Clam structures

Although the clam structures are of interest as ammonium ion binders, they are by no means the only azacrown compounds of interest in this application. Sutherland and coworkers have examined a number of azacrowns as primary ammonium ion bind-ers - . In addition, Metcalfe and Stoddart have utilized bis-azacrowns to bind secondary ammonium cations. 

Pedersen patented a series of ftis-crowns related to the above except that the side chain was bound on each side to a crown. Cram " and Sutherland have both reported similar structures. Pedersen suggested the name clams for such species but the name has not found wide acceptance. 

A number of bridged crown ethers have been prepared. Although the Simmons-Park in-out bicyclic amines (see Sect. 1.3.3) are the prototype, Lehn s cryptands (see Chap. 8) are probably better known. Intermediates between the cryptands (which Pedersen referred to as lanterns ) and the simple monoazacrowns are monoazacrowns bridged by a single hydrocarbon strand. Pedersen reports the synthesis of such a structure (see 7, below) which he referred to as a clam compound for the obvious reason . Although Pedersen appears not to have explored the binding properties of his clam in any detail, he did attempt to complex Na and Cs ions. A 0.0001 molar solution of the clam compound is prepared in ethanol. The metal ions Na and Cs are added to the clam-ethanol solutions as salts. Ultraviolet spectra of these solutions indicate that a small amount of the Na is complexed by the clam compound but none of the Cs . 

One of the first applications of the HPLC method was the investigation of differences in toxin profiles between shellfish species from various localities ( ). It became apparent immediately that there were vast differences in these toxin profiles even among shellfish from the same beach. There were subtle differences between the various shellfish species, and butter clams had a completely different suite of toxins than the other clams and mussels. It was presumed that all of the shellfish fed on the same dinoflagellate population, so there must have been other factors influencing toxin profiles such as differences in toxin uptake, release, or metabolism. These presumptions were strengthened when toxin profiles in the littleneck clam (Prototheca Staminea) were examined. It was found that, in this species, none of the toxin peaks in the HPLC chromatogram had retention times that matched the normal PSP toxins. It was evident that some alteration in toxin structure had occurred that was unique in this particular shellfish species. 

For (203), models indicated that the isomer containing cis-syn-cis hydrogen atoms on the cyclohexane ring should be able to form clam-type complexes, provided the cyclohexane ring is in the flexible or twist conformation. The models suggested that the cavity defined by the ten oxygen donors would be ideal for K+. However, for the potassium and barium thiocyanate complexes, configurations of type (204) do not occur in the solid state. Instead, two molecules of the bis-crown coordinate simultaneously to two alkali metal ions - both these 2 2 complexes have structures of type (205). 

The shells of molluscs, such as clam, oyster abalone, scallop and fresh water snail, use CaC03 as the principal constituent for an extraordinary array of diverse structures. Several approaches have led, and will lead further in the future, to a greater understanding of how these complex forms are generated. 

Work on the chemical structure and properties of the poisons from Alaska butter clam siphons, the hepatopancreas of California mussels, and axenic cultures of G. catenella carried on in the Biological Laboratories and with Rapoport at the University of California definitely established that the sea mussel did not alter the poison obtained from G. catenella. The poison from all three sources had identical structures (31). The situation with the Alaska butter clam may be different however in light of the different saxitoxin derivatives recently found in the dinoflagellates in that region. Perhaps the clam converts the sulfo and sulfate derivatives to the more toxic saxitoxin. 

Note The B and C series of the PSP (R4 - SO ) have not been included in this table because they form their STX, NEO and GTX counterparts (11) on treatment with acid during the preparation of clam extracts. For the structure of tetrodotoxin see (8,9). 

The kidney of the giant clam Tridacna maxima yielded an arsenic-containing sugar sulfate (213), the structure of which was determined by X-ray crystallography [218]. 

Suzuki, T. Tomoyuki, T. Uda, K. Kinetic properties and structural characteristics of an unusual two-domain arginine kinase of the clam Corbicula japonica. FEBS Lett., 533, 95-98 (2003)... 

Intake water tunnels are generally made from concrete, and absorption of water by concrete is the main reason for corrosion in reinforcement. In intake structures the problems are due to concrete failure from salts penetrating into the concrete and corroding the rebar. Hard, dense concrete with ample cover to reinforcement and without cracks and porosity has good resistance to corrosion against seawater. In Indian nuclear power plants, the experience with concrete intake tunnels with respect to corrosion behavior is not bad except that special care is required for protection against algae, clams, mussels, etc. which attach to the tunnel surface. 

Demolition Clam. A small plastic case designed to hold approx 0.5 lb of plastic HE. Another design of the demolition clam w/o case consists of a ret angular block of PEX (1.7 lb) provided with 4 permanent magnets and connections for 2 delay-type firing devices. The demolition clam is used to destroy steel structures such as gasoline storage tanks, pipe lines, vehicles, etc (Refs 1 2)... 

Chemical studies on Nautilus pompilius (a cephalopod) and Mercenaria mercenaria (a clam) indicate that matrix proteins are composed of two structural units (1) a polypeptide with a strong affinity to Ca2+ ions which is soluble in strong CaCl2 solutions, and (2) a high molecular weight protein insoluble in CaCl2 with no affinity to calcium and which is arranged in the form of sheets and layers. 

Cyclopheophorbide enol (122) a nonmetalated chlorophyll a derivative was isolated from a New Zealand sponge (Darwinella oxeata) and its structure determined by X-ray measurements (113). Although 132,173-cyclopheophorbide enol (122) was first isolated from natural sources, it had previously been synthesized during a study of ring E enolization of chlorophyll derivatives (114). A new pheophorbide a-related compound named chlorophyllone a (123) was isolated from extracts of the short-necked clam Ruditapes philippinarum (115). Compound 123 exhibits antioxidative activity. 

McLeese, D.W., Zitko, V., Peterson, M.R. (1979) Structure lethality relationships for phenols, anilines and other aromatic compounds in shrimp and clams. Chemosphere 2, 53-57. 

There are seven living classes of molluscs,23 including the worm-like Aplacophora, the chitons of the Polyplacophora, the limpet-like creatures of the Monoplacophora and the Gastropods which includes the abalone, marine snails, slugs, nudibranchs and conch. The next three are comprised of the Cephalopods (cuttlefish, squid and octopus), the Bivalves (clams, oysters) and the Scaphopoda (Tusk shells). Figure 6.5 shows that the most prolific order within Mollusca is the Aplysiomorpha (Anaspidea) with 507 articles and 384 structures published since 1951. There have been a total of 1684 publications and 1225 chemical structures reported from the order Mollusca. One of the most well-known structure classes from molluscs are the dolastatins, which are from the Anaspidea order. 

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