Inherent Photoluminescence Properties of Poly(propyl ether imine) Dendrimers

Synthesis and Studies of Pyridoneimine-Functionalized PETIM Dendrimers

Pyridinoimine-functionalized poly(ether imine) (PETIM) dendrimers of 1-3 generations, possessing 4-16 moieties at the peripheries, are synthesized. Chloride-functionalized dendrimers are reacted with N-methylamino pyridine, under basic conditions, which led to functionalization of the peripheries of a dendrimer with pyridoneimine moieties. Variable-temperature 1H NMR studies are performed to assess the contributing resonance forms of pyridoneimine in the dendrimers. Solvatochromism and 15N NMR studies aid further the assessment of the contributing resonance forms. Comparison with derivatives that possess 1 and 2 pyridoneimines illustrates the contributing resonance forms between nonaromatic pyridoneimine and zwitter ionic aromatic imidopyridinium species.

Hydrolyzation-Triggered Ultralong Room-Temperature Phosphorescence in Biobased Nonconjugated Polymers

Amorphous nonconjugated room-temperature phosphorescent (RTP) polymers have aroused ever-increasing attention. However, the variety of such polymers is still rare due to limited preparation strategies. Herein, we report a facile strategy to achieve ultralong RTP emission in biobased nonconjugated polymers through a hydrolyzation process. The investigated polymers are synthesized by free radical solution copolymerization using biomass methyl isoeugenol and maleic anhydride as monomers. Noticeably, the obtained polymers carry no conventional fluorescent units but can exhibit blue fluorescence. More interestingly, after hydrolysis in sodium hydroxide aqueous solution, the resulting hydrolyzed polymers emit both enhanced blue emission and persistent RTP (up to 400 ms) under air conditions, with reversible emission performance switched via the uptake and removal of water. Also worthy to be highlighted is that the emission can be remarkably regulated by the cations in carboxylate or the substituents on the benzene ring. The as-obtained polymers demonstrate potential applications in anticounterfeiting and information encryption.

Effect of Metal Ions on the Intrinsic Blue Fluorescence Property and Morphology of Aromatic Amino Acid Self-Assembly

Metal ions are known to strongly bind with different proteins and peptides, resulting in alteration of their different physicochemical properties. In this work, we investigate the effect of metal ions of different nuclear charges and sizes on the intrinsic blue luminescence of the self-assembled structures formed by aromatic amino acids, namely, phenylalanine and tryptophan, using spectroscopic and imaging techniques. The study reveals that the intrinsic blue fluorescence of amino acid assemblies is influenced by metal ions and the pH of the medium. The metal ions with a higher charge to radius ratio promote clusterization which results in the enhancement of the intrinsic fluorescence, an effect known as "clusteroluminescence" of the amino acids aggregates. The imaging study reveals that metal ions with a higher charge to size ratio inhibit the large fibrillation of aromatic amino acids by promoting the formation of small nonfibrillar aggregates through increased hydrophobicity in the medium. The nanoaggregates are assumed to be responsible for the enhancement in the blue "clusteroluminescence".

Underlying Mechanisms for the Modulation of Self-Assembly and the Intrinsic Fluorescent Properties of Amino Acid-Functionalized Gold Nanoparticles

The origin of the blue fluorescence of proteins and peptides in the visible region has been a subject of intense debate despite several efforts. Although aromatic amino acids, namely tryptophan (Trp), tyrosine (Tyr), and phenylalanine (Phe) are responsible for the intrinsic luminescence of proteins and peptides, the underlying mechanism and contributions of these amino acids to the unusual blue fluorescence are still not well resolved. In the present endeavor, we show that the clusterization of both aromatic and aliphatic amino acids on the surface of the gold nanoparticles (Au NPs) leads to clusteroluminescence, which could be linked to the unusual fluorescence properties of the proteins and peptides and have been ignored in the past. The amino acid monomers initially form small aggregates through clusterization, which provides the fundamental building blocks to establish the amyloid structure as well as the luminescence property. Because of the clusterization, these Au NPs/nano-aggregate systems are also found to exhibit remarkable stability against the freeze-thaw cycle and several other external stimuli, which can be useful for biological and biomedical applications.

Radiation-Induced In Situ-Printed Nonconjugated Fluorescent Nonwoven Fabric with Superior Fluorescent Properties

A new technique is proposed for the in situ printing of fluorescent fabrics with superior fluorescent properties that have the potential for continuous roll-to-roll production in the industry. Nonconjugated chemical moieties were covalently connected to polyethylene/polypropylene nonwoven fabric (PE/PP NWF) to successfully prepare fluorescent PE/PP NWF, which emits a bright blue light and has a high quantum yield (∼83.35%) that can be attributed to a unique aggregation-induced emission effect. The fluorescent PE/PP NWF exhibits excellent fluorescent stability under high shear forces during accelerated laundering and in harsh chemical environments. The fluorescent PE/PP NWF can also be tailored into diverse shapes and printed in situ with high resolution. The versatility of the method was also demonstrated by fabricating fluorescent materials with different polymer matrices such as Nylon 66 fiber and PE terephthalate membrane.

Successive outermost-to-core shell directionality of the protonation of poly(propyl ether imine) dendritic gene delivery vectors

The protonation behaviour of polycationic compounds has direct relevance to their ability to condense and deliver nucleic acids. This report pertains to a study of the protonation behaviour of polycationic poly(propyl ether imine) (PETIM) dendritic gene delivery vectors that are constituted with tertiary amine core moiety and branch sites, n-propyl ether linkages, and primary amine peripheries. The ability of this series of dendrimers to condense nucleic acids and mediate endosomal escape was studied by unravelling the protonation behaviour of the dendrimers aided by pH metric titrations and 1H and 15N NMR spectroscopies. The results demonstrate protonation of the primary and tertiary amines of outermost-to-core shells occurring in a successive stepwise fashion, in contrast to other polycationic vectors. Theoretical calculations based on the Ising model rationalize further the finer details of protonation at each shell. The protonation pattern correlates with the endosomal buffering and nucleic acid condensation properties of this PETIM-based dendritic gene delivery vectors. The study establishes that the protonation behaviour is a critical and essential parameter to assess the gene condensation and delivery vector properties of a polycationic compound.

Facile one-pot synthesis of novel water-soluble fluorescent hyperbranched poly(amino esters)

Two kinds of water-soluble fluorescent hyperbranched poly(amino esters) were first synthesized by a convenient one-pot approach via the A₂ + B₃ Michael addition reaction of trimethylolpropane triacrylate and aliphatic diamines.

pH dependent one-/two-photon fluorescence emission properties and mechanism of the dendrimer PAMAM triphenylamine imine

pH dependent fluorescence emission of PTS-G0 and ETS were compared, to better understand intrinsic fluorescence phenomena of PAMAM dendrimers.

A new microscopic insight into membrane penetration and reorganization by PETIM dendrimers

Dendrimers are highly branched polymeric nanoparticles whose structure and topology, largely, have determined their efficacy in a wide range of studies performed so far. An area of immense interest is their potential as drug and gene delivery vectors. Realizing this potential, depending on the nature of cell surface-dendrimer interactions, here we report controlled model membrane penetration and reorganization, using a model supported lipid bilayer and poly(ether imine) (PETIM) dendrimers of two generations. By systematically varying the areal density of the lipid bilayers, we provide a microscopic insight, through a combination of high resolution scattering, atomic force microscopy and atomistic molecular dynamics simulations, into the mechanism of PETIM dendrimer membrane penetration, pore formation and membrane re-organization induced by such interactions. Our work represents the first systematic observation of a regular barrel-like membrane spanning pore formation by dendrimers, tunable through lipid bilayer packing, without membrane disruption.

Poly-amidoamine structure characterization: amide resonance structure of imidic acid (HO–CN) and tertiary ammonium

The dendrimer PAMAM has an amide resonance structure,i.e.imidic acid (HO–CN), and a tertiary ammonium structure, which can be characterized using¹⁵N/¹H/2D NH/¹³C NMR, IR and MS.

A study using quantum chemical theory methods on the intrinsic fluorescence emission and the possible emission mechanisms of PAMAM

Structural units imidic acid (HO–CN) and tertiary ammonium in PAMAM dendrimers were proven to give fluorescence emission by TDDFT methods.

Uncovering a broad class of fluorescent amine-containing compounds by heat treatment

In a heating process, the fluorescence peaks of amine-containing compounds shift gradually from the ultraviolet spectral region to the visible region.

Dendrimers - from organic synthesis to pharmaceutical applications: an update

Dendrimers are a relatively new class of monodisperse polymers, which have tree-like spherical structures with well-defined sizes and shapes. Their unique structure has a significant impact on their physical and chemical properties. Research on dendrimers is of significant interest to scientists from all areas and their utility in various scientific fields, including pharmaceuticals, is expanding. The present review is comprehensive and covers different aspects of dendrimers viz. (1) synthesis, (2) properties and (3) pharmaceutical applications. The emphasis is on their applications as well as the current ongoing research status for drug targeting.

Design of biocompatible dendrimers for cancer diagnosis and therapy: current status and future perspectives

In the past decade, nanomedicine with its promise of improved therapy and diagnostics has revolutionized conventional health care and medical technology. Dendrimers and dendrimer-based therapeutics are outstanding candidates in this exciting field as more and more biological systems have benefited from these starburst molecules. Anticancer agents can be either encapsulated in or conjugated to dendrimer and be delivered to the tumour via enhanced permeability and retention (EPR) effect of the nanoparticle and/or with the help of a targeting moiety such as antibody, peptides, vitamins, and hormones. Imaging agents including MRI contrast agents, radionuclide probes, computed tomography contrast agents, and fluorescent dyes are combined with the multifunctional nanomedicine for targeted therapy with simultaneous cancer diagnosis. However, an important question reported with dendrimer-based therapeutics as well as other nanomedicines to date is the long-term viability and biocompatibility of the nanotherapeutics. This critical review focuses on the design of biocompatible dendrimers for cancer diagnosis and therapy. The biocompatibility aspects of dendrimers such as nanotoxicity, long-term circulation, and degradation are discussed. The construction of novel dendrimers with biocompatible components, and the surface modification of commercially available dendrimers by PEGylation, acetylation, glycosylation, and amino acid functionalization have been proposed as available strategies to solve the safety problem of dendrimer-based nanotherapeutics. Also, exciting opportunities and challenges on the development of dendrimer-based nanoplatforms for targeted cancer diagnosis and therapy are reviewed (404 references).

Multicharged and/or water-soluble fluorescent dendrimers: properties and uses

The fluorescence of water-soluble dendritic compounds can be due to the whole structure or to fluorophores used as core, as peripheral groups, or as branches. Highly sophisticated precisely defined structures with other functional groups usable for material or biological purposes have been synthesised, but many recent examples have shown that dendrimers can be used as versatile platforms for statistically linking various types of functional groups.