Dendrimer labeling

Shinkai et al. described the synthesis of dendritic saccharide sensors based on a PAMAM dendrimer labeled with eight boronic acid residues [183]. The dendritic compound showed enhanced binding affinity for D-galactose and d-fructose. The fact that the dendritic boronic acid functions as a saccharide sponge is ascribed primarily to the cooperative action of two boronic acids to form an intramolecular 2 1 complex. When one boronic acid binds a saccharide, its counterpart cannot participate in dimer formation and seeks a guest. 

Fig. 7. Plot of absorption maximum vs generation number for polyether dendrimers labeled with a focal point solvatochromic group...

Coordination causes electron-spin density redistribution in the N-O fragment the contribution of resonance structure II increase. The redistribution of spin density results in changes in the parallel component of the nitrogen hyperfine tensor. TEMPO and anthraquinone (AQ) have been used in this way to probe the Lewis acidity of alumina and Li and Mg doped alumina matrices.176 The differences in the Lewis acidic strength towards TEMPO and anthraquinone are discussed. An interesting study has appeared aimed to study the guest-host interaction between poly(amidoamine) dendrimers labelled with nitroxides and several porous solids including alumina.177... 

Steady-state fluorescence spectra and decays of excitations of a phosphorus-containing dendrimer labeled with 12 internal (pyrene) labels 31-[G j] and of an iminophosphorane model compound bearing two labels (Scheme 25) dissolved in different solvents revealed that the interior of dendrimers contained, as... 

The ESR studies of labeled dendrimers intended to clarify their role as MRI contrast agents have been described in several papers. Spin labeling of several different dendrimers (DAB and PAMAM, at different generations) let the authors calculate the rates of nitroxide reduction due to superoxide, by observing the change of the low-field spectral peaks in the ESR spectra as a function of time (Table 3). Dendrimers labeled with nitronylnitroxides work well as contrast agents in MRI, and therefore their characterization by means of ESR is of interest. ... 

Qualmann and Kessels have reported the synthesis of carborane-containing lysine dendrimers (123) (Fig. 72), with a better defined number of boron atoms, for use as protein labels in immunocytochemistry using electron microscopic techniques such as electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI).149... 

Use of sulfo-NHS-LC-SPDP or other heterobifunctional crosslinkers to modify PAMAM dendrimers may be done along with the use of a secondary conjugation reaction to couple a detectable label or another protein to the dendrimer surface. Patri et al. (2004) used the SPDP activation method along with amine-reactive fluorescent labels (FITC or 6-carboxytetramethylrhodamine succinimidyl ester) to create an antibody conjugate, which also was detectable by fluorescent imaging. Thomas et al. (2004) used a similar procedure and the same crosslinker to thiolate dendrimers for conjugation with sulfo-SMCC-activated antibodies. In this case, the dendrimers were labeled with FITC at a level of 5 fluorescent molecules per G-5 PAMAM molecule. 

Dissolve the purified SPDP-modified dendrimer of step 5 in 50 mM sodium phosphate, 0.15M NaCl, pH 7.5, or in DMSO at a concentration of at least lOmg/ml. Add a 10-20 X molar excess of an amine-reactive fluorescent molecule (i.e., NHS-rhodamine or a hydrophilic NHS-Cy5 derivative see section on fluorescent probes). React with mixing for 1 hour at room temperature. Purify the fluorescently labeled SPDP-modified dendrimer using gel filtration or ultrafiltration. Follow the method of either step 7 or 8 to conjugate the dendrimer to another protein or molecule. 

A similar type of biotin-dendritic multimer also was used to boost sensitivity in DNA microarray detection by 100-fold over that obtainable using traditional avidin-biotin reagent systems (Stears, 2000 Striebel et al., 2004). With this system, a polyvalent biotin dendrimer is able to bind many labeled avidin or streptavidin molecules, which may carry enzymes or fluorescent probes for assay detection. In addition, if the biotinylated dendrimer and the streptavidin detection agent is added at the same time, then at the site of a captured analyte, the biotin-dendrimer conjugates can form huge multi-dendrimer complexes wherein avidin or streptavidin detection reagents bridge between more than one dendrimer. Thus, the use of multivalent biotin-dendrimers can become universal enhancers of DNA hybridization assays or immunoassay procedures. 

Figure 7.20 The multivalent surface of dendrimers can be used to couple biotin groups and labels for detection in immunoassays. One such conjugate was made by coupling NHS-biotin and a maleimido-iron chelate to an amine-dendrimer for use in an unique carbonyl metallo assay method.

Figure 7.21 Dendrimers that are fluorescently labeled as well as biotinylated create enhanced detection reagents for use in (strept)avidin-biotin-based assays. Large complexes containing multiple fluorescent dendrimers can bind to antigens and form a highly sensitive detection system that exceeds the detection capability of fluorescently labeled antibodies.

Add a quantity of the SCN-Bzl-DTPA bifunctional chelating agent to obtain the desired molar excess of label over the amount of dendrimer present. The optimal ratio may be determined experimentally by preparing a series of dendrimer-chelate conjugates using different molar ratios and choosing the one that works the best in the intended application. 

Kobayashi, H., Wu, C., Kim, M.K., Paik, C.H., Carrasquillo, J.A., and Brechbiel, M.W. (1999) Evaluation of the in vivo biodistribution of indium-111 and yttrium-88 labeled dendrimer-1 B4M-DTPA and its conjugation with anti-Tac monoclonal antibody. Bioconjug. Chem. 10, 103-111. 

Qualmann, B., Kessels, M.M., Musiol, H.J., Sierralta, W.D., Jungblut, P.W., and Morodeg L. (1996) Synthesis of boron-rich lysine dendrimers as protein labels in electron microscopy. Angew. Chem. Int. 

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