Search

Spectrally discriminating CH 3 OH and CD 3 OD, and even detecting CH 3 OH contents in the CD 3 OD solvent, are important yet have not been achieved so far, likely owing to their very similar chemical/physical properties. Herein, dynamic transesterification reactions, which can be achieved via two-step proton transfers, can be signaled via ultraviolet UV-visible (UV/vis) absorption and fluorescence spectroscopies under mild experimental conditions. Introduction of strong electron-withdrawing groups, such as -NO 2 , to the aromatic ring (benzoic acid moiety or phenol moiety) of carboxylate esters to activate the esters is important for transesterification reactions and is an intriguing method for modulating the selectivity of the spectral response. The rate constant of the transesterification reaction enhanced with increasing the total number of strong electron-withdrawing groups. Furthermore, the rate constants of esters in which substituent(s) are connected to the phenol moiety are higher than those of corresponding esters in which substituent(s) are connected to the benzoic acid moiety. In transesterification systems, added aliphatic amines mainly play two roles: (i) lowering the energy barrier of the first transesterification step via the formation of intermolecular hydrogen bonding in ternary systems and (ii) deprotonating the released 4-nitrophenol in UV/vis absorption spectral systems to generate an UV/vis absorption spectral signal reporter, i.e., nitrophenolate anions. As a result of the methanol-mediated transesterification reaction, spectral-sensing systems can be established for discriminating CH 3 OH and CD 3 OD and even detecting low CH 3 OH contents in the CD 3 OD solvent, owing to the kinetic isotope effect. This is the first example of spectral recognition between CD 3 OD and CH 3 OH.

To realize strong donor-acceptor face-to-face stacking for efficient through-space charge transfer-type thermally activated delayed fluorescence, a conceptually new design strategy is proposed to couple flexible bridges with adequate rigidity via built-in intramolecular hydrogen bonds (IHBs). The resulting emitter ACE-CN has a planarized benzyl methyl ether bridge self-anchored by the C-H···O IHB and shows a high photoluminescence quantum efficiency of 93%. The solution- and vacuum-processed devices exhibited high external quantum efficiencies of 11.8% and 24.7%, respectively.

A facile synthesis of a binuclear Ag I complex 2 of a bis(carbone) ligand L and its application as a carbone-transfer agent for the generation of other transition-metal complexes of Au I ( 3 ), Ni II ( 4 ), and Pd II ( 5 ) is presented. Complex 2 was synthesized through multiple synthetic routes under mild reaction conditions using the tetracationic [ L H 4 ][OTf·Cl] 2 precursor salt, the dicationic [ L H 2 ][OTf] 2 ylide salt, and the free ligand L . The first two synthesis routes require no prior isolation of the air-, moisture-, and temperature-sensitive free ligand L , thus affording complex 2 with high yield and purity. Multinuclear NMR techniques, high-resolution mass spectrometry, and single-crystal X-ray diffraction analysis confirmed the identity of complex 2 as a binuclear Ag I complex of L with a molecular formula of [ L 2 Ag 2 ][OTf] 2 and a 16-membered-ring metallomacrocyclic structure. During the transmetalation reaction with Au I , the binuclear nature of complex 2 remains intact to give analogous complex 3 ([ L 2 Au 2 ][OTf] 2 ). However, the dimeric structure was disrupted upon the carbone-transfer reaction with Ni II and Pd II , yielding mononuclear C-N-C pincer-type complexes 4 ([ L NiCl][OTf]) and 5 ([ L PdCl][OTf]), respectively. These results demonstrated the versatile use of complex 2 as a carbone-transfer agent to other transition metals regardless of the type or size of the metals or the geometry they prefer.

We have described the chemical synthesis of d-Sortase A in large quantity and high purity by a hydrazide ligation strategy. The d-Sortase was fully active toward d-peptides and D/L hybrid proteins, and the ligation efficiency was unaffected by the chirality of the C-terminus substrate. This study points toward using d-sortase ligation as a modern ligation method for d-proteins and D/L hybrid proteins and expands the chemical protein synthesis toolbox in biotechnology.

The introduction of signal amplification to molecular spectral sensing systems is an intriguing topic in supramolecular analytical chemistry. In this study, click chemistry was used to generate a triazole moiety to bridge with a long hydrophobic alkyl chain (C n ) and another short alkyl chain (C m ) bearing a 1,4,7-triazacyclonane (TACN) group for efficiently generating a self-assembling multivalent catalyst, C n -triazole-C m -TACN·Zn 2+ ( n and m represent the carbon numbers of both alkyl chains, respectively; n = 16, 18, and 20; m = 2 and 6), to catalyze the hydrolysis of 2-hydroxypropyl-4-nitrophenyl phosphate (HPNPP) when Zn 2+ was added. The triazole moiety introduced adjacent to the TACN group plays an important role in improving the selectivity of Zn 2+ because the triazole moiety can participate in the coordination interaction between the Zn 2+ and neighboring TACN group. The supplementary triazole complexing increases the space requirement for coordinated metal ions. This catalytic sensing system also shows high sensitivity, with a favorable limit of detection down to 350 nM, even if only UV-vis absorption spectra rather than more sensitive fluorescence techniques were used for signaling, and can be used to determine the concentration of Zn 2+ in tap water, which demonstrates the practical application feasibility.

The mechanochemical cascade reaction of [60]fullerene with 3-benzylidene succinimides, diethyl 2-benzylidene succinate, or 2-benzylidene succinonitrile in the presence of an inorganic base has been investigated under solvent-free and ball-milling conditions. This protocol provides an expedient method to afford various [60]fullerene-fused cyclopentanes, showing advantages of good substrate scope, short reaction time, and solvent-free and ambient reaction conditions. Furthermore, representative fullerene products have been applied in inverted planar perovskite solar cells as efficient cathode interlayers.

How to distinguish D 2 O and H 2 O and determine the trace H 2 O content in D 2 O solvent, by using molecule-based spectral probes, is an intriguing topic in analytical chemistry, yet considerably few examples remain up to now, likely due to the very similar physical/chemical properties between D 2 O and H 2 O. In this work, we found that both the hydrolysis reactions to release fluorescent amines and aggregation-induced emission (AIE) of imines, functioning as dual fluorescence signals to distinguish D 2 O and H 2 O, could be modulated by changing the imine structures. The hydrophobicity of imines showed an important contribution to the ability of modulating the hydrolysis reactions and AIE, demonstrating a significant difference on fluorescence signals in D 2 O and H 2 O solvents. Among all tested imines, probe 3, condensed from 2-naphthylamine and salicylaldehyde, was found to have the potential ability to act as an ideal candidate for probing the H 2 O content in D 2 O solvent, particularly in a low H 2 O content range, using the ratiomeric emission signals.

Imitating and incorporating the multiple key structural features observed in natural enzymes into a minimalistic molecule to develop an artificial catalyst with outstanding catalytic efficiency is an attractive topic for chemists. Herein, we designed and synthesized one class of minimalistic dipeptide molecules containing a terminal -SH group and a terminal His-Phe dipeptide head linked by a hydrophobic alkyl chain with different lengths, marked as HS-C n +1 -His-Phe ( n = 4, 7, 11, 15, and 17; n + 1 represents the carbon atom number of the alkyl chain). The His (-imidazole), Phe (-CO 2 - ) moieties, the terminal -SH group, and a long hydrophobic alkyl chain were found to have important contributions to achieve high binding ability leading to outstanding absolute catalytic efficiency ( k cat / K M ) toward the hydrolysis reactions of carboxylic ester substrates., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Disulfide-rich proteins are useful as drugs or tool molecules in biomedical studies, but their synthesis is complicated by the difficulties associated with their folding. Here, we describe a removable glycosylation modification (RGM) strategy that expedites the chemical synthesis of correctly folded proteins with multiple or even interchain disulfide bonds. Our strategy comprises the introduction of simple O-linked β- N -acetylglucosamine (O-GlcNAc) groups at the Ser/Thr sites that effectively improve the folding of disulfide-rich proteins by stabilization of their folding intermediates. After folding, the O-GlcNAc groups can be efficiently removed using O-GlcNAcase (OGA) to afford the correctly folded proteins. Using this strategy, we completed the synthesis of correctly folded hepcidin, an iron-regulating hormone bearing four pairs of disulfide-bonds, and the first total synthesis of correctly folded interleukin-5 (IL-5), a 26 kDa homodimer cytokine responsible for eosinophil growth and differentiation.

The β 2 -adrenergic receptor (β 2 AR) is a G-protein-coupled receptor (GPCR) that responds to the hormone adrenaline and is an important drug target in the context of respiratory diseases, including asthma. β 2 AR function can be regulated by post-translational modifications such as phosphorylation and ubiquitination at the C-terminus, but access to the full-length β 2 AR with well-defined and homogeneous modification patterns critical for biochemical and biophysical studies remains challenging. Here, we report a practical synthesis of differentially modified, full-length β 2 AR based on a combined native chemical ligation (NCL) and sortase ligation strategy. An array of homogeneous samples of full-length β 2 ARs with distinct modification patterns, including a full-length β 2 AR bearing both monoubiquitination and octaphosphorylation modifications, were successfully prepared for the first time. Using these homogeneously modified full-length β 2 AR receptors, we found that different phosphorylation patterns mediate different interactions with β-arrestin1 as reflected in different agonist binding affinities. Our experiments also indicated that ubiquitination can further modulate interactions between β 2 AR and β-arrestin1. Access to full-length β 2 AR with well-defined and homogeneous modification patterns at the C-terminus opens a door to further in-depth mechanistic studies into the structure and dynamics of β 2 AR complexes with downstream transducer proteins, including G proteins, arrestins, and GPCR kinases.

Although dynamic reactions of imines have been extensively studied, the dynamic behaviors manipulated by chirality remain nearly unexplored. In this work, enantioselective amine exchange reactions were demonstrated as a first example via the reaction of enantiomeric chiral amines such as natural amino acids with a series of innovative axially chiral 1,1'-binaphthyl-2,2'-diamine (BNDA)-based imines that were prepared from the condensation reactions between BNDA and salicylaldehyde (SA) or its derivatives. This enantioselective dynamic behavior can be directly indicated by the degree of the fluorescence response of the R -configuration of imines to the d-enantiomer of chiral amine, because the released BNDA can serve as the fluorescence signal output when the amine exchange reaction occurs, which is far higher than the response to its l-enantiomer under identical experimental conditions. For the S -configuration of chiral imines, the fluorescence response is the opposite. The enantioselective exchange reaction can be tuned by altering the electron-withdrawing or electron-donating capability of the substituent at position 4 or 5 of the SA part of chiral imines. Not only o -OH groups in SA-based imines but also protic solvents used as reaction media were found to be important to the dynamic behavior at high rates.

This work describes polyimide (PI) ultrafine fibrous membranes (UFMs) with aligned fibrous structures, fabricated via the high-speed electrospinning procedure. Organo-soluble intrinsically photosensitive PI is utilized as the fiber-forming agent. The effects of different rotating speeds on the fiber morphology and properties are studied. The aligned UFMs possess hydrophobicity, favorable optical properties, and improved deformation durability. The extension strength of the UFMs reinforces obviously with the increased rotating speed and reaches the maximum of 9.18 MPa at 2500 rpm. In addition, due to the photo-cross-link nature of the PI resin, the UFMs present lithography capability, which can obtain micro-sized patterns on aluminum substrates, and even part of the fibrous structure was retained after development. This work shows promise in manufacturing fiber-based photolithographic hierarchical structures on flexible substrates, which exhibit potential in achieving multiple functions on fiber-based electronic devices., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

The combination of distinct peptide ligation techniques to facilitate chemical protein synthesis represents one of the long-standing goals in the field. A new combination ligation method of N-to-C sequential native chemical ligation and Ser/Thr ligation (NCL-STL) is described for the first time. This method relies on the peptide salicylaldehyde S , S -propanedithioacetal (SAL PDT )-ester prepared by a new 1,3-propanedithiol-mediated reaction. The peptide SAL PDT -ester, which is compatible with NCL, can be fully activated by N -chlorosuccinimide (NCS)/AgNO 3 in aqueous solution to afford peptide SAL-ester for use in the subsequent STL. The practicality of the combined NCL-STL method is illustrated by the synthesis of S-palmitoylated matrix-2 (S-palm M2) ion channel from Influenza A virus and S-palmitoylated interferon-induced transmembrane protein 3 (S-palm IFITM3). This approach expands the multiple-segments peptide ligation toolkit for producing important and complex custom-made protein samples by chemical protein synthesis.

Chemical synthesis can produce water-soluble globular proteins bearing specifically designed modifications. These synthetic molecules have been used to study the biological functions of proteins and to improve the pharmacological properties of protein drugs. However, the above advances notwithstanding, membrane proteins (MPs), which comprise 20-30% of all proteins in the proteomes of most eukaryotic cells, remain elusive with regard to chemical synthesis. This difficulty stems from the strong hydrophobic character of MPs, which can cause considerable handling issues during ligation, purification, and characterization steps. Considerable efforts have been made to improve the solubility of transmembrane peptides for chemical ligation. These methods can be classified into two main categories: the manipulation of external factors and chemical modification of the peptide. This Account summarizes our research advances in the development of chemical modification especially the two generations of removable backbone modification (RBM) strategy for the chemical synthesis of MPs. In the first RBM generation, we install a removable modification group at the backbone amide of Gly within the transmembrane peptides. In the second RBM generation, the RBM group can be installed into all primary amino acid residues. The second RBM strategy combines the activated intramolecular O-to-N acyl transfer reaction, in which a phenyl group remains unprotected during the coupling process, which can play a catalytic role to generate the activated phenyl ester to assist in the formation of amide. The key feature of the RBM group is its switchable stability in trifluoroacetic acid. The stability of these backbone amide N-modifications toward TFA can be modified by regulating the electronic effects of phenol groups. The free phenol group is acylated to survive the TFA deprotection step, while the acyl phenyl ester will be quantitatively hydrolyzed in a neutral aqueous solution, and the free phenol group increases the electron density of the benzene ring to make the RBM labile to TFA. The transmembrane peptide segment bearing RBM groups behaves like a water-soluble peptide during fluorenylmethyloxycarbonyl based solid-phase peptide synthesis (Fmoc SPPS), ligation, purification, and characterization. The quantitative removal of the RBM group can be performed to obtain full-length MPs. The RBM strategy was used to prepare the core transmembrane domain Kir5.1[64-179] not readily accessible by recombinant protein expression, the influenza A virus M2 proton channel with phosphorylation, the cation-specific ion channel p7 from the hepatitis C virus with site-specific NMR isotope labels, and so on. The RBM method enables the practical engineering of small- to medium-sized MPs or membrane protein domains to address fundamental questions in the biochemical, biophysical, and pharmaceutical sciences.

We propose a versatile yet practical transferring technique to fabricate a high performance and extremely stable silver nanowire (AgNW) transparent electrode on arbitrary substrates. Hydroxylated poly(ethylene glycol) terephthalate (PET) or poly(dimethylsiloxane) (PDMS) deposited with AgNWs was selectively decorated to lower its polar surface energy, so that the AgNWs were easily and efficiently transferred into an epoxy resin (EPR) as a freestanding film (AgNWs-EPR) or onto various substrates. The AgNWs-EPR capped with alkanethiolate monolayers exhibits high conductivity, low roughness, ultraflexibility, and strong corrosion resistance. Using the transferring process, AgNWs-EPR was successfully constructed on rough, adhesive, flimsy, or complex curved substrates, including PET, thin optically clear adhesive, papers, a beaker, convex spherical PDMS, and leaves. A flexible touch panel enabling multitouch and a curved transparent heater on a beaker were first fabricated by using the composite film. These demonstrations suggest that the proposed technique for AgNWs is a promising strategy toward the next generation of flexible/portable/wearable electronics.

Chemical protein synthesis can provide access to proteins with post-translational modifications or site-specific labelings. Although this technology is finding increasing applications in the studies of water-soluble globular proteins, chemical synthesis of membrane proteins remains elusive. In this report, a general and robust removable backbone modification (RBM) method is developed for the chemical synthesis of membrane proteins. This method uses an activated O-to-N acyl transfer auxiliary to install in the Fmoc solid-phase peptide synthesis process a RBM group with switchable reactivity toward trifluoroacetic acid. The method can be applied to versatile membrane proteins because the RBM group can be placed at any primary amino acid. With RBM, the membrane proteins and their segments behave almost as if they were water-soluble peptides and can be easily handled in the process of ligation, purification, and mass characterizations. After the full-length protein is assembled, the RBM group can be readily removed by trifluoroacetic acid. The efficiency and usefulness of the new method has been demonstrated by the successful synthesis of a two-transmembrane-domain protein (HCV p7 ion channel) with site-specific isotopic labeling and a four-transmembrane-domain protein (multidrug resistance transporter EmrE). This method enables practical synthesis of small- to medium-sized membrane proteins or membrane protein domains for biochemical and biophysical studies.

A new synthetic method for peptide thioesters is described using Fmoc solid-phase peptide synthesis (Fmoc-SPPS). This method employs a novel enamide motif to facilitate irreversible intramolecular N-to-S acyl migration, which can efficiently afford the desired peptide thioesters (3 h, 30 °C) under the final trifluoroacetic acid (TFA) cleavage conditions. The acyl-transfer-mediated approach for synthesis of peptide thioesters tolerated different C-terminal residues and was used to synthesize human C-C motif chemokine 11 (hCCL11) via native chemical ligation.

Total chemical synthesis provides a unique approach for the access to uncontaminated, monodisperse, and more importantly, post-translationally modified membrane proteins. In the present study we report a practical procedure for expedient and cost-effective synthesis of small to medium-sized membrane proteins in multimilligram scale through the use of automated Fmoc chemistry. The key finding of our study is that after the attachment of a removable arginine-tagged backbone modification group, the membrane protein segments behave almost the same as ordinary water-soluble peptides in terms of Fmoc solid-phase synthesis, ligation, purification, and mass spectrometry characterization. The efficiency and practicality of the new method is demonstrated by the successful preparation of Ser64-phosphorylated M2 proton channel from influenza A virus and the membrane-embedded domain of an inward rectifier K(+) channel protein Kir5.1. Functional characterizations of these chemically synthesized membrane proteins indicate that they provide useful and otherwise-difficult-to-access materials for biochemistry and biophysics studies.

The formation of a hitherto unknown three-coordinate dicationic hydrido boron complex is described. Interestingly, supporting ligand carbodicarbene gave unprecedented reaction with BH3 without using more highly electrophilic Lewis acid precursors. Spectroscopic, crystallographic, and computational analysis was performed to understand the electronic features of these species.

The chemical synthesis of proteins provides synthetic chemists with an interesting challenge and supports biological research through the generation of proteins that are not produced naturally. Although it offers advantages, studies of solid phase peptide synthesis have established limits for this technique: researchers can only prepare peptides up to 50 amino acids in length in sufficient yields and purity. Therefore, researchers have developed techniques to condense peptide segments to build longer polypeptide chains. The method of choice for chemical synthesis of these longer polypeptides is convergent condensation of unprotected protein fragments by the native chemical ligation reaction in aqueous buffer. As researchers apply this strategy to increasingly difficult protein targets, they have needed to overcome diverse problems such as the requirement for a thiol-containing amino acid residue at the ligation site, the difficulty in synthesizing thioester intermediates under mild conditions, and the challenge of condensing multiple peptide segments with higher efficiency. In this Account, we describe our research toward the development of new thioester equivalents for protein chemical synthesis. We have focused on a simple idea of finding new chemistry to selectively convert a relatively "low-energy" acyl group such as an ester or amide to a thioester under mild conditions. We have learned that this seemingly unfavorable acyl substitution process can occur by the coupling of the ester or amide with another energetically favorable reaction, such as the irreversible hydrolysis of an enamine or condensation of a hydrazide with nitrous acid. Using this strategy, we have developed several new thioester equivalents that we can use for the condensation of protein segments. These new thioester equivalents not only improve the efficiency for the preparation of the intermediates needed for protein chemical synthesis but also allow for the design of new convergent routes for the condensation of multiple protein fragments.

An operationally simple method for the synthesis of peptide thioesters is developed using standard Fmoc solid-phase peptide synthesis procedures. The method relies on the use of a premade enamide-containing amino acid which, in the final TFA cleavage step, renders the desired thioester functionality through an irreversible intramolecular N-to-S acyl transfer.

A detailed investigation of the absorption and CD signals of Ag(I)-cysteine (Cys) aqueous solutions at buffered or varying pH has allowed us to suggest that coordination polymers are formed upon mixing Ag(I) and Cys bearing a Ag(I)-Cys repeat unit. The formation of the coordination polymers are shown to be facilitated by both the Ag(I)···Ag(I) interaction and the interaction between the side chains in the polymeric backbone. The former allows for an immediate spectral sensing of Cys with enantiomeric discrimination capacity with both high sensitivity and selectivity, and the contribution of the side-chain/side-chain interaction serves to guide extended sensing applications by means of modulating this interaction. With our preliminary data on the corresponding Cu(I)-Cys and Au(I)-Cys systems that exhibited similar spectral signals, we conclude that the M(I)-SR coordination polymers (M = Cu, Ag, or Au) could in general function as spectral sensing ensembles for extended applications. This sensing ensemble involves the formation of coordination polymers with practically no spectral background, thus affording high sensing sensitivity and selectivity.

Biomarkers for colorectal cancer (CRC) early diagnosis are currently lacking. The purpose of this study was to interpret molecular events in the early stage of CRC that may bring about new biomarkers for early diagnosis. Methylation isotope labeling assistant gel-enhanced liquid chromatography-mass spectrometry (GeLC-MS) strategy was developed to improve protein identification in quantitative proteome analysis between pooled early stage CRC and pooled normal counterparts. Expression of candidate biomarkers were in situ verified in a 372-dots tissue array, and their relative concentrations in sera were validated in 84 CRC patients and healthy individuals. Altogether, 501 proteins showing consistent differential expression were discovered. Function analysis highlighted the ubiquitination-proteasome and glycolysis/gluconeogenesis pathways as the most regulated pathways in CRC. Two glycol-proteins, alpha1 antitrypsin (A1AT) and cathepsin D (CTSD), which play central role in proteasome regulation, were further examined due to their possible importance in human cancers. Consistent with proteome data, CRC specimens expressed less A1AT and more CTSD than normal counterparts in both tissue and serum levels. By combining CTSD and A1AT, 96.77% of CRC tissues were distinguished from normal tissues by immunohistochemical analysis on a tissue array (P<0.0001). Combined CTSD and A1AT should be strongly considered for clinical use in early diagnosis of early stage CRC, and the methylation assistant GeLC-MS approach is competent for a global quantitative proteome study.