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Amar H. Flood

Bio: Amar H. Flood is an academic researcher from Indiana University. The author has contributed to research in topics: Rotaxane & Supramolecular chemistry. The author has an hindex of 47, co-authored 172 publications receiving 9921 citations. Previous affiliations of Amar H. Flood include Calvin College & Pennsylvania State University.


Papers
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Journal ArticleDOI
TL;DR: Two switchable, palindromically constituted bistable [3]rotaxanes have been designed and synthesized with a pair of mechanically mobile rings encircling a single dumbbell, supporting the hypothesis that the cumulative nanoscale movements within surface-bound molecular muscles can be harnessed to perform larger-scale mechanical work.
Abstract: Two switchable, palindromically constituted bistable (3)rotaxanes have been designed and synthesized with a pair of mechanically mobile rings encircling a single dumbbell. These designs are reminiscent of a "molecular muscle" for the purposes of amplifying and harnessing molecular mechanical motions. The location of the two cyclobis(paraquat-p-phenylene) (CBPQT 4+ ) rings can be controlled to be on either tetrathiafulvalene (TTF) or naphthalene (NP) stations, either chemically ( 1 H NMR spectroscopy) or electrochemically (cyclic voltammetry), such that switching of inter-ring distances from 4.2 to 1.4 nm mimics the contraction and extension of skeletal muscle, albeit on a shorter length scale. Fast scan-rate cyclic voltammetry at low temperatures reveals stepwise oxidations and movements of one-half of the (3)rotaxane and then of the other, a process that appears to be concerted at room temperature. The active form of the bistable (3)rotaxane bears disulfide tethers attached covalently to both of the CBPQT4+ ring components for the purpose of its self-assembly onto a gold surface. An array of flexible microcantilever beams, each coated on one side with a monolayer of 6 billion of the active bistable (3)rotaxane molecules, undergoes controllable and reversible bending up and down when it is exposed to the synchronous addition of aqueous chemical oxidants and reductants. The beam bending is correlated with flexing of the surface- bound molecular muscles, whereas a monolayer of the dumbbell alone is inactive under the same conditions. This observation supports the hypothesis that the cumulative nanoscale movements within surface-bound "molecular muscles" can be harnessed to perform larger-scale mechanical work.

599 citations

Journal ArticleDOI
TL;DR: This tutorial review will focus on the privileged C-H hydrogen bond donor of the 1,2,3-triazole ring systems as elucidated from anion-binding studies with macrocyclic triazolophanes and other receptors.
Abstract: The supramolecular chemistry of anions provides a means to sense and manipulate anions in their many chemical and biological roles. For this purpose, Click chemistry facilitated the synthetic creation of new receptors and thus, an opportunity to aid in the recent re-examination of CH⋯anion hydrogen bonding. This tutorial review will focus on the privileged C–H hydrogen bond donor of the 1,2,3-triazole ring systems as elucidated from anion-binding studies with macrocyclic triazolophanes and other receptors. Triazolophanes are shape-persistent and planar macrocycles that direct four triazole and four phenylene CH groups into a 3.7 A cavity. They display strong (log K(Cl−) = 7), size-dependent halide binding (Cl− > Br− ≫ F− ≫ I−) and a rich set of binding equilibria. For instance, the too large iodide (4.4 A) can be sandwiched between two pyridyl-based triazolophanes with extreme positive cooperativity. Computational studies verify the triazole's hydrogen bond strength indicating it approaches the traditional NH donors from pyrrole. These examples, those of transport, sensing (e.g., ion-selective electrodes), templation, and versatile synthesis herald the use of triazoles in anion-receptor chemistry.

554 citations

Journal ArticleDOI
TL;DR: The investigated system is a unique example of an artificial linear nanomotor that behaves as an autonomous linear motor and operates with a quantum efficiency up to ≈12% and works in mild environmental conditions.
Abstract: Light excitation powers the reversible shuttling movement of the ring component of a rotaxane between two stations located at a 1.3-nm distance on its dumbbell-shaped component. The photoinduced shuttling movement, which occurs in solution, is based on a “four-stroke” synchronized sequence of electronic and nuclear processes. At room temperature the deactivation time of the high-energy charge-transfer state obtained by light excitation is ≈10 μs, and the time period required for the ring-displacement process is on the order of 100 μs. The rotaxane behaves as an autonomous linear motor and operates with a quantum efficiency up to ≈12%. The investigated system is a unique example of an artificial linear nanomotor because it gathers together the following features: (i) it is powered by visible light (e.g., sunlight); (ii) it exhibits autonomous behavior, like motor proteins; (iii) it does not generate waste products; (iv) its operation can rely only on intramolecular processes, allowing in principle operation at the single-molecule level; (v) it can be driven at a frequency of 1 kHz; (vi) it works in mild environmental conditions (i.e., fluid solution at ambient temperature); and (vii) it is stable for at least 103 cycles.

426 citations

Journal ArticleDOI
17 Dec 2004-Science
TL;DR: Several types of molecular electronics devices, such as molecular rectifiers and molecular switch tunnel junctions, have withstood scientific scrutiny and will most likely consist of hybrid devices that combine molecular with existing electronics.
Abstract: Molecular electronics devices hold great promise for electronics applications. But how have the devices fared so far? In their Perspective, Flood et al ., review recent advances in this field. They conclude that several types of molecular electronics devices, such as molecular rectifiers and molecular switch tunnel junctions, have withstood scientific scrutiny: In these devices, the observed effects are indeed molecular in origin. Future practical devices will most likely consist of hybrid devices that combine molecular with existing electronics.

418 citations

Journal ArticleDOI
TL;DR: A reversibly operating nanovalve that can be turned on and off by redox chemistry is demonstrated and traps and releases molecules from a maze of nanoscopic passageways in silica by controlling the operation of redox-activated bistable [2]rotaxane molecules tethered to the openings of nanopores leading out of a nanoscale reservoir.
Abstract: In everyday life, a macroscopic valve is a device with a movable control element that regulates the flow of gases or liquids by blocking and opening passageways. Construction of such a device on the nanoscale level requires (i) suitably proportioned movable control elements, (ii) a method for operating them on demand, and (iii) appropriately sized passageways. These three conditions can be fulfilled by attaching organic, mechanically interlocked, linear motor molecules that can be operated under chemical, electrical, or optical stimuli to stable inorganic porous frameworks (i.e., by self-assembling organic machinery on top of an inorganic chassis). In this article, we demonstrate a reversibly operating nanovalve that can be turned on and off by redox chemistry. It traps and releases molecules from a maze of nanoscopic passageways in silica by controlling the operation of redox-activated bistable [2]rotaxane molecules tethered to the openings of nanopores leading out of a nanoscale reservoir.

417 citations


Cited by
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28 Jul 2005
TL;DR: PfPMP1)与感染红细胞、树突状组胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作�ly.
Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1(PfPMP1)与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员,通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

18,940 citations

Journal ArticleDOI
TL;DR: The basis for the unique properties and rate enhancement for triazole formation under Cu(1) catalysis should be found in the high ∆G of the reaction in combination with the low character of polarity of the dipole of the noncatalyzed thermal reaction, which leads to a considerable activation barrier.
Abstract: The Huisgen 1,3-dipolar cycloaddition reaction of organic azides and alkynes has gained considerable attention in recent years due to the introduction in 2001 of Cu(1) catalysis by Tornoe and Meldal, leading to a major improvement in both rate and regioselectivity of the reaction, as realized independently by the Meldal and the Sharpless laboratories. The great success of the Cu(1) catalyzed reaction is rooted in the fact that it is a virtually quantitative, very robust, insensitive, general, and orthogonal ligation reaction, suitable for even biomolecular ligation and in vivo tagging or as a polymerization reaction for synthesis of long linear polymers. The triazole formed is essentially chemically inert to reactive conditions, e.g. oxidation, reduction, and hydrolysis, and has an intermediate polarity with a dipolar moment of ∼5 D. The basis for the unique properties and rate enhancement for triazole formation under Cu(1) catalysis should be found in the high ∆G of the reaction in combination with the low character of polarity of the dipole of the noncatalyzed thermal reaction, which leads to a considerable activation barrier. In order to understand the reaction in detail, it therefore seems important to spend a moment to consider the structural and mechanistic aspects of the catalysis. The reaction is quite insensitive to reaction conditions as long as Cu(1) is present and may be performed in an aqueous or organic environment both in solution and on solid support.

3,855 citations

01 Jan 2016
TL;DR: The principles of fluorescence spectroscopy is universally compatible with any devices to read and is available in the digital library an online access to it is set as public so you can download it instantly.
Abstract: Thank you very much for downloading principles of fluorescence spectroscopy. As you may know, people have look hundreds times for their favorite novels like this principles of fluorescence spectroscopy, but end up in malicious downloads. Rather than reading a good book with a cup of tea in the afternoon, instead they cope with some harmful bugs inside their desktop computer. principles of fluorescence spectroscopy is available in our digital library an online access to it is set as public so you can download it instantly. Our digital library spans in multiple locations, allowing you to get the most less latency time to download any of our books like this one. Kindly say, the principles of fluorescence spectroscopy is universally compatible with any devices to read.

2,960 citations

Journal ArticleDOI
Naomi J. Halas1, Surbhi Lal1, Wei-Shun Chang1, Stephan Link1, Peter Nordlander1 

2,702 citations

01 Dec 1991
TL;DR: In this article, self-assembly is defined as the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds.
Abstract: Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.

2,591 citations