Structural imaging of transient excited-state species is a key goal of molecular physics, promisi... more Structural imaging of transient excited-state species is a key goal of molecular physics, promising to unveil rich information about the dynamics underpinning photochemical transformations. However, separating the electronic and nuclear contributions to the spectroscopic observables is challenging, and typically requires the application of high-level theory. Here, we employ site-selective ionisation via ultrashort soft X-ray pulses and time-resolved Coulomb explosion imaging to interrogate structural dynamics of the ultraviolet photochemistry of carbon disulfide. This prototypical system exhibits the complex motifs of polyatomic photochemistry, including strong non-adiabatic couplings, vibrational mode couplings, and intersystem crossing. Immediately following photoexcitation, we observe Coulomb explosion signatures of highly bent and stretched excited-state geometries involved in the photodissociation. Aided by a model to interpret such changes, we build a comprehensive picture of ...
We present an investigation of the ultrafast dynamics of the polycyclic aromatic hydrocarbon fluo... more We present an investigation of the ultrafast dynamics of the polycyclic aromatic hydrocarbon fluorene initiated by an intense femtosecond infrared laser pulse and probed by a weak visible pulse. Using a multichannel detection scheme (mass spectra, electron and ion velocity-map imaging), we provide a full disentanglement of the complex dynamics of the vibronically excited parent molecule, its excited ionic states, and fragments. We observed channels resulting from both multiphoton- and tunnel-ionization regimes. In particular, we observed the formation of the unstable tetracation of fluorene, above-threshold ionization features in the photoelectron spectra, and evidence of ubiquitous secondary fragmentation. We produced a global fit of all observed time-dependent photoelectron and photoion channels. This global fit includes four parent ions extracted from the mass spectra, 15 kinetic-energy-resolved ionic fragments extracted from ion velocity map imaging, and five photoelectron chann...
The complex conformational space of the non-proteinogenic cyclic amino acid pipecolic acid has be... more The complex conformational space of the non-proteinogenic cyclic amino acid pipecolic acid has been explored in the gas phase for the first time. Solid pipecolic acid samples were vaporized by laser ablation and expanded in a supersonic jet where the rotational spectral signatures owing to nine different conformers were observed by Fourier transform microwave spectroscopy. All species were identified by comparison of the experimental rotational and nuclear quadrupole coupling constants with those predicted theoretically. Observation of type-III conformers, leading difference compared with the conformational behavior of the analog amino acid proline, has been interpreted by an increment in steric hindrance when increasing the number of carbons present in the ring.
Carvedilol (CRV) is an important medicament for heart arrhythmia. The aim of this work was the in... more Carvedilol (CRV) is an important medicament for heart arrhythmia. The aim of this work was the interpretation of its vibrational spectra with consideration on the solvent effect. Infrared and Raman spectra were recorded in solid state as well in solution. The experimental spectra were evaluated using DFT quantum chemical calculations computing the optimized structure, atomic net charges, vibrational frequencies and force constants. The same calculations were done for the molecule in DMSO and aqueous solutions applying the PCM method. The calculated force constants were scaled to the experimentally observed solid state frequencies. The characters of the vibrational modes were determined by their potential energy distributions. Solvent effects on the molecular properties were interpreted. Based on these results vibrational spectra were simulated.
The bioactive amino monosaccharide D-glucosamine has been generated in the gas phase via laser ab... more The bioactive amino monosaccharide D-glucosamine has been generated in the gas phase via laser ablation of D-glucosamine hydrochloride. Three cyclic a-4 C 1 pyranose forms have been identified using Fourier transform microwave techniques. Stereoelectronic hyperconjugative forces -essentially linked with the anomeric or gauche effect -and cooperative OHÁ Á ÁO, OHÁ Á ÁN and NHÁ Á ÁO chains, extended along the entire molecule, are found to be the main factors driving the conformational behavior. The orientation of the NH 2 group within each conformer has been determined by the values of the nuclear quadrupole coupling constants. The results have been compared with those recently obtained for the archetypical D-glucose.
Gas-Phase Conformational Characterization of Trace Amine Neurotransmitters: a rotational spectroscopy study
Tese no âmbito do Doutoramento em Quimica, ramo de Espectroscopia Molecular apresentada ao Depart... more Tese no âmbito do Doutoramento em Quimica, ramo de Espectroscopia Molecular apresentada ao Departamento de Quimica da Faculdade de Ciencias e Tecnologia da Universidade de Coimbra
On the use of metallic nanoparticulated catalysts for in-situ oil upgrading
Fuel, 2021
An exhaustive review on the application of different metal-based nanoparticles for the upgrading ... more An exhaustive review on the application of different metal-based nanoparticles for the upgrading of heavy oils has been performed. Particular emphasis has been put on those catalysts used for in-situ upgrading using various thermal treatment methods aiming at extracting heavy oils in a more effective manner. Different types of catalysts have been identified, such as monometallic (Mg,
Proceedings of the 71st International Symposium on Molecular Spectroscopy, 2016
The multiconformational landscape of the non-proteinogenic cyclic amino acid pipecolic acid has b... more The multiconformational landscape of the non-proteinogenic cyclic amino acid pipecolic acid has been explored in the gas phase. Solid pipecolic acid (m.p. 280 • C) was vaporized by laser ablation (LA) and expanded in a supersonic jet where the rotational spectra of seven conformers were obtained by broadband microwave spectroscopy (CP-FTMW). All conformers were conclusively identified by comparison of the experimental spectroscopic constants with those predicted theoretically. The relative stability of the conformers rests on a delicate balance of the different intramolecular hydrogen bonds established between the carboxylic and the amino groups.
Solid samples of phenylglycinol were vaporized by laser ablation and investigated through rotatio... more Solid samples of phenylglycinol were vaporized by laser ablation and investigated through rotational spectroscopy in a supersonic expansion using two different techniques: chirped pulse Fourier transform microwave spectroscopy and narrow band molecular beam Fourier transform microwave spectroscopy. One conformer, bearing an O-H•••N and an N-H•••'IT intramolecular hydrogen bonds, could be successfully identified by comparison of the experimental rotational and 14 N nuclear quadruple coupling constants with those predicted theoretically.
The bioactive amino monosaccharide D-glucosamine has been generated in gas phase via laser ablati... more The bioactive amino monosaccharide D-glucosamine has been generated in gas phase via laser ablation of D-glucosamine hydrochloride. Three cyclic α-4 C1 pyranose forms have been identified using Fourier transform microwave techniques. Stereoelectronic hyperconjugative forcesessentially linked with the anomeric or gauche effectand cooperative OH … O, OH … N and NH … O chains, extended along the entire molecule, are found to be the main factors driving the conformational behavior. The orientation of the NH2 group within each conformer has been determined by the values of the nuclear quadrupole constants. The results have been compared with those recently obtained for the archetypical D-glucose.
Proceedings of the 69th International Symposium on Molecular Spectroscopy, 2014
A laser ablation method has been successfully used to vaporize the bioactive amino monosaccharide... more A laser ablation method has been successfully used to vaporize the bioactive amino monosaccharide D-glucosamine. Three cyclic α-4 C 1 pyranose forms have been identified using a combination of CP-FTMW and LA-MB-FTMW spectroscopy. Stereoelectronic hyperconjugative factors, like those associated with anomeric or gauche effects, as well as the cooperative OH• • • O, OH• • • N and NH• • • O chains, extended along the entire molecule, are the main factors driving the conformational behavior. All observed conformers exhibit a counter-clockwise arrangement (cc) of the network of intramolecular hydrogen bonds. The results are compared with those recently obtained for D-glucose. a a
Four and six conformers of the neurotransmitters octopamine and synephrine, respectively, have be... more Four and six conformers of the neurotransmitters octopamine and synephrine, respectively, have been identified in the gas phase using a laser ablation device in combination with a molecularbeam Fourier transform microwave spectrometer operating in the 4-10 GHz frequency range. The identification of all of the conformers was based on a comparison of the experimental rotational and 14 N quadrupole coupling constants with those predicted by ab initio calculations, as well as the relative values of their electric dipole moment components. The conformational preferences have been rationalized in terms of the various intramolecular forces operating in the different conformers of the studied molecules. All observed species are characterized by an intramolecular hydrogen bond of the type O-H•••N established in the side chain of the neurotransmitters, which adopts an extended disposition in their most stable forms. For conformers with a folded side chain, an extra N-H•••π hydrogen-bond-type interaction is established between the amino group and the π system of the aromatic ring.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2014
BSN-006 is an important compound in drug industry. Structure was analyzed by means of DFT/(B3LYP)... more BSN-006 is an important compound in drug industry. Structure was analyzed by means of DFT/(B3LYP) functional with 6-311++G(d,p) set. Far, Mid-infrared and micro-Raman spectroscopic investigations were performed. Experimental results are in consistent with the theoretical calculations. Hydrogen bonds were also discussed after potential energy scan calculations. Optimized geometric structure of BSN-006.
Conformational isomerism of trimethylphosphate (TMP) has been studied de novo. TMP monomers were ... more Conformational isomerism of trimethylphosphate (TMP) has been studied de novo. TMP monomers were isolated in low temperature xenon matrices at different substrate temperatures and characterized using FTIR spectroscopy. At the lowest temperature, three different conformers, with overall molecular symmetries C 3 , C 1 and C s , were shown to co-exist in the matrix. Increase of the sample temperature led to conformational cooling, with the two minor conformers being depopulated successively, following an order of increasing stability. Initially, the less stable C s conformer converted to the C 1 form and, at higher temperatures, the C 1 conformer converted to the global energy minimum, C 3 . Interpretation of the experimental data was supported by extensive calculations of the vibrational spectra and barriers to the conformational interconversion.
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Papers by Alcides Simao