Pyranosylmagellanicus a novel structural class of polyhalogenated acetogenins from Ptilonia magellanica

Three naturally occurring pyranosyl-like polyhalogenated metabolites 1-3 as well as their likely biogenetic precursor, the linear compound 4, have been isolated from the red alga Ptilonia magellanica. They are the first compounds within the genus that incorporate chlorine in their network. Compound 3 have structural features reminiscent of the universal chemical signal AI-2 (autoinducer-2) for bacterial communication.     

Isomers of C(20): an energy profile II

Semi-empirical calculations, at the PM3 level provided within the Winmopac v2.0 software package, are used to geometrically optimize and determine the absolute energies (heats of formation) of a variety of C(20) isomers that are predicted to exist in and around the bowl and cage isomers. Using the optimized Cartesian coordinates for the bowl and the cage isomers, a saddle-point calculation was performed. The output file generated, containing energy, distance, and geometry information, is then organized into a graphical format. The resulting graph, which plots the energy of the 20-atom system as a function of the distance from the geometric midpoint, is a two-dimensional energy profile. This profile illustrates an estimation of the contours on the potential energy surface, showing energy minima and maxima that are encountered as the bowl evolves into the cage structure, or vice-versa. To expand the surface into three dimensions, geometry optimizations were performed on the sets of Cartesian coordinates that correspond to energy minima in the bowl-cage profile. Based on these optimizations, eight additional isomers of C(20) have been identified and are predicted to be energetically stable. These additional isomers were subsequently subjected to saddle-point calculations in order to identify those isomers that lie adjacent to one another on the three-dimensional surface. Two isomers that are adjacent to each other will exhibit an energy profile that progresses smoothly from the potential well of each isomer up to the saddle point separating them. Consequently, these adjacent pairs of isomers establish a step-wise transformation between the bowl and the cage. This process, which extends out over the three-dimensional surface, is predicted to require less energy than that of the direct, two-dimensional transformation predicted in the bowl-cage profile.     

Influence of cluster size on the structures and stability of trimetallic nitride fullerenes M3N@C80.

To provide insight into the influence of encaged clusters on the structures and stability of trimetallic nitride fullerenes (TNFs), extensive density functional theory calculations were performed on Sc3N@C80, Y3N@C80, and La3N@C80 as well as their encaged clusters. The calculated results demonstrated that both Sc3N and Y3N units are planar, whereas La3N units are pyramidal inside C80-I(h), and that both of the Y3N@C80 and La3N@C80 cages deform considerably in the planes of Y3 and La3. The calculated results suggest that M-cage attraction/repulsion and M-M repulsion interactions determine the geometries of these three complex molecules and the dynamics of the corresponding encaged clusters. These calculated findings distinctly reveal the influence of the size of the encaged clusters on the structures and stability of TNFs and may rationalize their significant differences in yields and chemical reactivity.     

A highly directional fourfold hydrogen-bonding motif for supramolecular structures through self-assembly of fullerodendrimers

Supramolecular dendrimers resulting from the dimerization of fullerene-functionalized dendrons through a quadruple hydrogen-bonding motif were prepared. The synthetic strategy is based on the esterification of a tert-butoxycarbonyl (Boc)-protected 2-ureido-4-[1H]pyrimidinone precursor possessing an alcohol function with fullerodendrons bearing a carboxylic acid unit at the focal point. Subsequent acidic treatment to cleave the protecting group and reaction of the resulting amine with octylisocyanate affords the targeted compounds. As demonstrated by the results of MALDI-TOF mass spectrometry and 1H NMR spectroscopy, both of the 2-ureido-4-[1H]pyrimidinone derivatives form self-assembled dimers spontaneously through hydrogen-bonding interactions, thus leading to supramolecular structures containing two or ten fullerene moieties.     

Blending Non‐Group‐3 Transition Metal and Rare‐Earth Metal into a C80 Fullerene Cage with D5h Symmetry

Rare‐earth metals have been mostly entrapped into fullerene cages to form endohedral clusterfullerenes, whereas non‐Group‐3 transition metals that can form clusterfullerenes are limited to titanium (Ti) and vanadium (V), and both are exclusively entrapped within an I_h‐C₈₀ cage. Non‐Group‐3 transition‐metal‐containing endohedral fullerenes based on a C₈₀ cage with D_5h symmetry, V_xSc_3?xN@D_5h‐C₈₀ (x=1, 2), have now been synthesized, which exhibit two variable cluster compositions. The molecular structure of VSc₂N@D_5h‐C₈₀ was unambiguously determined by X‐ray crystallography. According to a comparative study with the reported Ti‐ and V‐containing clusterfullerenes based on a I_h‐C₈₀ cage and the analogous D_5h‐C₈₀‐based metal nitride clusterfullerenes containing rare‐earth metals only, the decisive role of the non‐Group‐3 transition metal on the formation of the corresponding D_5h‐C₈₀‐based clusterfullerenes is unraveled.     

A Supramolecular [10]CPP Junction Enables Efficient Electron Transfer in Modular Porphyrin–[10]CPP⊃Fullerene Complexes

Efficient photoinduced electron transfer was observed across a [10]cycloparaphenylene ([10]CPP) moiety that serves as a rigid non‐covalent bridge between a zinc porphyrin and a range of fullerenes. The preparation of iodo‐[10]CPP is the key to the synthesis of a porphyrin–[10]CPP conjugate, which binds C₆₀, C₇₀, (C₆₀)₂, and other fullerenes (K_A>10⁵ m ^?1). Fluorescence and pump–probe spectroscopy revealed intramolecular energy transfer between CPP and porphyrin and also efficient charge separation between porphyrin and fullerenes, affording up to 0.5 μs lifetime charge‐separated states. The advantage of this approach towards electron donor–acceptor dyads is evident in the case of dumbbell‐shaped (C₆₀)₂, which gave intricate charge‐transfer behavior in 1:1 and 2:1 complexes. These results suggest that [10]CPP and its cross‐coupled derivatives could act as supramolecular mediators of charge transport in organic electronic devices.     

Synthesis of chlorinated fullerenes C60Cln (n = 2, 4) from C60Cl6 and their Arbuzov-type reaction with P(OEt)3

Reduction of C₆₀Cl₆ with triphenylphosphine was demonstrated to be a useful method for the preparation of a mixture of low-chlorinated fullerenes C₆₀Cl_n (n?=?2, 4). Individual chlorofullerene 1,4-C₆₀Cl₂ was isolated by preparative gel permeation chromatography and characterized spectroscopically for the first time. The Arbuzov-type reaction of C₆₀Cl_n with P(OEt)₃ produced C₆₀[PO(OEt)₂]₃H as a major isolable product, which was further hydrolyzed to C₆₀[PO(OH)₂]₃H.     

Synthesis,Isolation and Structures of Trifluoromethylated Fullerenes D2‐C76, C76(1)(CF3)10–18

High‐temperature trifluoromethylation of fullerene C₇₆ chlorination products followed by HPLC separation of C₇₆(CF₃)_n derivatives resulted in the isolation and X‐ray structural characterization of thirteen C₇₆(1)(CF₃)_n compounds including nine new isomers such as one isomer of C₇₆(1)(CF₃)₁₀, two C₇₆(1)(CF₃)₁₂, three C₇₆(1)(CF₃)₁₄, one C₇₆(1)(CF₃)₁₆, and two isomers of C₇₆(1)(CF₃)₁₈. Depending on their addition patterns, C₇₆(1)(CF₃)_n isomers are divided into three subgroups and discussed in terms of trifluoromethylation pathways and relative formation energies.