Factors controlling the reactivity of divalent metal ions towards pheophytin a

An Update in Computational Methods for Environmental Monitoring: Theoretical Evaluation of the Molecular and Electronic Structures of Natural Pigment-Metal Complexes

Metals are beneficial to life, but the presence of these elements in excessive amounts can harm both organisms and the environment; therefore, detecting the presence of metals is essential. Currently, metal detection methods employ powerful instrumental techniques that require a lot of time and money. Hence, the development of efficient and effective metal indicators is essential. Several synthetic metal detectors have been made, but due to their risk of harm, the use of natural pigments is considered a potential alternative. Experiments are needed for their development, but they are expensive and time-consuming. This review explores various computational methods and approaches that can be used to investigate metal-pigment interactions because choosing the right methods and approaches will affect the reliability of the results. The results show that quantum mechanical methods (ab initio, density functional theory, and semiempirical approaches) and molecular dynamics simulations have been used. Among the available methods, the density functional theory approach with the B3LYP functional and the LANL2DZ ECP and basis set is the most promising combination due to its good accuracy and cost-effectiveness. Various experimental studies were also in good agreement with the results of computational methods. However, deeper analysis still needs to be carried out to find the best combination of functions and basis sets.

Chlorophyll a π-Cation Radical as Redox Mediator in Superoxide Dismutase (SOD) Mimetics

The extensive speciation of copper(II) chloride in organic solvents varies with concentration, temperature, pressure and oxygen content, providing the ability to switch between different chlorophyll transmetalation pathways. We found that one of them is exceptionally suitable for the formation and stabilisation of the chlorophyll π-cation radical. This is due to unique redox cycling, which is coupled to the generation and transformation of various reactive oxygen species. In the presence of a proton donor, our system shows behavior which resembles that of superoxide dismutase (SOD). Regardless of light, chlorophyll acts as an electron transfer mediator.

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.

Divalent Cations: A Molecular Glue for Protein Materials

Among inorganic materials, divalent cations modulate thousands of physiological processes that support life. Their roles in protein assembly and aggregation are less known, although they are progressively being brought to light. We review the structural roles of divalent cations here, as well as the novel protein materials that are under development, in which they are used as glue-like agents. More specifically, we discuss how mechanically stable nanoparticles, fibers, matrices, and hydrogels are generated through their coordination with histidine-rich proteins. We also describe how the rational use of divalent cations combined with simple protein engineering offers unexpected and very simple biochemical approaches to biomaterial design that might address unmet clinical needs in precision medicine.

Porpholactone Chemistry: An Emerging Approach to Bioinspired Photosensitizers with Tunable Near-Infrared Photophysical Properties

Chlorophylls, known as the key building blocks of natural light-harvesting antennae, are essential to utilize solar energy from visible to near-infrared (NIR) region during the photosynthesis process. The fundamental studies for the relationship between structure and photophysical properties of chlorophylls disclosed the importance of β-peripheral modification and thus boosted the fast growth of NIR absorbing/emissive porphyrinoids via altering the extent of π-conjugation and the degree of distortion from the planarity of macrocycle. Despite the tremendous progress made in various porphyrin-based synthetic models, it still remains a challenge to precisely modulate photophysical properties through fine-tuning of β-peripheral structures in the way natural chlorophylls do. With this in mind, we initiated a program and focused on meso-C₆F₅-substituted porpholactone (F₂₀TPPL), in which one β-pyrrolic double bond was replaced by a lactone moiety, as an attractive platform to construct the bioinspired library of NIR porphyrinoids. In this Account, we summarize our recent contributions to the bioinspired design, synthesis, photophysical characterization, and applications of porpholactones and their derivatives. We have developed a general, convenient method to directly prepare porpholactones in large scale up to gram, which forms the chemical basis of porpholactone chemistry. By modulation of the saturation level and in particular regioisomerization of β-dilactone moieties, a synthetic library constituted by a series of porpholactones and their derivatives has been established. Thanks to the electron-withdrawing nature of lactone moiety, derivation of the saturation levels gives help to build stable models for chlorin, bacteriochlorin, and tunichlorin. It is worth noting that regioisomerization of dilactone moieties mimics the relative orientation of β-substituents in natural chlorophylls and hemes, which was considered as the key factor to tune NIR absorption and reactivity. Porpholactones can illustrate the capability of fine-tuning photophysical properties including the excited triplet states by subtle alteration of β-peripheral structures in the presence of transition metals and lanthanides (Ln). Furthermore, they can serve as efficient photosensitizers for singlet oxygen and NIR Ln, showing potential applications in cell imaging and photocytotoxicity studies. The high luminescence, tunable structures, high cellular uptake, and intense NIR absorption render them as promising and competitive candidates for theranostics in vitro and in vivo. Therefore, extending the studies of "porpholactone chemistry" not only tests the fundamental understanding of the structure-function relationship that governs NIR photophysical properties of natural tetrapyrrole cofactors such as chlorophylls but also provides the guiding principles for the bioinspired design of NIR luminescent molecular probes with various applications. Taken together, as a new synthetic porphyrin derivative, porpholactone chemistry shines light on synthetic porphyrin, bioinorganic, and lanthanide chemistry.

Formulation of Ethyl Cellulose Microparticles Incorporated Pheophytin A Isolated from Suaeda vermiculata for Antioxidant and Cytotoxic Activities

BACKGROUND

This study is designed to discover a method for delivering an efficient potent pheophytin a (pheo-a) into more absorbed and small polymeric ethyl cellulose (EC) microparticles.

METHODS

Silica gel and Sephadex LH-20 columns were used to isolate pheo-a from the chloroform extract of the edible plant, Suaeda vermiculata. Pheo-a was incorporated into EC microparticles using emulsion-solvent techniques. The antioxidant activity of pheo-a microparticles was confirmed by the level of superoxide radical (SOD), nitric oxide (NO), and reducing power (RP) methods. Meanwhile, the cytotoxic effect of the product was investigated on MCF-7 cells using MTT assay.

RESULTS

Pheo-a was isolated from S. vermiculata in a 12% concentration of the total chloroform extract. The structures were confirmed by NMR and IR spectroscopic analysis. The formulated microparticles were uniform, completely dispersed in the aqueous media, compatible as ingredients, and had a mean diameter of 139 ± 1.56 µm as measured by a particle size analyzer. Pheo-a demonstrated a valuable antioxidant activity when compared with ascorbic acid. The IC₅₀ values of pheo-a microparticles were 200.5 and 137.7 µg/mL for SOD, and NO respectively. The reducing power of pheo-a microparticles was more potent than ascorbic acid and had a 4.2 µg/mL for IC₅₀ value. Pheo-a microparticles did not show notable cytotoxicity on the MCF-7 cell line (IC₅₀ = 35.9 µg/mL) compared with doxorubicin (IC₅₀ = 3.2 µg/mL).

CONCLUSIONS

the results showed that water-soluble pheo-a microparticles were prepared with a valuable antioxidant activity in a wide range of concentrations with a noteworthy cytotoxic effect.