Spider silk has outstanding mechanical properties despite being spun at close to ambient temperatures and pressures using water as the solvent. The spider achieves this feat of benign fibre processing by judiciously controlling the folding and crystallization of the main protein constituents, and by adding auxiliary compounds, to create a composite material of defined hierarchical structure. Because the 'spinning dope' (the material from which silk is spun) is liquid crystalline, spiders can draw it during extrusion into a hardened fibre using minimal forces. This process involves an unusual internal drawdown within the spider's spinneret that is not seen in industrial fibre processing, followed by a conventional external drawdown after the dope has left the spinneret. Successful copying of the spider's internal processing and precise control over protein folding, combined with knowledge of the gene sequences of its spinning dopes, could permit industrial production of silk-based fibres with unique properties under benign conditions.

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Liquid crystalline spinning of spider silk.

Strength and structure of spiders' silks.

THE orb web of the garden spider Araneus diadematus, like those of other ecribellate orb spiders, relies on the remarkable extensibility of its sticky capture spiral to intercept and entrap prey1,2. The spiral strands consist of core fibres and an all-enveloping aqueous coat, which forms into a pattern of droplets3. The core fibres are paired and probably made of typical spider silk4,5. The aqueous solution droplets are more or less evenly spaced6 and are required to allow the special mode of extension of the fibres3,7. Knowledge of the chemical composition and general physical properties of this liquid phase is necessary to understand its function in web mechanics and prey capture8. We have now investigated the chemical composition of this aqueous solution and found the droplets to be a concentrated solution of hygroscopic substances related to neurotransmitters. We offer an explanation as to the function and origin of this solution.

Compounds in the droplets of the orb spider's viscid spiral

The garden spider's web filters from the air insects that arrive with considerable kinetic energy. Critical for the absorption of this energy are the tensile strength and extensibility of the silk [1, 2]. To channel this energy, the fine threads must stick firmly to the prey rather than slide off. Thus, adhesiveness may be as important to a web's success as the mechanics of its silk [3]. Although thread mechanics has recently attracted much attention [ 4 8 ] , next to nothing is known about the glue. We have now identified the glue in the web of araneid orb spiders as microscopic nodules made of glycoprotein. The nodules sit astride the capture threads beneath the visible droplets. The finding puts to rest the old notion that the viscous coat itself is the principal adhesive, whereas in reality it is a water reservoir that maintains thread elasticity [6, 8] and also supports glue formation. Orb webs and their builders fall into two categories classified by the silk that renders the web sticky. Cribellate spiders use very fine silk of nm diameter which they comb, in hackled bands of several hundred threads at a time, onto support threads of/~m diameter [9]. We do not understand how this hackled silk functions nor do we understand the mechanism of its adhesiveness [9]. Ecribellate spiders (e.g., the garden cross spider Araneus diadematus) lack cribellure silk. Instead they catch insects using threads of #m diameter coated with an aqueous solution that forms droplets. Coat and droplets are crucial for the function of the capture spiral [8]. The high water content of the coat (80 %) plasticizes the threads and renders them elastic [6]. The droplets, powered by surface tension, keep the threads tight by reeling them in when slackened and unraveling them again when stretched [8]. Chemical analysis of the coat shows high concentrations of five major water-soluble organic compounds [10] and low concentrations of inorganic salts [11, 12] as well as one or more glycoproteins [13 16]. These glycoproteins are the only identified compounds that have sufficiently long side chains to act as glue sensu strictu rather than adhere by virtue of being a highly viscous solution. We now report that the glycoprotein may be concentrated inside distinct structures, nodules that sit astride the capture threads. The nodules, "droplets within droplets" [17], have so far been ignored by research and textbooks on spider orb webs. We have studied nodule morphology, development, function, and chemistry. Nodules, along with the droplets of the viscous coat, form within minutes after the sticky silk has been laid down (Fig. l a c ) . In Araneus, like all ecribellate orb weavers, sticky silk is confined to the capture spiral and consists of a pair of core threads each paid out f rom the central spigot of a triad, the other two spigots providing the aqueous solution of the coat [18]. The two threads immediately merge and the coat flows into distinct droplets connected by a fine layer of liquid [19]. We observed that nodules and droplets correlated in spacing as well as size

Glycoprotein glue beneath a spider web's aqueous coat

Orb web hygroscopicity was examined in three species of araneid spiders, Argiope aurantia, Argiope trifasciata, and Araneus cavaticus. Both whole webs and fractions generated from them (water-soluble and -insoluble fractions; ethanol-soluble and -insoluble subfractions [Etsol and -insol]) were examined at various relative humidities. In general, the water-soluble fraction, consisting of low molecular weight components (LMW) of the adhesive spiral cover, was more hygroscopic than the water-insoluble (protein) fraction. As the Et-sol of the water extract was typically more hygroscopic than the Et-insol, it appears that organic LMW are more responsible for water adsorption by the adhesive spiral cover than inorgnic LMW. Hygroscopicity measurements made on individual synthetic or commercially obtained LMW compounds known to be in the web (both organic and inorganic) agree with this interpretation.



As a first attempt toward correlating web hygroscopicity with composition, the water-soluble web fractions from the three species were examined by proton nuclear magnetic resonance (1H-NMR) spectroscopy and the molar percentages of the organic LMW were estimated. To accomplish this, it was necessary to identify the principal organic LMW in the web of A. trifasciata (since, unlike the situation in other araneids which have been studied, GABamide is not the principal organic LMW in A. trifasciata). Using 1H-NMR and thin layer chromatography this compound was identified as N-acetylputrescine. While considerable interspecific variation in the molar percentages of GABamide, N-acetylputrescine, isethionic acid, and N-acetyltaurine was observed, interspecific differences in Et-sol hygroscopicities were not apparent.

Comparative study of orb web hygroscopicity and adhesive spiral composition in three araneid spiders

Über die Chemie der Spinnwebe, I

Das Spreitungsalkaloid Stenusin aus dem KurzflüglerStenus comma (Coleoptera: Staphylinidae)

Über Arthropodenabwehrstoffe, LIX. Platambin, ein Wehrstoff des Schwimmkäfers Platambus maculatus (Coleoptera: Dytiscidae)

Quasi-axiale Substituenten (z. B. Wasserstoff und Chlor) am C-9 von 1,2,3,4-Tetraphenyl-9H-tribenzo[a,c,e]cyclohepten (1) werden leicht unter Bildung quasi-axialer Organometall-Verbindungen ausgetauscht. Lediglich im Fall des 9-Lithio-9-methyl-Derivates 17 konnte ein Gleichgewicht 17A ⇄ 17B zwischen einer quasi-aquatorialen und einer quasi-axialen Lithium-Verbindung nachgewiesen werden. Zahlreiche stereospezifisch verlaufende Abwandlungen der neuen Organometalle werden beschrieben und die konformativ bedingten Reaktivitatsunterschiede diskutiert.



Studies on Seven-Membered Ring Systems, XV. Organolithium Derivatives of the Conformationally Rigid Tetraphenyltribenzocycloheptariene (1,2,3,4-Tetraphenyl-9H-tribenzo[a,c,e]cycloheptene)



Quasi-axial substituents (e. g. hydrogen and chlorine) at C-9 of 1,2,3,4-tetraphenyl-9H-tribenzo-[a,c,e]cycloheptene (1) are easily exchanged with formation of quasi-axial organometallic compounds. Only in the case of the 9-lithio-9-methyl derivative 17 an equilibrium 17A ⇄ 17B between a quasi-equatorial and a quasi-axial lithium compound was found. Various stereospecific reactions of the new organometallics are reported and the reactivity differences of conformational origin are discussed.

Untersuchungen an Siebenring‐Systemen, XV. Organolithium‐Derivate des konformativ starren Tetraphenyltribenzocycloheptatriens (1,2,3,4‐Tetraphenyl‐9H‐tribenzo[a,c,e]cyclohepten)

Gleditsia triacanthos L. (honey locust), a plant of the widespread family Leguminosae, shows strong nyctinastic behaviour. Guided by the bioassay, a number of turgor influencing substances - PLMF 1, PLMF 3, PLMF 4, PLMF 5 and PLMF 6 - could be isolated and characterized from aqueous extracts of this plant. Structure and biological relevance of this phenolic-acid-glycosidesulfates are confirmed by synthesis. The multitude and the graduated biological activity of that factors suggests a biological way of irritation, who is after all responsible for the nyctinasty of G. triacanthos.

Pflanzenabwehrstoffe XXIX [1]. Isolierung, Charakterisierung und Synthese von Turgorinen aus Gleditsia triacanthos L. / Plant Defense Substances XXIX [1]. Isolation, Characterization and Synthesis of Turgorines from Gleditsia triacanthos L.

Dietlinde Krauß

Papers

Über die Chemie der Spinnwebe, I

Das Spreitungsalkaloid Stenusin aus dem KurzflüglerStenus comma (Coleoptera: Staphylinidae)

Über Arthropodenabwehrstoffe, LIX. Platambin, ein Wehrstoff des Schwimmkäfers Platambus maculatus (Coleoptera: Dytiscidae)

Untersuchungen an Siebenring‐Systemen, XV. Organolithium‐Derivate des konformativ starren Tetraphenyltribenzocycloheptatriens (1,2,3,4‐Tetraphenyl‐9H‐tribenzo[a,c,e]cyclohepten)

Pflanzenabwehrstoffe XXIX [1]. Isolierung, Charakterisierung und Synthese von Turgorinen aus Gleditsia triacanthos L. / Plant Defense Substances XXIX [1]. Isolation, Characterization and Synthesis of Turgorines from Gleditsia triacanthos L.