Surface Modifications and Applications of Organic & Inorganic Surfaces

1. Surface Modifications and Applications of Organic & Inorganic Surfaces Hyuk Yu (yu@chem.wisc.edu) Department of Chemistry University of Wisconsin Madison, WI 53706-1396 LSU Chemistry Colloquium Baton Rouge, LA March 5, 2004

2. Goals Personal Perspective • Outline what appears to be pivotal in the fundamental knowledge base and corresponding applications of surfaces. • What we have learned. • What need to be learned. • What the future holds, in terms of biomedical • applications

3. Contributors & Collaborators • Principal Contributors: • Dong X. Lin, Seagate, Minneapolis • Abukar Wehelie, Intel, Houston • Zhihao Yang, Eastman Kodak, Rochester, NY • Sangwook Park, LG Chem, Korea • Jeffrey Galloway, Sandia National Labs. • Dr. Keiji Tanaka, Kyushu Univ., Japan • Dr. Xiqun Jiang, Nanjing Univ., China • Thorsteinn Adalsteinsson, MPI-Golum, Germany • Dr. Junwei Li, Chemistry, Lehigh University • Weiguo Cheng, in residence, to leave for NALCO

4. Contributors & Collaborators • Principal Collaborators: • Charles M. Strother, M.D., Radiology,U.W.- Madison & • Baylor College of Medicine, Houston • Richard Frayne, M.D., Ph.D., Radiology, U.W.- Madison& Univ. of Calgary • Orhan Unal, Medical Physics, U.W.-Madison • Frank Denes, C-PAM & Biological systems Engineering, U.W.-Madison

5. Starting Point • Liquid Surfaces: flat & smooth; facile dynamics to establish equi-chemical potential. • Amorphous Solid Surfaces: rough & irregular; dynamics-limited quasi-equilibrium; passivation required to make them smooth; In case of amorphous polymer surfaces, the passivation route is effective through glass transition

6. Water Surface: Air/Water Interface Flat and smooth Irving Langmuir, Science 1936,84, 379. “I plan to tell you of the behaviour of molecules and atoms that held at the surfaces of three-dimensional solids and liquids. . . . I will show you that we can have adsorbed films which really constitute two-dimensional gases, two-dimensional liquids and two-dimensional solids”

7. Historical Milestones Air/Water Interface Pliny the elder (Gaius Plinius Secundus), AD 23-79 : “that all sea water is made smooth by oil, and so divers sprinkle oil on their face because it calms the rough element and carries light down with them”; . . . Historia Naturalis. Benjamin Franklin:. . .where the waves began to form, and there the oil, though not more than a teaspoonful, produced an instant calm, . . . perhaps half an acre as smooth as a looking glass”; Phil. Trans. Roy. Soc.(1774), 64, 445. Lord Rayleigh: “The earlier part of Miss Pockels’ letter covers nearly the same ground as some of my own recent work, . . . , raising many important questions. I hope soon to find opportunity for repeating some of Miss Pockels’ experiment” Agnes Pockels: “MY LORD-Will you kindly excuse my venturing to trouble you with German letter on a scientific subject?. . .; Nature (1891) 43, 437. Irving Langmuir: “The constitution and fundamental properties of solids & liquids. II Liquids”; J. Am. Chem. Soc. (1917) 39, 1848.

8. Early examples of chemistry on A/W monolayer • In low surface pressure, i.e., in low surface density, permanganate solution oxidizes oleic acid monolayer through its double bond at C 9 position. • At high surface pressure, oleic acid monolayer is no longer oxidized, for its chain conformation gives rise to a hydrocarbon insulation layer of 10Å thick. • This is a clear chemical evidence for flatness of Air/Water interface in macroscopic length scales. • Alexander & Rideal, Proc. R. Soc. London 1937, A163, 70. Surface roughtness of A/W is 3.2Å by X-ray reflectometry Braslau et al., Phys. Rev. Lett. 1985, 54, 114. Braslau et al., Phys. Rev. A 1988, 38, 2457.

9. Changes on Polar Groups Covered Hydrocarbon Polymer (PE, PP PS) Surfaces

10. Time dependent aging of oxygen plasma treated the polymer surfaces • Lower pressures, 100-250 mT:O2+ etching & functionalization of electron deposited surfaces. • Higher pressures, 500-700 mT: oxygen atom etching & functionalization of almost neutral surfaces • Oxygen containing groups, e.g., carbonyl, carboxyl, alcohol, etc. remain on the surfaces. • Water contact angle comes almost to zero. • It changes significantly within a few days upon aging in wet atmosphere, 18-95% relative humidity.

11. Aging Time Dependence of Water Contact Angle Oxygen plasma treated, aged in 18% RH

12. Functional group translocation hypothesis Oxygen plasma generated hydrophilic surface functional groups, will likely migrate into the polymer interior driven by surface energy.

13. Surface topography of PS film prior to the plasma treatment

14. Surface topography of PS film, treated by O2 plasma at 100mT, 40W, 1min

15. Surface roughness of PS films Film roughness in a spatial range of 2 m does not change with time, hence it is unlikely to be responsible for the contact angle changes.

16. The relative concentrations of different carbon binding states in O2 plasma treated PS surface vs. aging time Plasma: 100 mT, 40W, 1min; aged in 18% RH; 45˚ takeoff angle

17. SFG vibrational spectra of PS surface with & without oxygen plasma treatments

18. SFG vibrational spectra of the plasma treated PS surface at different aging times

19. Reorientation of Polar Functional Groups on PS Surface aged in air

20. Summary • The water contact angle of the plasma modified PS surface increases markedly within two days of storage in air under 18-95% RH. • Surface roughness can be ruled out as the main cause for the change of water contact angle. • The depth profile of oxygen is essentially unaffected by aging as deduced from XPS measurements, indicating that reorganization of chain segments is confined in a layer thinner than the probing depth of XPS (3 nm). • Sum frequency generation (SFG) spectral changes with time provide direct support for the reactions in plasma treatment involving aromatic ring opening, followed by the formation of oxygen contained polar groups as side chains. • When the treated surfaces are aged in air at different RH, the intensity of CH2 vibration increases with time, while that of CH3 vibration decreases, indicating that the side chains with polar functional groups reorient toward the polymer interior, while the PS surface is covered mostly by polymer backbone. The final surfaces are not those of untreated PS.

21. Conversion of Inorganic Surfaces to Functional Biomembrane Mimetic Surfaces

22. Monolayers to Mimic Biomembrane Bilayers

23. Biomembrane Mimetic Surface Modification of Silica Substrates Preserving Functionality of Membrane Proteins self-assembled on Phospholipid Monolayers? • Advantages for using solid substrates: • Stable and Robust • Very large surface area (>300 cm2/g)

24. Biomembrane Mimetic Surfaces • Lipase on/in phospholipid self-assembled monolayers (SAMs) • Monolayer structure and dynamics • Diffusion of lipase in phospholipid SAMs • Lipase activity on/in phospholipid SAMs

25. Preparation of Phospholipid SAMs on Silica

26. Self-Assembling of Phosphoipids on Native Oxide of Si Wafer loading the immobilized lipid monolayer with free lipids(DLPC/NBD-PE)

27. Lateral Diffusion of a Probe (NBD-PE) in lipid SAMs D=1.9±0.4x10-9 cm2/s (at 22°C) • References: • In transfered lipid bilayers, D=1~4x10-8 cm2/s at 30°C (M. Stelzle, R. Miechlich, E. Sackman, Biophys. J. 1992, 63, 1346.) • In DMPC liposomes, D=2x10-10 cm2/s at 22.5°C(A. B. Smith, H. M. McConnell, Proc. Natl. Acad. Sci. 1978, 75, 2759)

28. Fluorescent dye labeling of lipase

29. Lateral Diffusion of Lipase on Phospholipid SAMs D=2.7±0.4x10-10 cm2/s

30. Hydrolysis Reaction of Umbelliferone Esters

31. Hydrolysis of Umbelliferone Stearate by Lipase at Phospholipid SAM on Silica Gel

32. Experimental Test of Interfacial Activation of Lipase by the Lipid SAMs • UMB esters were loaded to the monolayer in CHCl3/MeOH • Hydrolysis condition: in 0.1M phosphate buffer, pH=7.0, 23°C • 1 mL of Pseudomonas sp. lipase solution (ca.. 0.4 mg/mL) was added to hydrolyze the UMB substrate. • The fluorescence of elute was monitored.

34. Summary • A phospholipid monolayer on silica substrates (SiO2/Si) is constructed through a novel method, by a self-assembling process. • Such a monolayer is highly stable and structurally mimicks biomembranes. • The partially localized phospholipid SAMs show the dynamic properties (e.g. diffusion) close to those of biomembranes. • A biomembrane enzyme, lipase, localized to the monolayers are protected from denaturation. • Interfacial activation of lipase by the lipid SAMs is observed, indicating the viability of the monolayers as the biomembrane mimetic.

35. Endovascular biomedical applications

36. Hydrazine Plasma Functionalization of PE Surface

37. DTPA[Gd(III)] Complex & Water

38. Gd3+ has 7 unpaired 4f electrons, hence T1 of proton NMR of inner-sphere water is much shorter than bulk water.

39. Contrast Agent N O O/H2O Gd3+ DTPA C X-ray structure of Gd DTPA(H2O)2-, top view(hydrogen atoms are omitted) R: rotational correlation time of the chelate kex: water/proton exchange rate

40. Imaging Mechanism • Interplay between the rotational mobility of ligand and the exchange rate of inner sphere water; • Caravan et al., Chem. Rev. 1999, 99, 2293-2352. • Difference exists for the imageability between spatially confined DTPA[Gd(III)] within a thin slab from a surface and that spatially dispersed in bulk.

41. Scan Parameters 2D SPGR TR = 18 ms, TE = 4.1 ms, Flip angle = 30º Acquisition Matrix = 256 X 256 PE Slice thickness = 2-3 mm FOV = 16 cm X 16 cm and RBW = ± 32 kHz 2D SE TR = 300 ms, TE = 9.0 ms, Flip angle = 30º Acquisition Matrix = 256 X 256 PE Slice thickness = 2-3 mm FOV = 16 cm X 16 cm and RBW = ± 32 kHz 1.5 T GE CV Scanner (40mT/m, 150 mT/m/ms)

42. Agarose Gel Encapsulation of Functionalized PE Rods

43. MRI of Gel Encapsulated of PE Rods(soaked for 1 hour)

44. MRI of Gel Encapsulated of PE Rods(soaked for 10 hours)

45. Design III 6F Cath filled with 4% Gd III/5 after 30min

46. Catheter filled with Gd(III) solution

47. Catheter coated with encapsulated DTPA-Gd3+ covalently linked

48. Summary Working Hypothesis: For artificial surfaces to be biomembrane mimetic, (structurally and functionally), they must manifest all the equilibrium and dynamics of at least monolayers of phospholipids. MRI of endovascular medical devices, catheters & guide wires: For diagnostic and interventional endovascular devices to be magnetically imageable, contrast agent functionalization on the surfaces with thin-layer hydrogel encapsulation suffices.

49. Conversion of Gold Surface to Viable Biomembrane Mimetic Surface

50. Chemistry of SAMs on Gold Surface