A 1000-year-old mystery solved: Unlocking the molecular structure for the medieval blue from Chrozophora tinctoria, also known as folium

The molecular structure of the medieval watercolor known as folium has finally been solved in the 21st century. The interdisciplinary approach taken was the key to producing extracts that had been prepared following medieval instructions, and shows the blue/purple chromophore as the major dye in Chrozophora tinctoria fruits (shell). A multi-analytical characterization of its structure was made using HPLC-DAD-MS, GC-MS, NMR (¹H, ¹³C, COSY, HSQC, HMBC, INADEQUATE), and computational studies. The results demonstrate that the blue compound corresponds to 6'-hydroxy-4,4'-dimethoxy-1,1'-dimethyl-5'-{[3,4,5-trihydroxy-6-(hydroxymethyl)tetrahydro-2H-pyran-2-yl]oxy}-[3,3'-bipyridine]-2,2',5,6(1H,1'H)-tetraone, a hermidin derivative, which we named chrozophoridin. Experimental data and computational modeling studies show that this mono-glycosylated dimer is represented by two stable isomers (atropisomers). This is an indispensable piece of knowledge for the characterization of this medieval dye in works of art such as medieval manuscript illuminations and for testing its stability and contributes to the preservation of our cultural heritage.

A molecular insight into the phototoxic reactions observed with vemurafenib, a first-line drug against metastatic melanoma

The electronic properties of vemurafenib (VB) provide a rational basis for understanding its strong UVA-induced phototoxicity. Thus, solvation of hydrophobic VB by hydrogen bonding solvents controls its photophysical, photochemical and photosensitizing properties. Addition of phosphate buffered saline (PBS) to methanol (MeOH) induces a bathochromic shift of the VB absorbance spectrum and a fluorescence emission (λmax = 450 nm, quantum yield (Φ) = 0.011). Phosphorescence (λmax = 461 nm) is observed at 77 K in MeOH. 308 nm laser flash spectroscopy demonstrates that the lifetimes (τ) and quantum yields of the VB triplet state ((3)T(*)(1)) in deaerated MeOH (τMeOH = 0.41 μs, λmax ∼ 380 nm), MeOH-PBS and HSA solutions markedly depend on the microenvironment. A long-lived radical (half-life >200 μs) is also formed. The state (3)T(*)(1) is quenched by O2 and electron donors (Cys and 2'-deoxyguanosine) at a rate constant >1 × 10(9) M(-1) s(-1). UVA-irradiation of VB in air-saturated MeOH or MeOH-PBS solutions produces a UVA-absorbing photoproduct (Φ ∼ 5 × 10(-4)). VB photosensitizes Trp destruction by type I (radical formation) and type II (singlet oxygen ((1)O2) formation) photodynamic reactions (Φ = 0.005). Singlet oxygen production is further demonstrated by the VB-photosensitized His oxidation (ΦMeOH = 0.006).

Ohmic heating assisted synthesis of coumarinyl porphyrin derivatives

Efficient access to coumarinyl porphyrin derivatives bearing pyrano[3,2-c]coumarin motifs is disclosed. Conditions used ohmic heating and water, in Knoevenagel and hetero-Diels–Alder reactions between a beta-vinylporphyrin and α-methylenechromanes.

Saliramophenol, an unprecedented natural t-butylphenol derivative from Salicornia ramosissima J. Woods

A unique skeleton-type compound with four t-butyl groups, named saliramophenol, was identified in Salicornia ramosissima J. Woods aerial parts.

The chemical composition of hexane extract from bark of Juniperus brevifolia

The phytochemical analysis of the bark of Juniperus brevifolia was undertaken for the first time. The GC-MS analysis of the hexane extract from bark of "cedro-do-mato" (J. brevifolia) allowed to identify three rare compounds for the first time in Juniperus genus: 6,7-dehydroferrugin-12-methyl ether, 11-hydroxy-6,7-dehydroferruginol and 6,7-dehydrohinokiol. The results also showed that the chemical composition of the extract were essentially abietane-type diterpenoids with alcohol function (44.9%) and with carbonyl function (8.6%). Fatty acids such palmitic, oleic, stearic and docosanoic acids were the second most abundant family of identified compounds (9.5%) and its value increased (12.7%) after alkaline hydrolysis, mainly due to docosanoic and tetradocosanoic acids. Sterols like sitosterol and stigmast-4-en-3-one, were also present (6.6%), along with esters of sterols (8.4%). Significant quantities of the long-chain aliphatic alcohols (ca 3.7%) were identified in the hexane extract only after alkaline hydrolysis.

Structure elucidation of xanthone derivatives: studies of nuclear magnetic resonance spectroscopy

1H and 13C NMR spectra remain the first tool used by chemists to perform the structure elucidation of their products on a routine basis. It is common to provide NMR data on both proton and carbon spectra based on one-dimensional experiments, but often only proton resonances are assigned. The increasing complexity of natural compounds and their synthetic related derivatives imply the use of some more recent 1D and 2D NMR techniques. The purpose of this review is to describe the main NMR features of the most common and important classes of xanthones and also to discuss the application of several 1D and 2D NMR techniques in the structure elucidation of these compounds. A brief discussion of these NMR techniques from the point of view of structure elucidation of organic compounds will also be considered. The calculated NMR chemical shifts in the structure elucidation of xanthones and the use of NMR to study their mode of action in biological activities will be also described.

Study of the behaviour of amino acids in aqueous solution by time-domain NMR and high-resolution NMR

The study of protein hydration by time-domain NMR is complicated by the great number of interactions involved, resulting from the presence of several amino acids and the possible modifications produced by the various structures. Moreover, a good comprehension of the molecular interactions of the simple amino acids in solution is essential to elucidate the mechanism of the biological functions of proteins. Measurements of transverse relaxation rates of the protons of water (R(2) = 1/T(2)) in aqueous solutions of amino acids such as L-glycine, L-asparagine, L-arginine and L-tryptophan were carried out in order to study the effects of chemical exchange and molecular diffusion on the amplitude of R(2). The values of R(2) measured by the Carr-Purcell-Meiboom-Gill (CPMG) sequence were studied while varying the solution pH and the parameters of the CPMG sequence. The dependence of R(2) on pH and tau (inter-pulse delay between the first and the second pulses of the CPMG sequence) is interpreted in terms of chemical exchange between the protons of water and those of the labile amino acid groups. This interpretation was confirmed by the analysis of the proton spectra acquired using a 300 MHz NMR spectrometer.

Electrochemical and spectroscopic studies of the oxidation mechanism of the herbicide propanil

Electrochemical oxidation of propanil in deuterated solutions was studied by cyclic, differential pulse, and square wave voltammetry using a glassy carbon microelectrode. The oxidation of propanil in deuterated acid solutions occurs at the nitrogen atom of the amide at a potential of +1.15 V vs Ag/AgCl. It was also found that, under the experimental conditions used, protonation at the oxygen atom of propanil occurs, leading to the appearance of another species in solution which oxidizes at +0.60 V. The anodic peak found at +0.79 V vs Ag/AgCl in deuterated basic solutions is related to the presence of an anionic species in which a negative charge is on the nitrogen atom. The electrochemical data were confirmed by the identification of all the species formed in acidic and basic deuterated solutions by means of NMR spectroscopy. The results are supported by electrochemical and spectroscopic studies of acetanilide in deuterated solutions.