Free-radical distributions in emulsion polymerization which employs oil-soluble radical generators

The use of oil-soluble radical generators for emulsion polymerization is considered. When radicals are formed in pairs within particles of a seed latex, the occurrence of radical desorption leads to complex kinetics. Use of radical balances and realistic simplifications produce a method for a relatively simple calculation of radical populations in the particles. Examples are restricted, for illustration purposes, to cases where the average number of radicals per particle, n , is less than one. Very low rates of radical desorption cause a substantial increase in n . As the desorption rate increases, the value of n decreases. n increases slowly with radical generation rate. Large decreases in the chain termination rate coefficient (which may accompany a gel effect) can have a negligible effect on the value of n . Radical distributions obtained from oil-soluble initiators can be slightly broader than those expected from the use of water-soluble initiators. The kinetics of emulsion polymerization will be similar for the two types of radical generator when radicals from oil-soluble generators can desorb from the polymer particles.     

Formation of a cyclobutylidene ring: intramolecular [2 + 2] cycloaddition of allyl and vinylidene C=C bonds under mild conditions

Intramolecular [2 + 2] cycloaddition of two C=C bonds in vinylidene complexes [Ru(eta5-C9H7){=C=C(R)H}(PPh3){kappa1-(P)-PPh2(C3H5)][BF4] affords cyclobutylidene complexes [Ru(eta5-C9H7){kappa2-(P,C)-(=CC(R)HCH2CHCH2PPh2)}(PPh3)][BF4], which can be also obtained by reaction of terminal alkynes with [Ru(eta5-C9H7)(PPh3){kappa3-(P,C,C)-PPh2(C3H5)}][PF6]. The reaction proceeds under mild conditions via vinylidene complexes, and the activation parameters were determined by kinetic studies.     

Thermodynamic Parameters for the Association of Fluorinated Benzenesulfonamides with Bovine Carbonic Anhydrase II

This paper describes a calorimetric study of the association of a series of seven fluorinated benzenesulfonamide ligands (C₆H_nF_5?nSO₂NH₂) with bovine carbonic anhydrase II (BCA). Quantitative structure–activity relationships between the free energy, enthalpy, and entropy of binding and pK_a and log P of the ligands allowed the evaluation of the thermodynamic parameters in terms of the two independent effects of fluorination on the ligand: its electrostatic potential and its hydrophobicity. The parameters were partitioned to the three different structural interactions between the ligand and BCA: the Zn^II cofactor–sulfonamide bond (≈65 % of the free energy of binding), the hydrogen bonds between the ligand and BCA (≈10 %), and the contacts between the phenyl ring of the ligand and BCA (≈25 %). Calorimetry revealed that all of the ligands studied bind in a 1:1 stoichiometry with BCA; this result was confirmed by ¹⁹F NMR spectroscopy and X‐ray crystallography (for complexes with human carbonic anhydrase II).     

New spherical-cutoff methods for long-range forces in macromolecular simulation

New atom- and group-based spherical-cutoff methods have been developed for the treatment of nonbonded interactions in molecular dynamics (MD) simulation. A new atom-based method, force switching, leaves short-range forces unaltered by adding a constant to the potential energy, switching forces smoothly to zero over a specified range. A simple improvement to group-based cutoffs is presented: Switched group-shifting shifts the group–group potential energy by a constant before being switched smoothly to zero. Also introduced are generalizations of atom-based force shifting, which adds a constant to the Coulomb force between two charges. These new approaches are compared to existing methods by evaluating the energy of a model hydrogen-bonding system consisting of two N-methyl acetamide molecules and by full MD simulation. Thirty-five 150 ps simulations of carboxymyoglobin (MbCO) hydrated by 350 water molecules indicate that the new methods and atom-based shifting are each able to approximate no-cutoff results when a cutoff at or beyond 12 Å is used. However, atom-based potential-energy switching and truncation unacceptably contaminate group–group electrostatic interactions. Group-based potential truncation should not be used in the presence of explicit water or other mobile electrostatic dipoles because energy is not a state function with this method, resulting in severe heating (about 4 K/ps in the simulations of hydrated MbCO). The distance-dependent dielectric (? ∝? r) is found to alter the temperature dependence of protein dynamics, suppressing anharmonic motion at high temperatures. Force switching and force shifting are the best atom-based spherical cutoffs, whereas switched group-shifting is the preferred group-based method. To achieve realistic simulations, increasing the cutoff distance from 7.5 to 12 Å or beyond is much more important than the differences among the three best cutoff methods. © 1994 by John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

The microwave spectrum and conformation of bromomethyl cyclopropane

The microwave spectrum of gaseous bromomethyl cyclopropane

is reported in the range 12 to 36 GHz. Lines of the ⁷⁹Br and ⁸¹Br species of cis and gauche forms are assigned and partial r₀-structures derived. The rotational constants in MHz are: gauche C₃H₅CH₂⁷⁹Br, A = 11 469.285, B = 1 374.777, C = 1 295.394; gauche C₃H₅CH₂⁸¹Br, A = 11 400.100, B = 1 364.088, C = 1 283.952; cis C₃H₅CH₂⁷⁹Br, A = 8 759.918, B = 1 597.413, C = 1 522.141; cis C₃H₅CH₂⁸¹Br, A = 8 716.552, B = 1 583.761, C = 1 509.017.     

Mesoporous sodium four-coordinate aluminosilicate nanoparticles modulate dendritic cell pyroptosis and activate innate and adaptive immunity

Pyroptosis is a programmed cell death widely studied in cancer cells for tumour inhibition, but rarely in dendritic cell (DC) activation for vaccine development. Here, we report the synthesis of sodium stabilized mesoporous aluminosilicate nanoparticles as DC pyroptosis modulators and antigen carriers. By surface modification of sodium-stabilized four-coordinate aluminium species on dendritic mesoporous silica nanoparticles, the resultant Na-^IVAl-DMSN significantly activated DC through caspase-1 dependent pyroptosis via pH responsive intracellular ion exchange. The released proinflammatory cellular contents further mediated DC hyperactivation with prolonged cytokine release. In vivo studies showed that Na-^IVAl-DMSN induced enhanced cellular immunity mediated by natural killer (NK) cells, cytotoxic T cells, and memory T cells as well as humoral immune response. Our results provide a new principle for the design of next-generation nanoadjuvants for vaccine applications.

Na-^IVAl-DMSN acts as both antigen carriers and modulators to “hyperactivate” dendritic cells (DCs) via potassium (K⁺) efflux dependent pyroptosis, eventually leading to enhanced adaptive and innate immunity.     

Fluorotamoxifen. A Caveat on the Generality of Electrophilic Destannylation

A one-step synthesis of fluorotamoxifen from tamnoxifen is described. Attempts to achieve synthesis of the title compound by fluorodestannylation or transmetallation were unsuccessful.