A study of the binding of manganese (II) with the sodium salts of nucleosides in aqueous solutions by the13C NMR method

The binding of manganese(II) with nucleosides — adenosine (A), guanosine (G), cytidine (C), and uridine (U) — in an alkaline D₂O solution has been investigated by the¹³C NMR method. It has been established that the structure of the paramagnetic Mn(II)—nucleoside complexes differs substantially in neutral and in alkaline media. The broadening of the resonance lines (C-2′, C-3′ > C-1′, C-4′ > C-5′) shows the localization of the Mn(II) in the C-2′ and C-3′ hydroxyls of the ribose in an alkaline medium. It has been shown for the case of U that the degree of complex-formation depends on the pH of the solution. It is assumed that the nucleoside forms intramolecular complexes (I) with Mn(OH)₂.     

Reduction of Hg(II) salts in aqueous acidic solutions by SO2

Kinetic studies of the reduction of Hg(II) salts in aqueous acidic solutions by SO₂ in mild conditions have revealed that SO₂ quantitatively reduces Hg(II) to metal in the examined HClO₄ concentration range (2–8M^–1).

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Hg(II) . , HClO₄ (2–8 .^–1) SO₂ Hg(II) .

     

A 13C NMR study of the structure of sulfur-stabilized carbanions

The structure of the lithium and potassium salts of φSCH₃,φSOCH₃,φSO₂CH₃,φSO(NCH₃)CH₃ has been studied by ¹³C NMR in different solvents. The results show that the metalated carbon is nearly pyramidal in and nearly planar in φSOCH₂^?M⁺, whatever the solvent are cation are φSO₂CH₂^? φSCH₂^?M⁺ and φSO(NCH₃)CH₂^?M⁺ are in an intermediate hydridization state, cation and solvent dependent. For the sulfoxide, a four-center chelate is proposed, stable to strong solvating agents and only disrupted by cryptands. It is very likely responsible for the planar configuration of the anionic carbon.The low temperature study of φSOCH₂Li shows the existence of aggregates in THF. HMPA or external lithium salts disrupt these associations, giving rise to other species.The ¹³C NMR parameters of the whole series of sulfur-stabilized carbanions are quite consistent with the date reported for phosphorous and arsenic ylids: the

coupling constants appear to be a good probe of the geometry of the anionic carbon, whereas the chemical shifts are rather insensitive to its hybridization state.     

Withasteroids ofPhysalis. V. A study of the1H and13C NMR spectra of the withasteroids visconolide and 28-hydroxywithaperuvin C

The PMR and¹³C NMR spectra of new withasteroids — visconolide and 28-hydroxywithaperuvin C, isolated fromPhysalis viscosa L. — have been investigated. A detailed analysis of the spectral characteristics obtained is given. For visconolide is proposed the structure of 4,12,17,28-pentahydroxy-1-oxo-5, 6-epoxy-22R-witha-2,24-dienolide, and for 28-hydroxywithaperuvin C that of 6,14,17,20R, 28-pentahydroxy-l-oxo-22R-witha-2, 4, 24-trienolide.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 657–663, September–October, 1985.     

NMR 13C study of the structure of polyethyleneimine

The NMR ¹³C (CMR) spectrum of high molecular weight (M = 20,000) branched polyethyleneimine (PEI) obtained by polymerization of ethyleneimine (EI) in aqueous and alcoholic solutions at 50° with 1,3-dichloropropanol as initiator, contains 8 lines. The lines were identified using CMR spectra of model compounds, i.e. linear PEI, regularly branched PEI, diethylenetriamine and ethyleneimine pentamer. It has been shown that the deshielding effect of the nitrogen atoms on the α-atoms of carbon decreases in the folowing order: N_tert > N_sec > N_prim; with the atoms of carbon in the β-position, the effect increases in the opposite order.A quantitative estimation has been made of the distribution of the diads of elementary units containing the same and different nitrogen atoms. The data have been used to draw some conclusions about the structure of the PEI macromolecule.     

13C high-resolution NMR study of undoped polyacetylene

¹³C NMR spectra of undoped polyacetylene,(CH)_x, have been measured. The existence of 3.4 mol% methylene moieties as defects in the (CH)_x chains has been observed in trans-(CH)_x. Measurements of partially cis-to-trans isomerized (CH)_x suggest the existence of isolated cis regions.     

A 13C and 1H NMR investigation of the bonding in norbornenyl complexes of palladium(II) and platinum(II)

The modes of bonding in several norbornenyl complexes of palladinm(II) and platinum(II) has been investigated by both ¹H and ¹³C NMR spectroscopy. Analysis of internal ¹H¹H, ¹³C¹H, and ¹⁹⁵Pt¹³C coupling constants indicate considerable distortion of the norbornenyl ligand in these complexes relative to organic norbornenes. The nature of this distortion is compatible with a π-homoallylic bonding scheme.     

13C NMR study of alcohols complexed with nitroxide radical

The contact shifts of carbon nuclei in 8 alcohols complexed with 2,2,6,6-tetramethylpiperidine nitroxide radical were determined from the ¹³C NMR spectra and explained by hydrogen bonding and collision interactions.     

13C NMR study of ethers complexed with nitroxide radical

The contact shifts of carbon nuclei in 5 ethers complexed with 2,2,6,6-tetramethylpiperidine nitroxide radical were determined from the ¹³C NMR spectra and explained by collision interactions.     

13C NMR study of ethers complexed with nitroxide radical

The contact shifts of carbon nuclei in five ethers complexed with 2,2,6,6-tetramethylpiperidine nitroxide radical were determined from the ¹³C NMR spectra and explained by collision interactions.     

A 13CNMR study of the carbohydrate portion of ristocetin A

A ¹³C NMR study of the antibiotic ristocetin A establishes two changes which must be made to the structures hitherto accepted for the carbohydrate portion of the antibiotic.     

Chiral relaxation reagents (CRR) in 13C NMR spectroscopy

Enantiomers and chiral relaxation reagents (CRR) afford diastereomeric complexes, which differ clearly in their ¹³C spin-lattice relaxation times.     

NMR study (1H, 13C and 29Si) of the methylallylsilanes

¹H, ¹³C and ²⁹Si NMR data for the compounds (CH₃)_xSi(CH₂CHCH₂)_4-x are reported. The ¹H resonances from the π system are indicative of the electron-supplying inductive effect (+I) of the (CH₃SiCH₂, moiety but the corresponding ¹³C_π chemical shifts seem to be influenced by a sterically induced polarization of the C-H bonds. The ¹³C_All, ¹³C_Me and ²⁹Si chemical shift data reveal an important neighbour anisotropy contribution originating from the π system. Ultraviolet study of the compounds mentioned above gives indication of a σ—π conjugation in accordance with PES and ab initio results [1—5]. The trend observed in the various coupling constants is too small to be Interpreted.     

13C NMR spectra of some methylplatinum(IV) complexes

The ¹³C NMR spectra of some methylplatinum(IV) Schiff-base and related complexes have been recorded. The results are interpreted in terms of the differing effects of various donor atoms on a platinumcarbon bond in the trans position.     

NMR (1H, 13C, 29Si) study of some allylhalogenosilanes

¹H, ¹³C and ²⁹Si NMR spectra of the allylchlorosilanes (CH₂CH-CH₂-)_xSiCl_4?x and of triallylbromosilane have been analysed. Results are discussed in terms of inductive and steric effects and of contributions of diamagnetic anisotropy. There is no conclusive evidence for (p-d)π conjugation.     

13C NMR study of the 1-isopropyl-indanyl-ion in methylene chloride solution

¹³C NMR study of the reaction between 3-isopropyl indene and trifluoromethane sulfonic acid in methylene chloride solution at ?70° shows the presence of 1-isopropyl indanyl cation. Proposed assignments of the chemical shifts show charge delocalisation due to the aromatic ring.     

NMR (195Pt and 13C) contribution to the study of some Pt(II), Pt(IV) and mixed-valence thioamido complexes

The ¹⁹⁵Pt and ¹³C chemical shifts (δ_Pt and δ_c) are reported for platinum(II), platinum(IV) and class II mixed-valence complexes, with general formula [PtL₄]X₂, cis- and trans-PtL₂X₂, PtL₂X₄ and Pt₂L₄X₆ (where L may be thiourea, 2-imidazolidine-thione, tetrahydro 2-pyrimidinethione, thiocaprolactam, pyridine-2-thione and tetramethylthiourea, and X may be Cl or Br). The ¹⁹⁵Pt chemical shifts can be understood in view of ¹³C data in terms of variations of electronegativities and σ-donor abilities of ligands attached to platinum.