Chloroform

Example 28

[Figure (not displayed)]

A typical protocol used for the synthesis of the PNAEP₆₇-PnBA₅₀₀ diblock copolymer was as follows: PNAEP₆₇ macro-CTA (0.185 g, 14.6 μmol), deionised water (4.501 g, corresponding to a 20% w/w solution) and KPS (1.320 mg, 4.9 μmol; PNAEP₆₇/KPS=3.0) were weighed into a 10 mL round-bottom flask charged with a magnetic flea. HCl (10 μL, 0.2 M) was added to reduce the pH to 3.0. This flask was then immersed in an ice bath, and the solution was degassed with nitrogen for 30 min. nBA (1.500 g) was weighed into a separate 14 mL vial and degassed with nitrogen in an ice bath for 30 min. An AsAc stock solution (0.01% w/w) was weighed into a second 14 mL vial and degassed with nitrogen in an ice bath for 30 min. After 30 min nBA (1.05 ml, 7.32 mmol; target DP=500) was added to the flask using a degassed syringe and needle under nitrogen. The flask contents were then stirred vigorously to ensure thorough mixing and degassed for 5 min before being immersed in an oil bath set at 30° C. After 1 min, AsAc (0.09 ml, 4.9 μmol; KPS/AscAc molar ratio=1.0) was added to the flask. The nBA polymerisation was allowed to proceed for 1 h before being quenched by exposing the reaction solution to air and immersing the reaction vial in an ice bath. ¹H NMR spectroscopy analysis of the disappearance of vinyl signals indicated a final nBA conversion of 99%. Chloroform GPC analysis of this copolymer indicated a M_n of 86.6 kg mol⁻¹ and an M_w/M_n of 1.56. Other diblock copolymer compositions were obtained by adjusting the nBA/PNAEP₆₇ molar ratio.

Example 1

This example describes an exemplary nanostructure (i.e. nanocomposite tecton) and formation of a material using the nanostructure.

A nanocomposite tecton consists of a nanoparticle grafted with polymer chains that terminate in functional groups capable of supramolecular binding, where supramolecular interactions between polymers grafted to different particles enable programmable bonding that drives particle assembly (FIG. 4). Importantly, these interactions can be manipulated separately from the structure of the organic or inorganic components of the nanocomposite tecton, allowing for independent control over the chemical composition and spatial organization of all phases in the nanocomposite via a single design concept. Functionalized polystyrene polymers were made from diaminopyridine or thymine modified initiators via atom transfer radical polymerization, followed by post-functionalization to install a thiol group that allowed for particle attachment (FIG. 5). The polymers synthesized had three different molecular weights (˜3.7, ˜6.0, and ˜11.0 kDa), as shown in FIG. 6, with narrow dispersity (Ð<1.10), and were grafted to nanoparticles of different diameters (10, 15, 20, and nm) via a “grafting-to” approach.

Once synthesized, nanocomposite tectons were functionalized with either diaminopyridine-polystyrene or thymine-polystyrene were readily dispersed in common organic solvents such as tetrahydrofuran, chloroform, toluene, and N,N′-dimethylformamide with a typical plasmonic resonance extinction peak at 530-540 nm (FIG. 7A) that confirmed their stability in these different solvents. Upon mixing, diaminopyridine-polystyrene and thymine-polystyrene coated particles rapidly assembled and precipitated from solution, resulting in noticeable red-shifting, diminishing, and broadening of the extinction peak within 1-2 minutes (example with 20 nm gold nanoparticles and 11.0 kDa polymers, FIG. 7B). Within 20 minutes, the dispersion appeared nearly colorless, and large, purple aggregates were visible at the bottom of the tube. After moderate heating (˜55° C. for ˜1-2 minutes for the example in FIG. 7B), the nanoparticles redispersed and the original color intensity was regained, demonstrating the dynamicity and complete reversibility of the diaminopyridine-thymine directed assembly process. Nanocomposite tectons were taken through multiple heating and cooling cycles without any alteration to assembly behavior or optical properties, signifying that they remained stable at each of these thermal conditions (FIG. 7C).

A key feature of the nanocomposite tectons is that the sizes of their particle and polymer components can be easily modified independent of the supramolecular binding group's molecular structure. However, because this assembly process is driven via the collective interaction of multiple diaminopyridine and thymine-terminated polymer chains, alterations that affect the absolute number and relative density of diaminopyridine or thymine groups on the nanocomposite tecton surface impact the net thermodynamic stability of the assemblies. In other words, while all constructs should be thermally reversible, the temperature range over which particle assembly and disassembly occurs should be affected by these variables. To better understand how differences in nanocomposite tecton composition impact the assembly process, nanostuctures were synthesized using different nanoparticle core diameters (10-40 nm) and polymer spacer molecular weights (3.7-11.0 kDa), and allowed to fully assemble at room temperature (˜22° C.) (FIG. 8). Nanocomposite tectons were then monitored using UV-Vis spectroscopy at 520 nm while slowly heating at a rate of 0.25° C./min, resulting in a curve that clearly shows a characteristic disassembly temperature (melting temperature, T_m) for each nanocomposite tecton composition.

From these data, two clear trends can be observed. First, when holding polymer molecular weight constant, T_m increases with increasing particle size (FIG. 8A). Conversely, when keeping particle diameter constant, T_m drastically decreases with increasing polymer length (FIG. 8B). To understand these trends, it is important to note that nanocomposite tecton dissociation is governed by a collective and dynamic dissociation of multiple individual diaminopyridine-thymine bonds, which reside at the periphery of the polymer-grafted nanoparticles. The enthalpic component of nanocomposite tecton bonding behavior is therefore predominantly governed by the local concentration of the supramolecular bond-forming diaminopyridine and thymine groups, while the entropic component is dictated by differences in polymer configuration in the bound versus unbound states.

All nanocomposite tectons possess similar polymer grafting densities (i.e. equivalent areal density of polymer chains at the inorganic nanoparticle surface, FIG. 9) regardless of particle size or polymer length. However, the areal density of diaminopyridine and thymine groups at the periphery of the nanocomposite tectons is not constant as a function of these two variables due to nanocomposite tecton geometry. When increasing inorganic particle diameter, the decreased surface curvature of the larger particle core forces the polymer chains into a tighter packing configuration, resulting in an increased areal density of diaminopyridine and thymine groups at the nanocomposite tecton periphery; this increased concentration of binding groups therefore results in an increased T_m, explaining the trend in FIG. 8A.

Conversely, for a fixed inorganic particle diameter (and thus constant number of polymer chains per particle), increasing polymer length decreases the areal density of diaminopyridine and thymine groups at the nanocomposite tecton periphery due to the “splaying” of polymers as they extend off of the particle surface, thereby decreasing T_m in a manner consistent with the trend in FIG. 8B. Additionally, increasing polymer length results in a greater decrease of system entropy upon nanocomposite tecton assembly, due to the greater reduction of polymer configurations once the polymer chains are linked via a diaminopyridine-thymine bond; this would also be predicted to reduce T m. Within the temperature range tested, all samples were easily assembled and disassembled via alterations in temperature. Inorganic particle diameter and polymer length are therefore both effective handles to control nanocomposite tecton assembly behavior.

Importantly, because the nanocomposite tecton assembly process is based on dynamic, reversible supramolecular binding, it should be possible to drive the system to an ordered equilibrium state where the maximum number of binding events can occur. The particle cores and polymer ligands are polydisperse (FIG. 10) and ordered arrangements represent the thermodynamically favored state for a set of assembled nanocomposite tectons. When packing nanocomposite tectons into an ordered lattice, deviations in particle diameter would be expected to generate inconsistent particle spacings that would decrease the overall stability of the assembled structure. However, the inherent flexibility of the polymer chains should allow the nanocomposite tectons to adopt a conformation that compensates for these structural defects. As a result, an ordered nanocomposite tecton arrangement would still be predicted to be stable if it produced a larger number of diaminopyridine-thymine binding events than a disordered structure and this increase in binding events outweighed the entropic penalty of reduction in polymer chain configurations.

To test this hypothesis, multiple sets of assembled nanocomposite tectons were thermally annealed at a temperature just below their T_m, allowing particles to reorganize via a series of binding and unbinding events until they reached the thermodynamically most stable conformation. The resulting structures were analyzed with small angle X-ray scattering, revealing the formation of highly ordered mesoscale structures where the nanoparticles were arranged in body-centered cubic superlattices (FIG. 11). The body-centered cubic structure was observed for multiple combinations of particle size and polymer length, indicating that the nanoscopic structure of the composites can be controlled as a function of either the organic component (via polymer length), the inorganic component (via particle size), or both, making this nanocomposite tecton scheme a highly tailorable method for the design of future nanocomposites.

Example 125

[Figure (not displayed)]

Methyl 4-((5-(benzyloxy)-2-methoxyphenyl)(ethyl)amino)butanoate (184). 5-(Benzyloxy)-N-ethyl-2-methoxyaniline (146) (0.681 g, 2.65 mmol), DIEA (0.92 mL, 5.3 mmol), and methyl 4-iodobutyrate (0.72 mL, 5.3 mmol) in DMF (5 mL) were stirred at 70° C. for 5 days. The reaction mixture was cooled to rt, diluted with EtOAc (60 mL), washed with water (4×50 mL), brine (75 mL), dried over Na₂SO₄ and evaporated. The residue was purified by chromatography on a silica gel column (2.5×30 cm bed, packed with CHCl₃), eluant: 5% MeOH in CHCl₃ to get compound 184 (0.72 g, 76%) as a dark amber oil.

Methyl 4-(ethyl(5-hydroxy-2-methoxyphenyl)amino)butanoate (186). Ester 184 (0.72 g, 2.0 mmol) was stirred under reflux with 6 mL of water and 6 mL of conc HCl for 1.5 hrs and then evaporated to dryness to give acid 185 as a brown gum. The crude acid was dissolved in 50 mL of methanol containing 1 drop (cat.) of methanesulfonic acid ant the solution was kept for 2 hrs at rt. After that the mixture was concentrated in vacuum and the residue was mixed with 20 mL of saturated NaHCO₃. The product was extracted with EtOAc (3×40 mL). The extract was washed with brine (40 mL), dried over Na₂SO₄ and evaporated. The residue was purified by chromatography on a silica gel column (2.5×30 cm bed, packed with CHCl₃), eluant: 5% MeOH in CHCl₃ to get compound 186 (0.444 g, 83%) as a brown oil.

N-(6-(dimethylamino)-9-(4-(ethyl(4-methoxy-4-oxobutyl)amino)-2-hydroxy-5-methoxyphenyl)-3H-xanthen-3-ylidene)-N-methylmethanaminium chloride (187). To a stirred suspension of tetramethylrhodamine ketone 101 (0.234 g, 0.830 mmol) in 10 mL of dry chloroform was added oxalyl chloride (72 μL, 0.82 mmol) upon cooling to 0-5° C. The resulting red solution was stirred for 0.5 h at 5° C., and the solution of compound 186 (0.222 g, 0.831 mmol) in dry chloroform (5 mL) was introduced. The reaction was allowed to heat to rt, stirred for 72 h, diluted with CHCl₃ (100 mL and washed with sat. NaHCO₃ solution (2×30 mL) The organic layer was extracted with 5% HCl (3×25 mL). The combined acid extract was washed with CHCl₃ (2×15 mL; discarded), saturated with sodium acetate and extracted with CHCl₃ (5×30 mL). The extract was washed with brine (50 mL), dried over Na₂SO₄ and evaporated. The crude product was purified by chromatography on silica gel column (2×50 cm bed, packed with CHCl₃/MeOH/AcOH/H₂O (100:20:5:1)), eluant: CHCl₃/MeOH/AcOH/H₂O (100:20:5:1) to give the product 187 (0.138 g, 29%) as a purple solid.

4-((4-(6-(dimethylamino)-3-(dimethyliminio)-3H-xanthen-9-yl)-5-hydroxy-2-methoxyphenyl)(ethyl)amino)butanoate (188). Methyl ester 187 (0.136 g, 0.240 mmol) was dissolved in 5 mL of 1M KOH (5 mmol). The reaction mixture was kept at rt for 1.5 hrs and the acetic acid (1 mL) was added. The mixture was extracted with CHCl₃ (4×30 mL), and combined extract was washed with brine (20 mL), filtered through the paper filter and. The crude product was purified by chromatography on silica gel column (2×50 cm bed, packed with MeCN/H₂O (4:1)), eluant: MeCN/H₂O/AcOH/(4:1:1) to give the product 188 (0.069 g, 98%) as a purple solid.

N-(6-(dimethylamino)-9-(4-((4-(2,5-dioxopyrrolidin-1-yloxy)-4-oxobutyl)(ethyl)amino)-2-hydroxy-5-methoxyphenyl)-3H-xanthen-3-ylidene)-N-methylmethanaminium chloride (189). To a solution of the acid 188 (69 mg, 0.12 mmol) in DMF (2 mL) and DIEA (58 μL, 0.33 mmol) was added N-hydroxysuccinimide trifluoroacetate (70 mg, 0.33 mmol). The reaction mixture was stirred for 30 min, diluted with chloroform (100 mL) and washed with water (5×50 mL), brine (50 mL), filtered through paper and concentrated in vacuum. The crude product was purified by precipitation from CHCl₃ solution (5 mL) with ether (20 mL) to give compound 189 (55 mg, 67%) as a purple powder.