Hirshfeld Atomic Charges Research Articles

Theoretical Design of New Grafted Molecules d-Glucosamine-Oxyresveratrol-Essential Amino Acids: DFT Evaluation of the Structure-Antioxidant Activity.

In the pursuit of innovative high-performance materials suitable for antioxidant applications, the density functional theory was employed to design a series of compounds derived from small biodegradable organic molecules. This study involved grafting the negatively charged unit d-glucosamine (GleN) and essential amino acids onto the 3 and 4' carbons of the backbone of trans-2,4,3',5'-tetrahydroxystilbene (trans-OXY), respectively. The aim was to prevent trans-OXY degradation into the cis region and enhance its electronic and antioxidant properties. Theoretical calculations using DFT/PW91/TZP in water revealed that the designed biomolecules (GleN-OXY-AA) outperformed both free OXY units and essential amino acids in terms of antioxidant efficacy, as indicated by the bond dissociation energy (BDE) findings. Notably, GleN-OXY-Ile and GleN-OXY-Trp compounds exhibited an average BDE of 66.355 kcal/mol, translating to 1.82 times the activity of t-OXY and 1.55 times the action of ascorbic acid (Vit C). AIM analysis demonstrated that the proposed biomaterials favored the formation of quasi-rings through intramolecular H···O hydrogen bonds, promoting π-electron delocalization and stabilization of radical, cationic, and anionic forms. Quantum calculations revealed the release of hydrogen atoms or electrons from sites of reduced electronegativity, visually identified by MEP maps and estimated by Hirshfeld atomic charges.

Comprehensive Study on the Adsorption and Degradation of Dichlorodiphenyltrichloroethane on Bifunctional Adsorption-Photocatalysis Material TiO2/MCM-41 Using Quantum Chemical Methods.

The adsorption and degradation capacities of dichlorodiphenyltrichloroethane (DDT) on a photocatalyst composed of TiO2 supported on the mesoporous material MCM-41 (TiO2/MCM-41) were investigated using density functional theory and real-time density functional theory methods. The van der Waals interactions within the PBE functional were adjusted by using the Grimme approach. The adsorption of DDT was evaluated through analyses involving adsorption energy, Hirshfeld atomic charges, Wiberg bond orders, molecular electrostatic potential, noncovalent interaction analysis, and bond path analysis. The findings reveal that DDT undergoes physical adsorption on pristine MCM-41 or MCM-41 modified with Al or Fe due to the very small bond order (only about 0.15-0.18) as well as the change in total charge of DDT after adsorption is close to 0. However, it chemically adsorbs onto the TiO2/MCM-41 composite through the formation of Ti···Cl coordination bonds because the maximum bond order is very large, about 1.0 (it can be considered as a single bond). The adsorption process is significantly influenced by van der Waals interactions (accounting for approximately 30-40% of the interaction energy), hydrogen bonding, and halogen bonding. MCM-41 is demonstrated to concurrently function as a support for the TiO2 photocatalyst, creating a synergistic effect that enhances the photocatalytic activity of TiO2. Based on the computational results, a novel photocatalytic mechanism for the degradation of DDT on the TiO2/MCM-41 catalyst system was proposed.

DFT and Docking Calculations of the Structural, Electronic, Biological and Conductivity Properties of the Synthetic Complex [Cu(hfac)2(L)2][PF6]2

AbstractIn the present research, we report a theoretical study of Cu II complex based on TTF ligand [Cu(hfac)2(L)2][PF6]2 (in neutral and oxidized states +1 and +2, of biological interest and various applications in magnetic conducting materials. It is an organic/inorganic hybrid material involving a coordination between a paramagnetic transition metal and a nitrogenous aromatic TTF linked through a covalent transition conjugate bridge. The optimized structures of neutral and oxidized metal transition complexes obtained using the Density Functional Theory (DFT) method are consistent with the experimental results. Several properties including geometrical parameters, Hirshfeld atomic charges, energies of Frontier Molecular Orbitals (FMOs), and energy gap (ΔEgap) between the Highest Occupied Molecular Orbital (HOMO), and the Lowest Unoccupied Molecular Orbital (LUMO) are calculated for optimized complexes. The results reveal that oxidation leads to more stable aromatic systems and reduces the energy gap. The analysis of the charges as well as the distribution of the spin density in the frontier orbitals shows that the oxidation takes place at the ligand level. More precisely the ylidene C3=C4 bond is the most sensitive molecular part to oxidation. A significant degeneracy of molecular orbitals is also observed. No metallic contribution in the HOMO of Cu complex reveals a strong electronic localization at the end of the chain, and, at the same time a delocalization along the chain, this is also in favor of a good conductivity and excellent catalytic activity of this compounds.

Extension of the D3 and D4 London dispersion corrections to the full actinides series.

Efficient dispersion corrections are an indispensable component of modern density functional theory, semi-empirical quantum mechanical, and even force field methods. In this work, we extend the well established D3 and D4 London dispersion corrections to the full actinides series, francium, and radium. To keep consistency with the existing versions, the original parameterization strategy of the D4 model was only slightly modified. This includes improved reference Hirshfeld atomic partial charges at the ωB97M-V/ma-def-TZVP level to fit the required electronegativity equilibration charge (EEQ) model. In this context, we developed a new actinide data set called AcQM, which covers the most common molecular actinide compound space. Furthermore, the efficient calculation of dynamic polarizabilities that are needed to construct CAB6 dispersion coefficients was implemented into the ORCA program package. The extended models are assessed for the computation of dissociation curves of actinide atoms and ions, geometry optimizations of crystal structure cutouts, gas-phase structures of small uranium compounds, and an example extracted from a small actinide complex protein assembly. We found that the novel parameterizations perform on par with the computationally more demanding density-dependent VV10 dispersion correction. With the presented extension, the excellent cost-accuracy ratio of the D3 and D4 models can now be utilized in various fields of computational actinide chemistry and, e.g., in efficient composite DFT methods such as r2SCAN-3c. They are implemented in our freely available standalone codes (dftd4, s-dftd3) and the D4 version will be also available in the upcoming ORCA 6.0 program package.

ThemetaandparaOH Substitution Effect onC‐Phenyl‐Nitrilimine Bond‐Shift Isomers

AbstractThe geometric and electronic structure of 1,3‐dipolar species, in particular of nitrile imines, can be surprisingly intricate. A particular example is theC‐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 themetaandparaOH substituted derivatives. These two nitrile imines were generated in an argon matrix by UV‐irradiation of 2H‐tetrazole precursors and found to photoisomerize to carbodiimidesvia1H‐diazirines. The different effects of the OH substitution inmetaandparapositions on the bond‐shift isomerism are rationalized with the support of Natural Resonance Theory and Hirshfeld atomic charges. The understanding of how substitution affects the structural characteristics ofC‐phenyl‐nitrilimines, opens a door to modulate the chemistry of those compounds (e. g. in cycloaddition reactions) by appropriate tuning of their substitution (substituent type and position).

Fullerenol-based toxic fluoride gas sensing: A promising way to monitoring Li-ion battery status

In order to demonstrate the feasibility of fullerenol-based toxic fluoride gas sensing, the density functional theory is utilized for adsorption mechanism study. The dominant adsorption conformations of HF/PF5/POF3 is analyzed according to Boltzmann distribution based on Gibbs free energy. The intermolecular interaction of these dominant conformation is revealed by the independent gradient model based on Hirshfeld partition (IGMH) method, which shows that the main driving force of adsorption is the hydrogen bond. After considering the thermodynamic correction, the adsorption free energy of fullerenols with HF turns from negative to positive at 95 °C, showing a transition between adsorption and desorption. The superior recovery characteristic is thus indicated. The Hirshfeld atomic charge shows that HF exhibit as an electron acceptor during the adsorption process. The charge transfer and density of states analysis illustrate the significant bonding effect that existed between fullerenol and gas. And the energy gap shows a decrease after adsorption, which results in an increase in conductivity. It can be deduced that fullerenol can transform the presence of the toxic fluoride gas into an electrical signal, and therefore exhibit a promising way as gas sensor for Li-ion battery status monitoring.

Aryl Boronic Acids in Columnar Stacked Co-crystalline Materials: Key-Factors Governing the Assembly with Quinones.

The assembly of aryl boronic acids B with quinones Q into columnar mixed stacked materials, as previously observed in the solid-state, has been here subjected to a detailed theoretical analysis focusing on the properties of the isolated synthons (HOMO-LUMO energies, electron affinity, ionization potential, reorganization hole/electron energies, partial Hirshfeld atomic charges and conformation stabilities) as well as those of the 1 : 1 adducts (Hirshfeld analysis, IRI surfaces, Hirshfeld atomic charges, hydrogen bond and slipped stacked π-π contributions). The overall picture obtained throught this study shows an intricate pattern of interconnected factors contributing to the formation and stability of the Bx Qy adducts, and it unveils the importance of parameters such as HOMO-LUMO gap, polarization and charge transfer, in addition to the more evident hydrogen bond and slipped-stacked π-π interactions in the formation of 1 : 1 adducts. An explanation has been also given for the presence in some Bx Qy adducts of the rare anti-anti conformation for the BO-H group with respect to the most studied and common anti-syn conformation.

DFT investigation of temozolomide drug delivery by pure and boron doped C24 fullerene-like nanocages.

In this paper, the DFT/M05-2X-D3/6-31+G(d,p) theoretical chemistry method is used to probe the adsorption ability of pure and boron doped C24 toward the temozolomide (TMZ) anticancer drug. The study is conducted in both gas and aqueous phases. The positive values of the Gibbs free energy of formation (12.03, 9.14 and 2.51 kcal mol-1) show that the adsorption of TMZ on C24 is not allowed. However, the boron-doped C24 (BC23) forms a very stable molecular complex with TMZ in the gas phase, characterized by the adsorption energy and Gibbs free energy values of -32.07 and -21.27 kcal mol-1 respectively. Analysis of Hirshfeld's atomic charge revealed the transfer of 0.6395e from TMZ to BC23, which is confirmed by the value of the dipole moment of the complex (13.42 D in the gas phase) as well as its molecular electrostatic potential map. The change in the frontier molecular orbital energy difference of BC23 is found to be 21.67% proving the good sensitivity of the cage toward the drug. The TMZ-BC23 molecular complex is very stable in water though the sensitivity of the cage is hugely reduced in that solvent. The reliability of these results was confirmed by checking the outcomes at both wB97XD/6-31+G(d,p) and B3LYP-D3/6-31+G(d,p) levels. This work shows that pristine BC23 is a better adsorbent of TMZ than some reported nanomaterials from the theoretical chemistry point of view.

Experimental and DFT research for the effects of sodium on the heterogeneous reaction between NO and semichar derived fromO2/CO2 pretreatments

The excessive emission of NO is endangering the ecological environment and the health of humans. In-depth research on the reduction mechanisms of NO is crucial to regulating NO emissions. In this research, the influence of sodium on the heterogeneous reaction of NO by semichar derived from O2/CO2 pretreatments were investigated through the experimental and density functional theory (DFT) method. According to the results of atomic dipole corrected Hirshfeld atomic charge (ADCH), the additional Na and oxygen-containing compound altered the semichar's charge distribution of. The additional Na weakened the positive effects of the marginal hydrogen. And the charge of the carbon, which was attached to the phenol group, changed from negative to positive due to the strong electron-trapping ability of the phenol group. The energy potential diagrams between NO and semichars derived from O2/CO2 pretreatments without/with sodium addition reflected that sodium was beneficial to reduce NO. Compared with pure O2/CO2 pretreatments, the additional sodium decreased the energy gap of the NO reduction by 144.68 kJ/mol. On the other hand, the temperature-programmed reduction (TPR) results were performed to identify the accuracy of the calculation results. The experimental results illustrated that adding sodium enhanced the NO reducibility of semichar, expressing great consistency with the theoretical results.

Investigation of the synergetic regulation of O2/Ar preheating treatment and sodium salt addition on semichar combustion characteristics

Using Raman spectroscopy, temperature-programmed desorption (TPD) and laser-induced breakdown spectroscopy (LIBS), the relationship between microstructural characteristics and molecular emissions was determined. It can be concluded that the enhancement of C2 and CN emissions was related to the generation of small aromatic rings and C(O) groups. Compared with the Ar preheating treatment, the presence of additional amount of O2 and sodium salt accelerated the dissociation of the large aromatic ring skeleton, leading to the significant enhancement of small aromatic rings, C(O) and CONa groups. Subsequently, the combustion performance of preheated semichar was investigated by the TG-DTG method. The experimental results demonstrated that pretreatment under oxidizing atmospheres (without and with sodium salt addition) enhanced the comprehensive combustion index (S) and the combustion stability (Rw) of semichars. The corresponding combustion activation energy (E) was weakened. Furthermore, the DFT method was used to analyse the combustion behaviours of semichars. This result demonstrated that preheating treatment (with or without sodium participation) altered the distribution of the Hirshfeld atomic charge (ADCH) of preheated samples, and the combustion essence of semichar was the fracture and recombination of aromatic clusters. For the semichar preheated in the O2/Ar atmosphere, the energy gap of the most optimized pathway was 436.26 kJ/mol. When sodium participated in the oxidizing pretreatment, the energy gap of the most optimized pathway was 413.80 kJ/mol. The positive effect of sodium on the combustion performance of semichar was identified, which was in good agreement with the experimental results.

Experimental and theoretical study on efficient CO2 absorption coordinated by molecules and ions of DBN and 1,2,4-triazole formed deep eutectic solvents

Deep eutectic solvents (DESs) as a new class of designer solvents have attracted intensive attention in CO2 capture, while the interactions between CO2 and underlying molecules and/or ions in DESs are poorly understood. Here, superbase 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) and 1,2,4-triazole (Tz) formed DESs with different DBN/Tz molar ratios were used to absorb CO2, wherein DES [2DBN:Tz] achieved the highest weight capacity approaching 0.19 g CO2/g DES at 25 °C. The ionicity of the DESs was determined by proton transfer from Tz to DBN and showed a positive correlation with absorption capacity. Density functional theory calculation was also used to elucidate the proton transfer between molecular and ionic pairs in [DBN:Tz] and their interactions with CO2. Both Hirshfeld atomic charge and electrostatic potential analyses revealed that DBN and Tz− acted as electron-rich nucleophiles could form DBN-CO2 and Tz-CO2− adducts with electrophilic CO2, which were also confirmed by carbon nuclear magnetic resonance and Fourier transform infrared spectroscopy. Moreover, a two-paths CO2 capture process through synergistic effect of DBN molecules and Tz− ions in the DESs was proposed and demonstrated.

Empirical electronic polarizabilities for use in refractive index measurements at 589.3 nm: Hydroxyl polarizabilities

Abstract Refractive indices of minerals and inorganic compounds can be calculated from their chemical compositions using the additivity rule for electronic polarizabilities and converting the sum of polariz-abilities α using the Anderson-Eggleton relationship:αAE=(nD2-1)Vm4π+(4π3-2.26)(nD2-1) with the molar volume Vm solved for the mean refractive index nD at 589.3 nm. Whereas the polariz-ability of cations is a single parameter, the polarizability of anions is described by a two-parameter term α−=α−o10−No/Van1.20 with α– = anion polarizability, Van = anion molar volume, and the two least-squares parameters α−o (corresponding to free-ion polarizability) and No. For hydroxyls, Shannon and Fischer (2016) introduced different parameter sets for non-H-bonded hydroxyls (α−o = 1.79 Å3, No = 1.792 Å3.6) and moderately strong H-bonded hydroxyls (α−o = 1.73 Å3, No = 2.042 Å3.6). In an effort to understand the lower polarizability of the H-bonded hydroxyl ions, we have evaluated observed and calculated polarizabilities, O-H, H∙∙∙O, O∙∙∙O distances, and O-H∙∙∙O angles in 10 minerals with non-hydrogen-bonded hydroxyls (mean <O∙∙∙O> distance 3.143 Å, mean <H∙∙∙O> distance 2.352 Å), in seven minerals with H-bonded-hydroxyls (<O∙∙∙O> = 2.739 Å, <H∙∙∙O> = 1.856 Å), and in 10 minerals with very strongly H-bonded hydroxyls (<O∙∙∙O> = 2.531 Å, <H∙∙∙O> = 1.525 Å). On the basis of quantum chemical cluster calculations using atomic parameters of well determined crystal structures of hydroxyl containing compounds, we found that calculated intrinsic polariz-abilities of OH are correlated with the hydrogen bond lengths H∙∙∙O and O∙∙∙O between donor and acceptor of the H-bond. This is demonstrated for LiOH, brucite [Mg(OH)2], portlandite [Ca(OH)2], clinometaborite (β-HBO2), sassolite (H3BO3), archerite (KH2PO4), kalicinite (KHCO3), metaborite (γ-HBO2), and NaPO2(OH)2. Thus, we find that these summed intrinsic polarizabilities for OH-bonds which are involved in H-bonding are significantly lower than the corresponding summed intrinsic polarizabilities for OH-bonds not involved in H-bonding. We attribute the reduction in polarizability of hydroxyl ions in clinometaborite, sassolite, archerite, kalicinite and metaborite, and the compound NaPO2(OH)2 to the presence of H-bonds and a reduction of Hirshfeld atomic charge on the O atom.

Achieving simultaneous hydrogen evolution and organic pollutants degradation through the modification of Ag3PO4 using Cs2AgBiBr6 quantum dots and graphene hydrogel

The Ag3PO4/Cs2AgBiBr6 quantum dots/graphene hydrogel (ACGH) photocatalytic system was designed. The Cs2AgBiBr6 quantum dots (CABBQDs) and graphene hydrogel (rGH) solved the insufficient redox ability and easy photocorrosion of Ag3PO4, at the same time, the novel system achieved full-spectrum-driven photoreforming to use for efficient photocatalytic hydrogen evolution and simultaneous organic compounds photodegradation. The feasibility study of alternative sacrificial agents evaluated higher simultaneous photocatalytic activity in tetracycline hydrochloride (TC) compared to general sacrificial agents (methanol, Na2S/Na2SO3, acid orange and glucose). The yield of hydrogen production and simultaneous photodegradation efficiency of TC were 5965.8 μmol/g and 98.32 % respectively in 6 h. And the hydrogen production rate in TC solution was more than twice that of general sacrificial agents within 24 h. Meanwhile, the mechanism exploration elucidated the photogenerated charge transfer path to generate the water splitting and photoinduced oxidizing species (h+, OH, ·O2-). The Hirshfeld atomic charges on TC and methanol molecules were calculated by density functional theory to predict the initial attack sites. Results indicated that the CCO and CNC fragments on TC molecules were inferred as nucleophilic attack and radical attack sites. And more electrons on TC could give to ACGH constantly for hydrogen production than methanol. The yield of hydrogen production and simultaneous degradation efficiency of TC remained at 3683.24 μmol/g and 93.22 % respectively in six photocatalytic cycle experiments, showing the reusability of ACGH. The simultaneous hydrogen production and degradation of organic pollutants of ACGH could proceed in actual municipal wastewater.

Stability, atomic charges, bond‐order analysis, and the directionality of lone‐electron pairs on nitriles and isocyanides

AbstractThe carbon atoms in :CN and the nitrogen atoms in CN: are always the global electrostatic minima in the whole molecules of nitriles and isocyanides. The global molecular electrostatic potential minima (Vmin) values and the electrostatic potential isosurfaces higher than Vmin by 10 kcal/mol were investigated and visualized based on the optimized geometrical structures at B3LYP‐D3(BJ)/def2‐QZVP level for a series of nitriles and isocyanides with the selected 21 functional groups. The relative stability between RCN: and :CNR was quantified with isomerization energies and bond dissociation enthalpies by single‐point energy (SPE) calculations at B2PLYP‐D3(BJ)/cc‐pVTZ level. The bond dissociation enthalpies of RCN: were evaluated, and the standard molar enthalpies of formation for RCN: and R· were also calculated to estimate the bond dissociation enthalpies. The theoretical results show that the directionality of the lone pairs influences electrostatic distribution. The population analyses in terms of Hirshfeld and ADCH atomic charges and bond‐order analyses via Laplacian and fuzzy bond orders were also discussed in detail.

Research on the gamma irradiation decomposition products of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105)

In this work, 60Co gamma-ray source was used to irradiate LLM-105 at room temperature with the radiation doses of 100, 300, 500, 696, and 900 kGy under vacuum. High-performance liquid chromatography coupled with electrospray mass spectrometry (HPLC–MS) and 1H nuclear magnetic resonance (NMR) demonstrated the main radiolysis product in gamma-irradiated LLM-105 was 2,6-diamino-3,5-dinitropyrazine (ANPZ). The relationship between ANPZ content and irradiation dose indicated that LLM-105 was a stable explosive under gamma irradiation. The sensitivity is not expected to change based on the chemical analyses performed on irradiated LLM-105. The radiation decomposition mechanism of LLM-105 was clarified by Atomic dipole moment corrected Hirshfeld (ADCH) atomic charges and electronic localization function (ELF).

Effect of CO2 on the As2O3 adsorption over carbonaceous surface: Experiment and quantum chemistry study

The adsorption characteristics of the As2O3 over carbonaceous surface in the presence of CO2 were systematically studied by experiment and density functional theory (DFT). The experimental results show that CO2 has a negative effect on the adsorption of arsenic by activated carbon. In addition, quantum chemistry calculations were employed to study the mechanism for CO2 influence on arsenic adsorption. Calculation results show that carbonaceous surface tends to react with CO2 compared to As2O3 in the flue gas. Compared to the As2O3 adsorption over the complete carbonaceous surface, there is a noticeable decrease for the adsorption energy over the defective carbonaceous surface. Besides, with the pre-assembled CO2 adsorption over the carbonaceous surface, the As2O3 adsorption energy decreases, indicating CO2 has the negative effect on As2O3 adsorption. By means of Hirshfeld atomic charges analysis, CO2 adsorbed on carbonaceous surface would weaken the activity of adsorption sites and inhibit the As2O3 adsorption. The experiment and theoretical study figured out the influences mechanism of CO2 on the As2O3 adsorption and provide a theoretical foundation for gaseous arsenic removal using carbonaceous surface.

DFT investigation on the application of pure and doped X12N12 (X = B and Al) fullerene-like nano-cages toward the adsorption of temozolomide.

The sensitivity of pure and doped X12N12 (X = B and Al) fullerene-like nano-cages (FLNs) toward the anti-cancer drug temozolomide (TMZ) is probed herein at DFT/M06-2X-D3/6-311G(d,p) theoretical level in both gas phase and water. A noticeable affinity of the FLNs toward TMZ was observed along with the negative gas-phase adsorption energies −1.37 and −2.09 eV for the most stable configurations of pure B12N12 and Al12N12 pristines, respectively. Considerable charge transfer from TMZ to the FLNs was also revealed via NBO analysis and the Hirshfeld atomic charges, making the dipole moment vector of the molecular complexes to be oriented from the nano-cages to the TMZ moiety. Furthermore, a percentage decrease in the HOMO-LUMO energy gap (ΔEg) of 38.09 and 17.72% was obtained for the B12N12 and Al12N12 nano-cages, respectively. The percentage change in ΔEg was found to be reduced upon doping and solvation of the FLNs. Finally, a recovery time in vacuum ultraviolet light of 1.06 s is found for the complex with pure B12N12, which in addition to the above-mentioned parameters make this boron nitride cage the best sensor for TMZ, among the FLNs considered in the present work.

How Substitution Combines with Non-Covalent Interactions to Modulate 1,4-Naphthoquinone and Its Derivatives Molecular Features-Multifactor Studies.

Substitution is well-known to modulate the physico-chemical properties of molecules. In this study, a combined, multifactor approach was employed to determine a plethora of substitution patterns using –Br and –O-H in 1,4-naphthoquinone and its derivatives. On the basis of classical Density Functional Theory (DFT), 25 models divided into three groups were developed. The first group contains 1,4-naphthoquinone and its derivatives substituted only by –Br. The second group consists of compounds substituted by –Br and one –O-H group. As a result of the substitution, an intramolecular hydrogen bond was formed. The third group also contains –Br as a substituent, but two –O-H groups were introduced and two intramolecular hydrogen bonds were established. The simulations were performed at the B97XD/6-311++G(2d,2p) level of theory. The presence of substituents influenced the electronic structure of the parent compound and its derivatives by inductive effects, but it also affected the geometry of the 2 and 3 groups, due to the intramolecular hydrogen bonding and the formation of a quasi-ring/rings. The static DFT models were applied to investigate the aromaticity changes in the fused rings based on the Harmonic Oscillator Model of Aromaticity (HOMA). The OH stretching was detected for the compounds from groups 2 and 3 and further used to find correlations with energetic parameters. The evolution of the electronic structure was analyzed using Hirshfeld atomic charges and the Substituent Active Region (cSAR) parameter. The proton reaction path was investigated to provide information on the modulation of hydrogen bridge properties by diverse substitution positions on the donor and acceptor sides. Subsequently, Car–Parrinello Molecular Dynamics (CPMD) was carried out in the double-bridged systems (group 3) to assess the cooperative effects in double –O-H-substituted systems. It was determined that the –O-H influence on the core of the molecule is more significant than that of –Br, but the latter has a major impact on the bridge dynamics. The competitive or synergic effect of two –Br substituents was found to depend on the coupling between the intramolecular hydrogen bridges. Thus, the novel mechanism of a secondary (cooperative) substituent effect was established in the double-bridged systems via DFT and CPMD results comparison, consisting of a mediation of the bromine substitutions’ influence by the cooperative proton transfer events in the hydrogen bridges.

Selective Bromocyclization of 5-Amino-4-Alkenyl-1,2,4-Triazole-3-Thione

Here, we present a study on the regioselectivity cyclization of 5-amino-4-alkenyl-1,2,4-triazole-3-thiones. The presence of various nucleophilic centers causes the possibility of cyclization of an alkenyl fragment on different heteroatoms and the formation of a few alternative structures. Elemental bromine was utilized as an electrophilic agent, and two 6-(bromomethyl)-6-R-5,6-dihydro[1,3]thiazolo[2,3-c][1,2,4]triazol-3-amine hydrobromide salts were obtained as the only products when taking reaction in chloroform, acetic acid, or acetonitrile. The 1H and 13C APT NMR spectra analysis proved the formation of the 1,3-thiazolinium ring upon cyclization reaction. DFT calculations at the ωB97X-D3/6-311G(d,p) level of theory were utilized to analyze molecular electrostatic potential, electron localization function, and Hirshfeld atomic partial charges the intermediate bromonium cation. These theoretical calculations explain the experimentally observed regioselectivity.

Catalyst-free formal [3 + 2] cycloaddition of stabilized N,N-cyclic azomethine imines to 3-nitrobenzofurans and 3-nitro-4H-chromenes: access to heteroannulated pyrazolo[1,2-a]pyrazoles.

We have studied the [3 + 2]-cycloaddition of various N,N-cyclic azomethine imines to 3-nitrobenzofurans. This process is a rare example of their dearomatization. We have also extended this process to the related 3-nitro-4H-chromenes as dipolarophiles. Both reactions provide access to benzofuro- and chromeno-condensed pyrazolo[1,2-a]pyrazoles with 100% atom economy in a diastereoselective manner under mild eco-friendly conditions. Finally, on the basis of DFT calculations, the mechanistic insights into the mentioned [3 + 2]-cycloadditions and explanations of the experimentally determined limitations of the method are given. Hirshfeld atomic charge values of push-pull heterocycles were suggested as a criterion for a priori assessment of the possibility of their dipolar cycloaddition with N,N-cyclic azomethine imines.