Electrochemical, spectroscopic, and DFT study of C60(CF3)n frontier orbitals (n = 2-18): the link between double bonds in pentagons and reduction potentials

The frontier orbitals of 22 isolated and characterized C(60)(CF(3))(n) derivatives, including seven reported here for the first time, have been investigated by electronic spectroscopy (n = 2 [1], 4 [1], 6 [2], 8 [5], 10 [6], 12 [3]; the number of isomers for each composition is shown in square brackets) fluorescence spectroscopy (n = 10 [4]), cyclic voltammetry under air-free conditions (all compounds with n 相似文献   

Synthesis, spectroscopic and electrochemical characterization, and DFT study of seventeen C70(CF3)n derivatives (n=2, 4, 6, 8, 10, 12)

Eight new C70(CF3)n derivatives (n=2, 6, 10, 12) have been synthesized and characterized by UV/Vis and 19F NMR spectroscopy, cyclic voltammetry, and quantum chemical calculations at the DFT level of theory. Nine previously known derivatives of C70(CF3)n with n=2-12 were also studied by cyclic voltammetry (and seven of them by UV/Vis spectroscopy for the first time). Most of the 17 compounds exhibited two or three reversible reductions at scan rates from 20 mV s(-1) up to 5.0 V s(-1). In general, reduction potentials for the 0/- couple are shifted anodically relative to the C70 0/-) couple. However, the 0/- E1/2 values for a given composition are strongly dependent on the addition pattern of the CF3 groups. The data show that the addition pattern is as important, if not more important in some cases, than the number of substituents, n, in determining E1/2 values. An analysis of the DFT-predicted LUMOs indicates that addition patterns that have non-terminal double bonds in pentagons result in derivatives that are strong electron acceptors.     

Redox state of the photosynthetic electron transport chain in wild-type and mutant leaves of Arabidopsis thaliana: Impact on photosystem II fluorescence

In addition to the photosynthetic linear electron transport, several alternative electron transport routes exist in thylakoids of higher plants. The plastoquinone (PQ) pool acts as a common electron carrier in these pathways. In the cyclic electron flow around photosystem I (PSI), reduced ferredoxin is used by the ferredoxin-quinone reductase (FQR) to reduce the PQ pool. Chlororespiratory pathway consists in the reduction of the PQ pool by the NAD(P)H dehydrogenase (NDH). These alternative pathways and their role in photosynthesis are still not fully understood. In the present study, the accumulation kinetics of quinone acceptors was measured by fluorescence induction in leaves of Arabidopsis thaliana wild-type and mutants altered in alternative electron pathways after various light- and dark-adaptation conditions. Results show that NDH activity can be probed by fluorescence induction during light-to-dark transition of plants. Also, the activity of FQR pathway did not affect directly the FI kinetics. However, the accumulation kinetics of reduced PQ under actinic light was dependant on the redox state of PSI acceptors prior to illumination.     

8-或6-(3-氯苯甲酰)香豆素衍生物的合成、表征、生物活性及与牛血清白蛋白的相互作用

合成了2个新化合物7-羟基-8-(3-氯苯甲酰基)-4-甲基香豆素(1)和7-羟基-6-(3-氯苯甲酰基)-4-甲基香豆素(2). X射线单晶衍射分析表明, 2个化合物的晶体同属于单斜晶系, P2₁/c空间群, 化合物1: a=1.21527(14) nm, b=1.01550(12) nm, c=1.5045(2) nm, β=112.377(2)°, V=1.7169(4) nm³, D_c=1.396 g/cm³, Z=4, F(000)=752, R₁=0.0415, wR₂=0.0981[I>2σ(I)], S=1.063; 化合物2: a=2.0168(2) nm, b=0.76229(12) nm, c=2.25497(17) nm, β=123.987(6)° , V=0.8745(6) nm³, D_c=1.454 g/cm³, Z=8, F(000)=1296, R₁=0.0604, wR₂=0.1384[I>2σ(I)], S=0.948. 抗菌实验结果表明, 2个化合物对大肠杆菌(E. coli)、 枯草杆菌(B. subtilis)和金色葡萄球菌(S. aureus) 均有中等程度的抑制作用; 体外抗氧化实验结果表明, 2个化合物对超氧阴离子自由基(O₂^-·)、 羟基自由基(·OH)和二苯代苦味肼基自由基(DPPH·)均有良好的清除能力. 采用荧光光谱法研究了不同温度下2个化合物与牛血清白蛋白(BSA)的相互作用, 结果表明, 2个化合物对BSA 的荧光猝灭均属于静态猝灭; 热力学数据表明, 化合物1(ΔH>0, ΔS>0, ΔG<0)与BSA主要以疏水作用力相结合, 化合物2(ΔH<0, ΔS<0, ΔG<0)与BSA主要以氢键或范德华力相结合; BSA与化合物1和化合物2间的距离分别为2.59和2.38 nm, 说明2个化合物与BSA 之间可能发生了非辐射能量转移.     

Halide ion complexes of decaborane (B10H14) and their derivatives: noncovalent charge transfer effect on second-order nonlinear optical properties

Quantum molecular engineering has been performed to determine the second-order nonlinear optical (NLO) properties in different halo complexes of decaborane (B(10)H(14)) and their derivatives using the density functional theory (DFT) method. These decaborane halo complexes of X(-)@B(10)H(14) (X = F, Cl, Br, and I) are found to possess noncovalent charge transfer interactions. The static polarizability (α(0)) and first hyperpolarizability (β(0)) among these complexes increase by moving down the group from F to I, partly due to the increase in size of their anionic radii and the decrease in their electron affinities. A two-level approximation has been employed to investigate the origin of β(0) values in these halo complexes, which show very consistent results with those by the finite-field method. Furthermore, in the same line, two experimentally existing complexes, I(-)@B(10)H(14) and I(-)@2,4-I(2)B(10)H(12), are found to have considerably large β(0) values of 2859 and 3092 a.u., respectively, which are about three times larger than a prototypical second-order NLO molecule of p-nitroaniline, as reported by Soscun et al. [Int. J. Quantum Chem.2006, 106, 1130-1137]. Besides this, the special effects of solvent, counterion, and bottom substitutions have also been investigated. Interestingly, 2,4-alkali metal-substituted decaborane iodide complexes show remarkably large second-order NLO response with β(0) amplitude as large as 62436 a.u. for I(-)@2,4-K(2)B(10)H(12) complex, which are explained in terms of their transition energies, frontier molecular orbitals and electron density difference plots. Thus, the present investigation provides several new comparative insights into the second-order NLO properties of halo complexes of decaborane, which possess not only large first hyperpolarizabilities, but also high tunability to get a robustly large second-order NLO response by alkali metal substitution effects.     

Synthesis and characterization of (Z)-5-arylmethylidene-rhodanines with photosynthesis-inhibiting properties

A series of rhodanine derivatives was prepared. The synthetic approach, analytical and spectroscopic data of all synthesized compounds are presented. Lipophilicity of all the discussed rhodanine derivatives was analyzed using the RP-HPLC method. The compounds were tested for their ability to inhibit photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts and reduce chlorophyll content in freshwater alga Chlorella vulgaris. Structure-activity relationships between the chemical structure, physical properties and biological activities of the evaluated compounds are discussed. For majority of the tested compounds the lipophilicity of the compound and not electronic properties of the R1 substituent were decisive for PET-inhibiting activity. The most potent PET inhibitor was (5Z)-5-(4-bromobenzylidene)-2-thioxo-1,3-thiazolidin-4-one (IC(50) = 3.0 μmol/L) and the highest antialgal activity was exhibited by (5Z)-5-(4-chlorobenzylidene)-2-thioxo-1,3-thiazolidin-4-one (IC(50) = 1.3 μmol/L).     

ON THE NATURE OF THE INTERMEDIATE ELECTRON ACCEPTOR (A1) IN THE PHOTOSYSTEM I REACTION CENTER

Abstract— A sodium dodecyl sulfate-Photosystem I (PSI) complex has been prepared and characterized with respect to its electron acceptors. Component X and iron-sulfur centers A and B are absent from this preparation but the intermediate electron acceptor (A₁) is present. Flash-induced absorbance changes at 25°C show charge separation, followed by a back-reaction with a half-time of 5 µs. The spectrum of the flash-induced change from 350 to 550 nm indicates a contribution from the intermediate electron acceptor, A₁, as well as from P700⁺. EPR studies show that A₁ is associated with a free-radical signal having a g-value of 2.0025 and a linewidth of 12 gauss. A, would appear to be associated with a monomeric form of either Chi α or pheophytin a.     

The vibrational spectrum of the secondary electron acceptor, A1, in photosystem I

Photosystem I (PSI) is a multisubunit protein complex which carries out light-induced, transmembrane charge separation in oxygenic photosynthesis. In PSI, the electron-transfer pathway consists of chlorophyll and phylloquinone molecules, as well as iron-sulfur clusters. There are two phylloquinone molecules, which are located in structurally symmetric positions in the reaction center. It has been proposed that both phylloquinone molecules are active as the A1 secondary electron acceptor in bidirectional electron-transfer reactions. The PSI A1 acceptors are of interest because they have the lowest reduction potential of any quinone found in nature. In this work using light-induced FT-IR spectroscopy, isotope-edited spectra are presented, which attribute vibrational bands to the carbonyl stretching vibrations of A1 and A1- and the quinoid ring stretching vibration of A1. Bands are assigned by comparison with hybrid Hartee-Fock density functional calculations, which predict vibrational frequencies, amplitudes, and isotope shifts for the phylloquinone singlet and radical anion states. The results are consistent with an environmental interaction increasing the frequency of the singlet CO vibration and decreasing the frequency of the anion radical CO vibration, relative to model compounds. This environmental interaction may be the asymmetric hydrogen bond to A1/A1-, electrostatic interactions with charged amino acid side chains, or a pi-pi interaction with the indole ring of a nearby tryptophan. Such differential effects on the structure of A1 and A1- may be associated with a destabilization of the anion radical. These studies give novel information concerning the effect of the protein matrix on the PSI electron-transfer cofactor.     

In Vitro Inhibition Effect of Some Dihydroxy Coumarin Compounds on Purified Human Serum Paraoxonase 1 (PON1)

Human serum paraoxonase 1 (PON1; EC 3.1.8.1) is a high-density lipoprotein associated, calcium-dependent enzyme that hydrolyses aromatic esters, organophosphates and lactones and can protect the low-density lipoprotein against oxidation. In this study, in vitro inhibition effect of some dihydroxy coumarin compounds namely 6,7-dihydroxy-3-(2-methylphenyl)-2H-chromen-2-one (A), 6,7-dihydroxy-3-(3-methylphenyl)-2H-chromen-2-one (B) and 6,7-dihydroxy-3-(4-methylphenyl)-2H-chromen-2-one (C) on purified PON1 were investigated by using paraoxon as a substrate. PON1 was purified using two-step procedures, namely ammonium sulphate precipitation and Sepharose-4B-l-tyrosine-1-naphthylamine hydrophobic interaction chromatography. The purified enzyme had a specific activity of 11.76?U/mg. The dihydroxy coumarin derivatives of A and B compounds inhibited PON1 enzyme activity in a noncompetitive inhibition manner with K _i of 0.0080?±?0.256 and 0.0003?±?0.018?mM values, respectively. C compound exerted an uncompetitive inhibition of PON1 enzyme activity with K _i of 0.0010?±?0.173?mM. Moreover, dihydroxy coumarin derivatives of A, B and C compounds were effective inhibitors on purified human serum PON1 activity with IC₅₀ of 0.012, 0.022 and 0.003?mM values, respectively. IC₅₀ value of unsubstituted 6,7 dihydroxy coumarin was found as 0.178?mM. The present study has demonstrated that PON1 activity is very highly sensitive to studied coumarin derivatives.     

Structures and electronic properties of Al7x0,- and Al13 X1,2,12- clusters with X=F, Cl, and Br

The structures, binding energies, and electronic properties for Al7X, Al7X-, Al13X-, Al13X2-, and Al13X12- (X = F, Cl, Br) were studied at the B3LYP/6-311+G(2d,p) level. Among the systems studied, Al7 and Al13 clusters in Al7X and Al13X- reveal alkali-like and halogen-like superatom characters, respectively. Al7 can bind with one halogen atom to form a salt-like compound as Al7+delta-X-delta. Al13- can combine with one halogen atom to form a diatomic halogen anion Al13X-. However, when adding more halogens, the superatom structure would be destroyed, resulting in low-symmetry compounds with the center Al atom moving toward the cluster surface. The structures of Al13X1,2,12- (X = F, Cl, Br) are similar to those of X = I; however, their binding energies and electron structures are much different. In addition, the analyses of the calculated NBO charges show that Cl and Br have similar properties, but much different from F, when interacting with the Al clusters. The Al-Cl and Al-Br bonds have more covalent character in Al7X and Al13X2,12-, in contrast to the corresponding Al-F bond, which has prominent ionic character.     

Novel non-peptide GPIIb/IIIa antagonists: synthesis and biological activities of 2-[4-[2-(4-amidinobenzoylamino)-2-(substituted)acetyl]-3-(2-methoxy-2-oxoethyl)-2-oxopiperazinyl] acetic acids

To improve the in vitro and in vivo potency of our first low molecular weight GPIIb/IIIa antagonist 1 (TAK-029), a series of 2-[4-[2-(4-amidinobenzoylamino)-2-(substituted)acetyl]-3-(2-methoxy-2-oxoethyl)-2-oxopiper-azinyllacetic acids were synthesized through modification of the glycine moiety of 1 and evaluated for their ability to inhibit in vitro adenosine 5'-diphosphate (ADP)-induced platelet aggregation of guinea pig platelet rich plasma (PRP). Among the compounds examined, the (3S,2S)-4-methoxyphenylalanine derivative 4h showed the most potent antagonistic activity with an IC50 value of 13 nM. Dose-dependent inhibition of ex vivo platelet aggregation was achieved with oral administration of 4h (0.3-1.0 mg/kg) to guinea pigs. Complete inhibition was observed for up to 8 h, and 43% inhibition could still be observed 24 h after oral administration of 1.0 mg/kg. The long-lasting antiplatelet effect of 4h suggests that 4h would be suitable for once-a-day dosing. Structure-activity relationships (SAR) were examined in the series of the phenylalanine derivatives. An increase in the electron density around the 4-position of the phenyl ring of the phenylalanine moiety led to an increase in the antiplatelet activity, suggesting the existence of a hydrophobic and electrostatic interaction site in addition to the ionic binding sites in the GPIIb/IIIa.     

Electrochemical study of a reconstituted photosynthetic electron-transfer chain

A multi-enzyme electron-transfer chain involving solubilized photosystem I (PSI) as photocatalytic unit, cytochrome c6 and ferredoxin as electron carriers and ferredoxin/NADPH oxidoreductase (FNR) as electron acceptor was reconstituted in an electrochemical cell and studied by cyclic voltammetry. The working gold electrodes were modified to react selectively with cytochrome c6. Quantitative analysis of the photocatalytic current under continuous illumination allowed the determination of the values kon and koff for the ferredoxin/PSI interaction. An efficient recycling system for NADPH was established, and the dissociation constant of the oxidized ferredoxin/semiquinone FNR complex was extracted by modeling the catalytic efficiency of the chain as a function of ferredoxin concentration. The value determined hereby is consistent with a shift of -50 to -100 mV of the reduction potential of ferredoxin when complexed with FNR.     

Mesomorphic properties of achiral halogen-substituted banana-shaped compounds

Three banana-shaped achiral compounds, derivatives of 4,6-dichloro-1,3-phenylene bis-[4-(4- n -octyloxyphenyliminomethyl) benzoate], were synthesized by varying the substituent ( X =H, F and Cl). Their mesomorphic properties were investigated by differential scanning calorimetry, polarizing optical microscopy, and X-ray analysis. The compound with X = H exhibited an enantiomeric nematic phase. The compounds with X = F and Cl formed a nematic phase on heating, while on cooling they formed a nematic phase at high temperature and a smectic A phase at a lower temperature (monotropic). A schematic representation of the mesophase structures for the compound with X = F is also illustrated.     

Photophysical and electronic properties of five PCBM-like C60 derivatives: spectral and quantum chemical view

By means of transient UV-visible absorption spectra/fluorescence spectra, combined with electronic structure calculations, the present work focuses on characterizing the photophysical and electronic properties of five PCBM-like C(60) derivatives (F1, F2, F3, F4, and F5) and understanding how these properties are expected to affect the photovoltaic performance of polymer solar cells (PSCs) with those molecules as acceptors. Spectral data reveal that the fluorescence quantum yields (Φ(F)) are enhanced and the triplet quantum yields (Φ(T)) are lowered for the five PCBM-like C(60) derivatives as compared to those of the pristine C(60), suggesting that functionalization of a C═C double bond perturbs the fullerene's π-system and breaks the I(h) symmetry of pristine C(60), which results in modifications of photophysical properties of the fullerene derivatives. PBEPBE/6-311G(d,p)//PBEPBE/6-31G(d) level of electronic structure calculations yields the HOMO-LUMO gaps and LUMO energies, showing that the electron-withdrawing effect induced by the side chain functional groups perturbs LUMO energies, from which different open circuit voltages V(oc) are resulted. The predicted V(oc) from our calculation agrees with previous experiment results. Basically, we found that functionalization of a C═C double bond sustains the fullerene structure and its electron affinitive properties. Adducted side chains contribute to adjust the HOMO-LUMO gap and LUMO levels of the acceptors to improve open circuit voltage. The results could provide fundamental insights for understanding how structural modifications influence the photovoltaic performance, which paves a way for guiding the synthesis of new fullerene derivatives with improved performance in polymer solar cells.     

Synthesis and in vitro cytotoxic activities of sorafenib derivatives

A series of novel sorafenib derivatives have been designed and synthesized.The cytotoxic activities of these compounds were tested in three tumor cell lines.Most of the compounds showed potent antiproliferative activity against the tested cell lines with IC50= 0–20 mmol/L.Some compounds demonstrated competitive antiproliferative activities to sorafenib against all three cancer cell lines.Among them,compound 5g demonstrated significant inhibitory activity against A549,ACHN and MDAMB-231 cell lines with IC50values of 1.29,1.99,3.11 mmol/L,respectively.     

Theoretical, thermodynamic, spectroscopic, and structural studies of the consequences of one-electron oxidation on the Fe-X bonds in 17- and 18-electron Cp*Fe(dppe)X complexes (X = F, Cl, Br, I, H, CH3)

The compounds Cp*Fe(dppe)X ([Fe]X) and the corresponding cation radicals [Fe*]X*+ are available for the series X = F, Cl, Br, I, H, CH3. This has allowed for a detailed investigation of the dependence of the nature of Fe-X bonding on the identity of X and the oxidation state (charge) of the complex. Cyclic voltammetry demonstrates that the electrode potentials for the [Fe]X0/+ couples decrease in the order I > Br > Cl > H > F > CH3. An "inverse halide order" is seen, in which the most electronegative X leads to the most easily oxidized complex. This suggests that F is the best donor among the halides. The halide trend is also reflected in NMR spectroscopic data. M?ssbauer spectroscopy data also suggest that the F ligand is a strong donor (relative to H and CH3) in [Fe*]X*+. DFT calculations on CpFe(dpe)X ([Fe]X) model complexes nicely reproduce the trend in the electrode potentials for the [Fe*]X0/+ couples. Analysis of the theoretical data within the halogen series indicates that the energy of the [Fe]X HOMO does not correlate with the extent of its Fe(d(pi))-X(p(pi)) antibonding character, which varies in the order I > Br > Cl > F, but rather depends on the destabilizing electrostatic effect caused by X. This effect varies in the order F > Cl > Br > I. A thermochemical cycle that incorporates the [Fe*]X0/+ and [Fe*]0/+ electrode potentials was used to investigate the effect of the oxidation state of the complex on the homolytic bond dissociation energy (BDEhom), defined for the processes Fe-X --> Fe* + X* and Fe-X*+ --> Fe*+ + X*. For all X, it was found that a one-electron oxidation leads to a weakening of the Fe-X bond. This trend was reproduced by the DFT calculations. On the other hand, IR nu(Fe-X) spectroscopy data showed an increase in the stretching frequencies for X = H and Cl upon oxidation. X-ray crystallographic data showed a shortening of the Fe-Cl bond upon oxidation. The trends in IR and Fe-Cl bond distances were reproduced in the DFT calculations. The combined data therefore suggest that oxidation leads to weaker, but shorter, Fe-X bonds. A second thermochemical cycle was applied to investigate the effect of the one-electron oxidation on the heterolytic bond dissociation energies (BDEhet), defined for the processes Fe-X --> Fe+ + X- and Fe-X*+ --> Fe2+ + X-. In this case, the oxidation led to bond strengthening in all cases. The computed BDE values have been analyzed within Ziegler's transition state methodology and decomposed into two components, one electrostatic and one covalent, describing the interaction between the unrelaxed fragments. In all the computed BDEhom and BDEhet values of the [Fe]X models the electrostatic component is important. This helps to understand their respective variations upon oxidation.     

Impact of electron acceptor on three-photon absorption cross-section of the fluorene derivatives

Small three-photon absorption (3PA) cross-section values of present nonlinear organic molecules limit their practical applications. Although electron donors and electron acceptors have a great effect on 3PA cross-section, little is known about how the strength and situation of electron acceptors influence the 3PA cross-section value of a compound. The present work reports 3PA effects of two fluorene derivatives with symmetric D-π-π(A)-π-D archetype, which are named as 2,7-bis(4-methoxyphenylacetylene)-9-fluorenone (FATT) and 2,7-bis(4-methoxyphenylacetylene)-9-thoine-fluorene (TSATL). Large 3PA cross-section and ideal 3PA-induced optical limiting effects have been found in the two fluorene derivatives. The two molecules both have a different electron acceptor on the fluorene core, by which the 3PA cross-section value for FATT is enhanced by nearly 3-fold compared with that for TSATL. The mechanism of this significant enhancement in 3PA cross-section has been investigated by density functional theory (DFT) and configuration interaction singles (CIS) method with use of 6-311+G basis set in combination with conductor polarizable continuum model (CPCM). The theoretical results show that increase of electronegative character of the electron acceptor on the core is responsible for the increase of 3PA cross-section values of the two molecules.     

Search for more stable C58X18 isomers: stabilities and electronic properties of seven-membered ring C58X18 fullerene derivatives (X = H, F, and Cl)

Stimulated by recent preparation and characterization of the first C58F18 fullerene derivative, with a heptagon in the framework (Science, 2005, 309, 278), we have performed systematic density functional studies on the stabilities and electronic properties of two different structures C58X18 (A) and C58X18 (B), where X = H, F, and Cl. The large energy gaps between the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals (between 2.64 and 3.45 eV) and the aromatic character (with nucleus independent chemical shifts from -10.0 to -13.9 ppm) of C58X18 (A) and C58X18 (B) indicate that they possess high stabilities. Further investigations show that the heats of formation of C58X18 fullerene derivatives are highly exothermic, suggesting that adding nine X2's releases much of the strain of pure C58 fullerene and leads to stabilities of the derivatives. Lower in energy and stronger in aromatic character than C58F18 (B), which has been experimentally characterized, C58F18 (A) should also be isolated. In addition, C58F18 and C58Cl18 are predicted to possess large electron affinities, especially for C58F18 (B) and C58Cl18 (B) with values of 3.00 and 3.06 eV, respectively, even larger than that (2.50 eV) of C60F18. Hence, C58F18 and C58Cl18 can serve as good electron-acceptors with possible photonic/photovoltaic application. The IR spectra of C58X18 are simulated to facilitate identification of different isomers experimentally. In addition, the electronic spectra and second-order hyperpolarizabilities of C58X18 are predicted by ZINDO and sum-over-states model. With the addition of 9X2, both the static and frequency-dependent second-order hyperopolarizabilities of C58X18 greatly decrease compared to those of C58.