Modulating the pro-apoptotic activity of cytochrome c at a biomimetic electrified interface

Nanocatalytic NO gas therapy against orthotopic oral squamous cell carcinoma by single iron atomic nanocatalysts

Oral squamous cell carcinoma (OSCC) has been being one of the most malignant carcinomas featuring high metastatic and recurrence rates. The current OSCC treatment modalities in clinics severely deteriorate the quality of life of patients due to the impaired oral and maxillofacial functions. In the present work, we have engineered the single-atom Fe nanocatalysts (SAF NCs) with a NO donor (S-nitrosothiol, SNO) via surface modification to achieve synergistic nanocatalytic NO gas therapy against orthotopic OSCC. Upon near-infrared laser irradiation, the photonic hyperthermia could effectively augment the heterogeneous Fenton catalytic activity, meanwhile trigger the thermal decomposition of the engineered NO donor, thus producing toxic hydroxyl radicals (•OH) and antitumor therapeutic NO gas at tumor lesion simultaneously, and consequently inducing the apoptotic cell death of tumors via mitochondrial apoptosis pathway. This therapeutic paradigm presents an effective local OSCC therapeutics in a synergistic manner based on the nanocatalytic NO gas therapy, providing a promising antitumor modality with high biocompatibility.

Potential-Modulated Surface-Enhanced Raman Spectroscopy of Tolmetin at Gold Nanoparticle Film Functionalized Polarizable Liquid-Liquid Interfaces

An aqueous colloidal suspension of gold nanoparticles (AuNPs) may be condensed into a thin fractal film at the polarizable liquid-liquid interface formed between two immiscible electrolyte solutions upon injection of millimolar concentrations of sodium chloride to the aqueous phase. By adjusting the interfacial polarization conditions (negative, intermediate, and positive open-circuit potentials), the morphology of the film is modified, resulting in unique surface plasmon properties of the film, which enable in situ surface-enhanced Raman spectroscopy (SERS). Intense SERS signals are observed at the polarizable liquid-liquid interface when micromolar concentrations of tolmetin, a nonsteroidal anti-inflammatory drug, are entrapped in the AuNP fractal film. The change in the signal intensity, averaged over multiple spectra, with respect to the concentration of tolmetin, depends on the polarization conditions and suggests the presence of chemical-induced damping effects on the surface plasmons of the gold film.

Time-resolved absorption measurements quantify the competition of energy and electron transfer between quantum dots and cytochrome c

We applied transient absorption spectroscopy to study the early photodynamics in a system composed of CdTe quantum dots (QDs) and cytochrome c (Cyt c) protein. In the QDs and Cyt c mixtures, about 25 % of the excited QD electrons quickly relax (∼23 ps) to the ground state and roughly 75 % decay on slower time scale - mostly due to quenching by Cyt c. On the basis of the assumed model, we estimated the contribution of electron transfer and other mechanisms to this quenching. The primary quenching mechanism is probably energy transfer but electron transfer makes a significant contribution (∼8 %), resulting in photoreduction of Cyt c. The lifetime of one fraction of reduced Cyt c (35-90 %) is ∼ 1 ms and the lifetime of the remaining fraction was longer than the ∼ 50-ms time window of the experiment. We speculate that, in the former fraction, the back electron transfer from the reduced Cyt c to QDs occurs and the latter fraction of Cyt c is stably reduced.

Potential‐Modulated Ion Distributions in the Back‐to‐Back Electrical Double Layers at a Polarised Liquid|Liquid Interface Regulate the Kinetics of Interfacial Electron Transfer

Biphasic interfacial electron transfer (IET) reactions at polarisable liquid|liquid (L|L) interfaces underpin new approaches to electrosynthesis, redox electrocatalysis, bioelectrochemistry and artificial photosynthesis. Herein, using cyclic and alternating current voltammetry, we demonstrate that under certain experimental conditions, the biphasic 2-electron O₂ reduction reaction can proceed by single-step IET between a reductant in the organic phase, decamethylferrocene, and interfacial protons in the presence of O₂. Using this biphasic system, we demonstrate that the applied interfacial Galvani potential difference Δ o w φ provides no direct driving force to realise a thermodynamically uphill biphasic IET reaction in the mixed solvent region. We show that the onset potential for a biphasic single-step IET reaction does not correlate with the thermodynamically predicted standard Galvani IET potential and is instead closely correlated with the potential of zero charge at a polarised L|L interface. We outline that the applied Δ o w φ required to modulate the interfacial ion distributions, and thus kinetics of IET, must be optimised to ensure that the aqueous and organic redox species are present in substantial concentrations at the L|L interface simultaneously in order to react.

A method for quantifying how the activity of an enzyme is affected by the net charge of its nearest crowded neighbor

The electrostatic effects of protein crowding have not been systematically explored. Rather, protein crowding is generally studied with co‐solvents or crowders that are electrostatically neutral, with no methods to measure how the net charge (Z) of a crowder affects protein function. For example, can the activity of an enzyme be affected electrostatically by the net charge of its neighbor in crowded milieu? This paper reports a method for crowding proteins of different net charge to an enzyme via semi‐random chemical crosslinking. As a proof of concept, RNase A was crowded (at distances ≤ the Debye length) via crosslinking to different heme proteins with Z = +8.50 ± 0.04, Z = +6.39 ± 0.12, or Z = −10.30 ± 1.32. Crosslinking did not disrupt the structure of proteins, according to amide H/D exchange, and did not inhibit RNase A activity. For RNase A, we found that the electrostatic environment of each crowded neighbor had significant effects on rates of RNA hydrolysis. Crowding with cationic cytochrome c led to increases in activity, while crowding with anionic “supercharged” cytochrome c or myoglobin diminished activity. Surprisingly, electrostatic crowding effects were amplified at high ionic strength (I = 0.201 M) and attenuated at low ionic strength (I = 0.011 M). This salt dependence might be caused by a unique set of electric double layers at the dimer interspace (maximum distance of 8 Å, which cannot accommodate four layers). This new method of crowding via crosslinking can be used to search for electrostatic effects in protein crowding.

On the origin of chaotrope-modulated electrocatalytic activity of cytochrome c at electrified aqueous|organic interfaces

Electrochemical, spectroscopic and computational methods are used to demonstrate that electrified aqueous|organic interfaces are a suitable bio-mimetic platform to study and contrast the accelerated electrocatalytic activity of cytochrome c towards the production of reactive oxygen species (ROS) in the presence of denaturing agents such as guanidinium chloride and urea.