63Cu NMR spectroscopy of copper(I) complexes with various tridentate ligands: CO as a useful 63Cu NMR probe for sharpening 63Cu NMR signals and analyzing the electronic donor effect of a ligand

63Cu NMR spectroscopic studies of copper(I) complexes with various N-donor tridentate ligands are reported. As has been previously reported for most copper(I) complexes, 63Cu NMR signals, when acetonitrile is coordinated to copper(I) complexes of these tridentate ligands, are broad or undetectable. However, when CO is bound to tridentate copper(I) complexes, the 63Cu NMR signals become much sharper and show a large downfield shift compared to those for the corresponding acetonitrile complexes. Temperature dependence of 63Cu NMR signals for these copper(I) complexes show that a quadrupole relaxation process is much more significant to their 63Cu NMR line widths than a ligand exchange process. Therefore, an electronic effect of the copper bound CO makes the 63Cu NMR signal sharp and easily detected. The large downfield shift for the copper(I) carbonyl complex can be explained by a paramagnetic shielding effect induced by the copper bound CO, which amplifies small structural and electronic changes that occur around the copper ion to be easily detected in their 63Cu NMR shifts. This is evidenced by the correlation between the 63Cu NMR shifts for the copper(I) carbonyl complexes and their nu(C[triple bond]O) values. Furthermore, the 63Cu NMR shifts for copper(I) carbonyl complexes with imino-type tridentate ligands show a different correlation line with those for amino-type tridentate ligands. On the other hand, 13C NMR shifts for the copper bound 13CO for these copper(I) carbonyl complexes do not correlate with the nu(C[triple bond]O) values. The X-ray crystal structures of these copper(I) carbonyl complexes do not show any evidence of a significant structural change around the Cu-CO moiety. The findings herein indicate that CO complexation makes 63Cu NMR spectroscopy much more useful for Cu(I) chemistry.     

Density functional computations of 99Ru chemical shifts: relativistic effects, influence of the density functional, and study of solvent effects on fac-[Ru(CO)3I3]-

Solvent effects on the 99Ru NMR chemical shift of the complex fac-[Ru(CO)3I3]- are investigated computationally using density functional theory. Further, benchmark calculations of the 99Ru shift for a set of ten Ru complexes have been performed in order to calibrate the computational model and to determine the importance of relativistic effects on the 99Ru nuclear magnetic shielding and on the chemical shift. A computational model for fac-[Ru(CO)3I3]- that includes both explicit solvent molecules and a continuum model is shown to yield the best agreement with experiment. Relativistic corrections are shown to be of minor importance for determining 99Ru chemical shifts. On the other hand, the nature of the density functional is of importance. In agreement with literature data for ligand trends of 99Ru chemical shifts, the chemical shift range for different solvents is also best reproduced by a hybrid functional.     

α'-三氟甲基-含氟β-二酮镧系螯合物的合成及其用作位移试剂的研究

本文合成了α'-三氟甲基-含氟β-二酮镧系螯合物Ln{CF3CF2[CF2OCF(CF3)]nCOCHCOC(CH3)3}3[n=1; Ln=Eu(1a), Pr(1b), Nd(1c),Sm(1d), Gd(1e), Tb(1f), Dy(1g), Er(1h). n=2; Ln=Eu(2a), Pr(2b), Nd(2c),Sm(2d), Gd(2e), Tb(2f), Dy(2g), Er(2h)], 并研究了它们的位移性能. 1a、1b、2a和2b在用作位移试剂时, 不仅具备Ln(fod)3(Ln=Eu, Pr)的所有优点, 而且还有另外两个优点: (1)在底物存在时, 试剂自身的叔丁基峰明显向高场迁移, 特别是在醇类化合物存在下, δ-Bu^t接近于0ppm, 因此, 1a和2a的t-Bu峰总是处于底物ω-甲基的高场, 不干扰图谱的解析. (2)1b和2b虽为镨类螯合物, 但与1a与2a一样, 都能得到非常清晰的一级图谱. c、f和g均使谱峰向高场迁移, 而h却使谱峰向低场迁移. c的位移能力略低于b. f、g和h的位移能力极强.     

The influence of solvation on the stability constants of Ag<Superscript>+</Superscript>-18-crown-6 complexes in acetonitrile-dimethylsulfoxide mixtures at 298.15 K

The influence of the composition of acetonitrile-dimethylsulfoxide solvents on the stability of silver(I) complexes with 18-crown-6 ether was studied potentiometrically. An increase in the concentration of dimethylsulfoxide decreased the stability of the coordination compound. It was shown on the basis of the thermodynamic characteristics of solvation of the reagents that a determining factor of complex formation equilibrium shifts was the solvation effect of the Ag⁺ ion. An equation was suggested for predicting the stability of silver(I) coordination compounds with crown ethers and pyridine-type ligands in binary mixtures of aprotic solvents from changes in the solvation state of the central ion.     

Stereospecificity and enantioselectivity in the binding of the platinum(II) complex [PtCl2(tmdz)] (tmdz = 5,5,7-trimethyl-1,4-diazacycloheptane) to dinucleotides and oligonucleotides

The two stereoisomers formed on reaction of each of the enantiomers of [PtCl2(tmdz)] with d(GpG) have been identified by using one- and two-dimensional 1H NMR spectroscopy. For both isomers formed with the R enantiomer the 3'-H8 shifts are downfield from those for the 5'-H8. For the S enantiomer the reverse is observed, showing that the bulky tmdz ligand determines the pattern of shifts. Models of these isomers generated by molecular mechanics show that the bulky tmdz ligand limits the rotation of the guanine bases and enforces right-handed (R2) canting for both isomers formed by the R enantiomer and left-handed (L1) canting for those formed by the S enantiomer. The pattern of H8 shifts is the opposite to that expected for these cantings; this suggests that other factors may play a role in determining these shifts. The interactions between the tmdz and d(GpG) ligands are also shown by molecular mechanics and the broadness of the H8 NMR signals to influence the tendency of the coordinated guanine bases to rotate about their Pt-N7 bonds. Reaction of each of the enantiomers with a 52 base-pair nucleotide, with a total of six GpG binding sites, resulted in the formation of only one of the stereoisomers in each case, the first reported case of complete stereoselectivity, or stereospecificity, in the reaction of Pt complexes with DNA. The observed stereoisomers were identified by comparison with the properties of the d(GpG) complexes. Molecular mechanics models of the adducts with duplex DNA show that the nonformation of one stereoisomer is consistent with the steric bulk of the tmdz ligand preventing closure from the monofunctional adduct to the bifunctional adduct. Enantioselectivity is also observed in that the R enantiomer forms more monofunctional adducts than bifunctional (59:41), whereas the S enantiomer forms more bifunctional adducts (27:73). The origins of this enantioselectivity must be at the level of monofunctional adduct formation and this has been investigated by molecular mechanics modelling.     

13C and 19F chemical shifts of bridgehead halogenated adamantanes

The ¹³C chemical shifts of the sixteen bridgehead substituted mono-, di-, tri- and tetrahaloadamantanes (halo = F, Cl, Br, I) and four mixed 1,3-dihaloadamantanes are reported. The effect of bridgehead halogens on the shift values of carbons in β and δ positions is well correlated by the simple additivity relationship based on substituent shifts of 1-monohaloadamantanes. A substituted α-carbon is shifted upfield with an increase in the number of halogens at other bridgehead positions and this shift is relatively greater in the order F < Cl < Br < I. This observed upfield shift of α-carbons is opposite to the downfield shift expected from additivity. An unsubstituted bridgehead γ-carbon is moved to lower fields by one, two and three bromines (or iodines) at other bridge-heads while, in contrast, a third fluorine weakly shields the remaining unsubstituted γ-carbon. Some special noncumulative effects of halogens operating across the 1,3-bridgehead positions of adamantane are indicated by the data. The ¹⁹F chemical shifts of 1-fluoro-, 1,3-difluoro-, 1,3,5-trifluoro- and 1,3,5,7-tetrafluoroadamantanes are contrary to expectations based on inductive effects in that they move progressively upfield. Other 1-fluoroadamantanes with chloro, bromo, or methyl groups present also show substituent-induced chemical shifts which shield the fluorine.     

Effects of amino acid phi,psi propensities and secondary structure interactions in modulating H alpha chemical shifts in peptide and protein beta-sheet.

H alpha chemical shifts are often used as indicators of secondary structure formation in protein structural analysis and peptide folding studies. On the basis of NMR analysis of model beta-sheet and alpha-helical peptides, together with a statistical analysis of protein structures for which NMR data are available, we show that although the gross pattern of H alpha chemical shifts reflects backbone torsion angles, longer range effects from distant amino acids are the dominant factor determining experimental chemical shifts in beta-sheets of peptides and proteins. These show context-dependent variations that aid structural assignment and highlight anomalous shifts that may be of structural significance and provide insights into beta-sheet stability.     

Structure determination of protein-protein complexes using NMR chemical shifts: case of an endonuclease colicin-immunity protein complex

Nuclear magnetic resonance (NMR) spectroscopy provides a range of powerful techniques for determining the structures and the dynamics of proteins. The high-resolution determination of the structures of protein-protein complexes, however, is still a challenging problem for this approach, since it can normally provide only a limited amount of structural information at protein-protein interfaces. We present here the determination using NMR chemical shifts of the structure (PDB code 2K5X) of the cytotoxic endonuclease domain from bacterial toxin colicin (E9) in complex with its cognate immunity protein (Im9). In order to achieve this result, we introduce the CamDock method, which combines a flexible docking procedure with a refinement that exploits the structural information provided by chemical shifts. The results that we report thus indicate that chemical shifts can be used as structural restraints for the determination of the conformations of protein complexes that are difficult to obtain by more standard NMR approaches.     

Temperature-Dependent Terahertz Spectra of Isonicotinamide in the Form I Studied Using the Quasi-Harmonic Approximation

Anharmonicity of molecular vibrational motions is closely associated with the thermal property of crystals. However, the origin of anharmonicity is still not fully understood. Low-frequency vibrations, which are usually defined in the terahertz (THz) range, show excellent sensitivity to anharmonicity. In this work, anharmonicity of isonicotinamide in the form I was investigated by using temperature-dependent terahertz time-domain spectroscopy and the quasi-harmonic approximation (QHA) approach at PBE-D3 and PBE-MBD levels. Both DFT calculations suggest the variation of π-π stacking conformation dominates in the thermal expansion of the unit cell. Frequency shifts of the modes in THz range obtained by QHA approach are found to be qualitatively consistent with experimental observations, demonstrating QHA approach is a useful tool for the interpretation of frequency shifts of modes induced by temperature.     

Mixed quantum-classical molecular dynamics analysis of the molecular-level mechanisms of vibrational frequency shifts

A detailed analysis of the origins of vibrational frequency shifts of diatomic molecules (I2 and ICl) in a rare gas (Xe) liquid is presented. Specifically, vibrationally adiabatic mixed quantum-classical molecular dynamics simulations are used to obtain the instantaneous frequency shifts and correlate the shifts to solvent configurations. With this approach, important mechanistic questions are addressed, including the following: How many solvent atoms determine the frequency shift? What solvent atom configurations lead to blue shifts, and which lead to red shifts? What is the effect of solute asymmetry? The mechanistic analysis can be generally applied and should be useful in understanding what information is provided by infrared and Raman spectra about the environment of the probed vibrational mode.     

13C NMR study of halogen bonding of haloarenes: measurements of solvent effects and theoretical analysis

Solvent effects on the NMR spectra of symmetrical (X = F (1), X = Cl (2), X = Br (3), X = I (4), X = NO2 (5), X = CN (6)) and unsymmetrical (X = I, Y = MeO (7), Y = PhO (8)) para-disubstituted acetophenone azines X-C6H4-CMe=N-N=CMe-C6H4-Y and of models X-C6H4-CMe=N-Z (X = I, Z = H (9), Z = NH2 (10)), 4-iodoacetophenone (11), and iodobenzene (12) were measured in CDCl(3), DMSO, THF, pyridine, and benzene to address one intramolecular and one intermolecular issue. Solvent effects on the (13)C NMR spectra are generally small, and this finding firmly establishes that the azine bridge indeed functions as a "conjugation stopper," an important design concept in our polar materials research. Since intermolecular halogen bonding of haloarenes do occur in polar organic crystalline materials, the NMR solution data pose the question as to whether the absence of solvent shifts indicates the absence of strong halogen bonding in solution. This question was studied by the theoretical analysis of the DMSO complexes of iodoarenes 4, 9-12, and of iodoacetylene. DFT and MP2 computations show iodine bonding, and characteristic structural and electronic features are described. The nonrelativistic complexation shifts and the change in the spin-orbit induced heavy atom effect of iodine compensate each other, and iodine bonding thus has no apparent effect on Ci in the iodoarenes. For iodides, complexation by DMSO occurs and may or may not manifest itself in the NMR spectra. The absence of complexation shifts in the NMR spectra of halides does not exclude the occurrence of halogen bonding in solution.     

An infrared study on the chemisorption of tertiary phosphines on coinage and platinum group metal surfaces

The chemisorption of dimethylphenyl-, methyldiphenyl- and triphenylphosphine on evaporated gold, silver, copper, rhodium, iridium, palladium, platinum and nickel surfaces has been studied by means of infrared reflection–absorption spectroscopy (IRAS). Multilayers of physisorbed phosphine are formed on the surfaces of all metals studied except nickel after deposition from dilute toluene solution. The deposition rate varies for different metal surfaces and it is sometimes quite slow. The standard immersion time was 20 h in this study to secure that an equilibrium between the surface and the solution is reached. Several minutes of ultrasonic treatment are required to get rid of the physisorbed phosphine, leaving a very thin layer of chemisorbed phosphine on the metal surface. Most of the absorption bands in IRAS spectra of these thin layers show significant shifts, which are especially large for dimethylphenylphosphine. It is evident that the electron distribution in the entire phosphine molecules is changed and that the chemisorption to the coinage and platinum group metal surfaces is strong. Infrared spectra of coordination compounds of gold(I), silver(I) and copper(I) with dimethylphenyl-, methyldiphenyl- and triphenylphosphine and of the corresponding phosphine oxides have served as reference material for the chemisorbed phosphines. The spectra of the coordination compounds show similar shifts and intensity changes as the IRAS spectra of tertiary phosphines chemisorbed on the coinage and platinum group metals. This suggests that the studied phosphines are as strongly bound to the coinage and platinum group metal surfaces as to the monovalent coinage metal ions known to form very stable complexes with tertiary phosphines.     

UV raman examination of alpha-helical peptide water hydrogen bonding

UV resonance Raman spectra (UVRS) of an alpha-helical, 21 residue, mainly Ala peptide (AP) in the dehydrated solid state were compared to those in aqueous solution at different temperatures. The UVRS amide band frequencies of a dehydrated solid alpha-helix peptide show frequency shifts compared to those in aqueous solution due to the loss of amide backbone hydrogen bonding to water; the amide II and amide III bands of the solid alpha-helix downshift, while the amide I band upshifts. The shifts are identical in direction but smaller than those that occur for alpha-helices in aqueous solution as the temperature increases; water hydrogen bonding strengths decrease as the temperature increases. The UV Raman amide band frequency shifts can be used to monitor alpha-helix hydrogen bonding.     

Inclusion complex of 2-naphthylamine-6-sulfonate with beta-cyclodextrin: intramolecular charge transfer versus hydrogen bonding effects

The photophysical characteristics of the ground and excited states of 2-naphthylamine-6-sulfonate (2-NA-6-S) were investigated in different solvents and in beta-cyclodextrin (beta-CD). The spectral shifts are well correlated with Kamlet-Taft relationship. Multiple linear regression analysis indicated that both non-specific dipolar interaction and specific hydrogen bonding interactions play competitive roles in determining the position of the absorption maximum, while the dipolar interaction is the dominating parameter in determining the emission maximum. For the Stokes shift, both the nonspecific interaction and the hydrogen donation property of the solvent are participating equally. The molecular encapsulation of 2-NA-6-S by beta-CD in aqueous solution has been studied by different spectroscopic techniques. Fluorescence measurements show that the dielectric constant of beta-CD experienced by the included 2-NA-6-S is intermediate between water and methanol. The changes observed in the absorption and fluorescence spectra of 2-NA-6-S upon inclusion in beta-CD allowed the association constant to be calculated and found to be 465+/-100 and 495+/-100 M-1, respectively. The changes observed for the chemical shifts of 2-NA-6-S and beta-CD 1H NMR spectra and the corresponding 1H NMR spectra of their mixture confirmed the formation of the inclusion complex and showed that 2-NA-6-S is encapsulated in beta-CD cavity in a tilted equatorial approach.     

NMR spectroscopy can characterize proteins encapsulated in a sol-gel matrix

Proteins encapsulated within sol-gel matrices (SG) have the potential to fill many scientific and technological roles, but these applications are hindered by the limited means of probing possible structural consequences of encapsulation. We here present the first demonstration that it is possible to obtain high-resolution, solution NMR measurements of proteins encapsulated within a SG matrix. With the aim of determining the breadth of this approach, we have encapsulated three paramagnetic proteins with different overall charges: the highly acidic human Fe3+ cytochrome b5 (cyt b5); the highly basic horse heart cytochrome c (cyt c); and the nearly neutral, sperm whale cyanomet-myoglobin. The encapsulated anionic and neutral proteins (cyt b5; myoglobin) undergo essentially free rotation, but show minor conformational perturbations as revealed by shifts of contact-shifted peaks associated with the heme and nearby amino acids.     

Substituent effects in heterocyclic systems. 1H-NMR Study of methyl 3,5-diarylisoxazolium iodides

Methyl 3-aryl-5-phenylisoxazolium iodides (I) and methyl 3-phenyl-5-arylisoxazolium iodides (II) were synthesized from the corresponding isoxazoles in moderate yields. The ¹H-nmr chemical shifts for H-4, series I and II, and the quaternary methyl group series II were found to correlate with values. The rho value observed for H-4 series II was 3.3 times that observed in series I. The correlation observed in series I contrasts with the lack of (poor) correlations reported in the corresponding isoxazole and chalcone systems. The rho value observed in the correlation of the quaternary methyl group series II correlates well with an estimate based on methyl pyridinium salt data. The chemical shifts of the quaternary methyl group series I showed little or no variation. Swain-Lupton and DSP treatments did not show improved correlations over the single parameter results. However, interpretation of these treatments reveals that similar processes are occuring in all three cases. The results for H-4 series I showed that the reduction of transmission of the substituent effect in series I compared to that in series II was essentially due to equal reduction of both inductive and resonance effects. The mechanism of transmission seems to differ only in degree and not type.     

Linear correlation between 1H and 13C chemical shifts of ferriheme proteins and model ferrihemes

The (1)H{(13)C} HMQC experiment at natural-abundance (13)C provides a very useful way of determining not only (1)H but also (13)C chemical shifts of most heme substituents, without isotopic labeling of the hemin. This is true both in model low-spin ferriheme complexes and in low-spin ferriheme proteins, even when the proton resonances are buried in the protein diamagnetic region, because the carbon shifts are much larger than the proton shifts. In addition, in many cases, the protohemin methyl cross peaks are fairly linearly related to each other, with the slope of the correlation, δ(C)/δ(H), being approximately -2.0 for most low-spin ferriheme proteins. The reasons why this should be the case, and when it is not, are discussed.     

Redox active macrocyclic receptors for neutral guests

A novel series of triazine-appended macrocyclic complexes has been investigated as potential hydrogen bonding receptors for complementarily disposed heterocycles. Cocrystallization of a melamine-appended azacyclam complex of Cu(II) has been achieved with barbitone, the barbiturate anion and thymine. In each case, a complementary DAD/ADA hydrogen bonding motif between the melamine group and the heterocycle has been identified by X-ray crystallography. Electrochemical studies of the copper macrocycles in both nonaqueous and aqueous solution show anodic shifts of the Cu(II/)(I) redox couple of more than 60 mV upon addition of guest molecules with matching H-bonding motifs. The Zn(II) analogues have been synthesized via transmetalation of the Cu(II) complex, and their guest binding properties investigated by NMR spectroscopy. (1)H NMR shifts of up to 0.8 ppm were observed upon addition of guest, and stability constants are similar to those obtained electrochemically.     

Exploring new 129Xe chemical shift ranges in HXeY compounds: hydrogen more relativistic than xenon

Among rare gases, xenon features an unusually broad nuclear magnetic resonance (NMR) chemical shift range in its compounds and as a non-bonded Xe atom introduced into different environments. In this work we show that (129)Xe NMR chemical shifts in the recently prepared, matrix-isolated xenon compounds appear in new, so far unexplored (129)Xe chemical shift ranges. State-of-the-art theoretical predictions of NMR chemical shifts in compounds of general formula HXeY (Y = H, F, Cl, Br, I, -CN, -NC, -CCH, -CCCCH, -CCCN, -CCXeH, -OXeH, -OH, -SH) as well as in the recently prepared ClXeCN and ClXeNC species are reported. The bonding situation of Xe in the studied compounds is rather different from the previously characterized cases as Xe appears in the electronic state corresponding to a situation with a low formal oxidation state, between I and II in these compounds. Accordingly, the predicted (129)Xe chemical shifts occur in new NMR ranges for this nucleus: ca. 500-1000 ppm (wrt Xe gas) for HXeY species and ca. 1100-1600 ppm for ClXeCN and ClXeNC. These new ranges fall between those corresponding to the weakly-bonded Xe(0) atom in guest-host systems (δ < 300 ppm) and in the hitherto characterized Xe molecules (δ > 2000 ppm). The importance of relativistic effects is discussed. Relativistic effects only slightly modulate the (129)Xe chemical shift that is obtained already at the nonrelativistic CCSD(T) level. In contrast, spin-orbit-induced shielding effects on the (1)H chemical shifts of the H1 atom directly bonded to the Xe center largely overwhelm the nonrelativistic deshielding effects. This leads to an overall negative (1)H chemical shift in the range between -5 and -25 ppm (wrt CH(4)). Thus, the relativistic effects induced by the heavy Xe atom appear considerably more important for the chemical shift of the neighbouring, light hydrogen atom than that of the Xe nucleus itself. The predicted NMR parameters facilitate an unambiguous experimental identification of these novel compounds.     

Substituent effects in heterocyclic systems by carbon-13 nuclear magnetic resonance. Isoxazoles

The carbon-13 nmr spectra of a series of 3-aryl-5-phenylisoxazoles (I) and 3-phenyl-5-arylisoxazoles (II) have been recorded and the signals assigned. Carbon-13 data for series I show little effect of substituent on the chemical shift of the isoxazole ring carbons. However, a plot of the carbon-13 chemical shift of carbon-5 in the isoxazole system I versus the chemical shift of carbon-3 in the 3-(4′-aryl)-1-phenylpropenones gives a straight line (r = .989) with a slope of 0.35. In series II, the chemical shifts of both carbon-4 and -5 are relatively sensitive to substituent effects. Fair correlations between Hammett sigma values and the chemical shifts of these two carbons are found; dual substituent parameter treatment improves the correlations. The results obtained from correlations with carbon-4 in series II are similar to those obtained from β-carbons of a number of styrene systems. The data show that carbon-4 in series II is approximately 20% less sensitive to substituent effects than the previously reported data for carbon-3 of 2-arylfurans. Transmission of substituent effects in the isoxazole system compare well with those of the benzothiazole system.