pH-Controlled Self-Assembling of meso-Tetrakis(4-sulfonatophenyl)porphyrin−Chitosan Complexes

Kinetics, Equilibrium, and Thermodynamics for Conjugation of Chitosan with Insulin-Mimetic [meso-Tetrakis(4-sulfonatophenyl)porphyrinato]oxovanadate(IV)(4-) in an Aqueous Solution

This study investigated the conjugation of chitosan with the insulin-mimetic [meso-tetrakis(4-sulfonatophenyl)porphyrinato]oxovanadate(IV)(4-), VO(tpps), in an aqueous medium as a function of conjugation time, VO(tpps) concentrations, and temperatures. To validate the synthesis of chitosan-VO(tpps) conjugate, UV-visible and Fourier transform infrared spectrophotometric techniques were utilized. Conjugate formation is ascribed to the electrostatic interaction between the NH3+ units of chitosan and the SO3- units of VO(tpps). Chitosan enhances the stability of VO(tpps) in an aqueous medium (pH 2.5). VO(tpps) conjugation with chitosan was best explained by pseudo-second-order kinetic and Langmuir isotherm models based on kinetic and isotherm studies. The Langmuir equation determined that the maximal ability of VO(tpps) conjugated with each gram of chitosan was 39.22 μmol at a solution temperature of 45 °C. Activation energy and thermodynamic studies (Ea: 8.78 kJ/mol, ΔG: -24.52 to -27.55 kJ/mol, ΔS: 204.22 J/(mol K), and ΔH: 37.30 kJ/mol) reveal that conjugation is endothermic and physical in nature. The discharge of VO(tpps) from conjugate was analyzed in freshly prepared 0.1 mol/L phosphate buffer (pH 7.4) at 37 °C. The release of VO(tpps) from the conjugate is a two-phase process best explained by the Higuchi model, according to a kinetic analysis of the release data. Taking into consideration all experimental findings, it is proposed that chitosan can be used to formulate both solid and liquid insulin-mimetic chitosan-VO(tpps) conjugates.

Adsorption properties of heavy metals and antibiotics by chitosan from larvae and adult Trypoxylus dichotomus

Chitosan was prepared by hydrothermal deacetylation from multi-step protein purification chitin based on Trypoxylus dichotomus, for treating heavy metals and antibiotics. Chitosan with higher deacetylation degree and lower molecular weight were synthesized. The adult chitosan was composed of nanofibers arranged more evenly, showing higher yield, thermal stabilities and antimicrobial properties. The adsorption capacities of Cu²⁺ and Fe³⁺ were 462 and 270 mg/g, lower than 934 mg/g of Pb²⁺. Levofloxacin and tetracycline hydrochloride adsorption capacity were 26 and 22 mg/g, lower than 67 mg/g of sulfamethoxazole. In addition, compared with single pollutants, the adsorption of sulfamethoxazole and Pb²⁺ can increase by 6% and 5% when they act as composite contaminants. The adsorption procedure can be well described by pseudo-second-order kinetics and Langmuir isothermal model, indicating it a homogeneous monolayer chemisorption. Therefore, the Trypoxylus dichotomus source chitosan prepared by hydrothermal deacetylation has potential applications in the adsorption of complex pollutants.

Chitosan nanocomposites with CdSe/ZnS quantum dots and porphyrin

Water-soluble nanocomposites based on CdSe/ZnS quantum dots (QDs) and hydrophobic tetraphenylporphyrin (TPP) molecules passivated by chitosan (CS) have been formed. Magnetic circular dichroism (MCD) spectra evidence TPP presence in both monomeric and agglomerated forms in the nanocomposites. The nanocomposites demonstrate more pronounced singlet oxygen generation compared to free TPP in CS at the same concentration due to the intracomplex Förster resonance energy transfer (FRET) with a 45% average efficiency.

Supramolecular assembly of calix[4]resorcinarenes and chitosan for the design of drug nanocontainers with selective effects on diseased cells

Effective delivery systems for anticancer drugs were prepared through the self-assembly of calix[4]resorcinarenes and chitosan in an aqueous medium.

Thermochemical research of chitosan complexes with sulfonated metallophthalocyanines

The complexation processes of chitosan with cobalt(II)tetrasulfophthalocyanine (CoPc) and copper(II)tetrasulfophthalocyanine (CuPc) were studied calorimetrically in solution. It was established that CoPc forms two types of complexes with chitosan, while CuPc forms a single type of complex with chitosan, in which copper(II)tetrasulfophthalocyanine is in dimerized form. The complexes are thermodynamically stable, which was allowed to study them in a solid form by different methods. Joint application of DSC and TG/DTG methods allowed us to identify the temperature intervals for evaporation of physically and chemically bounded water and thermal decomposition of chitosan and its complexes. The glass transition temperature of chitosan (110.8 °C) is greater than the glass transition temperature of the complexes with CuPc (74.7 °C) and CoPc (71.2 °C). Using SEM images and X-ray data of heated, unheated chitosan and its complexes, it was shown that the complexes are predominantly amorphous. Heating of chitosan and its leads to increasing of amorphous phase. Modification of chitosan by phthalocyanines leads to decreasing of thermal stability of complexes insignificantly.

Supramolecular Hybrid Material Based on Engineering Porphyrin Hosts for an Efficient Elimination of Lead(II) from Aquatic Medium

Porphyrins show great promise for future purification demands. This is largely due to their unique features as host binding molecules that can be modified at the synthetic level, and largely improved by their incorporation into inorganic based materials. In this study, we assessed the efficacy of a hybrid material obtained from the immobilization of 5,10,15,20-tetrakis(pentafluorophenyl)-porphyrin on silica surface to remove Pb(II), Cu(II), Cd(II), and Zn(II) ions from water. The new organic-inorganic hybrid adsorbent was fully characterized by adequate techniques and the results show that the hybrid exhibits good chemical and thermal stability. From batch assays, it was evaluated how the efficacy of the hybrid was affected by the pH, contact time, initial metal concentration, and temperature. The adsorption kinetic and isotherms showed to fit the recent developed fractal-like pseudo-second-order model and Langmuir–Freundlich model respectively. The highest adsorption capacities for Pb(II), Cu(II), Cd(II), and Zn(II) ions were 187.36, 125.17, 82.45, and 56.23 mg g⁻¹, respectively, at pH 6.0 and 25 °C. This study also shows that metal cations from real river water samples can be efficient removed in the presence of the new adsorbent material.

The chitosan - Porphyrazine hybrid materials and their photochemical properties

Three magnesium sulfanyl porphyrazines differing in the size of peripheral substituents (3,5-dimethoxybenzylsulfanyl, (3,5-dimethoxybenzyloxy)benzylsulfanyl, 3,5-bis[(3,5-bis[(3,5-dimethoxybenzyloxy)benzyloxy]benzylsulfanyl) were exposed to visible and ultraviolet radiation (UV A + B + C) in order to determine their photochemical properties. The course of photochemical reactions in dimethylformamide solutions and the ability of the systems to generate singlet oxygen were studied by UV-Vis spectroscopy, which additionally gave information on aggregation processes. The porphyrazines were found to be stable upon visible light irradiation conditions, but when exposed to high energy UV radiation, the efficient photodegradation of these macrocycles was observed. Therefore, these three magnesium sulfanyl porphyrazines were incorporated into chitosan matrix. The obtained thin films of chitosan doped with porphyrazines were subjected to polychromatic UV-radiation and studied by spectroscopic methods (UV-Vis, FTIR), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Application of chitosan as a polymer matrix for porphyrazines was found to be successful method that effectively stopped the unwelcome degradation of macrocycles, thus worth considering for their photoprotection. In addition, the surface properties of the hybrid material were determined by contact angle measurements and calculation of surface free energy. Intermolecular interactions between these novel porphyrazines and chitosan were detected. The mechanism of photochemical reactions occurring in studied systems has been discussed.

Characterization of bioactive chitosan and sulfated chitosan from Doryteuthis singhalensis (Ortmann, 1891)

Chitosan was extracted from the pen of squid Doryteuthis singhalensis and characterized using FT-IR, NMR, CHN, SEM and DSC analysis. Purified chitosan was sulfated with chlorosulfonic acid in N,N-dimethylformamide and the added sulfate group was confirmed with FT-IR analysis. The molecular weight and degree of deacetylation (DDA) of chitosan was found 226.6kDa and 83.76% respectively. Chitosan exhibited potent antioxidant activity evidenced by reducing power, chelating ability on ferrous ions and scavenging activity on DPPH, superoxide and hydroxyl radicals. The anticoagulant assay using activated partial thromboplastin time (APTT) and prothrombin time (PT) showed chitosan as a strong anticoagulant. The results of this study showed possibility of using D. singhalensis pen as a non-conventional source of natural antioxidants and anticoagulant which can be incorporated in functional food formulations.

Norfloxacin-loaded collagen/chitosan scaffolds for skin reconstruction: Preparation, evaluation and in-vivo wound healing assessment

Biomaterial scaffolds are versatile tools as drug carrier for treatment of wounds. A series of norfloxacin-loaded scaffolds were synthesized for treatment of wounds by combining collagen with two different types of chitosan using freeze-drying technique. Subsequently, scaffolds were screened in terms of morphology, water absorption and retention capacity, biodegradation, ex-vivo bioadhesive strength, in-vitro drug release biological compatibility, X-ray diffractometry, differential scanning calorimetry as well as in-vivo evaluation. The results indicate that the scaffold mechanical strength is dependent on the type of used chitosan. The prepared scaffolds contained interconnected porous architecture. The scaffolds had high water uptake and retention capacity with extended biodegradation rate. Scaffolds prepared with chitosan HCl showed superior bioadhesive strength compared to those prepared with low molecular weight chitosan. All scaffolds showed almost 100% drug release within 24h. As identified by the terahertz pulsed imaging measurements, there is single scaffold area with the same concentration. After 28 days of wound dressing with selected norfoloxacin-loaded or unloaded collagen/chitosan scaffolds in Albino rats, it was found that the tissue regeneration time was fast compared to non-treated wounds. Furthermore, the drug-loaded scaffolds showed normal structure of an intact epidermal layer as well as the underlying dermis as revealed by histopathological studies. The obtained results suggest that the investigated norfloxacin-loaded collagen/chitosan scaffold is a potential candidate for skin regeneration application.

Real-time analysis of porphyrin J-aggregation on a plant-esterase-functionalized surface using quartz crystal microbalance with dissipation monitoring

The J-aggregation of meso-tetra (4-sulfonatophenyl) porphine (TPPS4) on a plant-esterase-functionalized surface in a 1:1 v/v mixture of 0.05 M HCl/ethanol (pH ∼1.38) was analyzed in real time using a quartz crystal microbalance with dissipation monitoring (QCM-D). Simultaneous changes in frequency (Δf) and energy dissipation (ΔD) correlated well with mass and structural changes during the sequential phases of slow nucleation, rapid aggregation, and equilibration in J-aggregation. The time-dependent mass adsorption could be quantitatively analyzed with a model, which integrated two simple equations obtained when the surface concentration of TPPS4 (Γ(TPPS4)) was below and above the critical aggregation surface concentration (CASC). This study provides a new view for the protein-induced J-aggregation process, which may be helpful for understanding the interactions of self-assembled nanostructures with biomolecules.

Kinetics, mechanism and thermodynamics involved in sorption of meso-tetrakis(4-sulfonatophenyl)porphyrin onto chitosan in aqueous medium

Sorption of meso-tetrakis(4-sulfonatophenyl)porphyrin ( H 2 tpps ) onto chitosan has been investigated in aqueous medium. Kinetic and isotherm studies were carried out by considering the effects of various parameters, such as pH, initial concentration of H 2 tpps solution, and temperature. The kinetic data obtained from different batch experiments were analyzed using pseudo first-, second-order, intraparticle, and film diffusion kinetic models. The equilibrium sorption data was analyzed by using Tempkin, Langmuir and Freundlich models. The best results were achieved with the pseudo second-order kinetic, Langmuir and Freundlich isotherm models. The intraparticle diffusion and film diffusion are the rate limiting steps. The amount of sorbate adsorbed at equilibrium (qe) increased with increasing the initial concentration of H 2 tpps solution, showing maximum sorption capacity of 445.21 μmol.g-1. The activation energy (Ea) of sorption kinetics was found to be 19.47 kJ.mol-1. Thermodynamic parameters such as change in free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) were evaluated by applying the Van't Hoff equation. Thermodynamic activation parameters such as change in enthalpy of activation (ΔH‡), entropy of activation (ΔS‡), and free energy of activation (ΔG‡) were also calculated. The thermodynamics of H 2 tpps sorption onto chitosan in aqueous medium indicates its spontaneous and endothermic nature.

Characterization of mesoscale coiled-coil peptide-porphyrin complexes

Photoelectronically conductive self-assembling peptide-porphyrin assemblies have great potential in their use as biomaterials, owing largely to their environmentally responsive properties. We have successfully designed a coiled-coil peptide that can self-assemble to form mesoscale filaments and serve as a scaffold for porphyrin interaction. In our earlier work, peptide-porphyrin-based biomaterials were formed at neutral pH, but the structures were irregular at the nano- to microscale size range, as judged by atomic force microscopy. We identified a pH in which mesoscale fibrils were formed, taking advantage of the types of porphyrin interactions that are present in well-characterized J-aggregates. We used UV-visible spectroscopy, circular dichroism spectropolarimetry, fluorescence spectroscopy, and atomic force microscopy to characterize these self-assembling biomaterials. We propose a new assembly paradigm that arises from a set of unique porphyrin-porphyrin and porphyrin-peptide interactions whose structure may be readily modulated by changes in pH or peptide concentration.

Comparative study of the self-aggregation of rhodamine 6G in the presence of poly(sodium 4-styrenesulfonate), poly(N-phenylmaleimide-co-acrylic acid), poly(styrene-alt-maleic acid), and poly(sodium acrylate)

The interaction between rhodamine 6G and different polyelectrolytes is analyzed. Structural aspects differentiate these polyelectrolytes, such as the presence of aromatic groups and the number and localization of their respective charges, which may be directly attached to the aromatic groups or to the polymeric main chain. In the case of poly(sodium acrylate), which does not bear aromatic groups, the polyelectrolyte induces cooperative self-stacking between the dyes which is highly sensitive to the ionic strength, due to the predominance of long-range electrostatic interactions between the polymer and the dye. In the case of poly(sodium 4-styrenesulfonate), whose charge is directly attached to the aromatic groups, a high dispersant ability of the dyes is found and the interaction is less dependent on the ionic strength, due to the predominance of short-range aromatic-aromatic interactions between the dye and the polymer. Among the two polyelectrolytes studied for which the polymeric charge is directly attached to the main chain, and separated from the aromatic group, poly(styrene-alt-maleic acid) shows a lower dependence of the interaction on the ionic strength than poly(N-phenylmaleimide-co-acrylic acid) at a comonomer composition of 1:2, due to a higher linear aromatic density and a lower linear charge density, indicating the importance of hydrophobic forces. Both copolymers exhibit a high ability to induce cooperative self-aggregation of the dye.

Characterization and dissolution study of chitosan freeze-dried systems for drug controlled release

Freeze-dried systems (L) comprising chitosan (CS) and caffeine (CAF) have been developed for oral administration. Different proportions of CS and CAF have been used in the preparation of the systems. Hot stage microscopy (HSM), differential scanning calorimetry (DSC) and X-ray diffraction powder have been used to characterize the systems prepared. X-ray diffraction patterns showed that there were no interactions between CAF and CS molecules within the freeze-dried systems and the crystallinity of CAF was decreased. Swelling and dissolution tests were carried out in two different media (demineralized water and pH progressive medium) in order to establish their influence over CAF/CS system behaviour. Characteristic swelling behaviour of freeze-dried CS systems (imbibition and dissolution processes) was influenced by the proportions of CS and CAF in the formulations, and by the nature of the medium due to the pH-dependent solubility of CS. Release of CAF from lyophilized systems was conditioned by the swelling process and it should be possible to obtain a CAF/CS binary system with a specific time for total drug release including concrete proportions of both components. Furthermore, the freeze-drying process allowed us to obtain feasible systems for controlled release of CAF until the total amount of drug was released.