Studies on the biosynthesis of penicillins

A high yielding synthesis of the acyclic precursor of the penicillins, δ— (L—α—aminoadipyl)—L—cysteinyl—D— valine (LLD-ACV) was developed. Using this synthesis the isotopically enriched ACV peptides, δ-(DL-α—aminoadipyl)—L—cysteinyl—D— (3R)— [4-¹ ³C]—valine and δ—(L—α - aminoadipyl)—L— [3-¹ ³c]—cysteinyl-D— [¹ ³N]—valine were prepared. In an extension to this work the tetrapeptide, δ— (L—α—aminoadipyl)— L— cysteinyl—D— valylglycine (LLD-ACVG) was prepared.A putative intermediate in the biosynthesis of isopenicillin N, N— [δ— (L—α—aminoadipyl)—L—cysteinyl ]—N—hydroxy—D—valine (LLD-AC( N-OH) V), was synthesised from N—hydroxy—D—valine benzyl ester.A cell-free system capable of converting δ— (L—α—aminoadipyl )—L— cysteinyl—D—valine to isopenicillin N was obtained from cultures of the cephalosporin producing fungus Cephalosporium acremonium CW19. The cell-free system was used to test the importance of the above synthesised compounds in penicillin biosynthesis. N— [ δ— (L—α—aminoadipyl )—L—cysteinyl ]-N—hydroxy—D—valine was shown not to be a substrate for the enzyme "isopenicillin N synthetase" but to be a potent inhibitor of the LLD-ACV to isopenicillin N conversion. The tetrapeptide, δ— (L—α—aminoadipyl )—L—cysteinyl—D—valylglycine, was found to be a weak inhibitor of this conversion.The isotopically enriched ACV peptides were used to confirm the stereochemistry of the valine C3 centre in biosynthesised δ— (L—α— aminoadipyl)—L—cysteinyl—D—valine and to allow preliminary ¹ ³C n.m.r. studies on the biosynthesis of isopenicillin N

A user evaluation of hierarchical phrase browsing

Phrase browsing interfaces based on hierarchies of phrases extracted automatically from document collections offer a useful compromise between automatic full-text searching and manually-created subject indexes. The literature contains descriptions of such systems that many find compelling and persuasive. However, evaluation studies have either been anecdotal, or focused on objective measures of the quality of automatically-extracted index terms, or restricted to questions of computational efficiency and feasibility. This paper reports on an empirical, controlled user study that compares hierarchical phrase browsing with full-text searching over a range of information seeking tasks. Users found the results located via phrase browsing to be relevant and useful but preferred keyword searching for certain types of queries. Users experiences were marred by interface details, including inconsistencies between the phrase browser and the surrounding digital library interface

Subject Classification of Collection-level Descriptions Using DDC for Information Landscaping

Collection-level description (CLD) has emerged as an important tool for facilitating user access to large heterogeneous collections within digital library and hybrid information environments. Such metadata enables "information landscaping" techniques to be deployed, thereby allowing users to survey, discover and identify relevant collections. This can aid the precision of item-level queries by eliminating collections which may produce a significant number of false-drops or may contain no relevant items. The ability to provide suitable subject indexing and subject-based organization within such collection-level environments is an increasingly important user requirement, particularly for landscaping; yet it remains highly problematic owing to, for example, the broad subject coverage of many collections and the item-level nature of controlled vocabularies. In this paper we propose a methodology for the subject designation of collections using the Dewey Decimal Classification (DDC). The proposed approach allows the establishment of reliable, consistent and meaningful DDC class numbers to facilitate improved user browsing and searching tools within CLD systems. The methodology will be demonstrated using the Scottish Collections Network (SCONE) and alternative techniques to facilitate general subject analysis will also discussed

Dielectric Elastomers for Energy Harvesting

Dielectric elastomers are a type of electroactive polymers that can be conveniently used as sensors, actuators or energy harvesters and the latter is the focus of this review. The relatively high number of publications devoted to dielectric elastomers in recent years is a direct reflection of their diversity, applicability as well as nontrivial electrical and mechanical properties. This chapter provides a review of fundamental mechanical and electrical properties of dielectric elastomers and up-to-date information regarding new developments of this technology and it’s potential applications for energy harvesting from various vibration sources explored over the past decade

The Morphology ofTrypanosoma GambienseandTrypanosoma Rhodesiensein Cultures: And a Comparison with the Developmental Forms Described inGlossina Palpalis

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