Spectroscopic studies on the interaction of a water soluble porphyrin and two drug carrier proteins

Interaction of Aggregated Cationic Porphyrins with Human Serum Albumin

The interaction of an equilibrium mixture of monomeric and aggregated cationic trans-5,15-bis(N-methylpyridinium-4-yl)-10,15-bis-diphenylporphine (t-H₂Pagg) chloride salt with human serum albumin (HSA) has been investigated through UV/Vis absorption, fluorescence emission, circular dichroism and resonant light scattering techniques. The spectroscopic evidence reveals that both the monomeric t-H₂Pagg and its aggregates bind instantaneously to HSA, leading to the formation of a tight adduct in which the porphyrin is encapsulated within the protein scaffold (S₄₃₀) and to clusters of aggregated porphyrins in electrostatic interaction with the charged biomolecules. These latter species eventually interconvert into the final S₄₃₀ species following pseudo-first-order kinetics. Molecular docking simulations have been performed to get some insights into the nature of the final adduct. Analogously to hemin bound to HSA, the obtained model supports favorable interactions of the porphyrin in the same 1B subdomain of the protein. Hydrophobic and van der Waals energy terms are the main contributions to the calculated ΔG_bind value of -117.24 kcal/mol.

Functional Nano-Objects by Electrostatic Self-Assembly: Structure, Switching, and Photocatalysis

The design of functional nano-objects by electrostatic self-assembly in solution signifies an emerging field with great potential. More specifically, the targeted combination of electrostatic interaction with other effects and interactions, such as the positioning of charges on stiff building blocks, the use of additional amphiphilic, π-π stacking building blocks, or polyelectrolytes with certain architectures, have recently promulgated electrostatic self-assembly to a principle for versatile defined structure formation. A large variety of architectures from spheres over rods and hollow spheres to networks in the size range of a few tenths to a few hundred nanometers can be formed. This review discusses the state-of-the-art of different approaches of nano-object formation by electrostatic self-assembly against the backdrop of corresponding solid materials and assemblies formed by other non-covalent interactions. In this regard, particularly promising is the facile formation of triggerable structures, i.e. size and shape switching through light, as well as the use of electrostatically assembled nano-objects for improved photocatalysis and the possible solar energy conversion in the future. Lately, this new field is eliciting an increasing amount of understanding; insights and limitations thereof are addressed in this article. Special emphasis is placed on the interconnection of molecular building block structures and the resulting nanoscale architecture via the key of thermodynamics.

An update of label-free protein target identification methods for natural active products

Natural active products (NAPs) are derived from chemical substances found in nature that have biological activity and medicinal potential. Screening and revealing the protein targets of NAPs is an indispensable link in the pharmacological and toxicological understanding of NAPs. Proteins are the main factors executing cell functions, and cells rely on the function of proteins to complete various activities in the life cycle. The important mechanism of action of drugs is to regulate cell biological activities by interacting with proteins and other macromolecules. At present, the classic way to screen protein targets is based on the molecular label tracing method, which has a long cycle and changes the molecular structure and pharmacological effects of NAPs. Due to the shortcomings of molecular labelling methods, in recent years, scientists have tried to develop a variety of label-free protein target identification methods for NAPs and have made a certain amount of progress. This article reviews the current protein target identification methods for NAPs with the aim of providing a reference for research on NAP protein targets.

Self-Assembly and Multifaceted Bioactivity of a Silver(I) Quinolinate Coordination Polymer

Coordination polymers have emerged as a new class of potent biologically active agents due to a variety of important characteristics such as the presence of bioactive metal centers and linkers, low toxicity, stability, tailorable structures, and bioavailability. The research on intermediate metabolites has also been explored with implications toward the development of selective anticancer, antimicrobial, and antiviral therapeutic strategies. In particular, quinolinic acid (H2quin) is a recognized metabolite in kynurenine pathway and potent neurotoxic molecule, which has been selected in this study as a bioactive building block for assembling a new silver(I) coordination polymer, [Ag(Hquin)(μ-PTA)]n·H2O (1). This product has been prepared from silver oxide, H2quin, and 1,3,5-triaza-7-phosphaadamantane (PTA), and fully characterized by standard methods including single-crystal X-ray diffraction. Compound 1 has revealed distinctive bioactive features, namely (i) a remarkable antiviral activity against herpes simplex virus type 1 (HSV-1) and adenovirus 36 (Ad-36), (ii) a significant antibacterial activity against clinically important bacteria (Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa), and (iii) a selective cytotoxicity against HeLa (human cervix carcinoma) cell line. The present work widens a growing family of bioactive coordination polymers with potent antiviral, antibacterial, and antiproliferative activity.

Fluorescence Spectroscopy of Porphyrins and Phthalocyanines: Some Insights into Supramolecular Self-Assembly, Microencapsulation, and Imaging Microscopy

The molecular interactions of anionic tetrasulfonate phenyl porphyrin (TPPS) with poly(amido amine) (PAMAM) dendrimers of generation 2.0 and 4.0 (G2 and G4, respectively) forming H- or J-aggregates, as well as with human and bovine serum albumin proteins (HSA and BSA), were reviewed in the context of self-assembly molecular complementarity. The spectroscopic studies were extended to the association of aluminum phthtalocyanine (AlPCS4) detected with a PAMAM G4 dendrimer with fluorescence studies in both steady state and dynamic state, as well as due to the fluorescence quenching associated to electron-transfer with a distribution of lifetimes. The functionalization of TPPS with peripheral substituents enables the assignment of spontaneous pH-induced aggregates with different and well-defined morphologies. Other work reported in the literature, in particular with soft self-assembly materials, fall in the same area with particular interest for the environment. The microencapsulation of TPPS studies into polyelectrolyte capsules was developed quite recently and aroused much interest, which is well supported and complemented by the extensive data reported on the Imaging Microscopy section of the Luminescence of Porphyrins and Phthalocyanines included in the present review.

Spectroscopic Analysis of Apoferritin Associates with the Water-Soluble Porphyrins

The association behavior of apoferritin species with the anionic porphyrins, 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (H₂ TPPS^4- ) and its zinc(II) complex (ZnTPPS^4- ), which are water-soluble even in acidic solutions, was investigated for the first time through UV-Vis absorption and fluorescence spectroscopy in order to evaluate a potential ability of apoferritin as a stimuli-responsive molecular capsule. The absorption maximum wavelengths of both porphyrins were redshifted and the fluorescence intensity decreased, indicating the effective association between apoferritin species and the porphyrins, although it depended on the pH adjustment procedure. At pH 2, the ZnTPPS^4- associated with apoferritin subunits without demetallating and protonating, while the free base porphyrin formed the J-aggregate of the diprotonated species (H₄ TPPS^2- )_n , with extremely low fluorescence. As the concentration of apoferritin subunits increased, the H₂ TPPS^4- -subunits associates were formed accompanied by recovering the fluorescence. The association stoichiometries of 1 or 2 subunits/porphyrin obtained under neutral and acidic conditions. The significantly large association constant of ZnTPPS^4- as compared with that of H₂ TPPS^4- indicated that the coordination to the zinc(II) center strongly contributes to the association in addition to the electrostatic interaction between apoferritin subunits and the porphyrin under acidic conditions.

Binding of Two Tetrasulfophthalocyanines (Fe(III) and Metal-Free) to Lysozyme: Fluorescence Spectroscopic and Computational Approach

The interactions between tetrasulfophthalocyanines and lysozyme were studied using fluorescence spectroscopic and computational analyses. Lysozyme has been found to be widely studied as an anticancer agent, however, there are few reports of its interaction with phthalocyanines. Fe(III) tetrasulfophthalocyanine (FeTSPc) and free base tetrasulfophthalocyanine (TSPc) used in this study, were synthesized by our research group. Experimental results suggested that the metalled complex FeTSPc has a much higher affinity than TSPc. The binding stoichiometry between each tetrasulfophthalocyanine and lysozyme was 1:1. Stern-Volmer analysis suggested that the fluorescence quenching proceedes through a static process. Binding thermodynamics (ΔG, ΔH and ΔS) confirmed that mainly hydrogen bonds, van der Waals, and electrostatic forces are responsible for the binding process. We carried out molecular dynamics simulations, molecular docking, and binding energy calculations. Molecular dynamics simulations yielded the most populated cluster of lysozyme structures, and a representative structure from this cluster was used for the docking studies with these phthalocyanines. 1000 poses were generated for each ligand. The strudtures of the resulting complexes revealed that Arg 73 and Arg 112 are important for the binding affinity of the tetrasulfophthalocyanines, generating mainly an electrostatic favorable environment for the SO3- groups. In addition, hydrophobic contacts were involved with Trp 62, Trp 63 and Trp 108, explaining the fluorescence quenching observed experimentally. Binding energies were determined for these models, confirming that the interactions with lysozyme were more favorable for FeTSPc compared to TSPc. The understanding of the molecular mechanisms is relevant to characterize the nature of tetrasulfophthalocyanines in photodynamic therapy.

Identification of a novel mechanism for meso-tetra (4-carboxyphenyl) porphyrin (TCPP) uptake in cancer cells

Porphyrins are used for cancer diagnostic and therapeutic applications, but the mechanism of how porphyrins accumulate in cancer cells remains elusive. Knowledge of how porphyrins enter cancer cells can aid the development of more accurate cancer diagnostics and therapeutics. To gain insight into porphyrin uptake mechanisms in cancer cells, we developed a flow cytometry assay to quantify cellular uptake of meso-tetra (4-carboxyphenyl) porphyrin (TCPP), a porphyrin that is currently being developed for cancer diagnostics. We found that TCPP enters cancer cells through clathrin-mediated endocytosis. The LDL receptor, previously implicated in the cellular uptake of other porphyrins, only contributes modestly to uptake. We report that TCPP instead binds strongly ( K D = 42 nM ) to CD320, the cellular receptor for cobalamin/transcobalamin II (Cbl/TCN2). Additionally, TCPP competes with Cbl/TCN2 for CD320 binding, suggesting that CD320 is a novel receptor for TCPP. Knockdown of CD320 inhibits TCPP uptake by up to 40% in multiple cancer cell lines, including lung, breast, and prostate cell lines, which supports our hypothesis that CD320 both binds to and transports TCPP into cancer cells. Our findings provide some novel insights into why porphyrins concentrate in cancer cells. Additionally, our study describes a novel function for the CD320 receptor which has been reported to transport only Cbl/TCN2 complexes.

Recent Progress in Ionic Coassembly of Cationic Peptides and Anionic Species

Peptide assembly has been extensively exploited as a promising platform for the creation of hierarchical nanostructures and tailor-made bioactive materials. Ionic coassembly of cationic peptides and anionic species is paving the way to provide particularly important contribution to this topic. In this review, the recent progress of ionic coassembly soft materials derived from the electrostatic coupling between cationic peptides and anionic species in aqueous solution is systematically summarized. The presentation of this review starts from a brief background on the general importance and advantages of peptide-based ionic coassembly. After that, diverse combinations of cationic peptides with small anions, macro- and/or oligo-anions, anionic polymers, and inorganic polyoxometalates are described. Emphasis is placed on the hierarchical structures, value-added properties, and applications. The molecular design of cationic peptides and the general principles behind the ionic coassembled structures are discussed. It is summarized that the combination of interesting and unique characteristics that arise both from the chemical diversity of peptides and the wide range of anionic species may contribute in a variety of output, including drug delivery, tissue engineering, gene transfection, and antibacterial activity. The emergent new phenomena and findings are illustrated. Finally, the outlook for the peptide-based ionic coassembly systems is also presented.

Evaluation of polyvinylpyrrolidone and block copolymer micelle encapsulation of serine chlorin e6 and chlorin e4 on their reactivity towards albumin and transferrin and their cell uptake

Encapsulation of porphyrinic photosensitizers (PSs) into polymeric carriers plays an important role in enhancing their efficiency as drugs in photodynamic therapy (PDT). Porphyrin aggregation and low solubility as well as the preservation of the advantageous photophysical properties pose a challenge on the design of efficient PS-carrier systems. Block copolymer micelles (BCMs) and polyvinylpyrrolidone (PVP) are promising drug delivery vehicles for physical entrapment of PSs. BCMs exhibit enhanced dynamics as compared to the less flexible PVP network. In the current work the question is addressed how these different dynamics affect PS encapsulation, release from the carrier, reaction with serum proteins, and cellular uptake. The porphyrinic compounds serine-amide of chlorin e6 (SerCE) and chlorin e4 (CE4) were used as model PSs with different lipophilicity and aggregation properties. ¹H NMR and fluorescence spectroscopy were applied to study their interactions with PVP and BCMs consisting of Kolliphor P188 (KP). Both chlorins were well encapsulated by the carriers and had improved photophysical properties. Compared to SerCE, the more lipophilic CE4 exhibited stronger hydrophobic interactions with the BCM core, stabilizing the system and preventing exchange with the surrounding medium as was shown by NMR NOESY and DOSY experiments. PVP and BCMs protected the encapsulated chlorins against interaction with human transferrin (Tf). However, SerCE and CE4 were released from BCMs in favor of binding to human serum albumin (HSA) while PVP prevented interaction with HSA. Fluorescence spectroscopic studies revealed that HSA binds to the surface of PVP forming a protein corona. PVP and BCMs reduced cellular uptake of the chlorins. However, encapsulation into BCMs resulted in more efficient cell internalization for CE4 than for SerCE. HSA significantly lowered both, free and carrier-mediated cell uptake for CE4 and SerCE. In conclusion, PVP appears as the more universal delivery system covering a broad range of host molecules with respect to polarity, whereas BCMs require a higher drug-carrier compatibility. Poorly soluble hydrophobic PSs benefit stronger from BCM-type carriers due to enhanced bioavailability through disaggregation and solubilization allowing for more efficient cell uptake. In addition, increased PS-carrier hydrophobic interactions have a stabilizing effect. For more hydrophilic PSs, the main advantage of polymeric carriers like PVP or poloxamer micelles lies in their protection during the transport through the bloodstream. HSA binding plays an important role for drug release and cell uptake in carrier-mediated delivery to the target tissue.

Effects of bovine serum albumin (BSA) on the excited-state properties of meso-tetrakis(sulfonatophenyl) porphyrin (TPPS4)

To infer changes in the photophysical properties of porphyrins due to complexation with albumin, a combination of Z-scan and conventional spectroscopic techniques was employed. We measured the characteristics of excited states of meso-tetrakis(sulfonatophenyl) porphyrin bound to bovine serum albumin and observed that the binding reduces the intersystem crossing quantum yield and increases the internal conversion one. A reverse saturable absorption process was observed in the nanosecond timescale. These results are important for prediction of the efficiency of this complex in medical and optical applications, because associating porphyrins to proteins enables better accumulation in tumors and improves its stability in optical devices, but at the same time, decreases its triplet quantum yield.

Study of tetraphenylporphyrins as modifiers of insulin amyloid aggregation

Amyloid fibrils are rigid β-pleated protein aggregates that are connected with series of harmful diseases and at the same time are promising as base for novel nanomaterials. Thus, design of compounds able to inhibit or redirect those aggregates formation is important both for the biomedical aims and for nanotechnology applications. Here, we studied the effect of tetraphenylporphyrins (metal free, their Cu and Pd complexes, and those functionalized by carboxy and amino groups on periphery) on insulin amyloid self-assembling. The strongest impact on insulin aggregation was demonstrated by a metal-free porphyrin bearing four carboxy groups. This compound strongly suppresses insulin aggregation (about 88% reduction in amyloid-sensitive probe emission) inducing formation of fibrils with the length close to this of free insulin (1.7 ± 0.6 μm as compared with 1.4 ± 0.4 μm, respectively) with an essentially reduced tendency to lateral aggregation. Contrarily, the presence of tetraphenylporphyrin containing four amino groups only slightly affects fibrils' morphology and makes weaker impact on insulin aggregation yield (about 44% reduction). This is explained by the ability of aromatic carboxy groups of 5,10,15,20-(tetra-4-carboxyphenyl)porphyrin to interact with complementary protein-binding groups and thus stabilize the supramolecular complex. For 5,10,15,20-(tetra-4-aminophenyl)porphyrin, full protonation takes place in acidic medium of protein aggregation reaction; this results in the high positive charge of TPPN4 (equal or close to +6) and hence higher contribution of coulombic repulsion to interaction of TPPN4 with insulin. One more possible mechanism of the lower inhibition effect of TPPN4 as compared with TPPC4 could be the more restricted possibility of the former as compared with the latter to form H bonds with insulin groups. It was also shown that metal-free, Pd-containing, and Cu-containing tetraphenylporphyrins without peripheral substituents make almost the same impact on the protein self-assembling. We suppose this to be due to coordination saturation of these metal atoms.

β-Lactoglobulin as a Nanotransporter for Glabridin: Exploring the Binding Properties and Bioactivity Influences

Based on the fact that β-lactoglobulin (β-lg) can solubilize readily in water and bind many small hydrophobic molecules, a novel nanocomplexed glabridin with β-lg was developed by an antisolvent precipitation method. After binding to β-lg, the solubility of glabridin in aqueous solution was enhanced 21 times. Fluorescence spectroscopy of β-lg revealed that the interaction of glabridin with β-lg made the environment of Trp and Tyr residues on β-lg more hydrophilic. The morphology and crystal form of the nanocomplexed glabridin with β-lg was characterized and the changes in β-lg conformation was also been investigated. In combination with molecular docking modeling, the results revealed that glabridin was bound to β-lg by hydrophobic forces and hydrogen-bond interactions. Furthermore, the nanocomplexed glabridin with β-lg had a better 2,2-diphenyl-1-picrylhydrazyl radical-scavenging capacity and 2,2'-azino-bis-3-ethylbenzthiazoline-6-sulfonic acid radical-scavenging capacity compared to free glabridin at the same concentration during in vitro tests. Thus, nanocomplexing with β-lg, by virtue of its ability to enhance the solubility of glabridin in aqueous systems, provides a suitable opportunity as a nanocarrier molecule.

In situ ultra-fast heat deposition does not perturb the structure of serum albumin

MnTPPS is a metallic water soluble porphyrin with high potential to be used as a contrast agent in photoacoustic tomography. In order to fully understand the interaction between MnTPPS and serum albumin and to investigate the effect of the light induced fast in situ heat deposition by MnTPPS in the protein, we performed several experimental studies using fluorescence and circular dichroism spectroscopies, as well as photoacoustic calorimetry. To identify the possible binding site(s) of the metalloporphyrin in serum albumin and to help interpret the spectroscopic results, a molecular docking exercise was also carried out. The fluorescence data indicate a 1 : 1 stoichiometry for the complex BSA : MnTPPS. The molecular docking results suggest one binding site at the subdomain IB of albumin, where Trp-134 is found, as the main binding site for MnTPPS. The CD data indicate no significant conformational changes of the BSA secondary structure upon MnTPPS binding and even after several minutes of laser excitation of MnTPPS. TR-PAC results show that the in situ heat deposition from MnTPPS does not cause any significant transient conformational change to the BSA structure. In conclusion, this work demonstrates that MnTPPS, in addition to the necessary physical and chemical properties to be used as a contrast agent in photoacoustic tomography, can be effectively carried by albumin and that in situ heat release following light absorption does not cause any significant damage to the protein structure.

Spectroscopic investigation of the anticancer alkaloid piperlongumine binding to human serum albumin from the viewpoint of drug delivery

Piperlongumine (PL) is a very promising natural agent with a high potential for cancer treatment. To overcome the poor water solubility of PL, there is a need to develop a novel water-soluble formulation in which PL is non-covalently bound to human serum albumin (HSA). PL binding to HSA was studied by various spectroscopic techniques under simulated physiological conditions. Spectroscopic evidence showed that the interaction of PL with HSA could form a PL-HSA complex. The binding constant (Ka ) values increased with increasing temperature, and a similar dependence was observed for the number of binding sites (n) values. The number of PL molecules bound to HSA reached 8.1 when the temperature was raised to 308 K. Thermodynamic calculation results suggested that the binding reaction occurred spontaneously but was an entropy-driven process, and hydrophobic forces played a major role in stabilizing the complex. Furthermore, PL binding induced conformational and microenvironmental changes in HSA. Displacement studies indicated that PL and warfarin had separate binding regions in site I. Therefore, it would be possible to develop a novel water-soluble formulation involving PL and HSA. This study may provide some valuable information in terms of improving the poor water solubility of PL.

Tubulation of liposomes via the interaction of supramolecular nanofibers

We achieved tubulation of self-assembled lipid membranes, liposomes, via the interaction of supramolecular nanofibers, porphyrin J-aggregates. This structural change was reversible, and the deformation of the porphyrin J-aggregates caused reconstruction of the liposomes from the tubes. We discussed the tubulation mechanism and calculated the force provided by porphyrin J-aggregates for tubulation.

Core-Assisted Formation of Porphyrin J-Aggregates in pH-Sensitive Polyelectrolyte Microcapsules Followed by Fluorescence Lifetime Imaging Microscopy

A strategy assisted by an inorganic template was developed to promote the organized self-assembly of meso-(tetrakis)-(p-sulfonatophenyl)porphyrin (TPPS) on pH-sensitive core-shell polyelectrolyte microcapsules (PECs) of poly(styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH). A key feature of this strategy is the use of template CaCO₃ microparticles as a nucleation site endorsing inside-outside directional growth of porphyrin aggregates. Using this approach, TPPS self-assembly in positively charged PECs with CaCO₃ (PAH/PSS)₂PAH as a sequence of layers was successfully achieved using mild pH conditions (pH 3). Evidence for porphyrin aggregation was obtained by UV-vis with the characteristic absorption bands in PECs functionalized with porphyrins. Fluorescence lifetime imaging microscopy (FLIM) of the polyelectrolyte core-shell confirmed the presence of radially distributed needlelike structures sticking out from polyelectrolyte shells. Microscopic images also revealed a sequential process (adsorption, redistribution, and aggregation) for the directional growth (inside/outside) of TPPS aggregates, which highlights the importance of the core in the aggregation induction. Removing the CaCO₃ core alters the porphyrin interaction in the PEC environment, and aggregate growth is no longer favored.

Reversible Vesicle-to-Disk Transitions of Liposomes Induced by the Self-Assembly of Water-Soluble Porphyrins

Structural control of lipid membranes is important for mechanisms underlying biological functions and for creating high-functionality soft materials. We demonstrate the reversible control of vesicle structures (liposomes) using supramolecular assemblies. Specifically, water-soluble anionic porphyrin molecules interact with positively charged lipid membrane surfaces to form one-dimensional self-assembled structures (J-aggregates) under acidic conditions. Cryogenic transmission electron microscopy revealed that porphyrin J-aggregates on the membrane surface induced an extensive structural change from vesicles to layered disks. Neutralization of the solution deformed the porphyrin J-aggregates, thereby reforming nanosized liposomes from the layered disks.

Experimental and computational characterization of photosensitized conformational effects mediated by protoporphyrin ligands on human serum albumin

Metal-free and Zn-chelated protoporphyrins were bound to human serum albumin. Their binding parameters and locations were characterized and the effect of their irradiation on the conformation of the protein was demonstrated.

Effects of Visible-Light Irradiation of Protoporphyrin IX on the Self-Assembly of Tubulin Heterodimers

The formation and the effects of laser irradiation of the complex formed by protoporphyrin IX (PPIX) and tubulin was investigated. We have used tubulin as a model protein to investigate whether docked photoactive ligands can affect the structure and function of polypeptides upon exposure to visible light. We observed that laser irradiation in the Soret band prompts bleaching of the PPIX, which is accompanied by a sharp decrease in the intensity and average fluorescence lifetime of the protein (dominated by the four tryptophan residues of the tubulin monomer). The kinetics indicate non-trivial effects and suggest that the photosensitization of the PPIX bound to tubulin prompts structural alterations of the protein. These modifications were also observed through changes in the energy transfer between Trp residues and PPIX. The results suggest that laser irradiation produces localized partial unfolding of tubulin and that the changes prompt modification of the formation of microtubules in vitro. Measurements of singlet oxygen formation were inconclusive in determining whether the changes are prompted by reactive oxygen species or other excited state mechanisms.

Biophysical characterization of the interaction of human albumin with an anionic porphyrin

The manuscript describes the characterization of the interaction between meso-tetrakis(p-sulfonatophenyl)porphyrin (TSPP) and human serum albumin (HSA). TSPP is a candidate for the photosensitization of structural and functional changes in proteins while HSA provides both an excellent protein model and binding and functional characteristics that could be explored in future applications of the approach. A combination of optical spectroscopic techniques (e.g., fluorescence spectroscopy, fluorescence lifetime, circular dichroism, etc.) and computational docking simulations were applied to better characterize the TSPP/HSA interaction. Recent advances have revealed that the complex formed by TSPP and HSA has become potentially relevant to biomedical applications, biomaterials research and protein photosensitized engineering. The study has determined a likely location of the binding site that places TSPP at a site that overlaps partially with the low affinity site of ibuprofen and places one of the SO3− groups of the ligand in proximity of the Trp214 residue in HSA. The characterization will enable future studies aimed at photosensitizing non-native functions of HSA for biomedical and biomaterial applications.

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A novel protocol involving extensive dialysis and centrifugation eliminated aggregated protoporphyrins from the solution.

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Reliable FRET between Trp214 and the porphyrin ligands was established.

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FRET and docking simulations converge to a model consistent with experimental X-ray data.

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Photosensitization mediated by the porphyrin ligands prompts localized conformational changes in HSA.

Combined use of optical spectroscopy and computational methods to study the binding and the photoinduced conformational modification of proteins when NMR and X-ray structural determinations are not an option

The functions of proteins depend on their interactions with various ligands and these interactions are controlled by the structure of the polypeptides. If one can manipulate the structure of proteins, their functions can in principle be modulated. The issue of protein structure-function relationship is not only a central problem in biophysics, but is becoming clear that the ability to "artificially" modify the structure of proteins could be relevant in fields beyond the biomedical area to provide, for instance, light responses in proteins which would not possess such properties in their native state. This chapter presents an overview of the combination of optical electronic and vibrational spectroscopy with various computational methods to investigate the binding between photoactive ligands and proteins.

Partial Unfolding of Tubulin Heterodimers Induced by Two-Photon Excitation of Bound meso-Tetrakis(sulfonatophenyl)porphyrin

The water-soluble porphyrin meso-tetrakis(p-sulfonatophenyl)porphyrin (TSPP) can be noncovalently bound to tubulin and used as a photosensitizer, which upon irradiation triggers photochemical reactions that lead to conformational changes of the protein. These conformational changes in turn inhibit tubulin's primary function of polymerizing into microtubules. We explored the possibility of using two-photon excitation of the bound porphyrin to induce photosensitized protein unfolding. Although TSPP has a relatively low cross section (∼30 GM) our results did find that two-photon excitation of the ligand causes partial unfolding of the tubulin host and the inhibition of the in vitro formation of microtubules. Conversely, irradiating tubulin alone caused no such effects despite the large irradiance per pulse (97-190 GW/cm(2)). The conformational changes were characterized using spectroscopic studies and provide a promising protocol for the future application of non-native photosensitization of proteins.

Ferrocenyl based pyrazoline derivatives with vanillic core: synthesis and investigation of their biological properties

Synthesis of four novel series of ferrocenyl based pyrazoline derivatives with vanillic core are described and microbiological, BSA and DNA binding studies conducted.

Resonance Raman and vibrational mode analysis used to predict ligand geometry for docking simulations of a water soluble porphyrin and tubulin

The ability to modify the conformation of a protein by controlled partial unfolding may have practical applications such as inhibiting its function or providing non-native photosensitive properties. A water-soluble porphyrin, meso-tetrakis (p-sulfonatophenyl) porphyrin (TSPP), non-covalently bound to tubulin can be used as a photosensitizer, which upon irradiation can lead to conformational changes of the protein. To fully understand the mechanism responsible for this partial unfolding and determine the amino acid residues and atoms involved, it is essential to find the most likely binding location and the configuration of the ligand and protein. Techniques typically used to analyze atomic position details, such as nuclear magnetic resonance and X-ray crystallography, require large concentrations, which are incompatible with the dilute conditions required in experiments for photoinduced mechanisms. Instead, we develop an atomistic description of the TSPP-tubulin complex using vibrational mode analysis from density functional theory calculations correlated to resonance Raman spectra of the porphyrin paired with docking simulations. Changes in the Raman peaks of the porphyrin molecule correlate with changes in its structural vibrational modes when bound to tubulin. The data allow us to construct the relative geometry of the porphyrin when bound to protein, which are then used with docking simulations to find the most likely configuration of the TSPP-tubulin complex.

Encapsulation of photoactive porphyrinoids in polyelectrolyte hollow microcapsules viewed by fluorescence lifetime imaging microscopy (FLIM)

Fluorescence Lifetime Imaging Microscopy (FLIM) was used to investigate the encapsulation of porphyrinoids in multilayer hollow microcapsules assembled layer by layer with poly(styrene sulfonate) (PSS) and poly(allylamine hydrochloride) (PAH).

Supramolecular intracellular delivery of an anionic porphyrin by octaarginine-conjugated per-O-methyl-β-cyclodextrin

A convenient and efficient method for intracellular delivery of a water-soluble anionic porphyrin has been developed by utilizing its supramolecular interaction with per-O-methyl-β-cyclodextrin bearing an octaarginine chain as a cell-penetrating peptide.

Protoporphyrins enhance oligomerization and enzymatic activity of HtrA1 serine protease

High temperature requirement protein A1 (HtrA1), a secreted serine protease of the HtrA family, is associated with a multitude of human diseases. However, the exact functions of HtrA1 in these diseases remain poorly understood. We seek to unravel the mechanisms of HtrA1 by elucidating its interactions with chemical or biological modulators. To this end, we screened a small molecule library of 500 bioactive compounds to identify those that alter the formation of extracellular HtrA1 complexes in the cell culture medium. An initial characterization of two novel hits from this screen showed that protoporphyrin IX (PPP-IX), a precursor in the heme biosynthetic pathway, and its metalloporphyrin (MPP) derivatives fostered the oligomerization of HtrA1 by binding to the protease domain. As a result of the interaction with MPPs, the proteolytic activity of HtrA1 against Fibulin-5, a specific HtrA1 substrate in age-related macular degeneration (AMD), was increased. This physical interaction could be abolished by the missense mutations of HtrA1 found in patients with cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL). Furthermore, knockdown of HtrA1 attenuated apoptosis induced by PPP-IX. These results suggest that PPP-IX, or its derivatives, and HtrA1 may function as co-factors whereby porphyrins enhance oligomerization and the protease activity of HtrA1, while active HtrA1 elevates the pro-apoptotic actions of porphyrin derivatives. Further analysis of this interplay may shed insights into the pathogenesis of diseases such as AMD, CARASIL and protoporphyria, as well as effective therapeutic development.

Comparative study of the structural and vibroelectronic properties of porphyrin and its derivatives

Density functional theory (DFT and time-dependent-DFT (TD-DFT) were employed to investigate the vibroelectronic structural properties of porphyrin and some derivatives: unsubstituted porphyrin (TPyr), meso-tetraphenylporphyrin (TPP), meso-tetrakis(p-sulfonatophenyl)porphyrin (TSPP), protonated-TPyr (H₂TPyr), deuterated-H₂TPyr (D₄TPyr), protonated-TPP (H₂TPP) and deuterated-H₂TPP (D₄TPP), protonated TSPP (H₂TSPP), deuterated-H₂TSPP (D₄TSPP), dicationic TSPP (H₆TSPP) and deuterated-H₆TSPP (D₈TSPP). The possible internal conversion (IC) and intersystem crossing (ISC) processes of these compounds were investigated. Finally, the relaxed ground state potential energy surface (PES) (S₀), and singlet (S_n, n = 1–24) and triplet (T_n) excited state PESs of the TSPP molecule were calculated as function of the dihedral angle (C_α-C_m-C_ϕ-C(ph)) rotation. The results of the calculations indicated that while the meso-substitutions caused a significant shift in frequencies when the meso-carbons within the parent-porphine (or TPyr) are involved in the vibrational motion of molecules; the protonation of the N atoms at the porphine/porphyrin core causes a significant blue shift when the H on the N atoms within the pyrroline are dominantly involved in the vibrational motions. The deuteration of N atoms not only caused a red-shift in the frequencies of the corresponding peaks below 1600 cm⁻¹, but also produced new vibrational modes of frequencies in the 2565–2595 cm⁻¹ range caused by the N-D bond stretching. Similarly, the deuteration of O atoms within the sulfonato groups (-SO₃⁻) exhibited a new peak at around 2642 cm⁻¹ due to O-D bond stretching. The measured Raman spectrum of the H₂TSPP is assigned based on the predicted Raman spectra of the compounds studied here and measured Raman spectrum of the TPP (from our previous work). The IR spectrum is assigned based on our calculations and measured IR spectra obtained from the literature. The results of the TD-DFT calculations did not only indicate that the meso-substitution and protonation of the porphyrin bring about a significant read shift in the electronic transitions; but also provided a strong evidence for the IC from the Soret band to Q-bands beside possibility of the ISC process; its existence depend on the other excited state process such as much faster vibrational relaxation; the IC and etc. The ground state PES curve (S₀) of the ionic TSPP exhibited two minima at the dihedral angle (C_α-C_m-C_ϕ-C) of about 66° (corresponds to the lowest ground state) and 110° (corresponds to next energetically stable state or the local minima). The energy deference between these two minima is 0.0132 eV (or 106 cm⁻¹) and the highest potential energy barrier when undergoing from the lowest ground state to this local state is only 0.0219 eV (177 cm⁻¹; which is compatible with the thermal energy (kT) at 298 K is 207.2 cm⁻¹.

Photoinduced partial unfolding of tubulin bound to meso-tetrakis(sulfonatophenyl) porphyrin leads to inhibition of microtubule formation in vitro

The irradiation of the complex formed by meso-tetrakis (sulfonatophenyl) porphyrin (TSPP) and tubulin was investigated as well as its effects on the structure and function of the protein. We have used tubulin as a model target to investigate whether photoactive ligands docked to the protein can affect the structure and function of the protein upon exposure to visible light. We observed that laser irradiation prompts bleaching of the porphyrin which is accompanied by a sharp decrease (∼2 ns) in the average fluorescence lifetime of the protein and a change in the dichroic spectrum consistent with a decrease of helical structure. The result indicated the photoinduced partial unfolding of tubulin. We also observed that such partial conformational change inhibits the formation of microtubules in vitro. We investigated whether photosensitization of reactive oxygen species was responsible for these effects. Even upon removal of O2 the protein still undergoes conformational changes indicating that irradiation of the bound porphyrin does not require the presence of O2 to prompt conformational and functional effects opening the possibility that other mechanisms (e.g., charge transfer) are responsible for the photoinduced mechanism.

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.

Development of (111)In-labeled porphyrins for SPECT imaging

OBJECTIVES

The aim of this research was the development of (111)In-labeled porphyrins as possible radiopharmaceuticals for the imaging of tumors.

METHODS

Ligands, 5, 10, 15, 20-tetrakis (3, 5-dihydroxyphenyl) porphyrin) (TDHPP), 5, 10, 15, 20-tetrakis (4-hydroxyphenyl) porphyrin (THPP) and 5, 10, 15, 20-tetrakis (3,4-dimethoxyphenyl) porphyrin) (TDMPP) were labeled with (111)InCl3 (produced from proton bombardment of natCd target) in 60 min at 80 ºC. Quality control of labeled compounds was performed via RTLC and HPLC followed by stability studies in final formulation and presence of human serum at 37 ºC for 48 h as well as partition coefficient determination. The biodistribution studies performed using tissue dissection and SPECT imaging up to 24h.

RESULTS

The complexes were prepared with more than 99% radiochemical purity (HPLC and RTLC) and high stability to 48 h. Partition coefficients (calculated as log P) for (111)In-TDHPP, (111)In-THPP and (111)In-TDMPP were 0.88, 0.8 and 1.63 respectively.

CONCLUSION

Due to urinary excretion with fast clearance for (111)In-TDMPP, this complex is probably a suitable candidate for considering as a possible tumor imaging agent.

Femto- to micro-second photobehavior of photosensitizer drug trapped within a cyclodextrin dimer

The interactions of 5,10,15,20-tetrakis(4-sulfonatophenyl)-porphyrin (TSPP, a singlet oxygen photosensitiser molecule) with a hexa-2,4-diynediyl bridged β-cyclodextrin dimer (CD-CD) in aqueous solutions of pH 7 were studied using steady-state UV-visible absorption/emission and femto- to millisecond time-resolved spectroscopy. TSPP forms 1 : 1 complexes with CD-CD (K(e) = 1.9 × 10(8) M(-1) at 293 K). The value of K(e) indicates a high affinity of TSPP to form complexes with CD-CD. The chemical nano-cavity has a notable effect on the fluorescence lifetimes of the Q(x) state (9.3 ns in water and 10.8 ns in CD-CD). The rotational times (410 ps for TSPP in water and 0.03 ns (12%) and 1.1 ns (88%) for the TSPP:CD-CD complexes) indicate the robustness of the formed entities, and fast depolarization of emission, most probably involving the porphyrin skeleton and phenyl ring motions. The ultrafast femtosecond component (60-100 fs) of TSPP is moderately affected by the confining environment, which instead strongly influences the ps component (1-2 ps in water and 5 ps within CD-CD) assigned to the vibrational relaxation of the Q(x) state. Moreover, a 50 ps component emerges in the emission transients in the 640-720 nm range, and which is assigned to a thermalization of the hot Q(x) state. The effect of O2 on the triplet state of the encapsulated TSPP was also studied and discussed in light of the shielding effect of the CD-CD cavity. We observed comparable quantum yield (0.62 and 0.69) of the generated singlet molecular oxygen of TSPP without and with CD-CD. We believe that our results on the molecular interaction between TSPP and CD-CD from femtosecond to millisecond regime at both ground and electronically first excited states give relevant information for improving our understanding of this kind of caged drugs, and thus for a better design of drug:nanocarrier complexes. A particular implication for the use of CD-CD as a drug carrier is the high affinity of this host for complex formation with TSPP, while the yield of singlet oxygen generation is still high.