Synthesis of alkyl-branched main chain copolyimides and their effect on the pretilt angles of liquid crystal alignment

Three series of copolyimides containing long alkyl branches were synthesized using the twostep method via poly(amic acid) precursors and chemical imidization. Most of the copolyimides prepared are soluble in polar organic solvents. Good liquid crystal alignment was achieved by buffing the copolyimide films spin-coated onto indium tin oxide glass substrates. The measured liquid crystal pretilt angles range from 0.16° to 15.54°. The Titan simulation program was used to calculate the dipole of each dianhydride structure and correlate with the observed pretilt angles. Main chain copolyimides with a long alkyl side chain, small dipole, and linear, symmetric and rigid core structures are favourable for generating large pretilt angles.     

Delineation of G‐Quadruplex Alkylation Sites Mediated by 3,6‐Bis(1‐methyl‐4‐vinylpyridinium iodide)carbazole‐Aniline Mustard Conjugates

A new G‐quadruplex (G‐4)‐directing alkylating agent BMVC‐C3M was designed and synthesized to integrate 3,6‐bis(1‐methyl‐4‐vinylpyridinium iodide)carbazole (BMVC) with aniline mustard. Various telomeric G‐4 structures (hybrid‐2 type and antiparallel) and an oncogene promoter, c‐MYC (parallel), were constructed to react with BMVC‐C3M, yielding 35 % alkylation yield toward G‐4 DNA over other DNA categories (<6 %) and high specificity under competition conditions. Analysis of the intact alkylation adducts by electrospray ionization mass spectroscopy (ESI‐MS) revealed the stepwise DNA alkylation mechanism of aniline mustard for the first time. Furthermore, the monoalkylation sites and intrastrand cross‐linking sites were determined and found to be dependent on G‐4 topology based on the results of footprinting analysis in combination with mass spectroscopic techniques and in silico modeling. The results indicated that BMVC‐C3M preferentially alkylated at A15 (H26), G12 (H24), and G2 (c‐MYC), respectively, as monoalkylated adducts and formed A15–C3M–A21 (H26), G12–C3M–G4 (H24), and G2–C3M–G4/G17 (c‐MYC), respectively, as cross‐linked dialkylated adducts. Collectively, the stability and site‐selective cross‐linking capacity of BMVC‐C3M provides a credible tool for the structural and functional characterization of G‐4 DNAs in biological systems.     

Photo-alignment of liquid crystals using a crosslinked discotic film

A new photo-alignment layer using a crosslinked discotic compound was demonstrated. This discotic compound exhibits excellent solubility in common organic solvents, the possibility of low temperature processing and good thermal stability. A linearly polarized long wavelength ultraviolet (LPUV) light (λ = 350 nm) was used to initiate the crosslinking process and induce liquid crystal alignment on the discotic film surface. The induced LC directors were found parallel to the electric field direction of the LPUV light. A 1.2° pre-tilt angle was achieved using a single exposure at a 30° oblique angle.     

Preparation of Superconducting Na(x)(H2O)yCoO2 using NaMnO4 as the deintercalation and oxidation agent

We have used aqueous NaMnO4 solution as the deintercalation and oxidation agent to treat gamma-Na0.7CoO2 powders and to successfully obtain superconducting sodium cobalt oxyhydrates, Nax(H2O)yCoO2, with onset Tc approximately 4.6 K without using highly toxic Br2/CH3CN solution. Chemical analyses indicate that the sodium content x decreases with increasing concentration of NaMnO4 solution and depends slightly on the immersion time. Unlike using a high concentration of aqueous KMnO4 as the deintercalation and oxidation agent, all the hydrated products are the c approximately 19.6 A phase with bilayers of water molecules intercalated between the CoO2 layers and sodium layers because of the absence of K+ in the Na+ layers.     

Synthesis of graft copolymers by reaction of polymethyl methacrylate with heterochain polyesters

Summary Graft copolymers were obtained by the interaction of polymethyl methacrylate with heterochain polyesters, their properties were studied and a hypothesis was put forward on their structure.The thermomechanical curves and x-ray pictures were obtained in the laboratories directed by G. L. Slonimskii and A. I. Kitaigorodskii, to whom we express our sincere thanks.     

Alkaline Earth Metal Ion Induced Coil–Helix–Coil Transition of Lysine–Coumarin–Azacrown Hybrid Foldamers with OFF–OFF–ON Fluorescence Switching

A new metal‐ion‐responsive and fluorescent foldamer, OPLM₈ , composed of eight lysine–coumarin–azacrown units, has been designed and synthesized. The flexible OPLM₈ can be forced into a well‐defined helix structure only upon the addition of alkaline earth metal ions. The structural change is based on the crown ether moieties being positioned in the requisite arrangement along the peptide chain, that is, at i, i+4 spacing, such that the alkaline earth metal ions can mediate the formation of four sandwich complexes between them. Moreover, varying the chelator‐to‐metal‐ion ratio from 2:1 to 1:1 resulted in disassembly of the sandwich complexes leading to collapse of the helical structure to a random coil. These metal‐ion‐induced structural transitions could not only be monitored by the CD amplitude change but also easily probed by unique “OFF–OFF–ON” fluorescence intensity changes from 0.7‐fold to 14‐fold as the structure changed from the folded helix to a random coil. To further verify that the helix formation was indeed induced by metal‐ion complexation, two kinds of control octamers with only four metal‐ion chelators on the side chains were studied. One, which was capable of forming two sandwich complexes between the i and i+4 residues, displayed a negative Cotton couplet with the magnitude of its A value close to half that of OPLM₈ , and the second had four metal‐ion chelators positioned in the same turn, and hence was incapable of forming intramolecular metal complexes and showed different induced CD signals. Collectively, the photospectroscopic data and the results of the control studies suggest that alkaline earth metal ions can efficiently promote the flexible octamer OPLM₈ into a well‐organized helix by the formation of sandwich complexes between substituents at an i, i+4 spacing.     

A restricted sum formula among multiple zeta values

For positive integers α₁,α₂,…,αr with αr?2, the multiple zeta value or r-fold Euler sum is defined as