Evaluation of aluminum phthalocyanine chloride and DNA interactions for the design of an advanced drug delivery system in photodynamic therapy

Unraveling the intrinsic and photodynamic effects of aluminum chloride phthalocyanine on bioenergetics and oxidative state in rat liver mitochondria

Previous research has revealed that mitochondria are an important target for photodynamic therapy (PDT), which might be employed as a therapeutic approach for several malignancies, including hepatocellular carcinoma (HCC). In this study, we investigated both intrinsic toxicity and photodynamic effects of the photosensitizer (PS) aluminum chloride phthalocyanine (AlClPc) on mitochondrial functions. Several aspects of mitochondrial bioenergetics, structure, and oxidative state were investigated in the isolated mitochondria obtained from rat liver by differential centrifugation. Additionally, experiments were conducted to demonstrate the intrinsic and photodynamic effects of AlClPc on the viability of HepG2 cells. AlClPc interacted with mitochondria regardless of photostimulation; however, at the maximum utilized concentration (40 μM), photostimulation reduced its interaction with mitochondria. Although AlClPc hindered catalase (CAT) and glutathione reductase (GR) activities intrinsically, it had no discernable capacity to generate oxidative stress or impact bioenergetics in mitochondria without photostimulation, as one would anticipate from an ideal PS. When exposed to light, however, AlClPc had a substantially unfavorable influence on mitochondrial function, strengthening its intrinsic inhibitory action on CAT, producing oxidative stress, and jeopardizing mitochondrial bioenergetics. In terms of oxidative stress parameters, AlClPc induced lipid peroxidation and decreased the level of reduced glutathione (GSH) in mitochondria. Regarding bioenergetics, AlClPc promoted oxidative phosphorylation uncoupling and photodynamic inactivation of complex I, complex II, and the FoF1-ATP synthase complex, lowering mitochondrial ATP production. Lastly, AlClPc exhibited a concentration-dependent decrease in the viability of HepG2 cells, regardless of the presence or absence of photostimulation. While the harmful photodynamic effects of AlClPc on mitochondrial bioenergetics hold promise for treating HCC and other malignancies, the inherent toxic impacts on HepG2 cells underscore the need for caution in its application for this purpose.

Aluminium in dermatology - Inside story of an innocuous metal

Aluminium, the third most abundant element in the earth's crust, was long considered virtually innocuous to humans but has gained importance in the recent past. Aluminium is ubiquitous in the environment, with various sources of exposure like cosmetics, the food industry, occupational industries, the medical field, transport and electronics. Aluminium finds its utility in various aspects of dermatology as an effective haemostatic agent, anti-perspirant and astringent. Aluminium has a pivotal role to play in wound healing, calciphylaxis, photodynamic therapy and vaccine immunotherapy with diagnostic importance in Finn chamber patch testing and confocal microscopy. The metal also finds significance in cosmetic procedures like microdermabrasion and as an Nd:YAG laser component. It is important to explore the allergic properties of aluminium, as in contact dermatitis and vaccine granulomas. The controversial role of aluminium in breast cancer and breast cysts also needs to be evaluated by further studies.

Development of Liposomes Loaded with Chloroaluminum Phthalocyanine for Application of Photodynamic Therapy in Breast Cancer

Chloraluminium phthalocyanine (ClAlPc) has potential therapeutic effect for the treatment of cancer; however, the molecule is lipophilic and may present self-aggregation which limits its clinical success. Thus, nanocarriers like liposomes can improve ClAlPc solubility, reduce off-site toxicity and increase circulation time. For this purpose, developing suitable liposomes requires the evaluation of different lipid compositions. Herein, we aimed to develop liposomes containing soy phosphatidylcholine (SPC), 1,2-distearoyl-sn-glycero- 3-phosphoethanolamine-N-[amino(polyethylene glycol)-2000] (DSPEPEG2000), cholesterol and oleic acid loaded with ClAlPc using the surface response methodology and the Box-Behnken design. Liposomes with particle size from 110.93 to 374.97 nm and PdI from 0.265 to 0.468 were obtained. The optimized formulation resulted in 69.09 % of ClAlPc encapsulated, with particle size and polydispersity index, respectively, at 153.20 nm and 0.309, providing stability and aggregation control. Atomic force microscopy revealed vesicles in a spherical or almost spherical shape, while the analyzes by Differential Scanning Calorimetry (DSC), Powder X-ray Diffraction (PXRD), and Fourier transform infrared spectroscopy (FTIR) suggested that the drug was adequately incorporated into the lipid bilayer of liposomes, in its amorphous state or molecularly dispersed. In vitro studies conducted in breast cancer cells (4T1) showed that liposome improved phototoxicity compared to the ClAlPc solution. ClAlPc-loaded liposomes also enhanced the production of ROS 3-fold compared to the ClAlPc solution. Finally, confocal microscopy and flow cytometry demonstrated the ability of the liposomes to enter cells and deliver the fluorescent ClAlPc photosensitizer with dose and time-dependent effects. Thus, this work showed that Box-Behnken factorial design was an effective strategy for optimizing formulation development. The obtained ClAlPc liposomes can be applied for photodynamic therapy in breast cancer cells.

Synthesis, characterization, DNA interaction, molecular docking, and α-amylase and α-glucosidase inhibition studies of a water soluble Zn(II) phthalocyanine

In this study, 2(3),9(10),16(17),23(24)-tetrakis-[(N-methyl-(1-benzylpiperidin-4-yl)oxy)phthalocyaninato]zinc(II) iodide (ZnPc-2) was synthesized and characterized using spectral methods (FT-IR, 1H-NMR, UV-Vis and mass spectroscopy). The interaction of ZnPc-2 with DNA was investigated by using the UV/Vis titrimetric method, thermal denaturation profile, agarose gel electrophoresis and molecular docking studies. Additionally, the antidiabetic activity of ZnPc-2 was revealed spectroscopically by studying α-amylase and α-glucosidase inhibition activities. The spectroscopic results indicated that ZnPc-2 effectively binds to calf thymus-DNA (CT-DNA) with a Kb value of 7.5 × 104 M-1 and interacts with CT-DNA via noncovalent binding mode. Gel electrophoresis results also show that ZnPc-2 binds strongly to DNA molecules and exhibits effective nuclease activity even at low concentrations. Furthermore, docking studies suggest that ZnPc-2 exhibits a stronger binding tendency with DNA than the control compounds ethidium bromide and cisplatin. Consequently, due to its strong DNA binding and nuclease activity, ZnPc-2 may be suitable for antimicrobial and anticancer applications after further toxicological tests. Additionally, antidiabetic studies showed that ZnPc-2 had both α-amylase and α-glucosidase inhibition activity. Moreover, the α-glucosidase inhibitory effect of ZnPc-2 was approximately 3500 times higher than that of the standard inhibitor, acarbose. Considering these results, it can be said that ZnPc-2 is a moderate α-amylase and a highly effective α-glucosidase inhibitor. This suggests that ZnPc-2 may have the potential to be used as a therapeutic agent for the treatment of type 2 diabetes.

A review of DNA nanoparticles-encapsulated drug/gene/protein for advanced controlled drug release: Current status and future perspective over emerging therapy approaches

In the last ten years, the field of nanomedicine has experienced significant progress in creating novel drug delivery systems (DDSs). An effective strategy involves employing DNA nanoparticles (NPs) as carriers to encapsulate drugs, genes, or proteins, facilitating regulated drug release. This abstract examines the utilization of DNA NPs and their potential applications in strategies for controlled drug release. Researchers have utilized the distinctive characteristics of DNA molecules, including their ability to self-assemble and their compatibility with living organisms, to create NPs specifically for the purpose of delivering drugs. The DNA NPs possess numerous benefits compared to conventional drug carriers, such as exceptional stability, adjustable dimensions and structure, and convenient customization. Researchers have successfully achieved a highly efficient encapsulation of different therapeutic agents by carefully designing their structure and composition. This advancement enables precise and targeted delivery of drugs. The incorporation of drugs, genes, or proteins into DNA NPs provides notable advantages in terms of augmenting therapeutic effectiveness while reducing adverse effects. DNA NPs serve as a protective barrier for the enclosed payloads, preventing their degradation and extending their duration in the body. The protective effect is especially vital for delicate biologics, such as proteins or gene-based therapies that could otherwise be vulnerable to enzymatic degradation or quick elimination. Moreover, the surface of DNA NPs can be altered to facilitate specific targeting towards particular tissues or cells, thereby augmenting the accuracy of delivery. A significant benefit of DNA NPs is their capacity to regulate the kinetics of drug release. Through the manipulation of the DNA NPs structure, scientists can regulate the rate at which the enclosed cargo is released, enabling a prolonged and regulated dispensation of medication. This control is crucial for medications with limited therapeutic ranges or those necessitating uninterrupted administration to attain optimal therapeutic results. In addition, DNA NPs have the ability to react to external factors, including alterations in temperature, pH, or light, which can initiate the release of the payload at precise locations or moments. This feature enhances the precision of drug release control. The potential uses of DNA NPs in the controlled release of medicines are extensive. The NPs have the ability to transport various therapeutic substances, for example, drugs, peptides, NAs (NAs), and proteins. They exhibit potential for the therapeutic management of diverse ailments, including cancer, genetic disorders, and infectious diseases. In addition, DNA NPs can be employed for targeted drug delivery, traversing biological barriers, and surpassing the constraints of conventional drug administration methods.

Spectroscopic, calorimetric and cytotoxicity studies on the combined binding of daunorubicin and acridine orange to a DNA tetrahedron

Chemotherapy-phototherapy (CTPT) combination drugs co-loaded by targeted DNA nanostructures can achieve controlled drug delivery, reduce toxic side effects and overcome multidrug resistance. Herein, we constructed and characterized a DNA tetrahedral nanostructure (MUC1-TD) linked with the targeting aptamer MUC1. The interaction of daunorubicin (DAU)/acridine orange (AO) alone and in combination with MUC1-TD and the influence of the interaction on the cytotoxicity of the drugs were evaluated. Potassium ferrocyanide quenching analysis and DNA melting temperature assays were used to demonstrate the intercalative binding of DAU/AO to MUC1-TD. The interactions of DAU and/or AO with MUC1-TD were analyzed by fluorescence spectroscopy and differential scanning calorimetry. The number of binding sites, binding constant, entropy and enthalpy changes of the binding process were obtained. The binding strength and binding sites of DAU were higher than those of AO. The presence of AO in the ternary system weakened the binding of DAU to MUC1-TD. In vitro cytotoxicity studies demonstrated that the loading of MUC1-TD augmented the inhibitory effects of DAU and AO and the synergistic cytotoxic effects of DAU + AO on MCF-7 cells and MCF-7/ADR cells. Cell uptake studies showed that the loading of MUC1-TD was beneficial in promoting the apoptosis of MCF-7/ADR cells due to its enhanced targeting to the nucleus. This study has important guiding significance for the combined application of DAU and AO co-loaded by DNA nanostructures to overcome multidrug resistance.

The Management of Parkinson's Disease: An Overview of the Current Advancements in Drug Delivery Systems

Parkinson's disease (PD) has significantly affected a large proportion of the elderly population worldwide. According to the World Health Organization, approximately 8.5 million people worldwide are living with PD. In the United States, an estimated one million people are living with PD, with approximately 60,000 new cases diagnosed every year. Conventional therapies available for Parkinson's disease are associated with limitations such as the wearing-off effect, on-off period, episodes of motor freezing, and dyskinesia. In this review, a comprehensive overview of the latest advances in DDSs used to reduce the limitations of current therapies will be presented, and both their promising features and drawbacks will be discussed. We are also particularly interested in the technical properties, mechanism, and release patterns of incorporated drugs, as well as nanoscale delivery strategies to overcome the blood-brain barrier.

High-Affinity DNA Nanomatrix: A Platform Technology for Synergistic Drug Delivery and Photothermal Therapy

With the advent of nucleosome/nucleotide intercalating drugs, DNA-based nanocarriers have recently gained impetus. However, most of the newly proposed DNA nanosystems are rather complex, thereby having low scalability and translatability. In this study, we propose a simple DNA nanomatrix core encapsulated within a chitosan shell, which is expected to enhance the encapsulation efficiency of intercalating drugs. This has been demonstrated using proflavine hemisulfate (PfHS), a model intercalating agent that shows improved ROS generation, among other anticancerous properties. The release of the drug from the nanomatrix is triggered by providing a heat trigger using IR-792 perchlorate, a known NIR photothermal sensitizer.

Indocyanine green assembled free oxygen-nanobubbles towards enhanced near-infrared induced photodynamic therapy

Photodynamic therapy (PDT) has shown a promising capability for cancer treatment with minimal side effects. Indocyanine green (ICG), the only clinically approved near-infrared (NIR) fluorophore, has been used as a photosensitizer for PDT in clinical application. However, the main obstacle of directly utilizing ICG in the clinic lies in its low singlet oxygen (¹O₂) quantum yield (QY) and instability in aqueous solution. To improve the PDT efficacy of ICG, free ICG molecules were assembled with free oxygen nanobubbles (NBs-O₂) to fabricate ICG-NBs-O₂ by hydrophilic-hydrophobe interactions on the gas-liquid interface. Interestingly, ¹O₂ QY of ICG-NBs-O₂ solution was significantly increased to 1.6%, which was estimated to be 8 times as high as that of free ICG solution. Meanwhile, ICG-NBs-O₂ exhibited better aqueous solution stability compared with free ICG. Furthermore, through establishing tumor models in nude mice, the therapeutic efficacy of ICG-NBs-O₂ was also assessed in the PDT treatment of oral cancer. The tumor volume in ICG-NBs-O₂ treated group on day 14 decreased to 0.56 of the initial tumor size on day 1, while the tumor volume in free ICG treated group increased to 2.4 times. The results demonstrated that ICG-NBs-O₂ showed excellent tumor ablation in vivo. Therefore, this facile method provided an effective strategy for enhanced PDT treatment of ICG and showed great potential in clinical application.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material (measurements of the singlet oxygen quantum yield of ICG-NBs-O₂, time-dependent temperature changes during the laser irradiation, photographs of Cal27 tumor-bearing nude mice and complete blood count of health male balb/c mice analysis) is available in the online version of this article at 10.1007/s12274-022-4085-0.

DNA polymer films used as drug delivery systems to early-stage diagnose and treatment of breast cancer using 3D tumor spheroids as a model

The present study examines the designer of DNA polymeric films (DNA-PFs) associated with aluminum chloride phthalocyanine (AlClPc) (DNA-PFs-AlClPc), as a promising drug delivery system (DDS), applicable for breast cancer treatment and early-stage diagnosis using photodynamic therapy (PDT). This study starts evaluating (MCF7) as a model for breast cancer cell behavior associated with DNA-PFs. Analyses of the morphological behaviors, biochemical reaction, and MCF7 cell adhesion profile on DNA-PFs were evaluated. SEM and AFM analysis allowed the morphological characterization of the DNA-PFs. Cell viability and cell cycle kinetics studies indicate highly biocompatible material capable of anchoring MCF7 cells, allowing the attachment and support of cell in the same structure where the insertion of AlClPc (DNA-PFs-AlClPc). The application of visible light photoactivation based on classical PDT protocol over the DNA-PFs-AlClPc showed a reduction in cell viability with increased cell death proportional to the fluency energy range from 600, 900, and 1800 mJ cm^-2. The 3D organoid system mimics the tumor microenvironment which was precisely observed in human breast cancer in early-stage progression in the body. The results observed indicate that the viability was reduced by more than 80% in monolayer culture and around 50% in the 3D organoid cell culture at the highest energy fluency (1800 mJ cm^-2). We could also point out that with low energy fluency (100 mJ cm^-2,), the DNA-PFs-AlClPc did not show a cytotoxic effect on MCF7 cells, enabling this user dose for the photodiagnosis of early-stage human breast cancer detection in the initial stage of progression.

Dopamine-loaded nanoparticle systems circumvent the blood-brain barrier restoring motor function in mouse model for Parkinson's Disease

Parkinson's disease (PD) is a progressive and chronic neurodegenerative disease of the central nervous system. Early treatment for PD is efficient; however, long-term systemic medication commonly leads to deleterious side-effects. Strategies that enable more selective drug delivery to the brain using smaller dosages, while crossing the complex brain-blood barrier (BBB), are highly desirable to ensure treatment efficacy and decrease/avoid unwanted outcomes. Our goal was to design and test the neurotherapeutic potential of a forefront nanoparticle-based technology composed of albumin/PLGA nanosystems loaded with dopamine (ALNP-DA) in 6-OHDA PD mice model. ALNP-DA effectively crossed the BBB, replenishing dopamine at the nigrostriatal pathway, resulting in significant motor symptom improvement when compared to Lesioned and L-DOPA groups. Notably, ALNP-DA (20 mg/animal dose) additionally up-regulated and restored motor coordination, balance, and sensorimotor performance to non-lesioned (Sham) animal level. Overall, ALNPs represent an innovative, non-invasive nano-therapeutical strategy for PD, considering its efficacy to circumvent the BBB and ultimately deliver the drug of interest to the brain.

Tailoring the growth and proliferation of human dermal fibroblasts by DNA-based polymer films for skin regeneration

The use of DNA as a functional biomaterial for therapeutic, diagnostic, and drug delivery applications has been prominent in recent years, but its use as a scaffold for tissue regeneration is still limited. This study aimed to evaluate the biocompatibility and interaction of DNA-based polymeric films (DNA-PFs) with primary human fibroblasts (PHF) for regenerative medicine and wound healing purposes. The morphological characterization of the films was performed by scanning electron microscopy, SEM-energy-dispersive X-ray spectroscopy, and atomic force microscopy analysis. Cell viability, cell cycle kinetics, oxidative stress, and migration studies were carried out at 48 and 72 hr of incubation and compared to control cells. Cell adhesion was impaired in the first 24 hr, DNA-PFs with higher concentrations of DNA (1.0 and 2.0 g/L) this effect was not seen in DNA-PFs (0.5 g/L), explained by the difference in topography and roughness of DNA-PFs, but it was overcome after 48 hr of incubation. PHF seeded on DNA films showed higher proliferation and migration rates than the control after 48 hr of incubation, with the maintenance of cell morphology and lower cytotoxicity and oxidative stress during the evaluation time. Therefore, these results indicate that DNA-PFs are highly biocompatible and provide a suitable microenvironment for dermal fibroblasts to maintain their activity, helping build new and more complex biomaterials suitable for future tissue repair applications.

Thermoresponsive Hydrogel-Loading Aluminum Chloride Phthalocyanine as a Drug Release Platform for Topical Administration in Photodynamic Therapy

Phthalocyanine aluminum chloride (Pc) is a clinically viable photosensitizer (PS) to treat skin lesions worsened by microbial infections. However, this molecule presents a high self-aggregation tendency in the biological fluid, which is an in vivo direct administration obstacle. This study proposed the use of bioadhesive and thermoresponsive hydrogels comprising triblock-type Pluronic F127 and Carbopol 934P (FCarb) as drug delivery platforms of Pc (FCarbPc)-targeting topical administration. Carbopol 934P was used to increase the F127 hydrogel adhesion on the skin. Rheological analyses showed that the Pc presented a low effect on the hydrogel matrix, changing the gelation temperature from 27.2 ± 0.1 to 28.5 ± 0.9 °C once the Pc concentration increases from zero to 1 mmol L^-1. The dermatological platform showed matrix erosion effects with the release of loaded Pc micelles. The permeation studies showed the excellent potential of the FCarb platform, which allowed the partition of the PS into deeper layers of the skin. The applicability of this dermatological platform in photodynamic therapy was evaluated by the generation of reactive species which was demonstrated by chemical photodynamic efficiency assays. The low effect on cell viability and proliferation in the dark was demonstrated by in vitro assays using L929 fibroblasts. The FCarbPc fostered the inhibition of Staphylococcus aureus strain, therefore demonstrating the platform's potential in the treatment of dermatological infections of microbial nature.

Cholesterol-rich nanoemulsion (LDE) as a novel drug delivery system to diagnose, delineate, and treat human glioblastoma

We have prepared and characterized a cholesterol-rich nanoemulsion called LDE, a mimic of classic lipoprotein macromolecules, that can be applied as a new drug delivery system for aluminum phthalocyanine chloride (PcAlCl). The LDE containing PcAlCl system prepared herein had mean size and zeta potential of 127 nm and -29 mV, respectively, and encapsulation rate efficiency was 81%, and stability of 17 months. Compared to classical liposomes, LDE was more efficient, especially in brain diseases like glioblastoma (GBM), as revealed by tests on the U-87 MG cell line. The LDEPc formulation did not display dark cytotoxicity, as expected. The best light dose for LDEPc was 1.0 J·cm^-2: its activity was 55% higher than PcAlCl in a compatible organic medium. In the U-87 MG cells, apoptosis was the preferential pathway activated by PDT. These results strongly support the use of LDE as a new theranostic system.

Expanding the Limits of Photodynamic Therapy: The Design of Organelles and Hypoxia-Targeting Nanomaterials for Enhanced Photokilling of Cancer

Photodynamic therapy (PDT) is a minimally invasive clinical protocol that combines a nontoxic photosensitizer (PS), appropriate visible light, and molecular oxygen for cancer treatment. This triad generates reactive oxygen species (ROS) in situ, leading to different cell death pathways and limiting the arrival of nutrients by irreversible destruction of the tumor vascular system. Despite the number of formulations and applications available, the advancement of therapy is hindered by some characteristics such as the hypoxic condition of solid tumors and the limited energy density (light fluence) that reaches the target. As a result, the use of PDT as a definitive monotherapy for cancer is generally restricted to pretumor lesions or neoplastic tissue of approximately 1 cm in size. To expand this limitation, researchers have synthesized functional nanoparticles (NPs) capable of carrying classical photosensitizers with self-supplying oxygen as well as targeting specific organelles such as mitochondria and lysosomes. This has improved outcomes in vitro and in vivo. This review highlights the basis of PDT, many of the most commonly used strategies of functionalization of smart NPs, and their potential to break the current limits of the classical protocol of PDT against cancer. The application and future perspectives of the multifunctional nanoparticles in PDT are also discussed in some detail.

Conjugate of chitosan nanoparticles with chloroaluminium phthalocyanine: Synthesis, characterization and photoinactivation of Streptococcus mutans biofilm

BACKGROUND

Antimicrobial photodynamic therapy (aPDT) using chloroaluminium phthalocyanine (ClAlPc) has high oxidative power allowing for the control of biofilms, especially when the photosensitizer is administered in an appropriate release vehicle. This study aimed to develop/characterize the ClAlPc encapsulated in chitosan nanoparticles (CSNPs), and evaluate its antimicrobial properties against S. mutans biofilms.

METHODS

CSNPs were prepared by ion gelation, and characterization studies included particle size, polydispersion index (IPd), zeta potential, accelerated stability, absorption spectrum and ClAlPc quantification. The S. mutans biofilms were formed in bovine dentin blocks at 37 °C for 48 h under microaerophilic conditions. 8 μM ClAlPc was combined with a diode laser (InGaAlP) at 660 nm and 100 J/cm². The aPDT toxicity was verified by dark phototoxicity. The antimicrobial activity was verified by CFU/mL and biofilm was analyzed by scanning electron microscopy (SEM). The number of viable bacteria was analyzed by ANOVA and Tukey HSD tests (α = 0.05).

RESULTS

The characterization revealed that the ClAlPc nanoparticles were found in nanometer-scale with adequate photophysical and photochemical properties. The aPDT mediated by ClAlPc + CSNPs nanoconjugate showed a significant reduction in the viability of S. mutans (1log10 CFU/mL) compared to the negative control (PBS, p < 0.05). The aPDT mediated by ClAlPc was similar to PBS (p > 0.05). SEM revealed change in biofilm morphology following the treatment of bacteria with aPDT ClAlPc + CSNPs. Cells were arranged as single or in shorted chains. Irregular shapes of S. mutans were found.

CONCLUSION

ClAlPc nanoparticles are considered stable and aPDT mediated by ClAlPc + CSNPs nanoconjugate was effective against S. mutans biofilm.

A Schiff-base receptor based chromone derivate: Highly selective fluorescent and colorimetric probe for Al(III)

Upon excitation of the visible light, probes show colorimetric and fluorescent responses to the specific metal ion, which can be easily detected by the naked eye. Owing to the excitation of the visible light at 423 nm, a novel and simple Schiff-base receptor based chromone derivative called 7-methoxychromone-3-carbaldehyde-(indole-3-formyl) hydrazone (MCIH2) had been investigated as a selective and sensitive probe for Al³⁺ with colorimetric and fluorescent responses. Upon addition of Al³⁺ to compound MCIH2 solution, compound MCIH2 could respond to Al³⁺ with a good selective colorimetric signal, which was easily observed from colorless to yellow-green by the naked eye. Furthermore, a remarkable fluorescence emission enhancement with an "OFF-ON" signal by over 700-fold was triggered, but other various metal ions had no such significant effects on the fluorescence emission. In addition, the detection limit of compound MCIH2 for recognizing Al³⁺ was evaluated to be as low as 1 × 10^-7 M level, which was sufficiently low for sensing Al³⁺ widely distributed in various environmental and biological systems.

Theoretical and experimental studies concerning monomer/aggregates equilibrium of zinc phthalocyanine for future photodynamic action

Monomeric zinc phthalocyanine has been studied as a promising active photosensitizer in photodynamic therapy against cancer, in which its aggregate form is non-active. This paper aimed to describe the monomer/aggregates equilibrium of zinc phthalocyanine in binary water/DMSO mixtures. To reach this aim theoretical calculation, electronic absorption, static and time-resolved fluorescence, and resonance light scattering was used. Zinc phthalocyanine shows a complex water dependence behavior in the mixture. At least three distinct steps were observed: (i) until 30% water zinc phthalocyanine is essentially in the monomeric form, changing to (ii) small slipped cofacial-aggregates around 30% to 40% water and finally to (iii) a staircase arrangement of large aggregates at higher water percent. The staircase arrangement is driven by the intermolecular coordination between the pyrrolic nitrogen lone-pairs and the central metal zinc. The water-Zn coordination governs the fluorescence quenching by a static mechanism. These results have direct relevance in the better understanding on the behavior of zinc phthalocyanine in vivo and when incorporated in drug delivery systems for clinical applications in photodynamic therapy.