113Cd NMR Research Articles

Heterobimetallic Alkoxides [CdIIMV(OiPr)7]2 (M = Nb, Ta) as Potential Precursors to Pyrochlore Cd2M2O7

Attempts to synthesize Cd–M (M = Nb, Ta) heterobimetallic complexes by salt metathesis reaction resulted in the unexpected structural motif [I2CdII2MV(OiPr)7]2 [M = Nb (2), Ta (3)]. Multinuclear NMR analysis revealed the coexistence of multiple products in solution. Donor solvents influenced the formation of different intermediate species in solution, as was proven by 113Cd NMR spectroscopic data. The isolation of trimetallic [I2Cd{Ta(OiPr)6}K(HOiPr)2]4 (4) and the adduct [I2CdTa(OiPr)5(thf)] (5) provided insight into the reaction mechanism. By exploiting the Lewis acidic nature of cadmium alkoxides, different compounds could be synthesized and thoroughly characterized by spectroscopic methods and single‐crystal X‐ray diffraction studies. Heterobimetallic compounds with the formula [CdIIMV(OiPr)7]2 [M = Nb (6), Ta (7)] produced pyrochlore phases from an amorphous ceramic homogenate, which indicates their potential as single‐source precursors, as was confirmed by thermogravimetric/differential thermal analysis, which showed that complexes 6 and 7 undergo facile two‐step thermal decomposition at 600 °C to produce Cd2Nb2O7 and Cd2Ta2O7, respectively. Variable‐temperature X‐ray diffraction analysis of 6 additionally proved the formation of crystalline Cd2Nb2O7 phase.

Chiral Discrimination of Diamines by a Binaphthalene-Bridged Porphyrin Dimer.

A pair of 1,1'-binaphthalene-bridged bisporphyrins, (R)- and (S)-H1, were designed to examine their chiral discrimination abilities toward a range of model diamines by using UV-vis absorption, CD, and 1H NMR spectroscopy with the assistance of DFT molecular modeling. The spectroscopic titrations revealed that (R)-/(S)-H1 could encapsulate (R)-/(S)-DACH and (R)-/(S)-PPDA in the chiral bisporphyrin cavities, leading to the selective formation of sandwich-type 1:1 complexes via dual Zn-N coordination interactions. In particular, the chiral recognition energy (ΔΔG°) toward (R)-/(S)-DACH was evaluated to be -4.02 kJ mol-1. The binding processes afforded sensitive CD spectral changes in response to the stereostructure of chiral diamines. Remarkable enantiodiscrimination effects were also detected in the NMR titrations of (R)-/(S)-H1, in which the nonequivalent chemical shift (ΔΔδ) can reach up to 0.57 ppm for (R)-/(S)-DACH. However, due to the large steric effect, another chiral diamine ((R)-/(S)-DPEA) could not be sandwiched in the chiral bisporphyrin cavity; therefore, (R)-/(S)-DPEA could hardly be discriminated by (R)-/(S)-H1. The present results demonstrate a chiral bisporphyrin host with integrated CD and NMR chiral sensing functions and also highlight the binding-mode-dependent character of its enantiodiscrimination performance for different chiral guests.

Identification and antimicrobial activity of the sesquiterpene lactone mixture extracted from Smallanthus sonchifolius dried leaves

The present study aimed to identify and screen the antibacterial activity of a mixture of sesquiterpene lactones (SLs) obtained from the dichloromethane extract of Smallanthus sonchifolius leaves. Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Salmonella enterica strains were used as bacterial tests. The identification and quantification of compounds were established by GC/MS and 1H, 13C 2D NMR spectroscopic analysis. The antimicrobial activity was measured by the disk diffusion method and minimal inhibitory concentration assay (MIC). In vitro antimicrobial assays showed that the mixture of SLs found (uvedalin and enhydrin) displays poor antibacterial activity against the Gram-negative bacteria and appreciable antibacterial properties against the Gram-positive bacterial strain tested when 90 µg of the SLs mixture per disk was used. The MIC determination against S. aureus revealed that a concentration of 750 µg of SLs mixture mL−1 should be necessary to inhibit the strain. These results indicate that the SLs mixture of enhydrin and uvedalin from yacon leaves presents promising antibacterial properties against S. aureus and apparent lack of activity against the Gram-negative bacterial strains tested at the concentrations applied.

Probing the local structure of Prussian blue electrodes by 113Cd NMR spectroscopy.

We demonstrate that 113Cd NMR is a potent technique to monitor the local electronic and structural states of the Prussian blue electrode during Li+ intercalation, providing an atomic-scale insight into the reaction mechanism.

Direct Observation of Nanosecond Water Exchange Dynamics at a Protein Metal Site

Nanosecond ligand exchange dynamics at metal sites within proteins is essential in catalysis, metal ion transport, and regulatory metallobiochemistry. Herein we present direct observation of the exchange dynamics of water at a Cd2+ binding site within two de novo designed metalloprotein constructs using 111mCd perturbed angular correlation (PAC) of γ-rays and 113Cd NMR spectroscopy. The residence time of the Cd2+-bound water molecule is tens of nanoseconds at 20 °C in both proteins. This constitutes the first direct experimental observation of the residence time of Cd2+ coordinated water in any system, including the simple aqua ion. A Leu to Ala amino acid substitution ∼10 Å from the Cd2+ site affects both the equilibrium constant and the residence time of water, while, surprisingly, the metal site structure, as probed by PAC spectroscopy, remains essentially unaltered. This implies that remote mutations may affect metal site dynamics, even when structure is conserved.

Triterpene saponins and megastigmane glucosides from Camellia bugiamapensis

Two new triterpene saponins, camelliosides I and J (1 and 2), two new megastigmane glycosides, camellistigosides A and B (3 and 4), and two known megastigmane glycosides, icariside B1 (5) and (6S,9R)-roseoside (6), were isolated from a methanol extract of the Camellia bugiamapensis leaves using various chromatographic separation techniques. Their structures were elucidated based on spectroscopic analyses, including HR ESI MS, CD, 1D and 2D NMR. Their inhibitory effects on LPS-induced NO production in RAW264.7 cells were evaluated. This is the first report of the chemical constituents and biological activity of C. bugiamapensis.

MAGE (Melanoma-Associated Antigen) Protein Purification and Stability Studies Using CD Spectroscopy and NMR

MAGE (Melanoma-Associated Antigen) Protein Purification and Stability Studies Using CD Spectroscopy and NMR

Band-Selective 2D HSQMBC: A Universal Technique for Detection and Measurement of 35,37Cl Isotope Effects for 13C Nuclei.

A novel technique that allows efficient measurement of the 35,37Cl isotope pattern for any 13C resonance has been developed. The band-selective CLIP-HSQMBC experiment is reliable and universally applicable for the indirect measurement of the 35,37Cl isotope shift of 13C resonances. The experiment provides advantages over conventional 1D 13C NMR and the recently developed bs-HSQC experiments. The utility and performance of the bs-CLIP-HSQMBC experiment is demonstrated for polyhalogenated synthons in a synthetic route and for a polyhalogenated marine natural product.

Synthesis, characterization and structures of cadmium(II) and mercury(II) complexes with bis(dipiperidinylphosphino)methylamine dichalcogenides

Two new bidentate phosphine dichalcogenide ligands of the type MeN(Pip2PE)2 [(Pip=piperidinyl; E=S (1) or Se (2)] and their cadmium(II) and mercury(II) chloride complexes MCl2{MeN(Pip2PE)2} [M=Cd; E=S (3); Se (4) or M=Hg; L=S (5); Se (6)] were prepared and characterized by elemental analysis, IR, multinuclear (31P, 77Se and 113Cd) NMR spectroscopy and single crystal X-ray analyses. Ligands 1and2 were found to adopt anti conformation structures in the solid state, in which both PE groups are trans to each other. Complexes 3–6 are comprised of one ligand coordinated in a bidentate fashion to the metal centre in a distorted tetrahedral arrangement [98.46(3)–121.24(4)°]. The PS bond lengths of 1.999(15)–2.003(14)Å in complex 3 are slightly elongated compared to those in the free ligand [1.933(15)–1.950(14)Å]. The results are discussed and compared with closely related analogues.

Porous Coordination Polymer Based on Bipyridinium Carboxylate Linkers with High and Reversible Ammonia Uptake.

The zwitterionic bipyridinium carboxylate ligand 1,1'-bis(4-carboxyphenyl)-4,4'-bipyridinium (pc1) in the presence of cadmium chloride affords novel porous coordination polymers (PCPs): [Cd4(pc1)3Cl6]·CdCl4·guest (1) crystallizing in the P3̅1c space group. In the structure, [Cd4Cl6(CO2)6] building units are linked together by six pc1 ligands, leading to a 3D high-symmetrical network exhibiting hexagonal channels along the c axis. The walls of this PCP consist of cationic electron-acceptor bipyridinium units. The PCP 1 reversibly adsorbs H2O and CH3OH up to about 0.1 g/g at saturation showing the adsorption isotherms characteristic of a moderately hydrophilic sorbent. Adsorption of ammonia (NH3) follows a different pattern, reaching an exceptional uptake of 0.39 g/g (22.3 mmol/g) after the first adsorption cycle. Although the crystalline structure of 1 collapses after the first adsorption, the solid can be regenerated and maintains the capacity of 0.29 g/g (17 mmol/g) in the following cycles. We found that the high NH3 uptake is due to a combination of pore filling taking place below 150 h·Pa and chemisorption occurring at higher pressures. The latter process was shown to involve two phenomena: (i) coordination of NH3 molecules to Cd(2+) cations as follows from (113)Cd NMR and (ii) strong donor-acceptor interactions between NH3 molecules and pc1 ligands.

Modulating Hydrogen Bonded Self-assembled Patterns and Morphological Features by a Change in Side Chain of Third Amino Acid of Synthetic γ- Amino Acid Based Tripeptides

Self-assembled structure and functions of peptides could be achieved by the design and synthesis of hybrid peptides. Here, we report structural and morphological studies of designed hybrid tripeptides Boc-Gpn-Aib-Xaa-OMe (where Xaa=Leu(L) for 1 and Phe(F) for 2), which show different conformations both in solid and solution states. The conformational modulations are achieved by the design and synthesis of reported peptides 1 and 2 by suitable choice of conventional and non-conventional amino acid building blocks and slight change in side-chain of third amino acids of tripeptides. The conformational modulations exhibited by peptides 1 and 2 are well probed and confirmed using Single crystal XRD, FT-IR, CD and 2D NMR studies. The morphological studies of peptides 1 and 2 show different self-assembled morphological preferences in THF – water (1:1) under similar experimental conditions.

Two new sesquiterpenes from the aerial parts of Schizonepeta tenuifolia

Two new sesquiterpenes named petafolias A–B were isolated from the aerial parts of Schizonepeta tenuifolia. Their structures were elucidated by various spectroscopic techniques (UV, IR, MS, CD, 1D, and 2D NMR).

Diarylpentanol constituents from the aerial part of Stelleropsis tianschanica

Five diarylpentanol derivatives including two new compounds stellerasme A (1), stellerasme B (2) were isolated from the aerial parts of Stelleropsis tianschanica. Their structures were elucidated by various spectroscopic techniques (UV, IR, MS, CD, 1D and 2D NMR). All compounds were evaluated for their cytotoxicity activity against HeLa and KB cell lines, and compound 1 showed selective activities against HeLa cell line with an IC50 value of 7.4 μM.

Precise and rapid isotopomic analysis by 1H–13C 2D NMR: Application to triacylglycerol matrices

An optimized HSQC sequence was tested and applied to triacylglycerol matrices to determine their isotopic and metabolomic profiles. Spectral aliasing and non-uniform sampling approaches were used to decrease the experimental time and to improve the resolution, respectively. An excellent long-term repeatability of signal integrals was achieved enabling to perform isotopic measurements. Thirty-two commercial vegetable oils were analyzed by this methodology. The results show that this method can be used to classify oil samples according to their geographical and botanical origins.

Expression, purification and characterization of the recombinant cysteine-rich antimicrobial peptide snakin-1 in Pichia pastoris

Snakin-1 (SN-1) is a small cysteine-rich plant antimicrobial peptide with broad spectrum antimicrobial activity which was isolated from potato (Solanum tuberosum). Here, we carried out the expression of a recombinant SN-1 in the methylotrophic yeast Pichia pastoris, along with its purification and characterization. A DNA fragment encoding the mature SN-1 was cloned into pPIC9 vector and introduced into P. pastoris. A large amount of pure recombinant SN-1 (approximately 40 mg/1L culture) was obtained from a fed-batch fermentation culture after purification with a cation exchange column followed by RP-HPLC. The identity of the recombinant SN-1 was verified by MALDI-TOF MS, CD and 1H NMR experiments. All these data strongly indicated that the recombinant SN-1 peptide had a folding with six disulfide bonds that was identical to the native SN-1. Our findings showed that SN-1 exhibited strong antimicrobial activity against test microorganisms and produced very weak hemolysis of mammalian erythrocytes. The mechanism of its antimicrobial action against Escherichia coli was investigated by both outer membrane permeability assay and cytoplasmic membrane depolarization assay. These assays demonstrated that SN-1 is a membrane-active antimicrobial peptide which can disrupt both outer and cytoplasmic membrane integrity. This is the first report on the recombinant expression and purification of a fully active SN-1 in P. pastoris.

A new sandwich-type polyoxometalates containing mixed transition metals, [Cd2Zn2(H2O)2(P2W15O56)2]16−: Syntheses, spectrochemical characterization and its electrocatalytical activity comparison with [M4(H2O)2(P2W15O56)2]16− (M = Cd2+ and Zn2+) and [P2W15O56]12−

The mixed-metal sandwich-type polyoxometalate [Cd2Zn2(H2O)2(P2W15O56)2]16− (abbreviated Cd2Zn2P4W30) has been synthesized and characterized by FT-IR, 31P NMR, 113Cd NMR spectroscopies, cyclic voltammetry (CV) and elemental analysis. The electrochemical behavior of this sandwich-type complex in aqueous solution has been investigated, and also systematic comparisons of that have been made by [M4(H2O)2(P2W15O56)2]16− (M=Cd2+ and Zn2+) (abbreviated M4P4W30) and [P2W15O56]12− (abbreviated P2W15). All these compounds show successive reduction processes of the tungsten centers in a negative potential range, but in some cases, the electrochemistry involves redox reactions originating from cadmium ions. These sandwich-type complexes have efficient electrocatalytic activities towards the reduction of nitrite. However, there is a significant decrease in efficiency as the number of cadmium centers in the complex increases.

Microcystbiopterins A–E, five O-methylated biopterin glycosides from two Microcystis spp. bloom biomasses

Five previously undescribed biopterin glycosides, microcystbiopterin A–E, were isolated from the extracts of two bloom materials of Microcystis spp. collected from a fishpond (IL-337) and Lake Kinneret (IL-347), Israel. The structure of the pterins was established by interpretation of their UV, CD, 1D and 2D NMR spectra and HR mass measurements. Microcystbiopterin D is the first heptose containing pterin glycoside to be reported in the literature. Their antimicrobial and cytotoxic properties were evaluated but all were found not active in both assays.

Rapid Determination of Polymer Stereoregularity Using Band-Selective 2D HSQC

We report the use of band-selective 2D HSQC NMR spectroscopy to rapidly determine the stereoregularity of polymers usually analyzed by 1D 13C NMR spectroscopy. This approach reduced the time required to characterize the triad stereosequences of polyacrylonitrile from about an hour to a few minutes, and can be performed with sufficient 13C resolution to resolve higher-order stereosequences, such as the pentads of polypropylene.

Magnesium and cadmium containing Heusler phases REPd2Mg, REPd2Cd, REAg2Mg, REAu2Mg and REAu2Cd

Twenty-eight new Heusler phases REPd2Mg, REPd2Cd, REAg2Mg, REAu2Mg and REAu2Cd with different rare earth elements were synthesized from the elements in sealed niobium ampoules in a water-cooled sample chamber of an induction furnace. The samples were characterized by powder X-ray diffraction. The cell volumes show the expected lanthanide contraction. The structures of YPd2Cd, GdPd2Cd, GdAu2Cd, Y1.12Ag2Mg0.88 and GdAg2Mg were refined based on single crystal diffractometer data. The magnetic properties were determined for fifteen phase pure samples. LuAu2Mg is a weak Pauli paramagnet with a susceptibility of 1.0(2) × 10−5 emu mol−1 at room temperature. The remaining samples show stable trivalent rare earth ions and most of them order magnetically at low temperatures. The ferromagnet GdAg2Mg shows the highest ordering temperature of TC = 98.3 K. 113Cd and 89Y MAS NMR spectra of YAu2Cd and YPd2Cd confirm the presence of unique crystallographic sites. The resonances are characterized by large Knight shifts, whose magnitude can be correlated with electronegativity trends.

Two new compounds from the leaves of Indocalamus latifolius

Two new compounds, erythro-syringylglycerol-9-O-trans-4-hydroxycinnamate 7-O-β-d-glucopyranoside (1) and indocalatin A (2), together with three known ones, 5,7,3′-trihydroxy-6-C-β-d-digitoxopyranosyl-4′-O-β-d-glucopyranosyl flavonoid (3), 5,4′-dihydroxy-3′,5′-dimethoxy-7-O-[β-d-apiose-(1→2)]-β-d-glucopyranosyl flavonoid (4), and tricin-6-C-β-boivinopyranosyl-8-C-β-glucopyranoside (5), were isolated from the 95% EtOH extract of Indocalamus latifolius leaves. Their molecular structures were determined by UV, IR, HRESIMS, CD, and 1D and 2D NMR data analyses.