Spectroscopic observation of the formyl cation in a condensed phase

Science

Volumn 276, Issue 5313, 1997, Pages 776-779

  De Rege, Peter J F ^a   Gladysz, John A ^b   Horváth, István T ^a  

^a EXXONMOBIL UPSTREAM RESEARCH COMPANY   (United States)

^b UNIVERSITY OF UTAH   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

CARBON MONOXIDE; CHEMISTRY; INFRARED SPECTROSCOPY; NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY; PHASE EQUILIBRIA; PRESSURE EFFECTS; SOLUTIONS; SPECTROSCOPIC ANALYSIS;

FORMYL CATION;

IONS;

CARBON MONOXIDE; CARBONIC ACID; CATION; FORMYLPEPTIDE;

ARTICLE; CHEMICAL REACTION; INFRARED SPECTROSCOPY; NUCLEAR MAGNETIC RESONANCE; PRIORITY JOURNAL; PROTON TRANSPORT;

EID: 0031547982     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.276.5313.776     Document Type: Article

References (21)

1. S. P. A. Fodor et al., Science 251, 767 (1991).
2. C. S. Dulcey et al., ibid. 252, 551 (1991).
3. D. A. Stenger et al., J. Am. Chem. Soc. 114, 8435 (1992).
4. R. Singhvi et al., Science 264, 696 (1994).
5. S. A. Sundberg et al., J. Am. Chem. Soc. 117, 12050 (1995).
6. L. M. Tender, R. L. Worley, H. Fan, G. P. Lopez, Langmuir 12, 5515 (1996).
7. M. Mrksich et al., Proc. Natl. Acad. Sci. U.S.A. 93, 10775 (1996).
8. E. Kim, Y. Xia, G. M. Whitesides, Nature 376, 581 (1995).
9. _, J. Am. Chem. Soc. 118, 5722 (1996).
10. The PDMS mold is formed by curing its prepolymer (Sylgard 184, Dow Corning) on a fluorinated master having a negative pattern of the μFN formed in photoresist (Hoechst 6612, 1.5 μm thick) on its surface [Y. Xia et al., Science 273, 347 (1996)].
11. 2 (oxygen pressure ≈ 0.8 torr, load coil power ≈ 200 W; Technics Plasma, Florence, KY) for 15 s to render the μFN hydrophilic, although many other conditions of reaction are possible, including wet chemical oxidation of the surface.
12. We found that capillaries remained effectively isolated from each other for long periods of time (>1 hour) except in the case where both the surface and the μFN had contact angles for the fluid of ∼10° or less. In that case, the capillary force at the point of contact between the PDMS and substrate is high and evidently disrupts conformal contact between them. Wherever we encountered this problem, we used selective oxidation of the μFN, an oxidation confined to its interior walls, to keep the liquid pinned in the capillaries (E. Delamarche, H. Schmid, B. Michel, H. Biebuyck, A. Bernard, unpublished data).
13. 3, Pierce) to promote the adhesion of the IgGs to the surface by amide bond formation. Alternatively, the self-assembly of a monolayer of an alkyl disulfide terminated by N-hydroxysuccinimide esters on Au provided an equivalent type of activated surface. In either case, coupling of the IgGs to the surface proceeded in the μFN for 1 hour with the use of a 1 mg/ml solution of IgG [chicken polyclonal IgG (Sigma) or mouse monoclonal IgG prepared at the University of Zürich, clone X7B3] in acetate buffer. Conditions for coupling were controlled by monitoring the amount of deposited IgG with an ellipsometer or an optical grating coupler with nonpattemed samples. After coupling, the μFN was carefully removed from the substrate under a flow of phosphate-buffered saline (PBS, ∼10 ml) to prevent spreading of IgGs from their channels into adjacent channels or other parts of the surface. The patterned substrate was rinsed three times with 1 ml of PBS, three times with 1 ml of 0.5% Tween 20 in PBS, and three times with 1 ml of deionized water and finally dried. Regions of the surface outside the μFN (and therefore free of IgGs), or regions only partially derivatized by IgGs, were blocked by their exposure to a 1% solution of BSA in PBS for 1 hour to prepare the sample for immunoassays.
14. E. Delamarche et al., Langmuir 12, 1997 (1996).
15. A. Bernard and H. R. Bosshard, Eur. J. Biochem. 230, 416 (1995).
16. Generally, blockage of capillaries occurred in our experiments because of occlusion by dust particles, inherent structural instability of the elastomeric channels (E. Delamarche et al., Adv. Mater., in press), or variability in the wetting of the surface. Typically, these effects became noticeable when the dimensions of the capillaries approached 1 μm.
17. We noticed a complete absence of deposited IgGs, as measured by SEM or fluorescence from a tagged IgG, in micrometer-sized capillaries only 50 μm downstream from the filling pad when concentrated solutions of IgG (∼1 mg/ml) filled, but did not flow through, these capillaries. This result emphasizes the competition between flow through the network, adsorption at interfaces, and the poor recovery of concentration of proteins by their diffusion from the bulk reservoir into narrow capillaries. Thus, simple filling is usually not adequate for efficient chemical reaction with dilute solutions in μFNs.
18. J. M. Harris, Poly(Ethylene Glycol)Chemistry: Biotechnical and Biochemical Applications (Plenum, New York, 1992).
19. PDMS treated in our plasma had a useful lifetime of ∼15 min in air before reconstruction of the surface made the interface hydrophobic again. Storing the treated PDMS under water maintained its hydrophilicity for >1 week. The surface tension of the buffer could also be lowered by adding ethanol (up to 5% of the buffer solution by volume); this step markedly improved the flow of buffer through the capillary network without noticeably affecting the attachment of the IgGs we used or their recognition by antispecies IgGs.
20. G. P. López, H. A. Biebuyck, R. Härter, A. Kumar, G. M. Whitesides, J. Am. Chem. Soc. 115, 10774 (1993).
21. A.B. was supported by the Swiss National Science Foundation NFP36 project. We thank H. Rothuizen for help in designing the fluidic network, B. Kunz for help with the fluorescence microscope and for supplying mouse monoclonal antibodies, and P. Guéret and H. R. Bosshard for their support.