Coordination of copper(II) ions by the fragments of neuropeptide gamma containing D1, H9, H12 residues and products of copper-catalyzed oxidation

A potentiometric, spectroscopic (UV-Vis, CD and EPR) and mass spectrometric (ESI-MS) study of Cu(II) binding to the (1-2,7-21)NPG, Asp(1)-Ala-Ile(7)-Ser-His(9)-Lys-Arg-His(12)-Lys-Thr-Asp-Ser-Phe-Val-Gly-Leu-Met(21)-NH(2), and Ac-(1-2,7-21)NPG, Ac-Asp(1)-Ala-Ile(7)-Ser-His(9)-Lys-Arg-His(12)-Lys-Thr-Asp-Ser-Phe-Val-Gly-Leu-Met(21)-NH(2), fragments of neuropeptide gamma were carried out. The results clearly indicate the stabilization of the 1 N {NH(2), β-COO(-)}, 2 N {NH(2), β-COO(-), N(Im)} and 3 N {NH(2), β-COO(-), 2N(Im)} complexes by the coordination of the β-carboxylate group of the D(1) residue. For the (1-2,7-21)NPG the CuH(2)L complex with 3 N {NH(2), β-COO(-), 2N(Im)}, the binding mode dominates in a wide pH range of 4-8.5. With the sequential increase of pH, deprotonated amide nitrogens are involved in copper coordination. For the Ac-(1-2,7-21)NPG peptide the imidazole nitrogen atoms are the primary metal binding sites forming macrochelates in the pH range 4 to 7. The CuHL complex with 4 N {N(Im), N(-), N(-), N(Im)} coordination mode is formed in pH range 6-9. Deprotonation and co-ordination of the third amide nitrogen were detected at pH ～8.6. Metal-catalyzed oxidation (MCO) of proteins is mainly a site-specific process in which one or a few amino acids at metal-binding sites on the protein are preferentially oxidized. To elucidate the products of the copper(II)-catalyzed oxidation of the (1-2,7-21)NPG and Ac-(1-2,7-21)NPG, the liquid chromatography-mass spectrometry (LC-MS) method and Cu(II)/hydrogen peroxide as a model oxidizing system were employed. In the presence of hydrogen peroxide with 1?:?4 peptide-H(2)O(2) molar ratio for the Ac-(1-2,7-21)NPG peptide the oxidation of the methionine residue to methionine sulfoxide and for (1-2,7-21)NPG to sulfone was observed. For the Cu(II)-peptide-hydrogen peroxide in 1?:?1?:?4 molar ratio systems, oxidation of the histidine residues to 2-oxohistidines was detected. Under experimental conditions the (1-2,7-21)NPG and Ac-(1-2,7-21)NPG undergo fragmentations by cleavage of the S(8)-H(9), H(9)-K(10), R(11)-H(12) and H(12)-K(13) peptide bonds supporting the participation of the H(9) and H(12) residues in the coordination of copper(II) ions. For the (1-2,7-21)NPG peptide chain the involvement of the D(1) residue in the coordination of metal ions is supported by the alkoxyl radical modification of this amino acid residue.     

Zn(pybox)-complex-catalyzed asymmetric aqueous Mukaiyama-aldol reactions

Catalytic asymmetric aldol reactions in aqueous media have been developed using chiral zinc complex. The aldol products have been obtained in high yields, high diastereocontrol, and good level of enantioselectivity. Various aromatic and alpha,beta-unsaturated aldehydes and silyl enol ethers derived from ketones can be employed in this reaction to provide the aldol adducts in good to high yield. The elaborated catalytic system has been found as selective for aliphatic aldehydes as well.     

Aryl H-phosphonates. 12. Synthetic and (31)P NMR studies on the preparation of nucleoside H-phosphonothioate and nucleoside H-phosphonodithioate monoesters

Transformation of nucleoside H-phosphonate monoesters into the corresponding H-phosphonothioate and H-phosphonodithioate derivatives and possible side-reactions that may accompany this process were studied using (31)P NMR spectroscopy. These provided new insight into a possible mechanism involved in this transformation and constituted the basis for development of efficient methods for the preparation of nucleoside H-phosphonothioate and nucleoside H-phosphonodithioate monoesters using readily available H-phosphonate monoesters as starting materials.     

On Chloralose-Cyclodextrin Complexes by ESI-Mass Spectrometry

α-Chloralose is a useful mild anaesthetic, providing stable but not deep anaesthesia. Host–guest complexes of α-chloralose with α-, β- and γ-cyclodextrin (CD) were studied using electrospray ionisation (ESI-MS) mass spectrometry and molecular modelling (MD). As it is currently administered, chloralose is transported in a convenient water-soluble complex, and released to react on a physiological level with the reactor sites. It is believed that the chloraloses (α and its isomer β) are encapsulated within the CD cavity. However, the ESI spectra did not reveal such the presence of inclusion compounds. Searching of alternative mechanisms of transportation of these anaesthetic agents, we found that outer-cavity complexes of inserted chloraloses, as found from MD calculations, do have a reasonable stability.     

Kinetics of the Formation of the Blue Complex CrO(O2)2 Formed by Dichromate and H2O2 in Acid Solutions. A Stopped-Flow Investigation Using Rapid-Scan UV-VIS Detection

Summary.  The kinetics of the CrO(O₂)₂ formation by H₂O₂ and Cr₂O₇ ²⁻ in aqueous acidic media was measured at 293 ± 2 K in a pH range between 2.5 and 3.3. Using the stopped-flow method with rapid scan UV-VIS detection, the rate law of the formation of CrO(O₂)₂ was determined. For the media HClO₄, HNO₃ and CH₃COOH, the reaction order in the Cr₂O₇ ²⁻ concentration was found to be 0.5. For [H₂O₂] as well as for [H⁺], the reaction was first order in all acids used. In HCl and H₂SO₄ media the reaction was first order in Cr₂O₇ ²⁻. At T = 293 ± 2 K the rate constant for the formation of Cr(O)(O₂)₂ was found to be (7.3 ± 1.9) · 10² M^−3/2 s⁻¹ in HClO₄. Corresponding author. E-mail: grampp@ptc.tu-graz.ac.at Received January 30, 2002; accepted (revised) June 5, 2002     

Kinetics of the Formation of the Blue Complex CrO(O2)2 Formed by Dichromate and H2O2 in Acid Solutions. A Stopped-Flow Investigation Using Rapid-Scan UV-VIS Detection

 The kinetics of the CrO(O₂)₂ formation by H₂O₂ and Cr₂O₇ ²⁻ in aqueous acidic media was measured at 293 ± 2 K in a pH range between 2.5 and 3.3. Using the stopped-flow method with rapid scan UV-VIS detection, the rate law of the formation of CrO(O₂)₂ was determined. For the media HClO₄, HNO₃ and CH₃COOH, the reaction order in the Cr₂O₇ ²⁻ concentration was found to be 0.5. For [H₂O₂] as well as for [H⁺], the reaction was first order in all acids used. In HCl and H₂SO₄ media the reaction was first order in Cr₂O₇ ²⁻. At T = 293 ± 2 K the rate constant for the formation of Cr(O)(O₂)₂ was found to be (7.3 ± 1.9) · 10² M^−3/2 s⁻¹ in HClO₄.     

A chiral iron(II)-pybox catalyst stable in aqueous media. Asymmetric Mukaiyama-aldol reaction

Among various transition metals, iron is nontoxic, cheap and hence of great potential synthetic use. We report herein a water stable chiral Lewis acid containing an iron(II) ion and a pybox-type ligand. The resulting cationic aqua complex of C₂-symmetry is an effective Lewis acid catalyst for asymmetric Mukaiyama-aldol reactions in aqueous media. The aldol products have been obtained in good yields, syn-diastereoselectivities and ca. 70% levels of enantioselectivity.     

Modern Theoretical Approaches to Modeling the Excited-State Intramolecular Proton Transfer: An Overview

The excited-state intramolecular proton transfer (ESIPT) phenomenon is nowadays widely acknowledged to play a crucial role in many photobiological and photochemical processes. It is an extremely fast transformation, often taking place at sub-100 fs timescales. While its experimental characterization can be highly challenging, a rich manifold of theoretical approaches at different levels is nowadays available to support and guide experimental investigations. In this perspective, we summarize the state-of-the-art quantum-chemical methods, as well as molecular- and quantum-dynamics tools successfully applied in ESIPT process studies, focusing on a critical comparison of their specific properties.     

Soft X-ray laser diagnostics of exploding aluminum wire plasmas

The evolution of current-driven thin single Al wire plasmas was studied with soft X-ray shadowgraphy and interferometry using a very compact capillary discharge-driven =46.9 nm laser probe. Wires of 25 m diameter excited by current pulses with a 78 A/ns increase rate were observed to expand uniformly at a rate of 3.5 m/ns. In contrast, an increase in the rate of energy deposited per unit mass was observed to give rise to significant early plasma instabilities. The results illustrate the use of table-top soft X-ray lasers as a new tool for the diagnostics of dense pulse power driven plasmas. PACS 52.70.Kz; 52.59.Qy; 52.25.Vy; 52.50.Nr