Structure and tunneling splitting spectra of methyl groups of tetramethylpyrazine in complexes with chloranilic and bromanilic acids.

The crystal and molecular structure of the 2,3,5,6-tetramethylpyrazine (TMP) complex with 2,5-dibromo-3,6-dihydroxy-p-quinone (bromanilic acid, BRA) has been studied and the results are compared with TMP CLA (2,5-dichloro-3,6-dihydroxy-p-quinone (chloranilic acid, CLA) complex. The X-ray structure of TMP BRA complex indicates the formation of dimeric units, in which two BRA(-) anions are connected by two O-H···O (2.646(2) Å) hydrogen bonds, whereas the cations and anions are joined together by strong N(+)-H···O(-) (2.657(2) Å) hydrogen bonds. The results are analyzed in terms of both the methyl group surroundings and the C-H···O and N(+)-H···O(-) (or N···H-O) bridge formations. Both effects, the strength of the N(+)-H···O(-) hydrogen bonds and steric hindrance for the rotations, are responsible for the CH3 group dynamics. For the TMP CLA and TMP BRA complexes, the inelastic neutron backscattering spectra were also investigated. In the case of TMP CLA, four tunneling signals have been observed in the energy range ±30 µeV, which indicates four inequivalent methyl groups in the crystal structure at the lowest temperature. No tunneling splitting is observed in the case of the TMP BRA complex, most probably due to the overlapping with the elastic peak. The tunneling results are consistent with the (1)H NMR spin-lattice relaxation time investigations in a wide temperature range, which also point to the CH3 group tunneling effect in the case of TMP CLA.

Mycorrhizal fungi modulate phytochemical production and antioxidant activity of Cichorium intybus L. (Asteraceae) under metal toxicity.

Cichorium intybus (common chicory), a perennial plant, common in anthropogenic sites, has been the object of a multitude of studies in recent years due to its high content of antioxidants utilized in pharmacy and food industry. Here, the role of arbuscular mycorrhizal fungi (AMF) in the biosynthesis of plant secondary metabolites and the activity of enzymatic antioxidants under toxic metal stress was studied. Plants inoculated with Rhizophagus irregularis and non-inoculated were grown on non-polluted and toxic metal enriched substrata. The results presented here indicate that AMF improves chicory fitness. Fresh and dry weight was found to be severely affected by the fungi and heavy metals. The concentration of hydroxycinnamates was increased in the shoots of mycorrhizal plants cultivated on non-polluted substrata, but no differences were found in plants cultivated on metal enriched substrata. The activity of SOD and H2O2 removing enzymes CAT and POX was elevated in the shoots of mycorrhizal plants regardless of the cultivation environment. Photochemical efficiency of inoculated chicory was significantly improved. Our results indicate that R. irregularis inoculation had a beneficial role in sustaining the plants ability to cope with the deleterious effects of metal toxicity.

4,4'-, 5,5'-, and 6,6'-dimethyl-2,2'-bipyridyls: the structures, phase transitions, vibrations, and methyl group tunneling of their complexes with chloranilic acid.

The crystal and molecular structures of 4,4(')- and 6,6(')-dimethyl-2,2(')-bipyridyl complexes with 2,5-dichloro-3,6-dihydroxy-p-benzoquinone (chloranilic acid, CLA) have been determined and compared with those of the complex with the 5,5(')-derivative, which is known to possess interesting antiferroelectric properties. In the crystalline state, all three compounds form hydrogen bonded chains with N(+)-H···O(-) and O-H···N bridges on both sides of the bipyridyl constituent. The comparison of three derivatives indicates that the N(+)-H···O(-) hydrogen bonds are shortest for the 5,5(')-dimethyl complex. The 4,4(')- and 6,6(')-derivatives do not show any ferroelectric feature. The 6,6(')-one is, however, characterized by a continuous phase transition, revealed in the differential scanning calorimetry, dilatometric, and dielectric characteristics. The tunneling splitting measured by neutron backscattering in the energy range ±30 µeV for the neat dimethyl bipyridyls and their complexes with CLA indicates that the different splittings are primarily due to the crystal packing effect and that charge transfer between interacting compounds plays only a minor role.

The structure of diaminodurene and the dynamics of the methyl groups.

Diaminodurene crystallizes in the orthorhombic space group Pbca, with eight molecules in the unit cell. Four inequivalent methyl groups with different environments exist in a molecule. The amino groups are also different, which is well reflected in infrared spectra. Two tunneling modes are resolved at 23.7 and 7.0 microeV at 4.5 K. Their intensities are consistent with the presence of two further unresolved tunneling modes. Quasielastic spectra are composed of three Lorentzians of equal intensities. The two low activation energies and tunnel modes are modeled into consistent rotational potentials. The third activation energy and a librational band are used to guess the strength of the two stronger rotational potentials. The internal modes related to the torsional/librational vibrations mix with ring torsions in the range of 70-220 cm(-1). This way the tunnel modes couple to ring torsions whose energy determines the broadening of both tunnel bands. The calculations for free molecules yield mode frequencies a little bit lower than the experimental inelastic neutron scattering (INS) values. Application of theoretical methods elaborated for the crystalline state leads to a satisfactory consistency. It is also valid for bending modes of NH(2) groups, which in the solid state show much higher frequencies than in the gas phase, as expected.

X-ray diffraction and inelastic neutron scattering study of 1:1 tetramethylpyrazine chloranilic acid complex: temperature, isotope, and pressure effects.

The x-ray diffraction studies of the title complex were carried out at room temperature and 14 K for H/D (in hydrogen bridge) isotopomers. At 82 K a phase transition takes place leading to a doubling of unit cells and alternation of the hydrogen bond lengths linking tetramethylpyrazine (TMP) and chloranilic acid molecules. A marked H/D isotope effect on these lengths was found at room temperature. The elongation is much smaller at 14 K. The infrared isotopic ratio for O-H(D)...N bands equals to 1.33. The four tunnel splittings of methyl librational ground states of the protonated complex required by the structure are determined at a temperature T=4.2 K up to pressures P=4.7 kbars by high resolution neutron spectroscopy. The tunnel mode at 20.6 microeV at ambient pressure shifts smoothly to 12.2 microeV at P=3.4 kbars. This is attributed to an increase of the strength of the rotational potential proportional to r(-5.6). The three other tunnel peaks show no or weak shifts only. The increasing interaction with diminishing intermolecular distances is assumed to be compensated by a charge transfer between the constituents of deltae/e approximately 0.02 kbar(-1). The phase transition observed between 3.4 and 4.7 kbars leads to increased symmetry with only two more intense tunneling bands. In the isotopomer with deuterated hydrogen bonds and P=1 bar all tunnel intensities become equal in consistency with the low temperature crystal structure. The effect of charge transfer is confirmed by a weakening of rotational potentials for those methyl groups whose tunnel splittings were independent of pressure. Density functional theory calculations for the model TMP.(HF)2 complex and fully ionized molecule TMP+ point out that the intramolecular rotational potential of methyl groups is weaker in the charged species. They do not allow for the unequivocal conclusions about the role of the intermolecular charge transfer effect on the torsional frequencies.

Low frequency internal modes of 1,2,4,5-tetramethylbenzene, tetramethylpyrazine and tetramethyl-1,4-benzoquinone INS, Raman, infrared and theoretical DFT studies.

The results of inelastic neutron scattering (INS), Raman and infrared (IR) studies on 1,2,4,5-tetramethylbenzene (durene), tetramethylpyrazine (TMP) and tetramethyl-1,4-benzoquinone (TMBQ) in the solid state are reported. The observed frequencies are analyzed on the basis of DFT calculations. The low frequency region, below 400 cm(-1), related to the torsional and bending out-of-plane vibrations of the CH(3) groups, is of particular interest. The detailed analysis is possible due to the simulation of the INS spectra by using the auntie-CLIMAX program. It is shown that the observed low frequency INS bands are dramatically shifted, compared to the calculated ones, towards higher frequencies. Although one cannot exclude deficiencies of theoretical methods as applied to low frequency modes, it seems more probable the interpretation based on an existence of non-conventional CH(...)pi, CH(...)N, CH(...)O hydrogen bonds formed by the methyl groups in crystalline phases.

Inelastic neutron scattering study of tetramethylpyrazine in the complex with chloranilic acid.

The tunnel splitting of the methyl librational ground states in the hydrogen bonded tetramethylpyrazine-chloranilic acid (TMP-CLA) complex are determined for temperatures T≤28 K by high resolution neutron spectroscopy. Three tunnel modes are resolved at T = 2.4 K. Their relative intensities show that the crystal structure must be different from the proposed space group. Tunnelling and methyl librational modes from the measured density of states are combined into rotational potentials. There are discrepancies of activation energies calculated for these potentials and those obtained from quasielastic scattering of neutrons at T≥50 K due to structural differences in the two respective temperature regimes. Rotational potentials in TMP-CLA are significantly weaker as in pure TMP.

Inelastic neutron scattering studies on dichloro-1,4-benzoquinones.

Inelastic neutron scattering (INS) spectra of 2,6-dichloro- and 2,5-dichloro-1,4-benzoquinone were compared with Raman and infra-red (IR) spectra and analysed in detail below 1800 cm(-1). The analysis was based on calculations tending towards simulation of spectra by using GAUSSIAN (HF, DFT/B3LYP and BLYP/6-31G(d,p)), and auntieCLIMAX programs. The correlations between calculated and experimental (either INS or Raman and IR) frequencies enabled to analyse the problem of scaling factors (SFs). The advantages of INS technique was shown in studies of low frequency vibrations with participation of H-atoms. The macroscopic lattice effect at low temperatures on INS spectra is discussed.

Heavy metal concentrations in Enchytraeidae (Oligochaeta) in the Niepolomice Forest.

Enchytraeidae were investigated as a part of a broad study of Niepolomice Forest ecosystem functioning. Animals were collected in oak-hornbeam (Tilio-Carpinetum) and in mixed oak-pine (Pino-Quercetum) stands. The highest cadmium concentration was observed in oak-hornbeam from the northern part of the forest (32.33+/-23.22 mg kg(-1) dry mass), with lower ones in mixed oak-pine (13.60+/-21.42 mg kg(-1) dry mass) and southern oak-hornbeam stands (11.84+/-7.52 mg kg(-1) dry mass). Lead concentrations were higher in mixed oak-pine (47.73+/-23.36 mg kg(-1) dry mass) and southern oak-hornbeam (52.20+/-45.19 mg kg(-1) dry mass) stands than in northern, oak-hornbeam (9.20+/-6.46 mg kg(-1) dry mass). The copper concentration was similar in animals from all forest types studied (147.94+/-106.38 mg kg(-1) dry mass in mixed oak-pine, 138.35+/-64.76 mg kg(-1) dry mass in northern oak-hornbeam, and 138.27+/-80.08 mg kg(-1) dry mass in southern oak-hornbeam). The lowest concentration of zinc in animals was found in northern oak-hornbeam (1015.27+/-300.28 mg kg(-1) dry mass) and higher concentrations, in mixed oak-pine (2233.81+/-1825.41 mg kg(-1) dry mass) and southern oak-hornbeam (2366.60+/-1987.52 mg kg(-1) dry mass). The concentrations of available metals in litter trended with those in the animals, but only the relation between lead concentration in animals and available lead in litter was significant. The spatial distribution of metal concentrations in the whole forest suggests a relationship between forest type and the content of cadmium, lead, and zinc in animals. The spatial distribution of heavy metal content in enchytraeids was investigated in selected plots as well. The coefficients of variation indicated that lead had the most diverse distribution and zinc the most homogeneous.

Liquid crystalline properties and IR spectra of 2'-hydroxy-4'-octyloxyazobenzenes.

New azobenzene derivatives, namely 3,5-dichloro, 2,6-dimethyl and 3-chloro-4-methyl derivatives of 2'-hydroxy-4'-octyloxyazobenzene were synthesized and their properties were compared with those of 4-chloro, 4-methyl and 4-nitroderivatives. Special attention was paid to the characteristics of intramolecular O-H...N hydrogen bond reflected in IR spectra of CCl(4) solutions and neat crystalline samples. The spectra were analyzed based on DFT calculations. In all cases of solutions very strong hydrogen bonds are manifested in broad bands centered at about 2700-2800 cm(-1) of low intensity typical of resonance assisted H-bonds. On the other hand, in cases of neat crystalline samples, a broad, intensified absorption is extended down to approximately 600 cm(-1) forming a continuum resembling a Hadzi's trio. However, neither broad maxima nor minima can be assigned to delta(OH) or gamma(OH) overtones. The studies of the H/D isotope effect on the continuum seem to indicate on the role of resonance couplings between nu(OH) vibrators of neighboring molecules as well as hot bands arising from the coupling between high and low frequency modes. These couplings modify the dynamic pattern of the potential for the proton motion leading to a decrease of the barrier for the proton transfer.

Inelastic neutron scattering (INS) studies on 2,5-dihydroxy-1,4-benzoquinone (DHBQ).

Inelastic neutron scattering (INS) spectra of solid 2,5-dihydroxy-1,4-benzoquinone were measured and compared with IR and Raman data. The INS spectrum is very well reproduced in the region below 1000 cm(-1) by DFT calculations on the B3LYP/6-311++G** level using Gaussian and Climax programs. To get a better agreement one should take into account additional interactions of OH groups in the solid state leading to an increase of the gamma(OH) frequency and to a decrease of frequencies for modes in which the delta(OH) participates. The studies of the deuterated compound in IR enabled to correct the assignment of gamma(OH) vibrations. Highly asymmetric nu(OH) band observed in IR spectrum with sharp maximum at about 3300 cm(-1) is discussed in terms of a stochastic approach to the analysis of hydrogen bonded systems.

Inelastic neutron scattering studies on low frequency vibrations of pentachlorophenol.

Inelastic neutron scattering (INS) and DFT theoretical studies on pentachlorophenol (PCP) and d-PCP were performed. IR and Raman spectra were also measured for comparison. A special attention was focused on low frequency modes in INS spectra, which provide information about modes into which the co-ordinates of the hydrogen and chlorine atoms are involved. The intensity of respective INS bands is discussed based on the cross-sections of nuclei and calculated relative amplitudes of vibrations. The appearance of overtones and summation frequencies in INS spectra was evidenced.

Vibrational spectra of the adduct of 1,8-bis(dimethylamino)naphthalene with dichloromaleic acid (DMAN x DCM).

The infra-red (IR), Raman (R) and inelastic incoherent neutron scattering (IINS) spectra, particularly in low frequency region, of the title ionic adduct were studied. It is shown that all low frequency vibrations (below 200 cm(-1)) of (CH3)2N groups of protonated 1,8-bis(dimethylamino)naphthalene (DMAN)--clearly observed in IINS spectra--are sensitive to the environment, i.e. to the type of counterion forming short contacts with C-H bonds of methyl groups. The internal frequencies were also calculated by ab initio method. The results are consistent with numerous observations of the counteranion effect on the geometry of the protonated DMAN. The conclusions are compared with structural and NMR studies reported recently for the 1,8-bis(dimethylamino)naphthalene with dichloromaleic acid (DMAN x DCM) adduct. The single crystal R polarized spectra taken over the frequency range 20-3200 cm(-1) were analyzed in detail. We have shown that a substantial difference in the IR spectrum of the dichloromaleic acid (DCM) anion in the DMAN adduct and in the potassium salt results from different geometries of OHO hydrogen bonds. In the case of potassium salt the chains of longer intermolecular hydrogen bonds are formed described by means of a double minimum potential.