The Structurally Regular trans-1,4-Poly(chloroprene)

Radiation polymerization of large crystals of chloroprene formed within the temperature range -130 to -180°C has yielded the stereoregular trans-1,4-poly(2-chloro-1,3-butadiene). The monomer was found to have a glass transition temperature of ca. -180°C. Polymerization of monomer rapidly cooled to below -180°C was difficult and gave only structurally irregular polymer in low yield.     

Synthesis and tautomerism of spiro-pyrazolines

An experimental study on the synthesis, tautomerism, and acid promoted structural changes of spiro-pyrazolines is described. The target was achieved through a [3+2]-dipolar cycloaddition of an alkene with nitrile imines generated in situ and was isolated in high yield. The synthesized cycloadduct displayed a tendency to exhibit an imine–enamine type of tautomerism as evidenced by X-ray crystal and NMR studies. Furthermore, addition of an acid resulted in the transformation of an imine tautomer to an enamine. The current report constitutes a first formal observation of this kind of tautomerism observed in spiro-indoline pyrazolines.     

The structure and helicity of perfluorooctanonitrile, CF3–(CF2)6–CN

New molecular structural data is presented for a cyanide terminated oligomer of polytetrafluoroethene. The target molecule, CF₃–(CF₂)₆–CN, has been seeded within a pulsed supersonic expansion of argon. The result of this action is to cool the species to rotational temperatures below 4 K. Within this state, the pure rotational spectrum of the oligomer has been recorded using two types of Fourier transform microwave spectroscopy. A total of 111 transitions have been identified involving rotational J levels between 6 and 40. Only a- and b-type transitions were observed. The spectrum has been analyzed using a Hamiltonian containing all three rotational constants and one centrifugal distortion constant, D_J. The experimental spectroscopic constants have been used to develop an effective molecular structure by scaling the quantum chemical calculated structure. The data shows that the seven carbon perfluorinated chain for the isolated oligomer twists ≈104°. This compares well to the C₇F₁₃-twist of ≈97° anticipated from the X-ray structure of phase II polytetrafluoroethene.     

BKP方程族的Pfaffian解

本文从约化的角度考虑BKP方程族的Pfaffian形式的解.证明了通过施加适当的微分约束,KP方程族的格拉姆行列式的解很自然的约化为BKP方程族的解.     

Ab initio treatment of the chemical reaction precursor complex Br(2P)-HCN. 2. Bound-state calculations and infrared spectra

Rovibronic energy levels and properties of the Br(2P)-HCN complex were obtained from three-dimensional calculations, with HCN kept linear and the CN bond frozen. All diabatic states that correlate to the 2P3/2 and 2P1/2 states of the Br atom were included and spin-orbit coupling was taken into account. The 3 x 3 matrix of diabatic potential surfaces was taken from the preceding paper (paper 1). In agreement with experiment, we found two linear isomers, Br-NCH and Br-HCN. The calculated binding energies are very similar: D0 = 352.4 cm(-1) and D0 = 349.1 cm(-1), respectively. We established, also in agreement with experiment, that the ground electronic state of Br-NCH has |Omega| = (1/2) and that Br-HCN has a ground state with |Omega| = (3/2), where the quantum number, Omega, is the projection of the total angular momentum, J, of the complex on the intermolecular axis R. This picture can be understood as being caused by the electrostatic interaction between the quadrupole of the Br(2P) atom and the dipole of HCN, combined with the very strong spin-orbit coupling in Br. We predicted the frequencies of the van der Waals modes of both isomers and found a direct Renner-Teller splitting of the bend mode in Br-HCN and a smaller, indirect, splitting in Br-NCH. The red shift of the CH stretch frequency in the complex, relative to free HCN, was calculated to be 1.98 cm(-1) for Br-NCH and 23.11 cm(-1) for Br-HCN, in good agreement with the values measured in helium nanodroplets. Finally, with the use of the same potential surfaces, we modeled the Cl(2P)-HCN complex and found that the experimentally observed linear Cl-NCH isomer is considerably more stable than the (not observed) Cl-HCN isomer. This was explained mainly as an effect of the substantially smaller spin-orbit coupling in Cl, relative to Br.     

Ruthenium‐Grafted Vinylhelicenes: Chiroptical Properties and Redox Switching

The properties of mono‐ and bis‐Ru–vinyl[6]helicene complexes ( 2 a and 2 b , respectively), recently synthesized by using molecular engineering of helicenes based on the grafting of lateral organometallic substituents on the π‐helical backbone through a vinyl bridge, are presented. These helicene derivatives are thoroughly characterized, with special attention given to their chiroptical properties and redox switching activity. The UV/Vis and electronic circular dichroism (ECD) spectra of P and M enantiopure species, both in the neutral and oxidized states ([ 2 a ] ^{. +}, [ 2 b ] ^{. +}, and [ 2 b ]²⁺), are analyzed with the aid of quantum‐chemical calculations. The extended π‐conjugation facilitated by the vinyl moiety, clearly visible in the electronic structures of 2 a , b , introduces new active bands in the ECD spectra that consequently lead to a significant increase in optical rotation of Ru–vinylhelicenes compared with the organic precursors. The vibrational circular dichroism (VCD) spectra were measured and calculated for both the organic and organometallic species and constitute the first examples of VCD for metal‐based helicene derivatives. Finally, the redox‐triggered chiroptical switching activity of 2 a , b is examined in detail by using ECD spectroscopy. The modifications of the ECD spectra in the UV/Vis and NIR region are well reproduced and rationalized by calculations.     

DNA Damage Checkpoint Responses in the S Phase of Synchronized Diploid Human Fibroblasts

We investigated the hypothesis that the strength of the activation of the intra‐S DNA damage checkpoint varies within the S phase. Synchronized diploid human fibroblasts were exposed to either 0 or 2.5 J m^?2 UVC in early, mid‐ and late‐S phase. The endpoints measured were the following: (1) radio‐resistant DNA synthesis (RDS), (2) induction of Chk1 phosphorylation, (3) initiation of new replicons and (4) length of replication tracks synthesized after irradiation. RDS analysis showed that global DNA synthesis was inhibited by approximately the same extent (30 ± 12%), regardless of when during S phase the fibroblasts were exposed to UVC. Western blot analysis revealed that the UVC‐induced phosphorylation of checkpoint kinase 1 (Chk1) on serine 345 was high in early and mid S but 10‐fold lower in late S. DNA fiber immunostaining studies indicated that the replication fork displacement rate decreased in irradiated cells at the three time points examined; however, replicon initiation was inhibited strongly in early and mid S, but this response was attenuated in late S. These results suggest that the intra‐S checkpoint activated by UVC‐induced DNA damage is not as robust toward the end of S phase in its inhibition of the latest firing origins in human fibroblasts.