Photoinduced electron transfer in a protein-surfactant complex: probing the interaction of SDS with BSA

Photoinduced fluorescence quenching electron transfer from N,N-dimethyl aniline to different 7-amino coumarin dyes has been investigated in sodium dodecyl sulfate (SDS) micelles and in bovine serum albumin (BSA)-SDS protein-surfactant complexes using steady state and picosecond time resolved fluorescence spectroscopy. The electron transfer rate has been found to be slower in BSA-SDS protein-surfactant complexes compared to that in SDS micelles. This observation has been explained with the help of the "necklace-and-bead" structure formed by the protein-surfactant complex due to coiling of protein molecules around the micelles. In the correlation of free energy change to the fluorescence quenching electron transfer rate, we have observed that coumarin 151 deviates from the normal Marcus region, showing retardation in the electron transfer rate at higher negative free energy region. We endeavored to establish that the retardation in the fluorescence quenching electron transfer rate for coumarin 151 at higher free energy region is a result of slower rotational relaxation and slower translational diffusion of coumarin 151 (C-151) compared to its analogues coumarin 152 and coumarin 481 in micelles and in protein-surfactant complexes. The slower rotational relaxation and translational diffusion of C-151 are supposed to be arising from the different location of coumarin 151 compared to coumarin 152 and coumarin 481.     

Relative stabilities of weakly coordinating anions: a computational study

This article describes BP86/SV(P) (DFT) calculations on a representative set of weakly coordinating anions (WCAs) of type [M(L)n]-, their parent neutral Lewis acids M(L)(n-1) and their ate complexes with fluoride, that is, [FM(L)(n)](n-1) (M=B, L=F, OTeF5, C6H5, C6F5, C6H3(CF3)2, CF3; M=P, As, Sb, L=F, OTeF5; M=Al, L=OC(CF3)3). Compounds with fluoride bridges, that is, Sb(n)F(5n) and [Sb(n)F(5n+1)]- (n=2, 3, 4), Al2(L)5F and [(L)3Al-F-Al(L)3]- (L=OC(CF3)3), (F4C6[1,2-B(L)2]2, [F4C6[1,2-B(L)2]2F]-, [F4C6[1,2-B(L)2]2OMe]- (L=C6F5) were also calculated. Based on these BP86/SV(P) and auxiliary MP2/TZVPP, G2, and CBS-Q calculations the relative stabilities and coordinating abilities of these WCAs were established with regard to the fluoride ion affinities (FIA) of the parent Lewis acids, the ligand affinity (LA) of the WCAs, the decomposition of a given WCA in the presence of a hard (H+, proton decomposition PD) and a soft electrophile (Cu+, copper decomposition CuD), the position of the HOMO, the HOMO-LUMO gap, and population analyses of the anions providing partial charges for all atoms. To obtain data that is more reliable, the assessed quantities were calculated through isodesmic reactions. If parts of the calculations could not be done isodesmically, higher levels such as MP2/TZVPP, G2, and CBS-Q were used to obtain reliable values for these reactions. Although the obtained results can not be taken as absolute, the relative ordering of the stabilities of all WCAs will undoubtedly be correct, since a single methodology was chosen for the investigation. To include media effects the decomposition reactions of a subset of 14 WCAs with the SiMe3+ and [Cp2ZrMe]+ ions were also calculated in PhCl and 1,2-F2C6H4 (COSMO solvation model). We found that in most cases gas-phase calculations and solution calculations give comparable results for the stability of the anion. Applications of the LA and FIA that allow one to decide, on thermodynamic grounds, which WCA or Lewis acid is the most suitable for a given problem are sketched.     

阴离子插层镁铝水滑石结构及相互作用的理论研究

采用密度泛函理论(DFT)计算了MgAl-LDHs层板与无机阴离子(F^-、Cl^-、NO₃^-、CO₃^2-、SO₄^2-)和有机阴离子(水杨酸根离子([HO(C₆H₄)COO]^-)、苯甲酸根离子([(C₆H₅)COO]^-)、对二甲氨基苯甲酸根离子([p-(CH₃)₂N(C₆H₄)COO]^-)、十二烷基磺酸根离子[C₁₂H₂₅SO₃]^-、己烷基磺酸根离子[C₆H₁₃SO₃]^-、丙烷基磺酸根离子[C₃H₇SO₃]^-)间的相互作用,获得稳定超分子几何结构及相互作用能。层板主体与客体间存在较强的超分子作用,包括主客体间静电作用和氢键等。主、客体间相互作用能数值大小顺序为CO₃^2- > SO₄^2- > F^-> Cl^-> NO₃^-;[p-(CH₃)₂N(C₆H₄)COO]^-> [(C₆H₅)COO]^-> [HO(C₆H₄)COO]^-和[C₁₂H₂₅SO₃]^-> [C₆H₁₃SO₃]^- > [C₃H₇SO₃]^-。另外,还采用自然键轨道(NBO)计算和分析了LDHs 层板与阴离子间作用机理,从二阶微扰理论计算得到的稳定化能变化趋势与相互作用能数据基本吻合。     

Interactions of weakly coordinating anions with tripalladium sandwich complexes

An understanding of the interaction of weakly coordinating ligands with zero-valent palladium complexes is of importance to understanding the potential catalytic mechanisms and properties of these complexes. We have used a combination of multi-nuclei NMR, microanalysis and single crystal X-ray diffraction to characterize a series of tripalladium ditropylium sandwich complexes that possess one or more triflate [CF₃SO₃]⁻ ligands. The influence of the strong electronic effects on the triflate ligand cause a significant change in the internal bond lengths and angles of the complexes which are coupled to systematic shifts of the tropylium ¹H and ¹³C resonances in the NMR spectra. The use of the Advanced Light Source (ALS) permitted crystallographic characterization of only the third example of a complex containing a Pd-FBF₃ bond.     

金属络阴离子在笼形聚氨肟树脂上的吸附行为

研究了Ce（NO3）_6~3-、VO_3~-、Cr2O_7~2-、CrO_4~2-、MoO_4~2-、WO_4~2-、MnO_4~-、Fe（CN）_6~2-、Fe（CN）_6~3-、和PtCl_6~2-等金属络阴离子在笼形聚氨肟树脂（CAO）上的吸附行为。发现Ce（NO3）-6~2-离子在强酸性介质中不被CAO树脂吸附但被还原为Ce3+。其它金属络阴离子被酸处理笼形聚氨肟树脂（ACAO）所吸附，吸附容量顺序是：MnO_4~-＞Fe（CN）_6~2-＞Cr2O_7~2-＞MoO_4~2-＞PtCl_6~2-＞CrO_4~2-＞VO_3~-＞Fe（CN）_6~3-＞WO_4~2-减处理笼形聚氨肟树脂（BCAO）不吸附CrO_4~2-离子，但可吸附Cr2O_7~2-、MnO_4~2-和PtCl_6~-等离子。吸附容量顺序：MnO_4~-＞Cr2O_7~2-＞PtCl_6~2-根据吸附动力学研究结果，认为ACAO树脂通过离聚体的离子场对外来给阴离子进行多层吸附，但金属络阴离子在BCAO树脂大分子场力作用下在树脂表面形成单吸附层。     

Isobutene homo- and isobutene-isoprene copolymerization initiated by protic initiators associated with a series of novel, weakly coordinating counteranions

The highly electrophilic borane B(C₆F₅)₃ reacts with a variety of carboxylic acids RCO₂H to form 1:1 and 1:2 adducts [RCO₂H][B(C₆F₅)₃] and [RCO₂H][B(C₆F₅)₃]₂. These adducts exhibit enhanced acidities, and the 1:2 adduct of n-decanoic (stearic) acid in particular is an excellent initiator for the carbocationic polymerization of isobutene and copolymerization of isobutene with isoprene in methylene chloride and methyl chloride. High conversions to high molecular weight polyisobutene and isobutene-isoprene copolymers are obtained at unusually high temperatures, consistent with the anion [n-C₁₇H₃₅CO₂ BC₆F₅)_{3 2}]⁻ being very weakly coordinating. Interestingly, the system also exhibits a surprising, as yet not understood, dependence of polymer molecular weights on the nature of R in methyl chloride.     

Polyethyl substituted weakly coordinating carborane anions: a sequential dehydrogenative borylation-hydrogenation route

Polyethylated carborane monoanions based on [closo-CB11H12]- with up to five B-ethyl groups can be prepared by a sequential Rh-catalysed dehydrogenative borylation then hydrogenation.     

Gas-phase ion/ion reactions of transition metal complex cations with multiply charged oligodeoxynucleotide anions

Multiply deprotonated hexadeoxyadenylate anions, (A6-nH)(n-), where n = 3-5, have been subjected to reaction with a range of divalent transition-metal complex cations in the gas phase. The cations studied included the bis- and tris-1,10-phenanthroline complexes of CuII, FeII, and CoII, as well as the tris-1,10-phenanthroline complex of RuII. In addition, the hexadeoxyadenylate anions were subjected to reaction with the singly charged FeIII and CoIIIN,N'-ethylenebis(salicylideneiminato) complexes. The major competing reaction channels are electron-transfer from the oligodeoxynucleotide anion to the cation, the formation of a complex between the anion and cation, and the incorporation of the transition-metal into the oligodeoxynucleotide. The latter process proceeds via the anion/cation complex and involves displacement of the ligand(s) in the transition-metal complex by the oligodeoxynucleotide. Competition between the various reaction channels is governed by the identity of the transition-metal cation, the coordination environment of the metal complex, and the oligodeoxynucleotide charge state. In the case of the divalent metal phenanthroline complexes, competition between electron-transfer and metal ion incorporation is particularly sensitive to the coordination number of the reagent metal complexes. Both electron-transfer and metal ion incorporation occur to significant extents with the bis-phenanthroline ions, whereas the tris-phenanthroline ions react predominantly by metal ion incorporation. To our knowledge this work reports the first observations of the gas-phase incorporation of multivalent transition-metal cations into oligodeoxynucleotide anions and represents a means for the selective incorporation of transition-metal counter-ions into gaseous oligodeoxynucleotides.     

Reversible electrochemical generation of a rhodium(II) porphyrin: thwarting disproportionation with weakly coordinating anions

We report electrochemical generation of a stable Rh(II) porphyrin (Rh(II)(F(28)TPP)) from a four-coordinate Rh(I) precursor [Rh(I)(F(28)TPP)](-) dissolved in weakly coordinating electrolyte solutions. This work provides the first example of an unambiguously reversible one-electron electrochemical oxidation of a Rh(I)(por), and demonstrates that electrochemical oxidation can be performed under conditions that are compatible with alkane activation. These studies begin to classify those media capable of supporting a stable Rh(II)(por), and those that induce disproportionation.     

Stannylium ions, a tin(II) arene complex, and a tin dication stabilized by weakly coordinating anions

The reactivity of aryl‐substituted stannylenes, Ar₂Sn ( 4 ), towards silylarenium borates, [R₃SiArH][B(C₆F₅)₄] ( 3 ), was investigated. The reaction with 2,3,4‐trimethyl‐6‐tert‐butylphenyl (mebp)‐substituted stannylene gave silyl‐substituted stannylium ions 2 a , b , which were characterized by NMR spectroscopy supported by the results of quantum‐mechanical computations of molecular structures and magnetic properties. The tri‐iso‐propylphenyl‐substituted stannylium ions 2 c , d undergo a decomposition reaction in toluene to give the dicationic tin–arene complex [Sn(C₇H₈)₃]²⁺ ( 5 ) in the form of the [B(C₆F₅)₄] salt in high yields. The 5 [B(C₆F₅)₄]₂ salt was identified by single crystal X‐ray diffraction analysis and by Mössbauer spectroscopy. The bonding situation was investigated by using natural bond orbital (NBO) and quantum theory of atoms in molecules (QTAIM) calculations. The substitution of the weakly coordinating borate anion by the carboranate [CB₁₁H₆Br₆]^? results in replacement of the toluene ligands and formation of tin(II) carboranate with only weak Sn²⁺–anion interactions as suggested by the solid‐state structure of the isolated salt.     

Thermodynamic analysis of a hydrophobic binding site: probing the PDZ domain with nonproteinogenic peptide ligands

[structure: see text] Isothermal titration calorimetry (ITC) is used to study the thermodynamic consequences of systematically modifying the hydrophobic character of a single residue in a series of protein-binding ligands. By substituting standard and nonproteinogenic aliphatic amino acids for the C-terminal valine of the hexapeptide KKETEV, binding to the third PDZ domain (PDZ3) of the PSD-95 protein is characterized by distinct changes in the Gibbs free energy (DeltaG), enthalpy (DeltaH), and entropy (TDeltaS) parameters. One notable observation is that peptide binding affinity can be improved with a nonstandard residue.     

Abnormal binding in a carbene complex formed from an imidazolium salt and a metal hydride complex

2-Pyridylmethylimidazolium salts and IrH5(PPh3)2 give an [(N-C)IrH2(PPh3)2]+ species with the imidazole ring bound in the 'wrong way': at C-5, not at the expected C-2.     

Reactions of carbon dioxide with metal carbonyl anions

The reactivity of a series of metal carbonyl anions with CO₂ has been found to parallel their relative nucleophilicities. The highly nucleophilic species, C₅H₅Fe(CO)^?₂, reacts readily to give the dimer, (C₅H₅Fe(CO)₂)₂, and carbonate while Co(CO)^?₄ is unreactive. The reaction of ¹³CO₂ with C₅H₅Fe(CO)^?₂ results in the formation of the ¹³CO enriched dimer.     

Cyclic dimer of a fused porphyrin zinc complex as a novel host with two pi-electronically coupled binding sites

Upon complexation with 4,4[prime or minute]-bipyridine, a cyclic dimer of a fused porphyrin zinc complex, having two pi-electronically coupled binding sites, shows a strong negative cooperativity in the second guest binding, to allow stepwise formation of 1 : 1 and 1 : 2 inclusion complexes.     

The chemistry of metal carbonyl anions : III. Sodium-potassium alloy: An efficient reagent for the production of metal carbonyl anions

Reduction of several metal carbonyl dimers including Mn₂](CO)₁₀, [C₅H₅Fe(C0)₂]₂, Co₂(CO)₈, and [C₅H₅M(CO)₃]₂ (M = Cr, Mo and W) by sodium—potassium alloy (NaK) in tetrahydrofuran at room temperature provides a rapid and clean method for the production of the corresponding metal carbonyl anions in high yield. Isolation and characterization of [n-Bu₄N] [Fe(CO)₂C₅H₅] from the iron dimer reduction is described. Reductions of other carbonyls including M(CO)₆ (M = Cr, Mo and W) and Re₂(CO)₁₀ proceed more slowly than previously established methods and provide principally M₂(CO)₁₀^2? and Re(CO)₅₅^?. Methods for the preparation of Re(CO)₅^? are critically considered. The reaction of NaK with [C₅H₅NiCO]₂ is discussed in relation to previously reported results. Infrared solution spectra of a number of carbonyl anions in THF, obtained in a special infrared solution cell, are reported.     

Anion effect on the nanostructure of a metal ion binding self-assembling peptide

Effects of copper salts containing different anions (SO(4)(2)(-), Cl(-), and NO(3)(-)) on the self-assembly of a designed peptide EAK16(II)GGH with affinity for Cu(2+) have been investigated. The peptide secondary structure, self-assembled nanostructures, and surface activity were observed to depend strongly on the type of anion. Over a salt concentration range from 0.05 to 10.0 mM, SO(4)(2)(-) induced long fiber formation, whereas Cl(-) and NO(3)(-) caused short fiber formation. The fiber length increased with copper sulfate concentration, but the concentration of copper chloride and copper nitrate did not affect the peptide nanostructures significantly. Analysis by Fourier transform infrared spectroscopy (FTIR) revealed that the addition of the copper salts tended to cause the peptide conformation to change from alpha-helix/random coil to beta-sheet, the extent to which depended on the anion type. This evidence of the anion effect was also supported by surface tension measurements using the axisymmetric drop shape analysis-profile (ADSA-P) technique. An explanation for the effect of anions on the peptide self-assembly was proposed. The divalent anion SO(4)(2)(-) might serve as a bridge by electrostatically interacting with two lysine residues from different peptide molecules, promoting beta-sheet formation. The extensive beta-sheet formation may further promote peptide self-assembly into long fibers. On the other hand, monovalent anions Cl(-) and NO(3)(-) may only electrostatically interact with one charged residue of the peptide; hence, a mixed secondary structure of alpha-helix/random coil and beta-sheet was observed. This observation might explain the predominant formation of short fibers in copper chloride and copper nitrate solutions.