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Anthropogenic ecological ecosystems create favourable conditions for the growth of the nitrophilous medicinal species Chelidonium majus in six urban parks in Southern Poland. This study focuses on the concentrations of trace elements in the soils, leaves, stems, and rhizomes of greater celandine. The soil samples were taken only in the humus horizon (A), which averaged approximately 15 cm in thickness under the clumps of Ch. majus. Regarding the reaction, the soil samples tested can be described as slightly acidic (5.6–6.8 in KCl) to alkaline (7.1–7.4 in H2O). Organic carbon content at all sites is high, ranging from 3.2% to 13.6%, while the highest total nitrogen (Nt) content is 0.664%. The average total phosphorus (Pt) content in all samples is 548.8 mg/kg (and its range is 298–940 mg/kg), such values indicating its anthropogenic origin. In terms of heavy metals, Zn has the highest content in the analysed soil samples compared to the other elements, and its range is from 394.50 mg/kg to 1363.80 mg/kg in soil. In rhizomes, Zn also has the highest values (178.7–408.3 mg/kg), whereas, in stems and leaves, it varies (from 80.6 to 227.5 and from 57.8 to 297.4 mg/kg, respectively). Spearman’s rank correlation showed high correlations between the content of Pb, Zn, Cd, and As in the soil and rhizomes of Ch. majus. Despite soil contamination with Pb, Cd, and Zn, Ch. majus does not accumulate them in its tissues. However, the translocation of Hg and Cr from rhizomes to leaves was observed. The different concentrations of metals in each park result from the degree of diversity of the parent rocks on which the soil was formed.

The problem of aromaticity in heterocyclic rings of uracil and its 5-halogenoderivatives (5XU) was analyzed theoretically by calculating modified harmonic oscillator model of aromaticity (HOMA) for Heterocycle Electron Delocalization (HOMHED), nucleus-independent chemical shift parameters (NICS) and the so-called scan experiments, using helium-3 atom as a magnetic probe. The impact of halogen electronegativity on C5 atom’s NBO charges was also investigated. Water, as a polar environment, has a negligible impact on 5XU aromaticity. The most stable diketo tautomer shows a very low aromaticity while the “rare” dihydroxy form (tautomer No 6) is aromatic and resembles benzene. This is in agreement with traditional drawing of chemical formula of uracil’s six-membered ring, directly showing three alternating single and double bonds in its tautomer No 6. No good correlation between magnetic and geometric indexes of aromaticity for the studied 5XU tautomers was found. Linear correlation between the magnitude of NICS minimum, as well as the distance of the minimum above uracil ring plane center from 3He NMR chemical shift scan plot with respect to halogen electronegativity were observed. A strong linear dependence of magnetic index of aromaticity and the electronegativity of 5X substituent was observed.

5-Fluorouracil (5-FU) is one of anticancer drugs with broad activity. Due to its severe side effects, recent studies concentrate on new ways of directed 5-FU delivery and its release in ill tissue. One of selective carriers could be cyclodextrins and liposomes. The combination of novel methods, leading to formation of inclusion complexes (IC) between host molecule of β-cyclodextrin (β-CD) or 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) and 5-FU guest and its subsequent encapsulation in dipalmitoylphosphatidylcholine (DPPC) liposomes is studied experimentally in the present work. Several methods are applied to proof the encapsulation of the analysed drug and its release over time at 37 and 41 °C. The 5-FU release from complex of liposomal form of 5-fluorouracil and β-cyclodextrin (L[DPPC/5-FU]:β-CD) and complex of liposomal form of 5-fluorouracil and (2-hydroxypropyl)-β-cyclodextrin (L[DPPC/5-FU]:HP-β-CD) was followed using UV–Vis and fluorescence spectroscopy, proton nuclear magnetic resonance (1H NMR) and differential scanning calorimetry (DSC) techniques. The electronic and NMR spectra analysis were additionally supported by molecular modeling, including prediction of spectral changes in vacuum and in water using density functional theory (DFT-B3LYP-D3). From the observed changes the fastest release from liposomes (within 1 h) was observed for the 5-FU complexes with HP-β-cyclodextrin at 41 °C.

The presented study focuses on the interaction of the well-known neurotoxin muscimol with water. Two approaches for the water solvent are applied – the explicit and the implicit. The muscimol-water clusters were obtained by the molecular dynamics simulations and the first solvation shell was kept for further studies. Implicit water was mimicked via the polarized continuum model (PCM). All three tautomeric forms of the free muscimol molecule are considered in the calculations. The combined theoretical and experimental vibrational IR and Raman studies determined the stability of the prevailing zwitterion form in water. We proved that water molecules in the first solvation shell are crucial for the correct prediction of structural and spectroscopic parameters of muscimol due to its ability to form strong hydrogen bonds. We believe that our findings will shed some light on the binding preferences of muscimol with the γ-aminobutyric acid (GABA) receptor.

Exponential dependencies between locally calculated geometric and magnetic indexes of aromaticity, harmonic oscillator model of aromaticity (HOMA) and nucleus independent chemical shifts (NICS)(0), NICS(1) and NICS(1)zz, and the number of conjugated benzene rings in linear acenes, from benzene to decacene were observed at B3LYP/6-311+G** level of theory. Correlations between HOMA and NICS indexes showed exponential dependencies and were fitted with simple three-parameter function. Similar correlations between both indexes of aromaticity and proton and carbon nuclear isotropic shieldings of individual acene rings were observed. Contrary to proton data, the predicted 13 C nuclear isotropic shieldings of carbon atoms belonging to inner rings in polyacenes were less shielded, indicating lower aromaticity and therefore, higher reactivity.

We report on the density functional theory (DFT) modelling of structural, energetic and NMR parameters of uracil and its derivatives (5-halogenouracil (5XU), X = F, Cl, Br and I) in vacuum and in water using the polarizable continuum model (PCM) and the solvent model density (SMD) approach. On the basis of the obtained results, we conclude that the intramolecular electrostatic interactions are the main factors governing the stability of the six tautomeric forms of uracil and 5XU. Two indices of aromaticity, the harmonic oscillator model of aromaticity (HOMA), satisfying the geometric criterion, and the nuclear independent chemical shift (NICS), were applied to evaluate the aromaticity of uracil and its derivatives in the gas phase and water. The values of these parameters showed that the most stable tautomer is the least aromatic. A good performance of newly designed xOPBE density functional in combination with both large aug-cc-pVQZ and small STO(1M)&minus, 3G basis sets for predicting chemical shifts of uracil and 5-fluorouracil in vacuum and water was observed. As a practical alternative for calculating the chemical shifts of challenging heterocyclic compounds, we also propose B3LYP calculations with small STO(1M)&minus, 3G basis set. The indirect spin&ndash, spin coupling constants predicted by B3LYP/aug-cc-pVQZ(mixed) method reproduce the experimental data for uracil and 5-fluorouracil well.

In this study we report on UV-vis, IR and Raman studies of non-covalent copper phthalocyanine (CuPc) – flake graphene oxide (GO) complex in water and in the solid phase. Experimental results were supported by molecular modeling of structure, electronic and vibrational parameters for free CuPc and its 1 : 1 complexes with water, benzene, phenol, neutral and deprotonated benzoic acid. HOMO-LUMO gaps for these complexes were calculated and compared with data derived from the absorption edge of Q-band in the recorded UV-vis spectra for free CuPc and its adduct with GO in water. Small but non-negligible changes in position of spectral bands observed as result of CuPc interaction with GO were consistent with theoretical models predicted by density functional theory (DFT). Both the observed spectroscopic changes and theoretical shifts of spectral bands supported a direct interaction between CuPc and GO. The interaction site of CuPc was copper ion - small molecules were bound preferably to Cu2+ and its vicinity as an additional axial ligand forming a kind of T-shaped structure. In case of benzene and phenol sandwich type complexes were formed.

Phosphorus nitride (PN) is the simplest molecule formed solely by phosphorus and nitrogen. It represents an interesting model for materials, where phosphorus is directly attached to nitrogen. Nevertheless, both theoretical and experimental studies often provide an incomplete picture on the structural, electronic, and spectral properties of PN. Theoretical predictions often suffer from insufficient level of theory, incomplete basis set, or from neglecting several effects, for example, zero‐point vibrational correction (ZPVC). Therefore, we performed an extensive benchmark study on structural, electronic, and spectral properties of PN at the Hartree‐Fock, density functional theory (DFT), or even the coupled‐cluster levels. We paid special attention to the basis set effect. We tested three variants of Dunning's aug‐cc‐pVXZ basis sets with the size from double‐ζ to sextuple‐ζ, as well as Jensen's aug‐pc‐n, aug‐pcJ‐n, and aug‐pcSseg‐n basis sets, where n = 1‐4. Obtained energetics, PN distance, dipole moment, vibrational frequencies, and nuclear magnetic resonance (NMR) parameters were extrapolated to the complete basis set limit (CBS) using three‐ or two‐parameter formulas. The 31P NMR shieldings estimated with the aug‐cc‐pVXZ and aug‐cc‐pV(X + d)Z basis sets strongly depend on the basis set size providing scattered convergence patterns toward CBS. The Hartree‐Fock self‐consistent field (HF‐SCF) NMR parameters evinced similar behavior as the coupled‐cluster data. The only smooth convergence was achieved using the aug‐cc‐pCVXZ basis sets that include core‐valence effects. The KT3 functional underestimated the phosphorus CBS shieldings by about 12 ppm compared to coupled cluster with singles and doubles (CCSD) (T). Nevertheless, KT3 unambiguously surpasses the HF‐SCF and CCSD levels that provide 31P shieldings that are lower by about 150 ppm and 24 ppm compared to CCSD(T). The convergence of nitrogen shieldings was regular for all basis set hierarchies and all theoretical methods. Relativistic and vibrational effects on selected properties were also discussed.

Static electric properties, from the dipole moment to the second-hyperpolarizability tensor γ, of the 3-membered, isoelectronic ring molecules, fluorene (FL), carbazole (CR), and dibenzofuran (DBF), have been calculated at various levels of approximation. The electron correlation effects have been included at the coupled-cluster (CC) level, using CCSD and CC2 versions of the method. DFT calculations with the CAM-B3LYP functional have also been performed, and the results are compared to the CC values. The electric property-tailored Pol basis set and its more compact Z3Pol version have been employed in all static calculations. Differences between dipole polarizability values computed at the Pol and Z3Pol bases have been found to be almost negligible. Therefore, all components of the frequency-dependent dipole polarizability tensor α(-ω;ω) have been determined at the CAM-B3LYP/Z3Pol level. Divergence occurring at electronic resonances has been eliminated using the complex polarization propagator (CPP) formalism, explicitly introducing an imaginary iΓ parameter to account approximately for the finite lifetime of the excited state. The imaginary part of the dipole polarizability Im α(-ω;ω) has been calculated for a wide range of external radiation energies up to 10 eV, and its maxima have been compared to the calculated vertical electronic excitation energies.

We report on nucleus-independent magnetic shielding (NICS) scans over the centers of six- and five-membered rings in selected metal phthalocyanines (MPc) and fullerene C60 for more accurate characterization of local aromaticity in these compounds. Detailed tests were conducted on model aromatic molecules including benzene, pyrrole, indole, isoindole, and carbazole and subsequently applied to H2 Pc, ZnPc, Al(OH)Pc, and CuPc. Similar behavior of three selected magnetic probes, Bq, 3 He, and 7 Li+ , approaching perpendicularly the ring centers, was observed. For better visualization of shielding zone over the centers of aromatic rings, we introduced a simple mathematical procedure: the first and second derivatives of scan curves with respect to magnetic probe position enabled their additional examination. It allowed an easier localization of curve minimum and discrimination between areas in space varying by the magnetic field magnitude and to illustrate local aromaticity of two different kinds of rings in MPc with better resolution. Our results supported earlier reports on very low aromaticity indexes of pyrrole ring incorporated into MPc and significant aromaticity of the central macrocycle. No direct dependence between harmonic oscillator model of aromaticity and NICS was observed. Instead, a correlation between position of scan curve minimum and its magnitude were observed. In addition, the NICS values and 3 He chemical shifts in the middle of neutral C60 and C606- anion agreed well with the reported experimental NMR values for He@C60 and He@C606- .

Conformational propensities of N-t-butoxycarbonyl-glycine-(E/Z)-dehydrophenylalanine N′-methylamides (Boc-Gly-(E/Z)-ΔPhe-NHMe) in chloroform were investigated by NMR and IR techniques. The low-temperature crystal structure of the E isomer was determined by single crystal X-ray diffraction and the experimental data were elaborated by theoretical calculations using DFT (B3LYP, M06-2X) and MP2 approaches. The β-turn tendencies for both isomers were determined in the gas phase and in the presence of solvent. The obtained results reveal that the configuration of ΔPhe residue significantly affects the conformations of the studied dehydropeptides. The tendency to adopt β-turn conformations is significantly lower for the E isomer (Boc-Gly-(E)-ΔPhe-NHMe), both in gas phase and in chloroform solution.

A theoretical investigation on the planarity of molecular structure of zinc phthalocyanine (ZnPc) and its aromaticity has been performed using B3LYP and M06-2X density functionals combined with selected Pople-type basis sets. The effect of the applied calculation method on the optimized structure of ZnPc and ZnPc∙∙∙H2O, both in the gas phase and in the polar solvent, was analyzed. To quantify the aromaticity of the ZnPc and ZnPc∙∙∙H2O complexes, both the geometric and magnetic criteria, i.e., Harmonic Oscillator Model of Aromaticity (HOMA) index and the nucleus-independent chemical shift (NICS) values at the centers or 1 A above the centers of structural subunits, were calculated. The energies of highest energy occupied molecular orbital (HOMO) and lowest energy unoccupied molecular orbital (LUMO) and energy gaps were also estimated. The results show that the free ZnPC molecule is flat in the gas phase and nonplanar in the polar environments (DMSO and water). ZnPC∙∙∙H2O is nonpolar in the gas phase and polar solvent which is in agreement with recent X-ray reports. Both HOMA and NICS indexes indicate the presence of highly aromatic macrocycle and benzene rings while these parameters for pyrrolic ring are significantly smaller than in free pyrrole. The presence of polar solvents practically does not change aromaticity of the ring subunits of the studied compounds.

Self‐consistent field Hartree–Fock (SCF‐HF), density functional theory (B3LYP, KT1, KT2, and KT3), and coupled‐cluster calculations of the nuclear magnetic shielding constants of BH and BH3 molecules have been conducted to characterize the convergence of individual results obtained with correlation‐ and polarization‐consistent basis sets. The individual 11B and 1H NMR parameters were estimated in the complete basis set limit and compared with benchmark literature results. The SCF‐HF and density functional theory B3LYP predicted boron shieldings and shielding anisotropies of BH significantly differed from the results obtained by coupled‐cluster with single, double, and perturbative treatment of triple excitations, CCSD(T) approach. The best agreement between the CCSD(T)/complete basis set limit estimated boron shieldings was obtained for KT3 density functional (~5.7 ppm). The 1H NMR parameters predicted at B3LYP and CCSD(T) levels of theory differed by less than 1 ppm, and the SCF‐HF calculated proton shieldings and shielding anisotropies also nicely agreed with our coupled‐cluster results. The 1J(11B1H) parameters, calculated with B3LYP and KT3 functionals, accurately reproduced the earlier reported benchmark value for BH molecule. The SCF‐HF, B3LYP, and KT3 calculated boron shieldings of BH3 differed from the CCSD(T) values by 13.2, −16.8, and −2.1 ppm, respectively.

The development of novel molecularly imprinted polymers (MIP) sorbents for specific chemical compounds require a lot of tedious and time-consuming laboratory work. Significant quantities of solvents and reagents are consumed in the course of the verification of appropriate configurations of polymerization reagents. Implementation of molecular modeling in the MIP sorbent development process appears to provide a solution to this problem. Appropriate simulations and computations facilitate the determination of the nature of interaction between the reagents and thus the selection of the best configuration of chemicals for the preparation of the sorbent. The article presents literature information on major computer software used for molecular modeling, its application in the development of MIP sorbents, as well as the advantages resulting from the implementation of computer-assisted techniques. The appropriate choice of polymerization reagents and conditions allows for a significant reduction of the adverse environmental impact of the entire laboratory process.

Structural and selected Raman features of pristine single-walled carbon nanotubes (SWCTNs) with diameters from 0.4 to 1.2 nm and total lengths up to 2.15 nm were studied using the density functional theory (DFT) at the UB3LYP/6-31G* level. Models of different lengths (1, 4, 6 and 10 adjacent bamboo-units) of zigzag (n, 0) SWCNTs, for n ranging from 5 to 15, were studied. Highly systematic changes of individual CC bond lengths and angles along the nanotube axis were observed and described for the longest models. Predicted Raman active radial breathing mode (RBM) vibrational frequencies regularly decreased upon increasing the nanotube diameter and only a negligible effect of the tube length was observed. The changes in calculated RBM frequencies with increasing diameter were close to values estimated using empirical formulas. The experimental G-mode characteristics were reasonably well reproduced using the 4-unit model, especially for tubes with the diameter d > 1 nm. Raman features were also determined for cyclacenes representing the shortest models of SWCNTs. Calculated RBM frequencies of cyclacenes match closely the values for longer SWCNT models but are too inaccurate in the case of the G-mode. For the first time, the Raman properties of SWCNTs were also determined using the Cartesian coordinate tensor (CCT) transfer technique, thus providing reasonable frequencies of Raman active bands for long tubes consisting of 10 bamboo-units.

We present measurements of 1H and 13C shielding for (2E)- and (2Z)-2-(acetyloamino)-N,N-dimethyl-3-phenylacrylamide isomers in solutions. Practically the same values of the shielding were obtained using internal and external referencing. For the interpretation, we explore DFT calculations of shieldings performed at the rovibrationally averaged geometries. The comparison of the experimental and theoretical results is verified both for the shielding and chemical shift. It appears that some inaccuracies in the calculations of the chemical shift can be reduced due to the error compensation while subtracting the reference shielding. As shown the measurement of magnetic shielding can be useful for molecular structural studies.

Chemical characterization and separation of individual fullerenes from a raw reaction mixture need new and efficient tools, including rapid spectroscopic techniques. Recent "molecular surgery" synthesis of endohedral complexes of fullerenes with selected atoms and small molecules has opened a new path for experimental and theoretical studies on structural and spectroscopic properties of these molecular systems. Among them are fullerenes with molecular hydrogen confined within a nanoscale cavity. In this work we report on quantum-chemical prediction of nuclear magnetic shielding (and chemical shift) and indirect spin-spin coupling constant in free HD and H2 molecules, as well as models of confined dihydrogen using the coupled cluster with single and double excitations (CCSD) and density functional theory (DFT) levels of theory. Inspired with the recent experimental NMR studies on HD and H2 molecules confined inside C60 fullerene we systematically investigated the sensitivity of (1)H nuclear magnetic shielding of H2 and indirect spin-spin coupling constant (1)JHD in HD molecules to the interatomic separation in the gas phase, in the presence of benzene and inside fullerene cages of different size. The sensitivity of both NMR parameters to confinement is discussed in terms of very weak non-covalent interactions of HD and H2 with fullerene cage.

The molecular geometries of carbazole and its 17 nitro derivatives were optimized at the B3LYP/6-311++G(2d,2p) level of theory. The harmonic oscillator model of aromaticity and nucleus-independent chemical shift descriptors of π-electron delocalization were calculated to estimate the aromaticity of the carbazole five- and six-membered rings. The biggest changes in the value of both descriptors were observed for the pyrrole ring. The nitro group attached to 3 and/or 6 positions of the carbazole ring system exerts only a slight influence on the benzene ring aromaticity.

Theoretical modeling of noble gas interaction with furan as a simple heterocyclic ring was performed. The structures of neon–furan and argon–furan complexes were calculated at the MP2, M06-2X, CAM-B3LYP, APFD, and VSXC levels of theory using 6-311++G** basis set. The predicted 21Ne and 39Ar NMR chemical shifts for the Ne–furan and Ar–furan complexes calculated with pcS-3 and aug-pcS-3 basis sets were sensitive to the presence of the aromatic furan ring. Our results indicate a higher sensitivity of the neon and argon NMR probes than the previously reported 3He NMR spectroscopic parameters in studies of small heterocyclic rings containing the oxygen atom.

Rapid growth of nanoscience and nanotechnology requires new and more powerful modeling tools. Efficient theoretical modeling of large molecular systems at the ab initio and Density Functional Theory (DFT) levels of theory depends critically on the size and completeness of the basis set used. The recently designed variants of STO-3G basis set (STO-3Gel, STO-3Gmag), modified to correctly predict electronic and magnetic properties were tested on simple models of pristine and functionalized carbon nanotube (CNT) systems and fullerenes using the B3LYP and VSXC density functionals. Predicted geometries, vibrational properties, and HOMO/LUMO gaps of the model systems, calculated with typical 6-31G* and modified STO-3G basis sets, were comparable. The (13)C nuclear isotropic shieldings, calculated with STO-3Gmag and Jensen's polarization consistent pcS-2 basis sets, were also identical. The STO-3Gmag basis sets, being half the size of the latter one, are promising alternative for studying (13)C nuclear magnetic shieldings in larger size CNTs and fullerenes.

In this work, regular convergence patterns of the structural, harmonic, and VPT2-calculated anharmonic vibrational parameters of ethylene towards the Kohn–Sham complete basis set (KS CBS) limit are demonstrated for the first time. The performance of the VPT2 scheme implemented using density functional theory (DFT-BLYP and DFT-B3LYP) in combination with two Pople basis sets (6-311++G** and 6-311++G(3df,2pd)), the polarization-consistent basis sets pc-n, aug-pc-n, and pcseg-n (n = 0, 1, 2, 3, 4), and the correlation-consistent basis sets cc-pVXZ and aug-cc-pVXZ (X = D, T, Q, 5, 6) was tested. The BLYP-calculated harmonic frequencies were found to be markedly closer than the B3LYP-calculated harmonic frequencies to the experimentally derived values, while the calculated anharmonic frequencies consistently underestimated the observed wavenumbers. The different basis set families gave very similar estimated values for the CBS parameters. The anharmonic frequencies calculated with B3LYP/aug-pc-3 were consistently significantly higher than those obtained with the pc-3 basis set; applying the aug-pcseg-n basis set family alleviated this problem. Utilization of B3LYP/aug-pcseg-n basis sets instead of B3LYP/aug-cc-pVXZ, which is computationally less expensive, is suggested for medium-sized molecules. Harmonic BLYP/pc-2 calculations produced fairly accurate ethylene frequencies. Graphical Abstract In this study, the performance of the VPT2 scheme implemented using density functional theory (DFT-BLYP and DFT-B3LYP) in combination with the polarization-consistent basis sets pc-n, aug-pc-n, and pcseg-n (n = 0, 1, 2, 3, 4), and the correlation-consistent basis sets cc-pVXZ and aug-cc-pVXZ (X = D, T, Q, 5, and 6) was tested. For the first time, we demonstrated regular convergence patterns of the structural, harmonic, and VPT2-calculated anharmonic vibrational parameters of ethylene towards the Kohn–Sham complete basis set (KS CBS) limit Electronic supplementary material The online version of this article (doi:10.1007/s00894-015-2902-z) contains supplementary material, which is available to authorized users.

Structure and energy calculations of pristine and COOH-modified model single wall carbon nanotubes (SWCNTs) of different length were performed at B3LYP/6-31G* level of theory. From 1 to 9 COOH groups were added at the end of the nanotube. The differences in structure and energetics of partially and fully functionalized SWCNTs at one end of the nanotube are observed. Up to nine COOH groups could be added at one end of (9,0) zigzag SWCNT in case of full functionalization. However, for (5,5) armchair SWCNT, the full functionalization was impossible due to steric crowding and rim deformation. The dependence of substituent attachment energy on the number of substituents at the carbon nanotube rim was observed. Figure Structure and energy calculations of pristine and COOH-modified model single wall carbon nanotubes (SWCNTs) of different length were performed at B3LYP/6-31G* level of theory and from 1 to 9 COOH groups was added at the end of the nanotube

The performance of more than 40 density functionals in predicting indirect spin-spin coupling constants (SSCCs) in the Kohn-Sham basis set limit was tested. For comparison, similar calculations were performed using the RHF, SOPPA, SOPPA(CC2), and SOPPA(CCSD) methods, and the results were estimated toward the complete basis set (CBS) limit. The SSCCs of nine small molecules (N(2), CO, CO(2), NH(3), CH(4), C(2)H(2), C(2)H(4), C(2)H(6), and C(6)H(6)) were calculated using the dedicated Jensen pcJ-n polarization-consistent basis sets and used for the CBS limit estimations within the Kohn-Sham limit. These CBS results were compared with calculations using the aug-cc-pVTZ-J basis set. Among the 41 studied DFT methods, the tHCTHhyb, HSEh1PBE, HSE2PBE, wB97XD, wB97, and wB97X functionals reproduced accurately the experimental (1)J(XH) SSCCs and (3)J(HH60) and (2)J(HH(gem)) in ethane. Similarly, the functionals HSEh1PBE, HSE2PBE, wB97XD, wB97, and wB97X predicted accurately (1)J(CC), and B98, B97-1, B97-2, PBE1PBE, B1LYP, and O3LYP provided accurate (1)J(CO) results in the CO molecule. A very good performance for the calculation of the SSCCs based on the use of the relatively small basis set aug-cc-pVTZ-J was observed.

L-threonine (L-Thr) is one of two essential α- amino acids with a hydroxyl group in the side chain. It is also one of two essential α-amino acids with a chiral side chain (the second one is L-isoleucine). Its diastereomer, L-allo- threonine (L-aThr), is rarely present in nature. In L-Thr, Cα and Cβ are L- and D- chiral, respectively. In L-aThr, both of these atoms are L-chiral. Bis(L- threoninato)copper(II), Cu(L-Thr)2, is part of the exchangeable pool of copper(II) in human blood plasma, whereas the bis(L-allo- threoninato)copper(II), Cu(L-aThr)2, does not regularly appear in the living organisms. One L-Thr, as well as L-aThr, can bind to Cu(II) via amino nitrogen (Nam), carboxylato oxygen (O), and hydroxy oxygen (Oh) atoms, in three coordination modes, as presented in Figure 1: 1. a glycine-like (via Nam and O atoms) – marked with G 2. an amino-hydroxy (via Nam and Oh atoms) – marked with No 3. a carboxy-hydroxy (via O and Oh atoms) – marked with Oo, yielding six possible coordination modes in Cu(L-Thr)2 and in Cu(L-aThr)2. Fig.1. Three coordination modes of binding of L-Thr to Cu(II) Information on the actual coordination modes to Cu(II) in Cu(L-Thr)2 and Cu(L-aThr)2 complex in aqueous solution are available from the experimental data, such as visible absorption and circular dichroism measurements. According to them, at physiological pH value, 7.4, both L-Thr and L- aThr ligands coordinate to Cu(II) in a glycine- like coordination mode. At higher pH values increasing up to ~ 9.4, coordination via Nam and Oh atoms to Cu(II) was observed in Cu(L- Thr)2, whereas only one Nam coordinated in Cu(L-aThr)2.1, 2 To examine the relative stabilities of these coordination modes and possible conformations of both systems in the gas phase, quantum chemical B3LYP/LanL2DZ{;D95v+ (d)}; conformational analyses were performed.3 They resulted in 196 and 267 gas-phase Cu(L- Thr)2 and Cu(L-aThr)2 conformers, respectively.3 The glycine-like mode is calculated as the most stable for both complexes.3 Intramolecular hydrogen bonds, as the most dominant weak molecular interaction in both copper compounds, generally create an important effect on molecular stability and relative energy of the two systems. For example, the position of the hydroxyl group in the physiological Cu(L-Thr)2 complex causes the described restriction of its conformational space, compared to Cu(L-aThr)2. To model the solvent effects, calculations with the polarizable continuum model (PCM) were performed.3 As initial structures, the five lowest-energy gas-phase conformers for each of the coordination modes were optimized by using B3LYP/LanL2DZ{;D95v+(d)}; in the aqueous medium using PCM.3 As a result, we found generally that the most stable gas-phase conformers are also the most stable ones in aqueous solution.3 The versatility of gas-phase and aqueous Cu(L- Thr)2 and Cu(L-aThr)2 minima obtained will be presented. As a conclusion, our data may explain why Cu(L-aThr)2 is not present in the body. Acknowledgement: M.M. is grateful for the financial support of “Scholarship of the Scholarship Foundation of the Republic of Austria for Postdocs” given via Österreichische Austauschdienst. This work has been supported by the Croatian Science Foundation under the Project No. IP-2014-09-3500. Computational resources were provided by the Graz University of Technology and by the Isabella cluster (isabella.srce.hr) at the Zagreb University Computing Centre. References: [1] P. Grenouillet, R. P. Martin, A. Rossi, M. Ptak, Biochim. Biophys. Acta, 322, 185 (1973). [2] V. Noethig-Laslo, N. Paulić, Monatsh. Chem. Chem. Mon., 128, 1101 (1997). [3] M. Marković, M. Ramek, C. Loher, J. Sabolović, Inorg. Chem., 55, 7694 (2016).