Исследование структуры бивня мамонта методом ИК спектроскопии

The structure of mammoth tusk was investigated by infrared spectroscopy, including after heat treatment. The whole complex of functional groups of the tusk components - hydroxyapatite, collagen and water - was revealed. It was found that collagen in the IR spectrum is represented mainly by characteristic absorption bands of amide and aliphatic groups. After heat treatment at 600 °C, the organic part is completely removed from the sample. It was found that hydroxyapatite in mammoth tusk is presented in a carbonate-substituted form, however, heat treatment at 900 °C leads to the removal of carbonate anion and water from the sample, which is accompanied by the transition of hydroxyapatite from the nonstoichiometric state to the stoichiometric state.

Atmospheric Carbon Dioxide Capture as Carbonate into a Luminescent Trinuclear Cd(II) Complex with Tris(2-aminoethyl)amine Tripodal Ligand

Spontaneous atmospheric CO2 capture as carbonate anion occurred in the synthesis of a trinuclear Cd(II) complex with tris(2-aminoethyl)amine ligand. In reaction two types of compounds were obtained and structurally characterized by X-ray diffraction on a single crystal: initially [{Cd(tren)}3(tren)](ClO4)6·2H2O (1) and subsequently [{Cd(tren)}3(tren)][{Cd(tren)}3(µ3-ηCO3)](ClO4)10 (2). The carbonate anion replaces partially the bridging tren molecule and coordinates in a µ3 fashion. The luminescent properties of the compounds were investigated.

Mechanism of 8-Aminoquinoline Directed Ni-Catalyzed C(sp3)-H Functionalization: Paramagnetic Ni(II) Species, and the Deleterious Effect of Na2CO3 as a Base

<p>Studies into the mechanism of 8-aminoquinoline-directed nickel-catalyzed C(sp³)–H arylation with iodoarenes are described, in an attempt to determine the catalyst resting state and optimize catalytic performance. Paramagnetic complexes are identified that are undergo the key C–H activation step. Hammett analysis using electronically different aryl iodides suggests a concerted oxidative addition mechanism for the C–H functionalization step; DFT calculations were also performed to support this finding. When Na₂CO₃ is used as the base the rate determination step for C–H functionalization appears to be 8-aminoquinoline deprotonation and binding to Ni. The carbonate anion was also observed to provide a deleterious NMR inactive low-energy off-cycle resting state in catalysis. Replacement of Na₂CO₃ with NaO<i>^t</i>Bu not only improved catalysis at milder conditions but also eliminated the need for carboxylic acid and phosphine additives.</p>

Mechanism of 8-Aminoquinoline Directed Ni-Catalyzed C(sp3)-H Functionalization: Paramagnetic Ni(II) Species, and the Deleterious Effect of Na2CO3 as a Base

<p>Studies into the mechanism of 8-aminoquinoline-directed nickel-catalyzed C(sp³)–H arylation with iodoarenes are described, in an attempt to determine the catalyst resting state and optimize catalytic performance. Paramagnetic complexes are identified that are undergo the key C–H activation step. Hammett analysis using electronically different aryl iodides suggests a concerted oxidative addition mechanism for the C–H functionalization step; DFT calculations were also performed to support this finding. When Na₂CO₃ is used as the base the rate determination step for C–H functionalization appears to be 8-aminoquinoline deprotonation and binding to Ni. The carbonate anion was also observed to provide a deleterious NMR inactive low-energy off-cycle resting state in catalysis. Replacement of Na₂CO₃ with NaO<i>^t</i>Bu not only improved catalysis at milder conditions but also eliminated the need for carboxylic acid and phosphine additives.</p>

Mechanism of 8-Aminoquinoline Directed Ni-Catalyzed C(sp3)-H Functionalization: Paramagnetic Ni(II) Species, and the Deleterious Effect of Na2CO3 as a Base

<p>Studies into the mechanism of 8-aminoquinoline-directed nickel-catalyzed C(sp³)–H arylation with iodoarenes are described, in attempts to determine the catalyst resting state and optimize catalytic performance. Paramagnetic complexes are identified that are undergo the key C–H activation step. Hammett analysis using electronically different aryl iodides suggests a concerted oxidative addition mechanism for the C–H functionalization step; DFT calculations were also performed to support this finding. When Na₂CO₃ is used as the base the rate determination step for C–H functionalization appears to be 8-aminoquinoline deprotonation and binding to Ni. The carbonate anion was also observed to provide a deleterious NMR inactive low-energy off-cycle resting state in catalysis. Replacement of Na₂CO₃ with NaO<i>^t</i>Bu not only improved catalysis at milder conditions but also eliminated the need for carboxylic acid and phosphine additives.</p>

Formation and characterization of crosslinks, including Tyr–Trp species, on one electron oxidation of free Tyr and Trp residues by carbonate radical anion

Exposure of free Tyr and Trp to a high concentration of carbonate anion radicals (CO3˙−), under anaerobic conditions, result in the formation of Tyr–Trp species, as well as dityrosine and ditryptophan crosslinks.

A bis-copper(II)–[D-βVal3,7]ascidiacyclamide complex enveloping two square pyramids and sharing an apex atom from a carbonate anion

The four azole rings place structural restrictions on ascidiacyclamide (ASC). As a result, the structure of ASC exists in an equilibrium between two major forms (i.e. folded and square). [D-βVal3,7]Ascidiacyclamide (βASC) was synthesized by replacing two D-Val-Thz (Val is valine and Thz is thiazole) blocks with D-β-Valine (D-βVal-Thz). This modification expands the peptide ring; the original 24-membered macrocycle of ASC becomes a 26-membered ring. Circular dichroism (CD) spectra showed that, in solution, the structural equilibrium is maintained with βASC, but the folded form is dominant. A copper complex was prepared, namely [[D-βVal3,7]ascidiacyclamide(2−)]aqua-μ-carbonato-dicopper(II) monohydrate, [Cu2(C38H54N8O6S2)(CO3)(H2O)]·H2O, to determine the effect of the change in ring size on the coordinated structure. The obtained bis-CuII–βASC complex contains two water molecules and a carbonate anion. Two CuII ions are chelated by three N-donor atoms of two Thz–Ile–Oxz (Ile is isoleucine and Oxz is oxazoline) units. An O atom of the carbonate anion bridges two CuII ions, forming two square pyramids. These features are similar to the previously reported structure of the CuII–ASC complex, but the two pyramids are enveloped inside the peptide and share one apex. In the CuII–ASC complex, the apex of each square pyramid is an O atom of a water molecule, and the two pyramids are oriented toward the outside of the peptide. The incorporated β-amino acids of βASC make the space inside the peptide large enough to envelop the two square pyramids. The observed structural changes in the bis-CuII–βASC complex arising from ring expansion are particularly interesting in the context of the previously reported structure of the CuII–ASC complex.