Myoglobin-CO substate structures and dynamics: multidimensional vibrational echoes and molecular dynamics simulations

Spectrally resolved infrared stimulated vibrational echo data were obtained for sperm whale carbonmonoxymyoglobin (MbCO) at 300 K. The measured dephasing dynamics of the CO ligand are in agreement with dephasing dynamics calculated with molecular dynamics (MD) simulations for MbCO with the residue histidine-64 (His64) having its imidazole epsilon nitrogen protonated (N(epsilon)-H). The two conformational substate structures B(epsilon) and R(epsilon) observed in the MD simulations are assigned to the spectroscopic A(1) and A(3) conformational substates of MbCO, respectively, based on the agreement between the experimentally measured and calculated dephasing dynamics for these substates. In the A(1) substate, the N(epsilon)-H proton and N(delta) of His64 are approximately equidistant from the CO ligand, while in the A(3) substate, the N(epsilon)-H of His64 is oriented toward the CO, and the N(delta) is on the surface of the protein. The MD simulations show that dynamics of His64 represent the major source of vibrational dephasing of the CO ligand in the A(3) state on both femtosecond and picosecond time scales. Dephasing in the A(1) state is controlled by His64 on femtosecond time scales, and by the rest of the protein and the water solvent on longer time scales.     

Simplified electron ejection in Fourier transform ion cyclotron resonance mass spectrometry by suspended trapping

Suspended trapping is used to eject electrons in negative-ion Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometric experiments. In contrast to electron ejection by resonant excitation of the trapping motion, suspended trapping involves allowing the electrons to escape along the z-axis (perpendicular to the trap plates) while the trapping potential is briefly removed. The duration of this event is sufficiently short (～10 μs) so that ion losses are negligible; the overall effect is that of a ‘high-pass mass filter’. Suspended trapping is simpler to implement and more generally applicable to various cell geometries than resonant electron ejection. The effectiveness of the suspended trapping technique is not compromised by the anharmonicity of the potential well in ‘elongated’ ICR traps, but depends simply on the time it takes the electrons to escape the cell. Finally, a small, positive offset potential (～+0.25 V) applied to the trap plates during the suspended trapping event increases the efficiency of the ejection.     

Mixed nitrosyl/phosphinidene and nitrene/phosphinidene clusters of ruthenium

Reaction of the aminophosphinidene complex [Ru5(CO)15(mu 4-PNPri2)] 1 with [PPN][NO2] (PPN = Ph3P=N=PPh3) led to the mixed nitrosyl/phosphinidene cluster complex [PPN][Ru5(CO)13(mu-NO)(mu 4-PNPri2)] 2 which is transformed into the novel nitrene/phosphinidene cluster [Ru5(CO)10(mu-CO)2(mu 3-CO)(mu 4-NH)(mu 3-PNPri2)] 3 via treatment with triflic acid.     

Synthetic, structural and spectroscopic studies of (pseudo)halo(1,3-di-tert-butylimidazol-2-ylidine)gold complexes

A series of (pseudo)halo(1,3-di-tert-butylimidazol-2-ylidine)gold complexes [(But2Im)AuX](X = Cl, Br, I, CN, N3, NCO, SCN, SeCN, ONO2, OCOCH3, CH3) have been synthesized and characterised spectroscopically and structurally. 13C NMR chemical shifts for the carbene carbon vary widely with differing ancillary anion, correlating well with the sigma-donor ability of the latter and with the M-C(carbene) bond distance. These results reinforce the notion that N-heterocyclic carbene ligands are primarily sigma-donor ligands with little pi-acceptor ability.     

Metal to ligand group transfer reactions : II. Reactions of some π-allylrhodium(I) complexes with trifluoroacetic acid and alkyl,acyl and trimethyltin halides

Rh(π-C₃H₅)(PF₃)₃ (I), reacts with trifluoroacetic acid to form propene and [Rh(CF₃COO)(PF₃)₂]₂ (II). I reacts with t-butyl bromide to give [RhBr(PF₃)₂]₂ and a mixture of propene and 2-methyl-1-propene and with n-propyl bromide to give propene and [RhBr(PF₃)₂]₂. Rh(π-C₃H₅)(PPh₃)₂ (III), and t-butyl bromide yield propene and 2-methyl-1-propene. In these reactions a mechanism involving β-hydrogen abstraction and hydrogen migration via the metal to carbon is proposed. When III reacts with Me₃SnCl the Me₃Sn—moiety migrates intact to the π-allyl group. I reacts with acetyl chloride to give propene, [RhCl(PF₃)₂]₂ and the carbonyl rhodium complex Rh₂Cl₂(PF₃)₃(CO). II does not apparently undergo phosphine ligand exchange unlike the analogous halogeno-bridged dimers.     

Modeling the similarities and differences between the sodalite cages (β-cages) in the generic materials

Initially in this review the sodalite framework [T₁₂O₂₄]^6– (T=Al, Si] is modeled with regular tetrahedra and disordered T atoms. Equations are given for calculating atomic coordinates from the unit cell parameter a and the T—O distancet; the expansion or contraction of the sodalite-cage is related quantitatively to changes ina through the cooperative twists of TO₄ tetrahedra about 4 axes and changes in < TOT bridge angles. The fully expanded cage has=0° and the maximum value ofa. The equations are general for any framework formed by isomorphous substitution of T by atoms other than Al, Si and for any SiAl ratio. The model and equations are extended to the zeolite A framework, which can be built from fully expanded sodalite cages. With the cooperative tilt of the TO₄ tetrahedra of zeolite A, described by Depmeier, the major variable features of the zeolite A framework are explained quantitatively. The faujasite framework has twisted-cages (>0), as in sodalite examples, and is quantitatively modeled most conveniently from sodalite examples with similar-cage contents. The review is extended to structures with T-ordering and distorted tetrahedra. Methods are given for estimating a for sodalites from a knowledge of the cavity contents, especially the sizes of cations and anions, and so on, present. Ways of predicting cavity sites in zeolite A as a function of cation size are presented, and the principal cavity sites in the faujasite-cage region are discussed. Finally the review considers isomorphous replacement of T atoms (Si or Al) by B, Be, Fe, Ga, Ge, and P; many of these substituted frameworks are stabilized by templates, or guest molecules, which reside in the cavities. Templates also stabilize Si, Al frameworks with high SiAl ratios. The modeling approach reviewed here is tested on a range of isomorphously substituted frameworks isotypic with sodalite; observed and calculated values of twist and 12O₂₄]^12– with distorted tetrahedra; these are structures with Al-O-Al bridges, which violate Loewenstein's Rule.     

Mesoporous silica-supported uranyl: synthesis and photoreactivity

A mesoporous silica-supported uranyl material (U(aq)O(2)(2+)-silica) was prepared by a co-condensation method. Our approach involves an I(-)M(+)S(-) scheme, where the electrostatic interaction between the anionic inorganic precursor (I(-)), surfactant (S(-)), and cationic mediator (M(+)) provides the basis for the stability of the composite material. The synthesis was carried out under acidic conditions, where the anionic sodium dodecyl sulfate provided the template for the uranyl cation and silicate to condense. Excitation with visible or near-UV light of aqueous suspensions of U(aq)O(2)(2+)-silica generates an excited state that decays with k(0) = 1.5 x 10(4) s(-1). The reaction of the excited state with aliphatic alcohols exhibits kinetic saturation and concentration-dependent kinetic isotope effects. For 2-propanol, the value of k(C)3(H)7(OH)/k(C)()3(D)7(OH) decreases from 2.0 at low alcohol concentrations to 1.0 in the saturation regime at high alcohol concentrations. Taken together, the data describe a kinetic system controlled by chemical reaction at one extreme and diffusion at the other. At low [alcohol], the second-order rate constants for the reaction of silica-U(aq)O(2)(2+) with methanol, 2-propanol, 2-butanol, and 2-pentanol are comparable to the rate constants obtained for these alcohols in homogeneous aqueous solutions containing H(3)PO(4). Under slow steady-state photolysis in O(2)-saturated suspensions, U(aq)O(2)(2+)-silica acts as a photocatalyst for the oxidation of alcohols with O(2).     

Syntheses of gold-manganese and gold-rhenium clusters, [(Ph3PAu)3M(CO)4] and [(Ph3PAu)4M(CO)4] (M = Mn, Re), and the crystal structure of [(Ph3PAu)4Mn(CO)4]BF4

The specific additions of one, three or four Ph₃PAu groups to [M(CO)₅]⁻ (M=Mn, Re) are described. Thus [M(CO)₅] ⁻ in THF reacts with [(Ph₃PAu)₃O]BF₄ to give [(Ph₃PAu)₄Mn(CO)₄]BF₄. An X-ray crystal structure of the M = Mn example shows the cation to have a trigonal bipyramidal Au₄Mn core with the Mn in an equatorial site. The previously known neutral (Ph₃PAu)₃M(CO)₄ clusters are formed by addition of two Ph₃PAu groups, using the mixed reagent [(Ph₃PAu) ₃O]BF₄/[ppn][Co(CO)₄], to Ph₃PAuM(CO)₅, which itself is readily prepared from [M(CO)₅]⁻ and Ph₃PAuCl.     

Mono-cyclopentadienyl complexes of lanthanum: synthesis and characterization of anilido derivatives

Use of the bulky cyclopentadienyl ligand [η⁵-C₅H₂(SiMe₃)₃-1,2,4]⁻ (Cp?) allows for the isolation of monomeric, mono-ring lanthanide species. As previously reported, (Cp?)K reacts with LaI₃(THF)₄ (THF=tetrahydrofuran) in THF/pyridine to form the mono-ring complex (Cp?)LaI₂(py)₃ (1) (py=pyridine); a minor product of this reaction is the bis-ring species (Cp?)₂LaI(py) (2). The solid state structure of 2 reveals a monomeric compound containing a pseudo-tetrahedral metal center exhibiting no unusual intramolecular contacts. Addition of one equiv of KNHAr (Ar=2,6-ⁱPr₂C₆H₃) to complex 1 in THF generates the mono-anilido compound (Cp?)LaI(NHAr)(THF)₂ (3), which may be converted to the more stable pyridine adduct (Cp?)LaI(NHAr)(py)₂ (4) by the addition of pyridine to 3. An X-ray crystal structure of 3 indicated a trigonal bipyramidal metal center with the anilido group oriented trans to the iodide atom (N1-La1-I1=123.1(3)°). A structural study on the bis-pyridine adduct 4 revealed a similar C_s-symmetric structure with a slightly increased N_anilido-La-I angle of 132.1(2)°. Addition of KNHAr to the di-iodo bipyridine adduct (Cp?)LaI₂(bipy)(py) (5), in which the two iodide atoms are cis-disposed, yields the mono-anilido complex (Cp?)LaI(NHAr)(bipy)(py) (6) (bipy=2,2^′-bipyridine); this compound may also be prepared by the addition of bipy to (Cp?)LaI(NHAr)(py)₂ (4). An X-ray diffraction study shows that the lanthanum center in 6 is octahedrally coordinated by a Cp? ring, an iodide, an anilido group, a pyridine molecule and two nitrogens of a bipy molecule. In this case, the anilido moiety and the iodide ligand are arranged in a cis fashion (N_anilido-La-I=111.2(2)°), resulting in a complex with C₁ symmetry. Both (Cp?)LaI(NHAr)(py)₂ (4) and (Cp?)LaI(NHAr)(bipy)(py) (6) are inactive as catalysts for the hydroamination/cyclization of 2-amino-hex-5-ene.     

Electrochemical Detection of MS2 Phage Using a Bead‐based Immunoassay and a NanoIDA

A microbead based sandwich immunoassay for MS2 bacteriophage was developed using an interdigitated array (IDA) electrode with nanoscale dimensions (220 nm electrode width, 620 nm gap). The IDA was fabricated using an electron beam lithographic lift‐off technique. After an antibody‐assisted capture of MS2 using paramagnetic microbeads, a β‐galactosidase labeled secondary antibody was used to convert p‐aminophenyl‐β‐D ‐galactopyranoside (PAPG) into the redox active p‐aminophenol (PAP). Amperometric detection of PAP with IDA electrodes at +300 and ?200 mV vs. a Ag/AgCl reference electrode was used to measure the result, detecting MS2 concentrations as low as 10 ng/mL.