13C Shifts Research Articles

Structural and spectroscopic studies of Au(III) and Pd(II) chloride complexes and organometallics with 2-benzylpyridine

Abstract Au(III) and Pd(II) chloride complexes with 2-benzylpyridine (2bzpy) – [Au(2bzpy)Cl3] and trans-[Pd(2bzpy)2Cl2], as well as Au(III) chloride organometallics with monoanionic form of 2bzpy, deprotonated in the benzyl side group at the ortho-carbon C(2′) (2bzpy*) – [Au(2bzpy*)Cl2], were studied by 1H, 13C and 15N NMR. 1H, 13C and 15N coordination shifts (i.e. differences of chemical shifts for the same atom in the complex and ligand molecules) were discussed in relation to the molecular structures and the coordination modes, as well as to the factors influencing nuclear shielding. Analogous NMR measurements were performed for the new (2bzpyH)[AuCl4] salt, studied also by single crystal X-ray diffraction.

1H, 13C and 15N chemical shift assignments of unliganded Bcl-xL and its complex with a photoresponsive Bak-derived peptide

Here we report the (1)H, (13)C and (15)N resonance assignments of free Bcl-x(L) and of Bcl-x(L) in complex with an azobenzene-modified peptide derived from the BH3 domain of the pro-apoptotic Bak. The spectra suggest predominantly folded proteins; chemical shift difference analysis provides a detailed view of the reorganization occurring on peptide binding.

1H, 13C, and 15N Chemical Shift Assignments for the IIA(Chitobiose)-HPr Complex of the N,N'-Diacetylchitobiose Branch of the Escherichia coli Phosphotransferase System

1H, 13C, and 15N Chemical Shift Assignments for the IIA(Chitobiose)-HPr Complex of the N,N'-Diacetylchitobiose Branch of the Escherichia coli Phosphotransferase System

1H, 13C, and 15N Chemical Shift Assignments for a yeast protein

1H, 13C, and 15N Chemical Shift Assignments for a yeast protein

Backbone and side chain 1H, 13C, and 15N Chemical Shift Assignments for Hen Egg White Lysozyme mutant WT-ALA

Backbone and side chain 1H, 13C, and 15N Chemical Shift Assignments for Hen Egg White Lysozyme mutant WT-ALA

Backbone 1H, 13C, and 15N chemical shift assignments of reduced yeast iso-1 cytochrome c

Backbone 1H, 13C, and 15N chemical shift assignments of reduced yeast iso-1 cytochrome c

Backbone 1H, 13C, and 15N chemical shift assignments of reduced horse heart cytochrome c

Backbone 1H, 13C, and 15N chemical shift assignments of reduced horse heart cytochrome c

Electronic structure and magnetic properties of 31P@C60-SWCNT as peapods

Design of the NMR quantum computer of 1D spin chains based on 31P@C60-SWCNT as peapods was studied. Electronic structure and magnetic properties of 31P@C60 encapsulating fullerenes within SWCNT as peapods was investigated by quantum chemical calculation. Characterization of chemical shifts of 13C, principle g-tensor and A-tensor of hyperfine structure for phosphorus atom with electronic spin S = 3/2 and nuclear spin I = 1/2 were studied. The excited energy and wavelength at 1512 nm and 728 nm confirmed assignment of the first and second states as van Hove transitions. Molecular design of carbon peapods is important to control quantum spin qubits, splitting by spin-local interaction and dipole-dipole interaction based on p-orbital spin density distribution under hybrization of molecular orbital at excited state and grand state.

13C and 15N chemical shift assignments of cAMP bound Cyclic Nucleotide-Binding Domain from a bacterial Cyclic Nucleotide-Gated channel

13C and 15N chemical shift assignments of cAMP bound Cyclic Nucleotide-Binding Domain from a bacterial Cyclic Nucleotide-Gated channel

Distinct microbial and faunal communities and translocated carbon in Lumbricus terrestris drilospheres

Lumbricus terrestris is a deep-burrowing anecic earthworm that builds permanent, vertical burrows with linings (e.g., drilosphere) that are stable and long-lived microhabitats for bacteria, fungi, micro- and mesofauna. We conducted the first non-culture based field study to assess simultaneously the drilosphere (here sampled as 0–2 mm burrow lining) composition of microbial and micro/mesofaunal communities relative to bulk soil. Our study also included a treatment of surface-applied 13C- and 15N-labeled plant residue to trace the short-term (40 d) translocation of residue C and N into the drilosphere, and potentially the assimilation of residue C into drilosphere microbial phospholipid fatty acids (PLFAs). Total C concentration was 23%, microbial PLFA biomass was 58%, and PLFAs associated with protozoa, nematodes, Collembola and other fauna were 200-to-300% greater in the drilosphere than in nearby bulk soil. Principal components analysis of community PLFAs revealed that distributions of Gram-negative bacteria and actinomycetes and other Gram-positive bacteria were highly variable among drilosphere samples, and that drilosphere communities were distinct from bulk soil communities due to the atypical distribution of PLFA biomarkers for micro- and mesofauna. The degree of microbial PLFA 13C enrichment in drilosphere soils receiving 13C-labeled residue was highly variable, and only one PLFA, 18:1ω9c, was significantly enriched. In contrast, 11 PLFAs from diverse microbial groups where enriched in response to residue amendment in bulk soil 0–5 cm deep. Among control soils, however, a significant δ13C shift between drilosphere and bulk soil at the same depth (5–15 cm) revealed the importance of L. terrestris for translocating perennial ryegrass-derived C into the soil at depth, where we estimated the contribution of the recent grass C (8 years) to be at least 26% of the drilosphere soil C. We conclude that L. terrestris facilitates the translocation of plant C into soil at depth and promotes the maintenance of distinct soil microbial and faunal communities that are unlike those found in the bulk soil.

Investigating the nuclear magnetic resonance of the structure of electrolyte based on a LiClO4—ethylene carbonate solution

We establish the molecular structure of LiClO4 solution in ethylene carbonate with different lithium perchlorate concentrations (from the strongest dilution 0.01 M to 3 M). Agreement with the experimental NMR spectra is achieved. Calibration molecular structures for calculating the chemical shifts of 1H, 7Li, 13C, 17O, and 35Cl nuclei are proposed.

Three-dimensional triple-resonance NMR Spectroscopy of isotopically enriched proteins

correlates the amide ‘H and “N shifts with the 13C shift of the carbonyl resonance of the preceding amino acid. A second experiment (HNCA) correlates the intraresidue amide ‘H and 15N shifts with the CLY chemical shift. This experiment often also provides a weak correlation between the amide NH and 15N resonances of one amino acid and the Ca resonance of the preceding amino acid. A third experiment (HCACO) correlates the Ha and GY shifts with the intraresidue carbonyl shift. Finally, a 3D relay experiment, HCA( CO)N, correlates Ha and Cal resonances of one residue with the “N frequency of the succeeding residue. The principles of these experiments are described in terms of the operator formalism. To optimize spectral resolution, special attention is paid to removal of undesired J splittings in the 3D spectra. Technical details regarding the implementation of these triple-resonance experiments on a commercial spectrometer are also provided. The experiments are demonstrated for the protein calmodulin ( 16.7 kDa).

Validation of Relativistic DFT Approaches to the Calculation of NMR Chemical Shifts in Square-Planar Pt(2+) and Au(3+) Complexes.

Recently implemented hybrid density functional methods of calculating nuclear magnetic shielding using the two-component zeroth-order regular approximation approach (J. Phys. Chem. A2009, 113, 11495) have been employed for a series of compounds containing heavy transition-metal atoms. These include Pt(2+), Pd(2+), and Au(3+) organometallics and metal complexes with azines, some of which exhibit interesting biological and catalytic activities. In this study we investigate the effects of geometry, exchange-correlation functional, solvent, and scalar relativistic and spin-orbit corrections on the nuclear magnetic shielding-mainly for (13)C and (15)N atoms connected to a heavy-atom center. Our calculations demonstrate that the B3LYP method using effective core potentials and a cc-pwCVTZ-PP/6-31G** basis set augmented with the polarizable continuum model of the dimethylsulfoxide solvent provides geometries for the complexes in question which are compatible with the experimental NMR results in terms of both the trends and the absolute values of the (13)C shifts. The important role of the exact exchange admixture parameter for hybrid functionals based on B3LYP and PBE0 is investigated systematically for selected Pt(2+) and Au(3+) complexes. The (13)C and (15)N NMR chemical shifts are found to be best reproduced by using a B3LYP or PBE0 approach with 30% and 40-50% exact exchange admixtures for the Pt(2+) and Au(3+) complexes, respectively. The spin-orbit contributions to the (15)N NMR chemical shifts reflect metal-ligand bonding that is much more ionic for the Au(3+) than for the Pt(2+) complex. Finally, an optimized density functional method is applied to a series of transition-metal complexes to estimate the scope and the limitations of the current approach.

NMR crystallography of 2-acylamino-6-[1H]-pyridones: Solid-state NMR, GIPAW computational, and single crystal X-ray diffraction studies

Abstract 2-Acylamino-6-[1H]-pyridones [acyl = RCO, where R = methyl (1), ethyl (2), iso-propyl (3), tert-butyl (4), and 1-adamantyl (5)] have been synthesized and characterized by NMR spectroscopy. From three congeners, 2, 3 and 5, also single crystal X-ray structures have been solved. For these derivatives GIPAW calculations acts as a “bridge” between solid-state NMR data and calculated chemical shifts based on X-ray determined geometry. In crystals all three compounds exist as pyridone tautomers possessing similar six-membered ring structure stabilized by intramolecular C O⋯HN hydrogen bond. Theoretical GIPAW calculated and experimental 13C and 15N CPMAS NMR shifts are in excellent agreement with each other.

Environmental effects of Deccan volcanism across the Cretaceous–Tertiary transition in Meghalaya, India

The Um Sohryngkew section of Meghalaya, NE India, located 800–1000 km from the Deccan volcanic province, is one of the most complete Cretaceous–Tertiary boundary (KTB) transitions worldwide with all defining and supporting criteria present: mass extinction of planktic foraminifera, first appearance of Danian species, δ13C shift, Ir anomaly (12 ppb) and KTB red layer. The geochemical signature of the KTB layer indicates not only an extraterrestrial signal (Ni and all Platinum Group Elements (PGEs)) of a second impact that postdates Chicxulub, but also a significant component resulting from condensed sedimentation (P), redox fluctuations (As, Co, Fe, Pb, Zn, and to a lesser extent Ni and Cu) and volcanism. From the late Maastrichtian C29r into the early Danian, a humid climate prevailed (kaolinite: 40–60%, detrital minerals: 50–80%). During the latest Maastrichtian, periodic acid rains (carbonate dissolution; CIA index: 70–80) associated with pulsed Deccan eruptions and strong continental weathering resulted in mesotrophic waters. The resulting super-stressed environmental conditions led to the demise of nearly all planktic foraminiferal species and blooms (> 95%) of the disaster opportunist Guembelitria cretacea. These data reveal that detrimental marine conditions prevailed surrounding the Deccan volcanic province during the main phase of eruptions in C29r below the KTB. Ultimately these environmental conditions led to regionally early extinctions followed by global extinctions at the KTB.

Stable carbon and hydrogen isotope fractionation of dissolved organic groundwater pollutants by equilibrium sorption

Linear free energy relationships (LFERs) were established which relate equilibrium vapor-liquid isotope effects to stable carbon and hydrogen isotope enrichment factors for equilibrium sorption to geosorbents. The LFERs were established for normal, cyclic or branched alkanes, monoaromatic hydrocarbons, and chloroethenes. These LFERs predict that isotopic light compounds sorb more strongly than their heavy counterparts. Defining fractionation as in classical literature by "heavy divided by light", carbon enrichment factors for equilibrium sorption were derived which ranged from -0.13±0.04‰ (benzene) to -0.52±0.19‰ (trichloroethene at 5-15 °C). Hydrogen enrichment factors for sorption of 14 different compounds were between -2.4 and -9.2‰. For perdeuterated hydrocarbons the predicted enrichment factors ranged from -19±5.4‰ (benzene) to -64±30‰ (cyclohexane). Equilibrium sorption experiments with a soil and activated carbon as sorbents were performed in the laboratory for perdeuterocyclohexane and perdeuterotoluene. The measured D/H enrichments agreed with the LFER prediction for both compounds and both sorbents within the uncertainty estimate of the prediction. The results of this work suggest that equilibrium sorption does create only very small isotope shifts for (13)C in groundwater pollutants in aquifers. It is also suggested that deuterium shifts are expected to be higher, especially for strongly sorbing pollutants.

13C and 15N Chemical Shift Assignments for the fd Bacteriophage

13C and 15N Chemical Shift Assignments for the fd Bacteriophage

Cutting Off Functional Loops from Homodimeric Enzyme Superoxide Dismutase 1 (SOD1) Leaves Monomeric β-Barrels

Demetallation of the homodimeric enzyme Cu/Zn-superoxide dismutase (SOD1) is known to unleash pronounced dynamic motions in the long active-site loops that comprise almost a third of the folded structure. The resulting apo species, which shows increased propensity to aggregate, stands out as the prime disease precursor in amyotrophic lateral sclerosis (ALS). Even so, the detailed structural properties of the apoSOD1 framework have remained elusive and controversial. In this study, we examine the structural interplay between the central apoSOD1 barrel and the active-site loops by simply cutting them off; loops IV and VII were substituted with short Gly-Ala-Gly linkers. The results show that loop removal breaks the dimer interface and leads to soluble, monomeric β-barrels with high structural integrity. NMR-detected nuclear Overhauser effects are found between all of the constituent β-strands, confirming ordered interactions across the whole barrel. Moreover, the breathing motions of the SOD1 barrel are overall insensitive to loop removal and yield hydrogen/deuterium protection factors typical for cooperatively folded proteins (i.e. the active-site loops act as a "bolt-on" domain with little dynamic influence on its structural foundation). The sole exceptions are the relatively low protection factors in β-strand 5 and the turn around Gly-93, a hot spot for ALS-provoking mutations, which decrease even further upon loop removal. Taken together, these data suggest that the cytotoxic function of apoSOD1 does not emerge from its folded ground state but from a high energy intermediate or even from the denatured ensemble.

1H, 13C, and 15N Chemical Shift Assignments for a complex of PDZ2 from PTP-BL with the C-terminus of RIL (reversion induced LIM)

1H, 13C, and 15N Chemical Shift Assignments for a complex of PDZ2 from PTP-BL with the C-terminus of RIL (reversion induced LIM)

1H, 13C, and 15N Chemical Shift Assignments for a complex of PDZ2 from PTP-BL with the C-terminus of APC (adenomatous polyposis coli)

1H, 13C, and 15N Chemical Shift Assignments for a complex of PDZ2 from PTP-BL with the C-terminus of APC (adenomatous polyposis coli)