Probe lipophilic

Organic-soluble lanthanide chelates have been used to probe lipophillic systems. The compound 4-(4-dipentylamino-( )- S-styryl)-l-(2,2,2-trifluoroethyl)pyridinium perchlorate (22) was employed as a probe in dimyristoylphosphatidylcholine vesicles. Probe molecules assembled in the inner and outer shells of the vesicle as evidenced by the presence of two signals in the NMR spectrum (376 MHz). Even though addition of Eu(fod)3 promoted vesicle fusion, only one of the signals shifted. The shifted signal was likely from the probe molecule on the outer shell, as the internal P signal of the phospholipid did not shift in the presence of Eu(fod)3 ". 

If the photoequilibrium concentrations of the cis and trans isomers of the photoswitchable ionophore in the membrane bulk and their complexation stability constants for primary cations are known, the photoinduced change in the concentration of the complex cation in the membrane bulk can be estimated. If the same amount of change is assumed to occur for the concentration of the complex cation at the very surface of the membrane, the photoinduced change in the phase boundary potential may be correlated quantitatively to the amount of the primary cation permeated to or released from the membrane side of the interface under otherwise identical conditions. In such a manner, this type of photoswitchable ionophore may serve as a molecular probe to quantitatively correlate between the photoinduced changes in the phase boundary potential and the number of the primary cations permselectively extracted into the membrane side of the interface. Highly lipophilic derivatives of azobis(benzo-15-crown-5), 1 and 2, as well as reference compound 3 were used for this purpose (see Fig. 9 for the structures) [43]. Compared to azobenzene-modified crown ethers reported earlier [39 2], more distinct structural difference between the cis... 

Figure 7.22b is a similar plot for the other two lipids considered olive oil (unfilled symbols) and octanol (filled symbols). Both lipids can be described by a bilinear relationship, patterned after the case in Fig. 7.19d [Eq. (7.44)]. Octanol shows a declining log Pe relationship for very lipophilic molecules (log Kd > 2). The probe set of 32 molecules does not have examples of very hydrophilic molecules, with log Kd < —2, so the expected hydrophilic ascending part of the solid curve in Fig. 7.22b is not fully shown. Nevertheless, the shape of the plot is very similar to that reported by Camenisch et al. [546], shown in Fig. 7.8c. The UWL in the latter study (stirred solutions) is estimated to be 460 pm (Fig. 7.8b), whereas the corresponding value in unstirred 96-well microtiter late assay is about 2300 pm. For this reason, the high point in Fig. 7.22b is 16 x 10-6 cm/s, whereas it is 70 x 10 6 cm/s in Fig. 7.8c.

Furthermore, the membrane retentions of the lipophilic probe molecules are dramatically decreased in the presence of the sink condition in the acceptor wells, as shown in Fig. 7.27. All molecules show R < 35%, with progesterone and phenazo-pyridine showing the highest values, 34% and 26%, respectively. 

The strategy for the development of the oral absorption model at pION is illustrated in Fig. 7.58. The human jejunal permeabilities reported by Winiwarter et al. [56] were selected as the in vivo target to simulate by the in vitro model. In particular, three acids, three bases and two nonionized molecules studied by the University of Uppsala group were selected as probes, as shown in Fig. 7.58. They are listed in the descending order of permeabilities in Fig. 7.58. Most peculiar in the ordering is that naproxen, ketoprofen, and piroxicam are at the top of the list, yet these three acids are ionized under in vivo pH conditions and have lipophilicity (log Kj) values near or below zero. The most lipophilic molecules tested, verapamil and carbamazepine... 

The studies on phospholipid bilayers with defined amounts of charged component are helpful to explain the partition characteristics in biological membranes. Liposome water partition data of propranolol in lipids from kidney epithelial cells (a common model system in pharmaceutical sciences for the uptake into the gastrointestinal tract) have been successfully described with partition models developed for pure bilayers or defined mixtures [159]. Since lipophilic cations and anions can be used as probes for the membrane potential, their interaction with microbial and mitochondrial membranes has been studied... 

The relatively nonpolar squaraine rotaxane 14c was found to interact with cells in a very similar way to the well-known lipophilic dye Nile Red this probe rapidly accumulates at lipophilic sites inside a living cell, such as the endoplasmic reticulum and intracellular lipid droplets [55], The red emission band for probe 14c is quite narrow and permits the acquisition of multicolor images. It displayed high chemical stability and low toxicity. 

Fluorescence Properties of Methyl 8-(2-Anthroyl) Octanoate, a Solvatochromic Lipophilic Probe, Chem. Phys. Lipids 59, 17— 28. 

In order to prepare successful NIR molecular probe dyes, NIR dyes must meet the following criteria adequate response to analytes, high lipophilicity and/or reactive functional groups, absorbance maxima compatible with available laser diodes, high fluorescence quantum yield, molar absorptivity, and high photostability. 

Substituting hx = 3.6 cm and K ip/w = K - into Eq. 28 Johnson et al. calculated solute lateral diffusion coefficients in stratum corneum bilayers from macroscopic permeability coefficients. Measurements with highly ionized or very hydrophilic compounds were not performed because of the possible transport along a nonlipoidal pathway. Comparison of the computed Aat values with experimentally determined data for fluorescent probes in extracted stratum corneum lipids [47] showed a highly similar curve shape. The diffusion coefficient for the lateral transport showed a bifunctional size dependence with a weaker size dependence for larger, lipophilic compounds (> 350 Da), than... 

Less frequently used at present is electron spin resonance spectroscopy, which is based on the use of spin probes as model componnds or covalent spin labeling of drugs. Microviscosity and micropolarity of the molecnlar environment of the probe can be derived from electron spin resonance spectra. Moreover, the spectra allow us to differentiate isotropic and anisotropic movements, which result from the incorporation of the probe into liposomal structures. Quantitative distribution of the spin probes between the internal lipid layer, the snrfactant, and the external water phase is to be determined noninvasively. On the basis of the chemical degradation of drugs released from the lipid compartment, agents with reductive features (e.g., ascorbic acid) allow us to measure the exchange rate of the drugs between lipophilic compartments and the water phase [27,28]. 

Grams, Y. Y. and Bouwstra, J. A., Penetration and distribution of three lipophilic probes in vitro in human skin focusing on the hair follicle. J. Control. Release, 83, 253-62, 2002. 

Solvent extraction has become a common technique for the determination of formation constants, P , of aqneons hydrophilic metal complexes of type MX , particularly in the case when the metal is only available in trace concentrations, as the distribntion can easily be measnred with radioactive techniques (see also section 4.15). The method reqnires the formation of an extractable complex of the metal ion, which, in the simplest and most commonly used case, is an nn-charged lipophilic complex of type MA. The metal-organic complex MA serves as a probe for the concentration of metal ions in the aqueous phase through its equilibrium with the free section 4.8.2. This same principle is used in the design of metal selective electrodes (see Chapter 15). Extractants typically used for this purpose are P-diketones like acetylacetone (HAA) or thenoyltrifluoroacteone (TTA), and weak large organic acids like dinonyl naph-talene sulphonic acid (DNNA). 

A new class of lipophilic ferrichrome analogs carrying acetoxymethyl ester moieties 203 has been synthesized and shown to penetrate rapidly through cell membranes. Intracellular esterase mediated hydrolysis transformed the lipophilic termini from hydrophobic to hydrophilic. The intracellular retention was visualized in hepatoma cells by labeling these analogs with a fluorescent naphthy-imide probe . Their fluorescence analogs retained their fluorescent properties for extended periods in comparison to hydrophobic derivatives 204 lacking the cleavable substituents. 

The dyes used for probing lipid membranes consist of a fluorophore with a long lipophilic tail. The lipophilic tail inserts itself into the membrane thus locating the fluorophore label on the membrane. These products are used as lipid labels and in cell tracking as part of biophysical studies. There are two main classes of fluorophore, aminostyryls and indocarbocyanines. The most widely used indocarbocya-nine is the 18-carbon derivative of Cy3 known as dil, (3.72). 

It is at present still difficult to correlate the absolute intensity of the SHG with the number of cationic complexes at the membrane surface. Therefore, a quantitative discussion, showing how the permselective uptake of primary cations forming SHG active complexes into the membrane side of the phase boundary corresponds to the increase in the membrane potential, is not possible yet. Lipophilic derivatives of photoswitchable azobis(benzo-15-crown-5) were recently shown as a molecular probe to determine photoinduced changes in the amount of the primary cation uptake into the membrane phase boundary in relation to the photoinduced EMF changes under otherwise identical conditions. 

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