C2 Carbon Atom Research Articles

Molecular modelling of luciferyl adenylate deprotonation in the active site of Photinus pyralis luciferase

Firefly bioluminescence is a product of chemical reactions that involve luciferin chromophore oxidation in the active site of luciferase proteins. We perform a series of classical molecular dynamic simulations and combined quantum and molecular mechanics (QM/MM) calculations to expose the molecular mechanism of C4 carbon atom deprotonation in luciferyl adenylate molecule. QM/MM calculations confirm that ND-protonated His245 residue is a suitable proton acceptor in the wild-type Photinus pyralis luciferase. Classical molecular dynamic simulations reveal oxygen-binding cavities inside the protein including the one located close to the C4 atom of luciferin. In mutant forms that lack direct interactions with the His245 side chain, a proton wire comprising water molecules stimulates either protonation of the phosphate group of the luciferyl adenylate forming an unstable intermediate or keto–enol tautomerisation of luciferin. The comparison of the ionisation potentials of molecular systems with the ‘deprotonated’ C4 carbon atom revealed that the ionisation energy for the enol tautomeric form is close to the system with the His245 proton acceptor. Thus, the existence of the keto–enol tautomerisation channel might explain bioluminescence in case of the absence of the amino acid proton acceptor.

SYNTHESIS AND ANALGESIC ACTIVITY OF METHYL-1-ANTIPYRYL-4-AROYL-2,3-DIOXO-2,3,5,10-TETRAHYDROBENZO[B]PYRROLO[2,3-E][1,4]DIAZEPINE-10A(1H) –CARBOXYLATES

In order to obtain new biologically active compounds, methyl-1-antipyryl-4-aroyl-2,3-dioxo-2,3,5,10-tetrahydrobenzo[b]pyrrolo[2,3-e][1,4]diazepine was synthesized-10a(1H)-carboxylates by reacting 1-antipyryl-4-aroyl-5-methoxycarbonyl-1H-pyrrole-2,3-diones with o-phenylenediamine. The structures of the obtained compounds were confirmed by 1H NMR, IR spectroscopy, X-ray diffraction and elemental analysis. The presence of several electrophilic centers in the structure of antipyryl-substituted 1H-pyrrole-2,3-diones gives them a high reactivity with respect to binucleophilic reagents. Apparently, the described interaction is carried out by the initial nucleophilic attack of one aminogroup of o-phenylenediamine on the C5 carbon atom of the pyrrole-2,3-dione ring, followed by the attack of another aminogroup on the carbonyl carbon atom of the aroyl fragment, closing the diazepine ring. The described reaction is a convenient preparative method for the synthesis of previously undescribed methyl-1-antipyryl-4-aroyl-2,3-dioxo-2,3,5,10-tetrahydrobenzo[b]pyrrolo[2,3-e][1,4]diazepine-10a(1H)-carboxylates, which are of interest as pharmacological substances. The described interaction proceeds quickly and with high yields. The obtained compounds were screened for analgesic activity, as a result of which a more pronounced effect was found in some products compared to the reference drug (diclofenac sodium). A preliminary assessment of acute toxicity was carried out, according to which the derivatives of 2,3,5,10-tetrahydrobenzo[b]pyrrolo[2,3-e][1,4]diazepine proved to be safe for further studies. The survival rate of animals in all groups is 100% after 24 h and 100% after 14 days. Screening of analgesic activity was performed by the hot plate method. Registration of time was carried out from the moment of placement on a hot surface until the appearance of a behavioral response to nociceptive stimulation 60 and 120 min after the administration of substances. For citation: Lyadov V.A., Makrushin D.E., Denislamova E.S., Maslivets A.N., Triandafilova G.A., Solodnikov S.I. Synthesis and analgesic activity of methyl-1-antipyryl-4-aroyl-2,3-dioxo-2,3,5,10-tetrahydrobenzo[b]pyrrolo[2,3-e][1,4]diazepine-10a(1H) –carboxylates. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 5. P. 17-23. DOI: 10.6060/ivkkt.20246705.6939.

Understanding of the stability of acyclic nitronic acids in the light of molecular electron density theory

In the present work, the electronic structure and stability of acyclic nitronic acids were studied. Depending on the different substituents, the analyzed compounds can be classified as pseudo(mono)radical or zwitterionic nitronic acids. ELF topological analysis of the electron density of nitronic acids containing in their structure EWG substituent (-NO2 (1); –COOCH3 (2); –NO2, –CH3 (5); –COOCH3, –OCH3 (6); –NO2, –H (7); –COOH3, –H (8)) permits establishing a pseudo(mono)radical electronic structure with a pseudoradical centers at the C1 carbon atom. In turn, ELF analysis of the compounds 3, 4, 9 and 10 containing substituent belonging to the EGD group (-CH3 (3); –OCH3 (4); –CH3, –H (9); –COH3, –H (10)) and based on the presence of C1–N2 double bond and absence of pseudoradical centre allows for the classification of these compounds as a zwitterionic nitronic acids. Nitronic acids containing EDG substituents in their structure are the most stable among the analyzed nitronic acids. In turn, nitronic acids containing EWG groups are characterized by higher reactivity in chemical reactions compared to other analyzed nitronic acids.

Enantioselective Intramolecular ortho Photocycloaddition Reactions of 2-Acetonaphthones.

2-Acetonaphthones, which bear an alkenyl group tethered to its C1 carbon atom via an oxygen atom, were found to undergo an enantioselective intramolecular ortho photocycloaddition reaction. A chiral oxazaborolidine Lewis acid leads to a bathochromic absorption shift of the substrate and enables an efficient enantioface differentiation. Visible light irradiation (λ=450 nm) triggers the reaction which is tolerant of various groups at almost any position except carbon atom C8 (16 examples, 53-99 % yield, 80-97 % ee). Consecutive reactions were explored including a sensitized rearrangement to tetrahydrobiphenylenes, which occurred with full retention of configuration. Evidence was collected that the catalytic photocycloaddition occurs via triplet intermediates, and the binding mode of the acetonaphthone to the chiral Lewis acid was elucidated by DFT calculations.

Enantioselective Intramolecular ortho Photocycloaddition Reactions of 2‐Acetonaphthones

Abstract2‐Acetonaphthones, which bear an alkenyl group tethered to its C1 carbon atom via an oxygen atom, were found to undergo an enantioselective intramolecular ortho photocycloaddition reaction. A chiral oxazaborolidine Lewis acid leads to a bathochromic absorption shift of the substrate and enables an efficient enantioface differentiation. Visible light irradiation (λ=450 nm) triggers the reaction which is tolerant of various groups at almost any position except carbon atom C8 (16 examples, 53–99 % yield, 80–97 % ee). Consecutive reactions were explored including a sensitized rearrangement to tetrahydrobiphenylenes, which occurred with full retention of configuration. Evidence was collected that the catalytic photocycloaddition occurs via triplet intermediates, and the binding mode of the acetonaphthone to the chiral Lewis acid was elucidated by DFT calculations.

Studies of the Chemical Reactivity of a Series of Benzimidazolyl-Chalcone by Quantum Chemical Approaches

This theoretical chemical reactivity study was conducted using the Density Functional Theory (DFT) method at the B3LYP/6-311G(d,p) level of calculation. It involved a series of five (05) Benzimidazolyl-Chalcone (BZC) and allowed the prediction of the chemical reactivity of these compounds. The DFT global chemical reactivity descriptors (HOMO and LUMO energies, chemical hardness, energy, electronic chemical potential and electrophilicity) were examined to predict the relative stability and reactivity of BZCs. Thus BZC-4 which has a boundary orbital energy gap of ΔEgap = 3.650 eV is the most polarisable, most reactive, good nucleophile.and it is a soft molecule. The values of the global reactivity descriptors confirmed the high chemical reactivity of BZC-4. Local reactivity indices as well as dual descriptors were calculated to indicate the likely sites of electrophilic and nucleophilic attack of the different compounds studied. The analysis of the local indices and the dual descriptors revealed that the nitrogen heteroatom N13 is the preferential site of electrophilic attack and the carbon atom C1 should be the most reactive site with respect to a nucleophilic attack. the Hierarchical Ascending Classification analysis allowed us to group all five (5) compounds studied into three categories. The most active which are BZC-1 and BZC-5, the moderately active BZC-2, and the compounds BZC-3 and BZC-4, the least active. Moreover, this classification is consistent with the value of the Larvicide concentrations (LC100 (μg/mL)).
 Keywords : Benzimidazolyl-Chalcone (BZC), Global descriptors, Local descriptors, Dual descriptors

Montmorillonite Catalyzed Synthesis of Novel Steroid Dimers.

The reactions of sterols (androst-5-en-3β-ol-17-one, diosgenin, and cholesterol) and their tosylates with hydroquinone aimed at the synthesis of O,O-1,4-phenylene-linked steroid dimers were studied. The reaction course strongly depended on the conditions used. The study has shown that the major reaction products are the elimination products and unusual steroid dimers resulting from the nucleophilic attack of the hydroquinone C2 carbon atom on the steroid C3 position, followed by an intramolecular addition to the C5-C6 double bond. A different reaction course was observed when montmorillonite K10 was used as a catalyst. The reaction of androst-5-en-3β-ol-17-one under the promotion of this catalyst afforded the O,O-1,4-phenylene-linked steroid dimer in addition to the disteroidal ether. The formation of the latter compound was suppressed by using 3-tosylate as a substrate instead of the free sterol. The reactions of androst-5-en-3β-ol-17-one tosylate and cholesteryl tosylate with hydroquinone catalyzed by montmorillonite K10 carried out under optimized conditions afforded the desired dimers in 31% and 67% yield, respectively.

Exploring the Mechanism of the Intramolecular Diels-Alder Reaction of (2E,4Z,6Z)-2(allyloxy)cycloocta-2,4,6-trien-1-one Using Bonding Evolution Theory.

In the present work, the bond breaking/forming events along the intramolecular Diels-Alder (IMDA) reaction of (2E,4Z,6Z)-2(allyloxy)cycloocta-2,4,6-trien-1-one have been revealed within bonding evolution theory (BET) at the density functional theory level, using the M05-2X functional with the cc-pVTZ basis set. Prior to achieving this task, the energy profiles and stationary points at the potential energy surface (PES) have been characterized. The analysis of the results finds that this rearrangement can proceed along three alternative reaction pathways (a-c). Paths a and b involve two steps, while path c is a one-step process. The first step in path b is kinetically favored, and leads to the formation of an intermediate step, Int-b. Further evolution from Int-b leads mainly to 3-b1. However, 2 is the thermodynamically preferred product and is obtained at high temperatures, in agreement with the experimental observations. Regarding the BET analysis along path b, the breaking/forming process is described by four structural stability domains (SSDs) during the first step, which can be summarized as follows: (1) the breaking of the C-O bond with the transfer of its population to the lone pair (V(O)), (2) the reorganization of the electron density with the creation of two V(C) basins, and (3) the formation of a new C-C single bond via the merger of the two previous V(C) basins. Finally, the conversion of Int-b (via TS2-b1) occurs via the reorganization of the electron density during the first stage (the creation of different pseudoradical centers on the carbon atoms as a result of the depopulation of the C-C double bond involved in the formation of new single bonds), while the last stage corresponds to the non-concerted formation of the two new C-C bonds via the disappearance of the population of the four pseudoradical centers formed in the previous stage. On the other hand, along path a, the first step displays three SSDs, associated with the depopulation of the V(C2,C3) and V(C6,C7) basins, the appearance of the new monosynaptic basins V(C2) and V(C7), and finally the merging of these new monosynaptic basins through the creation of the C2-C7 single bond. The second step is described by a series of five SSDs, that account for the reorganization of the electron density within Int-a via the creation of four pseudoradical centers on the C12, C13, C3 and C6 carbon atoms. The last two SSDs deal with the formation of two C-C bonds via the merging of the monosynaptic basins formed in the previous domains.

Synthesis and Crystal Structure of Ethyl 5-(4-Bromophenyl)-7-methyl-3-oxo-2,3-dihidro-5H-thiazolo[3,2-a]pyrimidine-6-carboxylate

Thiazolopyrimidines are attractive to medical chemists as new antitumor agents due to their high inhibitory activity against the replication process of tumor cells and the easy modification of their structure by changing the number and nature of substituents. The presence of asymmetric C5 carbon atoms requires the development of racemic mixture separation procedures for these heterocycles. One of the most effective methods is the crystallization of a racemic compound in the form of a conglomerate. The prerequisite for such separation is the construction of chiral, supramolecular ensembles in the crystalline state. Halogen-π interactions were chosen as supramolecular synthons. In this context, ethyl 7-methyl-3-oxo-2,3-dihidro-5H-thiazolo[3,2-a]pyrimidine-6-carboxylate containing a 4-bromophenyl fragment at C5 was synthesized. The crystal structure of the resulting compound was established using SCXRD. The role of the halogen-π interaction on the formation of one-dimensional homochiral chains is revealed.

(2-Hydroxy-3-Methoxybenzylidene)thiazolo[3,2-a]pyrimidines: Synthesis, Self-Assembly in the Crystalline Phase and Cytotoxic Activity.

A series of new 2-hydroxy-3-methoxybenzylidenethiazolo[3,2-a]pyrimidines with different aryl substituents at the 5 position are synthesized and characterized by 1H/ 13C NMR and IR-spectroscopy and mass-spectrometry, as well as single crystal X-ray diffraction (SCXRD). It was demonstrated that the type of hydrogen bonding can play a key role in the chiral discrimination of these compounds in the crystalline phase. The hydrogen bond of the O-H...N type leads to 1D supramolecular heterochiral chains or conglomerate crystallization in the case of the formation of homochiral chains. The hydrogen bond of O-H...O type gave racemic dimers, which are packed into 2D supramolecular layers with a parallel or angular dimers arrangement. Halogen bonding of the N...Br or O...Br type brings a new motif into supramolecular self-assembly in the crystalline phase: the formation of 1D supramolecular homochiral chains instead 2D supramolecular layers. The study of cytotoxicity against various tumor cells in vitro was carried out. It was found that 2-hydroxy-3-methoxybenzylidenethiazolo[3,2-a]pyrimidines with 3-nitrophenyl substituent at C5 carbon atom demonstrated a high efficiency against M-HeLa (cervical adenocarcinoma) and low cytotoxicity against normal liver cells.

P-TSA·H2O catalyzed metal-free and environmentally benign synthesis of 4-aryl quinolines from arylamine, arylacetylene, and dimethyl sulfoxide.

An environmentally benign and metal-free synthesis of 4-aryl quinolines is reported by employing readily available arylamine, arylacetylene, and DMSO in the presence of 20 mol% p-TSA·H2O. In the present protocol, the solvent DMSO serves as a reactant cum solvent for providing the C2 carbon atom of the quinoline skeleton. Notably, the reaction proceeds effectively and efficiently without the involvement of any metal catalyst, ligand, and co-catalyst as additives and inert atmospheric reaction conditions. This method provides high atom economy and good yields, and two C-C and one C-N bonds are formed in a single step through a three-component reaction.

The global and local Reactivity of C,N-diarylnitryle imines in [3+2] cycloaddition processes with trans-β-nitrostyrene according to Molecular Electron Density Theory: A computational study

The regioselectivity of the [3+2] cycloaddition reactions between trans-β-nitrostyrene and C,N-diarylnitryle imine analogues as three atom components (TACs) has been studied with the use of Conceptual Density Functional Theory in the framework of Molecular Electron density Theory. Global and local reactivity indices were determined. Presented quantum-chemical computations showed that, for the reaction of nitroalkene with diphenylnitryle imine, the most favourable reaction path is determined by the nucleophilic attack of C3 carbon atom of TAC on an electrophilic Cα carbon atom of nitroalkene. Therefore, the creation of 1,3,4-triphenyl-5-nitro-Δ2-pyrazoline, according to channel B, is more probable. Similarly, to presented conclusion, for reactions of nitroalkene with nitryle imines containing ED group at para position of the phenyl ring also the most favourable reaction paths run through channel B leading to 1,3,4-triphenyl-5-nitro-Δ2-pyrazolines. In turn, reactions of nitroalkene with nitryle imines containing EW group at para position of the phenyl ring have the opposite preference and the most favourable reaction paths is channel A leading to 1,3,5-triphenyl-4-nitro-Δ2-pyrazolines.

Mechanism of formation and ion mobility separation of protomers and deprotomers of diaminobenzoic acids and aminophthalic acids.

Aminobenzoic acids are well-established candidates for understanding the formation of isomeric ions in positive mode electrospray ionization as they yield both N- and O-protomers (prototropic isomers) at the amine and carbonyl sites, respectively. In the present work, a combination of ion mobility-mass spectrometry and density functional theory calculations to determine the protonation and deprotonation behaviour of four diamino benzoic acid and four aminophthalic acid isomers is presented. The additional COOH group on the ring of aminophthalic acids provides experimental evidence regarding the mechanism of intramolecular NH3+ → O proton transfer, which has been the subject of debate in recent years. To determine the proton acceptor O atom, ion mobility spectra of the fragments of protomers were used as a new method for the confidential assignment of the O-protomer structure, confirming only short-distance intramolecular NH3+ → O proton transfer. Additionally, the substitution pattern both influences the basicity of the protonation sites and enables these molecules to form internal hydrogen bonds with the protonated or deprotonated sites. The formation of the hydrogen bonds in the deprotonated aminophthalic acids changed the charge distribution and subsequently their ion mobility-derived collision cross sections in nitrogen (CCSN2) leading to separation of the four isomers studied. Finally, an interesting effect of the substitution pattern was observed as a synergistic electron-donating effect of the amine groups of 3,5-diaminobenzoic acid on enhancing the basicity of the carbon atom C2 of the ring and previously unreported formation of a C-protomer within aminobenzoic acid systems.

Effect of modification of betulinic acid at the C3-carbon atom of homolupane triterpenoids on the antiproliferative activity in vitro

In search of new cytotoxic derivatives based on the lupane scaffold, methyl betulonate and methyl 20,29-dihydrobetulonate were conjugated with Reformatsky reagents to provide homolupanes extended at the C3-carbon atom. Further transformations of the functional groups afforded a series of derivatives with 2-hydroxyethyl and allyl alcohol moieties. Their varying antiproliferative activity in vitro was then investigated in four cancer cell lines and in normal human BJ fibroblasts. In cervical carcinoma HeLa cells, derivatives 5, 6 and 17 were the most promising with lower micromolar IC50s and no toxicity to fibroblasts, thus showing a high therapeutic index. In addition, induction of apoptosis was found in HeLa cells after 24 h treatment with compounds 5, 6, 13 and 29. This newly synthesized series is more interesting than the published lupane and homolupane triterpenes and saponins, due to their nontoxicity towards healthy human cells and stronger cytotoxicity to various cancer cell lines. This approach increases their potential as anticancer agents.

Photochemical Ring Contraction of 5,5-Dialkylcyclopent-2-enones and in situ Trapping by Primary Amines.

If substituted in the 5,5-position, cyclopent-2-enones undergo a smooth photochemical rearrangement to ketenes. A concomitant cyclopropane formation occurs due to a 1,3-shift of the C5 carbon atom from the carbonyl carbon atom (C1) to carbon atom C3. In this study, the cyclopropyl-substituted ketene intermediates were trapped in situ by primary amines providing an efficient entry into 2,2-disubstituted cyclopropaneacetic amides (24 examples, 49-95% yield). A remarkable feature of the reaction is the fact that the photochemical rearrangement can occur from either the first excited singlet (S1) or the respective triplet state (T1). In line with experimental results (triplet quenching, sensitization), XMS-CASPT2 calculations support the existence of efficient reaction pathways to the intermediate ketene both on the singlet and on the triplet hypersurface.

A molecular electron density theory study on the Chichibabin reaction: The origin of regioselectivity

A Molecular Electron Density Theory (MEDT) study was performed on the nucleophilic amination of pyridine and benzene to elucidate the observed regioselectivity in the Chichibabin reaction. For this purpose, three possible reaction paths were considered between NaNH2 and the 2-, 3- and 4-positions of pyridine. The reaction of NaNH2 and benzene was also investigated. The results indicated that in each reaction, the first step involves the nucleophilic attack of the NH2‾ ion toward the aromatic system to produce an anionic intermediate. The second step, proceeds via hydride elimination of the anionic intermediate to produce the corresponding aromatic amine. This step is more favourable both kinetically and thermodynamically for the reaction at the 2-position of pyridine relative to the 4-position. In contrast to the Parr functions analysis which indicates that the 4-position is activated more electrophilically in pyridine, the PES analysis reveals that the 2-position attack with the NH2‾ ion is more favourable both thermodynamically and kinetically. The results for the reaction of sodium amide and benzene indicated that this reaction is not feasible due to the high activation barriers. In consistent with the experimental results, the ELF analysis indicated that in the first step of the reaction between pyridine and sodium amide, the formation of the C2–N bond takes place via a pseudoradical coupling between the C2 carbon atom of pyridine and the N atom of NaNH2. These variations occur in the second-half of the first step of the reaction. NCI analysis on the reaction revealed that the more attractive forces between the fragments, make the transition states for the 2-position attack more stable relative to the others. Thus, the NCI analysis can satisfactorily describe the observed regioselectivity in the Chichibabin reaction.

Crystalline State Hydrogen Bonding of 2-(2-Hydroxybenzylidene)Thiazolo[3,2-a]Pyrimidines: A Way to Non-Centrosymmetric Crystals

Thiazolopyrimidines are attractive to medical chemists as new antitumor agents due to their high inhibiting activity towards the tumor cells replication process and easy modification of their structure by varying of the number and nature of substituents. The presence of asymmetric C5 carbon atoms requires the development of racemic mixture separation procedures for these heterocycles. One of the more effective ways is the crystallization of a racemic compound as a conglomerate. A prerequisite for such separation is the formation of non-centrosymmetric crystals presenting Sohncke space groups. For the construction of chiral supramolecular ensembles in a crystalline state, hydrogen bonds were chosen as supramolecular synthons. In this context, salicylic derivatives at the C2 atom of thiazolopyrimidines were synthesized. The crystal structures of the obtained compounds were established by SCXRD. The regularities of the solvent’s influence on the crystal packaging were revealed. The conditions for the preparation of crystals with the chiral space group due to intermolecular hydrogen bonds were discovered.

Visible Light‐Mediated Dearomative Hydrogen Atom Abstraction/ Cyclization Cascade of Indoles

AbstractThe photochemical synthesis of yet unknown 2‐oxospiro[azetidine‐3,3′‐indolines] (17 examples, 80–95 % yield), 2,4‐dioxospiro[azetidine‐3,3′‐indolines] (eight examples, 87–97 % yield), and 1‐oxo‐1,3‐dihydrospiro[indene‐2,3′‐indolines] (17 examples, 85–97 % yield) is described. Starting from readily accessible 3‐substituted indoles, a dearomatization of the indole core was accomplished upon irradiation at λ=420 nm in the presence of thioxanthen‐9‐one (10 mol%) as the sensitizer. Based on mechanistic evidence (triplet energy determination, deuteration experiments, by‐product analysis) it is proposed that the reaction proceeds by energy transfer via a 1,4‐ or 1,5‐diradical intermediate. The latter intermediates are formed by excited state hydrogen atom transfer from suitable alkyl groups within the C3 substituent to the indole C2 carbon atom. Subsequent ring closure proceeds with pronounced diastereoselectivity to generate a 4‐ or 5‐membered spirocyclic dearomatized product with several options for further functionalization.

Visible Light-Mediated Dearomative Hydrogen Atom Abstraction/ Cyclization Cascade of Indoles.

The photochemical synthesis of yet unknown 2‐oxospiro[azetidine‐3,3′‐indolines] (17 examples, 80–95 % yield), 2,4‐dioxospiro[azetidine‐3,3′‐indolines] (eight examples, 87–97 % yield), and 1‐oxo‐1,3‐dihydrospiro[indene‐2,3′‐indolines] (17 examples, 85–97 % yield) is described. Starting from readily accessible 3‐substituted indoles, a dearomatization of the indole core was accomplished upon irradiation at λ=420 nm in the presence of thioxanthen‐9‐one (10 mol%) as the sensitizer. Based on mechanistic evidence (triplet energy determination, deuteration experiments, by‐product analysis) it is proposed that the reaction proceeds by energy transfer via a 1,4‐ or 1,5‐diradical intermediate. The latter intermediates are formed by excited state hydrogen atom transfer from suitable alkyl groups within the C3 substituent to the indole C2 carbon atom. Subsequent ring closure proceeds with pronounced diastereoselectivity to generate a 4‐ or 5‐membered spirocyclic dearomatized product with several options for further functionalization.

Effect of fullerene on the anisotropy, domain size and relaxation of a perpendicularly magnetized Pt/Co/C60/Pt system

(a) Spinterface formation on a single C60 unit. The surface cobalt atom Co2 is bonded to the C2 carbon atom of C60. (b)- (e) Domain images near the coercive field for samples Pt/Co/C60/Pt having C60 thickness 0, 0.5, 1.6 and 3.2 nm, respectively.