1H Diffusion-ordered Spectroscopy Research Articles

Synthesis, Characterization, and Spectroscopic Studies of 2,6-Dimethylpyridyl-Linked Cu(I)-CNC Complexes: The Electronic Influence of Aryl Wingtips on Copper Centers.

Six new Cu(I) complexes containing pincer ligands of the type 2,6-bis(3-alkyl/arylimidazol-2-ylidene) methylpyridine I(R/R'Ar) ĈN̂C, where R = trifluoroethyl (TFE) and R' = 4-CF3, 4-NO2, 4-CN, 4-H, and 4-CH3, have been synthesized. These complexes, namely, [Cu(I(TFE)ĈN̂C)]PF6, 1-TFE; [Cu(ICF3Ar ĈN̂C]PF6, 2-CF3; [Cu(INO2Ar ĈN̂C)]PF6, 3-NO2; [Cu(ICNAr ĈN̂C]PF6, 4-CN; [Cu(IHAr ĈN̂C)]2(PF6)2, 5-H; and [Cu(ICH3Ar ĈN̂C)]2(PF6)2, 6-CH3, were fully characterized by 1H, 13C, and HMBC NMR spectroscopy, elemental analysis, electrochemical studies, and single-crystal X-ray crystallography. The crystallographic data revealed different structures and copper nuclearities for the complexes bearing aryl wingtips with electron-withdrawing (2-CF3, 3-NO2, and 4-CN) and electron-donating (5-H and 6-CH3) substituents. The solution-phase conductivity measurements in acetonitrile revealed a mix-electrolyte behavior for these complexes, supporting the presence of both mono- and binuclear forms of each complex. The fast monomer-dimer equilibrium of the Cu-CNC complexes at room temperature is reflected in their simple 1H NMR spectra in acetonitrile. However, both mono- and binuclear forms were identifiable in 1H diffusion-ordered spectroscopy (DOSY) at low temperatures. The dynamic behavior of these complexes in solution was further examined by variable-temperature 1H NMR (VT 1H NMR) experiments, and the relevant thermodynamic parameters were determined. The process was also probed by one-dimensional rotating-frame Overhauser enhancement spectroscopy (1D ROESY) experiments to elucidate the coexisting species in solution. The 2,6-dimethylpyridyl-linked Cu-CNC complexes also presented a quasi-reversible Cu(II)/Cu(I) couple in cyclic voltammetry studies, wherein a clear influence of the aryl wingtips on the E1/2 values was observed. Furthermore, the percent buried volumes (% Vbur) of the complexes were calculated, showing a similar steric hindrance around copper in all complexes. These findings support the importance of electronic effects, induced by the aryl wingtips, on the preferred coordination geometry, copper nuclearity, and redox properties of the Cu-CNC complexes.

Unexpected Photocatalytic Degeneration of NAD + for Inducing Apoptosis of Hypoxia Cancer Cells

Unexpected Photocatalytic Degeneration of NAD ⁺ for Inducing Apoptosis of Hypoxia Cancer Cells

Binary mixture (1:1) of Triton X100 and Propranolol hydrochloride in an aqueous solution of NaCl: Whether mixed micelles are formed, possible clarification in 1H DOSY NMR experiment

Micellisation of the binary mixture (1:1) of non-ionic surfactant Triton X100 and surface-active drug Propranolol hydrochloride is examined in an aqueous solution of NaCl (0.3 molkg−1) in the temperature interval T = (273.15–313.15) K with steps of 5 K. Propranolol hydrochloride has two critical micellar concentrations (cmc) if the solution contains NaCl (0.3 molkg−1), while its binary mixture with Triton X100 (1:1) has one critical micellar concentration. The interaction coefficient (β) between structurally different micellar building units is β > 0, which means that there are antagonistic interactions in the binary mixed micelle, i.e., the molar excess Gibbs free energy is higher than zero, which probably originates from the increase in the degree of hydrophobic hydration when incorporating the naphthalene ring (part of Propranolol hydrochloride) into the Triton X100 micelle. The change of the molar Gibbs free energy of mixing is lower than zero. Thus the driving force for the formation of the binary mixed micelle originates from the entropy of mixing structurally different particles. The Diffusion-Ordered SpectroscopY (DOSY) experiment makes it possible to determine, based on the change (reduction) of the self-diffusion coefficient (D) of a surfactant concerning the D value in the monomeric state, whether the observed surfactant (whose concentration in the solution must be lower than its monocomponent cmc values) with another surfactant particle (from a binary mixture of surfactants) forms a binary mixed micelle. DOSY experiment was performed in an aqueous solution without NaCl. If the total concentration of the examined binary mixture is higher than its critical micellar concentration, it decreases the self-diffusion coefficient of both components, suggesting the formation of the binary mixed micelle. The self-diffusion coefficient of Triton X100 is significantly lower than that of propranolol hydrochloride, indicating that non-ionic surfactant dominates in the binary mixed micelle.

Crown ether and crown ether/K+ complex assisted DOSY NMR: A versatile tool for positional isomers identification in aqueous solution

Diffusion-ordered spectroscopy (DOSY) is a powerful and efficient technique for the analysis of complex mixtures, relying on their differential in self-diffusion coefficient. However, DOSY is often struggled to separate signals pertaining to isomeric species, especially positional isomers. Here, for the first time, we describe the novel design of 18-crown ether-6 (18C6) and 18C6/K+ complex as matrixes to discriminate and identify positional isomeric mixtures of phenylenediamine, nitroaniline, phthalic acid, dimethoxybenzoic acid, aminophthalic acid and even amino acids using 1H DOSY spectrum. The superior performance of 18C6 and 18C6/K+ complex as matrix depends on that they can interact with different components with varying binding energy as demonstrated by MMMF calculations and the DFT calculation. The methodology presented here is simple yet efficient. Moreover, the crown ether and crown ether/K+ complex provide the dual mode discrimination for both amino and carboxylic substituted positional isomers.

Controlling the Chain Folding for the Synthesis of Single-Chain Polymer Nanoparticles Using Thermoresponsive Polymers

Synthetic polymer single-chain nanoparticles (SCNPs) are an emerging new class of nanomaterials that possess similar folded structures as natural proteins. However, most SCNPs reported so far are p...

Di(hydroperoxy)cycloalkane Adducts of Triarylphosphine Oxides: A Comprehensive Study Including Solid-State Structures and Association in Solution.

Four new di(hydroperoxy)cycloalkane adducts (Ahn adducts) of p-Tol3PO (1) and o-Tol3PO (2), namely, p-Tol3PO·(HOO)2C(CH2)5 (3), o-Tol3PO·(HOO)2C(CH2)5 (4), p-Tol3PO·(HOO)2C(CH2)6 (5), and o-Tol3PO·(HOO)2C(CH2)6 (6), have been synthesized and fully characterized. Their single crystal X-ray structures have been determined and analyzed. The 31P NMR data are in accordance with hydrogen bonding of the di(hydroperoxy)alkanes to the P═O groups of the phosphine oxides. Due to their high solubility in organic solvents, natural abundance 17O NMR spectra of 1-6 could be recorded, providing the signals for the P═O groups and additionally the two different oxygen nuclei in the O-OH groups in the adducts 3-6. The association and mobility of 3-6 were explored by 1H DOSY (diffusion ordered spectroscopy) NMR, which indicated persistent hydrogen bonding of the adducts in solution. Competition experiments with phosphine oxides allowed ranking of the affinities of the di(hydroperoxy)cycloalkanes for the different phosphine oxide carriers. On the basis of variable temperature 31P NMR investigations, the Gibbs energies of activation ΔG‡ for the adduct dissociation processes of 3-6 at different temperatures, as well as the enthalpy ΔH‡ and entropy ΔS‡ of activation, have been determined. IR spectroscopy of 3-6 corroborated the hydrogen bonding, and in the Raman spectra, the ν(O-O) stretching bands have been identified, confirming the presence of peroxy groups in the solid materials. The high solubilities in selected organic solvents have been quantified.

Ternary deep eutectic solvents catalyzed d-glucosamine self-condensation to deoxyfructosazine: NMR study

Ternary deep eutectic solvents (TDESs) comprising choline chloride (ChCl), glycerol and l-arginine were synthesized as catalysts and solvents for the conversion of d-glucosamine (GlcNH2) into deoxyfructosazine (DOF). The interactions between these three components in the prepared TDESs were studied by 1H-, 35Cl-NMR spectra and 1H diffusion-ordered spectroscopy (DOSY) measurements. The chemical shift changes of active hydrogen in the 1H-NMR spectra of TDES system and widening of signals in the 35Cl-NMR spectra confirmed the hydrogen bonding interaction between the components, which was further supported by the decrease of diffusion coefficients (D) of the TDES components according to 1H DOSY measurements. The influences of reaction temperature and l-arginine content in the TDESs on the yield of DOF were also studied. The experimental results have shown that when the molar ratio of ChCl, glycerol, and l-arginine was 1:2:0.1, DOF was the major product with a yield of 22.6% at 90 °C for 120 min. The chemical shift titration indicated that the carboxyl group of l-arginine in the TDES is the catalytical active site, so the mechanism of the catalytic reaction between GlcNH2 and the TDES was proposed. Moreover, a reaction intermediate, dihydrofructosazine, was identified in the self-condensation reaction of GlcNH2 by an in situ1H NMR technique.

Bipyrrolidine salan alkoxide complexes of lanthanides: synthesis, characterisation, activity in the polymerisation of lactide and mechanistic investigation by DOSY NMR.

Four dimeric lanthanide alkoxide complexes bearing ONNO bipyrrolidine salan ligands (LMeH2/LtBuH2) have been prepared with Nd, Sm and Yb. Depending on the metal and substituents, these complexes adopt varying coordination geometries. While investigating the hydrolytic degradation of these complexes, three dimeric mixed alkoxide/hydroxide and bis-hydroxide products were also prepared, isolated and characterised. Despite paramagnetism, 1H NMR and diffusion ordered spectroscopy (DOSY) allowed additional characterisation alongside elemental and single-crystal X-ray diffraction analyses. These systems were very active for the controlled ring-opening polymerisation (ROP) of rac-lactide (LA), under industrially relevant melt conditions and in solution, yielding complete conversion within 5 minutes at [Ln] : [LA] ratios of up to 3000 : 1 in toluene, and at 80 °C, whilst retaining low dispersities (Đ = 1.1). 1H DOSY NMR spectroscopy was employed to monitor polymer growth from the metal centres in situ, and revealed a dinuclear catalytically active species.

A Supramolecular Investigation on the Interactions between Ethyl terminated Bis–viologen Derivatives with Sulfonato Calix[4]arenes

AbstractHerein, we report the synthesis and guest‐host complexation between isomeric xylylene interconnected ethyl terminated bis‐viologens (EDV) with p‐sulfonatocalix[4]arene (SC4 A). Guest‐host interactions between EDV and SC4 A were monitored by CV (cyclic voltammetry), 1H and DOSY (Diffusion Ordered Spectroscopy) NMR titrations. CV titrations showed a partial inclusion complex formation between EDV and SC4 A which is further confirmed by 1H NMR and DOSY titrations. It is evident from 1H NMR titrations that all the three isomers of EDV forms a stable inclusion complex with SC4 A where SC4 A caps the terminal. o‐ and m‐ isomers of EDV interacts differently than their corresponding p‐isomer. 1H NMR titration reveals that o‐ and m‐xylylene units are incorporated into the SC4 A cavity whereas p‐xylylene unit is only partially included into the cavity during the interaction. Further, it is observed that the ethyl terminated viologen adopts axial orientation in concordance with previous reports. DOSY measurements further confirmed the formation of inclusion complex between the bis‐viologen and SC4 A and indicated the formation of aggregates at higher concentrations of SC4 A. Results clearly indicate that the bis‐viologens possess multiple binding sites for the multivalent SC4 A host and based on the concentration of SC4 A, several types of interactions exists between the two predicting a complex binding model.

Dynamic Phosphonic Bridges in Aqueous Uranyl Clusters

AbstractThe uranyl cage clusters (UO2)22(O2)15(PHO3)20(H2O)1026– (U22) and (UO2)28(O2)20(PHO3)24(H2O)1232– (U28) can be probed in aqueous solutions by using a combination of 1H Diffusion‐Ordered Spectroscopy (DOSY) and 1H‐31P Heteronuclear‐Single Quantum Coherence (HSQC) spectroscopy. This class of clusters is ideal for 1H NMR analysis in D2O because of the covalent character of the H–P bond in the phosphonic bridges. 1H DOSY indicates that the clusters are stable in solution and provides hydrodynamic radii of 9.8 ± 0.4 Å for the U22 and 12.3 ± 0.5 Å for the U28 clusters. Furthermore, 1H‐31P HSQC delivers unequivocal signal assignment for both nuclei, which enables solution dynamics to be monitored by variable‐temperature experiments, and reveals the presence of phosphonic‐bridge conformers. The results provide some of the first dynamic information about steady conformational changes in these enormous actinide macroions.

Generation of a Dynamic System of Three‐Dimensional Tetrahedral Polycatenanes

Generation of a Dynamic System of Three‐Dimensional Tetrahedral Polycatenanes

Specific and Cooperative Interactions between Oximes and PAMAM Dendrimers As Demonstrated by 1H NMR Study

Oximes are important in the treatment of organophosphate (OP) poisoning, but have limited biological half-lives. Complexing these drugs with a macromolecule, such as a dendrimer, could improve their pharmacokinetics. The present study investigates the intermolecular interactions that drive the complexation of oxime-based drug molecules with fifth generation poly(amidoamine) (PAMAM) dendrimers. We performed steady-state binding studies of two molecules, pralidoxime and obidoxime, employing multiple NMR methods, including 1D titration, (1)H-(1)H 2D spectroscopy (COSY, NOESY), and (1)H diffusion-ordered spectroscopy (DOSY). Several important insights were gained in understanding the host-guest interactions occurring between the drug molecules and the polymer. First, the guest molecules bind to the dendrimer macromolecule through a specific interaction rather than through random, hydrophobic encapsulation. Second, this specificity is driven primarily by the electrostatic or H-bond interaction of the oxime at a dendrimer amine site. Also, the average strength for each drug and dendrimer interaction is affected by the surface modification of the polymer. Third, individual binding events between oximes and a dendrimer have a negative cooperative effect on subsequent oxime binding. In summary, this report provides a novel perspective important for designing host systems for drug delivery.

Aggregation States of Asphaltenes: Evidence of Two Chemical Behaviors by 1H Diffusion-Ordered Spectroscopy Nuclear Magnetic Resonance

The mean molecular weight and particle size of asphaltene aggregates extracted from Buzurgan feedstock have been evaluated by measuring the diffusivity by means of 1H diffusion-ordered spectroscopy (DOSY) nuclear magnetic resonance (NMR). This technique, recently applied in the petroleum industry, appeared as a key tool to investigate the behavior of asphaltenes diluted in toluene over a wide range of concentrations (from 0.01 to 15 wt %). The results show that the diffusivity is highly dependent upon solute concentration. Indeed, interactions occurring in dilute systems differ from interactions occurring in the semi-dilute regime. In the dilute regime (below 0.25 wt %), physical characterization of the nanoaggregates detected by 1H DOSY NMR could be achieved. An average molecular weight of roughly 6900 g mol−1 (taken at the highest diffusion peak and given as a polystyrene equivalent) with a range of 1500−85000 g mol−1 was obtained, while a mean radius of 15.6 Å was determined from the solute diffusivity at infinite dilution [D∞asp ∼ (2.4 ± 0.1) × 10−10 m2 s−1 for Buzurgan asphaltenes]. Average masses (Mn and Mw) were also calculated from DOSY NMR data and compared to results obtained from size exclusion chromatography (SEC) analyses. We also used DOSY NMR techniques to investigate the molecular dynamics of asphaltenes. A concentration of 0.25 wt % was found to represent the onset of the aggregation process. We believe DOSY NMR allowed us to observe the beginning of aggregation in phase transition. The asphaltene system is very polydisperse. At low concentrations, it is a polydisperse diluted system, but increasing the solute concentration induces a distinction of different aggregates, presenting various sizes in a macroscopic homogeneous phase. When the distinction occurs, there is a zone that is richer in high molecular weight aggregates of asphaltenes, and as a result, a second zone is impoverished in high molecular weight aggregates. In a microscopic point of view, there is a difference in nano or macroaggregate concentration, whereas in a macroscopic point of view, an average density is observed. For the first time, a clear separation between two families of aggregates of asphaltenes is presented in the diffusion dimension for concentrations higher than 3 wt %. 1H DOSY spectra and diffusion profiles confirm these results. The key point of this study resides in the detection and presentation of two classes of aggregates of asphaltenes achieved for concentrated solutions, without any assumption concerning the composition of the mixture.

1H Diffusion-Ordered Spectroscopy (DOSY) Nuclear Magnetic Resonance (NMR) as a Powerful Tool for the Analysis of Hydrocarbon Mixtures and Asphaltenes

Heavy crude oils are more and more of interest for the oil industry to meet the growing worldwide energy demand. Asphaltenes, which are the heaviest and least reactive molecules in crude oils, have received great attention over the last few decades, because they are responsible for many problems occurring during hydrotreatment and hydroconversion. 1H diffusion-ordered spectroscopy (DOSY) nuclear magnetic resonance (NMR) based on pulsed field gradient (PFG) sequences is a powerful tool to analyze polydisperse samples. The key advantage of such a technique compared to traditional NMR diffusion sequences, such as pulsed field gradient spin−echo (PFGSE), is to obtain both physical and chemical information in a single experiment. 1H DOSY NMR has been carried out on different types of samples to obtain a deeper insight into the physicochemical properties of petroleum samples, because diffusion coefficients are both sensitive to molecular weights and sizes. The application of DOSY NMR to analyze hydrocarbon mixtures and asphaltenes is assessed. It is shown that both solute and solvent diffusion coefficients decrease with an increasing concentration of solute. Different types of intermolecular interactions were observed on petroleum samples depending upon the sample concentration. Dilute and semi-dilute regimes have also been detected. 1H DOSY spectra applied to diesel and asphaltene samples in toluene are presented and interpreted to demonstrate the potential of DOSY techniques to analyze heterogeneous petroleum samples. The data obtained for the diesel sample enable us to establish that monoaromatics were connected to long alkyl chains, whereas di- or triaromatic molecules were linked to shorter hydrocarbon chains. However, a clear conclusion could not be reached for the asphaltene sample because there were only a few aromatic protons that were not detected. This observation is most consistent with a continental model of these asphaltenes.