Fusing C60 units without Stone–Wales bond rotations

Abstract  

Using ab-initio calculation, we have explored new chemical paths for the coalescence of C₆₀ units into higher fullerenes and novel structures. Besides the Stone–Wales paradigm used for rationalizing the fusion of fullerenes and nanotubes, we demonstrated that an alternative path exists for the fusion of two C₆₀ units. This path uses successive “π–π” additions and subsequent bond reorganizations to lead to a specific C₁₂₀ peanut-like structure. The energies of the chemical barriers, the intermediate structures, and the final product are markedly lower than their counterparts found in the chemical paths based on Stone–Wales bond rotations. The results rationalize the existence of a temperature range in which peanut-like structures are obtained during thermal treatment of peapod structures.     

Prenylated Flavonoids and C-15 Isoprenoid Analogues with Antibacterial Properties from the Whole Plant of Imperata cylindrica (L.) Raeusch (Gramineae)

The local botanical Imperata cylindrica in Cameroon was investigated for its antibacterial potency. The methanol extract afforded a total of seven compounds, including five hitherto unreported compounds comprising three flavonoids (1–3) and two C-15 isoprenoid analogues (4 and 5) together with known derivatives (6 and 7). The novelty of the flavonoids was related to the presence of both methyl and prenyl groups. The potential origin of the methyl in the flavonoids is discussed, as well as the chemophenetic significance of our findings. Isolation was performed over repeated silica gel and Sephadex LH-20 column chromatography and the structures were elucidated by (NMR and MS). The crude methanol extract and isolated compounds showed considerable antibacterial potency against a panel of multi-drug resistant (MDR) bacterial strains. The best MIC values were obtained with compound (2) against S. aureus ATCC 25923 (32 µg/mL) and MRSA1 (16 µg/mL).     

Interface induced crystal structures of dioctyl-terthiophene thin films

Temperature dependent structural and morphological investigations on semiconducting dioctyl-terthiophene (DOTT) thin films prepared on silica surfaces reveals the coexistence of surface induce order and distinct crystalline/liquid crystalline bulk polymorphs. X-ray diffraction and scanning force microscopy measurements indicate that at room temperature two polymorphs are present: the surface induced phase grows directly on the silica interface and the bulk phase on top. At elevated temperatures the long-range order gradually decreases, and the crystal G (340 K), smectic F (348 K), and smectic C (360 K) phases are observed. Indexation of diffraction peaks reveals that an up-right standing conformation of DOTT molecules is present within all phases. A temperature stable interfacial layer close to the silica-DOTT interface acts as template for the formation of the different phases. Rapid cooling of the DOTT sample from the smectic C phase to room temperature results in freezing into a metastable crystalline state with an intermediated unit cell between the room temperature crystalline phase and the smectic C phase. The understanding of such interfacial induced phases in thin semiconducting liquid crystal films allows tuning of crystallographic and therefore physical properties within organic thin films.     

Guttiferone BL with antibacterial activity from the fruits of Allanblackia gabonensis

Allanblackia genus, an endless source of bioactive compounds, was investigated for its antibacterial properties. The chemical study of the methanol extract from the fruits of Allanblackia gabonensis resulted in the isolation of the undescribed guttiferone BL (1) along with the known kaempferol (2), morelloflavone (3), morelloflavone 7″-O-β-D-glucopyranoside (4), β-sitosterol 3-O-β-D-glucopyranoside and β-sitosterol. Their structures were determined using spectrometry and spectroscopic techniques. The antibacterial activity was evaluated against five Gram-negative and two Gram-positive strains using a broth micro-dilution method. Compounds displayed low to significant activity against the tested bacterial strains with MICs ranging from 8 to 512 μg/mL. Morelloflavone (3) presented significant activity against E. coli ATCC8739 (MIC = 8 μg/mL) while guttiferone BL (1) exhibited low activity (MICs = 256–512 μg/mL) against all the tested strains. The crude extract also had moderate to significant activity against the tested bacterial strains.     

Ester-functionalized phthalonitriles and zinc phthalocyanines via palladium-catalyzed cyanation of 4,5-dichlorophthalates

Dicyanophthalates 3 were synthesized via Pd-catalyzed two-fold cyanation of the corresponding 4,5-dichlorophthalates with Zn(CN)₂. Appropriate modification of reaction conditions allowed one-pot synthesis of the corresponding zinc phthalocyanines 7 bearing eight peripheral alkyl ester groups. Powder X-ray diffraction study of a mesogenic zinc phthalocyanine bearing branched alkyl substituents revealed a rare case of a transition between two columnar rectangular liquid crystalline mesophases with different symmetry.     

Synthesis of glucosidic derivatives with a spacer arm by reverse hydrolysis using almond β-D-glucosidase

Glucosidase-catalysed synthesis of glucosides with a spacer arm on the anomeric carbon is reported. By using the acceptor as solvent at an elevated temperature, much higher yields of product have been obtained than previously observed.     

Computation of the contribution from the cavity effect to protein-ligand binding free energy

We present results of the investigation of the cavity creation/annihilation effect in view of formation of the protein-ligand (PL) complexes. The protein and ligand were considered as rigid structures. The change of the cavity creation/annihilation free energy DeltaG(cav) was calculated for three PL complexes using the thermodynamic integration procedure with the original algorithm for growing the interaction potential between the cavity and the water molecules. The thermodynamic cycle consists of two stages, annihilation of the cavity of the ligand for the unbound state and its creation at the active site of the protein (bound state). It was revealed that for all complexes under investigation, the values of DeltaG(cav) are negative and favorable for binding. The main contribution to DeltaG(cav) appears due to the annihilation of the cavity of the ligand. All computations were made using the parallel version of CAVE code, elaborated in our preceding work.     

Hierarchical Surface Atomic Structure of a Manganese‐Based Spinel Cathode for Lithium‐Ion Batteries

The increasing use of lithium‐ion batteries (LIBs) in high‐power applications requires improvement of their high‐temperature electrochemical performance, including their cyclability and rate capability. Spinel lithium manganese oxide (LiMn₂O₄) is a promising cathode material because of its high stability and abundance. However, it exhibits poor cycling performance at high temperatures owing to Mn dissolution. Herein we show that when stoichiometric lithium manganese oxide is coated with highly doped spinels, the resulting epitaxial coating has a hierarchical atomic structure consisting of cubic‐spinel, tetragonal‐spinel, and layered structures, and no interfacial phase is formed. In a practical application of the coating to doped spinel, the material retained 90 % of its capacity after 800 cycles at 60 °C. Thus, the formation of an epitaxial coating with a hierarchical atomic structure could enhance the electrochemical performance of LIB cathode materials while preventing large losses in capacity.     

Structures of the high-temperature solid phases of the odd-numbered fatty acids from tridecanoic acid to tricosanoic acid

Crystal structures of the high-temperature phases of odd-numbered fatty acids (C(n)H(2n-1)OOH) from tridecanoic acid (C(13)H(25)OOH) to tricosanoic acid (C(23)H(45)OOH) are presented in this article. They have been determined from high-quality X-ray powder-diffraction patterns. Two types of high-temperature phases are adopted: one monoclinic A2/a with Z=8 for the fatty acids with n=13 and n=15, denoted as C', and one monoclinic P2(1)/a with Z=4 for the longer-chain fatty acids, denoted as C'. It appears that the packing arrangement of the alkyl chains and of the carboxyl groups is similar in all of the structures. However, the arrangement at the methyl-group interface differs between the C' and C' forms. A survey of the intermolecular interactions involved in these polymorphs coupled with a study of the effects of temperature on the structures have led us to a better understanding of the arrangement of the molecules within the high-temperature solid phases of odd-numbered fatty acids.