Regioselective Synthesis and Characterization of Tris- and Tetra-Prato Adducts of MN@C (M = Y, Gd).

The tris- and tetra-adducts of MN@C metallofullerenes were synthesized and characterized for the first time. The 1,3-dipolar cycloaddition (Prato reaction) of YN@-C and GdN@-C with an excess of -ethylglycine and formaldehyde provided tris- and tetra-fulleropyrrolidine adducts in a regioselective manner. Purification by HPLC and analyses of the isolated peaks by NMR, MS, and vis-NIR spectra revealed that the major products were four tris- and one tetra-isomers for both YN@-C and GdN@-C.

Structures of GdN@C Prato Bis-Adducts: Crystal Structure, Thermal Isomerization, and Computational Study.

The structures of two bis-ethylpyrrolidinoadducts of GdN@C, obtained by regioselective 1,3-dipolar cycloadditions, were elucidated by single crystal X-ray, visible-near infrared (vis-NIR) spectra, studies on their thermal isomerization, and theoretical calculations. The structure of the minor-bis-adduct reveals a -symmetric carbon cage with [6,6][6,6]-addition sites and with an endohedral GdN cluster that is completely flattened. This is the first example of a crystal structure of GdN@C derivatives.

Larger Substituents on Amide Cavitands Induce Bigger Cavities.

A series of quinoxaline cavitands bearing pendant amide groups with various substituent sizes (Et, Pr, Bu) were synthesized, and their cavity size/structure were investigated by X-ray and NMR analyses. In the case of the Et or Pr amide cavitand, the conformation of the molecule was in the vase form, while the bulky Bu amide cavitand gave the kite conformation at room temperature. X-ray crystal structures of Et and Pr cavitands clearly showed the intramolecular H-bondings to influence the conformation and the cavity sizes dependent on the bulkiness of functional groups.

Micelle vs. vesicle formation controlled by distal functionalization of C-PEG conjugates.

An amphiphilic C-PEG conjugate was modified by the addition of cationic moieties in the hydrophobic C part to provide the related bis- and tris-adducts and their self-assembling structures were compared. All of these materials were water-soluble and their supramolecular structures were investigated in the aqueous phase using tensiometry, DLS, and STEM techniques. While mono- and bis-adducts formed micelle-type supramolecular structures, the tris-one with two additional cationic pyrrolidine groups showed the formation of larger particles as indicated by DLS data.

Synthesis, Characterization, and DFT Analysis of Bis-Terpyridyl-Based Molecular Cobalt Complexes.

Terpyridine ligands are widely used in chemistry and material sciences owing to their ability to form stable molecular complexes with a large variety of metal ions. In that context, variations of the substituents on the terpyridine ligand allow modulation of the material properties. Applying the Stille cross-coupling reaction, we prepared with good yields a new series of terpyridine ligands possessing quinoline-type moieties in ortho, meta, and para positions and dimethylamino substituents at central or distal positions.

Endohedral metal-induced regioselective formation of bis-Prato adduct of Y3N@I(h)-C80 and Gd3N@I(h)-C80.

Regioselective bisaddition of M3N@Ih-C80 (M = Y, Gd) was observed for the first time in the Prato reaction with N-ethylglycine and formaldehyde. The main kinetic bisadduct of Y3N@C80 was determined to be a [6,6],[6,6] adduct by (1)H and (13)C NMR and vis/NIR spectroscopy, and it converted to a mixture of regioisomers upon heating via a sigmatropic rearrangement. The main kinetic bisadduct of Gd3N@C80 (the [6,6],[6,6] adduct on the basis of vis/NIR data) existed stably under thermal conditions without isomerization.

Water-soluble fullerene materials for bioapplications: photoinduced reactive oxygen species generation.

The photoinduced reactive oxygen species (ROS) generation from several water-soluble fullerenes was examined. Macromolecular or small molecular water-soluble fullerene complexes/derivatives were prepared and their (1)O(2) and O(2)˙(-) generation abilities were evaluated by ESR spin-trapping methods. As a result, efficient (1)O(2) generation was detected from photoexcited C(60), not only in organic solvents, but also in aqueous media and especially from small molecule C(60)-carboxylic acid derivatives.

Essential factors for control of the equilibrium in the reversible rearrangement of M₃N@I(h)-C₈₀ fulleropyrrolidines: exohedral functional groups versus endohedral metal clusters.

The effects of exohedral moieties and endohedral metal clusters on the isomerization of M3N@I(h)-C80 products from the Prato reaction through [1,5]-sigmatropic rearrangement were systematically investigated by using three types of fulleropyrrolidine derivatives and four different endohedral metal clusters. As a result, all types of derivatives provided the same ratios of the isomers for a given trimetallic nitride template (TNT) as the thermodynamic products, thus indicating that the size of the endohedral metal clusters inside C80 was the single essential factor in determining the equilibrium between the [6,6]-isomer (kinetic product) and the [5,6]-isomer. In all the derivatives, the [6,6]- and [5,6]-Prato adducts with larger metal clusters, such as Y3N and Gd3N, were equally stable, which is in good agreement with DFT calculations.

C60 pyrrolidine bis-carboxylic acid derivative as a versatile precursor for biocompatible fullerenes.

A C60 Prato derivative with bis-(t)Bu ester was prepared as a stable and convenient scaffold for the development of fullerene derivatives such as water-soluble C60-PEG conjugates, fulleropeptides via solid phase synthesis, and bis-functionalized C60.

Water-soluble C60- and C70-PVP polymers for biomaterials with efficient (1)O2 generation.

Highly water-soluble fullerene polymers were successfully prepared by a simple direct free-radical copolymerization of N-vinylpyrrolidone and intact C60 or C70 as a radical-capping agent. Using AIBN as a radical initiator, the polymers (C60- or C70-PVP) with significantly high molecular weight (~30 kDa) and with efficient (1)O2 generation were obtained.

Prato reaction of M3N@I(h)-C80 (M = Sc, Lu, Y, Gd) with reversible isomerization.

The 1,3-dipolar cycloaddition of an azomethine ylide (Prato reaction) with M(3)N@I(h)-C(80) (denoted as M(3)N@C(80); M = Sc, Lu, Y, Gd) was carried out to obtain fulleropyrrolidinebis(carboxylic acid) derivatives as scaffolds for the preparation of various functionalized M(3)N@C(80) materials. The formation of two monoadduct isomers (the [6,6]- and [5,6]-adducts) were detected by HPLC and identified by NMR and vis/NIR spectroscopies. In each Prato reaction with M(3)N@C(80), the initial addition gave a [6,6]-adduct of the I(h)-C(80) cage, and subsequently, a [5,6]-adduct was obtained by complete or partial thermal isomerization via a rearrangement reaction.

Photoswitching tripodal single molecular tip for noncontact AFM measurements: synthesis, immobilization, and reversible configurational change on gold surface.

Tripodal molecules consisting of a tetrasubstituted adamantane with three phenylacetylene legs and a reversibly photoswitching apex were designed as "single molecular tips" for both chemical and topographical characterization of the substrate surface. By covalent attachment onto gold-coated AFM tips through three S-Au bonds, these rigid tripodal molecules are expected to act as sharp, robust, and stationary molecular tips whose configuration can be reversibly changed upon irradiation with UV or visible light. In this report, the full account of the syntheses of two photoswitching tripodal molecular tips, their immobilization onto Au(111) surfaces, and the detection of photoinduced configurational change on Au(111) surface by SPM measurements are documented.