Hydrophobic cations

Both the 3i4- and 2.5i2-helical backbones have been found suitable for the design of antimicrobial /9-peptides. In order to cluster polar residues on one face of the helix, amphiphilic 3i4-helical /9-peptides have been constructed from hydro-phobic-cationic-hydrophobic or hydrophobic-hydrophobic-cationic residue triads... 

It is obvious from the above conditions that the transfer of strongly hydrophylic Zf anions from phase w to s and of strongly hydrophobic X2 anions from phase 5 to vr is much more difficult compared to the transfer of the common hydrophylic-hydrophobic cations. In the equilibrium state, the Galvani potential is defined in terms of the Nernst equation (4) ... 

Taking into account that both the voltammetric maximum and the depression in drop time-potential curves were affected by the ion pair formation equilibrium of Na DPA in LM, it is concluded that Na which has been transferred from NB to W may be adsorbed at the interface from the side of W inducing the adsorption of DPA as a counterion from the NB side. At the interface, the adsorbed Na may exist as an ion pair, which is denoted as Na DPAj, hereafter. The possibility of the interfacial ion pair formation between a hydrophobic cation (or anion) in an organic phase and a hydrophilic anion (or cation) in an aqueous phase has been proposed by Girault and Schiffrin [32], and Kakiuchi et al. [33]. 

Feibush, B. and Santasania, C. T., Hydrophilic shielding of hydrophobic, cation- and anion-exchange phases for separation of small analytes direct injection of biological fluids onto high performance chromatographic columns, /. Chromatogr., 544, 41, 1991. 

As the concentration of the internal solution of the ion-selective electrode is constant, this type of electrode indicates the cation activity in the same way as a cation electrode (or as an anion electrode if the ion-exchanger ion is a hydrophobic cation). 

The recent crystallization of the small water-soluble transcriptional regulator of Bacillus subtilis multidrug transporter Bmr, BmrR, which binds hydrophobic cations from the cytosol [64, 65] provides a good example for an interaction determined primarily by van der Waals interactions. Interestingly, the same drugs, which bind to the water-soluble BmrR are also substrates for the transmembrane multidrug transporter Bmr. As will be discussed below, the latter interactions could well be of different nature. 

Hydrophobe, cationic modifled cellulose ethers (DCFs) are drug delivery vehicles speciflcally designed to interact with mucosae. DCE s are closely related to cationic polysaccharides used safely and effectively for many years in topical personal care products. 

The aforementioned methodology has been applied to measure the kinetics of a series of monovalent ions by using the oxidation of LBPC [26-29], As the redox probe LBPC is oxidized to the stable hydrophobic cation LBPC+, and the electrode reaction is accompanied by either anion ingress from the aqueous phase (4.12) or cation expulsion from the organic phase (4.13), which depends on the type of ions and their relative affinity for both liquid phases. 

The soil properties observed with these chemicals suggest that the chemical structural requirements for an hydrophobic cationic surfactant appear to be ... 

As a rather strongly hydrophilic anion, nitrate requires an ISE membrane containing a strongly hydrophobic cation, as described on p. 169. This function was fulfilled in the first nitrate electrode from Orion Research by cation V [180] in nitro-p-cymene 5. The electrode can be used in the pH range 4-7. In other commercial electrodes, the ion-exchanger ion is a tetra-alkylammonium salt, for example in the electrode from Coming Co., substance XIII in solvent 6 [27]. An ISE with a renewable membrane surface was found to be very useful (see section 4.1 and fig. 4.4), in which the ion-exchanger solution contains the nitrate of crystal violet VII dissolved in nitrobenzene [191]. The NOj ISE also responds to nitrites that can be removed by addition of aminosulphonic acid. 

The membrane potentials of cells and organelles such as mitochondria can be measured using the distribution of hydrophobic cations (dibenzyldimethyl-ammonium [43, 44, 158,195], tetraphenylphosphonium [96,157], butyltri-phenylphosphonium [132]). The ion concentration in the supernatant is measured the ion-exchanger ion is XV. 

An improved adsorption of DNA bases has been observed at a chemically modified electrode based on a Nafion/ruthenium oxide pyrochlore (Pb2Ru2-x FhxOj-y modified GC (CME). Nafion is a polyanionic perfiuorosulfonated ionomer with selective permeability due to accumulation of large hydrophobic cations rather than small hydrophilic ones. The Nafion coating was demonstrated to improve the accumulation of DNA bases, while the ruthenium oxide pyrochlore proved to have electrocatalytic effects towards the oxidation of G and A. The inherent catalytic activity of the CME results from the Nafion-bound oxide surface being hydrated. The catalytically active centers are the hydrated surface-boimd oxy-metal groups which act as binding centers for substrates [50]. 

Mazumder A, Gupta M, Perrin DM, Sigman DS, Rabinovitz M, Pommier Y. Inhibition of human immunodeficiency virus type 1 integrase by a hydrophobic cation The phenanthroline-cuprous complex. AIDS Res Human Retro 1995 11 115-125. 

H. Hauser, M.C. Phillips and M.D. Barratt, Differences in the interaction of inorganic and organic (hydrophobic) cations with phosphatidylserine membranes, Biochem. Biophys. Acta 413 (1975) 341-353. 

B AZrP can be used as a precursor to prepare assemblies of several aromatic hydrophobic cations (Fig. 5). In addition to the favorable electrostatic interactions,... 

Small hydrophobic cations derived from naphthalene, anthracene, and pyrene and larger molecules such as rhodamine and fluorescein can be readily intercalated into the a-ZrP galleries. Inorganic complexes, ruthenium tris bipyridine derivatives, and others can also be intercalated into the galleries of a-ZrP. This list has... 

The process through which a linear string of amino acid residues newly synthesized at a ribosome folds into a complex, three-dimensional, biologically active protein structure remains poorly understood. Consider how protein-folding contrasts with RNA-folding. Proteins have 20 distinct monomeric units, RNA only four. The amino acids include aromatic, hydrophobic, cationic, and anionic chemical properties compared to four comparable RNA nucleosides. Moreover, secondary and tertiary structures were fundamentally inter-linked in proteins, but are essentially distinct in RNA molecules. 

Because of their well-recognized physicochemical properties (relatively high hydrophobicity, cationic character, and short length) reversed-phase, size-exclusion, and cation exchange chromatographies are particularly appropriate to purify bioactive peptides from the immune system of invertebrates. The sensitivity of HPLC, MS, Edman degradation, and liquid growth inhibition assays allow one to use from narrow (e.g., 2.1-mm internal diameter) down to micro-or nano-columns. 

The cationic surfactant is selected on the basis of the amount of conditioning desired, the more hydrophobic cationic such as a dihydrogenated tallow dimethyl ammonium chloride provides a high level of conditioning, while the same molecular architecture based on di-palmityl-dimethyl ammonium chloride provides a lower level of conditioning. Still milder conditioning for oily hair can be provided by mono alkyl chain cationics such as dodecyl-trimethyl ammonium chloride. 

When strongly hydrophobic cationic surfactants are present in the mobile phase the hydrophobic surface of the stationary phase becomes dynamically conditioned with respect to the adsorption of the surfactant. This confers an ion-exchange capability on the stationary phase. Cassidy and Elchuk (32, 33) reported use of cetylpyridinium chloride to coat the stationary phase "permanently", but used tetrabutyl and tetramethylammonium salts in the mobile phase. Their equilibration procedure also employed the use of acetonitrile in the initial conditioning step, thus increasing the overall cost of the analysis. Knox and Hartwick (36)... 

Wei et al. studied the separation of amines (aniline, ephedrine, codeine, cocaine, thebaine) and quaternary ammonium compounds (berberine, jatrorrhi-zine) on a bare silica stationary phase [44], A thorough study of the separation mechanism revealed a complex multifunctional mechanism. Contributions from differential electrophoretic migration were superimposed on hydrophobic, cation-exchange, and normal-phase interactions. Retention was highly dependent on the pH (optimal pH 8.3), ionic strength, and the amount of organic modifier. As the content of acetonitrile exceeded 80%, retention was consistent with a normal-phase mechanism. 

The tetraanlonlc porphyrins associate strongly with moderately hydrophobic cations such as CTAC, R N+ and the vlologens. These complexes are readily detected spectroscopically for both 3 and 4 however, efforts to measure precise values of the association constant are frustrated due to the fact that multiple association complexes are formed (eqs. 5, 6), where p4- =... 

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