Flattened cone

An unusual scoop conformation of 24 has been characterised in the hydrate (C-methylcalix[4]resordnarene)(H20) [65]. The scoop conformation is a hybrid of the bowl and flattened cone conformations and there are two intramolecular O-H... 0 hydrogen bonds from adjacent resorcinol units. Adjacent 24 molecules form O-H... 0 hydrogen bonds and there are additional links via water molecules resulting a 2D sheet structure. The sheets pack in a bi-layer arrangement. 

The flexibility of the calix[4]arene basis is reflected in the molecular structure of 54a as determined by X-ray diffraction analysis (Fig. 22). The calix[4]arene adopts a flattened cone conformation with intramolecular 7i-stacking of two terpyridyl... 

Figure 3 shows the typical shape of a smoke-plume in a stable atmosphere. In this case, there is a vertical temperature gradient such that the air aloft is hotter and less dense then the air near the ground - a so-called temperature inversion - and the resulting absence of ambient vertical motion causes the plume to fan out under the influence of the prevailing horizontal airflow. In comparison with its profile for neutral stability, the flattened cone of the stable-atmosphere plume may be supposed to retain a... 

In order to elucidate relationships between surface active and film forming properties of food proteins, it is useful to examine the surface active properties of proteins whose physical and molecular properties are well characterized e.g. -casein, bovine serum albumin (BSA), lysozyme ( ), and -lactoglobulin (b-Lg) (2jL). These represent a range of tertiary structures for soluble proteins. Lysozyme is a rigid and roughly ellipsoidal molecule, whereas the hydrophobic -casein molecule is mostly a random coil structure. The b-Lg molecule consists almost entirely of antiparallel -sheet strands organized into a flattened cone ( ). 

Figure 11. X-ray crystal structure of 104 (a) shows a flattened cone conformation and (b) shows the dimeric form. (Reprinted with permission from 2002CEJ1134, Copyright 2002, John Wiley Sons Inc.)...

Scleroscope An instrument for measuring impact resilience by dropping a ram with a flattened-cone tip from a specified height onto the specimen, then noting the height of rebound. 

ABSTRACT. The introduction of acetic acid units on p.t-butylealix [4] arene, in a controlled way, leads to a series of new lipophilic complexones (3,5,7) with different structures and properties. The tetraacid derivative (3) shows a cone structure and its alkali and ammonium salts are soluble in water whereas the other two ligands (5) and (7) show a "flattened cone" structure. All new ligands are able to extract divalent metal cations from water to methylene chloride. 

The H NMR spectrum of (7) (Fig. 3) indicates a "flattened cone structure" for this new macrobicyclic compound. The two carboxylic groups are located on the... 

Different solid state structures of p-fert-butylcalix[7]arene C[7] have been determined by X-ray crystallography. The most common conformation found was the so-called double-cone-pinched [90] one (Fig. 7.25a) in which a tetrameric conelike (blu in Fig. 7.25a) and a trimeric %-cone-Uke (yellow in Fig. 7.25a) substructures were stabilized by the strong intramolecular H-bonds between OH groups. The structure reported by Perrin et al. [91] for p-ethylcalix[7]arene lb (Fig. 7.25b) is characterized by a more flattened %-cone-like trimeric subunit and by a tetrameric subunit with the two central phenolic rings inverted with respect to... 

Depending on the reaction conditions and the nature of the ester side chain in the cinnamates, the resorc[4]arenes can adopt different conformational states, namely, 1,2-altemate, 1,3-altemate, or flattened-cone). In particular, when ( )-2,4-dimethoxycinnamic acid methyl ester 1 was reacted with BF3 Et20 at room temperature, only the 1,2-altemate 2a and flattened-cone 2b stereoisomers were obtained in a 2 3 ratio and 75 % overall yield. In the 1,2-altemate conformation, the assignment of the 12- and 16-OMe signals, by INEPT experiments in conjunction with DIF NOE measurements, allowed to establish the correct stereochemistry at C(14). On the other hand, the presence in the H- and C-NMR spectra of only one signal for both external (H-5) and internal (H-28) aromatic protons and the related carbons, as well as a similar pattern for the methoxy group and the aliphatic... 

A different pattern of reaction products was obtained with the ethyl 3 and isopropyl 5 cinnamic esters. In both cases, comparable chemical yields were obtained, but in addition to the 1,2-altemate (4a, 6a, respectively) and the flattened-cone (4b, 6b, respectively), a third type of stereoisomers (namely, 4c and 6c) emerged from the reaction mixture. An accurate analysis of H and NMR spectra pointed out the existence of two symmetry planes. DIF NOE experiments revealed the proximity of the methine and the methylene groups with the aromatic protons. Therefore, on the basis of only NMR evidences, 4c and 6c were assigned the 1,3-altemate conformation with the pseudoequatorial side chains in an all -cis position. Later, thanks to the obtainment of suitable crystals for X-ray analysis, the stereoisomer 4c was definitively reassigned the chair conformation [6]. 

Notably, not only the 2,4-dimethoxycinnamates underwent the BF3-Et20 mediated tetramerization reaction, and this has proved the versatility of the reaction. In fact, also 2,4-dimethoxycinnamic acid amides such as 12 (Scheme 8.5), derived from the mixed anhydride of 2,4-dimethoxycinnamic acid with 1- or d-vaUne ethyl ester, upon treatment with BF3-Et20 yielded the amido-resorc[4]arenes 13a-C which proved to be chiral for the presence of four axial pendants containing the chiral valine residue [9]. A novel flattened-partial cone conformation was isolated for the first time from the reaction mixture, together with three other stereoisomers (namely, 1,2-altemate, flattened-cone, and chair). The flattened-cone stereoisomer, which was identified by molecular modeling as the most stable, proved to form as minor product in kinetic conditions, and to become the main component of the reaction mixture under more drastic conditions (namely, substrate/ BF3 Et20 = 1 400 M ratio). The chiral amido-resorc[4]arenes 13a-c were obtained in enantiomerically pure forms, as checked by enantioselective HPLC. 

Treatment of tetraalcohol 25b with glutaroyl, adipoyl and pimeloyl dichlorides in the presence of Et3N gave the corresponding double-spanned resorcarenes 26 (n=l), 27 (n = 2), and 28 ( = 3) [15], in which the insertion of the methylene bridges led to the formation of a cavity shaped architecture resembling a basket (Scheme 8.8) H- and C-NMR spectra. X-ray analysis, as well as molecular dynamic studies agreed that the basket derivative had a frozen flattened-cone conformation. 

The crown ether bridge in calix[4]arene 19 freezes the calixarene stmcture in a rigid flattened-cone conformation also pushing the two metal ions apart. The bimetallic complex 19—Zu2 cleaves HPNP eight times less effectively than the flexible 2—Zu2 [17], thus confirming that a certain degree of flexibility is beneficial and is an important requisite in a supramolecular catalyst. 

---