Formation Of Reversible Complex Research Articles

On the origin of carbon sources in the electrochemical upgrade of CO2 from carbon capture solutions

•Reacting bicarbonate and carbamate species on Ag electrodes requires energy input •On Ag electrodes, the carbon source is the free and dissolved CO2 during RCC •Carbamate species can only participate in RCC at highly negative potentials •Methods to measure and report dissolved CO2 concentration during RCC are developed Carbon capture and utilization (CCU) is a crucial technology for mitigating the effects of climate change. One approach to CCU is reactive carbon capture (RCC), which integrates (1) the capture and concentration of CO2 in a capture medium via the reversible formation of a chemical complex with a molecular capture agent, such as an amine, and (2) the direct transformation of the CO2 complex into a fuel or chemical. CO2 capture media present a large degree of speciation, where carbon exists in different molecular configurations with different energy states and barriers to reaction. In this work, a combination of first principle modeling and experimental electrochemical characterization methods reveal that unbound dissolved CO2 is the primary carbon species being consumed during the electrochemical reduction of bicarbonate and amine-based CO2 capture solutions on silver electrodes. Carbon in the CO2-absorber complex occurs to serve as a second carbon source only at highly negative potential. Carbon capture and utilization (CCU) is a crucial technology for mitigating the effects of climate change. One approach to CCU is reactive carbon capture (RCC), which integrates (1) the capture and concentration of CO2 in a capture medium via the reversible formation of a chemical complex with a molecular capture agent, such as an amine, and (2) the direct transformation of the CO2 complex into a fuel or chemical. CO2 capture media present a large degree of speciation, where carbon exists in different molecular configurations with different energy states and barriers to reaction. In this work, a combination of first principle modeling and experimental electrochemical characterization methods reveal that unbound dissolved CO2 is the primary carbon species being consumed during the electrochemical reduction of bicarbonate and amine-based CO2 capture solutions on silver electrodes. Carbon in the CO2-absorber complex occurs to serve as a second carbon source only at highly negative potential.

Mechanism of melanogenesis inhibition by Keggin-type polyoxometalates.

Abnormal melanin overproduction can result in hyperpigmentation syndrome in human skin diseases and enzymatic browning of fruits and vegetables. Recently, our group found that Keggin-type polyoxometalates (POMs) can efficiently inhibit tyrosinase activity. However, it remains unclear whether Keggin-type POMs exhibit optimal effects in vivo. Additionally, the inhibitory effect and mechanism of action of POMs on cellular tyrosinase activity and melanogenesis have been rarely reported. Here we demonstrate that our screened and synthesised PMo11Zn and GaMo12 show superior inhibitory effects on melanin formation as well as inhibition of cellular tyrosinase activity compared to other Keggin-type POMs. Intriguingly, we reveal that Keggin-type POMs competitively bind to tyrosinase mainly through more interactions with Cu2+ ions and the amino acid residue is capable of forming van der Waals, cation-π and hydrogen bonds, resulting in a reversible non-covalent complex formation. Our findings provide valuable insights into the design, synthesis and screening of polyoxometalates as multifunctional metallodrugs and food preservatives against hyperpigmentation.

Heteroprotein complex coacervation of lactoferrin and osteopontin: Phase behaviour and thermodynamics of formation

This research describes the formation of reversible heteroprotein complex coacervates between the bioactive milk proteins lactoferrin (LF) and osteopontin (OPN) within specific combinations of pH (∼4–6), ionic strength (≤30 mM added NaCl), protein stoichiometry (LF:OPN mass mixing ratios of ∼ 2–8) and total protein concentration (≤∼8% w/v). Electrostatic attraction between these proteins is possible across a wide range of pH values due to the acidic isoelectric point of OPN (∼ pH 3.5) and the basic isoelectric point of LF (∼ pH 8.7). Thermodynamic analysis of the OPN-LF interaction indicated that the protein-protein binding had enthalpic and entropic contributions which resulted in liquid-liquid phase separation given the appropriate combination of intrinsic and extrinsic conditions. The complex coacervates were found to be a concentrated protein phase (∼27% protein, w/w) which was highly hydrated (>70% moisture, w/w) and occurred spontaneously within LF: OPN ratios naturally found in human milk. The structure, biological functionality, and applications of heteroprotein complexes and/or complex coacervates between LF and OPN will be explored in separate work.

Covalently Immobilizable Tris(Pyridino)-Crown Ether for Separation of Amines Based on Their Degree of Substitution.

A great number of biologically active compounds contain at least one amine function. Appropriate selectivity can only be accomplished in a few cases upon the substitution of these groups, thus functionalization of amines generally results in a mixture of them. The separation of these derivatives with very similar characteristics can only be performed on a preparative scale or by applying pre-optimized HPLC methods. A tris(pyridino)-crown ether was designed and synthetized for overcoming these limitations at a molecular level. It is demonstrated, that this selector molecule is able to distinguish protonated primary, secondary and tertiary amines by the formation of reversible complexes with different stabilities. This degree of substitution-specific molecular recognition of amines opens the door to develop separation processes primarily focusing on the purification of biologically active compounds in a nanomolar scale.

Responsive fluorescence enhancement for in vivo Cu(II) monitoring in zebrafish larvae

Several neurodegenerative diseases are ascribed to disorders caused by the secretion of Cu ions. However, a majority of the current techniques for copper ion detection are restricted to in vivo monitoring and nonspecific interactions. Their methods are limited to the systematic analysis of Cu ions in living organisms. Thus, a synthetic molecular fluorophore, 5-amino 2,3-dihydroquinolinimine (NDQI), has been developed and successfully utilized in in vivo monitoring of the distribution of Cu(II) in zebrafish larvae. The reversible formation of the NDQI-Cu complex allows its use with high metal concentrations and in oxidative stress conditions. The NDQI-directed strategy developed here can quantitatively differentiate cells with different Cu(II) concentrations. Remarkably, dynamic distribution of Cu(II) in the intestine and liver can be observed.

Manufacturing of polystyrene panels with tunable colors

In this study, the synthesis of polyamine functional grafts that capable of reversible metal complexation with the transition metals has been achieved on the surface of commercial polystyrene (PS) panels. The brushes were generated via surface-initiated photo-iniferter polymerization (SI-PMP) on the active sites of PS panels. The active dithiocarbamate sites were created on the surface of the PS in four steps. First, the panels reacted with chlorosulfonic acid to obtain chlorosulfonic functionality on the surface without losing transparency. Diethanolamine was easily tethered to the surface of the PS panel from the chlorosulfonyl group. Then hydroxyl groups belonging to the diethanolamine were mesylated by methane sulfonylchloride, and resulting mesylated panels were reacted with pyridinium N,N′-diethyldithiocarbamate salt to get the dithiocarbomate functionality on the surface of the panel. After generation of the initiation sites on the panel, glycidyl methacrylate (GMA) was grafted via SI-PMP under UV light irradiation. The resulting PGMA brushes were converted to polyamine grafts via ring-opening reaction of epoxy groups with triethylenetetramine in a yield of 0.032 mmol amine per cm2. The functional surface grafts were employed for reversible metal complex formation with metal ions. The surface topologies and functionalities of modified panels were determined with SEM, AFM and FTIR.

Photoassisted Charge Transfer Between DMF and Substrate: Facile and Selective N,N-Dimethylamination of Fluoroarenes.

A reversible Van der Waals complex formation between the electron-deficient fluorinated aromatic ring and N,N-dimethylformamide (DMF) molecules followed by light irradiation resulted in charge transfer (CT) process. The complex was stabilized by ammonium formate and further decomposed to form the C-N bond. Control experiments revealed that the simultaneous SN Ar pathway also contributes to product formation. This methodology is mild, metal-free, and effective for the amination of a variety of substrates. The reproducibility of this methodology was also verified on gram-scale reactions. The CT states were supported by control UV/Vis spectroscopy and computational studies.

Reversible Addition of Carbon Dioxide to Main Group Metal Complexes at Temperatures about 0 °C.

The reaction of dialane [LAl-AlL] (1; L=dianion of 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene, dpp-bian) with carbon dioxide results in two different products depending on solvent. In toluene at temperatures of about 0 °C, the reaction gives cycloadduct [L(CO2 )Al-Al(O2 C)L] (2), whereas in diethyl ether, the reaction affords oxo-bridged carbamato derivative [L(CO2 )(Et2 O)Al(μ-O)AlL] (3). The DFT and QTAIM calculations provide reasonable explanations for the reversible formation of complex 2 in the course of two subsequent (2+4) cycloaddition reactions. Consecutive transition states with low activation barriers were revealed. Also, the DFT study demonstrated a crucial effect of diethyl ether coordination to aluminium on the reaction of dialane 1 with CO2 . The optimized structures of key intermediates were obtained for the reactions in the presence of Et2 O; calculated thermodynamic parameters unambiguously testify the irreversible formation of the product 3.

Cyclodextrins as a Key Piece in Nanostructured Materials: Quantitation and Remediation of Pollutants.

Separation and pre-concentration of trace pollutants from their matrix by reversible formation of inclusion complexes has turned into a widely studied field, especially for the benefits provided to different areas. Cyclodextrins are non-toxic oligosaccharides that are well known for their host–guest chemistry, low prices, and negligible environmental impact. Therefore, they have been widely used as chiral selectors and delivery systems in the pharmaceutical and food industry over time. However, their use for extraction purposes is hampered by their high solubility in water. This difficulty is being overcome with a variety of investigations in materials science. The setting-up of novel solid sorbents with improved properties thanks to the presence of cyclodextrins at their structure is still an open research area. Some properties they can offer, such as an increased selectivity or a good distribution along the surface of a solid support, which provides better accessibility for guest molecules, are characteristics of great interest. This systematic review reports the most significant uses of cyclodextrins for the adsorption of pollutants in different-origin samples based on the works reported in the literature in the last years. The study has been carried out indistinctly for quantitation and remediation purposes.

Dual‐Functioning Molecular Carrier of Superoxide Radicals for Stable and Efficient Lithium–Oxygen Batteries

AbstractLow round‐trip efficiency and poor cycle stability remain the major challenges associated with lithium–oxygen (Li–O2) batteries. These issues are primarily triggered by or correlated to the radical species produced during the operation of Li–O2 cells, which lead to significant deterioration of the electrolytes and air electrodes. Regulation of the reactivity of these radical species would thus open up opportunities to suppress such side reactions. Herein, a dual‐functioning molecule that is capable of mitigating the reactivity of radical species produced in a Li–O2 cell by reversibly forming stable intermediate complex during both the discharge and charge processes is introduced. Specifically, 5,5‐dimethyl‐1‐pyrroline N‐oxide (DMPO) is exploited, which has been widely used as a chemical agent to detect oxygen radicals, to induce the reversible formation of an intermediate complex, DMPO–O2−, in the presence of superoxide radicals. It is demonstrated that DMPO mediates the O2−‐involved electrochemical reaction, leading to significant suppression of side reactions and a remarkably improved oxygen efficiency. Unexpectedly, it is also observed that upon charging, DMPO actively scavenges the superoxides from the surface of discharge products, thus substantially lowering the charging overpotential. The combined radical mediation and scavenging of superoxides result in cycle stability of a practical Li–O2 cell over 200 cycles with a specific capacity of 1000 mAh g−1. The findings indicate the importance of controlling the reactivity of radical species and suggest a new pathway toward the realization of stable and efficient Li–O2 batteries.

Numerical analysis of time-dependent inhibition kinetics: comparison between rat liver microsomes and rat hepatocyte data for mechanistic model fitting

Time-dependent inhibition (TDI) may confound drug interaction predictions. Recently, models were generated for an array of TDI kinetic schemes using numerical analysis of microsomal assays. Additionally, a distinct terminal inactivation step was identified for certain mechanism based inhibitors (MBI) following reversible metabolite intermediate complex (MIC) formation. Longer hepatocyte incubations potentially allow analysis of slow TDI and terminal inactivation. In the experiments presented here, we compared the quality of TDI parameterization by numerical analysis between hepatocyte and microsomal data. Rat liver microsomes (RLM), suspended rat hepatocytes (SRH) and sandwich-cultured rat hepatocytes (SCRH) were incubated with the prototypical CYP3A MBI troleandomycin and the substrate midazolam. Data from RLM provided a better model fit as compared to SRH. Increased CYP3A expression after dexamethasone (DEX) induction improved the fit for RLM and SRH. A novel sequential kinetic scheme, defining inhibitor metabolite production prior to MIC formation, improved the fit compared to direct MIC formation. Furthermore, terminal inactivation rate constants were parameterized for RLM and SRH samples with DEX-induced CYP3A. The low expression of CYP3A and experimental error in SCRH resulted in poor data for model fitting. Overall, RLM generated data better suited for elucidation of TDI mechanisms by numerical analysis.

Cyclodextrin-Based Nanosystems as Drug Carriers for Cancer Therapy.

Cyclodextrins have been of great interest as excellent candidates for fabricating versatile nano-drug delivery systems due to their commercial availability, easy functionalization, low immunogenicity, biocompatibility and safety. The possibility of reversible inclusion complex formation between cyclodextrins and various guest molecules in association with versatile exclusive properties of cyclodextrins offer a route towards the fabrication of highly sophisticated nanostructures with enormous potential for cancer treatment. The current review discusses important recent advances in the fabrication and development of cyclodextrin-based nanostructures for cancer therapy. Firstly, the formation of inclusion complexes between cyclodextrin derivatives and anticancer compounds, as well as their application, are summarized. Secondly, the cyclodextrins -based nanosystems including cyclodextrin-containing polymers, cyclodextrin-based supramolecular necklaces, which consist of polyrotaxanes and polypseudorotaxanes and cyclodextrin based hydrogels accompanied by their applications in cancer treatment are highlighted. In the end, the future perspective of this field is discussed. Numerous investigations in this area pave the way for the flourishing of the next generation of nano-therapeutics towards enhanced cancer therapy.

The chemical physics of sequential infiltration synthesis-A thermodynamic and kinetic perspective.

Sequential infiltration synthesis (SIS) is an emerging materials growth method by which inorganic metal oxides are nucleated and grown within the free volume of polymers in association with chemical functional groups in the polymer. SIS enables the growth of novel polymer-inorganic hybrid materials, porous inorganic materials, and spatially templated nanoscale devices of relevance to a host of technological applications. Although SIS borrows from the precursors and equipment of atomic layer deposition (ALD), the chemistry and physics of SIS differ in important ways. These differences arise from the permeable three-dimensional distribution of functional groups in polymers in SIS, which contrast to the typically impermeable two-dimensional distribution of active sites on solid surfaces in ALD. In SIS, metal-organic vapor-phase precursors dissolve and diffuse into polymers and interact with these functional groups through reversible complex formation and/or irreversible chemical reactions. In this perspective, we describe the thermodynamics and kinetics of SIS and attempt to disentangle the tightly coupled physical and chemical processes that underlie this method. We discuss the various experimental, computational, and theoretical efforts that provide insight into SIS mechanisms and identify approaches that may fill out current gaps in knowledge and expand the utilization of SIS.

β-Cyclodextrin: A Green and Efficient Supramolecular Catalyst for Organic Transformations.

β-Cyclodextrin is cyclic oligosaccharide possessing hydrophobic cavity, which binds the substrates selectively and catalyze number of organic transformations with high selectivity. It catalyzes the reaction by non-covalent supramolecular bonding with reversible formation of host-guest complexes as seen in enzymes. This account summarizes our efforts in designing a good number of important organic transformations using β-cyclodextrin and its derivatives. These reactions were performed in neat, aqueous as well as organic media. Greener synthetic routes to a variety of biologically relevant organic molecules has been developed. The temperature, solvent and catalyst amount plays in important role in these reactions. β-Cyclodextrin activates variety of organic compounds like aldehydes, ketones, anhydride, oximes, amines, nitriles and increases the rate of reactions.

A novel chimaeric flocculation protein enhances flocculation in Saccharomyces cerevisiae

Yeast flocculation is the reversible formation of multicellular complexes mediated by lectin-like cell wall proteins binding to neighbouring cells. Strong flocculation can improve the inhibitor tolerance and fermentation performance of yeast cells in second generation bioethanol production. The strength of flocculation increases with the size of the flocculation protein and is strain dependent. However, the large number of internal repeats in the sequence of FLO1 from Saccharomyces cerevisiae S288c makes it difficult to recombinantly express the gene to its full length. In the search for novel flocculation genes resulting in strong flocculation, we discovered a DNA sequence, FLONF, that gives NewFlo phenotype flocculation in S. cerevisiae CEN.PK 113-7D. The nucleotide sequence of the internal repeats of FLONF differed from those of FLO1. We hypothesized that a chimaeric flocculation gene made up of a FLO1 variant derived from S. cerevisiae S288c and additional repeats from FLONF from S. cerevisiae CCUG 53310 would be more stable and easier to amplify by PCR. The constructed gene, FLOw, had 22 internal repeats compared to 18 in FLO1. Expression of FLOw in otherwise non-flocculating strains led to strong flocculation. Despite the length of the gene, the cassette containing FLOw could be easily amplified and transformed into yeast strains of different genetic background, leading to strong flocculation in all cases tested. The developed gene can be used as a self-immobilization technique or to obtain rapidly sedimenting cells for application in e.g. sequential batches without need for centrifugation.

Microwave-assisted synthesis of cyclopentadienone iron tricarbonyl complexes: molecular structures of [{\u03b74-C4R2C(O)C4H8}Fe(CO)3] (R\u2009=\u2009Ph, 2,4-F2C6H3, 4-MeOC6H4) and attempts to prepare Fe(II) hydroxycyclopentadienyl\u2013hydride complexes

Microwave irradiation of 1,6-diynes, RC≡C(CH2)4C≡CR, with Fe(CO)5 in dimethylether leads to the facile and clean formation of cyclopentadienone complexes [{η4-C4R2C(O)C4H8}Fe(CO)3] in good yields resulting from a [2 + 2 + 1] cycloaddition. The molecular structures of three examples (R = Ph, 2,4-F2C6H3, 4-MeOC6H4) have been obtained. The addition of HBF4 leads to the clean and reversible formation of cationic hydroxycyclopentadienyl complexes [{η5-C4R2C(OH)C4H8}Fe(CO)3][BF4]. Sequential addition of hydroxide and acid has also been carried out in an attempt to prepare hydroxycyclopentadienyl–hydride complexes. These were largely unsuccessful but in one case a Shvo-type complex with a bridging hydride was detected by 1H NMR spectroscopy. Reasons for the differing behaviour of [{η4-C4(SiMe3)2C(O)C4H8}Fe(CO)3] and the related aryl-functionalised derivatives are considered.Graphical Microwave irradiation of 1,6-diynes, RC≡C(CH2)4C≡CR, with Fe(CO)5 gives cyclopentadienone complexes [{η4-C4R2C(O)C4H8}Fe(CO)3], the molecular structures of three (R = Ph, 2,4-F2C6H3, 4-MeOC6H4) being carried out. Sequential addition of hydroxide and acid was carried out in an attempt to prepare hydroxycyclopentadienyl–hydride complexes, and while largely unsuccessful, in one case a Shvo-type complex with a bridging hydride was suggested by 1H NMR spectroscopy.

Sedimentation Boundary Structure of Multi-Component Solutions with Rapidly Reversible Interactions

The coupled transport behavior of macromolecular mixtures with rapidly reversible complex formation is of great interest in the study of protein interactions by many different methods. Complicated transport patterns arise even for simple bimolecular reactions, when all species exhibit different migration velocities, yet are coupled by mass action law. Although partial differential equations are available to describe the spatial and temporal evolution of such systems given particular initial conditions, these are often not useful to fit imperfect experimental data, and do not yield any insight into the transport mechanism and phase behavior of the systems in parameter space. For two-component systems, based on the limit of non-diffusing species migrating under constant force, we have previously derived simple algebraic relationships describing the number, amplitude, and velocity of sedimentation boundaries, which are consistent with the principle that the time-average velocity of all co-sedimenting components must match in each boundary. These can be considered ‘effective particles’, and their properties can be related to parameters extracted from experimental sedimentation profiles. Here, we generalize this effective particle theory to N-component systems. These can have N-2 reaction boundaries of successively lower velocity and number of components. We report algebraic relationships for velocities and composition. The concentration space is subdivided into regions exhibiting different boundary patterns with discontinuous transitions along characteristic subspaces. The extension of the effective particle theory provides physical insights into the coupled co-migration processes, and can be used to interpret boundary patterns derived from experimentally measured sedimentation coefficient distributions. It can be used to plan multi-component sedimentation velocity experiments to determine binding constants and complex stoichiometries.

Dynamic Coordination of Eu-Iminodiacetate to Control Fluorochromic Response of Polymer Hydrogels to Multistimuli.

New fluorochromic materials that reversibly change their emission properties in response to their environment are of interest for the development of sensors and light-emitting materials. A new design of Eu-containing polymer hydrogels showing fast self-healing and tunable fluorochromic properties in response to five different stimuli, including pH, temperature, metal ions, sonication, and force, is reported. The polymer hydrogels are fabricated using Eu-iminodiacetate (IDA) coordination in a hydrophilic poly(N,N-dimethylacrylamide) matrix. Dynamic metal-ligand coordination allows reversible formation and disruption of hydrogel networks under various stimuli which makes hydrogels self-healable and injectable. Such hydrogels show interesting switchable ON/OFF luminescence along with the sol-gel transition through the reversible formation and dissociation of Eu-IDA complexes upon various stimuli. It is demonstrated that Eu-containing hydrogels display fast and reversible mechanochromic response as well in hydrogels having interpenetrating polymer network. Those multistimuli responsive fluorochromic hydrogels illustrate a new pathway to make smart optical materials, particularly for biological sensors where multistimuli response is required.

Mechanistic Study of Arylsilane Oxidation through 19F NMR Spectroscopy.

The mechanism of the oxidation of arylsilanes to phenols has been investigated using 19F NMR spectroscopy. The formation of silanols in these reactions results from a rapid background equilibrium between silanol and alkoxysilane; the relative rates of reaction of these species was evaluated by modeling of concentration profiles obtained through 19F NMR spectroscopic reaction monitoring. Combining these results with a study of initial rates of phenol formation, and of substituent electronic effects, a mechanistic picture involving rapid and reversible formation of a pentavalent peroxide ate complex, prior to rate-limiting aryl migration, has evolved.

Thermoresponsive UCST‐Type Behavior of Interpolymer Complexes of Poly(ethylene glycol) and Poly(poly(ethylene glycol) methacrylate) Brushes with Poly(acrylic acid) in Isopropanol

Upper critical solution temperature (UCST)‐type thermoresponsive behavior of poly(ethylene glycol)–poly(acrylic acid) (PEG–PAA) and poly(poly(ethylene glycol) methacrylate)–poly(acrylic acid) (PPEGMA–PAA) interpolymer complexes has been observed in isopropanol. For these investigations, PPEGMA and PAA with various average molecular weights have been synthesized by atom transfer radical polymerization. It has been found that both the PEG and PPEGMA have lower cloud point temperatures (Tcp) than its mixed polymer solutions with PAA, whereas PAA does not show such behavior in the investigated temperature range. These findings indicate the reversible formation of interpolymer complexes with variable structure and composition in the solutions of the polymer mixtures in isopropanol. Increasing the ethylene glycol/acrylic acid molar ratio or the molecular weight of either the PAA or the H‐acceptor PEG component of the interpolymer complexes increases the UCST‐type cloud point temperatures of these interpolymer systems. The polymer–polymer interactions by hydrogen bonds between PAA and PEG or PPEGMA and the correlations between Tcp and structural parameters of the components revealed in the course of these investigations may be utilized for exploring well‐defined UCST‐type material systems for various applications. image