富勒烯C60、C70的超分子化学

介绍了富勒烯Ｃ６０、Ｃ７０与环糊精、冠醚、杯芳烃等主体形成超分子的进展和一些潜在的应用前景。     

浅谈富勒烯C60、C70发现的偶然性与必然性

1985年英国萨塞克斯大学(University of Sussex)的波谱学家H.W.Kroto与美国莱斯大学(Rice University)两名教授R.E.Smalley和R.F.Curl合作研究,发现碳元素可以形成由60个或70个碳原子构成的有笼状结构的C60和C70分子[1],这一发现引起科学界特别是物理学和化学界的强烈反响,成为本世纪后半叶的重大科学发现之一.11年后,三位科学家因为发现C60并提出其分子结构模型而荣获1996年诺贝尔化学奖.回顾C60的发现过程,应当承认,确有偶然性的一面,但从人类的认识规律和科学技术发展背景分析,C60的发现又有着历史的必然性.     

Octapalladium Strings Trap C60 and C70 Fullerenes Affording Metal-Chain-Wired Bucky Balls

Reactions of Pd₈ strings supported by meso-Ph₂PCH₂P(Ph)CH₂P(Ph)CH₂PPh₂ (meso-dpmppm) ligands, [Pd₈(meso-dpmppm)₄(L)₂]⁴⁺ (L=CH₃CN ( 1 ), XylNC ( 2 )) with C₆₀ resulted in the exclusive formation of unprecedented metal-chain-wired C₆₀ bucky balls, [{Pd₄(meso-dpmppm)₂(L)}₂(C₆₀)]⁴⁺ (L=CH₃CN ( 11 ), XylNC ( 12 )), in which a C₆₀ fullerene is trapped in the central Pd–Pd junction, as unambiguously established by spectroscopic, X-ray crystallographic, and theoretical techniques. The similar reaction of Pd₈ strings supported by rac-dpmppm, [Pd₈(rac-dpmppm)₄(CH₃CN)₂]⁴⁺ ( 3 ) also afforded a racemic mixture of [{Pd₄((R*,R*)-dpmppm)₂(CH₃CN)}₂(C₆₀)]⁴⁺ ( 13 ) without scrambling the Pd₄ fragments with (R,R)- and (S,S)-dpmppm ligands. Consequently, those of enantiopure chiral Pd₈ strings, [Pd₈((R*,R*)-dpmppm)₄(CH₃CN)₂]⁴⁺, certainly afforded chiral bucky balls of [{Pd₄((R*,R*)-dpmppm)₂(CH₃CN)}₂(C₆₀)]⁴⁺ ( 13 _RR and 13 _SS ), that exhibit mirror-image circular dichroism spectra. The reactions of 1 and 2 were also applied for trapping a C₇₀ fullerene to give 2 : 1 adducts of [{Pd₄(meso-dpmppm)₂(L)}₂(C₇₀)]⁴⁺ (L=CH₃CN ( 21 ), XylNC ( 22 )). These results provide useful information for creating a platform to develop dimensionally and chirality controlled metal–carbon nanocomposite materials.     

Iron Sulfido Derivatives of the Fullerenes C(60) and C(70)

Toluene solutions of C(60) react upon UV irradiation with Fe(2)S(2)(CO)(6) to give C(60)[S(2)Fe(2)(CO)(6)](n)() where n = 1-6. C(60)[S(2)Fe(2)(CO)(6)](n)() where n = 1-3 have been isolated and characterized. Crystallographic studies of C(60)S(2)Fe(2)(CO)(6) show that the S-S bond of the Fe(2) reagent is cleaved to give a dithiolate with idealized C(2)(v)() symmetry. The addition occurred at a 6,6 fusion, and the metrical details show that the Fe(2) portion of the molecule resembles C(2)H(4)S(2)Fe(2)(CO)(6). IR spectroscopic measurements indicate that the Fe(2)(CO)(6) subunits in the multiple-addition species (n > 1) interact only weakly. UV-vis spectra of the adducts show a shift to shorter wavelength with addition of each S(2)Fe(2)(CO)(6) unit. Photoaddition of the phosphine complex Fe(2)S(2)(CO)(5)(PPh(3)) to C(60) gave C(60)[S(2)Fe(2)(CO)(5)(PPh(3))](n)(), where n = 1-3. (31)P{(1)H} NMR studies show that the double adduct consists of multiple isomers. Photoaddition of Fe(2)S(2)(CO)(6) to C(70) gave a series of adducts C(70)[S(2)Fe(2)(CO)(6)](n)() where n = 1-4. HPLC analyses show one, four, and three isomers for the adducts, respectively.     

Chromatographic Behavior of C60 and C70 Fullerenes at Subambient Temperature with n-Alkanes Mobile Phases

The influence of temperature on the retention and separation of C60 and C70 fullerenes was studied under HPLC conditions. Particularly, chromatographic experiments were conducted using moderate carbon loaded octadecylsilica stationary phase and homologous series of n-alkanes including n-pentane, n-hexane and n-heptane as the mobile phases. All studies were performed across wide range of subambient temperature from −80 to +20 °C. From practical point of view the best chromatographic conditions for baseline separation of the components of interest were selected. The retention of analytes was strongly affected by temperature and below minus 30 °C strong deviation from van't Hoff behavior was observed. To explore this phenomenon selected thermodynamic parameters including changes of enthalpy (ΔH^o) and changes of entropy (ΔS^o) were estimated. Positive values of the ΔH^o and ΔS^o at low temperature region may indicate the lack of the interaction with the stationary phase ligands. A possible retention mechanism at different temperatures for C60 and C70 molecules has been discussed.     

Theoretical studies of C60/C70 fullerene derivatives: C60O and C70O

A semiempirical (AM1) calculation on the structures and stabilities of isomers of the fullerene derivatives C₆₀O and C₇₀O is carried out. The ozonolysis reaction mechanism and the thermodynamics of the compounds are studied. The two isomers of C₆₀O (56 bond and 66 bond) formed by an oxygen atom bridging across a C-C bond have an epoxide-like or an annulene-like structure. According to the ozonolysis reaction mechanism and kinetic factor analysis, the possible products of this ozonolysis reaction are C₆₀O with oxygen bridging over the 66 bond (C_2v) as an epoxide-like isomer and that with oxygen bridging over the 56 bond (C_s) as an annulene-like isomer. Further, the sixteen isomers of C₇₀O (both epoxide-like and annulene-like structures) have been studied with respect to the same reaction mechanism. The most possible product in this ozonolysis reaction contains oxygen bridging across in the upper part (66 bond in C₇₀O-2 or C₇₀O-4) as an epoxide-like structure. The other possible product is C₇₀O-8 (annulene-like structure), in which oxygen bridges across an broken equatorial CC bond in C₇₀ (D_5h). The vibrational frequency analysis and the electronic structure of the selected C₆₀O and C₇₀O isomers are generated for experimental characterisation. The experimental results indicate that C₆₀O and C₇₀O may decompose into the odd number fullerenes C₅₉ and C₆₉. We therefore studied the structures of C₅₉ and C₆₉ also.     

ChemInform Abstract: Structural Characterization of C60 and C70 Fullerenes by Small-Angle Neutron Scattering.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Fullerenes制备中C60和C70含量不同的热力学解释

本文计算了不同温度下气相反应7/6 C60=C70的热力学函数, 讨论了C60与C70之间相互转化的热力学条件。结果表明, 温度高于2828K时气相中C60比C70稳定, 温度低于2828K时气相中C70比C60稳定, 解释了由石墨制备Fullerenes时, C60和C70含量不同的原因。     

Selective Encapsulation and Chiral Induction of C60 and C70 Fullerenes by Axially Chiral Porous Aromatic Cages

Chiral induction has been an important topic in chemistry, not only for its relevance in understanding the mysterious phenomenon of spontaneous symmetry breaking in nature but also due to its critical implications in medicine and the chiral industry. The induced chirality of fullerenes by host–guest interactions has been rarely reported, mainly attributed to their chiral resistance from high symmetry and challenges in their accessibility. Herein, we report two new pairs of chiral porous aromatic cages (PAC), R- PAC-2 , S- PAC-2 (with Br substituents) and R- PAC-3 , S- PAC-3 (with CH₃ substituents) enantiomers. PAC-2 , rather than PAC-3 , achieves fullerene encapsulation and selective binding of C₇₀ over C₆₀ in fullerene carbon soot. More significantly, the occurrence of chiral induction between R- PAC-2 , S- PAC-2 and fullerenes is confirmed by single-crystal X-ray diffraction and the intense CD signal within the absorption region of fullerenes. DFT calculations reveal the contribution of electrostatic effects originating from face-to-face arene-fullerene interactions dominate C₇₀ selectivity and elucidate the substituent effect on fullerene encapsulation. The disturbance from the differential interactions between fullerene and surrounding chiral cages on the intrinsic highly symmetric electronic structure of fullerene could be the primary reason accounting for the induced chirality of fullerene.     

富勒烯(C60/70)-丙烯酸的自由基共聚

富勒烯及其衍生物在超导、光电、磁学等领域展现出奇特性能[1],富勒烯的化学修饰成为化学工作者们关注的热点之一,而其中合成含富勒烯的新型聚合物是一个非常重要的方面.     

Transalkylation of Higher Trifluoromethylated Fullerenes with C70: A Pathway to New Addition Patterns of C70(CF3)8

We report three new isomers of C₇₀(CF₃)₈, structurally related to p⁷mp‐C₇₀(CF₃)₁₀, that are inaccessible by direct trifluoromethylation, but can be easily identified among the products of the transalkylation of higher trifluoromethylfullerenes with C₇₀. The reported compounds are characterized by UV/Vis, 1 D and 2 D COSY ¹⁹F NMR spectroscopy, and DFT calculations. A rather unusual addition pattern is observed in p⁶,i‐C₇₀(CF₃)₈ in which one addend is attached remotely from the others; polarization of the adjacent unsaturated bonds by the addend makes the molecule readily oxidizable.     

Stable Non‐IPR C60 and C70 Fullerenes Containing a Uniform Distribution of Pyrenes and Adjacent Pentagons

The most abundant fullerenes, C₆₀ and C₇₀, and all the pure carbon fullerenes larger than C₇₀, follow the isolated‐pentagon rule (IPR). Non‐IPR fullerenes containing adjacent pentagons (APs) have been stabilized experimentally in cases where, according to Euler’s theorem, it is topologically impossible to isolate all the pentagons from each other. Surprisingly, recent experiments have shown that a few endohedral fullerenes, for which IPR structures are possible, are stabilized in non‐IPR cages. We show that, apart from strain, the physical property that governs the relative stabilities of fullerenes is the charge distribution in the cage. This charge distribution is controlled by the number and location of APs and pyrene motifs. We show that, when these motifs are uniformly distributed in the cage and well‐separated from one other, stabilization of non‐IPR endohedral and exohedral derivatives, as well as pure carbon fullerene anions and cations, is the rule, rather than the exception. This suggests that non‐IPR derivatives might be even more common than IPR ones.     

C70NH的结构和光谱的理论研究

摘要本文用INDO系列方法对C70NH的8种异构体构型进行计算，结果表明最稳定的构型是N原子加在C3-C3键和C4-C4键上形成具有CS对称性且不开环的三元环结构。研究了这两种最稳定构型的电荷分布，指出了C70NH的8种构型的^13CNMR谱。进行了UV-Vis光谱计算，结果表明C70NH主峰与C70一致，并在500nm以上产生特征吸收峰；C70NH与C70。相比将发生UV谱带红移的现象，同时讨论了谱带红移的原因。     

Fluorescent Bis-Calix[4]arene-Carbazole Conjugates: Synthesis and Inclusion Complexation Studies with Fullerenes C60 and C70

Supramolecular chemistry has become a central theme in chemical and biological sciences over the last decades. Supramolecular structures are being increasingly used in biomedical applications, particularly in devices requiring specific stimuli-responsiveness. Fullerenes, and supramolecular assemblies thereof, have gained great visibility in biomedical sciences and engineering. Sensitive and selective methods are required for the study of their inclusion in complexes in various application fields. With this in mind, two new fluorescent bis-calix[4]arene-carbazole conjugates (4 and 5) have been designed. Herein, their synthesis and ability to behave as specific hosts for fullerenes C₆₀ and C₇₀ is described. The optical properties of the novel compounds and their complexes with C₆₀ and C₇₀ were thoroughly studied by UV-Vis and steady-state and time-resolved fluorescence spectroscopies. The association constants (K_a) for the complexation of C₆₀ and C₇₀ by 4 and 5 were determined by fluorescence techniques. A higher stability was found for the C₇₀@4 supramolecule (K_a = 5.6 × 10⁴ M⁻¹; ΔG = −6.48 kcal/mol). Evidence for the formation of true inclusion complexes between the host 4 and C₆₀/C₇₀ was obtained from NMR spectroscopy performed at low temperatures. The experimental findings were fully corroborated by density functional theory (DFT) models performed on the host–guest assemblies (C₆₀@4 and C₇₀@4).     

Fullerenes against COVID-19: Repurposing C60 and C70 to Clog the Active Site of SARS-CoV-2 Protease

The persistency of COVID-19 in the world and the continuous rise of its variants demand new treatments to complement vaccines. Computational chemistry can assist in the identification of moieties able to lead to new drugs to fight the disease. Fullerenes and carbon nanomaterials can interact with proteins and are considered promising antiviral agents. Here, we propose the possibility to repurpose fullerenes to clog the active site of the SARS-CoV-2 protease, M^pro. Through the use of docking, molecular dynamics, and energy decomposition techniques, it is shown that C₆₀ has a substantial binding energy to the main protease of the SARS-CoV-2 virus, M^pro, higher than masitinib, a known inhibitor of the protein. Furthermore, we suggest the use of C₇₀ as an innovative scaffold for the inhibition of SARS-CoV-2 M^pro. At odds with masitinib, both C₆₀ and C₇₀ interact more strongly with SARS-CoV-2 M^pro when different protonation states of the catalytic dyad are considered. The binding of fullerenes to M^pro is due to shape complementarity, i.e., vdW interactions, and is aspecific. As such, it is not sensitive to mutations that can eliminate or invert the charges of the amino acids composing the binding pocket. Fullerenic cages should therefore be more effective against the SARS-CoV-2 virus than the available inhibitors such as masinitib, where the electrostatic term plays a crucial role in the binding.     

Theoretical studies on structures and UV-Vis spectra of C70O

Systematic studies on eight isomers of C₇₀O were performed by means of INDO methods. It has been indicated that the O atom is mainly added to the C₁-C₂ or C₃-C₃ bond and an epoxide feature with C_s symmetry is formed. Based on the optimized geometries, the UV-Vis spectra were calculated. It has been found that the main peaks of C₇₀O resemble those of C₇₀ and the characteristic absorptions beyond 460 nm are produced, which is in agreement with the experimental results. Theoretical assignments about the absorptions were canied out and the reason for the red-shift of the absorptions was discussed. C₇₀O is probably composed of four isomers according to the calculated results. Project supported by the National Natural Science Foundation of China.     

Theoretical Characterization of Chiral Carbon Nanotube Encapsulating Ellipsoidal C70

The molecular orientation of ellipsoidal C70 in carbon nanotubes is carefully studied by first principles calculations. Using （14, 7） single-wall carbon nanotube （SWCNT） as a prototype material, we explored that the weak chemical interaction between SWCNT and C70 was the crucial factor to determine the molecular orientation. However, the small energy difference makes the distinguishment of two possible molecular orientations difficult. By simulating scanning tunneling microscope images and optical properties, we found that local electronic states sensitively depended on the molecular orientation of ellipsoidal C70, which provided a practical way of using scanning tunneling microscope to recognize the molecular orientation of ellipsoidal C70.     

Magnetic Silicon Fullerenes: Experimental Exploration and Theoretical Insight

The present article summarizes progress in research on silicon clusters with encapsulated metal atoms, and specifically focuses on the recent identification of magnetic silicon fullerenes. Considering that C\(_{20}\) forms the smallest known fullerene, the Si\(_{20}\) cluster is of particular interest in this context. While the pure hollow Si\(_{20}\) cage is unstable due to the lack of \(sp^2\) hybridization, endohedral doping with a range of metal atoms has been considered to be an effective way to stabilize the cage structure. In order to seek out suitable embedded atoms for stabilizing Si\(_{20}\), a broad search has been made across elements with relatively large atomic radius. The rare earth elements have been found to be able to stabilize the Si\(_{20}\) cage in the neutral state by forming R@Si\(_{20}\) fullerene cages. Among these atoms, Eu@Si\(_{20}\) has been reported to yield a stable magnetic silicon fullerene. The central europium atom has a large magnetic moment of nearly 7.0 Bohr magnetons. In addition, based on a stable Eu\(_2\)Si\(_{30}\) tube, a magnetic silicon nanotube has been constructed and discussed. These magnetic silicon fullerenes and nanotubes may have potential applications in the fields of spintronics and high-density magnetic storage.