Replacement Of Carbon Atoms Research Articles

Thermodynamic Study of Alkylsilane and Alkylsiloxane-Based Ionic Liquids.

The thermodynamic properties of ionic liquids (ILs) bearing alkylsilane and alkylsiloxane chains, as well as their carbon-based analogs, were investigated. Effects such as the replacement of carbon atoms by silicon atoms, the introduction of a siloxane linkage, and the length of the alkylsilane chain were explored. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to study the thermal and phase behavior (glass transition temperature, melting point, enthalpy and entropy of fusion, and thermal stability). Heat capacity was obtained by high-precision drop calorimetry and differential scanning microcalorimetry. The volatility and cohesive energy of these ILs were investigated via the Knudsen effusion method coupled with a quartz crystal microbalance (KEQCM). Gas phase energetics and structure were also studied to obtain the gas phase heat capacity as well as the energy profile associated with the rotation of the IL side chain. The computational study suggested the existence of an intramolecular interaction in the alkylsiloxane-based IL. The obtained glass transition temperatures seem to follow the trend of chain flexibility. An increase of the alkylsilane chain leads to a seemingly linear increase in molar heat capacity. A regular increment of 30 J·K-1·mol-1 in the molar heat capacity was found for the replacement of carbon by silicon in the IL alkyl chain. The alkylsilane series was revealed to be slightly more volatile than its carbon-based analogs. A further increase in volatility was found for the alkylsiloxane-based IL, which is likely related to the decrease of the cohesive energy due to the existence of an intramolecular interaction between the siloxane linkage and the imidazolium headgroup. The use of Si in the IL structure is a suitable way to significantly reduce the IL's viscosity while preserving its large liquid range (low melting point and high thermal stability) and low volatilities.

Activation of Z-scheme heterojunction of peroxymonosulfate for augmented visible-light-induced photocatalytic decomposition of tetracycline and enhanced antimicrobial efficacy with O-doped g-C3N4@Co3O4

The widespread use of graphitic carbon nitride (CN) for environmental pollutant removal has been hampered by intrinsic limitations, notably facile electron-hole recombination and a limited surface area. This work successfully synthesized OCN/Co3O4 composite materials. Furthermore, the implementation of a peroxymonosulfate (PMS) reaction system remarkably enhanced the material’s capability to degrade Escherichia coli (E. coli) and tetracycline hydrochloride (TC). Compared with CN, the composite material possessed a notably larger specific surface area, affording it a profusion of reactive sites. Additionally, the replacement of carbon atoms with oxygen atoms in the original CN structure profoundly altered its electronic configuration. The characterization through UV–Vis diffuse reflectance spectra, photoluminescence, transient photocurrent responses, and electrochemical impedance spectroscopy also confirmed the excellent optical and electrochemical attributes of OCN/Co3O4. Experimental results illustrated OCN/Co3O4/Vis/PMS completely degraded E. coli at an initial concentration of 1 × 107 CFU mL−1 within 1 h and reduced TC with the adding concentration of 10 mg/L by 99.2% in only 20 min. An analysis was conducted on reactive oxygen species (ROS) using electron paramagnetic resonance spectroscopy and radical quenching experiments. The test results demonstrated the generation of ROS including •O2−, •OH, h+, and SO4•− within the reaction system. This work explored the degradation mechanism in the OCN/Co3O4/Vis/PMS system, providing innovative insights for the design of eco-friendly, efficient catalysts as well as the enhancement of TC and E. coli degradation through the synergistic activation of photocatalytic PMS.

Boron-containing fullerene-based salts with cyclic carbonate solvents as electrolytes for Li-ion batteries and beyond.

Replacement of carbon atoms by a heteroatom in fullerene is a promising route that enhances the electronic properties of fullerenes and results in hetero fullerene-based effective agents ensuring applications in vivid fields of the solar cell, cathode materials for batteries, etc. Towards the development of new electrolyte salts, attention has been paid to facilitating ion mobility in particular and moderate stability of the anions in addition. From the atomistic molecular dynamics simulation studies, for the first time, we uncover that the boron-containing hetero fullerene, C59B- anion-based LiC59B, and NaC59B salts in cyclic carbonate solvents can act as efficient electrolytes by improving the transport phenomenon of the metal ions in solution, importantly for Li+ and satisfactorily for Na+ as compared to their commonly used BF4- anion based salts. Additionally, our study revealed that apart from LiC59B, and NaC59B salts, C58B22- based MgC58B2 salt can facilitate the ionic conductivity of the electrolyte. The properties of the proposed electrolyte under an electric field and different temperatures were investigated. Some of the bulk properties of the used electrolytes to some extent were found to be improved in the presence of these salts. The first principle-based electrochemical calculations further justify the stability of the proposed anions. The initial investigation from the Reactive force-field (ReaxFF) based atomistic simulations study elucidates that LiC59B reduces the decomposition of the EC solvent compared to LiBF4 and facilitates solvent stability.

Adsorption of hazardous gases on Cyclo[18]carbon and its analogues

Density functional theory calculations were performed to study the adsorption behavior of hazardous gases (NH3, CO2, CO, and NO) on twelve adsorbents (cyclo[18]carbon (C18) and its analogues Al9N9, B9N9, C6B6N6, C12B3N3, C14B2N2, d-C14B2N2, C16BN, C17Si; cyclo[12]carbon (C12) and its analogues Al6N6 and B6N6). The molecular electrostatic potential (MESP) maps of C18 revealed its polyynic structure with alternating electron-rich and electron-deficient regions. The most negative-valued MESP point (Vmin) indicates that the replacement of carbon atoms of C18/C12 by BN/AlN/Si units increases the electron-rich environment in the molecules. In general, NH3 and CO2 are found to be physisorbed on C18/C12 and its analogues. An important result is that the Vmin of C18/C12 and its analogues is linearly correlated with the NH3 and CO2 adsorption energies. The quantum theory of atoms in molecules (QTAIM) results indicate that the interactions of NH3 and CO2 with C18/C12 and its analogues are non-covalent in nature. In general, CO and NO are found to be chemisorbed on C18/C12 and its analogues. In contrast to the cases of NH3 and CO2 adsorption, the Vmin of C18/C12 and its analogues is generally inversely related to the CO and NO adsorption energies. The QTAIM results indicate the strong covalent character of the bonding for CO/C18, CO/C6B6N6, CO/d-C14B2N2, CO/C12, NO/C18, NO/C17Si, and NO/C12 systems. The adsorption process significantly influenced the chemical potential and/or hardness, especially for CO– and NO-adsorbed C18/C12 and its analogues.

Enhancement of absorption capacity, optical and non-linear optical properties of graphene oxide nanosheet

We studied the absorption capacity, optoelectronic and non-linear optical (NLO) properties of graphene oxide nanosheet (GON) and its doped derivatives with aluminum (-Al) atoms. The investigations have been performed using three functionals (B3LYP, B3LYP-D3 and ωB97XD) of the density functional theory (DFT) associated to the basis set 6-31+G(d,p). Aluminum atoms were incorporated into GON at different sites in order to search for suitable candidates that could lead to the enhancement of NLO properties and decrease the band gap value of pristine graphene oxide. As per our molecular investigations, several doped molecular design schemes based on push–pull models of GON were proposed. The best electronic and NLO configurations responses highlight the doped derivatives which were obtained by replacement of carbon atoms which support the functional groups present on the honeycomb lattice of GON with –Al atoms.

Infrared Spectrum for the New Nanomolecules ASi, CSi, TSi and Gsi

The core of the work is based on the replacement of carbon atoms by silicon atoms, on the basis of four standard bases of DNA: A, C, G and T (adenine, cytosine, guanine, thymine). Determining with minimum computational methods via ab initio Hartree-Fock methods, infrared spectrum and their peak absorbance frequencies. The option for simple replacement of carbon by silicon is due to the peculiar characteristics between both. Atomic interactions under non-carbon conditions were studied, with only the Hydrogen, Silicon, Nitrogen and Oxygen atoms, in CNTP, for the four standard bases of DNA, A, C, G and T, thus obtaining by quantum chemistry four new compounds, named here as: ASi, CSi, GSi and TSi. Computational calculations admit the possibility of the formation of such molecules, their existence being possible via quantum chemistry. Calculations obtained in the ab initio Unrestricted and Restrict Hartree-Fock method, (UHF and RHF) in the set of bases used Effective core potential (ECP) minimal basis, UHF CEP-31G (ECP split valance) and UHF CEP-121G (ECP triple-split basis), CC-pVTZ (Correlation-consistent valence-only basis sets triple-zeta) and 6-311G**(3df, 3pd) (Gaussian functions quadruple-zeta basis sets).

Infrared Spectrum for the New Exobiological Nanomolecules Asi, Csi, Tsi and Gsi

The core of the work is based on the replacement of carbon atoms by silicon atoms, on the basis of four standard bases of DNA: A, C, G and T (adenine, cytosine, guanine, thymine). Determining with minimum computational methods via ab initio Hartree-Fock methods, infrared spectrum and their peak absorbance frequencies. The option for simple replacement of carbon by silicon is due to the peculiar characteristics between both. Atomic interactions under non-carbon conditions were studied, with only the Hydrogen, Silicon, Nitrogen and Oxygen atoms, in CNTP, for the four standard bases of DNA, A, C, G and T, thus obtaining by quantum chemistry four new compounds, named here as: ASi, CSi, GSi and TSi. Computational calculations admit the possibility of the formation of such molecules, their existence being possible via quantum chemistry. Calculations obtained in the ab initio Unrestricted and Restrict Hartree-Fock method, (UHF and RHF) in the set of basis used Effective core potential (ECP) minimal basis, UHF CEP-31G (ECP split valance) and UHF CEP-121G (ECP triple-split basis), CC-pVTZ (Correlation-consistent valence-only basis sets triple-zeta) and 6-311G**(3df, 3pd) (Gaussian functions quadruple-zeta basis sets).

EFFECT OF NANOCARBON ADDITIVES ON STABILITY OF POLYMER COMPOSITES

This review briefly describes a state of research on the effect of fullerenes and carbon nanotubes (CNTs) on a durability of various polymer composite materials under extreme conditions. Fullerenes C60, C70, fullerene soot and CNTs integrated into the polymer matrix effectively prevent both thermal and thermo-oxidative degradation, as well as photo-oxidation processes. The stabilization mechanism of the carbon nanocompounds (CNC) is likewise and consists of the substantial end-capping termination of oxidation destructive chains on the nanocarbon skeleton. At that, the data array unequivocally indicates the predominant addition of carbon-centered alkyl radicals. Various polymer composite materials based on polyolefins, polyacrylates, polyamides, polycarbonates, elastomers are involved into the consideration. The approaches described are mostly aimed to increase the level of stabilizing activity of the polymer composites using different combinations of nanocarbon additives. The optimal dosage of CNC and interfacial compatibility between the polymer and fillers can significantly increase the heat resistance of the composites. The replacement of carbon atoms in the fullerene molecule with heteroatoms can also change its electronic properties and improve the antiradical and antioxidant activity. Areas for the effective use of fullerene C60 in aqueous media can be significantly expanded by modification with hydrophilic polymers. Thus, the performance of CNC integrated in the polymer composites is similar with those for strong synthetic stabilizers. CNC have good prospects for real industrial applications.

Carbon-Based Band Gap Engineering in the h-BN Analytical Modeling.

The absence of a band gap in graphene is a hindrance to its application in electronic devices. Alternately, the complete replacement of carbon atoms with B and N atoms in graphene structures led to the formation of hexagonal boron nitride (h-BN) and caused the opening of its gap. Now, an exciting possibility is a partial substitution of C atoms with B and N atoms in the graphene structure, which caused the formation of a boron nitride composite with specified stoichiometry. BC2N nanotubes are more stable than other triple compounds due to the existence of a maximum number of B–N and C–C bonds. This paper focused on the nearest neighbor’s tight-binding method to explore the dispersion relation of BC2N, which has no chemical bond between its carbon atoms. More specifically, the band dispersion of this specific structure and the effects of energy hopping in boron–carbon and nitrogen–carbon atoms on the band gap are studied. Besides, the band structure is achieved from density functional theory (DFT) using the generalized gradient approximations (GGA) approximation method. This calculation shows that this specific structure is semimetal, and the band gap energy is 0.167 ev.

Probing Peripheral H-Bonding Functionalities in BN-Doped Polycyclic Aromatic Hydrocarbons.

The replacement of carbon atoms at the zigzag periphery of a benzo[fg]tetracenyl derivative with an NBN atomic triad allows the formation of heteroatom-doped polycyclic aromatic hydrocarbon (PAH) isosteres, which expose BN mimics of the amidic NH functions. Their ability to form H-bonded complexes has never been touched so far. Herein, we report the first solution recognition studies of peripherally NBN-doped PAHs to form H-bonded DD·AA- and ADDA·DAAD-type complexes with suitable complementary H-bonding acceptor partners. The first determination of Ka in solution showed that the 1:1 association strength is around 27 ± 1 M-1 for the DD·AA complexes in C6D6, whereas it rises to 1820 ± 130 M-1 for the ADDA·DAAD array in CDCl3. Given the interest of BN-doped polyaromatic hydrocarbons in supramolecular and materials chemistry, it is expected that these findings will open new possibilities to design novel materials, where the H-bonding properties of peripheral NH hydrogens could serve as anchors to tailor the organizational properties of PAHs.

Variable electronic transport properties of double carbon-nanotube junctions via substitutional Fe, Co, and Mn atom doping

Electronic and transport properties of carbon-nanotube (CNT) hybrid junction CNT(3,3)/CNT(6,0)/CNT(3,3) are investigated and compared with substitutionally doped junction with transition metal atoms, iron, cobalt, and manganese; using density functional theory combined with non-equilibrium Green's function formalism. Transmission coefficient and current–voltage (I–V) characteristics are calculated for all configurations. The results indicate a smooth increase of current with voltage in pristine junction up to 0.75 V while in the case of higher voltages, the increase accelerates significantly and the conductance for the voltages between 1 and 1.5 becomes almost constant, about 40μA V. The replacement of carbon atoms with Fe, Co, and Mn in the scattering region causes rather substantial reduction of the transmission and conductance of the hybrid junction. It causes the current to reduce nearly 25% at the voltage of 1.5 V compared to the pristine one. It also appears that, there is no serious difference in the I–V characteristics for different impurity atoms, except some deviation in manganese conductance from the other two impurities’ curves. These results can be useful for future CNTs based nano-electronic applications.

ChemInform Abstract: Silicon‐Containing Amino Acids: Synthetic Aspects, Conformational Studies, and Applications to Bioactive Peptides

AbstractReview: 135 refs.

Silicon-Containing Amino Acids: Synthetic Aspects, Conformational Studies, and Applications to Bioactive Peptides.

Unnatural α-amino acids form a family of essential molecules used for, among other applications, the synthesis of modified peptides, to improve resistance to proteolytic enzyme degradation, and to modulate physico- and biochemical properties of bioactive peptides as well as chiral inducers in asymmetric synthesis. Among them, silicon-containing unnatural amino acids are becoming an interesting new class of building blocks. The replacement of carbon atoms in bioactive substances with silicon is becoming increasingly popular. Peptides containing silyl amino acids hold great promise for maintaining or reinforcing the biological activity of active compounds, while they simultaneously enhance their resistance to enzyme degradation. In addition, the lipophilicity of the silicon atom facilitates their membrane crossing and their bioavailability. Nowadays, the interest of the pharmaceutical industry in peptide- and protein-based therapies is increasing. In this respect, silicon-containing amino acids and peptides are likely to be a significant part of future innovations in this area, and more generally in the area of biomolecules. In this process, commercial availability of silicon-containing amino acids is necessary: new syntheses have been developed, and work in this area is ongoing. This review aims to be a comprehensive and general summary of the different methods used to prepare silicon-containing amino acids and their implications on conformational structures and biological applications when they are incorporated into bioactive molecules.

Synthesizing MnO2nanosheets from graphene oxide templates for high performance pseudosupercapacitors

A facile method to synthesize layered manganese oxide nanosheets was developed for the first time by using graphene oxide as a template. The in situ replacement of carbon atoms on the graphene oxide framework by edge-shared [MnO6] octahedra provides a new methodology to synthesize graphene-based two-dimensional nanomaterials. The transformation of graphene oxide into δ-type MnO2 nanosheets results in an especially high surface area (157 m2 g−1), which is the highest value amongst today's MnO2 nanomaterials. Moreover, the MnO2 nanosheets demonstrated prominent capacitance (∼1017 F g−1 at a scan rate of 3 mV s−1, and ∼1183 F g−1 at a current density of 5 A g−1) and remarkable rate capability (∼244 F g−1 at a high scan rate of 50 mV s−1 and ∼559 F g−1 at a high current density of 25 A g−1), indicating their promise in high energy and power density pseudosupercapacitors.

Synthesis and Olfactory Characterization of Novel Silicon‐Containing Acyclic Dienone Musk Odorants

AbstractWith an odor threshold value of 0.54 ng L–1 air, (3E,5E)‐7,7‐dimethyl‐5‐tert‐butylocta‐3,5‐dien‐2‐one (1a) constitutes the most potent member of a new family of acyclic musk odorants with ionone aspects. Replacement of the quaternary carbon atoms of 1a with silicon atoms leads to the (di)sila analogues 1b (replacement of the carbon atom C‐7), 1c (replacement of the quaternary carbon atom of the 5‐tert‐butyl group), and 1d (replacement of both quaternary carbon atoms). Compounds 1b–1d were prepared in multistep syntheses, and their olfactory properties were characterized. The disila analogue 1d turned out to be the weakest compound of the series (197 ng L–1 air), with only very faint musky aspects. The 7‐sila analogue 1b was very floral, of iononeand rose character, and also had a distinct musky note (1.63 ng L–1 air). The 5‐trimethylsilyl analogue 1c was the most musky sila odorant of the series (10.6 ng L–1 air), with rosy but not ionone‐like facets. Thus, exchange of one or both tert‐butyl groups of 1a for a trimethylsilyl substituent had quite dramatic effects on the odor, and steric bulk at the carbon atom C‐5 seems to be important for creating a musk odor impression.

The magnetic property of carbon-doped TiO 2

Despite carbon and TiO 2 are nonmagnetic, we detected ferromagnetism at room temperature over samples of carbon-doped TiO 2. The materials were prepared by standard solid-state reaction and sintered either in an argon or nitrogen atmosphere. According to Raman results, the samples sintered in nitrogen showed lower D-bond (disordered) and G-bond (graphitic) concentration, plausibly a result of nitrogen incorporation into the carbon-doped TiO 2 materials. All the samples are ferromagnetic at room temperature. With increase of carbon concentration, there is decline of magnetic moment per carbon (in carbide form) due to antiferromagnetic interaction among the carbon atoms. Compared to the sample sintered in argon, the one sintered in nitrogen is lower in magnetic moment due to partial replacement of carbon atoms by nitrogen atoms. We found that the electrons-mediated mechanism is more suitable than the holes-mediated one for the explanation of ferromagnetism of the carbon-doped TiO 2 materials.

A TD-DFT investigation of two-photon absorption of fluorene derivatives

We report time-dependent density functional theory (TD-DFT) calculations on the two-photon absorption (TPA) properties of fluorene and derivatives. The influence of donor and acceptor groups and of dimerisation is investigated. Firstly the choice of a DFT functional and of the basis set is performed by comparison of experimental and calculated excitation energies and two-photon cross sections. Then, the calculations display an enhancement of the cross section with acceptor groups or with a combination of one donor and one acceptor groups (push-pull), at some positions on the cycles. Moreover, the largest cross section is obtained for bifluorene. The replacement of carbon atoms by nitrogen atoms, giving heterocycles, is not efficient. In chloroform as solvent, the excitation energy decreases and the two-photon cross section increases, mainly with a polar molecule. Finally, a rationalization of the results is given based on the three-level model by analysis of the transition moments and of the molecular orbitals.

Carbon modified TiO2 photocatalysts for water purification

Carbon modified TiO2 photocatalysts for water purification Carbon can form different structures with TiO2: carbon-doped TiO2, carbon coated TiO2 and composites of TiO2 and carbon. The presence of carbon layer on the surface of TiO2 as well as the presence of porous carbon in the composites with TiO2 can increase the concentration of organic pollutants on the surface of TiO2, facilitating the contact of the reactive species with the organic molecules. Carbon-doped TiO2 can extend the absorption of the light to the visible region by the narrowing of the band gap and makes the photocatalysts active under visible light irradiation. TiO2 loaded carbon can also work as a photocatalyst, on which the molecules are adsorbed in the pores of carbon and then they undergo the photocatalytic decomposition with UV irradiation. Enhanced photocatalytic activity for the destruction of some organic compounds in water was noticed on the carbon coated TiO2 and TiO2 loaded activated carbon, mostly because of the adsorptive role of carbon. However, in carbon-doped TiO2, the role of carbon is somewhat different, the replacement of carbon atom with Ti or oxygen and formation of oxygen vacancies are responsible for extending its photocatalytic activity towards the visible range.

6-Membered P-Heterocycles: Ring-Condensed 1,3,2-Diheterophosphorinane 2-Chalcogenides

Literature publications (up to the end of 2006) relating to the synthesis, biological significance and conformational behaviour of carbocycle- and heterocycle-condensed six-membered tetracoordinate P(V) 1,3,2-diheterophosphorinanes are reviewed. The replacement of carbon atoms of cyclohexane by P and O and/or N to form 1,3,2-dioxa-, 1,3,2- oxaza- or 1,3,2-diazaphosphorinanes introduces lone pair electrons instead of hydrogens and changes the bond angles and bond lengths, and can thereby lead to significantly different stereostructural preferences of the hetero ring as compared with those of cyclohexane. Although monocyclic 1,3,2-diheterophosphorinanes often exist in a chair conformation in both the solid and solution states, the existence of conformations other than a chair can predominate in some cases for steric and stereoelectronic reasons associated with the presence of bulky groups on the P-containing ring or in polycyclic rigid systems. After a brief account on the most important pharmacological and stereochemical features, involving the configuration assignment and conformation determination of P-diheterophosphorinanes, the present review mainly focuses on the synthesis and stereostructural studies of carbo- and heterocycle-condensed derivatives, where the fused ring may exert considerable effects on the conformational behaviour of the P-hetero ring.

Electronic States of BCN Alloy Nanotubes in a Simple Tight-Binding Model

Electronic states are calculated in boron carbonitride (BCN) alloy nanotubes with a simple tight-binding model. Random replacement of carbon atoms with boron and nitrogen (B–N) ones in metallic carbon nanotubes mainly causes level broadening and the nanotubes remain metallic. On the other hand, the energy gap of boron nitride (BN) nanotubes always survives under random substitution of B–N atoms by carbon ones while it becomes smaller than the original gap. Further, the optical gap does not correspond well with the band gap of the density of states in nanotubes with high B–N concentration. This can be understood in terms of localized states associated with carbon impurities in a BN nanotube.