Angela Mammana

Interactions of a Tetraanionic Porphyrin with DNA: from a Z-DNA Sensor to a Versatile Supramolecular Device

The anionic nickel(II) porphyrin NiTPPS is able to selectively sense the spermine induced left-handed Z-form of DNA while it is completely silent in the presence of right-handed B-DNA. Interactions between the DNA and the porphyrin can be easily modulated by pH and temperature. The resulting Z-DNA-porphyrin-spermine complex behaves as a supramolecular reversible information storage system and as a reversible AND logic gate.

Porphyrins as spectroscopic sensors for conformational studies of DNA

Molecular systems containing two or more interacting porphyrins show remarkable spectroscopic features that allow for a very sensitive detection of conformational changes on the microscale level by different methods, such as fluorescence and electronic circular dichroism (ECD). Covalent porphyrin-DNA assemblies can provide a CD profile (exciton couplet) within the porphyrin Soret band region which is very diagnostic for DNA conformational changes. Additionally, covalently linked porphyrins have been shown to function as DNA molecular caps and to stabilize the non-self-complementary non-Watson-Crick guanine-adenine DNA sequence via their strong π-π stacking.

A Chiroptical Photoswitchable DNA Complex

The interesting structural, electronic, and optical properties of DNA provide fascinating opportunities for developing nanoscale smart materials by integrating DNA with opto-electronic components. In this article we demonstrate the electrostatic binding of an amine-terminated dithienylethene (DET) molecular switch to double-stranded synthetic polynucleotides. The DET switch can undergo photochemical ring-closure and opening reactions. Circular dichroism (CD) and UV-vis spectroscopy show that both the open, 1o, and the closed, 1c, forms of the switch bind to DNA. Upon addition of DNA to a solution of 1o or 1c, the UV-vis spectrum displays a hypochromic effect, indicative of an interaction between the switch and the DNA. The chirality of the DNA double-helix is transmitted to the switching unit which displays a well-defined CD signal upon supramolecular complexation to the DNA. Additionally, the CD signal of the DNA attenuates, demonstrating that both components of the complex mutually influence each others structure; the DNA induces chirality in the switch, and the switch modifies the structure of the DNA. Modulation of the chiroptical properties of the complex is achieved by photochemically switching the DET between its ring open and closed isomers. A pH dependence study of the binding shows that when the pH is increased the switches lose their binding ability, indicating that electrostatic interactions between protonated amines and the negatively charged phosphate backbone are the dominant driving force for binding to the DNA. A comparison of poly(deoxyguanylic-deoxycytidylic) acid [poly(dGdC)(2)] polynucleotides with poly(deoxyadenylic-deoxythymidylic) acid [poly(dAdT)(2)] shows distinct differences in the CD spectra of the complexes.

Reversible “Chiral Memory” in Ruthenium Tris(phenanthroline)–Anionic Porphyrin Complexes

In the last few years, transfer and memory of chirality have been attracting growing interest for potential technological applications. In general, this phenomenon occurs through two steps: 1) transfer of chirality from a chiral template to an achiral covalent or noncovalent “polymeric” species and 2) “removal” of the chiral cast which leaves its chirality permanently imprinted on the “polymer”. The chiral memory relies on the kinetic inertness of the “polymeric” species and most examples rely on systems that have a “static” memory: that is, once imprinted and memorized, chirality becomes an intrinsic but nontunable feature of the complex. Only recently has a system with a “dynamic memory” for which it is possible to cyclically store and release the “memorized chirality” been reported. We report herein a new and more intriguing “dynamic” supramolecular memory system (SuMe). We have recently reported that the L and D enantiomers of [Ru(1,10-phenanthroline)3] 2+ ([Ru(phen)3] , lmax = 262 nm, Figure 1) induce chiral aggregation of various achiral anionic porphyrins. Our interest in this complex system stems from two considerations. Firstly, porphyrins are ideal building blocks for supramolecular architectures because of their unique spectroscopic properties (extinction coefficients of ca. 10 and intense emission signals, the position and intensity of which can be tuned by insertion of a central metal ion) and the possibility of modulation of their self-aggregation. Secondly, ruthenium (II) complexes can transfer two kind of molecular information—energy and chirality—to porphyrins and their aggregates. 5] The interaction between meso-tetrakis(4-sulfonatophenyl)porphine (H2TPPS4, lmax = 412 nm, Figure 1) and an equimolar amount of [Ru(phen)3] 2+ (pH 6.0, NaCl (0.3m)) is indicated by variations in the absorption spectra of both [Ru(phen)3] 2+ and H2TPPS4. The strongest evidence of interaction, however, comes from the appearance of an induced circular dichroism (ICD) band in the absorption region (Soret band) of the achiral porphyrin (Figure 2). The relationship between chirality of the cationic metal complex and that transferred to the anionic porphyrins is straightforward because interactions of H2TPPS4 with the Land D[Ru(phen)3] 2+ lead to mirror-image ICD signals (Figure 2). At a pH value lower than 3 and in the presence of millimolar concentration of salt, the protonated species of H2TPPS4 (H4TPPS4, pKa 5, lmax = 436 nm) is zwitterionic and self-assembles to give both face-to-face (H, lmax = 422 nm) and edge-to-edge aggregates (J, lmax = 490 nm, Figure 3). Yashima and co-workers have shown very Figure 1. Structure of the anionic porphyrin H2TPPS4 and of the L and D enantiomers of [Ru(phen)3] .

Transfer of Chirality for Memory and Separation

Transfer of chirality is an intriguing issue worth studying to understand better the origin of life and for possible technological applications. In the last few years we have been working in this area studying the chain of events that begins with induction, reaches a permanent transfer (chiral memory) and extends in some cases to a (quasi-)reversible situation in which induced and permanently memorized chirality coexists. This can happen thanks to a designed blend of thermodynamics and kinetics.

Interactions of Λ and Δ enantiomers of ruthenium(II) cationic complexes with achiral anionic porphyrins

The interactions between Lambda and Delta enantiomers of ruthenium(II)-phenanthroline cationic complex ([Ru(phen)(3)](2+)) and three anionic porphyrins have been characterized by absorption, circular dichroism (CD), fluorescence, and resonance light scattering (RLS). The three porphyrins used in this study have been chosen for the different number (two or four) and reciprocal (symmetrical, cis or trans) disposition of the anionic (4-sulphonatophenyl) peripheral groups in the meso positions. All the techniques evidence the formation of inorganic-organic hybrids. In particular, CD and fluorescence measurements show that the inorganic moiety is able to transfer to porphyrins not only chirality (as shown from the appearance of an induced CD signal (ICD) in the absorption region of porphyrins) but, most likely, also energy.

Electroless Deposition of Nickel on Photografted Polymeric Microscale Patterns

This report demonstrates the electroless deposition of Ni onto micropatterns of poly (acrylic acid) (PAA) photografted to phthalimide-terminated self-assembled monolayers (SAMs). PAA is spin-coated onto phthalimide SAMs and covered with a photomask. UV irradiation selectively binds PAA to exposed regions of the surface, allowing PAA on unexposed regions to be rinsed off. A Pd catalyst is then selectively adsorbed to regions of the surface where PAA is bound. The adsorbed catalyst selectively initiates Ni plating upon immersion of the substrate into a Ni(SO4 ) bath.

Photochemical Immobilization of Polymers on a Surface: Controlling Film Thickness and Wettability

In this manuscript, we demonstrate the control of film thickness and surface wettability in the photochemical immobilization of poly (vinyl alcohol) (PVA) to a self‐assembled monolayer (SAM) containing a phthalimide chromophore. Surface attachment is characterized by ellipsometry and contact angle measurements. The wettability of the resulting films is shown to depend on the chemical composition of the polymer. The film thickness is shown to depend on the irradiation time and molecular weight of the polymer. Using a photomask, micropatterns of polymers can be grafted to the SAM. The photopatterned surface can be “developed” by coating with a thin layer of a mixture containing poly (styrene) (PS) and triphenylsulfonium triflate.