Rapid oxygen isotopic exchange between bicarbonate and water during photosynthesis.

Whether rapid oxygen isotopic exchange between bicarbonate and water occurs in photosynthesis is the key to determine the source of oxygen by classic 18O-labeled photosynthetic oxygen evolution experiments. Here we show that both Microcystis aeruginosa and Chlamydomonas reinhardtii utilize a significant proportion (>16%) of added bicarbonate as a carbon source for photosynthesis. However, oxygen isotopic signal in added bicarbonate cannot be traced in the oxygen in organic matter synthesized by these photosynthetic organisms. This contradicts the current photosynthesis theory, which states that photosynthetic oxygen evolution comes only from water, and oxygen in photosynthetic organic matter comes only from carbon dioxide. We conclude that the photosynthetic organisms undergo rapid exchange of oxygen isotope between bicarbonate and water during photosynthesis. At the same time, this study also provides isotopic evidence for a new mechanism that half of the oxygen in photosynthetic oxygen evolution comes from bicarbonate photolysis and half comes from water photolysis, which provides a new explanation for the bicarbonate effect, and suggests that the Kok-Joliot cycle of photosynthetic oxygen evolution, must be modified to include a molecule of bicarbonate in addition to one molecule of water which in turn must be incorporated into the cycle instead of two water molecules. Furthermore, this study provides a theoretical basis for constructing a newer artificial photosynthetic reactor coupling light reactions with the dark reactions.

Phosphate buffer interferes dissolution of prazosin hydrochloride in compendial dissolution testing.

The purpose of this study was to elucidate the lack of supersaturation behavior in the dissolution profile of prazosin hydrochloride (PRZ-HCl) in the compendial dissolution test. The equilibrium solubility was measured by a shake-flask method. Dissolution tests were performed by a compendial paddle method with a phosphate buffer solution (pH 6.8, 50 mM phosphate). The solid form of the residual particles was identified by Raman spectroscopy. In the pH range below 6.5, the equilibrium solubility in phosphate buffer was lower than that in the unbuffered solutions (pH adjusted by HCl and NaOH). Raman spectra showed that the residual solid was a phosphate salt of PRZ. In the pH range above 6.5, the pH-solubility profiles in the phosphate buffer solutions and the unbuffered solutions were the same. The residual solid was a PRZ freebase (PRZ-FB). In the dissolution test, PRZ-HCl particles first changed to a phosphate salt within 5 min, then gradually changed to PRZ-FB after several hours. Since the intestinal fluid is buffered by the bicarbonate system in vivo, the dissolution behavior in vivo may not be properly evaluated using a phosphate buffer solution. For drugs with a low phosphate solubility product, it is necessary to consider this aspect.

The effect of buffer species on biorelevant dissolution and precipitation assays - Comparison of phosphate and bicarbonate buffer.

Biorelevant solubility and dissolution testing is an important tool during pharmaceutical development, however, solubility experiments performed using biorelevant media often do not properly match the solubility data observed in human intestinal fluids. Even though the bicarbonate buffer is the predominant buffer system in the small intestine, in vitro assays are commonly performed using non-volatile buffer systems like phosphate and maleate. In the current study, bicarbonate- and phosphate-buffered biorelevant media were applied to solubility, dissolution, and precipitation testing for a broad range of model compounds. It was found that the medium affects primarily the dissolution kinetics. However, with the knowledge of the unique buffering properties of bicarbonate buffer in the diffusion layer, it was not always possible to predict the effect of buffer species on solubility and dissolution when changing from phosphate to bicarbonate buffer. This once again highlights the special role of bicarbonate buffer for simulating the conditions in the human intestinal fluids. Moreover, it is necessary to further investigate the factors which may cause the differences in solubility and dissolution behavior when using phosphate- vs. bicarbonate-buffered biorelevant media.

Dissolution Kinetics of Nifedipine-Ionizable Polymer Amorphous Solid Dispersion: Comparison Between Bicarbonate and Phosphate Buffers.

PURPOSE: The intestinal fluid pH is maintained by the bicarbonate buffer system that shows unique properties regarding drug dissolution. Nevertheless, current compendial dissolution tests use phosphate buffers. The purpose of the present study was to investigate the effect of bicarbonate and phosphate buffers on the dissolution profiles of amorphous solid dispersions (ASD) composed of ionizable polymers. METHODS: Hydroxypropylmethylcellulose acetate succinate (HPMCAS), amino methacrylate copolymer (AMC), and hydroxypropylmethylcellulose (HPMC) were employed as acidic, basic, and neutral polymers, respectively. Nifedipine (NIF) was used as a model drug. Dissolution profiles were measured in pH 6.5 bicarbonate and phosphate buffers by a mini-scale paddle dissolution test. The pH of bicarbonate buffers was maintained by the floating lid method. RESULTS: The pH change of the bicarbonate buffer was suppressed to less than + 0.25 pH for 3 h by the floating lid method. In all cases, the NIF concentration was supersaturated against the solubility of crystalline NIF. The dissolution rates of HPMCAS and AMC ASDs were 1.5 to 2.0-fold slower in the bicarbonate buffer than in the phosphate buffer when compared at the same buffer capacity. The dissolution profile of HPMC ASD was not affected by the buffer species. The higher the buffer capacity and ionic strength, the faster the dissolution rate of HPMCAS ASD. CONCLUSION: The dissolution rate of ASDs with ionizable polymers would be overestimated by using unphysiological phosphate buffer solutions. It is important to use a biorelevant bicarbonate buffer solution for dissolution testing.

Effects of Stromal and Lumenal Side Perturbations on the Redox Potential of the Primary Quinone Electron Acceptor QA in Photosystem II.

The primary quinone electron acceptor QA is a key component in the electron transfer regulation in photosystem II (PSII), and hence accurate estimation of its redox potential, Em(QA-/QA), is crucial in understanding the regulatory mechanism. Although fluorescence detection has been extensively used for monitoring the redox state of QA, it was recently suggested that this method tends to provide a higher Em(QA-/QA) estimate depending on the sample status due to the effect of measuring light [Kato et al. (2019) Biochim. Biophys. Acta 1860, 148082]. In this study, we applied the Fourier transform infrared (FTIR) spectroelectrochemistry, which uses non-reactive infrared light to monitor the redox state of QA, to investigate the effects of stromal- and lumenal-side perturbations on Em(QA-/QA) in PSII. It was shown that replacement of bicarbonate bound to the non-heme iron with formate upshifted Em(QA-/QA) by ∼55 mV, consistent with the previous fluorescence measurement. In contrast, an Em(QA-/QA) difference between binding of 3-(3,4-dichlorophenyl)-1,1-dimethylurea and bromoxynil was found to be ∼30 mV, which is much smaller than the previous estimate, ∼100 mV, by the fluorescence method. This ∼30 mV difference was verified by the decay kinetics of the S2QA- recombination. On the lumenal side, Mn depletion hardly affected the Em(QA-/QA), confirming the previous FTIR result. However, removal of the extrinsic proteins by NaCl or CaCl2 wash downshifted the Em(QA-/QA) by 14-20 mV. These results suggest that electron flow through QA is regulated by changes both on the stromal and lumenal sides of PSII.

Spontaneous assembly of redox-active iron-sulfur clusters at low concentrations of cysteine.

Iron-sulfur (FeS) proteins are ancient and fundamental to life, being involved in electron transfer and CO2 fixation. FeS clusters have structures similar to the unit-cell of FeS minerals such as greigite, found in hydrothermal systems linked with the origin of life. However, the prebiotic pathway from mineral surfaces to biological clusters is unknown. Here we show that FeS clusters form spontaneously through interactions of inorganic Fe2+/Fe3+ and S2- with micromolar concentrations of the amino acid cysteine in water at alkaline pH. Bicarbonate ions stabilize the clusters and even promote cluster formation alone at concentrations >10 mM, probably through salting-out effects. We demonstrate robust, concentration-dependent formation of [4Fe4S], [2Fe2S] and mononuclear iron clusters using UV-Vis spectroscopy, 57Fe-Mössbauer spectroscopy and 1H-NMR. Cyclic voltammetry shows that the clusters are redox-active. Our findings reveal that the structures responsible for biological electron transfer and CO2 reduction could have formed spontaneously from monomers at the origin of life.

Fabrication of gelatin microspheres containing ammonium hydrogen carbonate for the tunable release of herbicide.

The major challenge in utilizing pesticides lies in identifying the precise application that would improve the efficiency of these pesticides and decline their environmental and health hazards at the same time. Such application requires the development of specific formulations that enable controlled, stimuli-responsive release of the pesticides. Gelatin is a relatively cheap material characterized by temperature-sensitivity and abundant amino acid groups, which makes it suitable for the storage and controlled release of pesticides. In this study, gelatin microspheres were prepared by emulsion and cross-linking, then they were loaded with 2,4-dichlorophenoxyacetic acid sodium (2,4-D Na) as a model herbicide. To achieve temperature-tunable release of 2,4-D Na from the microspheres, NH4HCO3 was added to the formulations at different concentrations. The prepared formulations were characterized by SEM, FTIR, and size distribution analyzes, and their drug loading capacities were determined. Based on bioassay experiments, the 2,4-D Na-NH4HCO3-loaded gelatin microspheres can effectively control the spread of dicotyledonous weeds. Therefore, the strategy proposed herein can be used to develop novel, effective herbicide formulations.

Observation of Intact and Proteolytically Cleaved Amyloid-Beta (1-40)-Oleuropein Noncovalent Complex at Neutral pH by Mass Spectrometry.

Mass spectrometry analyses carried out on mass spectrometers equipped with soft ionization sources demonstrated their utility in the assessment of the formation of noncovalent complexes and the localization of the binding sites. Direct analyses by mass spectrometry of the noncovalent complex formed in acidic and mildly acidic environments by amyloid beta (1-40) peptide and oleuropein have been previously described, and, in several studies, the absorption, metabolism, excretion, and the implications in the prevention and therapy of Alzheimer's disease of oleuropein have been investigated. Our paper presents modifications of the method previously employed for noncovalent complex observation, namely, the amyloid beta (1-40) pretreatment, followed by an increase in the pH and replacement of the chemical environment from ammonium acetate to ammonium bicarbonate. The formation of noncovalent complexes with one or two molecules of oleuropein was detected in all chemical solutions used, and the amyloid beta (17-28) binding site was identified via proteolytic experiments using trypsin prior to and after noncovalent complex formation. Our results highlight the importance of further studies on the effect of oleuropein against amyloid beta aggregation.

Minute Cu2+ coupling with HCO3- for efficient degradation of acetaminophen via H2O2 activation.

Homogeneous Cu2+-mediated activation of H2O2 has been widely applied for the removal of organic contaminants, but fairly high dosage of Cu2+ is generally required and may cause secondary pollution. In the present study, minute Cu2+ (2.5 µM) catalyzed H2O2 exhibited excellent efficiency in degradation of organic pollutants with the assistant of naturally occurring level HCO3- (1 mM). In a typical case, acetaminophen (ACE) was completely eliminated within 10 min which followed the pseudo-first-order kinetics. Singlet oxygen and superoxide radical rather than traditionally identified hydroxyl radical were the predominant reactive oxygen species (ROS) responsible for ACE degradation. Meanwhile, Cu3+ was deduced through Cu+ and p-hydroxybenzoic acid formation analysis. CuCO3(aq) was the main complex with high reactivity for the activation of H2O2 to form ROS and Cu3+. The removal efficiency of ACE depended on the operating parameters, such as Cu2+, HCO3- and H2O2 dosage, solution initial pH. The presence of Cl-, HPO42-, humic acid were found to retard ACE removal while other anions such as SO42- and NO3- had no obvious effect. ACE exhibited lower degradation efficiency in real water matrices than that in ultra-pure water. Nevertheless, 58-100% of ACE was removed from domestic wastewater, lake water and tap water within 60 min. Moreover, eight intermediate products were identified and the possible degradation pathways of ACE were proposed. Additionally, other typical organic pollutants including bisphenol A, norfloxacin, lomefloxacin hydrochloride and sulfadiazine, exhibited great removal efficiency in the Cu2+/H2O2/HCO3- system.

Computational Exploration of the Mechanism of Critical Steps in the Biomimetic Synthesis of Preuisolactone A, and Discovery of New Ambimodal (5 + 2)/(4 + 2) Cycloadditions.

Computational studies with ωB97X-D density functional theory of the mechanisms of the steps in Trauner's biomimetic synthesis of preuisolactone A have elaborated and refined mechanisms of several unique processes. An ambimodal transition state has been identified for the cycloaddition between an o-quinone and a hydroxy-o-quinone; this leads to both (5 + 2) (with H shift) and (4 + 2) cycloaddition products, which can in principle interconvert via α-ketol rearrangements. The origins of periselectivity of this ambimodal cycloaddition have been investigated computationally with molecular dynamics simulations and tested further by an experimental study. In the presence of bicarbonate ions, the deprotonated hydroxy-o-quinone leads to only the (5 + 2) cycloaddition adduct. A new mechanism for a benzilic acid rearrangement resulting in ring contraction is proposed.

Fast Screening of Biomembrane-Permeable Compounds in Herbal Medicines Using Bubble-Generating Magnetic Liposomes Coupled with LC-MS.

A novel strategy based on the use of bionic membrane camouflaged magnetic particles and LC-MS was developed to quickly screen the biomembrane-permeable compounds in herbal medicines. The bionic membrane was constructed by bubble-generating magnetic liposomes loaded with NH4HCO3 (BMLs). The lipid bilayer structure of the liposomes enabled BMLs to capture biomembrane-permeable compounds from a herbal extract. The BMLs carrying the compounds were then separated from the extract by a magnetic field. Upon heat treatment, NH4HCO3 rapidly decomposed to form CO2 bubbles within the liposomal bilayer, and the captured compounds were released from BMLs and analyzed by LC-MS. Jinlingzi San (JLZS), which contains various natural ingredients, was chosen to assess the feasibility of the proposed method. As a result, nine potential permeable compounds captured by BMLs were identified for the first time. Moreover, an in vivo animal study found that most of the compounds screened out by the proposed method were absorbed into the blood. The study provides a powerful tool for rapid and simultaneous prediction of multiple biomembrane-permeable components.

Airway Surface Liquid pH Regulation in Airway Epithelium Current Understandings and Gaps in Knowledge.

Knowledge on the mechanisms of acid and base secretion in airways has progressed recently. The aim of this review is to summarize the known mechanisms of airway surface liquid (ASL) pH regulation and their implication in lung diseases. Normal ASL is slightly acidic relative to the interstitium, and defects in ASL pH regulation are associated with various respiratory diseases, such as cystic fibrosis. Basolateral bicarbonate (HCO3-) entry occurs via the electrogenic, coupled transport of sodium (Na+) and HCO3-, and, together with carbonic anhydrase enzymatic activity, provides HCO3- for apical secretion. The latter mainly involves CFTR, the apical chloride/bicarbonate exchanger pendrin and paracellular transport. Proton (H+) secretion into ASL is crucial to maintain its relative acidity compared to the blood. This is enabled by H+ apical secretion, mainly involving H+/K+ ATPase and vacuolar H+-ATPase that carry H+ against the electrochemical potential gradient. Paracellular HCO3- transport, the direction of which depends on the ASL pH value, acts as an ASL protective buffering mechanism. How the transepithelial transport of H+ and HCO3- is coordinated to tightly regulate ASL pH remains poorly understood, and should be the focus of new studies.

Generating tumor-selective conditionally active biologic anti-CTLA4 antibodies via protein-associated chemical switches.

Anticytotoxic T lymphocyte-associated protein 4 (CTLA4) antibodies have shown potent antitumor activity, but systemic immune activation leads to severe immune-related adverse events, limiting clinical usage. We developed novel, conditionally active biologic (CAB) anti-CTLA4 antibodies that are active only in the acidic tumor microenvironment. In healthy tissue, this binding is reversibly inhibited by a novel mechanism using physiological chemicals as protein-associated chemical switches (PaCS). No enzymes or potentially immunogenic covalent modifications to the antibody are required for activation in the tumor. The novel anti-CTLA4 antibodies show similar efficacy in animal models compared to an analog of a marketed anti-CTLA4 biologic, but have markedly reduced toxicity in nonhuman primates (in combination with an anti-PD1 checkpoint inhibitor), indicating a widened therapeutic index (TI). The PaCS encompass mechanisms that are applicable to a wide array of antibody formats (e.g., ADC, bispecifics) and antigens. Examples shown here include antibodies to EpCAM, Her2, Nectin4, CD73, and CD3. Existing antibodies can be engineered readily to be made sensitive to PaCS, and the inhibitory activity can be optimized for each antigen's varying expression level and tissue distribution. PaCS can modulate diverse physiological molecular interactions and are applicable to various pathologic conditions, enabling differential CAB antibody activities in normal versus disease microenvironments.

Efficient Adsorption of Methylene Blue by Porous Biochar Derived from Soybean Dreg Using a One-Pot Synthesis Method.

Soybean dreg is a by-product of soybean products production, with a large consumption in China. Low utilization value leads to random discarding, which is one of the important sources of urban pollution. In this work, porous biochar was synthesized using a one-pot method and potassium bicarbonate (KHCO3) with low-cost soybean dreg (SD) powder as the carbon precursor to investigating the adsorption of methylene blue (MB). The prepared samples were characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM), elemental analyzer (EA), Brunauer-Emmett-Teller (BET), X-ray diffractometer (XRD), Raman spectroscopy (Raman), Fourier transform infrared spectrometer (FTIR), and X-ray photoelectron spectroscopy (XPS). The obtained SDB-K-3 showed a high specific surface area of 1620 m2 g-1, a large pore volume of 0.7509 cm3 g-1, and an average pore diameter of 1.859 nm. The results indicated that the maximum adsorption capacity of SDB-K-3 to MB could reach 1273.51 mg g-1 at 318 K. The kinetic data were most consistent with the pseudo-second-order model and the adsorption behavior was more suitable for the Langmuir isotherm equation. This study demonstrated that the porous biochar adsorbent can be prepared from soybean dreg by high value utilization, and it could hold significant potential for dye wastewater treatment in the future.

EndoPil: A Magnetically Actuated Swallowable Capsule for Weight Management: Development and Trials.

Intragastric balloons (IGBs), by occupying the stomach space and prolonging satiety, is a promising method to treat obesity and consequently improves its associated comorbidities, e.g. coronary heart disease, diabetes, and cancer. However, existing IGBs are often tethered with tubes for gas or liquid delivery or require endoscopic assistance for device delivery or removal, which are usually uncomfortable, costly, and may cause complications. This paper presents a novel tetherless, magnetically actuated capsule (EndoPil) which can deploy an IGB inside the stomach after being swallowed and being activated by an external magnet. The external magnet attracts a small magnet inside the EndoPil to open a valve, triggering the chemical reaction of citric acid and potassium bicarbonate to produce carbon dioxide gas, which inflates a biocompatible balloon (around 120 mL). A prototype, 13 mm in diameter and 35 mm in length, was developed. Simulations and bench-top tests were conducted to test the force capability of the magnetic actuation mechanism, the required force to activate the valve, and the repeatability of balloon inflation. Experiments on animal and human were successfully conducted to demonstrate the safety and feasibility of inflating a balloon inside the stomach by an external magnet.

Yolk-shell structured Au nanorods@mesoporous silica for gas bubble driven drug release upon near-infrared light irradiation.

Drug release systems co-encapusulated with ammonium bicarbonate (ABC) could facilitate drug release upon acidic or thermal stimulations to improve therapeutic effect. However, it is not easy to control drug release rate, owing to relative stable temperature and acidic condition in living body. Besides, the additional loaded ABC reduces drug loading capacity. Herein, a near-infrared light triggered rapid drug release system with high loading capacity was developed by loading ABC and doxorubicin into yolk-shell structured Au nanorods@mesoporous silica. Gas bubbles were generated from the thermolysis of ABC utilizing photothermal effect of Au nanorods to extrude drug molecules. The mesoporous silica shell was finally destroyed along with growing bubbles, resulting in burst drug release. The photothermal therapeutic effect of Au nanorods also contributed in tumor treatment. The excellent therapeutic effect was demonstrated in cancer cells and tumor-bearing mice, which provides a new reference to achieve controllable rapid drug release in cancer medicine.

Tyrosine-EDC Conjugation, an Undesirable Side Effect of the EDC-Catalyzed Carboxyl Labeling Approach.

Carbodiimide-catalyzed carboxyl and amine conjugation (amidation) has been widely used to protect carboxyl groups. N-(3-(Dimethylamino)propyl)-N'-ethylcarbodiimide (EDC) is the most common carbodiimide reagent in protein chemistry due to its high catalytic efficiency in aqueous media. The reaction has also been applied in different proteomic studies including protein terminomics, glycosylation, and interaction. Herein, we report that the EDC-catalyzed amidation could cause a +155 Da side modification on the tyrosine residue and severely hamper the identification of Tyr-containing peptides. We revealed the extremely low identification rate of Tyr-containing peptides in different published studies employing the EDC-catalyzed amidation. We discovered a +155 Da side modification occurring specifically on Tyr and decoded it as the addition of EDC. Consideration of the side modification in a database search enabled the identification of 13 times more Tyr-containing peptides. Furthermore, we successfully developed an efficient method to remove the side modification. Our results also imply that chemical reactions in proteomic studies should be carefully evaluated prior to their wide applications. Data are available via ProteomeXchange with identifier PXD020042.

Lipopolysaccharide directly inhibits bicarbonate absorption by the renal outer medullary collecting duct.

Acidosis is associated with E. coli induced pyelonephritis but whether bacterial cell wall constituents inhibit HCO3 transport in the outer medullary collecting duct from the inner stripe (OMCDi) is not known. We examined the effect of lipopolysaccharide (LPS), on HCO3 absorption in isolated perfused rabbit OMCDi. LPS caused a ~ 40% decrease in HCO3 absorption, providing a mechanism for E. coli pyelonephritis-induced acidosis. Monophosphoryl lipid A (MPLA), a detoxified TLR4 agonist, and Wortmannin, a phosphoinositide 3-kinase inhibitor, prevented the LPS-mediated decrease, demonstrating the role of TLR4-PI3-kinase signaling and providing proof-of-concept for therapeutic interventions aimed at ameliorating OMCDi dysfunction and pyelonephritis-induced acidosis.

Antibacterial Effects of Bicarbonate in Media Modified to Mimic Cystic Fibrosis Sputum.

Cystic fibrosis (CF) is a hereditary disease caused by mutations in the gene encoding an epithelial anion channel. In CF, Cl- and HCO3- hyposecretion, together with mucin hypersecretion, leads to airway dehydration and production of viscous mucus. This habitat is ideal for colonization by pathogenic bacteria. We have recently demonstrated that HCO3- inhibits the growth and biofilm formation of Pseudomonas aeruginosa and Staphylococcus aureus when tested in laboratory culture media. Using the same bacteria our aim was to investigate the effects of HCO3- in artificial sputum medium (ASM), whose composition resembles CF mucus. Control ASM containing no NaHCO3 was incubated in ambient air (pH 7.4 or 8.0). ASM containing NaHCO3 (25 and 100 mM) was incubated in 5% CO2 (pH 7.4 and 8.0, respectively). Viable P. aeruginosa and S. aureus cells were counted by colony-forming unit assay and flow cytometry after 6 h and 17 h of incubation. Biofilm formation was assessed after 48 h. The data show that HCO3- significantly decreased viable cell counts and biofilm formation in a concentration-dependent manner. These effects were due neither to extracellular alkalinization nor to altered osmolarity. These results show that HCO3- exerts direct antibacterial and antibiofilm effects on prevalent CF bacteria.

Preparation and Characterisation of Activated Carbon from Palm Mixed Waste Treated with Trona Ore.

This study explores the use of a novel activating agent and demonstrates the production and characterisation of activated carbon (AC) from a combine palm waste (CPW) in 3:2:1 proportion by weight of empty fruit bunch, mesocarp fibre and palm kernel shell. The resulting biomass was processed by a microwave-assisted method using trona and compared with material produced by conventional routes. These results demonstrate the potential of trona ore as an activating agent and the effectiveness of using a combined palm waste for a single stream activation process. It also assesses the effectiveness of trona ore in the elimination of alcohol, acids and aldehydes; with a focus on increasing the hydrophilicity of the resultant AC. The optimum results for the conventional production technique at 800 °C yielded a material with SBET 920 m2/g, Vtotal 0.840 cm3/g, a mean pore diameter of 2.2 nm and an AC yield 40%. The optimum outcome of the microwave assisted technique for CPW was achieved at 600 W, SBET is 980 m2/g; Vtotal 0.865 cm3/g; a mean pore diameter 2.2 nm and an AC yield of 42%. Fourier transform infrared spectrometry analyses showed that palm waste can be combined to produce AC and that trona ore has the capacity to significantly enhance biomass activation.