Funnel complexes

Y. Rondelez, M.-N. Rager, A. Duprat, O. Reinaud, Calix[6]arene-based cuprous funnel complexes a mimic for the substrate access channel to metalloenzyme active sites, J. Am. Chem. Soc., 2002, 124, 1334-1340. 

Coordination to Cn(II) generates five-coordinate complexes as distorted sqnare-based pyramids (SBPs). The local environment constrains one of the arms in an axial position and the other two in equatorial positions, trans to each other. Two remaining sites are present one endo, at which the access is controlled by the cavity, and one exo, located trans to the endo one and typically occupied by small molecules such as H2O. This constitutes the first generation of calix[6]arene ligands or funnel complexes that constrain copper to a mononuclear environment, and are thus a sophisticated structural model for enzymes such as PHM and D/SH (Figure... 

Figure 15 Ligand exchange at the Zn(It) center of the funnel complexes based on the /zexa-fBu-calix[6]tris(hnidazole) ligand. The equilibrium constants Xl /eioh (exchange of L = EtOH for L at 298 K in CDCI3) are given in parentheses. XEtoH/2H20 = 0.4mol When no endo coordination can be detected, XL/2H2O <...

Nuclearity has a strong impact on reactivity, as evidenced by the different reactivity of mono versus binuclear copper oxidation enzymes (aromatic vs aliphatic oxidation) or the specific roles of the different Zn centers in alkaline phosphatase. Some nuclearities (e.g., binuclear metal complexes) correspond to thermodynamic sinks. In that case, preorganization is not required. Less stable nuclearities require a platform in order to be maintained during the catalytic process. Mononuclear systems correspond to this situation. In particular, monocopper centers need to be embedded to be protected. The funnel complex strategy was developed for that purpose. Porphyrin complexes can be protected from deactivation pathways by grafting them... 

This complex should be used when the organolithium is in solution in a hydrocarbon solvent. For organolithium reagents prepared in ether (see Note 4), the same complex may be used or, more conveniently, copper iodide (Cull can be used. The Cul purchased from Prolabo or Merck 4 Company, Inc. may be used directly. Other commercial sources of Cul (Fluka, Aldrich Chemical Company, Inc., Alfa Products, Morton/Thiokol, Inc.) furnish a salt which affords better results when purified. 1 mol of Cul is stirred for 12 hr with 500 ml of anhydrous tetrahydrofuran, then filtered on a sintered glass funnel ( 3), washed twice with 50 ml of anhydrous tetrahydrofuran, once with 50 ml of anhydrous ether and finally dried under reduced pressure (0.1 imO for 4 hr. 

A. Heptoic anhydride enanthic anhydride). In a 250-ml. round-bottomed three-necked flask, equipped with a stirrer, dropping funnel, and thermometer, are placed 15.8 g. (16.1 ml., 0.2 mole) of dry pyridine (Note 1) and 25 ml. of dry benzene (Note 2). I hen 14.8 g. (15.5 ml., 0.1 mole) of heptoyl chloride (Note 3) is added rapidly to the stirred solution. The temperature rises only slightly, and a pyridinium complex separates. While stirring is continued, 13.0 g. (14.1 ml., 0.1 mole) of heptoic acid (Note 3) is added from the dropping funnel over a period of 5 minutes. The temperature rises rapidly to 50-65° (Note 4), and pyridine hydrochloride is formed. After stirring for 10 minutes, the solid is collected on a chilled Buchner funnel and washed twice with 25-ml. portions of dry benzene (Note 5). 

The interiors of rhodopseudomonad bacteria are filled with photosynthetic vesicles, which are hollow, membrane-enveloped spheres. The photosynthetic reaction centers are embedded in the membrane of these vesicles. One end of the protein complex faces the Inside of the vesicle, which is known as the periplasmic side the other end faces the cytoplasm of the cell. Around each reaction center there are about 100 small membrane proteins, the antenna pigment protein molecules, which will be described later in this chapter. Each of these contains several bound chlorophyll molecules that catch photons over a wide area and funnel them to the reaction center. By this arrangement the reaction center can utilize about 300 times more photons than those that directly strike the special pair of chlorophyll molecules at the heart of the reaction center. 

The excess lithium aluminum hydride and the metallic complexes are decomposed by the careful addition of 82 ml. of distilled water, from a dropping funnel, to the well-stirred mixture. The reaction mixture is stirred for an additional 30 minutes, filtered with suction, and the solid is washed with several 100-ml. portions of ether. After the ether is removed from the filtrates, the residual oil is distilled under reduced pressure. The yield of laurylmethylamine, a colorless liquid boiling at 110-115°/1.2-1.5 mm., is 121-142 g. (81-95%) (Note 6). 

In a 3-1. three-necked round-bottomed flask, fitted with a sealed stirrer, a dropping funnel, and a reflux condenser, is placed 80 g. (1.1 moles) of dimethylformamide (Note 1). The flask is immersed in an ice bath, and the internal temperature is maintained at 10-20°, while 169 g. (1.1 moles) of phosphorus oxychloride is added through the dropping funnel over a period of 15 minutes. An exothermic reaction occurs with the formation of the phosphorus oxychloride-dimethylformamide complex. The ice bath is removed, and the mixture is stirred for 15 minutes (Note 2). 

A. N,N-Dimeihyljormamide-dimelhyl sulfate complex. In a 500-ml. four-necked flask equipped with mechanical stirrer, reflux condenser with calcium chloride drying tube, dropping funnel, and thermometer is placed 73 g. (1.0 mole) of dimethyl-formamide, and 126 g. (1.0 mole) of dimethyl sulfate is added dropwise with stirring at 50-60° (Note 1). After the addition is complete, the mixture is heated for another 2 hours at 70-80°. The dimethylformamide complex forms as a viscous, colorless or pale yellow ether-insoluble oil. 

Procedure. To 10.0 mL of the solution containing up to 200 fig of copper in a separatory funnel, add 5.0 mL of 10 per cent hydroxylammonium chloride solution to reduce Cu(II) to Cu(I), and 10 mL of a 30 per cent sodium citrate solution to complex any other metals which may be present. Add ammonia solution until the pH is about 4 (Congo red paper), followed by lOmL of a 0.1 per cent solution of neo-cuproin in absolute ethanol. Shake for about 30 seconds with 10 mL of chloroform and allow the layers to separate. Repeat the extraction with a further 5 mL of chloroform. Measure the absorbance at 457 nm against a blank on the reagents which have been treated similarly to the sample. 

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