Degradable self-assembling dendrons for gene delivery: experimental and theoretical insights into the barriers to cellular uptake

This paper uses a combined experimental and theoretical approach to gain unique insight into gene delivery. We report the synthesis and investigation of a new family of second-generation dendrons with four triamine surface ligands capable of binding to DNA, degradable aliphatic-ester dendritic scaffolds, and hydrophobic units at their focal points. Dendron self-assembly significantly enhances DNA binding as monitored by a range of experimental methods and confirmed by multiscale modeling. Cellular uptake studies indicate that some of these dendrons are highly effective at transporting DNA into cells (ca. 10 times better than poly(ethyleneimine), PEI). However, levels of transgene expression are relatively low (ca. 10% of PEI). This indicates that these dendrons cannot navigate all of the intracellular barriers to gene delivery. The addition of chloroquine indicates that endosomal escape is not the limiting factor in this case, and it is shown, both experimentally and theoretically, that gene delivery can be correlated with the ability of the dendron assemblies to release DNA. Mass spectrometric assays demonstrate that the dendrons, as intended, do degrade under biologically relevant conditions over a period of hours. Multiscale modeling of degraded dendron structures suggests that complete dendron degradation would be required for DNA release. Importantly, in the presence of the lower pH associated with endosomes, or when bound to DNA, complete degradation of these dendrons becomes ineffective on the transfection time scale-we propose this explains the poor transfection performance of these dendrons. As such, this paper demonstrates that taking this kind of multidisciplinary approach can yield a fundamental insight into the way in which dendrons can navigate barriers to cellular uptake. Lessons learned from this work will inform future dendron design for enhanced gene delivery.     

Multimetal Fischer carbene complexes of Group VI transition metals: synthesis, structure and substituent effect investigation

Fischer carbene complexes of tungsten with substituents containing up to two additional different transition metals, with all the metals in electronic contact with the carbene carbon atom, were synthesised and studied both in solution and in the solid state. For the complexes of the type [W(CO)(5){C(OR')R}], the substituents chosen were heteroaromatic 2-benzo[b]thienyl (2-BT), or 2-BT π-bonded to a chromium tricarbonyl fragment ([Cr(CO)(3)(2-η(6)-BT)]) or ferrocenyl (Fc) as the R-substituent, while the OR'-substituent was systematically varied between an ethoxy or a titanoxy group, to yield the complexes 1b (R' = Et, R = 2-BT), 2b (R' = Et, R = [Cr(CO)(3)(2-η(6)-BT)]), 3b (R' = TiCp(2)Cl, R = 21-BT), 4b (R' = TiCp(2)Cl, R = [Cr(CO)(3)(2-η(6)-BT)]), 5b (R' = Et, R = Fc) and 6b (R' = TiCp(2)Cl, R = Fc). The structural features and their relevance to bonding in the multimetal carbene compounds of both these tungsten and the analogous chromium complexes were investigated as they represent indicators of possible reactivity sites in multimetal carbene assemblies. The possibility of using DFT calculations to quantify the effect of metal-containing substituents on the carbene ligands was tested and correlated with experimental parameters by employing methods such as vibrational spectroscopy, molecular orbital analysis, and cyclic voltammetry.     

Simultaneous monitoring of pH, CO2 and O2 using an optical imaging fiber

The interdependence of pH, CO₂ and O₂ during chemical and biochemical processes has driven the need to monitor them simultaneously, continuously and in situ, in order to exert better control over such reactions. We present the fabrication and performance of a multi-analyte imaging fiber sensor that allows pH, CO₂ and O₂ to be monitored simultaneously with rapid response. Sensing elements are fabricated by covalently immobilizing fluorescent indicators within polymer matrices via photopolymerization, resulting in the formation of distinct regions of analyte-sensitive polymer at the fiber's distal end. The multianalyte sensor's working range is 0%–100% for O₂ and 0%–10% for CO₂ in the pH range 5.5–7.5. The sensor was used to monitor the pH, CO₂ and O₂ changes during a beer fermentation.     

Electrical characterization of argon-ion sputtered n-GaAs

Epitaxially grown n-type GaAs was sputtered with 0.5 keV Ar ions at doses of 10¹² and 10¹⁵ ions/cm². The sputter-induced defects in the GaAs were characterized using deep-level transient spectroscopy (DLTS) and the effect of these defects on the characteristics of Au Schottky barrier diodes (SBD's) fabricated on the sputtered GaAs was evaluated by current-voltage measurements. It was found that the barrier height of the SBD's decreased with ion dose from 0.97 eV for unsputtered diodes to 0.48 eV after sputtering at a dose of 10¹⁵/cm². DLTS showed the presence of a multitude of sputter-induced defects at and near the GaAs surface. The defects formed during the initial stages of sputtering had the same properties as some of the primary defects introduced during electron and proton irradiation of GaAs. Isochronal annealing at temperatures of up to 350°C showed that although some defects were removed by annealing, others appeared.     

Flow Invariance on Stratified Domains

This paper studies conditions for invariance of dynamical systems on stratified domains as originally introduced by Bressan and Hong. We establish Hamiltonian conditions for both weak and strong invariance of trajectories on systems with non-Lipschitz data. This is done via the identification of a new multifunction, the essential velocity multifunction. Properties of this multifunction are investigated and used to establish the relevant invariance criteria.     

Film thickness dependence of the magnetic resonance in Fe–SiO2 nanocomposites

The magnetic properties of Fe–SiO₂ nanogranular composite thin films were studied as a function of film thickness and Fe concentration, f, using ferromagnetic resonance at X-band (9.4 GHz) and Q-band (35 GHz). Films with an Fe volume percent ranging from 17% to 70% were fabricated from a mosaic target using RF sputtering techniques. Film thickness was varied between 10 and 200 nm. From measurements made at room temperature with the external field applied parallel and perpendicular to the film plane, it was possible to determine an almost linear dependence of the effective anisotropy field with Fe concentration. Small differences observed between X- and Q-band, specially at low f, were attributed to the effects that the different fields applied during the experiment cause on the magnetic state of the sample. No systematic change of the effective field or the g value was observed in films of different thickness. The absorption line width, on the other hand, was found to depend on film thickness indicating a larger distribution of particle shape and size with increasing film thickness. A maximum in the line width was observed around f30–35% and is probably caused by the transition from single domain ferromagnetic clusters to superparamagnetic particles.     

The level structure of85Rb and87Rb from (n,n′γ) reaction measurements

Detection of gamma rays resulting from inelastic scattering of neutrons in the energy range 550 to 2,100 keV from a natural rubidium sample was used to determine the level structure of⁸⁵Rb and⁸⁷Rb. Decay gammas were observed with time-gated Ge(Li) and intrinsic germanium detectors with good energy resolution. Level and decay schemes up to 2 MeV excitation were constructed for both⁸⁵Rb and⁸⁷Rb. Several new levels were found, some seen previously in particle reactions were confirmed and their energies accurately established. Comparison of the excitation functions with Hauser-Feshbach theory led to the assignment of spins and parities for several levels.