Structural studies of {Li} 2-lithiopyrrolidines using NMR spectroscopy

A selection of N-substituted 2-lithiopyrrolidines were prepared and their structures were investigated by ⁶Li and ¹³C NMR spectroscopy. Evidence is presented for aggregation and dynamic solvation effects, depending on the nature of the N-substituent and substituents on the pyrrolidine ring. Studies were performed with N-Boc (coordinating carbonyl group), N-methoxyethyl (coordinating methoxy group) and N-alkyl (no coordinating group) heterocycles to represent three different classes of organolithiums: dipole-stabilized, unstabilized and chelated, and unstabilized.     

A binaphthyl-containing Eu(III) complex and its interaction with human serum albumin: a luminescence study

On binding to human serum albumin (HSA), the Eu(III) luminescent emission enhancement of a complex containing a binaphthyl chromophore enables the determination of binding constants, showing no chiral discrimination for the (R)- (K= 8200 +/- 810 M(-1)) and (S)-enantiomers (K= 7710 +/- 460 M(-1)).     

Synthesis of chiral building blocks for use in drug discovery

In the past decade there has been a significant growth in the sales of pharmaceutical drugs worldwide, but more importantly there has been a dramatic growth in the sales of single enantiomer drugs. The pharmaceutical industry has a rising demand for chiral intermediates and research reagents because of the continuing imperative to improve drug efficacy. This in turn impacts on researchers involved in preclinical discovery work. Besides traditional chiral pool and resolution of racemates as sources of chiral building blocks, many new synthetic methods including a great variety of catalytic reactions have been developed which facilitate the production of complex chiral drug candidates for clinical trials. The most ambitious technique is to synthesise homochiral compounds from non-chiral starting materials using chiral metal catalysts and related chemistry. Examples of the synthesis of chiral building blocks from achiral materials utilizing asymmetric hydrogenation and asymmetric epoxidation are presented.     

Intramolecular general acid catalysis of phosphate transfer. nucleophilic attack by oxyanions on the PO3 2- group

Phosphate transfer from the 8-dimethylammonium-naphthyl-1-phosphate monoanion 4m to water and to a range of nucleophiles shows general acid catalysis by the neighboring NH(+) group, through the strong intramolecular hydrogen bond. Reactivity is insensitive to the charge on the nucleophile, so that fluoride and oxyanions displace dimethylaminonaphthol from the PO3(2-) group as effectively as do amines of the same basicity. Reactivity is (predictably) relatively insensitive to the basicity of the nucleophile and to the alpha-effect. A strong intramolecular hydrogen bond is present in the product, but also in the reactant, as evidenced by major perturbations in the pK(a)'s of the phosphate and dimethylamino groups, to 3.94 and 9.31, respectively, and by ab initio calculations. Rate accelerations are of the order of 10(6)-fold despite this stabilization: the strength of the hydrogen bond is evidently significantly enhanced in the transition state. The evidence suggests that it also depends remarkably strongly on the degree of ionization of the reacting phosphate group and will be significantly reduced for the neutral PO(OH)2 group. Thus, the hydrolysis of the substrate cation 4+ shows a correspondingly greater, >10(8)-fold acceleration.     

The conductance of lanthanide (III) sulfate solutions in D2O

The formation constants of the LnSO ₄ ⁺ complexes are reported for La³⁺, Pr³⁺, Sm³⁺, Dy³⁺, Yb³⁺, and Lu³⁺ in D₂O and for Sm³⁺ and Lu³⁺ in water at 25°C. Formation constants which were calculated from conductance data are identical with those obtained in H₂O within the limits of the assumptions made in the mathematical analysis.     

Phosphine and phosphonite complexes of a ruthenium(II) porphyrin. 1. Synthesis,structure, and solution state studies

We have investigated the effect of complexation of different phosphorus ligands on the stability, solid state structure, and spectroscopic properties (NMR, IR, UV-vis) of a 5,15-diphenyl-substituted ruthenium porphyrin, (MeOH)Ru(II)(CO)(DPP) 2 [DPP = 5,15-bis(3',5'-di-tert-butyl)phenyl-2,8,12,18-tetraethyl-3,7,13,17-tetramethylporphyrin]. The ligands used are PPh(3), diphenyl(phenylacetenyl)phosphine (DPAP), bis(diphenylphosphino)acetylene (DPPA), tris(phenylacetenyl)phosphine [(PA)(3)P], and diethyl (phenylacetenyl)phosphonite [PAP(OEt)(2)]. The mono-phosphine complexes (PR(3))Ru(II)(CO)(DPP) are readily formed in solution in quantitative yields. The complexes display association constants ranging from 1.2 x 10(4) M(-1) for PPh(3) to 4.8 x 10(6) M(-1) for PAP(OEt)(2). The weak association of PPh(3) does not correlate with its pK(a), delta((31)P), or cone angle value and is attributed to steric effects. Due to their kinetic lability, which is shown by 2D NMR spectroscopy, and the weakening of the carbonyl ligand via a trans effect, the mono-phosphine complexes could not be isolated. IR spectroscopy gives the relative order of pi-acceptor strength as PPh(3) < DPAP, DPPA < (PA)(3)P < PAP(OEt)(2), whereas the relative order of the sigma-donor strength is PPh(3) < (PA)(3)P < DPAP, DPPA < PAP(OEt)(2), based on the calculated pK(a) values and on the (31)P((1)H) NMR chemical shifts of the ligands. The chemical shift differences in the (31)P9(1)H)) NMR spectra upon ligand binding display a linear correlation with the calculated pK(a) values of the protonated ligands HPR(3)(+); we propose that the pK(a), and probably other electronic properties, of a specific phosphorus ligand can be estimated on the basis of the chemical shift difference Deltadelta((31)P) upon complexation to a metalloporphyrin. The bis-phosphine complexes can be isolated in pure form by crystallization from CHCl(3)-MeOH solutions using excess ligand. Association of the second ligand is in the same order of magnitude as the first binding for the phosphines, but the second phosphonite binding is decreased by a factor of about 100. The solid state structures show only marginal differences in the geometrical parameters. The calculated and the crystallographic cone angles of the ligands generally do not match, apart from the values obtained for PAP(OEt)(2).     

Self-Assembly of Ribbons and Frameworks Containing Large Channels Based upon Methylene-Bridged Dithio-, Diseleno-, and Ditelluroethers

Homoleptic copper(I) and silver(I) complexes [M(n)(L-L)(2)(n)()](BF(4))(n)() (M = Cu or Ag; L-L = MeECH(2)EMe; E = S, Se or Te) have been prepared and characterized by analysis, FAB mass spectrometry, and IR and multinuclear NMR spectroscopy ((1)H, (77)Se, (125)Te, (63)Cu and (109)Ag). The single-crystal X-ray structures of [Cu(n)()(MeSeCH(2)SeMe)(2)(n)()](PF(6))(n)() (orthorhombic, P2(1)2(1)2(1), a = 10.879(7) ?, b = 16.073(7) ?, c = 9.19(1) ?, Z = 4) and [Ag(n)()(MeSeCH(2)SeMe)(2)(n)()](BF(4))(n)() (monoclinic, P2(1)/c, a = 14.546(9) ?, b = 14.65(1) ?, c = 30.203(9) ?, Z = 4) reveal extended three-dimensional cationic frameworks in the solid state which contain large cylindrical or rectangular channels accommodating the PF(6)(-) or BF(4)(-) counterions. In contrast, a single-crystal X-ray structure of [Cu(n)()(MeSCH(2)SMe)(2)(n)()](PF(6))(n)().nMeNO(2) (orthorhombic, Pbcn, a = 15.506(3) ?, b = 8.934(2) ?, c = 25.859(3) ?, Z = 8) shows tetrahedral Cu(I) ions coordinated to bridging dithioethers forming an cationic ribbon-like arrangement of 8-membered rings. Adjacent rings are linked by the Cu atoms. Variable temperature NMR studies have been used to probe various exchange processes occurring in solution in these systems.     

Determination of proline in wine using flow injection analysis with tris(2,2'-bipyridyl)ruthenium(II) chemiluminescence detection

Flow injection methodology is described for the determination of proline in red and white wines using tris(2,2′-bipyridyl)ruthenium(II) chemiluminescence detection. Selective conditions were achieved for proline at pH 10, while other amino acids and wine components did not interfere. The precision of the method was less than 1.00% (R.S.D.) for five replicates of a standard (4 × 10⁻⁶ M) and the detection limit was 1 × 10⁻⁸ M. The level of proline in white and sparkling wines using the developed methodology was equivalent to those achieved using HPLC-FMOC amino acid analysis. SPE removal of phenolic material was required for red wines to minimize Ru(bipy)₃³⁺ consumption and its associated effect on accuracy.     

Construction of a hybrid quadrupole/fourier transform ion cyclotron resonance mass spectrometer for versatile MS/MS above 10 kDa

Technological advancements including an open-cylindrical Penning trap with capacitively coupled ICR cell, selective ion accumulation with a resolving quadrupole, and a voltage gradient used during ion extraction from an octopole ion trap, have individually improved dynamic range and sensitivity in Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS). Documented here is a new instrument utilizing these technologies toward the robust detection and fragmentation of biomolecules >10 kDa. Up to 55-fold enhancement in ion population by selective ion accumulation combined with 10- to 20- fold signal-to-noise improvement by application of a DC voltage gradient to an accumulation octopole during the ion transfer event offers improved signal-to-noise (or speed) of MS/MS experiments, for proteins from Methanococcus jannaschii and Saccharomyces cerevisiae whole cell lysates. After external quadrupole filtering with a 40 m/z window, three proteins were fragmented (and identified) in parallel from the database of Methanococcus jannaschii. Electron capture dissociation (ECD) of an intact yeast protein provides extensive sequence information resulting in a high degree of localization for an N-terminal acetylation. Hybrid fragmentation, infrared multiphoton dissociation (IRMPD) followed by low energy electrons (ECD), with the electron source located laterally off the z-axis and external to the magnet bore, presents a strategy for identification of proteins by means of the sequence tag approach. Automated implementation of diverse MS(n) approaches in a Q-FTMS instrument promises to help realize "top-down" proteomics in the future.