John B. Grutzner

Coherent broad-band decoupling—An alternative to proton noise decoupling in carbon-13 nuclear magnetic resonance spectroscopy

Abstract Phase modulation of the decoupler carrier frequency with a 50% duty cycle square wave is shown to be an efficient method for broad-band decoupling. Experimental and theoretical studies show that this coherent broad-band decoupling is more effective than random noise decoupling for many applications. In the particular case of proton decoupled carbon-13 NMR spectroscopy, coherent broad-band decoupling is the method of choice because it is more efficient and is simpler to apply than random noise decoupling. Signal/noise improvements by a factor of 2 or more are observed because of the better decoupling even when the resolution is limited by computer criteria.

The conversion of 2,3-butanediol to methyl ethyl ketone over zeolites

In situ DRIFTS and differential reaction studies of 2,3-butanediol dehydration over a series of well-characterized ZSM-5, mordenite, β- and Y-zeolites show that dehydration to methyl ethyl ketone is favored on ZSM-5 but is facile on all the zeolites. At the temperatures above 400 K needed to allow transport into and out of the zeolite channels, aldol condensation and ultimately aromatization narrow the window of practical utility of this family of catalysts.

Phosphorus nuclear magnetic resonance studies of phosphoglucomutase and its metal ion complexes.

Abstract The 31 P nuclear magnetic resonance of the covalently bound phosphate group at the active site of phosphoglucomutase has been examined by means of Fourier transform nuclear magnetic resonance spectroscopy. At a pD of 7.9, the chemical shift of the 31 P nucleus is 3.8 ± 0.1 ppm downfield from 85% H 3 PO 4 ; this shift is close to that of phosphoserine (dianionic form). Proton decoupling experiments suggest that the phosphorus of the enzymic phosphate group is coupled to protons with chemical shifts similar to those of phosphoserine. In D 2 O, with proton decoupling, the ratio of the longitudinal and transverse diamagnetic relaxation times in solutions of 1.6 m m phosphoenzyme yields an approximate correlation time of 10 −7 s for the 31 P nucleus of the enzyme. This is within the range of values expected for tumbling of the entire protein molecule and suggests that the covalently attached phosphate group is immobilized or “frozen” at the active site of the enzyme by means of noncovalent interactions with adjacent groups. Consistent with this, the p K a of the enzymic phosphate is significantly lower than that of phosphoserine. Binding of the diamagnetic activator, Mg 2+ , causes little or no change in the chemical shift of the resonance of the enzymic phosphorus from pD = 5.3 to 7.6, a downfield shift (−0.5 ± 0.1 ppm) at pD = 8.6, but an upfield shift (0.8 ±0.1 ppm) for that of phosphoserine, suggesting that bound Mg 2+ is not coordinated to the enzymic phosphate. Independent evidence against direct coordination is provided by the paramagnetic effects of Ni 2+ bound at the active site on the relaxation rates of the enzymic phosphorus. By assessing the paramagnetic effect of bound Ni 2+ on both the longitudinal and transverse relaxation rates of the observed resonance, and by using correlation times determined for water proton relaxation induced by the Ni 2+ complex, a range of Ni 2+ to phosphorus distances of 4 to 6 A is calculated. These distances suggest a second sphere interaction between the enzyme-bound metal and the enzymic phosphate group. Bound Ni 2+ also markedly decreases the integrated intensity of the 31 P resonance. Although the reason for this intensity decrease is incompletely explained, the present data establish the close proximity of the bound metal ion and the active site phosphoserine on phosphoglucomutase.

Conformational equilibria in cyclohexyltrimethylstannane and cyclohexyltrimethylplumbane by low temperature 13C NMR spectroscopy

The variable temperature carbon-13 NMR spectra of cyclohexyltrimethylstannane and cyclohexyltrimethylplumbane have been recorded, and at −69°C, the chair-chair conformational interconversion is “frozen”. A values (A = -ΔG° = RTln K) for the (CH3)3Sn (1.06 ± 0.14) and (CH3)3Pb (0.67 ± 0.06) groups are derived.

Robinlin: A novel bioactive homo-monoterpene from Robinia pseudoacacia L. (Fabaceae)

A bioactivity-directed fractionation of the ethanolic extracts of Robinia pseudoacacia L. (Fabaceae) afforded robinlin (1), a novel homo-monoterpene. The structure of 1 was elucidated by spectral analyses of the parent compound as well as its derivatives; 1 showed strong bioactivity in the brine shrimp lethality test (BST).

Conversion of biomass to ethanol: Isomerization of xylose over HY zeolite

Xylose, a pentose indigestible to most yeasts, was converted to ethanol by a two-step isomerization and fermentation. HY zeolite was used to catalyze the isomerization of xylose, and the xylulose produced was directly used as the carbon source in ethanol fermentation. Zeolite catalysts offer pH compatibility with yeast fermentation and the ability to carry out isomerization at higher temperature where equilibrium xylulose concentration is higher. Initial rate studies indicate that xylose consumption follows pseudo-first-order kinetics, with a specific rate constant of 6.2×10−4 L/solution/g zeolite/h.

The use of

The unique chemical and biological properties of β-lactam antibiotics and, in particular, the importance of penicillins and cephalosporins in the treatment of a variety of bacterial infections have stimulated investigations in various laboratories concerned with elucidation of the biosynthetic pathways leading to the formation of these antibiotics. Most of the present knowledge of some of these processes has been obtained from tracer studies involving 14C labelled precursors (Abraham & Newton 1967). The recent advances in the instrumentation required for recording 13C n.m.r.(c.m.r.) spectra, as well as commercial availability of simple 13C enriched compounds suitable for the synthesis of appropriate precursors, prompted us to examine the usefulness of c.m.r. spectroscopy in biosynthetic studies of cephalosporin C (Neuss, Nash, Lemke & Grutzner 1971).

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The structure of the cyclooctatetraene dimer of m. p. 53° has been a matter of controversy. Structure I was proposed by Jones(3} and could be reconciled with a proposed mechanism of conversion of the dimer to bullvalene(4). Schroder(5) has proposed structure II because the material afforded the all cis-cyclobutanetetracarboxylic acid on ozonolysis and peracid oxidation. However, there is still a possibility that I could yield ciclobutanetetracarboxilic acid on oxidation by way of its valence tautomer III.

C n.m.r. (C.m.r.) Spectroscopy in Biosynthetic Studies Of

Computational and experimental methods have been utilized to examine the facile dimerization of diazirinyl radicals. Two potential dimers were investigated using density functional theory. Both were shown to have low-barrier reaction coordinates leading to formation of HCN and N2. A cross-over experiment was employed to establish the relative contributions of C–N and N–N dimers towards product formation. The N–N dimerization was found to be dominant under the current conditions, and the corresponding reaction coordinate energetics were further explored using coupled-cluster methods. A detailed mechanism for dimer decomposition is presented. The competition between unimolecular and bimolecular reactions of diazirinyl radicals is explored under high dilution conditions. The high reactivity of the diazirinyl radical as a nitrogen atom transfer agent suggests a possible bimolecular contribution for “prompt” NO formation in hydrocarbon combustion with diazirinyl radicals as intermediates.

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Broadening and additional splitting due to second-order effects in off-resonance proton-decoupled 13C n.m.r. spectra provide evidence that carbon atoms are adjacent to one another.