The role of Duschinsky rotation in intersystem crossing: A case study of uracil

The intersystem crossing rate for the transition between the lowest excited singlet and triplet electronic states of uracil was studied by means of ab initio methods. The rate was evaluated using the timedependent approach based on the correlation function and its two approximations: the second-order cumulant expansion and the short-time approximation. The normal modes of the singlet and triplet states are related by the Duschinsky transformation, i.e., by rotation and translation. It was found that for singlet-triplet adiabatic energy gaps below 6000 cm-1, the inclusion of the Duschinsky rotation is necessary for quantitative results. Above energy gaps of 6000 cm-1, the rates obtained with and without the Duschinsky rotation are similar. The cumulant expansion approximates well the correlation function. The short-time approximation, although crude, can be used as the first estimate of the rate

A study of the low-lying singlet and triplet electronic states of chlorophyll A and B

Chlorophylls have been extensively investigated both experimentally and theoretically owing to the fact that they are essential for photosynthesis. We have studied two forms of chlorophyll, chlorophyll a and chlorophyll b, by means of density functional theory. Optimization of S0, S1 and T1 states was performed with the B3-LYP functional. The computed fluorescence lifetimes show good agreement with the available experimental data. The electronic adiabatic energies of S1 and T1 states are 2.09/2.12 and 1.19/1.29 eV for chlorophyll a and chlorophyll b respectively. We discussed the implications of this results on the triplet formation. Also, the calculated vertical ionization potentials shows good agreement with the experimental results. [Projekat Ministarstva nauke Reoublike Srbije, br. 172040

A simulation of free radicals induced oxidation of dopamine in aqueous solution

Understanding the basic chemistry between highly reactive free radicals and dopamine is an important step in characterizing the antioxidative activity of catecholamine neurotransmitters. In this work, we simulated the reactions between dopamine and hydroxyl, peroxyl and methoxy radicals in aqueous solution by employing first principle molecular dynamics based on density functional theory and the BLYP functional. The simulations provide mechanistic insight into the reaction mechanisms but underestimate reaction timescales. The failure of the BLYP functional to address the formal hydrogen atom transfer barriers between dopamine and free radicals is attributed to the self-interaction error.This is peer-reviewed version of the article: B. Milovanović, J. Ilić, I.M. Stanković, M. Popara, M. Petković, M. Etinski, Chemical Physics 524, (2019) 26-30, [https://doi.org/10.1016/j.chemphys.2019.05.001][http://cer.ihtm.bg.ac.rs/handle/123456789/2949

Conifers as green renewable inhibitors for steel acid cleaning

While traditional corrosion inhibitors are quite effective at protecting metal, they also pollute the environment. Since conifers are renewable plants, there has been a lot of interest in using plant extracts as green corrosion inhibitors [1,2]. They fit industry standards and make excellent raw materials for corrosion inhibitors. However, because of the high dosage and unclear composition of these corrosion inhibitors, they have not been successfully used in industry. In this work black pine (Pinus nigra, PN) and Pančić spruce essential oils were synthesized from fresh needles, which were further tested as a mixture of green organic substances that inhibit steel corrosion. In addition, the active substances of black pine essential oil (α-pinene, β-pinene, and caryophyllene) were tested under the same conditions and their effect on the corrosion rate was compared with the effect of black pine essential oil. The influence of phytochemicals (bornyl-acetate, borneol, and camphene) on the effectiveness of the essential oil of Pančić's spruce, as well as on the adsorption on steel, was evaluated by theoretical and surface methods. Through experiments and theoretical calculation, the corrosion inhibition effect of these inhibitors on steel was studied in 1 M HCl solution at 25 C. The optimal inhibitor concentration as well as the time of immersion were assessed by Electrochemical impedance spectroscopy. It has been demonstrated that all inhibitors become more effective over time. At the same concentration of 80 ppm, the most prevalent component of the PN essential oil, α-pinene, demonstrated a poorer corrosion prevention efficacy than β-caryophyllene, that reached 96% inhibition efficiency. Both PN and Pančić essential oil were mixed types of inhibitors with prevalent influence on the inhibition of the cathodic reaction, as shown by polarization measurements. SEM and XPS analysis confirmed the presence of borneol and bornyl-acetate, along with non-soluble oxides that formed a protective film on metal surface. Binding mechanism of the Pančić essential oil inhibitor molecules was resolved with the analysis of the projected density of states [3]. The theoretical calculations [4] indicated that some of the phytochemicals in Pančić essential oil bond to the steel by chemisorption (bornyl-acetate and borneol) while others by physisorption (camphene). This has also been confirmed by values of adsorption free energy determined from Langmuir Isotherm

Tuning charge transfer states in the G-octet-metal ion complexes for the potential nanotechnological applications

Here we study G-octet-metal ion complexes (M-G8) which act as models for the G-quadruplex supramolecular arrangement within DNA. We used DFT based molecular dynamics (BLYP-D3/DZVP+PW+GTH) for the configuration sampling purposes and calculated electronic excitations to initially populated (Franck-Condon) states. We use descriptors based on one-electron transition density matrix to seize charge transfer content of the selected excited states. We use TDDFT formalism (CAM-B3LYP/6-31G(d)) to calculate one-electron transition density matrices and absorption spectrum

Influence of the metal ions on the charge transfer states in the G-octet-metal ion complexes

In this work, we study G-octet-metal ion complexes which act as models for the G-quadruplex supramolecular arrangement within DNA. We used DFT based molecular dynamics (BLYP-D3/DZVP+PW+GTH) for configuration sampling purposes and calculated electronic excitations to initially populated (Franck-Condon) states. To capture charge transfer content of the excited states, we used descriptors who rely on the analysis of the one-electron transition density matrix acquired from the TDDFT calculation (CAM-B3LYP/6-31G(d))

Peptides and their constituents as steel corrosion inhibitors: an experimental and theoretical approach

Ekološki prihvatljivi inhibitori privlače pažnju mnogih istraživača zbog povoljnih svojstava: biorazgradivost, netoksičnost, dostupnost i obnovljivost. U njih spadaju i amonokiseline (AK), kao sastojci od vitalnog značaja za sva živa bića. U radu je ispitan inhibitorski efekat nekoliko AK na čeliku u 1 M HCl: tri samostalne AK, glicin, glutaminska kiselina i cistein; smeša ove tri AK, kao i njihov dipeptid (glicin i glutaminska kiselina) i tripeptid glutation (glicin, glutaminska kiselina i cistein). Inhibitorska efikasnot AK je određena elektrohemijskim merenjima. Meren je ugao kvašenja površine čelika sa adsorbovanim inhibitorom, energija veza inhibitora i supstrata je određivana XPS metodom, a topografija AFM. Razlike u vezivanju inhibitora za supstrat su analizirane teorijskim proračunima.Green eco-friendly inhibitors have become very popular due to their remarkable properties such as biodegradability, environmental acceptability, safety, availability, and renewability. Amino acids (ACs) are one of them, as constituents of vital importance for all living beings. Several AC systems were examined in this study as steel inhibitors in 1 M HCl solution: three ACs separately, glycine, glutamic acid and cysteine; their mixture, as well as their dipeptide (glycine and glutamic acid) and tripeptide glutathione (glycine, glutamic acid and cysteine). Their inhibition efficiency was evaluated and compared by electrochemical methods. The steel surface with adsorbed inhibitor was analyzed by contact angle measurements, AFM and XPS. The intrinsic differences in adsorption between these green inhibitors were analyzed by theoretical calculations

Inhibicija korozije ugljeničnog čelika u 1 M HCl pomoću ekološki prihvatljivog inhibitora (Pančićeva omorika): kombinovanje eksperimentalnih i teorijskih metoda

Etarsko ulje Pančićeve omorike analizirano je gasnom hromatografijom u kombinaciji sa masenom spektrometrijom (GC/MS). Eektrohemijska merenja su pokazala da u koncentaciji od 200 ppm ovaj zeleni inhibitor smanjuje brzinu korozije čelika sa značajnom efikasnošću od 93 % nakon 4 h. Polarizaciona mjerenja su pokazala da je etarsko ulje inhibitor mešovitog tipa. Inhibirana i neinhibirana površina čelika je analizirana skenirajućom elektronskom mikroskopijom (SEM), i merenjem kontaktnog ugla. Adsorpcija organskih aktivnih supstanci na površini čelika prati Lengmirovu adsorpcionu izotermu i rendgenska fotoelektronska spektroskopija (XPS) je pružila dublji uvid u mehanizam inhibicije korozije. Eksperimentalne studije su upotpunjene teorijskim proračunima.Picea omorika essential oil was analyzed by gas chromatography combined with mass spectrometry (GC/MS). Electrochemical measurements showed that this green inhibitor reduces the corrosion rate of steel with a significant efficiency of 93% after 4 h at a concentration of 200 ppm. Polarization measurements showed that the essential oil is a mixed type inhibitor. The inhibited and non-inhibited surface of the steel was analyzed by scanning electron microscopy (SEM) and contact angle measurements. X-ray photoelectron spectroscopy (XPS) provided a deeper insight into the mechanism of corrosion inhibition. The adsorption of organic active substances on the steel surface follows the Langmire adsorption isotherm. Experimental studies were completed with the theoretical studies

Investigation of the spin-forbidden process in thymine

The intersystem crossing rate from the lowest singlet to the lowest triplet state of thymine was studied by means of the ab initio methods. The rate was calculated employing the time-dependent approach based on the correlation function. The normal modes of the singlet and triplet electronic states are related by the Duschinsky transformation, i. e. by rotation and translation. The correlation function was calculated using the Condon approximation for the spin-orbit matrix element and harmonic approximation for the nuclear motion. The intersystem crossing rate strongly depends on the singlet-triplet adiabatic energy gap and on the normal mode mixing

Effect of temperature on rate of the spin-forbidden transition in uracil and thymine

The intersystem crossing rates of uracil and thymine molecules in interaction with the heat bath were studied by means of the ab initio methods. The rates were calculated employing the time-dependent approach based on the correlation function. The normal modes of the singlet and triplet electronic states were related by the Duschinsky transformation. The correlation function was calculated using the Condon approximation for the spin-orbit matrix element and harmonic approximation for the nuclear motion. The excess vibrational energy in the initial singlet excited electronic state decreases the rate of the triplet formation in uracil and thymine. This decrease is more pronounced for uracil. Also, it was found that the change of the adiabatic energy gap can significantly modify the rate of the triplet formation