Solar thermal pasteurization: a simple way to disinfect water.

This work is a review of a simple system for solar water pasteurisation with natural circulation discussed in our recent papers where it was designed, sized and simulated in different locations where the need for safe drinkable water was evident. Such model includes the full thermo-hydraulics, and the exergy and exergo-economic balance. In this report we critically analysed the simulated results in terms of productivity of the system and of daily and annual-average costs of purified water in order to deduce its potential socioeconomic impacts in the proposed contexts

Chromophore-Protein Coupling beyond Nonpolarizable Models: Understanding Absorption in Green Fluorescent Protein

The nature of the coupling of the photoexcited chromophore with the environment in a prototypical system like green fluorescent protein (GFP) is to date not understood, and its description still defies state-of-the-art multiscale approaches. To identify which theoretical framework of the chromophore protein complex can realistically capture its essence, we employ here a variety of electronic-structure methods, namely, time-dependent density functional theory (TD-DFT), multireference perturbation theory (NEVPT2 and CASPT2), and quantum Monte Carlo (QMC) in combination with static point charges (QM/MM), DFT embedding (QM/DFT), and classical polarizable embedding through induced dipoles (QM/MMpol). Since structural modifications can significantly affect the photophysics of GFP, we also account for thermal fluctuations through extensive molecular dynamics simulations. We find that a treatment of the protein through static point charges leads to significantly blue-shifted excitation energies and that including thermal fluctuations does not cure the coarseness of the MM description. While TDDFT calculations on large cluster models indicate the need of a responsive protein, this response is not simply electrostatic: An improved description of the protein in the ground state or in response to the excitation of the chromophore via ground-state or state-specific DFT and MMpol embedding does not significantly modify the results obtained with static point charges. Through the use of QM/MMpol in a linear response formulation, a different picture in fact emerges in which the main environment response to the chromophore excitation is the one coupling the transition density and the corresponding induced dipoles. Such interaction leads to significant red-shifts and a satisfactory agreement with full QM cluster calculations at the same level of theory. Our findings demonstrate that, ultimately, faithfully capturing the effects of the environment in GFP requires a quantum treatment of large photoexcited regions but that a QM/classical model can be a useful approximation when extended beyond the electrostatic-only formulation

Modeling The Fluorescence Of Protein-embedded Tryptophans With Ab Initio Multiconfigurational Quantum Chemistry: The Limiting Cases Of Parvalbumin And Monellin

We show that a quantum-mechanics/molecular-mechanics strategy based on ab initio (i.e., first principle) multiconfigurational perturbation theory can reproduce the spectral properties of a tryptophan residue embedded in the contrasting hydrophobic and hydrophilic environments of parvalbumin and monellin, respectively. We show that the observed absorption and emission energies can be reproduced with a less than 3 kcal mol(-1) error. The analysis of the computed emission energies based on a protein disassembly scheme and protein electrostatic potential mapping allows for a detailed understanding of the factors modulating the tryptophan emission. It is shown that for rnonellin, where the tryptophan is exposed to the solvent, the fluorescence wavelength is controlled not only by the distribution of the point charges of the protein-solvent environment but also by specific hydrogen bonds and, most important, by the environment-induced change in chromophore structure. In contrast, in parvalbumin, where the chromophore is embedded in the protein core, the structure and emission maxima are the same as those of an isolated 3-methylindole fluorophore. Consistently, we find that in parvalbumin the solvation does not change significantly the computed emission energy

Effects Of The Protein Environment On The Spectral Properties Of Tryptophan Radicals In Pseudomonas Aeruginosa Azurin

Many biological electron-transfer reactions involve short-lived tryptophan radicals as key reactive intermediates. While these species are difficult to investigate, the recent photogeneration of a long-lived neutral tryptophan radical in two Pseudomonas aeruginosa azurin mutants (Az48W and ReAz108W) made it possible to characterize the electronic, vibrational, and magnetic properties of such species and their sensitivity to the molecular environment. Indeed, in Az48W the radical is embedded in the hydrophobic core while, in ReAz108W it is solvent-exposed. Here we use density functional theory and multiconfigurational perturbation theory to construct quantum-mechanics/molecular-mechanics models of Az48W* and ReAz108W* capable of reproducing specific features of their observed UV-vis, resonance Raman, and electron paramagnetic resonance spectra. The results show that the models can correctly replicate the spectral changes imposed by the two contrasting hydrophobic and hydrophilic environments. Most importantly, the same models can be employed to disentangle the molecular-level interactions responsible for such changes. It is found that the control of the hydrogen bonding between the tryptophan radical and a single specific surface water molecule in ReAz108W\u27 represents an effective means of spectral modulation. Similarly, a specific electrostatic interaction between the radical moiety and a Val residue is found to control the Az48W* excitation energy. These modulations appear to be mediated by the increase in nitrogen negative charge (and consequent increase in hydrogen bonding) of the spectroscopic D-2 state with respect to the D-0 state of the chromophore. Finally, the same protein models are used to predict the relaxed Az481Ar* and ReAz108W* D-2 structures, showing that the effect of the environment on the corresponding fluorescence maxima must parallel that of Do absorption spectra

DFT modeling of structures and redox potentials of wild-type, Nickel-substituted and mutated (N47S/M121L, HPAz) Azurin

Azurin (Az) from Pseudomonas aeruginosa is a redox active protein belonging to the family of cupredoxins. Cupredoxins span a wide range of reduction potentials (E0) going from stellacyanin having the lowest potential of ca. 184mV to rusticyanin showing the higher potential of ca. 680mV. Several works have been devoted to the understanding of the factors influencing E0 by changing primary coordination sphere ligands or exploring secondary coordination sphere mutations. To this goal, a series of Az mutants have been designed and showed that E0 could be tuned over a very broad range (between 90mV and 640mV) without significantly perturbing the metal binding site. Among these mutants, the HPAz variant showed the highest E0 value (970mV) ever reported for Az while a significant lowering of E° value (-590mV) has been reached in a Ni-substituted Az. In this paper, we computed the B3LYP energies and Gibbs free energies of oxidized and reduced models of wild-type Az, Ni-substituted Az and two mutants (N47S/M121L and HPAz) of the protein Az to estimate their E0. The results show that the employed strategy is able to reproduce the experimental lowering or increasing of E0 among the studied Az proteins

Computational Photochemistry

This chapter discusses photochemical reaction path concept and its use in mechanistic investigations. The field of computational photochemistry is a relatively young field, especially when applied to the study of ultrafast reactions, but it is now established as a branch of computational chemistry and as a powerful, sometimes unique, way to simulate the molecular mechanism underlying fundamental chemical and biological events such as vision, primitive photosynthesis, phototropism, photochromism, bleaching, fluorescence, phosphorescence. These days, computational strategies are available for locating conical intersection and singlet/triplet crossing points and for constructing inter-state “photochemical” reaction pathways. These tools comprise methodologies for the optimisation of low-lying crossings between pair of potential energy surfaces and the computation of relaxation paths from a photoexcited reactant (For example, from theFranck-Condon (FC) structure) to a deactivation channel

Recent Applications of a QM/MM scheme at the CASPT2//CASSCF/AMBER (or CHARMM) level of theory in Photochemistry and Photobiology

The excited-state properties of chemically different chromophores embedded in diverse protein environments or in solution can be nowadays correctly evaluated by means of a hybrid quantum mechanics/molecular mechanics (QM/MM) computational strategy based on multiconfigurational perturbation theory and complete-active-space-self-consistent-field geometry optimization. In particular, in this article we show how a QM/MM strategy has been recently developed in our laboratory and has been successfully applied to the investigation of the fluorescence of the green fluorescent protein (GFP) and how the same strategy (embedding the chromophores in methanol solution) has been combined with retrosynthetic analysis to design a prototype light-driven Z/E molecular switch featuring a single reactive double bond and the same electronic structure and photoisomerization mechanism of the chromophore of the visual pigment Rhodopsin

Life Cycle Assessment of Gratzel-type cell production for non conventional photovoltaics from novel Organic Dyes

In the context of a constant energy demand growth, the interest of the scientific community is progressively moving towards renewable energy sources. Among these, photovoltaics has a prominent role. With the aim of overcoming the limits of silicon production, research turned itself to the development of new photovoltaic technologies based on alternative materials, such as organic compounds. The Dye Sensitized Solar Cells, also known as Grätzel-type cells, have attracted much interest, especially in the last decade. This is due to their potentially lower economic and environmental costs compared with traditional silicon-based cells even though they are not efficient enough yet to be industrially competitive. In this study we present the preliminary results obtained through a multidisciplinary project for the design and synthesis of new organic sensitizers for solar cells together with a life cycle assessment of a Grätzel-type panel production. The life cycle analysis has been developed based on preliminary and estimated production data along all the project stages in order to evaluate environmental impacts and energy consumption associated with the production process. This analysis will be pivotal in understanding the environmental dynamics, the benefits and drawbacks associated with the production of dye sensitized solar cells in comparison with other competitor photovoltaic technologies

Life Cycle Inventory datasets for nano-grid configurations

Datasets concerning some user-scale Smart Grids, named Nano-grids, are reported in this paper. First several Solar Home Systems composed of a photovoltaic plant, a backup generator and different types of lithium-ion batteries are provided. Then, the inventory analysis of hybrid Nano-grids integrating batteries and hydrogen storage is outlined according to different scenarios. These data inventory could be useful for any academic or stakeholder interested in reproducing this analysis and/or developing environmental sustainability assessment in the field of Smart Grids. For more insight, please see “Environmental analysis of a Nano-Grid: a Life Cycle Assessment” by Rossi F, Parisi M.L., Maranghi S., Basosi R., Sinicropi A. [1]