2D-COLOC

Comment Triad assignments were deduced using the 2D COLOC experiment. 

Moreover in 87-94, which have different esterification sites, a 2D COLOC spectra is necessary for the identification of the sites of attachment of the various substitution groups long-range carbon-proton shift correlations are observed between the carbonyl carbon of p-coumaroyl acid residues and H-6" of the glucose moiety, or between the carbonyl carbon of the trans-p-coumarovl or the cis-p-coumaroyl unit and H of glucose supporting the esterification and H-7 " of coumaric acid residue. This work also led to the structural revision of two of these flavonol glycosides, 92 and 93. 

The NMR techniques discussed so far provide information about proton-proton interactions (e.g., COSY, NOESY, SECSY, 2D y-resolved), or they allow the correlation of protons with carbons or other hetero atoms (e.g., hetero COSY, COLOC, hetero /resolved). The resulting information is very useful for structure elucidation, but it does not reveal the carbon framework of the organic molecule directly. One interesting 2D NMR experiment, INADEQUATE (Incredible Natural Abundance Double Quantum Transfer Experiment), allows the entire carbon skeleton to be deduced directly via the measurement of C- C couplings. 

Total assignment of the H and 13C NMR chemical shifts as well as the relative configuration of the Diels-Alder adducts 33-35 was accomplished with the help of 2D (111-111 COSY, H-111 NOESY (NOESY = nuclear Overhauser enhancement spectroscopy), H- C XHCORR (XHCORR = nucleus X-hydrogen correlation), H-13C COLOC) and NOE difference spectroscopy <1996JHC697>. 

C. Roldan. Implementation computacional usando el metodo de colocation con funciones de base radial para el modelo de stokes en 2d de fluidos newtonianos con aplicaciones en flujos de polimeros. Diploma thesis, EAFIT University, 2005. 

One of six chromenone glycosides isolated from the tubers of Eranthis hyemalis and structurally identified by a combination of FAB-MS and 2D (COSY, COLOC) NMR techniques was compound (15), a / -D-glucopyranoside of 7-(hydroxymethyl)-2,3-dihydro-2-(l-hydroxy-l-methylethyl)-4-methoxy-5/7-furo[3,2- ][l]benzopyran-5-one <91HCA611). 

In addition, 3D imaging also allows the trained eye to identify other important parameters such as e.g. the distance between the probes and whether the probes are colocalized (2D systems simply cannot reveal this). Furthermore, the documented improved accuracy and precision of 3D images help avoid potential mistakes such as image distortion and magnification common with 2D imaging technology. 

The assignments are based on 2D COSY and COLOC experiments, as well as the chemical shifts and results of the DEPT spectrum. All the assignments, except C7 and C9 which are interchanged, are consistent with published values for amoxicillin trihydrate dissolved in dimethyl sulphoxide [23], although there are some chemical shift differences due to solvent effects. 

The structural elucidation of these sesquiterpenes, given the difficulty in determining the linking sites of the respective ester groups when more than three kinds of acid are involved as esters in the molecule, necessitates the use of nmr experiments (selective INEPT [10], Coloc [11] or HMBC 2D [12]), selective hydrolysis processes or X-ray crystallographic methods [13], From comparison of the chemical shifts of similar compounds, it is not easy to establish the exact position of each ester. 

Several ID and 2D NMR techniques have become standard tools for structure elucidation studies of the resveratrol oligomers. The most commonly employed of these include the one-bond i3C- H HETCOR and HMQC, as well as, the two- and three-bond C- H FLOCK [106], COLOC [67,72,88,106], andHMBC [53,71,78] pulse sequences. Typical 2 Vc-h coupling constant values used for these experiments range between. 7=8-12 Hz. Other commonly used H- H correlation methods include standard COSY [64] and NOESY [67,72,78] pulse sequences however, the most widely employed experiment concerning proton-proton... 

The domain is concerned with mainly two varieties of CH 2D experiments the one-bond correlation and the long range (two- or three-bond) correlation. These experiments were formerly run in the so-called normal mode acquisition with modulation) and were named CH COSY (XH CORR or HETCOR) and COLOC (long range). These acron rms are now being replaced with HMQC ( Heteronuclear Multiple Quantum Correlation) and HMBC (Heteronuclear Multiple Bond Correlation) and they are run in the reverse mode ( H acquisition with C modulation). The differences between normal and reverse experiments are sensitivity (a factor of 5) and resolution (in the dimension of acquisition ). 

The structure of a glycopeptide (14.) obtained by a rearrangement during attempted glycosylation of H-Ddz serine benzyl ester, has been determined by the COLOC technique. The structure determination of peracetylated glycosphingoliplds by unidimensional and 2D H-n.m.r. techniques at 360 and 500 MHz has been reported. The... 

COSY = homonuclear chemical shift correlation spectroscopy NOESY = 2D nuclear Overhauser effect (NOE) spectroscopy HMQC = heteronuclear mulltiple-quantum coherence RELAY = relayed coherence transfer COLOC = correlation via long-range coupling HMBC = heteronuclear long-range coupling INADEQUATE = incredible natural abundance double quantum transfer experiment. 

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