Murburn Model of Photosynthesis: Effect of Additives like Chloride and Bicarbonate

Oxygenic photosynthesis essentially involves photo-lysis (splitting of water to release oxygen), photo-reduction (formation of NADPH), and photo-phosphorylation (synthesis of ATP) reactions. These reactions use photoactive pigments such as chlorophylls and carotenoids. Z-scheme and Kok-Joliot cycle, the acclaimed and deterministic model of photosynthesis, are founded on the classical enzyme reaction mechanisms that depend solely on affinity-based interactions of enzymes with the substrates at defined active sites, for explaining electron/moiety transfers. In contrast, the new murburn model is built on stochastic collisions between diffusible reactive species (DRS) and other milieu components (including enzymes, substrates and ions). This novel perspective explains fast kinetics and action spectrum, and affords a spontaneously probable/evolvable biochemical system. The murburn perspective proposes that the photo-excitation of pigments in the chloroplast leads to effective charge separation and DRS-formation. DRS are stabilized/utilized by a pool of redox-active components via disordered/parallel bimolecular interactions at the thylakoid membrane interface. Herein, we provide details of how murburn model is a thermodynamically, kinetically, and mechanistically viable mechanism for the formation of ATP, NADPH and oxygen. The murburn model also provides more viable explanations for several classical experimental observations in photosynthesis (Emerson enhancement effect, Jagendorf/Racker experiments, etc.) and the non-specific effects of diverse additives (such as chloride and bicarbonate)

Comprehensive Analyses of the Enhancement of Oxygenesis in Photosynthesis by Bicarbonate and Effects of Diverse Additives: Z-scheme Explanation Versus Murburn Model

The Z-scheme electron transport chain (ETC) explanation for photosynthesis starts with the serial/sequential transfer of electrons sourced from water molecules bound at Photosystem II via a deterministic array of redox centers (of various stationary/mobile proteins), before "sinking" via the reduction of NADP+ bound at flavin-enzyme reductase. Several research groups’ finding that additives (like bicarbonate) enhance the light reaction had divided the research community because it violated the Z-scheme. The untenable aspects of the Z-scheme perception were demonstrated earlier and a murburn bioenergetics (a stochastic/parallel paradigm of ion-radical equilibriums) model was proposed to explain photophosphorylation and Emerson effect. Herein, we further support the murburn model with accurate thermodynamic calculations, which show that the cost of one-electron abstraction from bicarbonate [491 kJ/mol] is lower than water [527 kJ/mol]. Further, copious thioredoxin enables the capture of photoactivated electrons in milieu, which aid in the reduction of nicotinamide nucleotides. The diffusible reactive species (DRS) generated in milieu sponsor phosphorylations and oxygenic reactions. With structural analysis of Photosystems and interacting molecules, we chart out the equations of reactions that explain the loss of labeled O-atom traces in delocalized oxygenesis. Thus, this essay discredits the Z-scheme and explains key outstanding observations in the field

Potential and limitations of CsBi3I10 as a photovoltaic material

Herein we demonstrate the dry synthesis of CsBi3I10 both as a free-standing material and in the form of homogeneous thin films, deposited by thermal vacuum deposition. Chemical and optical characterization shows high thermal stability, phase purity, and photoluminescence centered at 700 nm, corresponding to a bandgap of 1.77 eV. These characteristics make CsBi3I10 a promising low-toxicity material for wide bandgap photovoltaics. Nevertheless, the performance of this material as a semiconductor in solar cells remains rather limited, which can be at least partially ascribed to a low charge carrier mobility, as determined from pulsed-radiolysis time-resolved microwave conductivity. Further developments should focus on understanding and overcoming the current limitations in charge mobility, possibly by compositional tuning through doping and/or alloying, as well as optimizing the thin film morphology which may be another limiting factor

Hand-drawn resistors, capacitors, diodes, and circuits for a pressure sensor system on paper

Hand-written fabrication techniques offer new ways of developing customizable, biodegradable and low-cost electronic systems. In this work, a new level of complexity is demonstrated for hand-written electronics by fabricating passive components, circuits and a sensorsystem on paper. The system comprises a pencil-written graphite force-sensitive-resistor, a pencil-drawn RC-filter, a pen-written half-wave rectifier, and a commercial front-end voltage amplifier. The sensor system exhibits a linear response for pressures up to 1.2 kPa, and a sensitivity of 51 mV kPa-1 . Furthermore, the electrical and mechanical performance of the single components and circuits is studied. Diodes fabricated through pen-written deposition of silver and nickel contacts on amorphous Indium-Gallium-Zinc-Oxide coated paper show rectification ratios up to 1:8. Tensile and compressive bending measurements applied to all pencil-written components for radii down to 0.1 mm indicate minor influence of strain. Similar results are obtained for circuits created from these individual components. Diodes and half-wave rectifiers show a stable behavior when bent to a radius of 5 mm. The presented techniques can enable the development of flexible and eco-friendly wearables and sensors for consumer and healthcare applications, and are an effective way for school-pupils to explore the world of electronics

Murburn concept: A stochastic principle for evolution and synthesis of cellular functions

As three points are minimally required to define/confine any area, the study of life can be systematized with the following three essential/prioritized biological principles: (a) Cell theory affords a factual/spatial demarcation of life from non-life, and discretizes/unitizes the organization of complex living beings. (b) Central dogma gives a blueprint for retaining/perpetuating genetic information/identity in time, also deterministically governing cellular protein concentrations and thereby their affinity-driven outcomes. (c) Murburn concept founds a stochastic basis for understanding the operational continuum of the principles of physics that govern the thermodynamics, kinetics and overall mechanics of sustenance/disruption of cellular life

Explanations for the enhancement of oxygenic photosynthesis by bicarbonate and diverse additives: Affinity-driven binding with photosystems versus murburn model

The classical explanation of photosynthesis starts with the abstraction of electrons from water molecules bound to the MnComplex of Photosystem II. These electrons are then passed/transported via sequentially ordered redox centers of various biomolecules, before finally being used for the reduction of NADP+ bound to flavin-enzyme reductase. The finding by several research groups that additives like bicarbonate/chloride ions enhance the light reaction cannot be satisfactorily explained by affinity-based binding of such species to Photosystems and the research community is divided on this topic. Recently, we had demonstrated that the classical deterministic/serial ETC perception was flawed and applied murburn bioenergetics (a stochastic/parallel paradigm of ion-radical equilibriums) to explain the physiological Emerson effect and overall phenomenology of photophosphorylation (Manoj et al., J. Biomol. Str. Dyn. 2021). Herein, we elucidate that bicarbonate could enhance the light reaction by virtue of aiding murburn interactive equilibriums in milieu. Our accurate thermodynamic calculations show that the one-electron abstraction from bicarbonate [ ° ≈ 491 kJ/mol] is comparable with water [ ° ≈ 527 kJ/mol]. With structural analysis of photosystems and their interactions with known electron donors/systemic components, we chart out the thermodynamics of probabilistic reactions that explain delocalized O2-evolution. Copious thioredoxin enables the capture of photoactivated electrons, which reduce the nicotinamide nucleotides whereas the diffusible reactive species (DRS) generated in milieu sponsor phosphorylations and thermogenic/oxygenic reactions. These considerations provide a satisfactory resolution of outstanding observations reported in literature, e.g. Stemler & Radmer, Science, 1977; Radmer & Ollinger, FEBS Lett., 1980; Clausen et al., Plant Physiol., 2005

Assessing the operational feasibility of ‘Z-scheme electron transport chain’ in chloroplasts

We summarize salient components of the Z-Scheme electron transport chain within chloroplasts. Banking on the skepticism kindled by Robert Emerson’s reproducible observations, we explore the working of its various elements using updated information on the distribution of components within the chloroplast architecture, structure-function correlations of relevant redox proteins, thermodynamics, kinetics, and evolutionary principles. Through a set of simple models/simulations and a series of intriguing queries, we moot several theoretical premises and highlight evidences/arguments that question the physiological feasibility of Z-scheme. Finally, we also point to new avenues for furthering research in this field

Murburn concept in cellular function and bioenergetics, Part 1: Understanding murzymes at the molecular level

Bioenergetics is the study of how life-activities are powered within the cell. This also deals with the interactive exchange of matter/radiation between cellular components and their environment, and the accompanying changes thereof. The acclaimed bioenergetics paradigm has relied on ‘electron transport chains’ and selective/stoichiometric electrogenic ‘ion-pumping’ mediated by vectorial protein-embedded membranes. Therein, an electrochemical gradient was deemed to be the driving force for chemical reactions leading to ATP production, physical thermogenesis by uncoupling proteins, and complex electromechanical processes like information relay along the axon. On one hand, this vitally deterministic perception requires the membrane proteins to “intelligently” manipulate ion-fluxes and generate/harness an electrochemical gradient by a gambit-type logic, and at the other hand, also seeks that the same gradient should cyclically control the membrane-proteins’ activity. Our recent pursuits have questioned such traditional perspectives, and advocated the alternate explanation of murburn concept, leading to a revamping of the macroscopic treatments of overall thermodynamic, kinetic, mechanistic and evolutionary (probability) considerations. The current review aims to consolidate the murburn paradigm of bioenergetics, wherein murzymes initiate redox processes by effective charge separation (ECS) and diffusible reactive species (DRS) formation, enabling cells to work as simple chemical engines (SCE). Herein, we discuss the reaction chemistry of some simple enzyme systems and also delve into protein complex arrays mediated powering routines like mitochondrial respiration-thermogenesis and chloroplast-centered photosynthesis. Further, we remark that the “water-ion-molecules” phase continuum is actually discretized into dynamically fluctuating coacervates, and express concern over the marginalization of sound chemico-physical ideas by the bioenergetics community