Compendium

Supramolecular and Host-Guest Chemistry

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Supramolecular and Host-Guest Chemistry

A Tier 2 deep-dive into “chemistry beyond the molecule” — the design and synthesis of molecular assemblies bound by non-covalent interactions, the engineering of synthetic hosts (crown ethers, cryptands, cyclodextrins, calixarenes, cucurbiturils, pillararenes, cavitands, MOFs), the construction of mechanically interlocked architectures (rotaxanes, catenanes, molecular machines), templated and self-assembly strategies (DNA origami, peptide amphiphiles, coordination cages), chemosensing approaches (indicator displacement assays, fluorescent probes), supramolecular catalysis in confined cavities, and pharmaceutical applications including the Sugammadex case. Lehn (Strasbourg) coined “supramolecular chemistry” in 1978; the 1987 Nobel (Pedersen-Cram-Lehn) institutionalized it; the 2016 Nobel (Sauvage-Stoddart-Feringa) confirmed molecular machines as a mature discipline.

See also

Non-covalent interactions — the toolkit

Supramolecular chemistry is built from interactions weaker than covalent bonds (<5 kcal/mol typical, vs ~80-100 kcal/mol for C-C) but additive and directional enough to specify three-dimensional architecture. Understanding the rank-order of strength, geometry, and solvent dependence of each is foundational.

Hydrogen bonding

D-H···A where D = electronegative donor (N, O, F, sometimes S, C-H acidic), A = electronegative acceptor with lone pair. Energy 1-40 kcal/mol depending on D, A, and geometry. Strong H-bonds (e.g., [F-H-F]⁻) approach 40 kcal/mol — three-center four-electron character. Moderate H-bonds in water-water, OH···O=C (1.6-2.0 Å, ~5 kcal/mol). Weak H-bonds — C-H···O, C-H···π — 0.5-2 kcal/mol; structurally significant in aggregate (Desiraju 1991).

Etter’s rules (Margaret Etter 1990 Acta Cryst) — empirical H-bond pairing in cocrystals. Jeffrey-Saenger Hydrogen Bonding in Biological Structures (Springer 1991) — classic monograph.

π-π stacking

Aromatic-aromatic; face-to-face (sandwich, 3.3-3.8 Å parallel) or T-shaped (edge-to-face). Hunter-Sanders model (1990) — electrostatic between quadrupole moments dominates; benzene-benzene weakly attractive (~2 kcal/mol), perfluoroarene-arene strongly attractive (~3-4 kcal/mol; opposite quadrupole signs). Charge-transfer complexes (TTF-TCNQ, viologen-dialkoxynaphthalene) drive Stoddart’s mechanically interlocked architectures.

Halogen bonding

R-X···Y where X = halogen (typically I, Br, less Cl), Y = Lewis base. σ-hole on X opposite the R-X bond — anisotropic positive electrostatic potential. Strength 1-40 kcal/mol; iodine > bromine > chlorine. Directionally tight (R-X···Y angle ~180°). Resnati-Metrangolo (Politecnico Milano) established the modern field 1996-2000s. Applications: crystal engineering, anion recognition, catalysis (XB activator catalysis — Huber Aachen, Bolm Aachen, Takemoto Kyoto).

Standard XB donors: pentafluoroiodobenzene C₆F₅I (CAS 827-15-6, Sigma 308005), 1,4-diiodotetrafluorobenzene (CAS 392-57-4, TCI D2207), N-iodosaccharin (CAS 27866-72-2, Sigma 660795), 1-iodoperfluoroalkanes (1-iodoperfluorohexane CAS 355-43-1, Apollo Scientific PC2090).

Chalcogen, pnictogen, tetrel bonding

σ-Hole analogues with S, Se, Te (chalcogen); P, As (pnictogen); Si, Ge (tetrel). Weaker than halogen bonds typically; emerging in catalyst and receptor design. Pioneers: Berkessel, Matile (Geneva), Beer (Oxford), Resnati. Benzotellurazoles (Beer 2017 Nat Chem) are textbook ChB receptors.

Cation-π and anion-π

Cation-π: K⁺, NH₄⁺, Me₃NH⁺ above benzene face. Free energy ~5-20 kcal/mol gas phase; reduced in water but still significant. Dougherty (Caltech) seminal work 1996; ubiquitous in protein recognition (Phe/Trp/Tyr coordinating Arg/Lys/quaternary ammonium — acetylcholine binding to nicotinic receptor classic example).

Anion-π: electron-poor arenes (hexafluorobenzene, perfluoronaphthalene, tetracyanoquinodimethane, naphthalene diimides) interact with anions through quadrupole-induced electrostatics. Matile-Mareda (Geneva) exploited in anion-π catalysis (2013 Nat Chem).

Hydrophobic effect

In aqueous solvent, non-polar surfaces aggregate because solvating them requires structuring water cages (negative entropy). Driving force in protein folding, micelle formation, cyclodextrin-guest inclusion. ~25 cal/(mol·Å²) free energy per buried surface area at 25 °C. Chandler 2005 Nature 437:640 — modern view distinguishing small (entropy-dominated) vs large (enthalpy-dominated) hydrophobic surfaces.

Van der Waals / dispersion

Induced-dipole–induced-dipole; ~0.5-2 kcal/mol per pair. Sum over many atoms — collective dispersion is a substantial contributor to organic crystal lattice energy (~10-20 kcal/mol) and to host-guest binding inside hydrophobic cavities. Properly described only with dispersion-corrected DFT (D3/D4 — Grimme; see computational-chemistry-deep) or post-HF methods.

Coordination bonds

Metal–ligand dative bonds bridge the supramolecular/coordination boundary. Reversibility (especially Pd-pyridine ~20-25 kcal/mol) makes them ideal for self-assembled cages: Fujita Pd₆L₄ octahedron and Pd₁₂L₂₄ sphere, Raymond Fe₄L₆ tetrahedron, Nitschke subcomponent self-assembly.

Cooperativity and the chelate effect

A multidentate host binds a single guest more strongly than the sum of its mono-dentate analogues — chelate effect. Origin partly enthalpic (preorganization) but largely entropic: tying donors into one molecule pays the rotational/translational entropy cost only once.

Pedersen’s crown ethers (1967) demonstrated this dramatically: 18-crown-6 binds K⁺ in MeOH with K_a ~10⁶ M⁻¹, while six free dimethyl ether molecules bind ~10⁻¹ M⁻¹ collectively. Six log units of cooperativity.

Macrocyclic effect — a macrocycle binds tighter than an open-chain analogue with the same donors. Origin: preorganization (Cram’s principle — “the more highly hosts and guests are organized for binding before they complex, the more stable will be their complexes”). Cram 1986 Angew Chem 25:1039.

Allosteric cooperativity — positive (Hill coefficient n>1) or negative (n<1). Designed allosteric hosts: Shinkai porphyrin-crown clamshells (1992), Anslyn metalloreceptors.

The classical hosts

Crown ethers (Pedersen 1967)

Charles Pedersen at DuPont accidentally observed dibenzo-18-crown-6 (CAS 14187-32-7, Sigma 122769) formation as a byproduct in 1967 and within weeks recognized cation complexation. J Am Chem Soc 1967 89:7017. Crown ethers are macrocyclic polyethers, named [m]-crown-n where m = total atoms, n = oxygens.

Common members and selectivities:

  • 12-crown-4 (CAS 294-93-9, Sigma 194905). Li⁺ selective (cavity 1.2-1.5 Å radius ≈ Li⁺ 0.76 Å).
  • 15-crown-5 (CAS 33100-27-5, TCI C1147). Na⁺ selective (cavity 1.7-2.2 Å ≈ Na⁺ 1.02 Å).
  • 18-crown-6 (CAS 17455-13-9, Sigma 186651). K⁺ selective (cavity 2.6-3.2 Å ≈ K⁺ 1.38 Å); K_a ≈ 10⁶ M⁻¹ in MeOH.
  • dibenzo-18-crown-6. Pedersen’s original.
  • dicyclohexano-18-crown-6. cis-syn-cis, cis-anti-cis isomers; lipophilic; phase-transfer catalyst.

Solubilization of inorganic salts in organic solvents (KMnO₄ in benzene = “purple benzene”; KF in MeCN as anhydrous fluoride source). Phase-transfer catalysis (Starks 1971 — but quaternary ammonium PTC competes). Stripping K⁺ for solubilizing carbanions (potassium tert-butoxide / 18-crown-6).

Cryptands (Lehn 1969)

Jean-Marie Lehn at Strasbourg extended crowns into three-dimensional bicyclic polyazapolyether cages — cryptands. [2.2.2]cryptand (CAS 23978-09-8, Sigma 291110) encapsulates K⁺ with K_a ~10¹⁰ M⁻¹ in MeOH — four orders tighter than 18-crown-6 due to full 3D shielding. Naming [a.b.c] denotes ethyleneoxy bridges between N caps.

  • [2.1.1]cryptand. Li⁺ selective.
  • [2.2.1]cryptand (CAS 31250-06-3, Sigma 291102). Na⁺ selective.
  • [2.2.2]cryptand. K⁺ selective; “Kryptofix 222.”
  • [3.2.2]cryptand, [3.3.3]cryptand. Larger; Cs⁺, Rb⁺.

Cryptands stabilize bizarre oxidation states: “Na anion” Na⁻ (Dye, Michigan State; sodide salts of [2.2.2]cryptand-Na⁺ Na⁻ — first electride/sodide). Also useful in radiopharmaceutical labeling — Kryptofix 222 sequesters K⁺ counterion for ¹⁸F⁻ fluorination of PET tracers (FDG synthesis).

Cyclodextrins (CDs)

Cyclic oligomers of α-1,4-linked D-glucopyranose units from enzymatic degradation of starch by cyclodextrin glucanotransferase (CGTase, EC 2.4.1.19). Truncated-cone shape with hydrophobic interior (cavity diameter 5-8 Å) and hydrophilic exterior (primary 6-OH on narrow rim, secondary 2,3-OH on wide rim).

  • α-CD (6 glucose units; CAS 10016-20-3; Sigma C4642, Wacker Cavamax W6 Pharma). Cavity 4.7-5.3 Å; binds small alkanes, simple aromatics.
  • β-CD (7 units; CAS 7585-39-9; Sigma C4767, Wacker Cavamax W7 Pharma). Cavity 6.0-6.5 Å; benzene, naphthalene, steroids, many drugs. Most widely used.
  • γ-CD (8 units; CAS 17465-86-0; Sigma C4892, Wacker Cavamax W8 Pharma). Cavity 7.5-8.3 Å; large molecules — fullerene C₆₀ forms 2:1 inclusion.

Industrial CGTase strains: Bacillus macerans, B. circulans, B. stearothermophilus. Roquette Kleptose, Wacker Cavamax/Cavasol product lines.

Modified CDs:

  • HP-β-CD (2-hydroxypropyl-β-cyclodextrin; CAS 128446-35-5; Cavasol W7 HP, Roquette Kleptose HPB). DS ~0.6-0.9; FDA Inactive Ingredient list; major pharmaceutical solubilizer (Sporanox/itraconazole oral solution, Geodon/ziprasidone IM injection, Vfend/voriconazole IV).
  • SBE-β-CD (Captisol) (sulfobutylether-β-CD sodium; CAS 182410-00-0). Ligand Pharmaceuticals/Cydex; DS ~6.5; sulfonate anionic; Sigma 821110. Used in Abilify Maintena, Nexterone, Vyondys 53. Captisol-enabled Veklury (remdesivir IV) was the first FDA-approved COVID-19 antiviral.
  • RM-β-CD (randomly methylated). RAMEB, DIMEB.
  • G2-β-CD (2-O-maltosyl-β-CD).

Calixarenes (Gutsche, Cram)

Cyclic arenes connected by methylene bridges from base-catalyzed condensation of p-tert-butylphenol and formaldehyde — von Baeyer 1872 first observed; Gutsche systematized 1970s-80s. Named after Greek calix (chalice/vase) for cup shape.

Common members:

  • p-tert-butylcalix[4]arene (CAS 60705-62-6, Sigma 200735). Cone conformation; cavity ~3 Å; selectively binds Cs⁺, Na⁺ depending on lower-rim derivatization.
  • p-tert-butylcalix[6]arene (CAS 78092-53-2, Sigma 245518). Larger; binds quaternary ammoniums.
  • p-tert-butylcalix[8]arene (CAS 68971-82-4, Sigma 232017). Even larger; sometimes guest of choice for fullerenes.

Conformations of calix[4]arene: cone, partial cone, 1,2-alternate, 1,3-alternate. Lower-rim alkylation locks the conformer. Ion-selective electrodes (Bühlmann, ETH; Diamond, DCU) for Cs⁺ in nuclear waste streams use calixarene-crown hybrids — calix[4]arene-bis(crown-6) — exemplified in the SREX-CSSX process (Savannah River cesium extraction from Hanford tank waste).

Resorcinarenes (resorcin[4]arenes) — analogous structure from resorcinol; Aoyama, MacGillivray; deeper cavity for cavitand synthesis (below).

Cucurbiturils (Mock, Kim)

Pumpkin-shaped (Latin cucurbita) macrocycles from glycoluril + formaldehyde cyclization — Behrend 1905 first isolated (without structure), Mock (Illinois Chicago) 1981 elucidated structure, Kim Kimoon (POSTECH/IBS Korea) developed homologue series 2000-2010s. Cucurbit[n]uril abbreviated CB[n].

  • CB[5] (CAS 259886-49-2). Cavity 4.4 Å; H₂, He, N₂ guests. AldRich 545058.
  • CB[6] (CAS 80262-43-3, Sigma 376140). Cavity 5.8 Å; alkylammoniums.
  • CB[7] (CAS 259886-51-6, Sigma 545104). Cavity 7.3 Å; the workhorse for biological applications.
  • CB[8] (CAS 259886-50-5, Sigma 545112). Cavity 8.8 Å; can host two guests simultaneously → ternary complexes.

CB[7] binds bicyclic diammonium guests with K_a >10¹⁵ M⁻¹ in water — the strongest synthetic host-guest interaction ever measured (Isaacs, Maryland; J Am Chem Soc 2005 127:15959 and 2007 129:3713). Exceeds avidin-biotin (~10¹⁵). Driving force: hydrophobic effect + cation-dipole at the two carbonyl-rimmed portals.

Pillararenes (Ogoshi 2008)

Tomoki Ogoshi (Kanazawa/Kyoto) reported pillar[5]arene 2008 — formaldehyde + 1,4-dimethoxybenzene → planar-chiral cylindrical pillar with ten ether oxygens lining a hydrophobic channel. Subsequent pillar[6,7,8,9,10] homologues. Cavity ~4.7 Å (pillar[5]) suits paraquat dication, neutral diamines, alkyl chains, fragrance guests. Per-functionalization via the methoxy groups → water-soluble (carboxylates, sulfonates) and amphiphilic variants. Pillar[5]arene CAS 1268177-04-1, Sigma 902004.

Cavitands (Cram)

Donald Cram coined “cavitand” 1982. Resorcin[4]arene with lower rim bridged by methylene bridges → bowl-shaped vase that interconverts (vase ↔ kite) with temperature, solvent, pH. Self-assembly of two cavitands → hexameric capsules (Reinhoudt, Rebek). Carcerands (Cram 1985) — irreversible covalent capsules trapping guests permanently. Hemicarcerands — reversible at elevated T. Carceplexes can stabilize reactive species (cyclobutadiene, benzyne, o-benzyne stable inside molecular shell — Cram-Warmuth 1991 J Am Chem Soc).

MOFs as molecular hosts

Metal-organic frameworks bridge supramolecular host design and crystalline porous solids. Cross-link mof-cof-perovskite-catalog for the full catalog.

  • HKUST-1 (Cu₃(BTC)₂; Cu-BTC, basolite C 300). Chui-Williams 1999 Science 283:1148. Hong Kong University of Science and Technology #1. SBU = paddlewheel Cu₂(O₂CR)₄; BTC = 1,3,5-benzenetricarboxylate. ~1500 m²/g BET; Lewis-acidic open Cu sites; gas adsorption (CO₂, NH₃, H₂O), heterogeneous catalysis (Lewis acid). BASF Basolite C 300 — first MOF commercialized.
  • MIL-101(Cr) and MIL-101(Fe). Férey-Serre IUL/CNRS Versailles 2005 Science 309:2040. Cr/Fe trimer + terephthalate; mesoporous (12 and 16 Å cages); 3000+ m²/g BET; spectacular thermal/water stability for MOFs.
  • ZIF-8 (Zn(2-methylimidazole)₂). Yaghi-Park-Côté 2006. Sodalite topology, 11.6 Å cage with 3.4 Å six-ring window; mimics zeolite topology. BASF Basolite Z 1200. Excellent for gas separation, hydrophobicity, biomolecule encapsulation.
  • UiO-66 (Zr₆O₄(OH)₄(BDC)₆). Cavka-Lillerud 2008 J Am Chem Soc 130:13850. Univ. i Oslo. Zr₆ cluster with 12 BDC linkers; exceptional thermal (500 °C) and aqueous stability; defect engineering (missing-linker, missing-cluster) tunes properties.

Other landmark host MOFs: MOF-5 (Yaghi 1999, IRMOF series), MOF-74 (open metal site for CO₂ binding), PCN-222/MOF-525 (porphyrin biocatalysis), NU-1000 (Northwestern), MIL-53 (breathing framework), Mg-DOBDC, Co-MOF-74 (CO binding).

MOFs as supramolecular hosts: enantioselective separation (Lin chiral MOF), drug delivery (MIL-100/MIL-101 ibuprofen loading; Horcajada-Serre-Couvreur), gas storage (H₂, CH₄), heterogeneous catalysis (encapsulated enzymes, Frustrated Lewis Pair chemistry).

Mechanically interlocked molecules

The 2016 Nobel (Sauvage-Stoddart-Feringa) recognized molecular machines built around mechanical bonds. Two molecules are “mechanically interlocked” if you cannot separate them without breaking a covalent bond, yet no covalent bond connects them. The two archetypes are catenanes (interlocked rings) and rotaxanes (ring on axle with stoppers).

Catenanes

Sauvage (Strasbourg) introduced metal-template Cu(I) coordination of two phenanthroline-containing macrocycles 1983, then ring-closure of one — 27% yield, dramatic improvement over Wasserman’s 1960 statistical (<1%) and Schill’s 1969 covalent template (multi-step) routes. Sauvage J Am Chem Soc 1984 106:3043.

Stoddart’s [2]catenane templated by π-stacking — donor naphthalene/dialkoxynaphthalene ring + acceptor bipyridinium (paraquat) ring; clipping by alkyl bromide + amine condensation. >90% yield routinely. Stoddart Chemical & Engineering News 1991, Angew Chem 1989 28:1396.

Rotaxanes

Axle threaded through ring; stoppers prevent dethreading. Synthetic strategies:

  • Capping (Schill 1969). Thread first, then attach stoppers.
  • Clipping (Stoddart). Build ring around axle.
  • Slipping (Anelli 1991). Stoppers small enough that ring slips on at elevated T, then trapped on cooling.
  • Active-metal template (Leigh 2009). Cu(I) inside ring catalyzes a bond-forming step on the axle exclusively through the ring.

Molecular shuttles, switches, motors

A bistable rotaxane with two recognition stations on the axle and a single ring → shuttle. Stoddart-Heath molecular electronics (UCLA-Caltech, 2000s) demonstrated 160 kbit Stoddart-Heath crossbar with bistable [2]rotaxanes.

Leigh (Manchester) hydrogen-bonded rotaxane “molecular machines” — light, redox, or chemically driven shuttle motion.

Feringa (Groningen) light-driven unidirectional rotation — chiral overcrowded alkene; UV photoisomerization + thermal helix inversion → four-step 360° rotation. Nature 1999 401:152. Subsequent designs achieve MHz rotation; integrated into nanocars (Tour, Rice; Feringa-Tour collaboration 2017).

Sauvage molecular muscle — interlocked rotaxane dimer that extends/contracts by 27% on metal-ion exchange (Cu/Zn).

Molecular motors at work

Feringa nanocar 2011 Nature 479:208 — four photo-driven motor wheels; verified to “drive” on Cu(111) surface via STM tip pulse. Nanocar Race I (2017, Toulouse) — five teams raced motor molecules along Au surface tracks; verified motion at <1 nm resolution.

Light-driven motor applications: artificial muscles, surface-bound rotor arrays (Browne-Feringa, Faisca-Vögel), drug-delivery vesicle membrane-pumping (Garcia-Lopez 2017 Nature 548:567 — motor molecules drilled cancer cell membranes).

Self-assembly

A larger principle: emergent ordered structures from many copies of a building block with directional interactions. The key insight (Whitesides 2002 Science 295:2418): self-assembly is the only feasible route to molecular structures with >10⁶ components, because covalent synthesis scales linearly in yield × steps.

Coordination cages

Fujita Pd-pyridyl chemistry — Pd(II)(en)(NO₃)₂ + 4 pyridyl ditopic ligand → Pd₆L₄ octahedral cage (Fujita 1995 Nature 378:469). Subsequent Pd₁₂L₂₄ sphere (Fujita 2010 Nature 466:589) — 24 ligand vertices, 12 Pd edges; molecular weight ~10 kDa; encapsulates organic guests for confined-cavity reactions.

Raymond (Berkeley) Fe₄L₆ tetrahedral host — 1,5,9-triamino-cyclononane caps + naphthalene bis-catecholate linker → chiral M₄L₆ tetrahedron (Caulder-Raymond 1998 J Am Chem Soc 120:8923). Ga(III) and Fe(III) variants. Catalyst inside cavity — see “supramolecular catalysis” below.

Nitschke (Cambridge) subcomponent self-assembly — Fe(II) or Zn(II) ion + bidentate pyridyl aldehyde + amine assemble in situ via imine condensation around metal centers → M₄L₆ tetrahedra, M₈L₆ cubes, M₁₂L₂₄ spheres in one pot. Acc Chem Res 2014 47:2063.

Stang Pt-pyridyl coordination-driven self-assembly (Utah) — Pt(II)(PEt₃)₂ corners + dipyridyl edges → squares, triangles, prisms.

DNA nanotechnology

DNA self-assembly trades the 4-base code for programmable Watson-Crick pairing.

Seeman (NYU) — pioneer; immobile Holliday junctions 1982; first 3D DNA cube 1991; nanomechanical DNA devices 2000s.

Rothemund DNA origami 2006 Nature 440:297. Long M13mp18 single-strand scaffold (~7249 nt) + hundreds of short “staple” oligos fold into arbitrary shapes via designed crossover hybridization. Smiley face, map of Americas, octahedron, dolphin, gear. caDNAno (Douglas-Shih, Harvard Wyss) — open-source design CAD; 2009.

3D DNA origami (Douglas-Dietz-Liedl-Högberg-Bald-Shih 2009 Nature 459:414) — square/hexagonal close-packed helix bundles. Wireframe DNA origami (Bathe MIT, Wyss-Högberg 2015) — vertex-edge polyhedra.

DNA origami applications: nanoscale rulers (DNA-PAINT super-resolution microscopy — Jungmann), drug delivery (Shih DNA nanorobot — Douglas 2012 Science), single-molecule force spectroscopy, electron-microscopy alignment, neutron-scattering probes.

DNA bricks (Yin Harvard 2012) — 32-mer bricks self-assemble into 3D voxelated structures by sticky-end logic.

DNA computing (Adleman 1994 Science; Winfree-Qian DNA strand-displacement circuits) and dynamic DNA nanotechnology (Yurke Bell Labs invader strands, Pierce Caltech HCR — hybridization chain reaction).

Peptide and protein self-assembly

Peptide amphiphiles (Stupp, Northwestern) — palmitoyl-VVVAAAEEEE-RGD-style design; hydrophobic tail + β-sheet “structural” peptide + bioactive epitope. Self-assemble in water into high-aspect-ratio nanofibers (~7 nm diameter, microns long). Science 2001 294:1684 (Stupp). Used in regenerative medicine — spinal cord injury repair (Tysseling-Mattiace 2008), bone regeneration, angiogenesis induction.

Coiled-coil peptides — heptad-repeat α-helices that bundle into oligomers (parallel or antiparallel dimers, trimers, tetramers, pentamers). Designed by Woolfson (Bristol), DeGrado (UCSF). Computational protein design (Baker, Washington — Nobel 2024) extends to de novo β-barrel, jellyroll, TIM-barrel, and three-dimensional cage architectures via Rosetta scoring + RFdiffusion deep-learning backbone generation. King-Baker-Yeates 2014 Nature 510:103 — designed 25 nm dodecahedral protein nanocages.

Amyloid β-sheets — both pathological (Alzheimer’s Aβ, Parkinson’s α-synuclein) and engineered (Aggrescan / TANGO design rules; functional amyloids in CsgA E. coli curli fibers).

Block copolymer self-assembly

Cross-link polymer-chemistry and soft-matter-and-self-assembly. AB diblocks self-assemble into spherical, cylindrical, gyroid, lamellar morphologies depending on χN and f; periodicity 10-100 nm. Directed self-assembly (DSA) for sub-10 nm lithography — Intel, IBM, Samsung development programs.

Templated synthesis

Templates direct bond-forming events to produce structures inaccessible to statistical synthesis.

Anion templation

Beer (Oxford), Vögtle, Sessler — anion-templated catenane and rotaxane synthesis. Cl⁻, SO₄²⁻ hydrogen-bond to amide rings → preorganize for olefin metathesis ring-closure → high-yield interlocked product. Beer Angew Chem 2002 41:3829.

Metal-template synthesis

Sauvage Cu(I) phenanthroline as above. Leigh, Goldup expanded with Cu(I), Pd(II), Au(I), Cu(II) templates; “active-metal template” route where metal is also catalyst for the bond-forming step.

Dynamic covalent chemistry (DCC)

Reversible covalent bonds (imine, hydrazone, disulfide, boronic ester, olefin metathesis, transesterification) interconvert in a library → thermodynamic product dominates. Lehn coined DCC 1999. Sanders, Otto, Stoddart, Nitschke. Used for self-sorting libraries, dynamic combinatorial library screening (Sanders, Otto; Chem Soc Rev 2010 39:1747).

Imprinting

Molecularly imprinted polymers (MIPs) — Wulff (Düsseldorf) 1972, Mosbach (Lund). Polymerize functional monomers + cross-linker around a template molecule → cavity-complementary cross-linked matrix. After template removal, the cavity rebinds selectively. Applications: solid-phase extraction (SupelMIP Sigma 53322), affinity chromatography, sensor recognition layers, drug delivery imprinted matrices.

Chemosensing — recognition reporting

Translate molecular recognition into a measurable readout (UV-Vis, fluorescence, conductance, mass).

Fluorescent chemosensors

  • PET (photoinduced electron transfer) sensors. Fluorophore-spacer-receptor architecture. de Silva (Queen’s Belfast, 1989) — PET quenched when receptor unoccupied; binding switches off PET → fluorescence ON. Crown-anthracene Na⁺ sensor, calix-cyclam Hg²⁺ sensor.
  • ICT (intramolecular charge transfer) sensors. Push-pull dye where binding modulates donor or acceptor strength → wavelength shift. DANSL, dansyl-functionalized aza-crowns.
  • FRET sensors. Two fluorophores; binding changes distance/orientation → energy transfer modulated.
  • AIE (aggregation-induced emission). Tang (HKUST) 2001 — tetraphenylethylene (TPE), hexaphenylsilole turn ON in aggregated state. Inverts the ACQ (aggregation-caused quenching) problem of planar fluorophores.

Real sensors: K⁺ in physiology (Minta-Tsien BAPTA Ca²⁺ analogues, K⁺-binding triazacryptand Frangioni), pH (BCECF, SNARF, pHrodo from Invitrogen), Zn²⁺ (TSQ, Zinpyr — Lippard), NO (DAF-FM, Lin Jianjun), reactive oxygen species (DHE, MitoSOX, dihydrofluorescein).

Indicator displacement assays (IDA) and dimensional displacement assays (DA)

Anslyn (Texas Austin) 1990s-2000s. Pair a host with a colorimetric/fluorescent dye indicator — analyte displaces indicator → optical change. Avoids functionalizing host with a fluorophore for every new analyte.

Classic IDA: Anslyn’s boronic acid receptors + alizarin red S indicator for sugar sensing (saccharides bind boronate, displace alizarin); citrate sensor (guanidinium copper complex + pyrocatechol violet displaced by citrate). Anslyn Acc Chem Res 2001 34:963 “Indicator-Displacement Assays.”

Differential receptor arrays — “chemical noses”

Multiple cross-reactive receptors trained statistically against analyte mixtures. Lewis (Caltech) carbon-black polymer-composite resistive array; Suslick (Illinois) colorimetric porphyrin/pH-dye array; Anslyn cross-reactive boronic-acid arrays for protein/glycoprotein discrimination. Principal component analysis or LDA classifies analyte fingerprints.

Electrochemical sensors

Beer ferrocene-amide rotaxanes, Sessler calix[4]pyrrole sensors, Steed urea-anion receptors with ferrocene or quinone reporters — anion binding shifts redox potential.

Mass-spec recognition

Schalley (FU Berlin) ESI-MS competition experiments quantify binding constants of host-guest pairs from mass ratios.

Supramolecular catalysis

Catalysis by encapsulation in a designed cavity — analog of an enzyme active site. The cavity provides: (1) substrate preorganization, (2) effective-molarity enhancement of co-encapsulated reagents, (3) microenvironment effects (polarity, pH, electrostatics), (4) selective product release.

Rebek tennis ball / softball / jelly doughnut

Julius Rebek (Scripps) 1993 — two glycoluril-derived molecules form a “tennis ball” hemispherical assembly bound by 8 hydrogen bonds. Guests bound inside; constrictive binding. J Am Chem Soc 1993 115:797.

Extension to “softball” (Rebek 1995, larger cavity for two-guest binding). Catalyzes [2+2] cycloadditions and Diels-Alder by templating substrates. Demonstrated autocatalysis — the encapsulated product is itself a host, enabling exponential self-replication.

Raymond Fe₄L₆ / Ga₄L₆ tetrahedron

Raymond cage K12[Ga₄L₆] where L = N,N’-bis(2,3-dihydroxybenzoyl)-1,5-diaminonaphthalene; ΔΔΔΔ or ΛΛΛΛ chirality. Anionic interior (charge -12) encapsulates cationic guests (R₃NMe⁺, tropylium cation).

Catalytic feats:

  • Aza-Cope rearrangement of encapsulated enammonium salt: ~10⁵-fold rate acceleration (Fiedler-Bergman-Raymond 2004 J Am Chem Soc 126:3674).
  • C-H activation by Ir(I) and Pt(II) cations encapsulated; reactivity altered by confinement.
  • Acid catalysis in basic solution: Pluth-Bergman-Raymond 2007 Science 316:85 — orthoformate hydrolysis catalyzed by Ga₄L₆ that protonates orthoformate inside cavity at pH 10. Apparent pK_a shifted by >5 units by the anion-lined cavity.
  • Aldol, Mukaiyama aldol, Nazarov cyclization with cation-stabilization inside cage.

Raymond-Bergman Acc Chem Res 2009 42:1650 — comprehensive review.

Fujita Pd cage chemistry

Fujita Pd₆L₄ octahedron, Pd₁₂L₂₄ sphere stabilize encapsulated species: photo-induced [2+2] alkene dimerization (regiochemistry controlled by host); Diels-Alder of normally unreactive partners; siloxane oligomer cyclization; o-benzyne dimerization (Inokuma 2010 Nat Chem) — “crystalline sponge” method observing in capsule via single-crystal XRD of guest in soaked Pd₁₂L₂₄ crystal.

Encapsulated enzymes — biocatalysis hybrids

Embed enzymes (lipase, peroxidase, lysozyme) inside MOFs (ZIF-8, PCN-333, NU-1000) or organic capsules. Tsung, Farha, Lin, Ma groups — “biomimetic encapsulation” extends enzyme operating range (pH, T, organic solvent). Cytochrome c in NU-1000 retains activity in 90 °C aqueous; lipase in ZIF-8 active in toluene.

Catalysis by anion receptors

Jacobsen (Harvard) hydrogen-bond-donor catalysis — thiourea or squaramide hydrogen-bonds anion leaving group of substrate, stabilizing developing charge in SN1, Mannich, Pictet-Spengler. Asymmetric variants with chiral thioureas (Takemoto, Connon, Jacobsen) routine for organocatalysis. Many of the privileged motifs are recognizable supramolecular receptors.

Pharmaceutical applications

Cyclodextrin solubilization

Cyclodextrins solubilize hydrophobic drugs by inclusion of the drug’s hydrophobic portion in the CD cavity. Patient-administered formulations:

  • Sporanox IV/oral solution (itraconazole + HP-β-CD). Janssen 1997 onward. HP-β-CD ~40% w/v dissolves antifungal triazole.
  • Vfend IV (voriconazole + SBE-β-CD/Captisol). Pfizer 2002.
  • Geodon IM (ziprasidone + SBE-β-CD). Pfizer 2001.
  • Abilify Maintena IM (aripiprazole + sulfobutylether-β-CD). Otsuka.
  • Veklury IV (remdesivir + SBE-β-CD/Captisol). Gilead; first FDA-approved COVID-19 antiviral 2020. SBE-β-CD enabled solubilization at clinically useful concentrations.
  • Nexterone IV (amiodarone + SBE-β-CD). Baxter — alternative to Tween/benzyl-alcohol formulations.

CD inclusion shifts apparent solubility 10-1000× without modifying the drug molecule. Stability boost (light, oxidation, hydrolysis) sometimes incidental. Mouth-feel improvement (CD masks bitter); taste-modified pediatric formulations.

Sugammadex (Bridion) — the textbook host-drug

Sugammadex (Anton Bom, Organon Newhouse Scotland 2002; FDA 2015) is a γ-cyclodextrin derivative with eight per-6-thiopropionate groups on the narrow rim (8 negatively charged carboxylates). It selectively encapsulates rocuronium (and vecuronium), neuromuscular-blocking steroidal aminosteroids used in anesthesia.

Binding constant K_a ~10⁷ M⁻¹ in saline; complete reversal of neuromuscular block within ~3 minutes (vs ~10-30 minutes for traditional neostigmine + glycopyrrolate). Eliminates anticholinergic side effects. Approved EU 2008, FDA 2015 (delayed over hypersensitivity concerns); now standard rescue agent in ORs globally. Anesthesiology multiple 2010s reviews. Merck (post-Organon merger) markets as Bridion. Annual sales >$1B by 2023.

Sugammadex represents the most successful supramolecular drug ever — a host molecule whose mechanism of action is host-guest complexation. Other sequestering antidotes are following: detoxifying scaffolds for digoxin (Digibind antibody Fab is biological, not synthetic supramolecular), local-anesthetic overdose (Intralipid emulsion, not strictly supramolecular but lipid sequestration), chelation therapy for heavy metals (DMSA, DMPS, deferoxamine, deferasirox — small-molecule chelators).

Calixarene drug candidates

  • Mecamylamine + p-sulfonatocalix[4]arene — IP/research stage; reverses nicotine binding.
  • Calixarene sulfonate as virucidal — Garcia-España, Sansone — interacts with viral surface proteins.
  • MTC-220 — calix[6]arene-based hepatitis B antiviral (clinical research stage).

Cucurbituril sequestering antidotes

Calabadion (Isaacs, Maryland 2012) — acyclic cucurbituril derivative binds neuromuscular blockers (cisatracurium, rocuronium) and reverses anesthetic narcotics (methamphetamine, ketamine in vivo). Eikenboom Maryland Innovation Initiative spin-out commercialization. Pre-clinical; potential next-generation Sugammadex covering non-steroidal blockers.

MOF drug delivery

MIL-100(Fe), MIL-101(Fe), UiO-66 loaded with ibuprofen, doxorubicin, busulfan, cisplatin. Horcajada-Couvreur (Villejuif) — biocompatible “BioMOFs.” Slow release via framework degradation. Pre-clinical to early clinical (NanoBiotix in radiotherapy enhancer NBTXR3 uses HfO₂ nanoparticles — different field).

Pillararene and rotaxane drug platforms

Stoddart-Sauvage rotaxanes investigated as drug-delivery platforms (controlled release on switch trigger). Pillararene-based supramolecular vesicles for targeted delivery (Huang, Zhejiang — pillar[5]arene-grafted polymers; Wang).

Computational supramolecular chemistry

Cross-link computational-chemistry-deep for methods detail.

  • Force-field-based binding energy. OPLS-AA, AMBER GAFF, CHARMM CGenFF for hosts + guests in explicit solvent; PMF (potential of mean force) via umbrella sampling or metadynamics.
  • DFT for cavity binding. Dispersion-corrected DFT essential (D3, D4 — Grimme; or vdW-DF) since vdW dominates inside hydrophobic cavities. M06-2X, ωB97X-D, B3LYP-D3 typical functionals; def2-TZVP basis.
  • MM-PBSA / MM-GBSA. Post-processing binding-affinity estimate from MD trajectory. Used widely for host-guest competitions and drug-receptor in CADD.
  • Alchemical free energy. Thermodynamic integration, Bennett acceptance ratio, λ-dynamics; gold-standard for relative binding energies, ~1 kcal/mol accuracy.
  • SAMPL challenges. Statistical assessment of modeling of proteins and ligands — community blind-prediction tests; host-guest sub-challenges (cucurbiturils, octa-acid cavitand, Gibb deep-cavity hosts) since 2010.

Workflows — practical playbook

Determine a binding constant

  1. ITC (isothermal titration calorimetry). MicroCal/Malvern PEAQ-ITC, TA Instruments Affinity ITC. Direct ΔH and K_a from one titration; ΔG, ΔS derived. Best for K_a 10³-10⁸ M⁻¹ in single titration; tighter binding via competitive ITC.
  2. NMR titration. Track guest chemical shift vs [host] added; fit to 1:1 or 1:2 model in Bindfit (Open Data Fit, Hibbert-Thordarson). K_a 10²-10⁵ M⁻¹ range; larger requires displacement.
  3. UV-Vis or fluorescence titration. Sensitive for chromophore/fluorophore-active hosts or guests; K_a 10³-10⁸ M⁻¹.
  4. Competition / displacement. Indicator-displacement (Anslyn) when host has known binding to a reporter dye.
  5. Mass spec. Schalley competition method.

Synthesize a host

  1. Choose target architecture based on guest size, shape, charge. Cavity-diameter selection rules: alkali metals → crown size match; tetrahedral cations → cryptand; alkyl/aryl guests in water → CD or CB or pillararene; large neutral organics → MOF cage; chiral guests → chiral cavitand or M₄L₆.
  2. Template strategy if needed (metal, anion, or thermodynamic via DCC).
  3. Workup — extensive purification (Soxhlet wash, recrystallization, prep HPLC); supramolecular hosts often contain residual templates/guests that confound binding assays.
  4. Characterize — ¹H/¹³C NMR (often with VT to slow conformer averaging), HRMS, IR, XRD if crystalline, ITC against benchmark guest, computational structure.

Design a chemosensor

  1. Define analyte and matrix (water, plasma, organic solvent, gas phase). Specify required sensitivity and selectivity.
  2. Pick recognition motif — receptor with K_a appropriate for analyte concentration; selectivity against likely interferents.
  3. Pick reporter — fluorescence (most sensitive), absorbance, electrochemistry, mass change.
  4. Couple recognition to reporter — PET, ICT, FRET, AIE, displacement.
  5. Characterize sensor — LOD, dynamic range, response time, reversibility, interference profile, matrix effects.

Industrial applications beyond pharma

Food and fragrance

Cyclodextrin encapsulation: HSE clinker odor control (β-CD sequesters volatile sulfur), fragrance microencapsulation in textiles (β-CD-grafted cotton — Febreze Glade, P&G), aroma masking in pharmaceuticals, ethanol-removal from wine (Wacker AROMARES). Vacuolation of garlic odor via β-CD.

Cosmetics and consumer products

Encapsulation of unstable actives (vitamin C, retinol, fragrance) in β-CD or HP-β-CD. Sustained release in deodorants, antiperspirants, hair care.

Agrochemicals

β-CD inclusion of pheromones (codling moth, gypsy moth) for slow release in confusion-mating biopesticides. Reduces application rate and frequency.

Chromatographic separation

CD-bonded chiral stationary phases (Chiralpak CD-Ph, Astec Cyclobond) for enantiomer separation. Calixarene and crown-ether stationary phases for alkali-metal separation (Sigma-Aldrich Custom Chiral phases).

Nuclear waste cleanup

Calix[4]arene-bis(crown-6) extracts Cs⁺ selectively from acidic tank waste — Hanford / Savannah River CSSX (Caustic-Side Solvent Extraction); patented 1996 ORNL; deployed Savannah River Salt Waste Processing Facility 2018-present.

Gas storage and separation

MOFs: H₂ storage (MOF-5 ~7.5 wt% at 77 K, 80 bar; UMCM-1; NU-100), CH₄ storage for natural-gas vehicles (HKUST-1, MOF-74 series at 65 bar surpass DOE 2025 target 0.5 g/g), CO₂ capture (Mg-MOF-74, mmen-Mg2(dobpdc) — McDonald-Long-Smit 2015 Nature).

Crystal engineering

Supramolecular architectures in the solid state. Cocrystals (a multi-component crystal where each component is solid alone at RT and which is not a salt) bridge organic synthesis, supramolecular chemistry, and pharma. FDA Regulatory Classification of Pharmaceutical Co-Crystals (2018) clarified that cocrystals are not salts — separate IP and approval considerations.

Cocrystal design

Etter, Desiraju synthons — recurring H-bond patterns. Carboxylic acid + amide → R₂²(8); pyridine + carboxylic acid → strong N-H···O=C + O-H···N pair. Predict cocrystal partners (coformers) from synthon analysis.

Pharmaceutical cocrystals

  • Caffeine + oxalic acid cocrystal. Trask-Motherwell-Jones 2005.
  • Carbamazepine + saccharin (CBZ-SAC). Better dissolution than parent CBZ.
  • Sildenafil + acetylsalicylic acid (research stage).
  • AMG 517 + sorbic acid (Amgen).
  • Caffeine cocrystal galantamine (Janssen Alzheimer’s).
  • Entresto (sacubitril/valsartan) — Novartis; sodium-bonded supramolecular complex (debatably cocrystal-vs-salt).

Mechanochemistry for cocrystals

Liquid-assisted grinding (LAG) — Jones (Cambridge), Friščić (McGill) — solvent-free or solvent-drop ball-mill cocrystallization. Scalable; eliminates solvent recovery; rapid screening. Cross-link green-chemistry-and-process-intensification.

Foldamers — folded synthetic polymers

Gellman (Wisconsin), Moore (Illinois), Huc (Bordeaux), Lehn — non-natural backbones (β-peptides, peptoids, aromatic amide foldamers, aryl-ureas) that fold into defined helices, sheets, hairpins by hydrogen-bonding and stacking. Bridge to supramolecular chemistry — foldamers are “molecular Lego” with secondary structure for binding pockets.

Applications: protein-protein interaction inhibitors, antimicrobials (cf. peptide antibiotics resistant to proteases), molecular machines as foldamer rotors and shuttles.

Adjacent

Further reading

  • Anslyn, E.V., Dougherty, D.A. — Modern Physical Organic Chemistry. University Science Books, 2006 — chapters on non-covalent interactions, host-guest binding, supramolecular thermodynamics.
  • Steed, J.W., Atwood, J.L. — Supramolecular Chemistry, 2nd ed. Wiley, 2009 — the comprehensive textbook; encyclopedic coverage of hosts, machines, sensors, crystal engineering.
  • Lehn, J.-M. — Supramolecular Chemistry: Concepts and Perspectives. VCH, 1995 — founding monograph from the Nobel laureate.
  • Cram, D.J. — Container Molecules and Their Guests. RSC, 1994 — cavitands and carcerands from Cram’s perspective.
  • Stoddart, J.F. — “The Master of Chemical Topology” (assorted reviews 2010-2020 Angew Chem, Acc Chem Res) — mechanically interlocked architectures.
  • Sauvage, J.-P., ed. — From Non-Covalent Assemblies to Molecular Machines. Wiley-VCH, 2010.
  • Rebek, J. — Hydrogen-Bonded Capsules: Molecular Behavior in Small Spaces. World Scientific, 2016.
  • Schneider, H.-J., ed. — Supramolecular Systems in Biomedical Fields. RSC, 2013 — cyclodextrins, cucurbiturils, MOFs in pharma.
  • Crabtree, R.H. — The Organometallic Chemistry of the Transition Metals, 7th ed. Wiley, 2019 — chapters on metal-templated assembly and cage chemistry.
  • Smith, M.B. — March’s Advanced Organic Chemistry, 8th ed. Wiley, 2020 — pericyclic, condensation, and template-controlled bond-forming chemistry underpinning host synthesis.

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