Vesicles, fibres, films and crystals: A low-molecular-weight-gelator [Au(6-thioguanosine)2]Cl which exhibits a co-operative anion-induced transition from vesicles to a fibrous metallo-hydrogel

We describe a simple coordination compound of Au(i) and 6-thioguanosine, [Au(6-tGH)2]Cl, that has a rich self-assembly chemistry. In aqueous solution, the discrete complex assembles into a supramolecular fibre and forms a luminescent hydrogel at concentrations above about 1 mM. Below this concentration, the macromolecular structure is a vesicle. Through appropriate control of the solvent polarity, the gel can be turned into a lamellar film or crystallised. The molecular structure of [Au(6-tGH)2]Cl was determined using single crystal X-ray diffraction, which showed bis-6-thioguanosine linearly coordinated through the thione moiety to a central Au(i) ion. In the vesicles, the photoluminescence spectrum shows a broad, weak band at 550 nm owing to aurophilic interactions. Co-operative self-assembly from vesicle to fibre is made possible through halogen hydrogen bonding interactions and the aurophilic interactions are lost, resulting in a strong photoluminescence band at 490 nm with vibronic structure typical of an intraligand transition. The vesicle-fibre transition is also revealed by a large increase of ellipticity in the circular dichroism spectrum with a prominent peak near 390 nm owing to the helical structure of the fibres. Atomic force microscopy shows that at the same time as fibres form, the sample gels. Imaging near the vesicle-fibre transition shows that the fibres form between vesicles and a mechanism for the transition based on vesicle collisions is proposed.


Vesicles
Figure S3 -additional AFM images of fibres forming between vesicles.Figure S20 -1 H NMR COSY spectrum at 363 K with correlations due to protons on 2,2'sulfinyldiethanol indicated.

Au-S bond lengths for coordinated thione and thiolate ligands
Literature structural data on C-S bond lengths          After a few days (acetone) or a few weeks (isopropanol) crystals start to form (grey dots) in the gel.The silicon can then be removed and analyzed using AFM to observe the crystal growth.The remaining crystals can be left to grow and then analyzed using XRD.
On searching the CCDC for similar structures with linear coordination of sulfur to gold there are 99 hits.
Of these 47 have been assigned to thione C=S  Of the 47 which have been assigned to the thione forms, the range of bond lengths is 1.653-1.779 Å h a mean bond length of 1.721 Å.

Figure S2 -
Figure S2 -comparison of PXRD of a polycrystalline sample of [Au(6-tGH)2]Cl with the powder pattern computed from the single crystal XRD structure.

Figure
Figure S4 -electron micrographs of the xerogel formed from 6 mM gels.

Figure
Figure S5 -electron micrographs of the xerogel after addition of acetone.

Figure S6 -
Figure S6 -Powder X-ray diffraction data for the xerogel.

Figure S7 -
Figure S7 -Powder X-ray diffraction data for crystals made by addition of isopropanol.

Figure S8 -
Figure S8 -Schematic of the relevant crystal planes.

Figure S10 -
Figure S10 -Schematic of the vapour diffusion method for crystallization from the xerogel.

Figure S11 -
Figure S11 -AFM images of crystals forming after vapour in-diffusion of acetone.

Figure S13 -
Figure S13 -Inversion test and heating / cooling of the gel.

Figure S15 -
Figure S15 -Temperature-dependent 1 H NMR spectra of the gel.

Figure S16 - 1 H
Figure S16 -1 H NMR spectrum at 363 K with proton assignments to the molecule.

Figure S23 -
Figure S23 -Schematic model of the vesicles.

Figure S24 -
Figure S24 -Calculated and experimental CD spectra.

Figure S26 -
Figure S26 -Luminescence decay curves below and above the minimum gelation concentration.

Figure S28 -
Figure S28 -Rheological data for the chloride anion effect.

Figure S3 :
Figure S3: Two in situ AFM images at 1 mM of [Au(6-tGH)2]Cl showing the vesicles (bright spots), fibres and the molecular strands forming between vesicles (examples indicated by red arrows in image (b)).

Figure S5 :
Figure S5: SEM images of films of [Au(6-tGH)2]Cl made by addition of an equal volume of acetone to a 10 mM gel.Lamellae and crystals are observed.

Figure S6 :
Figure S6: (a) PXRD of c = 10 mM [Au(6-tGH)2]Cl xerogels.(1) Xerogel before freeze drying; (2) after freeze drying; (3) further drying under vacuum for one week and (4) after drying under vacuum for two weeks.(b) The xerogel made by freeze drying and two weeks of vacuum drying (black line) compared to PXRD for the oxidation product of the reducing agent used to prepare Au(I); 2,2-sulfinyldiethanol.The three most intense peaks from the 2,2-sulfinyldiethanol pattern are indicated by green arrows.

Figure S9 :
Figure S9: Olex2 images of the crystal structure of 1.(a) a view normal to the cb plane of the unit cell that shows the chain alignment in the crystal.(b) A view normal to the ac plane of the unit cell showing the chain stacking.

Figure S10 :
Figure S10: Vapor diffusion setup for crystallization of 1 on silicon chips.The blue antisolvent (acetone or isopropanol) diffuses slowly in to the inner vial where the gel (yellow) and the silicon (brown line) are.After a few days (acetone) or a few weeks (isopropanol) crystals start to form (grey dots) in the gel.The silicon can then be removed and analyzed using AFM to observe the crystal growth.The remaining crystals can be left to grow and then analyzed using XRD.

Figure S11 :
Figure S11: AFM images of c = 5 mM [Au(6-tGH)2]Cl on silicon.Acetone was vapour-diffused into the sample as the antisolvent.(a) individual fibres and rigid, needle-shaped crystals.(b) crystals (top left) forming on top of the gel, visible in the background as a dense network of fibres.

Figure S12 :
Figure S12: (a) Photographs showing the transformation from gel to crystals (left to right) during vapor diffusion of acetone into a 10 mM gel.(b) Optical micrograph of the crystals of 1 at 40x magnification.

Figure S13 :
Figure S13: Inversion test on a 4 mM aqueous sample of [Au(6-tGH)2]Cl: (a) before, (b) during, and (c) after heating.(a) Sample at room temperature in the gel state.(b) The sample heated to 100 o C and in the liquid state.(c) The sample after cooling for 48 h to room temperature.Gel has reformed.

Figure S16: 1 H
Figure S16: 1 H NMR of 4.5 mM sample of [Au(6-tGH)2]Cl in D2O recorded on a 500 MHz at 363 K with proton assignments to molecule.

Figure S17 :
Figure S17: COSY spectrum of 4.5 mM sample of [Au(6-tGH)2]Cl in D2O recorded on a 500 MHz instrument at 363 K with the correlations of sugar protons indicated.

Figure S19 :
Figure S19: (a) The four peaks from the oxidation product of the reducing agent (2,2'-sulfinyldiethanol), used to prepare Au(I), show prominently in the 1 H NMR of a 4.5 mM sample in D2O recorded on a 500 MHz at 298 K. (b) 1 H NMR of the reactant mixture from the first step of the coordination reaction in D2O recorded on a 500 MHz instrument: chloroauric acid (HAuCl4) and 2,2'-thiodiglycol.These form Au(I) and 2,2'-sulfinyldiethanol which can sometimes be crystallised under alternative crystallisation conditions.The four peaks from the oxidation product of the reducing agent, 2,2'-sulfinyldiethanol remain sharp at 298 K confirming that it is not part of the supramolecular structure of [Au(6-tGH)2]Cl, 1.

Figure S22 :
Figure S22: Excitation and emission spectra of 1 at 5 µM concentration.The excitation wavelength was λexc = 300 nm for the emission spectrum and the emission wavelength λem = 440 nm for the excitation spectrum.

Figure S23 :
Figure S23: Model of 1 monomers in the vesicle wall.The red areas indicate the hydrophilic sugar groups which form the wetted internal and external surfaces.The blue areas indicate the hydrophobic nucleobases and yellow indicates the Au ions.The alignment of the Au ions facilitates aurophilic interactions.

Figure S24 :
Figure S24: Calculated CD spectrum of monomeric [Au(6-tGH)2] + using the B3LYP functional and the 6-31G(d,p) basis set for the non-metallic atoms and the LanL2DZ basis set for Au (dashed black line).Experimental CD data for [Au(6-tGH)2]Cl just under the gel point at 1 mM (red line).

Figure S25 :
Figure S25: CD spectra at different temperatures.(a) 3 mM of [Au(6-tGH)2]Cl at room temperature, about 290K (blue line) and at 333 K (grey line).(b) ellipticity at 390 nm for samples at 2.5, 3.0 and 3.5 mM concentrations of aqueous [Au(6-tGH)2]Cl.(c) Heat-cool cycle for a 4 mM gel sample.The black line is the spectrum of the gel at 20 o C before heating, the red line shows the spectrum recorded at 70 o C and the blue line shows the spectrum after cooling to 20 o C for 8 h.

Figure S27 : 7 .Figure S28 :
Figure S27: (a) Circular dichroism spectra and (b) absorbance spectra of [Au(6-tGH)2]Cl gels at a concentration of 3 mM in isopropanol/water mixtures.The colour scale indicates the volume percentage of isopropanol.

Figure S29 :
Figure S29: Discrete particles of gel formed when NaCl is added to a dilute (0.1-0.2 mM) sample of [Au(6-tGH)2]Cl .Photograph taken under illumination by an Hg lamp.