Structure-Function Relationships in Pectin Emulsification

The emulsifying characteristics of pectins isolated from six different okra genotypes were investigated and their structure-function relationships have been evaluated. Emulsion formation and stabilization of acidic oil-in-water emulsions (pH 2.0, φ = 0.1) were studied by means of droplet size distribution, ζ-potential measurements, viscometry, interfacial composition analysis and fluorescence microscopy. Fresh and aged emulsions differed in terms of droplet size distribution, interfacial protein and pectin concentrations (Γ) depending on the molecular properties of pectin that was used. Specifically, pectins with intermediate length of RG-I branching with molar ratio of (Ara + Gal)/Rha between 2 and 3 exhibit the optimum emulsification capacity whereas samples with the molar ratio outside this range do not favour emulsification. Additionally, low amounts of RG-I segments (HG/RG-I > 2) improve long term stability of emulsions as opposed to the samples that contain high amounts of RG-I (HG/RG-I < 2) which lead to long term instability. Protein was not found to be the controlling factor for the stability of the dispersions. The present results show that rational design of pectin should be sought before application as functional ingredient in food and/or pharmaceutical systems.

Matrix-assisted diffusion-ordered NMR spectroscopy with an invisible, tuneable matrix

Perfluorooctanoate is a useful “invisible matrix” for mixture analysis by diffusion-ordered NMR (DOSY) with pH-controlled diffusion resolution.

1H and 19F NMR in drug stress testing: the case of voriconazole

Stress tests form an important part of drug development, and of subsequent accreditation.

Relaxation-encoded NMR experiments for mixture analysis: REST and beer

A new family of NMR experiments for mixture analysis (Relaxation-Encoded Selective TOCSY, REST) allows the extraction of component subspectra from mixtures.

A new tool for NMR analysis of complex systems: selective pure shift TOCSY

A new NMR experiment aids the identification of components in complex systems, including mixtures.

Convection in liquid-state NMR: expect the unexpected

Temperature gradients in liquid NMR samples cause convection, attenuating signals in experiments that use field gradients. Different spectrometers and probes show surprisingly different dependences of convection velocity v_max on temperature T.

Increasing the quantitative bandwidth of NMR measurements

The frequency range of quantitative NMR is increased to hundreds of kHz, yielding accurate integrals even for ¹⁹F.

Impact of bread making on fructan chain integrity and effect of fructan enriched breads on breath hydrogen, satiety, energy intake, PYY and ghrelin

Recently, there has been considerable interest in the satiety inducing properties of inulin type fructans (ITF) as a tool for weight management. As a staple food, breads provide an excellent vehicle for ITF supplementation however the integrity of the ITF chains and properties upon bread making need to be assessed. Breads enriched with 12% fructooligosaccharides (FOS) and 12% inulin were baked and the degree of polymerisation of fructans extracted from the breads were compared to those of pure compounds. An acute feeding study with a single blind cross-over design was conducted with 11 participants to investigate the effect of ITF enriched breads on breath hydrogen, self-reported satiety levels, active ghrelin, total PYY and energy intake. Size exclusion chromatography indicated that little or no depolymerisation of inulin occurred during bread making, however, there was evidence of modest FOS depolymerisation. Additionally, ITF enriched breads resulted in increased concentrations of exhaled hydrogen although statistical significance was reached only for the inulin enriched bread (p = 0.001). There were no significant differences between bread types in reported satiety (p = 0.129), plasma active ghrelin (p = 0.684), plasma PYY (p = 0.793) and energy intake (p = 0.240). These preliminary results indicate that inulin enriched bread may be a suitable staple food to increase ITF intake. Longer intervention trials are required to assess the impact of inulin enriched breads on energy intake and body weight.

Sample convection in liquid-state NMR: why it is always with us, and what we can do about it

Many NMR experiments on liquids suffer if the sample convects. This is particularly true for applications, such as the measurement of diffusion, that rely on spatial labelling of spins. It is widely assumed that, in most well-conducted experiments with stable temperature regulation, samples do not convect. Unfortunately this is not the case. It is shown here that typical NMR samples show measurable convective flow for all but a very narrow range of temperatures; convection is seen both above and below this range, which can be as small as a degree or so for a mobile solvent such as chloroform. This convection is driven by both vertical and horizontal temperature gradients. Measurements of convection velocity are presented for a range of samples, sample tubes, probes, and temperatures. Both decreasing sample tube inner diameter and changing sample tube material from glass to sapphire can slow convection markedly, with sapphire tubes being particularly effective. Such tubes are likely to be particularly helpful for accurate measurement of diffusion by NMR.

Measuring couplings in crowded NMR spectra: pure shift NMR with multiplet analysis

Integrating the PSYCHE method for pure shift NMR into 2D J spectroscopy allows each multiplet in a complex proton NMR spectrum to be cleanly extracted.

“Perfecting” pure shift HSQC: full homodecoupling for accurate and precise determination of heteronuclear couplings

Full suppression of proton–proton couplings in pure shift HSQC spectra simplifies their analysis, as demonstrated for high precision RDC measurements.

A simple flowcell for reaction monitoring by NMR

A simple, cheap and flexible flowcell based on a standard 5 mm NMR tube, designed for the monitoring of reactions but of wide applicability, is described. No modification of the NMR instrument is needed, allowing the system to be employed with any conventional NMR probe and magnet. The system is robust and economical in use of reagents, and can be used for studying both homogeneous and heterogeneous reactions.

Constant time gradient HSQC-iDOSY: practical aspects

An improved constant time gradient HSQC-iDOSY pulse sequence is presented, and the corresponding form of the Stejskal-Tanner equation is derived. The pulse sequence is particularly well suited to the problem of analysing mixtures of chemically cognate species, where the high spectral resolution afforded by 1H-13C correlation methods is needed for DOSY experiments to give good diffusion resolution. Its use is illustrated for a mixture of rutin and its aglycone quercetin.

Global amplification of mRNA by template-switching PCR: linearity and application to microarray analysis

Conventional approaches to target labelling for expression microarray analysis typically require relatively large amounts of total RNA, a serious limitation when the sample available is small. Here we explore the cycle-dependent amplification characteristics of Template-Switching PCR and validate its use for microarray target labelling. TS-PCR identifies up to 80% of the differentially expressed genes identified by direct labelling using 30-fold less input RNA for the amplification, with the equivalent of 1000-fold less starting material being used for each hybridisation. Moreover, the sensitivity of microarray experiments is increased considerably, allowing the identification of differentially expressed transcripts below the level of detection using targets prepared by direct labelling. We have also validated the fidelity of amplification and show that the amplified material faithfully represents the starting mRNA population. This method outperforms conventional labelling strategies, not only in terms of sensitivity and the identification of differentially expressed genes, but it is also faster and less labour intensive than other amplification protocols.

Further observations on the size, shape, and hydration of casein micelles from novel analytical ultracentrifuge and capillary viscometry approaches

The size, shape, and hydration of casein micelles were estimated using a combination of sedimentation velocity (time-derivative analysis) in the analytical ultracentrifuge and capillary viscometry applied to skimmed milk. On the basis of sedimentation time-derivative and Wales-van Holde analyses the casein micelles appear as large spherical molecules of s0T,b = 845S, Mw approximately 2.8 x 10(8), hydrodynamic radius approximately 77.8 nm, and ks/[eta] = 1.6. The molecular hydration (i.e., the extent of chemically bound and physically entrained solvent) was calculated to be 3.4 g/g. These results appear to be in good agreement with comparable results from electron microscopy and dynamic light scattering.

Silicon-29 diffusion-ordered NMR spectroscopy (DOSY) as a tool for studying aqueous silicates

The first use of silicon-29 diffusion-ordered NMR spectroscopy (DOSY) is reported, in a study of the speciation of aqueous silicates.

One-dimensional DOSY

A new NMR experiment for correlating diffusion coefficients and chemical shifts is presented. This experiment provides the same information as the conventional DOSY experiment, but only requires a single dimension because a nonuniform magnetic field gradient is used to encode the diffusion information into the lineshapes of the peaks in the chemical shift dimension. By fitting the resulting lineshapes, the diffusion coefficient for each peak in the spectrum can be extracted. Using this experiment, a qualitative DOSY spectrum can be generated using the results from a single one-dimensional experiment. Quantitative results can be determined with the use of reference experiments.

Analyzing and correcting spectrometer temperature sensitivity

Stability and reproducibility of the spectrometer are fundamental to the success of many modern NMR experiments. Variation in room temperature is a particularly important source of instability, in part because it can cause coherent artifacts in NMR spectra. Small changes in room temperature lead to corresponding changes in the phases, amplitudes, and frequencies of NMR signals. These can lead in turn to apparently random spectral artifacts such as t(1)-noise in two-dimensional (2D) NMR and to the incomplete cancellation of signals in difference spectra, but also, importantly, to F(1) satellite signals in 2D spectra. These "parallel diagonals" arise from the use of air conditioning, which typically forces room temperature to oscillate within a fixed band. Work to identify, quantify, and suppress sources of temperature sensitivity in a modern 300-MHz spectrometer has led to a greater than 10-fold improvement in the signal-to-artifact ratio.

A general high-yield route to bis(salicylaldimine) zinc(II) complexes: application to the synthesis of pyridine-modified salen-type zinc(II) complexes

A general, direct, and high-yield synthesis of bis(salicylaldimine) zinc complexes from the ligands and Et(2)Zn is reported. This synthetic method is particularly valuable, not only because it allows the efficient preparation of salen-type complexes of zinc but also because it can be used to prepare bifunctional pyridine-modified zinc(II) bis(salicylidene) complexes, which are potentially useful compounds for applications in asymmetric catalysis and materials chemistry. The synthesis and complete structural characterization of a new series of pyridine-modified zinc(II) bis(salicylidene) ligands is discussed.

Binding of a porphyrin conjugate of Hoechst 33258 to DNA. II. NMR spectroscopic studies detect multiple binding modes to a 12-mer nonself-complementary duplex DNA

We have probed by 1H NMR spectroscopy the molecular basis of the interaction between Hoechst 33258 conjugated to a des-metalloporphyrin and a non self-complementary duplex DNA sequence, designed on the known chemical nuclease selectivity of this system. The imino NMR spectra are consistent with two distinct families of structure, that is, PORHOE binding either way along the duplex. 2D spectral, T2, and linewidth data suggest multiple species within the two conformational families.

Acid-catalyzed degradation of clarithromycin and erythromycin B: a comparative study using NMR spectroscopy

One of the major drawbacks in the use of the antibiotic erythromycin A is its extreme acid sensitivity, leading to degradation in the stomach following oral administration. The modern derivative clarithromycin degrades by a different mechanism and much more slowly. We have studied the pathway and kinetics of the acid-catalyzed degradation of clarithromycin and of erythromycin B, a biosynthetic precursor of erythromycin A which also has good antibacterial activity, using (1)H NMR spectroscopy. Both drugs degrade by loss of the cladinose sugar ring and with similar rates of reaction. These results suggest that erythromycin B has potential as an independent therapeutic entity, with superior acid stability compared with erythromycin A and with the advantage over clarithromycin of being a natural product.

Randomized acquisition for the suppression of systematic F1 artifacts in two-dimensional NMR spectroscopy

2D spectra, particularly for homonuclear correlation, can show a variety of artifactual signals in the F1 domain. Common sources include carry-over of signal modulation from one transient to the next ("rapid pulsing artifacts") and systematic variations in room temperature ("parallel diagonals"). In both cases there is one very simple expedient which can greatly reduce the impact of these sources of error. Multidimensional data sets are almost invariably recorded by simply incrementing or decrementing evolution periods, largely for reasons of convenience and historical precedent. If instead the sampling of the evolution periods is carried out in random order, the perturbations responsible for the sharp F1 signals in the conventional experiment manifest themselves as t1 noise. Since the randomized acquisition redistributes coherent artifactual signals randomly in F1, the maximum artifactual signal is substantially reduced in the randomized experiment and no longer appears in the form of misleading distinct peaks.

Refined high-field NMR solution structure of a binary-addressed pyrene/perfluoro-azide complementary DNA oligonucleotide system shows extensive distortion in the central nick region

The structural analysis of the photoactivated binary system of complementary-addressing nucleic acid sequences (1:2:3) by high-resolution NMR spectroscopy and restrained molecular dynamics is reported. The binary system comprised a 12 base-pair target DNA sequence, pdGTATCAGTTTCT (1), and two hexanucleotides, (dAGAAACp-L-Az (2) and Pyr-pdTGATAC (3)), complementary to neighbouring sites in the target DNA. Oligonucleotide (2) is conjugated with a p-azidotetrafludrobenzyl group (Az) via a linker group (L), and the other oligonucleotide (3) is equipped with the photosensitizing pyrenyl-1-methylamino group (Pyr). We now extend the structural analysis of 1:2:3, which was previously based on qualitative 2D 1H-NMR data and thermodynamic analysis of complex formation from UV-visible thermal denaturation experiments. In the current work structural refinement was performed by separate molecular dynamics runs for six different starting structures based on 318 proton-proton distance-range constraints, evaluated from the 1H-NOESY spectrum (tau(mix) = 200 ms, 600 MHz) using complete relaxation matrix analysis (NMR/TRIAD/MARDIGRAS). Additional Watson-Crick hydrogen bond restraints were included in the calculations based on the detected signals from the exchangeable protons, using REFOPT(NY) methods. The final averaged structure obtained from the six refined co-ordinate sets showed a considerable degree of axis bend (62.5 degrees) with the bending point in the middle of the duplex in the region of the backbone nick between the two short oligonucleotides. The complex behaves dynamically as the equivalent of two short B-DNA-like duplexes displaying a hinge-like flexing at their junction. In all final structures the Pyr function location was very restricted, the aromatic group lying in the duplex minor groove near residues 4T, 5C and 2T. In contrast, the location of the perfluoroazido group was different in all the final structures, indicating the high flexibility of this group in the duplex. The only feature common to all six final azido group orientations was the outside location on the side of the major groove. The distance between the Pyr and Az groups varied from 11 A to 24 A for the six final structures (17 A, final average structure). The dynamics of duplex denaturation for 1:2:3 was probed by monitoring the temperature-induced NMR line broadening of the imino protons in a 1D variable temperature NMR experiment. The melting of 1:2:3 starts both from the ends and from the middle part of the duplex at the backbone break between the two short oligonucleotides reflecting the destabilisation of the pyrene-arylazido nick region in the duplex.

Maxillary canine restoration: a case report

The replacement of a single tooth with osseointegrated dental implants presents a unique challenge to both the prosthodontist and the surgeon. When anterior teeth are replaced, it is difficult to design an occlusal scheme that will direct forces down the long axis of an implant. This is especially true when the canine is involved. Wide-diameter implants offer advantages, such as increased surface area of implant to bone, stronger prosthetics, stronger implants, and less screw loosening or breakage when compared to standard-diameter implants. The single-stage technique is advantageous in terms of soft-tissue predictability, and it eliminates the need for second-stage surgery.

Cross-correlated quadrupolar spin relaxation and carbon-13 lineshapes in the (13)CD(2) spin grouping

Lineshape calculations are reported for a spin system consisting of a spin-12 nucleus scalar-coupled to two magnetically equivalent spin-1 nuclei, e.g., a CD(2) group. It is found that, because of the differential line broadening, the peak height ratio of the five spin-12 nucleus transitions is expected to deviate from the integrated intensity ratio of 1:2:3:2:1. The deviation is dependent on the extent of cross-correlation between the two quadrupolar interactions. The theoretical predictions for peak height ratios and for bandshapes are tested for the carbon-13 spectrum of perdeuterated ethylene glycol, and iterative fitting is used to obtain an estimate of the extent of the correlation between the quadrupolar interactions for the two deuterons.

Automated shimming with normal spectrometer hardware: 3D profile edge shimming

A novel method is proposed for automated magnetic field homogeneity adjustment in high-resolution NMR. The method uses measurements of the edge frequencies of slice profiles recorded under static gradients to obtain three-dimensional magnetic field maps and does not require significant extra spectrometer hardware. Results are presented for the "cold" shimming of 5- and 10-mm-diameter probes in a 400-MHz narrow bore magnet. Copyright 1998 Academic Press.

A three-dimensional DOSY-HMQC experiment for the high-resolution analysis of complex mixtures

A three-dimensional experiment is described in which NMR signals are separated according to their proton chemical shift, 13C chemical shift, and diffusion coefficient. The sequence is built up from a stimulated echo sequence with bipolar field gradient pulses and a conventional decoupled HMQC sequence. Results are presented for a model mixture of quinine, camphene, and geraniol in deuteriomethanol. Copyright 1998 Academic Press.

Dependence of the 1H NMR chemical shifts of ring F resonances on the orientation of the 27-methyl group of spirostane-type steroidal sapogenins

A relationship between the 1H NMR chemical shifts of the ring F resonances and orientation of the H3-27 group has been derived for the establishment of 25R- and 25S-stereochemistry in spirostane type of steroidal sapogenins.

Contrast-modified gradient echo imaging using rotary echo preparatory pulses

The use of on-resonance 121 binomial composite pulses in two- or three-dimensional magnetization-prepared gradient-recalled echo magnetic resonance imaging experiments generates rotary echoes, leading to an increase in contrast range that is, in part, determined by the ratio of T2 to T1. In comparison with other fast gradient-recalled echo imaging techniques designed for enhanced T2 contrast, this method is more robust with respect to radiofrequency field inhomogeneity and less sensitive with respect to motion artifacts. Three-dimensional parametric images may be calculated using least-squares fitting based on a simple model for steady-state longitudinal magnetization during the imaging sequences.

The spatial dependence of spin-echo signals

The signals in NMR spin echoes which are refocused by 90 degrees pulses are spatially modulated. The spatial modulation is not normally observed in images or profiles obtained using Hahn or stimulated echoes, but may cause errors if the sample structure varies on the distance scale of the modulation. Localized spectra measured using stimulated echoes will also show errors under these conditions. Simple Fourier-transform arguments show that conditions which allow the modulation to become visible in an image or profile have the effect of introducing a second echo into the time-domain acquisition window. Phase cycling may be used to remove the spatial dependence of the signals.

Off-resonance binomial composite pulses in 2D and 3D fat/water imaging at 0.5 T

A new method of acquiring two-dimensional (2D) and three-dimensional (3D) fat/water decomposed images on a 0.5 T magnetic resonance (MR) imaging system is described. The method uses a gradient-recalled echo (GRE) sequence incorporating a composite 121 pulse, originally used for magnetization transfer contrast (MTC) experiments, for frequency-selective pre-saturation. By applying the 121 pulse off resonance, a sharp discrimination between the chemically shifted water and fat signals may be obtained using a composite pulse as short as 4 ms. Phantom studies demonstrate that suppression ratios as high as 50:1 are achievable. The new method has been applied to volunteers and patients, and good fat/water images of limb, abdomen, head and neck obtained. The new method can be incorporated into other pulse sequences related to GRE, such as phase contrast (PC) and time-of-flight (TOF), and represents the first practical (i.e. rapid) method for 3D fat/water imaging at an operating field as low as 0.5 T.

Direct observation of the magnetization exchange dynamics responsible for magnetization transfer contrast in human cartilage in vitro

Saturating irradiation far off-resonance can lead to diminution in the water signal seen in MRI, giving rise to magnetization transfer contrast. This results from transfer of magnetization between "solid" protons with restricted motion, which give rise to a band some tens of kilohertz wide, and the narrow signal from mobile protons. In the work reported here a high-power pulse spectrometer, which can detect signals from both mobile and immobile protons, was used to investigate the dynamics of magnetization transfer in cartilage in vitro. Magnetization transfer in modified Hoffman-Forsén inversion transfer experiments was well-described by a single rate constant model; full analytical solutions are offered for the resultant biexponential magnetization recovery curves. The use of pulsed methods to generate magnetization contrast may in some circumstances offer advantages over the steady-state saturation methods used hitherto.

The distribution of Langerhans cells and CD1a antigen in healthy and diseased human gingiva

The distribution of CD1a antigen in gingival epithelium of clinically healthy gingiva was examined and compared with the distribution in gingival epithelium of adult periodontitis lesions. Cryostat sections were examined with monoclonal antibodies to CD1a antigen using the ABC immunoperoxidase technique. In healthy gingiva, CD1a was limited to Langerhans cells (LC) which were observed throughout the length of the external epithelium and orosulcular epithelium. The numbers of LC expressed either per unit length of orosulcular epithelium or per mm2 were similar to the numbers in external gingiva. Junctional epithelium contained few if any dendritic LC. The numbers of LC in pocket epithelium of adult periodontitis lesions were significantly lower compared with orosulcular epithelium of healthy tissue and compared with external gingiva of diseased tissue (p less than 0.005). In many sections, no LC were identified in pocket epithelium. In 5 of 8 adult periodontitis sites, CD1a was also observed in association with the membranes of suprabasal keratinocytes in external and pocket epithelium in areas where no LC were identified. These findings provide further evidence that changes in gingival epithelial cells occur in periodontal disease which are analogous to those documented in dermatological diseases and suggest that epithelium may play a role in gingival homeostasis and in the pathogenesis of periodontal diseases.

Two-dimensional NMR spectroscopy of siomycin A. Proton--carbon-13 chemical shift correlation

A trial application of a recent two-dimensional nuclear magnetic resonance experiment to the polypeptide antibiotic siomycin A is described. Proton--carbon-13 chemical shift correlation measures the proton and carbon-13 chemical shift for each directly bonded CH group in a molecule, in a single experiment. The resultant map of correlated chemical shifts enables the carbon-13 spectrum to be assigned directly from the known proton shifts, and allows individual proton signals to be identified without problems of overlap. The signal-to-noise ratio available from such techniques should enable their application to aqueous protein solutions using currently available high-field spectrometers.

Application of 31P-NMR saturation transfer techniques to investigate phospholipid motion and organization in model and biological membranes

The potential of 31P-NMR saturation transfer experiments for determining motional characteristics (in the millisecond to second time scale) of phospholipids in model and biological membranes is demonstrated. A technique to separate membrane phospholipid 31P-NMR signals from those of small water-soluble phosphates in intact cells in liver tissue is also illustrated.

Rupture of the quadriceps tendon: diagnosis by arthrography

Arthrography revealed an abnormal tract of contrast agent dissecting from the suprapatellar bursa into the soft tissue anterior to the patella and downward to a level 9 cm beneath the tibial plateau in a patient with complete rupture of the quadriceps tendon. The bursal anatomy of the anterior portion of the knee is reviewed in relation to the capsule-forming structures of the quadriceps expansion. The use of knee arthrography for the assessment of quadriceps tendon injury is advocated.

Ganymede: Observations by Radar

Radar cross-section measurements indicate that Ganymede scatters to Earth 12 percent of the power expected from a conducting sphere of the same size and distance. This compares with 8 percent for Mars, 12 percent for Venus, 6 percent for Mercury, and about 8 percent for the asteroid Toro. Furthermore, Ganymede is considerably rougher (to the scale of the wavelength used, 12.6 centimeters) than Mars, Venus, or Mercury. Roughness is made evident in this experiment by the presence of echoes away from the center of the disk. A perfectly smooth target would reflect only a glint from the center, whereas a very rough target would reflect power from over the entire disk.

Mars Radar Observations, a Preliminary Report

Radar observations of a narrow belt of the surface of Mars, centered at 16 degrees south latitude, show a very rugged terrain, with elevation differences greater than 13 kilometers from peak to valley. For nearby points, the relative altitude is measured to 40 meters at best; the precision is worse for points at different latitudes, or widely separated in longitude, because of orbital uncertainties. Some of the larger craters have been resolved, and their depth and, in some cases, the height of the raised rim have been measured. Where high resolution photographs, are available, the correlation is excellent.