Nebulized water cooling of the canopy affects leaf temperature, berry composition and wine quality of Sauvignon blanc.

BACKGROUND: The present paper details a new technique based on spraying nebulized water on vine canopy to counteract the negative impact of the current wave of hot summers with temperatures above 30 °C, which usually determine negative effects on vine yield, grape composition and wine quality. RESULTS: The automatized spraying system was able to maintain air temperature at below 30 °C (the threshold temperature to start spraying) for all of August 2013, when in the canopy of uncooled vines the temperature was as high as 36 °C. The maintenance of temperature below 30 °C reduced leaf stress linked to high temperature and irradiance regimes as highlighted by the decrease of H2 O2 content and catalase activity in the leaves. A higher amount of total polyphenols and organic acids and lower sugars characterized the grapes of cooled vines. Wine from these grapes had a higher content of some volatile thiols like 3-sulfanylhexanol (3SH) and 3-sulfanylhexylacetate (3SHA), and lower content of 4-methyl-4-sulfanylpentan-2-one (4MSP). CONCLUSION: Under conditions of high temperature and irradiance regimes, water nebulization on the vine canopy can represent a valid solution to reduce and/or avoid oxidative stress and associated effects in the leaves, ensure a regular berry ripening and maintain high wine quality. The consumption of water during nebulization was acceptable, being 180 L ha-1 min-1 , which lasted an average of about 1 min to reduce the temperature below the threshold value of 30 °C. A total of 85-90 hL (from 0.8 to 0.9 mm) of water per hectare per day was required. © 2016 Society of Chemical Industry.

Binding energies of the π-stacked anisole dimer: new molecular beam-laser spectroscopy experiments and CCSD(T) calculations.

Among noncovalent interactions, π-π stacking is a very important binding motif governed mainly by London dispersion. Despite its importance, for instance, for the structure of bio-macromolecules, the direct experimental measurement of binding energies in π-π stacked complexes has been elusive for a long time. Only recently, an experimental value for the binding energy of the anisole dimer was presented, determined by velocity mapping ion imaging in a two-photon resonant ionisation molecular beam experiment. However, in that paper, a discrepancy was already noted between the obtained experimental value and a theoretical estimate. Here, we present an accurate recalculation of the binding energy based on the combination of the CCSD(T)/CBS interaction energy and a DFT-D3 vibrational analysis. This proves unambiguously that the previously reported experimental value is too high and a new series of measurements with a different, more sensitive apparatus was performed. The new experimental value of 1800±100 cm(-1) (5.15±0.29 kcal mol(-1)) is close to the present theoretical prediction of 5.04±0.40 kcal mol(-1). Additional calculations of the properties of the cationic and excited states involved in the photodissociation of the dimer were used to identify and rationalise the difficulties encountered in the experimental work.

Noncovalent interactions in the gas phase: the anisole-phenol complex.

The present paper reports on an integrated spectroscopic study of the anisole-phenol complex in a molecular beam environment. Combining REMPI and HR-LIF spectroscopy experimental data with density functional computations (TD-M05-2X/M05-2X//N07D) and first principle spectra simulations, it was possible to locate the band origin of the S(1) ← S(0) electronic transition and determine the equilibrium structure of the complex, both in the S(0) and S(1) electronic states. Experimental and computational evidence indicates that the observed band origin is due to an electronic transition localized on the phenol frame, while it was not possible to localize experimentally another band origin due to the electronic transition localized on the anisole molecule. The observed structure of the complex is stabilized by a hydrogen bond between the phenol, acting as a proton donor, and the anisole molecule, acting as an acceptor through the lone pairs of the oxygen atom. A secondary interaction involving the hydrogen atoms of the anisole methyl group and the π electron system of the phenol molecule stabilizes the complex in a nonplanar configuration. Additional insights about the landscapes of the potential energy surfaces governing the ground and first excited electronic states of the anisole-phenol complex, with the issuing implications on the system photodynamic, can be extracted from the combined experimental and computational studies.

Integrated experimental and computational spectroscopy study on π-stacking interaction: the anisole dimer.

Integrated experimental and computational results help to clarify the nature of the intermolecular interactions in a simple, isolated π-stacked dimer prepared in a molecular beam. The properties of bimolecular anisole complexes are examined and discussed in terms of the local/supramolecular nature of the electronic wavefunctions. Experimental resonance-enhanced multi-photon ionization spectra of clusters with different isotopic compositions confirmed the fundamentally localized nature of the S(1)←S(0) electronic transition. A detail analysis of the experimental results however shows the existence of non-negligible excitonic coupling for the excited-state wavefunctions leading to the doubling of the single-molecule vibronic levels in the S(1) state, with a splitting of about 30 cm(-1). Theoretical simulation of the vibrationally resolved electronic spectra and computations of the excitonic coupling convincingly support the experimental findings. The overall combined experimental/theoretical study allows a detailed description of the stacking interaction in the anisole dimer.

Isotopomeric conformational changes in the anisole-water complex: new insights from HR-UV spectroscopy and theoretical studies.

Resonance enhanced multiphoton ionization and rotationally resolved S1<--S0 electronic spectra of the anisole-2H2O complex have been obtained. The experimental results are compared with high level quantum mechanical calculations and with data already available in the literature. Quite surprisingly, the equilibrium structure of the anisole-2H2O complex in the S0 state shows some non-negligible differences from that of the isotopomer anisole-1H2O complex. Actually, the structure of the deuterated complex is more similar to the corresponding structure of the anisole-1H2O complex in the S1 state. In anisole-water, two equivalent H(D) atoms exist as revealed by line splitting in the rotationally resolved spectra. It is possible to suggest a mechanism for the proton/deuteron exchange ruled by a bifurcated transition state for the exchange reaction, with both water hydrogen atoms interacting with the anisole oxygen atom. From the analysis of all of the available experimental data and of computational results, we can demonstrate that in the S1 excited state the hydrogen bond in which the water molecule acts as an acid is weaker than in the electronic ground state but is still the principal interaction between water and the anisole molecules.

On the properties of microsolvated molecules in the ground (S0) and excited (S1) states: the anisole-ammonia 1:1 complex.

State-of-the-art spectroscopic and theoretical methods have been exploited in a joint effort to elucidate the subtle features of the structure and the energetics of the anisole-ammonia 1:1 complex, a prototype of microsolvation processes. Resonance enhanced multiphoton ionization and laser-induced fluorescence spectra are discussed and compared to high-level first-principles theoretical models, based on density functional, many body second order perturbation, and coupled cluster theories. In the most stable nonplanar structure of the complex, the ammonia interacts with the delocalized pi electron density of the anisole ring: hydrogen bonding and dispersive forces provide a comparable stabilization energy in the ground state, whereas in the excited state the dispersion term is negligible because of electron density transfer from the oxygen to the aromatic ring. Ground and excited state geometrical parameters deduced from experimental data and computed by quantum mechanical methods are in very good agreement and allow us to unambiguously determine the molecular structure of the anisole-ammonia complex.