Toward a Theoretical Quantitative Estimation of the λmax of Anthraquinones-Based Dyes

Density Functional Theory Study of Cu6 Nanoclusters as a Phenylalanine Detector

Research on amino acids is an attractive area because of their application in metabolism, cancer treatment, growth, and repair of body tissue, and RNA and DNA syntheses. Twenty amino acids are primarily responsible for protein synthesis. In our study, we used a Cu6 nanocluster as an amino acid detector. For the investigation, we adsorbed amino acids on the Cu6 nanocluster and studied their UV-visible spectra. It is observed that all of the Cu6-amino acid complexes have peaks at near 380 nm wavelength except the Cu-phenylalanine complex, where two UV-visible peaks are found at wavelengths 351 nm (excitation energy 3.49 eV) and 403 nm (excitation energy 3.02 eV), respectively, which originated from the HOMO - 2 to LUMO (28%) and HOMO - 1 to LUMO (38%) transitions. Due to this unique transition, the Cu6 nanocluster can be used for the detection of the phenylalanine amino acid out of the 20 amino acids.

Near-Infrared Emitting Poly(amidoamine) Dendrimers with an Anthraquinone Core toward Versatile Non-Invasive Biological Imaging

Today, there is a very strong demand for versatile near-infrared (NIR) imaging agents suitable for non-invasive optical imaging in living organisms (in vivo imaging). Here, we created a family of NIR-emitting macromolecules that take advantage of the unique structure of dendrimers. In contrast to existing fluorescent dendrimers bearing fluorophores at their periphery or in their cavities, a NIR fluorescent structure is incorporated into the core of the dendrimer. Using the poly(amidoamine) dendrimer structure, we want to promote the biocompatibility of the NIR-emissive system and to have functional groups available at the periphery to obtain specific biological functionalities such as the ability to deliver drugs or for targeting a biological location. We report here the divergent synthesis and characterization by NMR and mass spectrometries of poly(amidoamine) dendrimers derived from the fluorescent NIR-emitting anthraquinone core (AQ-PAMAF). AQ-PAMAFs ranging from the generation -0.5 up to 3 were synthesized with a good level of control resulting in homogeneous and complete dendrimers. Absorption, excitation, and emission spectra, as well as quantum yields, of AQ-PAMAFs have been determined in aqueous solutions and compared with the corresponding properties of the AQ-core. It has been demonstrated that the absorption bands of AQ-PAMAFs range from UV to 750 nm while emission is observed in the range of 650-950 nm. Fluorescence macroscopy experiments confirmed that the NIR signal of AQ-PAMAFs can be detected with a satisfactory signal-to-noise ratio in aqueous solution, in blood, and through 1 mm thick tissue-mimicking phantom. The results show that our approach is highly promising for the design of an unprecedented generation of versatile NIR-emitting agents.

Photoinduced phenomena in water solution of melamine explaining the photostability of the compound

Two tautomers of melamine (triamino and imino-diamino) were studied at the BLYP/aug-cc-pVDZ theoretical level. It was found that the two tautomers are bridged with the ¹πσ^* excited-state reaction path. The high photostability of melamine in water solution was explained with the mechanism of ring deformation which occurs along the ¹ππ^* excited-state reaction path. The two mechanisms are investigated at the TD BLYP level of theory using the linear interpolation in internal coordinates approach.

Photoprotection assessment of olive (Olea europaea L.) leaves extract standardized to oleuropein: In vitro and in silico approach for improved sunscreens

Olive leaves contain higher amount of polyphenols than olive oil and represent a waste product from olive harvest and pruning of olive trees. The most abundant compound in olive leaves is oleuropein. Benefits of the topical application of olive leaves extract were previously reported, but little information is available on its photoprotective potential and the result of the association of this extract with organic UV filters in topical sunscreen formulations. The olive leaves extract photoprotective potential is less explored for both oral and topical photoprotection in comparison with other plants extracts and polyphenols, such as Polypodium leucotomos extract and resveratrol. There are increasing efforts towards developing more efficient sunscreens and a photoprotection assessement along with a better understanding of the photochemistry of naturally occurring sunscreens could aid the design of new and improved commercial sunscreen formulations. This study was designed to investigate the photoprotective potential of olive leaves extract standardized for oleuropein performing a set of in vitro and in silico tools as an innovative approach, highlighting yeast assays, in vitro Sun Protection Factor (SPF) and molecular modelling studies of UV absorption. This study supports the use of olive leaves extract for photoprotection, as an effective photoprotective, anti-mutagenic and antioxidant active, also showing a synergistic effect in association with UV filters with an improvement on in vitro SPF of sunscreen formulations.

Near-IR luminescent lanthanide complexes with 1,8-diaminoanthraquinone-based chromophoric ligands

1,8-Anthraquinone derivatives can act as low energy, visible light sensitizers for near-IR emitting lanthanides.

Structural and optical properties of Purpurin for dye-sensitized solar cells

In this work, we reported a combined experimental and theoretical study on molecular structure, vibrational spectra and Homo-Lumo analysis of Purpurin and TiO2/Purpurin. The geometries, electronic structures, molecular orbital analysis of natural dye sensitizer Purpurin were studied based on density functional theory (DFT) using the hybrid functional B3LYP. Fourier transform infrared (FT-IR) and FT-Raman spectra have been recorded and extensive spectroscopic investigations have been carried out on Purpurin. The optimized geometries, wave number and intensity of the vibrational bands of Purpurin have been calculated using density functional level of theory (DFT/B3LYP) employing 6-311G (d,p) basis set. Based on the comparison between calculated and experimental results, assignments of the fundamental vibrational modes are examined. Features of the electronic absorption spectrum in the visible and near-UV regions were assigned based on TD-DFT calculations. The calculated results suggest that the three excited states with the lowest excited energies in 1,2,4, trihydroxy 9-10 anthraquinone was due to photo-induced electron transfer processes. Frontier molecular orbitals (FMO), LUMO, HOMO, and energy gap, of these dyes have been analyzed to show their effect on the process of electron injection and dye regeneration. Interaction between HOMO and LUMO of Purpurin are investigated to understand the recombination process and charge transfer process involving these dyes. We also performed analysis of I-V characteristics to investigate the role of charge transfer and the stability of the dye molecule.

Dye chemistry with time-dependent density functional theory

In this perspective, we present an overview of the determination of excited-state properties of "real-life" dyes, and notably of their optical absorption and emission spectra, performed during the last decade with time-dependent density functional theory (TD-DFT). We discuss the results obtained with both vertical and adiabatic (vibronic) approximations, choosing relevant examples for several series of dyes. These examples include reproducing absorption wavelengths of numerous families of coloured molecules, understanding the specific band shape of amino-anthraquinones, optimising the properties of dyes used in solar cells, mimicking the fluorescence wavelengths of fluorescent brighteners and BODIPY dyes, studying optically active biomolecules and photo-induced proton transfer, as well as improving the properties of photochromes.

The role of tryptophans in the UV-B absorption of a UVR8 photoreceptor – a computational study

Absorption spectra of different amino acid models of UVR8.

Hydrogen peroxide contributes to the ultraviolet-B (280-315 nm) induced oxidative stress of plant leaves through multiple pathways

Solar UV-B (280-315 nm) radiation is a developmental signal in plants but may also cause oxidative stress when combined with other environmental factors. Using computer modeling and in solution experiments we show that UV-B is capable of photosensitizing hydroxyl radical production from hydrogen peroxide. We present evidence that the oxidative effect of UV-B in leaves is at least twofold: (i) it increases cellular hydrogen peroxide concentrations, to a larger extent in pyridoxine antioxidant mutant pdx1.3-1 Arabidopsis and; (ii) is capable of a partial photo-conversion of both 'natural' and 'extra' hydrogen peroxide to hydroxyl radicals. As stress conditions other than UV can increase cellular hydrogen peroxide levels, synergistic deleterious effects of various stresses may be expected already under ambient solar UV-B.

UV/Visible spectra of a series of natural and synthesised anthraquinones: experimental and quantum chemical approaches

Root decoctions of anthraquinone-containing plants are often taken as postpartum tonic and aphrodisiac. Anthraquinones are known for their diverse biological activities, especially antioxidant and anticancer. A series of 35 anthraquinones was generated by isolation from Rubiaceae plants and synthesis. Their UV/vis spectrum depends on the nature and relative positions of auxochromic substituents on the basic skeleton. To predict the maximum absorption bands for the current series of anthraquinones, excited sate calculations were performed using TD-DFT, CIS, ZINDO methods. The results showed that the use of PBE0 or its combination with B3LYP and B3P86 hybrid functionals are the most suitable to reproduce accurately the experimental λ_MAX. The structure–property relationships (SPRs) were established based on structural and electronic properties of the anthraquinones and showed (i) the importance of the number and position of OH groups and (ii) the positive contribution of the electrophilicity and hardness as electronic descriptors on position and amplitude of the maximum absorption bands.

Time-dependent density functional theory study of UV/vis spectra of natural styrylpyrones

Natural styrylpyrones isolated from fungi are known for various biological activities including antioxidant activity by scavenging free radicals. UV/vis spectra play an important role in elucidating chemical structures of these compounds via identification of chromophore units. With the aim of predicting the UV/vis spectra of a series of natural styrylpyrones, we tested TD-DFT, CIS and ZINDO methods in gas and in PCM solvent. The results showed that the individual or combined B3P86 and B3LYP hybrid functionals are suitable to predict the maximum wavelength absorption bands (λmax) for styrylpyrones. The structure property relationship (SPR) study emphasized the role of (i) structural parameters (e.g., hydrogen bond and the length of conjugated double bonds) and (ii) electronic descriptors (e.g., ionization potential, electronic affinity, hardness and electrophilicity) in bathochromic and hypsochromic shifts of maximum wavelength absorption bands (λmax) of styrylpyrone derivatives.

Acene-modified triphenylamine dyes for dye-sensitized solar cells: a computational study

A series of metal-free acene-modified triphenylamine dyes (benzene to pentacene, denoted as TPA-AC1 to TPA-AC5) are investigated as organic sensitizers for application in dye-sensitized solar cells (DSSCs). A combination of density functional theory (DFT), density functional tight-binding (DFTB), and time-dependent DFT (TDDFT) approaches is employed. The effects of acene units on the spectra and electrochemical properties of the acene-modified TPA organic dyes are demonstrated. The dye/(TiO(2))(46) anatase nanoparticle systems are also simulated to show the electronic structures at the interface. The results show that from TPA-AC1 to TPA-AC5 with increasing sizes of the acenes, the absorption and fluorescence spectra are systematically broadened and red-shifted, but the oscillator strength and electron injection properties are reduced. The molecular orbital contributions show increasing localization on the bridging acene units from TPA-AC1 to TPA-AC5. From the theoretical examination of some key parameters including free enthalpy related to the electron injection, light-harvesting efficiency, and the shift of semiconductor conduction band, TPA-AC3 with an anthracene moiety demonstrates a balance of the above crucial factors. TPA-AC3 is expected to be a promising dye with desirable energetic and spectroscopic parameters in the DSSC field, which is consistent with recent experimental work. This study is expected to deepen our understanding of TPA-based organic dyes and assist the molecular design of new metal-free dyes for the further optimization of DSSCs.

Prediction of the maximum absorption wavelength of azobenzene dyes by QSPR tools

The maximum absorption wavelength (λ(max)) of a large data set of 191 azobenzene dyes was predicted by quantitative structure-property relationship (QSPR) tools. The λ(max) was correlated with the 4 molecular descriptors calculated from the structure of the dyes alone. The multiple linear regression method (MLR) and the non-linear radial basis function neural network (RBFNN) method were applied to develop the models. The statistical parameters provided by the MLR model were R(2)=0.893, R(adj)(2)=0.893, q(LOO)(2)=0.884, F=1214.871, RMS=11.6430 for the training set; and R(2)=0.849, R(adj)(2)=0.845, q(ext)(2)=0.846, F=207.812, RMS=14.0919 for the external test set. The RBFNN model gave even improved statistical results: R(2)=0.920, R(adj)(2)=0.919, q(LOO)(2)=0.898, F=1664.074, RMS=9.9215 for the training set, and R(2)=0.895, R(adj)(2)=0.892, q(ext)(2)=0.895, F=314.256, RMS=11.6427 for the external test set. This theoretical method provides a simple, precise and an alternative method to obtain λ(max) of azobenzene dyes.

Computational evidence for the role of Arabidopsis thaliana UVR8 as UV-B photoreceptor and identification of its chromophore amino acids

A homology model of the Arabidopsis thaliana UV resistance locus 8 (UVR8) protein is presented herein, showing a seven-bladed β-propeller conformation similar to the globular structure of RCC1. The UVR8 amino acid sequence contains a very high amount of conserved tryptophans, and the homology model shows that seven of these tryptophans cluster at the 'top surface' of the UVR8 protein where they are intermixed with positive residues (mainly arginines) and a couple of tyrosines. Quantum chemical calculations of excitation spectra of both a large cluster model involving all twelve above-mentioned residues and smaller fragments thereof reveal that absorption maxima appearing in the 280-300 nm range for the full cluster result from interactions between the central tryptophans and surrounding arginines. This observation coincides with the published experimentally measured action spectrum for the UVR8-dependent UV-B stimulation of HY5 transcription in mature A. thaliana leaf tissue. In total these findings suggest that UVR8 has in fact in itself the ability to be an ultraviolet-B photoreceptor in plants.

Spectral properties of spirooxazine photochromes: TD-DFT insights

A large series of photochromes of the spirooxazine family has been investigated using density functional theory and time-dependent density functional theory, aiming at designing molecules with an open-ring merocyanine form absorbing at the longest possible wavelength. A complete methodological assessment (basis set, solvent effects, functionals) has been performed, allowing the design of efficient multilinear regressions for two solvents (cyclohexane and toluene). These regressions allow the estimate of the absorption wavelength of open spirooxazine with an error limited to about 5 nm. The thermodynamic and spectral properties of several isomers have been considered, and it turned out that only TTC and CTC structures may appear experimentally. These structures present similar stabilities and absorption wavelengths. The impact of the auxochromic groups on the UV/vis spectra was assessed and novel promising substitution patterns have been unravelled. It is shown that using a strong push moiety on the same side of the molecule as the pull group may be an effective procedure for tuning the visible spectra. In particular, several spirooxazines with absorption wavelength predicted to be close to or larger than 700 nm are proposed.