The dependence of cyclopolymerizability of acrylic and methacrylic anhydrides on various conditions: New interpretation of temperature dependency of cyclization constant in radical cyclopolymerization of nonconjugated dienes

The cyclization constant K_c in the radical cyclopolymerization of acrylic and methacrylic anhydrides was evaluated in detail under various conditions. No linear relationship between in K_c and 1/T was observed; cyclization was acceleratively enhanced at elevated temperatures. The K_c values also increased with decreased monomer concentration and increased solvent polarity. These increasing dependencies of K_c are ascribed to the increased significance of depropagation, demonstrating a new interpretation of the temperature dependence of the cyclization constant in the radical cyclopolymerization of nonconjugated dienes.     

Mechanistic studies on the binding of nitric oxide to a synthetic heme-thiolate complex relevant to cytochrome p450

The synthetic heme-thiolate complex (SR) in methanol binds nitric oxide (k(on) = (2.7 +/- 0.2) x10(6) M(-)(1) s(-)(1) at 25 degrees C) to form SR(NO). The binding of NO to the SR complex in a noncoordinating solvent, such as toluene, was found to be almost 3 orders of magnitude faster than that in methanol. The activation parameters DeltaH(), DeltaS(), and DeltaV() for the formation of SR(NO) in methanol are consistent with the operation of a limiting dissociative mechanism, dominated by dissociation of methanol in SR(MeOH). In the presence of an excess of NO, the formation of SR(NO) is followed by subsequent slower reactions. The substantially negative activation entropy and activation volume values found for the second observed reaction step support an associative mechanism which involves attack of a second NO molecule on the thiolate ligand in the initially formed SR(NO) complex. The following slower reactions are strongly accelerated by a large excess of NO or by the presence of NO(2)(-) in the SR/NO reaction mixture. They can be accounted for in terms of dynamic equilibria between higher nitrogen oxides (NO(x)()) and reactive SR species, which lead to the formation of a nitrosyl-nitrite complex of SR(Fe(II)) as the final product. This finding is clearly supported by laser flash photolysis studies on the SR/NO reaction mixture, which do not reveal simple NO photolabilization from SR(Fe(III))(NO), but rather involve the generation of at least three photoinduced intermediates decaying with different rate constants to the starting material. The species formed along the proposed reaction pathways were characterized by FTIR and EPR spectroscopy. The results are discussed in terms of their relevance for the biological function of cytochrome P450 enzymes and in context of results for the reaction of NO with imidazole- and thiolate-ligated iron(III) hemoproteins.     

Unique oxidation reaction of amides with pyridine-N-oxide catalyzed by ruthenium porphyrin: direct oxidative conversion of N-acyl-L-proline to N-acyl-L-glutamate

Oxidations of alkanes, alkenes, and aromatic rings with pyridine N-oxides are efficiently catalyzed by ruthenium porphyrins under mild conditions. We show here that the oxidation of N-acyl cyclic amines with RuIVtetraarylporphyrin dichloride-2,6-substituted pyridine N-oxides directly gives N-acyl amino acids in modest to good yield via oxidative C-N bond cleavage. N-Acylpyrrolidines and N-acylpiperidines were converted to N-acyl-gamma-aminobutyric acids and N-acyl-delta-aminovaleric acids, respectively. This type of reaction is a novel one in which the C-N bond is cleaved selectively at the less substituted carbon. Notably, the proline residue in proline-containing peptides was selectively converted to glutamate. A large intramolecular kinetic isotope effect (kH/kD = 9.8) was observed in the oxidation of N-benzoyl[2,2,-d2]pyrrolidine, indicating that the reaction should involve an alpha-hydrogen atom abstraction process as the rate-determining step. N-Acylcarbaldehyde, the putative intermediate ring-opened form of alpha-hydroxylated N-acyl cyclic amine, was readily oxidized with the oxidizing system to afford the corresponding N-acylamino acid in good yield. Further, lactams (1-methyl-2-pyrrolidone and 1-methyl- 2-piperidone) were also oxidized to give the corresponding imides (1-methylsuccinimide and 1-methylpiperidine-2,6-dione).     

Energy spectrum of superfluid turbulence with no normal-fluid component

The energy of superfluid turbulence without the normal fluid is studied numerically under the vortex filament model. Time evolution of the Taylor-Green vortex is calculated under the full nonlocal Biot-Savart law. It is shown that for k<2pi/l the energy spectrum is very similar to the Kolmogorov's -5/3 law which is the most important statistical property of the conventional turbulence, where k is the wave number of the Fourier component of the velocity field and l is the average intervortex spacing. The vortex length distribution converges to a scaling property reflecting the self-similarity of the tangle.     

Mechanical and dielectric absorption of poly(vinyl chloride) and some related polymers

The mechanical and dielectric low temperature absorptions of poly(vinyl chloride) (PVC) and several modified PVC's have been studied over the temperature range from ?60 to +60°C. with some tests extending to ?150°C. and others to +170°C. The results indicate that the low-temperature absorption near ?50°C (β₂ absorption) decreases in intensity with chlorination, while the absorption at a higher temperature near 0°C (β₁ absorption) decreases in intensity with hydrogenation. The apparent activation energies of the β₁ and β₂ absorptions were calculated to be 16 kcal/mole and 10.7 kcal/mole, respectively. Besides, the β₂ absorption markedly decreases in intensity with addition of plasticizer, while the intensity of β₁ absorption is not much affected by increasing plasticizer content. From these results, the β₁ and β₂ processes are concluded to be the results of molecular motion in crystalline and amorphous region in PVC, respectively. For samples of reduced Cl content, another low-temperature absorption was located near ?120°C (γ absorption) and attributed to the presence of short sequences of ethylene units. It has also been observed that the temperature location of the high temperature absorption near 100°C (α absorption) shifts linearly to higher temperature with increasing chlorine content and to lower temperature with increasing hydrogen content.     

Rotating superfluid turbulence

Almost all studies of vortex states in helium II have been concerned with either ordered vortex arrays or disordered vortex tangles. This work numerically studies what happens in the presence of both rotation (which induces order) and thermal counterflow (which induces disorder). We find a new statistically steady state in which the vortex tangle is polarized along the rotational axis. Our results are used to interpret an instability that was discovered experimentally by Swanson et al. [Phys. Rev. Lett. 50, 190 (1983)]] and the vortex state beyond the instability that has been unexplained until now.     

Measurement of Masseteric Oxygenation by Near-Infrared Spectroscopy during Chewing

To non-invasively determine the condition of the masticatory muscles during chewing in real time, we used near-infrared spectroscopy and measured the masseter muscle. It increased in size, while the deoxy Hb in this muscle experienced the change in the short cycle by chewing. Periodic change of deoxy Hb was in agreement with the vertical movement of the lower jaw. It was found that the amount of increase in the deoxy Hb differs depending on the hardness of food being chewed. Moreover, by carrying out simultaneous measurement of the masseter muscles on both side of the jaw it was possible to determine the predominant muscles currently used in chewing.     

Generating asymptotically optimal broadcasting schedules to minimize average waiting time

The performance of a Video-on-Demand broadcasting scheme is commonly evaluated by the maximum waiting time encountered by the customer before viewing can start. This paper addresses the issue of minimizing the average waiting time. Recently, we proposed Harmonic Block Windows scheduling to specifically minimize the average waiting time for given bandwidth. Here, we present an efficient heuristic algorithm that generates asymptotically optimal Harmonic Block Windows schedules. Using simulation, we demonstrate that, as we increase the “block size”, the normalized average waiting time of these schedules approaches the theoretical minimum achievable by any “fixed start points” schedule.     

Fluorescence Response and Self-Assembly of a Tweezer-Type Synthetic Receptor Triggered by Complexation with Heme and Its Catabolites

There is increasing interest in the development and applications of synthetic receptors that recognize target biomolecules in aqueous media. We have developed a new tweezer-type synthetic receptor that gives a significant fluorescence response upon complexation with heme in aqueous solution at pH 7.4. The synthetic receptor consists of a tweezer-type heme recognition site and sulfo-Cy5 as a hydrophilic fluorophore. The receptor–heme complex exhibits a supramolecular amphiphilic character that facilitates the formation of self-assembled aggregates, and both the tweezer moiety and the sulfo-Cy5 moiety are important for this property. The synthetic receptor also exhibits significant fluorescence responses to biliverdin and bilirubin, but shows very weak fluorescence responses to flavin mononucleotide, folic acid, and nicotinamide adenine dinucleotide, which contain smaller π-scaffolds.