Strong Amide Research Articles

Designing multifunctional, 3D cross-linked network binder for actual use in high performance lithium ion batteries silicon based anodes

Binders have been proved to be an economical and effective approach for accelerating the industrial application of silicon based anodes. Herein, a 3D network binder (H-PAN-g-ECH) with multifunctional groups, is constructed by crosslinking polyacrylonitrile (PAN) hydrolysate (H-PAN) with epichlorohydrin (ECH). Strong polar groups carboxylate (-COO-) and amide (-CONH2) obtained from hydrolysis of PAN as well as the original cyanide (-CN) enhance the adhesive ability of H-PAN-g-ECH to not only active material but also current collector, and thus sustain the structure integrity of the electrode. In addition, the network structure proposed by linking H-PAN with short-chain molecules endows H-PAN-g-ECH with facilitated Li-ion transmission and improved mechanical property to accommodate the great volume variation of Si during cycling. The as-prepared H-PAN-g-ECH possesses multiple interfacial adhesion and robust mechanical performance, which improves the electrochemical property of silicon anode with high areal capacity. In combination with good processability, H-PAN-g-ECH is verified to be a superior binder in use of practical Si based anodes.

Frustration of H-Bonding and Frustrated Packings in a Hexamorphic Crystal System with Reversible Crystal-Crystal Transitions.

The study of transitions between polymorphic phases is a less investigated chapter of the widely studied book of polymorphism. In this paper, we discuss the phase behavior of a new compound that has been rationally designed to show frustration of H-bonds for the strong amide N-H donor, which cannot be involved in H-bonding nor in van der Waals interactions. The compound (ImB) is a showcase of almost all possible cases of transitions between polymorphs [monotropic/enantiotropic, fast/slow, diffusive/displacive, and single-crystal-to-single-crystal (SCSC)] and of relation between polymorphs with different Z'. Six crystal phases (I, II, III, IV, V, and VI) were identified for it with five crystal-crystal transitions. Two transitions are reversible/SCSC/fast. Of the three monotropic transitions, all non-SCSC, one is slow, and the others are fast. Of the two enantiotropic SCSC transitions, one does not exhibit undercooling, while the other shows strong undercooling. Phase III, with Z' = 6, is stable at room temperature between phase II (Z' = 1), stable at high temperature, and phase IV (Z' = 2), stable at low temperature. All six polymorphs are based on the same O-H···O═C H-bonding synthon, which produces infinite chains in five polymorphs and ring tetramers in one. The sequence of reversible SCSC transitions IV ⇆ III ⇆ II involves a remarkable ping pong of the symmetry rules by which H-bonded chains are built. Based on all of this, a possible roadmap for prediction of SCSC transitions in crystals is shortly outlined.

Synergistic effects of graphene quantum dots nanocarriers and folic acid targeting agent on enhanced killing of breast cancer cells by tamoxifen

AbstractIn this study, a new targeted and controlled‐release drug delivery system based on graphene quantum dots (GQDs) was fabricated. The fluorescent GQDs were synthesized via an environmentally‐friendly chemical oxidation method, using graphene oxide (GO) as a precursor and hydrogen peroxide and ammonia solution as oxidants. Folic acid (FA), as a targeting agent, was bound to GQDs through strong amide covalent bindings, and tamoxifen (TMX), as a hydrophobic anticancer drug, was non‐covalently attached to the nanocarrier via π–π stacking bonds. The as‐prepared GQDs and TMX/FA‐GQDs were characterized using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), UV/Vis spectroscopy (UV/Vis), and photoluminescence spectroscopy (PL). The resulting TMX/GQDs demonstrated pH‐sensitive release behaviour with an overall release of 85% and 58% at pH 5.5 and 7.4, respectively, after 120 h. Also, the MTT assay test performed on MCF‐7 cells presented negligible toxicity of the nanocarriers, even at high concentrations. At the same time, the targeted nanocarrier, TMX/FA‐GQDs, showed much more toxicity towards MCF‐7 cells than the non‐targeted one and free TMX.

Enhancing Long-Term Durability of Electrochemical Reactors Producing Formate from CO2 and Water Designed for Integration with Solar Cells.

Artificial photosynthetic cells producing organic matter from CO2 and water have been extensively studied for carbon neutrality, and the research trend is currently transitioning from proof of concept using small-sized cells to large-scale demonstrations for practical applications. We previously demonstrated a 1 m2 size cell in which an electrochemical (EC) reactor featuring a ruthenium (Ru)-complex polymer (RuCP) cathode catalyst was integrated with photovoltaic cells. In this study, we tackled the remaining issue to improve the long-term durability of cathode electrodes used in the EC reactors, demonstrating high Faradaic efficiencies exceeding 80% and around 60% electricity-to-chemical energy-conversion efficiencies of a 75 cm2 sized EC reactor after continuous operation for 3000 h under practical conditions. Introduction of a pyrrole derivative containing an amino group in the RuCP coupled with UV-ozone treatment to create carboxyl groups on the carbon supports effectively reduced the detachment of the RuCP catalyst by forming a strong amide linkage. A newly developed chemically resistant graphite adhesive prevented the carbon supports from peeling off of the conductive substrates. In addition, highly durable anodes composed of IrOx-TaOy/Pt-metal oxide/Ti were adopted. Even though the EC reactor was installed at an inclined angle of 30°, which is approximately the optimal angle for receiving more solar energy, the crossover reactions were sufficiently suppressed because the porous separator film impeded the transfer of oxygen gas bubbles from the anode to the cathode. The intermittent operation improved the energy-conversion efficiency because the accumulated bubbles were removed at night.

Spectroscopic, crystallographic, and Hirshfeld surface characterization of nine-membered-ring-containing 9-meth-oxy-3,4,5,6-tetra-hydro-1H-benzo[b]azonine-2,7-dione and its parent tetra-hydro-car-ba-zole.

9-Meth-oxy-3,4,5,6-tetra-hydro-1H-benzo[b]azonine-2,7-dione, C13H15NO3, (I), and 6-meth-oxy-1,2,3,4-tetra-hydro-car-ba-zole, C13H15NO, (II), represent the structures of a benzoazonine that contains a nine-membered ring and its parent tetra-hydro-car-ba-zole. The mol-ecules of (I) pack together via strong amide N-H⋯O hydrogen bonding and weak C-H⋯O inter-actions, whereas the parent tetra-hydro-car-ba-zole (II) packs with C/N-H⋯π inter-actions, as visualized by Hirshfeld surface characterization.

Roles of Hydrogen, Halogen Bonding and Aromatic Stacking in a Series of Isophthalamides

The synthesis and spectroscopic characterisation of six bis(5-X-pyridine-2-yl)isophthalamides (X = H, F, Br, Cl, I, NO2) are reported, together with five crystal structure analyses (for X = H, F to I). The isophthalamides span a range of conformations as syn/anti (H-DIP; I-DIP), anti/anti- (F-DIP; Br-DIP) and with both present in ratio 2:1 in Cl-DIP. The essentially isostructural F-DIP and Br-DIP molecules (using strong amide…amide interactions) aggregate into 2D molecular sheets that align with either F/H or Br atoms at the sheet surfaces (interfaces), respectively. Sheets are linked by weak C-H⋯F contacts in F-DIP and by Br⋯Br halogen bonding interactions as a ‘wall of bromines’ at the Br atom rich interfaces in Br-DIP. Cl-DIP is an unusual crystal structure incorporating both syn/anti and anti/anti molecular conformations in the asymmetric unit (Z’ = 3). The I-DIP•½(H2O) hemihydrate structure has a water molecule residing on a twofold axis between two I-DIPs and has hydrogen and N⋯I (Nc = 0.88) halogen bonding. The hydrate is central to an unusual synthon and involved in six hydrogen bonding interactions/contacts. Contact enrichment analysis on the Hirshfeld surface demonstrates that F-DIP, Cl-DIP and Br-DIP have especially over-represented halogen···halogen interactions. With the F-DIP, Cl-DIP and Br-DIP molecules having an elongated skeleton, the formation of layers of halogen atoms in planes perpendicular to the long unit cell axis occurs in the crystal packings. All six DIPs were analysed by ab initio calculations and conformational analysis; comparisons are made between their minimized structures and the five crystal structures. In addition, physicochemical properties are compared and assessed.

Understanding the histology and hematobiochemical aspects of Kadaknath an Indian black fowl with an appealing taste native to Dhar district Madhya Pradesh

ABSTRACT 1. The Kadaknath, an Indian fowl, is popular for its taste and health benefits. However, there is scarcity of information on its histology, haematology and biochemistry. 2. Histology was conducted on various organs, including brain, heart, intestine, liver, kidney and the lung. For haematology investigation Mispa Count Plus was used (AGAPPE Diagnostic, India). 3. Biochemical analysis involved determination of blood sugar, serum creatinine, serum urea, serum bilirubin, SGPT, serum protein and the alkaline phosphatase. The organs contained significant amounts of proteins characterised by strong amide (amide I-β-sheet) bands within mid and NIR region. 4. Hydrated fatty acids were not found in mid IR region, although NIR revealed traces substantiated by strong – OH bending within 10 680/cm -10 400/cm. 5. This work reported the usefulness of attenuated total reflectance (ATR) in understanding nutritive benefits of Kadaknath chickens and can assist avian practitioners in the detection of infections or pathological conditions.

A Planar‐Chiral Palladium Complex Derived from a Weak Oxygen Donor N,N‐Diisopropyl Ferrocenecarboxamide Ligand

AbstractThe reaction of chiral 2‐iodoferrocenecarboxamide, palladium(II) acetate, and triphenylphosphine ligand in acetonitrile has been resulted in the formation of an air‐stable chiral (Sp)‐2‐(N,N‐diisopropyl ferrocenecarboxamide) triphenylphosphine palladium(II) iodide complex. The isolated chiral palladium complex was thoroughly characterized by multi‐nuclear (1H, 13C, 31P) NMR, IR spectroscopy, mass spectrometry, polarimetry, CHN analysis, cyclic voltammetry and single crystal X‐ray crystallography (XRD). The single‐crystal XRD analysis reveals a square planar geometry around the palladium atom with a strong amide oxygen‐Pd bond [2.095(6) Å]. The palladium complex crystallized in the C2‐chiral space group having a Flack parameter value of 0.011(14), which is close to 0 and indicative of the enantiomeric purity of the palladium complex. The electrochemical study reveals a two‐electron redox couple due to the ferrocenyl Fe(II) atom and the palladacyclic Pd(II) center. In differential pulse voltammetry (DPV), two peaks were observed at 450 mV and 590 mV vs. Ag/AgCl. Further, the synthesized chiral palladacyle has also been explored in Suzuki‐Miyaura coupling reaction as a substrate and as a catalyst for Tsuji‐Trost coupling and phosphonation reactions.

Impact of bPNA Backbone Structural Constraints and Composition on Triplex Hybridization with DNA.

We report herein a study on the impact of bifacial peptide nucleic acid (bPNA) amino acid composition and backbone modification on DNA binding. A series of bPNA backbone variants with identical net charge were synthesized to display either 4 or 6 melamine (M) bases. These bases form thymine-melamine-thymine (TMT) base-triples, resulting in triplex hybrid stem structures with T-rich DNAs. Analyses of 6 M bPNA-DNA hybrids suggested that hybrid stability was linked to amino acid secondary structure propensities, prompting a more detailed study in shorter 4 M bPNAs. We synthesized 4 M bPNAs predisposed to adopt helical secondary structure via helix-turn nucleation in 7-residue bPNAs using double-click covalent stapling. Generally, hybrid stability improved upon stapling, but amino acid composition had a more significant effect. We also pursued an alternative strategy for bPNA structural preorganization by incorporation of residues with strong backbone amide conformational preferences such as 4R- and 4S-fluoroprolines. Notably, these derivatives exhibited an additional improvement in hybrid stability beyond both unsubstituted proline bPNA analogues and the helically patterned bPNAs. Overall, these findings demonstrate the tunability of bPNA-DNA hybrid stability through bPNA backbone structural propensities and amino acid composition.

Methylated tetra-amide derivatives of paramagnetic complexes for magnetic resonance biosensing with both BIRDS and CEST.

Paramagnetic agents that utilize two mechanisms to provide physiological information by magnetic resonance imaging (MRI) and magnetic resonance spectroscopic imaging (MRSI) are described. MRI with chemical exchange saturation transfer (CEST) takes advantage of the agent's exchangeable protons (e.g., -OH or -NHx , where 2 ≥ x ≥ 1) to create pH contrast. The agent's incorporation of non-exchangeable protons (e.g., -CHy , where 3 ≥ y ≥ 1) makes it possible to map tissue temperature and/or pH using an MRSI method called biosensor imaging of redundant deviation in shifts (BIRDS). Hybrid probes based upon 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate chelate (DOTA4- ) and its methylated analog (1,4,7,10-tetraazacyclododecane-α, α', α″, α‴-tetramethyl-1,4,7,10-tetraacetate, DOTMA4- ) were synthesized, and modified to create new tetra-amide chelates. Addition of several methyl groups per pendent arm of the symmetrical chelates, positioned proximally and distally to thulium ions (Tm3+ ), gave rise to favorable BIRDS properties (i.e., high signal-to-noise ratio (SNR) from non-exchangeable methyl proton peaks) and CEST responsiveness (i.e., from amide exchangeable protons). Structures of the Tm3+ probes elucidate the influence of methyl group placement on sensor performance. An eight-coordinate geometry with high symmetry was observed for the complexes: Tm-L1 was based on DOTA4- , whereas Tm-L2 and Tm-L3 were based on DOTMA4- , where the latter contained an additional carboxylate at the distal end of each arm. The distance of Tm3+ from terminal methyl carbons is a key determinant for sustaining BIRDS temperature sensitivity without compromising CEST pH contrast; however, water solubility was influenced by introduction of hydrophobic methyl groups and hydrophilic carboxylate. Combined BIRDS and CEST detection of Tm-L2, which features two high-SNR methyl peaks and a strong amide CEST peak, should enable simultaneous temperature and pH measurements for high-resolution molecular imaging in vivo.

Additive Manufacturing of α-Amino Acid Based Poly(ester amide)s for Biomedical Applications.

α-Amino acid based polyester amides (PEAs) are promising candidates for additive manufacturing (AM), as they unite the flexibility and degradability of polyesters and good thermomechanical properties of polyamides in one structure. Introducing α-amino acids in the PEA structure brings additional advantages such as (i) good cytocompatibility and biodegradability, (ii) providing strong amide bonds, enhancing the hydrogen-bonding network, (iii) the introduction of pendant reactive functional groups, and (iv) providing good cell–polymer interactions. However, the application of α-amino acid based PEAs for AM via fused deposition modeling (FDM), an important manufacturing technique with unique processing characteristics and requirements, is still lacking. With the aim to exploit the combination of these advantages in the creation, design, and function of additively manufactured scaffolds using FDM, we report the structure–function relationship of a series of α-amino acid based PEAs. The PEAs with three different molecular weights were synthesized via the active solution polycondensation, and their performance for AM applications was studied in comparison with a commercial biomedical grade copolymer of l-lactide and glycolide (PLGA). The PEAs, in addition to good thermal stability, showed semicrystalline behavior with proper mechanical properties, which were different depending on their molecular weight and crystallinity. They showed more ductility due to their lower glass transition temperature (Tg; 18–20 °C) compared with PLGA (57 °C). The rheology studies revealed that the end-capping of PEAs is of high importance for preventing cross-linking and further polymerization during the melt extrusion and for the steadiness and reproducibility of FDM. Furthermore, our data regarding the steady 3D printing performance, good polymer–cell interactions, and low cytotoxicity suggest that α-amino acid based PEAs can be introduced as favorable polymers for future AM applications in tissue engineering. In addition, their ability for formation of bonelike apatite in the simulated body fluid (SBF) indicates their potential for bone tissue engineering applications.

Supramolecular Antiparallel β-Sheet Formation by Tetrapeptides Based on Amyloid Sequence.

Self-assembly of short peptides has emerged as an interesting research field for a wide range of applications. Recently, several truncated fragments of long-chain peptides or proteins responsible for different neurodegenerative diseases were studied to understand whether they can mimic the property and function of native peptides or not. It was reported that such a kind of peptide adopts a β-sheet structure in the disease state. It was observed that aromatic amino acid-rich peptide fragments possess a high tendency to adopt a β-sheet conformation. In this article, we are first time reporting the crystal structure of two tetrapeptides: Boc-GAII-OMe (Peptide 1) and Boc-GGVV-OMe (Peptide 2), composed of aliphatic amino acids, and the sequences are similar to the Aβ-peptide fragments Aβ29-32 and Aβ37-40 , respectively. In the solid-state, they are self-assembled in an antiparallel β-sheet fashion. The peptide units are connected by the strong amide hydrogen-bonding (N-H···O) interactions. Apart from that, other noncovalent interactions are also present, which help to stabilize the cross-β-sheet arrangement. Interestingly, in the crystal structure of Peptide 1, noncovalent C···C interaction between the electron-deficient carbonyl carbon, and the electron-rich sp3-carbon atom is observed, which is quite rare in the literature. The calculated torsion angles for these peptides are lying in the β-sheet region of the Ramachandran plot. FT-IR studies also indicate the formation of an antiparallel β-sheet structure in the solid-state. Circular dichroism of the peptides in the aqueous solution also suggests the presence of predominantly β-sheet-like conformation in the aqueous solution. Under cross-polarized light, Congo Red stained both peptides showed green-gold color due to birefringence indicating their amyloidogenic nature. This result indicates that the short peptide composed of aliphatic amino acid is capable of forming a β-sheet structure in the absence of aromatic amino acid and also can mimic the function of the native amyloid peptide.

Preliminary study on immobilization of plant esterase on functionalized multi-walled carbon nanotubes (MWCNTs) for biosensor application

The functionalization of multi-walled carbon nanotubes (MWCNTs) is extremely important to increase their solubility. This study reported the efficient functionalization of MWCNTs via acid treatment introducing carboxyl group at the side wall of MWCNTs by mixing the concentrated nitric and sulfuric acid. Plant esterase enzyme extracted from wheat flour called alpha naphthyl acetate esterase (ANAE) was immobilized onto functionalized MWCNTs via covalent attachment of amine group in ANAE and carboxyl group of functionalized MWCNTs. In order to characterize the functionalization of MWCNTs and immobilization of enzyme, Fourier transform infrared (FTIR) spectroscopy have been used to confirm the existence of these functional groups. The FTIR spectrums revealed that the several peaks formed at 1992.39, 2324.14, 2880.85 and 3029.51 cm−1 which can be assigned to the C=O symmetric stretching, O−H stretch from strongly hydrogen-bonded –COOH, H−C stretch modes of H−C=O in the carboxyl group, and O-H stretch from carboxyl groups (O=C−OH and C−OH) respectively. The immobilization of ANAE on functionalized MWCNTs confirmed by observation of the peak at 3646.81 cm−1 and 3850.91 cm−1 introduced the strong amide linkages between carboxylic acid groups and amine group on the MWCNTs. This proposed framework can be applied for fabrication of screen printed electrode as biosensor for detection of pesticide.

Transformation of bone mineral morphology: From discrete marquise-shaped motifs to a continuous interwoven mesh

Continual bone apposition at the cranial sutures provides the unique opportunity to understand how bone is built. Bone harvested from 16-week-old Sprague Dawley rat calvaria was either (i) deproteinised to isolate the inorganic phase (i.e., bone mineral) for secondary electron scanning electron microscopy or (ii) resin embedded for X-ray micro-computed tomography, backscattered electron scanning electron microscopy, and micro-Raman spectroscopy. Interdigitated finger-like projections form the interface between frontal and parietal bones. Viewed from the surface, bone mineral at the mineralisation front is comprised of nanoscale mineral platelets arranged into discrete, ~0.6–3.5 μm high and ~0.2–1.5 μm wide, marquise-shaped motifs that gradually evolve into a continuous interwoven mesh of mineralised bundles. Marquise-shaped motifs also contribute to the burial of osteoblastic–osteocytes by contributing to the roof over the lacunae. In cross-section, apices of the finger-like projections resemble islands of mineralised tissue, where new bone apposition at the surface is evident as low mineral density areas, while the marquise-shaped motifs appear as near-equiaxed assemblies of mineral platelets. Carbonated apatite content is higher towards the internal surface of the cranial vault. Up to 4 μm from the bone surface, strong Amide III, Pro, Hyp, and Phe signals, distinct PO43− bands, but negligible CO32– signal indicate recent bone formation and/or delayed maturation of the mineral. We show, for the first time, that the extracellular matrix of bone is assembled into micrometre-sized units, revealing a superstructure above the mineralised collagen fibril level, which has significant implications for function and mechanical competence of bone.

δ-Azaproline and Its Oxidized Variants.

Peptides featuring backbone N-amino substituents exhibit unique conformational properties owing to additional electrostatic, hydrogen-bonding, and steric interactions. Here, we describe the synthesis and conformational analysis of three δ-azaproline derivatives as potential proline surrogates. Our studies demonstrate stereoelectronic tuning of heterocyclic ring pucker, cis/trans amide propensity, and amide isomerization barriers within a series of oxidation state variants. A combination of NMR, X-ray diffraction, and density functional theory calculations shows that electron density and hybridization at the δ position play a dominant role in the conformational preferences of each analogue. Both δ-azaproline and γ,δ-dehydro-δ-azaproline exhibit strong trans amide rotamer propensities irrespective of ring conformation, while a novel residue, γ-oxo-δ-azaproline, features rapid amide isomerization kinetics and isoenergetic amide bond geometries influenced by torsional strain and H-bonding interactions. The introduction of the δ heteroatom in each residue allows the decoupling of structural effects that are typically linked in proline and its pyrrolidine-substituted analogues. δ-Azaproline derivatives thus represent useful probes of prolyl amide isomerism with potential applications in peptidomimetic drug design and protein folding.

Order, Disorder, and Reorder State of Lysozyme: Aggregation Mechanism by Raman Spectroscopy.

Lysozyme, like many other well-folded globular proteins, under stressful conditions produces nanoscale oligomer assembly and amyloid-like fibrillar aggregates. With engaging Raman microscopy, we made a critical structural analysis of oligomer and other assembly structures of lysozyme obtained from hen egg white and provided a quantitative estimation of a protein secondary structure in different states of its fibrillation. A strong amide I Raman band at 1660 cm-1 and a N-Cα-C stretching band at ∼930 cm-1 clearly indicated the presence of a substantial amount of α-helical folds of the protein in its oligomeric assembly state. In addition, analysis of the amide III region and Raman difference spectra suggested an ample presence of a PPII-like secondary structure in these oligomers without causing major loss of α-helical folds, which is found in the case of monomeric samples. Circular dichroism study also revealed the presence of typical α-helical folds in the oligomeric state. Nonetheless, most of the Raman bands associated with aromatic residues and disulfide (-S-S-) linkages broadened in the oligomeric state and indicated a collapse in the tertiary structure. In the fibrillar state of assembly, the amide I band became much sharper and enriched with the β-sheet secondary structure. Also, the disulfide bond vibration in matured fibrils became much weaker compared to monomer and oligomers and thus confirmed certain loss/cleavage of this bond during fibrillation. The Raman band of tryptophan and tyrosine residues indicated that some of these residues experienced a greater hydrophobic microenvironment in the fibrillar state than the protein in the oligomeric state of the assembly structure.

Diagnosis of EGFR exon21 L858R point mutation as lung cancer biomarker by electrochemical DNA biosensor based on reduced graphene oxide /functionalized ordered mesoporous carbon/Ni-oxytetracycline metallopolymer nanoparticles modified pencil graphite electrode

In this present work we made a novel, fast, selective and sensitive electrochemical genobiosensor to detection of EGFR exon 21 point mutation based on two step electropolymerization of Ni(II)-oxytetracycline conducting metallopolymer nanoparticles (Ni-OTC NPs) on the surface of pencil graphite electrode (PGE) which was modified by reduced graphene oxide/carboxyl functionalized ordered mesoporous carbon (rGO/f-OMC) nanocomposite. ssDNA capture probe with amine groups at the5′ end which applied as recognition element was immobilized on the rGO/f-OMC/PGE surface via the strong amide bond. Ni-OTC metallopolymer NPs were electropolymerized to rGO/ssDNA-OMC/PGE surface and then hybridization fallows through the peak current change in differential pulse voltammetry (DPV) using Ni-OTC NPs as a redox label. The biosensor was characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), FT-IR spectroscopy, energy dispersive X-ray spectroscopy (EDX), cyclic voltammetry and Nitrogen adsorption–desorption analysis. The Ni-OTC current response verified only the complementary sequence indicating a significant reduction current signal in comparison to single point mismatched and non-complementary and sequences. Under optimal conditions, the prepared biosensor showed long-term stability (21 days) with a wide linear range from 0.1 µM to 3 µM with high sensitivity (0.0188 mA/µM) and low detection limit (120 nM).

Reconciling Simulated Ensembles of Apomyoglobin with Experimental HDX Data

Hydrogen/deuterium exchange (HDX) is a powerful tool to investigate protein conformational dynamics at equilibrium. In the classic model of HDX, each of the amide hydrogens of a protein can either exist in an “open” conformation, where HDX can occur with the exchange rate kint, or in a “closed” conformation, where HDX rate, kex, gets much slower. The extent of protection for a residue i, is characterized by a protection factor, PFi = kex,i/kint,i, which is related to the effective free energy difference between open and closed states, ΔG, through ln(PFi ) = βΔGi. However, it has been challenging to make direct connections between molecular simulations of native-state protein dynamics, both in predicting HDX PF from trajectory data, and in using experimental protection factors as restraints in simulated ensembles. In this study, we propose an expression, ln(PF)= βc<Nc> + βh<Nh> + β0, to predict the protection factors based on the average number of heavy-atom contacts <Nc> and hydrogen bonds <Nh> observed in simulations. The model parameters are trained on ultra-long, all-atom trajectories of proteins with experimentally measured protection factors (BPTI and ubiquitin). Using Bayesian inference to propagate the uncertainties in model parameters, we then use this model to refine conformational ensembles of apomyoglobin at neutral pH. To minimize bias, we simulated apomyoglobin using a range of weak to strong amide exposure restraints. We applied a transition-based reweighting method, TRAM, to construct a Multi-ensemble Markov model from the combined simulation data, and then used our Bayesian Inference of Conformational Populations (BICePs) algorithm to refine a conformational ensemble that best matched the experimental structural data. The resulting ensemble shows a partially-disordered F/H helix, and atomically detailed information that was previously missing from 2D NMR studies.

Methyl matters: An autonomic rapid self-healing supramolecular poly(N-methacryloyl glycinamide) hydrogel

Poly(N-acryloyl glycinamide) (PNAGA) with a protein-like thermoresponsive gelation behavior in water has been developed as a high strength self-healable supramolecular polymer(SP) hydrogels recently. However, harsh conditions, such as high temperature treatment and long waiting time, were required for achieving the complete healing due to strong dual amide hydrogen bonding interactions. In this study, to create an autonomic rapid self-healing SP hydrogel, we deliberately introduced a methyl into the opposite side to dual amide to synthesize N-methacryloyl glycinamide (MNAGA) monomer. Rheological analysis, dynamic light scattering(DLS), Fourier transform infrared (FTIR) spectroscopy, and Gaussian calculation revealed that one substitution methyl caused a considerable perturbation to the hydrogen bonding interaction, thus leading to the increased starting gelling concentration and pronounced decrease in mechanical properties of PMNAGA hydrogel compared to PNAGA hydrogel. The PMNAGA hydrogel was shown to exhibit rapid autonomic reparability without any external intervention, and dynamic swelling measurement indicated this PMNAGA hydrogel could evolve from permanent to transient network due to the metastable hydrogen bonding crosslinkage, depending on its environmental temperature. This intriguing robust, autonomous healing and autolytic PMNAGA hydrogel holds great potential as a short-term embolic agent for blocking blood vessel and artificial tears for moistening eyes.

Highly Enantioselective Fluorescent Recognition of Both Unfunctionalized and Functionalized Chiral Amines by a Facile Amide Formation from a Perfluoroalkyl Ketone.

The H8 BINOL-based perfluoroalkyl ketone (S)-2 is found to exhibit highly enantioselective fluorescent enhancements toward both unfunctionalized and functionalized chiral amines. It greatly expands the substrate scope of the corresponding BINOL-based sensor. A dramatic solvent effect was observed for the reaction of the amines with compound (S)-2. In DMF, cleavage of the perfluoroalkyl group of compound (S)-2 to form amides was observed but not in other solvents, such as methylene chloride, chloroform, THF, hexane, and perfluorohexane. Thus, the addition of another solvent, such as THF, can effectively quench the reaction of compound (S)-2 with amines in DMF to allow stable fluorescent measurement. This is the first example that the formation of strong amide bonds under very mild conditions is used for the enantioselective recognition of chiral amines. The mechanism of the reaction of compound (S)-2 with chiral amines is investigated by using various analytical methods including mass spectrometry as well as NMR and UV/Vis absorption spectroscopy.