Folded alkyl chains in water-soluble capsules and cavitands

Gavette, Jesse V.; Zhang, Kang‐Da; Ajami, Dariush; Rebek, Julius

doi:10.1039/c4ob01032a

Cited by 27 publications

(28 citation statements)

References 16 publications

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“…A folded conformation of the diene at the tapered end of the cavity is proposed (Figure and Figure S14) and places H 2 and H 13 deepest within the cavity. This conformation is in accord with observations of longer n ‐alkanes (C14–C18) that are encapsulated in folded conformations . These subtleties are depicted in the cartoons of Figure e, where the discontinuity occurs with the terminally folded C14.…”

Section: Figuresupporting

confidence: 87%

“…Theterminal olefinic protons (H 1a = H 14a and H 1b = H 14b )s how ÀDd value of only 4.26 and 4.21 ppm, respectively.Afolded conformation of the diene at the tapered end of the cavity is proposed (Figure 2a nd Figure S14) and places H 2 and H 13 deepest within the cavity.T his conformation is in accord with observations of longer n-alkanes (C14-C18) that are encapsulated in folded conformations. [9] These subtleties are depicted in the cartoons of Figure 2e,where the discontinuity occurs with the terminally folded C14. Complete COSY spectra and the assignments for 2c-f inside 1a·1 a are available in Figures S5-S14.…”

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Cavitands as Containers for α,ω‐Dienes and Chaperones for Olefin Metathesis

Petsalakis

Theodorakopoulos

et al. 2018

Angew Chem Int Ed

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Described herein is the behavior of a,w-dienes sequestered within cavitands in aqueous (D 2 O) solution. Hydrophobic forces drive the dienes into the cavitands in conformations that best fill the available space.Shorter dienes (C9 and C10) bind in compressed conformations that tumble rapidly in the cavitands.L onger dienes induce capsule formation between cavitands with self-complementary hydrogen bonding sites,w here the dienes exist in extended conformations.Incavitands unable to form capsules,longer dienes adopt folded structures.T he wider open ends allowt he synthesis of medium-sized cycloalkenes by ring-closing metathesis reactions with the Hoveyda-Grubbs-II catalyst. Yields of cycloheptene and cyclooctene were enhanced by the chaperones in water when compared with reactions of the free dienes in either aqueous media or chloroform, and even cyclononene could be prepared within the cavitand.Molecularcontainerhostshavereceivedmuchattentionfor their ability to confine guest molecules and affect their reactivity.T he use of self-assembly has expanded the use of these containers for the promotion of reactions in small spaces. [1] We recently reported the synthesis and characterization of the deep cavitand 1a [2] (Figure 1). Thes elfcomplementary pattern of hydrogen bond donors and acceptors on the upper rim was devised by de Mendoza, [3] who showed that dimerization to host capsules occurs with suitable guests in organic solvents.W ef ound that pyridinium or methylimidazolium "feet" provided good solubility in water, and the formation of capsules occurs even in aqueous solutions when large hydrophobic guests are present. [4] To prevent such dimerization, we exhaustively N-methylated the benzimidazolones of the upper rim to form the octamethyl urea 1b (Supporting Information). Thec avitand 1b showed good solubility in water (D 2 O), where it exists as avelcrand [5] dimer in the absence of guests.H erein we report the complexation of symmetrical aliphatic a,w-dienes (C9-C14) with cavitands 1a and 1b,a nd their applications for olefin metathesis in otherwise reluctant cyclizations.Alkenes bound inside synthetic host structures are not often reported [6] because the NMR signals of the olefinic protons are rarely observed given the overlap with the signals of the cavitands. [7] We used commercially available a,w-dienes:C 91 ,8-nonadiene (2a), C10 1,9-decadiene (2b), C11 1,10-undecadiene (2c), C12 1,11-dodecadiene (2d), and C14 1,13-tetradecadiene (2f). TheC13 1,12-tridecadiene (2e) was synthesized by reaction of 10-bromo-1-decene with allylmagnesium bromide. [8] Brief sonication of these a,w-dienes (0.5 mm)w ith 1a (0.5 mm)i nw ater (D 2 O) gave host-guest complexes with 1 HNMR signals of the guest characteristically upfield-shifted by the shielding of the aromatic panels of the host structure (Figure 2; Supporting Information). Thelonger a,w-dienes 2c, 2d, 2e,and 2fshow signals that are spread out between d = 1.5 and À2.0 ppm (Figure 2). Thes ignals for terminal vinyl hydrogen of C11 appears at d = 0.05 ppm (Dd = À...

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Section: Figuresupporting

confidence: 87%

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confidence: 99%

Cavitands as Containers for α,ω‐Dienes and Chaperones for Olefin Metathesis

Petsalakis

Theodorakopoulos

et al. 2018

Angew Chem Int Ed

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“…In a preliminary study, DFT calculations were performed by using a water polarizable continuum model (PCM) and showed that for TEMPONE@ 1 2 , the ketone group of the guest pushes one of the eight walls of capsule 1 2 slightly out of the ideal shape (Figure 2). The two orientational isomers are within 0.5 kcal mol −1 and even if deformed, the hydrogen‐bonding network of the capsule is nearly optimum (Figure 2b) 20a…”

Section: Resultsmentioning

confidence: 99%

EPR Studies of the Binding Properties, Guest Dynamics, and Inner‐Space Dimensions of a Water‐Soluble Resorcinarene Capsule

Ayhan

Casano

Karoui

et al. 2015

Chemistry A European J

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Nitroxide free radicals have been used to study the inner space of one of Rebek's water-soluble capsules. EPR and (1) H NMR spectroscopy, ESI-MS, and DFT calculations showed a preference for the formation of 1:2 complexes. EPR titrations allowed us to determine binding constants (Ka ) in the order of 10(7) M(-2) . EPR spectral-shape analysis provided information on the guest rotational dynamics within the capsule. The interplay between optimum hydrogen bonding upon capsule formation and steric strain for guest accommodation highlights some degree of flexibility for guest inclusion, particularly at the center of the capsule where the hydrogen bond seam can be barely distorted or slightly disturbed.

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“…The cavitand is stable over a wide pH range. Whereas a number of water-soluble, deep cavitand hosts are available (3-10), cavitand 1 bound long-chain guest alkanes and related difunctional compounds (bola-amphiphiles) in folded conformations (11). Folded alkyls inside a γ-cyclodextrin were initially characterized by Turro et al (12), and folded bola-amphiphiles were reported by Kim and co-workers in cucurbiturils (13); even stranger shapes inside deep containers have been encountered recently by Gibb and co-workers (14).…”

Section: Resultsmentioning

confidence: 99%

Water-soluble cavitands promote hydrolyses of long-chain diesters

Shi

Mower

Blackmond

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Water-soluble, deep cavitands serve as chaperones of long-chain diesters for their selective hydrolysis in aqueous solution. The cavitands bind the diesters in rapidly exchanging, folded J-shape conformations that bury the hydrocarbon chain and expose each ester group in turn to the aqueous medium. The acid hydrolyses in the presence of the cavitand result in enhanced yields of monoacid monoester products. Product distributions indicate a two-to fourfold relative decrease in the hydrolysis rate constant of the second ester caused by the confined space in the cavitand. The rate constant for the first acid hydrolysis step is enhanced approximately 10-fold in the presence of the cavitand, compared with control reactions of the molecules in bulk solution. Hydrolysis under basic conditions (saponification) with the cavitand gave >90% yields of the corresponding monoesters. Under basic conditions the cavitand complex of the monoanion precipitates from solution and prevents further reaction.M onofunctionalization of symmetrical compounds poses a general problem: When identical functional groups on a substrate are truly remote, they act independently, and reactions result in a statistical mixture of products. For example, hydrolysis of diesters ( Fig. 1) separated by a long methylene chain exhibits equal rate constants at each site (k 1 = k 2 ), which sets an upper limit of 36.8% for the yield of the monoester. This maximum occurs when comparable amounts of unreacted diester and doubly reacted diacid product are present ( Fig. 1), a factor that often complicates isolation of the desired monoester product.Special circumstances can favor monofunctionalization. When the monofunctionalized compound has fortuitously different properties (such as solubility) and can be removed to a different phase (1) as it is formed, good yields can result. Likewise, when the sites are not remote--as in diesters of oxalic acid--reaction at one site greatly modifies reactivity at the other site and affects the yield of the monofunctionalized product. We describe here the application of synthetic container compounds (cavitands) as molecular chaperones to address the monofunctionalization problem. Whereas the present examples involve only hydrolysis of long-chain diesters, the predictable influence of the cavitand promises wider applications in other reactions of symmetrical, difunctional substrates. Results and DiscussionWe recently reported the synthesis of deep cavitand 1 (Fig. 2) and its capacity to sequester hydrophobic and amphiphilic species in water (2). The eight methyl groups of cavitand 1 broaden its upper rim and prevent dimerization through hydrogen bonding into a capsule. The cavitand is stable over a wide pH range. Whereas a number of water-soluble, deep cavitand hosts are available (3-10), cavitand 1 bound long-chain guest alkanes and related difunctional compounds (bola-amphiphiles) in folded conformations (11). Folded alkyls inside a γ-cyclodextrin were initially characterized by Turro et al. (12), and folded bola-amphiphiles ...

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Folded alkyl chains in water-soluble capsules and cavitands

Cited by 27 publications

References 16 publications

Cavitands as Containers for α,ω‐Dienes and Chaperones for Olefin Metathesis

Cavitands as Containers for α,ω‐Dienes and Chaperones for Olefin Metathesis

EPR Studies of the Binding Properties, Guest Dynamics, and Inner‐Space Dimensions of a Water‐Soluble Resorcinarene Capsule

Water-soluble cavitands promote hydrolyses of long-chain diesters

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