A study of the self-assembly of water-soluble porphyrins in aqueous solution

In nature, self-assembly processes of biologically active organic molecules often occur, resulting in formation of dimers and higher oligomers of various and sometimes complex structures. This natural occurrence of self-organization has been the subject of research, with the aim of understanding and possibly modulating the aggregation behavior of biological molecules. The meso-tetrakis(4-phosphonatophenyl) porphyrin, H2TPPP was synthesized, purified, and characterized. Its self-assembly was studied in aqueous solutions as a function of pH and time. The variations on the λmax and shape of the Soret band of this porphyrin in the absorption spectra when altering the pH indicated the pH dependency in the hierarchical self-assembly of H2TPPP in aqueous solution. The aggregation as a function of time was monitored via fluorescence spectroscopy, where the emission intensity decrease suggests self-quenching and aggregation. Small angle x-ray scattering experiments were conducted in an attempt to obtain structural information for the self-organized porphyrin complexes. Analytical ultracentrifugation techniques confirmed reported SAXS results and also revealed the self-associative behavior of the aggregates

Synthesis, characterization, and self-assembly of porphyrins conjugated to superparamagnetic colloidal particles for enhanced photodynamic therapy

Porphyrins and their derivatives are often used as photosensitizers in photodynamic therapy (PDT), which is a noninvasive antitumor treatment. The photochemical process for PDT involves exciting a photosensitizing agent with visible light, which induces cytotoxicity in the presence of oxygen as a result of forming reactive oxygen species (ROS). The ROS are the responsible components for invoking cell death and destruction of tumors. Although this mechanism is an effective cancer therapeutic, it still has many shortcomings. One major challenge of PDT concerns improving the tumor selectivity and specificity of photosensitizers because porphyrins have nonspecific affinity to tumor cells. The discussed research introduces a potential drug delivery vehicle to enhance the efficacy of cancer therapeutics and overcome the aforementioned issues. Specifically, hybrid composite particles composed of superparamagnetic polypeptide-coated silica nanoparticles conjugated to porphyrins were designed to improve the mechanism of tumor cell destruction via controlled assembly and transport. Along the path of developing these nanocomposites, porphyrin self-assembly was explored to understand the dynamics of porphyrins alone. A series of complementary experiments and analytical methods were used, including UV-Vis and fluorescence spectroscopy measurements, small angle X-ray scattering (SAXS), cryogenic transmission electron microscopy (cryo-TEM) and freeze-fracture transmission electron microscopy (FF-TEM). Whereas UV-Vis and fluorescence techniques enabled us to determine the type of aggregates formed, AUC and SAXS provided complementary details and information about the size of the assemblies in solution. Cryo-TEM and FF-TEM provided direct visualization of the aggregates

Characterization of the self-assembly of meso-tetra(4-sulfonatophenyl) porphyrin (H \u3csub\u3e2\u3c/sub\u3eTPPS \u3csup\u3e4-\u3c/sup\u3e) in aqueous solutions

The aggregation of meso-tetra(4-sulfonatophenyl)porphyrin (H 2TPPS 4-) in phosphate solutions was investigated as a function of pH, concentration, time, ionic strength, and solution preparation (either from dilution of a freshly prepared 2 mM stock or by direct preparation of μM solution concentrations) using a combination of complementary analytical techniques. UV-vis and fluorescence spectroscopy indicated the formation of staggered, side-by-side (J-type) assemblies. Their size and self-associative behavior were determined using analytical ultracentrifugation and small-angle X-ray scattering. Our results indicate that in neutral and basic solutions of H 2TPPS 4-, porphyrin dimers and trimers are formed at micromolar concentrations and in the absence of NaCl to screen any ionic interactions. At these low concentrations and pH 4, the protonated H 4TPPS 2- species self-assembles, leading to the formation of particularly stable aggregates bearing 25 ± 3 macrocycles. At higher concentrations, these structures further organize or reorganize into tubular, rod-like shapes of various lengths, which were imaged by cryogenic and freeze-fracture transmission electron microscopy. Micron-scale fibrillar aggregates were obtained even at micromolar concentrations at pH 4 when prepared from dilution of a 2 mM stock solution, upon addition of NaCl, or both. © 2011 American Chemical Society

Reformulation of etoposide with solubility-enhancing rubusoside

Etoposide (ETO), a widely used anti-cancer drug, is constrained by its low aqueous solubility and by side effects from both the drug and its solubilizing excipients. In this study, a recently discovered natural solubilizer rubusoside (RUB) was used to achieve the solubilization of ETO. Dynamic light scattering and freeze-fracture transmission electron microscopy studies showed that ETO and RUB formed ETO-RUB nanoparticles (∼6 nm in diameter). The powder of ETO-RUB nanoparticles was completely reconstitutable in water and remained stable in this solution at 25 and 37°C for at least 24h. Under other physiologic conditions, ETO solution was clear and free of precipitation at 25°C, but underwent various structural transformations. In PBS and simulated intestinal fluid, RUB-solubilized ETO underwent epimerization and equilibrated to cis-ETO. In simulated gastric fluid, RUB-solubilized ETO degraded to 4\u27-demethylepipodophyllotoxin-beta-d-glucoside and 4\u27-demethylepipodophyllotoxin. Higher temperatures favored epimerization or degradation. Furthermore, a side-by-side comparison with DMSO-solubilized ETO confirmed that the RUB-solubilized ETO showed no significant differences in cytotoxicity in colon, breast and prostate cancer cell lines. RUB effectively solubilized and stabilized etoposide, which sets the stage for further toxicology, bioavailability, and efficacy investigations

Characterization of the Self-Assembly of <i>meso</i>-Tetra(4-sulfonatophenyl)porphyrin (H₂TPPS^4–) in Aqueous Solutions

The aggregation of <i>meso</i>-tetra­(4-sulfonatophenyl)­porphyrin (H₂TPPS^4–) in phosphate solutions was investigated as a function of pH, concentration, time, ionic strength, and solution preparation (either from dilution of a freshly prepared 2 mM stock or by direct preparation of μM solution concentrations) using a combination of complementary analytical techniques. UV–vis and fluorescence spectroscopy indicated the formation of staggered, side-by-side (J-type) assemblies. Their size and self-associative behavior were determined using analytical ultracentrifugation and small-angle X-ray scattering. Our results indicate that in neutral and basic solutions of H₂TPPS^4–, porphyrin dimers and trimers are formed at micromolar concentrations and in the absence of NaCl to screen any ionic interactions. At these low concentrations and pH 4, the protonated H₄TPPS^2– species self-assembles, leading to the formation of particularly stable aggregates bearing 25 ± 3 macrocycles. At higher concentrations, these structures further organize or reorganize into tubular, rod-like shapes of various lengths, which were imaged by cryogenic and freeze-fracture transmission electron microscopy. Micron-scale fibrillar aggregates were obtained even at micromolar concentrations at pH 4 when prepared from dilution of a 2 mM stock solution, upon addition of NaCl, or both

Yielding Behavior in Colloidal Glasses: Comparison between “Hard Cage” and “Soft Cage”

Rheological measurements are utilized to examine the yielding behavior of a polystyrene (PS) core and poly­(<i>N</i>-isopropylacrylamide) (PNIPAM) shell microgel system with varying shell/core ratio. For a shell/core ratio of 0.15 at high concentrations, the suspensions show a typical hard sphere (HS) yielding response where the loss modulus (<i>G</i>″) exhibits a single peak due to cage breaking. As a result of tighter cages and less cage distortion prior to yielding, the peak location of <i>G</i>″ decreases with volume fraction. For a shell/core ratio of 1.10, which behaves like a soft jammed glass at high concentration, the suspensions exhibit a one-step yielding behavior similar to that of HS glass. However, the location of the peak in <i>G</i>″ increases with volume fraction, demonstrating the important role of particle deformation in the breakage of cages. For an intermediate shell/core ratio of 0.34, the system displays a two-step yielding behavior, as observed in previous reports for attractive glasses. By increasing the volume fraction, the strain of the first peak increases while the second one decreases. In addition, as the effective volume fraction increases to 112%, the two peaks merge into one broad peak. It is demonstrated that the first peak of <i>G</i>″ is due to deformation of the shell, and the second peak of <i>G</i>″ is attributed to cage breaking as a result of the cores colliding with each other. Combining these results, a yielding state diagram from typical HS to soft jammed glass is demonstrated

A novel solubility-enhanced curcumin formulation showing stability and maintenance of anticancer activity

Curcumin (CUR) is an active food compound, but its insolubility and instability in water contributes to low bioavailability. In this study, the solubility of CUR was enhanced by utilizing the solubilizing properties of rubusoside (RUB). The solubility of CUR in water increased linearly from 61 μg/mL to 2.318 mg/mL in the presence of RUB ranging from 1% to 10% (w/v). Dynamic light scattering and transmission electron microscopy studies found that CUR and RUB formed CUR-RUB nanoparticle (∼8 nm) complexes. The RUB-solubilized CUR was stable in physiological conditions and did not precipitate when diluted or degrade when spray-dried to a completely reconstitutable powder. Furthermore, cell viability assays demonstrated the efficacy of RUB-solubilized CUR against human colon, breast, and pancreatic cancer cell lines. The development of this new solubilized, stable, and biologically active CUR formulation lays the foundation for future bioavailability improvement. © 2011 Wiley-Liss, Inc. and the American Pharmacists Association