Complexes of lasalocid 2-naphthylmethyl ester with monovalent metal cations studied by mass spectrometry, spectroscopic and semiempirical methods

Lasalocid acid is an ionophore able to carry protons and cations through the cell membrane. Its 2-naphthylmethyl ester (NAFB) and its complexes with Li⁺, Na⁺ and K⁺ cations were synthesized and their structures were studied by ESI-MS, ¹H NMR, ¹³C NMR, FTIR and PM5 methods. The ESI-MS spectra indicate that NAFB forms stable complexes with Li⁺, Na⁺ and K⁺ cations of exclusively 1:1 stoichiometry and that the complexation of Li⁺ cations by NAFB is favoured. The NMR and FTIR spectra indicate that the oxygen atom of the ketone group of the NAFB molecule is involved in the coordination of the cations, and the strength of this process is dependent on the type of cation. We find that the intramolecular O(3)?CH···O(2) hydrogen bond in NAFB and its complexes is partially broken in acetonitrile solution and that this process is independent of the type of cation. The PM5 semiempirical calculations allow visualisation of all structures and determination of the hydrogen bond parameters.     

X-ray crystallographic, FT-IR, and density functional theory studies of the salt formed between dipicrylamine and 1,5,7-triazabicyclo[4.4.0]dec-1-ene

The DPA-TBD (dipicrylamine-1,5,7-triazabicyclo[4.4.0]dec-1-ene) salt has been synthesized and characterized by FT-IR spectroscopy, X-ray single-crystal diffraction, and theoretical study. In the FT-IR spectrum of the crystalline DPA-TBD salt, an unexpected intense band at 1742 cm(-1) is present. The optimized geometry and the FT-IR spectra of the DPA salt were calculated at the B3LYP/6-31G+(d) level and give an explanation of the nature of this band as the ν(C═N═C) vibration. For comparison, the calculated IR spectra of the DPA anion, hydrogen-bonded DPA anion, and neutral DPA and TBD molecules as well as for the TBD cation are also shown. The presence of the free DPA anion in the gas phase was directly detected in the negative ion mode electrospray ionization MS spectra. The fragmentation of the DPA anion is also discussed.     

Pyrene-1-Carboxylate in Water and Glycerol Solutions: Origin of the Change of p<Emphasis Type="Italic">K</Emphasis> Upon Excitation

Pyrene-1-carboxy acid has a pK of 4 in the ground state, and a pK of 8 in the excited state. Fluorescence spectra of the acid and base forms are presented as a function of solvent and temperature. Ab initio quantum calculations indicate that the bond between the ring system and the carboxyl group has aromatic character that becomes stronger upon excitation. This stabilization helps to account for the increase in pK upon excitation.     

Many-orbital cluster expansion for the exchange-repulsion energy in the interaction of closed-shell systems

The energy of exchange repulsion between two closed-shell systems described by determinantal wave functions has been represented as a sum of contributions arising from the interaction of two, three and four orbitals at a time. These contributions have been calculated for the interaction of two neon atoms. It has been found that in the van der Waals minimum region the two-orbital components are of secondary importance and that about 90% of the total exchange energy originates from the three-orbital interactions ofL-shell electrons. The four-orbital as well as the double-exchange terms have been found negligible. The approximate algorithms for evaluation of the exchange repulsion energy have been tested and discussed.This work was partly supported by the Polish Academy of Sciences within the project MR-I.9.     

Intermolecular potentials based on symmetry-adapted perturbation theory with dispersion energies from time-dependent density-functional calculations

Recently, three of us have proposed a method [Phys. Rev. Lett. 91, 33201 (2003)] for an accurate calculation of the dispersion energy utilizing frequency-dependent density susceptibilities of monomers obtained from time-dependent density-functional theory (DFT). In the present paper, we report numerical calculations for the helium, neon, water, and carbon dioxide dimers and show that for a wide range of intermonomer separations, including the van der Waals and short-range repulsion regions, the method provides dispersion energies with accuracies comparable to those that can be achieved using the current most sophisticated wave-function methods. If the dispersion energy is combined with (i) the electrostatic and first-order exchange interaction energies as defined in symmetry-adapted perturbation theory (SAPT) but computed using monomer Kohn-Sham (KS) determinants, and (ii) the induction energy computed using the coupled KS static response theory, (iii) the exchange-induction and exchange-dispersion energies computed using KS orbitals and orbital energies, the resulting method, denoted by SAPT(DFT), produces very accurate total interaction potentials. For the helium dimer, the only system with nearly exact benchmark values, SAPT(DFT) reproduces the interaction energy to within about 2% at the minimum and to a similar accuracy for all other distances ranging from the strongly repulsive to the asymptotic region. For the remaining systems investigated by us, the quality of the SAPT(DFT) interaction energies is so high that these energies may actually be more accurate than the best available results obtained with wave-function techniques. At the same time, SAPT(DFT) is much more computationally efficient than any method previously used for calculating the dispersion and other interaction energy components at this level of accuracy.     

Spectroscopic, semiempirical and X-ray structural study of the 2:1 complex of a cyclic diamide of o-phthalic acid with water molecule

Cyclic diamide of o-phthalic acid with 3,6-dioxa-octyl-1,8-diamine (CPhDA) was synthesised by a new method and its hydrate structure has been studied by X-ray diffraction, FT-IR, NMR and PM5 semiempirical methods. The crystal of this compound is orthorhombic, space group Pbcn, with a = 16.7033(11), b = 8.8823(5), c = 19.6182(12) and Z = 8. The IR spectrum of the crystal is consistent with the results obtained by the X-ray study and provides spectroscopic evidence for the formation of the H-bonded complex with water molecules. The calculated structure of the complex and the structural parameters are comparable with those determined by the X-ray method.     

Intramolecular hydrogen bonds with large proton polarizability in semisalts of mono- and di-N-oxides of N,N′-tetraalkyl-o-xylyldiamines

Heteroconjugated NO⁺H … N NO … H⁺N and homoconjugated NO⁺H … ON NO … H⁺ON intramolecular hydrogen bonds formed in semisalts of mono- and di-N-oxides of N,N′-tetraalkyl-o-xylyldiamines were studied by IR and NMR spectroscopy. All these hydrogen bonds show large proton polarizability. In the case of the heteroconjugated hydrogen bonds the proton transfer equilibrium shifts from compounds 1 to 3 to the left hand side since the interaction of the hydrogen bond with the solvent environment decreases in this series of compounds. With compound 1 the hydrogen bonds are slightly weaker and longer, hence the wavenumber dependence of the intensity of the continuum caused by these hydrogen bonds is slightly changed with compound 1 compared with compound 2. In the case of compound 3 the intensity of the continuum decreases because of increasing screening of the hydrogen bonds. In the series of homoconjugated hydrogen bonds, from compound 4 to 6 the intense continuum vanishes, and only the band of the 0–1 proton transition at 950 cm⁻¹ remains. The vanishing of the continuum is caused by increasing screening of the hydrogen bonds against their solvent environments by bulky groups, and thus, this change demonstrates again that the interaction of the hydrogen bond with large proton polarizabilities is a necessary prerequisite for IR continua to appear.     

X-ray and spectroscopic studies of the molecular structure of bis(8-oxy-1-methylquinolinium) hydroiodide

Bis(8-oxy-1-methylquinolinium) hydroiodide has been studied by X-ray diffraction, FT-IR, ¹H and ¹³C NMR spectroscopy. In the crystalline state a homoconjugated OH  O⁻ hydrogen bond is formed. As indicated by the X-ray data this hydrogen bond is very short (2.457 Å) and structurally symmetrical. The existence of this bond is manifested in the FT-IR spectra by an intense and broad band in the 1500–400 cm⁻¹ region. This type of absorption indicates that this hydrogen bond can be described by one very broad potential energy minimum in which the proton shows a large proton polarizability due to its fast fluctuations, i.e., it shows the so-called Zundel’s polarizability.