Kinetics and thermodynamics of amine and diamine signaling by a trifluoroacetyl azobenzene reporter group

Enlightening the Path to Protein Engineering: Chemoselective Turn-On Probes for High-Throughput Screening of Enzymatic Activity

Many successful stories in enzyme engineering are based on the creation of randomized diversity in large mutant libraries, containing millions to billions of enzyme variants. Methods that enabled their evaluation with high throughput are dominated by spectroscopic techniques due to their high speed and sensitivity. A large proportion of studies relies on fluorogenic substrates that mimic the chemical properties of the target or coupled enzymatic assays with an optical read-out that assesses the desired catalytic efficiency indirectly. The most reliable hits, however, are achieved by screening for conversions of the starting material to the desired product. For this purpose, functional group assays offer a general approach to achieve a fast, optical read-out. They use the chemoselectivity, differences in electronic and steric properties of various functional groups, to reduce the number of false-positive results and the analytical noise stemming from enzymatic background activities. This review summarizes the developments and use of functional group probes for chemoselective derivatizations, with a clear focus on screening for enzymatic activity in protein engineering.

Recent Advances in Chemodosimeters Designed for Amines

The analysis of amines has long been a very important task in science, industry, and healthcare. To date, this task has been accomplished by using expensive and time-consuming methods. Colorimetric and fluorescent chemodosimeters enable the fast, accurate, and sensitive analysis of various species with inexpensive instruments or the naked eye. Accordingly, the studies on these probes have gained great momentum in the last 20 years. In this review, amine chemodosimeters developed in the last 10 years were investigated. The investigated chemodosimeters are metal-free structures based on small organic compounds. The strategies for the detection, differentiation, and quantification of amines were discussed by considering the reaction types.

A reaction-based sensing scheme for volatile organic amine reagents with the chromophoric-fluorogenic dual mode

In this study, we present the classical Michael's addition reaction-based sensing scheme for volatile organic amine reagents such as ethylenediamine, N, N-dimethylethylenediamine and diethylenetriamine using a near-infrared fluorescent dye TCF1. Obvious spectral changes in the UV-vis absorption and fluorescence spectra of TCF1 were observed upon addition of these amine reagents with an effective catalyst DBU, resulting in significant and fast color changes detectable by the naked-eye. TCF1 showed an efficient response to these amine reagents with a low detection limit, especially for diethylenetriamine. NMR and MS spectral analysis proved that the mechanism of the detection was based on the classical Michael addition, which was also verified by the theoretical calculations. In addition, a portable test paper incorporated with TCF1 had also successfully realized the detection of a low concentration of these amine reagents.

Intramolecularly Cross-Linked Polymers: From Structure to Function with Applications as Artificial Antibodies and Artificial Enzymes

Cross-linking of polymers significantly alters their physical properties, greatly expanding their everyday utility. Indeed, the polymeric networks resulting from linkages between polymer chains are found in everyday materials from soft contact lenses and automobile tires to enamel coatings and high-performance adhesives. In contrast, intramolecularly cross-linked polymers have received far less attention until recent years, in large part because they are synthetically more challenging to prepare. In this Account, we trace our own efforts to develop the chemistry of intramolecularly cross-linked macromolecules, starting with dendrimers. Dendrimers provided an excellent starting point for investigating intramolecular cross-linking because they are single molecular entities. We showed that the end groups of dendrimers can be extensively cross-linked using the ring-closing metathesis reaction and that the discrete structure of the dendrimer provides unique opportunities for characterizing the number and location of the cross-links as well as some physical properties of the macromolecule such as its size and rigidity. Increasing the number of ring-closing metathesis reactions correlated with a reduction in size and an increase in rigidity. The general strategy applied to dendrimers was extended to star polymers and hyperbranched polyglycerols. Each of these macromolecules has a core or an initiating group from which the branches emanate. Linking the end groups or branches of these polymers presents a unique opportunity to chemically remove the core of the cross-linked macromolecule in a process that is reminiscent of that used to produce covalent molecular imprinted polymers. Recognizing this analogy, we sought a compelling application for cross-linked dendrimers, the first example of unimolecular imprinting, where a single polymer contains a single molecular imprint. The quality of the imprinting was mixed but pointed to an alternative general strategy for molecular imprinting in polymers. The effort also focused attention on synthetic antibodies and the general biomimicry provided by this class of macromolecules. Indeed, cross-linking of polymers either covalently or non-covalently bears a loose resemblance to folding of proteins into defined three-dimensional shapes. The synthesis and study of cross-linked linear polymers, often called single-chain nanoparticles (SCNPs), has emerged as a very active area of research in the past few years. Our experience with the cross-linking of branched polymers combined with an interest in performing organic synthesis within living cells led us to develop copper-containing SCNPs as artificial clickases. These polymeric clickases exhibit all of the hallmarks of enzymatic catalysis. One clickase containing a polyacrylamide backbone performs low-concentration copper-assisted alkyne-azide click reactions at unprecedented rates. Another performs click reactions within living cells. Other organic transformations can be performed intracellularly, and some of the most advanced SCNPs engage in concurrent and tandem catalysis with a naturally occurring biocatalyst. By tracing our own efforts, this Account provides a few entry points into the broader literature and also points to both the remaining challenges and overall promising future envisioned for this unique class of functional macromolecules.

Macroscopic helical chirality and self-motion of hierarchical self-assemblies induced by enantiomeric small molecules

Transfer of molecular chirality to supramolecular chirality at nanoscale and microscale by chemical self-assembly has been studied intensively for years. However, how such molecular chirality further transfers to the macroscale along the same path remains elusive. Here we reveal how the chirality from molecular level transfers to macroscopic level via self-assembly. We assemble a macrostripe using enantiomeric camphorsulfonic acid (CSA)-doped polyaniline with hierarchical order. The stripe can twist into a single-handed helical ribbon via helical self-motion. A multi-scale chemo-mechanical model is used to elucidate the mechanism underlying its chirality transfer and induction. The molecular origin of this macroscopic helical chirality is verified. Results provide a comprehensive understanding of hierarchical chirality transfer and helical motion in self-assembled materials and even their natural analogues. The stripe exhibits disparate actuation behaviour under stimuli of enantiomeric amines and integrating such chiral perception with helical self-motion may motivate chiral biomimetic studies of smart materials.

Chirality transfer by chemical self-assembly has been studied intensively for years but chirality transfers along the same path remains elusive. Here the authors use a multiscale chemo-mechanical model to elucidate the mechanism underlying the chirality transfer via self-assembly in hierarchical camphorsulfonic acid doped polyaniline.

Amine detection with distyrylbenzenedialdehyde-based Knoevenagel adducts

Eight acceptor-substituted distyrylbenzene (DSB) derivatives were obtained by postfunctionalization of dialdehyde precursor 1 using Knoevenagel condensation. Solubility in a water/THF 9:1 mixture was achieved through the addition of branched oligoethylene glycol side chains. The acceptor compounds discriminate primary and secondary amines in aqueous solution. The fluorescence responses were analyzed by the multivariate analysis of variance (MANOVA) protocol, a statistical tool. In contrast to 1, the adducts show reactivity toward secondary and aromatic amines. Nitroolefin 2f is the most active dosimeter molecule. Reaction with amines is completed after less than 3 min, and the limit of detection (LOD) is improved by a factor of 10. Propylenediamine can be detected at 75 μM. This is a 10-fold improvement for the detection limit when compared to the detection limit of the starting dialdehyde.

Detection of amines with extended distyrylbenzenes by strip assays

We herein describe the synthesis and property evaluation of three novel aldehyde-substituted pentameric phenylenevinylenes carrying branched oligo(ethylene glycol) (swallowtail, Sw) substituents. The targets were synthesized by a combination of Heck coupling and Wittig or Horner reactions of suitable precursor modules. If the pentameric phenylenevinylene carries only two of these Sw substituents, it is no longer water-soluble. When six of the Sw substituents are attached, regardless of their position, the pentameric phenylenevinylenes are well water-soluble. The dialdehydes were investigated with respect to their amine-sensing capabilities both in water as well as in the solid state, sprayed onto thin layer chromatography (TLC) plates (alox, silica gel, reversed phase silica gel). The recognition of amine vapors using the sprayed-on phenylenevinylene dialdehydes is superb and allows the identification of different amines on regular silica TLC plates via color changes, analyzed by a statistical tool, the multivariate analysis of variance (MANOVA) protocol.

Aldehyde-appended distyrylbenzenes: amine recognition in water

Change in water: Aqueous solutions of aldehyde-substituted, water-soluble distyrylbenzenes reacted with amines to give imines or aminals with dramatically changed fluorescence. This approach allowed the detection and recognition of amines in water (see figure).

Dynamic multi-component covalent assembly for the reversible binding of secondary alcohols and chirality sensing

Reversible covalent bonding is often employed for the creation of novel supramolecular structures, multi-component assemblies, and sensing ensembles. In spite of remarkable success of dynamic covalent systems, the reversible binding of a mono-alcohol with high strength is challenging. Here we show that a strategy of carbonyl activation and hemiaminal ether stabilization can be embodied in a four-component reversible assembly that creates a tetradentate ligand and incorporates secondary alcohols with exceptionally high affinity. Evidence is presented that the intermediate leading to binding and exchange of alcohols is an iminium ion. Further, to demonstrate the use of this assembly process we explored chirality sensing and enantiomeric excess determinations. An induced twist in the ligand by a chiral mono-ol results in large Cotton effects in the circular dichroism spectra indicative of the alcohol’s handedness. The strategy revealed in this study should prove broadly applicable for the incorporation of alcohols into supramolecular architecture construction.

Aldehyde cruciforms: dosimeters for primary and secondary amines

We demonstrate that aldehyde-substituted donor-acceptor cruciforms [1,4-bis(arylethynyl)-2,5-distyrylbenzenes] are useful dosimeters for primary amines, primary diamines, and secondary amines. The 1,n-diamines are particularly reactive towards this dosimeter and can be detected in less than 100 ppm concentration. Using a single aldehyde-functionalized cruciform in seven different solvents allowed us to discern fourteen different amines by digital photography and statistical evaluation of the response patterns extracted as red, green, blue (RGB) values.

Dynamic multicomponent hemiaminal assembly

A simple approach to generating in situ metal-templated tris-(2-picolyl)amine-like multicomponent assemblies with potential applications in molecular recognition and sensing is reported. The assembly is based on the reversible covalent association between di-(2-picolyl)amine and aldehydes. Zinc ion is best for inducing assembly among the metal salts investigated, whereas 2-picolinaldehyde is the best among the heterocyclic aldehydes studied. Although an equilibrium constant of 6.6×10(3) M(-1) was measured for the assembly formed by 2-picolinaldehdye, di-(2-picolyl)amine, and zinc triflate, the equilibrium constants for other systems are in the 10(2) M(-1) range. X-ray structural analysis revealed that zinc adopts trigonal-bipyramidal geometry within the assembled ligand. The diversity and equilibrium of the assemblies are readily altered by simply changing concentrations, varying components, or adding counteranions.

Molecular recognition of organic ammonium ions in solution using synthetic receptors

Ammonium ions are ubiquitous in chemistry and molecular biology. Considerable efforts have been undertaken to develop synthetic receptors for their selective molecular recognition. The type of host compounds for organic ammonium ion binding span a wide range from crown ethers to calixarenes to metal complexes. Typical intermolecular interactions are hydrogen bonds, electrostatic and cation-π interactions, hydrophobic interactions or reversible covalent bond formation. In this review we discuss the different classes of synthetic receptors for organic ammonium ion recognition and illustrate the scope and limitations of each class with selected examples from the recent literature. The molecular recognition of ammonium ions in amino acids is included and the enantioselective binding of chiral ammonium ions by synthetic receptors is also covered. In our conclusion we compare the strengths and weaknesses of the different types of ammonium ion receptors which may help to select the best approach for specific applications.

N-acyl triazenes as tunable and selective chemodosimeters toward cyanide ion

A novel type of chemodosimeters has been developed on the basis of a displacement reaction. N-Acyl-triazenes are found to be highly selective and tunable chemodosimeters toward cyanide. When N-acetyl-triazene 1a was titrated with various anions (-CN, F-, Cl-, AcO-, H2PO4-, -SCN, ClO4-, and HSO4-) in acetonitrile, significant absorption changes (from colorless to deep purple) resulted in the cases of -CN and F-, and small changes in the cases of AcO- and H2PO4-. N-Isopropanoyl-triazene 1b showed significant response only toward -CN, weaker response toward F-, and little response toward other anions in acetonitrile. Both of the triazenes 1a and 1b responded only to -CN in methanol-water, because of the analyte's strong nucleophilicity toward the acyl group and weak hydrogen-bonding ability as compared to other anions examined. The N-acyl-triazenes can be used for the naked eye detection of cyanide.

Functional liquid crystal films selectively recognize amine vapours and simultaneously change their colour

During recent years, cholesteric liquid crystals have found only a few applications, one of them being temperature detection; in this study, however, we intend to show that the combination of cholesteric liquid crystals and molecules with a trifluoroacetyl function can be applied to optically detect amine vapours.

Fluorescence modulation in anion sensing by introducing intramolecular H-bonding interactions in host–guest adducts

Fluorescence signaling in anion binding is modulated from quenching to enhancement by intramolecular H-bonding stabilization of anion-ionophore adducts; the intramolecular H-bonding is suggested to suppress the quenching processes otherwise possible and increase the conformational rigidity of the anionic adducts, leading to fluorescence enhancement in a selective fashion towards cyanide ion, among the various anions examined.

Molecular imprinting science and technology: a survey of the literature for the years up to and including 2003

Over 1450 references to original papers, reviews and monographs have herein been collected to document the development of molecular imprinting science and technology from the serendipitous discovery of Polyakov in 1931 to recent attempts to implement and understand the principles underlying the technique and its use in a range of application areas. In the presentation of the assembled references, a section presenting reviews and monographs covering the area is followed by papers dealing with fundamental aspects of molecular imprinting and the development of novel polymer formats. Thereafter, literature describing attempts to apply these polymeric materials to a range of application areas is presented.

Detection of Amines and Unprotected Amino Acids in Aqueous Conditions by Formation of Highly Fluorescent Iminium Ions

Properly substituted coumarin aldehydes can be used to detect amines and amino acids under neutral, high ionic strength conditions by the formation of highly fluorescent iminium ions. The fluorescence of one sensor increases by 26-fold upon the addition of glycine. This strong florescent response is attributed to hydrogen bonding of the chromophore carbonyl by the acidic iminium proton.

Molecular Recognition of Anions through Hydrogen Bonding Stabilization of Anion−Ionophore Adducts: A Novel Trifluoroacetophenone-Based Binding Motif

[reaction: see text] A novel trifluoroacetophenone-based binding motif has been developed that recognizes anions such as carboxylates through reversible formation of anion-ionophore adducts that are stabilized by intramolecular H-bonding. The intramolecular H-bonding resulted in more than 10-fold enhancement in the binding affinity and an enthalpy gain (DeltaH degrees ) of 3.0 kcal/mol for the binding of an acetate ion when compared to the case without the intramolecular H-bonding.