Quantum dot on a rope

The conjugation of nanoparticles (NPs) typically yields supramolecular materials which are fairly rigid, and the electronic coupling between the NP and other structural units of these compounds is fixed by covalent bonds. Here, we report on a novel bichromophor system constructed from a quantum dot tethered to a semiconducting polymer, which demonstrates the possibility of the dynamic interunit coupling in the NP supramolecules. The NP bichromophoric system was made on the basis of the layer-by-layer assembled (LBL) films of an anionic polyelectrolyte with poly(p-phenylene ethynylene) backbone, aPPE, and poly(allylamine hydrochloride) PAH polycation. To conjugate CdTe NPs to the (aPPE/PAH)(m) LBL film, we took advantage of the reactive groups of NP stabilizer, that is, -COOH, and the aminogroups on PAH. Tethering of CdTe was accomplished by using poly(ethyleneglycole), PEG, chains with two reactive terminals such as t-BOC-NH-PEG-COO-NHS. The evidence for successful conjugation of NPs to the LBL films can be seen both in AFM images and in optical data. The latter also indicate that the light quanta emitted by the NPs originate from the light absorption of the polymer film, which proves the presence of the aPPE-->NP energy-transfer process. The average separation distance between the NPs tethered to the LBL films can be changed by altering the dielectric properties of the solvent affecting PEG tether coiling (water/alcohol mixture). The reduced emission intensity of aPPE was found to follow the extension of the PEG tether. The quenching of aPPE is reversible when the original composition of the solvent mixture is restored. Thus, CdTe-PEG-aPPE is an example of an organized NP system with tunable optical coupling. Variable electronic coupling offers a convenient structural platform for new nanotechnological devices for which spatial control translates into a higher level of sophistication. PEG molecules afford a wide variety of polymer chain configurations with different reactive terminals, which makes possible the preparation of diverse NP superstructures.     

Magneto-optical rotation in molecules

A quantum-mechanical theory for the magneto-optica rotation in diamagnetic polyatomic molecules is formulated using the timedependent second-order perturbation theory. The treatment is not restricted to molecules having non-degenerate excited wave functions. The contributions of the induced magnetic moment and the perturbed Boltzmann factor are included. The results are compared with some of the former theories.

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Zusammenfassung Es wird eine quantenmechanische Theorie für die magneto-optische Drehung in diamagnetischen mehratomigen Molekülen unter Anwendung der zeitabhängigen Störungstheorie zweiter Ordnung formuliert. Die Behandlung ist nicht auf Moleküle mit nicht-entarteten angeregten Zuständen beschränkt. Die Beiträge des induzierten magnetischen Moments und des gestörten Boltzmann-Faktors sind eingeschlossen. Die Ergebnisse werden mit denen einiger früherer Theorien verglichen.

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Résumé La théorie des perturbations dépendantes du temps, limitée au second ordre, est utilisée pour formuler une théorie quantique de la polarisation rotatoire magnétique dans les molécules polyatomiques diamagnétiques. L'étude est étendue aux molécules ayant des fonctions d'onde excitées dégénérées. On tient compte de l'effet du moment magnétique induit et du facteur de Boltzmann perturbé. Les résultats sont comparés à ceux de certaines théories antérieures.

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The work reported in this paper has been supported in part by the King Gustaf VI Adolf's 70-Years Fund for Swedish Culture, the Knut and Alice Wallenberg's Foundation, and in part by the U.S. Public Health Service Research Grant under Contract CA 06850-01 with Uppsala University.

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On leave from: Department of Materials Science, The University of Electro-Communications, Chofu-shi, Tokyo, Japan.

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I should like to thank Professor P. O. Löwdin for valuable discussions. This paper is dedicated to Professor Masao Kotani on his sexagenary birthday.     

铵根离子在水溶液中的跳跃转动机理

铵根离子的动力学行为与生命体内的生物和化学过程密切相关.依据流体力学理论,由于铵根离子与水分子之间存在多个强氢键,其转动应较慢,但实验结果并非如此,其转动的微观机理尚不清晰.本文分子动力学模拟研究表明,水溶液中铵根离子主要以快速、大角度的跳跃方式进行转动,像水分子一样遵从扩展分子跳跃转动模型.通过微观转动模式的分解和两种转动弛豫时间的比较发现,相对其氢键骨架的扩散转动,跳跃转动对其转动速率贡献更大,并随浓度增大不断强化.与水分子氢键交换方式相比,铵根离子更倾向于在非氢键相连的水分子间发生交换.     

A Big Jump in Nacre-inspired Strong,Tough Composites

To achieve structural order and strength-toughness balance similar to natural composites like nacre has been highly challenging, especially in a practically viable manner. Liu et al. developed a continuous preparation method to construct such high performance composites through a superspreading strategy at the oil/water/hydrogel interface. Exploiting the strong shear force at the interface, nanoparticles, such as nanosheets and nanotubes oriented and stacked together rapidly(as short as 358 ms) and the composites revealed the tensile strength and fracture toughness far higher those of natural nacre(9.0 and 20.4 times higher). This work has been published in Nature, 2020.     

Internal rotation in mononitro-n-alkyl radicals

Internal rotation in the C·H₂(CH₂) _n NO₂ (n ≤ 7) type radicals has been studied. 44 potential functions of the internal rotation, V(φ), have been calculated taking advantage of the B3LYP/6-311++(3df,3pd) and MP2/6-311++(3df,3pd) methods. The trends observed in the series of parameters characterizing the internal rotation have been explained in view of the electron clouds conjugation, the inductive effect of the end groups, the gauche effect, and the rotation tops interaction. The coefficients of V(φ) have been shown to depend predominantly on the nearest surrounding of the rotation axis. Based on this, the generalized functions, V _av(φ), have been developed, their coefficients being dependent exclusively on the rotating bond position. Such functions are convenient for molecular modeling applications.     

Internal rotation in nitric acid

The torsional region of the gas phase infrared spectrum of nitric acid and nitric acid-d₁ has been reassigned, showing that besides a ground state torsional series also torsional series due to excited deformational states are present. Barriers to internal rotation have been calculated.     

Phenyl group rotation in polystyrene and the nature of twofold anisotropic internal rotation

A review of the experimental evidence for phenyl group rotation in various polystyrenes and improvements in the interpretation of spin relaxation data for dilute solutions of randomly coiled polymers led to a new calculation of the correlation time for phenyl group rotation from nuclear magnetic resonance (NMR) data. Both ¹³C and ¹⁹F NMR data were reconsidered by using a model which includes motional modulation of the dipole–dipole interaction by overall rotatory diffusion, backbone rearrangements, and internal anisotropic rotation. The choice of a twofold potential to characterize local resistance to internal phenyl group rotation strongly influences the estimate of the rate of phenyl group rotation. The magnetic resonance data are found to be consistent with a correlation time for phenyl group rotation which is one to six times longer than the average correlation time for backbone rearrangement.     

Hindered rotation and exchange in trimethylsilylanilides

A series of trimethylsilylanilides were prepared and characterized as amide—imidate mixtures. Low temperature NMR spectra reveal both hindered rotation and exchange processes for the formanilides and benzanilides and exchange for the acetanilides. Isomer ratios and free energies of activation are reported and used to postulate a mechanism for the exchange process.     

Exponential probe rotation in glass-forming liquids

Using time resolved optical depolarization, we have studied the rotational behavior of molecular probes in supercooled liquids near the glass transition temperature T(g). Simultaneously, the dynamics of the liquid immediately surrounding these rigid probes is measured by triplet state solvation experiments. This direct comparison of solute and solvent dynamics is particularly suited for assessing the origin of exponential orientational correlation functions of probe molecules embedded in liquids which exhibit highly nonexponential structural relaxation. Polarization angle dependent Stokes shift correlation functions demonstrate that probe rotation time and solvent response time are locally correlated quantities in the case of smaller probe molecules. Varying the size of both guest and host molecules shows that the size ratio determines the rotational behavior of the probes. The results are indicative of time averaging being at the origin of exponential rotation of probes whose rotational time constant is slower than solvent relaxation by a factor of 20 or more.     

Restricted rotation in substituted propane epoxides

Dynamic nmr spectroscopy is used to show that 1,1-diaryl-2-methyl-1,2-epoxypropanes display restricted rotation.     

Anisotropic rotation of spin-probes in polymers

The observed change in the ESR spectra of a nitroxide spin-probe as it passes through the transition >T_g found in amorphous polymers is explained in terms of a change in the anisotropic rotation of the probe. The degree of anisotropy factor ? is calculated for various polymers and probes, and shows the most marked change with Tempol Benzoate (I) in atactic polypropylene and plasticized polystyrene. Results for a steroid nitroxide probe are also presented.     

Different buckling regimes in direct electrospinning: A comparative approach to rope buckling

Understanding the dynamics of direct electrospinning is the key to control fiber morphologies that are critical for the development of new electrospinning methods and novel materials. Here, we propose the theory for direct electrospinning based on theories for (liquid) “rope coiling” and experimentally test it. For the experiments, the buckling of microscale liquid ropes formed from polymer solutions is studied systematically using three different electrospinning setups and for different polymer concentrations. We show that different buckling regimes exist, whose dynamics are governed by an interplay of electrical, inertial, and viscous forces, and that three different buckling regimes emerge depending on the dominant forces. For low polymer concentrations, we observe an inertial regime similar to that observed for viscous liquid ropes at high velocities. By increasing the polymer concentration and consequently decreasing the rope velocity, we enter an inertial‐electrical regime for which discontinuities occur in the buckling frequency as a function of applied voltage. These observations can be accounted for quantitatively by replacing the gravitational forces in viscous rope coiling theory with the electrical forces of our electrospinning experiment. Finally, for the highest polymer concentration, we observe a purely electrical regime for a solidified rope; this regime is well described by “elastic” rope coiling theory. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 451–456     

Specific rotation of anabasine

Conclusions The iodomethylation of N-benzoylanabasine gave two isomeric products, one of which is dl-N-benzoyl-anabasine methiodide, while the other is the methiodide that is formed from the purel-N-benzoylanabasine.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1325–1326, June, 1973.