A B3LYP and MP2 theoretical investigation into host-guest interaction between calix[4]arene and Li+ or Na+

The DFT-B3LYP and MP2 methods with 6-311G** and 6-311++G** basis sets have been applied to study the complexation energies of the host-guest complexes between the cone calix[4]arene and Li⁺ or Na⁺ on the B3LYP optimized geometries. A comparison of the complexation energies obtained from the MP2(full) with those from MP2(fc) method is also carried out. The result shows that it is essential to introduce the diffuse basis set into the geometry optimizations and complexation energy calculations of the alkali-metal cation-π interaction complexes of calix[4]arene, and the D _e values show a maximum of 21.13 kJ mol⁻¹ (14.45% of relative error) between the MP2(full)/6-311++G** and MP2(fc)/6-311++G** method. For Li⁺ cation, the complexation is mainly energetically stabilized by the lower rim/cation (namely O–Li⁺) interaction. However, binding energies and NBO analyses confirm that Na⁺ cation prefers to enter the calix[4]arene cavity and the cation-π interaction is predominant, which contradicts the previous low-level theoretical studies. Furthermore, the complexation with Li⁺ is preferred over that with Na⁺ by at least 12.70 kJ mol⁻¹ at MP2(full)/6-311++G**//B3LYP/6-311++G** level.      

Ab initio and DFT study on the electrophilic addition reaction of bromine to tetracyclo[5.3.0.02,6.03,10]deca–4,8–diene

The electronic and geometric structures of tetracyclo[5.3.0.0^2,6.0^3,10]deca-4,8-diene (hypostrophene) have been investigated by ab initio and DFT/B3LYP methods using the 6-31G* and 6-311G* basis sets. The double bonds of hypostrophene are endo-pyramidalized. The cationic intermediates and products formed in the addition reaction have been investigated using the HF/6-311G*, HF/6-311G**, and B3LYP/6-311G* methods. The bridged bromonium cation was more stable than the U-type cation. Considering that the bridged cation does not isomerize to the less stable U-type cation, it is not possible for the U-type product to be obtained in the reaction. The bridged bromonium cation transformed into the more stable N-type cation and the N-type product was obtained via this cation. The thermodynamic stability of the exo, exo and exo, endo isomers of the N-type dibromide molecule were almost identical. The N-type product was 16.6 kcal mol⁻¹ more stable than the U-type product. Figure General energy diagram of the hypostrophene–bromine (HS–Br₂) system (kcal mol⁻¹) (MP2/6-311G*//HF/6-311G*)     

Density functional theory investigation of electrophilic addition reaction of bromine to tricyclo[4.2.2.22,5]dodeca-1,5-diene1

The geometry and the electronic structure of tricyclo[4.2.2.2^2,5]dodeca-1,5-diene (TCDD) molecule were investigated by DFT/B3LYP and /B3PW91 methods using the 6-311G(d,p) and 6-311++G(d,p) basis sets. The double bonds of TCDD molecule are syn-pyramidalized. The structure of π-orbitals and their mutual interactions for TCDD molecule were investigated. Potential energy surface (PES) of the TCDD-Br₂ system was studied by B3LYP/6-311++G(d,p) method and the configurations [molecular charge-transfer (CT) complex, transition states (TS1 and TS2), intermediate (INT) and product (P)] corresponding to the stationary points (minima or saddle points) were determined. Initially, a molecular CT-complex forms between Br₂ and TCDD. With a barrier of 22.336 kcal mol^-1 the CT-complex can be activated to an intermediate (INT) with energy 15.154 kcal mol^-1 higher than that of the CT-complex. The intermediate (INT) then transforms easily (barrier 5.442 kcal mol^-1) into the final, N-type product. The total bromination is slightly exothermic. Accompanying the breaking of Br-Br bond, C1-Br, C5-Br and C2-C6 bonds are formed, and C1 = C2 and C5 = C6 double bonds transform into single bonds. The direction of the reaction is determined by the direction of intramolecular skeletal rearrangement that is realized by the formation of C2-C6 bond.

<Emphasis Type="Italic">Ab initio</Emphasis> and DFT investigation of electrophilic addition reaction of bromine to <Emphasis Type="Italic">endo,endo</Emphasis>-tetracyclo[4.2.1.1<Superscript>3,6</Superscript>.0<Superscript>2,7</Superscript>]dodeca-4,9-diene

Full geometric optimization of endo,endo-tetracyclo[4.2.1.1^3,6.0^2,7]dodeca-4,9-diene (TTDD) has been carried out by ab initio and DFT/B3LYP methods and the structure of the molecule investigated. The double bonds of TTDD molecule are endo pyramidalized. The structure of π-orbitals and their mutual interactions for TTDD molecule were investigated. The cationic intermediates and products obtained as a result of the addition reaction have been studied using the HF/6-311G(d), HF/6-311G(d,p) and B3LYP/6-311G(d) methods. The bridged bromonium cation isomerized into the more stable N- and U-type cations and the difference between the stability of these cations is small. The N- and U-type reaction products are obtained as a result of the reaction, which takes place via the cations in question. The stability of exo, exo and exo, endo isomers of N-type product are nearly the same and the formation of both isomers is feasible. The U-type product basically formed from the exo, exo-isomer. Although the U-type cation was 0.68 kcal mol⁻¹ more stable than the N-type cation, the U-type product was 4.79 kcal mol⁻¹ less stable than the N-type product. Figure The energy diagram of TTDD–Br₂ system (kcal mol⁻¹)(MP2/6-311G*//HF/6-311G*)     

Zwitterionic conformers of pyrrolysine and their interactions with metal ions—a theoretical study

A total of 16 pyrrolysine conformers in their zwitterionic forms are studied in gas and simulated aqueous phase using a polarizable continuum model (PCM). These conformers are selected on the basis of our study on the intrinsic conformational properties of non-ionic pyrrolysine molecule in gas phase [Das and Mandal (2013) J Mol Model 19:1695?1704]. In aqueous phase, the stable zwitterionic pyrrolysine conformers are characterized by full geometry optimization and vibrational frequency calculations using B3LYP/6-311++G(d,p) level of theory. Single point calculations are also carried out at MP2/6-311++G(d,p) level. Characteristic intramolecular hydrogen bonds present in each conformer, their relative energies, theoretically predicted vibrational spectra, rotational constants and dipole moments are systematically reported. The calculated relative energy range of the conformers at B3LYP/6-311++G(d,p) level is 5.19 kcal mol^?1 whereas the same obtained by single point calculations at MP2/6-311++G(d,p) level is 4.58 kcal mol^?1. A thorough analysis reveals that four types of intramolecular H-bonds are present in the conformers; all of which play key roles in determining the energetics and in imparting the observed conformations to the conformers. The vibrational frequencies are found to shift invariably toward the lower side of frequency scale corresponding to the presence of the H-bonds. This study also points out that conformers with diverse structural motifs may differ in their thermodynamical stability by a narrow range of relative energy. The effects of metal coordination on the relative stability order and structural features of the conformers are examined by complexing five zwitterionic conformers of pyrrolysine with Cu⁺² through their carboxylate groups. The interaction enthalpies and Gibbs energies, rotational constants, vibrational frequencies and dipole moments of the metal complexes calculated at B3LYP level are also reported. The zwitterionic conformers of pyrrolysine are not stable in gas phase; after geometry optimization they are converted to the non-ionic forms.     

Bis-dibenzo[a.i]fluorenylidene, does it exist as stable 1,2-diradical?

The geometries, energies, and electronic properties of the two possible configurations of bis-[dibenzo[a.i]fluorenylidene] were investigated theoretically by density functional theory DFT B3LYP at the UB3LYP/6-311?+?G(2d,p) // UB3LYP/6-31?+?G(d,p) level of theory. According to the performed calculations, it was found that the singlet is 3.4?kcal?mol^-1 lower in energy compared to triplet state at room temperature. This gap is compared with those of other alkenes like ethylene, (61.9?kcal?mol^-1) tetra-tert-butyethylene, (6.4?kcal?mol^-1) and bis-fluorenylidene (19.5?kcal?mol^-1). These results confirm the experimental findings of the paramagnetic properties determined by Franzen and Joschek. The low singlet-triplet gap in the case of bis-[dibenzo[a.i]fluorenylidene] is the result of a steric destabilization of the singlet due to strain and stabilization of the triplet electronic state by delocalization of each free electron within each aromatic moiety. This correlates with the special electronic structure of the triplet state of this compound, where facial interaction of two hydrogen atoms lying close to the lobes of each p-orbital occupied with a single electron at the distorted double bond in the triplet electronic state.

Normal coordinate analyses of 3,5-dichlorophenylcyanamide

The structure of 3,5-dichlorophenylcyanamide c-C₆H₃Cl₂–NHCN was investigated by DFT-B3LYP and ab initio MP2 calculations with the 6-311+G** basis set. The planar to perpendicular rotational barrier was calculated to be of about 5 kcal mol^–1 at both levels of calculation. The stability of the planar structure of the molecule was explained on the basis of conjugation effects between the cyanamide–NHCN moiety and the phenyl c-C₆H₅ ring in agreement with earlier NMR results. The CNC and the HNC bond angles were calculated to be about 120° especially by MP2 calculation, which is consistent with sp² (planar –NH–CN group) and not sp³ (pyramidal –NH–CN group) structure. The vibrational frequencies of the d₀, d₁ and d₃ species of 3,5-dichlorophenylcyanamide and the potential energy distributions among symmetry coordinates of the normal modes of the parent molecule were computed at the DFT-B3LYP level. The calculated infrared and Raman spectra of the molecule were plotted. Complete vibrational assignments were made on the basis of isotopic substitution and normal coordinate calculations.Figure Potential curves for the internal rotation in 3,5-dichlorophenylcyanamide as determined by DFT-B3LYP/6-311+G** (solid) and MP2/6-311+G** (dotted) calculations     

Theoretical potential scans and vibrational spectra of vinyl selenonyl halides CH2=CH–SeO2X (X is F, Cl and Br)

The structure and conformational stability of vinyl selenonyl fluoride, chloride and bromide CH₂=CH–SeO₂X (X is F, Cl and Br) were investigated using density functional B3LYP/6-311+G** and ab initio MP2/6-311+G** calculations. From the calculations the molecules were predicted to exist only in the non-planar gauche conformation with the vinyl C=C group almost eclipsing one of the selenonyl Se=O bonds as a result of conjugation between the two moieties. Single-minimum potential scans were calculated at the DFT level for the molecules. The vibrational frequencies were computed using B3LYP/6-311+G**. Normal coordinate calculations were then carried out and potential energy distributions were calculated for the three molecules in the gauche conformation.Figure Potential function for the asymmetric torsion in vinyl selenonyl fluoride (dotted line), chloride (dashed line) and bromide (solid line) as determined at the DFT-B3LYP/6-311+G** level     

Reactions of permanganyl chloride with allene in low-temperature matrices

The light-induced (546 nm) reaction of MnO₃Cl with allene has been investigated in low-temperature argon matrices at 11 K. IR spectroscopic studies in combination with isotopic enrichment experiments (¹⁸O, D) and DFT calculations (B3LYP/LanL2DZ) allowed the identification of (O)₂MnCl(OCCH₂CH₂) (1), and (O)₂MnCl(H₂COCCH₂) (2) as the products. Possible ways for their formation are first of all discussed qualitatively in the context of the literature available, and then quantitatively with the background of DFT data (B3LYP/6-311G(d)) obtained for starting materials, products, transition states and intermediates. The most reasonable interpretation involves two-state reactivity.     

Absolute configuration of (−)-myrtenal by vibrational circular dichroism

The VCD spectrum of the monoterpene (−)-myrtenal (1) was compared with theoretical spectra using ab initio density functional theory (DFT) calculations at the B3LYP/6-31G(d,p), B3LYP/6-31G+(d,p), B3LYP/6-311G+(d,p), B3LYP/DGDZVP, and B3PW91/DGTZVP levels of theory. Conformational analysis of 1 indicated that the lowest energy conformer was s-trans-C2-C10, which contributes more than 98.5% to the total conformational population regardless of the employed level of theory. The use of a recently developed confidence level algorithm demonstrated that VCD spectra calculated for the main conformer, using the indicated hybrid functionals and basis set, gave no significant changes, from where it follows that B3LYP/DGDZVP calculations provide a superior balance between computer cost and VCD spectral accuracy. The DGDZVP basis set demanded around a quarter the time than the 6-311G+(d,p) basis set while providing similar results. The spectral comparison also provided evidence that the levorotatory enantiomer of myrtenal has the 1R absolute configuration.     

Computational Study of the Sulfonylated Amino Acid Hydroxamates Binding to the Zinc Ion within the Active Site of Carbonic Anhydrase

Abstract

The B3LYP/6–311+G(d,p) method and three ONIOM extrapolation methods ONI-OM (B3LYP/6–311+G(d,p): AM1); ONIOM(B3LYP/6–311+G(d,p): MNDO); ONIOM (B3LYP/6–311+G(d,p): HF/3-21G(d)) were used to characterize the complexes of Zn²⁺ cation with anionic sulfonylated amino acid hydroxamates (RSO₂NH-AA-CON(-)OH), possessing an unsubstituted RSO₂NH—amino acyl moiety. According to the R moiety we distinguish between pentafluorophenyl and 4-methoxyphenyl derivates. The amino acid hydroxamates included in the study were the Gly, Ala, and Leu derivates. Of the inhibitors investigated, the weakest zinc affinity exhibits the pentafluorophenyl derivate with Gly amino acid and the strongest affinity the 4-methoxyphenyl derivate with Leu amino acid. The inhibitors form bidentate coordination bonds with the zinc cation by means of the sulfonyl oxygen and the ionized hydroxamate nitrogen atoms, respectively. The zinc affinities computed using the B3LYP/6–311 +G(d,p)//HF/6–31 +G(d,p) method are in very good agreement with the full density functional theory (DFT) B3LYP/6–311+G(d,p)//B3LYP/6- 311+G(d,p) method and this method can be adopted to model larger complexes of inhibitors with the active site of carbonic anhydrase.     

Mechanistic investigation of the base-promoted cycloselenoetherification of pent-4-en-1-ol

The mechanism of phenylselenoetherification of pent-4-en-1-ol using some bases (pyridine, triethylamine, quinoline, 2,2′-bipyridine) as catalyst was examined through studies of kinetics of the cyclization, by UV-VIS spectrophotometry. It was demonstrated that the intramolecular cyclization is facilitated in the presence of bases caused by the hydrogen bond between base and alkenol’s OH-group. The obtained values for rate constants have shown that the reaction with triethylamine is the fastest one. Quantum chemical calculations (MP2(fc)/6-311+G**//B3LYP/6-311+G**) show, that the transition state of the cyclisation is S_N2 like.     

The simulation of UV spectroscopy and electronic analysis of temozolomide and dacarbazine chemical decomposition to their metabolites

The electronic features of anti-tumor agent, temozolomide, and its degradation products (MTIC and metabolite AIC) have been traced by means of UV absorption spectroscopy in vacuo and aqueous media. For comparison, electronic spectra of related structures and drugs (e.g., dacarbazine) were also investigated. These investigations were carried out using time-dependent density functional theory (TD-DFT) method while the conductor like screening model (COSMO) were applied for the inclusion of solvent effects in electronic spectra. From functional benchmarking, two methods; B3LYP and O3LYP were selected among several other methods with 6-311+G(2d,p) basis set aiming to get the best results in accord with the experimental values. An assessment of the obtained spectra has shown that O3LYP functional gives a mean absolute error (MAE) from experimental absorption peaks of 4.3 nm compared to the 7.2 nm MAE value at B3LYP level in aqueous media. Furthermore, since the structural and tautomeric conformers affect the electronic spectra, conformational preferences have been analyzed in temozolomide, dacarbazine, and their related structures. Temozolomide structure possesses two rotamers that differ in the orientation of carboxamide moiety with a small energy difference (energy difference of 1.39 kcal mol^?1 in vacuo and 0.35 kcal mol^?1 in aqueous media at B3LYP/6-311++G(2df,3pd). The more stable and meta-stable TMZ rotamer have shown their absorption maxima at 329–334 nm, respectively, at O3LYP level in aqueous media. Applying statistical calculation according to Boltzmann population formula at 25 °C and computed weighed mean estimates the λ_max of temozolomide at 331 nm, which is in notable agreement with the experimental value (330 nm). Moreover, molecular orbital composition analysis has been conducted in order to interpret these findings.

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Graphical Abstract Temozolomide and dacarbazine

     

Structure and electronic properties of azadirachtin

We performed a combined DFT and Monte Carlo ¹³C NMR chemical-shift study of azadirachtin A, a triterpenoid that acts as a natural insect antifeedant. A conformational search using a Monte Carlo technique based on the RM1 semiempirical method was carried out in order to establish its preferred structure. The B3LYP/6-311++G(d,p), wB97XD/6-311++G(d,p), M06/6-311++G(d,p), M06-2X/6-311++G(d,p), and CAM-B3LYP/6-311++G(d,p) levels of theory were used to predict NMR chemical shifts. A Monte Carlo population-weighted average spectrum was produced based on the predicted Boltzmann contributions. In general, good agreement between experimental and theoretical data was obtained using both methods, and the ¹³C NMR chemical shifts were predicted highly accurately. The geometry was optimized at the semiempirical level and used to calculate the NMR chemical shifts at the DFT level, and these shifts showed only minor deviations from those obtained following structural optimization at the DFT level, and incurred a much lower computational cost. The theoretical ultraviolet spectrum showed a maximum absorption peak that was mainly contributed by the tiglate group.     

Ab initio studies on the reactivity of the CF3OCH2O radical: Thermal decomposition vs. reaction with O2

Hydrofluoroethers are being considered as potential candidates for third generation refrigerants. The present investigation involves the ab initio quantum mechanical study of the decomposition mechanism of CF₃OCH₂O radical formed from a hydrofluoroether, CF₃OCH₃ (HFE-143a) in the atmosphere. The geometries of the reactant, products and transition states involved in the decomposition pathways are optimized and characterized at the DFT (B3LYP) level of theory using 6-311G(d,p) basis set. Energy calculations have been performed at the G2(MP2) and G2M(CC,MP2) level of theory. Two prominent decomposition channels, C-O bond scission and reaction with atmospheric O₂ have been considered for detailed investigation. Studies performed at the G2(MP2) level reveals that the decomposition channel involving C-O bond scission occurs with a barrier height of 23.8 kcal mol⁻¹ whereas the oxidative pathway occurring with O₂ proceeds with an energy barrier of 7.2 kcal mol⁻¹. On the other hand the corresponding values at G2M(CC,MP2) are 24.5 and 5.9 kcal mol⁻¹ respectively. Using canonical transition state theory (CTST) rate constants for the two pathways considered are calculated at 298 K and 1 atm pressure and found to be 5.9 × 10⁻⁶ s⁻¹ and 2.3 × 10⁻⁵ s⁻¹ respectively. The present study concludes that reaction with O₂ is the dominant path for the consumption of CF₃OCH₂O in the atmosphere. Transition states are searched and characterized on the potential energy surfaces involved in both of the reaction channels. The existence of transition state on the corresponding potential energy surface is ascertained by performing intrinsic reaction coordinate (IRC) calculation.     

Computational study of decomposition mechanisms and thermodynamic properties of molecular-type cracking patterns for the highly energetic molecule GZT

This study uses the Gaussian 03 program and density functional theory B3LYP with three basis set methods—[B3LYP/6-311+G(d,p), B3LYP/6-31+G(2d,p), and B3LYP/6-31G(d,p)]—to model the highly energetic ionic compound diguanidinium 5,5′-azotetrazolate (GZT) to research its decomposition mechanisms and thermodynamic properties. Molecular-type cracking patterns are proposed, which were initiated by heterocyclic ring opening, sequential cracking of the two five-membered rings of GZT, and simultaneous release of N₂ molecules; whereas proton transfer, bond-breaking, and atomic rearrangements were performed subsequently. Finally, 15 reaction paths and five transition states were obtained. All possible decomposition species and transition states, including intermediates and products, were identified, and their corresponding enthalpy and Gibbs free energy values were obtained. The results revealed that (1) the maximum activation energy required is 187.8 kJ mol^–1, and the enthalpy change (ΔH) and Gibbs free-energy change (ΔG) of the net reaction are ?525.1 kJ mol^–1 and ?935.6 kJ mol^–1, respectively; (2) GZT can release large amounts of energy, the main contribution being from the disintegration of the 5,5'-azotetrazolate anion (ZT^2?) skeleton (ΔH?=??598.3 kJ mol^–1); and (3) the final products contained major amounts of N₂ gas, but remaining gas molecules such as HCN and NH₃ were obtained, which are in agreement with experimental results. The detailed decomposition simulation results demonstrated the feasibility of this method to calculate the energies of the thermodynamic reactions for the highly energetic GZT and predict the most feasible pathways and the final products.     

Calculations of the C<Subscript>2</Subscript> fragmentation energies of higher fullerenes C<Subscript>80</Subscript> and C<Subscript>82</Subscript>

The C₂ fragmentation energies of the most stable isolated-pentagon-rule (IPR) isomers of the C₈₀ and C₈₂ fullerenes were evaluated with second-order Møller-Plesset (MP2) theory, density-functional theory (DFT) and the semiempirical self-consistent charge density-functional tight-binding (SCC-DFTB) method. Zero-point energy, ionization energy and empirical C₂ corrections were included in the calculation of fragmentation energies for comparison with experimental C₂ fragmentation energies of the fullerene cations. In the case of the most probable Stone-Wales pathway of C₂ fragmentation of C₈₀, the calculated \(D_{0} {\left( {{\text{C}}_{{{\text{80}}}} ^{ + } } \right)}\) agree well with experimental data, whereas in the case of C₈₂ fragmentation, the calculated \(D_{0} {\left( {{\text{C}}_{{{\text{82}}}} ^{ + } } \right)}\) exceed by up to 1.2 eV the experimental ones, which suggests that other IPR isomers may be present in sufficient amounts in experimental samples. Computer-intensive MP2 calculations and DFT calculations with larger basis sets do not yield much improved C₂ fragmentation energies, compared to those reported earlier with B3LYP/3-21G. On the other hand, semiempirical approaches such as SCC-DFTB, which are orders of magnitude less intensive, yield satisfactory fragmentation energies for higher fullerenes and may become a method of choice for routine calculations of fullerenes and carbon nanotubes.

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Figure C₂ fragmentation energies of C₈₀ and C₈₂ fullerenes have been calculated with B3LYP/6-31G* model chemistry, with semiempirical self-consistent-charge density-functional tight-binding (SCC-DFTB) method and with the more rigorous MP2 method. The influence of basis set extension and level of theory on the resulting fragmentation energies is discussed

     

Relationship between structure and entropy contributions in an anthraquinone mercapto derivative

The structural and thermodynamic properties of an anthraquinone derivative were studied by means of quantum-chemical calculations. Conformational analysis using ab initio and density functional theory methods revealed 14 low-energy conformers. In order to discuss similarities and differences in entropy of the conformers, the rotational and vibrational contributions to entropy were correlated with changes in conformer structure. The component of the moment of inertia perpendicular to the molecular plane gives significant input to ΔS _rot , whereas the largest contributions to the ΔS _vib have vibrations associated with the τ _S1C20 coordinate.

Ab initio studies on the decomposition kinetics of CF<Subscript>3</Subscript>OCF<Subscript>2</Subscript>O radical

The present study deals with the decomposition of CF₃OCF₂O radical formed from a hydrofluoroether, CF₃OCHF₂ (HFE-125), in the atmosphere. The study is performed using ab initio quantum mechanical methods. Two plausible pathways of decomposition of the titled species have been considered, one involving C-O bond scission and the other occurring via F atom elimination. The geometries of the reactant, products and transition states involved in the decomposition pathways are optimized and characterized at DFT (B3LYP) level of theory using 6-311G(d,p) basis set. Single point energy calculations have been performed at G2M(CC,MP2) level of theory. Out of the two prominent decomposition channels considered, the C-O bond scission is found to be dominant involving a barrier height of 15.3 kcal mol⁻¹ whereas the F-elimination path proceeds with a barrier of 26.1 kcal mol⁻¹. The thermal rate constants for the above two decomposition pathways are evaluated using canonical transition state theory (CTST) and these are found to be 1.78 × 10⁶ s⁻¹ and 2.83 × 10⁻⁷ s⁻¹ for C-O bond scission and F-elimination respectively at 298 K and 1 atm pressure. Transition states are searched on the potential energy surfaces involved during the decomposition channels and each of the transition states is characterized. The existence of transition states on the corresponding potential energy surface is ascertained by performing intrinsic reaction coordinate (IRC) calculation.     

Gas phase acidities of N-substituted amine-boranes

Complexation energies and acidities of 19 primary, secondary and tertiary amine-boranes were investigated using MP2/6-311+G(d,p) and B3LYP/6-311+G(d,p) methods. Gas phase acidities for free amines were also calculated. Acidity values for studied complexes range from 327.3 to 349.1 kcal mol^?1 and the most acidic are the ones with direct connection between deprotonation center and a π-system. Results obtained by both computational methods are in good agreement with each other and with known experimental data. Addition of BH₃ increases the acidity of amines by 30 to 50 kcal mol^?1. This enhancement effect was compared to the respective effect witnessed in phosphine-boranes and traced back to changes of charge delocalization on nitrogen. A question about the structural stability of several deprotonated amine-borane anions in the gas phase was also raised.