Popular science articles: March 2012

Controlling Liquid Drops with Texture Ratchets

Todd A. Duncombe^1,†,‡,
E. Yegân Erdem^2,†,§,
Ashutosh Shastry^3,†,¶,
Rajashree Baskaran⁴,
Karl F. Böhringer^5,*

Article first published online: 14 FEB 2012

Advanced Materials

Volume 24, Issue 12,pages 1545–1550, March 22, 2012

Controlled vibration selectively propels multiple microliter-sized drops along microstructured tracks, leading to simple microfluidic systems that rectify oscillations of the three-phase contact line into asymmetric pinning forces that propel each drop in the direction of higher pinning.

Sequence, Structure, and Function of Peptide Self-Assembled Monolayers

Ann K. Nowinski, Fang Sun, Andrew D. White, Andrew J. Keefe, and Shaoyi Jiang*

Department of Chemical Engineering, University of Washington, Seattle, Washington 98195, United States

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja3006868

Publication Date (Web): March 8, 2012

Cysteine is commonly used to attach peptides onto gold surfaces. Here we show that the inclusion of an additional linker with a length of four residues (-PPPPC) and a rigid, hydrophobic nature is a better choice for forming peptide self-assembled monolayers (SAMs) with a well-ordered structure and high surface density. We compared the structure and function of the nonfouling peptide EKEKEKE-PPPPC-Am with EKEKEKE-C-Am. Circular dichroism, attenuated total internal reflection Fourier transform IR spectroscopy, and molecular dynamics results showed that EKEKEKE-PPPPC-Am forms a secondary structure while EKEKEKE-C-Am has a random structure. Surface plasmon resonance sensor results showed that protein adsorption on EKEKEKE-PPPPC-Am/gold is very low with small variation while protein adsorption on EKEKEKE-C-Am/gold is high with large variation. X-ray photoelectron spectroscopy results showed that both peptides have strong gold–thiol binding with the gold surface, indicating that their difference in protein adsorption is due to their assembled structures. Further experimental and simulation studies were performed to show that -PPPPC is a better linker than -PC, -PPC, and -PPPC. Finally, we extended EKEKEKE-PPPPC-Am with the cell-binding sequence RGD and demonstrated control over specific versus nonspecific cell adhesion without using poly(ethylene glycol). Adding a functional peptide to the nonfouling EK sequence avoids complex chemistries that are used for its connection to synthetic materials.

UV-Induced Bursting of Cell-Sized Multicomponent Lipid Vesicles in a Photosensitive Surfactant Solution

Antoine Diguet†‡§, Miho Yanagisawa

, Yan-Jun Liu†‡§, Elodie Brun†‡§, Sacha Abadie†‡§, Sergii Rudiuk†‡§, and Damien Baigl*†‡§

^† Department of Chemistry, Ecole Normale Supérieure, 24 rue Lhomond, 75005 Paris, France

^‡ Université Pierre et Marie Curie Paris 6, 4 place Jussieu, 75005 Paris, France

^§ UMR 8640, Centre National de la Recherche Scientifique, Paris, France

Department of Physics, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja211664f

Publication Date (Web): February 8, 2012

We study the behavior of multicomponent giant unilamellar vesicles (GUVs) in the presence of AzoTAB, a photosensitive surfactant. GUVs are made of an equimolar ratio of dioleoylphosphatidylcholine (DOPC) and dipalmitoylphosphatidylcholine (DPPC) and various amounts of cholesterol (Chol), where the lipid membrane shows a phase separation into a DPPC-rich liquid-ordered (L_o) phase and a DOPC-rich liquid-disordered (L_d) phase. We find that UV illumination at 365 nm for 1 s induces the bursting of a significant fraction of the GUV population. The percentage of UV-induced disrupted vesicles, called bursting rate (Y_burst), increases with an increase in [AzoTAB] and depends on [Chol] in a non-monotonous manner. Y_burst decreases when [Chol] increases from 0 to 10 mol % and then increases with a further increase in [Chol], which can be correlated with the phase composition of the membrane. We show that Y_burst increases with the appearance of solid domains ([Chol] = 0) or with an increase in area fraction of L_o phase (with increasing [Chol] ≥ 10 mol %). Under our conditions (UV illumination at 365 nm for 1 s), maximal bursting efficiency (Y_burst = 53%) is obtained for [AzoTAB] = 1 mM and [Chol] = 40 mol %. Finally, by restricting the illumination area, we demonstrate the first selective UV-induced bursting of individual target GUVs. These results show a new method to probe biomembrane mechanical properties using light as well as pave the way for novel strategies of light-induced drug delivery.

Flexible, All-Organic Chemiresistor for Detecting Chemically Aggressive Vapors

Srikanth Ammu, Vineet Dua, Srikanth Rao Agnihotra, Sumedh P. Surwade, Akshay Phulgirkar, Sanjaykumar Patel, and Sanjeev K. Manohar*

Department of Chemical Engineering, University of Massachusetts Lowell, Lowell, Massachusetts 01854, United States

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja300420t

Publication Date (Web): February 23, 2012

Chemiresistors made of thin films of single-walled carbon nanotube (CNT) bundles on cellulosics (paper and cloth) can detect aggressive oxidizing vapors such as nitrogen dioxide and chlorine at 250 and 500 ppb, respectively, at room temperature in ambient air without the aid of a vapor concentrator. Inkjet-printed films of CNTs on 100% acid-free paper are significantly more robust than dip-coated films on plastic substrates. Performance attributes include low sensor-to-sensor variation, spontaneous signal recovery, negligible baseline drift, and the ability to bend the sensors to a crease without loss of sensor performance.

Chemoenzymatic Synthesis of O-Mannosylpeptides in Solution and on Solid Phase

Robert Šardzík†, Anthony P. Green†, Nicolas Laurent†, Peter Both†, Carolina Fontana‡, Josef Voglmeir†, Martin J. Weissenborn†, Rose Haddoub†, Paola Grassi#, Stuart M. Haslam#, Göran Widmalm‡, and Sabine L. Flitsch*†

^† School of Chemistry, Manchester Interdisciplinary Biocentre, The University of Manchester, Manchester M1 7DN, U.K.

^‡ Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden

^# Division of Molecular Biosciences, Faculty of Natural Sciences, Imperial College London, London, SW7 2AZ, U.K.

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja211861m

Publication Date (Web): February 28, 2012

O-Mannosyl glycans are known to play an important role in regulating the function of α-dystroglycan (α-DG), as defective glycosylation is associated with various phenotypes of congenital muscular dystrophy. Despite the well-established biological significance of these glycans, questions regarding their precise molecular function remain unanswered. Further biological investigation will require synthetic methods for the generation of pure samples of homogeneous glycopeptides with diverse sequences. Here we describe the first total syntheses of glycopeptides containing the tetrasaccharide NeuNAcα2-3Galβ1-4GlcNAcβ1-2Manα, which is reported to be the most abundant O-mannosyl glycan on α-DG. Our approach is based on biomimetic stepwise assembly from the reducing end and also gives access to the naturally occurring mono-, di-, and trisaccharide substructures. In addition to the total synthesis, we have developed a “one-pot” enzymatic cascade leading to the rapid synthesis of the target tetrasaccharide. Finally, solid-phase synthesis of the desired glycopeptides directly on a gold microarray platform is described.

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