Search Results (118)

The design and the synthesis of molecule-based crystalline salts made up of simple cationic and/or anionic building blocks with multiple, occasionally stimulus-responsive, chemical (host–guest, catalytic, acid–base, or redox) and physical (optical, magnetic, or conducting) properties constitute two major goals in inorganic, organic, organometallic, and coordination chemistries. A deep knowledge of the basic features of molecular and supramolecular interactions that occur in the solid state is needed to progress along these tasks to obtain new advanced multifunctional materials. Inspired by the outstanding research of several groups on magnetic molecular salts from the mid-1970s to the present day, this review offers a personal portrayal of the history of molecular magnetism and molecular electronics and its current evolution toward molecular spintronics and quantum computing. We focus on the well-known families of molecular salts based on paramagnetic tetrathiafulvalenium/tetraselenafulvalenium or tetracyanoethenide/tetracyanoquinodimethanide organic radicals, cyclopentadienide/cyclooctatetraenide metallocenium complexes, and polyhalide/polycyanide, porphyrin/phthalocyanine, oxalate/dithiooxalate, or dithiolene/dithiolate metal complexes with first-, second-, or third-row transition metal (nd, n = 3–5) and lanthanide (4f) ions. This old but evergreen class of magnetic molecular salts provides illustrative “textbook” examples of advanced multifunctional materials such as molecular magnets and conductors, molecular magnetic conductors, molecular nanomagnets, and molecular quantum bits with potential nanotechnological applications in quantum information storage and processing. Full article

Copper is an indispensable trace element for maintaining metabolic homeostasis; however, the dysregulation and subsequent accumulation of Cu²⁺ are critically linked to neurodegenerative pathologies, including Alzheimer’s disease in humans. Consequently, the development of robust analytical tools for Cu²⁺ monitoring is of paramount importance. Here, we report a 2,2′-dipicolylamine porphyrin (DPAP)-based fluorescent sensor designed for the precise detection of metal cations. Photophysical investigations reveal that DPAP operates via a rapid turn-off fluorescence mechanism, achieving high-performance sensing in the parts-per-million range. Notably, the probe demonstrates exceptional sensitivity with detection limits of 26.3 nM for Cu²⁺ and 34.8 nM for Ni²⁺. Interference studies demonstrated the selectivity of DPAP for Cu²⁺ over a diverse range of competing metal ions such as Na⁺, Ag⁺, Ni²⁺, Cr³⁺, Pb²⁺, Al³⁺, Fe²⁺, Cd²⁺, and Zn²⁺. These results indicate that DPAP is a sensitive and selective probe suitable for copper ion detection. Full article

Tuberculosis, caused by Mycobacterium tuberculosis, remains a global health challenge, particularly due to multidrug-resistant strains. Photodynamic therapy using porphyrin-based photosensitizers offers a promising alternative by targeting the trehalose-rich cell wall of the bacillus. Motivated by prior experimental observations that shorter linkers improve efficacy, this study probes the molecular basis of linker-length-dependent activity in trehalose–porphyrin glycoconjugates. Here, we show that shorter linker lengths are consistent with improved activity in vitro and, in an Ag85B docking model, constrain conformational flexibility, reduce solvent exposure, and promote tighter packing consistent with stronger predicted interactions. Using computational docking, we analyzed binding scores, RMSD variability, steric clashes, and protein–ligand interactions for conjugates docked into Ag85B, a key enzyme in cell wall synthesis. Shorter linkers (0–2 carbons) were found to exhibit superior binding scores, lower RMSD variability, and stronger interactions with residues such as ARG 43, including unique π–cation interactions. In contrast, longer linkers displayed increased flexibility, reduced binding specificity, and greater solvent exposure. These findings, which support our experimental observations, suggest a molecular basis for linker-dependent efficacy and provide a framework for designing next-generation porphyrin-based therapeutics for tuberculosis treatment. Full article

The principal challenge in the development of efficient porphyrin-based photosensitizers is the intrinsic aggregation-induced quenching effect, which significantly impairs the generation efficiency of singlet oxygen (¹O₂) in photodynamic therapy (PDT). This study addresses this limitation through a supramolecular approach grounded in host-guest chemistry. Partially methyl-substituted cucurbit[6]uril (HMeQ[6]) was selected as the macrocyclic host owing to its smaller portal size and larger outer diameter, features that facilitate both strong binding affinity and effective spatial isolation. A porphyrin derivative functionalized with two cationic arms (DPPY) was designed and synthesized as the guest molecule. The results derived from ¹H NMR titration and UV spectroscopy analyses demonstrate that, in aqueous solution, these components self-assemble via host-guest interactions to form a 2:1 stoichiometric supramolecular complex (DPPY@HMeQ[6]) with a binding constant of 2.11 × 10⁵ M⁻¹. TEM, AFM, and DLS analyses indicate that this complex further assembles into nanosheet structures with dimensions of approximately 100 nm. Spectroscopic analyses reveal that encapsulation by HMeQ[6] effectively inhibits π-π stacking aggregation of DPPY molecules, resulting in an approximate threefold increase in fluorescence intensity and an extension of fluorescence lifetime from 3.2 ns to 6.2 ns. Relative to free DPPY, the complex demonstrates a sixfold enhancement in ¹O₂ generation efficiency. Subsequently, 4T1 cells, derived from mouse triple-negative breast tumors, were selected as the experimental model. These cells exhibit high invasiveness and metastatic potential, thereby effectively recapitulating the pathological progression of human triple-negative breast cancer. In vitro cellular assays indicate efficient internalization of the complex by 4T1 cells, inducing a concentration-dependent increase in reactive oxygen species (ROS) and oxidative stress following light irradiation. The in vitro cytotoxicity of the supramolecular photosensitizer was assessed employing the CCK-8 assay and flow cytometry techniques. The half-maximal inhibitory concentration (IC₅₀) against cancer cells is 1.8 μM, with apoptosis rates reaching up to 65.3%, while exhibiting minimal dark toxicity. This study expands the potential applications of methyl-substituted cucurbiturils within functional supramolecular assemblies and proposes a viable approach for the development of efficient and activatable supramolecular photosensitizers. Full article

The chirality transfer from chiral domains to achiral molecules is an important theoretical and applicative issue. In this work, we have investigated the interaction between two anionic chiral surfactants bearing a proline residue as hydrophilic head and the cationic, achiral porphyrin Zn(II) [5-{4-(3-trimethylammonium)propyloxyphenyl}-10,15,20-triphenylporphyrinyl]chloride to assess the effects of the structural variations in both units on the chirality transfer efficiency and amplification. We showed that the efficiency of transferring molecular information depends on the surfactant’s features, namely the chiral configuration of the polar head, the length of the aliphatic chain, and the aggregation state. At the same time, the presence of a coordinated metal and the peripheral charged group on the porphyrin macrocycle are key factors. In detail, the study of the hetero-aggregates formed at a surfactant concentration below the critical micellar concentration (cmc) indicates that the chirality depends on the synergy of hydrophobic effect, coordination interaction, and electrostatic forces. If the surfactant concentration is higher than the cmc, at a low concentration, porphyrins are included in micelles as monomers. Under these conditions, no chirality transfer is evident. When the porphyrin is in excess with respect to the micelles, an efficient asymmetry induction is again observed, transmitted from the chiral polar head to the porphyrin oligomers included in the micelle, through the polar heads and the hydrocarbon chains of the surfactants. Full article

Photodynamic inactivation (PDI) represents a promising strategy to overcome bacterial resistance by combining light, oxygen, and a photosensitizer (PS) to generate reactive oxygen species (ROS) that damage essential cellular components. Combining PDI with conventional antibiotics (ATBs) may further enhance bacterial eradication through complementary mechanisms. In this study, the tetracationic 5,10,15,20-tetra(4-N,N,N-trimethylammoniophenyl)porphyrin (TMAP⁴⁺) was evaluated in combination with ATBs: ampicillin (AMP) and rifampicin (RIF) against Staphylococcus aureus and cephalexin (CFX) against Escherichia coli. The photostability of all agents was assessed under the experimental irradiation conditions, and no evidence of physical interaction between TMAP⁴⁺ and the ATBs was detected. AMP and CFX remained photostable, while RIF exhibited only minimal photodegradation under white light, confirming its stability during PDI treatments. The antimicrobial assays revealed that irradiation significantly enhanced the bactericidal activity of TMAP⁴⁺. When combined with ATBs, photoactivated TMAP⁴⁺ led to a pronounced reduction in the minimum inhibitory concentration (MIC) values of AMP and RIF for S. aureus and of CFX for E. coli, indicating additive effects. Growth curve analyses corroborated these results, showing delayed bacterial growth and decreased maximal optical densities in the combined treatments compared to single agents. Overall, these findings demonstrate that the photodynamic process can potentiate the antimicrobial effect of conventional ATBs without compromising their stability, supporting the potential of PS–ATB combination therapies as a valuable approach to improve antibacterial efficacy and mitigate ATB resistance. Full article

A series of novel guanidino-aryl (GA) compounds containing phenanthrene, fluoranthene, fluorene, and naphthalene aromatic cores were synthesized to investigate their interactions with DNA, RNA, and G-quadruplex structures. Among the novel compounds, the phenanthrene-guanidino compound demonstrated the highest micromolar affinity for AT-DNA, possibly due to partial phenanthrene intercalation in addition to hydrogen bonding and electrostatic interactions of guanidine cation. All new guanidino-aryl GA compounds bind strongly to the Tel22 G-quadruplex structure with similar affinities regardless of aromatic core size. The 1:1 stoichiometric complex is stabilised by π-π stacking interactions with the top or bottom G-tetrad, together with strong electrostatic interactions of the guanidino cation. The guanidino-porphyrin PoGU displayed distinct binding stoichiometry, indicating possible sandwiching between two G-quadruplex structures. Within the GA compounds tested, guanidino-fluorene exhibited moderate antimetabolic activity against the HeLa cell line, without selectivity against the healthy cell line. Full article

Graphene quantum dots (GQDs) obtained by microwave-induced pyrolysis of glutamic acid and triethylenetetramine (trien) are fairly stable, emissive, water-soluble, and positively charged nano-systems able to interact with negatively charged meso-tetrakis(4-sulfonatophenyl) porphyrin (TPPS₄). The stoichiometric control during the preparation affords a supramolecular adduct, GQDs@TPPS₄, that exhibits a double fluorescence emission from both the GQDs and the TPPS₄ fluorophores. These supramolecular aggregates have an overall negative charge that is responsible for the condensation of cations in the nearby aqueous layer, and a three-fold acceleration of the metalation rates of Cu²⁺ ions has been observed with respect to the parent porphyrin. Addition of various metal ions leads to some changes in the UV/Vis spectra and has a different impact on the fluorescence emission of GQDs and TPPS₄. The quenching efficiency of the TPPS₄ emission follows the order Cu²⁺ > Hg²⁺ > Cd²⁺ > Pb²⁺ ~ Zn²⁺ ~ Co²⁺ ~ Ni²⁺ > Mn²⁺ ~ Cr³⁺ >> Mg²⁺ ~ Ca²⁺ ~ Ba²⁺, and it has been related to literature data and to the sitting-atop mechanism that large transition metal ions (e.g., Hg²⁺ and Cd²⁺) exhibit in their interaction with the macrocyclic nitrogen atoms of the porphyrin, inducing distortion and accelerating the insertion of smaller metal ions, such as Zn²⁺. For the most relevant metal ions, emission quenching of the porphyrin evidences a linear behavior in the micromolar range, with the emission of the GQDs being moderately affected through a filter effect. Deliberate pollution of the samples with Zn²⁺ reveals the ability of the GQDs@TPPS₄ adduct to detect sensitively Cu²⁺, Hg^2+, and Cd²⁺ ions. Full article

The treatment of trans-dihydroxo[5,10,15,20-tetrakis(3-pyridyl)porphyrinato]Sn(IV) or [Sn(OH)₂(TPyP)] with 1% nitric acid in a mixture of water and acetone resulted in the formation of an ionic complex 1 [Sn(OH)₂(TPy^HP)](NO₃)₄. Complex 1 was fully characterized by ¹H NMR spectroscopy, elemental analysis, UV-vis spectroscopy, powder X-ray diffraction, fluorescence spectroscopy, FT-IR spectroscopy, and single-crystal X-ray crystallography. X-ray crystallographic analysis confirmed that each peripheral pyridyl N atom is protonated to form tetra-cationic species {Sn(OH)₂(TPy^HP)}⁴⁺ stabilized by four NO₃⁻ counter anions. Intermolecular hydrogen bonding interaction between axial hydroxo ligands leads to the formation of a 1D porphyrin array. Nitrate anions also involve hydrogen bonding interactions with axial hydroxo ligands and the peripheral pyridinium groups. Full article

Porphyrins serve as photosensitizers (PS) in the realm of cancer photodynamic therapy (PDT). Upon excitation by laser light, porphyrins are capable of converting molecular oxygen into highly cytotoxic singlet oxygen (¹O₂). However, the rigid π-conjugated structure of porphyrins frequently results in the formation of aggregates in aqueous solutions, which leads to the self-quenching of the excited state. Cucurbit[n]urils exhibit the capacity to stably bind with porphyrins via host–guest interactions, effectively inhibiting their aggregation and potentially enhancing the therapeutic efficacy of PDT. In this study, water-soluble tetramethyl cucurbit[6]uril (TMeQ[6]) was selected as the host, while four propionic acid group-appended porphyrin cationic (TPPOR) was utilized as guests to construct a supramolecular photosensitizer (TPPOR-2TMeQ[6]) in a molar ratio of 2:1. Further experimental findings demonstrate that the presence of TMeQ[6] inhibits the aggregation of TPPOR through non-covalent interactions. This inhibition reduces the energy difference between the excited singlet and triplet states, thereby enhancing the conversion efficiency of ¹O₂. Moreover, TPPOR-2TMeQ[6] exhibits favorable biocompatibility and minimal dark toxicity against breast cancer cells (4T1). Upon intracellular excitation, the levels of reactive oxygen species (ROS) significantly increase, inducing oxidative stress in 4T1 cells and leading to apoptosis. Consequently, the findings of this study suggest that the enhanced photosensitization achieved through this supramolecular approach is likely to promote the anticancer therapeutic effects of PDT, thereby broadening the application prospects of porphyrins within PDT systems. Full article

The photodecomposition behavior of cationic porphyrin ZnTMAP⁴⁺ (zinc tetrakis-(N,N,N-trimethylanilinium-4-yl) porphyrin) in water and complexed with clay nanosheets was investigated by light irradiation to the Soret band of ZnTMAP⁴⁺. The decomposition of ZnTMAP⁴⁺ was observed by UV–visible absorption spectroscopy. While the decomposition quantum yield (ϕ_dec) was 3.4 × 10⁻⁴ in water, that was 9.4 × 10⁻⁷ on the exfoliated clay nanosheets. It was revealed that the photostability of ZnTMAP⁴⁺ was stabilized by the complex formation with clay. When ZnTMAP⁴⁺ was intercalated between the stacked clay nanosheets, ϕ_dec was further decreased to 4.9 × 10⁻⁷. The photostability increased by 361 times and 693 times for the exfoliated and stacked state, respectively. These results indicate that the flat clay surface has the potential to control intra- and intermolecular photochemical reactions. Full article

The synthesis of a new tetracationic porphyrin derivative is described. Contrary to the best known derivatives in the literature, which are derived from 5,10,15,20-tetrakis-4-pyridylporphyrin (TPyP), in this procedure we start from 5,10,15,20-tetrakis-(4-carboxymethoxyphenyl)porphyrin (TPPCOOMe), obtained by the condensation reaction between pyrrole and 4-formylbenzoate. The reaction is carried out in refluxed xylene, avoiding the use of halogenated solvents. The final product, 5,10,15,20-tetrakis-(4-(3-carbamoyl-pyridyl)-methylphenyl)porphyrin bromide (P15p), exhibits four cationic portions that make it soluble in water and suitable for G4 stabilization. The choice to synthesize a derivative of TPPCOOMe is based on the idea of having a possible stabilizer that, unlike those obtained from TPyP, shows the cationic moieties farther from the porphyrin core and thus closer to the phosphate groups present on the G4 loops. Full article

In this study, two distinct photocatalysts, namely tin(IV)porphyrin-sensitized titanium dioxide nanotubes (SnP-TNTs) and titanium dioxide nanofibers (TNFs), were synthesized and characterized using various spectroscopic techniques. SnP-TNTs were formed through the hydrothermal reaction of NaOH with TiO₂ (P-25) nanospheres in the presence of Sn(IV)porphyrin (SnP), resulting in a transformation into Sn(IV)porphyrin-imbedded nanotubes. In contrast, under similar reaction conditions but in the absence of SnP, TiO₂ (P-25) nanospheres evolved into nanofibers (TNFs). Comparative analysis revealed that SnP-TNTs exhibited a remarkable enhancement in the visible light photodegradation of model pollutants compared to SnP, TiO₂ (P-25), or TNFs. The superior photodegradation activity of SnP-TNTs was primarily attributed to synergistic effects between TiO₂ (P-25) and SnP, leading to altered conformational frameworks, increased surface area, enhanced thermo-chemical stability, unique morphology, and outstanding visible light photodegradation of cationic methylene blue dye (MB dye). With a rapid removal rate of 95% within 100 min (rate constant = 0.0277 min⁻¹), SnP-TNTs demonstrated excellent dye degradation capacity, high reusability, and low catalyst loading, positioning them as more efficient than conventional catalysts. This report introduces a novel direction for porphyrin-incorporated catalytic systems, holding significance for future applications in environmental remediation. Full article

Water-soluble metalloporphyrins, depending on the metal center, possess special spectral, coordination, and photochemical features. In nickel(II) porphyrins, the Ni(II) center can occur with low-spin or high-spin electronic configuration. In aqueous solution, the cationic nickel(II) complex (Ni(II)TMPyP⁴⁺, where H₂TMPyP⁴⁺ = 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin), exists in both forms in equilibrium. In this study, an equilibrium system involving the low-spin and high-spin forms of Ni(II)TMPyP⁴⁺ was investigated via application of irradiation, temperature change, and various potential axial ligands. Soret band excitation of this aqueous system, in the absence of additional axial ligands, resulted in a shift in the equilibrium toward the low-spin species due to the removal of axial solvent ligands. The kinetics and the thermodynamics of the processes were also studied via determination of the rate and equilibrium constants, as well as the ΔS, ΔH, and ΔG values. Temperature increase had a similar effect. The equilibrium of the spin isomers was also shifted by decreasing the solvent polarity (using n-propanol) as well as by the addition of a stronger coordinating axial ligand (such as ammonia). Since triethanolamine is an efficient electron donor in Ni(II)TMPyP⁴⁺-based photocatalytic systems, its interaction with this metalloporphyin was also studied. The results promote the development of efficient photocatalytic systems based on this complex. Full article