Popular science articles: April 2012

Printable Optical Sensors Based on H-Bonded Supramolecular Cholesteric Liquid Crystal Networks

Nicole Herzer†, Hilal Guneysu†, Dylan J. D. Davies†, Derya Yildirim†, Antonio R. Vaccaro†, Dirk J. Broer†, Cees W. M. Bastiaansen†‡, and Albertus P. H. J. Schenning*†

^† Functional Organic Materials & Devices, Eindhoven University of Technology, PO Box 513, Eindhoven, The Netherlands

^‡ Department of Materials, Queen Mary University of London, Mile End Road, London E1 4NS, U.K.

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja301845n

Publication Date (Web): April 23, 2012

A printable H-bonded cholesteric liquid crystal (CLC) polymer film has been fabricated that, after conversion to a hygroscopic polymer salt film, responds to temperature and humidity by changing its reflection color. Fast-responding humidity sensors have been made in which the reflection color changes between green and yellow depending on the relative humidity. The change in reflection band is a result of a change in helix pitch in the film due to absorption and desorption of water, resulting in swelling/deswelling of the film material. When the polymer salt was saturated with water, a red-reflecting film was obtained that can potentially act as a time/temperature integrator. Finally, the films were printed on a foil, showing the potential application of supramolecular CLC materials as low-cost, printable, battery-free optical sensors.

Three Distinct Water Structures at a Zwitterionic Lipid/Water Interface Revealed by Heterodyne-Detected Vibrational Sum Frequency Generation

Jahur A. Mondal, Satoshi Nihonyanagi, Shoichi Yamaguchi, and Tahei Tahara*

Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja300658h

Publication Date (Web): April 26, 2012

Lipid/water interfaces and associated interfacial water are vital for various biochemical reactions, but the molecular-level understanding of their property is very limited. We investigated the water structure at a zwitterionic lipid, phosphatidylcholine, monolayer/water interface using heterodyne-detected vibrational sum frequency generation spectroscopy. Isotopically diluted water was utilized in the experiments to minimize the effect of intra/intermolecular couplings. It was found that the OH stretch band in the Imχ⁽²⁾spectrum of the phosphatidylcholine/water interface exhibits a characteristic double-peaked feature. To interpret this peculiar spectrum of the zwitterionic lipid/water interface, Imχ⁽²⁾spectra of a zwitterionic surfactant/water interface and mixed lipid/water interfaces were measured. The Imχ⁽²⁾ spectrum of the zwitterionic surfactant/water interface clearly shows both positive and negative bands in the OH stretch region, revealing that multiple water structures exist at the interface. At the mixed lipid/water interfaces, while gradually varying the fraction of the anionic and cationic lipids, we observed a drastic change in the Imχ⁽²⁾spectra in which spectral features similar to those of the anionic, zwitterionic, and cationic lipid/water interfaces appeared successively. These observations demonstrate that, when the positive and negative charges coexist at the interface, the H-down-oriented water structure and H-up-oriented water structure appear in the vicinity of the respective charged sites. In addition, it was found that a positive Imχ⁽²⁾ appears around 3600 cm^–1 for all the monolayer interfaces examined, indicating weakly interacting water species existing in the hydrophobic region of the monolayer at the interface. On the basis of these results, we concluded that the characteristic Imχ⁽²⁾ spectrum of the zwitterionic lipid/water interface arises from three different types of water existing at the interface: (1) the water associated with the negatively charged phosphate, which is strongly H-bonded and has a net H-up orientation, (2) the water around the positively charged choline, which forms weaker H-bonds and has a net H-down orientation, and (3) the water weakly interacting with the hydrophobic region of the lipid, which has a net H-up orientation.

A Semisynthetic Fluorescent Sensor Protein for Glutamate

Matthias A. Brun, Kui-Thong Tan, Rudolf Griss, Anna Kielkowska, Luc Reymond, and Kai Johnsson*

Institute of Chemical Sciences and Engineering, Institute of Bioengineering, National Centre of Competence in Research Chemical Biology, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja3002277

Publication Date (Web): April 23, 2012

We report the semisynthesis of a fluorescent glutamate sensor protein on cell surfaces. Sensor excitation at 547 nm yields a glutamate-dependent emission spectrum between 550 and 700 nm that can be exploited for ratiometric sensing. On cells, the sensor displays a ratiometric change of 1.56. The high sensitivity toward glutamate concentration changes of the sensor and its exclusive extracellular localization make it an attractive tool for glutamate sensing in neurobiology.

What Really Drives Chemical Reactions on Contact Charged Surfaces?

Bilge Baytekin, H. Tarik Baytekin, and Bartosz A. Grzybowski*

Department of Chemistry and Department of Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja300925h

Publication Date (Web): April 11, 2012

Although it is known that contact-electrified polymers can drive chemical reactions, the origin of this phenomenon remains poorly understood. To date, it has been accepted that this effect is due to excess electrons developed on negatively charged surfaces and to the subsequent transfer of these electrons to the reactants in solution. The present study demonstrates that this view is incorrect and, in reality, the reactions are driven by mechanoradicals created during polymer–polymer contact.

Rapid, Sensitive, and Quantitative Detection of Pathogenic DNA at the Point of Care through Microfluidic Electrochemical Quantitative Loop-Mediated Isothermal Amplification†

Kuangwen Hsieh^2,‡,
Adriana S. Patterson^3,‡,
Dr. B. Scott Ferguson²,
Prof. Kevin W. Plaxco³,
Prof. H. Tom Soh^1,2,

^{Article first published online: 4 APR 2012
DOI: 10.1002/anie.201109115
Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

ingle-step DNA detection: A microfluidic electrochemical loop-mediated isothermal amplification platform is reported for rapid, sensitive, and quantitative detection of pathogen genomic DNA at the point of care (see picture). DNA amplification was electrochemically monitored in real time within a monolithic microfluidic device, enabling the detection of as few as 16 copies of Salmonella genomic DNA through a single-step process in less than an hour.}

Magnetic Click Colloidal Assembly

Stefano Sacanna*†, Laura Rossi‡, and David J. Pine†

^† Center for Soft Matter Research, Department of Physics, New York University, 4-6 Washington Place, New York, New York 10003, United States

^‡ Van’t Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute for Nano-materials Science,Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands

J. Am. Chem. Soc., 2012, 134 (14), pp 6112–6115

DOI: 10.1021/ja301344n

Publication Date (Web): March 27, 2012

We introduce a new class of spherical colloids that reversibly self-assemble into well-defined nonlinear structures by virtue of “magnetic patches”. This assembly is driven by tunable magnetostatic binding forces that originate from microscopic permanent magnets embedded underneath the surface of the particles. The resulting clusters form spontaneously in the absence of external magnetizing fields, and their geometry is determined by an interplay between magnetic, steric, and electrostatic interactions. Imposing an external magnetic field enables the clusters to unbind or change their geometry allowing, in principle, the creation of materials with a reconfigurable structural arrangement.

Carbon Nanotubes Induce Growth Enhancement of Tobacco Cells

Mariya V. Khodakovskaya†*, Kanishka de Silva†, Alexandru S. Biris‡§, Enkeleda Dervishi‡, and Hector Villagarcia†

^†Department of Applied Science, ^‡Nanotechnology Center, ^§Department of System Engineering, University of Arkansas at Little Rock, Arkansas 72204, United States

ACS Nano, 2012, 6 (3), pp 2128–2135

DOI: 10.1021/nn204643g

Publication Date (Web): February 23, 2012

Carbon nanotubes have shown promise as regulators of seed germination and plant growth. Here, we demonstrate that multiwalled carbon nanotubes (MWCNTs) have the ability to enhance the growth of tobacco cell culture (55–64% increase over control) in a wide range of concentrations (5–500 μg/mL). Activated carbon (AC) stimulated cell growth (16% increase) only at low concentrations (5 μg/mL) while dramatically inhibited the cellular growth at higher concentrations (100–500 μg/mL). We found a correlation between the activation of cells growth exposed to MWCNTs and the upregulation of genes involved in cell division/cell wall formation and water transport. The expression of the tobacco aquaporin (NtPIP1) gene, as well as production of the NtPIP1 protein, significantly increased in cells exposed to MWCNTs compared to control cells or those exposed to AC. The expression of marker genes for cell division (CycB) and cell wall extension (NtLRX1) was also up-regulated in cells exposed to MWCNTs compared to control cells or those exposed to activated carbon only.

Bidirectional Optical Sorting of Gold Nanoparticles

M. Ploschner*†, T. Čižmár‡, M. Mazilu†, A. Di Falco†, and K. Dholakia†

^† SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews KY16 9SS, United Kingdom

^‡ School of Medicine, Medical and Biological Science Building, University of St Andrews, St. Andrews KY16 9TF, United Kingdom

Nano Lett., 2012, 12 (4), pp 1923–1927

DOI: 10.1021/nl204378r

Publication Date (Web): March 26, 2012

We present a generic technique allowing size-based all-optical sorting of gold nanoparticles. Optical forces acting on metallic nanoparticles are substantially enhanced when they are illuminated at a wavelength near the plasmon resonance, as determined by the particle’s geometry. Exploiting these resonances, we realize sorting in a system of two counter-propagating evanescent waves, each at different wavelengths that selectively guide nanoparticles of different sizes in opposite directions. We validate this concept by demonstrating bidirectional sorting of gold nanoparticles of either 150 or 130 nm in diameter from those of 100 nm in diameter within a mixture.

Orthographic Processing in Baboons (Papio papio)

Science 13 April 2012:
Vol. 336 no. 6078 pp. 245-248
DOI: 10.1126/science.

ABSTRACT

Skilled readers use information about which letters are where in a word (orthographic information) in order to access the sounds and meanings of printed words. We asked whether efficient processing of orthographic information could be achieved in the absence of prior language knowledge. To do so, we trained baboons to discriminate English words from nonsense combinations of letters that resembled real words. The results revealed that the baboons were using orthographic information in order to efficiently discriminate words from letter strings that were not words. Our results demonstrate that basic orthographic processing skills can be acquired in the absence of preexisting linguistic representations.

Check out this video:

http://video.sciencemag.org/VideoLab/1556965049001/1

High density energy storage using self-assembled materials

High-Density Energy Storage Using Self-Assembled Materials

Christopher E. Wilmer, Omar K. Farha, Patrick E. Fuller

Northwestern University

Published in Science

Cavitand-Functionalized SWCNTs for N-Methylammonium Detection

Marco Dionisio†‡, Jan M. Schnorr†, Vladimir K. Michaelis§, Robert G. Griffin§, Timothy M. Swager*†, and Enrico Dalcanale*‡

^† Department of Chemistry and Institute for Soldier Nanotechnologies, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States

^‡ Dipartimento di Chimica Organica e Industriale,Università di Parma, and INSTM, UdR Parma, Parco Area delle Scienze 17A, 43124 Parma, Italy

^§ Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja301174m

Publication Date (Web): April 4, 2012

Single-walled carbon nanotubes (SWCNTs) have been functionalized with highly selective tetraphosphonate cavitand receptors. The binding of charged N-methylammonium species to the functionalized SWCNTs was analyzed by X-ray photoelectron spectroscopy and confirmed by ³¹P MAS NMR spectroscopy. The cavitand-functionalized SWCNTs were shown to function as chemiresistive sensory materials for the detection of sarcosine and its ethyl ester hydrochloride in water with high selectivity at concentrations as low as 0.02 mM. Exposure to sarcosine and its derivative resulted in an increased conductance, in contrast to a decreased conductance response observed for potential interferents such as the structurally related glycine ethyl ester hydrochloride.

Boronate-Mediated Biologic Delivery

Gregory A. Ellis†, Michael J. Palte‡, and Ronald T. Raines*†§

^†Department of Biochemistry, ^‡Medical Scientist Training Program and Molecular & Cellular Pharmacology Graduate Training Program, and ^§Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States

J. Am. Chem. Soc., 2012, 134 (8), pp 3631–3634

DOI: 10.1021/ja210719s

Publication Date (Web): February 3, 2012

Inefficient cellular delivery limits the landscape of macromolecular drugs. Boronic acids readily form boronate esters with the 1,2- and 1,3-diols of saccharides, such as those that coat the surface of mammalian cells. Here pendant boronic acids are shown to enhance the cytosolic delivery of a protein toxin. Thus, boronates are a noncationic carrier that can deliver a polar macromolecule into mammalian cells.

Solvent-Free Luminescent Organic Liquids**

Sukumaran Santhosh Babu, Junko Aimi, Hiroaki Ozawa, Naoto Shirahata, Akinori Saeki,
Shu Seki, Ayyappanpillai Ajayaghosh, Helmuth Mçhwald, and Takashi Nakanishi*

Thumbnail image of graphical abstract

Illuminating! Isolation of a π-core by covalently attached flexible hydrocarbon chains has been employed to synthesize blue-emitting oligo(p-phenylenevinylene) (OPV) liquids with tunable viscosity and optical properties. A solvent-free, stable, white-light emitting ink/paint, which can be applied onto various surfaces and even onto LEDs, was made by blending of liquid OPVs with emissive solid dopants.

High-Resolution EM of Colloidal Nanocrystal Growth Using Graphene Liquid Cells

Jong Min Yuk et al
DOI: 10.1126/science.1217654
Science 336, 61 (2012);

We introduce a new type of liquid cell for in situ transmission electron microscopy (TEM) based on
entrapment of a liquid film between layers of graphene. The graphene liquid cell facilitates

atomic-level resolution imaging while sustaining the most realistic liquid conditions achievable
under electron-beam radiation. We employ this cell to explore the mechanism of colloidal platinum
nanocrystal growth. Direct atomic-resolution imaging allows us to visualize critical steps in the process,
including site-selective coalescence, structural reshaping after coalescence, and surface faceting.

Why Spiders Don't Stick To The Web

In-Cell Fluorescence Activation and Labeling of Proteins Mediated by FRET-Quenched Split Inteins

Radhika Borra†, Dezheng Dong†, Ahmed Y. Elnagar†, Getachew A. Woldemariam†, and Julio A. Camarero*†‡

^†Department of Pharmacology and Pharmaceutical Sciences, and ^‡Department of Chemistry, University of Southern California, Los Angeles, California 90033, United States

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja300209u

Publication Date (Web): March 10, 2012

Methods to visualize, track, and modify proteins in living cells are central for understanding the spatial and temporal underpinnings of life inside cells. Although fluorescent proteins have proven to be extremely useful for in vivo studies of protein function, their utility is inherently limited because their spectral and structural characteristics are interdependent. These limitations have spurred the creation of alternative approaches for the chemical labeling of proteins. We report in this work the use of fluorescence resonance emission transfer (FRET)-quenched DnaE split inteins for the site-specific labeling and concomitant fluorescence activation of proteins in living cells. We have successfully employed this approach for the site-specific in-cell labeling of the DNA binding domain (DBD) of the transcription factor YY1 using several human cell lines. Moreover, we have shown that this approach can be also used for modifying proteins to control their cellular localization and potentially alter their biological activity.

Interaction of Nucleic Acids with the Glycocalyx

Michael J. Palte† and Ronald T. Raines*‡

^†Medical Scientist Training Program, Molecular & Cellular Pharmacology Graduate Training Program, and^‡Departments of Biochemistry and Chemistry, University of Wisconsin—Madison, Madison, Wisconsin 53706, United States

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja2106477

Publication Date (Web): March 8, 2012

Mammalian cells resist the uptake of nucleic acids. The lipid bilayer of the plasma membrane presents one barrier. Here, we report on a second physicochemical barrier for uptake. To create a sensitive probe for nucleic acid–cell interactions, we synthesized fluorescent conjugates in which lipids are linked to DNA oligonucleotides. We found that these conjugates incorporate readily into the plasma membrane but are not retained there. Expulsion of lipid–oligonucleotide conjugates from the plasma membrane increases with oligonucleotide length. Conversely, the incorporation of conjugates increases markedly in cells that lack the major anionic components of the glycocalyx, sialic acid and glycosaminoglycans, and in cells that had incorporated highly cationic lipids into their plasma membrane. We conclude that anionic oligosaccharides provide a formidable barrier to the uptake of nucleic acids by mammalian cells. This conclusion has implications for genomic stability, as well as the delivery of genes and siRNAs into mammalian cells.

Enzyme-Free Amplified Detection of DNA by an Autonomous Ligation DNAzyme Machinery

Fuan Wang, Johann Elbaz, and Itamar Willner*

Institute of Chemistry, Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel

J. Am. Chem. Soc., 2012, 134 (12), pp 5504–5507

DOI: 10.1021/ja300616w

Publication Date (Web): March 11, 2012

The Zn²⁺-dependent ligation DNAzyme is implemented as a biocatalyst for the amplified detection of a target DNA by the autonomous replication of a nucleic acid reporter unit that is generated by the catalyzed ligation process. The reporter units enhance the formation of active DNAzyme units, thus leading to the isothermal autocatalytic formation of the reporter elements. The system was further developed and applied for the amplified detection of Tay-Sachs genetic disorder mutant, with a detection limit of 1.0 × 10^–11 M. Besides providing a versatile paradigm for the amplified detection of DNA, the system reveals a new, enzyme-free, isothermal, autocatalytic mechanism that introduces means for effective programmed synthesis.

Magnetic Click Colloidal Assembly

Stefano Sacanna*†, Laura Rossi‡, and David J. Pine†

^† Center for Soft Matter Research, Department of Physics, New York University, 4-6 Washington Place, New York, New York 10003, United States

^‡ Van’t Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute for Nano-materials Science,Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja301344n

Publication Date (Web): March 27, 2012