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71.
Dr. Christina Rest Dr. Divya Susan Philips Torsten Dünnebacke Dr. Papri Sutar Dr. Angel Sampedro Jörn Droste Dr. Vladimir Stepanenko Prof. Dr. Michael Ryan Hansen Dr. Rodrigo Q. Albuquerque Prof. Dr. Gustavo Fernández 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(44):10005-10013
Besides their widespread use in coordination chemistry, 2,2’-bipyridines are known for their ability to undergo cis–trans conformational changes in response to metal ions and acids, which has been primarily investigated at the molecular level. However, the exploitation of such conformational switching in self-assembly has remained unexplored. In this work, the use of 2,2’-bipyridines as acid-responsive conformational switches to tune supramolecular polymerization processes has been demonstrated. To achieve this goal, we have designed a bipyridine-based linear bolaamphiphile, 1 , that forms ordered supramolecular polymers in aqueous media through cooperative aromatic and hydrophobic interactions. Interestingly, addition of acid (TFA) induces the monoprotonation of the 2,2’-bipyridine moiety, leading to a switch in the molecular conformation from a linear (trans) to a V-shaped (cis) state. This increase in molecular distortion along with electrostatic repulsions of the positively charged bipyridine-H+ units attenuate the aggregation tendency and induce a transformation from long fibers to shorter thinner fibers. Our findings may contribute to opening up new directions in molecular switches and stimuli-responsive supramolecular materials. 相似文献
72.
Two noncentrosymmetric quaternary tin chalcoarsenates, Cs(2)SnAs(2)S(9) (1) and Cs(2)SnAs(2)Se(9) (2), were synthesized by the polychalcoarsenate flux method. Compound 1 crystallizes in the orthorhombic space group Pmc2(1) with a = 7.386(3) A, b = 14.614(5) A, c = 14.417(5) A, and Z = 4. Compound 2 crystallizes in the monoclinic space group P2(1) with a = 7.715(5) A, b = 17.56(1) A, c = 7.663(5) A, beta = 115.86(1) degrees, and Z = 2. Both structures contain the same tin-centered molecular cluster anions [Sn[AsQ(2)(Q(2))][AsQ(Q(2))(2)]](2)(-) (Q = S, Se) separated by Cs cations. The Sn(4+) ion is in a distorted octahedral environment coordinated by two different pyramidal-shaped tridentate ligands, [AsQ(2)(Q(2))](3)(-) and [AsQ(Q(2))(2)](3)(-). These compounds absorb visible light at energies above 1.98 and 1.45 eV for 1 and 2, respectively. Differential thermal analysis revealed that 1 melts at 350 degrees C and on cooling gives a glass. The glass recrystallizes at 268 degrees C upon subsequent heating. Compound 2 melts at 258 degrees C. 相似文献
73.
Mahamood K. Nadira Divya P. V. Vineethkumar V. Prakash V. 《Journal of Radioanalytical and Nuclear Chemistry》2020,324(3):949-961
Journal of Radioanalytical and Nuclear Chemistry - The activity concentration of natural radionucides such as 40K, 226Ra and 232Th and radon surface and mass exhalation rates of the soil were... 相似文献
74.
J. T. Kunjappu A. J. Singh R. M. Iyer 《Journal of photochemistry and photobiology. A, Chemistry》1987,41(1)
Improved lasing efficiency and long-term photostability of laser dye 7-amino-4-methylcoumarin (C120) has been demonstrated in zone-refined material. Among the impurities found segregated, a high molecular weight compound, 7-acetylamino-4-methylcoumarin, was identified by mass spectrometry. Melting and spectral characteristics of the zone-melted fractions showed the migration of impurities to be in the direction of the zone movement. 相似文献
75.
Balaji V. S. Iyer Sachin Shanbhag Vinay A. Juvekar Ashish K. Lele 《Journal of Polymer Science.Polymer Physics》2008,46(21):2370-2379
In a topologically constraining environment the size of a flexible nonconcatenated ring polymer (macrocycles) and its dynamics are known to differ from that of linear polymers. Hence, the diffusion coefficient of ring polymers can be expected to be different from linear chains. We present here scaling arguments for the concentration and molecular weight dependence of self‐diffusion coefficient of ring polymers in semidilute solutions, and show that contrary to expectations these scaling relations are identical to what is known for linear polymers. At higher concentrations excluded volume interactions arising from possibilities of segmental overlap can become effective for large ring polymers. In this regime the diffusion coefficient of large ring polymers shows a relatively weaker dependence on concentration and molecular weight. ©2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2370–2379, 2008 相似文献
76.
M. Dubois D. Carrire R. Iyer M.A. Arunagirinathan J. Bellare J.-M. Verbavatz Th. Zemb 《Colloids and surfaces. A, Physicochemical and engineering aspects》2008,319(1-3):90-97
We show that nanodiscs stabilized with polymers order and pile up on a surface upon drying. The resulting surface films with an average thickness of one micron are made of collapsed cohesive layers with smectic long-range order. This occurs with and without plastifying stabilizing polymer and produces crevasses. The stacked discs undergo a two-to-three-dimensional crystallization while bottom layers close to the surface fuse and produce infinite bilayers. Small angle X-ray scattering experiments demonstrate that excess polymer is segregated from the crystalline stack. Water adsorption isotherms show that reversible swelling of the excess polymer does not destroy the compact stack of partially fused nanodiscs collapsed parallel to the surface. In the absence of chemical binding, the stacks of layered nanodiscs can be removed by simple washing with pure water. AFM, TEM and SEM experiments demonstrate that presence of crevasses is quenched by the presence of a plastifying polymer. 相似文献
77.
S. Kapoor C. Gopinathan R. M. Iyer 《Journal of Radioanalytical and Nuclear Chemistry》1988,125(1):91-96
Mixtures of methanol and isopropanol in a ratio (v/v) varying from 91 to 19 have been gamma-irradiated at 77 K and relative yields of trapped electrons have been measured. The reactivity of the trapped electrons towards acetone and uranyl nitrate has been studied at various methanol isopropanol ratios. On the basis of the results, an attempt has been made to assess the relative importance of the reaction of the electron with the solute prior to trapping with respect to the tunnelling reaction of the trapped electron with the solute. 相似文献
78.
We analyze the accretion of charged matter onto a rotating black hole immersed in an aligned dipolar magnetic field. We specialize
to motion in the equatorial plane and calculate the ‘Keplerian’ angular momentum distribution, the marginally stable and marginally
bound orbits, and the efficiency of mass-to-energy conversion as functions of the angular momentum of the black hole and of
the product of the dipole moment and the charge of the infalling matter. Although the detailed results are quite different
from those previously obtained in the case of an uniform magnetic field, the astrophysically relevant results are very similar;
when hydrodynamical accretion is considered, these effects of the magnetic field are always very small. But for test particles
the efficiency can be significantly increased for limited ranges of the parameters. 相似文献
79.
80.
Following the approach of optical reference geometry we derive the expression for the total force in the radial direction acting on a charged particle in magnetic fields superimposed on the static Schwarzschild background and show the possible existence of bound orbits for particles in the field of ultra compact objects at distancesr?3m wherein the Lorentz force counterbalances both the gravitational and centrifugal forces. 相似文献