Methods for peak assignment in low-resolution multidimensional NMR cross-correlation relaxometry.

Several NMR protocols are presented for assigning peaks in complex T1-T2 spectra, including the effects of varying the spectrometer frequency and the CPMG pulsing rate. Extensions into a third dimension based on chemical-shift; diffusion- and field-cycled weighted T1-T2 cross-correlation methods are also explored as a means of peak assignment. We illustrate the power of these novel techniques with reference to simple aqueous sucrose solutions, but the methodology should be generally applicable.

Ultrasonic Monitoring of Oil-in-Water Emulsions Undergoing Depletion Flocculation

The paper describes a three-part experiment on flocculating emulsions in order to determine whether ultrasonic spectroscopy could be used to detect and characterize the flocculation process. Three emulsions which represented unflocculated, partially flocculated, and fully flocculated systems were prepared. They were characterized independently using direct microscopic examination and their creaming behavior. Ultrasonic spectroscopic measurements of the flocculating emulsions showed large changes during the flocculation process, which were not readily modeled using single particle scattering theory. The ultrasonic properties of the unflocculated emulsion did not change during the measurement period. The results demonstrate that ultrasonic techniques are capable of detecting the flocculation process. There is clear potential to use ultrasonic techniques to characterize flocculated structures, but more work is needed on the theoretical analysis of the interaction of ultrasound with particle aggregates. Copyright 1997Academic Press

Isosteres of the DNA polymerase inhibitor aphidicolin as potential antiviral agents against human herpes viruses.

A variety of isosteres of the DNA polymerase inhibitor aphidicolin were synthesized as potential antiherpes agents. Modeling studies indicated that the bicyclooctane C, D rings of aphidicolin could be replaced by an aromatic moiety while maintaining the spatial arrangement of the hydroxyl group equivalent to the essential C18 hydroxyl group of aphidicolin. Of the racemic isosteres synthesized only 13, the compound with the greatest structural similarity to aphidicolin, showed any significant antiviral activity in primary assays. An enantioselective synthesis of the compound was carried out and the 4aS isomer 36 was shown to account for the observed antiviral activity noted against herpes simplex virus 1 and human cytomegalovirus.

Observations on the ultrastructure of the choanoflagellate Codosiga botrytis (Ehr.) Saville-Kent with special reference to the flagellar apparatus.

The ultrastructure of the choanoflagellate Codosiga botrytis is described with particular reference to the flagellar appendages, the flagellar rootlet system, the transition zone, the basal body and accessory centrioles, and the stalk. The controversial early reports of flagellar appendages in this species have been confirmed and they have been detected in 2 further species, Salpingoeca frequentissima and Monosiga sp. The appendages consist of a delicate bilateral vane 2 mum wide on either side of the axis, composed of extremely fine overlapping or interwoven fibrils. The flagellar root system consists of a large number of radiating microtubules associated with bands of electron-dense material near the basal body; striated roots are absent. The microtubules extend from several separate foci, those in any one group originating near a composite electron-dense band, and for a distance of 300 nm from the basal body they are separated by blocks of interstitial material. The flagellar basal body forms one of a diplosome pair of centrioles. The triplet microtubules of the accessory centriole are embedded in amorphous electron-dense material and the whole is enveloped in a sheath of similar appearance. The existence of a third centriole close to the diplosome pair is also reported. The relatively complex structure of the flagellar transitional zone is described. The stalk is composed of a core of circular lacunae, which may or may not contain finger-like protoplasmic extensions of the posterior end of the cell, surrounded by a continuation of the sheath material which encloses the remainder of the protoplast. In the stalk only there is a further closely sheathing layer about 15 nm thick which is regularly striated, the spacing of the striations in shadowcast material and sections being about 3 times that measured by negative staining. The structure of choanoflagellates differs widely from that of the algal class Chrysophyceae, the group in which they are included in some classifications, and from the remainder of the algae; they do not appear to have a place in either the algae or the plant kingdom. The structure of Codosiga botrytis is briefly compared with that of sponge choanocytes and collared cells in the Metazoa and some of the possible phylogenetic implications of this are indicated.