Adducts of rhodium(II) tetraacylates with methionine and its derivatives: 1H and 13C nuclear magnetic resonance spectroscopy and chiral recognition

Complexation of rhodium(II) dimeric tetraacylates: tetraacetate Rh₂AcO₄, tetratrifluoroacetate Rh₂TFA₄ , and (S)-Mosher’s acid salt Rh₂MTPA₄ with both enantiomerically pure and racemic methionine and its derivatives: hydrochloric salt of methionine, hydrochloric salt of methionine methyl ester, N-formyl methionine, N-phthaloyl methionine, N-phthaloyl methyl ester of methionine, and methyl ester of N,N-dimethylmethionine has been investigated by means of ¹H and ¹³C nuclear magnetic resonance (¹H and ¹³C NMR) and absorption electronic spectroscopy in the visible range. Complexation processes were investigated in D₂O or CDCl₃ solutions, depending on the ligands’ and rhodium salts’ solubilities. Some supporting measurements were performed in the solid phase, using ¹³C and ¹⁵N CPMAS NMR techniques.All ligands investigated form 1:1 and 1:2 adducts in the solution, depending on the rhodium salt to ligand molar ratios. The complexation site in the ligands (S atom) was deduced on the basis of the NMR parameter adduct formation shift (Δδ = δ_adduct ? δ_ligand) and calculated chemical shifts (DFT, NMR GIAO). In the cases of the Rh₂TFA₄ and Rh₂MTPA₄ adducts, decreasing the temperature within the range 220–254 K slowed down the ligand exchange and allowed us to observe the signals of all diastereoisomers in the ¹H and ¹³C NMR spectra.     

Cobalt-catalyzed versus uncatalyzed intramolecular Diels-Alder cycloadditions

The intramolecular [4+2] cycloadditions of dienynes was investigated using cobalt-based catalysts. Substrates without substitution on alkyne moiety were found to react under thermal activation. The use of a cobalt salt as catalyst made reactions cleaner by limiting the formation of byproducts. Cycloadditions with dienynes possessing a substituent on the alkyne pattern occurred only in presence of a cobalt catalyst which displayed a moderate to good activity depending on the substrate patterns.     

Adducts of nitrogenous ligands with rhodium(II) tetracarboxylates and tetraformamidinate: NMR spectroscopy and density functional theory calculations

Complexation of tetrakis(μ₂‐N,N'‐diphenylformamidinato‐N,N')‐di‐rhodium(II) with ligands containing nitrile, isonitrile, amine, hydroxyl, sulfhydryl, isocyanate, and isothiocyanate functional groups has been studied in liquid and solid phases using ¹H, ¹³C and ¹⁵N NMR, ¹³C and ¹⁵N cross polarisation–magic angle spinning NMR, and absorption spectroscopy in the visible range. The complexation was monitored using various NMR physicochemical parameters, such as chemical shifts, longitudinal relaxation times T₁, and NOE enhancements. Rhodium(II) tetraformamidinate selectively bonded only unbranched amine (propan‐1‐amine), pentanenitrile, and (1‐isocyanoethyl)benzene. No complexation occurred in the case of ligands having hydroxyl, sulfhydryl, isocyanate, and isothiocyanate functional groups, and more expanded amine molecules such as butan‐2‐amine and 1‐azabicyclo[2.2.2]octane. Such features were opposite to those observed in rhodium(II) tetracarboxylates, forming adducts with all kind of ligands. Special attention was focused on the analysis of Δδ parameters, defined as a chemical shift difference between signal in adduct and corresponding signal in free ligand. In the case of ¹H NMR, Δδ values were either negative in adducts of rhodium(II) tetraformamidinate or positive in adducts of rhodium(II) tetracarboxylates. Experimental findings were supported by density functional theory molecular modelling and gauge independent atomic orbitals chemical shift calculations. The calculation of chemical shifts combined with scaling procedure allowed to reproduce qualitatively Δδ parameters. Copyright © 2013 John Wiley & Sons, Ltd.     

13C and 15N CP/MAS, 1H–15N SCT CP/MAS and FTIR spectroscopy as tools for qualitative detection of the presence of zwitterionic and non‐ionic forms of ansa‐macrolide 3‐formylrifamycin SV and its derivatives in solid state

¹³C, ¹⁵N CP/MAS, including ¹H–¹³C and ¹H–¹⁵N short contact time CP/MAS experiments, and FTIR methods were applied for detailed structural characterization of ansa‐macrolides as 3‐formylrifamycin SV (1) and its derivatives (2–6) in crystal and in powder forms. Although HPLC chromatograms for 2/CH₃OH and 2/CH₃CCl₃ were the same for rifampicin crystals dissolved in respective solvents, the UV–vis data recorded for them were different in 300–375 nm region. Detailed solid state ¹³C and ¹⁵N CP/MAS NMR and FTIR studies revealed that rifampicin (2), in contrast to 3‐formylrifamycin SV (1) and its amino derivatives (3–6), can occur in pure non‐ionic or zwitterionic forms in crystal and in pure these forms or a mixture of them in a powder. Multinuclear CP/MAS and FTIR studies demonstrated also that 3–6 derivatives were present exclusively in pure zwitterionic forms, both in powder and in crystal. On the basis of the solid state NMR and FTIR studies, two conformers of 3‐formylrifamycin SV were detected in powder form due to the different orientations of carbonyl group of amide moiety. The PM6 molecular modeling at the semi‐empirical level of theory, allowed visualization the most energetically favorable non‐ionic and zwitterionic forms of 1–6 antibiotics, strongly stabilized via intramolecular H‐bonds. FTIR studies indicated that the originally adopted forms of these type antibiotics in crystal or in powder are stable in standard laboratory conditions in time. The results presented point to the fact that because of a possible presence of two forms of rifampicin (compound 2), quantification of the content of this antibiotic in relevant pharmaceuticals needs caution. Copyright © 2013 John Wiley & Sons, Ltd.     

Tris-(thiocyanato)-bis-(hexamethylenetetramine)-nona-(aquo) lanthanum(III): synthesis, crystal structure, IR and Raman characterization

The title compound (LaC₁₅H₄₂N₁₁O₉S₃) was prepared and characterized by means of X-ray, IR and Raman measurements. The crystals are orthorhombic: Pnma (No. 62), a = 21.117(2), b = 14.736(2), c = 10.082(1) Å, and Z = 4. The structure consists of polyhedra with a La(III) ion in the center of them and hexamethylene molecules, which link these polyhedra. Each La(III) ion coordinates seven molecules of water and two thiocyanate ions via nitrogen atoms. The IR and Raman spectra, which have been obtained and interpreted, are in good agreement with X-ray results.     

Ergodicity and Parameter Estimates for Infinite-Dimensional Fractional Ornstein-Uhlenbeck Process

Existence and ergodicity of a strictly stationary solution for linear stochastic evolution equations driven by cylindrical fractional Brownian motion are proved. Ergodic behavior of non-stationary infinite-dimensional fractional Ornstein-Uhlenbeck processes is also studied. Based on these results, strong consistency of suitably defined families of parameter estimators is shown. The general results are applied to linear parabolic and hyperbolic equations perturbed by a fractional noise. This work was partially supported by the GACR Grant 201/04/0750 and by the MSMT Research Plan MSM 4977751301.     

Ordered structures of syndiotactic poly(methyl methacrylates) studied by a combination of infrared,Raman, and NMR spectroscopy.

The C ? O stretching vibrations in Raman and infrared spectra of poly(methyl methacrylate) (PMMA) samples of various stereoregularity in solutions and in the solid state were measured. It was found that for ordered structures of syndiotactic (s) PMMA, transition dipole coupling of ester groups in ordered s-PMMA sequences leads to a splitting of the C ? O stretching vibration into three components with wavenumbers equal in the solid state and in solution, and of different activity in Raman and infrared spectra. A comparison of the time dependences of self-aggregation of s-PMMA as measured by NMR and infrared spectroscopy indicates that the first phase of the aggregation process is detected by both methods. NMR analysis of the effect of the degree of stereoregularity on the self-aggregation of s-PMMA shows that the prerequisite for the generation of a stable ordered structure is the mutual interaction of two s-sequences of a minimum length of 9 monomer units. The experimental data obtained lead to the conclusion that, in self-aggregated s-PMMA, some of the ester groups are in close contact, with the interacting s-sequences probably forming a double helix.     

Signed domination numbers of directed graphs

The concept of signed domination number of an undirected graph (introduced by J. E. Dunbar, S. T. Hedetniemi, M. A. Henning and P. J. Slater) is transferred to directed graphs. Exact values are found for particular types of tournaments. It is proved that for digraphs with a directed Hamiltonian cycle the signed domination number may be arbitrarily small.