Labeled guest

M. Sawada et al., Chiral recognition in host-guest complexation determined by the enantiomer-labeled guest method using fast atom bombardment mass spectrometry. J. Am. Chem. Soc. 117, 7726-7736 (1995)... 

Magnetic Resonance Study of Labeled Guest Molecules in Coal... 

One of the critical aspects of this approach is that two different experiments have to be performed between which the particular instrument conditions must be carefully kept constant in order not to affect the intensity ratios. This problem can be overcome by the enantiomer-labeled guest method [47]. It is based on the mass spectrometric examination of one enantiomer of the host with a pseudo-racemic mixture of the guest. In order to be able to detect both diastereomers separately, one enantiomer of the guest must be isotopically labeled, usually with deuterium. In the same experiment, both diastereotopic complexes are formed and their intensities can be compared directly. However, the stereochemical effect might additionally be superimposed by an unknown isotope effect. A way to separate stereochemical and isotope effects is to perform the same experiment with the second host enantiomer [4B]. In one experiment both stereochemical and isotope effects disfavor the same complex and thus work in the same direction. In the other experiment, they partly cancel each other. If both experiments have been performed, one can use the two experimental values for the intensity ratios of both diastero-meric complexes to deconvolute both effects [49]. 

RFDR methodology has been used to measure inter-fluorine distances of up to 12 A (-I-/-2 A) [255], this application is expected to be of great utility in the solid state NMR analysis of fluorine containing pharmaceuticals. RFDR can be used to provide distance measurements between a labelled nucleus and others of the same isotope at natural abundance. For instance, such measurements were made between a singly labelled guest molecule and the natural abundance carbons of the host in an organic clathrate [256]. 

B. Enantiomer-Labeled Method Synthesize one isotopically labeled guest enantiomer mix 1 1 with the second unlabeled enantiomer and add a small amount of enantiopure host record ESI mass spectrum and compare the intensities of both diastereomeric complexes directly to separate isotope and stereochemical effects, the other pseudoracemate needs to be subjected to the same experiment. 

An interesting way to analyze contribntions that make up constrictive binding is to measure the steric kinetic isotope effects (SKIEs) by comparing decomplexation rates of hemicarceplexes with isotopically labeled guests. The physical origin of a steric isotope effect is the smaller zero-point energy (ZPE) of the C-D bond as compared to that... 

The labeled guest polymer chains, < 114,(XX>, are reptating in the host matrix, =... 

Omnivorous reading made Carothers a brilliant and witty conversationalist in small groups of friends. Hill thought that, after a drink or two, Carothers became the funniest man alive. His humor was understated. When referring to a transmission box labeled positively infinitely variable, Carothers always added dryly, Within finite limits. At parties, he charmed guests by pulling from his pants pockets wooden blocks assembled into molecules. Stereochemical approaches to complicated compounds were becoming important in chemistry, he emphasized. 

Problems related to the use of a guest dye can be reduced if the polymer contains a fluorescent chemical group. Gohil and Salem [70] took advantage of such intrinsic fluorescence to characterize the in-plane distribution of orientation in biaxially drawn PET films. In these experiments, the chain-intrinsic fluorescent label is due to the formation of dimers by two terephthalic moieties, exclusively within the noncrystalline regions. A comparison between sequential and simultaneous drawing along the MD and TD directions was undertaken for a fixed MD draw ratio of 3.5 and various TD draw ratios. The orientational order was characterized by two "orientation ratios" Rmd and RTD such that... 

Shinkai et al. described the synthesis of dendritic saccharide sensors based on a PAMAM dendrimer labeled with eight boronic acid residues [183]. The dendritic compound showed enhanced binding affinity for D-galactose and d-fructose. The fact that the dendritic boronic acid functions as a saccharide sponge is ascribed primarily to the cooperative action of two boronic acids to form an intramolecular 2 1 complex. When one boronic acid binds a saccharide, its counterpart cannot participate in dimer formation and seeks a guest. 

There are several methods to enantiodifferentiate chiral ammonium ions by FAB-MS. One is the so-called enantiomer-labeled (EL) guest method. The method is based on the preparation of a mixture containing the enantiopure host (denoted as U) and the racemate of the guest. One of the guest enantiomers is isotopically labeled (e.g., [M5]+) and the other is not (e.g., [M ] ). Consequently, the signals for the two diastereomeric host-guest pairs (i.e., [U M/j] and [U-Ms] of equations (21) and (22)) appear at different miz ratios. 

The term "guest molecules , originally introduced to indicate specifically labeled marker molecules used in NMR studies of coal (7), is equally unsatisfactory for mobile phase components indigenous to the coal itself. Also, there appears to be insuMcient evidence for the presence of sizeable quantities of true "clathrates to rule out other possibilities, e.g., strong noncovalent bonding rather than physical entrapment. 

Fig. 12 The composite incommensurate structure of Sc-II, as viewed down the c axis. The eight-atom host framework is shown in grey, and the ID guest chains are shown in black. The insets show perspective views of (a) the body-centred guest structure of Fujihisa et al. and (b) the C-centred guest stmcture of McMahon et al. The crystallographic axes are labelled...

An extremely interesting class of problems concerns the behavior of guest molecules in host lipids, particularly when the host lipid system is in a condition where a solid fluid equilibrium exists in the plane of the membrane. Spin labels are ideal for the study of this problem. 

Coordination causes electron-spin density redistribution in the N-O fragment the contribution of resonance structure II increase. The redistribution of spin density results in changes in the parallel component of the nitrogen hyperfine tensor. TEMPO and anthraquinone (AQ) have been used in this way to probe the Lewis acidity of alumina and Li and Mg doped alumina matrices.176 The differences in the Lewis acidic strength towards TEMPO and anthraquinone are discussed. An interesting study has appeared aimed to study the guest-host interaction between poly(amidoamine) dendrimers labelled with nitroxides and several porous solids including alumina.177... 

A variety of spin probe methods have also been used to study the morphological features of the nano-channels present within MCM 41, as well as dynamical aspects connected to molecular diffusion in the inner pores,186-188 EPR has been used to investigate the adsorption and interactions of nitroxide-labelled de-ndrimers within porous silica.181 This method allows one to investigate the effective porosity of a solid surface (as a host) which is determined by the accessibility of the host surface to an adsorbed guest molecule. Information on the adsorption and interaction of dendrimers with the porous surface arises from computer-aided analysis of the EPR spectra based on of the well-established procedure proposed by Schneider and Freed.189... 

Fig. 79. I3C NMR spectra showing that when 2-methylpropene (isobutene) is intercalated in a synthetic hectorite r-butanol is formed when the guest species reacts with the interlamellar water. The peaks labeled 1 and 2 refer to the two distinct types of carbon atom in r-butanol (453).

Deuteration in adjacent molecules (solid solution of 13C-labeled UP as guest in deuterated UP as host). 

Irradiation of poly(ethylene glycol) labeled at the chain terminal with two 2-naphthyl groups 337 in NaY zeolite leads to formation of intramolecular photo-cyclomers 338 to the exclusion of intermolecular products [325] (Scheme 93). These results are explained in terms of the compartmentalization of the guest molecules in the supercages of NaY zeolite. Thus, this work demonstrates the util-... 

Aprotic solvents mimic the hydrophobic protein interior. However, a functional artificial receptor for flavin binding under physiological conditions must be able to interact with the guest even in competitive solvents. As found by spectroscopic measurements with phenothiazene-labeled cyclene, the coordinative bond between flavin and Lewis-acidic macrocyclic zinc in methanol was strong enough for this function. Stiochiometry of the complex was proved by Job s plot analysis. Redox properties of the assemblies in methanol were studied by cyclic voltammetry which showed that the binding motif allowed interception of the ECE reduction mechanism and stabilisation of a flavosemiquinone radical anion in a polar solvent. As a consequence, the flavin chromophore switched from a two-electron-one-step process to a two-step-one-electron-each by coordination. 

In CDCl3 DMSO-d6 85 15, T = 295 K, initial [13] = 10 mM. Uncertainty 40%. Change in receptor chemical shift (ppm) after addition of 200 mM guest salt. See structure of 13 for proton labeling. 

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