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The structural parameters of the three most stable isomers with formula Cl2O2, dichlorine peroxide, chloryl chloride and chlorine chlorite, were determined by high-level ab initio theory. The effects of core-valence electronic correlation as well as relativistic corrections were included in the calculations, and vibrational averaging of the so-obtained structures was performed. The bond distances agree with experimental data, where available, to within 0.01 Å, an unprecedented accuracy in particular for the floppy dichlorine peroxide molecule. The UV spectra of the three molecules were computed and decay pathways investigated. Under actinic UV radiation at 248 nm dichlorine peroxide decomposes principally according to ClOOCl → 2Cl + O2, in a synchronous concerted mechanism. In the low-energy tail region of this signal, the decay proceeds in a non-synchronous manner. There is also a low probability of the decay channel towards ClOO + Cl, whereas ClO molecules were not found. Chloryl chloride absorbs strongly around 300 nm. It disintegrates into ClO2 + Cl, where ClO2 seems to be formed mainly in excited electronic states which decompose further into Cl + O2. Hence chloryl chloride, though much less abundant in the stratosphere than dichlorine peroxide, also contributes to ozone depletion.

We present a physical model that explains the dependence of the UV cross section of ClOOCl on temperature in the actinic wavelength region measured before by J.J. Lin, A.F. Chen and Y.T. Lee [Chemistry — An Asian Journal, 6, 1664–1678 (2011)]. It was unclear why there are frequency regions in which the cross section decreases with increasing temperature and others in which it increases. This interesting behaviour is now shown to be due to the non-rigidity of the molecule and can be described in terms of the Boltzmann populations of the lowest torsional states and small, non-systematic variations in their absorption cross sections. Combination of these two ingredients produces the non-trivial temperature effect.

A new compound, 4-chlorobenzylammonium nitrate, was obtained by a reaction between 4-chlorobenzylamine and nitric acid, and characterized by X-ray diffraction and FT-IR spectroscopy. The phenyl ring and the nitro group were essentially coplanar in the obtained crystal. The aminomethyl substituent CH2 NH3+ lies out the plane of the aromatic ring as evidenced by the torsion angle Nl C7 C1 C6 of 88.2°. The crystal packing was formed by an infinite bi-dimensional layers with graph-set motif R48(16), and stabilized by N H⋯O hydrogen bond-type intermolecular interactions. In addition, molecular geometry in the electronic ground state, Hirshfeld surface, vibrational wavenumbers, molecular electronic plane (MEP), and Natural bond orbital (NBO) analysis were performed using the density functional theory (DFT/B3LYP) with 6-31+G* basis set. Theoretical and experimental results are in good agreement. The NBO analysis confirms that the N H⋯O intermolecular interactions notably affect crystal packing in this molecule.

We present the results of a systematic investigation, at the BHandHLYP/AVTZ density functional (DFT) level, of the tautomeric equilibria of 1,2,3- and 1,2,4-triazoles and their reactions with hydroxyl radicals in the gas phase. A total of twenty-six chemical reactions has been studied, and thermodynamical data and rate constants are reported. The reactions can be classified in two categories: hydrogen abstraction and OH addition. Nine of these reactions are favourable at room temperature. It was found that OH addition proceeds more rapidly than hydrogen abstraction, by several orders of magnitude. For the most stable tautomers, which presumably dominate in the gaz-phase, the fastest reactions are OH addition to 2H-1,2,3-triazole and site-specific OH addition to carbon atom 5 of 1H-1,2,4-triazole. In absolute values, however, the rate constants are rather small, k=5.82×10-20 cm3 s-1 and k=4.75×10-18 cm3 s-1 , respectively, at room temperature. Therefore, under the conditions of the troposphere, triazoles cannot be eliminated by reactions with OH. The accuracy of the computational approach has been demonstrated by studying the tautomeric equilibria of 1,2,3- and 1,2,4-triazoles in the gas phase. The computed equilibrium constants are in excellent agreement with those derived from spectroscopic observations. Additional assessment of the quality of the computed data was made by comparison with the results from high-level CCSD(T)-F12/AVTZ ab initio calculations for three exemplary structures. This comparison demonstrates the high accuracy of our DFT results of 0.29 kcal mol-1 for energy differences between stable isomers.

International audience; Internal rotation is a fundamental motion of end-standing methyl groups that provides important insight on the molecular physics of isolated molecules. The barrier heights of such large amplitude motions are highly sensitive to their molecular and electronic environment. Until now, it is still not possible to accurately determine barrier heights using quantum chemical calculations. To probe for the effect of molecular conformations on the barrier heights of substituted furan rings, the molecular jet Fourier transform microwave spectrum of 5-methyl furfural was recorded in the frequency range from 2 to 40 GHz. Quantum chemical calculations yielded two conformers with a trans and a cis orientation of the formyl group, which were both observed in the experimental spectrum. Torsional splittings due to the internal rotation of the methyl group were resolved and analyzed. The experimental spectra is reproduced with standard deviations close to the experimental accuracy, yielding sets of highly accurate rotational and internal rotation parameters. The results, especially the V3 potentials, are compared to quantum chemical calculations and discussed within the scope of the current literature of other methyl substituted furans, where the methyl group is in close proximity of the furan oxygen atom. Our work provides an accurate evaluation of the different case studies and highlights the bottle necks and future options of current available theoretical techniques.

Dioxygen difluoride is a tough molecule that has defied accurate theoretical description for many decades. In the present work we have identified the reason for this resistance: the flatness of the OO, and more important OF, stretching potential energy curves, which make it difficult to localise the global minimum. It is not related to the weak multi-reference character. Using high-level CCSD(T)-F12/VTZ-F12 ab initio theory, the global minimum has been properly located and vibrationally averaged bond lengths obtained. These vibrationally averaged parameters agree with experimental data to within 0.01 Å. Averaging was found essential to achieve this unprecedented accuracy. We have then simulated the IR and UV spectra, which compare well with experimental data and permit identification of the observed transitions.

A novel Cd(II) coordination polymer [Cd(C4H11N2)(μ-Cl)2Cl] n ·nH2O with a supramolecular structure has been synthesized by reaction of CdCl22·5H2O with piperazine. The compound was investigated by X-ray diffraction, electrochemistry, and IR spectroscopy. The CdCl3(C4H11N2)·H2O entity in the compound forms a 1D coordination polymer as a result of the bridging function of the chlorine atoms Cd–Cl2–Cd. Adjacent 1D coordination polymers are connected by (O,N,C)–H…Cl, (O,N)–H…Cl, and N–H…O hydrogen bonds, generating a three-dimensional supramolecular network. With this atomic arrangement, the complex can form an electroactive film on a platinum electrode by anodic oxidation in acetonitrile solution.

There has been a disagreement amongst experimentalists and between experimentalists and theoreticians as to the gas-phase structure of dimethyl peroxide. We have investigated this problem with high-level CCSD(T)-F12 and MRCI procedures. There can be no doubt anymore that, at the minimum of the potential energy surface, the COOC fragment has a trans-structure. The dynamical structure of the molecule can, however, be different and be explained by the very slow torsional motion. We have analysed the dynamical structure using numerical wavefunctions of the torsional motion and a fully optimized potential curve of MP2/aug-cc-pVTZ quality. Computational and all experimental results are shown to be in complete agreement. The problem that has persisted for more than thirty years, highlighted in a recent review article by Oberhammer titled "Gas phase structures of peroxides: experiments and computational problems", has been resolved.

The in vivo chlorophyll (Chl) fluorescence spectra of Solanum lycopersicum leaves were recorded in the spectral region 650-800nm using a spectroscopic method based on ultraviolet light emitting diode induced fluorescence spectroscopy (UV-LED IFS). These spectra have been used to analyze the interactive functions of cadmium (Cd(2+)) and zinc (Zn(2+)) on photosynthetic activities of S. lycopersicum plants. The fluorescence intensity ratios (F(690)/F(735)) of the chlorophyll bands at 685 and 730nm were calculated by evaluating curve fitted parameters using a Gaussian spectral function, for control as well as treated plants. The fluorescence induction kinetics (Kautsky effect) was also measured on dark adapted intact plant leaves at the chlorophyll bands for determining the variable chlorophyll fluorescence decrease ratio (R(Fd) values) and the stress adaptation index (Ap). In addition, metal accumulation in plants, plant growth and photosynthetic pigments content were estimated. It was found that the R(Fd)(690), R(Fd)(730) and Ap values decreased whereas the F(690)/F(735) ratio increased in the case of 10μM Cd(2+) treated plants, indicating an impairment of the photosynthetic efficiency. Zn(2+) supplementation, at low concentration (10 and 50μM), in combination with Cd(2+) protect the photochemical functions. However, the high Zn(2+) concentration exacerbated the negative effects of Cd(2+) and showed a severe decrease of R(Fd)(690), R(Fd)(730) and Ap values compared to Cd(2+) alone. It is seen that F(690)/F(735) ratios are strongly correlated with chlorophyll contents. The results demonstrate the usefulness of F(690)/F(735), Ap and R(Fd) values in determining the potential photosynthetic activity of an intact attached leaf in a non-destructive way.

The electrogeneration of pure 4,4′-di-tert-butylbiphenyl peroxide as an electrodeposit could be achieved on a platinum electrode through the anodic oxidation of p-tert butylphenol in the presence of Lutidine, in addition to several soluble oligomers. The electrochemical and theoretical studies have shown that the favored coupling reaction corresponds to the O–O bond, albeit it is generally being considered unstable. Without the strong base, a mixture of trimer, tetramer and pentamer was deposited. The peroxide product presents a different electroactivity to that of the phenolic compound, with the appearance of a redox process involving cathodic and anodic symmetrical peaks at −0.10/0.15 V versus SCE, which indicates the preference of the polymer to adhere onto the electrode surface. The thermal degradation has also been analyzed. Quantum-chemical calculations reveal the reason for the oxygen–oxygen coupling.

In this work it is shown that, with a new spectroscopic method based on ultraviolet light emitting diode-induced fluorescence spectroscopy (UV-LED IFS), the photosynthetic activity of an intact attached leaf can be measured in a non-destructive way within a few seconds. The effects of cadmium (Cd) toxicity on the photosynthetic activity of tomato plants (Solanum lycopersicum) were studied using various CdCl2 (cadmium chloride) concentrations. The Cd treatment decreases the photosynthetic activity, measured via a decline of the variable chlorophyll (chl) fluorescence decrease ratio (RFd) values, calculated at 690 and 730 nm. The chl fluorescence ratios of intensity (FIR) and band area were also calculated. It was found that the RFd(690) and RFd(730) values decreased whereas the FIR increased from 1 μM Cd treatment and this behaviour is enhanced with the increasing of Cd concentrations. At 10 and 25 μM Cd, the decrease in RFd values was associated with a strong decline in the chlorophyll-a + chlorophyll-b (chl-a + b). The chl-a + b decline could also be followed via an increase of the chl fluorescence ratio F690/F730. Our study demonstrates that the UV-LED IFS is a promising technique for early detection of Cd stress (from 1 μM) in tomato plants, before visual symptoms appear.

An investigation of the elastic properties of hexagonal phases of typical liquid crystal samples on an ordered hexagonal discotic hexa-n-octyloxytriphenylene (C 8 HET), a disordered one a triphenylene hexa-n-dodecanoate (C 11 HAT) and a hexacatenar phasmid was carried out. Characterization of their mechanical stability and analysis of light scattering were used; the same results were obtained for the three samples in spite of the differences in their molecular shapes and molecular orders in columns. From the instability of undulating columns submitted to a dilative strain normal to columns, we deduced an anomalously large value of the correlation length m (m ≃ 0.1 μm), compared to that of the smectic liquid crystals (m ≃ 20 A). Results from depolarized Rayleigh scattering showed that, although consisting of one-dimensional liquid-like structures, the studied samples in their hexagonal phases behaved elastically like three-dimensional solids. Considering the differences in molecular shapes and orders, this elastic behaviour was attributed to regular defects. Therefore, one can probably generalize this elastic behaviour as being due to the columnar hexagonal structure.

We analyze the structure, hydration, and pK(a) values of p-guanidinoethyl-phenol through a combined experimental and theoretical study. These issues are relevant to understand the mechanism of action of the tetrameric form, the antibacterial compound tetra-p-guanidinoethyl-calix[4]arene (Cx1). The investigated system can also be useful to model other pharmaceutical drugs bearing a guanidine function in the vicinity of an ionizable group and the effect of arginine on the pK(a) of vicinal ionizable residues (in particular tyrosine) in peptides. The p-guanidinoethyl-phenol monomer (mCx1) has two ionizable groups. One important particularity of this system is that it exhibits high molecular flexibility that potentially leads to enhanced stabilization in folded structures by direct, strong Coulombic interactions between the ionizable groups. The first pK(a) corresponding to ionization of the -OH group has experimentally been shown to be only slightly different from usual values in substituted phenols. However, because of short-range Coulombic interactions, the role of intramolecular interactions and solvation effects on the acidities of this compound is expected to be important and it has been analyzed here on the basis of theoretical calculations. We use a discrete-continuum solvation model together with quantum-mechanical calculations at the B3LYP level of theory and the extended 6-311+G(2df,2p) basis set. Both intra- and intermolecular effects are very large (~70 kcal/mol) but exhibit an almost perfect compensation, thus explaining that the actual pK(a) of mCx1 is close to free phenol. The same compensation of environmental effects applies to the second pK(a) that concerns the guanidinium group. Such a pK(a) could not be determined experimentally with standard titration techniques and in fact the theoretical study predicts a value of 14.2, that is, one unit above the pK(a) of the parent ethyl-guanidinium molecule.

The effects of zinc (Zn) on plant chlorophyll fluorescence were investigated in 10-day-old tomato ( Solanum lycopersicum ) seedlings subjected for 7 days to a series of zinc (10, 50, 100 and 150 μM) applied via the nutrient solution. The chlorophyll fluorescence spectra of leaves were recorded in the spectral region 650–800 nm using the spectroscopic technique of ultraviolet light emitting diode induced fluorescence spectroscopy (UV-LED IFS). These spectra have been used to analyze the effect of several doses of zinc on the photosynthetic activities of tomato plants. The fluorescence intensity ratios (FIR) at the two maxima ( F 690 / F 735 ) of control as well as treated tomato plants were calculated by evaluating curve-fitted parameters using a Gaussian spectral function. The variable chlorophyll fluorescence decrease ratio ( R Fd ) values were determined from the fluorescence induction kinetics curves recorded at 690 nm and 735 nm. In addition, Zn accumulation in plants, plant growth, photosynthetic pigments content and malondialdehyde level (MDA, an index of lipid peroxidation) were also estimated. The results indicated that the plants treated with 10 μM of zinc exhibited better growth, however, higher concentrations of zinc were harmful for plants. Excess Zn induced a decrease in the R Fd values, which was associated with a strong decline of the total chlorophylls content and an increase of MDA level. The total chlorophylls content decline could also be followed via an increase of the chlorophyll fluorescence ratio F 690 / F 735 .