Self-consistent Reaction Field Model Research Articles

Solvation of Potassium 5-Hydroxy Pentanoyl Trifluoroborate Salt in Aqueous Environment by Using FT-Raman and UV-Visible Spectra

The hydration process of potassium 5-hydroxypentanoyltrifluoroborate salt, K[C5H9BF3O2] and its 5-hydroxypentanoyltrifluoroborate [C5H9BF3O2]- anion have been studied by combining the experimental FT-Raman and ultraviolet-visible spectra in aqueous solution with hybrid B3LYP/6-311++G** calculations. Solvent effects have been considered with the self-consistent reaction field (SCRF) and solvation (SM) models. Here, the structures of [C5H9BF3O2].[H2O]n clusters of anion, with n from 1 to 5 implicit water molecules, were proposed in order to study the number of water molecules that could hydrate the anion. Calculations were performed in the gas phase and an aqueous solution to observe the effect of the medium on the dipole moment and volume values. Calculated solvation energies for all clusters were corrected by zero-point vibrational energy (ZPVE), non-electrostatic terms and by basis set superposition energy (BSSE). The dipole moment of salt in solution (10.19 D) suggests that the number of water molecules that could hydrate the anion vary between 3 and 4, in total agreement with the observed and predicted bands in the UV-Vis spectra for the salt and these two clusters in water between 180 and 400 nm. Comparisons among experimental and predicted Raman spectra show clearly the hydration effect because the bands attributed to OH, BF3 and C=O groups are shifted in solution, while, the predicted Raman spectra for all clusters in solution show strong changes in the intensities of many bands, in accordance with the corresponding experimental one. Evidently, the hydration occurs on the OH, BF3 and C=O groups.

Investigation of host-guest interactions between polyester dendrimers and ibuprofen using density functional theory (DFT)

Polyester dendrimers are mostly non-toxic and this advantage besides biodegradability gives them a great chance of success in the field of drug delivery. This study investigates electronic and structural characteristics of ibuprofen complexation with polyester G1 dendrimer using DFT calculations. Optimized structural geometries, interaction energies, NMR, NBO, and AIM analyses, revealed that the stability of G1:Ibu complex could be attributed to the intermolecular hydrogen bonds formed between the functional groups of polyester G1 dendrimer and ibuprofen molecule. All calculations were repeated using a self-consistent reaction field (SCRF) and polarizable continuum model (PCM) to consider implicit solvent effects and the outcomes were in line with gas phase calculations.

The structure of benzonitrile-water complex as unveiled by matrix isolation infrared spectroscopy: Is it linear or cyclic at low temperatures?

The hydrogen bonded interaction of benzonitrile (C6H5CN)-water (H2O) complexes have been studied experimentally using matrix isolation infrared spectroscopy to elucidate the structure(s) of the binary complexes produced at low temperatures. Computations performed at MP2 and B3LYP-D3 level of theory with aug-cc-pVDZ basis set predicted two complexes, of which global minimum complex A has a cyclic structure with the interactions occurring between ortho-hydrogen of C6H5CN and oxygen of H2O and the hydrogen of H2O with π-cloud of CN in C6H5CN. The linear acylic complex B, a local minimum is stabilized through a straight C-H⋯N interaction between nitrogen of C6H5CN and hydrogen of H2O and is present at a relative energy of ∼0.7 kcal/mol with respect to global minimum. While previous gas phase studies using a number of spectroscopic probes identify exclusively the cyclic global complex, our experiments performed under isolated conditions at low temperatures uniquely produced the acyclic linear C6H5CN-H2O complex, a local minimum in the potential energy surface. The CN stretching vibrational mode of C6H5CN was exploited as a unique marker to confirm the generation of local minimum. The effect of matrixes was simulated using Onsager self-consistent reaction field model and as a result, the linear complex (complex B) turned out to be energetically favored isomer under the influence of matrixes. The hydrogen bonding interaction in both the complexes was characterized using Atoms in Molecules, Natural Bond Orbital, Energy Decomposition and Non-Covalent Interaction analyses.

Synthesis and spectral properties of Methyl-Phenyl pyrazoloquinoxaline fluorescence emitters: Experiment and DFT/TDDFT calculations

Paper reports the synthesis and spectroscopic studies of two novel 1-Methyl-3-phenyl-1H-pyrazolo[3,4-b]quinoxaline (PQX) derivatives with 6-substituted methyl (MeMPPQX) or methoxy (MeOMPPQX) side groups. The optical absorption and fluorescence emission spectra are recorded in solvents of different polarity. Steady state and time-resolved spectroscopy provide photophysical characterization of MeMPPQX and MeOMPPQX dyes as materials for potential luminescence or electroluminescence applications. Measured optical absorption and fluorescence emission spectra are compared with quantum-chemical DFT/TDDFT calculations using long-range corrected xc-functionals, LRC-BLYP and CAM-B3LYP in combination with self-consistent reaction field model based on linear response (LR), state specific (SS) or corrected linear response (CLR) solvations. Performances of relevant theoretical models and approaches are compared. The reparameterized LRC-BLYP functional (ω = 0.231 Bohr−1) in combination with CLR solvation provides most accurate prediction of both excitation and emission energies. The MeMPPQX and MeOMPPQX dyes represent efficient fluorescence emitters in blue-green region of the visible spectra.

Computational study of the 1,3-dipolar cycloaddition between methyl 2-trifluorobutynoate and substituted azides in terms of reactivity indices and activation parameters

The 1,3-dipolar cycloaddition of methyl 2-trifluorobutynoate with various azides has been studied in terms of several theoretical approaches at DFT/B3LYP/6-311++G(d,p) level of theory. The mechanism of regioselectivity of these reactions was investigated through the evaluation of the potential energy surface of the cycloaddition process calculations and density DFT-based reactivity indices. These approaches were successfully applied to prediction of preferable regio-isomers for various reactions of 1,3-dipolar cycloadditions. The reactions were followed by performing transition state optimization, calculation of Intrinsic Reaction Coordinate and activation energies. Analysis of the geometries of the corresponding transition structures shows that the cycloaddition takes place along a single elementary step (one-step mechanism) but asynchronous mechanism. The calculation of the activation energies and reaction energies show that the 1,5-regioisomer for substituted phenyl azides as dipoles and the 1,4-regioisomer for substituted benzyl azides as dipoles are thermodynamically in all the cycloadditions reactions. The solvent effect was also studied in the solvent tert-butyl alcohol using self-consistent reaction field model. The observed regioselectivity was explained by using developed DFT-based reactivity descriptors, such as Fukui and Parr functions. The results were compared with experimental data to find a good agreement.

Experimental and Theoretical Study of the Raman Spectra of Ammonium Thiosulfate Solution

The Raman spectra of ammonium thiosulfate solution have been experimentally measured and several typical Raman peaks of S 2 o 3 2 − in ammonium thiosulfate solution were observed. We found that there is a linear relationship between the concentration of S 2 o 3 2 − and the corresponding intensity and area of the Raman peaks. To study the possible effect of intermolecular hydrogen bonds on the vibration of S 2 o 3 2 − , its Raman spectra were calculated using the Hartree–Fock Hamiltonian with the 6-31+G(d) basis set in the gas phase, hydrated phase (simulating intermolecular hydrogen bonds by adding two water molecules), and by the self-consistent reaction field model (SCRF). The study shows that in the gas and hydrated phases, the wavenumbers of peaks in the Raman spectra are in good agreement with the experimental values in the low-frequency region, and there is a red shift in the highfrequency region. In contrast, in both the low and high-frequency regions, the wavenumbers in the SCRF model are closer to the experimental values than those in the former two phases. This shows that the SCRF model is most suitable for the calculation of the Raman spectra of S 2 o 3 2 − in ammonium thiosulfate solution.

Hydrophobic-Radical Influence on the Structure and Vibrational Spectra of Zwitterionic Glycine and Alanine in the Condensed State

The structure and vibrational spectra of zwitterionic glycine and alanine in aqueous solution and the solid state were calculated in the B3LYP/6-311++G(d,p) approximation. The environment infl uence was taken into account by two methods, i.e., the self-consistent reaction fi eld (SCRF) model and a clear accounting for the effects of hydrogenbonds (complexes with water molecules). The geometric, energetic, and spectral characteristics required to establish that a hydrophobic radical affected the ability of glycine and alanine to form H-bonds were determined. It was found by comparison with experiment that zwitterionic glycine and alanine in the condensed states had to be surrounded with three water molecules, one of which was situated between the N+H3 and COO– ions, in order to calculate their vibrational (IR and Raman) spectra. The formation energies of the alanine complexes with water were 56.47 kcal/ mol and 12.55 kcal/mol greater than those of glycine for formation of a complex with one water molecule situated between the ionized groups and with three water molecules, respectively.

Theoretical Study of Different Solvent and Temperature Effects on Double-walled Carbon Nanotubes (DWNTs) and Calixarene with Amino Acid: A QM/MM Study

In this investigation, the interaction of Calixarene with amino acid (alanine) with double-walled carbon nanotubes (DWNTs) are examined, with OPLS, Amber and MM+ force field in molecular mechanic (MM) method. The calculations achieved by methods of Monte Carlo simulation in different temperatures. The calculations were carried out using HyperChem professional release 7.01 package of program. We investigate effects of gas phase (ϵ = 1) and in various solvent media with dielectric constants of water (ϵ = 78.39), DMSO (ϵ = 46.8), methanol (ϵ = 32.63), ethanol (ϵ = 24.55), CH2Cl2 (ϵ = 8.93) at seven temperatures on interaction of Calixarene with DWNTs, utilizing these force fields. The interaction of Calixarene with DWNTs in gas phase and five solvents such as water, DMSO, methanol, ethanol and dichloromethane has been processed applying the ab initio calculations. The calculations have been done with the GAUSSIAN 98 program according to Hartree-Fock (HF) theory at the HF/3-21G level. Thus, by utilizing a Hartree-Fock method, we studied the effects of different solvents on interaction of Calixarene with DWNTs within the Onsager self-consistent reaction field (SCRF) model, as well as the temperature effects on the stability of the interaction between Calixarene with DWNTs in various solvents.

Density Functional Theory Study of the Complexation of the Uranyl Dication with Anionic Phosphate Ligands with and without Water Molecules

The structures, vibrational frequencies and energetics of anhydrous and hydrated complexes of UO2(2+) with the phosphate anions H2PO4(-), HPO4(2-), and PO4(3-) were predicted at the density functional theory (DFT) and MP2 molecular orbital theory levels as isolated gas phase species and in aqueous solution by using self-consistent reaction field (SCRF) calculations with different solvation models. The geometries and vibrational frequencies of the major binding modes for these complexes are compared to experiment where possible and good agreement is found. The uranyl moiety is nonlinear in many of the complexes, and the coordination number (CN) 5 in the equatorial plane is the predominant binding motif. The phosphates are found to bind in both monodentate and bidentate binding modes depending on the charge and the number of water molecules. The SCRF calculations were done with a variety of approaches, and different SCRF approaches were found to be optimal for different reaction types. The acidities of HxPO4(3-x) in HxPO4(3-x)(H2O)4, x = 0-3 complexes were calculated with different SCRF models and compared to experiment. Phosphate anions can displace water molecules from the first solvation shell at the uranyl exothermically. The addition of water molecules can cause the bonding of H2PO4(-) and HPO4(2-) to change from bidentate to monodentate exothermically while maintaining CN 5. The addition of water can generate monodentate structures capable of cross-linking to other uranyl phosphates to form the types of structures found in the solid state. [UO2(HPO4)(H2O)3] is predicted to be a strong base in the gas phase and in aqueous solution. It is predicted to be a much weaker acid than H3PO4 in the gas phase and in solution.

Matrix Isolation Infrared and DFT Study of the Trimethyl Phosphite–Hydrogen Chloride Interaction: Hydrogen Bonding versus Nucleophilic Substitution

Trimethyl phosphite (TMPhite) and hydrogen chloride (HCl), when separately codeposited in a N(2) matrix, yielded a hydrogen bonded adduct, which was evidenced by shifts in the vibrational frequencies of the TMPhite and HCl submolecules. The structure and energy of the adducts were computed at the B3LYP level using 6-31++G** and aug-cc-pVDZ basis sets. While our computations indicated four minima for the TMPhite-HCl adducts, only one adduct was experimentally identified in the matrix at low temperatures, which interestingly was not the structure corresponding to the global minimum, but was the structure corresponding to the first higher energy local minimum. The Onsager self-consistent reaction field model was used to explain this observation. In an attempt to prepare the hydrogen bonded adduct in the gas phase and then trap it in the matrix, TMPhite and HCl were premixed prior to deposition. However, in these experiments, no hydrogen bonded adduct was observed; on the contrary, TMPhite reacted with HCl to yield CH(3)Cl, following a nucleophilic substitution, a reaction that is apparently frustrated in the matrix.

A Novel Approach for Deriving Force Field Torsion Angle Parameters Accounting for Conformation-Dependent Solvation Effects.

A procedure for deriving force field torsion parameters including certain previously neglected solvation effects is suggested. In contrast to the conventional in vacuo approaches, the dihedral parameters are obtained from the difference between the quantum-mechanical self-consistent reaction field and Poisson-Boltzmann continuum solvation models. An analysis of the solvation contributions shows that two major effects neglected when torsion parameters are derived in vacuo are (i) conformation-dependent solute polarization and (ii) solvation of conformation-dependent charge distribution. Using the glycosidic torsion as an example, we demonstrate that the corresponding correction for the torsion potential is substantial and important. Our approach avoids double counting of solvation effects and provides parameters that may be used in combination with any of the widely used nonpolarizable discrete solvent models, such as TIPnP or SPC/E, or with continuum solvent models. Differences between our model and the previously suggested solvation models are discussed. Improvements were demonstrated for the latest AMBER RNA χOL3 parameters derived with inclusion of solvent effects in a previous publication (Zgarbova et al. J. Chem. Theory Comput.2011, 7, 2886). The described procedure may help to provide consistently better force field parameters than the currently used parametrization approaches.

Mechanisms and Kinetics for the Thermal Decomposition of 2-Azido-N,N-Dimethylethanamine (DMAZ)

To gain insight into the mechanisms and kinetics of 2-azido-N,N-dimethylethanamine's (DMAZ's) thermal decomposition postulated reaction paths were simulated with ab initio and density functional theory quantum chemistry models. Four reaction types were modeled: (i) spin-allowed and spin-forbidden paths involving N-N(2) bond fission and nitrene formation, (ii) HN(3) elimination with the formation of (dimethylamino)ethylene, (iii) N-N(2) bond fission with the formation of molecules with three- or four-membered heterocyclic rings, and (iv) simple scission of C-H, C-N, and C-C bonds. The geometries of stationary points of the reactions were obtained with a MPWB1K/6-31+G(d,p) model. To locate and model the geometries of minimum energy intersystem crossing points for triplet nitrene formation and isomerization, unrestricted broken spin symmetry calculations were performed. Employed to model an analogous path for methyl azide's decomposition, this approach was found to yield results similar to those obtained with a CASSCF(10,8)/aug-cc-pVDZ model. Of the four reaction types studied, N-N(2) bond fissions with singlet or triplet nitrene formation were found to have the lowest barriers. Barriers for paths to cyclic products were found to be 2-4 kcal/mol higher. Kinetic rate expressions for individual paths were derived from the quantum chemistry results, and spin-allowed nitrene formation was found to be dominant at all temperatures and pressures examined. The expression 2.69 × 10(9) (s(-1))T(1.405) exp(-39.0 (kcal/mol)/RT), which was derived from QCISD(T)/6-31++G(3df,2p)//MPWB1K/6-31+G(d,p) results, was found to be representative of this reaction's gas-phase rate. Adjusted on the basis of results from self-consistent reaction field models to account for solvation by n-dodecane, the expression became 1.11 × 10(9) (s(-1))T(1.480) exp(-37.6 (kcal/mol)/RT). Utilizing this result and others derived in the study, a model of the decomposition of n-dodecane-solvated DMAZ was constructed, and it generated simulations that well-reproduce previously published measured data for the process.

Theoretical Study of Different Solvents and Temperatures Effects on Single-Walled Carbon Nanotube and Temozolomide Drug: A QM/MM Study

Recently, the majority of the investigation into computational chemistry has been focused on the examination of molecules submerged in various solvents and the interaction of anticancer drug with carbon nanotubes (CNTs). The most likely tendency is toward the interaction between anticancer drug and single-walled carbon nanotubes (SWCNTs). In this investigation, the interaction of Temozolomide, a common form of anticancer drug with open-end of SWCNT, are examined, with MM+, Amber and OPLS force field in molecular mechanic (MM) method. We investigate effects of water, methanol and a mixture of them on interaction of Temozolomide with SWCNT, utilizing these force fields. The interaction of Temozolomide with open-end of SWCNT in gas phase, water and methanol have been processed applying the abinitio calculations. The calculations have been done with the GAUSSIAN 98 program according to Hartree-Fock (HF) theory at the HF/STO-3G level. Gibbs free energy, enthalpy, entropy and dipole moment values are compared in gas phase, water and methanol in this research. Thus, by utilizing a Hartree-Fock method, we studied the effects of different solvents on interaction of Temozolomide with open-end SWCNT within the onsager self-consistent reaction field (SCRF) model, as well as the temperature effects on the stability of the interaction between Temozolomide and single-walled carbon in various solvents.

Investigation of Solvent Effects on Armchair Single-Walled Carbon Nanotubes: A QM/MD Study

In this research, we studied solvent effects on the relative energies, dipole moment values, and structural properties of water, methanol, ethanol, and mixtures of them surrounding single-walled carbon nanotubes (SWCNT), by using molecular dynamics simulation. Calculations were carried out with the Hyper Chem program. We used different force fields to determine energy and other types of geometrical parameters on the particular SWCNT. Because of the differences among force fields, the energy of a molecule calculated using two different force fields will not be the same. In this study, differences in force fields was illustrated by comparing the energy calculated by using force fields MM+, Amber and OPLS. The quantum Mechanics (QM) calculations were carried out with the GAUSSIAN 98 program based on density functional theory (DFT) at the B1LYP/3-21G level. In this study, we have compared gas phase and solvent calculations that considered solvents such as water, methanol and ethanol and a mixture of them. Therefore, we investigate polar solvents effects on SWCNT within the Onsager self-consistent reaction field (SCRF) model using a Hartree-Fock method and the temperature effect on the stability of SWCNT in various solvents.

Biophysical chemistry of macrocycles for drug delivery: a theoretical study

Ab initio (RHF/STO-3G) quantum chemical calculations using the self-consistent reaction field (SCRF) model were carried out to analyze the effect of solvent polarity on the relative Gibbs free energies, the dipole moments, and the structural stability of peptide macrocycles based on unsubstituted cyclo[Gly6] and its trisubstituted derivatives containing Me, NH2, or OH groups at the Cα atom. The macrocycles studied are stable in water at both room temperature and at body fever temperature, which is important for the design of a stable nanovehicle for drug delivery in water.

Intramolecular hydroxycarbene C-H-insertion: The curious case of (o-methoxyphenyl)hydroxycarbene.

The first C–H insertion of a hydroxycarbene species in the gas phase has been observed experimentally by means of high vacuum flash pyrolysis (HVFP) and subsequent matrix isolation: (o-Methoxyphenyl)glyoxylic acid gives non-isolable (o-methoxyphenyl)hydroxycarbene upon pyrolysis at 600 °C, which rapidly inserts into the methyl C–H bond. The insertion product, 2,3-dihydrobenzofuran-3-ol, was trapped in an excess of Ar at 11 K and characterized by infrared spectroscopy. The insertion process kinetically outruns the alternative [1,2]H-tunneling reaction to o-anisaldehyde, a type of reaction observed for other hydroxycarbenes. Traces of the dehydration product, benzo[b]furan, were also detected. The potential energy hypersurface including the insertion and hydrogen migration processes was computed at the all-electron coupled-cluster level of theory encompassing single and double substitutions and perturbatively included triple excitations [AE-CCSD(T)] in conjunction with a correlation-consistent double-ζ basis set (cc-pVDZ) by utilizing density functional theory (DFT) optimized geometries (M06-2X/cc-pVDZ) with zero-point vibrational energy (ZPVE) corrections. Exchange of the methoxy for a trifluoromethoxy group successfully prevents insertion and (o-trifluoromethoxy)benzaldehyde is produced instead; however, the carbene cannot be observed under these conditions. Thermal decomposition of (o-methoxyphenyl)glyoxylic acid in refluxing xylenes does not give the insertion product but yields o-anisaldehyde. This unanticipated outcome can be rationalized by protonation of the hydroxycarbene intermediate leading to the tautomeric formyl group. Thermochemical computations at M06-2X/cc-pVDZ in conjunction with a self-consistent solvent reaction field model support this suggested reaction pathway.

THE EFFECT OF DIFFERENT SOLVENTS AND TEMPERATURES ON STABILITY OF SINGLE-WALLED CARBON NANOTUBE: A QM/MD STUDY

In the present work, we have investigated solvent effects on the relative energies and dipole moment values and studied the structural properties of water, methanol, and ethanol surrounding single-walled carbon nanotube (SWCNT) and mixtures of them as well, using Molecular Dynamics simulation. Because some of the physicochemical parameters are related to structural properties of SWCNT, we used different force fields to determine energy and other types of geometrical parameters, on the particular SWCNT. Because of the differences among force fields, the energy of a molecule calculated using two different force fields will not be the same. In this study, the difference in the force fields is illustrated by comparing the calculated energies by using force fields such as MM+, AMBER, and BIO+. The Quantum Mechanics (QM) calculations were carried out with the GAUSSIAN 98 program based on HF/3-21G level. In this study, we have compared gas phase and solvent calculations that considered solvents such as water, methanol, ethanol, and mixtures of them. So, in this work, we investigated polar solvents effects on SWCNT within the Onsager self-consistent reaction field (SCRF) model using a Hartree–Fock method and the temperature effect on the stability of SWCNT in various solvents.

Conformational Preferences of Proline Analogues with a Fused Benzene Ring

The intrinsic conformational preferences of indoline-2-carboxylic acid (Inc) and its α-methylated derivative (αMeInc) have been investigated using quantum mechanical calculations. Specifically, the behavior of their N-acetyl-N'-methylamide derivatives, Ac-L-Inc-NHMe and Ac-L-αMeInc-NHMe, has been explored at the B3LYP/6-31+G(d,p) level. Such amino acids are analogues of proline and (α-methyl)proline, respectively, bearing a benzene ring fused to the C(γ)-C(δ) bond of the five-membered pyrrolidine ring. The additional aromatic group has been shown to significantly restrict the conformational space available to these residues by reducing the flexibility of both the five-membered cycle and the peptide backbone. The fused benzene ring also plays a critical role in determining the cis-trans arrangement of the amide bond involving the pyrrolidine nitrogen, which is also modulated by the presence of the α-methyl group in the αMeInc derivative. Furthermore, the influence of the environment on the conformational propensities of these compounds has been evaluated by using both a self-consistent reaction field model and a recently developed interface in a hybrid QM/MM scheme, in which the solvent molecules are treated explicitly with classical mechanics while the solute is described by quantum mechanics at the density functional theory level.

Accounting for Polarization Cost When Using Fixed Charge Force Fields. I. Method for Computing Energy

Although it is not currently standard practice, the cost to change the electronic polarization from one appropriate for the gas phase to that implied by the charge model should be considered when deriving force fields based on fits to certain types of experimental data and for using force fields to compute observables that involve changes in molecular polarization. We present mathematical expressions and a method to estimate this polarization cost implied by a fixed charge model force field, where the fixed charge model can be any combination of point charges, higher-order multipoles, or even distributed charge densities, as long as they do not change in response to environment. These expressions illuminate the relationship between polarization costs associated with fixed charge models, self-polarization energies of polarizable models, and quantum chemical based approaches that use continuum representations of the solvent, such as the self-consistent reaction field and polarizable continuum models. The technique takes account of the tensorial nature of the polarizabilities and includes quadrupole as well as dipole polarization. The consistency of this approach to one that estimates polarization cost using an implicit solvent quantum chemistry method (PCM) is demonstrated.

Conformation and vibrational spectra and assignment of 2-thenoyltrifluoroacetone

The conformational stabilities of different tautomers of 2-thenoyltrifluoroacetone (4,4,4-trifluoro-1-(2-thienyl)butane-1,3-dione, TTFA) in several solutions have been investigated at the B3LYP level using 6-311++G** basis set. The self-consistent Onsager reaction field model was used to study the solvent effects. It was determined that the energy differences of the most stable conformers (stabilized by the hydrogen bridge), which are negligible in the gas phase, increase in the solvent media. The harmonic vibrational frequencies were calculated at the B3LYP level using 6-31G** and 6-311G** basis sets. A complete vibrational assignment has been clearly provided for the experimental IR and Raman spectra of TTFA and its deuterated analogue, which shows coexisting of four conformations in the sample. This vibrational spectroscopy analyses confirms more content of the “A” forms in the solution than the “B” forms, although the reverse is true in the solid state, in agreement with the theoretical DFT calculations and the experimental X-ray results.