Octadecyl group

By immobilizing Mn(III)-tetrakis(4-sulfonatophenyl)-porphyrin on dioctadecyl-dimethyl ammonium chloride bilayer membranes incorporated into a PVC film, Kuniyoshi et al. [65] developed an epinephrine CL sensor, which allowed determination of epinephrine down to 3 pM with an RSD of 1.0% for 50 pM of this biological compound. Compared with the previously reported epinephrine CL sensor [66], the present authors noted that the alkaline carrier solution, at high concentration levels, caused gradual deterioration of the immobilized catalyst, and this problem could be solved by the use of immobilization techniques other than ion exchange, e.g., solubilization of the catalyst that has octadecyl groups in the bilayer molecules. 

Reverse-phase HPLC (RP-HPLC) separates proteins on the basis of differences in their surface hydophobicity. The stationary phase in the HPLC column normally consists of silica or a polymeric support to which hydrophobic arms (usually alkyl chains, such as butyl, octyl or octadecyl groups) have been attached. Reverse-phase systems have proven themselves to be a particularly powerful analytical technique, capable of separating very similar molecules displaying only minor differences in hydrophobicity. In some instances a single amino acid substitution or the removal of a single amino acid from the end of a polypeptide chain can be detected by RP-HPLC. In most instances, modifications such as deamidation will also cause peak shifts. Such systems, therefore, may be used to detect impurities, be they related or unrelated to the protein product. RP-HPLC finds extensive application in, for example, the analysis of insulin preparations. Modified forms, or insulin polymers, are easily distinguishable from native insulin on reverse-phase columns. 

Takeda et al. [104] found that the steady-state irradiation of A-octadecyl 6,8-dinitro-BlPS resulted in the formation of the closed form. This is in agreement with the femtosecond studies. However, the fade reaction showed three components when monitored at 500 nm in 1,2-dichloroethane. The first component was manifest as a bleach that occurred within the instrument response time of 25 nsec. This was followed by two longer components with 240-nsec and 3.4 psec lifetimes. The spiropyran ring-closed form evolved with two exponential components with lifetimes of 620 nsec and 4 p-sec. The Af-octadecyl group may affect the outcome compared to the A-methylated form. 

The effect of pore size on the retentive capacity of various octadecyl silica bonded phases is illustrated in Fig. 10. Exclusion effects become appreciable when bulky octadecyl groups (see Table V) are attached to the pore wall in 6 nm pore diameter silica (Si-60). As a result, the stationary... 

There is a report that the thermal stability of imidazolium salts is largely the same, despite a great difference in alkyl chain length between the butyl and octadecyl groups, suggesting simple extension of alkyl chain hardly afFects Id [30]. 

The most common R group is the octadecyl group (C-18), which leaves the silica particles coated with hydrocarbon chains. The silica particles are very small (—40 p dia. = 4 x 10 cm dia.) and very uniform in size. With very small, uniform particles, a molecule in the solvent can rapidly diffuse to the surface of the packing and undergo partitioning between the station-... 

Atwood et al. studied the dissolution of silica gel in the mobile phase by measuring the concentration of silica gel in the column effluent by atomic absorption. For uncoated silica gel and water as mobile phase at a flow rate of lml/min the concentration of silica gel in the column effluent was 38 ug/ml. For silica gel with chemically bonded octadecyl groups, no measurable amounts of silica gel were found 1n the effluent under the same experimental conditions (detection limit 0.3 ug/ml). The same was true for uncoated silica... 

Chemically bonded octadecyl groups on a pellicular support was used as stationary phase for the separation of a series of Mitragyna oxindole alkaloids4 with methanol - water (4 1) as mobile phase. 

The first reversed-phase separation of ergot alkaloids was reported by Jane and Wheals in connection with the analysis of LSD. Pellicular beads with chemically bonded octadecyl groups were used in combination with methanol - 0.1% aqueous ammonium carbonate (3 2) as mobile phase However, the mobile phase proposed by Vivilecchia et al.6 for the separation of the dihydro-ergotoxine alkaloids on octadecyl columns (acetonitrile - aqueous ammonium carbonate) has been... 

For the analysis of theophylline in biological fluids, a reversed-phase separation on a microparticulate stationary phase with chemically bonded octadecyl groups, and a mobile phase consisting of a 0.01 M sodium acetate buffer (pH 4.0) containing 4-10% acetonitrile, is widely used (Table 11.3 and Fig.11.I)27. 

Poly(aspartates) and poly(glutamates) with -alkyl chains as the side chains take on the liquid crystalline state under any conditions such as temperature variation, the side-chain length variation, etc., as the macroscopic structure, and also take various main-chain conformations. In poly(aspartates) and poly(glutamates) with long -alkyl side groups such as -octadecyl groups, between which the difference is the number of CH2 carbons between the C and ester carbonyl carbons, i.e., the former has one CH2 carbon and the latter two CH2 carbons. By elevating the temperature the latter forms a... 

Column A 30 X 4.6 L-column (porous silica gel with internal surfaces coated with octadecyl groups and external surfaces coated with glycerylpropyl groups) (Chemical Inspection and Testing Institute, Tolqro) B 250 X 4.6 Sumichiral OA-2500S ((R)-N-(3,5-dinitrobenzoyl)-... 

---