Lessons from chlorophylls: modifications of porphyrinoids towards optimized solar energy conversion

Cationic Porphyrins as Antimicrobial and Antiviral Agents in Photodynamic Therapy

Antimicrobial photodynamic therapy (APDT) has received a great deal of attention due to its unique ability to kill all currently known classes of microorganisms. To date, infectious diseases caused by bacteria and viruses are one of the main sources of high mortality, mass epidemics and global pandemics among humans. Every year, the emergence of three to four previously unknown species of viruses dangerous to humans is recorded, totaling more than 2/3 of all newly discovered human pathogens. The emergence of bacteria with multidrug resistance leads to the rapid obsolescence of antibiotics and the need to create new types of antibiotics. From this point of view, photodynamic inactivation of viruses and bacteria is of particular interest. This review summarizes the most relevant mechanisms of antiviral and antibacterial action of APDT, molecular targets and correlation between the structure of cationic porphyrins and their photodynamic activity.

The Influence of Lactic Acid Fermentation on Selected Properties of Pickled Red, Yellow, and Green Bell Peppers

Red, yellow, and green peppers are vegetables rich in natural pigments. However, they belong to seasonal vegetables and need to be treated to prolong their shelf life. One new approach to processing vegetables is to pickle them using lactic acid bacteria. The use of such a process creates a new product with high health value, thanks to the active ingredients and lactic acid bacteria. Therefore, this study aimed to evaluate the effect of the applied strain of lactic acid bacteria (LAB) on the chemical properties, including the content of active compounds (pigments) and the physical properties of the peppers. Levilactobacillus brevis, Limosilactobacillus fermentum, and Lactoplantibacillus plantarum were used for fermentation and spontaneous fermentation. The pigments, polyphenols content, and antioxidant properties were determined in the pickled peppers, as well as sugar content, color, dry matter, texture properties, and the count of lactic acid bacteria. In all samples, similar growth of LAB was observed. Significant degradation of chlorophylls into pheophytins was observed after the fermentation process. No significant differences were observed in the parameters tested, depending on the addition of dedicated LAB strains. After the fermentation process, the vitamin C and total polyphenols content is what influenced the antioxidant activity of the samples. It can be stated that the fermentation process changed the red bell pepper samples in the smallest way and the green ones in the highest way.

Light-Activated Phytochemicals in Photodynamic Therapy for Cancer: A Mini Review

Background: Cancer is a serious life-threatening disease often thought of as a deadly and painful disease with no permanent cure. With the advancement of medical science, there have been several clinically approved treatment options developed over the past decade. Photodynamic therapy (PDT) is one such approved minimally invasive light-based therapeutic option for many cancers. Selection of a suitable photosensitizer (PS) is an important step in PDT for improved therapeutic outcomes. Efforts to discover more efficient PSs continue for optimal PDT. Objective: This review discusses the available natural PS of plant origin, the role of phytochemicals in the application of PDT of cancer, specific localization of PS in various cell organelles, and photochemical reactions. Materials and methods: Owing to the substantial side effects, many biomedical research fields are currently focusing on natural compounds with chemotherapeutic potential with environmentally sustainable green approaches. Medicinal plant extracts have been used since ancient times for the treatment of various ailments. Plants are a natural source of many bioactive compounds with pharmaceutical potential and there have been some efforts made to discover potential new compounds from plants with photosensitizing properties for effective PDT outcomes. Results and conclusions: The PDT application in the current scenario raises some questions, such as most effective PS, its administration, the time of irradiation, light source, sensitivity of cells toward PS, and so forth. PDT effects can be direct or indirect. Owing to the direct effect of the PDT, most of the tumoral mass is destroyed. In the cancer cells that were not directly affected, secondary effects such as vascular effects, apoptosis induction, inflammation, and generation of an immune response may occur; however, the complex nature of PDT tissue response is not fully established.

Coordination Complexes as a New Generation Photosensitizer for Photodynamic Anticancer Therapy

Photodynamic therapy (PDT) has become an alternative to standard cancer treatment methods such as surgery, chemotherapy and radiotherapy. The uniqueness of this method relies on the possibility of using various photosensitizers (PS) that absorb and convert light emission in radical oxygen-derived species (ROS). They can be present alone or in the presence of other compounds such as metal organic frameworks (MOFs), non-tubules or polymers. The interaction between DNA and metal-based complexes plays a key role in the development of new anti-cancer drugs. The use of coordination compounds in PDT has a significant impact on the amount ROS generated, quantum emission efficiency (Φem) and phototoxic index (PI). In this review, we will attempt to systematically review the recent literature and analyze the coordination complexes used as PS in PDT. Finally, we compared the anticancer activities of individual coordination complexes and discuss future perspectives. So far, only a few articles link so many transition metal ion coordination complexes of varying degrees of oxidation, which is why this review is needed by the scientific community to further expand this field worldwide. Additionally, it serves as a convenient collection of important, up-to-date information.

Macrocyclic sulfone derivatives: Synthesis, characterization, in vitro biological evaluation and molecular docking

An artificial series of macrocycles based on 4,4'-sulfonyldiphenol intermediate was synthesized using a multistep procedure involving oxidation of bisphenol sulfide, etherification of phenolic hydroxyl groups, and final ring closure with different diamines. Different chemical species having aromatic, heteroaromatic, and aliphatic characters were incorporated into macrocyclic frameworks in the final step of ring closure. This simple and easily executable synthetic strategy was applied to synthesize 15 macrocycles (5a-o) in excellent yields. Characterization of the synthesized products was achieved through well-known modern spectroscopic techniques such as IR, NMR, and Mass. Macrocycles 5m and 5n were found to show significant AChE inhibition with IC₅₀ values of 76.9 ± 0.24 and 71.2 ± 0.77 μM, respectively. Macrocycle 5n was also found to be an active inhibitor of butyrylcholinesterase (BChE) with IC₅₀ score of 55.3 ± 0.54 μM. Among others, macrocycle 5l cyclized with o-phenylenediamine demonstrated moderate inhibition with IC₅₀ value of 81.1 ± 0.54 μM. Increasing interest in studying interactions of macrocycles with different enzymatic targets compelled us to design and synthesize sulfone-based macrocycles that might prove as highly potent class of biologically active compounds.

Cadmium ion-chlorophyll interaction - Examination of spectral properties and structure of the cadmium-chlorophyll complex and their relevance to photosynthesis inhibition

Chlorophyll was shown to spontaneously form a complex with cadmium, which is incorporated at the central position of the chlorophyll molecule porphyrin ring, where it replaces magnesium. The rate of complex formation depended on the ratio of Cd2+ ions to chlorophyll concentration in the solution. In solutions with chlorophyll concentration of C = 1 × 10^-5 M and Cd²⁺ concentrations of C = 1 × 10^-5 M, C = 1 × 10^-3 M and C = 9 × 10^-3 M, Cd-Chl complex formation was completed after 200 h, 50 h and 33 h, respectively. The formation of Cd-Chl complex followed the second order over all substrates reaction order, first order over Cd²⁺ concentration and first over Chl concentration. The pseudo second order reaction rate constant k, when Cd²⁺ concentration was equal Chl concentration have been obtained as k = 1.510 ± 0.023 × 10^-4 M^-1min^-1. Quantum chemistry computations showed that Cd-chlorophyll complex existed in two conformations in the methanol solution with cadmium ion placed either below or above the coordination plane. Two times smaller overlap integral of the Chl fluorescence spectrum with the Cd-Chl absorption spectrum I_Chl,Cd-Chl= 2.4223 × 10^-13 cm³/M in comparison with the overlap integral of the Chl fluorescence spectrum with the Chl absorption spectrum I_Chl,Chl= 4.6210 × 10^-13 cm³/M (twice lower probability of energy transfer Chl∗ → Cd-Chl than Chl∗ → Chl) and lower Förster critical distance for resonance energy transfer: R_{oChl→Cd-Chl}= 46.773 Å, R_oChl→Chl= 52.086 Å, indicated that in plants intoxicated with cadmium, taken up from the contaminated soil, the energy transfer between Chl and Cd-Chl in antennas will be disturbed, which may be one of the reasons for the inhibition of photosynthesis.

Absorption and Fluorescence Spectral Database of Chlorophylls and Analogues

Absorption spectra and fluorescence spectra are essential for use across the photosciences, yet such spectra along with the all-important values for molar absorption coefficient (ε) and fluorescence quantum yield (Φ_f ) often are found with great difficulty. Here, a literature survey concerning the vital class of chlorophyll compounds has led to identification of spectra for 150 members. Spectra in print form have been digitized (with baseline corrections) and assembled into a database along with literature references, solvent identity and values for ε and Φ_f (where available). The database encompasses photosynthetic tetrapyrroles wherein the chromophore is a porphyrin (e.g. chlorophyll c₁ , protochlorophyll a), chlorin (e.g. chlorophyll a, bacteriochlorophyll c) or bacteriochlorin (e.g. bacteriochlorophyll a). Altogether, the database contains 305 absorption spectra (from 19 porphyrins, 109 chlorins and 22 bacteriochlorins) and 72 fluorescence spectra (from 10 porphyrins, 30 chlorins and 4 bacteriochlorins). The spectral database should facilitate comparisons and quantitative calculations. All spectra are available in print form in the Supporting Information. The entire database in digital form is available with the PhotochemCAD program for free downloading and further use at http://www.photochemcad.com.

Stability of Chlorophyll a Monomer Incorporated into Cremophor EL Nano-Micelles under Dark and Moderate Light Conditions

In this paper, stability of chlorophyll a monomers encapsulated into the Cremophor EL nano-micelles was studied under dark and moderate light conditions, typical of a room with natural or artificial lighting, in the presence of oxygen. The pigment stability against visible light was determined using the dynamic light scattering and molecular spectroscopy (UV-Vis absorption and stationary fluorescence) methods. Chlorophyll a, at the molar concentration of 10-5 M, was dissolved in the 5 wt% Cremophor emulsion for comparison in the ethanolic solution. The stability of such a self-assembly pigment-detergent nano-system is important in the light of its application on the commercial-scale. The presented results indicate the high stability of the pigment monomeric molecular organization in the nano-emulsion. During the storage in the dark, the half-lifetime was calculated as about 7 months. Additionally, based on the shape of absorption and fluorescence emission spectra, chlorophyll aggregation in the Cremophor EL aqueous solution along with the time was excluded. Moreover, the average size of detergent micelles as chlorophyll carriers was not affected after 70 days of the nano-system storage. Pigment stability against the moderate white light (0.1 mW) did not differ significantly from storage conditions in the dark. The photooxidation products, detected by occurrence of new absorption and fluorescence emission bands, was estimated on the negligible level. The stability of such a self-assembly pigment-detergent nano-system would potentially broaden the field of chlorophyll a (chl a) application in the food industry, medicine or artificial photosynthesis models.

Anti-Hypochlorite, Antioxidant, and Catalytic Activity of Three Polyphenol-Rich Super-Foods Investigated with the Use of Coumarin-Based Sensors

The anti-hypochlorite activity of açaí (Euterpe oleracea Mart.), goji (Lycium barbarum L.) and schisandra (Schisandra chinensis) fruit extracts were assessed by determining the reactive chlorine species (RCS)-scavenging ability of these three "super-food" berries. In addition, the aqueous extracts obtained were employed as both the media and the catalyst in a green chemistry approach to the synthesis of a coumarin-based fluorescence turn-off sensor, which was then used for anti-hypochlorite activity testing. The aqueous extracts were also assessed for total phenolic content (TPC), using the Folin-Ciocalteu method, and the antioxidant activity using the ABTS^+• assay. Moreover, the main water-soluble polyphenolic constituents of the extracts were identified by the HPLC-PDA-ESI-MS technique. Among the extracts tested, açaí demonstrated the highest anti-hypochlorite and antioxidant activities, while the highest TPC value was found for the goji extract. All extracts demonstrated modest catalytic activity as Knoevenagel condensation catalysts.

Tuning the Photophysical Features of Self-Assembling Photoactive Polypeptides for Light-Harvesting

The LH1 complex is the major light-harvesting antenna of purple photosynthetic bacteria. Its role is to capture photons, and then store them and transfer the excitation energy to the photosynthetic reaction center. The structure of LH1 is modular and it cooperatively self-assembles from the subunits composed of short transmembrane polypeptides that reversibly bind the photoactive cofactors: bacteriochlorophyll and carotenoid. LH1 assembly, the intra-complex interactions and the light-harvesting features of LH1 can be controlled in micellar media by varying the surfactant concentration and by adding carotenoid and/or a co-solvent. By exploiting this approach, we can manipulate the size of the assembly, the intensity of light absorption, and the energy and lifetime of its first excited singlet state. For instance, via the introduction of Ni-substituted bacteriochlorophyll into LH1, the lifetime of this electronic state of the antenna can be shortened by almost three orders of magnitude. On the other hand, via the exchange of carotenoid, light absorption in the visible range can be tuned. These results show how in a relatively simple self-assembling pigment-polypeptide system a sophisticated functional tuning can be achieved and thus they provide guidelines for the construction of bio-inspired photoactive nanodevices.

Phototrophic purple bacteria as optoacoustic in vivo reporters of macrophage activity

Τhe morphology, physiology and immunology, of solid tumors exhibit spatial heterogeneity which complicates our understanding of cancer progression and therapy response. Understanding spatial heterogeneity necessitates high resolution in vivo imaging of anatomical and pathophysiological tumor information. We introduce Rhodobacter as bacterial reporter for multispectral optoacoustic (photoacoustic) tomography (MSOT). We show that endogenous bacteriochlorophyll a in Rhodobacter gives rise to strong optoacoustic signals >800 nm away from interfering endogenous absorbers. Importantly, our results suggest that changes in the spectral signature of Rhodobacter which depend on macrophage activity inside the tumor can be used to reveal heterogeneity of the tumor microenvironment. Employing non-invasive high resolution MSOT in longitudinal studies we show spatiotemporal changes of Rhodobacter spectral profiles in mice bearing 4T1 and CT26.WT tumor models. Accessibility of Rhodobacter to genetic modification and thus to sensory and therapeutic functions suggests potential for a theranostic platform organism.

Current optoacoustic probes for cancer imaging have limitations including background noise, long-term toxicity and scarce imaging depth in living tissue. Here the authors use Rhodobacter, purple bacteria rich in bacteriochlorophyll a, as an optoacoustic reporter to image tumor-associated macrophages in mice in vivo.

The impact of LED lighting on the yield, morphological structure and some bioactive components in alfalfa (Medicago sativa L.) sprouts

The aim of this study was to evaluate the impact of selected types of LED (light emitting diodes) lighting on the quality of alfalfa sprouts. In the experiment, cold white, warm white and multicolour: (red, green, blue-RGB) LEDs were applied, and dispersed sunlight was used as a control. The product was examined for the yield and the contents of dry matter, total polyphenols, ascorbic acid, chlorophylls, β-carotene, lutein, neoxanthin and violaxanthin. Cotyledons' mass in the whole plant increased under LED illumination and was up to 50% greater for sprouts grown in RGB light compared to those cultivated in dispersed sunlight. The highest chlorophyll and carotenoid pigment contents in cotyledons were observed under RGB LED and cold white treatments. Similarly, RGB LEDs allows one to obtain the product with the highest level of total phenolic compounds. The highest ascorbic acid content was observed in sprouts growing under sunlight, followed by RGB.

Macrocycle ring deformation as the secondary design principle for light-harvesting complexes

Natural light-harvesting is performed by pigment-protein complexes, which collect and funnel the solar energy at the start of photosynthesis. The identity and arrangement of pigments largely define the absorption spectrum of the antenna complex, which is further regulated by a palette of structural factors. Small alterations are induced by pigment-protein interactions. In light-harvesting systems 2 and 3 from Rhodoblastus acidophilus, the pigments are arranged identically, yet the former has an absorption peak at 850 nm that is blue-shifted to 820 nm in the latter. While the shift has previously been attributed to the removal of hydrogen bonds, which brings changes in the acetyl moiety of the bacteriochlorophyll, recent work has shown that other mechanisms are also present. Using computational and modeling tools on the corresponding crystal structures, we reach a different conclusion: The most critical factor for the shift is the curvature of the macrocycle ring. The bending of the planar part of the pigment is identified as the second-most important design principle for the function of pigment-protein complexes-a finding that can inspire the design of novel artificial systems.

Rapid Determination of Chlorophyll and Pheophytin in Green Tea Using Fourier Transform Infrared Spectroscopy

The chlorophyll, pheophytin, and their proportions are critical factors to evaluate the sensory quality of green tea. This research aims to establish an effective method to determine the quantification of chlorophyll and pheophytin in green tea, based on Fourier transform infrared (FT–IR) spectroscopy. First, five brands of tea were collected for spectral acquisition, and the chlorophyll and pheophytin were measured using the reference method. Then, a relation between these two pigments and FT–IR spectroscopy were developed based on chemometrics. Additionally, the characteristic IR wavenumbers of these pigments were extracted and proved to be effective for a quantitative determination. Successively, non-linear models were also built based on these characteristic wavenumbers, obtaining coefficients of determination of 0.87, 0.80, 0.85 and 0.89; and relative predictive deviations of 2.77, 2.62, 2.26 and 3.07 for the four pigments, respectively. These results demonstrate the feasibility of FT–IR spectroscopy for the determination of chlorophyll and pheophytin.

Phenolic Acid Content and Antioxidant Properties of Extruded Corn Snacks Enriched with Kale

Prohealth food contains specific components which have positive influence on the health and well-being of the consumer. An important position among bioactive compounds occurs for polyphenols. Many results have indicated that an increased intake of phenolic compounds may reduce the risk of cardiovascular diseases and type 2 diabetes. The objective of the study was production of extruded corn snacks with addition (0, 2, 4, 6, and 8%) of kale (Brassica oleracea L. var. sabellica)-a polyphenol-rich plant. Afterwards, high-performance liquid chromatography-mass spectrometry (LC-ESI-MS/MS) and antioxidant activity analyses of snack extracts were performed. In the corn snacks enriched with kale, fifteen phenolic acids were indicated. These were protocatechuic, 4-OH-benzoic, vanillic, trans-caffeic, cis-caffeic, trans-p-coumaric, cis-p-coumaric, trans-ferulic, cis-ferulic, salicylic, gentisic, syringic, 3-OH-cinnamic, trans-sinapic, and cis-sinapic acids. Both the qualitative and quantitative content of polyphenols increased with the addition of B. oleracea. Data from spectrophotometric analyses of the samples showed high DPPH radical scavenging potential of snacks enriched with 4, 6, and 8% of kale. Snacks enriched with kale contain high level of phenolic acids and, therefore, have great potential to make a valuable source of natural antioxidants. High-temperature short-time extrusion-cooking process had no negative impact on polyphenol's activity.

Spectroscopic and Theoretical Studies of Fluorescence Effects in 2-Methylamino-5-(2,4-dihydroxyphenyl)-1,3,4-thiadiazole Induced by Molecular Aggregation

The article presents the results of fluorescence analyses of 2-methylamino-5-(2,4-dihydroxyphenyl)-1,3,4-thiadiazole (MDFT) in an aqueous environment. MDFT dissolved in aqueous solutions with a pH value in the range from 1 to 4.5 yielded an interesting effect of two clearly separated fluorescence emissions. In turn, a single fluorescence was observed in MDFT dissolved in water solutions with a pH value from 4.5 to 12. As it was suggested in the previous investigations of other 1,3,4-thiadiazole compounds, these effects may be associated with conformational changes in the structure of the analysed molecule accompanied by aggregation effects. Crystallographic data showed that the effect of the two separated fluorescence emissions occurred in a conformation with the –OH group in the resorcyl ring bound on the side of the sulphur atom from the 1,3,4-thiadiazole ring. The hypothesis of aggregation as the mechanism involved in the change in the spectral properties at low pH is supported by the results of (Time-Dependent) Density Functional Theory calculations. The possibility of rapid analysis of conformational changes with the fluorescence spectroscopy technique may be rather important outcome obtained from the spectroscopic studies presented in this article. Additionally, the presented results seem to be highly important as they can be easily observed in solutions and biologically important samples.

Capillary coating as an important factor in optimization of the off-line and on-line MEKC assays of the highly hydrophobic enzyme chlorophyllase

The choice between bare and coated capillaries is a key decision in the development and use of any methods based on capillary electrophoresis. In this work several permanently and dynamically coated capillaries were successfully implemented in a previously developed micellar electrokinetic chromatography (MEKC) assay of the plant membrane enzyme chlorophyllase. The results obtained demonstrate the rationale behind the use of capillary coating, which is crucial for successful optimization of both the off-line mode and the on-line/electrophoretically mediated microanalysis assay mode. The application of an amine permanently coated capillary (eCAP) is a simple way to significantly increase the repeatability of migration times and peak areas, and to ensure a strong electroosmotic flow that considerably decreases the overall analysis time. A dynamic coating (CEofix) allows one to apply an on-line incubation to control the reaction progress inside the capillary, and to increase the signal-to-noise ratio and peak efficiency. The dynamic coating is possible with use of both the normally applied uncoated silica capillary and the precoated amine capillary, which ensures more repeatable migration times. The strong points of the uncoated silica capillary are its attractive price and wide range of pH that can be applied. The characteristics presented may simplify the choice of capillary modification, especially in the case of hydrophobic analytes, MEKC-based separations, and other enzymatic assays.

Effect of Metals, Metalloids and Metallic Nanoparticles on Microalgae Growth and Industrial Product Biosynthesis: A Review

Microalgae are a source of numerous compounds that can be used in many branches of industry. Synthesis of such compounds in microalgal cells can be amplified under stress conditions. Exposure to various metals can be one of methods applied to induce cell stress and synthesis of target products in microalgae cultures. In this review, the potential of producing diverse biocompounds (pigments, lipids, exopolymers, peptides, phytohormones, arsenoorganics, nanoparticles) from microalgae cultures upon exposure to various metals, is evaluated. Additionally, different methods to alter microalgae response towards metals and metal stress are described. Finally, possibilities to sustain high growth rates and productivity of microalgal cultures in the presence of metals are discussed.

Metalloisoporphyrins: from synthesis to applications

An overview of the chemistry of isoporphyrin, the tautomer of porphyrin, whose existence was predicated by the Noble laureate Woodward, is presented with emphasis on hydroxy-isoporphyrins of tetra-aryl derivatives.