Self and directed assembly: people and molecules

Abstract

Self-assembly and directed-assembly are two very important aspects of supramolecular chemistry. As a young postgraduate student working in Canada with Tom Fyles my introduction to Supramolecular Chemistry was through the self-assembly of phospholipid membranes to form vesicles for which we were developing unimolecular and self-assembling transporter molecules. The next stage of my development as a scientist was in Japan with Seiji Shinkai where in a "Eureka" moment, the boronic acid templating unit (directed-assembly) of Wulff was combined with photoinduced electron transfer systems pioneered by De Silva. The result was a turn-on fluorescence sensor for saccharides; this simple result has continued to fuel my research to the present day. Throughout my career as well as assembling molecules, I have enjoyed bringing together researchers in order to develop collaborative networks. This is where molecules meet people resulting in assemblies worth more than the individual "molecule" or "researcher". My role in developing networks with Japan was rewarded by the award of a Daiwa-Adrian Prize in 2013 and I was recently rewarded for developing networks with China with an Inaugural CASE Prize in 2015.

Keywords: boronic acids; fluorescence; glucose sensor; self and directed assembly; supramolecular.

Scheme 1

Reaction of trimethylsilyl cyanide with tricarbonyl (η5-cyclohexadienyl)iron(1+) salts. Reproduced with permission from [3]. Copyright 1987 Royal Society of Chemistry.

Figure 1

(a) Supramolecular pore formers. Reproduced with permission from [6]. Copyright 1990 Elsevier. (b) Unimolecular ion channel. Reproduced with permission from [9]. Copyright 1993 The American Chemical Society.

Figure 2

An intelligent liquid crystal to read out saccharide structure as a color-change. Picture provided by Seiji Shinkai, Director of the ERATO Chemirecognics Project (1990–95) [13].

Scheme 2

Polymeric boronic acid receptor units developed by Wulff. Reproduced from [16]. Copyright 1982 International Union of Pure and Applied Chemistry.

Figure 3

Fluorescence photoinduced electron transfer (PET) pH sensor developed by A. P. De Silva.

Figure 4

Fluorescence PET sensor for saccharides.

Figure 5

(a) Glucose selective PET system. (b) Chiral discriminating PET system.

Figure 6

(a) Fluorescence photoinduced electron transfer (PET) cation sensors developed by A. P. De Silva. (b) Fluorescence photoinduced electron transfer (PET) saccharide sensor. (c) Fluorescence AND logic sensors for D-glucosamine hydrochloride.

Figure 7

(a) Pyrene diboronic acids (n = 3–8). (b) Pyrene monoboronic acid. (c) Block chart showing the relative stability K_rel of saccharide complexes. Obtained from the observed stability constants (K_obs) for D-glucose, D-galactose, D-fructose and D-mannose with pyrene diboronic acids (n = 3–8) divided by the observed stability constants (K_obs) with pyrene monoboronic acid, to yield relative values with saccharides.

Figure 8

Glysure Continuous Intravascular Glucose Monitoring (CIGM) System. Image provided by Nicholas P. Barwell Glysure Ltd. [56].

Figure 9

Chiral discrimination of D- and L-tartaric acid by (R)-8 at pH 5.6. [(R)-8] = 5.0 × 10⁻⁶ mol dm⁻³, at pH 5.6 in 0.05 mol dm⁻³ NaCl (52.1% methanol in water), λ_ex at 289 nm, 22 °C. The pH was kept at 5.6 with NaOH/HCl. (Left) Emission spectra. (Center) Normalized emission intensity) as a function of added tartaric acid concentration. Lines are fit to 1:1 binding isotherm (Right) Job plot of (R)-8 with D-tartaric acid at a constant total concentration [D-tartaric acid] + [R] = 5.0 × 10⁻⁶ mol dm⁻³; λ_em at 358 nm. Reproduced with permission from [61]. Copyright 2004 John Wiley and Sons.

Figure 10

Chiral discriminating sensor (relative stereochemistry shown) constructed using a good fluorophore (anthracene).

Figure 11

Fluorescence emission intensity-pH profile of: (a) Sensor 15: 1.0 × 10⁻⁶ mol dm⁻³ (λ_ex 370 nm, λ_em 435 nm. (b) Sensor 16: 1.0 × 10⁻⁶ mol dm⁻³ (λ_ex 335 nm, λ_em 390 nm). In 5.0 × 10⁻² mol dm⁻³ NaCl ionic buffer (52.1% methanol in water). Emission spectra of the sensors (c) 15 (1.0 × 10⁻⁶ mol dm⁻³), λ_ex 370 nm; (d) 16 (1.0 × 10⁻⁶ mol dm⁻³), λ_ex 335 nm. Sensors in 5.0 × 10⁻² mol dm⁻³ NaCl ionic buffer (52.1% methanol in water, w/w), 25 °C. Reproduced with permission from [64]. Copyright 2010 American Chemical Society.

Figure 12

Modular chiral discriminating d-PET systems (relative stereochemistry shown).

Figure 13

With Matthew Davidson and Steven Bull during “World Cup” lecture tour of Japan in 2002. (Left) Private photo taken in Osaka. (Right) Photo taken in Tokyo by Katsuhiko Ariga.

Figure 14

Preparation of chiral boron reagent and use as catalyst for aza-Diels–Alder reactions.

Figure 15

Chiral three component self-assembling system.