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排序方式： 共有227条查询结果，搜索用时 15 毫秒
71.
Yuwei Hu Chun‐Hua Lu Weiwei Guo Miguel Angel Aleman‐Garcia Jiangtao Ren Itamar Willner 《Advanced functional materials》2015,25(44):6867-6874
Shape memory acrylamide/DNA hydrogels include two different crosslinkers as stabilizing elements. The triggered dissociation of one of the crosslinking elements transforms the shaped hydrogel into an arbitrarily shaped (or shapeless) quasi‐liquid state. The remaining crosslinking element, present in the quasi‐liquid, provides an internal memory that restores the original shaped hydrogel upon the stimulus‐triggered regeneration of the second crosslinking element. Two pH‐sensitive shape memory hydrogels, forming Hoogsten‐type triplex DNA structures, are described. In one system, the shaped hydrogel is stabilized at pH = 7.0 by two different duplex crosslinkers, and the transition of the hydrogel into the shapeless quasi‐liquid proceeds at pH = 5.0 by separating one of the crosslinking units into a protonated cytosine–guanine–cytosine (C–G·C+ ) triplex. The second shaped hydrogel is stabilized at pH = 7.0, by cooperative duplex and thymine–adenine–thymine triplex (T–A·T) bridges. At pH = 10.0, the triplex units separate, leading to the dissociation of the hydrogel into the quasi‐liquid state. The cyclic, pH‐stimulated transitions of the two systems between shaped hydrogels and shapeless states are demonstrated. Integrating the two hydrogels into a shaped “two‐arrowhead” hybrid structure allows the pH‐stimulated cyclic transitions of addressable domains of the hybrid between shaped and quasi‐liquid states. 相似文献
72.
Metal ions (Ag+, Cu2+, Hg2+) are incorporated into an electropolymerized, poly(N‐isopropyl acrylamide), pNIPAM, thermosensitive polymer associated with an electrode using the “breathing‐in” method. The ion‐functionalized pNIPAM matrices reveal ion‐dependent gel‐to‐solid phase‐transition temperatures (28 ± 1 °C, 25 ± 1 °C, 40 ± 1 °C for the Ag+, Cu2+, and Hg2+‐modified pNIPAM, respectively). Furthermore, the ion‐functionalized polymers exhibit quasi‐reversible redox properties, and the ions are reduced to the respective Ag0, Cu0, and Hg0 nanocluster‐modified polymers. The metal‐nanocluster‐functionalized pNIPAM matrices enhance the electron transfer (they exhibit lower electron‐transfer resistances) in the compacted states. The electron‐transfer resistances of the metal‐nanocluster‐modified pNIPAM can be cycled between low and high values by temperature‐induced switching of the polymer between its contracted solid and expanded gel states, respectively. The enhanced electron‐transfer properties of the metal nanocluster‐functionalized polymer are attributed to the contacting of the metal nanoclusters in the contracted state of the polymers. This temperature‐switchable electron transfer across a Ag0‐modified pNIPAM was implemented to design a thermo‐switchable electrocatalytic process (the temperature‐switchable electrocatalyzed reduction of H2O2 by Ag0‐pNIPAM). 相似文献
73.
Huseyin Bekir Yildiz Ran Tel‐Vered Itamar Willner 《Advanced functional materials》2008,18(21):3497-3505
Different configurations of CdS nanoparticles (NPs) are linked to Au electrodes by electropolymerization of thioaniline‐functionalized CdS NPs onto thioaniline‐functionalized Au‐electrodes. In one configuration, thioaniline‐functionalized CdS NPs are electropolymerized in the presence of thioanline‐modified Au NPs to yield an oligoaniline‐crosslinked CdS/Au NPs array. The NP‐functionalized electrode generates a photocurrent with a quantum yield that corresponds to ca. 9%. The photocurrent intensities are controlled by the potential applied on the electrode, and the redox‐state of the oligoaniline bridge. In the oxidized quinoide state of the oligoaniline units, the bridges act as electron acceptors that trap the conduction‐band electrons that are transported to the electrode and lead to high quantum yield photocurrents. The reduced π‐donor oligoaniline bridges act as π‐donor sites that associate N,N′‐dimethyl‐4,4′‐bipyridinium, MV2+, by donor/acceptor interactions, Ka = 5270 M?1. The associated MV2+ acts as an effective trap of the conduction‐band electrons, and in the presence of triethanolamine (TEOA) as an electron donor, high photocurrent values are measured (ca. 12% quantum yield). The electropolymerization of thioaniline‐functionalized Au NPs and thioaniline‐modified CdS NPs in the presence of MV2+ yields a MV2+‐imprinted NP array. The imprinted array exhibits enhanced affinities toward the association of MV2+ to the oligoaniline π‐donor sites, Ka = 2.29 × 104 M?1. This results in the effective trapping of the conduction‐band electrons and an enhanced quantum yield of the photocurrent, ca. 34%. The sacrificial electron donor, TEOA, was substituted with the reversible donor I3?. A solar cell consisting of the imprinted CdS/Au NPs array, with MV2+ and I3?, was constructed. The cell generated a photocurrent with a quantum yield of 4.7%. 相似文献
74.
F. Shi Z. Liu G.‐L. Wu M. Zhang H. Chen Z. Q. Wang X. Zhang I. Willner 《Advanced functional materials》2007,17(11):1821-1827
In this Full Paper, we develop a novel approach for the generation of stable molecularly imprinted sites in polymeric films by combining the layer‐by‐layer (LbL) technique and photochemical crosslinking of the layered structure. After photo‐crosslinking, the imprinted films show high reproducibility and rapid loading and unloading of imprinted sites by the template molecules. Moreover, the competitive adsorption of template molecules and redox labels into the imprinted film using electrochemical methods indicates that the imprinted film has higher affinity for template molecules. We believe this approach may have some advantages over traditional ways of preparing imprinted sites in polymer matrices and it may open a new avenue for the functionalization of LbL films. 相似文献
75.
76.
A phase-space method for finding the accepting modes in a non-vertical radiationless vibronic transition and for recognizing the final state with the largest Franck—Condon factor is applied to a harmonic model of the S1 → S0 relaxation in trans-octatetraene. Input required for the analysis includes the energy gap between S1 and S0, normal mode frequencies, reduced masses, and eigenvectors (including the Duschinsky rotation matrix), and the molecule equilibrium configurations (bond lengths and angles) in S1 and S0. Some of these data are taken from published experimental results and some are calculated in this work. The energy gap of 0.132 au is much larger than the energy of a vertical transition, which is only 0.047 au. The phase-space method gives a closed-form analytic solution for how to divide the excess energy between the accepting modes. The final distribution includes a large excitation of the two CH2 end groups, where the motion of the two hydrogen atoms within each quasilocal CH2 group is antisymmetric; a symmetric stretch of the two central C-H bonds of the molecule; and small totally symmetric bending of the whole molecule. Comparison of Franck-Condon factors (exact within the harmonic model) of the final state obtained by the phase-space analysis and of other similar isoenergetic states shows that the phase-space method indeed chooses the most probable final energy distribution. Possible modifications of these results due to anharmonic effects are discussed. 相似文献
77.
Wei‐Ching Liao Yang Sung Sohn Marianna Riutin Alessandro Cecconello Wolfgang J. Parak Rachel Nechushtai Itamar Willner 《Advanced functional materials》2016,26(24):4262-4273
The synthesis of microcapsules consisting of DNA shells crosslinked by anti‐VEGF (vascular epithelial growth factor) or anti‐ATP (adenosine triphosphate) aptamers and loaded with tetramethylrhodamine‐modified dextran, TMR‐D, and Texas Red‐modified dextran, TR‐D, respectively, as fluorescence labels acting as models for drug loads, is described. The aptamer‐functionalized microcapsules act as stimuli‐responsive carriers for the triggered release of the fluorescent labels in the presence of the overexpressed cancer cell biomarkers VEGF or ATP. The VEGF‐ and ATP‐responsive microcapsules are, also, loaded with the anticancer drug doxorubicin (DOX), in the form of DOX‐functionalized dextran, DOX‐D. The release of DOX‐D from the respective microcapsules proceeds in the presence of VEGF or ATP as triggers. Preliminary cell experiments reveal that the ATP‐responsive DOX‐D‐loaded microcapsules undergo effective endocytosis into MDA‐MB‐231 cancer cells. The ATP‐responsive DOX‐D‐loaded microcapsules incorporated into the MDA‐MB‐231 cancer cells reveal impressive cytotoxicity as compared to normal epithelial MCF‐10A breast cells (50% vs 0% cell death after 24 h, respectively). The cytotoxicity of the ATP‐responsive DOX‐D‐loaded microcapsules toward the cancer cells is attributed to the effective unlocking of the microcapsules by overexpressed ATP, and to the subsequent release of DOX from the dextran backbone under acidic conditions present in cancer cells (pH = 6.2). 相似文献
78.
Wei‐Hai Chen Xu Yu Wei‐Ching Liao Yang Sung Sohn Alessandro Cecconello Anna Kozell Rachel Nechushtai Itamar Willner 《Advanced functional materials》2017,27(37)
Nanoparticles consisting of metal–organic frameworks (NMOFs) modified with nucleic acid binding strands are synthesized. The NMOFs are loaded with a fluorescent agent or with the anticancer drug doxorubicin, and the loaded NMOFs are capped by hybridization with a complementary nucleic acid that includes the ATP‐aptamer or the ATP‐AS1411 hybrid aptamer in caged configurations. The NMOFs are unlocked in the presence of ATP via the formation of ATP‐aptamer complexes, resulting in the release of the loads. As ATP is overexpressed in cancer cells, and since the AS1411 aptamer recognizes the nucleolin receptor sites on the cancer cell membrane, the doxorubicin‐loaded NMOFs provide functional carriers for targeting and treatment of cancer cells. Preliminary cell experiments reveal impressive selective permeation of the NMOFs into MDA‐MB‐231 breast cancer cells as compared to MCF‐10A normal epithelial breast cells. High cytotoxic efficacy and targeted drug release are observed with the ATP‐AS1411‐functionalized doxorubicin‐loaded NMOFs. 相似文献
79.
Stimuli‐responsive, drug‐loaded, DNA‐based nano‐ and micro‐capsules attract scientific interest as signal‐triggered carriers for controlled drug release. The methods to construct the nano‐/micro‐capsules involve i) the layer‐by‐layer deposition of signal‐reconfigurable DNA shells on drug‐loaded microparticles acting as templates, followed by dissolution of the core templates; ii) the assembly of three‐dimensional capsules composed of reconfigurable DNA origami units; and iii) the synthesis of stimuli‐responsive drug‐loaded capsules stabilized by DNA?polymer hydrogels. Triggers to unlock the nano‐/micro‐capsules include enzymes, pH, light, aptamer?ligand complexes, and redox agents. The capsules are loaded with fluorescent polymers, metal nanoparticles, proteins or semiconductor quantum dots as drug models, with anti‐cancer drugs, e.g., doxorubicin, or with antibodies inhibiting cellular networks or enzymes over‐expressed in cancer cells. The mechanisms for unlocking the nano‐/micro‐capsules and releasing the drugs are discussed, and the applications of the stimuli‐responsive nano‐/micro‐capsules as sense‐and‐treat systems are addressed. The scientific challenges and future perspectives of nano‐capsules and micro‐capsules in nanomedicine are highlighted. 相似文献
80.
This paper presents an analytical solution to the problem of the interaction between a thin plate that is adhesively bonded to the surface of an isotropic elastic halfspace and a concentrated Mindlin-type force that acts parallel to the bonded surface. The model is an idealization of a surface-stiffened region that has potential applications ranging from mechanics of thin films, thermal barrier coatings, layering created by attrition and wear of surfaces and functionally graded materials. The solution also illustrates the influence of the flexural plate model in mitigating the development of unbounded displacements during the application of localized loading directly at the bonded plate. 相似文献