The in vivo efficacy of phthalocyanine–nanoparticle conjugates for the photodynamic therapy of amelanotic melanoma

Oncologic photodynamic diagnosis and therapy: confocal Raman/fluorescence imaging of metal phthalocyanines in human breast cancer tissue in vitro

Raman microspectroscopy and confocal Raman imaging combined with confocal fluorescence were used to study the distribution and aggregation of aluminum tetrasulfonated phthalocyanine (AlPcS4) in noncancerous and cancerous breast tissues. The results demonstrate the ability of Raman spectroscopy to distinguish between noncancerous and cancerous human breast tissue and to identify differences in the distribution and aggregation of aluminum phthalocyanine, which is a potential photosensitizer in photodynamic therapy (PDT), photodynamic diagnosis (PDD) and photoimmunotherapy (PIT) of cancer. We have observed that the distribution of aluminum tetrasulfonated phthalocyanine confined in cancerous tissue is markedly different from that in noncancerous tissue. We have concluded that Raman imaging can be treated as a new and powerful technique useful in cancer photodynamic therapy, increasing our understanding of the mechanisms and efficiency of photosensitizers by better monitoring localization in cancer cells as well as the clinical assessment of the therapeutic effects of PDT and PIT.

Photodynamic therapy of melanoma using new, synthetic porphyrins and phthalocyanines as photosensitisers - a comparative study

Melanoma, a cancer that arises from melanocytes, is one of the most unresponsive cancers to known therapies and has a tendency to produce early metastases. Several studies showed encouraging results of the efficacy of photodynamic therapy (PDT) in melanoma, in different experimental settings in vitro and in vivo, as well as several clinical reports.

A new porphyrin for the preparation of functionalized water-soluble gold nanoparticles with low intrinsic toxicity

A potential new photosensitizer based on a dissymmetric porphyrin derivative bearing a thiol group was synthesized. 5-[4-(11-Mercaptoundecyloxy)-phenyl-10,15,20-triphenylporphyrin (PR-SH) was used to functionalize gold nanoparticles in order to obtain a potential drug delivery system. Water-soluble multifunctional gold nanoparticles GNP-PR/PEG were prepared using the Brust-Schiffrin methodology, by immobilization of both a thiolated polyethylene glycol (PEG) and the porphyrin thiol compound (PR-SH). The nanoparticles were fully characterized by transmission electron microscopy and (1)H nuclear magnetic resonance spectroscopy, UV/Vis absorption spectroscopy, and X-ray photoelectron spectroscopy. Furthermore, the ability of GNP-PR/PEGs to induce singlet oxygen production was analyzed to demonstrate the activity of the photosensitizer. Cytotoxicity experiments showed the nanoparticles are nontoxic. Finally, cellular uptake experiments demonstrated that the functionalized gold nanoparticles are internalized. Therefore, this colloid can be considered to be a novel nanosystem that could potentially be suitable as an intracellular drug delivery system of photosensitizers for photodynamic therapy.

Gold mining for PDT: Great expectations from tiny nanoparticles

Among many and various products, born by the modern nanotechnology, gold nanoparticles roused a special interest of biomedical researchers. Unique features of the nanoparticles allow to use them not only as effective transporters for therapeutic agents but also as basic components of nanocomposite preparations intended for targeted photodynamic and photothermal therapy of tumours. In the review, physical, chemical and biological properties of gold nanoparticles which can promote PDT efficiency of a designed nanocomposite, are briefly characterized, and promising trends in creation of gold-containing composite photosensitizers are analysed.

Synthesis, characterization and gas sensing properties of novel homo and hetero dinuclear ball-type phthalocyanines

A ball-type homodinuclear Co(ii)–Co(ii) phthalocyanine (2) and ball-type heterodinuclear Co(ii)–Fe(ii) phthalocyanine (3) were synthesized and their gas sensing properties were investigated.

Photophysical efficiency-boost of aqueous aluminium phthalocyanine by hybrid formation with nano-clays

Aluminium phthalocyanines, solubilized by nano-clay shuttles, retain high fluorescence efficiencies and singlet oxygen generation capabilities in aqueous ambience, qualifying them for photodynamic therapies.

Aptamer-functionalized gold nanoparticles as photoresponsive nanoplatform for co-drug delivery

Various platforms have been developed as innovative nanocarriers to deliver therapeutic agents to the diseased sites. Multifunctional surface modification allows an enhanced recognition and uptake of drug carriers by targeted cells. However, the development of drug resistance in some tumor cells plays a major role in the failure of chemotherapy. Drugs given in combination, called multidrug delivery approach, was designed to improve the therapeutic efficacy and has become an increasingly used strategy that is of great importance in clinical cancer treatments. In this study, aptamer-functionalized gold nanoparticles (Au NPs) have been used as a nanoplatform to codeliver two different anticancer drugs for improving the drug effectiveness. The surface of Au NPs (13 nm in diameter) was assembled with AS1411 aptamers, which tethered with 21-base pairs of (CGATCGA)3 sequence approached to the Au NPs. Both the photosensitizer 5,10,15,20-tetrakis(1-methylpyridinium-4-yl) porphyrin (TMPyP4) and the chemotherapeutic drug doxorubicin (Dox) were then physically attached to the AS1411-conjugated Au NPs (T/D:ds-NPs) and delivered to the target tumor cells such as HeLa and Dox-resistant MCF-7R cell lines. When exposed to a 632 nm light, reactive oxygen species induced by TMPyP4 molecules were generated inside the living cells, followed by cell damage. In addition, triggered release of the complementary drugs also occurred simultaneously during the photodynamic reaction. In the presence of Dox molecules, the toxicity toward the target cells was superior to individual drug treatment. Overall, a co-drug delivery platform was successfully established to improve the therapeutic efficacy in tumor cells. The improvement of the photodynamic-stimulated triggered release was enhanced, thus highly promising precise drug release in targeted drug delivery.

Perspectives on the application of nanotechnology in photodynamic therapy for the treatment of melanoma

Malignant melanoma is the most aggressive form of skin cancer and has been traditionally considered difficult to treat. The worldwide incidence of melanoma has been increasing faster than any other type of cancer. Early detection, surgery, and adjuvant therapy enable improved outcomes; nonetheless, the prognosis of metastatic melanoma remains poor. Several therapies have been investigated for the treatment of melanoma; however, current treatment options for patients with metastatic disease are limited and non-curative in the majority of cases. Photodynamic therapy (PDT) has been proposed as a promising minimally invasive therapeutic procedure that employs three essential elements to induce cell death: a photosensitizer, light of a specific wavelength, and molecular oxygen. However, classical PDT has shown some drawbacks that limit its clinical application. In view of this, the use of nanotechnology has been considered since it provides many tools that can be applied to PDT to circumvent these limitations and bring new perspectives for the application of this therapy for different types of diseases. On that ground, this review focuses on the potential use of developing nanotechnologies able to bring significant benefits for anticancer PDT, aiming to reach higher efficacy and safety for patients with malignant melanoma.

Anticancer efficacy of photodynamic therapy with hematoporphyrin-modified, doxorubicin-loaded nanoparticles in liver cancer

Photodynamic therapy (PDT) in combination with chemotherapy has great potential for cancer treatment. However, there have been very few attempts to developing cancer-targeted co-delivered systems of photosensitizers and anticancer drugs. We developed hematoporphyrin (HP)-modified doxorubicin (DOX)-loaded nanoparticles (HP-NPs) to improve the therapeutic effect of PDT in treating liver cancer. HP is not only a ligand for low density lipoprotein (LDL) receptors on the hepatoma cells but also a well-known photosensitizer for PDT. In vitro phototoxicity in HepG2 (human hepatocellular carcinoma) cells and in vivo anticancer efficacy in HepG2 tumor-bearing mice of free HP and HP-NPs were evaluated. The in vitro phototoxicity in HepG2 cells determined by MTT assay, annexin V-FITC staining and FACS analysis was enhanced in HP-NPs compared with free HP. Furthermore, compared with free HP-based PDT, in vivo anticancer efficacy in HepG2 tumor-bearing mice was markedly improved by HP-NPs-based PDT. Moreover, in both cases, the therapeutic effect was increased according to the irradiation time and number of PDT sessions. In conclusion, the HP-NPs prepared in this study represent a potentially effective co-delivery system of photosensitizer (HP) and anticancer drug (DOX) which improved the effects of PDT in liver cancer.

Pluronic-encapsulated natural chlorophyll nanocomposites for in vivo cancer imaging and photothermal/photodynamic therapies

A great challenge in developing nanotechnologies for cancer diagnosis and therapy has been the combined functionalities required for complicated clinical procedures. Among all requirements, toxicity has been the major hurdle that has prevented most of the nano-carriers from clinical use. Here, we extracted chlorophyll (Chl) from vegetable and encapsulated it into polymer (pluronic F68, Plu) micelles for cancer imaging and therapy. The results showed that the Chl-containing nanocomposites were capable of mouse tumor targeting, and the nanocomposite fluorescence within the tumor sites remained at high intensity more than two days after tail-vein injection. It is interesting that oral administration with the nanocomposites was also successful for tumor target imaging. Furthermore, the dietary Chl was found to be able to efficiently convert near-infrared laser irradiation to heat. The growths of melanoma cells and mouse tumors were effectively inhibited after being treated with the nanocomposites and irradiation. The suppression of the tumors was achieved by laser-triggered photothermal and photodynamic synergistic effects of Chl. As a natural substance from vegetable, Chl is non-toxic, making it an ideal nano-carrier for cancer diagnosis and treatment. Based on the results of this research, the Plu-Chl nanocomposites have shown promise for future clinical applications.

Drug delivery nanoparticles in skin cancers

Nanotechnology involves the engineering of functional systems at nanoscale, thus being attractive for disciplines ranging from materials science to biomedicine. One of the most active research areas of the nanotechnology is nanomedicine, which applies nanotechnology to highly specific medical interventions for prevention, diagnosis, and treatment of diseases, including cancer disease. Over the past two decades, the rapid developments in nanotechnology have allowed the incorporation of multiple therapeutic, sensing, and targeting agents into nanoparticles, for detection, prevention, and treatment of cancer diseases. Nanoparticles offer many advantages as drug carrier systems since they can improve the solubility of poorly water-soluble drugs, modify pharmacokinetics, increase drug half-life by reducing immunogenicity, improve bioavailability, and diminish drug metabolism. They can also enable a tunable release of therapeutic compounds and the simultaneous delivery of two or more drugs for combination therapy. In this review, we discuss the recent advances in the use of different types of nanoparticles for systemic and topical drug delivery in the treatment of skin cancer. In particular, the progress in the treatment with nanocarriers of basal cell carcinoma, squamous cell carcinoma, and melanoma has been reported.

Strategies for delivering porphyrinoid-based photosensitizers in therapeutic applications

Delivery strategies for porphyrinoid-based photosensitizers for use in therapeutic applications are based on a myriad of factors, which include porphyrinoid structure, solubility and cellular targets. These drug-delivery methods include encapsulation, hydrogels, protein carriers, nanoparticles and polymeric micelles among others. This article reviews the strategies for delivering porphyrinoids published to date and will focus on porphyrins, corroles, chlorins, bacteriochlorins, porphyrazines and phthalocyanines. Highlighted are the most recent and different strategies used for each of the corresponding porphyrinoid-based macrocycles.

Targeted in vivo photodynamic therapy with epidermal growth factor receptor-specific peptide linked nanoparticles

In targeted photodynamic therapy (tPDT), photosensitizers (PS) are targeted to disease tissue to reduce the dosage of PS and in addition to reduce the photo damage to the non-target tissue. We synthesized iron oxide nanoparticles (NP) armored with tumor targeting peptide and PS for targeted PDT. Chitosan covered Fe3O4 NPs (30 nm) were deposited with gold NPs to generate two distinct chemical surfaces. To the gold particles PS was attached with a lipoic acid linker. Human epidermal growth factor receptor (hEGFR)-specific peptide was also attached to the same particles via a nickel-nitrilotriacetic acid linker attached to the chitosan. Using these nanoparticles, peptide specific uptake and PDT mediated cell death of the SK-OV-3 cells (Her2(+) positive cells) were demonstrated by confocal microscopy, T2 imaging and viability assays. Peptide mediated preferential distribution of these NPs into tumor tissue was also shown in a xenograft tumor model. After one intravenous injection and one PDT dose, peptide bound NPs retarded tumor growth significantly compared to dark controls or treatments with NPs without peptide. The tumor retardation by targeted NPs was achieved at a PS concentration of 3.9 nmol/animal, whereas similar effect was seen with free PS at 220 nmol/animal. Therapeutic potential of these peptide containing NPs would be a useful in targeted PDT and in imaging the target tissue.

Nanoassembly of an amphiphilic cyclodextrin and Zn(ii)-phthalocyanine with the potential for photodynamic therapy of cancer

A photosensitising nanoassembly from non-ionic amphiphilic cyclodextrin and highly hydrophobic Zn-pthalocyanine with the capability to sustain the release of photosensitiser and showing photodynamic activity in cancer cells.

Synthesis of a novel water-soluble zinc phthalocyanine and its CT DNA-damaging studies

A novel 3-(4-methoxybenzylamino) propanoic acid substituted water-soluble zinc phthalocyanine (CNPcZn) was synthesized. The interaction between CNPcZn with calf thymus DNA (CT DNA) was studied using spectroscopic methods. The studies indicated that CNPcZn has strong affinity to CT DNA, and furthermore, CNZnPc showed excellent photodamaging activity to CT DNA. Above results indicated that such CNPcZn has great potential to be used as an effective photosensitizer in the field of photodynamic therapy.

Routes to some 3,6-disubstituted phthalonitriles and examples of phthalocyanines derived therefrom: An overview

The paper reviews a selection of synthetic pathways that provide access to 3,6-disubstituted phthalonitriles, precursors for the synthesis of 1,4,8,11,15,18,22,25-octasubstituted phthalocyanine derivatives. Early routes using Diels–Alder reactions for the synthesis of 3,6-dialkyl, 3,6-dialkoxymethyl, 3,6-dialkenyl and 3,6-diphenylphthalonitriles are appraised. However, the emphasis of the review focuses on the scope and applications of 2,3-dicyanohydroquinone as a starting material for obtaining 3,6-disubstituted phthalonitriles. The earliest example of the use of 2,3-dicyanohydroquinone concerned its O -alkylation to afford 3,6-dialkoxyphthalonitriles. These are immediate precursors to near-infrared absorbing phthalocyanine derivatives. Triflation of 2,3-dicyanohydroquinone extends the scope of the compound for phthalocyanine synthesis; the bis-triflate derivative is susceptible to S N Ar reactions and readily reacts with thiols to provide 3,6-bis(alkylsulfanyl) and 3,6-bis(arylsulfanyl)phthalonitriles. 3,6-Bis(phenylselenyl)phthalonitrile has also been obtained recently from the same precursor. Phthalocyanine derivatives obtained from them typically show a strongly bathochromically shifted Q-band absorption that is particularly sensitive to the central metal ion. The bis-triflate of 2,3-dicyanohydroquinone is also an ideal precursor for participation in cross-coupling reactions. Examples from the University of East Anglia group and elsewhere are presented which show the application of the nickel-catalyzed Negishi coupling reaction using alkylzinc halide derivatives. Yields of 3,6-dialkylphthalonitriles and 3,6-bis(substituted alkyl)phthalonitriles range from ca. 40 to 70%. Direct comparison for one example shows that the yield from the Negishi coupling method is higher than that using the Suzuki coupling protocol. Examples of the preparation of 3,6-diarylphthalonitriles from 2,3-dicyanohydroquinone bis-triflate using the Suzuki coupling reaction are reported with yields of the order of 65–70%. The review also includes a further application of 2,3-dicyanohydroquinone as a precursor to both monobromo and dibromo derivatives of 3,6-dibutoxyphthalonitrile. These compounds provide opportunities for cross-coupling at the brominated sites to provide more complex derivatives with the potential to serve as precursors of highly substituted phthalocyanine derivatives.

2,2,3,3-Tetrafluoropropoxy substituted oxo-titanium phthalocyanines axially ligated with common MALDI matrix materials

The synthesis of tetra and octa 2,2,3,3-tetrafluoropropoxy substituted oxo-titanium phthalocyanines (TiOPc) are reported. Using strongly chelating oxygen donor ligands, the reactions of TiOPc with catecholate (1a, 2a), 4-nitrocatecholate (1b, 2b) and caffeic acid (1c, 2c), ellagic acid (1d, 2d) and chlorogenic acid (1e, 2e) are described. The new compounds were characterized by mass, 1 H NMR, FT-IR, and UV-vis spectroscopic techniques as well as elemental analysis.

Applications of nanotechnology for melanoma treatment, diagnosis, and theranostics

Melanoma is the most aggressive type of skin cancer and has very high rates of mortality. An early stage melanoma can be surgically removed, with a survival rate of 99%. However, metastasized melanoma is difficult to cure. The 5-year survival rates for patients with metastasized melanoma are still below 20%. Metastasized melanoma is currently treated by chemotherapy, targeted therapy, immunotherapy and radiotherapy. The outcome of most of the current therapies is far from optimistic. Although melanoma patients with a mutation in the oncogene v-Raf murine sarcoma viral oncogene homolog B1 (BRAF) have an initially higher positive response rate to targeted therapy, the majority develop acquired drug resistance after 6 months of the therapy. To increase treatment efficacy, early diagnosis, more potent pharmacological agents, and more effective delivery systems are urgently needed. Nanotechnology has been extensively studied for melanoma treatment and diagnosis, to decrease drug resistance, increase therapeutic efficacy, and reduce side effects. In this review, we summarize the recent progress on the development of various nanoparticles for melanoma treatment and diagnosis. Several common nanoparticles, including liposome, polymersomes, dendrimers, carbon-based nanoparticles, and human albumin, have been used to deliver chemotherapeutic agents, and small interfering ribonucleic acids (siRNAs) against signaling molecules have also been tested for the treatment of melanoma. Indeed, several nanoparticle-delivered drugs have been approved by the US Food and Drug Administration and are currently in clinical trials. The application of nanoparticles could produce side effects, which will need to be reduced so that nanoparticle-delivered drugs can be safely applied in the clinical setting.

Unique diagnostic and therapeutic roles of porphyrins and phthalocyanines in photodynamic therapy, imaging and theranostics

Porphyrinic molecules have a unique theranostic role in disease therapy; they have been used to image, detect and treat different forms of diseased tissue including age-related macular degeneration and a number of different cancer types. Current focus is on the clinical imaging of tumour tissue; targeted delivery of photosensitisers and the potential of photosensitisers in multimodal biomedical theranostic nanoplatforms. The roles of porphyrinic molecules in imaging and pdt, along with research into improving their selective uptake in diseased tissue and their utility in theranostic applications are highlighted in this Review.

Shining light on nanotechnology to help repair and regeneration

Phototherapy can be used in two completely different but complementary therapeutic applications. While low level laser (or light) therapy (LLLT) uses red or near-infrared light alone to reduce inflammation, pain and stimulate tissue repair and regeneration, photodynamic therapy (PDT) uses the combination of light plus non-toxic dyes (called photosensitizers) to produce reactive oxygen species that can kill infectious microorganisms and cancer cells or destroy unwanted tissue (neo-vascularization in the choroid, atherosclerotic plaques in the arteries). The recent development of nanotechnology applied to medicine (nanomedicine) has opened a new front of advancement in the field of phototherapy and has provided hope for the development of nanoscale drug delivery platforms for effective killing of pathological cells and to promote repair and regeneration. Despite the well-known beneficial effects of phototherapy and nanomaterials in producing the killing of unwanted cells and promoting repair and regeneration, there are few reports that combine all three elements i.e. phototherapy, nanotechnology and, tissue repair and regeneration. However, these areas in all possible binary combinations have been addressed by many workers. The present review aims at highlighting the combined multi-model applications of phototherapy, nanotechnology and, reparative and regeneration medicine and outlines current strategies, future applications and limitations of nanoscale-assisted phototherapy for the management of cancers, microbial infections and other diseases, and to promote tissue repair and regeneration.

Distribution of phthalocyanines and Raman reporters in human cancerous and noncancerous breast tissue as studied by Raman imaging

There is a considerable interest in the developing new diagnostic techniques allowing noninvasive tracking of the progress of therapies used to treat a cancer. Raman imaging of distribution of phthalocyanine photosensitizers may open new possibilities of Photodynamic Therapy (PDT) to treat a wide range of neoplastic lesions with improved effectiveness of treatment through precise identification of malignant areas. We have employed Raman imaging and Raman spectroscopy to analyze human breast cancer tissue that interacts with photosensitizers used in the photodynamic therapy of cancer. PCA (Principal Component Analysis) has been employed to analyze various areas of the noncancerous and cancerous breast tissues. The results show that the emission spectra combined with the Raman images are very sensitive indicators to specify the aggregation state and the distribution of phthalocyanines in the cancerous and noncancerous breast tissues. Our results provide experimental evidence on the role of aggregation of phthalocyanines as a factor of particular significance in differentiation of the normal and tumourous (cancerous or benign pathology) breast tissues. We conclude that the Raman imaging reported here has a potential to be a novel and effective photodynamic therapeutic method with improved selectivity for the treatment of breast cancer.

Applications of nanotechnology in dermatology

What are nanoparticles and why are they important in dermatology? These questions are addressed by highlighting recent developments in the nanotechnology field that have increased the potential for intentional and unintentional nanoparticle skin exposure. The role of environmental factors in the interaction of nanoparticles with skin and the potential mechanisms by which nanoparticles may influence skin response to environmental factors are discussed. Trends emerging from recent literature suggest that the positive benefit of engineered nanoparticles for use in cosmetics and as tools for understanding skin biology and curing skin disease outweigh potential toxicity concerns. Discoveries reported in this journal are highlighted. This review begins with a general introduction to the field of nanotechnology and nanomedicine. This is followed by a discussion of the current state of understanding of nanoparticle skin penetration and their use in three therapeutic applications. Challenges that must be overcome to derive clinical benefit from the application of nanotechnology to skin are discussed last, providing perspective on the significant opportunity that exists for future studies in investigative dermatology.

Unmasking the chemistry and properties of non-peripherally octasubstituted phthalocyanines

The paper reviews the development of the chemistry, properties and applications of 1,4,8,11,15,18,22,25- (or non-peripheral) octasubstituted phthalocyanines that has been undertaken at the University of East Anglia over the last quarter of a century. The research has proved valuable for initiating and developing a number of areas of phthalocyanine science, not least because the compounds exhibit a number of properties seldom shared by Pc derivatives with other substitution patterns. In particular the compounds are obtained isomerically pure and the substituents' location at the non-peripheral sites as opposed to the peripheral positions ensures superior solubility and lower aggregation in most hydrophobic solvents. A further significant difference between isomeric non-peripheral (np)- and peripheral (p)-octasubstituted compounds is the effect of substituents on the energy of the Q-band, those at the former positions leading to more significant bathochromic shifts of this absorption band into the near infra-red. Examples of np-octasubstituted derivatives exhibit columnar mesophase behavior, a property shared by their p-octasubstituted counterparts. The favorable solubility of the np-octasubstituted compounds, including examples in which one of the four benzenoid rings bears different substituents from those on the other three (so called AAAB structures), in organic solvents facilitates their deposition as thin film formulations. A high degree of molecular organisation within Langmuir-Blodgett (LB) films of amphiphilic AAAB compounds has been investigated using various methods. Spin-coated films of certain AAAA and AAAB series of compounds have been shown to contain layer structuring and purpose designed AAAB compounds have been used in formation of self-assembled monolayers (SAMs). The use of LB and spin-coated films within electrical devices is described. Various applications of SAMs deposited on gold surfaces have been explored including gas sensing. Recent attention has focused on their use, when deposited onto gold nanoparticles, for applications in PDT, an approach complementing more conventional PDT studies. The principal challenge for obtaining the np-octasubstituted compounds is in preparing the precursor phthalonitriles. Though 3,6-dialkoxyphthalonitriles are readily prepared, early access to the 3,6-dialkylphthalonitriles was somewhat laborious. However, more convenient syntheses of the latter are now available through metal catalyzed cross-coupling reactions. Interesting contrasts in the reactivity of 3,6-dialkylphthalonitriles and 4,5-dialkylphthalonitriles have been uncovered. Thus reactions of the former with excess lithium in alcoholic solvents or with excess MeMgBr provide particularly ready access to examples of macrocycles that are hybrids of the Pc and tetrabenzoporphyrin structures. This level of reactivity is very different among the 4,5-dialkylphthalonitriles. Unexpectedly limited reactivity of np-octahexylsubstituted Si(OH)2Pc in condensation reactions has been exploited to provide a basis for the stepwise construction of m-oxo linked hetero-chromophore arrays. Finally, the unexpected construction of the novel EPR active Cd2Pc3 complexes from both np- and p-octaalkyl substituted CdPcs provided examples where both series behaved similarly – in contrast to behavior exhibited by alternatively substituted CdPcs investigated to date.