Fluorescent guests hosted in fluorescent dendrimers

Low-generation fluorescent polyurethane dendrimers via late-stage modification using azide-alkyne click chemistry

Protecting group free one-pot multicomponent Curtius reaction afforded a versatile MN₂ type dendron, ensuring late-stage modification of both dendron and dendrimer to afford highly fluorescent symmetrical and unsymmetrical (Janus) polyurethane dendrimers. Fluorescence study of these dendrimers exhibited the Förster resonance energy transfer (FRET) between blue and mint green fluorophores.

Bioinspired Artificial Photosynthetic Systems

Mimicking photosynthesis using artificial systems, as a means for solar energy conversion and green fuel generation, is one of the holy grails of modern science. This perspective presents recent advances towards developing artificial photosynthetic systems. In one approach, native photosystems are interfaced with electrodes to yield photobioelectrochemical cells that transform light energy into electrical power. This is exemplified by interfacing photosystem I (PSI) and photosystem II (PSII) as an electrically contacted assembly mimicking the native Z-scheme, and by the assembly of an electrically wired PSI/glucose oxidase biocatalytic conjugate on an electrode support. Illumination of the functionalized electrodes led to light-induced generation of electrical power, or to the generation of photocurrents using glucose as the fuel. The second approach introduces supramolecular photosensitizer nucleic acid/electron acceptor complexes as functional modules for effective photoinduced electron transfer stimulating the subsequent biocatalyzed generation of NADPH or the Pt-nanoparticle-catalyzed evolution of molecular hydrogen. Application of the DNA machineries for scaling-up the photosystems is demonstrated. A third approach presents the integration of artificial photosynthetic modules into dynamic nucleic acid networks undergoing reversible reconfiguration or dissipative transient operation in the presence of auxiliary triggers. Control over photoinduced electron transfer reactions and photosynthetic transformations by means of the dynamic networks is demonstrated.

The interaction of the excited states of safranine-O with low generation carboxyl terminated PAMAM dendrimers in an aqueous medium

The interaction of the singlet and triplet excited states of the synthetic dye safranine-O with carboxyl-terminated poly(amidoamine) (PAMAM) dendrimers was investigated in a buffer solution at pH 8. Low half-generation PAMAM dendrimers (G -0.5; G +0.5: G 1.5) were employed. The UV-vis absorption spectrum of the dye presents only a very small red shift in the presence of dendrimers. Fluorescence quenching was detected and it was interpreted by a static mechanism in terms of the association of the dye with the dendrimer. Laser flash photolysis experiments were carried out and transient absorption spectra of the triplet and radicals were obtained. The triplet state is quenched by the dendrimers with rate constants well below the diffusional limit. The quenching process was characterized as an electron transfer process and the quantum yield of radicals was estimated. It was found that radicals are formed with a high efficiency in the triplet quenching reaction.

Generation 3 PAMAM dendrimer TAMRA conjugates containing precise dye/dendrimer ratios

The synthesis, isolation, and characterization of generation 3 poly(amidoamine) (G3 PAMAM) dendrimer containing precise ratios of 5-carboxytetramethylrhodamine succinimidyl ester (TAMRA) dye (n = 1-3) per polymer particle are reported. Stochastic conjugation of TAMRA dye to the dendrimer was followed by separation into precise dye-polymer ratios using rp-HPLC. The isolated materials were characterized by rp-UPLC, MALDI-TOF-MS, and 1H NMR spectroscopy, UV-vis, and fluorescence spectroscopies.

The remarkable activity and stability of a dye-sensitized single molecular layer MoS2ensemble for photocatalytic hydrogen production

Single layer MoS₂synthesized by exfoliation with Li is demonstrated to take up the dye molecule, Eosin Y, with strong binding affinityviasulfur vacancies.

Hyperbranched poly(ether amine) (hPEA)/poly(vinyl alcohol) (PVA) interpenetrating network (IPN) for selective adsorption and separation of guest homologues

We here reported that hyperbranched poly(ether amine) (hPEA) and poly(vinyl alcohol) (PVA) interpenetrating network (hPEA/PVA-IPN) can be used for the selective adsorption and separation of guest homologues. A series of hyperbranched poly(ether amine) and poly(vinyl alcohol) interpenetrating networks (hPEA/PVA-IPNs) were fabricated by introducing poly(vinyl alcohol) chains into network of hyperbranched poly(ether amine), in which two independent networks of hyperbranched poly(ether amine) and poly(vinyl alcohol) were cross-linked through photodimerization of coumarin groups of hyperbranched poly(ether amine) and aldol condensation reaction between hydroxyl groups of poly(vinyl alcohol) and glutaraldehyde, respectively. The mechanical strength of interpenetrating networks can be enhanced by the introduction of poly(vinyl alcohol), and the tensile strength of interpenetrating networks increased with tens of times in compared with the pure hyperbranched poly(ether amine) network. The adsorption behavior of seven fluorescein dyes sharing with the same backbone and charge state onto hyperbranched poly(ether amine) and poly(vinyl alcohol) interpenetrating networks was then investigated in detail. Regardless of their charge states, these interpenetrating networks exhibited the quick adsorption to Rose Bengal (RB), Erythrosin B (ETB), Eosin B (EB), 4',5'-dibromofluorescein (DBF), and 4,5,6,7-tetrachlorofluorescein (TCF), with high adsorption capacity (Qeq) and very low adsorption of Calcein (Cal) and fluorescein (FR). The adsorption process was found to follow the pseudo-second-order kinetics, and the introduction of poly(vinyl alcohol) has no obvious effect on the adsorption behavior in this study. The big difference in the adsorption is indicative of the selective adsorption of hyperbranched poly(ether amine) and poly(vinyl alcohol) interpenetrating networks to fluorescein dyes. Based on the unique selective adsorption, the separation of several mixtures of fluorescein dyes such as RB/Cal, RB/FR, ETB/FR, and ETB/Cal was achieved by using hPEA/PVA-IPN as adsorbent.

Pharmacoinformatic approaches to understand complexation of dendrimeric nanoparticles with drugs

Nanoparticle based drug delivery systems are gaining popularity due to their wide spectrum advantages over traditional drug delivery systems; among them, dendrimeric nano-vectors are the most widely explored carriers for pharmaceutical and biomedical applications. The precise mechanism of encapsulation of drug molecules inside the dendritic matrix, delivery of drugs into specific cells, interactions of nano-formulation with biological targets and proteins, etc. present a substantial challenge to the scientific understanding of the subject. Computational methods complement experimental techniques in the design and optimization of drug delivery systems, thus minimizing the investment in drug design and development. Significant progress in computer simulations could facilitate an understanding of the precise mechanism of encapsulation of bioactive molecules and their delivery. This review summarizes the pharmacoinformatic studies spanning from quantum chemical calculations to coarse-grained simulations, aimed at providing better insight into dendrimer-drug interactions and the physicochemical parameters influencing the binding and release mechanism of drugs.

Isolation and characterization of precise dye/dendrimer ratios

Fluorescent dyes are commonly conjugated to nanomaterials for imaging applications using stochastic synthesis conditions that result in a Poisson distribution of dye/particle ratios and therefore a broad range of photophysical and biodistribution properties. We report the isolation and characterization of generation 5 poly(amidoamine) (G5 PAMAM) dendrimer samples containing 1, 2, 3, and 4 fluorescein (FC) or 6-carboxytetramethylrhodamine succinimidyl ester (TAMRA) dyes per polymer particle. For the fluorescein case, this was achieved by stochastically functionalizing dendrimer with a cyclooctyne "click" ligand, separation into sample containing precisely defined "click" ligand/particle ratios using reverse-phase high performance liquid chromatography (RP-HPLC), followed by reaction with excess azide-functionalized fluorescein dye. For the TAMRA samples, stochastically functionalized dendrimer was directly separated into precise dye/particle ratios using RP-HPLC. These materials were characterized using (1)H and (19)F NMR spectroscopy, RP-HPLC, UV/Vis and fluorescence spectroscopy, lifetime measurements, and MALDI.

Chemiluminescence determination of streptomycin in pharmaceutical preparation and its application to pharmacokinetic study by a flow injection analysis assembly

A novel and rapid method for the determination of streptomycin has been established by chemiluminescence (CL) based on significant intensity enhancement of streptomycin on the weak CL of N-bromosuccinimide (NBS) and eosin in alkaline medium. The method is simple, rapid and effective to determine streptomycin in the range of 8.0×10(-9)-1.0×10(-6)gmL(-1) with a determination limit of 2.25×10(-9)gmL(-1). The relative standard deviation is 1.95% for the determination of 2.0×10(-7)gmL(-1) streptomycin (n=11). The pharmacokinetics of streptomycin in plasma of rat coincides with the two-compartment open model. The T1/2α, T1/2β, CL/F, AUC(0-t), MRT, Tmax and Cmax were 18.83±1.24min, 82.14±3.07min, 0.0026±0.0011Lkg(-1)min(-1), 36044.50±105.02mgmin(-1)L(-1), 92.29±8.21min, 21.63±1.26min and 375.61±8.50μgmL(-1), respectively. There was no significant difference between the results obtained by CL and HPLC. The FI-CL method can be used to determine streptomycin in pharmaceutical preparation and biological samples. The established method is simple, rapid and sensitive without expensive instruments. The possible enhancement mechanism was also investigated.

Determination of ferulic acid by flow injection chemiluminescence analysis based on enhancement of the N-bromobutanimide-eosin-CrCl3 system in alkaline solution

A simple and sensitive flow injection chemiluminescence method has been developed for the determination of ferulic acid (FA) based on the significant enhancement effect of FA on the CL signal of the N-bromobutanimide (NBS)-eosin-CrCl3 system in alkaline solution. Under optimum conditions, the enhanced CL intensity is linearly related to the concentration of FA in its pharmaceutical preparations and human plasma samples. The corresponding linear regression equations were established over the 4.0 × 10(-10)-1.0 × 10(-7) g/mL for FA tablets and 2.0 × 10(-10)-1.0 × 10(-7) g/mL for plasma samples. The limit of detection for FA tablets and limit of quantification for plasma samples were 2.8 × 10(-10) g/mL (3 σ) and 3.04 × 10(-10) g/mL (10 σ), respectively. A complete analysis could be performed within 40 s, including washing and sampling, giving a throughput of ≈90/h. The proposed method was successfully applied to the determination of FA in pharmaceutical preparations and human plasma samples with satisfactory results. The recoveries of pharmaceutical preparations and human plasma samples at three different concentrations were 97.8-102.6% and 96.7-104.0%, respectively. Furthermore, the possible mechanism of CL reactions was also discussed briefly.

Photosensitization of Colloidal SnO2Semiconductor Nanoparticles with Xanthene Dyes

The photochemical behavior of xanthene dyes (fluorescein, erythrosine, and eosin) with colloidal SnO2nanoparticles was probed by UV-visible, steady state, and time resolved fluorescence measurements. The prepared SnO2nanoparticles were characterized by using UV-visible and powder XRD measurements. The xanthene dyes were adsorbed on the surface of colloidal SnO2nanoparticles through electrostatic interaction. Apparent association constant (Kapp) was calculated from the relevant fluorescence data. The larger value of apparent association constant indicates a strong association between xanthene dyes and SnO2nanoparticles. The fluorescence quenching is mainly attributed to electron transfer from the excited state xanthenes to the conduction band of colloidal SnO2. The electron transfer mechanism was explained based on the Rehm-Weller equation as well as the energy level diagram.

Sodium sensing in neurons with a dendrimer-based nanoprobe

Ion imaging is a powerful methodology to assess fundamental biological processes in live cells. The limited efficiency of some ion-sensing probes and their fast leakage from cells are important restrictions to this approach. In this study, we present a novel strategy based on the use of dendrimer nanoparticles to obtain better intracellular retention of fluorescent probes and perform prolonged fluorescence imaging of intracellular ion dynamics. A new sodium-sensitive nanoprobe was generated by encapsulating a sodium dye in a PAMAM dendrimer nanocontainer. This nanoprobe is very stable and has high sodium sensitivity and selectivity. When loaded in neurons in live brain tissue, it homogenously fills the entire cell volume, including small processes, and stays for long durations, with no detectable alterations of cell functional properties. We demonstrate the suitability of this new sodium nanosensor for monitoring physiological sodium responses such as those occurring during neuronal activity.

Fluorescence-based comparative binding studies of the supramolecular host properties of PAMAM dendrimers using anilinonaphthalene sulfonates: unusual host-dependent fluorescence titration behavior

This work describes the fluorescence enhancement of the anilinonaphthalene sulfonate probes 1,8-ANS, 2,6-ANS, and 2,6-TNS via complexation with PAMAM dendrimer hosts of Generation 4, 5 and 6. The use of this set of three very closely related probes allows for comparative binding studies, with specific pairs of probes differing only in shape (1,8-ANS and 2,6-ANS), or in the presence of a methyl substituent (2,6-TNS vs. 2,6-ANS). The fluorescence of all three probes was significantly enhanced upon binding with PAMAM dendrimers, however in all cases except one, a very unusual spike was consistently observed in the host fluorescence titration plots (fluorescence enhancement vs. host concentration) at low dendrimer concentration. This unprecedented fluorescence titration curve shape makes fitting the data to a simple model such as 1:1 or 2:1 host: guest complexation very difficult; thus only qualitative comparisons of the relative binding of the three guests could be made based on host titrations. In the case of G4 and G5 dendrimers, the order of binding strength was qualitatively determined to be 1,8-ANS<2,6-ANS indicating that the more streamlined 2,6-substituted probes are a better match for the dendrimer cavity shape than the bulkier 1,8-substituted probe. This order of binding strength was also indicated by double fluorometric titration experiments, involving both host and guest titrations. Further double fluorometric titration experiments on 2,6-ANS in G4 dendrimer revealed a host concentration-dependent change in the nature of the host: guest complexation, with multiple guests complexed per host molecule at very low host concentrations, but less than one guest per host at higher concentrations.

Nature of cationic poly(propylenimine) dendrimers in aqueous solutions as studied using versatile indicator dyes

Aqueous solutions of four cationic poly(propylenimine) low-generation dendrimers of different architecture and hydrophobicity have been examined as media for acid-base reactions of indicator dyes. The cationic dendrimers in solution can be considered as oligomers of cationic polyelectrolytes, or surfactant-like species, able to form micelles through self-association or sometimes even as unimolecular micelles. The dendrimers influence the ionization constants, tautomeric equilibria, and absorption/emission/excitation spectra of indicator dyes. The p K a values of the majority of the indicator dyes decrease in dendrimer solutions, often by 1-2 p K a units, similar to effects registered in micellar solutions of cationic surfactants. Analogously, the shifts of absorption band maxima indicate that the microenvironments of the dyes bound to the dendrimers are less polar than in water. However, some spectral effects denote the specificity of the dendrimers. The greatest difference between the dendrimers and spherical surfactant micelles is revealed by kinetic processes, especially of bromophenol blue alkaline fading in a dendrimer solution but not in a micellar surfactant solution. Within the dendrimer series, the most significant differences were observed for substances possessing n-dodecyl tails on the one hand and those without such hydrophobic portions on the other. For the last-named, the decrease in p K a's of indicators, band shifts of their anions, and in particular displacement of tautomeric equilibria compared with aqueous solutions are much smaller than for more hydrophobic dendrimers.

Nanoscience and nanotechnology: The bottom-up construction of molecular devices and machines

The bottom-up approach to miniaturization, which starts from molecules to build up nanostructures, enables the extension of the macroscopic concepts of a device and a machine to molecular level. Molecular-level devices and machines operate via electronic and/or nuclear rearrangements and, like macroscopic devices and machines, need energy to operate and signals to communicate with the operator. Examples of molecular-level photonic wires, plug/socket systems, light-harvesting antennas, artificial muscles, molecular lifts, and light-powered linear and rotary motors are illustrated. The extension of the concepts of a device and a machine to the molecular level is of interest not only for basic research, but also for the growth of nanoscience and the development of nanotechnology.

Photochemical conversion of solar energy

Energy is the most important issue of the 21st century. About 85% of our energy comes from fossil fuels, a finite resource unevenly distributed beneath the Earth's surface. Reserves of fossil fuels are progressively decreasing, and their continued use produces harmful effects such as pollution that threatens human health and greenhouse gases associated with global warming. Prompt global action to solve the energy crisis is therefore needed. To pursue such an action, we are urged to save energy and to use energy in more efficient ways, but we are also forced to find alternative energy sources, the most convenient of which is solar energy for several reasons. The sun continuously provides the Earth with a huge amount of energy, fairly distributed all over the world. Its enormous potential as a clean, abundant, and economical energy source, however, cannot be exploited unless it is converted into useful forms of energy. This Review starts with a brief description of the mechanism at the basis of the natural photosynthesis and, then, reports the results obtained so far in the field of photochemical conversion of solar energy. The "grand challenge" for chemists is to find a convenient means for artificial conversion of solar energy into fuels. If chemists succeed to create an artificial photosynthetic process, "... life and civilization will continue as long as the sun shines!", as the Italian scientist Giacomo Ciamician forecast almost one hundred years ago.