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1.
Heiko Kalpen Wolfgang Hnle Mehmet Somer Ulrich Schwarz Karl Peters Hans Georg von Schnering Roger Blachnik 《无机化学与普通化学杂志》1998,624(7):1137-1147
Bismuth(II) Chalcogenometallates(III) Bi2M4X8, Compounds with Bi24+ Dumbbells (M = Al, Ga and X = S, Se) The ternary bismuth(II) chalcogenometallates(III) Bi2M4X8 (with M = Al, Ga and X = S, Se) were synthesized from the binary chalcogenides M2X3 and Bi2X3 and elementary bismuth. All compounds are diamagnetic semiconductors with Eg (opt.) = 1.8–2.7 eV. The phases (except Bi2Al4Se8) are thermodynamically stable and decompose peritectically above 965–1020 K. Bi2Al4Se8 is metastable below 825 K and is obtained only by rapid quenching from T > 825 K. The isotypic compounds crystallize in a new tetragonal tP28 structure type (P4/nnc). The characteristic unit is the hitherto unknown clustercation Bi24+, with the mean bond length d(Bi–Bi) = 314.2 pm, the Raman frequency 102 cm–1 ≤ νs ≤ 108 cm–1, and the mean force constant of f = 0.68 N · cm–1. The Electron Localization Function, ELF, shows the covalent Bi–Bi bond, the lone electron pairs of the ψ-octahedrally coordinated Bi(II) cations, and the polar character of the Bi–X bonds. 相似文献
2.
《无机化学与普通化学杂志》2018,644(15):816-820
Dimethylsulfone reacts in the binary superacidic systems XF/MF5 (X = H, D; M = As, Sb) under the formation of the corresponding salts of the type [(CH3)2SO(OX)]+[MF6]–. The salts are characterized by low temperature vibrational spectroscopy. In case of [(CH3)2SO(OH)]+[SbF6]– a single‐crystal X‐ray structure analysis is reported. The salt crystallizes in the orthorhombic space group Pbca with eight formula units per unit cell [a = 10.3281(3) Å, b = 12.2111(4) Å, c = 13.9593(4) Å]. The experimental results are discussed together with quantum chemical calculations on the PBE1PBE/6‐311G++(3pd,3df) level of theory. 相似文献
3.
Jovica Stojanovi Tamara ?or?evi Ljiljana Karanovi 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(11):i91-i94
During an investigation of the insufficiently known system M1O–M2O–X2O5–H2O (M1 = Cd2+, Sr2+ and Ba2+; M2 = Cu2+, Ni2+, Co2+, Zn2+ and Mg2+; X = P5+, As5+ and V5+), single crystals of the novel compound dicadmium copper(II) bis[phosphate(V)], Cd2Cu(PO4)2, were obtained. This compound belongs to a small group of compounds adopting a Cu3(PO4)2‐type structure and having the general formula M12M2(XO4)2 (M1/M2 = Cd2+, Cu2+, Mg2+ and Zn2+; X = As5+, P5+ and V5+). The crystal structure is characterized by the interconnection of infinite [Cu(PO4)2]n chains and [Cd2O10]n double chains, both extending along the a axis. Exceptional characteristics of this structure are its novel chemical composition and the occurrence of double chains of CdO6 polyhedra that were not found in related structures. In contrast to the isomorphous compounds, where the M1 cations are coordinated by five O atoms, the Cd atom is coordinated by six. The dissimilarity in the geometry of M1 coordination between Cd2Cu(PO4)2 and the isomorphous compounds is mostly due to the larger ionic radius of the Cd cation in comparison with the Cu, Mg and Zn cations. Sharing a common edge, two CdO6 polyhedra form Cd2O10 dimers. Each such dimer is bonded to another dimer sharing common vertices, forming [Cd2O10]n double chains in the [100] direction. The Cu atoms, located on an inversion centre (site symmetry ), form isolated CuO4 squares interconnected by PO4 tetrahedra, forming [Cu(PO4)2]n chains similar to those found in related structures. Conversely, the [Cd2O10]n double chains, which were not found in related structures, are an exclusive feature of this structure. 相似文献
4.
H. A. Tajmir-Riahi 《Journal of the Iranian Chemical Society》2007,4(3):256-263
The enzyme Na+, K+-ATPase is an integral membrane protein which transports sodium and potassium cations against an electrochemical gradient. The transport of Na+ and K+ ions is connected to an oscillation of the enzyme between the two conformational states, the E1 (Na+) and the E2 (K+) conformations. The enzymatic activity of ATPase is largley affected by different ligands complexation. This review reports the effects of several drugs such as AZT (anti-AIDS), cis-Pt (antitumor), aspirin (anti-inflammatory) and vitamin C (antioxidant) on the stability and secondary structure of Na,K-ATPase in vitro. Drug-enzyme binding is mainly through H-bonding to the polypeptide C=O and C-N groups with two binding constants K1(AZT) = 5.30 × 105 M?1 and K2(AZT) = 9.80 × 103 M?1 for AZT and one binding constant for Kcis-Pt = 1.93 × 104 M?1, Kaspirin = 6.45 × 103 M?1 and Kascorbate = 1.04 × 104 M?1 for cis-Pt, aspirin and ascorbic acid. The enzyme secondary structure was altered from that of α-helix 19.8% (free protein) to almost 22–26% and the β-sheet from 25.6% to 18–22%, upon drug complexation with the order of induced stability AZT > cis-Pt > ascorbate > aspirin. 相似文献
5.
Sankar Muniappan Sophia Lipstman Israel Goldberg 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(7):o395-o399
Crystals of the title compounds, 20‐(4‐pyridyl)porphyrin‐54,104,154‐tribenzoic acid–dimethyl sulfoxide (2/5), C46H29N5O6·2.5C2H6OS, (I), and 20‐(4‐pyridyl)porphyrin‐54,104,154‐tribenzoic acid–4‐acetylpyridine–tetrahydrofuran (1/2/10), C46H29N5O6·2C7H7NO·10C4H8O, (II), consist of hydrogen‐bonded supramolecular chains of porphyrin units solvated by molecules of dimethyl sulfoxide [in (I)] and 4‐acetylpyridine [in (II)]. In (I), these chains consist of heterogeneous arrays with alternating porphyrin and dimethyl sulfoxide species, being sustained by COOH...O=S hydrogen bonds. They adopt a zigzag geometry and link on both sides to additional molecules of dimethyl sulfoxide. In (II), the chains consist of homogeneous linear supramolecular arrays of porphyrin units, which are directly connected to one another via COOH...N(pyridyl) hydrogen bonds. As in the previous case, these arrays are solvated on both sides by molecules of the 4‐acetylpyridine ligand via similar COOH(porphyrin)...N(ligand) hydrogen bonds. The two crystal structures contain wide interporphyrin voids, which accommodate disordered/diffused solvent molecules, viz. dimethyl sulfoxide in (I) and tetrahydrofuran in (II). 相似文献
6.
Maria V. Kashina Mikhail A. Kinzhalov Andrey S. Smirnov Daniil M. Ivanov Alexander S. Novikov Vadim Yu. Kukushkin 《化学:亚洲杂志》2019,14(21):3915-3920
The dihalomethanes CH2X2 (X=Cl, Br, I) were co‐crystallized with the isocyanide complexes trans‐[MXM2(CNC6H4‐4‐XC)2] (M=Pd, Pt; XM=Br, I; XC=F, Cl, Br) to give an extended series comprising 15 X‐ray structures of isostructural adducts featuring 1D metal‐involving hexagon‐like arrays. In these structures, CH2X2 behave as bent bifunctional XB/XB‐donating building blocks, whereas trans‐[MXM2(CNC6H4‐4‐XC)2] act as a linear XB/XB acceptors. Results of DFT calculations indicate that all XCH2–X???XM–M contacts are typical noncovalent interactions with estimated strengths in the range of 1.3–3.2 kcal mol?1. A CCDC search reveals that hexagon‐like arrays are rather common but previously overlooked structural motives for adducts of trans‐bis(halide) complexes and halomethanes. 相似文献
7.
《Acta Crystallographica. Section C, Structural Chemistry》2017,73(1):47-51
Porphyrin complexes of ruthenium are widely used as models for the heme protein system, for modelling naturally occurring iron–porphyrin systems and as catalysts in epoxidation reactions. The structural diversity of ruthenium complexes offers an opportunity to use them in the design of multifunctional supramolecular assemblies. Coproporphyrins and metallocoproporphyrins are used as sensors in bioassay and the potential use of derivatives as multiparametric sensors for oxygen and H+ is one of the main factors driving a growing interest in the synthesis of new porphyrin derivatives. In the coproporphyrin I RuII complex catena‐poly[[carbonylruthenium(II)]‐μ‐2,7,12,17‐tetrakis[2‐(ethoxycarbonyl)ethyl]‐3,8,13,18‐tetramethylporphyrinato‐κ5N ,N ′,N ′′,N ′′′:O ], [Ru(C44H52N4O8)(CO)]n , the RuII centre is coordinated by four N atoms in the basal plane, and by axial C (carbonyl ligand) and O (ethoxycarbonylethyl arm from a neighbouring complex) atoms. The complex adopts a distorted octahedral geometry. Self‐assembly of the molecules during crystallization from a methylene chloride–ethanol (1:10 v /v ) solution at room temperature gives one‐dimensional polymeric chains. 相似文献
8.
Mizuho Nisizawa 《Journal of polymer science. Part A, Polymer chemistry》1969,7(9):2715-2718
The effect of radiation on the breaking of secondary bonding in protein was studied by measuring the viscosity change at different radiation doses and urea concentrations. An experimental equation for the viscosity change was obtained, and the observed behavior was explained on the basis of the molecular mechanism. The general equation for the viscosity change is given by ηred = A(X ? Be?kx) + C log R, where ηred is the reduced viscosity of the solution, R is the dose of γ-radiation, X is the concentration of urea, and A, B, C, and k are adjustable constants. 相似文献
9.
Hydrogen exchange reactions between lithium and sodium compounds, MX (M=Li: X=H, CH3, NH2, OH, F; M=Na: X=CH3), and the corresponding hydrides, HX, have been modelled by means of ab initio calculations including electron correlation and zero point energy (ZPE) corrections. Small or no activation barriers (from the initial complexes) are encountered in systems involving lone pairs (10.8, 2.4, 0.0 kcal/mol for X=NH2, OH, F, respectively). Since the association energies of the initial complexes are much larger (21.0, 20.4, 23.5 kcal/mol, respectively; MP2/6–31+G*/6–31+G* + ZPE), such exchange reactions should occur spontaneously in the gas phase. The methyl systems (X=CH3) have the largest barriers: 26.7 (M=Li) and 31.7 (M=Na) kcal/mol (MP2/6–31+G*/6–31G* + ZPE), and the initial complexes are only weakly bound. The significance of these systems as models for hydrogen exchange reactions in complexes of electropositive transition metals is discussed. However, the gegenion-free exchange of hydrogen between CH3 and CH4 has a much lower, 11.8 kcal/mol barrier (MP2/6–31+G*/6–31+G* + ZPE). All the transition structures are highly ionic (charges on the metals > +0.8). The effect of aggregation has been considered by examining the hydrogen exchange between (LiX)2 and HX(X=H, CH3, NH2, OH). Although these dimer reactions formally involve six, instead of four electrons, no “aromatic” preference is observed. 相似文献
10.
Novel Copper(I) Clusters with 2‐(Diphenylphosphanyl)anilide Ligands. Synthesis and Crystal Structures of [Cu6X2(NHR)4] (X = Cl,Br, I; R = C6H4‐2‐PPh2)
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Treatment of copper(I) halides CuX (X = Cl, Br, I) with lithium 2‐(diphenylphosphanyl)anilide [Li(HL)] in THF led to the formation of hexanuclear copper(I) complexes [Cu6X2(HL)4] [X = Cl ( 1 ), Br ( 2 ), I ( 3 )]. In compounds 1 – 3 , the copper atoms are in a distorted octahedral arrangement and the amide ligands adopt a μ3‐κP,κ2N bridging mode. Additionally there are two μ2‐bridging halide ligands. Each of the [Cu6X2(HL)4] clusters comprises two copper atoms, which are surrounded by two amide nitrogen atoms in an almost linear coordination [Cu–N: 186.2(3)–188.0(3) pm] and four copper atoms, which are connected to an amide N atom, a P atom, and a halogen atom in a distorted trigonal planar fashion [Cu–N: 199.6(3)–202.3(3) pm)]. 相似文献
11.
Ignacio Viciano Slawomir Berski Sergio Martí Juan Andrés 《Journal of computational chemistry》2013,34(9):780-789
The electronic structure of iron‐oxo porphyrin π‐cation radical complex Por·+FeIV?O (S? H) has been studied for doublet and quartet electronic states by means of two methods of the quantum chemical topology analysis: electron localization function (ELF) η(r) and electron density ρ(r). The formation of this complex leads to essential perturbation of the topological structure of the carbon–carbon bonds in porphyrin moiety. The double C?C bonds in the pyrrole anion subunits, represented by pair of bonding disynaptic basins Vi=1,2(C,C) in isolated porphyrin, are replaced by single attractor V(C,C)i=1–20 after complexation with the Fe cation. The iron–nitrogen bonds are covalent dative bonds, N→Fe, described by the disynaptic bonding basins V(Fe,N)i=1–4, where electron density is almost formed by the lone pairs of the N atoms. The nature of the iron–oxygen bond predicted by the ELF topological analysis, shows a main contribution of the electrostatic interaction, Feδ+···Oδ?, as long as no attractors between the C(Fe) and C(O) core basins were found, although there are common surfaces between the iron and oxygen basines and coupling between iron and oxygen lone pairs, that could be interpreted as a charge‐shift bond. The Fe? S bond, characterized by the disynaptic bonding basin V(Fe,S), is partially a dative bond with the lone pair donated from sulfur atom. The change of electronic state from the doublet (M = 2) to quartet (M = 4) leads to reorganization of spin polarization, which is observed only for the porphyrin skeleton (?0.43e to 0.50e) and S? H bond (?0.55e to 0.52e). © 2012 Wiley Periodicals, Inc. 相似文献
12.
Compounds consisting of both cluster cations and cluster anions of the composition [(M6X12)(EtOH)6][(Mo6Cl8)Cl4X2] · n EtOH · m Et2O (M = Nb, Ta; X = Cl, Br) have been prepared by the reaction of (M6X12)X2 · 6 EtOH with (Mo6Cl8)Cl4. IR data are given for three compounds. The structures of [(Nb6Cl12)(EtOH)6][(Mo6Cl8)Cl6] · 3 EtOH · 3 Et2O 1 and [(Ta6Cl12)(EtOH)6][(Mo6Cl8)Cl6] · 6 EtOH 2 have been solved in the triclinic space group P1 (No. 2). Crystal data: 1 , a = 10.641(2) Å, b = 13.947(2) Å, c = 15.460(3) Å, α = 65.71(2)°, β = 73.61(2)°, γ = 85.11(2)°, V = 2005.1(8) Å3 and Z = 1; 2 , a = 11.218(2) Å, b = 12.723(3) Å, c = 14.134(3) Å, α = 108.06(2)°, β = 101.13(2)°, γ = 91.18(2)°, V = 1874.8(7) Å3 and Z = 1. Both structures are built of octahedral [(M6Cl12)(EtOH)6]2+ cluster cations and [(Mo6Cl8)Cl6]2– cluster anions, forming distorted CsCl structure types. The Nb–Nb and Ta–Ta bond lengths of 2.904 Å and 2.872 Å (mean values), respectively, are rather short, indicating weak M–O bonds. All O atoms of coordinated EtOH molecules are involved in H bridges. The Mo–Mo distances of 2.603 Å and 2.609 Å (on average) are characteristic for the [(Mo6Cl8)Cl6]2– anion, but there is a clear correlation between the number of hydrogen bridges to the terminal Cl and the corresponding Mo–Cl distances. 相似文献
13.
Behavior of cellulose in NaOH/Urea aqueous solution characterized by light scattering and viscometry
Cellulose was dissolved in 6 wt % NaOH/4 wt % urea aqueous solution, which was proven by a 13C NMR spectrum to be a direct solvent of cellulose rather than a derivative aqueous solution system. Dilute solution behavior of cellulose in a NaOH/urea aqueous solution system was examined by laser light scattering and viscometry. The Mark–Houwink equation for cellulose in 6 wt % NaOH/4 wt % urea aqueous solution at 25 °C was [η] = 2.45 × 10?2 weight‐average molecular weight (Mw)0.815 (mL g?1) in the Mw region from 3.2 × 104 to 12.9 × 104. The persistence length (q), molar mass per unit contour length (ML), and characteristic ratio (C∞) of cellulose in the dilute solution were 6.0 nm, 350 nm?1, and 20.9, respectively, which agreed with the Yamakawa–Fujii theory of the wormlike chain. The results indicated that the cellulose molecules exist as semiflexible chains in the aqueous solution and were more extended than in cadoxen. This work provided a novel, simple, and nonpollution solvent system that can be used to investigate the dilute solution properties and molecular weight of cellulose. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 347–353, 2004 相似文献
14.
I. Fischer-Hjalmars A. Henriksson-Enflo 《International journal of quantum chemistry》1980,18(2):409-419
Metal chelates [(C2H2X2)2M]n with ligating atoms X = NH, O, S and central atoms M = Be2+, Mg2+, Ni2+, Zn2+ (n = 0, ± 2), and M = Li+, Cu+ (n = ± 1, ?3), have been studied in our Laboratory for some years by ab initio calculations. In this article it is shown that certain features of the complexes are the same for all the different metals in our series. These features include a drastic reduction of the energy gap between unoccupied and occupied orbitals, when electrons are added to the positively charged complexes. This change of the energy gap is shown to be an effect of the ligand dimer [(C2H2X2)2]n. But this dimer can only exist when a positive ion, e.g., a metal ion, forms a bridge between the two monomers. The reduced energy gap implies a strong bathochromic shift of the electronic spectrum and low electrical resistivity. 相似文献
15.
Two iron–nitrosyl–porphyrins, nitrosyl[meso‐tetrakis(3,4,5‐trimethoxyphenylporphyrin]iron(II) acetic acid solvate ( 3 ) and nitrosyl[meso‐tetrakis(4‐methoxyphenylporphyrin]iron(II) CH2Cl2 solvate ( 4 ), were synthesized in quantitative yield by using a modified procedure with nitrous acid, followed by oxygen‐atom abstraction by triphenylphosphine under an argon atmosphere. These nitrosyl porphyrins are in the {FeNO}7 class. Under an argon atmosphere, these compounds are relatively stable over a broad range of pH values (4–8) but, under aerobic conditions, they release nitric oxide faster at high pH values than that at low pH values. The generated nitric‐oxide‐free iron(III)–porphyrin can be re‐nitrosylated by using nitrous acid and triphenylphosphine. The rapid release of NO from these FeII complexes at high pH values seems to be similar to that in nitrophorin, a nitric‐oxide‐transport protein, which formally possesses FeIII. However, because the release of NO occurs from ferrous–nitrosyl–porphyrin under aerobic conditions, these compounds are more closely related to nitrobindin, a recently discovered heme protein. 相似文献
16.
Supramolecular Tetrad Featuring Covalently Linked Bis(porphyrin)–Phthalocyanine Coordinated to Fullerene: Construction and Photochemical Studies
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Chandra B. KC Gary N. Lim Prof. Dr. Paul A. Karr Prof. Francis D'Souza 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(25):7725-7735
A multimodular donor–acceptor tetrad featuring a bis(zinc porphyrin)–(zinc phthalocyanine) ((ZnP–ZnP)–ZnPc) triad and bis‐pyridine‐functionalized fullerene was assembled by a “two‐point” binding strategy, and investigated as a charge‐separating photosynthetic antenna‐reaction center mimic. The spectral and computational studies suggested that the mode of binding of the bis‐pyridine‐functionalized fullerene involves either one of the zinc porphyrin and zinc phthalocyanine (Pc) entities of the triad or both zinc porphyrin entities leaving ZnPc unbound. The binding constant evaluated by constructing a Benesi–Hildebrand plot by using the optical data was found to be 1.17×105 M ?1, whereas a plot of “mole‐ratio” method revealed a 1:1 stoichiometry for the supramolecular tetrad. The mode of binding was further supported by differential pulse voltammetry studies, in which redox modulation of both zinc porphyrin and zinc phthalocyanine entities was observed. The geometry of the tetrad was deduced by B3LYP/6‐31G* optimization, whereas the energy levels for different photochemical events was established by using data from the optical absorption and emission, and electrochemical studies. Excitation of the zinc porphyrin entity of the triad and tetrad revealed ultrafast singlet–singlet energy transfer to the appended zinc phthalocyanine. The estimated rate of energy transfer (kENT) in the case of the triad was found to be 7.5×1011 s?1 in toluene and 6.3×1011 s?1 in o‐dichlorobenzene, respectively. As was predicted from the energy levels, photoinduced electron transfer from the energy‐transfer product, that is, singlet‐excited zinc phthalocyanine to fullerene was verified from the femtosecond‐transient spectral studies, both in o‐dichlorobenzene and toluene. Transient bands corresponding to ZnPc ? + in the 850 nm range and C60 ? ? in the 1020 nm range were clearly observed. The rate of charge separation, kCS, and rate of charge recombination, kCR, for the (ZnP–ZnP)–ZnPc ? +:Py2C60 ? ? radical ion pair (from the time profile of 849 nm peak) were found to be 2.20×1011 and 6.10×108 s?1 in toluene, and 6.82×1011 and 1.20×109 s?1 in o‐dichlorobenzene, respectively. These results revealed efficient energy transfer followed by charge separation in the newly assembled supramolecular tetrad. 相似文献
17.
Richard P. Wool 《Journal of Polymer Science.Polymer Physics》2005,43(2):168-183
A theory of the fracture of polymers with network microstructure was developed that was based on the vector, or rigidity percolation (RP) model of Kantor and Webman, in which the modulus, E, is related to the lattice bond fraction p, via E ~ [p ? pc]τ. The Hamiltonian for the lattice was replaced by the strain energy density function of the bulk polymer, U = σ2/2E, where σ is the applied stress and p was expressed in terms of the lattice perfection via the bond density ν, with the entanglement molecular weight, ν = ρ/Me and appropriate measures of crosslink density for rubber, thermosets, and carbon nanotubes. The stored mechanical energy, U, was released by the random fracture of νDo[p ? pc] over stressed hot bonds of energy Do ≈ 330 kJ/mol. The polymer fractured critically when p approached the percolation threshold pc, and the net solution was obtained as σ = (2EνDo [p ? pc])1/2 with a fracture energy, G1c ~ [p ? pc]. The fracture strength of amorphous and semicrystalline polymers in the bulk was well described by, σ = [EDoρ/16 Me]1/2, or σ ≈ 4.6 GPa/Me1/2. Fracture by disentanglement was found to occur in a finite molecular weight range, Mc < M < M*, where M*/Mc ≈ 8, such that the critical draw ratio, λc = (M/Mc)1/2, gave the molecular weight dependence of the fracture as G1c ~ [(M/Mc)1/2 ? 1]2. The critical entanglement molecular weight, Mc, is related to the percolation threshold, pc, via Mc = Me/(1 ? pc). Fracture by bond rupture was in accord with Flory's suggestion, G/G* = [1 ? Mc/M], where G* is the maximum fracture energy. Fracture of an ideal rubber with p = 1 was determined not to occur without strain hardening at λ > 4, such that the maximum stress, σ = E (λ ? 1/λ) = 3.75E. The fracture properties of rubber were found to behave as σ ~ ν, σ ~ E, and G1c ~ ν. For highly crosslinked thermosets, it was predicted that σ ~ (Eν)1/2, σ ~ (X ? Xc)1/2, and G1c ~ ν?1/2, where X is the degree of reaction of the crosslinking groups and Xc defines the gelation point. When applied to carbon nanotubes (SWNT and MWNT) of diameter d and hexagonal bond density ν = j/b2, the nominal stress as a function of diameter is σ(d) = [16 EDo(p ? pc) j/b]1/2/d ≈ 211/d (GPa.nm) and the critical force, Fc(d) ≈ 166 d (nN/nm), in which j = 1.15, b = 0.142 nm, E ≈ 1 Tpa, and Do = 518 kJ/mol. For polymer interfaces with Σ chains per unit area of length L and width X ~ L1/2, G1c is then ~ [p ? pc], where p ~ ΣL/X. The results predicted by the RP fracture model were in good agreement with a considerable body of fracture data for linear polymers, rubbers, thermosets, and carbon nanotubes. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 168–183, 2005 相似文献
18.
J. Oscar C. JimÉnez‐halla Eduard Matito LluÍs Blancafort Juvencio Robles Miquel Solà 《Journal of computational chemistry》2009,30(16):2764-2776
In this work, we analyze the geometry and electronic structure of the [XnM3]n?2 species (M = Be, Mg, and Ca; X = Li, Na, and K; n = 0, 1, and 2), with special emphasis on the electron delocalization properties and aromaticity of the cyclo‐[M3]2? unit. The cyclo‐[M3]2? ring is held together through a three‐center two‐electron bond of σ‐character. Interestingly, the interaction of these small clusters with alkali metals stabilizes the cyclo‐[M3]2? ring and leads to a change from σ‐aromaticity in the bound state of the cyclo‐[M3]2? to π‐aromaticity in the XM3? and X2M3 metallic clusters. Our results also show that the aromaticity of the cyclo‐[M3]2? unit in the X2M3 metallic clusters depends on the nature of X and M. Moreover, we explored the possibility for tuning the aromaticity by simply moving X perpendicularly to the center of the M3 ring. The Na2Mg3, Li2Mg3, and X2Ca3 clusters undergo drastic aromaticity alterations when changing the distance from X to the center of the M3 ring, whereas X2Be3 and K2Mg3 keep its aromaticity relatively constant along this process. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009 相似文献
19.
Susovan Bhowmik Soumyajit Dey Dipankar Sahoo Dr. Sankar Prasad Rath 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(41):13732-13744
The binding of a series of substituted phenols as axial ligands onto a diiron(III)? bisporphyrin framework have been investigated. Spectroscopic characterization revealed high‐spin states of the iron centers in all of the phenolate complexes, with one exception in the 2,4,6‐trinitrophenolate complex of diiron(III)? bisporphyrin, which only stabilized the pure intermediate‐spin (S=3/2) state of the iron centers. The average Fe? N (porphyrin) and Fe? O (phenol) distances that were observed with the 2,4,6‐trinitrophenolate complex were 1.972(3) Å and 2.000(2) Å, respectively, which are the shortest and longest distances reported so far for any FeIII? porphyrin with phenoxide coordination. The alternating shift pattern, which shows opposite signs of the chemical shifts for the meta versus ortho/para protons, is attributed to negative and positive spin densities on the phenolate carbon atoms, respectively, and is indicative of π‐spin delocalization onto the bound phenolate. Electrochemical data reveals that the E1/2 value for the FeIII/FeII couple is positively shifted with increasing acidity of the phenol. However, a plot of the E1/2 values for the FeIII/FeII couple versus the pKa values of the phenols shows a linear relationship for all of the complexes, except for the 2,4,6‐trinitrophenolate complex. The large deviation from linearity is probably due to the change of spin for the complex. Although 2,4,6‐trinitrophenol is the weakest axial ligand in the series, its similar binding with the corresponding FeIII? monoporphyrin only results in stabilization of the high‐spin state. The porphyrin macrocycle in the 2,4,6‐trinitrophenolate complex of diiron(III)? bisporphyrin is the most distorted, whilst the “ruffling” deformation affects the energy levels of the iron d orbitals. The larger size and weaker binding of 2,4,6‐trinitrophenol, along with heme? heme interactions in the diiron(III)? bisporphyrin, are responsible for the larger ring deformations and eventual stabilization of the pure intermediate‐spin states of the iron centers in the complex. 相似文献
20.
The phenomena of the high affinity of porphyrins to the human serum proteins, albumin, high-density lipoproteins (HDL) and low-density lipoproteins (LDL) is well established. Yet, evaluation of the activities of these proteins as endogenous porphyrin carriers, especially with respect to receptor-mediated porphyrin uptake into tumor cells, the merits of which are still in dispute, requires more quantitative protein-porphyrin binding data. As a continuation of previous studies on this issue, the binding of several porphyrin systems to each of the three proteins, employing previously developed spectral methodologies, was studied. The specific systems reported here are hematoporphyrin ester (HPE), which is a novel hematoporphyrin derivative (HPD)-like system, two porphyrin trimers (denoted O1 and O2) and a porphyrin dimer (denoted O3) isolated from HPE. Human serum albumin (HSA) was found to have a single high-affinity site for the monomeric components of HPE, with an equilibrium binding constant of 3.6 × 106. The equilibrium parameters determined for the binding of the three HPE-isolated oligomers to each of the serum proteins are: (1) Binding constants (Kb') of 2.3 × 106, 6.9 × 104 and 1.5 × 104 and number of sites per protein molecule (n) of 3, 1 and 5, for the binding of 01, 02 and 03, respectively, to HSA. (2) Kb’values of 15.5 × 103, 15.3 × 103 and 6.6 × 103 and n values of 1, 2 and 2, for the binding of O1, O2 and O3, respectively, to HDL. (3) Kb’values of 3.3 × 103, 2.28 × 104 and 8.0 × 103 and n values of 50, 20 and 16 for the binding of O1, O2 and O3, respectively, to LDL. These data are direct and clear support not only for the high affinity of porphyrins to serum proteins but specifically of stable oligomers that have been assigned critical roles in the photodynamic treatment of tumors. Of the three proteins, LDL is clearly the best camer, providing the highest drug payload with a moderate affinity (enough to bind and not too much to prevent release). These data are suggested to be promising for the postulated role of LDL in porphyrin uptake into tumor cells and to be useful in the future as benchmarks for novel porphyrin systems. 相似文献