AFM study of complement system assembly initiated by antigen-antibody complex

The shape and size of complement system C1 components assembled on a SiO₂ surface after classical activation by antigen-antibody complex was determined by tapping mode atomic force microscopy (AFM). The SiO₂ substrate was silanized and bovine leukemia virus proteins gp51 were covalently bound to the SiO₂ substrate. Self-assembly of complement system proteins was investigated by AFM. Uniform coating of silanized surface by gp51 proteins was observed by AFM. After incubation of gp51 coated substrate in anti-gp51 antibody containing solution, Ag-Ab complexes were detected on the substrate surface by AFM. Then after treatment of Ag-Ab complex modified substrate by guinea-pig blood serum containing highly active complement system proteins for 3 minutes and 30 minutes features 2–3 times and 5–8 times higher in diameter and in height if compared with those observed after formation of Ag-Ab complex, were observed respectively on the surface of SiO₂. This study revealed that AFM might be applied for the imaging of complement system assembly and provides valuable information that can be used to complement other well-established techniques.     

Accelerating charge transfer in a triphenylamine-subphthalocyanine donor-acceptor system

We have designed, synthesized and probed a dodecafluoro-subphthalocyaninato boron(III) unit, which bears a triphenylamine moiety in its axial position, as a novel electron donor-acceptor system.     

A fused donor-acceptor system based on an extended tetrathiafulvalene and a ruthenium complex of dipyridoquinoxaline

An application of the Horner-Wadsworth-Emmons reaction carried out on a ruthenium compound as the electrophilic precursor is described for the synthesis of fused donor-acceptor system 1 based on an extended tetrathiafulvalene and a ruthenium complex of dipyridoquinoxaline units.     

A study on vinyl polymerization initiated by a charge transfer complex

The mechanism of polymerization of methyl methacrylate initiated by a new charge transfer complex system of N,N-dimethylaniline-p-toluene sulphonyl chloride in acetonitrile medium at 50°C is reported.     

Polymerization of acrylonitrile initiated by styrene-arsenic sulfide complex

Arsenic sulfide interacts with styrene to form a complex which in DMSO at 80±0.1°C under N₂ atmosphere, initiates radical polymerization of acrylonitrile. The kinetic equation of the system isR _p [complex]^0.5 [AN]. The value ofk _p ² /k _t and energy of activation for the system are computed as 5.0×10^–1 l mol^–1 s^–1 and 98.2 kJ mol^–1, respectively. The polymerization is retarded by hydroquinone. The effect of polar and non-polar solvents has also been discussed. A possible mechanism for the reaction has also been proposed.     

Conversions of coordinated ligands by reducing thermolysis of some double complex compounds

Thermal decomposition of binary complexes [M(NH₃) _k ] _x [M′L _n ] _y (M = Ni, Co; M′ = Fe, Cr, Cu; L = CN⁻, SCN⁻, C₂O₄²⁻) in a hydrogen atmosphere showed conversion of coordinated CN⁻ groups into ammonia and hydrocarbons; SCN⁻ into ammonia, hydrogen sulfide, and hydrocarbons; and C₂O₄²⁻ into hydrocarbons and CO₂. In all cases, methane prevails in the resulting hydrocarbons; ethylene is the second in relative yield, which however strongly depends on the temperature and combination of the central ions of double complex salts. The yield of ethylene is especially high from the reduction of Co-Fe complexes at 350°C, Co₄-Fe₃ complexes at 500°C, Ni₃-Fe₂ and Ni₃-Cr₂ complexes at 350°C. The observed conversions of coordinated groups can be interpreted as arising from the catalytic effect caused by the reduced forms of the central atoms in the binary complexes to the interaction of ligands with hydrogen.     

Thermal activation of hydrocarbon C-H bonds initiated by a tungsten allyl complex

Gentle thermolysis of the allyl complex, CpW(NO)(CH(2)CMe(3))(eta(3)-H(2)CCHCMe(2)) (1), at 50 degrees C in neat hydrocarbon solutions results in the loss of neopentane and the generation of transient intermediates that subsequently activate solvent C-H bonds. Thus, thermal reactions of 1 with tetramethylsilane, mesitylene, and benzene effect single C-H activations and lead to the exclusive formation of CpW(NO)(CH(2)SiMe(3))(eta(3)-H(2)CCHCMe(2)) (2), CpW(NO)(CH(2)C(6)H(3)-3,5-Me(2))(eta(3)-H(2)CCHCMe(2)) (3), and CpW(NO)(C(6)H(5))(eta(3)-H(2)CCHCMe(2)) (4), respectively. The products of reactions of 1 with other methyl-substituted arenes indicate an inherent preference of the system for the activation of stronger arene sp(2) C-H bonds. For example, C-H bond activation of p-xylene leads to the formation of CpW(NO)(CH(2)C(6)H(4)-4-Me)(eta(3)-H(2)CCHCMe(2)) (5) (26%) and CpW(NO)(C(6)H(3)-2,5-Me(2))(eta(3)-H(2)CCHCMe(2)) (6) (74%). Mechanistic and labeling studies indicate that the transient C-H-activating intermediates are the allene complex, CpW(NO)(eta(2)-H(2)C=C=CMe(2)) (A), and the eta(2)-diene complex, CpW(NO)(eta(2)-H(2)C=CHC(Me)=CH(2)) (B). Intermediates A and B react with cyclohexene to form CpW(NO)(eta(3)-CH(2)C(2-cyclohexenyl)CMe(2))(H) (18) and CpW(NO)(eta(3)-CH(2)CHC)(Me)CH(2)C(beta)H(C(4)H(8))C(alpha)H (19), respectively, and intermediate A can be isolated as its PMe(3) adduct, CpW(NO)(PMe(3))(eta(2)-H(2)C=C=CMe(2)) (20). Interestingly, thermal reaction of 1 with 2,3-dimethylbut-2-ene results in the formation of a species that undergoes eta(3) --> eta(1) isomerization of the dimethylallyl ligand following the initial C-H bond-activating step to yield CpW(NO)(eta(3)-CMe(2)CMeCH(2))(eta(1)-CH(2)CHCMe(2)) (21). Thermolyses of 1 in alkane solvents afford allyl hydride complexes resulting from three successive C-H bond-activation reactions. For instance, 1 in cyclohexane converts to CpW(NO)(eta(3)-C(6)H(9))(H) (22) with dimethylpropylcyclohexane being formed as a byproduct, and in methylcyclohexane it forms the two isomeric complexes, CpW(NO)(eta(3)-C(7)H(11))(H) (23a,b). All new complexes have been characterized by conventional spectroscopic methods, and the solid-state molecular structures of 2, 3, 4, 18, 19, 20, and 21 have been established by X-ray crystallographic analyses.     

Ultrafast photoinduced electron transfer within a self-assembled donor-acceptor system

A photoactive supramolecular assembly that is based on the hydrogen-bonded system H1.G2, consisting of a methyl viologen-functionalized barbiturate host (H1) (1-(N-(3,5-bis[[(6-tert-butylacetylamino-2-pyridyl)amino]carbonyl])-phenylacetamide)-1'-methyl-4,4'-bipyridium) and a [Re(Br)(CO)3(barbi-bpy)] (barbi-bpy = 5-[4-(4'-methyl)-2,2'-bipyridyl]methyl-2,4,6-(1H,3H,5H)-pyrimidinetrione) complex as the guest (G2) is described. The host molecule contains a well-known electron accepting group (methyl viologen), whereas the guest system can act as an efficient electron donor in the excited state. Upon self-assembly, the resulting adduct (H1.G2) represents an interesting noncovalently linked donor-acceptor system. The H1.G2 complex has been characterized in acetonitrile-d3 using 1H NMR and diffusion-ordered NMR spectroscopy (DOSY). The photophysical properties of the components and of the assembly have been studied in dichloromethane, in which the assembly has a high binding constant (Kass > or = 2 x 10(5) M(-1)), using time-resolved fluorescence and transient absorption spectroscopy. A detailed investigation of the hydrogen-bonded complex H1.G2 revealed that, upon excitation of the rhenium compound G2, an ultrafast electron-transfer process occurs from the metal-based component to the acceptor unit. The kinetics of the forward and back electron-transfer processes have been determined.     

Unusual cycloaddition of a cage ketone with tetracyanoethylene by irradiation of the electron donor-acceptor complex.

The photochemical reaction of an electron donor-acceptor complex of a cage ketone containing a cyclobutane ring with tetracyanoethylene (TCNE) gave an unusual 1:1 adduct which is considered to be formed by interception of a 1, 4-radical cation by TCNE-..     

Two-photon microstructure-polymerization initiated by a coumarin derivative/iodonium salt system

Two-photon polymerization initiated by a bimolecular initiating system composed of 7-diethylamino-3-(2^′-benzimidazolyl)coumarin and diphenyliodonium hexafluorophosphate was investigated. The photosensitizer has been proven to possess large two-photon absorption cross-section for 800 nm femtosecond laser. The sensitizer/coinitiator system has high photosensitivity for the photopolymerization of methyl methacrylate. This photopolymer system has been demonstrated for fabricating three-dimensional microstructure.     

Competition between superexchange-mediated and sequential electron transfer in a bridged donor-acceptor system

The temperature- and solvent-dependence of photoinduced electron-transfer reactions in a porphyrin-based donor-bridge-acceptor (DBA) system is studied by fluorescence and transient absorption spectroscopy. Two competing processes occur: sequential and direct superexchange-mediated electron transfer. In a weakly polar solvent (2-methyltetrahydrofuran), only direct electron transfer from the excited donor to the appended acceptor is observed, and this process has weak temperature dependence. In polar solvents (butyronitrile and dimethylformamide), both processes are observed and the sequential electron transfer shows strong temperature dependence. In systems where both electron transfer processes are observed, the long-range superexchange-mediated process is more than two times faster than the sequential process, even though the donor-acceptor distance is significantly larger in the former case.     

Charge transfer in the electron donor-acceptor complex BH3NH3

As a simple yet strongly binding electron donor-acceptor (EDA) complex, BH(3)NH(3) serves as a good example to study the electron pair donor-acceptor complexes. We employed both the ab initio valence bond (VB) and block-localized wave function (BLW) methods to explore the electron transfer from NH(3) to BH(3). Conventionally, EDA complexes have been described by two diabatic states: one neutral state and one ionic charge-transferred state. Ab initio VB self-consistent field (VBSCF) computations generate the energy profiles of the two diabatic states together with the adiabatic (ground) state. Our calculations evidently demonstrated that the electron transfer between NH(3) and BH(3) falls in the abnormal regime where the reorganization energy is less than the exoergicity of the reaction. The nature of the NH(3)-BH(3) interaction is probed by an energy decomposition scheme based on the BLW method. We found that the variation of the charge-transfer energy with the donor-acceptor distance is insensitive to the computation levels and basis sets, but the estimation of the amount of electron transferred heavily depends on the population analysis procedures. The recent resurgence of interest in the nature of the rotation barrier in ethane prompted us to analyze the conformational change of BH(3)NH(3), which is an isoelectronic system with ethane. We found that the preference of the staggered structure over the eclipsed structure of BH(3)NH(3) is dominated by the Pauli exchange repulsion.     

Free-radical polymerization of monomer-polymer solutions initiated by a peroxide-tertiary aromatic amine system

The free-radical polymerization of styrene and methyl methacrylate initiated by the peroxide-tertiary aromatic amine system in the presence of dissolved aromatic polyethers and fluoroelastomer has been studied with the use of quantitative chemical, thermometric, and gravimetric analyses. It has been shown that the rate of polymerization of monomer-polymer solutions is higher than that of pure monomers. The influence of the content of dissolved polymers on the conversion of monomers corresponding to the onset of the gel effect has been estimated. In the presence of the polymer being added, this phenomenon manifests itself at a lower fractional conversion of the monomer. The greater the content of the polymer and the higher the viscosity of the reaction system, the sooner the rise in the rate of polymerization. The experimental evidence of this study makes it possible to control the synthesis of composite materials from monomer-polymer systems.     

Polymerization initiated by an electron donor–acceptor complex. VI. Polymerization of methyl methacrylate initiated by a liquid SO2–nicotine complex and carbon tetrachloride

A kinetic study has been made of polymerization of methyl methacrylate initiated by an electron donor–acceptor complex of liquid SO₂ (electron acceptor) and nicotine (donor) in the presence of carbon tetrachloride. It is concluded that the polymerization proceeds through free-radical intermediates similar to the cases of liquid SO₂–pyridine and liquid SO₂–poly(2-vinylpyridine) complexes. The overall rate of polymerization is proportional to the square root of both liquid SO₂ and nicotine concentrations, and the values of k_p/k_t^½ under various polymerization conditions are in satisfactory agreement with the literature values. For the activation energy of initiation, 13.6 kcal/mole is estimated from the k_p/k_t^½ values obtained at temperatures ranging from 0 to 80°C.     

Synthesis and properties of a dendritic FRET donor-acceptor system with cationic iridium(III) complex core and carbazolyl periphery

In order to enhance the photoluminescence of cyclometalated iridium(III) complexes, which are potentially useful for biolabeling and bioimaging, a series of benzyl ether branched dendritic moieties with carbazolyl termini were introduced to the cyclometalating C^N ligands of the heteroleptic Ir(III) complexes. The complexes also contain a bidentate bipyridine ligand with a carboxyl group for further bioconjugation or functionalization. The dendritic benzyl ether moieties with carbazolyl peripheral groups have demonstrated a dual function as both a F?rster resonance energy transfer (FRET) donor and an oxygen shield to the Ir(III) complex core. The peripheral carbazolyl groups absorb UV light more intensively and transfer energy efficiently to the Ir(III) complex core via the FRET effect, and thus the photoluminescence of the Ir(III) complex at around 560 nm is significantly enhanced. Furthermore, the benzyl ether dendrimers containing carbazolyl termini can shield the Ir(III) complex core to weaken the oxygen quenching effect, which leads to a further enhancement of the PL of the Ir(III) complex.     

Synthesis of a composite polymeric material in the system consisting of epoxy-anhydride matrix and analcime- and montmorillonite-containing rock

The conditions of synthesis of a composite material in the system consisting of an epoxy-anhydride polymeric matrix and an analcime-containing rock were studied. Addition of the filler allows the service characteristics to be improved by 20–25%. Samples with a low content of analcime-containing rock (up to 1 wt %) exhibit the best service characteristics.