NMR spectroscopy complexes

When the salt 152 was treated with [(COE)2IrCl]2, the product of C-Fl activation of the cyclooctene (COE) ligand 162 was obtained in 65% yield (Scheme 62) if -binding mode of the cyclooctene ligand in 162 was confirmed by X-ray crystallography and NMR spectroscopy. Complex 162 under the action of Fl2SiMes2 was converted into silylene derivative 163 observed by NMR spectroscopy <1999JA9871>. 

According to NMR spectroscopy, complexes -16 have a low configurational stability of the Ca atoms, giving rise to the formation of a mixture of the diaste-reomeric complexes Rs,Sc-16 and Rs, cT6 (Schemes 1.3.13 and 1.3.14). Addition of the Lewis acids Ti(OiPr)4 and ClTi(OiPr)3 causes their coordination to one of the sulfonimidoyl groups and establishment of an equilibrium between the cor-... 

Abstract Tubulin is a fascinating molecule that forms the cytoskeleton of the cells and plays an important role in cell division and trafficking of molecules. It polymerizes and depolymerizes in order to fulfill this biological function. This function can be modulated by small molecules that interfere with the polymerization or the depolymerization. In this article, the structural basis of this behavior is reviewed with special attention to the contribution of NMR spectroscopy. Complex structures of small molecules that bind to tubulin and microtubules will be discussed. Many of them have been determined using NMR spectroscopy, which proves to be an important method in tubulin research. 

NMR spectroscopy. Complex 22 was formed selectively by oxidative addition of allyl bromide to palladium(II) palladacycle 21. This structure is believed to result from cis oxidative addition of allyl bromide to palladacycle 21. 

Hagaman et al. (2012) studied interaction of benzoic acid with metal oxides using solid-state O NMR spectroscopy. Complexes formed by dry benzoic acid with mesoporous silica and nonporous titania and alumina were analyzed. Chemical reactions with silica were not observed, but the behavior of benzoic acid on silica was a function of the water content. The acid was characterized by high mobility as evidenced by a liquid-like, Lorentzian NMR resonance. Excess benzoic acid remained as the crystalline hydrogen-bonded dimer. Benzoic acid reacted with titania and alumina surfaces in equilibrium with air to form the corresponding titanium and aluminum benzoates. In both materials, the oxygen of the O-labeled acid was bound to the metal, showing the bond... 

Vanadium. The interactions betwen vanadate, uridine, and imidazole have been studied using C, 0, and V NMR spectroscopy. Complex formation between HSCH2CHOHCHOHCH2SH and vanadate has been investigated using V NMR spectroscopy. V NMR spectroscopy has been used to study the interaction of vanadate oligomers with a 90 kDa heat shock protein, Hsp90. The interaction of vanadate with aquatic humic substance has been studied using V NMR spectroscopy. ... 

The example of B5H9 serves to show how the chemical shift may be used as an aid to determining the stmcture of a molecule and, in particular, in deciding between alternative stmctures. There are many examples in the literature of this kind of application which is reminiscent of the way in which the chemical shift in NMR spectroscopy may be employed. However there is one important difference in using the two kinds of chemical shift. In XPS there are no interactions affecting closely spaced lines in the spectmm, however close they may be. Figure 8.15 illustrates this for the C lx lines of thiophene. In NMR spectroscopy the spectmm becomes more complex, due to spin-spin interactions, when chemical shifts are similar. 

The first quantitative model, which appeared in 1971, also accounted for possible charge-transfer complex formation (45). Deviation from the terminal model for bulk polymerization was shown to be due to antepenultimate effects (46). Mote recent work with numerical computation and C-nmr spectroscopy data on SAN sequence distributions indicates that the penultimate model is the most appropriate for bulk SAN copolymerization (47,48). A kinetic model for azeotropic SAN copolymerization in toluene has been developed that successfully predicts conversion, rate, and average molecular weight for conversions up to 50% (49). 

The formation of such materials may be monitored by several techniques. One of the most useful methods is and C-nmr spectroscopy where stable complexes in solution may give rise to characteristic shifts of signals relative to the uncomplexed species (43). Solution nmr spectroscopy has also been used to detect the presence of soHd inclusion compound (after dissolution) and to determine composition (host guest ratio) of the material. Infrared spectroscopy (126) and combustion analysis are further methods to study inclusion formation. For general screening purposes of soHd inclusion stmctures, the x-ray powder diffraction method is suitable (123). However, if detailed stmctures are requited, the single crystal x-ray diffraction method (127) has to be used. 

Another technique often used to examine the stmcture of double-heUcal oligonucleotides is two-dimensional nmr spectroscopy (see AfAGNETiC SPIN resonance). This method rehes on measurement of the nuclear Overhauser effects (NOEs) through space to determine the distances between protons (6). The stmcture of an oligonucleotide may be determined theoretically from a set of iaterproton distances. As a result of the complexities of the experiment and data analysis, the quality of the stmctural information obtained is debated. However, nmr spectroscopy does provide information pertaining to the stmcture of DNA ia solution and can serve as a complement to the stmctural information provided by crystallographic analysis. 

ColEl Regulation by RNA Hairpins. Rephcation of the E. coli plasmid ColEl is regulated by two short RNA molecules and a protein in a system that provides an example of the unique stmcmral elements accessible to RNA molecules. Multidimensional heteronuclear nmr spectroscopy has been used to characterize the complex formed between the two RNAs (25). Each of the RNA molecules fold back on the other to form a pair of hairpin... 

Generally, the most powerful method for stmctural elucidation of steroids is nuclear magnetic resonance (nmr) spectroscopy. There are several classical reviews on the one-dimensional (1-D) proton H-nmr spectroscopy of steroids (267). C-nmr, a technique used to observe individual carbons, is used for stmcture elucidation of steroids. In addition, C-nmr is used for biosynthesis experiments with C-enriched precursors (268). The availability of higher magnetic field instmments coupled with the arrival of 1-D and two-dimensional (2-D) techniques such as DEPT, COSY, NOESY, 2-D J-resolved, HOHAHA, etc, have provided powerful new tools for the stmctural elucidation of complex natural products including steroids (269). 

Application of NMR spectroscopy to heterocyclic chemistry has developed very rapidly during the past 15 years, and the technique is now used almost as routinely as H NMR spectroscopy. There are four main areas of application of interest to the heterocyclic chemist (i) elucidation of structure, where the method can be particularly valuable for complex natural products such as alkaloids and carbohydrate antibiotics (ii) stereochemical studies, especially conformational analysis of saturated heterocyclic systems (iii) the correlation of various theoretical aspects of structure and electronic distribution with chemical shifts, coupling constants and other NMR derived parameters and (iv) the unravelling of biosynthetic pathways to natural products, where, in contrast to related studies with " C-labelled precursors, stepwise degradation of the secondary metabolite is usually unnecessary. 

The formation of acyl halide-Lewis acid complexes have been observed by several methods. For example, both 1 1 and 1 2 complexes of acetyl chloride, with AICI3 can be observed by NMR spectroscopy. The existence of acylium ions has been demonstrated by X-ray diffraction studies on crystalline salts. For example, crystal structure determinations have been reported for /i-methylphenylacylium and acetylium ions as SbFg salts. There is also a good deal of evidence from NMR measurements which demonstrates that acylium ions can exist in nonnucleophilic solvents. " The positive charge on acylium ions is delocalized onto the oxygen atom. This delocalization is demonstrated in particular by the short O—C bond lengths in acylium ions, which imply a major contribution from the structure having a triple bond ... 

Compound 5 was analyzed by NMR spectroscopy to gain information relative to conformation and complexation preferences. When complexation with potassium cations was attempted, the N—CHj signals were affected more than others. When the cation present was Ag , the protons adjacent to sulfur were more strongly affected. This observation may indicate the relative binding sites for soft versus hard cations in this system. ... 

Diorganotin(IV) complexes 109 were characterized by NMR spectroscopy (96MI4). The downfield chemical shift of 6-H in 2-fluoroalkyl-4//-pyrido[l,2-n]pyrimidin-4-ones 111 is attributed to the anisotropic effect of the 4-carbonyl group (97JCS(P1)981). 

The complexation of 6, ciprofloxacin, and lomefloxacin with metals ions were studied in aqueous solution (pD 2.5 37 °C) by and NMR spectroscopy (99MI18). Titration experiments have revealed that the binding ability of 6 towards Al " " ion is much stronger than that of ciprofloxacin and lomefloxacin. Other metal ions (Ca " " and Mg " ") formed much weaker complexes. 

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