Presence Of Polyanions Research Articles

An improved preparation method of carbon aerogels derived from alginate / chitosan with a superiority of promoting nZVI for chromium(VI) ions removal from aqueous solution

CAs (carbon aerogels) are potential novel adsorbents for Cr(VI). However, their tradition preparation method presents a series of problems such as the tedious processes and the limited scaling up production caused by extreme conditions. Improved preparation methods are tried to explore so that supercritical process could be avoided. While the explanation of the adsorption behavior and mechanism remain incomplete in the presence of polyanions. In this paper, a series of sodium alginate/chitosan composite (SA/CTS) carbon aerogels with or without nZVI (nano zero-valent iron) doped are intentionally designed, which were prepared without supercritical process and expected to a significant improvement in Cr(VI) removal in wastewater while facilitating preparation and separation. The adsorption performance of carbon aerogels for Cr(VI) were investigated as functions of pH, adsorbent dosage and adsorption temperature. Following the study of adsorption behavior of Cr(VI) in the coexistence of polyanions, this work presented a detailed rationale for the different competing anions having different effects on Cr(VI) sorption. Four isotherms and three kinetic models were used to explain the adsorption behaviors. The maximum adsorption capacities of CTS900 and nZVI@CTS900 were estimated to be 183.85 mg/g and 204.35 mg/g at 35 °C using the Sips model, respectively, which showed favorable performance over carbon aerogel materials that have been reported so far. Besides the study of factors influencing adsorption, the mechanism of Cr(VI) sorption mainly involved electrostatic interactions, hydrogen bonding attraction, and redox reactions were demonstrated through the multi characteristic analysis. As a result, prepared CTSs and nZVI@CTSs perform acceptable application prospects in Cr(VI)-containing water and wastewater.

Chemical signal regulated injectable coacervate hydrogels.

In the quest for stimuli-responsive materials with specific, controllable functions, coacervate hydrogels have become a promising candidate, featuring sensitive responsiveness to environmental signals enabling control over sol-gel transitions. However, conventional coacervation-based materials are regulated by relatively non-specific signals, such as temperature, pH or salt concentration, which limits their possible applications. In this work, we constructed a coacervate hydrogel with a Michael addition-based chemical reaction network (CRN) as a platform, where the state of coacervate materials can be easily tuned by specific chemical signals. We designed a pyridine-based ABA triblock copolymer, whose quaternization can be regulated by an allyl acetate electrophile and an amine nucleophile, leading to gel construction and collapse in the presence of polyanions. Our coacervate gels showed not only highly tunable stiffness and gelation times, but excellent self-healing ability and injectability with different sized needles, and accelerated degradation resulting from chemical signal-induced coacervation disruption. This work is expected to be a first step in the realization of a new class of signal-responsive injectable materials.

Hydrophobic Composites Designed by a Nonwoven Cellulose-Based Material and Polymer/CaCO3 Patterns with Biomedical Applications.

Herein, we report a simple method to obtain hydrophobic surfaces by surface modification with calcium carbonate via diffusion-controlled crystallization using a cheap, versatile, and super-hydrophilic cellulose-based nonwoven material (NWM) as the substrate. To control the CaCO3 crystal growth, the ammonium carbonate diffusion method was applied in the presence of polyanions [poly(acid acrylic), poly(2-acrylamido-2-methylpropanesulfonic acid), and a copolymer which contains 55 mol % 2-acrylamido-2-methylpropanesulfonic acid and 45 mol % acrylic acid] or nonstoichiometric polyelectrolyte complexes with polycations [poly(allylamine hydrochloride) and chitosan] on a pristine NWM and on polycation-treated surfaces. The surface morphology obtained by calcite growth under surface or environmental functional groups' influence and the hydrophilic/hydrophobic character of the composite materials were followed and compared to that of the starting material. The obtained composite materials become hydrophobic, having a contact angle in the range of 110-135°. The capacity of tetracycline sorption and release by selected modified surfaces were followed and compared to the untreated NWM. Also, the biological properties were evaluated in terms of biocompatibility, antibacterial activity, and antifouling capability.

Native Mass Spectrometry Sheds Light on Formation of Deadly Heparin-PF4 Complexes

Native Mass Spectrometry Sheds Light on Formation of Deadly Heparin-PF4 Complexes

Anti-platelet factor 4/polyanion antibodies mediate a new mechanism of autoimmunity

Antibodies recognizing complexes of the chemokine platelet factor 4 (PF4/CXCL4) and polyanions (P) opsonize PF4-coated bacteria hereby mediating bacterial host defense. A subset of these antibodies may activate platelets after binding to PF4/heparin complexes, causing the prothrombotic adverse drug reaction heparin-induced thrombocytopenia (HIT). In autoimmune-HIT, anti-PF4/P-antibodies activate platelets in the absence of heparin. Here we show that antibodies with binding forces of approximately 60–100 pN activate platelets in the presence of polyanions, while a subset of antibodies from autoimmune-HIT patients with binding forces ≥100 pN binds to PF4 alone in the absence of polyanions. These antibodies with high binding forces cluster PF4-molecules forming antigenic complexes which allow binding of polyanion-dependent anti-PF4/P-antibodies. The resulting immunocomplexes induce massive platelet activation in the absence of heparin. Antibody-mediated changes in endogenous proteins that trigger binding of otherwise non-pathogenic (or cofactor-dependent) antibodies may also be relevant in other antibody-mediated autoimmune disorders.

L-Arginine ethylester enhances in vitro amplification of PrPSc in macaques with atypical L-type bovine spongiform encephalopathy and enables presymptomatic detection of PrPSc in the bodily fluids

Protease-resistant, misfolded isoforms (PrPSc) of a normal cellular prion protein (PrPC) in the bodily fluids, including blood, urine, and saliva, are expected to be useful diagnostic markers of prion diseases, and nonhuman primate models are suited for performing valid diagnostic tests for human Creutzfeldt-Jakob disease (CJD). We developed an effective amplification method for PrPSc derived from macaques infected with the atypical L-type bovine spongiform encephalopathy (l-BSE) prion by using mouse brain homogenate as a substrate in the presence of polyanions and l-arginine ethylester. This method was highly sensitive and detected PrPSc in infected brain homogenate diluted up to 1010 by sequential amplification. This method in combination with PrPSc precipitation by sodium phosphotungstic acid is capable of amplifying very small amounts of PrPSc contained in the cerebrospinal fluid (CSF), saliva, urine, and plasma of macaques that have been intracerebrally inoculated with the l-BSE prion. Furthermore, PrPSc was detectable in the saliva or urine samples as well as CSF samples obtained at the preclinical phases of the disease. Thus, our novel method may be useful for furthering the understanding of bodily fluid leakage of PrPSc in nonhuman primate models.

Lipid Membranes Facilitate Conformational Changes Required for Reovirus Cell Entry

Cellular entry of nonenveloped and enveloped viruses is often accompanied by dramatic conformational changes within viral structural proteins. These rearrangements are triggered by a variety of mechanisms, such as low pH, virus-receptor interactions, and virus-host chaperone interactions. Reoviruses, a model system for entry of nonenveloped viruses, undergo a series of disassembly steps within the host endosome. One of these steps, infectious subviral particle (ISVP)-to-ISVP* conversion, is necessary for delivering the genome-containing viral core into host cells, but the physiological trigger that mediates ISVP-to-ISVP* conversion during cell entry is unknown. Structural studies of the reovirus membrane penetration protein, μ1, predict that interactions between μ1 and negatively charged lipid head groups may promote ISVP* formation; however, experimental evidence for this idea is lacking. Here, we show that the presence of polyanions (SO4(2-) and HPO4(2-)) or lipids in the form of liposomes facilitates ISVP-to-ISVP* conversion. The requirement for charged lipids appears to be selective, since phosphatidylcholine and phosphatidylethanolamine promoted ISVP* formation, whereas other lipids, such as sphingomyelin and sulfatide, either did not affect ISVP* formation or prevented ISVP* formation. Thus, our work provides evidence that interactions with membranes can function as a trigger for a nonenveloped virus to gain entry into host cells. Cell entry, a critical stage in the virus life cycle, concludes with the delivery of the viral genetic material across host membranes. Regulated structural transitions within nonenveloped and enveloped viruses are necessary for accomplishing this step; these conformational changes are predominantly triggered by low pH and/or interactions with host proteins. In this work, we describe a previously unknown trigger, interactions with lipid membranes, which can induce the structural rearrangements required for cell entry. This mechanism operates during entry of mammalian orthoreoviruses. We show that interactions between reovirus entry intermediates and lipid membranes devoid of host proteins promote conformational changes within the viral outer capsid that lead to membrane penetration. Thus, this work illustrates a novel strategy that nonenveloped viruses can use to gain access into cells and how viruses usurp disparate host factors to initiate infection.

Microtubule‐Binding R3 Fragment from Tau Self‐Assembles into Giant Multistranded Amyloid Ribbons

AbstractTau protein and its fragments self‐assemble into amyloid fibrils in the presence of polyanions, such as heparin. By combining microscopy, scattering, and spectroscopy techniques, we studied the aggregation of the 26‐mer Tau‐derived peptide alone, Tau306–327, the third repeat fragment (R3) of the microtubule‐binding domain. We show that: i) the sole Tau306–327 can self‐assemble into amyloid fibrils without the need of aggregation‐promoting polyanions; ii) the resulting structures consist of surprisingly large, well‐ordered 2D laminated flat ribbons, with a log‐normal distribution of the lateral width, reaching the unprecedented lateral size of 350 nm and/or 45 individual protofilaments, that is, the largest amyloid laminated structures ever observed for Tau or any other amyloidogenic sequence. Our results provide insight into the molecular determinants of Tau aggregation and open new perspectives in the understanding of the assembly of amyloid fibrils and β‐sheet‐based biomaterials.

Microtubule-Binding R3 Fragment from Tau Self-Assembles into Giant Multistranded Amyloid Ribbons.

Tau protein and its fragments self-assemble into amyloid fibrils in the presence of polyanions, such as heparin. By combining microscopy, scattering, and spectroscopy techniques, we studied the aggregation of the 26-mer Tau-derived peptide alone, Tau(306-327), the third repeat fragment (R3) of the microtubule-binding domain. We show that: i) the sole Tau(306-327) can self-assemble into amyloid fibrils without the need of aggregation-promoting polyanions; ii) the resulting structures consist of surprisingly large, well-ordered 2D laminated flat ribbons, with a log-normal distribution of the lateral width, reaching the unprecedented lateral size of 350 nm and/or 45 individual protofilaments, that is, the largest amyloid laminated structures ever observed for Tau or any other amyloidogenic sequence. Our results provide insight into the molecular determinants of Tau aggregation and open new perspectives in the understanding of the assembly of amyloid fibrils and β-sheet-based biomaterials.

Evaluation of cellular uptake and intracellular trafficking as determining factors of gene expression for amino acid-substituted gemini surfactant-based DNA nanoparticles

BackgroundGene transfer using non-viral vectors offers a non-immunogenic and safe method of gene delivery. Cellular uptake and intracellular trafficking of the nanoparticles can impact on the transfection efficiency of these vectors. Therefore, understanding the physicochemical properties that may influence the cellular uptake and the intracellular trafficking can aid the design of more efficient non-viral gene delivery systems. Recently, we developed novel amino acid-substituted gemini surfactants that showed higher transfection efficiency than their parent compound. In this study, we evaluated the mechanism of cellular uptake of the plasmid/gemini surfactant/helper lipid nanoparticles and their effect on the transfection efficiency.ResultsNanoparticles were incubated with Sf 1 Ep cells in the presence of different endocytic inhibitors and gene expression (interferon-γ) was measured using ELISA. Clathrin-mediated and caveolae-mediated uptake were found to be equally contributing to cellular internalization of both P/12-7NH-12/L (parent gemini surfactant) and P/12-7NGK-12/L (amino acid-substituted gemini surfactant) nanoparticles. The plasmid and the helper lipid were fluorescently tagged to track the nanoparticles inside the cells, using confocal laser scanning microscopy. Transmission electron microscopy images showed that the P/12-7NGK-12/L particles were cylindrical while the P/12-7NH-12/L particles were spherical which may influence the cellular uptake behaviour of these particles. Dye exclusion assay and pH-titration of the nanoparticles suggested that high buffering capacity, pH-dependent increase in particle size and balanced DNA binding properties may be contributing to a more efficient endosomal escape of P/12-7NGK-12/L compared to the P/12-7NH-12/L nanoparticles, leading to higher gene expression.ConclusionAmino-acid substitution in the spacer of gemini surfactant did not alter the cellular uptake pathway, showing similar pattern to the unsubstituted parent gemini surfactant. Glycyl-lysine substitution in the gemini spacer improved buffering capacity and imparted a pH-dependent increase of particle size. This property conferred to the P/12-7NGK-12/L nanoparticles the ability to escape efficiently from clathrin-mediated endosomes. Balanced binding properties (protection and release) of the 12-7NGK-12 in the presence of polyanions could contribute to the facile release of the nanoparticles internalized via caveolae-mediated uptake. A more efficient endosomal escape of the P/12-7NGK-12/L nanoparticles lead to higher gene expression compared to the parent gemini surfactant.

Matrix synthesis of water-soluble polyaniline in the presence of polyelectrolytes

The matrix polymerization of aniline hydrochloride in the presence of polyanions with different chemical structures and molecular masses is studied. Poly(2-acrylamido-2-methyl-1-propanesulfonic acid) and poly(4-styrenesulfonic acid) or its sodium salt are used as polyelectrolyte matrices. It is shown that, if the polymerization of aniline hydrochloride is conducted in the presence of a polyelectrolyte matrix, water-soluble polyelectrolyte complexes in which polyaniline occurs in the form of an emeraldine salt are formed. The mechanism of polymerization is advanced. It is found that the sizes of polyaniline complexes in water are independent of the molecular mass of the polyelectrolyte matrix and its chemical structure.

Activity and Interactions of Liposomal Antibiotics in Presence of Polyanions and Sputum of Patients with Cystic Fibrosis

BackgroundTo compare the effectiveness of liposomal tobramycin or polymyxin B against Pseudomonas aeruginosa in the Cystic Fibrosis (CF) sputum and its inhibition by common polyanionic components such as DNA, F-actin, lipopolysaccharides (LPS), and lipoteichoic acid (LTA).MethodologyLiposomal formulations were prepared from a mixture of 1,2-Dimyristoyl-sn-Glycero-3-Phosphocholine (DMPC) or 1,2-Dipalmitoyl-sn-Glycero-3-Phosphocholine (DPPC) and Cholesterol (Chol), respectively. Stability of the formulations in different biological milieus and antibacterial activities compared to conventional forms in the presence of the aforementioned inhibitory factors or CF sputum were evaluated.ResultsThe formulations were stable in all conditions tested with no significant differences compared to the controls. Inhibition of antibiotic formulations by DNA/F-actin and LPS/LTA was concentration dependent. DNA/F-actin (125 to 1000 mg/L) and LPS/LTA (1 to 1000 mg/L) inhibited conventional tobramycin bioactivity, whereas, liposome-entrapped tobramycin was inhibited at higher concentrations - DNA/F-actin (500 to 1000 mg/L) and LPS/LTA (100 to 1000 mg/L). Neither polymyxin B formulation was inactivated by DNA/F-actin, but LPS/LTA (1 to 1000 mg/L) inhibited the drug in conventional form completely and higher concentrations of the inhibitors (100 to 1000 mg/L) was required to inhibit the liposome-entrapped polymyxin B. Co-incubation with inhibitory factors (1000 mg/L) increased conventional (16-fold) and liposomal (4-fold) tobramycin minimum bactericidal concentrations (MBCs), while both polymyxin B formulations were inhibited 64-fold.ConclusionsLiposome-entrapment reduced antibiotic inhibition up to 100-fold and the CFU of endogenous P. aeruginosa in sputum by 4-fold compared to the conventional antibiotic, suggesting their potential applications in CF lung infections.

Conformational Flexibility, Hydration and State Parameter Fluctuations of Fibroblast Growth Factor-10: Effects of Ligand Binding

Differential effects of ligand binding on local and global fibroblast growth factor-10 (FGF-10) flexibility and stability have been investigated utilizing a variety of experimental and computational techniques. Normal mode analysis was used to predict the low frequency motions and regional flexibility of FGF-10. Similarly, regional variations in local folding/unfolding equilibria were characterized with the COREX/BEST algorithm. Experimental adiabatic and isothermal compressibilities of FGF-10 alone and in the presence of polyanions are compared. Furthermore, the effect of polyanions on the coefficient of thermal expansion is compared. Measurements of density, heat capacity, compressibility, and expansibility were combined to calculate experimentally determined volume and enthalpy fluctuations. Global effects of polyanions on FGF-10 flexibility, thermodynamic fluctuations, and hydration vary depending on the size and charge density of the polyanion. Local effects of polyanions were investigated utilizing time-resolved fluorescence spectroscopy and red edge excitation spectroscopy (REES). Increased rigidity of the protein matrix or an increased solvent response surrounding the Trp residues is observed in the presence of polyanions. Similarly, time-resolved spectroscopy reveals increased ground state heterogeneity and increased dipole relaxation on the time scale of fluorescence for FGF-10 in the presence of polyanions. These polyanions increase heterogeneity, global flexibility, and fluctuations while increasing the melting temperature (Tm) of FGF-10.

Reversibly stable thiopolyplexes for intracellular delivery of genes

Novel polyaspartamide non-viral carriers for gene therapy were synthesized by introducing, on the same polymer backbone, positively charged groups, for electrostatic interactions with DNA, and thiol groups for the formation of disulfide bridges between polymer chains. The introduction of thiols was aimed to have a vector with low redox potential sensitivity: disulfide crosslinking in fact, being stable in extracellular environment, allowed either to have stable complexes in plasma, that can protect DNA from metabolism, or to be reduced inside the cell, where the excess of glutathion in reduced form maintains a low redox potential. The consequent destabilization of the complex after disulfide cleavage can release DNA selectively inside the cells. α,β-poly( N-2-hydroxyethyl)- d, l-aspartamide (PHEA) was used as starting polymer being a highly water-soluble synthetic polymer, already proposed with success as therapeutic carrier by our group. In this study, PHEA was firstly functionalised with ethylendiamine, obtaining a well defined copolymer with pendant primary amine groups (PHEA-EDA), to which N-succinimidyl 3-(2-pyridyldithio) propionate (SPDP) and 3-(carboxypropyl)trimethyl-ammonium chloride (CPTA) were linked in two subsequent steps, allowing the introduction of thiol and cationic groups respectively. Finally DTT treatment lead to the final PHEA-EDA-SH-CPTA thiopolycation, named PESC. The present work describes the synthesis and characterization of the thiopolycation PESC. 1H NMR spectroscopy detected the derivatization molar degrees in SPDP and CPTA; the formation of DNA complexes (thiopolyplexes), their stability in the presence of polyanions and the ability to release DNA under reductive conditions were studied by agarose gel electrophoresis. DNase II degradation study was carried out to detect the ability of thiopolyplex to stabilize DNA towards enzymatic metabolism. Thiopolyplexes were then characterized by Dynamic Light Scattering (DLS) and Zeta Potential analysis. Finally, in vitro toxicity profile (MTT) and gene transfer efficiency (Luciferase assay) were carried out to evaluate thiopolyplex biocompatibility, safety and efficacy to be used as gene delivery system.

Specific volume and compressibility of human serum albumin–polyanion complexes

The ultrasound velocimetry, densitometry, and differential scanning calorimetry have been used to study the formation of the complexes between human serum albumin (HSA) and polyanions heparin (HEP) and/or dextran sulfate (DS). The values of the ultrasound velocity and specific volume allowed us to determine the specific adiabatic compressibility, ϕ K/ β 0, which reflects the degree of volume compressibility of the complexes. We showed that in the presence of HEP and DS the adiabatic compressibility of HSA decreases with increasing concentration of polyanions. HEP more strongly interacts with HSA than DS. pH of electrolyte in the range 4.7–8.5 weakly affects the adiabatic compressibility. Changes of compressibility of HSA can be caused by increase of the hydration due to the formation of the HSA–polyanion complexes and due to partial unfolding of HSA. The HSA–polyanion interaction resulted in decrease of phase transition temperature of the protein. This evidences about protein destabilization in the presence of polyanions.

Interaction of Alzheimer's disease amyloid β peptide fragment 25–35 with tau protein, and with a tau peptide containing the microtubule binding domain

The interaction of amyloid beta (Abeta) 25-35 with tau protein and with the peptide 1/2R (KVTSKCGSLGNIHHKPGGG), has been investigated by chromatography, electron microscopy, and surface plasmon resonance (SPR). Abeta 25-35 comprises the minimum region of Abeta peptide that is able to aggregate into fibrils, and 1/2R contains residues 307-325 from the tau region involved in microtubule binding. The results of chromatography showed that Abeta 25-35 induces the aggregation of tau protein and of tau peptide 1/2R. Likewise, the results of electron microscopy showed that Abeta 25-35 increases the tau peptide polymerization observed in the presence of polyanions like heparin. A decrease in Abeta 25-35 aggregation induced by tau peptide was also observed by both techniques. No direct interaction between tau protein immobilized on the sensor surface and Abeta 25-35 could be detected by SPR. However, incubation of tau protein at room temperature produced the loss of capability of this protein for interacting with the active biosensor surface. The presence of Abeta 25-35 during the incubation of tau protein makes more efficient this loss of interacting capability with the sensor surface. These results clearly indicate that Abeta 25-35, the peptide region to which the cytotoxic properties of Abeta can be assigned, interacts with the peptide region of tau protein involved in microtubule binding. This interaction produces the aggregation of tau peptide and the concomitant disassembling of Abeta 25-35, offering thus an explanation to the lack of co-localization of neurofibrillary tangles and senile plaques in Alzheimer's disease, and suggesting the possibility that tau protein may have a protective action by preventing Abeta from adopting the cytotoxic, aggregated form.

Sulfhydryl Based Cationic Surfactants and the Impact of Polyanions on Disulfide Bond Formation: Implications for Gene Transfer Vectors

Compacting plasmid DNA (pDNA) into a small size is a fundamental necessity for the efficient in vivo transfer of nucleic acids to somatic cells. An approach for accomplishing this is to condense pDNA using cationic detergents with sulfhydryl groups, near their critical micelle concentration. In this study, a model surfactant was used to study how the rate of disulfide bond formation relates to environmental factors. It was shown that the thiol detergent had the ability to form a disulfide bond when oxidized and the presence of polyanions was significantly increased. The addition of a reducing agent disrupted the disulfide bonds initially, but this was followed by disulfide bond reformation in a short time period.

Pressure studies on the metallation of a supra-molecular porphyrin complex

The complex formation of meso-tetrakis-(1-methylpyridinium-4-yl)porphine p-toluenesulfonate (TMPyP) with zinc ions was examined at various pressures. By the application of high pressure, the second-order reaction rate constant for the metallation was increased to give the negative volume of activation (ΔV{). This result suggested that the activated complex is more strongly hydrated than the reactants. By the presence of anionic polyelectrolytes such as polyacrylic acid sodium salt (NaPAA, polymers with five molecular weight ranges from 1.1×103 to 6.6×105 were used) and poly(l-glutamic acid sodium salt) (Mw = 3.7×104), the metallation reaction was largely accelerated, whereas neither poly(l-lysine HBr salt) (Mw = 3.6×103) nor poly(ethylene glycol) (Mw = 1.1×104) affected the reaction at all. The acceleration effect of polyanions could be intuitively attributed to the accumulation of the cationic TMPyP in the vicinity of the polyanion to afford a supra-molecular porphyrin complex (polyanion-TMPyP), resulting in the increase in the collision probability of TMPyP with a zinc ion which was also accumulated in the polyanion domain. The degree of acceleration by the presence of NaPAA was the largest when the molecular weight was 2.5×103. The volume of activation (ΔV{) in the presence of polyanions was less negative in comparison with that for the spontaneous reaction, due to the more pronounced dehydration of the activated complex than the reactants in the vicinity of the polyanion. A good correlation between the ΔV{ value and the entropy of activation (ΔS{) for the metallation in the presence of various polyanions supported that the acceleration effect could be related to the solvation effects.

Synthesis, Characterization, and Luminescence Properties of Anthrylpolyamines: An Experiment for an Integrated, Advanced Laboratory Course

A 10-week, open-ended experiment for a junior/senior-level integrated laboratory course is described. The project involves the synthesis and instrumental characterization of two monosubstituted and two disubstituted anthrylpolyamines of varying lengths, as well as a detailed investigation of their photophysical and photochemical properties in the presence of polyanions of biological interest. Depending on the nature of the polyanion, emission quenching of the anthracene chromophore occurs by a template-directed excimer formation, or by an energy-transfer process. A correlation between the charge of the protonated anthrylpolyamines and the degree of emission quenching is also investigated. This project is ideally suited for introducing students to different quenching mechanisms within the context of a research-oriented, integrated laboratory experience.

Porphyrin aggregation in aqueous solutions: small angle and quasielastic light scattering results

The porphyrin trans-bis( N-methylpyridinium-4-yl)diphenylporphyine ( t-H 2P agg) is known to form in solution large assemblies and supramolecular structures in the presence of polyanions, such as nucleic acids, as a template support. We have studied the aggregation of the unbound porphyrin in 0.1 M NaCl aqueous solutions. The aggregation process was monitored by a time resolved small angle light scattering apparatus. The intensity profile of the scattered light as a function of the exchanged wavevector q, conforms to a scattered law for fractal aggregates in the range 0.2–31.4 μm −1. An analysis of the intensity data reveals a value of the fractal dimension d f equal to 2.5. Additional dynamic light scattering measurements confirm the presence of almost monodispersed aggregates in the mesoscopic range.