Rui Fausto

University of Coimbra | UC · Department of Chemistry

Probing quantum mechanical tunneling (QMT) in chemical reactions is crucial to understanding and developing new transformations. Primary H/D kinetic isotopic effects (KIEs) beyond the semiclassical maximum values of 7–10 (room temperature) are commonly used to assess substantial QMT contributions in one‐step hydrogen transfer reactions, because of...

Attention deficit and hyperactivity disorder (ADHD) is a prevalent neurodevelopmental condition, impacting approximately 10% of children globally. A significant proportion, around 30–50%, of those diagnosed during childhood continue to manifest ADHD symptoms into adulthood, with 2–5% of adults experiencing the condition. The existing diagnostic fra...

In this study, a commercial dental resin was reinforced by SiO2 nanoparticles (NPs) with different concentrations to enhance its mechanical functionality. The material characterization and finite element analysis (FEA) have been performed to evaluate the mechanical properties. Wedge indentation and 3-point bending tests were conducted to assess the...

Energy storage devices with liquid‐metal electrodes have attracted interest in recent years due to their potential for mechanical resilience, self‐healing, dendrite‐free operation, and fast reaction kinetics. Gallium alloys like Eutectic Gallium Indium (EGaIn) are appealing due to their low melting point and high theoretical specific capacity. Howe...

Two simple nitroxyl radicals, di-tert-butyl nitroxyl (DTBN) and 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) are solvated by one or two water, methanol, tert-butyl alcohol or phenol molecules. The resulting low temperature IR spectra of...

The thermal characterization of two binary systems of n-alkanes that can be used as Phase Change Materials (PCMs) for thermal energy storage at low temperatures is reported in this work. The construction of the solid–liquid binary phase diagrams was achieved using differential scanning calorimetry (DSC) and Raman spectroscopy. The solidus and liqui...

Integrating the principles of green chemistry to develop sustainable processes.

Water pollution poses a global threat to ecosystems and human health and is driven by the presence of various contaminants in wastewater, including nano- and microplastics. Despite the magnitude of this problem, the majority of global wastewater is released untreated into water bodies. To combat this issue, a multi-strategy approach is needed. This...

This annual review provides critical analysis of the literature on photochemistry and its applications for anyone wanting to keep up to date with the field. Combining reviews on the latest advances in photochemical research with specific topical highlights, this book is the primary resource for anyone wanting succinct and rich information. The volu...

Nitrile ylides are 1,3‐dipolar species with structures that are commonly described by propargylic and/or allenic resonance forms. Nevertheless, certain nitrile ylides exhibit a tendency to form dimers, suggesting the existence of structures characterized by an important carbenic contribution. To address the nitrile ylide carbenic nature, here we in...

Probing quantum mechanical tunneling (QMT) in chemical reactions is crucial to understand and develop new possibilities of molecular design. Primary H/D kinetic isotopic effects (KIEs) beyond the semiclassical maximum values of 7‒10 are commonly used to assess QMT contributions in one-step hydrogen transfer reactions, because H-atom QMT reactions a...

This work is a contribution to the thermal characterization of a selected binary system of two di-n-alkyl adipates that can be used as phase change material for thermal energy storage at low temperatures. The construction of the solid–liquid phase diagram using differential scanning calorimetry (DSC), complemented with Raman Spectroscopy studies fo...

Phenylpropiolic acid (C6H5C≡CCOOH, PPA) isolated in nitrogen and xenon cryogenic matrices was studied by infrared spectroscopy. The experimental studies were complemented by a series of quantum chemical calculations carried out at the density functional theory (B3LYP) and MP2 levels of theory (with different basis sets). The calculations predicted...

Piezoelectric nanogenerators (PENGs) have attracted great interest owing to their broad range application in environmental mechanical energy harvesting to power small electronic devices. In this study, novel flexible and high-performance double-layer sandwich-type PENGs based on one-dimensional (1-D) and two-dimensional (2-D) zinc oxide (ZnO) nanos...

We successfully synthesized millimeter-sized single crystals of the molecular erbium(III) complex Er(acac)3(cphen), where acac = acetylacetonate and cphen = 5-chloro-1,10-phenanthroline. The novelty of this work stems from the exhaustive examination of the polar and electronic properties of the obtained samples at the macro-, micro-, and nanoscale...

The molecular structure and photochemistry of dispiro[cyclohexane‐1,3′‐[1,2,4,5]tetraoxane‐6′,2′′‐tricyclo[3.3.1.13,7]decan]‐4‐one (TX), an antiparasitic 1,2,4,5‐tetraoxane was investigated using matrix isolation IR and EPR spectroscopies, together with quantum chemical calculations undertaken at the DFT(B3LYP)/6‐311++G(3df,3pd) level of theory, wi...

Crystal morphology is controlled by several physicochemical parameters such as the temperature, pressure, cooling rate, nucleation, diffusion, volatile composition, and viscosity. The development of different crystal morphologies is observed as a function of the cooling rate in many different rock types (i.e., glassy volcanic rocks, and archeometal...

The geometric and electronic structure of 1,3‐dipolar species, in particular of nitrile imines, can be surprisingly intricate. A particular example is the C‐phenyl‐nitrilimine, which exists as two energy minima that constitute bond‐shift isomers. To examine the effect of substituents in the phenyl ring, here we investigate the meta and para OH subs...

Ultraviolet-induced photodissociation and photo-isomerization of the three most stable conformers (SSC, GAC, and AAT) of glycolic acid are investigated in a low-temperature solid argon matrix using FTIR spectroscopy and employing laser radiation with wavelengths of 212 nm, 226 nm, and 230 nm. The present work broadens the wavelength range of photoc...

Monomers of benzimidazole trapped in an argon matrix at 15 K were characterized by vibrational spectroscopy and identified as 1H-tautomers exclusively. The photochemistry of matrix-isolated 1H-benzimidazole was induced by excitations with a frequency-tunable narrowband UV light and followed spectroscopically. Hitherto unobserved photoproducts were...

6-Bromopyridine-2-carbaldehyde (abbreviated as BPCA) is used both as a building block in supramolecular chemistry and as a ligand for transition metal catalysts and luminescent complexes. In this study, the structure and vibrational spectra of BPCA were investigated in both the room temperature neat crystalline phase and for the compound isolated i...

This chapter highlights the relevance of intramolecular hydrogen bonds (IMHBs) on the structure and properties (including reactivity) of molecules. A series of selected illustrative cases is provided, where IMHB impact the molecules' potential energy surfaces in a profound way, so that they ultimately are responsible in large amount for the propert...

Propiolamide (HC≡CCONH2, PA) has been isolated in low-temperature matrices (Ar, Xe, and N2) and studied by matrix isolation infrared (IR) spectroscopy and quantum chemical calculations undertaken at the DFT(B3LYP)/6-311++G(d,p) level of theory. In situ broadband UV light (λ>235 nm) irradiation of matrix-isolated PA led to the observation of new ban...

Monomers of meta-fluorophenol (mFP) were trapped from the gas phase into cryogenic argon and nitrogen matrices. The estimated relative energies of the two conformers are very close, and in the gas phase they have nearly equal populations. Due to the similarity of their structures (they only differ in the orientation of the OH group), the two confor...

Hydrogen bonding (HB) has been receiving attention from both experimental and theoretical researchers since its discovery in the 1920s due to its impact on many chemical and biological processes. However, despite the large number of investigations conducted on this topic, the nature of the HBs and, in particular, the estimation of intramolecular HB...

We present here a new example of chemical reactivity governed by quantum tunneling, which also highlights the limitations of the classical theories. The syn and anti conformers of a triplet 2-formylphenylnitrene, generated in a nitrogen matrix, were found to spontaneously rearrange to the corresponding 2,1-benzisoxazole and imino-ketene, respective...

The novel azo dye 2-(p-tolyldiazenyl)naphthalen-1-amine (2tona) was synthesized and structurally characterized by infrared, ¹H- and ¹³C NMR spectroscopies, complemented by density functional theory (DFT) calculations on the different possible isomeric species of the compound. The solvatochromism exhibited by 2tona in several solvents with different...

Quantum mechanical tunneling of heavy‐atoms and vibrational excitation chemistry are unconventional and scarcely explored types of reactivity. Once fully understood, they might bring new avenues to conduct chemical transformations, providing access to a new world of molecules or ways of exquisite reaction control. In this context, we present here t...

Organic polar crystalline materials, featuring the merits of lightweight, flexibility, and low fabrication costs, are emerging as promising alternatives for inorganic ferroelectrics, but so far, they are not competitive. The main reasons are the moderate polar properties of such materials and the fact that the temperature of the phase transition fr...

Herein, we describe studies relevant to heterocyclic chemistry carried out with low‐temperature matrix isolation technique in conjugation with infrared (IR) spectroscopy. These studies comprise structural characterizations, ultraviolet (UV) and thermal reactivity, IR‐induced processes, and quantum tunneling reactions. Focus is given mainly to examp...

The molecular structure, conformational space and UV-induced rotamerization and decarbonylation of 2-aminoacetanilide (2AA) were investigated by matrix isolation infrared spectroscopy and quantum chemical electronic structure calculations. The compound was isolated in a cryogenic (15 K) argon matrix, and four conformers were spectroscopically ident...

Plasmodium falciparum artemisinin‐resistance boosted the quest for novel plasmodial “fast killers,” uncovering antimalarial candidates OZ439 and E209, whose peroxide precursors are 1,2,4‐trioxolane (1) and 1,2,4,5‐tetraoxane (2), differing solely in the pharmacophore (trioxolane or tetraoxane). Combining X‐ray crystallography and vibrational spectr...

Anhydrous carbamazepine (CBZ) is an anti-convulsant drug commonly used to treat epilepsy and relieve trigeminal neuralgia. The presence of the dihydrate form in commercial CBZ tablets can change the dissolution rate of the active pharmaceutical ingredient (API), thus decreasing its activity. The hydration transformation can occur during wet granula...

5-Chlorosalicylaldehyde (abbreviated as 5CSA) is an important chemical used in the synthesis of fragrances, dyes, and pharmaceuticals. In this investigation, 5CSA isolated in solid N2, at 10 K, and in its neat amorphous and crystalline phases, at 50 and 190 K, respectively, were investigated by infrared spectroscopy and DFT(B3LYP)/6-311++G(d,p) cal...

Polycarbonate (PC)-ZnO films with different percentages of ZnO were prepared by a solution stirring technique and subjected to ultraviolet (UV; λ = 254 nm) irradiation. Structural parameters of the samples and the effects of UV irradiation on the surface properties of the PC and PC-ZnO nanocomposites were evaluated by X-ray diffraction (XRD), X-ray...

In this study, the YXXY¯ and the two equivalent ZXXZ¯/ZYYZ¯ polarized Raman spectra of a LiNbO3 single crystal have been recorded and used as a benchmark test for the density functional theory (DFT) calculation of the longitudinal modes and of their Raman activity. The theoretical approach, based on periodic boundary conditions and a linear combina...

Fumaric and maleic acids ((E)- and (Z)-HOOC-CH═CH-COOH, FA and MA) were studied experimentally by infrared spectroscopy in nitrogen matrixes and theoretically by quantum chemical calculations. The calculations, carried out at the DFT(B3LYP) and MP2 levels of theory, predicted the existence of at least 5 conformers of maleic acid and 10 conformers o...

A new benzyloxy containing ortho hydroxyl-substituted aryl Schiff base, trans 2-((2-(benzyloxy)benzylidene) amino)phenol (abbreviated as BBAP), was synthesized and characterized by 1H-, 13C-NMR and infrared spectroscopic techniques and elemental analysis. The conformational landscape of the compound, as well as its infrared spectra in argon and N2...

Although graphene films are the main candidate for replacing scarce and brittle metal‐oxide transparent conductors, the current challenges on graphene deposition and patterning are severely limiting their commercial application. Here, materials and methods that allow large‐scale, efficient, and low‐cost fabrication of highly transparent conductors...

Fulgurites are naturally occurring structures that are formed when lightning discharges reach the ground. In this investigation, the mineralogical compositions of core and shell compartments of a rare, iron-rich fulgurite from the Mongolian Gobi Desert were investigated by X-ray diffraction and micro-Raman spectroscopy. The interpretation of the Ra...

Semitransparent and Conductive Electrodes In article number 2101238, Mahmoud Tavakoli and colleagues demonstrate that graphene oxide‐coated liquid metal nanoparticles can be transformed to semitransparent and conductive electrodes, through a rapid, low‐cost, and scalable laser processing technique. The authors used an infrared laser source for simu...

The molecular and crystal structures of N-picryl-m-phenolidine (or, 3-(2,4,6-trinitrophenylamino)phenol; TAP) were investigated by quantum chemical electronic structure calculations (including state-of-the-art fully-periodic DFT calculations for the crystal) and single crystal X-ray diffraction. The molecule of the compound has four low-energy conf...

In this article, IR-induced and tunneling-driven reactions observed in cryogenic matrices are described in a historical perspective, the entangling of the two types of processes being highlighted. The story of this still ongoing fascinating scientific endeavor is presented here following closely our own involvement in the field for more than 30 yea...

The ending of estrogen production in the ovaries after menopause results in a series of important physiologic changes, including hair texture and growth. In this study we demonstrate that Raman spectroscopy can be used successfully as a tool to probe menopause-induced changes on hair, in particular when coupled with suitable chemometrics approaches...

A new methoxy-substituted ortho-hydroxyaryl Schiff base, 4-(3-methoxy-2-hydroxybenzylidene-amino) phenol was synthesized from 4-aminophenol and 2-hydroxy-3-methoxybenzaldehyde in methanol solution and characterized by 1H-NMR, 13C-NMR and infrared spectroscopies and elemental analysis. The compound was isolated in a cryogenic (10 K) argon matrix, an...

A novel derivative of the prominent ROY compound, 5-acetyl-2-((2-nitrophenyl)amino)thiophene-3-carbonitrile (AcROY), was synthesized in a two-steps procedure by the nucleophilic aromatic substitution reaction between 1-fluoro-2-nitrobenzene and 2-aminothiophene-3-carbonitrile, followed by Friedel–Crafts acylation...

Graphene encapsulated liquid metal particles is a novel and promising class of biphasic composite, with application in the next generation of electronic devices. Here, rapid, low‐cost, and scalable fabrication of solution processed large area rGO@EGaIn electrodes is demonstrated. rGO@EGaIn solution is first deposited over the substrate through spra...

A new tetramine bis(2-naphthol)-derivative was synthesized and its structure investigated by ¹H- and ¹³C NMR, UV-Vis absorption and fluorescence spectroscopies, as well as through density functional theory calculations (including time-dependent DFT). The effect of a series of metal ions (Ag ⁺, Al3 +, Ba2 +, Ca2 +, Cd2 +, Co2 +, Cs ⁺, Cu2 +, Fe2 +,...

We demonstrate here that selective vibrational excitation of a moiety, remotely attached in relation to the molecular reaction site, might offer a generalized strategy for inducing bond-breaking/bond-forming reactions with exquisite precision. As a proof-of-principle, the electrocyclic ring-expansion of a benzazirine to a ketenimine was induced, in...

A new Schiff base fluorescence probe for Cu²⁺ was designed and synthesized by reaction between 2-[(3-formylphenoxy)2-hydroxypropoxy]benzaldehyde and 4-aminophenol. The probe was characterized by elemental analysis, FTIR, ¹H- and ¹³C NMR, and fluorescence spectroscopies. DFT calculations were carried out to further characterize the structure of the...

In this article, a comprehensive study of the molecular structure, spectroscopy, and photochemistry of alprazolam (Xanax®; 8-chloro-1-methyl-6-phenyl-4H-[1,2,4] triazolo[4,3-a][1,4]benzodiazepine) is reported. The structure of the isolated molecule of the compound was investigated using density functional theory (DFT), revealing that the molecule e...

The prototropic tautomerism in 3(5)-aminopyrazoles was investigated by matrix isolation infrared (IR) spectroscopy, supported by DFT(B3LYP)/6-311++G(d,p) calculations. In consonance with the experimental data, the calculations predict tautomer 3-aminopyrazole (3AP) to be more stable than the 5-aminopyrazole (5AP) tautomer (calculated energy differe...

Attention deficit and hyperactivity disorder (ADHD) is one of the most common neurodevelopmental disorders of childhood. It affects ~10% of the world’s population of children, and about 30–50% of those diagnosed in childhood continue to show ADHD symptoms later, with 2–5% of adults having the condition. Current diagnosis of ADHD is based on the cli...

H-tunneling is a ubiquitous phenomenon, relevant to fields from biochemistry to materials science, but harnessing it for mastering the manipulation of chemical structures still remains nearly illusory. Here, we demonstrate how to switch on H-tunneling by conformational control using external radiation. This is outlined with a triplet 2-hydroxypheny...

A new Schiff base compound, 3-(5-bromo-2-hydroxybenzylideneamino)phenol (abbreviated as BHAP) was synthesized and characterized by 1H- and 13C- nuclear magnetic resonance and infrared spectroscopies. DFT/B3LYP/6-311++G(d,p) calculations were undertaken in order to explore the conformational space of both the E- and Z- geometrical isomers of the eno...

The monomers of 1,3-benzoxazole isolated in a cryogenic argon matrix were characterized by infrared spectroscopy. The photochemistry of matrix-isolated 1,3-benzoxazole, induced by excitation with a frequency-tunable narrowband UV light, was investigated. Irradiation at 233 nm resulted in a nearly quantitative conversion of 1,3-benzoxazole into 2-is...

This article reports on a detailed study of the structural, spectroscopic and magnetic properties of La0.57Nd0.10Sr0.18Ag0.15FeO3 (LNSAFO) ferrite nanoparticles, which were prepared using the solid state technique.The Rietveld analysis of the powder X-ray diffractogramsindicatedthat the material crystalizes in an orthorhombic structure, Pnma space...

Bjurböle L/LL4 ordinary chondrite was studied using scanning electron microscopy with energy dispersive spectroscopy, Raman spectroscopy, X-ray diffraction, magnetization measurements and Mössbauer spectroscopy. The phase composition and the relative iron fractions in the iron-bearing phases were determined. The unit cell parameters for olivine, or...

In this study, the polarized Raman spectra of the R3c LiNbO3 crystal are used as a benchmark test for density functional theory (DFT) full periodic boundary conditions linear combination of atomic orbitals (LCAO) calculation of the Raman tensors, according to the implementation in the CRYSTAL software. The theoretical approach used proved to provid...

The conformational stability, infrared spectrum, and photochemistry of phenyl 1-hydroxy-2-naphthoate (PHN) were studied by matrix isolation infrared spectroscopy and theoretical computations performed at the DFT(B3LYP)/6-311++G(d,p) level of theory. The main intramolecular interactions determining the relative stability of seven conformers of the m...

In 1975, Buchwalter and Closs reported one of the first examples of heavy-atom quantum mechanical tunneling (QMT) by studying the ring closure of triplet cyclopentane-1,3-diyl to singlet bicyclo[2.1.0]pentane in cryogenic glasses. Since then, no clear theoretical evidence has been provided to elucidate how the intersystem crossing (ISC) and QMT rel...

The Sari\c{c}i\c{c}ek howardite meteorite shower consisting of 343 documented stones occurred on 2 September 2015 in Turkey and is the first documented howardite fall. Cosmogenic isotopes show that Sari\c{c}i\c{c}ek experienced a complex cosmic ray exposure history, exposed during ~12-14 Ma in a regolith near the surface of a parent asteroid, and t...

New hexadentate chelates, H2L¹ and L¹, were synthesized. The Schiff base imine ligand, L¹, was prepared by reaction of 2,2′-[ethane-1,2-diylbis(oxy)]dibenzaldehyde and propanolamine, and characterized by infrared (IR), ¹H NMR and ¹³C NMR spectroscopies. The amine ligand, H2L¹, was prepared in the form of perchlorate salt ([H4L¹](ClO4)2,) by reducti...

The preferred conformations, infrared spectra and photochemistry of matrix-isolated 1H- and 2H- tautomers of ethyl tetrazole-5-carboxylate (ET5C) were investigated. Experimentally, isolated monomeric forms of the two tautomers were trapped in cryogenic argon matrices (15 K), and studied by infrared spectroscopy. Identification of the conformational...

This chapter focuses on the use of chemometric models developed from infrared (IR) spectroscopic data of blood serum as an auxiliary tool for autism spectrum disorder (ASD) diagnosis. In the introductory sections the fundamentals of IR spectroscopy are shortly reviewed and brief descriptions of the different chemometric methods used in the case stu...

The conformational behavior of carboxylic acids has attracted considerable attention, as it can be used as a gateway for the study of more complex phenomena. Here, we present an experimental and computational study of pyrrole-2-carboxylic acid (PCA) conformational space and the vibrational characterization of the compound by infrared spectroscopy....

Color polymorphism is an interesting property of chemical systems which present crystal polymorphs of different colors. It is a rare phenomenon, with only a few examples reported in the literature hitherto. Nevertheless, systems exhibiting color polymorphism have many potential applications in different domains, such as pigment, sensor, and technol...

In the first part of this work, we report the FTIR spectra of pure NH and isotopically substituted ND (10-15% D and 80-90% D) polycrystalline hypoxanthine, xanthine, adenine and guanine recorded in the 400–4000 cm⁻¹ range, as a function of temperature (10–300 K). We provide assignments of the stretching and out-of-plane bending amine (NH2) and imin...

This article presents a detailed comprehensive investigation of the ortho fluoro- and chloro- substituted benzoic acids both, as isolated molecules and in the crystalline phase. Quantum chemical calculations performed within the density functional theory (DFT) formalism are used to investigate the potential energy landscapes of the molecules, takin...

Monomers of 4-methoxyindole and 5-methoxyindole trapped in low-temperature xenon matrices (15-16 K) were characterized by IR spectroscopy, in separate experiments. Each compound was shown to adopt the most stable 1H-tautomeric form. The photochemistry of the matrix-isolated compounds was then investigated by exciting the matrices with narrowband UV...

The photophysical properties of Eu3+ and Tb3+ complexes of DOTAGA and DO3A-monoamide conjugates of the Pittsburgh compound B (PiB) chromophore, prepared using linkers of different lengths and flexibilities, and which form stable negatively charged (LnL1), and uncharged (LnL2) complexes, respectively, were studied as potential probes for optical det...