Chiara Deiana

The Formation and Self-Assembly of Long Prebiotic Oligomers Produced by the Condensation of Unactivated Amino Acids on Oxide Surfaces†

In situ IR and mass spectrometry evidence for the catalytic formation on SiO2 and TiO2 surfaces of glycine oligomers (poly-Gly) up to 16 units long by successive feeding with monomers from the vapor phase is presented. Parallel experiments carried out on hydroxyapatite resulted in the unreactive adsorption of Gly, thus indicating that the oligomerization was specifically catalyzed by the surfaces of SiO2 and TiO2 . Furthermore, the poly-Gly moved on the surface when contacted with H2 O vapor and formed self-assembled aggregates containing both helical and β-sheet-like structural motifs. These results indicate that polypeptides formed by the condensation of amino acids adsorbed on a mineral surface can evolve into structured supramolecular assemblies.

Direct Synthesis of Amides from Carboxylic Acids and Amines by Using Heterogeneous Catalysts: Evidence of Surface Carboxylates as Activated Electrophilic Species

“Rethinking amide-bond synthesis” is one of the most stimulating topics in current chemical research. A number of successful amide-forming reactions have been proposed to meet highly demanding synthetic challenges and/or large-scale production requirements. However, a general problem that affects these methods is the consumption of large amounts of chemicals, which typically include reagents that are required for the activation of carboxylic groups, thereby resulting in increased cost and waste production. In 2007, the American Chemical Society Green Chemistry voted “amide-bond formation avoiding poor atom-economy reagents” as a top priority in the search for better and more-sustainable reagents and methods. Catalyzed reactions are quite attractive for this purpose and many compelling studies of amidation reactions that are promoted by homogeneous and heterogeneous catalysts have been reported in recent years. The amidation mechanism for unactivated carboxylic acids and amines on heterogeneous catalysts, in particular the activation of the carboxylic moiety, has not yet been sufficiently explored. In their assessment of Bernal’s hypothesis by using ab initio methods, Rimola et al. proposed a mechanism that involved undissociated carboxylic groups for the formation of peptide bonds on the surface of an aluminosilicate. Herein, IR spectroscopy and high-resolution mass spectrometry (HRMS) provide evidence for the amidation of carboxylate moieties that are formed by the adsorption of formic and acetic acids onto the surface of TiO2 nanoparticles (Degussa P25) under mild conditions [about 323 K, the temperature of the samples in the IR beam, hereafter “beam temperature” (BT)] . In our view, this finding represents the starting point for the elucidation of the structural and energetic features of one of the potential pathways for amidation reactions on surfaces, thereby promoting the rational design of optimized materials and processes for heterogeneous catalytic approaches. Formic acid was properly dosed from the vapor phase onto dehydrated TiO2 nanoparticles (for the experimental details, see the Supporting Information, Materials and Methods and Figure S1) to ensure the adsorption of only formate species onto the surface. The attainment of this target was confirmed by the selective appearance in the IR spectrum of components at 1560 cm , with shoulders at 1580 and 1540 cm , and at 1361 cm , with a weak partner at 1412 cm , owing to the nasymCOO and nsymCOO stretches of the formate species, respectively; the signal at 1385 cm 1 corresponded to the H C O bending mode (Figure 1, curves a, b; for the full spectra, see the Supporting Information, Figures S1 B and S2). The same pattern was obtained by using HCOOD molecules, thus confirming the selective formation of HCOO species (see the Supporting Information, Figure S1 B’). Higher coverage resulted in the appearance of the nC=O band at about 1682 cm , which corresponded to HCOOH molecules that adsorbed in their non-dissociated form (see the Supporting Information, Figure S1 A). A proposal of the coordi[a] Dr. C. Deiana, Dr. Y. Sakhno, M. Fabbiani, Dr. M. Pazzi, Prof. M. Vincenti, Prof. G. Martra Department of Chemistry University of Torino Via P. Giuria 7, 10125 Torino (Italy) Fax: (+ 39) 0116707855 E-mail : gianmario.martra@unito.it [b] Dr. C. Deiana, Dr. Y. Sakhno, Prof. G. Martra Interdepartmental Centre of Excellence “Nanostructured Interfaces and Surfaces-NIS” University of Torino Via P. Giuria 7, 10125 Torino (Italy) [] These authors contributed equally to this work. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cctc.201300164. It contains descriptions of the materials, the IR and HRMS methods, and additional results, that is, IR spectra of: increasing/decreasing amounts of HCOOH on TiO2 ; the adsorption of HCOOH and 1-pentanamine onto TiO2 ; washed samples; reacted sample that had been degassed and hydrated with H2O or D2O; reverse-order admission of HCOOH and 1-pentanamine onto TiO2 ; adsorbed CO; the adsorption of CH3COOH and 1-pentanamine onto TiO2; increasing/decreasing amounts of CH3COOH on TiO2 ; D2O that had been admitted onto CH3COO /TiO2; a summary of the structures of the surface carboxylates; and HRMS spectra. Figure 1. Left : IR spectra within the range 1750–1300 cm 1 of a) TiO2 that had been outgassed at 723 K; b) after contact with HCOOH and subsequent outgassing; and c–e) after the admission of increasing amounts of 1-pentanamine. p, w) Spectra of TiO2 that had been outgassed at 723 K and then treated with 1-pentanamine (40 mbar) and water vapors (20 mbar), respectively, and outgassed at the BT for 1 h. Right: HRMS of the washing solution of the reacted sample. For the original spectrum, see the Supporting Information, Figure S3 A.

On the Simple Complexity of Carbon Monoxide on Oxide Surfaces: Facet-Specific Donation and Backdonation Effects Revealed on TiO2 Anatase Nanoparticles

Atomic-scale relationships between the structure of TiO2 surfaces and the physicochemical properties of surface sites, functional for titania-based applications, can be obtained from IR spectroscopy by using carbon monoxide (CO) as a molecular probe. In the literature, it is reported that strongly unsaturated cationic Ti sites (Lewis acid), which are important for reactivity, should cause a large upshift of the CO stretching frequency. By using IR spectroscopy of CO on TiO2 nanomaterials and theoretical analyses, here this model is challenged. It is shown that the stretching frequency of adsorbed CO results from a facet-dependent and synergic CO-surface donation (upshift) - surface-CO backdonation (downshift) mechanism. These results imply that the interaction of adsorbed molecules with the Ti centers is tuned by the surface oxygen atoms of the first coordination sphere, which play an active role as indirect electron density donors (Lewis base).

Surface features of TiO2 nanoparticles: combination modes of adsorbed CO probe the stepping of (101) facets

Integrated studies of CO adsorption on TiO2 materials of different morphology and surface complexity identify, for the first time, frustrated translational CO modes by detecting their combination with the CO stretching mode (νCO). All the considered materials exhibit IR spectra with low-intensity bands in the 2235-2205 cm(-1) range, a region where components due to strong Lewis acid Ti(4+) sites may be present as well. These observations lead to a powerful method for associating high-wavenumber bands to TiO2 surface features and interpreting IR spectra of drastically complex/defective TiO2 materials. The proposed band assignment is based on vibrational analyses of CO-TiO2 theoretical models, indicating that the frustrated translational mode with frequency in the 30-50 cm(-1) range involved in the observed combination bands is perpendicular to the Ti(4+) rows. Our results reveal that this low-energy CO mode is much more sensitive than νCO in probing the TiO2 surface topography, and that its higher-energy components can be specifically associated with the presence of steps on the (101) faces. In a broader perspective, the frustrated translational CO mode surface sensitivity could become a key tool for detecting specific defective sites on TiO2 surfaces.

Fast TiO2-catalyzed direct amidation of neat carboxylic acids under mild dielectric heating

The development of green protocols for amide bond formation is a major socioeconomic goal for chemical and pharmaceutical industries and an important challenge for academic research. We herein report a protocol for the quantitative conversion of carboxylic acids and amines to form amides at 100 °C in the presence of a TiO2 powder catalyst, under monomodal microwave irradiation. The sustainability of the process appears to be augmented by the ease with which the catalyst is recycled.

Activity patterns of metal oxide catalysts in the synthesis of N-phenylpropionamide from propanoic acid and aniline

The reactivities of various commercial and lab-made oxide samples (e.g., γ-Al2O3, CeO2, ZrO2 and TiO2) in the heterogeneous catalytic synthesis of N-phenylpropionamide (T, 383 K) from aniline and propanoic acid have been investigated. All the materials studied drive the direct synthesis of the amide to an extent depending on both the chemical and structural properties. A 0th-order kinetic dependence on the substrate concentrations suggests that the reaction proceeds via a Langmuir–Hinshelwood (L–H) pathway under kinetic control of the adsorption–desorption steps (the rate determining step, r.d.s.). The comparative analysis of the activity data on the basis of the relative surface specific kinetic constant discloses a superior surface reactivity of TiO2, CeO2 and ZrO2 over the γ-Al2O3 system, and also highlights marked differences in the catalytic functionality of the titania samples. IR spectroscopic studies of the carboxylic acids and amine adsorption and interaction patterns show the formation of the bidentate, bridging, and unidentate carboxylate intermediates accounting for the different amidation functionalities of the studied materials.

Surface Sites of Nanomaterials: Investigation of Local Structures by In Situ IR Spectroscopy

In this chapter, the possibilities to highlight atomic/molecular details of the surface of nanomaterials by IR spectroscopy of their interaction with molecules in controlled conditions are reviewed. For this objective, information on the experimental setups and procedures is also provided; particular attention has been devoted to the use of different probe molecules (CO, CH3CN, and H2O). Such molecules, when adsorbed in controlled conditions, become useful “molecular tools because of the sensitivity of their vibrational features to the physical/chemical properties of surface sites.