Helical-Ribbon and Tape Formation of Lipid Packaged [Ru(bpy)3]2+ Complexes in Organic Media

Anionic lipid amphiphiles with [RuII(bpy)3]2+ complex have been prepared. The metal complexes have been found to form ribbon and tape structures depending on chemical structures of lipid amphiphiles. Especially, the composites showed hypochromic effect and induced circular dichroism in organic media, and flexibly and weakly supramolecular control of morphological and optical properties have been demonstrated.

We also investigated the aggregation of [Ru II (bpy) 3 ](lipid) 2 and its interaction by obtaining luminescence spectra. The emission spectra of [Ru II (bpy) 3 ](lipid) 2 are shown in Figure 2c 3 ] 2+ maintains the process of photo-induced charge transfer based on the intramolecular factor of triplet [71,72]. In order to investigate the essential origin of the hypochromic effect, the self-assembly structure of [Ru II (bpy in EtOH because Na salt of amphiphiles 1-6 were molecularly dispersed in EtOH and displayed no assembled structures. These aggregation behaviors indicate that the hypochromic effect observed in the UV-Vis absorption spectra is related to the supramolecular self-assembly of ruthenium(II) complexes. In particular, we suggest that the helical aggregation is formed from closer interaction among [Ru II (bpy) 3 ] 2+ , leading to uniaxial elongation and formation of stable helicaltapes [20,[61][62][63][64][65].
On the other hand, in the case of nanosheets, the solvophobic region of [Ru II (bpy) 3 ] 2+ remains exposed to the surrounding solvent [20,[61][62][63][64][65], and leads to the creation of bigger and better-developed microsheet or urchin-like aggregation. The result indicates that the combination of discrete metal complexes and lipid amphiphiles enables delicate transformation between the variable structures. complexes. In particular, we suggest that the helical aggregation is formed from closer interaction among [Ru II (bpy)3] 2+ , leading to uniaxial elongation and formation of stable helicaltapes [20,[61][62][63][64][65].
On the other hand, in the case of nanosheets, the solvophobic region of [Ru II (bpy)3] 2+ remains exposed to the surrounding solvent [20,[61][62][63][64][65], and leads to the creation of bigger and better-developed microsheet or urchin-like aggregation. The result indicates that the combination of discrete metal complexes and lipid amphiphiles enables delicate transformation between the variable structures. In addition, both time-dependent TEM observation and UV-vis spectra were conducted, and the developed nanostructures with hypochromic effect remained relatively stable without precipitation In addition, both time-dependent TEM observation and UV-vis spectra were conducted, and the developed nanostructures with hypochromic effect remained relatively stable without precipitation for at least a month but with no distinct changes. The result indicates that the discrete metal complexes with lipid amphiphiles led to some rapid and stable growth of nanostructures among [Ru II (bpy) 3 ](lipids) 2 .
The circular dichroism (CD) spectra to determine the chiral conformation of lipid packaged metal complexes in EtOH are presented in Figure 4. In the metal complexes, circular dichroism appears in the absorbance region of 190 to 210 nm associated with those of only lipids, and signals corresponding to such conformation as helical structure was observed. In addition, induced circular dichroism (ICD) of [Ru II (bpy) 3 ](1) 2 and [Ru II (bpy) 3 ](2) 2 appears slightly in the absorbance peaks of ca. 450 nm associated with MLCT band of [Ru II (bpy) 3  The circular dichroism (CD) spectra to determine the chiral conformation of lipid packaged metal complexes in EtOH are presented in Figure 4. In the metal complexes, circular dichroism appears in the absorbance region of 190 to 210 nm associated with those of only lipids, and signals corresponding to such conformation as helical structure was observed. In addition, induced circular dichroism (ICD) of [Ru II (bpy)3](1)2 and [Ru II (bpy)3](2)2 appears slightly in the absorbance peaks of ca.  Wide-angle X-ray scattering (WAXS) measurements of [Ru II (bpy)3](lipid)2 solution in EtOH were conducted to further understand the structure of the supramolecular assembly. Figure 5 shows the WAXS pattern (λ = 1.488 Å,) taken for the EtOH solutions of [Ru II (bpy)3](lipid)2 at room temperature. The WAXD of the [Ru II (bpy)3](1)2 solution showed an intense (001) peak ( Figure 5a). These diffraction peaks indicate the presence of a lamellar structure with a long period of 54.6 Å. This value is smaller than twice the molecular length of 1 (ca. 24 Å, estimated by the space-filling model), indicating that the lipid compounds have orientation with regard to the layer made up of the lipid packaged ruthenium complexes. It suggests that the alkyl chains adopt more orientation in order to adapt to the layers consisting of these coordination compounds. Complexes [Ru II (bpy)3](lipid)2 (lipid = 2-6) also demonstrated a lamellar structure with tilt-orientation in d-spacing.   Wide-angle X-ray scattering (WAXS) measurements of [Ru II (bpy) 3 ](lipid) 2 solution in EtOH were conducted to further understand the structure of the supramolecular assembly. Figure 5 shows the WAXS pattern (λ = 1.488 Å,) taken for the EtOH solutions of [Ru II (bpy) 3 ](lipid) 2 at room temperature. The WAXD of the [Ru II (bpy) 3 ](1) 2 solution showed an intense (001) peak ( Figure 5a). These diffraction peaks indicate the presence of a lamellar structure with a long period of 54.6 Å. This value is smaller than twice the molecular length of 1 (ca. 24 Å, estimated by the space-filling model), indicating that the lipid compounds have orientation with regard to the layer made up of the lipid packaged ruthenium complexes. It suggests that the alkyl chains adopt more orientation in order to adapt to the layers consisting of these coordination compounds. Our spectroscopic and microscopic investigations reveal the details of the self-assembled structure of [Ru II (bpy)3](lipids)2 ( Table 2). Since hypochromic effects in UV-Vis absorption spectra (Figure 2a,b) are caused by the arrangement of the transition dipole moments, the ruthenium complexes are aligned parallel to each other in the bilayer structure of [Ru II (bpy)3](lipids)2, especially [Ru II (bpy)3](1)2 and [Ru II (bpy)3](2)2. In particular, the hypochromic effects are observed in absorption of [Ru II (bpy)3] 2+ , indicating that each ruthenium(II) complex form ordered arrays in the bilayer in the well-developed nanostructure. Thus, a possible molecular arrangement is proposed to be the 2D packing of [Ru II (bpy)3](lipids)2. Indeed, a close-packed simulation of the single-crystal structure [74] of [Ru II (bpy)3] 2+ reveals that the average separation between the closest couple of molecules can be estimated to be 5-6 Å, which is consistent with the interval of the lipids pattern [20,[61][62][63][64][65].  Our spectroscopic and microscopic investigations reveal the details of the self-assembled structure of [Ru II (bpy) 3 ](lipids) 2 ( Table 2). Since hypochromic effects in UV-Vis absorption spectra (Figure 2a,b) are caused by the arrangement of the transition dipole moments, the ruthenium complexes are aligned parallel to each other in the bilayer structure of [Ru II (bpy) 3 ](lipids) 2 , especially [Ru II (bpy) 3 ](1) 2 and [Ru II (bpy) 3 ](2) 2 . In particular, the hypochromic effects are observed in absorption of [Ru II (bpy) 3 ] 2+ , indicating that each ruthenium(II) complex form ordered arrays in the bilayer in the well-developed nanostructure. Thus, a possible molecular arrangement is proposed to be the 2D packing of [Ru II (bpy) 3 ](lipids) 2 . Indeed, a close-packed simulation of the single-crystal structure [74] of [Ru II (bpy) 3 ] 2+ reveals that the average separation between the closest couple of molecules can be estimated to be 5-6 Å, which is consistent with the interval of the lipids pattern [20,[61][62][63][64][65].
(Tokyo, Japan).). UV-vis spectra, fluorescence spectra, and circular dichroism spectra were obtained on RF-2500PC, RF-5300PC (Shimadzu Co.(Kyoto, Japan)), and J-820 (JASCO Co. (Tokyo, Japan)) spectrophotometers, respectively. IR absorption spectra were recorded on a PerkinElmer Spectrum 65 FT-IR spectrometer equipped with a diamond ATR (attenuated total reflectance) system, which enables the measurement of IR absorption spectrum of a sample located over the surface of the diamond crystal. Transmission electron microscopy was conducted on a Tecnai G2 F20 and Titan Themis 300 (FEI Co.(Hillsboro, OR, USA), operating at 200 kV. Transmission electron microscopes were prepared by transferring the surface layer of solutions on carbon-coated TEM grids. Emission quantum yield was conducted on Hamamatsu C9920-02 (Excitation: 470 nm), and phosphorescence lifetime was acquired using time-correlated single-photon counting (TCSPC) method using FluoroCube 3000U Horiba (Excitation: 340 nm (Nano LED) Repetition rate: 100 kHz). The 2D-WAXS (two-dimensional wide-angle X-ray scattering) measurements [76,77] using the high-brilliance synchrotron X-rays were carried out at BL-10C beamline with the wavelength of 0.1488 nm in Photon Factory of the High Energy Accelerator Research Organization, Tsukuba, Japan. The typical exposure time was in the range 10-30 s. The 2D-WAXS patterns were obtained using PILATUS-100K (DECTRIS). Polyethylene was used as a standard sample in order to calibrate the magnitude of the scattering vector, q, as defined by q = (4π/λ) sin (θ/2) with λ and θ being the wavelength of X-ray and the scattering angle, respectively. The 2D-WAXS patterns were further converted to one-dimensional profiles by conducting sector average. Each L-amino acid (aspartic acid and glutamic acid) (27 mmol) was dissolved in 10 mL of deionized water with cooling in an ice bath. The sodium hydroxide (53 mmol) in 5 mL of deionized water was added to the solution on vigorous stirring. Benzyl chloroformate (Z-Cl) (29 mmol) and aqueous NaOH (32.1 mmol in 5 mL of deionized water) was alternately added dropwise to the solution and the solution was stirred vigorously for 2 h in an ice bath. The solution was twice washed with 50 mL of diethylether to remove excess Z-Cl. The pH of aqueous layer was lowered to 3 to give turbid solution. The mixture was extracted to ethyl acetate, and the organic layer was washed with deionized water. The organic layer was dried over Na 2 SO 4 . After filtration, the filtrate was concentrated in vacuo and was reprecipitated from ethyl acetate/n-hexane to give white solid: L-2-aminoadipinic acid (18.5 mmol) was dissolved in 15 mL of deionized water, and sodium hydroxide (40 mmol) in 5 mL of deionized water was added to the solution with cooling in an ice bath. Benzyl chloroformate (Z-Cl) (28 mmol) and aqueous NaOH (22 mmol in 5 mL of deionized water) was alternately added dropwise to the solution and the solution was stirred vigorously for 2 h in an ice bath. The solution was twice washed with 15 mL of diethylether to remove excess Z-Cl. The pH of aqueous layer was lowered to 3 to give turbid solution. The solution was stored in refrigerator. The solid precipitated was filtered and collected to obtain white powder: Each Z-protected amino acid (1a, 2a, 3a) (5.3 mmol), 1-aminododecane (12 mmol), and trimethylamine (24 mmol) was dissolved in 100 mL of dry CHCl3 and stirred with cooling to 0 °C. Diethylphosphoryl cyanidate (DEPC) (29 mmol) was added to the mixture and stirred for 3 h in an ice bath. After being stirred for 5 days at room temperature, the solution was washed with 0.3 N HCl (50 mL, twice), deionized water (50 mL, once), saturated aqueous NaHCO3 (50 mL, twice), and deionized water (50 mL, once). The solution was dried over Na2SO4. After filtration, the filtrate was concentrated in vacuo and recrystallized from methanol to give white solid:  L-2-aminoadipinic acid (18.5 mmol) was dissolved in 15 mL of deionized water, and sodium hydroxide (40 mmol) in 5 mL of deionized water was added to the solution with cooling in an ice bath. Benzyl chloroformate (Z-Cl) (28 mmol) and aqueous NaOH (22 mmol in 5 mL of deionized water) was alternately added dropwise to the solution and the solution was stirred vigorously for 2 h in an ice bath. The solution was twice washed with 15 mL of diethylether to remove excess Z-Cl. The pH of aqueous layer was lowered to 3 to give turbid solution. The solution was stored in refrigerator. The solid precipitated was filtered and collected to obtain white powder: Each Z-protected amino acid (1a, 2a, 3a) (5.3 mmol), 1-aminododecane (12 mmol), and trimethylamine (24 mmol) was dissolved in 100 mL of dry CHCl 3 and stirred with cooling to 0 • C. Diethylphosphoryl cyanidate (DEPC) (29 mmol) was added to the mixture and stirred for 3 h in an ice bath. After being stirred for 5 days at room temperature, the solution was washed with 0.3 N HCl (50 mL, twice), deionized water (50 mL, once), saturated aqueous NaHCO 3 (50 mL, twice), and deionized water (50 mL, once). The solution was dried over Na 2 SO 4 . After filtration, the filtrate was concentrated in vacuo and recrystallized from methanol to give white solid:  Each didodecyl amino acid (1c, 2c, 3c) (1.3 mmol), sulfoacetic acid (1.3 mmol), and trimethylamine (4.6 mmol) was dissolved in 10 mL of DMF under N 2 gas. (Benzotriazol-1-yloxy)-tris(dimetylamino) phosphonium hexafluorophosphate) (BOP reagent) (1.3 mmol) in 2 mL of DMF were added to the solution in an ice bath. After being stirred for 2 days at room temperature, the solution was concentrated in vacuo. The residue was dissolved in 3 mL of methanol, and sodium hydroxide (1.6 mmol) in 1 mL of methanol was added to the solution. The precipitate was filtered and dried in vacuo to give a white solid: Yield 0.50 g (63%) (1(Na)); ν max (ATR)/cm −1 3283, 2917, 2850, 1639, 1543; 1 H NMR (d 6 -DMSO) δ 0.83-0.88 (t(6.26), 6H, *CH 3 ×2), 1.14-1.34 (m, 36H, (CH 2 ) 9 ×2), 1. 3.1.6. Synthesis of N',N"-Didodecyl-N α -4-Sulfobenzoyl-L-Aspartamide Sodium Salt (4(Na)), N',N"-Didodecyl-N α -4-Sulfobenzoyl-L-Glutamide Sodium Salt (5(Na)), N',N"-Didodecyl-L-2-N α -(4-Sulfobenzoylamino) Adipamide Sodium Salt (6(Na)) Each didodecyl amino acid (1c, 2c, 3c) (7.4 mmol), 4-sulfobenzoic acid potassium salt (2.1 mmol), and triethylamine (7.4 mmol) was dissolved in 20 mL of DMF under N 2 gas. BOP reagent (2.1 mmol) in 2 mL of DMF were dropped to the solution in an ice bath. After being stirred for 2 days at room temperature, the solution was concentrated in vacuo, and the residue was dissolved in 100 mL of chloroform. The solution was washed with saturated aqueous NaHCO 3 (50 mL, twice), saturated aqueous NaCl (50 mL, twice). The solution was dried over Na 2 SO 4 . After filtration, the filtrate was concentrated in vacuo and recrystallized from methanol to give white solid: Yield 0.81 g (57%) (4(Na)); ν max (ATR)/cm − [14] The composite of mixed-valence complexes with lipid amphiphiles were synthesized by the following procedure. An aqueous dispersion of the anionic amphiphile 1-6 (Na + salt, 0.20 mmol) was ultrasonically dissolved in 8 mL of deionized water. [Ru II (bpy) 3 ]Cl 2 in deionized water (0.047 mmol, 4 mL) was added to the solution. The solution was stored in a refrigerator. The resulting orange precipitate was collected by centrifugation, washed with deionized water, and dried in vacuo to give orange composite: Yield 0.14 g (36%) (

Conclusions
In conclusion, we have demonstrated that the lipid-packaged ruthenium complex [Ru II (bpy) 3 ](lipid) 2 (lipid = 1-6) displays morphological changes in ethanol, depending on the chemical structure of lipids. Formation of a bilayer structure with a metal complex causes morphological evolution from nanotapes to helical ribbons, giving rise to changes in absorption spectral intensities. The concept of lipid packaging could also be expanded to other useful coordination compounds and should allow us to further develop the nanochemistry of coordination materials. The biochemical and biomedical direction can also be considered to focus more on the self-assembly process. Biomimetic methodologies would typically employ both strong (coordinate bond formation) and weak noncovalent interactions (e.g., solvophobic interaction, electrostatic interaction, and so on) in a single process. Similar hierarchy of stronger to weaker interactions is thought to sequentially drive the formation of local structures in biology before the final product architecture is settled upon. The techniques of this type have already elegantly yielded entities displaying tertiary structure, such as some of helicates described in this study. Flexible self-assembly, in particular, will play an important role in the bottom-up manufacturing of novel materials in the evolving nanotechnology arena. More sophisticated sensors, as well as better and more useful catalytic applications, will undoubtedly emerge. Further developments in this concept can be anticipated with new intermolecular forces being employed. This approach offers interesting and undeveloped possibilities for switchable systems, self-assembly-based sensors, and molecular machines.

Conflicts of Interest:
The authors declare no conflict of interest.