Electrically driven directional motion of a four-wheeled molecule on a metal surface

• Tibor Kudernac,
• Nopporn Ruangsupapichat,
• Manfred Parschau,
• Beatriz Maciá,
• Nathalie Katsonis,
• Syuzanna R. Harutyunyan,
• Karl-Heinz Ernst
• & Ben L. Feringa

• 
  

  Nature

   

  479,

   

  208–211

   

  (10 November 2011)

  doi:10.1038/nature10587

  Received

   

  10 January 2011

   

  Accepted

   

  15 September 2011

   

  Published online

   

  09 November 2011


Propelling single molecules in a controlled manner along an unmodified surface remains extremely challenging because it requires molecules that can use light, chemical or electrical energy to modulate their interaction with the surface in a way that generates motion. Nature’s motor proteins^1, 2 have mastered the art of converting conformational changes into directed motion, and have inspired the design of artificial systems³ such as DNA walkers^4, 5 and light- and redox-driven molecular motors^{6, 7, 8, 9, 10, 11}. But although controlled movement of single molecules along a surface has been reported^{12, 13, 14, 15,16}, the molecules in these examples act as passive elements that either diffuse along a preferential direction with equal probability for forward and backward movement or are dragged by an STM tip. Here we present a molecule with four functional units—our previously reported rotary motors^6, 8, 17—that undergo continuous and defined conformational changes upon sequential electronic and vibrational excitation. Scanning tunnelling microscopy confirms that activation of the conformational changes of the rotors through inelastic electron tunnelling propels the molecule unidirectionally across a Cu(111) surface. The system can be adapted to follow either linear or random surface trajectories or to remain stationary, by tuning the chirality of the individual motor units. Our design provides a starting point for the exploration of more sophisticated molecular mechanical systems with directionally controlled motion.

Introduction to graphene

Curiosity Rover's Peculiar Mars Landing Described

Building Designed Granular Towers One Drop at a Time

Phys. Rev. Lett. 107, 208304 (2011) [5 pages]

Julien Chopin^* and Arshad Kudrolli^† 
Department of Physics, Clark University, Worcester, Massachusetts 01610, USA

 Received 27 August 2011; published 9 November 2011

A dense granular suspension dripping on an imbibing surface is observed to give rise to slender mechanically stable structures that we call granular towers. Successive drops of grain-liquid mixtures are shown to solidify rapidly upon contact with a liquid absorbing substrate. A balance of excess liquid flux and drainage rate is found to capture the typical growth and height of the towers. The tower width is captured by the Weber number, which gives the relative importance of inertia and capillary forces. Various symmetric, smooth, corrugated, zigzag, and chiral structures are observed by varying the impact velocity and the flux rate from droplet to jetting regime.

Conductive dense hydrogen

• M. I. Eremets
• & I. A. Troyan

• 
  

  Nature Materials

   

  10,

   

  927–931

   

  (2011)

  doi:10.1038/nmat3175

  Received

   

  27 May 2011

   

  Accepted

   

  18 October 2011

  Published online

   

  13 November 2011

  Molecular hydrogenis expected to exhibit metallic properties under megabar pressures. This metal is predicted to be superconducting with a very high critical temperature, T_c, of 200–400 K (ref. 1), and it may acquire a new quantum state as a metallic superfluid and a superconducting superfluid². It may potentially be recovered metastably at ambient pressures³. However, experiments carried out at low temperatures, T<100 K (refs 4, 5), showed that at record pressures of 300 GPa, hydrogen remains in the molecular insulating state. Here we report on the transformation of normal molecularhydrogen at room temperature (295 K) to a conductive and metallic state. At 200 GPa the Raman frequency of the molecular vibron strongly decreased and the spectral width increased, evidencing a strong interaction between molecules. Deuterium behaved similarly. Above 220 GPa, hydrogen became opaque and electrically conductive. At 260–270 GPa, hydrogen transformed into a metal as the conductance of hydrogen sharply increased and changed little on further pressurizing up to 300 GPa or cooling to at least 30 K; and the sample reflected light well. The metallic phase transformed back at 295 K into molecularhydrogen at  200 GPa. This significant hysteresis indicates that the transformation of molecular hydrogen into a metal is accompanied by a first-order structural transition presumably into a monatomic liquid state. Our findings open an avenue for detailed and comprehensive studies of metallic hydrogen.

Ultralight Metallic Microlattices

1. T. A. Schaedler¹,*, 
2. A. J. Jacobsen¹, 
3. A. Torrents², 
4. A. E. Sorensen¹, 
5. J. Lian³, 
6. J. R. Greer³, 
7. L. Valdevit²,
8. W. B. Carter¹

1. Science 18 November 2011: 
   Vol. 334 no. 6058 pp. 962-965 
   DOI: 10.1126/science.1211649

ABSTRACT

Ultralight (<10 milligrams per cubic centimeter) cellular materials are desirable for thermal insulation; battery electrodes; catalyst supports; and acoustic, vibration, or shock energy damping. We present ultralight materials based on periodic hollow-tube microlattices. These materials are fabricated by starting with a template formed by self-propagating photopolymer waveguide prototyping, coating the template by electroless nickel plating, and subsequently etching away the template. The resulting metallic microlattices exhibit densities ρ ≥ 0.9 milligram per cubic centimeter, complete recovery after compression exceeding 50% strain, and energy absorption similar to elastomers. Young’s modulus Escales with density as E ~ ρ², in contrast to the E ~ ρ³ scaling observed for ultralight aerogels and carbon nanotube foams with stochastic architecture. We attribute these properties to structural hierarchy at the nanometer, micrometer, and millimeter scales.

Measurement of Tear Glucose Levels with Amperometric Glucose Biosensor/Capillary Tube Configuration

Qinyi Yan†, Bo Peng†, Gang Su‡, Bruce E. Cohan§, Terry C. Major, and Mark E. Meyerhoff*†

^†Department of Chemistry, ^‡Bioinformatics Program,^§EyeLab Group, and Department of Surgery, The University of Michigan, Ann Arbor, Michigan 48109-1055, United States

Anal. Chem., 2011, 83 (21), pp 8341–8346

DOI: 10.1021/ac201700c

Publication Date (Web): September 30, 2011

Copyright © 2011 American Chemical Society

An amperometric needle-type electrochemical glucose sensor intended for tear glucose measurements is described and employed in conjunction with a 0.84 mm i.d. capillary tube to collect microliter volumes of tear fluid. The sensor is based on immobilizing glucose oxidase on a 0.25 mm o.d. platinum/iridium (Pt/Ir) wire and anodically detecting the liberated hydrogen peroxide from the enzymatic reaction. Inner layers of Nafion and an electropolymerized film of 1,3-diaminobenzene/resorcinol greatly enhance the selectivity for glucose over potential interferences in tear fluid, including ascorbic acid and uric acid. Further, the new sensor is optimized to achieve very low detection limits of 1.5 ± 0.4 μM of glucose (S/N = 3) that is required to monitor glucose levels in tear fluid with a glucose sensitivity of 0.032 ± 0.02 nA/μM (n = 6). Only 4–5 μL of tear fluid in the capillary tube is required when the needle sensor is inserted into the capillary. The glucose sensor was employed to measure tear glucose levels in anesthetized rabbits over an 8 h period while also measuring the blood glucose values. A strong correlation between tear and blood glucose levels was found, suggesting that measurement of tear glucose is a potential noninvasive substitute for blood glucose measurements, and the new sensor configuration could aid in conducting further research in this direction.

Is Mars Really Red?

Multifunctional Core–Shell Nanoparticles: Discovery of Previously Invisible Biomarkers

Davide Tamburro†‡§, Claudia Fredolini†‡, Virginia Espina†, Temple A. Douglas†, Adarsh Ranganathan†, Leopold Ilag‡, Weidong Zhou†, Paul Russo†, Benjamin H. Espina†, Giovanni Muto, Emanuel F. Petricoin, III†, Lance A. Liotta†, and Alessandra Luchini*†

Center for Applied Proteomics and Molecular Medicine,George Mason University, Manassas, Virginia 20110, United States

Department of Analytical Chemistry, Stockholm University, Stockholm 106 91, Sweden

Department of Hematology, Oncology and Molecular Medicine, Istituto Superiore di Sanità, Rome 00161, Italy

Department of Urology, S. Giovanni Bosco Hospital, Turin 10154, Italy

Department of Medicine and Experimental Oncology, University of Turin, 10125 Turin, Italy

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja207515j

Publication Date (Web): October 14, 2011

Copyright © 2011 American Chemical Society

Many low-abundance biomarkers for early detection of cancer and other diseases are invisible to mass spectrometry because they exist in body fluids in very low concentrations, are masked by high-abundance proteins such as albumin and immunoglobulins, and are very labile. To overcome these barriers, we created porous, buoyant, core–shell hydrogel nanoparticles containing novel high affinity reactive chemical baits for protein and peptide harvesting, concentration, and preservation in body fluids. Poly(N-isopropylacrylamide-co-acrylic acid) nanoparticles were functionalized with amino-containing dyes via zero-length cross-linking amidation reactions. Nanoparticles functionalized in the core with 17 different (12 chemically novel) molecular baits showed preferential high affinities (K_D < 10^–11 M) for specific low-abundance protein analytes. A poly(N-isopropylacrylamide-co-vinylsulfonic acid) shell was added to the core particles. This shell chemistry selectively prevented unwanted entry of all size peptides derived from albumin without hindering the penetration of non-albumin small proteins and peptides. Proteins and peptides entered the core to be captured with high affinity by baits immobilized in the core. Nanoparticles effectively protected interleukin-6 from enzymatic degradation in sweat and increased the effective detection sensitivity of human growth hormone in human urine using multiple reaction monitoring analysis. Used in whole blood as a one-step, in-solution preprocessing step, the nanoparticles greatly enriched the concentration of low-molecular weight proteins and peptides while excluding albumin and other proteins above 30 kDa; this achieved a 10,000-fold effective amplification of the analyte concentration, enabling mass spectrometry (MS) discovery of candidate biomarkers that were previously undetectable.

Beautiful TiO2 Nanostructures

Rational Design of 3D Dendritic TiO₂ Nanostructures with Favorable Architectures

Ziqi Sun†, Jung Ho Kim*†, Yue Zhao†, Fargol Bijarbooneh†, Victor Malgras†, Youngmin Lee‡, Yong-Mook Kang‡, and Shi Xue Dou†

Institute for Superconducting and Electronic Materials,University of Wollongong, Innovation Campus, Squires Way, North Wollongong, NSW 2500, Australia

Division of Advanced Materials Engineering, Kongju National University, 275 Budaedong, Cheonan, Chungnam, Republic of Korea

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja208468d

Publication Date (Web): October 31, 2011

Copyright © 2011 American Chemical Society

Controlling the morphology and size of titanium dioxide (TiO₂) nanostructures is crucial to obtain superior photocatalytic, photovoltaic, and electrochemical properties. However, the synthetic techniques for preparing such structures, especially those with complex configurations, still remain a challenge because of the rapid hydrolysis of Ti-containing polymer precursors in aqueous solution. Herein, we report a completely novel approach—three-dimensional (3D) TiO₂ nanostructures with favorable dendritic architectures—through a simple hydrothermal synthesis. The size of the 3D TiO₂ dendrites and the morphology of the constituent nano-units, in the form of nanorods, nanoribbons, and nanowires, are controlled by adjusting the precursor hydrolysis rate and the surfactant aggregation. These novel configurations of TiO₂ nanostructures possess higher surface area and superior electrochemical properties compared to nanoparticles with smooth surfaces. Our findings provide an effective solution for the synthesis of complex TiO₂ nano-architectures, which can pave the way to further improve the energy storage and energy conversion efficiency of TiO₂-based devices.

A step closer to solar cells-Dye sensitized solar cells

Science 4 November 2011: 
Vol. 334 no. 6056 pp. 629-634 
DOI: 10.1126/science.1209688

• RESEARCH ARTICLE

Porphyrin-Sensitized Solar Cells with Cobalt (II/III)–Based Redox Electrolyte Exceed 12 Percent Efficiency

1. Aswani Yella¹, 
2. Hsuan-Wei Lee², 
3. Hoi Nok Tsao¹, 
4. Chenyi Yi¹, 
5. Aravind Kumar Chandiran¹,
6. Md.Khaja Nazeeruddin¹, 
7. Eric Wei-Guang Diau³,*, 
8. Chen-Yu Yeh²,*, 
9. Shaik M Zakeeruddin¹,*, 
10. Michael Grätzel¹,*

ABSTRACT

The iodide/triiodide redox shuttle has limited the efficiencies accessible in dye-sensitized solar cells. Here, we report mesoscopic solar cells that incorporate a Co^(II/III)tris(bipyridyl)–based redox electrolyte in conjunction with a custom synthesized donor-π-bridge-acceptor zinc porphyrin dye as sensitizer (designated YD2-o-C8). The specific molecular design of YD2-o-C8 greatly retards the rate of interfacial back electron transfer from the conduction band of the nanocrystalline titanium dioxide film to the oxidized cobalt mediator, which enables attainment of strikingly high photovoltages approaching 1 volt. Because the YD2-o-C8 porphyrin harvests sunlight across the visible spectrum, large photocurrents are generated. Cosensitization of YD2-o-C8 with another organic dye further enhances the performance of the device, leading to a measured power conversion efficiency of 12.3% under simulated air mass 1.5 global sunlight.