Preparation of fluorine-containing polyethers

Polyethers were prepared from 3,3,3-trifluoro-1,2-epoxypropane by using both cationic and anionic initiators. Aluminum chloride and boron trifluoride were the two cationic initiators investigated. The polymer obtained with the use of aluminum chloride contained no functional endgroups other than hydroxyl, while the polymer prepared with boron trifluoride contained some terminal unsaturation. Potassium hydroxide and the monosodium salt of hexafluoropentanediol were investigated as anionic initiators. The polymer obtained by using potassium hydroxide also contained terminal unsaturation, while the polymer prepared with the monosodium salt of hexafluoropentanediol was terminated with primary hydroxyl groups capable of being used in polyurethanes. All polymers had molecular weights in the range from 970 to 4300. A fluorine-containing polyformal was prepared in high yield by the reaction of hexafluoropentanediol with trioxane. The same polymer was obtained in poor yield by the reaction of hexafluoropentanediol with dibutyl formal. Ring-opening polymerizations were attempted on two fluorinated cyclic ethers, 2,2,3,3,4,4-hexafluoropentamethylene oxide and 3,3,4,4-tetrafluorotetramethylene oxide. There was no reaction with anionic initiators. With most of the cationic initiators, there was no reaction. Boron trifluoride and phosphorus pentafluoride formed complexes with the ether, but would not cause ring opening.     

Population growth in random media. I. Variational formula and phase diagram

We consider an infinite system of particles on the integer lattice Z that: (1) migrate to the right with a random delay, (2) branch along the way according to a random law depending on their position (random medium). In Part I, the first part of a two-part presentation, the initial configuration has one particle at each site. The long-time limit exponential growth rate of the expected number of particles at site 0 (local particle density) does not depend on the realization of the random medium, but only on the law. It is computed in the form of a variational formula that can be solved explicitly. The result reveals two phase transitions associated with localization vs. delocalization and survival vs. extinction. In earlier work the exponential growth rate of the Cesaro limit of the number of particles per site (global particle density) was studied and a different variational formula was found, but with similar structure, solution, and phases. Combination of the two results reveals an intermediate phase where the population globally survives but locally becomes extinct (i.e., dies out on any fixed finite set of sites).     

Some observations on the collisional broadening and shift of the Sr 4607.33 Å line in H2/O2/Ar flames

Spectral profiles of the 4607.33 Å Sr emission line $\text{(}{}^1\text{P}{}_1\text{?}{}^1\text{S}{}_0\text{transition}\text{)}$ were measured with a pressure-scanned Fabry-Pérot interferometer in a set of pre-mixed, laminar shielded H₂/O₂/Ar flames at 1 atm with temperatures ranging from 1765 to 2365 K. Some additional integrated line profile measurements were carried out.From the full width at one-half maximum (FWHM), δλ_T, and shift of the optically thin line profiles, adiabatic cross sections for broadening and for shift were determined for SrAr and SrH₂O.     

Reversal of low-field CIDNP due to deuterium substitution

A perturbation method is applied to the problem of low-field CIDNP. It is shown that in the intermediate magnetic field region the most important deviation from the high-field formulae is due to a perturbation of the S—T₀ mixing by interaction with the T_± levels of the radical pair. In the case of a symmetrical radical pair this contribution decreases to zero and higher order contributions become dominant. An experimental example is the reversal of low-field CIDNP of ethane formed during the thermal decomposition of acetyl peroxide compared with that of ethane-d₃ during the decomposition of acetylperoxide-d₃. A qualitative rule is given for net CIDNP effects in the intermediate field region.     

Modular Design of Small Enzymatic Reaction Networks Based on Reversible and Cleavable Inhibitors

Systems chemistry aims to mimic the functional behavior of living systems by constructing chemical reaction networks with well‐defined dynamic properties. Enzymes can play a key role in such networks, but there is currently no general and scalable route to the design and construction of enzymatic reaction networks. Here, we introduce reversible, cleavable peptide inhibitors that can link proteolytic enzymatic activity into simple network motifs. As a proof‐of‐principle, we show auto‐activation topologies producing sigmoidal responses in enzymatic activity, explore cross‐talk in minimal systems, design a simple enzymatic cascade, and introduce non‐inhibiting phosphorylated peptides that can be activated using a phosphatase.