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Design and Self-Assembly of Molecular Prisms for Chemical Signature Detection

Explore the self-assembly of molecular prisms via Pt-based acceptors and clips for chemical signature detection of explosives. Results include synthesis details, spectroscopic studies, and potential sensor applications.

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Design and Self-Assembly of Molecular Prisms for Chemical Signature Detection

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  1. Self-Assembly of Molecular Prisms via Pt3 Organometallic Acceptorsand a Pt2 Organometallic ClipSushobhan Ghosh, Bappaditya Gole, Arun Kumar Bar, and Partha Sarathi Mukherjee*Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore-560 012, India Ref) Organometallics, Vol. 28, No. 15, 2009 Advanced Instrumental Analysis lab Ji Eun Park 09.08.13

  2. Introduction solution fluorescence  quenched efficiently by adding nitroaromatics  chemical signatures 4,4’,4’’-tris[ethynyl-trans-Pt- (PEt3)2(NO3)]triphenylamine +1,3-bis(3pyridylethynyl)benzene  trigonal prism 4,4’,4’’-tris(4-pyridylethynyl) triphenylamine + organometallic Pt2-clip  3c Ref) (a) Ghosh, S.; Mukherjee, P. S. Organometallics 2008, 27, 316. Schultheiss, N.; Ellsworths, J. M.; Bosch, E.; Barnes, C. L. Eur. J.Inorg. Chem. 2005, 45.

  3. Introduction new tripodal Pt3-organometallic acceptor  4,4’,4’’-tris[ethynyl-trans-Pt(PEt3)2(NO3)]triphenylethane + [1,8-bis(4-pyridylethynyl)anthracene] [2 + 3]  self-assembled prismatic derivative

  4. Results Synthesis of the Linkers Ref) (a) Ghosh, S.; Mukherjee, P. S. Organometallics 2008, 27, 316. Kryschenko, Y. K.; Seidel, R. S.; Muddiman, D. C.; Nepomuceno,A. I.; Stang, P. J. J. Am. Chem. Soc. 2003, 125, 9647

  5. Results Synthesis of the Linkers 31P{1H}NMR 195Pt ESI mass spectrum molecular ion [M+H+] m/z =1807.5 [M-4PEt3-NO3-]+ fragment m/z = 1274

  6. Results Synthesis of the Linkers · Cell dimensions of 1c  crystal system, cubic; space group, Pa ; α = 25.4754(5) Å; R=90° · The optimization of the tripodal linker density functional theory (DFT) calculations Gaussian 03 program, B3LYP functional · 6-31G for lighter elements (C, H, N, and O) & LanL2DZ for heavier elements (Pt and P). · X-ray structure analysis  I-C(central)-I angle ;110.97° · Pt environment angles 86.44° and 93.11°, Ref) Kryschenko, Y. K.; Seidel, R. S.; Muddiman, D. C.; Nepomuceno,A. I.; Stang, P. J. J. Am. Chem. Soc. 2003, 125, 9647

  7. Results Self-Assembly of Molecular Prisms 3a-d trigonal prism design ; two tritopic donors, six 90°corners, three linear linkers  [2+6+3] self-assembly reaction The major disadvantage of three-component self-assembly formation of a mixture

  8. Results Self-Assembly of Molecular Prisms 3a-d 3b ; yellow precipitate 31P NMR - solvent;CDCl3 - singlet at 15.6 ppm - 1JP-Pt (230 Hz) for the Pt satellites.

  9. Results Self-Assembly of Molecular Prisms 3a-d • 31P{1H} NMA ;singlet , 14ppm • 5 ppm upfield • shifted from the 31P{1H}NMR ; 1b

  10. Results Self-Assembly of Molecular Prisms 3a-d Upfield shift ; phosphorus signal of 1c downfield shift ; Hα, Hβ, H9 protons of the donor ligand

  11. Results Self-Assembly of Molecular Prisms 3a-d • 3a: • [M3a- 3NO3]3+ • m/z=1452.00 (calcd 1451.66) • [M3a- 4NO3]4+ • m/z=1073.49 (calcd 1073.18) • [M3a-5NO3]5+ • m/z=846.55 (calcd 845.67) Ref) (a) Ghosh, S.; Mukherjee, P. S. Organometallics 2008, 27, 316.

  12. Results Self-Assembly of Molecular Prisms 3a-d • [M3b-3NO3-]3+ • isotropic distribution pattern of the peak , • matched well with the theoretically expected pattern

  13. Results Self-Assembly of Molecular Prisms 3a-d

  14. Results Self-Assembly of Molecular Prisms 3a-d [M3d-3NO3]3+ m/z=1523.50 (calcd 1523.33) [M3d -5NO3]5+ m/z =890.1 (calcd 889.3)

  15. Results Self-Assembly of Molecular Prisms 3a-d Obtain single crystals for X-ray diffraction  fail Supramolecule 3d energy minimization is presented

  16. Results Absorption and Fluorescence Studies. 3b spectrum ; 1.5×10-5 M solution, 283 nm  π-π* transition 365 nm  metal-to-ligand (2b) charge transfe 3c spectrum ; 3×10-6M solution 430 and 383 nm  originating from the anthracene moiety of 1b 3d spectrum ; 421 and 398 nm corresponding to the anthracene part 309nm ; attributed to platinum-to-ligand (2d) charge transfer 3b-d  excited at 400 nm ; luminescent behavior & emit beteen400nm and 500 nm

  17. Results Absorption and Fluorescence Studies. 3b-d Fluorescence spectra in DMF solutions corresponding photophysical data Table S1

  18. Conclusion ·Pt3 organometallic acceptor (1c) & nanoscopic conjugated prisms (3a-d)  Pt-ethynyl functionality · tritopic planar donor (2c) and Pt2-organometallic clip (1b)  establish the versatility of directional bonding to obtain · Pt-ethynyl incorporation; assemblies fluorescent. · conjugated ethynyl functionality  assemblies π-electron rich and possible hosts · 3a, 3c, and 3d  chemical signature of many commercial explosives · Conjugated organic polyethynyl compounds  potential sensors for chemical explosives.

  19. Introduction of Heterofunctional Groups onto Molecular Hexagons via Coordination-Driven Self-Assembly Koushik Ghosh,† Jiming Hu,†,‡ Hai-Bo Yang,§ Brian H. Northrop,† Henry S. White,*,† and Peter J. Stang*,† <ref.> J. Org. Chem. 2009, 74, 4828–4833 Young Min Lee Organic Synthesis Lab. Department of Chemistry

  20. Abstract The design and synthesis of two new heterofunctional hexagons containing both redox-active ferrocenyl and host-guest crown ether functionalities has been achieved via coordination-driven self-assembly. The size and relative distribution of functional groups on the supramolecular metallacycles can be precisely controlled. The host-guest recognition properties of the crown ether moieties and their ability to complex cationic guests to form tris[2]pseudorotaxane complexes have been investigated. The functional moieties are shown to operate orthogonally, resulting in discrete supramolecular hexagons that are capable of carrying out a variety of functions both simultaneously and independently.

  21. Introduction • The design and creation of regularly shaped nanoscale objects, which can serve as the building blocks of supramolecular materials, • is an extremely important goal in material science. • They have recently introduced a variety of functionalized 120° • platinum acceptors and 120° organic donors and have quantitatively • assembled them to form molecular hexagons with six functional • groups on their periphery. • They envisioned that acceptor-donor-based coordination-driven • self-assembly is additionally useful because of the ability to modify • functional groups at both the donor and acceptor units. • Here they employ 120° acceptor units decorated with one functional group to self-assemble with 120° donor units decorated with another • functional group to form supramolecular hexagons with six • heterofunctional groups.

  22. Result Heterofunctional Hexagons 5 and 6 • Scheme 1. Self-Assembly of Heterofunctional Hexagons • With the 120° crown ether and ferrocene functionalized precursors in hand, in both donor and acceptor analogues, the self-assembly of heterofunctional hexagons was • investigated. • Upon mixing 120° ferrocenyl donor unit 1 with 120° crown ether functionalized unit 2 in CH2Cl2, heterofunctional hexagon • 5 was obtained . • Stirring 120° ferrocenyl acceptor • unit 3 with an equimolar amount of 120° crown ether donor unit 4 in • CH2Cl2 results in heterofunctional • hexagon 6.

  23. Result Tris[2]Pseudorotaxanes 8 and 9 • Scheme 2. Entry to Hexagonal Cavity-Cored Tris[2]pseudorotaxanes • These heterofunctionalized crown ether derivatives in hand, an investigation of the self-assembly • of tris[2]pseudorotaxanes was carried out to investigate any effect(s) of ferrocene substituents in the binding of crown ether • units. • Within 15 min of adding 3 equiv • of dibenzylammonium triflate salt 7 to a solution of hexagonal metallacycles 5 and 6, tris[2]pseudorotaxanes 8 and 9, respectively, were obtained.

  24. Result 1H and 31P NMR spectra of 5 (a) 195Pt satellites (b) < Hexagon 5 > • Figure 1. 1H(a) and 31P(b) NMR spectra of 5 in CD2Cl2

  25. Result 1H and 31P NMR spectra of 6 (a) (b) 195Pt satellites < Hexagon 6 > • Figure 3. 1H(a) and 31P(b) NMR spectra of 6 in CD2Cl2

  26. Result 1H and 31P NMR spectra of 8 (a) 195Pt satellites (b) < Tris[2]Pseudorotaxanes 8 > • Figure 2. 1H(a) and 31P(b) NMR spectra of 8 in CD2Cl2

  27. Result 1H and 31P NMR spectra of 9 (a) 195Pt satellites (b) < Tris[2]Pseudorotaxanes 9 > • Figure 4. 1H(a) and 31P(b) NMR spectra of 9 in CD2Cl2

  28. Result Partial 1H NMR spectra • In the corresponding 1H • NMR spectra, the-protons • showed a relatively • dramatic upfield shift • (0.41 ppm) as well as a • slight upfield shift of the • R-protons (0.04 ppm) due • to electron density transfer • from the pyridyl donor to • the metal acceptor. • A 0.45 ppm downfield • shift of the signal for the • benzylic methylene protons adjacent to the NH2+ center was observed, and protons • Hα, Hβ, and Hγ of of the • crown ether moiety exhibited upfield shifts. • Figure 8. Partial 1H NMR spectra of crown ether acceptor 2 (A), ferrocenyl donor 1 (B), mixed • hexagon 5 (C), and pseudorotaxane 8 (D).

  29. Result ESI-MS spectra of hexagon 5 and 6 • In the ESI mass spectra of • heterofunctionalized hexagon 5, a peak attributable to the loss of four triflate counterions, [M - 4OTf]4+ where M represents the intact assembly, was observed at • m/z = 1563.9. • The ESI/MS spectra of 6 exhibited characteristics very similar to those of 5. The ESI/MS spectra showed one charged state at • m/z = 1553.4 corresponding to • the [M - 4OTf]4+ species, and its isotopic resolution is in excellent agreement with the theoretical • distribution. • Figure 5. Calculated (top) and experimental (bottom) ESI-MS spectra of hexagon 5 (A) and 6 (B).

  30. Result ESI-MS spectra of 8 and 9 • Figure 6. Calculated (top) and experimental • (bottom) ESI-MS spectra of 8. • Figure 7. Calculated (top) and experimental • (bottom) ESI-MS spectra of 9. • The self-assembly of hexagonal cavity-cored tris[2]pseudorotaxanes 8 and 9 was also confirmed by ESI-MS spectrometry. • Two peaks at m/z = 1429.4 and 1824.8 were observed, corresponding to [M - 5OTf]5+ • and [M - 4OTf]4+, respectively, for 8, as were peaks attributable to [M - 5OTf]5+ and • [M - 4OTf]4+ of 9 at m/z = 1421.1 and 1813.4, respectively.

  31. Result Pseudorotaxane Stoichiometry and Binding Constant • The host:guest stoichiometry for • heterofunctional supramolecular • assemblies 8 and 9 was established • using the nonlinear leastsquares • fit method based 1H NMR titration • experiments. • Fitting the data to a 1:3 binding • mode for the hosts gave host-guest • association constants. • Figure 9. 1H NMR titration isotherms of 8 (A) and 9 (B), • recorded at 500 MHz in CD2Cl2 at 298 K, • indicating the change in chemical shift of the • proton signal corresponding to the γ-H of the • crown ether. • Table 1. Thermodynamic Binding Constants of Poly[2]pseudorotaxanes 8 and 9a

  32. Result Simulated molecular models of 5 and 8 • Figure 10. Simulated molecular models of 5 and 8, optimized with the molecular mechanics • force field. Color scheme: C = gray, O = red, N = blue, P = purple, Pt = yellow, and • R2NH2+ hydrogen atoms =green, Fe = purple all other hydrogen atoms have been • removed for clarity.

  33. Result Simulated molecular models of 6 and 9 • Figure 11. Simulated molecular models of 6 and 9, optimized with the molecular mechanics • force field. Color scheme: C = gray, O = red, N = blue, P = purple, Pt = yellow, • Fe = pink and R2NH2+ hydrogen atoms, green (all other hydrogen atoms have been • removed for clarity).

  34. Conclusion • They have provided two complementary approaches to generate • two new heterofunctional hexagons via coordination-driven self- • assembly from a ferrocenyl 120° di-Pt(II) acceptor/donor and a • complementary 120° crown ether decorated donor/acceptor unit • while exhibiting precise control of size and the distribution of the • ferrocene and crown ether moieties. • These heterofunctional hexagons are unique in not only their • discrete structures but also the presence of chemically different • units, since each unit introduces into the supramolecular structure • its own “pieces of information” (in the form of specific properties • such as recognition properties, redox levels, etc.) that are preserved • faithfully in the structure.

  35. A Catalytically Active, Permanently Microporous MOF with Metalloporphyrin Struts Abraham M. Shultz, Omar K. Farha, Joseph T. Hupp,* and SonBinh T. Nguyen* Received January 10, 2009 Undergraduate forth BAE CHANG GEUN

  36. Figure 1. Synthesis of ZnPO-MOF. The stick representation of the unit cell is shown on the right-hand side (yellow polyhedra ) Zn, red ) O, green ) F, blue ) N, gray ) C). Solvent molecules, hydrogens, and disordered atoms have been omitted for clarity.

  37. Figure 2. Space-filling models of the crystal structure of ZnPO-MOF (solvent omitted) showing channels down the a and b crystallographic axes (yellow ) Zn, red ) O, green ) F, blue ) N, gray ) C, black ) H): (a) 15 Å × 9 Å channels along the a axis; (b) 11 Å × 9 Å channels along the b axis. The channels along the c axis (not shown) are 8 Å × 9 Å.

  38. Figure 3. Plot of product concentrations vs time, showing the initial production of the various isomers of acetoxymethylpyridine (AMP) from N-acetylimidazole and pyridylcarbinols. The inset shows data at longer times.

  39. Conclusion To summarize, they have demonstrated that by appropriate design of organic building blocks (dipyridyl pillars, robust tetratopic carboxylates), metalloporphyrins can be successfully incorporated into a MOF possessing the features needed for effective catalysis, i.e., large pores, permanent microporosity, and fully reactant-accessible active sites. Proof-of-concept catalysis of an acyl-transfer reaction revealed ∼2400- fold rate enhancement, dominated by contributions from LA activation and reactant preconcentration. They hope to report shortly on variants of ZnPO-MOF featuringother metals as active sites and functioning catalytically by other mechanisms.

  40. Coordination-Driven Self-Assembly of Metallodendrimers Possessing Well-Defined and Controllable Cavities as Cores Peter J. Stang* et al. Department of Chemistry, University of Utah, 315 South 1400 East, Room 2020, Salt Lake City, Utah 84112 J. AM. CHEM. SOC. 9 VOL. 129, NO. 7, 2007 Kim You-Jung Undergraduate Junior

  41. Introduction • Supramolecular dendrimers are a recent and important subset of such self-assembled structures. • As a consequence, attention has recently turned to the self-assembly of dendrimers to provide well-defined nanoscale architectures via a variety of noncovalent interactions such as electrostatic interactions, hydrogen bonding and metal-ligand coordination. • In particular, cavity-cored dendrimers have recently received considerable attention because of their elaborate structures and potential applications in delivery and recognition.

  42. Introduction • Previously, Percec et al. reported a library of amphiphilic dendritic dipeptides that self-assemble into helical pores both in solution and in bulk. • In addition, the possibility to fine-tune the size and shape of the cavities in metallodendrimers would help provide an enhanced understanding of the geometrical requirements necessary for molecular self-assembly. • Furthermore, this strategy would likely give rise to the design and synthesis of novel supramolecular species with desired functionality arising from their unique interior cavities and dendritic exteriors.

  43. Introduction • Recently theyreported the self-assembly of the first metallodendrimers exhibiting a nonplanar hexagonal cavity with an internal core radius of approximately 1.6nm, by the combination of 120° dendritic donor subunits (substituted with Fréchet-type dendrons) and 120° di-Pt(Ⅱ) acceptor angular linkers in a 1:1 stoichiometric ratio. • Here they report the results obtained when they extended the investigations to the self-assembly of rhomboidal and “snowflake-shaped” metalloden- drimers possessing cavities of various size and shape at the core through the use of coordination-driven self-assembly (Figure 1).

  44. Result and Discussion Synthesis of 120° Angular Dendritic Donor Subunits The synthesis of [G0]-[G3] 120° donor building blocks 5a-d commenced with acylation of the commercially available compound 3,5-dibromo-phenol (1) to give 2 (Scheme 1). The 3,5-bis-pyridylethynyl-phenyl ester 3 was prepared by palladium-mediated coupling reaction from Ester 2 with 4-ethynylpyridine in reasonable yield (66%). Upon ester hydrolysis and etherification, the [G0]- [G3] 120° precursors 5a-d (Figure 2), substituted with Fréchet-type dendrons, were obtained in good yields.

  45. Result and Discussion Synthesis of [G0]-[G3]-Rhomboidal Metallodendrimers 7a-d. The combination of 60° units with 120° linking components will yield a molecular rhomboid. Stirring the [G0]-[G3] 120° angular donors 5a-d with an equimolar amount of the known 60° angular acceptor, 2,9-(trans Pt(PEt3)2NO3)2- phenanthrene (6), in CD2Cl2 for 14h resulted in [2+2] rhomboidal metallodendrimers 7a-d, respectively, in excellent yields (Scheme 2).

  46. The 31P{1H} NMR spectra of the [G0]-[G3] assemblies 7a-d displayed a sharp singlet (ca. 14.6 ppm) shifted up field from the signal of the starting platinum acceptor 6 by approximately 6.4 ppm. This change, as well as the decrease in coupling of the flanking 195Pt satellites (ca. ¢J ) –177Hz), is consistent with back-donation from the platinum atoms. In the 1H NMR spectrum of each assembly, the R- hydrogen nuclei of the pyridine rings exhibited 0.75- 0.78 ppm downfield shifts, and the â-hydrogen nuclei showed about 0.2 ppm downfield shifts, due to the loss of electron density that occurs upon coordination of the pyridine N atom with the Pt(II) metal center. It is noteworthy that two doublets were observed for these R-hydrogen nuclei, as this might be attributed to hindered rotation about the Pt-N(pyridyl) bond, which has been previously reported. Result and Discussion

  47. Result and Discussion In the ESI mass spectra of the [G0]-[G2] assemblies 7a-c, peaks attributable to the loss of nitrate counter ions, [M - 2NO3]2+ (m/z ) 1486.9 for 7a, m/z ) 1699.0 for 7b, and m/z ) 2123.8 for 7c) and [M - 3NO3]3+ (m/z ) 970.5 for 7a, m/z ) 1112.0 for 7b, and m/z ) 1394.8 for 7c), where M represents the intact assemblies, were observed (Figure 3)

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