The interacting effect of climate change and herbivory can trigger large-scale transformations of European temperate forests.

In many regions of Europe, large wild herbivores alter forest community composition through their foraging preferences, hinder the forest's natural adaptive responses to climate change, and reduce ecosystem resilience. We investigated a widespread European forest type, a mixed forest dominated by Picea abies, which has recently experienced an unprecedented level of disturbance across the continent. Using the forest landscape model iLand, we investigated the combined effect of climate change and herbivory on forest structure, composition, and carbon and identified conditions leading to ecosystem transitions on a 300-year timescale. Eight climate change scenarios, driven by Representative Concentration Pathways 4.5 and 8.5, combined with three levels of regeneration browsing, were tested. We found that the persistence of the current level of browsing pressure impedes adaptive changes in community composition and sustains the presence of the vulnerable yet less palatable P. abies. These development trajectories were tortuous, characterized by a high disturbance intensity. On the contrary, reduced herbivory initiated a transformation towards the naturally dominant broadleaved species that was associated with an increased forest carbon and a considerably reduced disturbance. The conditions of RCP4.5 combined with high and moderate browsing levels preserved the forest within its reference range of variability, defining the actual boundaries of resilience. The remaining combinations of browsing and climate change led to ecosystem transitions. Under RCP4.5 with browsing effects excluded, the new equilibrium conditions were achieved within 120 years, whereas the stabilization was delayed by 50-100 years under RCP8.5 with higher browsing intensities. We conclude that forests dominated by P. abies are prone to transitions driven by climate change. However, reducing herbivory can set the forest on a stable and predictable trajectory, whereas sustaining the current browsing levels can lead to heightened disturbance activity, extended transition times, and high variability in the target conditions.

Convalescent anti-SARS-CoV-2 plasma for the treatment of patients with COVID-19: a retrospective study RESCOVID-19.

PURPOSE: Convalescent plasma (CP) collected from people who recovered from COVID-19 became a rapidly available treatment modality in numerous countries, including the Czech Republic. The aims of our study were to evaluate the effectiveness and safety of CP in the treatment of COVID-19. METHODS: This retrospective observational study involved six Czech hospitals. This study enrolled patients with and without CP treatment who were hospitalized between April 2020 and April 2021. Propensity score matching and logistic regression analysis were performed to evaluate the influence of CP administration and its timing on the in-hospital survival of COVID-19 patients. RESULTS: A total of 1,498 patients were enrolled in the study; 406 (27%) were administered CP, and 1,092 (73%) were not treated with CP. The propensity score-matched control group consisted of 1,218 subjects. The survival of patients treated with CP was 79%, while that of patients in the matched control group was 62% (P<0.001). Moreover, the chance of survival was significantly greater when CP was administered within three days after the onset of COVID-19 symptoms than when CP was administered after four or more days (87% vs. 76%, P <0.001). In addition, adverse effects related to CP administration were recorded in only 2% of patients and were considered mild in all patients. CONCLUSIONS: Our study demonstrated that the administration of CP was safe and possibly associated with positive effects that were more pronounced if CP was administered within the first three days after the onset of COVID-19 symptoms.

Insights into localization, energy ordering, and substituent effect in excited states of azobenzenes from coupled cluster calculations of nuclear spin-induced circular dichroism.

Nuclear spin-induced circular dichroism (NSCD) is a molecular effect of differential absorption of left- and right-circularly polarized light due to nuclear spins in the molecule. In this work, new tools for its calculation are presented. Specifically, analytic expressions for the computation of the K term of NSCD have been derived and implemented for the second-order coupled cluster singles and doubles (CC2) model. NSCD results obtained thereby for three derivatives of azobenzenes have been compared with results from time-dependent density functional theory (TD-DFT). The complementary information that could be obtained from NSCD measurements compared to NMR for these three species is discussed.

Characteristic nuclear spin-induced optical rotation in oxygen-containing organic molecules.

Nuclear spin-induced optical rotation (NSOR) is a nuclear magneto-optic effect that manifests itself as a rotation of the plane of polarization of linearly polarized light. The effect is induced by ordered nuclear magnetic moments within a molecule. NSOR is sensitive to specific, localized interactions. Hence, the connection between the local chemical environment and the corresponding NSOR signal is crucial to understand. Despite the fact that contributions to better understand the connection have been made, the general systematics still remain unknown. In this paper, NSOR in oxygen compounds is investigated systematically to better understand the impact of oxygen atoms on the NSOR signal. NSOR signals are computed using density-functional theory methods for five different classes of oxygen compounds. The ability of NSOR to distinguish different molecules and individual nuclei in the molecules is studied and the information provided by NSOR is compared to conventional NMR spectroscopy. The results reveal that NSOR is capable of chemical distinction between nuclei and molecules, and by using NMR and NSOR together it is possible to distinguish nuclei near the oxygen atom.

Unexpected NMR shieldings of sp- and sp2-hybridized carbon atoms in graphyne systems.

Graphynes (GYs) are two-dimensional alloptropic forms of carbon consisting of periodically arranged sp- and sp2-hybridized carbon atoms in a planar structure. Graphynes can be formally created from graphene by inserting sp-hybridized carbon links into selected points of the graphene lattice. Depending on where the links are introduced, several forms of graphynes have been proposed with properties that make them potential candidates for new generation electronics or for applications in chemical processes. Since the applications of each form of GY depend on its structure, it is of interest to experimentally distinguish different forms of graphynes. In this paper we propose nuclear magnetic resonance (NMR) as a potential method of choice for such distinction. We computationally investigate on the DFT level the 13C-NMR chemical shifts for α-, ß-, γ-, rhombic, and 6,6,12-graphynes, and α- and γ-graphdiynes. We perform the calculations both in periodic systems and with approximate finite models. The results show that NMR chemical shifts in graphynes are dependent on the structure and reflect the local bonding around the carbon nucleus. Interestingly, NMR shifts of several graphynes show anomalous values, differing significantly from shifts found in typical sp2-hybridized systems. We analyze these results in terms of local structural parameters and qualitatively investigate the possible origins of these anomalous NMR shifts. The results show that NMR is a viable method for determining the structure of graphynes and their finite precursor molecules.

Landslides associated with recent road constructions in the Río Lucma catchment, eastern Cordillera Blanca, Peru.

Extensive road construction works recently took place in the remote eastern part of the Peruvian Cordillera Blanca, aiming at a better connection of isolated mountain communities with regional administrative centres. Here we document and characterize landslides associated with these road construction efforts in the Río Lucma catchment, Peru. We show that a total area of 321,332 m2 has been affected by landslides along the 47.1 km of roads constructed between 2015 and 2018. While landslides downslope the roads (48.2%) and complex landslides crossing the roads (46.4%) were the most frequent landslide types in relation to the position of the road; slide-type movement (60.7%) prevails over the flow-type movement (39.3%). Timewise, we found that 75.0% of landslides were observed simultaneously with road construction work, while the remaining 25.0% occurred up to seven months after the roads had been constructed. We plotted the lagged occurrence of these subsequent landslides against precipitation data, showing that 85.7% of them were observed during the wet season (November to April). We conclude that the majority of mapped landslides were directly associated with road constructions and that the road constructions also may set preconditions for landslides, which mainly occurred during the subsequent wet season.

Does polysaccharide glycogen behave as a promoter of amyloid fibril formation at physiologically relevant concentrations?

We investigated the influence of glycogen (GG), phytoglycogen (PG), mannan (MAN) and cinnamoyl-modified GG (GG-CIN) on amyloid fibril formation. We used hen egg-white lysozyme (HEWL) as a model system and amyloid beta peptide (1-42) (Aß1-42) as an Alzheimer's disease-relevant system. For brief detection of fibrils was used thioflavin T (ThT) fluorescence assay and the results were confirmed by transmission electron microscopy (TEM). We also deal with the interaction of polysaccharides and HEWL with isothermal titration calorimetry (ITC) and dynamic light scattering (DLS). We found that all polysaccharides accelerated the formation of amyloid fibrils from both HEWL and Aß1-42. At high but physiologically relevant concentrations of GG, amyloid fibril formation was extremely accelerated for HEWL. Therefore, on the basis of the herein presented in vitro data, we hypothesize, that dietary d-glucose intake may influence amyloid fibril formation not only by influencing regulatory pathways, but also by direct glycogen-amyloid precursor protein molecular interaction, as glycogen levels in tissues are highly dependent on d-glucose intake.

Chemically modified glycogens: how they influence formation of amyloid fibrils?

The formation of amyloid fibrils from certain proteins stays behind a number of pathologies, so-called amyloidoses. Glycosaminoglycans are polysaccharides and are known natural constituents of amyloids in vivo. However, little is known about the effect of other naturally abundant polysaccharides, and even less is known about the effect of chemically modified polysaccharides on the formation of amyloid fibrils. In the case of low-molecular weight compounds, aromatic substances are known to often influence amyloid formation significantly. We investigated the influence of glycogen (GG) and several modifications of GG with cinnamoyl groups, benzoyl groups and phenylacetyl groups. As model systems, hen egg-white lysozyme (HEWL) and amyloid beta peptide (1-42) (Aß1-42), which is an Alzheimer disease-relevant system, were used. The fluorescence of thioflavin-T (ThT) was used for the rapid detection of fibrils, and the fluorescence results were confirmed by transmission electron microscopy (TEM). Other techniques, such as isothermal titration calorimetry (ITC) and dynamic light scattering (DLS), were employed to determine the interactions between HEWL and the modifications. We achieved similar results with both model systems (HEWL and Aß1-42). We showed that π-π interactions played an important role in the process of amyloid fibril formation because fundamental changes were observed in this process even with a very small number of groups containing an aromatic ring. It was found that almost all GG modifications accelerated the formation of amyloid fibrils in both model systems, HEWL and Aß1-42, except for GG-Ph1 (1.6 mol% phenylacetyl groups), which had a retarding effect compared to all other modifications.

Reactive Oxygen Species (ROS)-Responsive Polymersomes with Site-Specific Chemotherapeutic Delivery into Tumors via Spacer Design Chemistry.

The lack of cellular and tissue specificities in conventional chemotherapies along with the generation of a complex tumor microenvironment (TME) limits the dosage of active agents that reaches tumor sites, thereby resulting in ineffective responses and side effects. Therefore, the development of selective TME-responsive nanomedicines is of due relevance toward successful chemotherapies, albeit challenging. In this framework, we have synthesized novel, ready-to-use ROS-responsive amphiphilic block copolymers (BCs) with two different spacer chemistry designs to connect a hydrophobic boronic ester-based ROS sensor to the polymer backbone. Hydrodynamic flow focusing nanoprecipitation microfluidics (MF) was used in the preparation of well-defined ROS-responsive PSs; these were further characterized by a combination of techniques [1H NMR, dynamic light scattering (DLS), static light scattering (SLS), transmission electron microscopy (TEM), and cryogenic TEM (cryo-TEM)]. The reaction with hydrogen peroxide releases an amphiphilic phenol or a hydrophilic carboxylic acid, which affects polymersome (PS) stability and cargo release. Therefore, the importance of the spacer chemistry in BC deprotection and PS stability and cargo release is herein highlighted. We have also evaluated the impact of spacer chemistry on the PS-specific release of the chemotherapeutic drug doxorubicin (DOX) into tumors in vitro and in vivo. We demonstrate that by spacer chemistry design one can enhance the efficacy of DOX treatments (decrease in tumor growth and prolonged animal survival) in mice bearing EL4 T cell lymphoma. Side effects (weight loss and cardiotoxicity) were also reduced compared to free DOX administration, highlighting the potential of the well-defined ROS-responsive PSs as TME-selective nanomedicines. The PSs could also find applications in other environments with high ROS levels, such as chronic inflammations, aging, diabetes, cardiovascular diseases, and obesity.

Nuclear spin-induced optical rotation of functional groups in hydrocarbons.

Nuclear spin-induced optical rotation (NSOR) is a nuclear magneto-optic effect manifesting as a rotation of the plane of polarization of linearly polarized light induced by nuclear magnetic moments within a molecule. NSOR probes molecular optical properties through localized nuclear interactions and has potential to be developed into a new spectroscopic tool. However, so far the connection between the molecular structure and NSOR response has not been systematically investigated. To obtain insight into this relation and to assess its viability as a foundation for a new spectroscopic method, NSOR of 1H and 13C nuclei in a set of hydrocarbon molecules with various structural motifs is theoretically investigated using density functional theory calculations. The results reveal that NSOR intensities are correlated with several structural features of the molecules, such as the position of the nucleus in the carbon chain, isomerism and presence of nearby unsaturated groups. Specific patterns connecting NSOR to the local chemical environment of the nucleus can be observed. It is also shown that this effect can be to a good approximation modelled as a sum of individual contributions from nearby chemical groups, allowing for a rapid estimation of its values. The demonstrated systematic dependence of the NSOR signal on the molecular structure is a desirable feature for theoretical and experimental development of new spectroscopic methods based on this phenomenon.

Rifampicin Nanoformulation Enhances Treatment of Tuberculosis in Zebrafish.

Mycobacterium tuberculosis, the etiologic agent of tuberculosis, is an intracellular pathogen of alveolar macrophages. These cells avidly take up nanoparticles, even without the use of specific targeting ligands, making the use of nanotherapeutics ideal for the treatment of such infections. Methoxy poly(ethylene oxide)- block-poly(ε-caprolactone) nanoparticles of several different polymer blocks' molecular weights and sizes (20-110 nm) were developed and critically compared as carriers for rifampicin, a cornerstone in tuberculosis therapy. The polymeric nanoparticles' uptake, consequent organelle targeting and intracellular degradation were shown to be highly dependent on the nanoparticles' physicochemical properties (the cell uptake half-lives 2.4-21 min, the degradation half-lives 51.6 min-ca. 20 h after the internalization). We show that the nanoparticles are efficiently taken up by macrophages and are able to effectively neutralize the persisting bacilli. Finally, we demonstrate, using a zebrafish model of tuberculosis, that the nanoparticles are well tolerated, have a curative effect, and are significantly more efficient compared to a free form of rifampicin. Hence, these findings demonstrate that this system shows great promise, both in vitro and in vivo, for the treatment of tuberculosis.

Spatial localization in nuclear spin-induced circular dichroism - a quadratic response function analysis.

Nuclear magneto-optic (NMO) effects are recently described phenomena originating from the interaction of light with local magnetic fields produced by nuclear spins. The phenomena border nuclear magnetic resonance and optical spectroscopy and are expected to provide rather unique spectroscopic features, borrowing from both localized response of the atomic nuclei as well as more global excitation properties of the whole molecule or its chromophore moieties. A number of quantum-chemical computational studies have been carried out, offering a reasonable agreement with nuclear magneto-optics experiments performed so far. However, the detailed structure-spectra relation is still poorly understood. In this report we address the question of locality of one of the NMO effects, namely nuclear spin-induced circular dichroism (NSCD). We implement an alternative computational approach for calculation of the NSCD intensities, based on residues of quadratic response functions, and use it to investigate the NSCD response of different nuclei in a model molecular system with well-defined separate chromophores. The results show that significant NSCD at a given energy only occurs at the nuclei which are located in the chromophore that is excited. We rationalize these findings using analysis via difference densities, and approximate sum-over-states calculations. This behaviour of NSCD opens a way to experimental studies of localization of excited states in molecules, potentially with resolution down to the order of bond-length.

Poly(ethylene oxide monomethyl ether)- block-poly(propylene succinate) Nanoparticles: Synthesis and Characterization, Enzymatic and Cellular Degradation, Micellar Solubilization of Paclitaxel, and in Vitro and in Vivo Evaluation.

Polyester-based nanostructures are widely studied as drug-delivery systems due to their biocompatibility and biodegradability. They are already used in the clinic. In this work, we describe a new and simple biodegradable and biocompatible system as the Food and Drug Administration approved polyesters (poly-ε-caprolactone, polylactic acid, and poly(lactic- co-glycolic acid)) for the delivery of the anticancer drug paclitaxel (PTX) as a model drug. A hydrophobic polyester, poly(propylene succinate) (PPS), was prepared from a nontoxic alcohol (propylene glycol) and monomer from the Krebs's cycle (succinic acid) in two steps via esterification and melt polycondensation. Furthermore, their amphiphilic block copolyester, poly(ethylene oxide monomethyl ether)- block-poly(propylene succinate) (mPEO- b-PPS), was prepared by three steps via esterification followed by melt polycondensation and the addition of mPEO to the PPS macromolecules. Analysis of the in vitro cellular behavior of the prepared nanoparticle carriers (NPs) (enzymatic degradation, uptake, localization, and fluorescence resonance energy-transfer pair degradation studies) was performed by fluorescence studies. PTX was loaded to the NPs of variable sizes (30, 70, and 150 nm), and their in vitro release was evaluated in different cell models and compared with commercial PTX formulations. The mPEO- b-PPS copolymer analysis displays glass transition temperature < body temperature < melting temperature, lower toxicity (including the toxicity of their degradation products), drug solubilization efficacy, stability against spontaneous hydrolysis during transport in bloodstream, and simultaneous enzymatic degradability after uptake into the cells. The detailed cytotoxicity in vitro and in vivo tumor efficacy studies have shown the superior efficacy of the NPs compared with PTX and PTX commercial formulations.

Post-disturbance recovery of forest carbon in a temperate forest landscape under climate change.

Disturbances alter composition, structure, and functioning of forest ecosystems, and their legacies persist for decades to centuries. We investigated how temperate forest landscapes may recover their carbon (C) after severe wind and bark beetle disturbance, while being exposed to climate change. We used the forest landscape and disturbance model iLand to quantify (i) the recovery times of the total ecosystem C, (ii) the effect of climate change on C recovery, and (iii) the differential factors contributing to C recovery. We reconstructed a recent disturbance episode (2008-2016) based on Landsat satellite imagery, which affected 39% of the forest area in the 16,000 ha study landscape. We subsequently simulated forest recovery under a continuation of business-asusual management until 2100. Our results indicated that the recovery of the pre-disturbance C stocks (C payback time) was reached 17 years after the end of the disturbance episode. The C stocks of a theoretical undisturbed development trajectory were reached 30 years after the disturbance episode (C sequestration parity). Drier and warmer climates delayed simulated C recovery. Without the fertilizing effect of CO2, C payback times were delayed by 5-9 years, while C parity was not reached within the 21st century. Recovery was accelerated by an enhanced C uptake compared to undisturbed conditions (disturbance legacy sink effect) that persisted for 35 years after the disturbance episode. Future climate could have negative impacts on forest recovery and thus further amplify climate change through C loss from ecosystems, but the effect is strongly contingent on the magnitude and persistence of alleviating CO2 effects. Our modelling study highlights the need to consider both negative and positive effects of disturbance (i.e., C loss immediately after an event vs. enhanced C uptake of the recovering forest) in order to obtain a comprehensive understanding of disturbance effects on the forest C cycle.

Polyelectrolyte pH-Responsive Protein-Containing Nanoparticles: The Physicochemical Supramolecular Approach.

We report on the physicochemical properties and self-assembly behavior of novel efficient pH-sensitive nanocontainers based on the Food and Drug Administration-approved anionic polymer Eudragit L100-55 (poly(methacrylic acid-co-ethyl acrylate) 1:1) and nonionic surfactant Brij98. The features of the interaction between Eudragit L100-55 and Brij98 at different pH values and their optimal ratio for nanoparticle formation were studied using isothermal titration calorimetry. The influence of the polymer-to-surfactant ratio on the size and structure of particles was studied at different pH values using dynamic light scattering and small-angle X-ray scattering methods. It was shown that stable nanoparticles are formed at acidic pH at polymer-to-surfactant molar ratios from 1:43 to 1:139. Trypsin was successfully encapsulated into Eudragit-Brij98 nanoparticles as a model bioactive component. The loading efficiency was determined by labeling trypsin with radioactive iodine-125. Eudragit-Brij98 nanoparticles effectively protected trypsin against pepsin digestion. The results showed that trypsin encapsulated into novel pH-sensitive nanocontainers retained more than 50% of its activity after treatment with pepsin compared with nonencapsulated trypsin. The described concept will contribute both to understanding the principles of and designing next-generation nanocontainers.

Galactosyl Pentadecene Reversibly Enhances Transdermal and Topical Drug Delivery.

PURPOSE: To study new skin penetration/permeation enhancers based on amphiphilic galactose derivatives. METHODS: Two series of alkyl and alkenyl galactosides were synthesized and evaluated for their enhancing effect on transdermal/topical delivery of theophylline (TH), hydrocortisone (HC) and cidofovir (CDV), reversibility of their effects on transepidermal water loss (TEWL) and skin impedance, interaction with the stratum corneum using infrared spectroscopy, and cytotoxicity on keratinocytes and fibroblasts. RESULTS: Initial evaluation identified 1-(α-D-galactopyranosyl)-(2E)-pentadec-2-ene A15 as a highly potent enhancer - it increased TH and HC flux through human skin 8.5 and 5 times, respectively. Compound A15 increased the epidermal concentration of a potent antiviral CDV 7 times over that reached by control and Span 20 (an established sugar-based enhancer). Infrared spectroscopy of human stratum corneum indicated interaction of A15 with skin barrier lipids but not proteins. These effects of A15 on the skin barrier were reversible (both TEWL and skin impedance returned to baseline values within 24 h after A15 had been removed from skin). In vitro toxicity of A15 on HaCaT keratinocytes and 3T3 fibroblasts was acceptable, with IC50 values over 60 µM. CONCLUSIONS: Galactosyl pentadecene A15 is a potent enhancer with low toxicity and reversible action.

Dodecyl Amino Glucoside Enhances Transdermal and Topical Drug Delivery via Reversible Interaction with Skin Barrier Lipids.

PURPOSE: Skin permeation/penetration enhancers are substances that enable drug delivery through or into the skin. METHODS: To search for new enhancers with high but reversible activity and acceptable toxicity, we synthesized a series of D-glucose derivatives, both hydrophilic and amphiphilic. RESULTS: Initial evaluation of the ability of these sugar derivatives to increase permeation and penetration of theophylline through/into human skin compared with a control (no enhancer) or sorbitan monolaurate (Span 20; positive control) revealed dodecyl 6-amino-6-deoxy-α-D-glucopyranoside 5 as a promising enhancer. Furthermore, this amino sugar 5 increased epidermal concentration of a highly hydrophilic antiviral cidofovir by a factor of 7. The effect of compound 5 on skin electrical impedance suggested its direct interaction with the skin barrier. Infrared spectroscopy of isolated stratum corneum revealed no effect of enhancer 5 on the stratum corneum proteins but an overall decrease in the lipid chain order. The enhancer showed acceptable toxicity on HaCaT keratinocyte and 3T3 fibroblast cell lines. Finally, transepidermal water loss returned to baseline values after enhancer 5 had been removed from the skin. CONCLUSIONS: Compound 5, a dodecyl amino glucoside, is a promising enhancer that acts through a reversible interaction with the stratum corneum lipids.

Vibrational Structure in Magnetic Circular Dichroism Spectra of Polycyclic Aromatic Hydrocarbons.

Absorption and magnetic circular dichroism (MCD) spectroscopies are powerful and simple methods to discriminate among various compounds. Polycyclic aromatic hydrocarbons provide particularly strong signal, which, for example, facilitates their detection in the environment. However, interpretation of the spectra is often based on quantum-chemical simulations, providing a limited precision only. In the present work, we use time-dependent density functional theory and complete active space second-order perturbation theories to understand spectral features observed in a series of naphthalene, anthracene, phenanthrene, and three larger compounds. The electronic computations provided reasonable agreement with the experiment for the smaller molecules, while a large error persisted for the bigger ones. However, many discrepancies could be explained by vibrational splitting of the electronic transitions across the entire spectral range. Compared to plain absorption, MCD spectral bands and their vibrational splitting were more specific for each aromatic molecule. The computational tools allowing simulations of detailed vibrational features in the electronic spectra thus promise to open a qualitatively new chapter in the spectroscopy of aromatic compounds.

System with embedded drug release and nanoparticle degradation sensor showing efficient rifampicin delivery into macrophages.

We have developed a biodegradable, biocompatible system for the delivery of the antituberculotic antibiotic rifampicin with a built-in drug release and nanoparticle degradation fluorescence sensor. Polymer nanoparticles based on poly(ethylene oxide) monomethyl ether-block-poly(ε-caprolactone) were noncovalently loaded with rifampicin, a combination that, to best of our knowledge, was not previously described in the literature, which showed significant benefits. The nanoparticles contain a Förster resonance energy transfer (FRET) system that allows real-time assessment of drug release not only in vitro, but also in living macrophages where the mycobacteria typically reside as hard-to-kill intracellular parasites. The fluorophore also enables in situ monitoring of the enzymatic nanoparticle degradation in the macrophages. We show that the nanoparticles are efficiently taken up by macrophages, where they are very quickly associated with the lysosomal compartment. After drug release, the nanoparticles in the cmacrophages are enzymatically degraded, with half-life 88±11 min.

Resolving Electronic Transitions in Synthetic Fluorescent Protein Chromophores by Magnetic Circular Dichroism.

The detailed electronic structures of fluorescent chromophores are important for their use in imaging of living cells. A series of green fluorescent protein chromophore derivatives is examined by magnetic circular dichroism (MCD) spectroscopy, which allows the resolution of more bands than plain absorption and fluorescence. Observed spectral patterns are rationalized with the aid of time-dependent density functional theory (TDDFT) computations and the sum-over-state (SOS) formalism, which also reveals a significant dependence of MCD intensities on chromophore conformation. The combination of organic and theoretical chemistry with spectroscopic techniques also appears useful in the rational design of fluorescence labels and understanding of the chromophore's properties. For example, the absorption threshold can be heavily affected by substitution on the phenyl ring but not much on the five-member ring, and methoxy groups can be used to further tune the electronic levels.