Quantitative analysis of thiols in consumer products on a microfluidic CE chip with fluorescence detection

A microchip CE-based method for the quantification of the thiols mercaptoethanoic acid (MAA) and 2-mercaptopropionic acid (2-MPA) in depilatory cream and cold wave lotions was developed. The thiols were first derivatized with the fluorogenic reagent ammonium-7-fluorobenzo-2-oxa-1,3-diazole-4-sulfonate (SBD-F). The derivatives were separated within only 20 s by microchip CE and detected by their fluorescence. Conventional CE with diode array detection and LC with fluorescence detection were used for validation. The internal standard 3-mercaptopropionic acid (3-MPA) provided RSDs of multiple injections of only 4% or less for the MCE approach. LOD is 2 microM, LOQ 6 microM, and the linear range comprises nearly three decades of concentration starting at the LOQ.     

Intramolecular hydroamination with homogeneous zinc catalysts: evaluation of substituent effects in N,N'-disubstituted aminotroponiminate zinc complexes

A series of symmetrical and unsymmetrical N,N'-disubstituted aminotroponimines (ATIHs) have been prepared. Substituents ranging from linear to cyclic alkyl groups, chelating ethers, and aryl groups were employed. The corresponding aminotroponiminate zinc complexes were then synthesized and characterized by a number of techniques, including by X-ray crystallography. Herein we report on the investigations into their activity in the intramolecular hydroamination of nonactivated alkenes. We also demonstrate that complexes bearing ligands with cyclic alkyl groups show superior activity in a number of selected reactions with functionalized aminoalkenes.     

Exploring base-pair-specific optical properties of the DNA stain thiazole orange

Double-stranded DNA offers multiple binding sites to DNA stains. Measurements of noncovalently bound dye-nucleic acid complexes are, necessarily, measurements of an ensemble of chromophores. Thus, it is difficult to assign fluorescence properties to base-pair-specific binding modes of cyanine dyes or, vice versa, to obtain information about the local environment of cyanines in nucleic acids by using optical spectroscopy. The feasibility to stain DNA and simultaneously probe local perturbations by optical spectroscopy would be a valuable asset to nucleic acid research. So-called FIT probes (forced intercalation probes) were used to pinpoint the location of the DNA stain thiazole orange (TO) in PNADNA duplexes. A detailed analysis of the base-pair dependence of optical properties is provided and enforced binding of TO is compared with "classical" binding of free TO-PRO1. UV-visible absorbance, circular dichroism (CD) and fluorescence spectroscopy, and melting-curve analyses confirmed site-specific TO intercalation. Thiazole orange exhibited base-specific responses that are not observed in noncovalent dye-nucleic acid complexes, such as an extraordinary dependence of the TO extinction coefficient (+/-60 % variation of the averaged epsilon(max) of 57,000 M(-1) cm(-1)) on nearest-neighbor base pairs. TO signals hybridization, as shown by increases in the steady-state fluorescence emission. Studies of TO fluorescence lifetimes in FIT-PNA and in DNADNA and PNADNA complexes highlighted four different fluorescence-decay processes that may be closed or opened in response to matched or single-mismatched hybridization. A very fast decay process (0.04-0.07 ns) and a slow decay process (2.33-3.95 ns) provide reliable monitors of hybridization, and the opening of a fast decay channel (0.22-0.48 ns) that resulted in an attenuation of the fluorescence emission is observed upon the formation of mismatched base pairs.     

Sequence-specific resonance assignment of soluble nonglobular proteins by 7D APSY-NMR spectroscopy

Based on sequence-specific resonance assignments, NMR is the method of choice for obtaining atomic-resolution experimental data on soluble nonglobular proteins. So far, however, NMR assignment of unfolded polypeptides in solution has been a time-consuming task, mainly due to the small chemical shift dispersion, which has limited practical applications of the NMR approach. This paper presents an efficient, fully automated method for sequence-specific backbone and beta-carbon NMR assignment of soluble nonglobular proteins with sizes up to at least 150 residues. The procedure is based on new APSY (automated projection spectroscopy) experiments which benefit from the short effective rotational correlation times in soluble nonglobular polypeptides to record five- to seven-dimensional NMR data sets, which reliably resolves chemical shift degeneracies. Fully automated sequence-specific resonance assignments of the backbone nuclei and C(beta) are described for the uniformly (13)C,(15)N-labeled urea-denatured 148-residue outer membrane protein X (OmpX) from E. coli. The method is generally applicable to systems with similar spectroscopic properties as unfolded OmpX, and we anticipate that this paper may open the door for extensive atomic-resolution studies of chemical denaturant-unfolded proteins, as well as some classes of functional nonglobular polypeptides in solution.     

Oligonuclear copper complexes of a bioinspired pyrazolate-bridging ligand: synthesis, structures, and equilibria in solution

The synthesis of a new bioinspired dinucleating ligand scaffold based on a bridging pyrazolate with appended bis[2-(1-methylimidazolyl)methyl]aminomethyl chelate arms is reported. This ligand forms very stable copper complexes, and a series of different species is present in solution depending on the pH. Interconversions between these solution species are tracked and characterized spectroscopically, and X-ray crystallographic structures of three distinct complexes that correspond to the species present in solution from acidic to basic pH have been determined. Overall, this provides a comprehensive picture of the copper coordination chemistry of the new ligand system. Alterations in the protonation state are accompanied by changes in nuclearity and pyrazolate binding, which cause pronounced changes in color and magnetic properties. Antiferromagnetic coupling between the copper(II) ions is switched on or off depending on the pyrazole binding mode.     

After 20 years, theoretical evidence that "AuF(7)" is actually AuF(5) x F(2)

Quantum-chemical calculations at the DFT (BP86, PBE, TPSS, B3LYP, PBE0), MP2, CCSD, and CCSD(T) levels have been carried out to characterize the putative AuF(7) reported in 1986 by Timakov et al. Our calculations indicate clearly that the species claimed to be AuF(7) had not been synthesized. Instead, a new gold fluoride complex AuF(7) x F2 was prepared. This complex is 205 kJ mol(-1) more stable than the proposed AuF(7) species, and the elimination of F(2) is calculated to be endothermic. This is consistent with the reported stability of the product. A reported experimental vibrational frequency at 734 cm(-1) was verified computationally to be the F-F stretching mode of the end-on coordinated F2 molecule. This result is in line with the recently published trends in the highest attainable oxidation states of the 5d transition metals where Au(V) remains the highest oxidation state of gold.     

High-valent technetium fluorides. Does TcF7 exist?

The structures and stabilities of technetium fluorides in high oxidation states have been studied quantum-chemically at density functional theory (B3LYP) and coupled-cluster (CCSD(T)) levels. The calculations indicate clearly that technetium heptafluoride, TcF7, has a good chance of existence and preparation, thus providing the first heptafluoride in the 4d series. The [TcF6]+ cation, a potential precursor, is also computed to be thermochemically stable against gas-phase elimination reactions. The problem with such highly fluorinated complexes appears thus to be mainly in difficult synthetic access under typical condensed-phase conditions. Matrix-isolation techniques or gas-phase experiments appear to be better suited as starting points.     

Cyanides,Isocyanides, and Hydrides of Zn,Cd and Hg from Metal Atom and HCN Reactions: Matrix Infrared Spectra and Electronic Structure Calculations

Zinc and cadmium atoms from laser ablation of the metals and mercury atoms ablated from a dental amalgam target react with HCN in excess argon during deposition at 5 K to form the MCN and MNC molecules and CN radicals. UV irradiation decreases the higher energy ZnNC isomer in favor of the lower energy ZnCN product. Cadmium and mercury atoms produce analogous MCN primary molecules. Laser ablation of metals also produces plume radiation which initiates H-atom detachment from HCN. The freed H atom can add to CN radical to produce the HNC isomer. The argon matrix also traps the higher energy but more intensely absorbing isocyanide molecules. Further reactions with H atoms generate HMCN and HMNC hydrides, which can be observed by virtue of their C−N stretches and intense M−H stretches. Computational modeling of IR spectra and relative energies guides the identification of reaction products by providing generally reliable frequency differences within the Zn, Cd and Hg family of products, and estimating isotopic shifts using to ¹³C and ¹⁵N isotopic substitution for comparison with experimental data.     

Ox-SLIM: Synthesis of and Site-Specific Labelling with a Highly Hydrophilic Trityl Spin Label

The combination of pulsed dipolar electron paramagnetic resonance spectroscopy (PDS) with site-directed spin labelling is a powerful tool in structural biology. Rational design of trityl-based spin labels has enabled studying biomolecular structures at room temperature and within cells. However, most current trityl spin labels suffer either from aggregation with proteins due to their hydrophobicity, or from bioconjugation groups not suitable for in-cell measurements. Therefore, we introduce here the highly hydrophilic trityl spin label Ox-SLIM. Engineered as a short-linked maleimide, it combines the most recent developments in one single molecule, as it does not aggregate with proteins, exhibits high resistance under in-cell conditions, provides a short linker, and allows for selective and efficient spin labelling via cysteines. Beyond establishing synthetic access to Ox-SLIM, its suitability as a spin label is illustrated and ultimately, highly sensitive PDS measurements are presented down to protein concentrations as low as 45 nm resolving interspin distances of up to 5.5 nm.