Tin-119 NMR Studies on adduct formation and stereochemistry of organoyltin(IV)trihalides

qazTin-119 and phosphorus-31 NMR spectra have been recorded for a series of adducts of RSnX₃ (R  Me, Ph; X  Cl, Br) with halide, tributylphosphine (P) and tributylphosphine oxide (L). The adducts were either 1:1 five coordinate or 1:2 six coordinate complexes. The tin-ll9 NMR spectra of mixtures of corresponding chloro and bromo complexes reveal, in most cases, all possible mixed halide species but much additional structural information is obtained from these spectra which could not be extracted from the spectra of individual compounds themselves. Thus in some cases, in the five coordinate species the Berry pseudorotation between isomers within a particular stoichiometry could be slowed on the NMR timescale which allowed a determination of the molecular structure. An equimolar mixture of [PhSnCl₅]²⁻ and [PhSnBr₅]²⁻ shows eleven of the twelve geometries possible for [PhSnCl_xBr_5−x]²⁻. In the six coordinate series [RSnX₄P]⁻ the tin-119 NMR spectra of the mixtures of [RSnCl₄P]⁻ and [RSnBr₄P]⁻ allow the geometry to be determined as trans. Application of the pairwise additivity model for calculation of the tin-119 chemical shift positions for the mixed halide systems are discussed.     

On the mechanism of action of thiamin enzymes, Crystal structure of 2-(α-hydroxyethyl)thiamin pyrophosphate (HETPP). Complexes of HETPP with zinc(II) and cadmium(II)

The crystal structure of the 2-(α-hydroxethyl) thiamin pyrophosphate (LH₂) was solved by X-ray diffraction. Crystallographic data: space group F2dd, a=7.922(4) Å, b=33.11(2) Å, c=36.232(10) Å, V=9503(9) ų, z=16. Metal complexes of the general formula K₂{[M(LH)Cl₂]₂} (M=Zn²⁺, Cd²⁺) were isolated from methanolic solutions and characterized by elemental analysis, IR, Raman, and ¹³C CP MAS NMR spectra. They were also characterized by ¹³C NMR, ³¹P NMR, ¹¹³Cd NMR, ES-MS, and ¹H NMR ROESY spectra in D₂O solutions. The data provide evidence for the bonding of the metals to the N(1′) atom of the pyrimidine ring and to the pyrophosphate group. The free ligand and the metal-coordinated ligand adopt the S conformation. Since thiamin cofactor, substrate, and metal ions are present in our system, the extracted results directly refer to thiamin catalysis and possible functional implications are correlated and discussed.     

13C NMR spectra of 1, 3, 6 -trihydroxy-7-methoxy-8-(3, 7 -dimethyl-2,6-octadienyl) xanthone and its dimethyl derivative

The ¹³C NMR spectra of 1, 3, 6-trihydroxy-7-methoxy-8-(3, 7-dimethyl-2, 6-octadienyl)xanthone and its dimethyl derivative are discussed. The data obtained confirmed the assigned structures. The geometrical configuration of the C₁₀ dienyl side-chain has been deduced as trans.     

Tellurium-125 NMR and mass spectra of dithiotellurides

The preparation, ¹²⁵Te NMR and mass spectra of some dithiotellurides, Te(RS)₂ (R = Ph, 2-PhCOOH, CPh₃, CH₂Ph, 3-PrCOOH, n-Bu, i-Pr, t-Bu) are discussed. The ¹²⁵Te chemical shifts have been found to lie within a range spanning ca. 690 ppm and correlate with the pK_a values of the parent thiols. The mass spectra of the alkyl derivatives (R = n-Bu, i-Pr, t-Bu) indicate an initial step-wise loss of alkenyl groups followed by the elimination of hydrogen sulfide from the resultant bis(hydrosulfido)-tellurium ion.     

Multinuclear NMR of cis-dicarbonylbis(dithiocarbamato)iron(II) complexes in chloroform solution

The ¹³C and ¹⁵SN NMR spectra of eleven cis-Fe(S₂CNRR′)₂(CO)₂ complexes, where R and R′ are organic substituents, have been measured at ambient temperature in CDCl₃ (0.08–0.16 M). The ¹³C absorptions for the carbonyl ligands correlate well with the force constants for the CO stretching vibrations in CHCl₃ solution. Each of the parameters (¹³CO absorption and k_cis for CO) correlate well with the aqueous solution pK_a for⁺H₂NRR′, corrected for the phenyl-containing substituents, high pK_a values corresponding to high ¹³CO absorptions and low k_cis CO force constants. [p ]Evidence was found in the ¹³C NMR spectra for hindered rotation about the CN bond in S₂CNC₂ in complexes with higher pK_a(corr) values and in the ¹³C spectra of the corresponding thiuram disulfides. [p ]The ¹⁵N (natural abundance) NMR spectra for each of the complexes was determined. Each revealed a single sharp absorption in a region of the ¹⁵N NMR spectrum which indicates substantial CN double bond character, as one would expect for coordinated dithiocarbamate ligands.     

Investigation of the solution behavior of tri-n-butylphosphine copper(I) and silver(I) acetates using P{H} NMR spectroscopy

³¹P{¹H} NMR spectra of metal-organic [(ⁿBu₃P)_mMO₂CMe] (M = Cu, Ag; m = 1, 1.5, 2, 2.5, 3, 3.5, 4) have been studied in the temperature range of 308-178 K. Exchange parameters were determined for the appropriate silver(I) complexes. Possible ligand exchange mechanisms based on dissociative and associative processes are discussed.     

Synthesis, crystal structure, luminescence and thermal decomposition kinetics of Eu(III) complex with 2,4-dichlorobenzoic acid and 2,2′-bipyridine

The complex of [Eu(2,4-DClBA)₃(bipy)]₂ (2,4-DClBA = 2,4-dichlorobenzoate; bipy = 2,2′-bipyridine) was obtained and characterized by elemental analysis, IR spectra, UV spectra, luminescence spectra, ¹H NMR spectra, single crystal X-ray diffraction and TG-DTG techniques. Two Eu³⁺ ions are connected by four carboxylate groups through bridging bidentate and bidentate chelating-bridging mode. The coordination number of europium ion is nine. The thermal decomposition behavior of the title complex under a static air atmosphere can be discussed by TG-DTG, SEM and IR techniques. The non-isothermal kinetics was investigated by using double equal-double steps method and Starink method. The mechanism function of the first decomposition step was determined. Meanwhile, the thermodynamic parameters (ΔH^≠, ΔG^≠ and ΔS^≠) and kinetic parameters (activation energy E and the pre-exponential factor A) were also calculated.     

Cadmium tri-tert-butoxysilanethiolates: Structural and spectroscopic models of metal sites in proteins

Syntheses and crystal structures of two molecular, heteroleptic cadmium complexes with CdS₂NO₂ and CdS₂N₂ kernels are described. Bis(tri-tert-butoxysilanethiolate)(1-methylimidazole)cadmium(II) and bis(tri-tert-butoxysilanethiolate)bis(1-methylimidazole)cadmium(II) coexist at equilibrium in chloroform solutions with varying concentrations of bis[bis(tri-tert-butoxysilanethiolate)cadmium(II)] and 1-methylimidazole. The equilibrium is characterized by solution ¹¹³Cd NMR spectra. Solid state CP MAS ¹³C, ²⁹Si, ¹¹³Cd NMR data for the complexes are also reported, analyzed and compared with the results obtained for cadmium-substituted proteins. The similarities and differences between the structures of cadmium complexes and their zinc analogues are discussed.     

Structure,bonding and lattice dynamics of tri- and tetraphenyltin derivatives as studied by Mössbauer and multinuclear NMR spectroscopy

The structure and bonding properties of a number of closely related tetraphenyltin- and triphenyltin chloride compounds have been studied by the ¹¹⁹Sn Mössbauer effect and multinuclear NMR spectroscopy. The comparison of liquid and solid state ¹³C and ¹¹⁹Sn NMR spectra and of glassy solution matrix and neat solid state Mössbauer spectra provides information about the extent of intermolecular association effects in these compounds. The results indicate that all materials with the exception of (p-CF₃Ph)₃SnCl are adequately described as monomeric solids with tetrahedral geometry around the metal atom. For the latter compound spectroscopic evidence for the presence of a five-coordinated tin species is presented.     

Mixed ligand octahedral Co3+ β-diketonates,with acetylacetone,benzoylacetone and dibenzoylmethane. Synthesis,separation of isomers and characterization

Three series of complexes were studied: Co(acetylacetonate)_n(dibenzoylmethanato)_3-n, Co(acetylacetonate)_n(benzoylacetonate)_3-n and Co(dibenzoylmethanato)_n(benzoylacetonate)_3-n. The product mixtures were separated by thin-layer chromatography. Complete separation of all compounds and stereoisomers was obtained. No attempt was made to separate optical isomers which exist for each single stereoisomer. Characterization was by elemental analyses, NMR spectroscopy and the separation characteristics. Electronic absorption spectra were measured in acetonitrile in the 200–800 nm region. Interpretation of the spectral data is provided in terms of ∏ → ∏^*, d → ∏^*, d → d^* transitions. The influence of geometrical isomerism is discussed.     

A N and N Nuclear Magnetic Resonance Study of Nitrogen Metabolism in Shoot-Forming Cultures of White Spruce (Picea glauca) Buds

Nitrogen-14 and nitrogen-15 nuclear magnetic resonance (NMR) spectra were recorded for freshly dissected buds of Picea glauca and for buds grown for 3, 6 and 9 weeks on shoot-forming medium. Resonances for Glu (and other αNH₂ groups), Pro, Ala, and the side chain groups in Gln, Arg, Orn, and γ-aminobutyric acid could be detected in in vivo¹⁵N NMR spectra. Peaks for α-amino groups, Pro, NO₃⁻ and NH₄⁺ could also be identified in ¹⁴N NMR spectra. Perfusion experiments performed for up to 20 hours in the NMR spectrometer showed that ¹⁵N-labeled NH₄⁺ and NO₃⁻ are first incorporated into the amide group of Gln and then in the αNH₂ pool. Subsequently, it also emerges in Ala and Arg. These data suggest that the glutamine synthetase/ glutamate synthase pathway functions under these conditions. The assimilation of NH₄⁺ is much faster than that of NO₃⁻. Consequently after 10 days of growth more than 70% of the newly synthesized internal free amino acid pool derives its nitrogen from NH₄⁺ rather than NO₃⁻. If NH₄⁺ is omitted from the medium, no NO₃⁻ is taken up during 9 weeks and the buds support limited growth by utilizing their endogenous amino acid pools. It is concluded that NH₄⁺ and NO₃⁻ are both required for the induction of nitrate- and nitrite reductase.     

Synthesis and characterization of cobalamines with anionic and neutral phosphorous donor ligands

In dimethyl formamide as solvent aquacobalamine reacts with the triorganyl phosphites 3–7 to give the corresponding (diorganylphosphito-P)cobalamines, their new β-axial ligands [P(O)(OR)₂]⁻ (3a–7a) being formed by partial hydrolysis. In methanol, however, additional methanolysis normally leads to (dimethylphosphito-P)cobalamine with the axial ligand [P(O)-(OMe)₂]⁻ (2a). Exceptions are P(OCH₂CH₂NMe₂)₃ (4) giving a complex with the only partially methanolized chiral ligand [P(O)(OCH₂CH₂NMe₂)- (OMe)]⁻ (4b), too, and the bicyclic phosphite 5 which is also coordinated in the unchanged, nonhydrolyzed form. All complexes are characterized by elementary analysis, electrophoresis, UVVis and ¹H, ³¹P NMR spectra. The chirality of the cobalamine moiety causes diatropism of the two organyl groups in the prochiral ligands [P(O)(OR)₂]⁻ which is well seen in the NMR spectra of the complexes with the methyl and phenyl derivatives 2a and 6a, whereas the spectra with ligands 3a and (in part) 4a are not resolved well enough to distinguish the two forms. With the chiral ligand 4b two diastereomers are obtained in different yields; this asymmetric induction is indicated by the intensities of the respective signals in the NMR spectra.     

13C NMR des alcaloïdes des Strychnos: Les dérivés de l'harmane et de l'usambarensine

¹³C NMR spectra of some tertiary and quaternary indole alkaloids are recorded and the signals assigned. Graphic interpretation of off-resonance spectra and substituent shielding effects together with the effect of N_b-methylation are utilized in the spectral interpretation.     

On the interaction of caffeine with nucleic acids: III. 1NMR studies of caffeine-5'-adenosine monophosphate and caffeine-poly(riboadenylate) interactions

1) The self-association of both caffeine (Cf) and 5'-adenosine monophosphate (AMP) in aqueous solution has been reinvestigated by ¹H NMR. The self-association process is characterized by an isodesmic model. The apparent self-association constants of the vertical stacking process are K_Cf= (10.6 ± 1.0) M^?1 and k_amp = (1.67 ± 0.17) M^?1. The arrangement of the monomeric units in the stacked aggregates is discussed in terms of isoshielding curves theoretically calculated by Giessner-Prettre and Pullman. Models are proposed which are consistent with these and further previous NMR data. 2) The interaction of Cf and AMP has been studied by ^?1 H NMR. The apparent association constant of the complex Cf-AMP is K_C-A = (7.3 ± 1.2) M^?1.Two models of the mutual arrangement of AMP and Cf in the complex are proposed on the basis of the calculated isoshielding curves considering both ring current and local atomic diamagnetic anisotropy effects. 3) The interaction of Cf and poly(riboadenylate), (rA)_n is indicated by a downfield shift of the H-8 line but an upfield shift of the H-2 line in the ¹H NMR spectra of (rA)_n. The concentration dependence of the ¹H NMR shifts of both Cf and (rA)_n can be explained by the existence of two binding mechanisms. We suggest (i) partial insertion of Cf between adjacent base residues of ordered single-stranded regions of (rA)_n and (ii) outside binding of Cf in form of monomeric Cf as well as of self-associated aggregates. The complex geometry of insertion proposed on the basis of the calculated isoshielding curves is characterized by a stronger overlapping of the Cf ring and the H-2 proton of (rA)_n as compared to the H-8 proton.     

Investigation of cobalt(II) substituted carboxypeptidase a interacting with azide and cyanate ions

Cobalt(II)-substituted carboxypeptidase A has been found to reversibly bind N3^? and NCO^?, but not NCS^?, in the pH range 5–10, thus including the pH range of activity of the enzyme. The pH dependence of the anion binding constant is affected by two ionizations, which are assigned as those regulating k_cat and K_M. The electronic and ₁H NMR spectra are consistent with a substantially pseudotetrahedral geometry of the anion derivatives.     

Structure and alignment of the membrane-associated peptaibols ampullosporin A and alamethicin by oriented 15N and 31P solid-state NMR spectroscopy

Ampullosporin A and alamethicin are two members of the peptaibol family of antimicrobial peptides. These compounds are produced by fungi and are characterized by a high content of hydrophobic amino acids, and in particular the α-tetrasubstituted amino acid residue α-aminoisobutyric acid. Here ampullosporin A and alamethicin were uniformly labeled with ¹⁵N, purified and reconstituted into oriented phophatidylcholine lipid bilayers and investigated by proton-decoupled ¹⁵N and ³¹P solid-state NMR spectroscopy. Whereas alamethicin (20 amino acid residues) adopts transmembrane alignments in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) or 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) membranes the much shorter ampullosporin A (15 residues) exhibits comparable configurations only in thin membranes. In contrast the latter compound is oriented parallel to the membrane surface in 1,2-dimyristoleoyl-sn-glycero-3-phosphocholine and POPC bilayers indicating that hydrophobic mismatch has a decisive effect on the membrane topology of these peptides. Two-dimensional ¹⁵N chemical shift - ¹H-¹⁵N dipolar coupling solid-state NMR correlation spectroscopy suggests that in their transmembrane configuration both peptides adopt mixed α-/3₁₀-helical structures which can be explained by the restraints imposed by the membranes and the bulky α-aminoisobutyric acid residues. The ¹⁵N solid-state NMR spectra also provide detailed information on the helical tilt angles. The results are discussed with regard to the antimicrobial activities of the peptides.     

NMR studies of the conformation of the natural sweetener rebaudioside A

Rebaudioside A is a natural sweetener from Stevia rebaudiana in which four β-d-glucopyranose units are attached to the aglycone steviol. Its ¹H and ¹³C NMR spectra in pyridine-d₅ were assigned using 1D and 2D methods. Constrained molecular dynamics of solvated rebaudioside using NMR constraints derived from ROESY cross peaks yielded the orientation of the β-d-glucopyranose units. Hydrogen bonding was examined using the temperature coefficients of the hydroxyl chemical shifts, ROESY and long-range COSY spectra, and proton-proton coupling constants.     

The effect of binding of spider-derived antimicrobial peptides, oxyopinins, on lipid membranes

Oxyopinins (Oxki1 and Oxki2) are antimicrobial peptides isolated from the crude venom of the wolf spider Oxyopes kitabensis. The effect of oxyopinins on lipid bilayers was investigated using high-sensitivity titration calorimetry and ³¹P solid-state NMR spectroscopy. High-sensitivity titration calorimetry experiments showed that the binding of oxyopinins was exothermic, and the binding enthalpies (ΔH) to 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) small unilamellar vesicles (SUVs) were − 18.1 kcal/mol and − 15.0 kcal/mol for Oxki1 and Oxki2, respectively, and peptide partition coefficient (K_p) was found to be 3.9 × 10³ M^− 1. ³¹P NMR spectra of 1,2-dielaidoyl-sn-glycero-3-phosphoethanolamine (DEPE) membranes in the presence of oxyopinins indicated that they induced a positive curvature in lipid bilayers. The induced positive curvature was stronger in the presence of Oxki2 than in the presence of Oxki1. ³¹P NMR spectra of phosphaditylcholine (PC) membranes in the presence of Oxki2 showed that Oxki2 produced micellization of membranes at low peptide concentrations, but unsaturated PC membranes or acidic phospholipids prevented micellization from occurring. Furthermore, ³¹P NMR spectra using membrane lipids from E. coli suggested that Oxki1 was more disruptive to bacterial membranes than Oxki2. These results strongly correlate to the known biological activity of the oxyopinins.     

Metabolic Biomarker Panels of Response to Fusarium Head Blight Infection in Different Wheat Varieties

Metabolic changes in spikelets of wheat varieties FL62R1, Stettler, Muchmore and Sumai3 following Fusarium graminearum infection were explored using NMR analysis. Extensive 1D and 2D ¹H NMR measurements provided information for detailed metabolite assignment and quantification leading to possible metabolic markers discriminating resistance level in wheat subtypes. In addition, metabolic changes that are observed in all studied varieties as well as wheat variety specific changes have been determined and discussed. A new method for metabolite quantification from NMR data that automatically aligns spectra of standards and samples prior to quantification using multivariate linear regression optimization of spectra of assigned metabolites to samples’ 1D spectra is described and utilized. Fusarium infection-induced metabolic changes in different wheat varieties are discussed in the context of metabolic network and resistance.