Electronic Supplementary Material (ESM)
Surface and self-organization of Sodium salt of 2-decyl pyridine-5-boronic acid and Sodium salt of 2-oxydecyl pyridine-5-boronic acid at two different pHs
Monali Maiti, Aparna Roy and Sumita Roy*
E-mail:
Department of Chemistry and Chemical Technology, Vidyasagar University,
Paschim Medinipur-721 102, India
Fig. S1 LC-Ms of 2-Decyl pyridine-5-boronic acid.
Fig. S2 1H NMR spectra of 2-Decyl pyridine-5-boronic acid.
2-Decyl pyridine-5-boronic acid: Yield (1.95 g, 51 %.), 1H NMR (400 MHz, DMSO-d6): δH 0.83-0.86 (t, J =5.84 Hz, 3H, CH3), 1.23-1.28 (m, 15H), 1.72 (m, 2H), 2.99-3.03 (t, J =7.56 Hz, 2H), 7.93-7.95 (d, J =8.0 Hz, 1H) 8.71-8.79 (dd, J =7.96 Hz, 6.68 Hz, 1H), 8.93 (s, 2H). MS (ESI+) for C15H26NO2B m/z 262 (M+H) +.
Fig. S3 LC-Ms of 2-Oxydecyl pyridine-5-boronic acid.
Fig. S4 1H NMR spectra of 2-Oxydecyl pyridine-5-boronic acid.
2-Oxydodecyl pyridine-5-boronic acid: Yield (4.78 g, 78 %.) 1H NMR (400 MHz, DMSO-d6): dH 0.86-0.88 (t, J = 6.44 Hz, 3 H), 1.11-1.28 (m, 14 H), 1.37-1.40 (m, 2 H), 1.70-1.77 (m, 2 H), 4.10-4.23( m, 2 H), 6.61-6.63 (d, J = 8.76 Hz, 1 H), 7.59-7.62 (dd, J = 3.24 Hz, 6.28 Hz, 1H), 8.15-8.16 (d, J = 2.40 Hz, 1 H). MS (ESI+) for C15H26NO3B m/z 280.2 (M+H) +.
Materials and Methods
General: 2,5-Dibromopyridine, 1-Iododecane, 5-Bromo-2-oxypyridine, Pyrene, DPH, Silver carbonate, Uranyl acetate, n-Butyllithium, Triisopropyl borate, 1-Bromodecane, Magnesium sulphate, Zinc chloride, Mg turnings and Pd(PPh3)4 were purchased from Aldrich Chemicals. Pyrene and DPH were used after recrystallization from ethanol. Other chemicals were procured locally and used as they were obtained. All organic solvents, Potassium chloride, Sodium hydroxide, Sodium bicarbonate, Borax, Fructose and Sucrose were purchased from Merck and the organic solvents were distilled and dried as required. Buffer solution of pH 9 was prepared by 0.025 M Borax and 0.1 M NaOH and pH 13 was made by 0.2 M KCl and 0.2 M NaOH. 1H NMR spectra were recorded using a Brucker 400 MHz instrument. LC-MS were taken in a Waters 2996 machine. The pH measurements were performed with a digital pH meter, Model pH L1613 (ELICO), using a glass electrode.
Solubility Test and Preparation of Aggregates: The amphiphiles are insoluble in water (pH 6.9) at room temperature (~30 oC) as the 3- pyridylboronic acid has two pKa values; pK1 ~ 4.0 and pK2 ~ 8.2. At first two buffer solutions of alkaline pH (9 and 13) was tried to dissolve the amphiphiles. But, it was still insoluble. After this we tried to dissolve the amphiphile by addition of carbohydrate (sucrose) at pH 13, the obtained pKa was11.97 for SDPB and 12.02 for SODPB in presence of 12 mM sucrose and the surfactants were soluble to give the stable clear solutions. However, the literatures demonstrate that sucrose is weaker binder and fructose is stronger binder of single chain boronic acid amphiphiles [1, 2]. Hence fructose was examined as a binder and it was found that 0.5 M fructose (pKa= 8.24 for SDPB and 8.58 for SODPB) was able to make the aggregate solutions stable at 30 °C. Therefore, a weighed amount of amphiphile was dissolved in a certain amount of buffer solution of pH 9 containing 0.5 M fructose / pH 13 containing 12 mM sucrose and shaken by hand to form homogeneous mixture at 30 °C. The mixtures were left to afford different types of aggregates as evidenced from transmission electron microscopy.
Surface Tension Measurement: Surface tension measurement was carried out with a Surface tensiometer (manual) using the Du Nuoy ring detachment method. Before each experiment, the platinum-iridium ring was thoroughly cleaned with ethanol-HCl solution and burnt in oxidizing flame by use of a Bunsen burner. The instrument was calibrated and accuracy was checked by measuring the surface tension of the triply distilled water. For surface tension measurement, a stock solution of SDPB and SODPB of the required concentrations were prepared and the surface tension (γ) was measured at different concentrations by adding a subsequent volume of stock solution to a beaker containing known volume of buffer solution of pH 9 containing fructose and buffer solution of pH 13 containing sucrose until the value almost reached saturation. For each concentration, the solution was equilibrated for 5 minutes and the average of three readings was taken. The CAC was then obtained from the break point of the plot of γ versus log C.
Fluorescence Measurements: The steady-state fluorescence spectra of the pyrene probe (~2×10-7 M) were measured on a HITACHI F-7000 spectrophotometer optical system equipped with a 150W Xe Lamp. A saturated solution of pyrene was prepared in buffer solutions containing different carbohydrates. A weighed amount of amphiphiles were then added to the saturated pyrene solutions. The samples were excited at 335 nm, and the emission spectrum was recorded between 350-550 nm with excitation and emission slit widths were both set at 1 nm. Each spectrum was blank subtracted and was corrected for lamp intensity variation during measurement. Steady-state fluorescence anisotropy (r) of DPH was obtained in the same instrument equipped with filter polarizers that uses L format configuration. DPH was excited at 350 nm and the fluorescence intensity was measured at 450 nm with band-pass 2.5 nm and 5 nm, respectively. Fluorescence anisotropy value was calculated by the given equation
r = (I║ - GI┴)/ (I║ + 2GI┴) (1)
where I║ and I┴ are the fluorescence intensities polarized parallel ( Ex. and Em. Polarisers at 0°) and perpendicular (Ex. Pol. at 0° and Em. Pol. at 90°) to the excitation light. G is the instrumentation correction factor (G = i90-0 / i90-90).
For anisotropy measurements a 2 mM solution of the probe was prepared in 20% methanol-water mixture. The final concentration of the probe was adjusted to 2 µM by addition of appropriate amount of stock solution.
DLS studies: The size of the aggregates was determined from DLS measurement by using a Zetasizer Nano S90 (Model No: ZEN 1690) Particle size analyzer (Malvern Instruments Ltd., UK) equipped with an He-Ne laser operated at 4 mW at l = 633 nm having a detection angle of 900. For DLS measurements, the respective buffer solutions of pH 9 and pH 13 of the amphiphiles were prepared in triply distilled water. The solution was filtered directly into the scattering cell through a Whatman syringe filter (sterile and endotoxin free, 0.45µm). Before measurement, the scattering cell was rinsed with the filtered solution and the sample solution was equilibrated for 15 minutes in the DLS optical system at 30 °C. The data acquisition was carried out for 10 minutes. Zeta (ζ) potential measurements were employed a Zetasizer Nano ZS90 (Model No: ZEN 3690, Malvern Instrument Lab., Malvern, U.K.) light scattering spectrometer equipped with a He-Ne laser working at 4 mW (λ = 633 nm).
XRD Measurements: A self-supported cast film for the X-ray diffraction study was prepared by dispersing the amphiphiles in respective buffer solutions containing fructose and sucrose. Few drops of this suspension were dispersed on a pre-cleaned glass plate and dried. Finally it was kept under vacuum for 48 h. The experiment was performed on a Pan analytica X′Pert pro X–Ray diffractometer using a Cu target (Cu Kα) and Ni filter at a scanning rate of 0.001s-1 between 2° to 12°, operating at a voltage of 40 kV and current 30 mA.
Transmission Electron Microscopy studies: Transmission electron microscopic measurements of the amphiphiles in two different buffer solutions were performed with a high-resolution transmission electron microscope (JEOL-JEM 2100, Japan) operating at 200 KeV. For all the cases the surfactant solutions were filtered by use of Whatman syringe filter (sterile and endotoxin free, 0.45µm). A drop of the amphiphile solution was put on a copper grid coated with carbon and allowed soaking 1-2 minutes; the surface solvent on the grid was removed by tapping in a filter paper followed by staining with 1.5% aqueous Uranyl acetate solution. The specimens were then dried in desiccators until before measurement.
Fig. S5 XRD pattern of the cast flim obtained from SODPB at (A) pH 9 containing fructose and (B) pH 13 containing sucrose.
Fig. S6 XRD pattern of the cast flim obtained from SDPB at pH 13 containing sucrose.
Fig. S7 XRD pattern of the cast flim obtained from SDPB at pH 9 containing fructose.
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