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Changes in the structure and properties of HZSM-5 zeolites used for extended periods as catalysts in the conversion of methanol to gasoline have been investigated. HZSM-5 samples were characterized using solid-state NMR spectroscopy (27Al and29Si MAS), infrared spectroscopy; chemical analysis, water and nitrogen adsorption, X-ray diffraction, X-ray photoelectron spectroscopy, and129Xe NMR spectroscopy of adsorbed xenon. Use of HZSM-5 in methanol conversion was found to cause dealumination of the zeolite lattice. The catalyst lifetime, however, increased after repeated use in MTG cycles. The dealumination is caused by water produced during methanol conversion, although the extralattice aluminum species formed appear to differ from those produced by calcination or mild hydrothermal treatment. The increase in catalyst lifetime is attributed to a decreased rate of coke formation in catalysts containing lower densities of acid sites.

The effect of calcination and hydrothermal treatments on the structure and properties of HZSM-5 zeolites with a range of aluminum contents has been investigated. Characterization of the treated zeolites was undertaken with solid-state NMR (27Al and29Si), infrared, nitrogen and water adsorption, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, chemical analysis, and129Xe NMR spectroscopy. Both calcination and hydrothermal treatment were found to cause dealumination of the zeolite lattice and formation of extralattice aluminum species of low symmetry which remain within the pores of the zeolite. HZSM-5 with low aluminum content was found to be more resistant to dealumination by either method and the degree of dealumination was greater when steam was present in the treatment.129Xe NMR was found to be a useful probe for the presence of extralattice aluminum in the pores of lattice dealuminated HZSM-5.

Oscillations of electric potential across a liquid membrane consisting of picric acid in nitrobenzene between two aqueous layers were studied. When fully described the oscillations were found to be characteristic of the structural class of a tastant present in the RHS of the liquid membrane. Smaller variations were observed in the pattern of oscillations and were apparently related to variations in the taste qualities within that class.

The peptide k-casein(98–111) corresponding to the sequence 98–111 of bovine k-casein (His-Pro-His-Pro-His-Leu-Ser-Phe-Met-Ala-Ile-Pro-Pro-Lys), which includes the aspartic protease sensitive region, was analysed by 2D 1H NMR spectroscopic techniques in DMSO-d6. The spectral peaks of all protons resolved at 400 MHz were assigned. The changes in the amide proton shifts with pH and temperature and the existence of particular cross peaks in the ROESY spectra were consistent with the central region of the peptide being in an extended chain in solution but with some type of distinct conformations at the N- and C-termini. The results are not consistent with the peptide having any helical structure at either low or high pH.

A novel nuclear magnetic resonance (NMR) assay has been developed to monitor lipase-catalyzed esterification reactions without the need to extract and purify the individual components. The technique measures ratios of ester:alcohol signals and has been shown to be both efficient and reproducible. The assay has proven useful as a quick screen for the effect of varying conditions on the extent of esterification in various biphasic solvent systems and can be applied to both saturated and unsaturated long-chain fatty acid and alcohol substrates. The NMR ratio technique has been used to quantitate the extent of reaction in theCandida cylindracea lipase-catalyzed synthesis of oleyl palmitate, stearyl palmitate, oleyl oleate, oleylgamma-linolenate and oleyl linoleate. The identity of these products was confirmed by high-resolution mass spectrometry.

The structure and distribution of the neutral side chains of three pectic polysaccharide fractions of kiwifruit, possessing widely differing degrees of branching, were studied by chemical methods, gel-permeation chromatography, and 13C-n.m.r. spectroscopy, following degradation with a purified endo-polygalacturonase. Three categories of side chain were identified: (a)(1 → 4)-linked β- d -galactosyl residues, which occurred in regions where the galacturonan backbone contained little rhamnose and small proportions of other neutral sugars; (b) side chains containing proportionately less galactose and more arabinose, xylose, and fucose, which occurred in regions where the galacturonan backbone contained increased proportions of rhamnose; and (c) large (1 → 4)-β- d -galactans, which were attached to the rhamnogalacturonan backbone. The possible contribution of these side chains to cell-wall breakdown during kiwifruit ripening is discussed.

119Sn NMR spectra were used to investigate the aquohalostannate(IV) complexes formed by SnCl4 and SnBr4 in aqueous and halogen acid solutions. Characteristic chemical shifts were assigned to the complex cations [SnX(H2O)5]3+, [SnX2(H2O)4]2+ and [SnX3(H2O)3]+, [SnX4(H2O)2], and the complex anions [SnX5(H2O)]− and [SnX6]2− (where X = Cl or Br); including the pairs of cis/trans or fac/mer isomers. The CPMAS spectra of crystalline solids containing [SnCl6]2− and cis- or trans-[SnCl4(H2O)2] assisted these assignments. The NMR data yielded quantitative estimates of the amounts of the various species in solution as a function of the tin concentration from 0.1 mol dm−3, where the hydrated stannic ion, Sn4+ (aq), is predominant, to near saturation where auto-complexing results in complex anion formation. Soluble hydrolysis products for which OH-bridged structures are proposed were detected in solutions without added HCl or HBr and increase in amount when NaOH is introduced. Solutions containing excess NaOH reveal [Sn(OH)6]2− which has a chemical shift of — 590 ppm and exhibits the Raman frequencies: 552 (v1), 425 (v2), 290 cm−1 (v5), appropriate for octahedral (Oh) symmetry. The 119Sn NMR spectra of tin(IV) mixed halide aqueous solutions consisted of signals ranging from — 600 ppm (H2O and Cl− ligands) to —2000 ppm (Br− ligands), due to the series of species represented by SnClxBry(H2O)z (where x+y+z = 6), and can be interpreted by relating the chemical shift of the tin nucleus to the sum of ligand electronegativities in a given complex. The solvent extraction of tin halides from aqueous acid solution by diethyl ether or isobutyl methyl ketone has been investigated and tin(IV) shown to be extracted in the form of both molecular [SnX4(H2O)2] and ion-pair H+(aq)[SnX5(H2O)]− complexes. These species can also be generated in solution by adding small amounts of water to [SnX6]2− in acetone. Conjoint use of NMR and Raman spectra enables the major species in these systems to be determined and allows the v(SnX) symmetric stretching frequencies to be identified and assigned.

When dl-[4-13C]aspartic acid was provided at regular intervals to Pseudomonas andropogonis cultures between two and three days growth, hydroxythreonine was specifically labelled at C-4 (4-fold enrichment), and rhizobitoxine was specifically labelled at C-4 and C-1 (4-fold and 2-fold enrichments, respectively). The result shows that aspartic acid is converted directly to the 2-amino-4-oxy-but-3-enoic acid moiety of rhizobitoxine. Various l-[U-14C]amino acids were added to P. andropogonis cultures after two days growth. [14C]Aspartic acid was rapidly (

Changes in the 1 H and 13 C NMR spectra over the temperature range −30 to +60°C are used to investigate conformational isomerism in N,N′-dimethylpiperazine, the N,N,N′,N′-tetramethylpiperazonium dication and trialkylpiperazonium monocations of the type MeN(CH 2 CH 2 ) 2 N(Me)R + , where R = Me, Et, n -Pr, i -Pr or CH 2 X (X = Cl, Br or I). Measurements of the rate of ring inverson of the heterocyclic cations ( 1–4 ) from line width data yield values of the enthalpy and entropy of activation; Δ H ≠ = 64 to 75 ± 2 kJ mol −1 and Δ S ≠ = 30 to 80 ± 10 J K −1 mol −1 . These are compared with the values derived from the activation energy (Δ G ≠ = 47 to 56 ± 1 kJ mol −1 ) obtained from the coalescence temperatures of NMR signals from appropriate sets of indicating nuclei. The related seven-membered heterocycle N,N,N′,N′-tetramethylhomopiperazonium dication ( 2 ) exhibits a higher barrier to ring inversion than those of the alkylpiperazonium derivatives. For the N,N,N′-trialkylpiperazonium ions ( 4–7 ) with unlike substituents on the quaternary nitrogen, the NMR spectra show that 70–75% of the ground state molecules have the bulkier group in the equatorial situation. Also reported are some 14 N coupling constants, 1 J ( 14 N, 13 C) of 2.5–4.0 Hz, and 3 J ( 14 N, 1 H) of 1.5–2.0 Hz, involving nitrogen atoms of the quaternary centres.

The technique of 129 Xe n.m.r. has been applied to the study of electric field effects in ZSM zeolites. For ZSM zeolites in the acid form, the chemical shift at zero coverage varies with aluminum content. This variation is explained by changes in the effective electric field experienced by xenon within the zeolite pores as the aluminium content and, hence, the proton concentration vary

DNA adducts of two acridine-linked aniline half-mustards have been isolated and identified. The compound where the half-mustard is attached to the DNA-targeting acridine moiety by a short linker chain alkylates both double- and single-stranded DNA exclusively at guanine N7, as do the majority of known aromatic and aliphatic nitrogen mustards. The longer-chain analogue, also containing a more reactive half-mustard, shows a strikingly different pattern, alkylating double-stranded DNA to yield primarily (> 90%) the adenine N1 adduct, together with < 10% of the adenine N3 adduct and only trace amounts of the guanine N7 adduct. In the presence of MgCl2 (which is known not to inhibit the interaction of drugs at minor groove sites), the adenine N3 adduct is the major product. The latter compound is the first known aniline mustard (and apparently the first known alkylating agent of any type) to preferentially alkylate adenine at the N1 position in duplex DNA. These results are consistent with previous work [Prakash et al. (1990) Biochemistry 29, 9799-9807], which showed that the preferred site of DNA alkylation by the corresponding long-chain acridine-linked aniline bis-mustards in general was at major groove sites of adenines and identifies the major site of alkylation as adenine N1 and not N7. This selectivity for adenine N1 alkylation is suggested to result from a preference for the acridine mustard side chain of these compounds to project into the major groove following intercalation of the acridine, coupled with structural distortion of the DNA helix to make the N1 positions of adenines adjacent to the intercalation sites more accessible.

Quaternary derivatives of naloxone and other compounds are assumed not to enter the central nervous system following systemic administration. We report that i.p. naloxone methylbromide (5 mg/kg) completely reversed the antinociceptive effect of systemically administered morphine (6 mg/kg) in acutely spinalised rats, although it had no effect in the same animals prior to the transection. Naloxone hydrochloride was effective both before and after transection. Nuclear resonance spectra confirmed the purity of both compounds. These results suggest that acute spinal transection allows rapid entry of quaternary naloxone into the spinal cord. Quaternary compounds therefore may need to be used with caution in spinalised animals.

Aqueous molybdate solutions which contain a series of polymeric oxomolybdenum(VI) complex ions have been investigated conjointly by 95Mo and 17O n.m.r. and Raman spectroscopy. The spectra provide evidence of the species [Mo7O24]6–, [Mo8O26]4–, [Mo36O112(H2O)16]8– believed to be formed successively prior to the point at which hydrous MoO3(‘molybdic acid’) precipitates from the acidified solution. This solid will redissolve and a further complex, probably [Mo2O5(H2O)6]2+, is the predominant form of MoVI in 2–6 mol dm–3 nitric or perchloric acid solutions. This species has characteristic vibrational frequencies νsym(Mo–O) 952, νasym(Mo–O) 925, and ν(Mo–O–Mo) 830 cm–1, and gives a 95Mo n.m.r. signal at δ–63 p.p.m. In halogen acid solutions additional complexes exist and spectroscopic evidence shows these to be polymeric oxohalogenomolybdenum(VI) species and the discrete complexes [MoO2X2(H2O)2](X = Cl or Br). Oxygenated organic solvents efficiently extract MoVI from halogen acid solutions in this form and the vibrational spectra of ether or ketone phases show the [MoO2X2(H2O)2] complexes to have cis-trans-cis disposition of ligands. Characteristic 95Mo chemical shifts of the halogeno-complexes [MoO2X2(H2O)2] occur at δ 157 (X = Cl), 217 (X = Br), and 187 p.p.m. for the mixed halide [MoO2ClBr(H2O)2]. I.r. and Raman spectra of the cis-[MoO2Cl4]2– anion have been observed and assigned by studying the crystalline Cs+ salt, but this complex is not present in significant amounts in molybdenum(VI) solutions in concentrated hydrochloric acid.

EXAFS and 129Xe NMR data are presented which show that adsorption of Mo(CO)6 in zeolite NaY followed by decomposition at 200 °C produces uniformly dispersed Mo2 clusters in the zeolite supercages; heating to 400 °C causes sintering to an average cluster size of three or four Mo atoms.

Recently, Kaptein et al. (I, 2) have described an elegant way of selecting particular multiplets (usually an AX spin system) out of a crowded ‘H NMR spectrum by using double-quantum coherence. This note offers an analysis of the selectivity of this experiment. The experiment, which they have called DOUBTFUL (I), works as follows. The standard 90°-~/2-1800-~/2-900 (where 7/2 = 1/4J) pulse sequence is used to create double-quantum coherence, as in the INADEQUATE experiment (3). The double-quantum coherence is allowed to evolve for some time t, and is then “read” with a final 90” pulse. The phases of the final pulse and the receiver are cycled so that only the signals that arrived via the double-quantum coherence are accumulated. The experiment is then repeated for a series of values of t,, the double-quantum evolution time, and all of the acquisitions for all of the t,‘s added together. In these types of experiments, the two members of each doublet appear in the spectrum 180” out of phase with each other. Since we will want to distinguish between positive and negative doublets, it is useful to add a spin echo at the end of the sequence to get the doublets in phase (4). The success of this experiment in selecting a multiplet out of a crowded spectrum is based on the double-quantum evolution time tI . Several theoretical analyses of this pulse sequence acting on an AX system have been published (5, 6) and from them it can be shown that the signal detected in this experiment is proportional to the product sin(2rJ(r/2)). cos(2mt,) where v is the double-quantum frequency relative to the carrier. If VA and vx are the Larmor frequencies of the A and X spins and v. is the rf carrier frequency then

New MS and NMR data for tagetitoxin required the structure to be revised to one consisting of two fused 6-membered heterocyclic rings.

The 119Sn chemical shifts of all ten trihalogenostannate(II) anions [SnClxBryIz]–(x+y+z= 3) are observed in diethyl ether extracts of tin(II) mixed-halide systems measured at –60°C. The tin(II) nuclear shielding order I < Br < Cl is the opposite of that found in tin(iv) halide systems. At room temperature, the tin resonance signals of tin(II) complexes in aqueous HCl, HBr, and Hl solutions, or their solvent extracts, are single peaks whose positions depend on the composition of the phase, showing that several species are in rapid equilibrium. The complex acids H [SnX3] exhibit 119Sn chemical shifts of δ=–40 (X = Cl), +135 (X = Br), and +350 (X = l) p.p.m. in ether extracts at room temperature.

Variable temperature 1H-nuclear magnetic resonance (NMR) has been used to study the interaction of the RNA trimer, GpCpA, with the intercalators ethidium bromide and the acridine derivatives; proflavin, 9-amino-acridine, acridine orange, acridine yellow and acriflavin. The complexes formed were studied at nucleic acid to drug ratios of 1:1 and 5:1, the latter being useful in defining the effects of structural variation in the acridine series and in determining the site of intercalation. All the intercalators greatly stabilized the oligonucleotide duplex, the average melting temperature (Tm) increasing by up to 30 degrees C. Significant changes in individual Tms and chemical shifts were observed for all the GpCpA protons. 9-Amino-acridine and acriflavin did not stabilize the GpCpA duplex as substantially as the other acridine derivatives. It is suggested that this intercalator:GpCpA system, and its associated NMR-derived Tm, is a useful physical probe for potential mutagens.

A set of empirical parameters which allows the prediction of the proton NMR chemical shifts at 70 C of non-exchangeable heterobase and anomeric protons in oligoribonucleotides has been constructed. The set is based on the highly flexible nature of oligoribonucleotide single strands and the wide range of conformational states which can be populated at relatively high temperatures (70 C or greater). A pairwise subtractive procedure, using 129 ribonucleotide oligomers (all 16 dimers, all 64 trimers, 37 tetramers, and 12 pentamers), shows that significant contributions to the observed chemical shift of protons in a given nucleoside residue are made by first, second, and third neighbors on the 3' and the 5' sides. The majority of the neighbors cause shielding effects with the exception of some first neighbors on the 5' side of a given residue. The magnitude of the shielding effects is greatest for the purine heterobases and follows the order A greater than G greater than C greater than U, with first neighbors on the 3'side showing more pronounced effects than second neighbors and these in turn showing larger effects than third neighbors. Second neighbors on the 5' side showed consistently greater shieldings than first neighbors, a result attributed to the deshielding effects of the first 5' neighbor phosphate group. The parameter Tables are applied to the prediction of proton chemical shifts in one heptamer, four hexamers, and two pentamers and give average absolute differences between predicted and observed shifts less than 0.030 ppm. The parameter approach represents an excellent method of generating initial assignments of proton chemical shifts for any single strand oligoribonucleotide.

Model bilayer systems from individual purified chloroplast thylakoid membrane lipids, from reconstituted mixtures of these purified lipids, and from leaf total polar lipid extracts have been prepared in water, and the longitudinal relaxation times ( T ' s 1 ) of the individual carbon atoms of the fatty acyl chains measured by 13 C-NMR spectroscopy. The T ' s 1 increasing distance of the carbon atoms from the polar headgroups in all cases, and as the results from each of the preparations are similar, all can be used as models of chloroplast membrane bilayers. Relaxation time measurements on intact chloroplast thylakoid membranes indicate the presence of chlorophyll resonances in the 13 C-NMR spectrum of the membrane.

The interaction of the polypeptide melittin with chloroplast membrane lipids has been studied by monolayer and 13 C-NMR techniques. Under conditions favouring the existence of a melittin monomer, the interaction of the polypeptide with monolayers of chloroplast lipids is largely confined to negatively charged lipids. Conditions favouring the formation of the melittin tetramer result in a marked interaction of the polypeptide with monolayers of uncharged lipids. 13 C-NMR measurements of the rate of motion of fatty acyl carbon atoms in multibilayers of chloroplast membrane lipids demonstrate that melittin penetrates deeply into the bilayer irrespective of the proportion of negatively charged lipids. It is concluded that interaction of melittin which chloroplast membrane lipids is the primary factor in its capacity to inhibit membrane-associated reactions in chloroplasts.

3α-Hydroxy-(13 S )-16- nor -pimar-7-en-15-oic acid and (13 S )-pimar-7-en-3α,15,16-triol, two new tricyclic diterpenoids, and kaur-16-en-3α,13-diol and kauran-3α,13,16α-triol, two new tetracyclic diterpenoids, have been isolated from the heartwood of the Fijian species Agathis vitiensis . The structures of the new compounds have been assigned from high field NMR measurements. Other constituents include agatharesinol, sitosterol, abietic acid and agathic acid.

Native intact bovine PTH was studied by proton nuclear magnetic resonance (NMR) techniques, at pH 3.5 and pH 6.3. The 1H-NMR spectra had good resolution and many multiplet structures were observed. Assignment of the NMR resonances corresponding to specific amino acids was approached using 1H chemical shifts, coupling constants, and pH dependence in the one-dimensional spectra and the 1H-1H connectivities revealed in two-dimensional homonuclear correlated spectroscopy (COSY) experiments. All the aromatic proton resonances were assigned. Two histidine residues had lower pK than the other two. The methyl groups of two residues were moved significantly downfield: using COSY and two-dimensional nuclear Overhauser enhancement spectroscopy (NOESY) correlations, these were assigned to an alanine residue close to both Trp-23 and Tyr-43, and a valine residue in close spatial proximity to Trp-23. The NOESY spectrum also showed cross-peaks between the residues of the upfield valine-leucine-isoleucine methyl envelope. Many of the H alpha protons moved upfield as the pH was increased. These results indicate that intact native PTH exists in a preferred conformation in solution at pH 6.5. Our studies have provided new information on the three-dimensional spatial proximity of several amino acids along the polypeptide chain. The observed interactions are consistent with the currently accepted model suggesting that the hormone has two separate structural domains associated with the amino- and carboxy-terminal regions of the molecule respectively. The potential implications of this model for the expression of biological activity are discussed.

Specific assignment of the non-exchangeable base and ribose anomeric protons is difficult for oligoribonucleotides with a high pyrimidine content. Problems arise from the narrow range of pyrimidine H-6 chemical shifts and the overlap of pyrimidine H-5 resonances with the ribose anomeric proton signals. To solve these problems two multiple pulse methods were used which depend on the scalar coupling between H-6 and H-5. The first method was double-quantum nmr which established the connectivity between specific pyrimidine H-6 and H-5 resonances. A refocussing pulse was added to the end of the double-quantum pulse sequence to improve the identification of several H-6 and H-5 connectivities in a single experiment. The second procedure involved homonuclear decoupled spin echo nmr to remove H-5 signals selectively from the ribose anomeric proton region. These techniques are illustrated by the assignment of the spectra of the oligoribonucleotides UpUpC, UpUpU, GpCpUpC, and UpApGpCpUpU.

Etude de complexes oxo de molybdene, zirconium et uranium par RMN de l'oxygene 17. La sensibilite est telle que la methode peut etre utilisee sans marquage isotopique de l'oxygene, l'abondance naturelle de 17 O etant suffisante