Sequential energy and electron transfer in aggregates of tetrakis[oligo(p-phenylene vinylene)] porphyrins and C60 in water

Chiral aggregation of oligo(p-phenylene vinylene)-functionalized Zn and free-base porphyrins is observed in water. The formation of mixed assemblies containing both porphyrins results in sequential energy transfer from OPV via zinc porphyrin to free-base porphyrin. Furthermore, the incorporation of C60 as electron acceptor yields a charge separated state by ultimate electron transfer

NMR nanoparticle diffusometry in hydrogels:enhancing sensitivity and selectivity

\u3cp\u3eFrom the diffusional behavior of nanoparticles in heterogeneous hydrogels, quantitative information about submicron structural features of the polymer matrix can be derived. Pulsed-gradient spin?echo NMR is often the method of choice because it measures diffusion of the whole ensemble of nanoparticles. However, in \u3csup\u3e1\u3c/sup\u3eH diffusion-ordered spectroscopy (DOSY), low-intensity nanoparticle signals have to be separated from a highly protonated background. To circumvent this, we prepared \u3csup\u3e19\u3c/sup\u3eF labeled, PEGylated, water-soluble dendritic nanoparticles with a \u3csup\u3e19\u3c/sup\u3eF loading of ∼% to enable background free \u3csup\u3e19\u3c/sup\u3eF DOSY experiments. \u3csup\u3e19\u3c/sup\u3eF nanoparticle diffusometry was benchmarked against \u3csup\u3e1\u3c/sup\u3eH diffusion-T\u3csub\u3e2\u3c/sub\u3e correlation spectroscopy (DRCOSY), which has a stronger signal separation potential than the commonly used \u3csup\u3e1\u3c/sup\u3eH DOSY experiment. We used bootstrap data resampling to estimate confidence intervals and stabilize 2D-Laplace inversion of DRCOSY data with high noise levels and artifacts, allowing quantitative diffusometry even at low magnetic field strengths (30 MHz). The employed methods offer significant advantages in terms of sensitivity and selectivity.\u3c/p\u3

Influence of supramolecular organization on energy transfer properties in chiral oligo(p-phenylene vinylene) porphyrin assemblies

A comparative study on oligo(p-phenylene vinylene) (OPV)-appended porphyrins contg. all trans-vinylene (either hydrophilic or lipophilic) or amide linkages (lipophilic) is presented. The type of supramol. arrangement obtained in org. solvents proves to be strongly dependent on the nature of the covalent connection. In the case of all trans-vinylene linkages, a J-type intermol. packing is obtained and the assemblies are only of moderate stability. Conversely, the supramol. structures obtained from the amide-linked system display an H-type stacking arrangement of enhanced stability and chirality as a consequence of intermol. hydrogen bonding along the stack direction, favorably interlocking the stacked building blocks. Interestingly, the obsd. differences in stability and organization are qual. illustrated by monitoring the sequential energy transfer process in both types of assemblies. Efficient intramol. energy transfer from the OPVs (donors) to the resp. porphyrin cores is followed by energy transfer from Zn-porphyrin (donor) to free-base porphyrin (acceptor) in both systems. However, the improved intermol. organization for the amide-linked system increases the energy transfer efficiency along the stack direction. In addn., the water-sol. (OPV)-appended porphyrin system forms highly stable assemblies in an aq. environment. Nevertheless, the poor energy transfer efficiency along the stack direction reveals a relative lack of organization in these assemblies

2D-Structures of Quadruple Hydrogen Bonded Oligo(p-phenylenevinylene)s on Graphite: Self-Assembly Behavior and Expression of Chirality

The two-dimensional pattern formation of chiral oligo(p-phenylenevinylene) derivatives of different lengths containing a self-complementary hydrogen bonding motif at the liquid/solid interface has been investigated and compared using scanning tunneling microscopy. Hydrogen bonding leads to dimer formation and the chirality of the molecules is expressed at the level of packing and orientation of the dimers with respect to the substrate symmetry. Differences in expression of molecular chirality are observed as a function of molecular length and the number of stereocenters they carry. Mixing of oligomers of different length does not lead to phase separation, but to the formation of heterodimers, stressing the important role of hydrogen bonding in the self-assembly process in both solution and at the liquid/solid interface

Scaling behavior of dendritic nanoparticle mobility in semidilute polymer solutions

\u3cp\u3eIn our studies on particle mobility in polymer solutions, we have investigated and determined self-diffusion coefficients of nanoparticles in semidilute solutions of poly(ethylene glycol) (PEG, M\u3csub\u3ew\u3c/sub\u3e = 6, 20, 35, and 100 kDa). Specially designed PEGylated dendrimers with well-defined sizes (d\u3csub\u3eh\u3c/sub\u3e = 3.4-11.0 nm) and with internal \u3csup\u3e19\u3c/sup\u3eF moieties allow for background-free \u3csup\u3e19\u3c/sup\u3eF NMR diffusion measurements. This way, we were able to assess the self-diffusion coefficients as a function of particle diameter and length scales (correlation length, tube diameter, polymer radius of gyration) with high resolution. Scaling arguments allowed us to visualize a clear crossover between particles probing a lower apparent viscosity to near macroviscosity when the nanoparticle size is comparable to the PEG polymer coil size. The same arguments are shown to correctly predict particle diffusion coefficients as a function of polymer concentration when the particles are smaller than the polymer coils.\u3c/p\u3

Complex coacervate core micelles with spectroscopic labels for diffusometric probing of biopolymer networks

\u3cp\u3eWe present the design, preparation, and characterization of two types of complex coacervate core micelles (C3Ms) with cross-linked cores and spectroscopic labels and demonstrate their use as diffusional probes to investigate the microstructure of percolating biopolymer networks. The first type consists of poly(allylamine hydrochloride) (PAH) and poly(ethylene oxide)-poly(methacrylic acid) (PEO-b-PMAA), labeled with ATTO 488 fluorescent dyes. We show that the size of these probes can be tuned by choosing the length of the PEO-PMAA chains. ATTO 488-labeled PEO\u3csub\u3e113\u3c/sub\u3e-PMAA\u3csub\u3e15\u3c/sub\u3e micelles are very bright with 18 dye molecules incorporated into their cores. The second type is a \u3csup\u3e19\u3c/sup\u3eF-labeled micelle, for which we used PAH and a \u3csup\u3e19\u3c/sup\u3eF-labeled diblock copolymer tailor-made from poly(ethylene oxide)-poly(acrylic acid) (mPEO\u3csub\u3e79\u3c/sub\u3e-b-PAA\u3csub\u3e14\u3c/sub\u3e). These micelles contain approximately 4 wt % of \u3csup\u3e19\u3c/sup\u3eF and can be detected by \u3csup\u3e19\u3c/sup\u3eF NMR. The \u3csup\u3e19\u3c/sup\u3eF labels are placed at the end of a small spacer to allow for the necessary rotational mobility. We used these ATTO- and \u3csup\u3e19\u3c/sup\u3eF-labeled micelles to probe the microstructures of a transient gel (xanthan gum) and a cross-linked, heterogeneous gel (κ-carrageenan). For the transient gel, sensitive optical diffusometry methods, including fluorescence correlation spectroscopy, fluorescence recovery after photobleaching, and super-resolution single nanoparticle tracking, allowed us to measure the diffusion coefficient in networks with increasing density. From these measurements, we determined the diameters of the constituent xanthan fibers. In the heterogeneous κ-carrageenan gels, bimodal nanoparticle diffusion was observed, which is a signpost of microstructural heterogeneity of the network.\u3c/p\u3

Triggered drug release from an antibody-drug conjugate using fast click-to-release chemistry in mice

\u3cp\u3eThe use of a bioorthogonal reaction for the selective cleavage of tumor-bound antibody-drug conjugates (ADCs) would represent a powerful new tool for ADC therapy, as it would not rely on the currently used intracellular biological activation mechanisms, thereby expanding the scope to noninternalizing cancer targets. Here we report that the recently developed inverse-electron-demand Diels-Alder pyridazine elimination reaction can provoke rapid and self-immolative release of doxorubicin from an ADC in vitro and in tumor-bearing mice.\u3c/p\u3

Visualization of various supramolecular assemblies of oligo(para- phenylenevinylene)-melamine and perylene bisimide

A melamine derivative has been covalently equipped with two oligo(para-phenylenevinylene) (OPV) chromophores. This procedure yields a bifunctional molecule with two hydrogen-bonding arrays available for complementary binding to perylene bisimide derivatives. Depending on the solvent, hydrogen-bonded trimers, tetramers, and dimers on a graphite surface are observed for pure OPV-melamine by using scanning tunneling microscopy (STM). Upon the addition of perylene bisimide, linear tapes of perylene bisimide, 12-membered rosettes that consist of alternating hydrogenbonded OPV-melamine and perylene bisimide moieties are visualized. These results provide direct evidence for the possible modes of hydrogen bonding within a supramolecular co-assembly in solution. Subsequently, the optical properties of pure OPV-melamine and co-assemblies with a perylene bisimide derivative were characterized in solution. In an apolar solvent, OPV-melamine self-assembles into chiral superstructures. Disassembly into molecularly dissolved species is reversibly controlled by concentration and tempera-ture. Complementary hydrogen bonding to a perylene bisimide derivative in an apolar solvent yields multicomponent, Ï€-stacked dye assemblies of enhanced stability that are characterized by fluorescence quenching of the constituent chromophores. Titration experiments reveal that a mixture of hydrogen-bonded oligomers is present in solution, rather than a single discrete assembly. The solution experiments are consistent with the STM results, which revealed various supramolecular assemblies. Our system is likely not to be optimally programmed to obtain a discrete co-assembled structure in quantitative yield. -© 2008 Wiley-VCH Verlag GmbH & Co. KGa

Heterogeneity of network structures and water dynamics in κ-carrageenan gels probed by nanoparticle diffusometry

\u3cp\u3eA set of functionalized nanoparticles (PEGylated dendrimers, d = 2.8-11 nm) was used to probe the structural heterogeneity in Na\u3csup\u3e+\u3c/sup\u3e/K\u3csup\u3e+\u3c/sup\u3e induced κ-carrageenan gels. The self-diffusion behavior of these nanoparticles as observed by \u3csup\u3e1\u3c/sup\u3eH pulsed-field gradient NMR, fluorescence recovery after photobleaching, and raster image correlation spectroscopy revealed a fast and a slow component, pointing toward microstructural heterogeneity in the gel network. The self-diffusion behavior of the faster nanoparticles could be modeled with obstruction by a coarse network (average mesh size <100 nm), while the slower-diffusing nanoparticles are trapped in a dense network (lower mesh size limit of 4.6 nm). Overhauser dynamic nuclear polarization-enhanced NMR relaxometry revealed a reduced local solvent water diffusivity near 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO)-labeled nanoparticles trapped in the dense network, showing that heterogeneity in the physical network is also reflected in heterogeneous self-diffusivity of water. The observed heterogeneity in mesh sizes and in water self-diffusivity is of interest for understanding and modeling of transport through and release of solutes from heterogeneous biopolymer gels.\u3c/p\u3