Hydrogenation from C60 to C60H60 was studied by an unrestricted broken spin symmetry Hartree–Fock approach implemented in semiempirical codes based on the
AM1 technique. The calculations focused on the successive addition of hydrogen molecules to the fullerene cage following the
identification of the cage target atoms by calculating the highest atomic chemical susceptibility at each step. The results
obtained are analyzed from energy, symmetry, and composition perspectives. 相似文献
Glucose oxidase (GOD) was covalently immobilized onto Fe3O4/SiO2 magnetic nanoparticles (FSMNs) using glutaraldehyde (GA). Optimal immobilization was at pH 6 with 3-aminopropyltriethoxysilane
at 2% (v/v), GA at 3% (v/v) and 0.143 g GOD per g carrier. The activity of immobilized GOD was 4,570 U/g at pH 7 and 50°C.
The immobilized GOD retained 80% of its initial activity after 6 h at 45°C while free enzyme retained only 20% activity. The
immobilized GOD maintained 60% of its initial activity after 6 cycles of repeated use and retained 75% of its initial activity
after 1 month at 4°C whereas free enzymes retained 62% of its activity. 相似文献
Dopamine receptors have been found in certain populations of non-neuronal cells in the brain, viz., discrete areas of ciliated ependyma and the ependymal cells of the choroid plexus. We have studied the presence of both tyrosine-hydroxylase-immunoreactive nerve fibers and dopamine receptors in the subcommissural organ (SCO), an ependymal brain gland that is located in the roof of the third ventricle and that secretes, into the cerebrospinal fluid, glycoproteins that aggregate to form Reissners fiber (RF). Antibodies against D2, D3, D4, and D5 dopamine receptors were used in immunoblots of bovine striatum, fresh SCO, and organ-cultured SCO, and in immunocytochemistry of the bovine, rat, and mouse SCO. Only a few tyrosine-hydroxylase fibers appeared to reach the SCO. However, virtually all the secretory ependymal and hypendymal cells of the SCO immunoreacted with antibodies against D2, D4, and D5 receptors, with the last-mentioned rendering the strongest reaction, especially at the ventricular cell pole of the secretory ependymocytes, suggesting that dopamine might reach the SCO via the cerebrospinal fluid. The antibodies against the four subtypes of receptors revealed corresponding bands in immunoblots of striatum and fresh SCO. Although the cultured SCO displayed dopamine receptors, dopamine had no apparent effect on the expression of the SCO-spondin gene/protein or on the release of RF-glycoproteins (SCO-spondin included) by SCO explants, suggesting that dopamine affects the function(s) of the SCO differently from the secretion of RF-glycoproteins.Financial support was provided by grants PI 030756 and Red CIEN, Instituto de Salud Carlos III, Spain (to J.M.P.F.), and 1030265 from Fondecyt, Chile (to E.M.R.) 相似文献
A density functional theory (DFT) study of cct-As, ccc, and cct-CO isomers of the ruthenium dihydride complex RuH2(CO)2(AsMe2Ph)2 is reported (see Scheme for the labeling isomer 34 structures of RuH2(CO)2(AsMe2Ph)2). Complex geometries and relative energies of different isomers have been calculated with both B3LYP and M06-2X functionals. The results show that the B3LYP calculated Boltzmann populations of cct-As, ccc, and cct-CO isomers are 65.5, 34.2, and 0.3%, respectively. These are in better agreement with the experimental data than those calculated at the M06-2X level. However, the calculations of 1H NMR chemical shifts were found to be better described with M06-2X than with B3LYP or with HF level of theories. In addition, a transition state between the two most stable isomers was determined through DFT/(B3LYP or M06-2X) calculations.
In this paper, we report a study on the structure and first hyperpolarizability of C60Cl2 and C60F2. The calculation results show that the first hyperpolarizabilities of C60Cl2 and C60F2 were 172 au and 249 au, respectively. Compared with the fullerenes, the first hyperpolarizability of C60Cl2 increased from 0 au to 172 au, while the first hyperpolarizability of C60F2 increased from 0 au to 249 au. In order to further increase the first hyperpolarizability of C60Cl2 and C60F2, Li@C60Cl2 and Li@C60F2 were obtained by introducing a lithium atom to C60Cl2 and C60F2. The first hyperpolarizabilities of Li@C60Cl2 and Li@C60F2 were 2589 au and 985 au, representing a 15-fold and 3.9-fold increase, respectively, over those of C60Cl2 and C60F2. The transition energies of four molecules (C60Cl2, Li@C60Cl2, C60F2, Li@C60F2) were calculated, and were found to be 0.17866 au, 0.05229 au, 0.18385 au, and 0.05212 au, respectively. A two-level model explains why the first hyperpolarizability increases for Li@C60Cl2 and Li@C60F2. 相似文献
Natural bond orbital (NBO) analyses and dissected nucleus-independent chemical shifts (NICSπzz) were computed to evaluate the bonding (bond type, electron occupation, hybridization) and aromatic character of the three lowest-lying Si2CH2 (1-Si, 2-Si, 3-Si) and Ge2CH2 (1-Ge, 2-Ge, 3-Ge) isomers. While their carbon C3H2 analogs favor classical alkene, allene, and alkyne type bonding, these Si and Ge derivatives are more polarizable and can favor “highly electron delocalized”? and “non-classical”? structures. The lowest energy Si 2CH2 and Ge 2CH2 isomers, 1-Si and 1-Ge, exhibit two sets of 3–center 2–electron (3c-2e) bonding; a π-3c-2e bond involving the heavy atoms (C–Si–Si and C–Ge–Ge), and a σ-3c-2e bond (Si–H–Si, Ge–H–Ge). Both 3-Si and 3-Ge exhibit π and σ-3c-2e bonding involving a planar tetracoordinated carbon (ptC) center. Despite their highly electron delocalized nature, all of the Si2CH2 and Ge2CH2 isomers considered display only modest two π electron aromatic character (NICS(0)πzz=--6.2 to –8.9 ppm, computed at the heavy atom ring center) compared to the cyclic-C 3H2 (–13.3 ppm).
A theoretical study of a sandwich compound with a metal monolayer sheet between two aromatic ligands is presented. A full
geometry optimization of the [Au3Cl3Tr2]2+ (1) compound, which is a triangular gold(I) monolayer sheet capped by chlorines and bounded to two cycloheptatrienyl (Tr)
ligands was carried out using perturbation theory at the MP2 computational level and DFT. Compound (1) is in agreement with
the 18–electron rule, the bonding nature in the complex may be interpreted from the donation interaction coming from the Tr
rings to the Au array, and from the back-donation from the latter to the former. NICS calculations show a strong aromatic
character in the gold monolayer sheet and Tr ligands; calculations done with HOMA, also report the same aromatic behavior
on the cycloheptatrienyl fragments giving us an insight on the stability of (1). The Au –Au bond lengths indicate that an
intramolecular aurophilic interaction among the Au(I) cations plays an important role in the bonding of the central metal
sheet.
Figure (a) Ground state geometry of complex 1; (b) Top view of compound 1 and Wiberg bond orders computed with the MP2/B1 computational method; (c) Lateral view of compound 1 and NICS values calculated with the MP2/B1 method; the values in parenthesis were obtained at the VWN/TZP level 相似文献
Density functional theory (DFT) calculations were used to study the effect of scandium doping on the structural, energetic, electronic, linear and nonlinear optical (NLO) properties of Be12O12, Mg12O12 and Ca12O12 nanoclusters. Scandium (Sc) doping on nanoclusters leads to narrowing of their Eg, which enhances their conductance greatly. Also, the polarizability (α) and first hyperpolarizability (β0) of nanoclusters were dramatically increased as Be, Mg or Ca atoms are substituted with a Sc atom. Among all clusters, α and β0 values for Sc-doped Ca12O12 were the largest. Consequently, the effect of the doping atom, as well as of cluster size, on electronic and optical properties was explored. Time dependent (TD)-DFT calculations were also carried out to confirm the β0 values; the results show that the higher value of first hyperpolarizability belongs to Sc-doped Ca12O12, which has the smallest transition energy (ΔEgn). The results obtained show that these clusters can be candidates for using in electronic devices and NLO materials in industry. 相似文献
Functional and reversible plasmonic resonances across the visible and near-infrared spectrum have opened new avenues for developing advanced next-generation nanophotonic devices. In this study, by using optothermally controlled phase-change material (PCM) for plasmonic nanostructures, we successfully induced highly tunable charge transfer plasmon (CTP) resonance modes. To this end, we have chosen a two-member dimer assembly consisting of gold cores and Ge2Sb2Te5 (GST) shells in distant, touching, and overlapping regimes. We show that switching between amorphous (dielectric) and crystalline (conductive) phases of GST allows for achieving tunable dipolar and CTP resonances and enables an effective interplay between these modes along the near-infrared spectrum. By analyzing electromagnetically calculated spectral responses for the dimer antenna in tunneling and direct charge transfer regimes, we confirmed that the induced CTPs in touching and overlapping regimes are highly controllable and pronounced in comparison to the quantum tunneling regime. We also use the precise, fast, and controllable switching between dipolar and CTP resonant modes to develop a telecommunication switch based on a simple metallodielectric dimer. The proposed structures can help designing optothermally controlled devices without morphological variations in the geometry of the design, and having strong potential for advanced plasmon modulation and fast data routing. 相似文献
A comparison of three labeling strategies for studies involving side chain methyl groups in high molecular weight proteins,
using 13CH3,13CH2D, and 13CHD2 methyl isotopomers, is presented. For each labeling scheme, 1H–13C pulse sequences that give optimal resolution and sensitivity are identified. Three highly deuterated samples of a 723 residue
enzyme, malate synthase G, with 13CH3,13CH2D, and 13CHD2 labeling in Ile δ1 positions, are used to test the pulse sequences experimentally, and a rationalization of each sequence’s
performance based on a product operator formalism that focuses on individual transitions is presented. The HMQC pulse sequence
has previously been identified as a transverse relaxation optimized experiment for 13CH3-labeled methyl groups attached to macromolecules, and a zero-quantum correlation pulse scheme (13CH3 HZQC) has been developed to further improve resolution in the indirectly detected dimension. We present a modified version
of the 13CH3 HZQC sequence that provides improved sensitivity by using the steady-state magnetization of both 13C and 1H spins. The HSQC and HMQC spectra of 13CH2D-labeled methyl groups in malate synthase G are very poorly resolved, but we present a new pulse sequence, 13CH2D TROSY, that exploits cross-correlation effects to record 1H–13C correlation maps with dramatically reduced linewidths in both dimensions. Well-resolved spectra of 13CHD2-labeled methyl groups can be recorded with HSQC or HMQC; a new 13CHD2 HZQC sequence is described that provides improved resolution with no loss in sensitivity in the applications considered here.
When spectra recorded on samples prepared with the three isotopomers are compared, it is clear that the 13CH3 labeling strategy is the most beneficial from the perspective of sensitivity (gains ≥2.4 relative to either 13CH2D or 13CHD2 labeling), although excellent resolution can be obtained with any of the isotopomers using the pulse sequences presented
here. 相似文献
In the present study, a method for easy and rapid synthesis of lipase nanohybrids was evaluated using cobalt chloride as an encapsulating agent. The synthesized nanohybrids exhibited higher activity (181%) compared to free lipase and improved catalytic properties at higher temperature and in harsh conditions. The nanohybrids retained 84% of their residual activity at 25 °C after 10 days. In addition, these nanohybrids also exhibited high storage stability and reusability. Collectively, the synthesis of carrier-free immobilized biocatalysts was performed rapidly within 24 h at 4 °C. Their high reusability and catalytic activities highlight the broad applicability of this method for catalysis in organic and aqueous media. 相似文献
Metal oxide semiconductors (MOS) are important and promising materials in optoelectronics, and it has been widely used in various catalytic applications such as gas sensing due to its high reactivity with many gases. In current work, mixtures of SnO2-WO3 (1:1) were prepared to synthesize nanostructured thin films by pulsed laser deposition as gas sensors. The sensitivity of sensors was measured for a relatively low concentration (200 ppm) of NO2 gas at room temperature; sensors prepared with target exposed to (200) laser shots have higher sensitivity with a maximum value of 96.49 % at time 65 s as compared with the sensors prepared with (150) laser shots where the sensitivity has a maximum value 71.82 % at time 110 s; XRD pattern shows a better crystalline and high intensity with increasing laser shots up to 200; scanning electron microscopy (SEM) micrographs show approximate homogeneity of grains that cover the substrate without cracks and pinholes with nanoparticles fall in micro and nanometer range 50–200 nm. The values of the direct band gap were found to be 2.07143 eV for films prepared with 150 laser shots and 2.02899 eV for films prepared with 200 laser shots which have higher absorbance than the former films due to the increment in thickness and particle size. Empirical equations between sensitivity and gas exposure time have been formulated with great coincidence with the experimental data. 相似文献
The C2 fragmentation energies of the most stable isolated-pentagon-rule (IPR) isomers of the C80 and C82 fullerenes were evaluated with second-order Møller-Plesset (MP2) theory, density-functional theory (DFT) and the semiempirical self-consistent charge density-functional tight-binding (SCC-DFTB) method. Zero-point energy, ionization energy and empirical C2 corrections were included in the calculation of fragmentation energies for comparison with experimental C2 fragmentation energies of the fullerene cations. In the case of the most probable Stone-Wales pathway of C2 fragmentation of C80, the calculated \(D_{0} {\left( {{\text{C}}_{{{\text{80}}}} ^{ + } } \right)}\) agree well with experimental data, whereas in the case of C82 fragmentation, the calculated \(D_{0} {\left( {{\text{C}}_{{{\text{82}}}} ^{ + } } \right)}\) exceed by up to 1.2 eV the experimental ones, which suggests that other IPR isomers may be present in sufficient amounts in experimental samples. Computer-intensive MP2 calculations and DFT calculations with larger basis sets do not yield much improved C2 fragmentation energies, compared to those reported earlier with B3LYP/3-21G. On the other hand, semiempirical approaches such as SCC-DFTB, which are orders of magnitude less intensive, yield satisfactory fragmentation energies for higher fullerenes and may become a method of choice for routine calculations of fullerenes and carbon nanotubes.
Figure C2 fragmentation energies of C80 and C82 fullerenes have been calculated with B3LYP/6-31G* model chemistry, with semiempirical self-consistent-charge density-functional tight-binding (SCC-DFTB) method and with the more rigorous MP2 method. The influence of basis set extension and level of theory on the resulting fragmentation energies is discussed
In this work, the structural, compositional, optical, and dielectric properties of Ga2S3 thin films are investigated by means of X-ray diffraction, scanning electron microscopy, energy dispersion X-ray analysis, and ultraviolet—visible light spectrophotometry. The Ga2S3 thin films which exhibited amorphous nature in its as grown form are observed to be generally composed of 40.7 % Ga and 59.3 % S atomic content. The direct allowed transitions optical energy bandgap is found to be 2.96 eV. On the other hand, the modeling of the dielectric spectra in the frequency range of 270–1,000 THz, using the modified Drude-Lorentz model for electron-plasmon interactions revealed the electrons scattering time as 1.8 (fs), the electron bounded plasma frequency as ~0.76–0.94 (GHz) and the reduced resonant frequency as 2.20–4.60 ×1015 (Hz) in the range of 270–753 THz. The corresponding drift mobility of electrons to the terahertz oscillating incident electric field is found to be 7.91 (cm2/Vs). The values are promising as they nominate the Ga2S3 thin films as effective candidates in thin-film transistor and gas sensing technologies. 相似文献
The interaction of cis-[PtCl2(Me2SO)2] with human serum albumin (HSA) and the sensitivity of the complex to heat denaturation as dependent on the duration of incubation
have been studied by UV absorption and fluorescence spectroscopy. Optimal conditions for cis-[PtCl2(Me2SO)2] binding to HSA have been determined. The results are compared with the data for the HSA-cisplatin complex. It has been found
that binding of HSA with cis-[PtCl2(Me2SO)2] does not result in significant structural changes of the protein. 相似文献
An experimental study has been carried out on the stability of adenine (one of the five nucleic acid bases) under hydrothermal conditions. The experiments were performed in sealed autoclaves at 300 degrees C under fugacities of CO(2), N(2) and H(2) supposedly representative of those in marine hydrothermal systems on the early Earth. The composition of the gas phase was obtained from the degradation of oxalic acid, sodium nitrite and ammonium chloride, and the oxidation of metallic iron. The results of the experiments indicate that after 200 h, adenine is still present in detectable concentration in the aqueous phase. In fact, the concentration of adenine does not seem to be decreasing after approximately 24 h, which suggests that an equilibrium state may have been established with the inorganic constituents of the hydrothermal fluid. Such a conclusion is corroborated by independent thermodynamic calculations. 相似文献
New methods are described for accurate measurement of multiple residual dipolar couplings in nucleic acid bases. The methods use TROSY-type pulse sequences for optimizing resolution and sensitivity, and rely on the E.COSY principle to measure the relatively small two-bond 2DCH couplings at high precision. Measurements are demonstrated for a 24-nt stem-loop RNA sequence, uniformly enriched in 13C, and aligned in Pf1. The recently described pseudo-3D method is used to provide homonuclear 1H-1H decoupling, which minimizes cross-correlation effects and optimizes resolution. Up to seven 1H-13C and 13C-13C couplings are measured for pyrimidines (U and C), including 1DC5H5, 1DC6H6, 2DC5H6, 2DC6H5, 1DC5C4, 1DC5C6, and 2DC4H5. For adenine, four base couplings (1DC2H2, 1DC8H8, 1DC4C5, and 1DC5C6) are readily measured whereas for guanine only three couplings are accessible at high relative accuracy (1DC8H8, 1DC4C5, and 1DC5C6). Only three dipolar couplings are linearly independent in planar structures such as nucleic acid bases, permitting cross validation of the data and evaluation of their accuracies. For the vast majority of dipolar couplings, the error is found to be less than ±3% of their possible range, indicating that the measurement accuracy is not limiting when using these couplings as restraints in structure calculations. Reported isotropic values of the one- and two-bond J couplings cluster very tightly for each type of nucleotide. 相似文献
In Escherichia coli, the F1FO ATP synthase b subunits house a conserved arginine in the tether domain at position 36 where the subunit emerges from the membrane. Previous
experiments showed that substitution of isoleucine or glutamate result in a loss of enzyme activity. Double mutants have been
constructed in an attempt to achieve an intragenic suppressor of the barg36→ile and the barg36→glu mutations. The barg36→ile mutation could not be suppressed. In contrast, the phenotypic defect resulting from the barg36→glu mutation was largely suppressed in the barg36→glu,glu39→arg double mutant. E. coli expressing the barg36→glu,glu39→arg subunit grew well on succinate-based medium. F1FO ATP synthase complexes were more efficiently assembled and ATP driven proton pumping activity was improved. The evidence
suggests that efficient coupling in F1FO ATP synthase is dependent upon a basic amino acid located at the base of the peripheral stalk. 相似文献