Markers molecules

Bilayer rigidity is a parameter which influences biodistribution and biodegradation of liposomes. In vitro a hydrophilic marker molecule (carboxyfluorescein) leaked much faster from the vesicles with bilayers in a fluid state than from bilayers in a gel state (Crommelin and Van Bommel, 1984). An indication of the bilayer rigidity can... 

FIGURE 5.2.3 Structures of some marker molecules of caramel color. 

Caramel color interacts with other food components. As an example, a concentration higher than 700 ppm caramel in cola increased the rate of hydrolysis of the aspartame, forming alpha-L-aspartyl-L-phenylalanine. Caramelization products inhibited enzymic browning by 85.8 and 72.2% when heated at pH 4 and 6, respectively, for 90 min. The highest inhibitory activity was found for the fraction with molecular weight of 1000 to 3000. Caramel is often used for adulteration of juices and other foods like honey or coffee. It can be determined by quantification of marker molecules such as 5-HMF, 4-Mel, and DFAs. ... 

Schneider M, O Luxenhofer, A Deissler, K Ballschmiter (1998) Cj-C, alkyl nitrates, benzyl nitrate and bifunctional nitrates measurements in California and South Atlantic air and global comparsion using C2Cj4 and CHBrj as marker molecules. Environ Sci Technol 32 3055-3062. 

The anti-DNA antibody has been used as a marker molecule of Systemic Lupus Erthematosus (SLE) which is a severe autoimmune disease. Enzyme immunoassay is the most reliable, widely used method of assay however, the electrochemical detection method reported here should be interesting for the purpose of a rapid and convenient diagnostic tool of SLE. 

Evaluation of the epithelial integrity can be performed by measuring the transepithelial electrical resistance (TEER). TEER values ranging from 150 ohms.cm2 up to 600 ohms.cm2 have been reported. An alternative method for assessing the monolayer integrity is to monitor the flux of hydrophilic marker molecules that pass the monolayers by the paracellular route (e.g., mannitol, Na-fluorescein, or atenolol). 

Extracellular marker molecules, such as mannitol, inulin, Na-fluorescein, and PEG-400, have been used to verify a tight epithelium they have also been used for testing the effects of enhancers and increased fluid absorption [159],... 

The enzyme or the chromogen detection system determines whether any endogenous material must first be destroyed. If a peroxidase marker molecule is to be used, endogenous peroxidase or peroxidase-like activity should be blocked. Because these preparations are more fragile than a fixed embedded sample, endogenous enzyme is inactivated with a weaker blocking solution than would... 

There are inherent problems associated with enzyme-mediated methods, regardless of the method used. The right conditions must be met, of course, for the enzyme action to take place. Unlike fluorochromes or gold particles (two other marker compounds), enzymes need to act chemically for the assay to work. Also, the enzyme action must only represent the marker molecule. Endogenous enzyme or enzyme-like activity can create problems only realized in systems that use enzymes. Also, the use of enzymes demands more attention to detail because of the increase in sensitivity that is often obtained. The problem of unwanted reactivity is enhanced in enzyme-mediated reactions more so than in others, in part because of the additional level of sensitivity brought about by the continuous action on a substrate. 

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. 

During cell fractionation, it is very important to analyze the purity of the fractions obtained. Whether or not the intended organelle is present in a particular fraction, and whether or not the fraction contains other components, can be determined by analyzing characteristic marker molecules. These are molecules that occur exclusively or predominantly in one type of organelle. For example, the activity of organelle-specific enzymes (marker enzymes) is often assessed. The distribution of marker enzymes in the cell reflects the compartmentation of the processes they catalyze. These reactions are discussed in greater detail here under the specific organelles. 

Figure 10.11 The use of ferritin as a label for the mechanism of growth of vesicles (adapted from Berclaz et al, 2001a b). Schematic representation of the possible vesicle formation and transformation processes when oleate, and oleic acid, are added to pre-formed vesicles which have been labelled, (a) The situation if only de novo vesicle formation occurs, (b) Growth in size of the pre-formed and labeled vesicles which may lead to division, either yielding vesicles that all contain marker molecules (case i, a statistical redistribution of the ferritin molecules) or also yielding vesicles that do not contain markers (case ii). Compare all this with Figure 10.9.

Schneider, M., O. Luxenhofer, A. Deissler, and K. Ballschmiter, C,-C 5 Alkyl Nitrates, Benzyl Nitrate, and Bifunctional Nitrates Measurements in California and South Atlantic Air and Global Comparison Using C2C14 and CHBr3 as Marker Molecules, Enriron. Sci. Technol., 32, 3055-3062 (1998). 

For the detection of viruses different SERS approaches are reported. One possibility is the direct detection of the DNA or the protein shell. Additionally, the presence of the DNA can also be detected indirectly via marker molecules. The third possibility is the detection via antibodies [28],... 

For an indirect detection of viral DNA the capture DNA is labeled with either a marker molecule and/or a SERS-active substrate. One approach is the use of a DNA hairpin. Here, the capture DNA is attached at one side to... 

As described earlier, the basic design of the micropump involves a drug reservoir attached to a pumping device with or without a sensor. The inclusion of a sensor with the device makes it a closed-loop system, where the device can check the levels of marker molecules such as glucose and deliver the therapeutic agent. In many systems the devices are implanted such that the reservoir can be charged when it is exhausted. The device may pump at a basal rate or may be controlled by a circuit connected in a closed loop with a sensor or by a handheld remote control device by the patient. 

Table 2.5 Marker molecules used to characterize ultrafiltration membranes...

Blood travels through the human body in more than 96,000 km of blood vessels and it is full of marker molecules [34], The physiological pH is usually 7.4 with a complex buffer system (bicarbonate-carbonic acid, hemoglobinate-hemoglobin, phosphate buffer) [35],... 

Figure 3 shows the results of sin investigation of the pH-sensitivity of a crosslinked poly(ortho ester) prepared from 3,9-bis(ethylidene 2,4,8,10-tetraoxaspiro [5,5] undecane), triethylene glycol, and 1,2,6-hexanetriol. In these studies, a marker molecule, p-nitroacetanilide was incorporated into the polymer, and the rate of release of p-nitroacetanilide was assumed to correspond to the rate of erosion of the polymer. This assumption is not entirely accurate because some diffusional release occurs. However, the method is a good measure for determining the changes in erosion rates with changes in external pH. 

---