Temperature-Sensitive Dendrimers

Dendrimers are three-dimensional hyperbranched, globular macromolecules that are capable of condensing DNA into small complexes, and thereby increase plasmid transfection efficiency (14). Dendrimers are typically stable in serum and not temperature sensitive, but are also non-biodegradable and cause significant cytotoxicity. 

HAB Haba, Y., Kojima, C., Harada, A., and Kono, K., Control of temperature-sensitive properties of poly(amidoamine) dendrimers using peripheral modification with various alkylatrride groups. Macromolecules, 39, 7451, 2006. 

Finally, temperature-sensitive, elastin-like peptide-modified dendrimers were synthesized for drug delivery by Kojima et al. [ 140]. Elastin is one of the major components of the extracellular matrix with temperature sensitivity. A repeat sequence of Val-Pro-Gly-Val-Gly was used to prepare the elastin-like peptide, which was conjugated to a PAMAM dendrimer G(4). The synthesized elastin-mimetic dendrimer-based polymer proved to be a potent drug carrier with both temperature- and pH-responsive properties. The same group reported fine-tuning of the temperature sensitivity by manipulation of the peptide chain length and the generation of dendrimer. 

X. Li, Y. Haba, K. Ochi, E. Yuba, A. Harada, and K. Kono, PAMAM dendrimers with an oxyethylene unit-enriched surface as biocompatible temperature-sensitive dendrimers, Bioconjug Chem, 24 (2), 282-90, 2013. 

Smart engineering has led to intriguing stimuli-sensitive dendrimer designs. pH-dependent release of pyrene from the interior of PPI dendrimers at low pH following protonation of the amine groups has been demonstrated (Pistohs et al. 1999). Temperature sensitivity of isobutyramide-incorporated dendrimers increased their water solubihty (Haba et al. 2004). Light-sensitive dendritic systems have also been reported (Puntoriero et al. 2007). 

Infrared spectroscopy of adsorbed CO is a useful characterization tool for dendrimer-templated supported nanoparticles, because it directly probes particle surface features. In these experiments, which are performed in a standard infrared spectrometer using an in-situ transmission or DRIFTS cell, a sample of supported DENs is first treated to remove the organic dendrimer. Samples are often reduced under H2 at elevated temperature, flushed with He, and cooled to room temperature. Dosing with CO followed by flushing to remove the gas-phase CO allows for the spectrum of surface-bound CO to be collected and evaluated. Because adsorbed CO stretching frequencies are sensitive to surface geometric and electronic effects, it is potentially possible to evaluate the relative effects of each on nanoparticle properties. 

Other applications of photochemistry include the development of sensitive fluorescent chemosensors for analysis of dilute solutions of inorganic cations and anions and the study of the diffusion of individual molecules in solution at room temperature. Fluorescent compoimds have been used as replacements for radioisotopes in the analysis of biological compoimds and the study of biologically active compounds and living systems. Photochemical reactions also offer alternative probes for the characterization of the microenvironments in diverse solid and liquid media, including crystals, zeolites, alumina, silica and clay surfaces, semiconductor surfaces, liquid crystals and host-guest inclusion complexes, polymer films, monolayers and supported multilayers of surfactant molecules, mi-celles, and dendrimers. ... 

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