Domenico A. Cristaldi

Durable contact active antimicrobial materials formed by a one-step covalent modification of polyvinyl alcohol, cellulose and glass surfaces.

In this work we have applied a direct covalent linkage of quaternary ammonium salts (QAS) to prepare a series of contact active antimicrobial surfaces based on widely utilized materials. Formation of antimicrobial polyvinyl alcohol (PVA-QAS), cellulose (cellulose-QAS) and glass (glass-QAS) surfaces was achieved by one step synthesis with no auxiliary linkers. The X-ray photoelectron spectroscopy (XPS) revealed tridentate binding mode of the antimicrobial agent. The antimicrobial activity of the prepared materials was tested on Bacillus cereus, Alicyclobacillus acidoterrestris, Escherichia coli and Pseudomonas aeruginosa. Active site density of the modified materials was examined and found to correlate with their antimicrobial activity. Stability studies at different pH values and temperatures confirmed that the linkage of the bioactive moiety to the surface is robust and resistant to a range of pH and temperatures. Prolonged long-term effectiveness of the contact active materials was demonstrated by their repeated usage, without loss of the antimicrobial efficacy.

Sequence, Stoichiometry, and Dimensionality Control in Porphyrin/Bis‐calix[4]arene Self‐Assemblies in Aqueous Solution

The use of a water-soluble octacationic bis-calix[4]arene with divergent cavities (BC(4)) as a templating agent for the assembly of a tetraanionic porphyrin (CuTPPS) has allowed the noncovalent synthesis of 2D or 3D multiporphyrin assemblies. Self-assembly of CuTPPS and BC(4) molecules proceeded under hierarchical control in a stepwise fashion to yield discrete and isolable supramolecular nanostructures containing up to 33 molecular elements (i.e., the CuTPPS/BC(4) 17:16 assembly, obtained in less than three hours). The formation of these species could be conveniently monitored by means of UV/Vis spectroscopy by following the absorbance of the Soret band at 412 nm. In particular, the attainment of the pivotal CuTPPS/BC(4) 5:4 species with a cruciform structure, as the key fork-point intermediate for the subsequent formation of the higher 2D and 3D assemblies, has been demonstrated by light-scattering studies and by an unequivocal synthesis of mixed-porphyrin/calixarene 5:4 species involving the use of two different types of metallated porphyrins, namely CuTPPS and MnTPPS. The remarkable stability of these assemblies permits a stepwise synthesis that makes it possible to choose the desired porphyrin sequence.

Sensing of linear alkylammonium ions by a 5-pyrenoylamido-calix(5)arene solution and monolayer using luminescence measurements†

Covalent chemisorption of a p-chloromethylphenyltrichlorosilane monolayer on silica substrates was achieved. A cone 5-pyrenoylamido-calix[5]arene bearing a 12-aminododecyl moiety at the lower rim was further covalently bonded, producing a 5-pyrenoylamido-calix[5]arene-based monolayer on silica. The surface chemical characterization of this hybrid material was carried out by X-ray photoelectron spectroscopy. The sensing properties of this pyrenoylamido-calix[5]arene system were probed by both NMR and luminescence measurements in solution. The optical recognition properties of the functional monolayer were similarly studied at room temperature by emission measurements. This system demonstrates to have significant recognition properties for the linear alkylammonium ions. As a result, n-dodecylammonium ions can be detected at ppm levels. The adopted synthetic procedure provided evidence to be useful in transferring molecular properties to a solid state device.

Photoactivity of hierarchically nanostructured ZnO–PES fibre mats for water treatments

A brush-like ZnO nanorods shell is grown by Chemical Bath Deposition on electrospun Zn(Ac)2 doped polyethersulfone fibres. The obtained mats are water resistant and photocatalytically active, thus resulting suitable for applications in water purification. The used procedure is simple, cost-effective and scalable to large volumes. The use of supported ZnO nanostructures onto fibrous mats paves the way to easily reusable photocatalyst that benefits the high surface area of nanostructures and limits the drawbacks associated to the use of nanoparticles and nanopowders (i.e. water turbidity, irradiation efficiency and photocatalyst recover), thus resulting suitable for use in membrane technology.

Covalent poly(methyl methacrylate) nanostructures on functionalized Si(100) surfaces

Material properties are strongly affected by the presence of surface chemical functionalities. In this study we show a platform for fabricating robust poly(methyl methacrylate) molecular architectures covalently bound to silylated Si(100) substrates, by an atom transfer radical polymerization approach. Infrared attenuated total reflectance spectra have shown increasing poly(methyl methacrylate) signals upon increasing reaction time and can be used to monitor the growth of these hybrid inorganic/organic structures. The chemical composition of these surface structures was investigated by X-ray photoelectron spectra. Surface morphology studies were carried out by atomic force microscopy and lithography. In our reaction conditions, the thickness of poly(methyl methacrylate) on Si(100) can be modulated in the nanometer range. Quantum mechanical DFT calculations have been performed to estimate the growth rate.

Long range order in Si(100) surfaces engineered with porphyrin nanostructures

Engineering of Si(100) with ordered organic nanostructures represents an advanced method to manufacture hybrid organic/inorganic systems useful for different applications. Well-ordered and densely packed molecules can be obtained by a self-assembly process that depends on directional inter-molecular interactions such as π–π stacking, electrostatic, dipole–dipole or van der Waals interactions, and other more complex forces. Macrocycles are well known to aggregate both in solution and in thin films as a result of some of the above-mentioned interactions. In our study, Si(100) substrates were functionalized with a covalent 4-ClCH2C6H4SiCl3 monolayer that binds to the surface using the –SiCl3 group and leaves a –CH2Cl group unreacted. The remaining alkyl chloride functionality at the top of the Si(100) substrate allowed additional covalent functionalization with a porphyrin monolayer that resulted in ordered, surface-confined porphyrin assemblies. X-ray photoelectron spectroscopy gave indication of the porphyrin grafting mode. Atomic force microscopy showed a long range order of these nanostructures. Emission measurements confirmed the porphyrin luminescence.

Functionalization of SnO2 Crystals with a Covalently‐Assembled Porphyrin Monolayer

The functionalization of micro- and nano-sized metal-oxide powders offers many advantages because of their large surface areas and, therefore, the large number of functional molecules that can be grafted onto the grain surfaces. Porphyrin molecules on large band-gap semiconducting metal oxides represent key materials for many different optical and electronic applications. Herein, we have proposed a general two-step procedure for the functionalization of metal-oxide crystals with dye-sensitizers. In particular, we functionalized SnO₂ nanoparticles with a monolayer of the bifunctional trichloro[4-(chloromethyl)phenyl]silane. Then, a monolayer of 5,10,15,20-tetrakis(4-hydroxyphenyl)-21H,23H-porphyne was covalently bound to the silanized SnO₂ grains. IR, UV/Vis, and luminescence measurements were used for optical characterization. The measured footprint of the grafted porphyrin molecules indicated total surface coverage of the grains. The surface electronic characterization was performed by using X-ray photoelectron spectroscopy. Emission measurements revealed two strong bands at 664.1 and 721.0 nm that were attributed to the porphyrin monolayer assembled on the surface of the SnO₂ crystals.

A contact active bactericidal stainless steel via a sustainable process utilizing electrodeposition and covalent attachment in water

A contact active bactericidal stainless steel was synthesized in water utilizing phenol electrodeposition, followed by covalent attachment of quaternary ammonium salts. The approach minimizes the amount of the antimicrobial agent and avoids its release into the environment. Gram negative and Gram positive bacteria were inactivated upon contact with the modified surface.

A photoelectron spectroscopy study of lava stones

In areas surrounding volcanoes, atmospheric agents remove surface layers from the emitted stones that go directly into the air and groundwater. The chemical composition of magmatic stones is currently studied using techniques that do not differentiate between bulk and surface composition. To the best of our knowledge there are no XPS investigations of magmatic stones. Therefore, in this study we report on the first surface chemical investigation of magmatic stones, and in particular of lapilli emitted by the Etna volcano (Sicily), using the X-ray photoelectron spectroscopy technique. Results show important differences between bulk and surface composition of major oxides. We found that Si, Fe, Ca and K segregate into the bulk, whereas Al, Na, P and Mn segregate on the surface. For example, the Mn surface concentration is 266.7% with respect to that observed in the bulk, and is due to the water soluble MnOOH species at the surface. The present study highlights the potentiality of the XPS technique in the investigation of the surface composition of magmatic materials.

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

Tritopic tris-calix[4]arene TC4 – possessing three divergent cavities linked to a tris-aminophenylamine core – forms, in the presence of tetra-anionic Cu(II) porphyrins CuTPPS or a combination of different metallo-porphyrins (CuTPPS, NiTPPS and MnTPPS), discrete 3 : 1 porphyrin/tris-calixarene complexes. The 3 : 1-(CuTPPS/TC4) complex in particular is shown to be a key building block for the assembly of supramolecular architectures of increasing complexity. Directional (radial vs. stacked) self-assembly of these nanostructures was achieved by alternate addition of selected hetero-components in a programmed fashion. Addition of TC4 and CuTPPS, in turn, leads to a radial growth of the assembly, whereas, addition of single-cavity calix[4]arene C4 stoppers followed by a CuTPPS topping, promotes a stacked growth. In the latter case, the use of chiral (R)- or (S)-C4 stoppers is seen to induce chirality in the whole assembly. Circular dichroism data ultimately suggest that porphyrin molecules located above/below the 3 : 1 core complex act as a “molecular glue”, by making the interaction between chiral calix[4]arenes (R)- or (S)-C4 and the achiral 3 : 1-(CuTPPS/TC4) complex stronger.