1,2,4‐Triazine‐Modified 2′‐Deoxyuridine Triphosphate for Efficient Bioorthogonal Fluorescent Labeling of DNA

In order to establish the Diels–Alder reaction with inverse electron demand for postsynthetic DNA modification, a 1,2,4‐triazine‐modified 2′‐deoxyuridine triphosphate was synthesized. The bioorthogonally reactive 1,2,4‐triazine group was attached at the 5‐position of 2′‐deoxyuridine by a flexible alkyl linker to facilitate its acceptance by DNA polymerases. The screening of four DNA polymerases showed successful primer extensions, using a mixture of dATP, dGTP, dCTP, and the modified 2′‐deoxyuridine triphosphate, by using KOD XL or Vent polymerase. The triazine moiety was stable under the conditions of primer extension, which was evidenced by labeling with a BCN‐modified rhodamine at room temperature in yields of up to 82 %. Two or three modified bases could be incorporated in quantitative yields when the modification sites were separated by three base pairs. These results establish the 1,2,4‐triazene group as a bioorthogonally reactive moiety in DNA, thereby replacing the problematic 1,2,4,5‐tetrazine for postsynthetic labeling by the Diels–Alder reaction with inverse electron demand.     

Functional Modification of Fibronectin by N‐Terminal FXIIIa‐Mediated Transamidation

A straightforward strategy is presented for the site‐specific incorporation of fluorophores or reactive probes into the extracellular matrix (ECM) protein fibronectin (Fn) by using the enzyme‐catalyzed transamidation by activated factor XIII. Characterization by SDS‐PAGE, western blotting, absorption measurements, mass spectrometry, and stepwise photobleaching for labeling quantification at the single‐molecule level showed that the labeling was efficient and restricted to the N‐terminal tails. The introduction of labels did not interfere with Fn fibrillogenesis, as verified by the incorporation of fluorescently labeled Fn into ECM and manually pulled Fn fibers. Site‐specific incorporation of an azide was used to create a template for bioorthogonal click chemistry reactions in a second bioconjugation step, thus offering versatile modification and application possibilities in the context of matrix biology and tissue engineering.     

Current Approaches for RNA Labeling in Vitro and in Cells Based on Click Reactions

Over recent years, click reactions have become recognized as valuable and flexible tools to label biomacromolecules such as proteins, nucleic acids, and glycans. Some of the developed strategies can be performed not only in aqueous solution but also in the presence of cellular components, as well as on (or even in) living cells. These labeling strategies require the initial, specific modification of the target molecule with a small, reactive moiety. In the second step, a click reaction is used to covalently couple a reporter molecule to the biomolecule. Depending on the type of reporter, labeling by the click reaction can be used in many different applications, ranging from isolation to functional studies of biomacromolecules. In this minireview, we focus on labeling strategies for RNA that rely on the click reaction. We first highlight click reactions that have been used successfully to label modified RNA, and then describe different strategies to introduce the required reactive groups into target RNA. The benefits and potential limitations of the strategies are critically discussed with regard to possible future developments.     

Trifunctional Saxitoxin Conjugates for Covalent Labeling of Voltage-Gated Sodium Channels**

Voltage-gated sodium ion channels (Na_Vs) are integral membrane protein complexes responsible for electrical signal conduction in excitable cells. Methods that enable selective labeling of Na_Vs hold potential value for understanding how channel regulation and post-translational modification are influenced during development and in response to diseases and disorders of the nervous system. We have developed chemical reagents patterned after (+)-saxitoxin (STX) – a potent and reversible inhibitor of multiple Na_V isoforms – and affixed with a reactive electrophile and either a biotin cofactor, fluorophore, or ‘click’ functional group for labeling wild-type channels. Our studies reveal enigmatic structural effects of the probes on the potency and efficiency of covalent protein modification. Among the compounds analyzed, a STX-maleimide-coumarin derivative is most effective at irreversibly blocking Na⁺ conductance when applied to recombinant Na_Vs and endogenous channels expressed in hippocampal neurons. Mechanistic analysis supports the conclusion that high-affinity toxin binding is a prerequisite for covalent protein modification. Results from these studies are guiding the development of next-generation tool compounds for selective modification of Na_Vs expressed in the plasma membranes of cells.     

Traceless affinity labeling of endogenous proteins for functional analysis in living cells

Protein labeling and imaging techniques have provided tremendous opportunities to study the structure, function, dynamics, and localization of individual proteins in the complex environment of living cells. Molecular biology-based approaches, such as GFP-fusion tags and monoclonal antibodies, have served as important tools for the visualization of individual proteins in cells. Although these techniques continue to be valuable for live cell imaging, they have a number of limitations that have only been addressed by recent progress in chemistry-based approaches. These chemical approaches benefit greatly from the smaller probe sizes that should result in fewer perturbations to proteins and to biological systems as a whole. Despite the research in this area, so far none of these labeling techniques permit labeling and imaging of selected endogenous proteins in living cells. Researchers have widely used affinity labeling, in which the protein of interest is labeled by a reactive group attached to a ligand, to identify and characterize proteins. Since the first report of affinity labeling in the early 1960s, efforts to fine-tune the chemical structures of both the reactive group and ligand have led to protein labeling with excellent target selectivity in the whole proteome of living cells. Although the chemical probes used for affinity labeling generally inactivate target proteins, this strategy holds promise as a valuable tool for the labeling and imaging of endogenous proteins in living cells and by extension in living animals. In this Account, we summarize traceless affinity labeling, a technique explored mainly in our laboratory. In our overview of the different labeling techniques, we emphasize the challenge of designing chemical probes that allow for dissociation of the affinity module (often a ligand) after the labeling reaction so that the labeled protein retains its native function. This feature distinguishes the traceless labeling approach from the traditional affinity labeling method and allows for real-time monitoring of protein activity. With the high target specificity and biocompatibility of this technique, we have achieved individual labeling and imaging of endogenously expressed proteins in samples of high biological complexity. We also highlight applications in which our current approach enabled the monitoring of important biological events, such as ligand binding, in living cells. These novel chemical labeling techniques are expected to provide a molecular toolbox for studying a wide variety of proteins and beyond in living cells.     

An Azide‐Modified Nucleoside for Metabolic Labeling of DNA

Metabolic incorporation of azido nucleoside analogues into living cells can enable sensitive detection of DNA replication through copper(I)‐catalyzed azide–alkyne cycloaddition (CuAAC) and strain‐promoted azide–alkyne cycloaddition (SPAAC) “click” reactions. One major limitation to this approach is the poor chemical stability of nucleoside derivatives containing an aryl azide group. For example, 5‐azido‐2′‐deoxyuridine (AdU) exhibits a 4 h half‐life in water, and it gives little or no detectable labeling of cellular DNA. In contrast, the benzylic azide 5‐(azidomethyl)‐2′‐deoxyuridine (AmdU) is stable in solution at 37 °C, and it gives robust labeling of cellular DNA upon addition of fluorescent alkyne derivatives. In addition to providing the first examples of metabolic incorporation into and imaging of azide groups in cellular DNA, these results highlight the general importance of assessing azide group stability in bioorthogonal chemical reporter strategies.     

Parameters affecting the chain extension and branching of PET in the melt state by polyepoxides

This article describes the chemical modification of polyethylene terephthalate (PET) with a variety of compounds containing reactive glycidyl group(s). Four different modifiers, namely, diglycidyl ether of bisphenol‐A (DGEBA), N,N′‐bis[3(carbo‐2′,3′‐epoxypropoxy) phenyl] pyromellitimide (BGPM), triglycidyl glycerol (TGG), and triglycidyl isocyanurate (TGIC) were compared for their reactivity toward PET in the melt phase. It was found that the presence of tertiary nitrogen in the structure of the epoxide modifiers plays the role of in‐built catalyst for their reaction with the end groups of PET. TGIC as a modifier was selected for the detailed investigation of the simultaneously occurring degradation and chain extension/branching reactions in a batch‐melt mixer. The reactions were followed by torque changes, analyzing the products for residual carboxyl content, and by determining insoluble content. It is shown that the rate of the reactive modification of PET melt by TGIC depends upon stoichiometry, temperature, rate of shear, and the chemical composition and the molecular weight (MW) of the PET resin. In general, the results indicate an increase in melt viscosity and insoluble content, whereas an overall decrease in carboxyl content occurs, as defined by the choice of mixing conditions and stoichiometry. Analysis of the batch kinetic data can be useful to define the process requirements for carrying out the reactive modification in continuous extrusion equipment. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 643–652, 2003     

A "tag-and-modify" approach to site-selective protein modification

Covalent modification can expand a protein's functional capacity. Fluorescent or radioactive labeling, for instance, allows imaging of a protein in real time. Labeling with an affinity probe enables isolation of target proteins and other interacting molecules. At the other end of this functional spectrum, protein structures can be naturally altered by enzymatic action. Protein-protein interactions, genetic regulation, and a range of cellular processes are under the purview of these post-translational modifications. The ability of protein chemists to install these covalent additions selectively has been critical for elucidating their roles in biology. Frequently the transformations must be applied in a site-specific manner, which demands the most selective chemistry. In this Account, we discuss the development and application of such chemistry in our laboratory. A centerpiece of our strategy is a "tag-and-modify" approach, which entails sequential installation of a uniquely reactive chemical group into the protein (the "tag") and the selective or specific modification of this group. The chemical tag can be a natural or unnatural amino acid residue. Of the natural residues, cysteine is the most widely used as a tag. Early work in our program focused on selective disulfide formation in the synthesis of glycoproteins. For certain applications, the susceptibility of disulfides to reduction was a limitation and prompted the development of several methods for the synthesis of more stable thioether modifications. The desulfurization of disulfides and conjugate addition to dehydroalanine are two routes to these modifications. The dehydroalanine tag has since proven useful as a general precursor to many modifications after conjugate addition of various nucleophiles; phosphorylated, glycosylated, peptidylated, prenylated, and even mimics of methylated and acetylated lysine-containing proteins are all accessible from dehydroalanine. While cysteine is a useful tag for selective modification, unnatural residues present the opportunity for bio-orthogonal chemistry. Azide-, arylhalide-, alkyne-, and alkene-containing amino acids can be incorporated into proteins genetically and can be specifically modified through various transformations. These transformations often rely on metal catalysis. The Cu-catalyzed azide-alkyne addition, Ru-catalyzed olefin metathesis, and Pd-catalyzed cross-coupling are examples of such transformations. In the course of adapting these reactions to protein modification, we learned much about the behavior of these reactions in water, and in some cases entirely new catalysts were developed. Through a combination of these bio-orthogonal transformations from the panel of tag-and-modify reactions, multiple and distinct modifications can be installed on protein surfaces. Multiple modifications are common in natural systems, and synthetic access to these proteins has enabled study of their biological role. Throughout these investigations, much has been learned in chemistry and biology. The demands of selective protein modification have revealed many aspects of reaction mechanisms, which in turn have guided the design of reagents and catalysts that allow their successful deployment in water and in biological milieu. With this ability to modify proteins, it is now possible to interrogate biological systems with precision that was not previously possible.     

Irreversible Protein Labeling by Paal–Knorr Conjugation

The application of new chemical reactions in a biological context has advanced bioconjugation methods for both fundamental research and commercial arenas. Recent adaptations of reactions such as Huisgen 1,3‐dipolar or Diels–Alder cycloadditions have enabled the labeling of specific residues in biomolecules by the attachment of molecules carrying azides, alkynes, or strained alkenes. Although these are fundamental tools, there is a need for the discovery of reactions that can label native proteins. We report herein the adaptation of the Paal–Knorr reaction to label lysine residues in proteins via pyrrole linkages.     

Biosynthetic Labeling and Two‐Color Imaging of Phospholipids in Cells

Phospholipids with a choline head group are abundant components of all biological membranes, performing critical functions in cellular structure, metabolism, and signaling. In spite of their importance, our ability to visualize choline phospholipids in vivo remains very limited. We present a simple and robust chemical strategy to image choline phospholipids, based on the metabolic incorporation of azidocholine analogues, that accurately reflects the normal biosynthetic incorporation of choline into cellular phospholipids. Azidocholine‐labeled phospholipids can be imaged in cells with high sensitivity and resolution, following derivatization with fluorophores, by bio‐orthogonal chemical reactions compatible with live‐cell imaging. We used this method to visualize the subcellular localization of choline phospholipids. We also demonstrate that double metabolic labeling with azidocholine and propargylcholine allows sensitive two‐color imaging of choline phospholipids. Our method represents a powerful approach to directly image phospholipids, and to study their dynamics in cells and tissues.     

Chemical toughening of epoxies. I. Structural modification of epoxy resins by reaction with hydroxy-terminated poly(butadiene-co-acrylonitrile)

In an attempt to toughen the epoxy resin matrix for fiber-reinforced composite applications, a chemical modification procedure of a commercially available bisphenol-A-based epoxy resin using reactive liquid rubber HTBN [hydroxy-terminated poly(butadiene-co-acrylonitrile)] and TDI (tolylene diisocyanate) is described. The progress of the reaction and the structural changes during modification process are studied using IR spectroscopy, viscosity data, and chemical analysis (epoxy value determination). The studies support the proposition that TDI acts as a coupling agent between the epoxy and HTBN, forming a urethane linkage with the former and an oxazolidone ring with the latter. The chemical reactions that possibly take place during the modification are discussed.     

From mechanism to mouse: a tale of two bioorthogonal reactions

Bioorthogonal reactions are chemical reactions that neither interact with nor interfere with a biological system. The participating functional groups must be inert to biological moieties, must selectively reactive with each other under biocompatible conditions, and, for in vivo applications, must be nontoxic to cells and organisms. Additionally, it is helpful if one reactive group is small and therefore minimally perturbing of a biomolecule into which it has been introduced either chemically or biosynthetically. Examples from the past decade suggest that a promising strategy for bioorthogonal reaction development begins with an analysis of functional group and reactivity space outside those defined by Nature. Issues such as stability of reactants and products (particularly in water), kinetics, and unwanted side reactivity with biofunctionalities must be addressed, ideally guided by detailed mechanistic studies. Finally, the reaction must be tested in a variety of environments, escalating from aqueous media to biomolecule solutions to cultured cells and, for the most optimized transformations, to live organisms. Work in our laboratory led to the development of two bioorthogonal transformations that exploit the azide as a small, abiotic, and bioinert reaction partner: the Staudinger ligation and strain-promoted azide-alkyne cycloaddition. The Staudinger ligation is based on the classic Staudinger reduction of azides with triarylphosphines first reported in 1919. In the ligation reaction, the intermediate aza-ylide undergoes intramolecular reaction with an ester, forming an amide bond faster than aza-ylide hydrolysis would otherwise occur in water. The Staudinger ligation is highly selective and reliably forms its product in environs as demanding as live mice. However, the Staudinger ligation has some liabilities, such as the propensity of phosphine reagents to undergo air oxidation and the relatively slow kinetics of the reaction. The Staudinger ligation takes advantage of the electrophilicity of the azide; however, the azide can also participate in cycloaddition reactions. In 1961, Wittig and Krebs noted that the strained, cyclic alkyne cyclooctyne reacts violently when combined neat with phenyl azide, forming a triazole product by 1,3-dipolar cycloaddition. This observation stood in stark contrast to the slow kinetics associated with 1,3-dipolar cycloaddition of azides with unstrained, linear alkynes, the conventional Huisgen process. Notably, the reaction of azides with terminal alkynes can be accelerated dramatically by copper catalysis (this highly popular Cu-catalyzed azide-alkyne cycloaddition (CuAAC) is a quintessential "click" reaction). However, the copper catalysts are too cytotoxic for long-term exposure with live cells or organisms. Thus, for applications of bioorthogonal chemistry in living systems, we built upon Wittig and Krebs' observation with the design of cyclooctyne reagents that react rapidly and selectively with biomolecule-associated azides. This strain-promoted azide-alkyne cycloaddition is often referred to as "Cu-free click chemistry". Mechanistic and theoretical studies inspired the design of a series of cyclooctyne compounds bearing fluorine substituents, fused rings, and judiciously situated heteroatoms, with the goals of optimizing azide cycloaddition kinetics, stability, solubility, and pharmacokinetic properties. Cyclooctyne reagents have now been used for labeling azide-modified biomolecules on cultured cells and in live Caenorhabditis elegans, zebrafish, and mice. As this special issue testifies, the field of bioorthogonal chemistry is firmly established as a challenging frontier of reaction methodology and an important new instrument for biological discovery. The above reactions, as well as several newcomers with bioorthogonal attributes, have enabled the high-precision chemical modification of biomolecules in vitro, as well as real-time visualization of molecules and processes in cells and live organisms. The consequence is an impressive body of new knowledge and technology, amassed using a relatively small bioorthogonal reaction compendium. Expansion of this toolkit, an effort that is already well underway, is an important objective for chemists and biologists alike.     

Investigations on the reactive surface modification of polycarbonate by surface‐reactive injection molding

A new procedure of surface modification was investigated in which the modification was coupled with the injection molding process. This procedure could save other commonly used surface modification procedures such as flame or plasma treatment. According to the procedure, a reactive modifier was applied to the surface of the mold cavity. On injection of the plastic melt, a chemical reaction took place, which attaches the modifier covalently to the resultant plastic part. In this contribution, conditions are considered for the modification of polycarbonate with poly(vinyl alcohol) and polyethylenimine as modifiers. The reaction in the melt was investigated and the modified surfaces of injection‐molded plates were characterized. The surface modification, realized with the new approach, was permanent. It allows for the introduction of special functional groups, which may be useful for further reactive processing stages such as reactive adhesive joining, reactive coating, metallization, or functionalization for special applications. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1186–1191, 2004     

Optimization of Caged Electrophiles for Improved Monitoring of Cysteine Reactivity in Living Cells

Cysteine residues play critical roles in protein function and are susceptible to numerous post‐translational modifications (PTMs) that serve to modulate the activity and localization of diverse proteins. Many of these PTMs are highly transient and labile, thus necessitating methods to study these modifications directly within the context of living cells. We previously reported a caged electrophilic probe, CBK1, that can be activated by UV for temporally controlled covalent modification of cysteine residues in living cells. To improve upon the number of cysteine residues identified in cellular cysteine‐profiling studies, the reactivity and uncaging efficiency of a panel of caged electrophiles were explored. We identified an optimized caged electrophilic probe, CIK4, that affords significantly improved coverage of cellular cysteine residues. The broader proteome coverage afforded by CIK4 renders it a useful tool for the biological investigation of cysteine‐reactivity changes and PTMs directly within living cells and highlights design elements that are critical to optimizing photoactivatable chemical probes for cellular labeling.     

Biomedical applications of tetrazine cycloadditions

Disease mechanisms are increasingly being resolved at the molecular level. Biomedical success at this scale creates synthetic opportunities for combining specifically designed orthogonal reactions in applications such as imaging, diagnostics, and therapy. For practical reasons, it would be helpful if bioorthogonal coupling reactions proceeded with extremely rapid kinetics (k > 10(3) M(-1) s(-1)) and high specificity. Improving kinetics would minimize both the time and amount of labeling agent required to maintain high coupling yields. In this Account, we discuss our recent efforts to design extremely rapid bioorthogonal coupling reactions between tetrazines and strained alkenes. These selective reactions were first used to covalently couple conjugated tetrazine near-infrared-emitting fluorophores to dienophile-modifed extracellular proteins on living cancer cells. Confocal fluorescence microscopy demonstrated efficient and selective labeling, and control experiments showed minimal background fluorescence. Multistep techniques were optimized to work with nanomolar concentrations of labeling agent over a time scale of minutes: the result was successful real-time imaging of covalent modification. We subsequently discovered fluorogenic probes that increase in fluorescence intensity after the chemical reaction, leading to an improved signal-to-background ratio. Fluorogenic probes were used for intracellular imaging of dienophiles. We further developed strategies to react and image chemotherapeutics, such as trans-cyclooctene taxol analogues, inside living cells. Because the coupling partners are small molecules (<300 Da), they offer unique steric advantages in multistep amplification. We also describe recent success in using tetrazine reactions to label biomarkers on cells with magneto-fluorescent nanoparticles. Two-step protocols that use bioorthogonal chemistry can significantly amplify signals over both one-step labeling procedures as well as two-step procedures that use more sterically hindered biotin-avidin interactions. Nanoparticles can be detected with fluorescence or magnetic resonance techniques. These strategies are now being routinely used on clinical samples for biomarker profiling to predict malignancy and patient outcome. Finally, we discuss recent results with tetrazine reactions used for in vivo molecular imaging applications. Rapid tetrazine cycloadditions allow modular labeling of small molecules with the most commonly used positron emission tomography isotope, (18)F. Additionally, recent work has applied this reaction directly in vivo for the pretargeted imaging of solid tumors. Future work with tetrazine cycloadditions will undoubtedly lead to optimized protocols, improved probes, and additional biomedical applications.     

Interphase effects in polymer-modified hydraulic cements

Earlier work has indicated the importance of interphase adhesion within these systems. The work here reported shows that, with reactive polymers, substantial chemical modification occurs at the surface of the polymer latex particle. With certain polymer types, such as polyethylene and polystyrene homopolymers, no evidence is found of such reactions; with others, such as poly(vinylidene chloride, vinyl chloride) and poly(ethyl acrylate, methyl methacrylate), substantial reaction occurs. Crosslinking and insolubilization frequently accompany these reactions, and the nature of the polymer is significantly altered.     

Chemical modification of poly(2,6-dimethyl-1,4-phenylene oxide) via phase transfer catalysis

The chemical modification of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) has been performed under phase transfer catalyzed (PTC) conditions. Four types of reactions: Williamson etherification, cyanide displacement, esterification, and heterocyclic group transfer have been identified as positive reactions involving the nucleophilic displacement on PPO. In reaction with alcohols, under PTC conditions, functional yields as high as 100% were obtained while for the esterification reaction functional yields of 92% were reached. Low conversions were found in reactions with cyanides and heterocylic compounds. Possible interactions of the reactive sites leading to additional crosslinking are being suggested. Minor changes in thermal stability of substituted PPO compared with the parent polymer were recorded. The modification of their permeation properties to gases was attributed to changes in polymer chain mobility and packing as well as to changes in polymer side chain polarity.     

Identification of rheological and structural characteristics of foamable poly(ethylene terephthalate) by reactive extrusion

The reactivity and efficiency of five low molecular weight multifunctional anhydride and epoxy compounds as chemical modifiers of a bottle grade poly(ethylene terephthalate) (PET) resin were evaluated by reactive extrusion under controlled conditions. The two dianhydrides and the three epoxy compounds were used at concentrations based on stoichiometry derived from the measured carboxyl and hydroxyl end group contents of the base resin. Measures of melt viscosity, melt strength, intrinsic viscosity and carboxyl group content were used as criteria of the extent of the modification. Correlations of die pressure with extrudate swell during extrusion, and melt flow index (MFI) with melt strength by off‐line testing of the extrudates permitted the ranking of the modifiers according to their chain‐extending/branching efficiency. For some systems molecular weight increases (related to die pressure/MFI/intrinsic viscosity) accompanied by broadening of the molecular weight distribution (related to die swell/melt strength) were considered excessive. Extrusion foaming experiments with one particular dianhydride modifier that increased the intrinsic viscosity of the resin from 0.71 to 0.9 dl g^?1 indicate that production of low‐density foams by a process involving one‐step reactive modification/gas injection foaming is feasible, at conditions not significantly different from those employed in the simple reactive modification of the PET resin. The rheological and structural parameters determined in this work may be used as criteria to specify PET foamable compositions in terms of types and concentrations of modifiers. Copyright © 2004 Society of Chemical Industry     

Transglutaminase-mediated N- and C-terminal fluorescein labeling of a protein can support the native activity of the modified protein

Fluorescein and its analogs are among the best fluorophores to label proteins and the labeling generally involves chemical modification of a translated protein. Using this methodology, labeling at a specific position remains difficult. It is known that the guinea pig liver transglutaminase (TGase)-catalyzed enzymatic modification method can allow terminal-specific fluorophore labeling of a protein by monodansylcadaverine. However, native activity of the fluorescent protein has not been investigated so far, nor has direct comparison between the chemical modification and the TGase-catalyzed modification been attempted. Therefore, we compared the possibility of fluorescein labeling via chemical labeling and via TGase-catalyzed modification. The latter method was found to be very practical and overcame some of the problems associated with the specificity of the former; fluorescein was covalently attached only to the N- or C-terminal site of glutathione S-transferase when the reaction was catalyzed by TGase and the resulting labeled protein completely retained its native activity. The TGase-mediated labeling occurred not only at room temperature but also at 4 degrees C to the same extent, which is more desirable for preventing the inactivation of proteins.     

Model Optimization for the Dynamic Simulation of Reactive Absorption Processes

The optimal design of reactive separations is impossible without reliable process models. Especially for the dynamic simulation and the model‐based control of complex reactive absorption processes the model development leads to a contradiction between the required model accuracy to reflect the process complexity and the feasibility of process simulations regarding the computation time. In this respect, we have developed a new rigorous dynamic two‐phase model based on the two‐film theory as a first step, which takes into account the influence of chemical reactions and additional driving forces in electrolyte systems on mass transfer considering thermodynamic nonidealities as well as the impact of column internals on the process hydrodynamics. For a model optimization, we have performed an analysis of different model approaches for complicated industrial absorption processes and determined an appropriate model complexity. Based on results of sensitivity studies, we have accomplished different model modifications leading to a stabilization of the numerical solution without affecting the good agreement between simulation results and the experimental data. This time‐optimized model can be considered superior as compared to previous approaches and facilitates for the first time a rigorous dynamic simulation of entire reactive absorption columns and the application within an on‐line process control system.