Solution NMR Spectra Research Articles

Solution NMR to Investigate Gating in the NaK Channel

The NaK channel is small bacterial non-selective cation channel that has proved to be an excellent model system to study basic biochemical and biophysical question concerning ion channels. NaK has been crystalized in the closed state and as an open channel using a truncated construct (NaKΔ19) missing the M0 helix. NaK shares a homologous architecture to tradition K+ channel pores such as KcsA, but it is non selective. However, small mutation in the selectivity filter can change NaK into a K+ selective channel. Solution NMR spectra of NaK solubilized in isotropic bicelles show superior spectral resolution, allowing for detailed solution NMR studies of NaK structure and dynamics in bicelles. Regulation of NaK is currently unknown, however the location of the amphipathic M0 helix on the membrane surface packed against two adjacent monomers makes it a likely contributor to channel gating. Preliminary work suggests that the full length NaK channel exists in at least two states in slow exchange at 45oC. Mutations to the M0 helix shift the equilibrium to a single population, supporting a role for the M0 helix in determining the structural and functional state of the channel. NaKΔ19 NMR spectra are also sensitive to addition of amino acids just before the M1 helix. This suggests that this region connecting the M0 helix to the M1 helix is important in determining NaK dynamics. Comparison of our results with functional studies highlights specific interactions between the M0 helix and the pore domain that determine the structural and functional state of the channel.

ChemInform Abstract: NMR Discrimination in Nonrigid Prochiral Solutes Dissolved in Chiral Liquid Crystals: Symmetry Considerations

AbstractReview: 39 refs.

Stacked naphthyls and weak hydrogen-bond interactions govern the conformational behavior of P-resolved cyclic phosphonamides: a combined experimental and computational study.

P-Enantiomerically pure cyclic phosphonamides have been synthesized via a cyclization reaction of (S,S)-aminobenzylnaphthols with chloromethylphosphonic dichloride. The reaction is highly stereoselective and gives almost exclusively (S,S,SP)-cyclic phosphonamides in good yields. Analysis of the X-ray crystal structures shows clearly that the cyclization reaction forces the two naphthyl rings into a stable parallel displaced stacking assembly and indicates also the existence of intramolecular CH···π interactions and weak forms of intermolecular hydrogen bondings, involving the oxygen and the chlorine atoms. QM computations and NMR spectra in solution confirm the stacked molecular assembly as the preferred arrangement of the two naphthyl groups.

An experimental and density functional study on conformational and spectroscopic analysis of 5-methoxyindole-2-carboxylic acid

In this article, a brief conformational and spectroscopic characterization of 5-methoxyindole-2-carboxylic acid (5-MeOICA) via experimental techniques and applications of quantum chemical methods is presented. The conformational analysis of the studied molecule was determined theoretically using density functional computations for ground state, and compared with previously reported experimental findings. The vibrational transitions were examined by measured FT-IR and FT-Raman spectroscopic data, and also results obtained from B3LYP and CAM-B3LYP functionals in combination with 6-311++G(d,p) basis set. The recorded proton and carbon NMR spectra in DMSO solution were analyzed to obtain the exact conformation. Due to intermolecular hydrogen bondings, NMR calculations were performed for the dimeric form of 5-MeOICA and so chemical shifts of those protons were predicted more accurately. Finally, electronic properties of steady compound were identified by a comparative study of UV absorption spectra in ethanol and water solution and TD-DFT calculations.

NMR discrimination in nonrigid prochiral solutes dissolved in chiral liquid crystals: symmetry considerations.

Enantiodiscrimination in the NMR spectra of flexible prochiral solutes dissolved in chiral liquid crystals (CLCs) is reviewed and compared with the analog phenomenon in such rigid solutes. In rigid prochiral solutes, the discrimination is brought about by the cancellation of improper symmetry elements upon dissolving in CLC within the frame of solute-solvent ordering mechanisms. If this reduction in symmetry renders the ordering of enantiotopic sites dissimilar, spectral discrimination may be observed. Symmetry considerations indicate that this is only possible for improper nonaxial groups lacking inversion symmetry. Nonrigid prochiral solutes consist of rapidly (on the NMR timescale) interconverting enantiomers, in which the racemization is accompanied by exchange of nonequivalent sites. These sites become, on the average, enantiotopically related, and in CLC, they exhibit spectral discrimination. The mechanism of the effect and the symmetry selection rules are different for the two cases. Specifically, the discrimination in flexible prochiral compounds results from the different ordering of the interchanging enantiomers in CLC. Using Altman's definition of average symmetry (Proc. R. Soc. A, 1967, 298, 184), selection rules for the phenomenon are derived. It follows that chiral discrimination in nonrigid prochiral solutes is much more abundant and can occur in all symmetry types except those possessing inversion. In particular, contrary to earlier thoughts, the effect can occur in compounds with axial symmetry. Illustrative examples of such studies with particular emphasis on compounds with average axial symmetry of the type D(3h), C(3v) and C(3h) are reviewed in this contribution.

Large variations in acidity of terminal amide bonds in histamine-containing peptides as measured by proton DNMR

The main objective of these studies is to quantitatively estimate pK variations of individual amide bonds as a function of the ionization state of end groups in peptides, determined on measuring macro- and micro- (if any) ionization constants. 1H NMR spectra of aqueous solutions of eight model substrates were consequently recorded using a water suppression sequence, within large pH ranges. A set of programs was devised to treat NMR data over the entirety of pH-dependent NMR patterns, in order to smooth out errors arising in handling individual spectra. Rates of amide proton abstraction by hydroxide ions were obtained from the coalescence of methylene coupled protons and the decrease of NH bond signal intensities, allowing us to estimate and discuss peptide pKs on assuming back reprotonation at a diffusion-limited rate. Cis–trans isomerization rates in two substrates bearing a tert-Butyloxycarbonyl terminal group were put in parallel with the acidity of carbamic protons.

Half- and Mixed-Sandwich Uranium Permethylpentalene Compounds

The synthesis and characterization of a series of U(IV) permethylpentalene complexes has been enabled by the development of an effective synthesis of the new Pn*U synthon [Pn*U(μ-Cl)4][Li(TMEDA)]2, which has allowed access to a set of half-sandwich Pn*U complexes. The compounds have been characterized via variable-temperature NMR and in some cases by structural analysis. The temperature dependence of the NMR solution spectra show a complex interplay between fluxional ligand dynamics and the effects of a paramagnetic f2 uranium center.

Synthesis and characterization of higher amino acid Schiff bases, as monosodium salts and neutral forms. Investigation of the intramolecular hydrogen bonding in all Schiff bases, antibacterial and antifungal activities of neutral forms

Schiff bases derived from 5-nitro-salicylaldehyde and 4-aminobutyric acid, 5-aminopentanoic acid and 6-aminohexanoic acid were synthesized both as monosodium salts (1a–3a) and neutral forms (1b–3b). The monosodium-Schiff bases were characterized by elemental analysis, 1H/13C NMR, IR, powder XRD, UV–vis spectra and conductivity measurements. The neutral-Schiff bases were characterized by elemental analysis, 1H/13C NMR, 2D NMR (HMQC), mass, IR, powder XRD, UV–vis spectra and conductivity measurements. The intramolecular hydrogen bonding and related tautomeric equilibria in all the Schiff bases were studied by UV–vis and 1H NMR spectra in solution. Additionally, the neutral-Schiff bases were screened against Staphylococcus aureus-EB18, S. aureus-ATCC 25923, Escherichia coli-ATCC 11230, Candida albicans-M3 and C. albicans-ATCC 16231.

Cu(II) and Zn(II) complexes of new 12- and 13-membered dioxopolyazacycloalkanes with pendant amide groups

The acid groups of the pendant arms of the ligands macrocyclic dioxotetraazacycloalkanediacetic acid, of 12- and 13-membered, were modified by amide groups. The modification was carried out using amidation reactions in a microwave reactor with the amines: N-butylamine, N-hexylamine, and phenylethylamine in presence of diisopropylcarbodiimide (DIC) and N-hydroxybenzotriazole (HOBt). Amidation of the pendant arms of the macrocyclic ligands increases the coordination sites of the molecules and decreases basicity the amino nitrogen atoms. Their Cu2+ chelates were characterized by electronic absorption spectra and their Zn2+ chelates were characterized by 1H NMR spectra in solution. Electronic spectra show that all the Cu2+ complexes derivatives from the ligands of 12-membered, have similar structures in acid and alkaline medium, but the complexes derived from the ligands of 13-members show a different geometry: octahedral geometry in acid medium and in a neutral or alkaline environment have a square planar structure, where the two nitrogen atoms of deprotonated amide and two amine nitrogen atoms are coordinated to the central metal ion. Coordination studies by 1H NMR of all ligands to zinc, indicating that the metal is coordinated with the donor atoms of the macrocyclic rings, besides the oxygen atoms of the amide carbonyl groups of the pendant arms.

π-Excess σ2 P,O Hybrid Ligands: Synthesis of the First 4-Methoxy-1H-1,3-benzazaphospholes

The synthesis of the first 4-methoxy-substituted 1,3-benzazaphosphole was accomplished by using a <i>C</i>,<i>O</i>-dilithium intermediate­ generated from <i>N</i>-(3-methoxyphenyl)-2,2-dimethylpropanamide and butyllithium. This intermediate was subjected either to direct phosphonylation or to a bromination and phosphonylation sequence; subsequent reductive cyclization with excess lithium aluminum hydride led to the desired product. In addition, <i>N</i>-(2,2-dimethylpropyl)-3-methoxy-2-phosphinoaniline, formed in a side reaction, was cyclized with (dimethoxymethyl)dimethylamine to give 1-(2,2-dimethylpropyl)-4-methoxy-1<i>H</i>-1,3-benzazaphosphole. The behavior of these +<i>M</i>-substituted π-excess aromatic σ² <i>P</i>-heterocycles towards moisture is reported, together with their ¹H, ¹³C, and ³¹P solution NMR spectra and a crystal-structure analysis. The new compounds represent potential σ² <i>P</i>,<i>O</i> hybrid or chelate ligands with a high π-density at the phosphorus atom.

Five-Coordinate [PtII(bipyridine)2(phosphine)]n+ Complexes: Long-Lived Intermediates in Ligand Substitution Reactions of [Pt(bipyridine)2]2+ with Phosphine Ligands

The reaction of [Pt(N-N)2](2+) [N-N = 2,2'-bipyridine (bpy) or 4,4'-dimethyl-2,2'-bipyridine (4,4'-Me2bpy)] with phosphine ligands [PPh3 or PPh(PhSO3)2(2-)] in aqueous or methanolic solutions was studied by multinuclear ((1)H, (13)C, (31)P, and (195)Pt) NMR spectroscopy, X-ray crystallography, UV-visible spectroscopy, and high-resolution mass spectrometry. NMR spectra of solutions containing equimolar amounts of [Pt(N-N)2](2+) and phosphine ligand give evidence for rapid formation of long-lived, 5-coordinate [Pt(II)(N-N)2(phosphine)](n+) complexes. In the presence of excess phosphine ligand, these intermediates undergo much slower entry of a second phosphine ligand and loss of a bpy ligand to give [Pt(II)(N-N)(phosphine)2](n+) as the final product. The coordination of a phosphine ligand to the Pt(II) ion in the intermediate [Pt(N-N)2(phosphine)](n+) complexes is supported by the observation of (31)P-(195)Pt coupling in the (31)P NMR spectra. The 5-coordinate nature of [Pt(bpy)2{PPh(PhSO3)2}] is confirmed by X-ray crystallography. X-ray crystal structural analysis shows that the Pt(II) ion in [Pt(bpy)2{PPh(PhSO3)2}]·5.5H2O displays a distorted square pyramidal geometry, with one bpy ligand bound asymmetrically. These results provide strong support for the widely accepted associative ligand substitution mechanism for square planar Pt(II) complexes. X-ray structural characterization of the distorted square planar complex [Pt(bpy)(PPh3)2](ClO4)2 confirms this as the final product of the reaction of [Pt(bpy)2](2+) with PPh3 in CD3OD. The results of density functional calculations on [Pt(bpy)2](2+), [Pt(bpy)2(phosphine)](n+), and [Pt(bpy)(phosphine)2](n+) indicate that the bonding energy follows the trend of [Pt(bpy)(phosphine)2](n+) > [Pt(bpy)2(phosphine)](n+) > [Pt(bpy)2](2+) for stability and that the formation reactions of [Pt(bpy)2(phosphine)](n+) from [Pt(bpy)2](2+) and [Pt(bpy)(phosphine)2](n+) from [Pt(bpy)2(phosphine)](n+) are energetically favorable. These calculations suggest that the driving force for the formation of [Pt(bpy)(phosphine)2](n+) from [Pt(bpy)2](2+) is the formation of a more energetically favorable product.

Bioinspired Insights into Silicic Acid Stabilization Mechanisms: The Dominant Role of Polyethylene Glycol-Induced Hydrogen Bonding

Mono- and disilicic acids were stabilized by uncharged polyethylene glycols (PEGs) in silica-supersaturated solutions (the starting solution contained 500 ppm/8.3 mM sodium orthosilicate, Na2SiO3·5H2O, expressed as SiO2) at pH = 7, most likely by hydrogen bonding between the silanol groups and -CH2-CH2-O-ether moieties. The stabilization was monitored by measuring molybdate-reactive silica and also by a combination of liquid- and solid-state (29)Si NMR spectroscopy. It depends on PEG concentration (20-100 ppm) and molecular weight (1550-20,000 Da). Two narrow (29)Si NMR signals characteristic for monosilicic acid (Q(0)) and disilicic acid (Q(1)) can be observed in (29)Si NMR spectra of solutions containing PEG 10000 with intensities distinctly higher than the control, that is, in the absence of PEG. Silica-containing precipitates are observed in the presence of PEG, in contrast to the gel formed in the absence of PEG. These precipitates exhibit similar degrees of silica polycondensation as found in the gel as can be seen from the (29)Si MAS NMR spectra. However, the (2)D HETCOR spectra show different (1)H NMR signal shifts: The signal due to H-bonded SiOH/H2O, which is found at 6 ppm in the control, is shifted to ~7 ppm in the PEG-containing precipitate. This indicates the formation of slightly stronger H-bonds than in the control sample, most likely between PEG and the silica species. The presence of PEG in these precipitates is unequivocally proven by (13)C CP MAS NMR spectroscopy. The (13)C signal of PEG significantly shifts and is much narrower in the precipitates as compared to the pristine PEG, indicating that PEG is embedded into the silica or at least bound to its surface (or both), and not phase separated. FT-IR spectra corroborate the above arguments. The H-bonding between silanol and ethereal O perturbs the band positions attributed to vibrations involving the O atom. This work may invoke an alternative way to envision silica species stabilization (prior to biosilica formation) in diatoms by investigating possible scenarios of uncharged biomacromolecules playing a role in biosilica synthesis.

NMR Structural Studies of Antimicrobial Peptides as In-Plane Helix of Membrane Proteins

Antibiotics from organic compounds are a long established part of our defense against bacterial pathogens. Their wide use has led to pathogens' increased drug resistance and the need to find novel classes of antimicrobial peptides as alternatives to antibiotics. Lactophoricin (LPcin), a cationic amphipathic peptide consists of 23-mer peptide, corresponds to the carboxy terminal 113-135 region of component-3 of proteose-peptone. LPcin is a good candidate as a peptide antibiotic because it has an antibacterial activity but no hemolytic activity. Three different analogs of LPcin, LPcin-yk2 which has mutant amino acids, LPcin-yk1 and LPcin-yk3 that has shorter mutant amino acids are recently developed by using peptide engineering in our laboratory. These three LPcin analogs show better antibioitic activities than wild-type LPcin and no toxicity at all. In order to understand the structural correlation between LPcin analogs structure and antimicrobial activity under the membrane environments, we tried to express and purify as large as amounts of LPcin and three different LPcin analogs. We finally optimized and succeed to overexpress in the form of fusion protein in Escherichia coli and purified with biophysical techniques like Ni-affinity chromatography, dialysis, entrifuge, chemical cleavage, and reversed-phase semiprep HPLC. In here, we will present the optimizing processes for high-yield expression and purification and solution NMR spectra and solid state NMR spectra for antimicrobial mechanisms.

Red emitting [Ir(C^N)2(N^N)]+complexes employing bidentate 2,2′:6′,2′′-terpyridine ligands for light-emitting electrochemical cells

2,2':6',2''-Terpyridine (tpy), 4'-(4-HOC6H4)-2,2':6',2''-terpyridine (1), 4'-(4-MeOC6H4)-2,2':6',2''-terpyridine (2), 4'-(4-MeSC6H4)-2,2':6',2''-terpyridine (3), 4'-(4-H2NC6H4)-2,2':6',2''-terpyridine (4) and 4'-(4-pyridyl)-2,2':6',2''-terpyridine (4) act as N^N chelates in complexes of the type [Ir(C^N)2(N^N)][PF6] in which the cyclometallating ligand, C^N, is derived from 2-phenylpyridine (Hppy) or 3,5-dimethyl-1-phenyl-1H-pyrazole (Hdmppz). The single crystal structures of eight complexes have been determined, and in each iridium(III) complex cation, the non-coordinated pyridine ring of the tpy unit is involved in a face-to-face π-stacking interaction with the cyclometallated ring of an adjacent ligand. Solution NMR spectra of the [Ir(ppy)2(N^N)](+) complexes are consistent with the presence of a non-classical hydrogen bond between the non-coordinated N-donor of the tpy domain and a CH unit of one pyridine ring of an adjacent ppy(-) ligand; the presence of the N···HC interaction was confirmed in one of the solid-state structures. The pendant pyridine ring of the coordinated tpy undergoes hindered rotation on the NMR timescale at 295 K. In CH2Cl2, the complexes are orange or red emitters, with λ(max)(em) in the range 580 to 642 nm; photoluminescence quantum yields (PLQY) are <10%, and lifetimes range from 54 to 136 ns. N-Methylation of the pendant 4'-(4-pyridyl) group in [Ir(dmppz)2(pytpy)][PF6] essentially quenches the emission. Light-emitting electrochemical cells (LECs) have been fabricated in a thin film configuration; the emission spectra of the LECs are red-shifted with respect to the PL spectra of the corresponding complex in thin film configuration. For the device incorporating [Ir(ppy)2(pytpy)][PF6], the PL to EL red-shift is extremely large and this is indicative of a different emitting state being involved. The most efficient devices used [Ir(ppy)2(1)][PF6], [Ir(ppy)2(2)][PF6] or [Ir(ppy)2(3)][PF6] in the emissive layer; the devices exhibited rapid turn-on times, but showed relatively low efficiencies in accordance with the solid state photoluminescence quantum yields.

NMR Study of the Structures of Repeated Sequences, GAGXGA (X = S, Y, V), in Bombyx mori Liquid Silk

The silk fibroin stored in the silk gland of the Bombyx mori silkworm, called "liquid silk", is spun out and converted into the silk fiber with extremely high strength and high toughness. Therefore it is important to determine the silk structure before spinning called Silk I at an atomic level to clarify the fiber formation mechanism. We proposed the repeated type II β-turn structure as Silk I in the solid state with the model peptide (AG)15 and several solid state NMR techniques previously. In this paper, the solution structure of native "liquid silk" was determined with solution NMR, especially for tandem repeated sequences with (GAGXGA)n (X = S, Y, V) and GAASGA motifs in the B. mori silk fibroin. The assignment of the (13)C, (15)N, and (1)H solution NMR spectra for the repetitive sequence motifs was achieved, and the chemical shifts were obtained. The program, TALOS-N, to predict the backbone torsion angles from the chemical shifts of proteins was applied to these motifs with (13)Cα, (13)Cβ, (13)CO, (1)Hα, (1)HN, and (15)N chemical shifts. The twenty-five best matches of torsion angles (ϕ, φ) were well populated and mainly fell into the regions for typical type II β-turn structures in the (ϕ, φ) map for the GAGXGA (X = S, Y, V) motifs. In contrast, (ϕ, φ) plots for motif GAASGA were scattered, indicating that the motif is in a disordered structure. Furthermore, inter-residue HN-Hα NOE cross peaks between i-th and (i+2)th residues in GAGXGA (X = S, Y, V) motifs were observed, supporting the repeated type II β-turn structure. Thus, we could show the presence of the repeated type II β-turn structure in "liquid silk".

A comparative study of selected disperse azo dye derivatives based on spectroscopic (FT-IR, NMR and UV–Vis) and nonlinear optical behaviors

In the present work, a combined experimental and quantum chemical study on ground state equilibrium structure, spectroscopic and nonlinear optical properties of selected disperse azo dye molecules are reported. The vibrational transitions were identified based on the recorded FT-IR spectra in the range of 4000–400cm−1 for solid state, simulated IR spectra and total energy distribution (TED) of vibrational modes. The chemical shifts were determined from the results of observed 1H and 13C NMR spectra in chloroform and dimethylsulfoxide solution. The DFT/gauge-invariant atomic orbital (GIAO) methodology was applied to predict the magnetic properties. Electronic properties were carried out by UV–Vis spectroscopy and TD-DFT/CIS approach. The nonlinear optical (NLO) features were addressed theoretically. A detailed description of spectroscopic and NLO behaviors of studied disperse azo dyes was reported with the help of comparison of experimental measurements and theoretical calculations.

NMR studies of thermo-responsive behavior of an amphiphilic poly(asparagine) derivative in water

The thermo-responsive behavior of a unique biocompatible polymer, poly(N-substituted α/β-asparagine) derivative (PAD), has been studied with several NMR methods. The 1H and 13C solution NMR measurements of the PAD in DMSO-d6 were used to investigate the isolated polymer and perform spectral assignments. By systematic addition of D2O we have tracked structural changes due to aggregation and observed contraction of hydrophilic side chains. Solution and cross polarization/magic angle spinning (CP/MAS) 13C NMR approaches were implemented to investigate the aggregates of the PAD aqueous solution during the liquid to gel transition as the temperature was increased. At temperatures near 20 °C, all of the peaks from the PAD were observed in the 13C CP/MAS and 13C solution NMR spectra, indicating the presence of polymer chain nodes. Increasing the temperature to 40 °C resulted in a partial disentanglement of the nodes due to thermal agitation and further heating resulted in little to no additional structural changes. Deuterium T1–T2 and T2–T2 two-dimensional relaxation spectroscopies using an inverse Laplace transform, were also implemented to monitor the water–PAD interaction during the phase transition. At temperatures near 20 °C the dynamical characteristics of water were manifested into one peak in the deuterium T1–T2 map. Increasing the temperature to 40 °C resulted in several distinguishable reservoirs of water with different dynamical characteristics. The observation of several reservoirs of water at the temperature of gel formation at 40 °C is consistent with a physical picture of a gel involving a network of interconnected polymer chains trapping a fluid. Further increase in temperature to 70 °C resulted in two non-exchanging water reservoirs probed by deuterium T2–T2 measurements.

Monomeric and dimeric structures analysis and spectroscopic characterization of 3,5-difluorophenylboronic acid with experimental (FT-IR, FT-Raman, 1H and 13C NMR, UV) techniques and quantum chemical calculations

The spectroscopic properties of 3,5-difluorophenylboronic acid (3,5-DFPBA, C6H3F2B(OH)2) were investigated by FT-IR, FT-Raman UV–Vis, 1H and 13C NMR spectroscopic techniques. FT-IR (4000–400cm–1) and FT-Raman spectra (3500–10cm–1) in the solid phase and 1H and 13C NMR spectra in DMSO solution were recorded. The UV spectra that dissolved in ethanol and water were recorded in the range of 200–400nm for each solution. The structural and spectroscopic data of the molecule have been obtained for possible three conformers from DFT (B3LYP) with 6-311++G(d,p) basis set calculations. The geometry of the molecule was fully optimized, vibrational spectra were calculated and fundamental vibrations were assigned on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method and PQS program. Hydrogen-bonded dimer of title molecule, optimized by counterpoise correction, was also studied B3LYP at the 6-311++G(d,p) level and the effects of molecular association through O–H⋯O hydrogen bonding have been discussed. 1H and 13C NMR chemical shifts were calculated by using the gauge-invariant atomic orbital (GIAO) method. The electronic properties, such as excitation energies, oscillator strength, wavelengths, HOMO and LUMO energies, were performed by time-dependent density functional theory (TD-DFT) results complements with the experimental findings. Total and partial density of state (TDOS and PDOS) and also overlap population density of state (OPDOS) diagrams analysis were presented. The effects due to the substitutions of boric acid group and halogen were investigated. The results of the calculations were applied to simulate spectra of the title compound, which show excellent agreement with observed spectra. Besides, frontier molecular orbitals (FMO), molecular electrostatic potential (MEP), nonlinear optical properties (NLO) and thermodynamic features were performed.

Complexes of lanthanide nitrates with tri-isopropylphosphine oxide

The complexes formed on reaction of tri-isopropylphosphine oxide ((C3H7)3PO=iPr3PO = L) and lanthanide nitrates have been studied. The new compounds have been characterised by elemental analysis, infrared and 31P NMR spectroscopy in CD2Cl2 solution. On reaction of lanthanide nitrates and L in 1:3 ratios, well defined Ln(NO3)3L3 are obtained for Ln=La–Eu with complexes for the heavier lanthanides forming mixtures of Ln(NO3)3L3 and Ln(NO3)3L2. Analytically pure complexes Ln(NO3)3L2 can be isolated for Yb and Lu. Single crystal X-ray structures for Ln(NO3)3L3, Ln=La (1), Ce (2), Pr (3), the ionic complex [Er(NO3)2L3(H2O)][NO3] (4) and Ln(NO3)3L2, Ln=Yb (5), Lu (6) are reported. The 31P solution NMR spectra of Ln(NO3)3L3 show that the complexes are fluxional at ambient temperature with spectra consistent with static structures observed at lower temperatures for some complexes. The structures and solution properties are discussed in terms of the steric and electronic properties of the ligand.

Synthesis and characterization of supramolecular complexes of a tetranuclear metallocycle with platinum(II) bis-ethynylphenylethynylpyridine organometallic complexes

A novel Pt(II) organometallic complex with 4-(4-ethynyl-phenylethynyl)-pyridine (DEBPy-H), namely [Pt(dppp)(DEBPy)2] (dppp = 1,3-bis-(diphenylphosphino)-propane), has been prepared by two synthetic routes. The DEBPy-H ligand was prepared by a shorter synthetic pathway and in higher yield than the method of previous reports. New Pt(II) organometallic complexes with DEBPy-H and four bidentate ligands [Pt(L–L)(DEBPy)2] (L–L = 1,2-bis-(diphenylphosphino)-benzene, bis-(dicyclohexyl)-ethane, 4,4′-dimethyl-2,2′-bipyridine, or 5,5′-dimethyl-2,2′-bipyridine) have also been prepared. These five Pt(II) complexes have two pyridyl units as an available coordination site that can operate as a metalloligand in nanoscale tectonics. A supramolecular complex of a tetranuclear metallocycle, [Pt(dppp)(DEBPy)2]2[Pt(dppp)]2(OTf)4, was synthesized from [Pt(dppp)(DEBPy)2] and [Pt(dppp)(OTf)2] as a corner connection through coordination-driven self-assembly. This supramolecular Pt(II) complex exists as a tetranuclear structure of the square type according to the interpretation of the ESI-mass and NMR spectra in solution. Five Pt(II) organometallics demonstrated the formation of similar tetranuclear metallocycles with [Pt(dppp)(OTf)2], as indicated by their ESI-mass and UV–vis spectra in solution.