Massimo Boiocchi

University of Pavia, Ticinum, Lombardy, Italy

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Publications (55)274.5 Total impact

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    ABSTRACT: From an EtOH/H2O solution, 0.3 M each of Ni2+ and cyclic triamine tacn (2; tacn=1,4,7-triazacyclononane), after 10 min refluxing and cooling at room temperature, copious and comparable amounts of blue crystals (containing the complex [Ni(tacn)(H2O)3]2+) and pink crystals (containing in the same cell both [Ni(H2O)6]2+ and [Ni(tacn)2]2+) precipitated. This unusual behaviour is ascribed to the fact that at the refluxing temperature the three species are present at the equilibrium in similar concentrations, which are frozen on cooling, due to the inertness of the macrocyclic complexes [Ni(tacn)(H2O)3]2+ and [Ni(tacn)2]2+.
    Chemistry - A European Journal 08/2014; · 5.93 Impact Factor
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    ABSTRACT: In this work, we report on two new asymmetric dicopper cryptates, characterized by alternate furanyl and p-xylyl spacers. The results of the potentiometric, UV-vis and X-ray diffraction studies are discussed. In particular, for one of the cages in the octaprotonated form, the crystal structure of the complex with nitrate is described. From the point of view of the anion binding in water, the new dicopper cryptates display stronger similarities to each other than to the symmetric analogues (i.e. p-xylyl and furan cryptates). The substitution of even only one spacer modifies the distance between the metal ions. This prevents the development of the CT band, typically accompanying the binding of halides by the furan cryptate, and favors the formation of complexes of different stoichiometry with the linear azide anion, not observed for the symmetric cryptates. The obtained results may be very helpful in the design of new molecular receptors based on dimetallic cryptates, in particular for the tuning of the sensitivity towards specific anionic substrates.
    Dalton Transactions 06/2014; · 4.10 Impact Factor
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    ABSTRACT: The selective binding of 99 Tc pertechnetate (99 TcO 4 À) in water is a big challenge. Recently, our group reported on the p-xylyl aza-cryptand, as the first molecular receptor for 99 TcO 4 À in aqueous solution. Here, we show that the introduction of a fluorescent unit in the azacryptand's framework leads to a new molecular system, able to selectively recognize and sense the pertechnetate anion at mM concentration. In water at pH 2, where the cage is in the hexaprotonated form, pertechnetate recognition is signalled by the quenching of the receptor's emission. Noticeably, environmentally ubiquitous anions, such as chloride, nitrate and sulfate do not interfere in the sensing, as they have no effect on our chemo-sensor's fluorescence. These unprecedented results are promising for the development of simple and smart devices for the recovery of 99 TcO 4 À from contaminated aqueous solutions.
    Chemical Science 01/2014; · 8.31 Impact Factor
  • Massimo Boiocchi, Luigi Fabbrizzi
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    ABSTRACT: In the presence of d(10) metal ions, prone to tetrahedral coordination, ligands containing two bidentate subunits will give rise to double-stranded helical complexes (helicates). Upon electrochemical oxidation of Cu(I) to Cu(II), the helicate complex tends to disassemble, thus giving rise to two mononuclear Cu(II) complexes with tetragonal geometry. Upon subsequent Cu(II)-to-Cu(I) electrochemical reduction, two Cu(I) complexes instantaneously re-assemble to give the helicate complex. A helicand containing a chiral subunit (e.g. 1,2-substituted cyclohexanediamine) contains a racemic mixture of the R,R and S,S enantiomers. The racemic helicand, reacting with Cu(I), forms dimetallic helicates, in which the two strands show the same chirality, whether R,R or S,S, thus obeying the principle of homochiral recognition.
    Chemical Society Reviews 01/2014; · 24.89 Impact Factor
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    ABSTRACT: The bis-bidentate ligand, obtained from Schiff base condensation of RR-1,2-cyclohexanediamine and 8-naphthylmethoxyquinoline-2-carbaldehyde (L-L), forms with [Cu(I)(MeCN)4]ClO4 a double strand helicate complex, made especially stable by the presence of four definite interstrand π-π interactions involving a quinoline subunit and a naphthylmethoxy substituent of the two strands. The [Cu(I)2(L-L)2](2+) complex, which does not decompose even on excess addition of either L-L or Cu(I), undergoes a two electron oxidation in MeCN, through two one-electron fully reversible steps, separated by 260 mV, as shown by cyclic voltammetry (CV) studies. The high stability of the mixed valence complex [Cu(I)Cu(II)(L-L)2](3+) with respect to disproportionation to [Cu(I)2(L-L)2](2+) and [Cu(II)2(L-L)2](4+) is essentially due to a favorable electrostatic term. Cu(II) forms with L-L a stable species, with a 1:1 stoichiometric ratio, but, in the absence of crystallographic data, it was impossible to assess whether it is of mono- or dinuclear nature. However, CV studies on an MeCN solution containing equimolar amounts of Cu(II) and L-L showed the presence in the reduction scan of two fully reversible waves, separated by about 250 mV, which indicated the presence in solution of a dicopper(II) double strand helicate complex, [Cu(II)2(L-L)2](4+). This work demonstrates that additional interstrand π-π interactions can favor the formation of unusually stable dicopper(I) and dicopper(II) helicate complexes.
    Inorganic Chemistry 09/2013; · 4.59 Impact Factor
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    ABSTRACT: This paper describes the structure and properties of the drug domperidone and a novel 1:1 domperidone succinate salt. The new salt is characterized by means of thermal, spectroscopic, microscopic and powder diffraction measurements. The crystal structures of the salt and, for the first time, of pure domperidone have been determined by means of single-crystal X-ray diffraction. In both structures, the piperidine ring of domperidone adopts the expected chair conformation, and supramolecular centrosymmetric R2(2)(8) motifs are formed by N-H...O hydrogen bonds between chlorine-substituted oxobenzimidazolyl groups. Further N-H...O hydrogen bonds occur between non-substituted oxobenzimidazolyl groups and the resulting C(4) motifs originates hydrogen-bonded chains, extending along the crystallographic b axis. In the salt, a single N-H...O hydrogen bond forms between the protonated nitrogen of the piperidine ring and the carboxylic O atom of the succinate ion. Two alternative and mutually exclusive positions for the nonsubstituted oxobenzimidazolyl group have also been observed; this disorder makes the hydrogen-bonded chains originating from the bicyclic group polar. The dissolution behaviour of the salt in dosage form is compared with two reference commercial products. The salt shows an increased solubility, a characteristic that could be of great advantage from a pharmaceutical view point.
    Acta crystallographica Section B, Structural science, crystal engineering and materials. 08/2013; 69(Pt 4):362-70.
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    ABSTRACT: Covalent linking of a Ru(terpy)2(2+) substituent improves recognition and sensing properties of the urea subunit toward anions. Urea's anion affinity is enhanced by the electrostatic attraction exerted by the Ru(II) cation and by the electron-withdrawing effect exerted by the entire polypyridine-metal complex. Such an enhancement of the anion affinity, which results from the combination of a through-space and a through-bond effect, is greater than that exerted by the classical neutral electron-withdrawing substituent nitrophenyl. Small yet significant modifications of π-π* and MLCT bands of the Ru(terpy)2(2+) chromophore, detected through UV-vis spectrophotometric titrations, allowed the determination of the constants for the formation of receptor-anion H-bond complexes in diluted MeCN solution. On (1)H NMR titration experiments, carried out under more concentrated conditions, the interaction of a second Cl(-) ion was observed, taking place through an outer-sphere mechanism. The Ru(terpy)2(2+) substituent favors the deprotonation of a urea N-H fragment on addition of a second equivalent of fluoride, with formation of HF2(-).
    Inorganic Chemistry 04/2013; · 4.59 Impact Factor
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    ABSTRACT: The anion binding tendencies of the two fluorogenic ureas L1H and L2H, containing the 2 anthracenyl and 1 pyrenyl moieties as signaling units, respectively, have been investigated in MeCN and DMSO by absorption, emission and 1H-NMR spectroscopies. The formation of stable 1:1 receptor:anion H bond complexes has been confirmed by structural studies on the crystalline [Bu4N][L1...Cl] and [Bu4N][L2H...CH3COO] salts. Complexation induces significant variations of the emission properties of L1H and L2H according to a multifaceted behavior, which depends upon the fluoro¬genic substituent, the solvent and the basicity of the anion. Poorly basic anions (Cl, Br) cause a red shift of the emission band(s). Carboxylates (CH3COO, C6H5COO) induce fluorescence quenching due to the occurrence of an electron transfer process taking place in the locally excited complex [*L H...X]. However, this excited complex may undergo an intra-complex proton transfer from one urea NH fragment to the anion, to give the tautomeric excited complex [L...HX]*, which emits at higher wavelength, the process being favoured by solvent polarity (DMSO > MeCN) and nature of the fluorogenic substituent (pyrene > anthracene). F displays a unique behavior: it forms with L1H a stable [LH...F], which in the excited state undergoes intra-complex proton transfer, to give the poorly emissive excited tautomer [L...HF]*. With L2H, on moderate addition of F, the 1:1 H bond complex forms and the blue fluorescence of pyrene is quenched. Large excess addition of F promotes deprotonation of the ground state complex, according to the equilibrium [L2H...F] + F- = [L2]- + HF2-. The deprotonated receptor [L2]- is distinctly emissive (yellow fluorescence), which generates the fluorimetric response ON1-OFF-ON2 of receptor L2H with respect to F-.
    Journal of the American Chemical Society 04/2013; · 10.68 Impact Factor
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    ABSTRACT: Asymmetric reactions involving (E)-3-aryl-1-(pyridin-2-yl-N-oxide)prop-2-en-1-ones and cyclic enol silyl ethers show good yields and excellent enantioselectivities (up to 99.9 % ee) when catalysed by bis(oxazoline)-Cu(II) complexes. Different reaction pathways can be followed by different enol silyl ethers: with 2-(trimethylsilyloxy)furan, a Mukaiyama-Michael adduct is obtained, whereas a hetero Diels-Alder cycloadduct was formed by using (1,2-dihydronaphthalen-4-yloxy)trimethylsilane. In the latter reaction, the absolute configuration of the product is consistent with a reagent approach to the less hindered Re face of the coordinated substrate in the reactive complex.
    Chemistry - A European Journal 07/2012; 18(37):11662-8. · 5.93 Impact Factor
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    ABSTRACT: he affinity of azacryptands towards perrhenate has been investigated by potentiometric, 1H NMR spectroscopic and ITC studies in aqueous solutions. The association constants could only be determined for the p-xylyl and m-xylyl azacryptands in the hexaprotonated form. The experimental results showed the outstanding affinity of the p-xylyl cryptand for perrhenate, attributable to the geometric complementarity between the anion and the cavity of the receptor. Single crystals of the inclusion complex could also be obtained. The X-ray diffraction studies indicate that the perrhenate anion is included in the cavity of the receptor and interacts with the ammonium groups by means of both direct and water-mediated H-bonding interactions. The receptors were also investigated in the presence of different anions (i.e. chloride, bromide, iodide, perchlorate and nitrate). The affinity trend demonstrates that the p-xylyl cryptand cavity is more suitable to host large anionic guests such as perrhenate, perchlorate and iodide, despite their low density charge. On the contrary, nitrate, bromide and chloride fit better into the smaller cavity of the m-xylyl cryptand. The higher affinity of the m-xylyl cage towards chloride over that of perrhenate was also demonstrated by the crystal structure of the 1:1 adduct.
    European Journal of Inorganic Chemistry 07/2012; 2012(21):3410–3417. · 3.12 Impact Factor
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    ABSTRACT: The complex between scandium triflate and pybox is a good enantioselective catalyst for the reaction between methyl (E)-4-aryl-2-oxo-3-butenoates (1) and enol silyl ethers (2). The main products with (4′S)-isopropyl-, (4′S)-phenyl-, and (4′S,5′S)-4-TIPS-pybox are methyl (4S,4aS,8aS)-4-aryl-8a-trialkylsiloxy-hexahydro-4H-chromen-2-carboxylates (7), which are obtained in good yield and enantioselectivities of more than 95 % ee. Because the reaction gives products with a trans ring junction that cannot derive from a conventional concerted hetero-Diels–Alder pathway, the mechanism involved in the enantioselective catalytic cycle and the origin of the stereoinduction were investigated. The structures of two desilylated products, 8b and 9b, were determined by X-ray crystal analysis. Their absolute configuration was then related to that of 7 by stereospecific isomerization and/or desilylation reactions. If aryl-butenoates 1 are coordinated to the catalyst, forming reacting complexes characterized by the five-membered structure 11, these rigid reacting intermediates give a face discrimination that is determined by the configuration of the pybox 4′-substituent. The resulting face-selective attack of enol silyl ethers to coordinated 1 gives an enantioselective tandem Mukaiyama–Michael addition/intramolecular ring closure reaction, which is an enantioselective formal hetero-Diels–Alder reaction, which rationalizes the absolute configuration of the reaction products.
    Annalen der Chemie und Pharmacie 05/2012; 2012(15). · 3.10 Impact Factor
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    ABSTRACT: Asymmetric reactions involving (E)‐3‐aryl‐1‐(pyridin‐2‐yl‐N‐oxide)prop‐2‐en‐1‐ones and cyclic enol silyl ethers show good yields and excellent enantioselectivities (up to 99.9 % ee) when catalysed by bis(oxazoline)–CuII complexes. Different reaction pathways can be followed by different enol silyl ethers: with 2‐(trimethylsilyloxy)furan, a Mukaiyama–Michael adduct is obtained, whereas a hetero Diels–Alder cycloadduct was formed by using (1,2‐dihydronaphthalen‐4‐yloxy)trimethylsilane. In the latter reaction, the absolute configuration of the product is consistent with a reagent approach to the less hindered Re face of the coordinated substrate in the reactive complex.
    Chemistry 01/2012; 18(37). · 5.83 Impact Factor
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    ABSTRACT: Carprofen co-crystals with selected co-formers were prepared by solvent evaporation and wet/dry grinding methods. Their effective formation was investigated by thermal analysis, FT-IR, X-ray single crystal and powder diffraction and SEM-EDS. This last technique has been applied for the first time to co-crystals since it provides unambiguous confirmation of co-crystal formation. Among the investigated co-formers we studied, only 4,4 0 -dipyridyl yields co-crystals. Two different crystal structures are obtained when the molar ratio of carprofen : 4,4 0 -dipyridyl is 2 : 1 (triclinic cell) and 1 : 1.5 (monoclinic cell). The asymmetric triclinic cell (Z ¼ 2) contains two carprofen and two half 4,4 0 -dipyridyl moieties while the monoclinic cell (Z ¼ 4) contains a single carprofen, and one and a half 4,4 0 -dipyridyl moieties. Several hydrogen-bond supramolecular synthons can be identified in the solid state. For both the 2 : 1 and 1 : 1.5 co-crystals, the main hydrogen-bond interaction consists of an O–H/N heterosynthon involving, as a donor, the COOH group of carprofen and, as a H-acceptor, the nitrogen of a 4,4 0 -dipyridyl molecule. The two co-crystals have characteristic FT-IR spectra and slightly different melting temperatures. X-Ray powder diffraction patterns of the 1 : 1 and 1 : 2 compositions reveal a mixture of phases, whose amount is quantified with Rietveld analysis.
    CrystEngComm 01/2012; 14(2):435. · 3.88 Impact Factor
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    ABSTRACT: New compounds of perphenazine and fumaric acid in 2 : 1 and 1 : 2 molar ratios have been prepared by solvent evaporation with the aim of increasing the drug solubility. Their physico-chemical properties were thoroughly characterized by differential scanning calorimetry, powder X-ray diffraction, Fourier infrared spectroscopy and scanning electron microscopy coupled with energy dispersive X-ray spectrometry. In addition, the crystal structure of the 2 : 1 salt was determined by single-crystal X-ray diffraction. The pharmaceutical characterization included solubility and dissolution studies in comparison with the commercial product Trilafon1. Perphenazine solubility is strongly pH-dependent: the binary systems show improved solubility and intrinsic dissolution rate compared with perphenazine, but only the capsule formulation containing the 1 : 2 dihydrate sample shows a quick and complete dissolution behaviour at neutral pH. This sample could represent an interesting perphenazine formulation to improve drug bioavailability and perhaps reduce in vivo variability even when the gastric fluid pH is increased by the presence of food.
    CrystEngComm 01/2012; 14:6035. · 3.88 Impact Factor
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    ABSTRACT: The influence of the positively charged N-methylpyridinium substituent on the anion binding tendencies of urea-based receptors has been investigated by comparing molecules 1 and 2. These receptors have been studied in acetonitrile, by performing UV-vis. and (1)H NMR titrations with several anions. UV-vis. titrations have also been performed in DMSO, MeOH and CHCl(3)/CH(3)CN mixture (1/1, v/v). In the case of 1, the presence of both H-donor and H-acceptor groups (urea and pyridine, respectively) favours aggregation and the formation of dimers in the solid state. In solution, this tendency to aggregate reduces affinity for anions with respect to the similar urea-based receptor 3. The methylation of the pyridyl group of 1 leads to the pyridinium-containing receptor 2. The pyridinium positive charge enhances the acidity of urea and increases anion affinity, as evidenced by the comparison of the binding constants. Both receptors (1-2) form stable adducts with all investigated anions. However, in the case of 2, the formation of 1 : 1 adducts with basic anions, such as acetate and fluoride, is followed by a proton transfer process. Quite interestingly, deprotonation does not involve the urea group, thus preserving the 1 : 1 adduct, as demonstrated by the (1)H NMR measurements. In particular, the proton transfer process takes place at the methylene group linking the pyridinium fragment to the receptor's skeleton. (1)H NMR studies indicate the formation of a stable neutral methine species, characterised by the loss of aromaticity by the pyridyl ring. These results open new perspectives in the field of anion recognition, as receptor 2 may by applied to the monitoring of both bound anion (through the urea unit) and excess anion in solution (through the development of the yellow methine species).
    Organic & Biomolecular Chemistry 12/2011; 9(24):8276-83. · 3.57 Impact Factor
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    ABSTRACT: The trisbenzimidazolium cyclophane receptor 23+ incorporates the F– anion in MeCN solution, which was inferred by spectrophotometric and 1H NMR titration experiments, with an association constant log K > 7. On the basis of geometric considerations, it is assumed that F– lies in the middle of the triangle 3C, whose vertices are the carbon atoms of the three imidazolium C–H fragments, and profits from three C–H···F H-bonds. No other anion is encapsulated by 23+ for reasons of size. The parent trisbenzimidazolium tripodal receptor 43+ does not exert size exclusion selectivity and forms 1:1 complexes not only with F–, but also with other mono- (Br–) and polyatomic anions (NO3–). X-ray diffraction studies on [4···Br]2+ and [4···NO3]2+ complexes indicated that, due to the steric restraints of the tripodal receptor, the anion is not positioned in the middle of the 3C triangle but stays below it, profiting from H-bonds. Cage effects are observed in the higher thermodynamic stability of the [2···F]2+ complex with respect to [4···F]2+ and in its resistance to excess F–. In fact, on addition of excess fluoride, the tripodal [4···F]2+ complex decomposes with deprotonation of a C–H fragment and formation of the very stable HF2– complex.
    Annalen der Chemie und Pharmacie 11/2011; 2011(32). · 3.10 Impact Factor
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    ABSTRACT: The tris-benzimidazolium cage LH(3)(3+), in MeCN solution, in the presence of OH(-), forms with Cu(I) and Ag(I) ions complexes of formula [M(I)(LH)](2+), in which each metal is linearly coordinated by two carbenes and one imidazolium N-H fragment remains intact. To achieve two-coordination, the two N-heterocyclic moieties of the cage make a saloon-door type motion, with a conformationally costless rotation of ca. 30° each. The two [M(I)(LH)](2+) complexes show high thermodynamic stability and are inert with respect to metal substitution, due to the mechanical constraints imposed by the ligating framework. Complexation with Cu(I) and Ag(I) with the reference unidentate carbene ligand Q, derived from the benzimidazolium precursor QH(+), was studied for comparison. Both metals in MeCN form 1:1 and 1:2 complexes with the carbene ligand Q according to two stepwise equilibria. Q complexes of both metals are labile with respect to metal substitution and those of Ag(I) are more stable than those of Cu(I). A significant cooperative effect has been observed with the formation of the [Ag(I)Q(2)](+) complex.
    Dalton Transactions 09/2011; 40(33):8367-76. · 4.10 Impact Factor
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    ABSTRACT: The study of the interactions of the three urea-based receptors AH, BH(+) and CH(2+) with a variety of anions, in MeCN, has made it possible to verify the current view that hydrogen bonding is frozen proton transfer from the donor (the urea N-H fragment in this case) to the acceptor (the anion X(-)). The poorly acidic, neutral receptor AH establishes two equivalent hydrogen bonds N-H···X(-), with all anions, including CH(3)COO(-) and F(-), in which moderate proton transfer from N-H to the anion takes place. The strongly acidic, dicationic receptor CH(2+) forms, with most anions, complexes in which two inequivalent hydrogen bonds are present: one involving moderate proton transfer (N-H···X(-)) and one in which advanced proton transfer has taken place, described as N(-)···H-X. The degree of proton advancement is directly related to the basic tendencies of the anion. The cationic receptor BH(+) of intermediate acidic properties only forms complexes with two inequivalent hydrogen bonds (moderate+advanced proton transfer) with CH(3)COO(-) and F(-), and complexes with two equivalent hydrogen bonds (moderate proton transfer) with all the other anions. Moreover, [B···HF] and [C···HF](+), on addition of a second F(-) ion, lose the bound HF molecule to give HF(2)(-). Release of CH(3)COOH, with the formation of [CH(3)COOH···CH(3)COO](-), also takes place with the [B···CH(3)COOH] complex in the presence of a large excess of anion.
    Chemistry - A European Journal 08/2011; 17(34):9423-39. · 5.93 Impact Factor
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    ABSTRACT: Diels-Alder and 1,3-dipolar cycloadditions involving (E)-3-aryl-1-(pyridin-2-yl-N-oxide)prop-2-en-1-ones as the 2π components are efficiently catalysed by bis(oxazoline)-Cu(II) complexes. The cycloadducts are obtained in quantitative yields with up to 98 % ee; absolute configurations were determined by X-ray analysis. The structure of the reactive complex, determined by X-ray analysis, is fully consistent with the stereochemical outcome of the catalysed process (approach of the diene or nitrone to the less hindered face of the coordinated pyridine-N-oxide derivative).
    Chemistry - A European Journal 01/2011; 17(2):516-20. · 5.93 Impact Factor
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    ABSTRACT: The reactivity of aromatic dicarboxylic acids, in combination with an axially-chiral, suitable dibenzylic alcohol, derived from BINOL, has been exploited in one-pot esterification reactions for the direct formation of several rigid, homochiral macrocycles. Cyclic adducts possessing, respectively, average molecular D(2) and D(3) symmetries, have been characterized in pure forms, with isolated yields and selectivities which are substantially different from those rising from purely statistical arguments. NMR and CD spectroscopies detect the structural and shape variability in the scaffolds, reflected both in terms of large changes in chemical shifts of selected proton resonances, and in terms of the variation of the CD signature related to the dihedral angle defined by the binaphthyl units embedded in the rigid cyclic skeleton. The crystal structure of two homochiral D(2) macrocycles show the formation of ordered nanostructures in the solid state, with the naphthyl rings of the binaphthyl units packing intermolecularly in an eclipsed-like conformation to yield nonhelical tubular arrangements. The larger D(3) cyclic adducts are able to afford stable complexes with C(60) in toluene solution, with comparable binding strengths, yet whose stoichiometries are dependent on small variations in the spacing units and therefore in the shapes of the internal cavities of the cyclic structures.
    Organic & Biomolecular Chemistry 04/2010; 8(7):1640-9. · 3.57 Impact Factor