Micelle-chelate

Surfactants such as sodium dodecyl sulfate (SDS) form micelles. .. Chelate structures were minimized using the empirical force field (EFF) method. ... 

Inspired by the many hydrolytically-active metallo enzymes encountered in nature, extensive studies have been performed on so-called metallo micelles. These investigations usually focus on mixed micelles of a common surfactant together with a special chelating surfactant that exhibits a high affinity for transition-metal ions. These aggregates can have remarkable catalytic effects on the hydrolysis of activated carboxylic acid esters, phosphate esters and amides. In these reactions the exact role of the metal ion is not clear and may vary from one system to another. However, there are strong indications that the major function of the metal ion is the coordination of hydroxide anion in the Stem region of the micelle where it is in the proximity of the micelle-bound substrate. The first report of catalysis of a hydrolysis reaction by me tall omi cell es stems from 1978. In the years that... 

Penetration enhancers are low molecular weight compounds that can increase the absorption of poorly absorbed hydrophilic drugs such as peptides and proteins from the nasal, buccal, oral, rectal, and vaginal routes of administration [186], Chelators, bile salts, surfactants, and fatty acids are some examples of penetration enhancers that have been widely tested [186], The precise mechanisms by which these enhancers increase drug penetration are largely unknown. Bile salts, for instance, have been shown to increase the transport of lipophilic cholesterol [187] as well as the pore size of the epithelium [188], indicating enhancement in both transcellular and paracellular transport. Bile salts are known to break down mucus [189], form micelles [190], extract membrane proteins [191], and chelate ions [192], While breakdown of mucus, formation of micelles, and lipid extraction may have contributed predominantly to the bile salt-induced enhancement of transcellular transport, chelation of ions possibly accounts for their effect on the paracellular pathway. In addition to their lack of specificity in enhancing mem-... 

Haapakka and Kankare have studied this phenomenon and used it to determine various analytes that are active at the electrode surface [44-46], Some metal ions have been shown to catalyze ECL at oxide-covered aluminum electrodes during the reduction of hydrogen peroxide in particular. These include mercu-ry(I), mercury(II), copper(II), silver , and thallium , the latter determined to a detection limit of <10 10 M. The emission is enhanced by organic compounds that are themselves fluorescent or that form fluorescent chelates with the aluminum ion. Both salicylic acid and micelle solubilized polyaromatic hydrocarbons have been determined in this way to a limit of detection in the order of 10 8M. 

See also Luminescent dendrimers antibacterial, 26 799 biocompatibility studies of, 26 800-801 in catalysis, 26 805-806 in cell targeting, 26 797-798 as chelators, 26 806-807 core and interior shells of, 26 789 cytotoxicity of, 26 800-801 in drug delivery, 26 792-795 in gene transfection, 26 791-792 as imaging agents, 26 795-797 luminescent, 26 801-804 medical applications of, 26 791-801 micelle-mimetic behavior of, 26 789 multiphoton applications of, 26 803-804... 

Figure 1 Schematic structures of micelle and liposome, their formation and loading with a contrast agent, (a) A micelle is formed spontaneously in aqueous media from an amphiphilic compound (1) that consists of distinct hydrophilic (2) and hydrophobic (3) moieties. Hydrophobic moieties form the micelle core (4). Contrast agent (asterisk gamma- or MR-active metal-loaded chelating group, or heavy element, such as iodine or bromine) can be directly coupled to the hydrophobic moiety within the micelle core (5), or incorporated into the micelle as an individual monomeric (6) or polymeric (7) amphiphilic unit, (b) A liposome can be prepared from individual phospholipid molecules (1) that consists of a bilayered membrane (2) and internal aqueous compartment (3). Contrast agent (asterisk) can be entrapped in the inner water space of the liposome as a soluble entity (4) or incorporated into the liposome membrane as a part of monomeric (5) or polymeric (6) amphiphilic unit (similar to that in case of micelle). Additionally, liposomes can be sterically protected by amphiphilic derivatization with PEG or PEG-like polymer (7) [1].

To increase the load of liposomes and micelles with reporter metals, we designed a new family of amphiphilic single-terminus modified polymers containing multiple chelating groups that could be incorporated into the hydrophobic domains of liposomes and micelles. The approach is based on the use of CBZ-protected polylysine (PL) with a free terminal amino group, which is derivatized into a reactive form with subsequent deprotection and incorporation of DTPA residues. This was initially suggested by us for heavy metal load on proteins and antibodies [17]. 

Using N-terminus modified polylysine, we developed a synthesis for an amphiphilic polychelator, A,a-(DTPA-polylysyl)glutaryl phosphatidyl ethanolamine (DTPA-PL-NGPE). This polychelator was incorporated into the liposomal membrane and micelle core during liposome or micelle preparation. This system sharply increased the number of chelated Gd atoms attached to a single lipid anchor. This increased the number of bound reporter metal atoms per vesicle and decreased the dosage of an administered... 

Figure 2 Chemistry of the polymeric chelates used for loading liposomes and micelles with multiple reporter metal atoms, (a) Synthesis of a single terminus-PDP-activated chelating polymer (DTPA-polylysine) starting from CBZ-protected polylysine and SPDR...

Micelles formed by self-assembled amphiphilic polymers (such as PEG-phosphatidyl ethanolamine) can also be loaded with amphiphilic PL-based chelates carrying diagnostically important metal ions such as In and Gd [20]. The final preparations are quite stable and serve as fast and efficient agents for scintigraphy or MR imaging. 

Similar experiments with PEG-phosphatidyl ethanolamine mixed micelles with a core-incorporated amphiphilic " In- or Gd-loaded chelating agent PAP demonstrated fast and efficient gamma and MR visualization of different compartments of the lymphatic system. Upon subcutaneous administration, the micelles penetrate the lymphatics and effect visualization (Figure 6). Micelles mostly stay within the lymph fluid rather than accumulate in the nodal macrophages (because of protective effect of surface PEG fragments) and rapidly move via the lymphatic pathway. 

Figure 6 Transverse MR images of axillary-subscapular lymph node area in the rabbit 4 min after s.c. administration of PEG (5 kDa) -phosphatidyl ethanolamine micelles containing coreincorporated Gd-loaded amphiphilic chelate DTPA-phosphatidyl ethanolamine. The dose was 0.5 pmol Gd per injection site. Fast and clear visualization of both lymph vessel (1) and lymph node (2) was achieved. Images were acquired by using a 1.5 Tesla GE Signa MRI scanner operated at fat suppression mode and Ti-weighted pulse sequence [20].

Two types of micellar systems have been described, the first one includes Gd complexes capable of self-organization resulting in a supramolecular assembly 103), while the other class of micelles, also named mixed micelles is made of several components a lipophilic gadolinium chelate, one or several phospholipid(s) and a non-ionic surfactant containing a polyoxyethylene chain 104,105). 

Hetaeric chromatography, 230, 231 effect of charge on hetaeron, 233 retention model of, 231-238 Hetaeron. 191, 230, 231, 240, 243, 249, 280 see also Complexing agent adsorption on the stationary phase, 231, 249,230 amphiphilic, 243 cetrimide, 248 decylsulfonate, 230 dodecylbenzenesulfonate, 230 formation constant of complexes, 276 lauryl sulfate, 230 metal chelating, 262 micelle formation, 230 optically active, 262 surface concentration of, 232... 

In another case, PAs were designed to function as magnetic resonance imaging (MRI) contrast agents (Bull et al. 2005) by covalently linking the peptide portion to a derivative of l,4,7,10-tetraazacyclododecane-l,4,7,10-tetraacetic acid followed by chelation of Gd ions by this moiety. The PAs were modified such that self-assembly produce either nanofibers or spherical micelles. The application of this self-assembling system could be extended to noninvasive MRI of PA scaffolds in vivo. 

Protein subunits will partially dissociate from crystalline ferritin in dilute salt solutions to yield a non-crystallizable ferritin. The non-crystallizable ferritin, in turn, in the presence of apoferritin appears to pick up protein subunits and by action yield crystalline ferritin molecules. The scheme for this process is shown in Fig. 6. The salient feature of this scheme is the initial formation of an iron micelle from soluble iron chelates which is then stabilized by protein subimits S5uithesized by the tissue (726). Harrison and Gregory 127) have used glacial acetic acid to dissociate apoferritin completely. When the pH is adjusted to 4 in the presence of thiol compoimds, apoferritin is rapidly formed, indicating strong subunit interaction. 

Fig. 6. A model for the synthesis of ferritin from protein subunits and the role of the iron micelle in the ultimate structural formation. Mobilization of the iron from the micelle by chelates is also indicated...

Fig. 25. (A) DELFIA (Dissociation Enhanced Lanthanide Fluoro-ImmunoAssay) system. This heterogeneous immunoassay system uses a primary antibody bound to a solid support, to which a variable amount of unlabeled antigen is bound. The secondary antibody is labeled with a non-phospho-rescent lanthanide chelate, which becomes phosphorescent after dissociation from the antibody, due to the addition of an enhancement solution [which typically contains a mixture of sensitizer (typically a (1-diketonate) and micelle inducing surfactant (5). (B) Heterogeneous fluoroimmunoassay using a secondary antibody directly labeled with a phosphorescent lanthanide chelate.

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