Supramolecular star polymers with compositional heterogeneity

Supramolecular Star Polymers with Compositional Heterogeneity

Ikhlas Gadwal,1 Swati De,1 Mihaiela C. Stuparu,2 Roey J. Amir,3 Se Gyu Jang,3 Anzar Khan1

1Department of Materials, ETH-Zurich, CH-8093 Zurich, Switzerland2Institute of Organic Chemistry, University of Zurich, CH-8057 Zurich, Switzerland3Materials Research Laboratory, University of California, Santa Barbara, California 93106

Correspondence to: A. Khan (E-mail: [email protected])

Received 5 December 2011; accepted 26 December 2011; published online 13 February 2012

DOI: 10.1002/pola.25956

ABSTRACT: We present the synthesis of supramolecular star poly-

mers with heterogeneous chemical compositions through potas-

sium cation-templated assembly of guanosine end-functionalized

random, diblock, and Y-shaped copolymers. The assembly and

disassembly processes of the synthesized star polymers have

been systematically examined on changing the concentration,

the temperature, the solvent, and the amount of cation using 1H

NMR, UV/vis, and CD spectroscopy. VC 2012 Wiley Periodicals,

Inc. J Polym Sci Part A: Polym Chem 50: 1844–1850, 2012

KEYWORDS: G-quadruplexes; guanosine assembly; supramolec-

ular structures; star polymers; structure-property relations

INTRODUCTION Supramolecular star polymers are branchedpolymeric architectures in which the branches radiate from acore that is formed via noncovalent interactions.1–6 Becauseof the noncovalent nature of the core, supramolecular starpolymers can undergo reversible assembly–disassemblyprocesses to polymer-arm and polymer-star forms, undercertain experimental conditions. The reversibility of thestructure formation7 brings interesting stimuli responsiveproperties to this unique class of materials. Hence, severalresearch groups have been involved in developing syntheticstrategies to the supramolecular star polymers. Todd andZimmerman described an elegant approach to hexa-arm starpolymers by using ditopic hydrogen bonding modules.1 Thegroups of Schubert and Fraser independently reported avariety of supramolecular star polymers (three to six arms)based on metal–ligand complex formation.2,3 Gibson and co-workers4 contributed a nice example by using pseudorotax-ane complexation to connect three polymer arms to a coremolecule. Bernard and coworkers5 used thymine and diami-nopyridine-based heterocomplementary hydrogen bondingunits to prepare triarm architectures. Barner-Kwollik and co-workers6 also produced triarm star polymers via a Hamiltonwedge-cyanuric acid bonding motif. Recently, Tam and co-workers utilized G-quadruplex formation8,9 of the guanosineend-functionalized methyl methacrylate-based homopolymersto give chemically homogeneous star polymers.10 Here, weuse the same motif—G-quadruplex formation8,9—to preparesupramolecular star polymers (Fig. 1). However, we aim atsystematically increasing the chemical complexity of thesynthesized branched systems and developing a structure–

property relationship in these complex architectures. We areparticularly attracted to the G-quadruplex motif due to itshigh reproducibility, quantitative yields, high thermal stabil-ity, complete reversibility, and the capacity to assemble aminimum of eight subunits.8,9 We chose to demonstrate ourobjective with the help of three different examples (Fig. 2).In the first example, the assembly precursor is a lineardiblock copolymer composed of polymethyl methacrylate(PMMA) and polystyrene (PS) segments (1). Assembly viathis precursor generates an octa-arm star polymer in whichthe star polymer core is surrounded by concentric PS andPMMA shells (18.K

þ). In the second system, the precursor iscomposed of randomly distributed hydrophilic ethylene gly-col and hydrophobic propylene glycol repeat units (2). Cat-ion-templated assembly using this precursor leads to the for-mation of a branched architecture in which the hydrophobicand hydrophilic elements are distributed randomly along thebranched architecture (28.K

þ). In the third system, a Y-shaped diblock copolymer bearing a guanosine molecule atits focal point is utilized (3). Assembly using this precursorgives rise to a star polymer in which the two chemically dif-ferent polymeric segments are distributed along thebranched structure in an alternating fashion (38.K

þ).11

RESULTS AND DISCUSSION

Synthesis of the Assembly PrecursorsSynthesis of precursors 1 and 2 was accomplished via anesterification reaction between hydroxy-equipped poly(sty-rene-b-methyl methacrylate) (Mn � 1600PS-b-1700PMMA g/mol) or poly(ethylene glycol-ran-popylene glycol) (Mn � 970

Additional Supporting Information may be found in the online version of this article.

VC 2012 Wiley Periodicals, Inc.

1844 JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 1844–1850

ARTICLE WWW.POLYMERCHEMISTRY.ORGJOURNAL OF

POLYMER SCIENCE

g/mol) and guanosine acid (Scheme 1). Synthesis of 3started with conjugate addition between hydroxy-ethyl acry-late and amino-functionalized polypropylene glycol (Mn �600 g/mol) thus giving rise to a polymer end-functionalizedwith two hydroxyl groups.12 One of the hydroxyl moietieswas converted into a polymerization initiator via reactionwith 2-bromoisobutyryl bromide. Atom transfer radical poly-merization (ATRP) from this macroinitiator gave access to PSarm (Mn � 2000 g/mol). This sequence led to the formationof Y-shaped diblock copolymer bearing a reactive hydroxylgroup at the focal point of the PS and polypropylene glycolchains. Esterification reaction between the hydroxyl groupand the guanosine acid afforded the desired Y-shaped pre-cursor 3 (Scheme 1).

Cation-Templated AssemblyBuilding blocks 1, 2, and 3 show well-defined proton signalsin DMSO-d6/DMF-d7 (Fig. 3). Noteworthy is the sharp signalsfrom the amide (!NH) and the amine (nNH2) protonsaround 10.7–10.8 and 6.5 ppm, respectively. This indicatesthat the building blocks do not self-associate via hydrogenbonding due to the highly competitive nature of this solvent.In chloroform, the proton signals are also well resolved (Sup-porting Information Figs. S1–S3) with the exception of theamide signal which is shifted and broadened, indicatingsome degree of self-association in absence of a potassiumcation to give ill-defined linear oligomers via hydrogen-bond-ing interactions.13

Addition of 0.125 equiv of KI (8:1 ratio of the polymer pre-cursor to the potassium ion) to the chloroform solution of 1,2, and 3 results in dramatic downfield shift of the amideproton (!NH) to about 12.3 ppm (Fig. 3). As expected for ahydrogen bonded cyclic quartet in the polymer core, the

amine protons split into two signals; one is hydrogen bondedand hence shifts downfield to about 9.5 ppm (hNH, Fig. 3)while the other is free and upfield shifted to about 6 ppm(nNH, Fig. 3). These signals are very weak at room tempera-ture due to the fast rotation of the amine protons aroundthe CAN bond, however, at low temperatures (0 to �20 �C,Fig. 4), the amine protons exchange slowly on the NMR timescale, and hence, signals of relatively high intensity can beobserved. Furthermore, the CH proton (*CH, Fig. 4) of theheterocyclic ring shows a pronounced upfield shift to 7.1ppm upon star formation presumably due to the aromaticstacking interactions. The singlet from the amide protondemonstrates formation of a well-defined guanosine octameras a polymer core in all cases. Addition of more potassiumcations did not lead to any changes in the assembly size asjudged by the unchanged proton spectra of all the systemsupon titration with potassium iodide salt (Supporting Infor-mation Figs. S4–S6).

UV–Vis SpectroscopyUV–vis spectroscopy of all the systems showed absorptionmaxima around 260 nm for the free polymer precursors 1,2, and 3 (Supporting Information Fig. S9). The absorptionmaxima of 28.K

þ is, however, shifted to 250 nm, while nochange was detected in this region in the case of 18.K

þ and38.K

þ that bear electronically active styrene repeat-units. Amarked difference in the UV–vis spectra of the free polymerprecursors and their respective star assemblies can beobserved at 290 nm at which the assemblies show a newabsorption band due to a specific stacked arrangement ofthe aromatic units in the G-quadruplex-based star polymercore.14

CD SpectroscopyTo investigate the stereochemical nature of the guanosine-based star polymer core, circular dichroism (CD) spectros-copy was used (Fig. 5). All the systems (18.K

þ, 28.Kþ, 38.K

þ)exhibit typical exciton couplets with two bands of oppositesigns at 265 and 290 nm, where kmax in absorption (250nm; Supporting Information Fig. S9) corresponds to zero CDintensity.15 This feature is diagnostic of a heteropolar (D4-symmetric) stacked chiral arrangement of the heterocyclicguanine chromophores of the supramolecular octamer at thestar polymer core.16 As expected, the precursor polymerchains 1, 2, and 3 do not exhibit any CD signal in the rangeof 250–320 nm (region of guanine absorption) due to ab-sence of any supramolecular chiral structure.

Variable Temperature NMR StudiesTemperature-dependent NMR spectroscopy was then used tostudy the thermal stability of the supramolecular assemblies(Fig. 4). The linear diblock copolymer star, 18.K

þ, remainsstable at 50 �C while the random copolymer star, 28.K

þ,starts to disintegrate at this temperature, as judged by theirheterocyclic CH (*CH) and the amide proton (!NH) signals.The Y-shaped diblock copolymer star, 38.K

þ, also begins todisintegrate into its building block at 50 �C. These data indi-cate the lower thermodynamic stability of the random andY-shaped diblock copolymer-based star polymers in

FIGURE 1 Chemical and cartoon representation of a polymeric

guanosine derivative and the G-quadruplex formation upon

addition of potassium salts. The anion remains at the complex

periphery and is not shown.

JOURNAL OFPOLYMER SCIENCE WWW.POLYMERCHEMISTRY.ORG ARTICLE

WWW.MATERIALSVIEWS.COM JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 1844–1850 1845

chloroform. In all cases, cooling the sample to room temper-ature restored the original proton spectra, thus demonstrat-ing the reversibility of the star formation.

Variable Concentration NMR StudiesDilution experiments in chloroform were then carried out toassess the range of concentrations over which the supramolec-

ular stars remain unbroken (Fig. 6). At 1 mM and higher con-centrations, all the systems remain intact. However, at 0.1 mMconcentration, 28.K

þ breaks significantly, and 38.Kþ dissociates

completely into its precursor polymer 3, whereas 18.Kþ shows

no disintegration at this concentration. These data show thatthe linear diblock copolymer star polymer, 18.K

þ, is more sta-ble to dilute conditions when compared with 28.K

þ and 38.Kþ.

FIGURE 2 Chemical structures of the assembly precursors and the resulting star polymers. The guanosine moiety is represented

graphically.


POLYMER SCIENCE


Mixed Solvents StudiesNext, we became interested in investigating the relativestabilities of the star polymers in mixed solvent systems, inwhich one solvent stabilizes the supramolecular interactions

while the other competes for the hydrogen bonding interac-tions (such as DMSO/DMF). This is accomplished by gradualaddition of DMSO/DMF to the chloroform solution of 18.K

þ,28.K

þ, and 38.Kþ (Fig. 7). Because of the insolubility of 1 in

DMSO, DMF was added to the chloroform solution of 18.Kþ

and almost complete dissociation was observed at 30% DMFaddition, whereas 15% DMSO addition is required to com-pletely break 28.K

þ and 38.Kþ into their precursors. The

higher amount of polar solvent needed to ‘‘denature’’ the lin-ear diblock copolymer star reflects on its comparativelyhigher stability. Although, due to the different chemical

SCHEME 1 Synthesis of the guanosine chain end functionalized star polymer precursors 1, 2, and 3.

FIGURE 3 1H NMR spectra of precursor polymers 1 (DMF-d7), 2

(DMSO-d6), and 3 (DMSO-d6) and their respective star poly-

mers in CDCl3 (1.25 mM). In all cases, tetramethylsilane (TMS)

was used as an internal standard. Solvent signals are shown

with a cross sign.

FIGURE 4 Variable-temperature 1H NMR spectra of 18.Kþ in

CDCl3. Refer to Supporting Information Figures S7 and S8 for

28.Kþ and 38.K

þ.



nature of the polar solvents involved, a direct comparison isnot possible. Furthermore, dissolution of 18.K

þ in CHCl3:DMF(1:1), and 28.K

þ and 38.Kþ in CHCl3:DMSO (1:1) resulted in

total disappearance of the CD signal, again, demonstratingthat the supramolecular stars disintegrate in the hydrogenbonding-competitive solvents (Supporting InformationFig. S14).

EXPERIMENTAL

Please see the Supporting Information for the synthesisdetails of the Y-shaped precursor, 3, and Figures S1–S16.

Synthesis, Guanosine acid: Suspension of hydroxy-guanosine(1.0 g, 3.0 mmol), triethylamine (TEA; 1 mL, 7 mmol), and 4-dimethylaminopyridine (DMAP; 0.1 g, 0.9 mmol) was stirredin dry acetonitrile at 25 �C for 10 min. To this suspension,succinic anhydride (0.46 g, 4.6 mmol) was added, and thereaction mixture was allowed to stir for additional 18 h. Af-ter which time the suspension was filtered and the solid wascollected and washed with minimum amount of DCM anddried under high vacuum conditions to afford 0.73 g of gua-nosine acid as a white solid (Yield ¼ 56%).1H NMR (d, ppm, 300 MHz, DMSO-d6): 10.83 (br s, 1H, NH),7.91 (s, 1H), 6.62 (br s, 2H, NH2), 6.01 (d, J ¼ 2.1 Hz, 1H),5.24 (dd, J ¼ 2.1 Hz, J ¼ 6.3 Hz, 1H), 5.13 (dd, J ¼ 2.1 Hz, J¼ 6.3 Hz, 1H), 4.26 (m, 2H), 4.14 (m, 1H), 2.45 (s, 4H), 1.52

(s, 3H), 1.33 (s, 3H); 13C NMR (d, ppm, 125 MHz, DMSO-d6):174.4, 172.7, 157.3, 154.4, 151.1, 136.6, 117.5, 113.9, 88.8,84.7, 84.2, 81.5, 64.6, 25.9, 25.8; ESI-MS: m/z ¼ 424.14[MþH]þ (calcd. 423.37 for C17H22N5O8), 446.12 [MþNa]þ

(calcd. 446 for C17H21N5O8Na).

FIGURE 5 CD spectra of 1 (a), 2 (b), and 3 (c) as solid line, and 18.Kþ (a), 28.K

þ (b), and 38.Kþ (c) as dashed line, in chloroform (a ¼

0.425 mM, b ¼ 0.134 mM, c ¼ 0.204 mM).

FIGURE 6 Variable-concentration 1H NMR spectra of 18.Kþ in

CDCl3. Refer to Supporting Information Figures S10 and S11

for 28.Kþ and 38.K

þ.


POLYMER SCIENCE


General esterification procedure: A mixture of guanosineacid (0.16 g, 0.4 mmol), EDCI.HCl (0.12 g, 0.6 mmol), HOBt(0.08 g, 0.6 mmol), DMAP (0.01 g, 0.1 mmol), and hydroxyl-terminated poly(styrene-b-methyl methacrylate) (1.0 g, 0.3mmol) in pyridine (10 mL) was stirred at 25 �C for 48 h.Pyridine was removed under reduced pressure, and thecrude solid was dissolved in minimum amount of DCM andprecipitated into 200 mL of methanol. The solid was isolatedby filtration and purified by column chromatography (DCM/MeOH; 95:5) to yield 0.3 g of 1 (Yield ¼ 29%).

1H NMR (d, ppm, 700 MHz, DMF-d7): 10.78 (s, 1H, NH), 7.96(s, 1H), 7.27–6.69 (br m, ArH), 6.14 (s, 1H), 5.38 (d, J ¼ 5.6Hz, 1H), 5.22 (d, J ¼ 2.8 Hz, 1H), 4.37 (m, 1H), 4.32 (m, 1H),4.24 (m, 1H), 3.89 (br m, 2H), 3.63–3.60 (br m), 2.59–2.53(m, 5H), 2.13–1.43 (br m), 1.03 (br s), 0.84 (br s); 13C NMR(d, ppm, 125 MHz, DMF-d7): 178.84, 178.59, 177.62, 173.02,158.02, 155.37, 151.90, 147.24–146.17, 138.76, 137.35,130.04, 129.30–128.59, 126.86, 126.39, 118.86, 114.72,90.11, 86.00, 85.42, 82.72, 65.59, 65.15, 55.42, 55.28, 54.37,53.79, 53.03, 52.51, 47.38, 45.81, 45.47, 41.29, 41.49, 27.78,25.92, 24.58, 22.76, 22.32, 21.91, 21.70, 20.69, 19.63, 18.89,17.50, 17.36; UV/vis (chloroform) kmax ¼ 258 nm; IR(cm�1): 2937, 1724, 1501, 1447, 1378, 1240, 1148, 986,748, 702, 533.

Polymers 2 and 3 were synthesized in a similar fashion butthe reaction mixture was stirred at 50 �C in the case of 2and precipitated in pentane instead of methanol.

Polymer 2(Yield ¼ 28%) 1H NMR (d, ppm, 700 MHz, DMSO-d6): 10.69(s, 1H, NH), 7.84 (s, 1H), 6.52 (br s, 2H, NH2), 6.01 (d, J ¼ 2.1Hz, 1H), 5.23 (d, J ¼ 6.3 Hz, 1H), 5.13 (dd, J ¼ 2.1 Hz, 5.6 Hz,1H), 4.90–4.84 (m, 1H), 4.26 (m, 2H), 4.13 (m, 1H), 3.60–3.30

(br m), 2.5 (m, 2H), 2.50 (m, 6H), 1.51(s, 3H), 1.46 (m, 2H),1.31 (s, 3H), 1.10 (t, J ¼ 8.4 Hz, 3H), 1.03 (br s), 0.87 (t, J ¼7.7 Hz, 3H); 13C NMR (d, ppm, 125 MHz, DMSO-d6): 172.28,171.94, 157.28, 154.29, 151.08, 136.71, 117.60, 113.95, 88.89,84.83, 84.30, 81.63, 74.95, 73.01, 72.81, 70.99–69.98, 68.43,64.93, 31.94, 29.39, 29.10, 27.63, 25.93, 19.45, 17.85, 17.02,14.36; UV/vis (chloroform) kmax ¼ 257 nm; IR (cm�1): 2868,1732, 1693, 1601, 1447, 1386, 1094.

Polymer 3(Yield ¼ 12%) 1H NMR (d, ppm, 700 MHz, DMSO-d6): 10.70(s, 1H, NH), 7.84 (s, 1H), 7.11–6.36 (br m, ArH), 6.01 (s, 1H),5.23 (m, 1H), 5.11 (m, 1H), 4.25 (m, 3H), 4.17–4.14 (m, 6H),3.98 (s, 3H), 3.53–3.22 (br m), 2.77–2.67 (m, 5H), 2.53 (s,6H), 2.33 (br s, 7H), 1.81–1.23 (br m), 1.02 (br s), 0.87 (brs, 12H), 0.77 (br s, 3H); 13C NMR (d, ppm, 125 MHz, DMSO-d6): 176.10, 171.76, 171.63, 156.69, 153.69, 150.48, 145.39–144.56, 136.09, 127.95, 127.20, 125.69, 113.33, 82.27, 84.19,83.69, 81.02, 75.85, 74.69, 74.60, 74.48, 74.29, 74.09, 73.91,72.42, 72.23, 71.30, 70.37, 70.08, 69.89, 69.81, 67.81, 64.31,62.15, 61.67, 61.35, 58.38, 54.77, 45.77, 45.90, 34.07, 33.97,28.36, 27.01, 25.30, 17.27, 13.58; UV/vis (chloroform) kmax

¼ 258 nm; IR (cm�1): 2922, 1739, 1609, 1496, 1455, 1370,1101, 748, 694, 541.

General self-assembly procedure: All the polymeric buildingblocks (1, 2, and 3) were thoroughly washed with Milliporewater to remove any metal-cation impurity that may bepresent in the material (these metal-cation impurities cancome from the multistep synthetic protocols necessary forthe preparation of the building blocks). After water wash thebuilding blocks were then dried thoroughly.

A stock solution of KI was prepared in acetone. Requiredamount of the KI solution was placed in a glass vial, and theacetone was removed completely under reduced pressure.Then, known amount of the desired polymer building block(1, 2, and 3) was added to this vial. Chloroform was thenadded, and the mixture was stirred overnight. Removal ofchloroform gave access to the octameric assemblies, 18.K

þ,28.K

þ, and 38.Kþ in the solid form. These solid and dry sam-

ples were used for further studies. Concentrations of thearm and the octamer were based on their respective molecu-lar weights.

CONCLUSIONS

Supramolecular star polymers with complex chemical struc-ture and compositional heterogeneity can be prepared viapotassium cation-templated assembly of carefully designedguanosine end-functionalized copolymer chains. The starpolymer formation is quantitative and completely reversible.Star polymers generated from linear diblock copolymer of PSand PMMA exhibit higher stability when compared with starsgenerated from random amphiphilic copolymer and Y-shapeddiblock copolymer precursors. This is presumably due to thefact that the linear block copolymer precursor gives rise to astar with a middle PS shell. This chemically nonpolar shellshields the hydrogen bonded guanosine-based octamer coreagainst changes in solvent polarity and temperature.7c,17 In

FIGURE 7 1H NMR spectra of 18.Kþ upon addition of DMF-d7 in

CDCl3. TMS was used as an internal standard. Refer to Sup-

porting Information Figures S12 and S13 for 28.Kþ and 38.K

þ.



the case of random copolymer precursor, the ethylene oxyunits are potential competitors for hydrogen bonding inter-actions and thus responsible for decreasing the stability ofthe supramolecular core.7c,17c Whereas in the case of Y-shaped copolymer precursor, increased steric demand of theprecursor and hence higher entropic penalty to form atightly packed supramolecular core seems to be a major fac-tor in lowering the thermodynamic stability of the resultingstar polymer. Hence, both the chemical nature and the struc-ture of the polymer arm determine the stability of theformed supramolecular star polymers. A careful tuning ofthese factors seems to be the key in designing new branchedmaterials with remarkable stability yet completereversibility.

A.K. thank A. D. Schluter (ETH) for financial and moral support.Financial support from Swiss National Science Foundation(SNSF) is gratefully acknowledged.

REFERENCES AND NOTES

1 (a) Todd, E. M.; Zimmerman, S. C. J. Am. Chem. Soc. 2007,

129, 14534–14535; (b) Todd, E. M.; Zimmerman, S. C. Tetrahe-

dron 2008, 64, 8558–8570.

2 (a) Hoogenboom, R.; Schubert, U. S. Chem. Soc. Rev. 2006,

35, 622–629, and references therein; (b) Hoogenboom, R.;

Wouters, D.; Schubert, U. S. Macromolecules 2003, 36,

4743–4749; (c) Hoogenboom, R.; Moore, B. C.; Schubert, U. S.

Chem. Commun. 2006, 4010–4012.

3 (a) Fraser, C. L.; Smith A. P. J. Polym. Sci, Part A: Polym.

Chem. 2000, 38, 4704–4716, and references therein; (b) Fraser,

C. L.; Smith, A. P.; Wu, X. J. Am. Chem. Soc. 2000, 122,

9026–9027; (c) Wu, X.; Collins, J. E.; McAlvin, J. E.; Cutts, R.

W.; Fraser, C. L. Macromolecules 2001, 34, 2812–2821.

4 Huang, F.; Nagvekar, D. S.; Slebodnick, C.; Gibson, H. W. J.

Am. Chem. Soc. 2005, 127, 484–485.

5 Chen, S.; Bertrand, A.; Chang, X.; Alcouffe, P.; Ladaviere, C.;

Gerard, J.-F.; Lortie, F.; Bernard, J. Macromolecules 2010, 43,

5981–5988.

6 Altintas, O.; Tuncab, U.; Barner-Kowollik, C. Polym. Chem.

2011, 2, 1146–1155.

7 For elegant work on the synthesis, self-assembly, and

thermo-responsiveness of AB-type of diblock copolymers con-

nected via quadruple hydrogen bonding interactions, see: (a)

Feldman, K. E.; Kade, M. J.; De Greef, T. F. A.; Meijer, E. W.;

Kramer, E. J.; Hawker, C. J. Macromolecules 2008, 41,

4694–4700; (b) Feldman, K. E.; Kade, M. J.; Meijer, E. W.;

Hawker, C. J.; Kramer, E. J. Macromolecules 2010, 43,

5121–5127; (c) De Greef, T. F. A.; Kade, M. J.; Feldman, K. E.;

Kramer, E. J.; Hawker, C. J.; Meijer, E. W. J. Polym. Sci, Part A:

Polym. Chem. 2011, 49, 4253–4260.

8 (a) Gellert, M.; Lipsett, M.; Davies, D. Proc. Natl. Acad. Sci.

USA 1962, 48, 2013–2018; (b) Pinnavaia, T.; Marshall, C.; Met-

tler, C.; Fisk, C.; Miles, H.; Becker, E. J. J. Am. Chem. Soc.

1978, 100, 3625–3627; (c) Gottarelli, G.; Masiero, S.; Spada, G.

P. J. Chem. Soc. Chem. Commun. 1995, 2555–2557; (d) Marlow,

A. L.; Mezzina, E.; Spada, G. P.; Masiero, S.; Davis, J. T.;

Gottarelli, G. J. Org. Chem. 1999, 64, 5116–5123; (e) Forman, S.

L.; Fettinger, J. C.; Pieraccini, S.; Gottarelli, G.; Davis, J. T.

J. Am. Chem. Soc. 2000, 122, 4060–4067; (f) Betancourt, J. E.;

Rivera, J. M. J. Am. Chem. Soc. 2009, 131, 16666–16668; (g)

Gonz�alez-Rodrıguez, D.; Van Dongen, J. L. J.; Lutz, M.; Spek, A.

L.; Schenning, A. P. H. J.; Meijer, E. W. Nat. Chem. 2009, 1,

151–155; (h) Kaucher, M. S.; Lam, Y.-F.; Pieraccini, S.; Gottarelli,

G.; Davis, J. T. Chem. Eur. J. 2005, 11, 164–173.

9 (a) Davis, J. T. Angew. Chem. Int. Ed. Engl. 2004, 43,

668–698; (b) Spada, G. P.; Gottarelli, G. Synlett 2004, 4,

596–602; (c) Davis, J. T.; Spada, G. P. Chem. Soc. Rev. 2007,

36, 296–313; (d) Lena, S.; Masiero, S.; Pieraccini, S.; Spada, G.

S. Mini-Rev. Org. Chem. 2008, 5, 262–273; (e) Lena, S.; Masiero,

S.; Pieraccini, S.; Spada, G. S. Chem. Eur. J. 2009, 15,

7792–7806.

10 Likhitsup, A.; Yu, S.; Ng, Y.-H.; Chai, C. L. L.; Tam, E. K. W.

Chem. Commun. 2009, 4070–4072.

11 Y-shaped polymers have been used to create beautiful or-

ganic-inorganic nano-architectures: (a) Zubarev, E. R.; Xu, J.;

Sayyad, A.; Gibson, J. D. J. Am. Chem. Soc. 2006, 128,

4958–4959; (b) Zubarev, E. R.; Xu, J.; Sayyad, A.; Gibson, J. D.

J. Am. Chem. Soc. 2006, 128, 15098–15099.

12 (a) Cai, Y.; Burguiere, C.; Armes, S. P. Chem. Commun.

2004, 802–803; (b) Cai, Y.; Tang, Y.; Armes, S. P. Macromole-

cules 2004, 37, 9728–9737.

13 (a) Giorni, T.; Grepioni, F.; Manet, I.; Mariani, P.; Masiero,

S.; Mezzina, E.; Pieraccini, S.; Saturni, L.; Spada, G. P.; Gottar-

elli, G. Chem. Eur. J. 2002, 8, 2143–2152; (b) Lena, S.; Branco-

lini, G.; Gottarelli, G.; Mariani, P.; Masiero, S.; Venturini, A.;

Pandoli, O.; Pieraccini, S.; Samori, P.; Spada, G. P. Chem. Eur.

J. 2007, 13, 3757–3764; (c) Kumar, A. M. S.; Sivakova, S.; Fox,

J. D.; Green, J. E.; Marchant, R. E.; Rowan, S. J. J. Am. Chem.

Soc. 2008, 130, 1466–1476; (d) Spada, G. P.; Lena, S.; Masiero,

S.; Pieraccini, S.; Surin, M.; Samori, P. Adv. Mater. 2008, 20,

2433–2438; (e) Ciesielski, A.; Lena, S.; Masiero, S.; Spada, G. P.;

Samori, P. Angew. Chem. Int. Ed. Engl. 2010, 49, 1963–1966.

14 For use of UV/Vis technique as a tool to study G-quartet for-

mation in oligonucleotides see: Mergny, J.-L.; Phan, A.-T.;

Lacroix, L. FEBS Lett. 1998, 435, 74–78.

15 Harada, N.; Nakanishi, K. Circular Dichroic Spectroscopy-

Exciton Coupling in Organic Stereochemistry; University Sci-

ence Book: Mill Valley CA, 1983.

16 (a) Masiero, S.; Trotta, R.; Pi, S.; Tito, S. D.; Perone, R.; Ran-

dazzo, A.; Spada, G. P. Org. Biomol. Chem. 2010, 8, 2683–2692;

(b) Gottarelli, G.; Spada, G. P. Circular Dichroism–Principles

and Applications; Nakanishi, K.; Berova, N.; Woody, R. W.,

Eds.; Wiley: Weinheim, 1994;105–119;(c) Bonazzi, S.; Capo-

bianco, M.; Miranda De Morais, M.; Garbesi, A.; Gottarelli, G.;

Mariani, P.; Ponzi Bossi, M. G.; Spada, G. P.; Tondelli, L. J. Am.

Chem. Soc. 1991, 113, 5809–5816; (d) Sakai, N.; Matile, S. Chir-

ality 2003, 15, 766–771; (e) Hennig, A.; Matile, S. Chirality 2008,

20, 932–937.

17 (a) Obert, E.; Bellot, M.; Bouteiller, L.; Andrioletti, F.; Lehen-

Ferrenbach, C.; Boue, F. J. Am. Chem. Soc. 2007, 129,

15601–15605; (b) Yoshikawa, I.; Sawayama, J.; Araki, K. Angew.

Chem. Int. Ed. Engl. 2008, 47, 1038–1041; (c) de Greef, T. F. A.;

Nieuwenhuizen, M. M. L.; Stals, P. J. M.; Fitie, C. F. C.; Pal-

mans, A. R. A.; Sijbesma, R. P.; Meijer, E. W. Chem. Commun.

2008, 4306–4308.


POLYMER SCIENCE


Supramolecular star polymers with compositional heterogeneity

Documents

Transcript of Supramolecular star polymers with compositional heterogeneity