Nanostructured surfaces by supramolecular self-assembly of linear oligosilsesquioxanes with biocompatible side groups

Linear oligomeric silsesquioxanes with polar side moieties (e.g., carboxylic groups and derivatives of N-acetylcysteine, cysteine hydrochloride or glutathione) can form specific, self-assembled nanostructures when deposited on mica by dip coating. The mechanism of adsorption is based on molecule-to-substrate interactions between carboxylic groups and mica. Intermolecular cross-linking by hydrogen bonds was also observed due to the donor–acceptor character of the functional groups. The texture of supramolecular nanostructures formed by the studied materials on mica was analysed with atomic force microscopy and their specific surface energy was estimated by contact angle measurements. Significant differences in the surface roughness, thickness and the arrangement of macromolecules were noted depending on the kind of functional groups on the side chains. Specific changes in the morphology of the surface layer were observed when mica was primed with a monolayer of small organic compounds (e.g., N-acetylcysteine, citric acid, thioglycolic or acid). The adsorption of both silsesquioxane oligomers and organic primers was confirmed with attenuated total reflectance infrared spectroscopy. The observed physiochemical and textural variations in the adsorbed materials correlate with the differences in the chemical structure of the applied oligomers and primers.


Analytical methods
Liquid state NMR ( 1 H, 13 C and 29 Si NMR) spectra for the precursors and condensed soluble materials were recorded in CDCl 3 or THF-d 8 as a solvent on a Bruker DRX-500 MHz spectrometer, with TMS as the reference. Solid-state 13 C and 29 Si CPMAS NMR spectra were recorded with high power decoupling (HP Dec) mode on an AV-400 Bruker spectrometer at 59.627 MHz. The peak positions were referenced to the signal of Q 8 M 8 (trimethylsilyl ester of cubic octameric silicate) as standard.
Mass spectrometry measurements (MALDI-TOF) were performed for LPSQ-Vi using a Voyager-Elite (PerSeptive Biosystems, USA) time-of-flight instrument equipped with a pulsed N 2 laser (337 nm, 4 ns pulse width) and timedelayed extraction ion source. An accelerating voltage of 20 kV was applied. Mass spectra were recorded in the linear positive ion mode using 1,8-dihydroxy-9-anthracenone (ditranol, DT) as the matrix and LiCl as the cationization agent.
Dichloromethane was used as mobile phase at the flow rate of 0.8 mL/min. Molecular masses were derived from a S3 calibration curve based on polystyrene standards. Phase transitions of polymers were studied by differential scanning calorimetry (DSC) technique (DuPont 2000 thermal analysis system).
Fourier transform infrared spectra were collected on a Nicolet 6700 spectrometer. The technique of attenuated total reflectance (ATR) was applied for IR measurements, using germanium crystal attachment together with the mercury cadmium telluride detector (MCTD). The spectra were obtained by adding 64 scans at a resolution of 2 cm −1 .

Surface characterization
Atomic Force Microscopy (AFM) images were recorded under ambient atmosphere using Nanoscope IIIa, MultiMode microscope (Veeco, Santa Barbara, CA). The analysis (tapping mode) was carried out at room temperature (unless otherwise indicated). The probes were commercially available rectangular silicon cantilevers (RTESP from Veeco) with nominal radius of curvature in the 10 nm range, spring constant 20-80 N m -1 , and a resonance frequency lying in the 264-369 kHz. The images were recorded with the highest available sampling resolution, that is, 512 x 512 data points. The applied eight ranges are −5 nm ÷ 5 nm, the offset of phase images is 15°. Rq can be defined as the standard deviation of the Z-values within the box cursor and is calculated using Equation S1 where Z i is the current Z-value, and N is the number of points within the box cursor. Rq is very sensitive to height deviations (peaks and valleys) in surface roughness profile due to the squaring of the values of amplitude in its calculation. The scan size of the analysed areas can be found in Table S1 and Figures S1-5 (the baseline was set automatically for the height level 0).
Contact-angle measurements: static contact angles of sessile droplets of deionized water and glycerol (Chempur, pure p.a., anhydrous) at the film-air interface were measured at room temperature with a Rame-Hart NRL contactangle goniometer equipped with a video camera JVC KYF 70B and drop-shape analysis software. The measurements were performed on untreated bare mica, mica coated with small organic primers, native and primed mica coated with PSAMs. Static, advancing, and receding contact angles were measured right after the deposition of the liquid onto the film surface. The values of contact angles (standard deviation estimated) are an average of at least three measurements taken on different areas of the same sample. They are reported for a short contact time, strictly S4 observed to diminish the effect of surface accommodation. Surface energies were estimated by the Owens-Wendt method using the values of advancing angles [Owens, D. K.; Wendt, R. C. J. Appl. Polym. Sci., 1969, 13, 1741-1747. MALDI-TOF mass spectrometry was used as a method for the determination of the structure of LPSQ-Vi. Linear oligomers with chain ends terminated with trimethylsilyl groups were detected. S5 13 С NMR (CD 3 OD), δ [ppm]: -0.5 (OSiMe 3 ); 11.4 (SiCH 2 ); 25.3 (CH 2 S); 31.6 (SCH 2 ); 170.9 (C=O) 29 Si NMR (CD 3 OD); δ [ppm]: -70 (-CH 2 -SiO 3/2 ); 11 (OSiMe 3 )

Synthesis of copolymeric derivatives of cysteine hydrochloride and thioglycolic acid (P2): the oligomers were
prepared by UV initiated thiol-ene addition of cysteine hydrochloride followed by addition of thioglycolic acid to LPSQ-Vi. DMPA (0.031 mmol) was added to a solution of cysteine hydrochloride (0.38 mmol) and LPSQ-Vi (0.15 g, 1.9 mmol Vi groups) in dry DMF (19 mL), placed in a quartz vessel. The mixture was irradiated for 45 min with UV light (350 nm). Volatiles were then removed under reduced pressure and the residue was dissolved in MeOH (18 mL) and placed in another quartz vessel. Thioglycolic acid (0.14 g, 1.52 mmol) and DMPA (10 mg) were added and the mixture was irradiated for 30 min with UV light. Volatiles were then removed under reduced pressure and the residue was dissolved in MeOH and precipitated into hexanes. The purification procedure was repeated thrice. The precipitate was dried under high vacuum at room temperature to a constant weight. A solid polymer was obtained (0.34 g, Y = 97%). Thioglycolic acid (0.07 g, 0.76 mmol) and DMPA (28 mg) were added and the mixture was irradiated for 45 min with UV light. Volatiles were then removed under reduced pressure and the residue was dissolved in THF and precipitated into hexanes. The purification procedure was repeated thrice. The precipitate was dried under high vacuum at room temperature to a constant weight. A solid polymer was obtained (0.20 g, Y = 98%

S7
Preparation of thin polysilsesquioxane films on solid supports: polymers (P1, P2, P3, P4) were dissolved in dry solvents (P1, P3, P4 in THF, P2 in methanol) at 0.04 wt % concentration. The solutions were filtered through 0.2 mm PTFE filters and placed in separate vessels. Dip coating was carried out at room temperature by the immersion of a freshly cleaved or primed muscovite mica support in the polymer solution for 5 s. All supports were mounted and moved vertically with a motorized linear slide (Zaber Technologies Inc.) (rate of immersion/extraction = 4 mm/s). The volume of liquid and the immersion level were constant. Dip-coated supports were then placed in a closed container and left for drying at room temperature for one day. Their surface was analyzed with AFM (tapping mode). Surface energy of all samples was estimated by contact angle measurements using water and glycerol as probe liquids.