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排序方式: 共有127条查询结果,搜索用时 31 毫秒
101.
102.
Liu Yangxue Wu Guanzhao Yang Zhen Rouh Hossein Katakam Nandakumar Ahmed Sultan Unruh Daniel Cui Zhonghua Lischka Hans Li Guigen 《中国科学:化学(英文版)》2020,63(5):692-698
New synthesis of multi-layer 3 D chiral molecules has been developed under novel conditions to give better outcomes. The aggregation-induced emission(AIE), UV irradiation/excitation, charge transfer(CT) and local excited(LE) ππ* transitions have been investigated on a representative individual enantiomer of pseudo C_2 asymmetry which was made possibly by differentiating moieties on phosphorous on N-phosphonyl ring of chiral sandwich framework. Meanwhile, a new tandem C–N/C–C coupling reaction was unexpectedly rendered providing a novel access to special benzo[a]carbazoles. 相似文献
103.
Lauren A. Brown Francis S. Wekesa Daniel K. Unruh Michael Findlater Brian K. Long 《Journal of polymer science. Part A, Polymer chemistry》2017,55(17):2824-2830
The α‐diimine‐ligated Fe‐complex, BIAN‐Fe(C6H6) , was synthesized and evaluated for the polymerization of l ‐lactide. Characterization of BIAN‐Fe(C6H6) reveals that it is redox non‐innocent and suggests that it is an Fe(I) species bearing a radical‐anionic ligand. We will demonstrate that BIAN‐Fe(C6H6) is active for the ring‐opening polymerization of l ‐lactide, and that polymer is produced with, or without, the use of an added external initiator. Interestingly, very high molecular weight polymers are produced in the absence of external initiator whereas polymer molecular weights that agree with theoretical calculations are produced in the presence of external initiator. To the best of our knowledge, BIAN‐Fe(C6H6) is the first Fe‐based α‐diimine catalyst reported to be active for the polymerization of l ‐lactide. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2824–2830 相似文献
104.
Trideep Rajale Shikha SharmaDaniel A. Stroud Daniel K. Unruh Emily MiaouKimberly Lai David M. Birney 《Tetrahedron letters》2014
An efficient Pd-catalyzed Suzuki cross-coupling reaction of sterically crowded 4-chlorocoumarin derivatives with air- and moisture-stable potassium organotrifluoroborates is developed. This methodology has been used to generate a series of novel alkyl, aryl, and vinyl substituted coumarin derivatives in good to excellent yields. The twisted conformation of the vinyl groups in the X-ray crystal structures of (2-oxo-4-vinyl-2H-chromen-3-yl)methyl acetate (2) and (2-oxo-4-vinyl-2H-chromen-3-yl)methyl 2,2,2-trichloroacetimidate (3), along with the atropisomerism of 3-(hydroxymethyl)-4-(2-methoxyphenyl)-2H-chromen-2-one (1d), are evidence of the steric crowding in these adducts. 相似文献
105.
Mechanochemical Rhodium(III)‐ and Gold(I)‐Catalyzed C−H Bond Alkynylations of Indoles under Solventless Conditions in Mixer Mills
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Gary N. Hermann Marvin T. Unruh Se‐Hyeong Jung Maik Krings Prof. Dr. Carsten Bolm 《Angewandte Chemie (International ed. in English)》2018,57(33):10723-10727
Mechanochemical activations in RhIII‐ and AuI‐catalyzed C?H alkynylations lead selectively to C2‐ and C3‐alkynylated indoles. The processes show excellent functional group tolerance, do not require additional heating and proceed under solventless conditions. Compared to solvent‐based standard protocols, the reaction times are shorter and the catalyst quantities lower resulting in high product yields under ambient atmosphere in mixer mills. 相似文献
106.
Xiaodan Ding Dr. Daniel K. Unruh Liulei Ma Evan J. van Aalst Dr. Eric W. Reinheimer Prof. Dr. Benjamin J. Wylie Prof. Dr. Kristin M. Hutchins 《Angewandte Chemie (International ed. in English)》2023,62(33):e202306198
Achieving substantial anisotropic thermal expansion (TE) in solid-state materials is challenging as most materials undergo volumetric expansion upon heating. Here, we describe colossal, anisotropic TE in crystals of an organic compound functionalized with two azo groups. Interestingly, the material exhibits distinct and switchable TE behaviors within different temperature regions. At high temperature, two-dimensional, area zero TE and colossal, positive linear TE (α=211 MK−1) are attained due to dynamic motion, while at low temperature, moderate positive TE occurs in all directions. Investigation of the solid-state motion showed the change in enthalpy and entropy are quite different in the two temperature regions and solid-state NMR experiments support motion in the solid. Cycling experiments demonstrate that the solid-state motions and TE behaviors are completely reversible. These results reveal strategies for designing significant anisotropic and switchable behaviors in solid-state materials. 相似文献
107.
It has long been recognized that the fluorescence lifetimes of amino acid residues such as tyrosine and tryptophan depend on the rotameric configuration of the aromatic side chain, but estimates of the rate of interchange of rotameric states have varied widely. We report measurements of the rotameric populations and interchange rates for tyrosine in N-acetyltyrosinamide (NATyrA), the tripeptide Tyr-Gly-Gly (YGG), and the pentapeptide Leu-enkephalin (YGGFL). The fluorescence lifetimes were analyzed to determine the rotameric interchange rates in the context of a model incorporating exchange among three rotameric states. Maximum entropy method analysis verified the presence of three fluorescence decay components for YGGFL and two for YGG and NATyrA. Rotameric exchange between the gauche(-) and trans states occurred on the nanosecond time scale, whereas exchange with the gauche(+) state occurred on a longer time scale. Good agreement was obtained with rotameric populations and exchange rates from molecular dynamics simulations. Quenching by iodide was used to vary the intrinsic fluorescence lifetimes, providing additional constraints on the determined interchange rates. The temperature dependence was measured to determine barriers to exchange of the two most populated rotamers of 3, 5, and 7 kcal/mol for NATyrA, YGG, and YGGFL, respectively. 相似文献
108.
We present measurements of the vibrational spectrum of a binary niobium-phosphate glass in the THz frequency range using inelastic neutron and Raman scattering. The spectra of these glasses show a low-frequency enhancement of the vibrational density of states (“boson peak”). Using a recently developed theory of vibrational excitations in disordered solids we are able to reconcile the measured neutron and Raman spectra using fluctuating elastic and Pockels constants as a model concept. As the spontaneous Raman susceptibility is a key parameter for Raman amplification our results suggest a significant gain profile for application of niobium-phosphate glasses in Raman amplifiers. 相似文献
109.
110.
Chester M. Mikulski Joseph Unruh Louis L. Pytlewski Nicholas M. Karayannis 《Transition Metal Chemistry》1979,4(2):98-103
Summary Methyl methylphenylphosphinate (L) complexes with 3d metal perchlorates were synthesized by interaction of L and metal salt solutions in triethyl orthoformate (61 molar ratio) and characterized by means of spectral, magnetic and conductance studies. In most cases (Mn+ = Cr3+, Mn2+, Co2+, Ni2+, Cu2+ or Zn2+), complexes involving 41 L: metal ratios, similar to those obtained with bulky triorganophosphine oxides and neutral phosphonate or phosphate esters, were formed. These complexes contain exclusively terminal L groups and were characterized as monomeric of the types [CrL4(OClO3)2](ClO4), [ML4(OH2)](ClO4)2 (M = Mn or Ni), [ML4(OClO3)](ClO4) (M = Co or Zn) and [CuL4](ClO4)2. In contrast, Fe2+ and Fe3+ perchlorates formed, rather unexpectedly, complexes involving 21 L: Fe ratios. These compounds appear to be binuclear and of the type [(O3ClO)(H2O)2LFeL2FeL(OH2)2(OClO3)](ClO4)n (n=2 for Fe2+; n=4 for Fe3+), containing both terminal and bridging coordinated L ligands. The bridging L groups in the iron complexes seem to be exclusively coordinated through the P=O oxygen, which acts as a bridging group between two adjacent Fe2+ or Fe3+ions, rather than functioning as bidentate bridging O,O-ligands, with both the P=O and methoxy oxygens involved in coordination. Spectral evidence suggests that L is a weaker ligand than triorganophosphine oxides and a stronger ligand than neutral phosphonate and phosphate esters, as anticipated. 相似文献