Observation and Analysis of Large Dynamic Frequency Shifts in the 1H NMR Signals of H-D in Deuterium-Substituted Dihydrogen Complexes.

A dynamic frequency shift (DFS) in the 1H NMR resonance of the HD unit of the deuterium-labeled dihydrogen complex [Ru(D)(η2-HD)(P3P3iPr)][BPh4] [P3P3iPr = P(CH2CH2CH2PiPr2)3] has been observed and analyzed. To the best of our knowledge, this is the first demonstration of the DFS for a H-D pair. The observed DFS of the center line relative to the outside lines in the H-D triplet is large, up to ∼11 Hz, because of the short H-D distance encountered in dihydrogen complexes. Analysis of the DFS as a function of the temperature, combined with density-functional-theory-calculated or least-squares-fitted electric-field-gradient (EFG) parameters, suggests an H-D bond length of 0.92-0.94 Å. A DFS was also observed in trans-[Fe(η2-HD)(H)(dppe)2]+, suggesting the DFS will be commonplace in dihydrogen complexes if appropriate conditions are employed for its observation. Possible applications of the DFS as a probe of the bond lengths, EFGs, and molecular motion, particularly in inorganic systems, are discussed.

Direct Observation of an Iron-Bound Terminal Hydride in [FeFe]-Hydrogenase by Nuclear Resonance Vibrational Spectroscopy.

[FeFe]-hydrogenases catalyze the reversible reduction of protons to molecular hydrogen with extremely high efficiency. The active site ("H-cluster") consists of a [4Fe-4S]H cluster linked through a bridging cysteine to a [2Fe]H subsite coordinated by CN- and CO ligands featuring a dithiol-amine moiety that serves as proton shuttle between the protein proton channel and the catalytic distal iron site (Fed). Although there is broad consensus that an iron-bound terminal hydride species must occur in the catalytic mechanism, such a species has never been directly observed experimentally. Here, we present FTIR and nuclear resonance vibrational spectroscopy (NRVS) experiments in conjunction with density functional theory (DFT) calculations on an [FeFe]-hydrogenase variant lacking the amine proton shuttle which is stabilizing a putative hydride state. The NRVS spectra unequivocally show the bending modes of the terminal Fe-H species fully consistent with widely accepted models of the catalytic cycle.

Diiron Dithiolate Hydrides Complemented with Proton-Responsive Phosphine-Amine Ligands.

The reaction of Fe2(pdt)(CO)6 with two equivalents of Ph2PC6H4NH2 (PNH2) affords the amido hydride HFe2(pdt)(CO)2(PNH2)(PNH) {[H1H]0, pdt2- = CH2(CH2S-)2}. Isolated intermediates in this conversion include Fe2(pdt)(CO)5-(κ1-PNH2) and Fe2(pdt)(CO)4(κ2-PNH2). X-ray crystallographic analysis of [H1H]0 shows that the chelating amino/amido-phosphine ligands occupy trans-dibasal positions. The 31P NMR spectrum indicates that [H1H]0 undergoes rapid proton exchange between the amido and amine centers. No exchange was observed for the hydride. Protonation of [H1H]0 gives [HFe2(pdt)(CO)2(PNH2)2]+ ([H21H]+), which contains two equivalent amino-phosphine ligands. Single-crystal X-ray crystallographic analysis of [H21H]+ also reveals hydrogen bonds between the exo amine protons with a THF molecule and BF4. Deprotonation of [H1H]0 with potassium tert-butoxide gave [HFe2(pdt)(CO)2(PNH)2]- ([1H]-), which was characterized spectroscopically. The complex has time-averaged C2 symmetry with two amido-phosphine ligands. FTIR spectroscopic measurements show that υCO shifts by approximately 20 cm-1 in the series [1H]-, [H1H]0, and [H21H]+. These shifts are comparable to those seen for the S-protonation of the (NC)2(CO)Fe-(µ-Scys)2Ni(Scys)2 site in the [NiFe]-hydrogenases.[1].

Spectroscopic Investigations of [FeFe] Hydrogenase Maturated with [(57)Fe2(adt)(CN)2(CO)4](2-).

The preparation and spectroscopic characterization of a CO-inhibited [FeFe] hydrogenase with a selectively (57)Fe-labeled binuclear subsite is described. The precursor [(57)Fe2(adt)(CN)2(CO)4](2-) was synthesized from the (57)Fe metal, S8, CO, (NEt4)CN, NH4Cl, and CH2O. (Et4N)2[(57)Fe2(adt)(CN)2(CO)4] was then used for the maturation of the [FeFe] hydrogenase HydA1 from Chlamydomonas reinhardtii, to yield the enzyme selectively labeled at the [2Fe]H subcluster. Complementary (57)Fe enrichment of the [4Fe-4S]H cluster was realized by reconstitution with (57)FeCl3 and Na2S. The Hox-CO state of [2(57)Fe]H and [4(57)Fe-4S]H HydA1 was characterized by Mössbauer, HYSCORE, ENDOR, and nuclear resonance vibrational spectroscopy.

Phosphine-iminopyridines as platforms for catalytic hydrofunctionalization of alkenes.

A series of phosphine-diimine ligands were synthesized by the condensation of 2-(diphenylphosphino)aniline (PNH2) with a variety of formyl and ketopyridines. Condensation of PNH2 with acetyl- and benzoylpyridine yielded the Ph2P(C6H4)N═C(R)(C5H4N), respectively abbreviated PN(Me)py and PN(Ph)py. With ferrous halides, PN(Ph)py gave the complexes FeX2(PN(Ph)py) (X = Cl, Br). Condensation of pyridine carboxaldehyde and its 6-methyl derivatives with PNH2 was achieved using a ferrous template, affording low-spin complexes [Fe(PN(H)py(R))2](2+) (R = H, Me). Dicarbonyls Fe(PN(R)py)(CO)2 were produced by treating PN(Me)py with Fe(benzylideneacetone)(CO)3 and reduction of FeX2(PN(Ph)py) with NaBEt3H under a CO atmosphere. Cyclic voltammetric studies show that the [FeL3(CO)2](0/-) and [FeL3(CO)2](+/0) couples are similar for a range of tridentate ligands, but the PN(Ph)py system uniquely sustains two one-electron reductions. Treatment of Fe(PN(Ph)py)X2 with NaBEt3H gave active catalysts for the hydroboration of 1-octene with pinacolborane. Similarly, these catalysts proved active for the addition of diphenylsilane, but not HSiMe(OSiMe3)2, to 1-octene and vinylsilanes. Evidence is presented that catalysis occurs via iron hydride complexes of intact PN(Ph)py.

Ruthenium hydrides containing the superhindered polydentate polyphosphine ligand P(CH2CH2P(t)Bu2)3.

The complex RuH2(N2)(P(2)P3(tBu)) (1) containing the extremely bulky PP3-type ligand P(2)P3(tBu) = P(CH2CH2P(t)Bu2)3 was synthesized by reduction of RuCl2(P(2)P3(tBu)) (2) with Na/NH3 under a N2 atmosphere. Like other complexes containing the P(2)P3(tBu) ligand, only three of the four donor phosphines are coordinated, and one of the phosphines remains as a dangling pendant phosphine. Reduction of RuCl2(P(2)P3(tBu)) (2) with a range of the more usual hydride reducing agents afforded the previously unknown ruthenium hydride complexes RuHCl(P(2)P3(tBu)) (3), RuH(BH4)(P(2)P3(tBu)) (6), RuH(AlH4)(P(2)P3(tBu)) (7), and the ruthenium(II) trihydride K[Ru(H)3(P(2)P3(tBu))] (8). The ruthenium tetrahydride containing a coordinated H2 ligand RuH2(H2)(P(2)P3(tBu)) (10) was synthesized by exchange of N2 in 1 by H2. Complexes 1, 3, 6, 7, and 8 were characterized by crystallography and multinuclear NMR spectroscopy.

Low oxidation state iron(0), iron(I), and ruthenium(0) dinitrogen complexes with a very bulky neutral phosphine ligand.

The synthesis of a series of iron and ruthenium complexes with the ligand P(2)P3(Cy), P(CH2CH2PCy2)3 is described. The iron(0) and ruthenium(0) complexes Fe(N2)(P(2)P3(Cy)) (1) and Ru(N2)(P(2)P3(Cy)) (2) were synthesized by treatment of [FeCl(P(2)P3(Cy))](+) and [RuCl(P(2)P3(Cy))](+) with an excess of potassium graphite under a nitrogen atmosphere. The Fe(I) and Ru(I) species [Fe(N2)(P(2)P3(Cy))](+) (3) and RuCl(P(2)P3(Cy)) (4) were synthesized by treatment of [FeCl(P(2)P3(Cy))](+) and [RuCl(P(2)P3(Cy))](+) with 1 equiv of potassium graphite under a nitrogen atmosphere. The cationic dinitrogen species [Fe(N2)H(P(2)P3(Cy))](+) (6) and [Ru(N2)H(P(2)P3(Cy))](+) (7) were formed by treatment of 1 and 3, respectively, with 1 equiv of a weak organic acid. The iron(II) complex Fe(H)2(P(2)P3(Cy)) (5) was also synthesized and characterized. Complexes [RuCl(P(2)P3(Cy))][BPh4], 1, 2, 3[BPh4], 4, 5, 6[BF4], and 7[BF4] were characterized by X-ray crystallography. The Fe(I) and Ru(I) complexes 3 and 4 were characterized by electron paramagnetic resonance (EPR) spectroscopy, and the Fe(I) complex has an EPR spectrum typical of a metal-centered radical.

New superhindered polydentate polyphosphine ligands P(CH2CH2P(t)Bu2)3, PhP(CH2CH2P(t)Bu2)2, P(CH2CH2CH2P(t)Bu2)3, and their ruthenium(II) chloride complexes.

The synthesis and characterization of the extremely hindered phosphine ligands, P(CH(2)CH(2)P(t)Bu(2))(3) (P(2)P(3)(tBu), 1), PhP(CH(2)CH(2)P(t)Bu(2))(2) (PhP(2)P(2)(tBu), 2), and P(CH(2)CH(2)CH(2)P(t)Bu(2))(3) (P(3)P(3)(tBu), 3) are reported, along with the synthesis and characterization of ruthenium chloro complexes RuCl(2)(P(2)P(3)(tBu)) (4), RuCl(2)(PhP(2)P(2)(tBu)) (5), and RuCl(2)(P(3)P(3)(tBu)) (6). The bulky P(2)P(3)(tBu) (1) and P(3)P(3)(tBu) (3) ligands are the most sterically encumbered PP(3)-type ligands so far synthesized, and in all cases, only three phosphorus donors are able to bind to the metal center. Complexes RuCl(2)(PhP(2)P(2)(tBu)) (5) and RuCl(2)(P(3)P(3)(tBu)) (6) were characterized by crystallography. Low temperature solution and solid state (31)P{(1)H} NMR were used to demonstrate that the structure of RuCl(2)(P(2)P(3)(tBu)) (4) is probably analogous to that of RuCl(2)(PhP(2)P(2)(tBu)) (5) which had been structurally characterized.

Ruthenium hydride complexes of the hindered phosphine ligand tris(3-diisopropylphosphinopropyl)phosphine.

The synthesis and characterization of the novel hindered tripodal phosphine ligand P(CH(2)CH(2)CH(2)P(i)Pr(2))(3) (P(3)P(3)(iPr)) (1) are reported, along with the synthesis and characterization of ruthenium chloro and hydrido complexes of 1. Complexes [RuCl(P(3)P(3)(i)Pr)][BPh(4)] (2[BPh(4)]), RuH(2)(P(3)P(3)(i)Pr) (3), and [Ru(H(2))(H)(P(3)P(3)(iPr))][BPh(4)] (4[BPh(4)]) were characterized by crystallography. Complex 2 is fluxional in solution, and low-temperature NMR spectroscopy of the complex correlates well with two dynamic processes, an exchange between stereoisomers and a faster turnstile-type exchange within one of the stereoisomers.

Analysis of hepatic glycogen-associated proteins.

Glycogen particles are associated with a population of proteins that mediate its biological functions, including: management of glucose flux into and out of the glycogen particle, maintenance of glycogen structure and regulation of particle size, number, and cellular location. A survey of the glycogen-associated proteome would be predicted to identify the relative representation of known members of this population, and associations with unexpected proteins that have the potential to mediate other functions of the glycogen particle. We therefore purified glycogen particles from both mouse and rat liver, using different techniques, and analyzed the resulting tryptic peptides by MS. We also specifically eluted glycogen-binding proteins from the pellet using malto-oligosaccharides. Comparison of the rat and mouse populations, and analysis of specifically eluted proteins allow some conclusions to be made about the hepatic glycogen sub-proteome. With the exception of glycogen branching enzyme all glycogen metabolic proteins were detected. Novel associations were identified, including ferritin and starch-binding domain protein 1, a protein that contains both a transmembrane endoplasmic reticulum signal peptide and a carbohydrate-binding module. This study therefore provides insight into the organization of the glycogen proteome, identifies other associated proteins and provides a starting point to explore the dynamic nature and cellular distribution of this metabolically important protein population.

Synthesis and redox properties of triarylmethane dye cation salts of anions [M6O19]2- (M = Mo, W).

Four salts have been isolated combining the triarylmethane dye cations pararosaniline (PR(+)) and crystal violet (CV(+)) with the hexametalates [M(6)O(19)](2-) (M = Mo, W). A new hexatungstic acid H(2)[W(6)O(19)]·4dma (dma = dimethylacetamide) was isolated and is a useful synthon for hexatungstate salts. Single-crystal X-ray diffraction confirmed the presence of PR(+) and [Mo(6)O(19)](2-) ions in [PR](2)[Mo(6)O(19)]·6dmf (dmf = dimethylformamide). A number of charge-assisted hydrogen bonds N-H···O exist between the cation -NH(2) functions and the anion oxygen atoms. Comparative cyclic voltammetry of salts [A]Cl (A = PR, CV), [Bu(4)N](2)[M(6)O(19)](2-) and A(2)[M(6)O(19)] was established in MeCN and Me(2)SO solutions and of solids in contact with the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide [emim][tfsa]. In the molecular solvents, the reversible potential for the process [Mo(6)O(19)](2-/3-) is less negative than the first reduction processes of the dye cations. In contrast, that for [W(6)O(19)](2-/3-) is more negative. Spectro-electrochemistry and bulk electrolysis experiments reveal significantly different pathways in the two cases. In contrast, in the [emim][tfsa] medium, a positive shift in reduction potential of at least 400 mV is seen for the anion processes but relatively little change for the dye cation processes. This means that initial reduction of the anions always precedes that of the dyes, providing significant simplification of the complex voltammetric data. Chemically modified electrodes can be used in the ionic liquid because of slow dissolution kinetics. However, reduced anion salts dissolve rapidly, allowing dissolved phase electrochemistry to be examined. The electrochemistries of the oxidized salts A(2)[M(6)O(19)] are essentially those of the individual ions, although low level interaction of A(+) with reduced anions [M(6)O(19)](3-,4-) is evident. The work establishes protocols for synthesis and handling of intensely absorbing and relatively insoluble salts which can now be applied to systems containing more complex polyoxometalate anions.

AMP-activated protein kinase does not associate with glycogen alpha-particles from rat liver.

The AMP-activated protein kinase (AMPK) is heterotrimer consisting of alpha catalytic subunit and beta/gamma regulatory subunits. It acts as a critical focal point for whole body and cellular mechanisms maintaining energy homeostasis by regulating carbohydrate and lipid metabolism, food intake, gene transcription, and protein synthesis. The AMPK beta subunit contains a glycogen-binding domain that has been shown to associate with glycogen particles in vitro and glycogen phosphorylase and glycogen synthase in cultured cells. To determine whether AMPK associates with glycogen particles in vivo, we developed a procedure to purify glycogen alpha-particles to apparent homogeneity from rat liver. Using immunoreactivity and mass spectrometry we determined that AMPK does not associate with the glycogen particle in livers from random-fed rats. This surprising finding indicates that the glycogen-binding properties of the AMPK beta subunit are likely regulated and responsive to the metabolic status of the hepatocyte.