Chemical Transformations in Individual Ultrasmall Biomimetic Containers

Author:

Chiu Daniel T.1,Wilson Clyde F.1,Ryttsén Frida2,Strömberg Anette2,Farre Cecilia2,Karlsson Anders2,Nordholm Sture2,Gaggar Anuj1,Modi Biren P.1,Moscho Alexander1,Garza-López Roberto A.3,Orwar Owe2,Zare Richard N.1

Affiliation:

1. Department of Chemistry, Stanford University, Stanford, CA 94305, USA.

2. Department of Chemistry, Göteborg University, Göteborg, SE-41296, Sweden.

3. Department of Chemistry, Pomona College, Claremont, CA 91711, USA.

Abstract

Individual phospholipid vesicles, 1 to 5 micrometers in diameter, containing a single reagent or a complete reaction system, were immobilized with an infrared laser optical trap or by adhesion to modified borosilicate glass surfaces. Chemical transformations were initiated either by electroporation or by electrofusion, in each case through application of a short (10-microsecond), intense (20 to 50 kilovolts per centimeter) electric pulse delivered across ultramicroelectrodes. Product formation was monitored by far-field laser fluorescence microscopy. The ultrasmall characteristic of this reaction volume led to rapid diffusional mixing that permits the study of fast chemical kinetics. This technique is also well suited for the study of reaction dynamics of biological molecules within lipid-enclosed nanoenvironments that mimic cell membranes.

Publisher

American Association for the Advancement of Science (AAAS)

Subject

Multidisciplinary

Reference34 articles.

1. We used a Brownian dynamics simulation program in which we treated a single enzyme and a single substrate as hard spheres. The radius of each molecule was estimated from the Stokes–Einstein law as described [

2. Ermak D. L., J. Chem. Phys. 62, 4189 (1975);

3. ]. The diffusion constants for the molecules were modeled by changing the time steps taken by the molecules and the constant velocities given to them. The trajectories were followed and the diffusion constants were calculated as described [

4. Turq P., Lantalme F., Friedman H. L., J. Chem. Phys. 66, 3039 (1977);

5. ]. We used D (enzyme) = 7 × 10 −11 m 2 s −1 and D (substrate) = 4.4 × 10 −10 m 2 s −1 . This model was later used to obtain an estimate of the number of collisions between enzyme and substrate and also between the different molecules and the phospholipid wall which was treated as a hard wall. Substrate-wall collisions scale as 1/ r and substrate-enzyme collisions scale as 1/ r 3 where r is the vesicle radius.

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