Atoms-in-Molecules Dual Parameter Analysis of Weak to Strong Interactions: Behaviors of Electronic Energy Densities versus Laplacian of Electron Densities at Bond Critical Points

Theoretical investigation on the covalence in AgRnX and XAgRn (X = F - I)

CCSD(T) calculations were performed to investigate the stabilities and interaction mechanisms of the AgRnX and XAgRn (X = F - I) series. Dissociation energies and frontier orbital properties demonstrate an increased trend of stabilities. Ag spd hybrids and Rn/X sp hybrids come into the σ_Ag-Rn and σ_Ag-X bonding orbital. The nature of Ag-Rn, Ag-X and Rn-X interactions were investigated by atoms in molecules (AIM) theory. The negative energy density and positive Laplacian values, as well as small electron densities at bond critical points (BCPs), characterize the moderate strength with partial covalence of interactions. BCP properties (-G/V and G/ρ), electron density deformations and natural resonance theory (NRT) results display increased covalence down the periodic table.

Combined TDDFT and AIM Insights into Photoinduced Excited State Intramolecular Proton Transfer (ESIPT) Mechanism in Hydroxyl- and Amino-Anthraquinone Solution

Time-dependent density functional theory (TDDFT) and atoms in molecules (AIM) theory are combined to study the photoinduced excited state intramolecular proton transfer (ESIPT) dynamics for eight anthraquinones (AQs) derivatives in solution. The calculated absorption and emission spectra are consistent with the available experimental data, verifying the suitability of the theory selected. The systems with the excited-state exothermic proton transfer, such as 1-HAQ, 1,5-DHAQ and TFAQ, emit completely from transfer structure (T), while the reactions for those without ESIPT including 1,4-DHAQ and AAAQ appear to be endothermic. Three reaction properties of three systems (1,8-DHAQ, DCAQ and CAAQ) are between the exothermic and endothermic, sensitive to the solvent. Energy scanning shows that 1,4-DHAQ and AAAQ exhibit the higher ESIPT energy barriers compared to 1-HAQ, 1,5-DHAQ and TFAQ with the "barrierless" ESIPT process. The ESIPT process is facilitated by the strengthening of hydrogen bonds in excited state. With AIM theory, it is observed that the change in electrons density ρ(r) and potential energy density V(r) at BCP position between ground state and excited state are crucial factors to quantitatively elucidate the ESIPT.

Structures and stabilities of naturally occurring cyclodextrins: a theoretical study of symmetrical conformers

A molecular modeling study of symmetrical conformers of α-, β-, and γ-cyclodextrins in the gas and aqueous phases was carried out using the M06-2X density functional method, with SMD employed as an implicit solvation model. Eight symmetrical conformers were found for each cyclodextrin. Values of geometrical parameters obtained from the modeling study were found to agree well with those obtained from X-ray diffraction structures. A vibrational analysis using harmonic frequencies was performed to determine thermodynamic quantities. The GIAO method was applied to determine proton and carbon-13 NMR chemical shifts, which were then compared with corresponding chemical shifts reported in the literature. Hydrogen-bonding patterns were analyzed using geometrical descriptors, and quantum chemical topology was explored by QTAIM analysis. The results of this study indicated that four of the eight conformers studied for each cyclodextrin are the most populated in aqueous solution. These results provide the foundations for future studies of host-guest complexes involving these cyclodextrins. Graphical abstract δΔG_solvation: variation of free Gibss energy of solvation.

Linear Four-Chalcogen Interactions in Radical Cationic and Dicationic Dimers of 1,5-(Dichalcogena)canes: Nature of the Interactions Elucidated by QTAIM Dual Functional Analysis with QC Calculations

The dynamic and static nature of extended hypervalent interactions of the ^BE···^AE···^AE···^BE type are elucidated for four center-seven electron interactions (4c-7e) in the radical cationic dimers (1·⁺) and 4c-6e in the dicationic dimers (1²⁺) of 1,5-(dichalcogena)canes (2: ^AE(CH₂CH₂CH₂)₂^BE: ^AE, ^BE = S, Se, Te, and O). The quantum theory of atoms-in-molecules dual functional analysis (QTAIM-DFA) is applied for the analysis. Total electron energy densities H_b(r_c) are plotted versus H_b(r_c) - V_b(r_c)/2 [= (ℏ²/8m)∇²ρ_b(r_c)] at bond critical points (BCPs) of the interactions, where V_b(r_c) values show potential energy densities at BCPs. Data from the fully optimized structures correspond to the static nature of the interactions. Those from the perturbed structures around the fully optimized ones are also plotted, in addition to those of the fully optimized ones, which represent the dynamic nature of interactions. The ^BE···^AE-^AE···^BE interactions in 1²⁺ are stronger than the corresponding ones in 1·⁺, respectively. On the one hand, for 1²⁺ with ^AE, ^BE = S, Se, and Te, ^AE···^AE are all classified by the shared shell interactions and predicted to have the weak covalent nature, except for those in 1a²⁺ (^AE = ^BE = S) and 1d²⁺ (^AE = ^BE = Se), which have the nature of regular closed shell (r-CS)/trigonal bipyramidal adduct formation through charge transfer (CT-TBP). On the other hand, ^AE···^BE are predicted to have the nature of r-CS/molecular complex formation through charge transfer for 1a²⁺, 1b²⁺ (^AE = Se; ^BE = S), and 1d²⁺ or r-CS/CT-TBP for 1c²⁺ (^AE = Te; ^BE = S), 1e²⁺ (^AE = Te; ^BE = Se), and 1f²⁺ (^AE = ^BE = Te). The ^BE···^AE-^AE···^BE interactions in 1·⁺ and 1²⁺ are well-analyzed by applying QTAIM-DFA.

Nature ofE2X2σ(4c–6e) of theX---E—E---Xtype at naphthalene 1,8-positions and model, elucidated by X-ray crystallographic analysis and QC calculations with the QTAIM approach

The nature ofE2X2σ(4c–6e) of theX-*-E-*-E-*-Xtype is elucidated for 1-(8-XC10H6)E–E(C10H6X-8′)-1′ [(1)E,X= S, Cl; (2) S, Br; (3) Se, Cl; (4) Se, Br] after structural determination of (1), (3) and (4), together with modelA[MeX---E(H)—E(H)---XMe (E= S and Se;X= Cl and Br)]. The quantum theory of atoms-in-molecules dual functional analysis (QTAIM-DFA) is applied. The total electron energy densitiesHb(rc) are plottedversus Hb(rc) –Vb(rc)/2 for the interactions at the bond critical points (BCPs; *), whereVb(rc) show the potential energy densities at the BCPs. Data for the perturbed structures around the fully optimized structures are employed for the plots, in addition to those of the fully optimized structures. The plots were analysed using the polar coordinate (R, θ) representation of the data of the fully optimized structures. Data containing the perturbed structures were analysed by (θp, κp), where θpcorresponds to the tangent line of the plot and κpis the curvature. Whereas (R, θ) shows the static nature, (θp, κp) represents the dynamic nature of interactions.E-*-Eare all classified as shared shell (S) interactions for (1)–(4) and as weak covalent (Cov-w) in nature (S/Cov-w). The nature ofpureCS (closed shell)/typical-HB (hydrogen bond) with no covalency is predicted forE-*-Xin (1) and (3),regularCS/typical-HB nature with covalency is predicted for (4), and an intermediate nature is predicted for (2). The NBO energies evaluated forE-*-Xin (1)–(4) are substantially larger than those in modelAdue the shortened length at the naphthalene 1,8-positions. The nature ofE2X2of σ(4c–6e) is well elucidatedviaQTAIM-DFA.

Behavior of interactions between hydrogen chalcogenides and an anthracene π-system elucidated by QTAIM dual functional analysis with QC calculations

The nature of the interactions between chalcogenides and the anthracene p-system, EH₂-*-p(C₁₄H₁₀), is predicted to be close to that of EH₂-*-p(C₁₀H₈), although the partial structures around the central rings can be found in EH₂-*-p(C₆H₆).

Gold setting the “gold standard” among transition metals as a hydrogen bond acceptor – a theoretical investigation

MP2/aug-cc-pVTZ-pp calculations show that the Au(i) atom of dimethylaurate behaves as a hydrogen-bond acceptor to a range of hydrogen-bond donors.

Redox trends in cyclometalated palladium(ii) complexes

Electrochemical and DFT studies on palladacycles revealed an increase in the metal–metal distance in the complexes leads to higher oxidation potentials.

Influence of the chelator structures on the stability of Re and Tc tricarbonyl complexes with iminodiacetic acid tridentate ligands: a computational study

The development of novel radiopharmaceuticals for nuclear medicine based on M(CO)3 (M = Tc, Re) complexes has attracted great attention. The versatility of this core and the easy production of the fac-[M(CO)3(H2O)3](+) precursor could explain this interest. The main characteristics of these tricarbonyl complexes are the high substitution stability of the three CO ligands and the corresponding lability of the coordinated water molecules, yielding, via easy exchange of a variety of bi- and tridentate ligands, complexes xof very high kinetic stability. Here, a computational study of different tricarbonyl complexes of Re(I) and Tc(I) was performed using density functional theory. The solvent effect was simulated using the polarizable continuum model. These structures were used as a starting point to investigate the relative stabilities of tricarbonyl complexes with various tridentate ligands. These complexes included an iminodiacetic acid unit for tridentate coordination to the fac-[M(CO)3](+) moiety (M = Re, Tc), an aromatic ring system bearing a functional group (-NO2, -NH2, and -Cl) as a linking site model, and a tethering moiety (a methylene, ethylene, propylene butylene, or pentylene bridge) between the linking and coordinating sites. The optimized complexes showed geometries comparable to those inferred from X-ray data. In general, the Re complexes were more stable than the corresponding Tc complexes. Furthermore, using NH2 as the functional group, a medium length carbon chain, and ortho substitution increased complex stability. All of the bonds involving the metal center presented a closed shell interaction with dative or covalent character, and the strength of these bonds decreased in the sequence Tc-CO > Tc-O > Tc-N.

Behavior of Halogen Bonds of the Y-X⋅⋅⋅π Type (X, Y=F, Cl, Br, I) in the Benzene π System, Elucidated by Using a Quantum Theory of Atoms in Molecules Dual-Functional Analysis

The nature of halogen bonds of the Y-X-✶-π(C6 H6 ) type (X, Y=F, Cl, Br, and I) have been elucidated by using the quantum theory of atoms in molecules (QTAIM) dual-functional analysis (QTAIM-DFA), which we proposed recently. Asterisks (✶) emphasize the presence of bond-critical points (BCPs) in the interactions in question. Total electron energy densities, Hb (rc ), are plotted versus Hb (rc )-Vb (rc )/2 [=(ħ(2) /8m)∇(2) ρb (rc )] for the interactions in QTAIM-DFA, in which Vb (rc ) are potential energy densities at the BCPs. Data for perturbed structures around fully optimized structures were used for the plots, in addition to those of the fully optimized ones. The plots were analyzed by using the polar (R, θ) coordinate for the data of fully optimized structures with (θp , κp ) for those that contained the perturbed structures; θp corresponds to the tangent line of the plot and κp is the curvature. Whereas (R, θ) corresponds to the static nature, (θp , κp ) represents the dynamic nature of the interactions. All interactions in Y-X-✶-π(C6 H6 ) are classified by pure closed-shell interactions and characterized to have vdW nature, except for Y-I-✶-π(C6 H6 ) (Y=F, Cl, Br) and F-Br-✶-π(C6 H6 ), which have typical hydrogen-bond nature without covalency. I-I-✶-π(C6 H6 ) has a borderline nature between the two. Y-F-✶-π(C6 H6 ) (Y=Br, I) were optimized as bent forms, in which Y-✶-π interactions were detected. The Y-✶-π interactions in the bent forms are predicted to be substantially weaker than those in the linear F-Y-✶-π(C6 H6 ) forms.

Dynamic and static behavior of the H...π and E...π interactions in EH₂ adducts of benzene π-system (E = O, S, Se and Te), elucidated by QTAIM dual functional analysis

Dynamic and static behavior of the interactions in the EH2 adducts of a benzene π-system (E = O, S, Se and Te) is elucidated by applying QTAIM-DFA (QTAIM dual functional analysis). Two types of H-*-π and E-*-π interactions are detected in the adducts, where the asterisk (*) emphasizes the existence of the bond critical point (BCP) on the interaction in question. Total electron energy densities Hb(rc) are plotted versus Hb(rc) -Vb(rc)/2 [=(ℏ(2)/8m)∇(2)ρb(rc)] at BCPs in QTAIM-DFA, where Vb(rc) are the potential energy densities at BCPs. Data from the fully optimized structures are analyzed by polar (R, θ) coordinate representation. Each plot for an interaction, containing data from the perturbed structures with those of the fully optimized one, shows a specific curve, which provides important information. The plot is expressed by (θp, κp): θp corresponds to the tangent line for the plot and κp is the curvature. θ and θp are measured from the y-axis and y-direction, respectively. Moreover, (R, θ) corresponds to the static nature, (θp, κp) represents the dynamic nature of interactions. While θ classifies the interaction in question, θp characterizes it. Both values are less than 90° for all H-*-π and E-*-π interactions examined in this study; therefore, they are all classified by the pure closed-shell interactions and predicted to have the character of vdW nature. However, it is suggested that E-*-π has the nature of the stronger interaction than the case of H-*-π for dynamic behavior in the same species evaluated at the MP2 and M06-2X levels. The nature of the interactions is well analyzed and specified by applying QTAIM-DFA.

Theoretical study of chlordecone and surface groups interaction in an activated carbon model under acidic and neutral conditions

Activated carbons (ACs) are widely used in the purification of drinking water without almost any knowledge about the adsorption mechanisms of the persistent organic pollutants. Chlordecone (CLD, Kepone) is an organochlorinated synthetic compound that has been used mainly as agricultural insecticide. CLD has been identified and listed as a persistent organic pollutant by the Stockholm Convention. The selection of the best suited AC for this type of contaminants is mainly an empirical and costly process. A theoretical study of the influence of AC surface groups (SGs) on CLD adsorption is done in order to help understanding the process. This may provide a first selection criteria for the preparation of AC with suitable surface properties. A model of AC consisting of a seven membered ring graphene sheet (coronene) with a functional group on the edge was used to evaluate the influence of the SGs over the adsorption. Multiple Minima Hypersurface methodology (MMH) coupled with PM7 semiempirical Hamiltonian was employed in order to study the interactions of the chlordecone with SGs (hydroxyl and carboxyl) at acidic and neutral pH and different hydration conditions. Selected structures were re-optimized using CAM-B3LYP to achieve a well-defined electron density to characterize the interactions by the Quantum Theory of Atoms in Molecules approach. The deprotonated form of surface carboxyl and hydroxyl groups of AC models show the strongest interactions, suggesting a chemical adsorption. An increase in carboxylic SGs content is proposed to enhance CLD adsorption onto AC at neutral pH conditions.

Nature of S2Se2 σ(4c–6e) at naphthalene 1,8-positions and models, elucidated by QTAIM dual functional analysis

The nature of ^BE–*–^AE–*–^AE–*–^BE σ(4c–6e) is primarily elucidated at naphthalene 1,8-positions: while the weak covalent nature is predicted for all ^AE–*–^AE, the HB nature with covalency or the CT-MC (MC formation through CT) nature is for ^AE–*–^BE.

Quantum chemical calculations with the AIM approach applied to the π-interactions between hydrogen chalcogenides and naphthalene

The nature of π-interactions in (EH₂)n–*–π(C₁₀H₈) (n = 1 and 2: E = O, S, Se and Te) is elucidated with QTAIM-DFA. They have the character of the vdW-nature of the pure-CS interactions, except for HHTe–*–π(C₁₀H₈), which seems stronger than others.

Investigation into the metallophilic interaction in coinage-metal halides: an ab initio study of CMX (CM = Cu and Ag, X = F - I)

Investigation of the metallophilic interactions of the title coinage-metal halide series, CMX (CM = Ag and Cu, X = F - I), and their cationic and anionic systems, were performed at CCSD(T) theoretical level with extended basis sets. Natural bond orbital analysis shows that the interactions come mainly from the overlap of the sp hybrid on the halogen and the spd hybrid on the coinage-metal atom. Electron density deformation analysis demonstrates a pronounced electron accumulation in the interaction region between the heavier X and the coinage-metal atoms, and suggests a covalent character of the interaction. Positive Laplacian values and negative total energy densities at bond critical points (BCPs) show the "intermediate" character of the interactions. Reduced density gradient analysis visualizes the interaction; a linear relationship between energy densities and eigenvalues can be found at BCPs.

On the properties of Au2P3z(z = −1, 0, +1): analysis of geometry, interaction, and electron density

Au₂P₃has been discovered to exhibit remarkable semiconductor properties among metal phosphides. A theoretical study focusing on the electron and interatomic interactions of Au₂P₃is performed and provides new insights for the synthesis of new materials.

Dynamic and static behavior of the E–E′ bonds (E, E′ = S and Se) in cystine and derivatives, elucidated by AIM dual functional analysis

AIM-DFA (AIM dual functional analysis) is applied to the E–E′ bonds (E, E′ = S and Se) in R-cystine (1), its derivatives and MeEE′Me. The nature of E–E′ is elucidated by (θ_p, κ_p: dynamic behavior) and (R, θ: static behavior), through AIM-DFA.

Dynamic and static behavior of hydrogen bonds of the X–H⋯π type (X = F, Cl, Br, I, RO and RR′N; R, R′ = H or Me) in the benzene π-system, elucidated by QTAIM dual functional analysis

The nature of the X–H-*-π interactions in X–H-*-π(C₆H₆) (X = F, Cl, Br, I, HO, MeO, H₂N, MeHN and Me₂N) was elucidated by applying QTAIM dual functional analysis. The interactions were all classified by pure closed-shell interactions and characterized to have the vdW nature.

Energetic study of 4(3H)-pyrimidinone: aromaticity of reactions, hydrogen bond rules, and support for an anomeric effect

4(3H)-Pyrimidinone is observed in nature in equilibrium with other tautomeric forms, mimicking the tautomeric equilibrium in pyrimidine nucleobases. In this work, the enthalpy of formation in the gaseous phase of 4(3H)-pyrimidinone was derived from the combination of the enthalpy of formation in the crystalline phase, obtained by static bomb combustion calorimetry, and the enthalpy of sublimation, obtained by Knudsen effusion. The gaseous phase enthalpy of formation of 4(3H)-pyrimidinone was interpreted in terms of isodesmic reactions that consider the enthalpic effects of hydroxypyridines and pyrimidine. After comparison of the experimental and computational results, the same type of isodesmic reactions was used to study the substituent effects of the hydroxyl functional group of 2-, 4-, and 5-hydroxypyrimidines. The influence of aromaticity on the energetics of hydroxypyrimidines was evaluated using the variation of nucleus-independent chemical shifts for several reactions. The influence of intramolecular hydrogen bonds was investigated using the quantum theory of atoms in molecules and the geometric rule of Baker and Hubbard to identify hydrogen bonds. The energetic results obtained were also interpreted in terms of an in plane anomeric effect in the pyrimidine ring.

Investigation of the distinction between van der Waals interaction and chemical bonding based on the PAEM-MO diagram

In recent years, the basic problem of understanding chemical bonding, nonbonded, and/or van der Waals interactions has been intensively debated in terms of various theoretical methods. We propose and construct the potential acting on one electron in a molecule-molecular orbital (PAEM-MO) diagram, which draws the PAEM inserted the MO energy levels with their major atomic orbital components. PAEM-MO diagram is able to show clear distinction of chemical bonding from nonbonded and/or vdW interactions. The rule for this is as follows. Along the line connecting two atoms in a molecule or a complex, the existence of chemical bonding between these two atoms needs to satisfy two conditions: (a) a critical point of PAEM exists and (b) PAEM barrier between the two atoms is lower in energy than the occupied major valence-shell bonding MO which contains in-phase atomic components (positive overlap) of the two considered atoms. In contrast to the chemical bonding, for a nonbonded interaction or van der Waals interaction between two atoms, both conditions (a) and (b) do not be satisfied at the same time. This is demonstrated and discussed by various typical cases, particularly those related to helium atom and H-H bonding in phenanthrene. There are helium bonds in HHeF and HeBeO molecules, whereas no H-H bonding in phenanthrene. The validity and limitation for this rule is demonstrated through the investigations of the curves of the PAEM barrier top and MO energies versus the internuclear distances for He2 , H2 , and He2 (+) systems.

The effect of fluorine substitution in alcohol–amine complexes

The effect of fluorine substitution on the hydrogen bond strength in alcohol–amine molecular complexes was investigated, with a combination of vapour phase infrared and near infrared spectroscopy and theoretical calculations.

Significant evidence of C⋯O and C⋯C long-range contacts in several heterodimeric complexes of CO with CH3–X, should one refer to them as carbon and dicarbon bonds!

An illustrated example of a ‘dicarbon bond’ formed between a pair of two carbon atoms of the OC⋯CH₃–Cl₃intermolecular complex, one corresponding to the methylated carbon in 1,1,1-trichloro-ethane (CH₃–Cl₃) and one to the carbon in the carbon dioxide (CO) molecule.

The nature of the interaction of dimethylselenide with IIIA group element compounds

The first systematic theoretical study of the nature of intermolecular bonding of dimethylselenide as donor and IIIA group element halides as acceptors was made with the help of the approach of Quantum Theory of Atoms in Molecules. Density Functional Theory with "old" Sapporo triple-ζ basis sets was used to calculate geometry, thermodynamics, and wave function of Me2Se···AX3 complexes. The analysis of the electron density distribution and the Laplacian of the electron density allowed us to reveal and explain the tendencies in the influence of the central atom (A = B, Al, Ga, In) and halogen (X = F, Cl, Br, I) on the nature of Se···A bonding. Significant changes in properties of the selenium lone pair upon complexation were described by means of the analysis of the Laplacian of the charge density. Charge transfer characteristics and the contributions to it from electron localization and delocalization were analyzed in terms of localization and delocalization indexes. Common features of the complexation and differences in the nature of bonding were revealed. Performed analysis evidenced that gallium and indium halide complexes can be attributed to charge transfer-driven complexes; aluminum halides complexes seem to be mainly of an electrostatic nature. The nature of bonding in different boron halides essentially varies; these complexes are stabilized mainly by covalent Se···B interaction. In all the complexes under study covalence of the Se···A interaction is rather high.

Electronic structure and gas-phase chemistry of protonated α- and β-quinonoid compounds: a mass spectrometry and computational study

RATIONALE

The use of quinonoid compounds against tropical diseases and as antitumor agents has prompted the search for new naturally occurring and synthetic derivatives. Among these quinonoid compounds, lapachol and its isomers (α- and β-lapachone) serve as models for the synthesis of new compounds with biological activity, and the use of electrospray ionization tandem mass spectrometry (ESI-MS/MS) analysis as a tool to elucidate and characterize these products has furnished important information about these compounds.

METHODS

ESI-MS/MS analysis under collision-induced dissociation conditions was used to describe the fragmentation mechanisms for protonated 1,4-naphthoquinone, 1,2-naphthoquinone, α-lapachone, and β-lapachone. The B3LYP/6-31+G(d,p) model was used to obtain proton affinities, gas-phase basicities, and molecular electrostatic potential maps, thus indicating the probable protonation sites. Fragmentation pathways were suggested on the basis of the relative enthalpies of the product ions.

RESULTS

The ESI-MS signals of the cationized molecules of ortho quinonoid compounds were more intense than those of the protonated molecule. Formation of the major product ions with m/z 187 from protonated α- and β-lapachone has been attributed to a retro-Diels-Alder (RDA) reaction.

CONCLUSIONS

MS/MS studies on lapachol isomers (α- and β-lapachone) will facilitate the interpretation of the liquid chromatography (LC)-MS/MS analysis of new metabolites. MS/MS data on the 1,4-naphthoquinone, 1,2-naphthoquinone, α-lapachone and β-lapachone core will help characterize new derivatives from in vitro/in vivo metabolism studies in complex matrices. The product ions revealed the major fragmentation mechanisms and these ions will serve as diagnostic ions to identify each studied compound.

Dynamic behavior of hydrogen bonds from pure closed shell to shared shell interaction regions elucidated by AIM dual functional analysis

The dynamic behavior of hydrogen bonds (HBs) was clarified for the wide range of interactions applying AIM dual functional analysis. Plots of H(b)(r(c)) versus H(b)(r(c)) - V(b)(r(c))/2 are analyzed in the polar (R, θ) representation, where H(b)(r(c)) and V(b)(r(c)) are total electron and potential energy densities at bond critical points, respectively, for the fully optimized structures. Data of the fully optimized structure and four perturbed ones around it are plotted for each interaction, which give a specific curve. The curve is analyzed by (θ(p), κ(p)): θ(p) corresponds to the tangent line from the y-direction and κ(p) is the curvature. Whereas (R, θ) correspond to the static nature, (θ(p), κ(p)) represent the dynamic nature of interactions. Indeed, HBs can be classified only by one parameter of θ, but θ(p) supplies more information necessary for better understanding of HBs. Although H(2)Se-*-HSeH and H(3)N-*-HNH(2) show the nature of pure CS (closed shell) of the vdW-type, H(2)S-*-HSH and H(2)O-*-HOH contain the nature of pure CS other than the vdW-type (HB-typical). The regular CS nature is observed for B-*-HF (B = HF, H(2)Se, H(2)S, H(2)O, and H(2)C═O). The HF-*-HF interaction is described as HB-typical, whereas others are by CT(MC)-type. The nature of H(3)N-*-HX (X = F, Cl, Br) is regular CS of the CT(TBP)-type. HBs in charged species, such as [HOH-*-OH](-) and [H(2)O-*-H-*-OH(2)], show the weak covalent nature of SS (shard shell). The dynamic behavior of HBs helps us to understand HBs in more detail, in addition to the static behavior.

Role of dG/dw and dV/dw in AIM analysis: an approach to the nature of weak to strong interactions

Role of dG(b)(r(c))/dw and dV(b)(r(c))/dw is revealed as the basic atoms-in-molecules (AIM) functions to evaluate, classify, and understand the nature of interactions, as well as G(b)(r(c)) and V(b)(r(c)). The border area between van der Waals (vdW) adducts and hydrogen-bonded (HB) adducts is shown to appear at around dG(b)(r(c))/dw = -dV(b)(r(c))/dw and that between molecular complexes (MC) and trigonal bipyramidal adducts (TBP) of chalcogenide dihalides appears at around 2dG(b)(r(c))/dw = -dV(b)(r(c))/dw. H(b)(r(c)) are plotted versus H(b)(r(c)) - V(b)(r(c))/2 at bond critical points (BCPs) in the AIM dual functional analysis. The plots incorporate the classification of interactions by the signs of ∇(2)ρ(b)(r(c)) and H(b)(r(c)). R [= (x(2) + y(2))(1/2)] corresponds to the energy for the interaction in question at BCPs, where (x, y) = (H(b)(r(c)), H(b)(r(c)) - V(b)(r(c))/2) and (x, y) = (0, 0) at the origin. The segment of lines for the plots (S) should correspond to energy, if the segment is substantially linear. The first derivative of S (dS) is demonstrated to be proportional to R. Relations between AIM functions, such as dV(b)(r(c))/dw, dG(b)(r(c))/dw, dH(b)(r(c))/d[H(b)(r(c)) - V(b)(r(c))/2], d(2)V(b)(r(c))/dw(2), d(2)G(b)(r(c))/dw(2), and d(2)H(b)(r(c))/d[H(b)(r(c)) - V(b)(r(c))/2](2), are also discussed. The results help us to understand the nature of interactions.

Gas-phase reactivity of 2-hydroxy-1,4-naphthoquinones: a computational and mass spectrometry study of lapachol congeners

In order to understand the influence of alkyl side chains on the gas-phase reactivity of 1,4-naphthoquinone derivatives, some 2-hydroxy-1,4-naphthoquinone derivatives have been prepared and studied by electrospray ionization tandem mass spectrometry in combination with computational quantum chemistry calculations. Protonation and deprotonation sites were suggested on the basis of gas-phase basicity, proton affinity, gas-phase acidity (ΔG(acid) ), atomic charges and frontier orbital analyses. The nature of the intramolecular interaction as well as of the hydrogen bond in the systems was investigated by the atoms-in-molecules theory and the natural bond orbital analysis. The results were compared with data published for lapachol (2-hydroxy-3-(3-methyl-2-butenyl)-1,4-naphthoquinone). For the protonated molecules, water elimination was verified to occur at lower proportion when compared with side chain elimination, as evidenced in earlier studies on lapachol. The side chain at position C(3) was found to play important roles in the fragmentation mechanisms of these compounds.