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Formation of Host-Guest Complexes

A macrocycle that bears anionic groups has been prepared which forms by far the most stable guanidinium and ammonium (NH4 ) complexes that are currently known in aqueous solution. The guanidinium ion complex (75) is the more [Pg.374]

Chiral crown ethers have been constructed around carbohydrates as sources of chirality. Variable-temperature H n.m.r. spectroscopy has shown that the 1 1 complexes of PhCH2NH3 NCS and the crowns (86) and (87) can be interpreted [Pg.376]

Alteration of the stereochemistry of 2,3-fusion of the ring in (87) and the effect this has on the ease of complexation with (primary alkyl)ammonium thiocyanates has been investigated. The manno-derivatives (H-2a,H-3a) and the altro-derivative (H-2a,H-3/3) have association constants K ) with Bu NH3 NCS in CDCI3 of 39 000 and 501 moP, respectively, the latter (very low) value being a consequence of at least one anti O—C—CO unit within the molecule. The H [Pg.377]

Thermodynamic parameters relating to the binding of cations with a wide range of crown ethers and crown esters have been published. [Pg.378]

Crown ethers have recently been shown to form crystalline, strictly stoicheiometric addition compounds with hexasubstituted benzene derivatives, e.g. (94), which are suited for systematic investigations of intra- and inter- [Pg.378]


The two-steps synthesis of thiophosphorylated cavitands is by far the best method to control the stereoselectivity of the resultant products. As for the P=0 partners, it is important to obtain the all-inward oriented P=S donating groups in high yields to benefit from cooperative effects of the P=S donor groups and the aromatic cavity in the formation of host-guest complexes. [Pg.70]

Only a few studies investigating the pressure effect on the formation of host-guest complexes have been carried out hitherto. A large effect of pressure has been observed for reactions in which atoms or molecules are compressed into the cavity of a container molecule without releasing other molecules out of the cavity. The volume of such a reaction is highly negative so that high pressure favors complex formation. One example is the incorporation of noble gas atoms into the cavity of buckminster fullerene Cgo which proceeds at 250 MPa and 600 °C [10]. [Pg.351]

Volumes of reaction were reported for the formation of host-guest complexes between crown ethers and the [2.2.2]cryptand as hosts and alkali metal ions (Na+,... [Pg.353]

Fig. 11.6. The formation of host-guest complexes between the molecular tweezers 2 and 3 and quinoid or aromatic guests 4-6. Fig. 11.6. The formation of host-guest complexes between the molecular tweezers 2 and 3 and quinoid or aromatic guests 4-6.
The Effect of Pressure on the formation of Host-Guest Complexes 367... [Pg.361]

Oxaziridines are accepted as intermediates in the photorearrangements of oximes to amides and lactams. The formation of host-guest complexes in acetophenone oxime derivatives that incorporate a crown ether moiety has been shown to stimulate triplet-derived Z-J -isomerization and to depress singlet-derived oxaziridine formation. Low yields of lactams (115>—(117) have been obtained on irradiation of D-nor-5a-androstan-16-one oxime (118) in methanol. The unusual formation of lactam (117), in which the chirality of the... [Pg.439]

In the context of crown ether hosts, non-covalent bonds of pole-pole, pole-dipole, and dipole-dipole types can all be employed [3-6] in the formation of host-guest complexes. Where the guest species is an alkali metal (i.e. Li, Na", K", Rb, Cs ), alkaline earth metal (i.e. Mg, Ca, Sr, Ba ), or harder transition or post-transition metal (e.g. Ag", TT, Hg, Pb, La, Ce ) cation [3-6,14], an electrostatic (M" O) pole-dipole interaction binds the guest to the host whilst the (M" X ) pole-pole interaction with the counterion (X ) is often retained. The features are exemplified by the X-ray crystal structure [15] shown in Fig. la for the 1 2 complex (1) (NaPF jj formed between dibenzo-36-crown-12 (1) and NaPF. Molecular complexes involving metal cations have considerable strengths even in aqueous solution and a template effect involving the metal cation is often observed during the synthesis of crown ether derivatives. [Pg.530]

Host molecules Formation of host-guest complexes ... [Pg.403]

The syn-anti isomerization of acetylbenzocrown ether oximes is stimulated by complex formation with sodium ion. The photolysis of the oximes is depressed by formation of host-guest complexes, which is attributed to enhanced intersystem crossing. ... [Pg.328]

The formation of host-guest complexes between crown ethers and organic ammonium cations and the high solubility and functionality of crown ethers in organic solvents enable the synthesis of molecular machines such as molecular elevators and molecular shuttles. Complexation of metal cations into the cavity of crown ethers contributes to the solubilization of metal cations in organic solvents and enhances the reactivity of... [Pg.6]

Inclusion of cationic molecules by hosts in organic solvents is also observed with other host molecules, such as crown ethers and calixarenes. Cat-ion/n and coordination interactions are the main driving forces in these complexes. However, the formation of host-guest complexes with neutral... [Pg.99]

Because the CDs possess hydrophobic inner surfaces and hydrophilic outer surfaces, they include hydrophobic molecules corresponding to their cavity sizes due to hydrophobic interactions. Thus, the CDs are well-known host molecules that increase the solubilities of hydrophobic guest molecules in water by the formation of host-guest complexes. Since p-CD has a low solubility in water compared to the a- and y-CDs, 2,6-dimethyl-P-cyclodextrin (Me2-P-CD) and randomly methylated P-cyclodextrin (RM-P-CD) have been used in many cases (Figure 5.3). [Pg.78]

Structural and conformational changes caused by interactions involving chiral molecules can be studied with CD spectroscopy. These experiments deal with, for example, the formation of host-guest complexes between asymmetric species, whose association constant can be determined from CD titrations. The case of an achiral chromophore (thus lacking a namral CD signal) that interacts with a chiral molecule is of particular interest. The resulting complex is obviously chiral and can exhibit circular dichroism in the absorption region of the achiral chromophore. [Pg.144]


See other pages where Formation of Host-Guest Complexes is mentioned: [Pg.144]    [Pg.212]    [Pg.235]    [Pg.212]    [Pg.235]    [Pg.187]    [Pg.5690]    [Pg.289]    [Pg.128]    [Pg.21]    [Pg.188]    [Pg.41]    [Pg.5689]    [Pg.372]    [Pg.269]    [Pg.303]    [Pg.1003]    [Pg.124]    [Pg.497]    [Pg.806]    [Pg.810]    [Pg.2025]    [Pg.15]    [Pg.18]    [Pg.120]    [Pg.498]    [Pg.498]    [Pg.416]    [Pg.160]   


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