Studio conformazionale di un derivato dendrimerico dell'acido L-glutammico tramite spettroscopia NMR e IR

Con questo lavoro si vuole proporre un modello conformazionale di una molecola dendrimerica tramite studi di spettroscopia NMR e FT-IR. Prima di inoltrarci nel fitto bosco di picchi spettroscopici introduciamo brevemente questa classe di composti [1a,b,c]. Le specie dendrimeriche sono dette tali in quanto strutturate da un corpo centrale (monomero di pochi u.m.a. ad esempio un amminoacido o un anello aromatico polifunzionalizzato) da cui si diramano vari bracci a loro volta ramificati. Se la molecola è molto grossa il risultato finale prende la forma di un granulo che presenta la superficie esterna ricca dei gruppi funzionali propri dei monomeri costituenti. L'utilizzo principale di questi composti comporta l'attivazione della loro superficie, ottenuta legando ai gruppi funzionali determinate molecole. È così possibile, per esempio, il veicolamento di farmaci a specifici siti attivi. Inoltre, sfruttando la formazione di legami non covalenti, alcuni dendrimeri sono utilizzati come fasi stazionarie in tecniche cromatografiche GC, HPLC, e scambio ionico. La possibilità di costruire dendrimeri con monomeri chirali ha portato queste molecole ad essere delle ottime candidate per lo studio degli effetti macroscopici della chiralità molecolare. In questo campo ci sono studi sulla chiralità del “core”, dei bracci dendrimerici o solo della superficie [2]. I gruppi funzionali superficiali possono essere di vario tipo e alcuni possono essere in grado di legarsi tra loro (ad esempio gruppi amminici e carbonilici con legami ad idrogeno). I legami possono avvenire sia tra due rami dendrimerici della stessa molecola (legami intramolecolari), sia tra gruppi funzionali di altre molecole (legami intermolecolari). Nel caso di legami ad idrogeno intermolecolari, quello che accade è l'aggregamento di due o più molecole dendrimeriche. Questo fenomeno genera lunghe catene di dendrimeri dette fibrille, le cui soluzioni assumono macroscopicamente l'aspetto di gel [3]. I gel dendrimerici ad una certa temperatura (o meglio in un intervallo di temperature) subiscono una transizione di fase, si rompono i legami ad idrogeno e le fibrille si scindono in dendrimeri liberi; questo processo non è sempre reversibile. Molto comuni sono i composti dendrimerici costruiti usando amminoacidi come monomeri, alcuni dei quali, ad esempio l'acido glutammico e la lisina, avendo più di un gruppo amminico o più di un gruppo carbossilico, sono in grado di legare, tramite legami ammidici, più molecole contemporaneamente. Questo fa si che alcuni dendrimeri vengano studiati dal punto di vista conformazionale per fare meglio luce sul tema del folding delle proteine [4]. Il dendrimero studiato in questa tesi, un trimero dell'acido glutammico, è troppo piccolo per essere considerato come un frammento significativo di una proteina; il nostro lavoro è comunque finalizzato allo studio conformazionale di questa molecola. Questo compito è stato affrontato utilizzando comuni tecniche di indagine spettroscopica NMR sia monodimensionali che bidimensionali, integrandole anche con alcuni spettri all'infrarosso che come vedremo sono stati cruciali per il fine del lavoro. I risultati verranno presentati grossomodo nell'ordine in cui sono stati registrati; i parametri sperimentali di ogni esperimento sono riportati in un capitolo a parte. In fine verrà formulata un'ipotesi conformazionale compatibile con i dati raccolti

Copper Carbonate Hydroxide as Precursor of Interfacial CO in CO2 Electroreduction

Copper electrodes are especially effective in catalysis of C2 and further multi-carbon products in the CO2 reduction reaction (CO2RR) and therefore of major technological interest. The reasons for the unparalleled Cu performance in CO2RR are insufficiently understood. Here, the electrode–electrolyte interface was highlighted as a dynamic physical-chemical system and determinant of catalytic events. Exploiting the intrinsic surface-enhanced Raman effect of previously characterized Cu foam electrodes, operando Raman experiments were used to interrogate structures and molecular interactions at the electrode–electrolyte interface at subcatalytic and catalytic potentials. Formation of a copper carbonate hydroxide (CuCarHyd) was detected, which resembles the mineral malachite. Its carbonate ions could be directly converted to CO at low overpotential. These and further experiments suggested a basic mode of CO2/carbonate reduction at Cu electrodes interfaces that contrasted previous mechanistic models: the starting point in carbon reduction was not CO2 but carbonate ions bound to the metallic Cu electrode in form of CuCarHyd structures. It was hypothesized that Cu oxides residues could enhance CO2RR indirectly by supporting formation of CuCarHyd motifs. The presence of CuCarHyd patches at catalytic potentials might result from alkalization in conjunction with local electrical potential gradients, enabling the formation of metastable CuCarHyd motifs over a large range of potentials

Operando Raman spectroscopy tracks oxidation-state changes in an amorphous Co oxide material for electrocatalysis of the oxygen evolution reaction

Transition metal oxides are of high interest in both energy storage (batteries) and production of non-fossil fuels by (photo)electrocatalysis. Their functionally crucial charge (oxidation state) changes and electrocatalytic properties are best investigated under electrochemical operation conditions. We established operando Raman spectroscopy for investigation of the atomic structure and oxidation state of a non-crystalline, hydrated, and phosphate-containing Co oxide material (CoCat), which is an electrocatalyst for the oxygen evolution reaction (OER) at neutral pH and is structurally similar to LiCoO2 of batteries. Raman spectra were collected at various sub-catalytic and catalytic electric potentials. 2H labeling suggests Co oxidation coupled to Co—OH deprotonation at catalytic potentials. 18O labeling supports O—O bond formation starting from terminally coordinated oxygen species. Two broad bands around 877 cm−1 and 1077 cm−1 are assigned to CoCat-internal H2PO4-. Raman peaks corresponding to terminal oxide (Co=O) or reactive oxygen species were not detectable; 1000–1200 cm−1 bands were instead assigned to two-phonon Raman scattering. At an increasingly positive potential, the intensity of the Raman bands decreased, which is unexpected and explained by self-absorption relating to CoCat electrochromism. A red-shift of the Co—O Raman bands with increasing potentials was described by four Gaussian bands of potential-dependent amplitudes. By linear combination of Raman band amplitudes, we can follow individually the Co(2+/3+) and Co(3+/4+) redox transitions, whereas previously published x-ray absorption spectroscopy analysis could determine only the averaged Co oxidation state. Our results show how electrochemical operando Raman spectroscopy can be employed as a potent analytical tool in mechanistic investigations on OER catalysis

The Emilia-Romagna region program in Silicon Valley program to support entrepreneurship: goals, experiences and outcomes

The purpose of this research project is to evaluate the impacts of the policies of the Emilia-Romagna region to encourage the development and internationalization of entrepreneurship. The study beyond this paper, aims to understand and identify the benefits of these programs for the regional ecosystem. and how the transversal competences affects entrepreneurship behaviour. This explorative research was conducted through the combination of three different approaches: 1. Data, theories and solutions collected on the field through the direct experience in Silicon Valley; 2. Qualitative and quantitative analysis using interview protocols and survey addressed to different actors involved in the ecosystem studied; 3. Support from literature. Time spent in San Francisco gave me the possibility to better understand the dynamics behind the Silicon Valley work environment and to go into the flow of this unique and inimitable reality. All this was possible thanks to the university of Bologna and in particular the professor and relator Sobrero Maurizio for the opportunity, support and collaboration during the whole project; the help of Dr. Luppi Elena in the survey construction; Dr. Mattarelli Elisa for the analysis of literature and the precious tips during the study of interview protocols; the collaboration of the regional consortium Art-ER, with the key figures of Mingozzi Irene (Silicon Valley hub manager) and D’Attorre Sara (Europe and international Dept); the availability of USmac and the two co-CEO Alfredo Coppola and Chris Burry for giving me the opportunity to attend the activities during the program in Silicon Valley; least but not last EIT Digital and in particular the CEO Eric Thelen, for the concession of a desk in San Francisco’s offices

Discovering Hidden Traps : in Nickel Oxide Nanoparticles for Dye-Sensitised Photocathodes

The finite nature of fossil fuels and their effect on the global climate, raised the need to find an alternative source of energy. This source should be environment compatible, cheap and abundant. The light coming from the Sun is a promising alternative. To be fruitful, the solar energy needs to be transformed in storable and transportable energy forms like electricityor fuels. Amongst the most studied techniques dye sensitised devices offer the possibility to be designed for both the scopes: solar-to-electricity and solar-to-fuel conversions. In these applications a photocathode and a photoanode, constructed by mesoporous semisconductor films sensitised with dyes, are placed in series with one another.It follows that the photocurrent generated by one electrode should be sustained by the photocurrent produced by the other electrode. At the moment there is a substantial difference between the conversion efficiencies and the photocurrent produced by photoanodes and photocathodes. In this thesis the reasons for this discrepancy are investigated. The main responsible of the bad performance is identified in the semiconductor normally used in photocathodes, Nickel Oxide (NiO). Electrochemical impedance spectroscopy was used to elucidate the electrical properties of mesoporous NiO films. The study revealed that NiO films are able to carry a large enough current to establish that conductivity is not a limiting factor. The recombination reactions were then accused as the cause of the power losses. A time resolved spectroscopic study revealed that NiO can host two kinds of holes. One of these holes is responsible for a fast dye-NiO recombination (100 ns) and the other one for a slow recombination (10 ms). A cell featuring only the slow dye-NiO recombination would possibly reach high efficiency. The characterisation of the species associated with these two holes was performed by density-of-state assisted spectroelectrochemistry. The holes were found to be trapped by Ni2+ and Ni3+ sites located on the NiO surface forming respectively Ni3+ and Ni4+ states. A study by fs and ns transient absorption spectroscopy revealed that Ni3+ sites can trap a hole in subpicosecond time scale and this hole relaxes into a Ni2+ trap in ns timescale. The control of the Ni2+/Ni3+ratio on the NiO surface was found  to be crucial for a high cell photovoltage. In the thesis these results are discussed and used to propose an explanation and some solutions to the poor performance of NiO-based dye sensitised cells

Effects on charge recombination of an electron accepting group in a Ru-dye for p-type Dye-Sensitized-Solar-Cells.

Studio degli effetti sulla ricombinazione e efficienza di un ligante elettron accettore in un colorante a base di Ruthenio per un a dye sensitized solar cell. Lo studio è stato eseguito tramite laser-flash-photolysis e spectro-electro-chemistry

Copper Carbonate Hydroxide as Precursor of Interfacial CO in CO2 Electroreduction

Copper electrodes are especially effective in catalysis of C-2 and further multi-carbon products in the CO2 reduction reaction (CO2RR) and therefore of major technological interest. The reasons for the unparalleled Cu performance in CO2RR are insufficiently understood. Here, the electrode-electrolyte interface was highlighted as a dynamic physical-chemical system and determinant of catalytic events. Exploiting the intrinsic surface-enhanced Raman effect of previously characterized Cu foam electrodes, operando Raman experiments were used to interrogate structures and molecular interactions at the electrode-electrolyte interface at subcatalytic and catalytic potentials. Formation of a copper carbonate hydroxide (CuCarHyd) was detected, which resembles the mineral malachite. Its carbonate ions could be directly converted to CO at low overpotential. These and further experiments suggested a basic mode of CO2/carbonate reduction at Cu electrodes interfaces that contrasted previous mechanistic models: the starting point in carbon reduction was not CO2 but carbonate ions bound to the metallic Cu electrode in form of CuCarHyd structures. It was hypothesized that Cu oxides residues could enhance CO2RR indirectly by supporting formation of CuCarHyd motifs. The presence of CuCarHyd patches at catalytic potentials might result from alkalization in conjunction with local electrical potential gradients, enabling the formation of metastable CuCarHyd motifs over a large range of potentials

Unveiling hole trapping and surface dynamics of NiO nanoparticles

The research effort in mesoporous p-type semiconductors is increasing due to their potential application in photoelectrochemical energy conversion devices. In this paper an electron-hole pair is created by band-gap excitation of NiO nanoparticles and the dynamics of the electron and the hole is followed until their recombination. By spectroscopic characterization it was found that surface Ni3+ states work as traps for both electrons and holes. The trapped electron was assigned to a N2+ state and the trapped hole to a Ni4+ state. The recombination kinetics of these traps was studied and related with the concept of hole relaxation suggested before.The timescale of the hole relaxation was foundto be in the order of tens of ns. Finally the spectrosc opic evidence of this relaxation is presented in a sensitized film

Photoinduced hole transfer from tris(bipyridine)ruthenium dye to a high-valent iron-based water oxidation catalyst

An efficient water oxidation system is a prerequisite for developing solar energy conversion devices. Using advanced time-resolved spectroscopy, we study the initial catalytic relevant electron transfer events in the light-driven water oxidation system utilizing [Ru(bpy)(3)](2+) (bpy = 2,2 '-bipyridine) as a light harvester, persulfate as a sacrificial electron acceptor, and a high-valent iron clathrochelate complex as a catalyst. Upon irradiation by visible light, the excited state of the ruthenium dye is quenched by persulfate to afford a [Ru(bpy)(3)](3+)/SO4- pair, showing a cage escape yield up to 75%. This is followed by the subsequent fast hole transfer from [Ru(bpy)(3)](3+) to the Fe-IV catalyst to give the long-lived Fe-V intermediate in aqueous solution. In the presence of excess photosensitizer, this process exhibits pseudo-first order kinetics with respect to the catalyst with a rate constant of 3.2(1) x 10(10) s(-1). Consequently, efficient hole scavenging activity of the high-valent iron complex is proposed to explain its high catalytic performance for water oxidation

Towards time resolved characterization of electrochemical reactions: electrochemically-induced Raman spectroscopy

Structural characterization of transient electrochemical species in the sub-millisecond time scale is the all-time wish of any electrochemist. Presently, common time resolution of structural spectro-electrochemical methods is about 0.1 seconds. Herein, a transient spectro-electrochemical Raman setup of easy implementation is described which allows sub-ms time resolution. The technique studies electrochemical processes by initiating the reaction with an electric potential (or current) pulse and analyses the product with a synchronized laser pulse of the modified Raman spectrometer. The approach was validated by studying a known redox driven isomerization of a Ru-based molecular switch grafted, as monolayer, on a SERS active Au microelectrode. Density-functional-theory calculations confirmed the spectral assignments to sub-ms transient species. This study paves the way to a new generation of time-resolved spectro-electrochemical techniques which will be of fundamental help in the development of next generation electrolizers, fuel cells and batteries