results confirm the existence of the synergic effect reported by Siggia and Hanna.     

Diffuse abdominal angiomatosis

We present a rare case of diffuse abdominal angiomatosis occurring in a 19-year-old male; particular attention is paid to the MR imaging features of this disease process.     

The thermodynamics of water and hydrogen solubility in fused silica

A statistical thermodynamic model of the solubility of water vapor in glass is developed as an extension of previous models of monatomic and diatomic gas solubility in glass. The model predicts the $\text{p}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ dependence of water vapor solubility in fused silica and indicates the binding energies of dissociated H and OH species to be about ?63 and ?99 kcal/mol, respectively. The OH binding energy is found to be slightly temperature dependent, namely E_OH(0) = ?81.3?0.0163T. The tendency of chemical solubility of H₂ to predominate over physical solubility above 500°C correlates with the model equations for H₂ solubility.     

UTILIZATION OF TOOLS FOR SUCCESSFUL. TROUBLESHOOTING OF STRUCTURAL PROBLEMS

A structural failure problem was solved using an integrated and iterative program of testing and analysis. The steps taken in solving the problem were: analytical calculations; operational testing; qualifications of analytical results; problem identification; design of corrective action; and confirmatory testing.     

Electrophilic tetraalkylammonium nitrate nitration. II. Improved anhydrous aromatic and heteroaromatic mononitration with tetramethylammonium nitrate and triflic anhydride,including selected microwave examples

A new one-pot nitration employing tetramethylammonium nitrate and trifluoromethanesulfonic anhydride in dichloromethane to provide a ready source of the nitronium triflate nitrating agent is presented. Rapid and selective nitration with a variety of aromatic and heteroaromatic substrates is achieved resulting in the synthesis of several novel organic compounds. A distinct advantage is the removal of undesired byproducts by aqueous workup. This very mild nitration permits large-scale syntheses and gives high isolated product yields that often require no further purification. This tetramethylammonium nitrate-based nitration also has been applied to microwave-assisted conditions, and the results with several compounds are outlined.