Altering the structures of 3D supramolecular assemblies from melamine and cyanuric acid derivatives in water.

Herein, we obtained two supramolecular assemblies with layered structures from melamine, N-methylmelamine, and hexynyl-cyanuric acid in water. By combination of X-ray diffraction, electron microscopy, and molecular dynamics studies, we found that introducing one methyl group in melamine alters the arrangement of the layers in these structures.

Photoluminescence of Two-Dimensional MoS2 Nanosheets Produced by Liquid Exfoliation.

Extraordinary properties of two-dimensional materials make them attractive for applications in different fields. One of the prospective niches is optical applications, where such types of materials demonstrate extremely sensitive performance and can be used for labeling. However, the optical properties of liquid-exfoliated 2D materials need to be analyzed. The purpose of this work is to study the absorption and luminescent properties of MoS2 exfoliated in the presence of sodium cholate, which is the most often used surfactant. Ultrasound bath and mixer-assisted exfoliation in water and dimethyl sulfoxide were used. The best quality of MoS2 nanosheets was achieved using shear-assisted liquid-phase exfoliation as a production method and sodium cholate (SC) as a surfactant. The photoluminescent properties of MoS2 nanosheets varied slightly when changing the surfactant concentrations in the range C(SC) = 0.5-2.5 mg/mL. This work is of high practical importance for further enhancement of MoS2 photoluminescent properties via chemical functionalization.

5-(Perylen-3-ylethynyl)uracil as an antiviral scaffold: Potent suppression of enveloped virus reproduction by 3-methyl derivatives in vitro.

Amphipathic nucleoside and non-nucleoside derivatives of pentacyclic aromatic hydrocarbon perylene are known as potent non-cytotoxic broad-spectrum antivirals. Here we report 3-methyl-5-(perylen-3-ylethynyl)-uracil-1-acetic acid and its amides, a new series of compounds based on a 5-(perylen-3-ylethynyl)-uracil scaffold. The compounds demonstrate pronounced in vitro activity against arthropod-borne viruses, namely tick-borne encephalitis virus (TBEV) and yellow fever virus (YFV), in plaque reduction assays with EC50 values below 1.9 and 1.3 nM, respectively, and Chikungunya virus (CHIKV) in cytopathic effect inhibition test with EC50 values below 3.2 µM. The compounds are active against respiratory viruses as well: severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) in cytopathic effect inhibition test and influenza A virus (IAV) in virus titer reduction experiments are inhibited - EC50 values below 51 nM and 2.2 µM, respectively. The activity stems from the presence of a hydrophobic perylene core, and all of the synthesized compounds exhibit comparable 1O2 generation rates. Nonetheless, activity can vary by orders of magnitude depending on the hydrophilic part of the molecule, suggesting a complex mode of action. A time-of-addition experiment and fluorescent imaging indicate that the compounds inhibit viral fusion in a dose-dependent manner. The localization of the compound in the lipid bilayers and visible damage to the viral envelope suggest the membrane as the primary target. Dramatic reduction of antiviral activity with limited irradiation or under treatment with antioxidants further cements the idea of photoinduced ROS-mediated viral envelope damage being the mode of antiviral action.

Hydrophobic Rose Bengal Derivatives Exhibit Submicromolar-to-Subnanomolar Activity against Enveloped Viruses.

Rose Bengal (RB) is an anionic xanthene dye with multiple useful biological features, including photosensitization properties. RB was studied extensively as a photosensitizer, mostly for antibacterial and antitumor photodynamic therapy (PDT). The application of RB to virus inactivation is rather understudied, and no RB derivatives have been developed as antivirals. In this work, we used a synthetic approach based on a successful design of photosensitizing antivirals to produce RB derivatives for virus photoinactivation. A series of n-alkyl-substituted RB derivatives was synthesized and evaluated as antiviral photosensitizers. The compounds exhibited similar 1O2 generation rate and efficiency, but drastically different activities against SARS-CoV-2, CHIKV, and HIV; with comparable cytotoxicity for different cell lines. Submicromolar-to-subnanomolar activities and high selectivity indices were detected for compounds with C4-6 alkyl (SARS-CoV-2) and C6-8 alkyl (CHIKV) chains. Spectrophotometric assessment demonstrates low aqueous solubility for C8-10 congeners and a significant aggregation tendency for the C12 derivative, possibly influencing its antiviral efficacy. Initial evaluation of the synthesized compounds makes them promising for further study as viral inactivators for vaccine preparations.

Impact of ozone treatment on dissolved organic matter in land-based recirculating aquaculture systems studied by Fourier transform ion cyclotron resonance mass spectrometry.

In land-based recirculating aquaculture systems (RAS), the accumulation of dissolved organic matter (DOM) can have detrimental effects on water quality impacting the system performance, microbial community, and consequently fish health and welfare. Ozone is used in the RAS water treatment process to improve water quality and remove DOM. However, little is known about the molecular composition of DOM in RAS and its transformation when exposed to ozone. In this study, we performed a detailed molecular characterization of DOM in RAS and explored its transformation induced by ozonation of RAS waters. Ultra-high resolution (UHR) Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) was used to characterize the DOM matrix of RAS waters (pump-sump and tanks) and to evaluate its transformation by ozonation. The analysis of DOM extracted from makeup water and feed samples allowed for the determination of DOM sources in RAS prior to ozonation. The CHO and unsaturated group of compounds were the most abundant class found in water samples. On the contrary, the DOM from feed samples was unique and consisted mainly of CHO, CHON and unsaturated group of compounds. After the ozonation of RAS waters, humic-like and unsaturated compounds [positive oxygen subtracted double bond equivalent per carbon (DBE-O)/C)] were decomposed, particularly the CHO-DOM that contained fewer -CH2- features. Fulvic-like compounds and several hundred saturated compounds [negative (DBE-O)/C)] were formed post ozonation, particularly the CHON and CHONS group of compounds that were associated with fish diets, makeup waters and transformation products from the ozonation of the RAS waters. This study showed that the high accuracy of the ultra-high resolution FTICR MS can be applied to characterize and monitor the changes of DOM at a molecular level in RAS waters. To our knowledge, this is the first study where FTICR MS was incorporated for the characterization of DOM and its sources in RAS.

Ultrafast Energy Transfer Determines the Formation of Fluorescence in DOM and Humic Substances.

Humification is a ubiquitous natural process of biomass degradation that creates multicomponent systems of nonliving organic matter, including dissolved organic matter (DOM) and humic substances (HS) in water environments, soils, and organic rocks. Despite significant differences in molecular composition, the optical properties of DOM and HS are remarkably similar, and the reason for this remains largely unknown. Here, we employed fluorescence spectroscopy with (sub)picosecond resolution to elucidate the role of electronic interactions within DOM and HS. We revealed an ultrafast decay component with a characteristic decay lifetime of 0.5-1.5 ps and spectral diffusion originating from excitation energy transfer (EET) in the system. The rate of EET was positively correlated to the fraction of aromatic species and tightness of aromatic species packing. Diminishing the number of EET donor-acceptor pairs by reduction with NaBH4 (decrease of the acceptor number), decrease of pH (decrease of the electron-donating ability), or decrease of the average particle size by filtration (less donor-acceptor pairs within a particle) resulted in a lower impact of the ultrafast component on fluorescence decay. Our results uncover the role of electronic coupling among fluorophores in the formation of DOM and HS optical properties and provide a framework for studying photophysical processes in heterogeneous systems of natural fluorophores.

The Oxidation-Induced Autofluorescence Hypothesis: Red Edge Excitation and Implications for Metabolic Imaging.

Endogenous autofluorescence of biological tissues is an important source of information for biomedical diagnostics. Despite the molecular complexity of biological tissues, the list of commonly known fluorophores is strictly limited. Still, the question of molecular sources of the red and near-infrared excited autofluorescence remains open. In this work we demonstrated that the oxidation products of organic components (lipids, proteins, amino acids, etc.) can serve as the molecular source of such red and near-infrared excited autofluorescence. Using model solutions and cell systems (human keratinocytes) under oxidative stress induced by UV irradiation we demonstrated that oxidation products can contribute significantly to the autofluorescence signal of biological systems in the entire visible range of the spectrum, even at the emission and excitation wavelengths higher than 650 nm. The obtained results suggest the principal possibility to explain the red fluorescence excitation in a large class of biosystems-aggregates of proteins and peptides, cells and tissues-by the impact of oxidation products, since oxidation products are inevitably presented in the tissue. The observed fluorescence signal with broad excitation originated from oxidation products may also lead to the alteration of metabolic imaging results and has to be taken into account.

Photoreactivity of humic-like polyphenol material under irradiation with different wavelengths explored by FTICR MS and deuteromethylation.

The goal of this study was to establish reactivity of lignin-derived synthetic polyphenolic material under irradiation by ultraviolet (254 nm) and visible (460 and 525 nm) light in order to deeper examine relationships between the optical properties of this complex mixture and its individual constituents. In all photoirradiation experiments, blue shift of the fluorescence spectrum was observed. We aimed at understanding whether these changes could be explained on the basis of the chromophore interactions hypothesis, which implies destruction of electron-acceptor pairs via free radical transformations to be responsible for the alteration of optical properties. For this, changes in molecular composition were explored by Fourier transform ion cyclotron resonance mass spectrometry. Irradiation with UV resulted in a pronounced oxidation of polyphenols, which was manifested in the van Krevelen diagram by the formation of components with higher O/C ratio. At the same time, irradiation by visible light had led to the appearance of more condensed molecules depleted of oxygen. Consideration of changes in relative contribution of 500 most abundant components in polyphenol materials revealed higher transformation yields under UV light as compared to the visible light. Further studies using deuteromethylation followed by Fourier transform ion cyclotron resonance mass spectrometry enabled to enumerate the number of carboxylic groups in individual components of the parent polyphenol material. It was shown that at all wavelengths irradiation mainly impacted carboxylic-rich unsaturated and aromatic compounds, which can be considered as strong electron-acceptors. We suggest that their transformation is responsible for the blue shift of fluorescence spectrum, thus emphasizing the role of chromophore interaction mechanism of the optical properties formation.

Optical Properties of Soil Dissolved Organic Matter Are Related to Acidic Functions of Its Components as Revealed by Fractionation, Selective Deuteromethylation, and Ultrahigh Resolution Mass Spectrometry.

The goal of this study was to establish a relationship between the optical properties of soil dissolved organic matter (DOM) and acidic functions carried out by its individual constituents. We obtained 12 fractions of DOM samples using sequential solid phase extraction on nonionic sorbent at steadily lowered pH values: 7, 5, 3, 2, which correspond to low bounds of pKa values of phenols, aliphatic, and aromatic carboxylic acids, and ketoacids. The structural studies were conducted with the use of NMR and selective deuteromethylation of isolated fractions coupled to ultrahigh resolution mass spectrometry. First, a gradual shift of molecular compositions was observed from reduced components to aromatic oxidized compounds isolated at pH 7 and 2, respectively. Changes in molecular compositions were accompanied by a red shift of fluorescence spectra. Further application of deuteromethylation enabled us to distinguish DOM constituents with different amounts of carboxylic groups. Moreover, identification of structural isomers in a single DOM sample was achieved. Statistical analysis revealed that red shift of fluorescence is facilitated by the increase of a contribution of aromatic poly(carboxylic acid)s with high conjugation lengths. Additionally, analysis of the labeled fractionated permafrost thaw DOM directly showed carboxyl-rich alicyclic molecules, while the same components from lower-latitude DOM were assigned to lignin-like species.

Dissection of the deep-blue autofluorescence changes accompanying amyloid fibrillation.

Pathogenesis of numerous diseases is associated with the formation of amyloid fibrils. Extrinsic fluorescent dyes, including Thioflavin T (ThT), are used to follow the fibrillation kinetics. It has recently been reported that the so-called deep-blue autofluorescence (dbAF) is changing during the aggregation process. However, the origin of dbAF and the reasons for its change remain debatable. Here, the kinetics of fibril formation in model proteins were comprehensively analyzed using fluorescence lifetime and intensity of ThT, intrinsic fluorescence of proteinaceous fluorophores, and dbAF. For all systems, intensity enhancement of the dbAF band with similar spectral parameters (∼350 nm excitation; ∼450 nm emission) was observed. Although the time course of ThT lifetime (indicative of protofibrils formation) coincided with that of tyrosine residues in insulin, and the kinetic changes in the ThT fluorescence intensity (reflecting formation of mature fibrils) coincided with changes in ThT absorption spectrum, the dbAF band started to increase from the beginning of the incubation process without a lag-phase. Our mass-spectrometry data and model experiments suggested that dbAF could be at least partially related to oxidation of amino acids. This study scrutinizes the dbAF features in the context of the existing hypotheses about the origin of this spectral band.