Determination of non-traditional intrinsic fluorescence (NTIF) emission sites in 1-(4-carbomethoxypyrrolidone)-PAMAM dendrimers using CNDP-based quenching studies |
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Authors: | Malgorzata?Konopka Anna?Janaszewska Kayla?AM?Johnson David?Hedstrand Donald?A?Tomalia Email authorView authors OrcID profile" target="_blank">Barbara?Klajnert-MaculewiczEmail authorView authors OrcID profile |
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Institution: | 1.Department of General Biophysics, Faculty of Biology and Environmental Protection,University of Lodz,Lodz,Poland;2.NanoSynthons LCC,Mt. Pleasant,USA;3.Department of Chemistry,University of Pennsylvania,Philadelphia,USA;4.Department of Physics,Virginia Commonwealth University,Richmond,USA |
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Abstract: | A unique photoluminescent phenomenon producing inexplicable, blue emissions λEx?=?365 nm; λEm?=?460 nm] in the absence of traditional aromatic fluorophores has been observed in a variety of surface functionalized poly(amidoamine) (PAMAM) dendrimers over the past two decades. This emission phenomenon, referred to as non-traditional intrinsic fluorescence (NTIF), originates from the intra-molecular clustering of electron-rich sub-fluorophores (i.e., tertiary amines and/or amido groups) residing in the interior of all PAMAM dendrimers. The intra-molecular clustering of these interior sub-fluorophores is hypothesized to account for the modest but reproducible, blue emissions observed for a variety of dendrimer surface moieties (i.e., –OH, –CO2H, and –NH2). Unexpectedly, a simple, one-step conversion of amine-terminated PAMAM dendrimers to 1-(4-carbomethyoxy) pyrrolidone-terminated dendrimers (4-CMP) was found to produce a 50-fold increase in blue NTIF emission compared to other surface moieties. In an effort to understand this new enhanced emission property, critical nanoscale design parameter (CNDP)-directed quenching experiments were devised to probe the increased NTIF emissions. Was it originating from the interior sub-fluorophoric tertiary amine/amido moieties or from the surface-attached, sub-fluorophoric pyrrolidone amido groups or both? Four generations of 4-CMP PAMAM dendrimers were examined. Two classical quenchers, namely, potassium iodide and acrylamide were selected to probe surface versus interior domains, respectively, as a function of predictable CNDPs associated with generation levels. With increasing dendrimer generation, quencher penetration into the dendrimer interior is impeded due to CNDP-directed generational congestion. Stern-Volmer plots for each quencher, as a function of generation, exhibited appropriate linear or non-linear correlations that corroborated behavior expected for two distinct region-specific emission sites. |
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