Recognition of guests bearing donor and acceptor hydrogen bonding groups by heteroditopic calix[4]arene receptors

Arduini, Arturo; Brindani, Elisabetta; Giorgi, Giovanna; Pochini, Andrea; Secchi, Andrea

doi:10.1016/s0040-4020(03)01126-8

Cited by 20 publications

(31 citation statements)

References 26 publications

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“…Variable‐temperature 1 H NMR experiments, carried out on 5 m M solutions (C 2 D 2 Cl 4 and CD 2 Cl 2 ) of ( 1 ⋅HCl) n , showed that complete disassembly occurs above 100 °C, whereas at temperatures below room temperature substantial broadening of all signals suggests a higher degree of aggregation of the polymeric material (Figure S4). Polymer ( 1 ⋅HCl) n also survives in the presence of considerable amounts of protic and ureido‐coordinating31 solvents (e.g. CDCl 3 /CD 3 OD 2:1 and CDCl 3 /[D 6 ]DMSO 4:1).…”

Section: Methodsmentioning

confidence: 99%

Anion‐Assisted Supramolecular Polymerization: From Achiral AB‐Type Monomers to Chiral Assemblies

et al. 2011

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Control over the self-assembly process of monomeric species by functional group modulation is highly desirable in the context of supramolecular polymer design. These materials, unlike covalently linked polymers, consist of monomeric arrays held together by reversible and highly directional noncovalent bonds. [1] Owing to the dynamic and reversible nature of noncovalent interactions, supramolecular polymers display unique topologies and unconventional properties (such as stimuli responsiveness [2] and self-healing [3] ) and are thus becoming cutting-edge species in modern materials science. Multiple hydrogen bonds, metal-ligand coordination, and p-p stacking are, by far, the most common weak forces used for engineering supramolecular polymers. [4] Recently, however, oligomeric and polymeric architectures based on host-guest inclusion complexes have started to become more and more popular. [5] Within this research frame, we have recently described a pH-responsive aminododecyloxy-calix[5]arene derivative (C5-NH 2 ) that, upon exposure to a variety of acids, selfassembles into linear oligomers. [6] Protonation activates the two latent self-complementary binding sites of this heteroditopic monomer precursor (i.e. a preorganized cone-shaped p-rich calix[5]arene cavity and a linear alkylamine pendant chain) and, according to a well-established host-guest recog-nition pattern, [7] which involves a concerted set of weak interactions (NH···O, CH-p, cation-p), [8] supramolecular oligomer formation readily occurs. However, because of the intrinsically saline nature of the monomers used, the growth of these supramolecular assemblies was found to be aniondependent. More specifically, the looser the ion-pairing interactions between the ammonium monomer and its counterion, the higher the degree of polymerization observed. [9] Although ion-pairing effects have been analyzed extensively in relation to simple one-to-one host-guest systems, [10] to the best of our knowledge they have not yet been examined in the context of supramolecular polymers derived from charged monomers. Elegant examples of polymeric species derived from crown ethers, [11] cryptands, [12] cyclodextrins, [13] cucurbiturils, [14] calixarenes, [15,16] and resorcinarenes [17] have been described, but in none of these instances-neither ABtype (self-complementary heteroditopic) [11a,b,d,e, 12a,b, 13a, 17a] nor AA/BB-type (complementary homoditopic) [11c, 12c, 14, 15, 17b] systems-has the role of the counterion in the growth of the polymer or the tuning of the supramolecular properties been addressed.Drawing on our earlier investigations on the simultaneous complexation of cations and anions [8,18] and on the design of heteroditopic [19] and heterotetratopic receptors [20] in an attempt to override the drawback of ion-pairing effects in AB-type salt monomers, we have now incorporated an ancillary anion-binding site (namely a ureido moiety) [21] into calix[5]arene C5-NH 2 with the aim of facilitating salt dissociation and ultimately making polymer formation mo...

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Section: Methodsmentioning

confidence: 99%

Anion‐Assisted Supramolecular Polymerization: From Achiral AB‐Type Monomers to Chiral Assemblies

et al. 2011

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“…Addition of dimethyl sulfoxide (DMSO) to a solution of 1 in chloroform led to a strong solvation of the hydrogen‐bond donor sites of the ureido functions 23. 24 This solvation caused a weakening of the binding ability of 1 toward ion‐paired salts25 and allowed the determination of the association constants by 1 H NMR spectroscopy. Table 2 shows that among the substrates investigated the longer C 12 and C 16 guest salts are more tightly bound than C 8 and C 10 by 1 as the result of capsular complexation.…”

Section: Methodsmentioning

confidence: 99%

A Calix[5]arene‐Based Heterotetratopic Host for Molecular Recognition of Long‐Chain, Ion‐Paired α,ω‐Alkanediyldiammonium Salts

et al. 2005

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Ion-pair recognition, that is, the simultaneous complexation of cation and anion guest species by neutral hosts, is an emerging field of topical interest in supramolecular chemistry with great potential for biological, analytical, and environmental applications.[1] It is well known that the ion-binding process with neutral receptors is adversely affected by the ionpairing of guest salts, [2] so that it is common practice to make use of salts with weakly coordinating counterions, [3] which result in enhanced host-guest associations. On the other hand, the ion-pairing interference can be circumvented either by using an appropriate combination of anion and cation receptors (binary host strategy) [4] or by designing specific heteroditopic receptors that take advantage of favorably positioned binding sites as well as induce positive cooperative and allosteric effects.[5] So far a plethora of heteroditopic receptors have been developed for inorganic ion pairs, [6] but much less has been reported for organic salts. [5c, 7] The molecular recognition of a,w-alkanediyldiammonium salts has been actively investigated with different classes of artificial homo(poly)topic receptors. Among these, cylindrical macrotricyclic hosts, [8] cucurbiturils, [9] crown ether [10] and glycoluril derivatives, [11] bimetallic porphyrin dimers, [12] as well as p-tert-butylcalix[5]arenes [13] have been employed. However, none of the receptors used so far has been equipped with complementary counterion-binding sites.Following our specific interest in the development of neutral multisite receptors for biogenic (poly)ammonium salts, [14] we report herein the synthesis and unique molecular recognition abilities of the first heterotetratopic receptor, 1, which consists of two convergent, conformationally fixed, cone calix[5]arene units (cation-binding sites) that are covalently linked at their upper rims by means of a 1,4-bis(ureido)phenylene spacer (anion-binding sites). Host 1 readily forms overall charge-neutral, unimolecular capsules (ligand-separated ion-pair complexes) of nanoscale dimensions by tight encapsulation [15] of linear a,w-alkanediyldiammonium ions, which range from 1,12-dodecane-to 1,16-hexadecanediammonium, inside the inner space defined by the two converging calix [5]arene cavities by simultaneously binding each of the two counteranions to the peripheral ureido functions through hydrogen bonds.The target biscalixarene 1 was synthesized in six steps from the known 31-benzyloxy-p-tert-butylcalix[5]arene (2) [16] according to the sequence illustrated in Scheme 1. The exhaustive O-alkylation of 2 with 4-methylpent-1-yl tosylate and K 2 CO 3 in CH 3 CN at reflux produced pentaether 3 in 77 % yield which, upon Pd/C-catalyzed hydrogenolysis in EtOAc, gave monohydroxy intermediate 4 in 93 % yield. The Scheme 1. Synthesis of 1: a) TsO(CH 2 ) 3 CH(CH 3 ) 2 , K 2 CO 3 , CH 3 CN, reflux, 12 h, 77 %; b) H 2 , Pd/C, EtOAc, room temperature, 4 h, 93 %; c) 68 % HNO 3 /AcOH, CH 2 Cl 2 , 08C, 25 min, 77 %; d) TsO(CH 2 ) 3 CH-(CH 3 ) 2 , NaH, ...

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“…Keywords: cyclophanes · hostguest systems · receptors · supramolecular chemistry · urea · X-ray diffraction orientations for binding. Besides calixarenes [7][8][9][10][11][12] and resorcinarenes, [13][14][15] little attention has been paid to other types of macrocyclic platforms as cores for urea-functionalized receptors. One such less-studied family of compounds are piperazine-reinforced cyclophanes.…”

Section: Introductionmentioning

confidence: 99%

Tri‐ and Tetraurea Piperazine Cyclophanes: Synthesis and Complexation Studies of Preorganized and Folded Receptor Molecules

Raatikainen

Beyeh

2010

Chemistry A European J

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A series of symmetrical tri- and tetrameric N-ethyl- and N-phenylurea-functionalized cyclophanes have been prepared in nearly quantitative yields (86-99 %) from the corresponding tri- and tetraamino-functionalized piperazine cyclophanes and ethyl or phenyl isocyanates. Their conformational and complexation properties have been studied by single-crystal X-ray diffraction, variable-temperature NMR spectroscopy, and ESI-MS analysis. The rigid 27-membered trimeric cyclophane skeleton assisted by a seam of intramolecular hydrogen bonds results in a preorganized ditopic recognition site with an all-syn conformation of the urea moieties that, complemented by a lipophilic cavity of the cyclophane, binds molecular and ionic guests as well as ion pairs. The all-syn conformation persists in acidic conditions and the triprotonated triurea cyclophane binds an unprecedented anion pair, H(2)PO(4)(-)⋅⋅⋅HPO(4)(2-), in the solid state. The tetra-N-ethylurea cyclophane is less rigid and demonstrates an induced-fit recognition of diisopropyl ether in the solid state. The guest was encapsulated within the lipophilic interior of a quasicapsule, formed by intramolecular hydrogen-bond-driven folding of the 36-membered cyclophane skeleton. In the gas phase, the essential role of the urea moieties in the binding was demonstrated by the formation of monomeric 1:1 complexes with K(+), TMA(+), and TMP(+) as well as the ion-pair complexes [KI+K](+), [TMABr+TMA](+) and [TMPBr+TMP](+). In the positive-mode ESI-MS analysis, ion-pair binding was found to be more pronounced with the larger tetraurea cyclophanes. In the negative mode, owing to the large size of the binding site, a general binding preference towards larger anions, such as the iodide, over smaller anions, such as the fluoride, was observed.

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Recognition of guests bearing donor and acceptor hydrogen bonding groups by heteroditopic calix[4]arene receptors

Cited by 20 publications

References 26 publications

Anion‐Assisted Supramolecular Polymerization: From Achiral AB‐Type Monomers to Chiral Assemblies

Anion‐Assisted Supramolecular Polymerization: From Achiral AB‐Type Monomers to Chiral Assemblies

A Calix[5]arene‐Based Heterotetratopic Host for Molecular Recognition of Long‐Chain, Ion‐Paired α,ω‐Alkanediyldiammonium Salts

Tri‐ and Tetraurea Piperazine Cyclophanes: Synthesis and Complexation Studies of Preorganized and Folded Receptor Molecules

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