New thiourea organocatalysts and their application for the synthesis of 5-(1H-indol-3-yl)methyl-2,2-dimethyl-1,3-dioxane-4,6-diones a source of chiral 3-indoylmethyl ketenes

The stereoselective properties of modified thiourea organocatalysts were tested in the Friedel–Crafts alkylation of indole with 5-arylidene-2,2-dimethyl-1,3-dioxane-4,6-diones, which produces chiral 5-((1H-indol-3-yl)(aryl)methyl)-2,2-dimethyl-1,3-dioxane-4,6-diones. Based on a tentative reaction mechanism for ((S)-N-benzyl-2-(3-(3,5-bis(trifluoromethyl)phenyl)thioureido)-N,3,3-trimethylbutanamide organocatalysts, modifications were applied in four selected regions. Systematic structure-stereoselectivity relationship study allowed designing the best efficient organocatalyst for the investigated Friedel–Crafts alkylation of indole with 5-arylidene-2,2-dimethyl-1,3-dioxane-4,6-diones.     

Evaluation of thermal properties of MMCp composites with silver alloy matrix

Journal of Thermal Analysis and Calorimetry - Silver, silver alloys, and composites with silver matrix are used mainly as electric contacts, circuit-breakers, and slide bearings. Contacts working...     

Key Intermediate Species Reveal the Copper(II)‐Exchange Pathway in Biorelevant ATCUN/NTS Complexes

The amino‐terminal copper and nickel/N‐terminal site (ATCUN/NTS) present in proteins and bioactive peptides exhibits high affinity towards Cu^II ions and have been implicated in human copper physiology. Little is known, however, about the rate and exact mechanism of formation of such complexes. We used the stopped‐flow and microsecond freeze‐hyperquenching (MHQ) techniques supported by steady‐state spectroscopic and electrochemical data to demonstrate the formation of partially coordinated intermediate Cu^II complexes formed by glycyl–glycyl–histidine (GGH) peptide, the simplest ATCUN/NTS model. One of these novel intermediates, characterized by two‐nitrogen coordination, t_1/2≈100 ms at pH 6.0 and the ability to maintain the Cu^II/Cu^I redox pair is the best candidate for the long‐sought reactive species in extracellular copper transport.     

Negative Ion Formation by Thermal Surface Ionization of Sulfur Dioxide

The generation of negative ions from SO₂ in the gas phase was studied using the thermal surface ionization method. Six anion types were measured: O⁻, S⁻, SO⁻, and SO₂⁻ and anions with m/z=96 and m/z=128. The most abundant anion formed was S⁻ and the formation routes are discussed for each of the six anions. O⁻, S⁻, and SO⁻ are formed via dissociative electron attachment to the molecule, whereas the generation of SO₂⁻ and anions with m/z=96 and m/z=128 are probably associated with the formation of H₂SO₄ in the gas inlet system and the ion source. Using statistical thermodynamics the dissociation temperatures of SO₂ and SO in the gas phase are calculated and values of above 1800 °C are obtained for both molecules. We also estimated the optimal filament temperatures for the formation of all anions measured, indicating that for SO₂ the optimal temperature is related to the electron affinity of the molecules: the optimal temperature increases with decreasing value of the electron affinity for the molecule corresponding to the respective anion.     

Key Intermediate Species Reveal the Copper(II)-Exchange Pathway in Biorelevant ATCUN/NTS Complexes

The amino-terminal copper and nickel/N-terminal site (ATCUN/NTS) present in proteins and bioactive peptides exhibits high affinity towards Cu^II ions and have been implicated in human copper physiology. Little is known, however, about the rate and exact mechanism of formation of such complexes. We used the stopped-flow and microsecond freeze-hyperquenching (MHQ) techniques supported by steady-state spectroscopic and electrochemical data to demonstrate the formation of partially coordinated intermediate Cu^II complexes formed by glycyl–glycyl–histidine (GGH) peptide, the simplest ATCUN/NTS model. One of these novel intermediates, characterized by two-nitrogen coordination, t_1/2≈100 ms at pH 6.0 and the ability to maintain the Cu^II/Cu^I redox pair is the best candidate for the long-sought reactive species in extracellular copper transport.     

Mössbauer investigation of the reaction of ferrate(VI) with sulfamethoxazole and aniline in alkaline medium

Mechanisms on the oxidation of sulfamethoxazole (SMX) and aniline by ferrate(VI) (Fe^VIO $_{4}{^{2-}}$ , Fe(VI)) in alkaline medium suggested the formation of Fe(VI)-SMX or Fe(VI)-aniline intermediates, respectively. Fe(V) and Fe(IV) as other intermediate iron species have also been proposed in the mechanism. In this paper, rapid freeze Mössbauer spectroscopy was applied in rapidly frozen samples to explore intermediate iron species in the reactions of SMX and aniline with Fe(VI). In both reactions, Fe(VI)-SMX and Fe(VI)-aniline intermediates were not seen in second-minute time scale. Fe(V) and Fe(IV) were also not observed. Fe(III) was the only final species of the reactions.     

Correlated development of a (2 × 2) reconstruction and a charge accumulation layer on the InAs(111)–Bi surface

We have studied the formation of a Bi-induced (2 × 2) reconstruction on the InAs(111)B surface. In connection to the development of the (2 × 2) reconstruction, a two dimensional charge accumulation layer located at the bottom of the InAs conduction band appears as seen through a photoemission structure at the Fermi level. Not well ordered Bi layers do not induce a charge accumulation. The Bi-induced reconstruction reduces the polarization of the pristine surface and changes the initial charge distribution. InAsBi alloying occurs below the surface where Bi acts as charge donor leading to the charge accumulation layer.     

Measuring in vivo protein half-life

Protein turnover critically influences many biological functions, yet methods have been lacking to assess this parameter in?vivo. Here, we demonstrate how chemical labeling of SNAP-tag fusion proteins can be exploited to measure the half-life of resident intracellular and extracellular proteins in living mice. First, we demonstrate that SNAP-tag substrates have wide?bioavailability in mice and can be used for the specific in?vivo labeling of SNAP-tag fusion proteins. We then apply near-infrared probes to perform noninvasive imaging of in?vivo-labeled tumors. Finally, we use SNAP-mediated chemical pulse-chase labeling to perform measurement of the in?vivo half-life of different extra- and intracellular proteins. These results open broad perspectives for studying protein function in living animals.     

Kinetic studies on chromium-glycinato complexes in acidic and alkaline media

Two solid complexes, fac–[Cr(gly)₃] and [Cr(gly)₂(OH)]₂, (where gly is glycinato ligand) were prepared and their acid-catalysed aquation products were identified. The structure of [Cr(gly)₃] was solved by X-ray diffraction, revealing a cationic 3D sublattice with perchlorate anions inside its cavities. Acid-catalysed aquation of [Cr(gly)₃] and [Cr(gly)₂(OH)]₂ leads to the same inert product, [Cr(gly)₂(H₂O)₂]⁺, in a two-stages process. At the first stage, intermediate complexes, [Cr(gly)₂(O–glyH)(H₂O)]⁺ and [Cr(gly)₂(H₂O)–OH–Cr(gly)₂(H₂O)]⁺, are formed respectively. Kinetics of the first aquation stage of [Cr(gly)₃] were studied in HClO₄ solutions. The dependencies of the pseudo first-order rate constants on [H⁺] are as follows: k _obs1H = k ₀ + k ₁ K _p1[H⁺], where k ₀ and k ₁ are rate constants for the chelate-ring opening via spontaneous and acid-catalysed reaction paths, respectively, and K _p1 is the protonation constant. The proposed mechanism assumes formation of the reactive intermediate as a result of proton addition to the coordinated carboxylate group of the didentate ligand. Some kinetic studies on the second reaction stage, the one-end bonded glycine liberation, were also done. The obtained results were analogous to those for stage I. In this case, the proposed reactive species are intermediates, protonated at the carboxylate group of the monodentate glycine. Base hydrolysis of two complexes, [Cr(gly)₂(O–gly)(OH)]⁻ and [Cr(gly)₂(OH)₂]⁻, was studied in 0.2–1.0 M NaOH. The pseudo first-order rate constants, k _obsOH, were [OH⁻] independent in the case of [Cr(gly)₂(O–gly)(OH)]⁻, whereas those for [Cr(gly)₂(OH)₂]⁻ linearly depended on [OH⁻]. The reaction mechanisms were proposed, where the OH⁻ -catalysed reaction path was rationalized in terms of formation of the reactive conjugate base, [Cr(gly)₂(OH)(O)]²⁻, as a result of OH⁻ ligand deprotonation. Activation parameters were determined and discussed.