Bottom-Up Hierarchical Self-Assembly of Chiral Porphyrins through Coordination and Hydrogen Bonds

Film thickness dependence of nanoscale arrangement of a chiral electron donor in its blends with an achiral electron acceptor

The nanoscale chiral arrangement in a bicomponent organic material system comprising donor and acceptor small molecules is shown to depend on the thickness of a film that is responsive to chiral light in an optoelectronic device. In this bulk heterojunction, a previously unreported chiral bis(diketopyrrolopyrrole) derivative was combined with an achiral non-fullerene acceptor. The optical activity of the chiral compound is dramatically different in the pure material and the composite, showing how the electron acceptor influences the donor's arrangement compared with the pure molecule. Mueller matrix polarimetric imaging shows the authenticity of this effect and the homogeneity of short range chiral orientations between the molecules, as well as more heterogeneous short and longer range arrangements in the films observed in linear dichroic and birefringent effects. The two-dimensional circular dichroism (CD) maps and spectra show the uniformity of the short range supramolecular interactions both in spun-cast films on quartz and blade-coated films on photovoltaic device substrates, where evidence for the chiral arrangement is uniquely provided by the synchrotron CD measurements. The external quantum efficiency of the devices depends upon the handedness of the light used to excite them and the film thickness, that influences the supramolecular arrangement and organization in the film, and determines the selectivity for left or right circularly polarised light. The difference in external quantum efficiency of the photovoltaic devices between the two handedness' of light correlates with the apparent differential absorbance (g-factor) of the films.

Chiral Assembly of Perovskite Nanocrystals: Sensitive Discrimination of Amino Acid Enantiomers

Chirality is a widespread phenomenon in nature and in living organisms and plays an important role in living systems. The sensitive discrimination of chiral molecular enantiomers remains a challenge in the fields of chemistry and biology. Establishing a simple, fast, and efficient strategy to discriminate the spatial configuration of chiral molecular enantiomers is of great significance. Chiral perovskite nanocrystals (PNCs) have attracted much attention because of their excellent optical activity. However, it is a challenge to prepare perovskites with both chiral and fluorescence properties for chiral sensing. In this work, we synthesized two chiral fluorescent perovskite nanocrystal assembly (PNA) enantiomers by using l- or d-phenylalanine (Phe) as chiral ligands. PNA exhibited good fluorescence recognition for l- and d-proline (Pro). Homochiral interaction led to fluorescence enhancement, while heterochiral interaction led to fluorescence quenching, and there is a good linear relationship between the fluorescence changing rate and l- or d-Pro concentration. Mechanism studies show that homochiral interaction-induced fluorescence enhancement is attributed to the disassembly of chiral PNA, while no disassembly of chiral PNA was found in heterochiral interaction-induced fluorescence quenching, which is attributed to the substitution of Phe on the surface of chiral PNA by heterochiral Pro. This work suggests that chiral perovskite can be used for chiral fluorescence sensing; it will inspire the development of chiral nanomaterials and chiral optical sensors.

Water-soluble porphyrin photosensitizers containing electron-withdrawing and electron-donating groups for photodynamic therapy

Photodynamic therapy is used to treat a variety of cancers. In this paper, water-soluble porphyrin photosensitizers (H2P1[Formula: see text]H2P3) for photodynamic therapy were synthesized, containing three groups -CH3, -CN, and -CF3. Density functional theory is used to optimize the structure of H2P1-H2P3 and calculate the [Formula: see text]E value. The smaller the value of [Formula: see text]E, the more favorable the electron transfer and thus the higher activity of the porphyrin photosensitizers. Due to the electron-withdrawing groups of -CN and -CF3, H2P2 and H2P3 have lower [Formula: see text]E values, higher reactive oxygen species yields compared with H2P1. The H2P2 porphyrin photosensitizers showed positive photodynamic therapeutic activity against hepatocellular carcinoma cells (HepG2) and good compatibility with human umbilical vein endothelial cells (HUVECs) by cellular anticancer activity assay. The anti-cancer mechanism of PSs was explained by living and dead cell staining experiment and intracellular reactive oxygen species experiment. PSs produced reactive oxygen species (ROS) in cancer cells under light irradiation, which induced cancer cell apoptosis.

Helicity Modulation in NIR-Absorbing Porphyrin-Ryleneimides

Peripheral substitution of a π-extended porphyrin with bulky groups produces a curved chromophore with four helical stereogenic units. The curvature and stereochemistry of such porphyrins can be controlled by varying the substituents, coordinated metal ions, and apical ligands. In particular, when the achiral saddle-shaped free bases are treated with large metal ions, i.e., CdII or HgII , the resulting complexes convert to chiral propeller-like configurations. X-ray diffraction analyses show that apical coordination of a water molecule is sufficient to induce a notable bowl-like distortion of the cadmium complex, which however retains its chiral structure. For phenyl- and tolyl-substituted derivatives, the conversion is thermodynamically controlled, whereas complexes bearing bulky 4-(tert-butyl)phenyl groups transform into their chiral forms upon heating. In the latter case, the chiral Hg porphyrin was converted into the corresponding free base and other metal complexes without any loss of configurational purity, ultimately providing access to stable, enantiopure porphyrin propellers.

Supramolecular Chirality in Porphyrin Self-assembly Systems in Aqueous Solution

Abstract:

The self-assembly process appears as a powerful and attractive strategy for constructing complex supramolecules by the spontaneous organization of appropriate building blocks. In this scenario, water-soluble porphyrinoids lend themselves as ideal paradigms to disclose the self-assembly phenomenon by exploiting their well-known tendency to build aggregates in aqueous media via weak non-covalent forces. Nevertheless, the spontaneous organization of achiral porphyrins can result in a final chiral superstructure moving away from single-molecule behaviour to supramolecular chirality. Therefore, over the years numerous attempts have been implemented to investigate how a porphyrin aggregate, made up of achiral monomers, becomes not-symmetric and which processes govern the bias for a certain enantiomeric assembly rather than another. Thus, in this mini-review, we exclusively discuss the main strategies for designing and building chiral aggregates in water from achiral porphyrin monomers, with particular regard to their chiroptical features.

Dissymmetrical tails-regulated helical nanoarchitectonics of amphiphilic ornithines: nanotubes, bundles and twists

How dissymmetrical tails (i.e. tails of different lengths) in one lipid molecule exert an impact on the structure and properties of the resulting assembly is an intriguing issue in both biological and material senses. However, the underlying mechanism that engenders such phenomena is still obscure, which prompted us to unmask it by exploring the self-assembly behaviours of artificial building blocks comprising dissymmetrical tails. Here, a series of Fmoc-protected ornithine lipids with dissymmetrical alkyl tails was designed and the dissymmetry of the two tails was found to hierarchically tune the self-assembled nanostructures from nanotubes to bundles and nanotwists. With the Fmoc-headgroup employed as a chromophorous probe, it was revealed that the alkyl chain dissymmetry controlled the interacting modes of van der Waals interactions between alkyl tails, π-π stacking between Fmoc motifs and hydrogen bonding formed by the three amide bonds in lipid bilayers. The counterbalance between those noncovalent interactions was responsible for such remarkable tuning ability towards self-assembly and emissive behaviours of the lipids, including circularly polarized light emission. This work provides insight into dissymmetrical tails-regulated biological structures and functions of natural lipids, and also sets up a novel strategy of rationally modulating chiral and emissive properties of supramolecular materials, i.e., tunable CPL materials, by exploitation of the tail dissymmetry.

Thermotropic chirality enhancement of nanoparticles constructed from foldamer/bis(amino acid) complexes

Herein, chiral nanoparticles are constructed by mixing an artificial foldamer bearing aza-18-crown-6 pendants with l-homocystine perchlorate salt, showing a thermotropic chirality enhancement due to the binding mode changes in the heating process.

Rational Design of Chiral Nanohelices from Self-Assembly of Meso-tetrakis (4-Carboxyphenyl) Porphyrin-Amino Acid Conjugates

In this article, meso-tetrakis (4-carboxyphenyl) porphyrins modified with different amino acids were designed, synthesized, and researched. The chiral self-assembly behavior of these porphyrin-amino acid molecules can be precisely controlled by adjusting the pH, constituent amino acids, and temperature, thereby giving rise to chiral nanostructures with precisely tailored helical pitch and handedness. This research provides a certain reference for the design and preparation of chiral nanomaterials and has potential application prospects in chiral resolution and chiral catalysis.

Spectrophotometric Study of Bridging N-Donor Ligand-Induced Supramolecular Assembly of Conjugated Zn-Trisporphyrin with a Triphenylamine Core

This article studies the supramolecular assembly behavior of a Zn-trisporphyrin conjugate containing a triphenylamine core (1) with bridging N-donor ligands using the UV-vis spectrophotometric titration method at micromolar concentrations. Our results show that pyridine, a non-bridging ligand, formed a 3:1 open complex with 1. The corresponding binding constant was estimated to be (2.7 ± 0.15) × 1014 M-3. In contrast, bridging ligands, 4,4-bipyridine (BIPY) and 1,3-di(4-pyridyl)propane (DPYP), formed stable 3:2 double-decker complexes with 1 in solution, which collapsed to yield a 3:1 open complex when excess BIPY or DPYP was added. The binding constants for forming BIPY and DPYP double-decker complexes were estimated to be (9.26 ± 0.07) × 1027 M-4 and (3.62 ± 0.16) × 1027 M-4, respectively. The UV-vis titration profiles supported the conclusion that the degradation of the 3:2 double-decker 1∙BIPY complex is less favorable compared to that of 1∙DPYP. Consequently, the formation of the 3:1 1∙DPYP open complex proceeded more readily than that of 1∙BIPY.

Chiral Metal Nanoparticle Superlattices Enabled by Porphyrin-Based Supramolecular Structures

Herein, we show that chiral metal nanoparticle superlattices can be produced through coassembly of achiral metal nanoparticles and porphyrin-based organic molecules. This chirality transfer from molecules to nanoparticle superstructures across three orders of magnitude in length scale is enabled by the hetero chain-chain van der Waals interactions. As far as we know, these are the first chiral nanoparticle assemblies based on chirality transfer through weak van der Waals forces. The dimensionality of the nanoparticle superlattices (1D chiral chains, 2D chiral sheets (cones), and 3D chiral particles) can be controlled based on a same synthetic chiral porphyrin molecule. Metalation of these porphyrin molecules with zinc cations results in the switching of molecular packing from J-type to H-type, which thereby produces 1D chiral nanoparticle chains. Functionalization of these zinc porphyrins with oleylamine can induce the assembly of nanoparticles into 2D chiral nanoparticle sheets.

Investigation of the Amide Linkages on Cooperative Supramolecular Polymerization of Organoplatinum(II) Complexes

Cooperative supramolecular polymerization of π-conjugated compounds into one-dimensional nanostructures has received tremendous attentions in recent years. It is commonly achieved by incorporating amide linkages into the monomeric structures, which provide hydrogen bonds for intermolecular non-covalent complexation. Herein, the effect of amide linkages is elaborately studied, by comparing supramolecular polymerization behaviors of two structurally similar monomers with the same platinum(II) acetylide cores. As compared to the N-phenyl benzamide linkages, N-[(1S)-1-phenylethyl] benzamide linkages give rise to effective chirality transfer behaviors due to the closer distances between the chiral units and the platinum(II) acetylide core. They also provide stronger intermolecular hydrogen bonding strength, which consequently brings higher thermo-stability and enhanced gelation capability for the resulting supramolecular polymers. Supramolecular polymerization is further strengthened by varying the monomers from monotopic to ditopic structures. Hence, with the judicious modulation of structural parameters, the current study opens up new avenues for the rational design of supramolecular polymeric systems.

Self-Assembly of Discrete Porphyrin/Calix[4]tube Complexes Promoted by Potassium Ion Encapsulation

The pivotal role played by potassium ions in the noncovalent synthesis of discrete porphyrin-calixarene nanostructures has been examined. The flattened-cone conformation adopted by the two cavities of octa-cationic calix[4]tube C4T was found to prevent the formation of complexes with well-defined stoichiometry between this novel water-soluble calixarene and the tetra-anionic phenylsulfonate porphyrin CuTPPS. Conversely, preorganization of C4T into a C_4v-symmetrical scaffold, triggered by potassium ion encapsulation (C4T@K⁺), allowed us to carry out an efficient hierarchical self-assembly process leading to 2D and 3D nanostructures. The stepwise formation of discrete CuTPPS/C4T@K⁺ noncovalent assemblies, containing up to 33 molecular elements, was conveniently monitored by UV/vis spectroscopy by following the absorbance of the porphyrin Soret band.

Tunable Supramolecular Chirogenesis in the Self-Assembling of Amphiphilic Porphyrin Triggered by Chiral Amines

Supramolecular chirality is one of the most important issues in different branches of science and technology, as stereoselective molecular recognition, catalysis, and sensors. In this paper, we report on the self-assembly of amphiphilic porphyrin derivatives possessing a chiral information on the periphery of the macrocycle (i.e., D- or L-proline moieties), in the presence of chiral amines as co-solute, such as chiral benzylamine derivatives. The aggregation process, steered by hydrophobic effect, has been studied in aqueous solvent mixtures by combined spectroscopic and topographic techniques. The results obtained pointed out a dramatic effect of these ligands on the morphology and on the supramolecular chirality of the final self-assembled structures. Scanning electron microscopy topography, as well as fluorescence microscopy studies revealed the formation of rod-like structures of micrometric size, different from the fractal structures formerly observed when the self-assembly process is carried out in the absence of chiral amine co-solutes. On the other hand, comparative experiments with an achiral porphyrin analogue strongly suggested that the presence of the prolinate moiety is mandatory for the achievement of the observed highly organized suprastructures. The results obtained would be of importance for unraveling the intimate mechanisms operating in the selection of the homochirality, and for the preparation of sensitive materials for the detection of chiral analytes, with tunable stereoselectivity and morphology.

Porphyrins Through the Looking Glass: Spectroscopic and Mechanistic Insights in Supramolecular Chirogenesis of New Self-Assembled Porphyrin Derivatives

The solvent driven aggregation of porphyrin derivatives, covalently linked to a L- or D-prolinate enantiomer, results in the stereospecific formation of species featuring remarkable supramolecular chirality, as a consequence of reading and amplification of the stereochemical information stored in the proline-appended group. Spectroscopic, kinetic, and topographic SEM studies gave important information on the aggregation processes, and on the structures of the final chiral architectures. The results obtained may be the seeds for the construction of stereoselective sensors aiming at the detection, for example, of novel emergent pollutants from agrochemical, food, and pharmaceutical industry.

The Self-Aggregation of Porphyrins with Multiple Chiral Centers in Organic/Aqueous Media: The Case of Sugar- and Steroid-Porphyrin Conjugates

An overview of the solvent-driven aggregation of a series of chiral porphyrin derivatives studied by optical methods (UV/Vis, fluorescence, CD and RLS spectroscopies) is herein reported. The investigated porphyrins are characterized by the presence in the meso-positions of glycol-, steroidal- and glucosteroidal moieties, conferring amphiphilicity and solubility in aqueous media to the primarily hydrophobic porphyrin platform. Aggregation of the macrocycles is driven by a change in bulk solvent composition, forming architectures with supramolecular chirality, steered by the stereogenic centers on the porphyrin peripheral positions. The aggregation behavior and chiroptical properties of the final aggregated species strongly depend on the number and stereogenicity of the ancillary groups that dictate the mutual spatial arrangement of the porphyrin chromophores and their further organization in larger structures, usually detectable by different microscopies, such as AFM and SEM. Kinetic studies are fundamental to understand the aggregation mechanism, which is frequently found to be dependent on the substrate concentration. Additionally, Molecular Mechanics calculations can give insights into the intimate nature of the driving forces governing the self-assembly process. The critical use of these combined methods can shed light on the overall self-assembly process of chirally-functionalized macrocycles, with important implications on the development of chiral porphyrin-based materials.

Morphology control in metallosupramolecular assemblies through solvent-induced steric demand

Controlling the supramolecular self-assembly of π-conjugated systems into defined morphologies is a prerequisite for the preparation of functional materials. In recent years, the development of sophisticated sample preparation protocols and modulation of various experimental conditions (solvent, concentration, temperature, etc.) have enabled precise control over aggregation pathways of different types of monomer units. A common method to achieve pathway control consists in the combination of two miscible solvents in defined proportions - a "poor" and "good" solvent. However, the role of solvents of opposed polarity in the self-assembly of a given building block still remains an open question. Herein, we unravel the effect of aggregation-inducing solvent systems of opposed polarity (aqueous vs. non-polar media) on the supramolecular assembly of a new bolaamphiphilic Pt(ii) complex. A number of experimental methods show a comparable molecular packing in both media driven by a synergy of solvophobic, aromatic and weak hydrogen-bonding interactions. However, morphological analysis of the respective aggregates in aqueous and non-polar media reveals a restricted aggregate growth in aqueous media into spherical nanoparticles and a non-restricted 2D-nanosheet formation in non-polar media. These findings are attributed to a considerably more efficient solvation and, in turn, increased steric demand of the hydrophilic chains in aqueous media than in nonpolar media, which can be explained by the entrapment of water molecules in the hydrophilic aggregate shell via hydrogen bonds. Our findings reveal that the different solvation of peripheral solubilizing groups in solvents of opposed polarity is an efficient method for morphology control in self-assembly.

Pre-Polymerization Enables Controllable Synthesis of Nanosheet-Based Porphyrin Polymers towards High-Performance Li-Ion Batteries

The precise regulation of nucleation growth and assembly of polymers is still an intriguing goal but an enormous challenge. In this study, we proposed a pre-polymerization strategy to regulate the assembly and growth of polymers by facilely controlling the concentration of polymerization initiator, and thus obtained two kinds of different nanosheet-based porphyrin polymer materials using tetrakis-5,10,15,20-(4-aminophenyl) porphyrin (TAPP) as the precursor. Notably, due to the π-π stacking and doping of TAPP during the preparation process, the obtained PTAPP-nanocube material exhibits a high intrinsic bulk conductivity reaching 1.49×10^-4  S m^-1 . Profiting from the large π-conjugated structure of porphyrin units, closely stacked layer structure and excellent conductivity, the resultant porphyrin polymers, as electrode materials for lithium ion batteries, deliver high specific capacity (≈650 mAh g^-1 at the current density of 100 mA g^-1 ), excellent rate performance and long-cycle stability, which are among the best reports of porphyrin polymer-based electrode materials for lithium-ion batteries, to the best of our knowledge. Therefore, such a pre-polymerization approach would provide a new insight for the controllable synthesis of polymers towards custom-made architecture and function.

Controlling J-Aggregates Formation and Chirality Induction through Demetallation of a Zinc(II) Water Soluble Porphyrin

Under acidic conditions and at high ionic strength, the zinc cation is removed from its metal complex with 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS₄) thus leading to the diacid free porphyrin, that subsequently self-organize into J-aggregates. The kinetics of the demetallation step and the successive supramolecular assembly formation have been investigated as a function of pH and ionic strength (controlled by adding ZnSO₄). The demetallation kinetics obey to a rate law that is first order in [ZnTPPS₄] and second order in [H⁺], according to literature, with k₂ = 5.5 ± 0.4 M⁻² s⁻¹ at 298 K (IS = 0.6 M, ZnSO₄). The aggregation process has been modeled according to an autocatalytic growth, where after the formation of a starting seed containing m porphyrin units, the rate evolves as a power of time. A complete analysis of the extinction time traces at various wavelengths allows extraction of the relevant kinetic parameters, showing that a trimer or tetramer should be involved in the rate-determining step of the aggregation. The extinction spectra of the J-aggregates evidence quite broad bands, suggesting an electronic coupling mechanism different to the usual Frenkel exciton coupling. Resonance light scattering intensity in the aggregated samples increases with increasing both [H⁺] and [ZnSO₄]. Symmetry breaking occurs in these samples and the J-aggregates show circular dichroism spectra with unusual bands. The asymmetry g-factor decreases in its absolute value with increasing the catalytic rate k_c, nulling and eventually switching the Cotton effect from negative to positive. Some inferences on the role exerted by zinc cations on the kinetics and structural features of these nanostructures have been discussed.

Long-Range Chiral Induction by a Fully Noncovalent Approach in Supramolecular Porphyrin-Calixarene Assemblies

The hierarchical assembly, in aqueous solution, of a new multi-metalloporphyrin/calixarene aggregate has been accomplished. In this supramolecular system transfer of chirality, from the outermost components to the central porphyrin reporter, takes place as a result of favorable and fully noncovalent long-range electronic communication.

Supramolecular block copolymers incorporating chiral and achiral chromophores for the bottom-up assembly of nanomaterials

The coordination of the chiral metalloporphyrin ([5,10,15,20-[4-([Formula: see text]-2-[Formula: see text]-octadecylamidoethyloxiphenyl]porphyrin] zinc (II)) and an achiral homologue to an amphiphilic block copolymer of poly(styrene-[Formula: see text]-4-vinyl pyridine) (PS-[Formula: see text]-P4VP) have been studied in solution and as cast material. The resulting chiral dye-polymer hybrid material has been accomplished via axial coordination between the zinc (II) metal ion in the core of the porphyrin ring and the pyridyl units of the block-copolymer in a non-coordinative solvent. The supramolecular organization and possible chirality transfer to the hybrid material have been studied in solution by UV-visible absorption spectroscopy, fluorescence spectroscopy, Nuclear Magnetic Resonance and Circular Dichroism. The morphology of the chiral and achiral doped polymers has been studied in solid state by Transmission Electron Microscopy and Atomic Force Microscopy. We show that the nanostructures formed depend greatly upon the nature of the side-chains on the porphyrins, where a chiral group leads to a very homogeneous phase-separated material, perhaps indicating that chiral side groups are useful for the preparation of this type of supramolecular hybrid.

Covalently Linked Bis(Amido-Corroles): Inter- and Intramolecular Hydrogen-Bond-Driven Supramolecular Assembly

Four bis-corroles linked by diamide bridges were synthesized through peptide-type coupling of a trans-A₂ B-corrole acid with aliphatic and aromatic diamines. In the solid state, the hydrogen-bond pattern in these bis-corroles is strongly affected by the type of solvent used in the crystallization process. Although intramolecular hydrogen bonds play a decisive role, they are supported by intermolecular hydrogen bonds and weak N-H⋅⋅⋅π interactions between molecules of toluene and the corrole cores. In an analogy to mono(amido-corroles), both in crystalline state and in solutions, the aliphatic or aromatic bridge is located directly above the corrole ring. When either ethylenediamine or 2,3-diaminonaphthalene are used as linkers, incorporation of polar solvents into the crystalline lattice causes a roughly parallel orientation of the corrole rings. At the same time, both NHCO⋅⋅⋅NH corrole hydrogen bonds are intramolecular. In contrast, solvation in toluene causes a distortion with one of the hydrogen bonds being intermolecular. Interestingly, intramolecular hydrogen bonds are always formed between the -NHCO- functionality located further from the benzene ring present at the position 10-meso. In solution, the hydrogen-bonds pattern of the bis(amido-corroles) is strongly affected by the type of the solvent. Compared with toluene (strongly high-field shifted signals), DMSO and pyridine disrupt self-assembly, whereas hexafluoroisopropanol strengthens intramolecular hydrogen bonds.

Large Synthetic Molecule that either Folds or Aggregates through Weak Supramolecular Interactions Determined by Solvent

Weak noncovalent interactions between large disclike molecules in poorly solvating media generally lead to the formation of fibers where the molecules stack atop one another. Here, we show that a particular chiral spacing group between large aromatic moieties, which usually lead to columnar stacks, in this case gives rise to an intramolecularly folded structure in relatively polar solvents, but in very apolar solvents forms finite aggregates. The molecule that displays this behavior has a C 3 symmetric benzene-1,3,5-tris(3,3'-diamido-2,2'-bipyridine) (BTAB) core with three metalloporphyrin units appended to it through short chiral spacers. Quite well-defined chromophore arrangements are evident by circular dichroism (CD) spectroscopy of this compound in solution, where clear exciton coupled bands of porphyrins are observed. In more polar solvents where the molecules are dispersed, a relatively weak CD signal is observed as a result of intramolecular folding, a feature confirmed by molecular modeling. The intramolecular folding was confirmed by measuring the CD of a C 2 symmetric analogue. The C 3 symmetric BTAB cores that would normally be expected to stack in a chiral arrangement in apolar solvents show no indication of CD, suggesting that there is no transfer of chirality through it (although the expected planar conformation of the 2,2'-bipyridine unit is confirmed by NMR spectroscopy). The incorporation of the porphyrins on the 3,3'-diamino-2,2'-bipyridine moiety spaced by a chiral unit leaves the latter incapable of assembling through supramolecular π-π stacking. Rather, modeling indicates that the three metalloporphyrin units interact, thanks to van der Waals interactions, favoring their close interactions over that of the BTAB units. Atomic force microscopy shows that, in contrast to other examples of molecules with the same core, disclike aggregates (rather than fibrillar one dimensional aggregates) are favored by the C 3 symmetric molecule. The closed structures are formed through nondirectional interlocking of porphyrin rings. The chiral spacer between the rigid core and the porphyrin moieties is undoubtedly important in determining the outcome in polar or less polar solvents, as modeling shows that this joint in the molecule has two favored conformations that render the molecule relatively flat or convex.

Chiral Selectivity of Porphyrin-ZnO Nanoparticle Conjugates

Recognition of enantiomers is one of the most arduous challenges in chemical sensor development. Although several chiral systems exist, their effective exploitation as the sensitive layer in chemical sensors is hampered by several practical implications that hinder stereoselective recognition in solid state. In this paper, we report a new methodology to efficiently prepare chiral solid films, by using a hybrid material approach where chiral porphyrin derivatives are grafted onto zinc oxide nanoparticles. Circular dichroism (CD) evidences that the solid-state film of the material retains supramolecular chirality due to porphyrin interactions, besides an additional CD feature in correspondence of the absorbance of ZnO (375 nm), suggesting the induction of chirality in the underlying zinc oxide nanoparticles. The capability of hybrid material to detect and recognize vapors of enantiomer pairs was evaluated by fabricating gas sensors based on quartz microbalances. Chiral films of porphyrin on its own were used for comparison. The sensor based on functionalized nanostructures presented a remarkable stereoselectivity in the recognition of limonene enantiomers, whose ability to intercalate in the porphyrin layers makes this terpene an optimal chiral probe. The chiroptical and stereoselective properties of the hybrid material confirm that the use of porphyrin-capped ZnO nanostructures is a viable route for the formation of chiral selective surfaces.

Kinetic and spectroscopic studies on the chiral self-aggregation of amphiphilic zinc and copper (l)-prolinate-tetraarylporphyrin derivatives in different aqueous media

The chiral self-aggregation of (l)-proline porphyrin derivatives depends on both the nature of the media and the coordinated metal ion.

Self-assembly of porphyrin hexamers via bidentate metal-ligand coordination

The supramolecular assembly of metal-porphyrin hexamers with bidentate ligands in chloroform solutions is demonstrated by UV/Vis and 1H NMR-titrations, and Small Angle Neutron Scattering (SANS) experiments. Titrations of zinc porphyrin hexamer Zn1 with 1,4-diazabicyclo[2,2,2]octane (DABCO) revealed that at a DABCO/Zn1 molar ratio of 3, intermolecular sandwich complexes are formed, which can be considered as "circular-shaped porphyrin ladders". These supramolecular complexes further aggregate into larger polymeric stacks, as a result of a combination of cooperativity effects, π-π stacking interactions, and chelate effects. The presence of rodlike assemblies in solution, formed by assembly of Zn1 and DABCO, is confirmed by SANS-experiments. Using a model for cylindrical assemblies, curve fitting calculations reveal that rods with an average length of 26 nm and a radius of 30-35 Å were formed, corresponding to columnar stacks of approximately 30 hexamer molecules. In contrast, the metal-free hexamer H21 did not form extended assemblies due to the absence of coordinative intermolecular interactions.

Boosting Self-Assembly Diversity in the Solid-State by Chiral/Non-Chiral ZnII -Porphyrin Crystallization

A chiral Zn^II porphyrin derivative 1 and its achiral analogue 2 were studied in the solid state. Considering the rich molecular recognition of designed metalloporphyrins 1 and 2 and their tendency to crystallize, they were recrystallized from two solvent mixtures (CH₂ Cl₂ /CH₃ OH and CH₂ Cl₂ /hexane). As a result, four different crystalline arrangements (1 a,b and 2 a,b, from 0D to 2D) were obtained. Solid-state studies were performed on all the species to analyze the role played by chirality, solvent mixtures, and surfaces (mica and HOPG) in the supramolecular arrangements. By means of combinations of solvents and substrates a variety of microsized species was obtained, from vesicles to flower-shaped arrays, including geometrical microcrystals. Overall, the results emphasize the environmental susceptibility of metalloporphyrins and how this feature must be taken into account in their design.

Chirality Enhancement of Porphyrin Supramolecular Assembly Driven by a Template Preorganization Effect

Cationic polylysine promotes, under neutral conditions, the spontaneous aggregation of opposite charged ZnTPPS in water. Spectroscopic investigations evidence a different preorganization of ZnTPPS onto the polypeptide matrix depending on the chain length. Spinodal decomposition theory in confined geometry is used to model this mechanism by considering the time evolution of a homogeneous distribution of randomly adsorbed particles (porphyrins) onto a rodlike polyelectrolyte (polymer) of variable length L.

Chemistry and engineering of cyclodextrins for molecular imaging

Cyclodextrins (CDs) are naturally occurring cyclic oligosaccharides bearing a basket-shaped topology with an "inner-outer" amphiphilic character. The abundance of hydroxyl groups enables CDs to be functionalized with multiple targeting ligands and imaging elements. The imaging time, and the payload of different imaging elements, can be tuned by taking advantage of the commercial availability of CDs with different sizes of the cavity. This review aims to offer an outlook of the chemistry and engineering of CDs for the development of molecular probes. Complexation thermodynamics of CDs, and the corresponding implications for probe design, are also presented with examples demonstrating the structural and physiochemical roles played by CDs in the full ambit of molecular imaging. We hope that this review not only offers a synopsis of the current development of CD-based molecular probes, but can also facilitate translation of the incremental advancements from the laboratory to real biomedical applications by illuminating opportunities and challenges for future research.

Macrophage-Instructed Intracellular Staphylococcus aureus Killing by Targeting Photodynamic Dimers

The survival of Staphylococcus aureus inside phagocytes is considered to be the sticking point of long-term chronic inflammation. Here, we fabricate peptide-chlorophyll-based photodynamic therapy (PDT) agents with "sandwich" dimeric structure to enhance the PDT effect and active targeting property to eliminate intracellular infections, which could be seen as prospective antibacterial agents for inflammation.

Metal-mediated linear self-assembly of porphyrins

Porphyrin derivatives are highly relevant to biological processes such as light harvesting and charge separation. Their aromatic electronic structure and their accessible HOMO-LUMO gap render porphyrins highly attractive for the development of opto- and electro-active materials. Due to the often difficult covalent synthesis of multiporphyrins, self-assembly using metal complexation as the driving force can lead to well defined objects exhibiting a controlled morphology, which will be required to analyse and understand the electronic properties of porphyrin wires. This article presents two assembly approaches, namely by peripheral coordination or by binding to a metal ion in the porphyrin core, that are efficient and well designed for future developments requiring interactions with a surface.

The role of counter-anions in the kinetics and chirality of porphyrin J-aggregates

Kinetics of the growth of TPPS₄ porphyrin J-aggregates slow down in the order H₂SO₄ > HCl > HBr > HNO₃ > HClO₄, in agreement with the Hofmeister series. The rate constants and the extent of chirality correlate with the structure-making or breaking abilities of the different anions with respect to the hydrogen bonding network of the solvent.

Tumor Microenvironment-Triggered Supramolecular System as an In Situ Nanotheranostic Generator for Cancer Phototherapy

The efficacy of photosensitizers in cancer phototherapy is often limited by photobleaching, low tumor selectivity, and tumor hypoxia. Assembling photosensitizers into nanostructures can improve photodynamic therapy efficacy and the safety profile of photosensitizers. Herein by employing supramolecular assembly, enhanced theranostic capability of Mn2+ -assisted assembly of a photosensitizer (sinoporphyrin sodium, DVDMS) is demonstrated. A tumor environment-triggered coassembly strategy is further developed to form Mn/DVDMS nanotheranostics (nanoDVD) for cancer phototherapy. MnO2 nanosheets serve as a highly effective DVDMS carrier and in situ oxygen and nanoDVD generator. In MCF-7 cells and xenograft tumors, MnO2 /DVDMS is reduced by glutathione (GSH) and H2 O2 and reassembled into nanoDVD, which can be monitored by activated magnetic resonance/fluorescence/photoacoustic signals. Intriguingly, the decrease of GSH, the production of O2 , and the formation of nanoDVD are shown to be synergistic with phototherapy to improve antitumor efficacy in vitro and in vivo, offering a new avenue for cancer theranostics.

Hierarchical self-assembly of squaraine and silica nanoparticle functionalized with cationic coordination sites for near infrared detection of ATP

Optical activity of hierarchical supramolecular assemblies based on organic dyes would create multiple functional architectures. In this work, three kinds of silica nanoparticles with or without functional groups were synthesized. For the first time, silica nanoparticles can induce positively charged squaraine (SQ) to aggregate to form supramolecular assemblies. Adenosine-5'-triphosphate (ATP) as building blocks was absorbed on the surface of silica nanoparticles through metal-anion coordination and electrostatic interactions, in which the aggregates of SQ was transferred to monomer. The thickness being composed of ATP and SQ on the outside of nanoparticles is about 5 nm. These supramolecular assemblies showed selective turn-on fluorescence response to ATP in near infrared (NIR) region over other ions through metal-anion coordination and electrostatic interactions. These functional silica nanoparticles possessing many advantages provide proof-of-principle "seed crystals" for construction of supramolecular assemblies and platforms for sensing with facile performance.

Porphyrin stacks as an efficient molecular glue to induce chirality in hetero-component calixarene–porphyrin assemblies

Porphyrins act as a sort of “molecular glue” in directional self-assembly of water-soluble multi-component porphyrin–calixarene architectures, allowing transfer of chirality to the supramolecular level.

Self-Assembly of Hierarchical Chiral Nanostructures Based on Metal-Benzimidazole Interactions: Chiral Nanofibers, Nanotubes, and Microtubular Flowers

Controlled hierarchical self-assembly of synthetic molecules into chiral nanoarchitectures to mimic those biological chiral structures is of great importance. Here, a low-molecular-weight organogelator containing a benzimidazole moiety conjugated with an amphiphilic l-glutamic amide has been designed and its self-assembly into various hierarchical chiral nanostructures is investigated. Upon gel formation in organic solvents, 1D chiral nanostructure such as nanofiber and nanotube are obtained depending on the solvents. In the presence of transition and rare earth metal ions, hierarchical chiral nanostructures are formed. Specifically, the addition of TbCl3 , EuCl3 , and AgNO3 leads to nanofiber structures, while the addition of Cu(NO3 )2 , Tb(NO3 )3 , or Eu(NO3 )3 provides the microflower structures and microtubular flower structures, respectively. While Eu(III) and Tb(III)-containing microtubular flowers keep the chirality, the Cu(II)-coordinated microflowers lose chirality. More interestingly, the nanofibers formed by the gelator coordinated with Eu(III) or Tb(III) ions show not only the supramolecular chirality but also the circularly polarized luminescence.