Stereochemistry of Gd3+ and Mn2+ interactions with D-gluconamide derivatives by 13C NMR spectroscopy

Natural abundance ¹³C nuclear magnetic resonance spectroscopy (¹³C NMR) was used to study the mode of binding of Gd³⁺ and Mn²⁺ to the polyol portion of several synthetic D-gluconamides. The results indicate that Gd³⁺ forms a single, unique binding structure requiring three oxygen atoms. The binding of Mn²⁺ to the polyol portion of these compounds appears to be nonspecific. The carbohydrate containing model compounds studied may be used to design new metal-ion chelating agents.     

Binding study of the drug cis-dichlorodiammineplatinum(II)to G p5′ and dGp5′ by high resolution proton and carbon-13 NMR spectroscopy

The molecular mode of action leading to the anticancer activity of the drug cis-diamminedichloroplatinum(II), cis-DDP or cis-platinum is still the subject of speculation. In the present high field (400 MHz) ¹H NMR study the results on coupling constants for cis- and trans-diammine bis(guanosine- 5′-monophosphate) and (d-guanosine-5′-monophosphate)platinum(II) complexes are presented and discussed. The ¹H and ¹³C NMR chemical shifts obtained are consistent with the drug binding to N7 of each guanine. It has been found that the drug induces different conformational changes in the nucleotide from the trans-DDP isomer.     

NMR studies on UO22+ complexes with pyridoxal

The interaction of pyridoxal with dioxouranium(VI) acetate was studied by ¹H and ¹³C NMR measurements in D₂O and CD₃OD.The results indicate that the preferred bonding site is the C-3O^? donor, and the major species obtained under the experimental conditions used is the equimolar complex.     

FT-IR and 1H NMR spectroscopic evidence of sugar ring conformational change in NH4GpG on complexation to form cis-[Pt(NH3)2(GpG)]+

The conformational change of the ribose ring in NH₄GpG and cis-[Pt(NH₃)₂(GpG)]⁺ was confirmed by FT-IR spectroscopic evidence as being C2′-endo, C3′-endo, anti, gg sugar ring pucker in the solid state. These results were compared with ¹H NMR spectral data in aqueous solution. The FT-IR spectrum of NH₄GpG shows marker bands at 802 cm^?1 and 797 cm^?1 which are assigned to the C3′-endo, anti, gg sugar-phosphate vibrations of ribose (?pG) and ribose (Gp?), respectively. The FT-IR spectrum of cis-[Pt(NH₃)₂(GpG)]⁺ (with N7N7 chelation in the GpG sequence) shows a marker band at 800 cm^?1 which is assigned to the C3′-endo, and a new shoulder band at 820 cm^?1 related to a C2′-endo ring pucker. The ribose conformation of (?pG) moiety in NH₄-GpG, C3′-endo, anti, gg changes into C2′-endo, anti, gg when a platinum atom is chelated to N7N7 in the GpG sequence.     

Cu2+-hyaluronic acid complex: Spectrophotometric detection

Hyaluronic forms a complex with Cu²⁺ showing an absorption band at 239 nm. The results indicate a 2:1 polymer-Cu²⁺ ratio in the complex formation with an equilibrium constant, 3 × 10³. Glucuronic acid, one of the monomers of hyaluronic acid, reacts with the cupric ion, showing a similar band at 235 nm, but the complex formation involves multiple equilibria. No complex formation was detected with N-acetylglucosamine—the other monomer of hyaluronic acid—and Cu²⁺. The absorption bands of the copper complexes with the polymer and glucuronic acid are attributed to a charge-transfer involving ligand to the metal ion.     

Application of luminescence and absorption spectroscopy and x-ray methods to studies of Ln+3 ions interaction with aminoacids

The Nd⁺³, Ho⁺³ and Eu⁺³ compounds with glycine, alanine and glutamic acid were synthesized and obtained as monocrystals.Absorption spectra in the range 8000–35 500 cm^?1 were measured along the crystallographic axes at room temperature on a Cary 14 spectrophotometerLuminescence spectra were recorded at the same temperature in the range 9000–16 600 cm^?1.Intensities of the ff transitions were analyzed on the basis of the Judd theory, taking the dependence of intensity on the crystallographic axis position into account.Considerable differences in hypersensitive transitions in crystals with alanine, glycine and glutamic acid, whose symmetry changed from triclinic to monoclinic, were explained in terms of differences in the MeO distances.     

13C NMR evidence for three slowly interconverting conformations of the dihydrofolate reductase-NADP+-folate complex

The 3-carboxamido-¹³C resonance of NADP⁺ in its complex with $\text{Lactobacillus}\text{casei}$ dihydrofolate reductase and folate has been studied as a function of pH. At low pH a single resonance is observed, while at high pH two resonances are observed, neither of which has the same chemical shift as that seen at low pH. The rates of interconversion between the three states of the complex represented by these resonances are < 19 s^?1 at 11°C.     

1H-1H and 13C-13C vicinal coupling constants and amino acid side chain conformation in peptides

The vicinal coupling constants ¹³C′-¹³C^γ were measured in aspartic acid and phenylalanine (85 % ¹³C enrichment) as free amino acids and in the peptides Asp-Pro and Gly-Pro-Phe. These coupling constants used in connection with those between the α -and the β-protons provide the unambiguous assignment of rotamers I and II in the Asp and Phe side chains. The method is generally applicable to other amino acids and residues even in large peptides. A possible set of J_g^c,c and J_t^c,c values is proposed for the use of carbon 13-carbon 13 vicinal coupling constants in the side chain conformational studies of amino acid residues with a free carboxyl group.     

Reaction of PtOH complexes with CO2: synthesis and X-ray structure of (PBz3)4Pt2(Ph)2(η1,η1,μ-CO3)·(toluene)

The reaction of (diphoe)Pt(CH₂CN)(OH) and trans-(PBz₃)₂Pt(Ph)(OH) with CO₂ is reported as producing dimeric, bridged carbonato complexes of the type: P₄Pt₂(R)₂(CO₃). The crystal and molecular structure of (PBz₃)₄Pt₂(Ph)₂(μ-CO₃)·(toluene) is also reported, showing η¹, η¹ bonding. The reaction is recognized to proceed in a stepwise fashion through bicarbonato intermediates.     

Solution and solid state behavior of Co2+, Ni2+ and Zn2+ tosylaminoacidate systems: Crystal and molecular structure of bis(N-tosylglycinato)tetraaquocobalt(II) and bis(N-tosyl-β-alaninato)tetraaquozinc(II) complexes

The interactions between N-tosylamino acids and cobalt(II), nickel(II) and zinc(II) ions in aqueous solution and in the solid state have been investigated. From concentrated aqueous solutions, compounds of general formula [M(II)(N-tosylaminoacidato)₂(H₂O)₄](M = Co(II), Ni(II) and N-tosylaminoacidato = N-tosylglycinate (Tsgly^?), N-tosyl-α- and -β-alaninate (Ts-α- and Ts-β-ala^?); M = Zn(II) and N-tosylaminoacidate = Tsgly^?, Ts-β-ala^?) and [Zn(II)(N- tosylaminoacidato)₂(H₂O)₂] were isolated and characterized by means of thermogravimetric, electronic and infrared spectra. For two of them: [Co(Tsgly)₂(H₂O)₄](I) and [Zn(Ts-β-ala)₂(H₂O)₄](II) the crystal and molecular structures were also determined. Both compounds crystallize in the monoclinic space group P2₁/c, with two formula units in a cell of dimensions: a = 13.007(6), b = 5.036(2), c = 18.925(7) Å, β = 102.33(3)° for (I) and a = 14.173(6), b = 5.469(2), c = 17.701(7) Å, β = 106.63(3)° for (II). The structures were solved by the heavy-atom method and refined by least-squares calculations to R = 0.031 and 0.064 for (I) and (II) respectively. The cobalt and zinc atoms lie in the centers of symmetry, each bonded to two amino- acid molecules through a carboxylic oxygen atom and four water molecules in a slightly tetragonally distorted octahedral geometry. The second carboxylic oxygen atom is not involved in metal coordination. Electronic and X ray-powder spectra suggest that the tetrahydrate complexes of Co²⁺, Ni²⁺ and Zn²⁺ ions of the same amino acids are isomorphous and isostructural. No coordinative interactions between ligand and metal ions were found in aqueous solution on varying the pH values before hydroxide precipitation.     

Zn2+, Mg2+, and H+ binding to d-fructose 1,6-bisphosphate studied by 31P and 1H NMR

The anomeric composition and mutarotation rates of fructose 1,6-bisphosphate were determined in the presence of 100 mm KCl at pH 7.0 by ³¹P NMR. At 23 and 37 °C the solution contains (15 ± 1)% of the α anomer. The anomeric rate constants at 37 °C are (4.2 ± 0.4) s^?1 for the β → α anomerization and (14.9 ± 0.5) s^?1 for the reverse reaction. A D₂O effect between 2.1 and 2.6 was found. From acid base titration curves it appeared that the pK values of the phosphate groups range from 5.8 to 6.0. Mg²⁺ and Zn²⁺ bind preferentially to the 1-phosphate in the α-anomeric position. Zn²⁺ has a higher affinity for this phosphate group than Mg²⁺ has. At increasing pH the fraction α anomer decreases slightly. At increasing Mg²⁺/fructose 1,6-bisphosphate ratios the fraction α anomer increases till 19% at a ratio of 20. Proton and probably Mg²⁺ binding decreases the anomerization rate. The time-averaged preferred orientation of the 1-phosphate along the C₁O₁ bond of the α conformer is strongly pH dependent, gauche rotamers being predominant at pH 9.4. In the presence of divalent cations the orientation is biased toward trans. A mechanistic model is proposed to explain the Zn²⁺, Mg²⁺, and pH-dependent behavior of the gluconeogenic enzyme fructose 1,6-bisphosphatase.     

New preparations and molecular structures of cis-MCl2(Ph2PCH2PPh2)2, M = Ru,Os and trans-RuCl2(Ph2PCH2PPh2)2

The title compounds were made by reacting bis(diphenylphosphino)methane (dppm) with reduced solutions of OsCl₆^4? and Ru₂OCl₁₀^4?. The crystal and molecular structures of these compounds have been determined form three-dimensional X-ray study. The cis-isomers crystallize with one CHCl₃ per molecule of the complex. All three compounds crystallize in the monoclinic space group P2₁/n with unit cell dimensions as follows: Cis-OsCl₂(dppm)₂·CHCl₃: a = 13.415(4) Å, b = 22.859(4) Å, c = 16.693(3) Å, β = 105.77(3)°, V = 4926(3) ų, Z = 4. cis-RuCl₂(dppm)₂·CHCl₃: a = 13.442(3) Å, b = 22.833(7) Å, c = 16.750(4) Å, β = 105.53(2)°, V = 4953(3) ų, Z = 4. trans-RuCl₂(dppm)₂: a = 11.368(7) Å, b = 10.656(6) Å, c = 18.832(12) Å; β = 103.90(6)°, V = 2213(7) ų; Z = 2. The structures were refined to R = 0.044 (R_w = 0.055) for cis-OsCl₂(dppm)₂·CHCl₃; R = 0.065 (R_w = 0.079) for cis-RuCl₂(dppm)₂·CHCl₃ and R = 0.028 (R_w = 0.038) for trans-RuCl₂(dppm)₂. The complexes are six coordinate with stable four-membered chelate rings. The PMP angle in the chelate rings is ca. 71° in each case.     

The crystal and molecular structure of [Co(NH3)5PO4]·3H2O,a Na+-K+ ATPase probe

The title compound, Co(NH₃)₅PO₄, prepared by a modified literature procedure, was used to study the inhibition of Na⁺-K⁺ ATPase and to serve as a structural model for ML₄(nucleotide) complexes. The structure was determined by single crystal X-ray diffraction techniques. The crystals are monoclinic, space group P2₁/n, a = 8.638(3), b = 14.517(2), c = 9.145(2) Å, and β = 112.71(2)°. The structure, solved by the heavy atom method to an R value of 3.3% for 1924 reflections, consists of a slightly distorted octahedron with the cobalt bound to the five amines and a monodentate phosphate. Solution structural data is taken from ³¹P NMR measurements. From comparison with other metal phosphate complexes it is concluded that multiple monodentate coordination of a di- or triphosphate closely resembles the coordination of a monophosphate This is based on the similarity of the MO bond angle which is 129.6° in the present example.     

Synthesis,FT-IR and 1H NMR studies of alkali and alkaline earth metal complexes with guanosine

The synthesis of complexes of Li(I), K(I), Mg(II), Ca(II) and Ba(II) with guanosine in basic non aqueous solutions is described. The complexes were of two types: (1) complexes having the general formula, M(Guo)_nX_m·YH₂O·ZC₂H₅OH, where M = Mg(II), Ca(II), Ba(II) and Li(I), n = 1,2,4, X = Cl^?, Br^?, NO₃^?, ClO₄^? and OH^?, m = 1,2, Y = 0?6 and X = 0?2, and (2) complexes with the general formula, M(GuoH-1)(OH)_n^?1·YH₂O, where M = K(I), Ca(Il) and Ba(II), GuoH-1 =Ionized guanosine at N₁, n = 1,2 and Y = 1?3. The complexes are characterized by their proton nuclear magnetic resonance (¹H NMR) and Fourier transform infrared (FT-IR) spectra. The FT-IR and ¹H NMR data of the non ionized nucleoside complexes suggest that the metal binding is through the N₇-site of guanine and that the anion (X) is hydrogen bonded to N₁H and NH₂ groups. In the N₁-ionized guanosine complexes the metal binding is via the O₆^? of guanine. All the complexes formed exhibited a transition of the sugar conformation from C₂′-endo/anti in the free nucleoside to C₃′-endo/anti in the metal complexes.     

Effects of phenoxide ligation: Synthesis and characterization of the [Mo2Fe6S8(SEt)3(OPh)6]3− ion

Reaction of phenol with an alkylthiolate-ligated double cubane complex effects phenolate substitution at the terminal positions; the product can be isolated as its benzyltriethylammonium salt. The phenolate cluster possesses unaltered magnetic properties and blue shifted optical spectra, and undergoes ligand exchange reactions with electrophiles as expected for terminal phenolate substitution. Increased isotropic proton NMR shifts and large negative shifts in corresponding first and second reduction potentials are consistent with increased donation of electron density to the [MoFe₃S₄]³⁺ cores for phenolate versus thiophenolate terminal ligands to iron. Similar behavior has been observed for Fe₄S₄, Fe₂S₂ and MoS₂Fe systems.