Polar Side Chains Research Articles

Preparation and Electrochromic Properties of Benzodithiophene-Isoindigo Conjugated Polymers with Oligoethylene Glycol Side Chains.

Functional polymers featuring good processability in non-halogenated, benzene-free green solvents are highly desired due to health and environmental concerns. Herein, a series of novel D-A type conjugated polymers, PBDT-IIDs, are designed and successfully prepared by "green" functionalization of the polymers with highly hydrophilic, highly polar, highly flexible, and biocompatible oligoethylene glycol (OEG) side chains in order to improve the processability. These series polymers are named PBDT-IID2, PBDT-IID3, and PBDT-IID4, respectively, according to the number of oxygen atoms in the side chain. After confirmation by structural characterization, the basic properties of PBDT-IIDs are also investigated. With the increase in the OEG side chain length, the polymer PBDT-IID4 not only has good solubility in the halogen solvent chlorobenzene, but also exhibits excellent solubility in the green halogen-free solvent methyltetrahydrofuran (Me-THF). As a result, the green solvent Me-THF can also be applied to prepare PBDT-IIDs' electrochromic active layers, except for chlorobenzene and toluene. The electrochromism of PBDT IIDs under both positive and negative voltages has a practical application potential. The several controllable switches between dark green and khaki (0-0.6 V) are expected to show great potential in the field of military camouflage. Furthermore, according to the principle of red, green, and blue (RGB) mixing, light blue-green in the reduced state (-1.6 V) can be used in the preparation of complementary ECDs to provide one of the three primary colors (green).

Ion Transport in 2D Nanostructured π-Conjugated Thieno[3,2-b]thiophene-Based Liquid Crystal.

Leveraging the self-assembling behavior of liquid crystals designed for controlling ion transport is of both fundamental and technological significance. Here, we have designed and prepared a liquid crystal that contains 2,5-bis(thien-2-yl)thieno[3,2-b]thiophene (BTTT) as mesogenic core and conjugated segment and symmetric tetra(ethylene oxide) (EO4) as polar side chains for ion-conducting regions. Driven by the crystallization of the BTTT cores, BTTT/dEO4 exhibits well-ordered smectic phases below 71.5 °C as confirmed by differential scanning calorimetry, polarized optical microscopy, temperature-dependent wide-angle X-ray scattering, and grazing incidence wide-angle X-ray scattering (GIWAXS). We adopted a combination of experimental GIWAXS and molecular dynamics (MD) simulations to better understand the molecular packing of BTTT/dEO4 films, particularly when loaded with the ion-conducting salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Ionic conduction of BTTT/dEO4 is realized by the addition of LiTFSI, with the material able to maintain smectic phases up to r = [Li+]/[EO] = 0.1. The highest ionic conductivity of 8 × 10-3 S/cm was attained at an intermedium salt concentration of r = 0.05. It was also found that ion conduction in BTTT/dEO4 is enhanced by forming a smectic layered structure with irregular interfaces between the BTTT and EO4 layers and by the lateral film expansion upon salt addition. This can be explained by the enhancement of the misalignment and configurational entropy of the side chains, which increase their local mobility and that of the solvated ions. Our molecular design thus illustrates how, beyond the favorable energetic interactions that drive the assembly of ion solvating domains, modulation of entropic effects can also be favorably harnessed to improve ion conduction.

Tenuous transcriptional threshold of human sex determination. II. SRY exploits water-mediated clamp at the edge of ambiguity.

Y-encoded transcription factor SRY initiates male differentiation in therian mammals. This factor contains a high-mobility-group (HMG) box, which mediates sequence-specific DNA binding with sharp DNA bending. A companion article in this issue described sex-reversal mutations at box position 72 (residue 127 in human SRY), invariant as Tyr among mammalian orthologs. Although not contacting DNA, the aromatic ring seals the domain's minor wing at a solvent-exposed junction with a basic tail. A seeming paradox was posed by the native-like biochemical properties of inherited Swyer variant Y72F: its near-native gene-regulatory activity is consistent with the father's male development, but at odds with the daughter's XY female somatic phenotype. Surprisingly, aromatic rings (Y72, F72 or W72) confer higher transcriptional activity than do basic or polar side chains generally observed at solvated DNA interfaces (Arg, Lys, His or Gln). Whereas biophysical studies (time-resolved fluorescence resonance energy transfer and heteronuclear NMR spectroscopy) uncovered only subtle perturbations, dissociation of the Y72F complex was markedly accelerated relative to wild-type. Studies of protein-DNA solvation by molecular-dynamics (MD) simulations of an homologous high-resolution crystal structure (SOX18) suggest that Y72 para-OH anchors a network of water molecules at the tail-DNA interface, perturbed in the variant in association with nonlocal conformational fluctuations. Loss of the Y72 anchor among SRY variants presumably "unclamps" its basic tail, leading to (a) rapid DNA dissociation despite native affinity and (b) attenuated transcriptional activity at the edge of sexual ambiguity. Conservation of Y72 suggests that this water-mediated clamp operates generally among SRY and metazoan SOX domains.

Myosin loop-4 is critical for optimal tropomyosin repositioning on actin during muscle activation and relaxation.

During force-generating steps of the muscle crossbridge cycle, the tip of the myosin motor, specifically loop-4, contacts the tropomyosin cable of actin filaments. In the current study, we determined the corresponding effect of myosin loop-4 on the regulatory positioning of tropomyosin on actin. To accomplish this, we compared high-resolution cryo-EM structures of myosin S1-decorated thin filaments containing either wild-type or a loop-4 mutant construct, where the seven-residue portion of myosin loop-4 that contacts tropomyosin was replaced by glycine residues, thus removing polar side chains from residues 366-372. Cryo-EM analysis of fully decorated actin-tropomyosin filaments with wild-type and mutant S1, yielded 3.4-3.6 Å resolution reconstructions, with even higher definition at the actin-myosin interface. Loop-4 densities both in wild-type and mutant S1 were clearly identified, and side chains were resolved in the wild-type structure. Aside from loop-4, actin and myosin structural domains were indistinguishable from each other when filaments were decorated with either mutant or wild-type S1. In marked contrast, the position of tropomyosin on actin in the two reconstructions differed by 3 to 4 Å. In maps of filaments containing the mutant, tropomyosin was located closer to the myosin-head and thus moved in the direction of the C-state conformation adopted by myosin-free thin filaments. Complementary interaction energy measurements showed that tropomyosin in the mutant thin filaments sits on actin in a local energy minimum, whereas tropomyosin is positioned by wild-type S1 in an energetically unfavorable location. We propose that the high potential energy associated with tropomyosin positioning in wild-type filaments favors an effective transition to B- and C-states following release of myosin from the thin filaments during relaxation.

Energy Transfer in Aqueous Light Harvesting Antennae Based on Brush-like Inter-Conjugated Polyelectrolyte Complexes.

Conjugated polyelectrolytes (CPEs) have the potential to serve as building blocks of artificial light-harvesting systems. This is primarily due to their delocalized electronic states and potential for hierarchical self-assembly. We showed previously that inter-CPE complexes composed of oppositely charged exciton-donor and exciton-acceptor CPEs displayed efficient electronic energy transfer. However, near ionic charge equivalence, complexed CPE chains become net-neutral and thus experience a precipitous drop in aqueous solubility. To increase the stability and to rationally manipulate the phase behavior of inter-CPE complexes, we synthesized a series of highly water-soluble exciton-donor CPEs composed of alternating ionic and polar nonionic fluorene monomers. The nonionic monomer contained oligo(ethyleneglycol) sidechains of variable length. We then formed exciton donor-acceptor complexes and investigated their relative energy transfer efficiencies in the presence of a fixed exciton-acceptor CPE. We find that, even when the polar nonionic sidechains become quite long (nine ethyleneglycol units), the energy transfer efficiency is hardly affected so long as the inter-CPE network retains a net polyelectrolyte charge. However, near the onset of spontaneous phase separation, we observe a clear influence of the length of the oligo(ethyleneglycol) sidechains on the photophysics of the complex. Our results have implications for the use of polyelectrolyte phase separation to produce aqueous light-harvesting soft materials.

The influenza hemagglutinin stem antibody CR9114: Evidence for a narrow evolutionary path towards universal protection

Human monoclonal antibodies (hmAbs) that protect against all influenza A and B strains are considered the road to universal influenza vaccines. Based on publicly-available data, we analyze the mechanistic and structural basis of pan-influenza protection by CR9114, a hemagglutinin (HA) stem-reactive antibody that protects against influenza subtypes from groups A1, A2, and B. The mechanistic basis of CR9114’s universal protection is not limited to in vitro neutralization, as CR9114 also protects in vivo from strains that escape its neutralizing activity: some H2 strains and influenza B. Fusion inhibition, viral egress inhibition, and activation of Fc-mediated effector functions are key contributors to CR9114’s universal protection. A comparative analysis of paratopes – between CR9114 (pan-influenza protection) and structurally similar VH1-69 hmAb CR6261 (influenza A1 protection) – pinpoints the structural basis of pan-influenza protection. CR9114’s heterosubtypic binding is conferred by its ability to bind HA with multiple domains: three HCDR loops and FR3. In contrast to other VH1-69 hmAbs, CR9114 uses a long and polar side chain of tyrosine (Y) residues on its HCDR3 for crucial H-bonds with H3, H5, and B HA. The recognition of a highly conserved epitope by CR9114 results in a high genetic barrier for escape by influenza strains. The nested, hierarchical structure of the mutations between the germline ancestor and CR9114 demonstrates that it is the result of a narrow evolutionary pathway within the B cell population. This rare evolutionary pathway indicates an immuno-recessive epitope and limited opportunity for vaccines to induce a polyclonal CR9114-like response.

Two‐Electron Tetrathiafulvalene Catholytes for Nonaqueous Redox Flow Batteries

AbstractTetrathiafulvalene (TTF) exhibits two reversible oxidation steps and is used as a novel multi‐electron catholyte for nonaqueous organic redox flow batteries. To increase solubility in polar organic solvents, TTF derivatives with polar side chains are synthesized. 4‐Methoxymethyltetrathiafulvalene emerges as a promising two‐electron catholyte because it is a liquid at room temperature and miscible with acetonitrile. Bulk‐electrolysis experiments and UV‐vis‐NIR absorption spectroscopy reveal excellent cycling stability for the first and second electrochemical oxidations. In the doubly oxidized state, the TTF derivatives show a reversible about 1 % loss of the state of charge per day, due to extrinsic effects. In a symmetric redox flow battery, 4‐methoxymethyltetrathiafulvalene shows a volumetric capacity loss of only 0.2 % per cycle with a Coulombic efficiency (CE) of 99.6 %. In an asymmetric redox flow battery with a pyromellitic diimide as two‐electron anolyte, the capacity loss is 0.8 % per cycle, with CE>99 % in each cycle.

Interplay between local protein interactions and water bridging of a proton antenna carboxylate cluster

Proteins that bind protons at cell membrane interfaces often expose to the bulk clusters of carboxylate and histidine sidechains that capture protons transiently and, in proton transporters, deliver protons to an internal site. The protonation-coupled dynamics of bulk-exposed carboxylate clusters, also known as proton antennas, is poorly described. An essential open question is how water-mediated bridges between sidechains of the cluster respond to protonation change and facilitate transient proton storage. To address this question, here I studied the protonation-coupled dynamics at the proton-binding antenna of PsbO, a small extrinsinc subunit of the photosystem II complex, with atomistic molecular dynamics simulations and systematic graph-based analyses of dynamic protein and protein-water hydrogen-bond networks. The protonation of specific carboxylate groups is found to impact the dynamics of their local protein-water hydrogen-bond clusters. Regardless of the protonation state considered for PsbO, carboxylate pairs that can sample direct hydrogen bonding, or bridge via short hydrogen-bonded water chains, anchor to nearby basic or polar protein sidechains. As a result, carboxylic sidechains of the hypothesized antenna cluster are part of dynamic hydrogen bond networks that may rearrange rapidly when the protonation changes.

Efficient Selective Sorting of Semiconducting Carbon Nanotubes Using Ultra-Narrow-Band-Gap Polymers.

Conjugated polymers with narrow band gaps are particularly useful for sorting and discriminating semiconducting single-walled carbon nanotubes (s-SWCNT) due to the low charge carrier injection barrier for transport. In this paper, we report two newly synthesized narrow-band-gap conjugated polymers (PNDITEG-TVT and PNDIC8TEG-TVT) based on naphthalene diimide (NDI) and thienylennevinylene (TVT) building blocks, decorated with different polar side chains that can be used for dispersing and discriminating s-SWCNT. Compared with the mid-band-gap conjugated polymer PNDITEG-AH, which is composed of naphthalene diimide (NDI) and head-to-head bithiophene building blocks, the addition of a vinylene linker eliminates the steric congestion present in head-to-head bithiophene, which promotes backbone planarity, extending the π-conjugation length and narrowing the band gap. Cyclic voltammetry (CV) and density functional theory (DFT) calculations suggest that inserting a vinylene group in a head-to-head bithiophene efficiently lifts the highest occupied molecular orbital (HOMO) level (−5.60 eV for PNDITEG-AH, −5.02 eV for PNDITEG-TVT, and −5.09 eV for PNDIC8TEG-TVT). All three polymers are able to select for s-SWCNT, as evidenced by the sharp transitions in the absorption spectra. Field-effect transistors (FETs) fabricated with the polymer:SWCNT inks display p-dominant properties, with higher hole mobilities when using the NDI-TVT polymers as compared with PNDITEG-AH (0.6 cm2 V–1 s–1 for HiPCO:PNDITEG-AH, 1.5 cm2 V–1 s–1 for HiPCO:PNDITEG-TVT, and 2.3 cm2 V–1 s–1 for HiPCO:PNDIC8TEG-TVT). This improvement is due to the better alignment of the HOMO level of PNDITEG-TVT and PNDIC8TEG-TVT with that of the dominant SWCNT specie.

Effect of amino acid on the surface adsorption and micellar properties of surface active ILs varying in cationic head groups

The interfacial along with bulk characteristics of the aqueous solutions of ILs with dissimilar cationic head group viz. 1-dodecyl-3-methylimidazolium bromide ([C12mim][Br]), and N-dodecyl-N-methylmorpholinium bromide ([Mor1,12][Br]) in the absence and the presence of an amino acid L-Methionine as an external additive have been examined by electrical conductivity, UV-Visible, surface tension, and DLS measurements. The CMC values, and the lowest maximum surface excess concentration (Гmax) achieved from all three techniques, and surface tension measurements respectively displayed more surface activity of the [C12mim][Br] than the [Mor1,12][Br]. Also, the morpholinium head group is less hazardous than imidazolium, it can be utilised to design ILs that are greener, mainly in combination with polar, small, and non-toxic side chains and anions.

Glycol bearing perylene monoimide based non-fullerene acceptors with increased dielectric permittivity

Perylene monoimide based electron acceptors have great properties for use in organic solar cells, like thermal stability, strong absorption, and simple synthesis. However, they typically exhibit low values for the dielectric permittivity. This hinders efficient exciton dissociation, limiting the achievable power conversion efficiencies. In this work, we present the synthesis and utilization of two new acceptor–donor-acceptor (A-D-A) molecules, comprising perylene monoimide as electron withdrawing A unit. Oligo ethylene glycol side chain modified carbazole (PMI-[C-OEG]) and fluorene (PMI-[F-OEG]) linkers were used as electron rich D units, respectively. The polar side chains are expected to increase the polarizability of the molecules and, thus, their permittivity according to the Clausius–Mossotti relationship. We found that the incorporation of glycol chains improved the dielectric properties of both materials in comparison to the reference compounds with alkyl chains. The permittivity increased by 18% from 3.17 to 3.75 for the carbazole-based non-fullerene acceptor PMI-[C-OEG] and by 12% from 3.10 to 3.47 for the fluorene-based acceptor PMI-[F-OEG]. The fabricated solar cells revealed power conversion efficiencies of 3.71 ± 0.20% (record 3.92%) with PMI-[C-OEG], and 1.21 ± 0.06% (record 1.51%) with PMI-[F-OEG].Graphical abstract

Positive and negative cluster ions of amino acids formed by electrospray droplet impact/secondary ion mass spectrometry (EDI/SIMS)

Cluster ions of amino acids (AAs) have been measured by several ionization methods such as electrospray, sonic spray, thermal desorption, and gas cluster ion beam (Arn+) bombardment. Prior research has primarily focused on positively charged cluster ions, whereas the formation of negatively charged cluster ions remains largely unexplored. In this study, mass spectra of both positive and negative cluster ions for 20 amino acids were measured by electrospray droplet impact/secondary ion mass spectrometry (EDI/SIMS). Because EDI is capable of generating abundant negative ions as well as positive ions, it is best suited for the comparative study on the dependence of polarity for AA cluster ions. For AAs with apolar side chains such as Ala, Val, Leu, and Ile, while large cluster sizes of positive cluster ions [n(AA) + H]+ (n = 11–21) were observed, negative cluster ions [n(AA) − H]− were observed with only n up to 3. The AAs with polar side chains (Ser, Thr, Asn, Gln, Tyr and Cys) gave similar n up to 7–12 for both [n(AA) + H]+ and [n(AA) − H]−. For basic AAs (Lys and Arg), the maximum n values observed for [n(AA) + H]+ are larger than those for [n(AA) − H]− and vice versa for acidic AA (Asp and Glu). A sharp intensity drop with n→(n+1) was observed for [n(AA) + H]+ with n of 12, 8, 8 and 11 for Pro, Ser, Thr, and Tyr, respectively. The magic number 8 for positive and 6 for negative cluster ions of Ser and Thr are in agreement with previous work. No magic numbers were observed for [n(AA) + H]+ and [n(AA) − H]− for acidic amino acids (Asp and Glu). The ligands (n−1)AAs in the negative clusters [AA − H]−⋅⋅⋅⋅(n−1)AA are bound more loosely than those in the positive clusters [AA + H]+ ⋅⋅⋅⋅(n−1)AA. The stability of amino acid cluster ions is critically affected by the polarities and structures of amino acids.

SARS-CoV-2 Delta variant isolates from vaccinated individuals

BackgroundThe SARS-CoV-2 Delta variant was first identified in the U.S. in March 2021 and has rapidly become the predominant lineage across the U.S. due to increased transmissibility, immune evasion and vaccine breakthrough. The aim of this study was to better understand the genetic diversity and the potential impact of mutations observed in SARS-CoV-2 viruses circulating in the U.S. in vaccinated individuals.ResultsWhole genome sequencing was performed on thirty-four SARS-CoV-2 positive samples using the Oxford Nanopore MinION. Evolutionary genomic analysis revealed two novel mutations, ORF1b:V2354F and a premature stop codon, ORF7a:Q94*, identified in a cluster of SARS-CoV-2 Delta isolates collected from vaccinated individuals in Colorado. The ORF1b:V2354F mutation, corresponding to NSP15:V303F, may induce a conformational change and result in a disruption to a flanking beta-sheet structure. The premature stop codon, ORF7a:Q94*, truncates the transmembrane protein and cytosolic tail used to mediate protein transport. This may affect protein localization to the ER-Golgi. In addition to these novel mutations, the cluster of vaccinated isolates contain an additional mutation in the spike protein, at position 112, compared to the Delta variant defining mutations. This mutation, S112L, exists in isolates previously obtained in the U.S. The S112L mutation substitutes a bulky hydrophobic side chain for a polar side chain, which results in a non-conservative substitution within the protein that may affect antibody-binding affinity. Additionally, the vaccinated cluster of isolates contains non-synonymous mutations within ORF8 and NSPs which further distinguish this cluster from the respective ancestral Delta variant.ConclusionsThese results show there is an emerging sub-lineage of the ancestral Delta variant circulating in the U.S. As mutations emerge in constellations, those with a potentially beneficial advantage to the virus may continue to circulate while others will cease.

Self-Healable, Self-Repairable, and Recyclable Electrically Responsive Artificial Muscles.

Elastomers with high dielectric permittivity that self‐heal after electric breakdown and mechanical damage are important in the emerging field of artificial muscles. Here, a one‐step process toward self‐healable, silicone‐based elastomers with large and tunable permittivity is reported. Anionic ring‐opening polymerization of cyanopropyl‐substituted cyclic siloxanes yields elastomers with polar side chains. The equilibrated product is composed of networks, linear chains, and cyclic compounds. The ratio between the components varies with temperature and allows realizing materials with largely different properties. The silanolate end groups remain active, which is the key to self‐healing. Elastomeric behavior is observed at room temperature, while viscous flow dominates at higher temperatures (typically 80 °C). The elasticity is essential for reversible actuation and the thermoreversible softening allows for self‐healing and recycling. The dielectric permittivity can be increased to a maximum value of 18.1 by varying the polar group content. Single‐layer actuators show 3.8% lateral actuation at 5.2 V µm–1 and self‐repair after a breakdown, while damaged ones can be recycled integrally. Stack actuators reach an actuation strain of 5.4 ± 0.2% at electric fields as low as 3.2 V µm–1 and are therefore promising for applications as artificial muscles in soft robotics.

Kir7.1 disease mutant T153I within the inner pore affects K+ conduction.

Inward-rectifier potassium channel 7.1 (Kir7.1) is present in the polarized epithelium, including the retinal pigmented epithelium. A single amino acid change at position 153 in the KCNJ13 gene, a substitution of threonine to isoleucine in the Kir7.1 protein, causes blindness. We hypothesized that the disease caused by this single amino acid substitution within the transmembrane protein domain could alter the translation, localization, or ion transport properties. We assessed the effects of amino acid side-chain length, arrangement, and polarity on channel structure and function. We showed that the T153I mutation yielded a full-length protein localized to the cell membrane. Whole cell patch-clamp recordings and chord conductance analyses revealed that the T153I mutant channel had negligible K+ conductance and failed to hyperpolarize the membrane potential. However, the mutant channel exhibited enhanced inward current when rubidium was used as a charge carrier, suggesting that an inner pore had formed and the channel was dysfunctional. Substituting with a polar, nonpolar, or short side-chain amino acid did not affect the localization of the protein. Still, it had an altered channel function due to differences in pore radius. Polar side chains (cysteine and serine) with inner pore radii comparable to wildtype exhibited normal inward K+ conductance. Short side chains (glycine and alanine) produced a channel with wider than expected inner pore size and lacked the biophysical characteristics of the wild-type channel. Leucine substitution produced results similar to the T153I mutant channel. This study provides direct electrophysiological evidence for the structure and function of the Kir7.1 channel's narrow inner pore in regulating conductance.

Influence of N Terminus Amino Acid on Peptide Cleavage in Solution through Diketopiperazine Formation.

Diketopiperazine (DKP) formation is an important degradation pathway for peptides and proteins. It can occur during synthesis and storage in either solution or the solid state. The kinetics of peptide cleavage through DKP formation have been analyzed for the model peptides Xaa1-Pro2-Gly4-Lys7 [Xaa = Gln, Glu, Lys, Ser, Phe, Trp, Tyr, Cha (β-cyclohexylalanine), Aib (α-aminoisobutyric acid), Gly, and Val] at multiple elevated temperatures in ethanol with ion mobility spectrometry-mass spectrometry (IMS-MS). When Xaa is an amino acid with a charged or polar side chain, degradation is relatively fast. When Xaa is an amino acid with a nonpolar alkyl side chain, the peptide is relatively stable. For these peptides, a bulky group on the α carbon speeds up dissociation, but the kinetic effects vary in a complicated manner for bulky groups on the β or γ carbon. Peptides where Xaa has a nonpolar aromatic side chain show moderate dissociation rates. The stability of these peptides is a result of multiple factors. The reaction rate is enhanced by (1) the stabilization of the late transition state through the interaction of an aromatic ring with the nascent DKP ring or lowering the activation energy of nucleophilic attack intermediate state through polar or charged residues and (2) the preference of the cis proline bond favored by the aromatic N-terminus. The number of unseen intermediates and transition state thermodynamic values are derived for each peptide by modeling the kinetics data. Most of the transition states are entropically favored (ΔS⧧ ∼ -5 to +31 J·mol-1·K-1), and all are enthalpically disfavored (ΔH⧧ ∼ 93 to 109 kJ·mol-1). The Gibbs free energy of activation is similar for all of the peptides studied here (ΔG⧧ ∼ 90-99 kJ·mol-1).

Investigation and Modeling of the Electrical Bias Stress in Electrolyte‐Gated Organic Transistors

AbstractElectrolyte‐gated organic transistors (EGOTs) are emerging as an important tool in advanced biosensing applications. However, their widespread exploitation is still limited by their poor operational stability. In order to understand the causes of this unreliability, the proposed study focuses on the influence of electrical bias stress (EBS) on EGOTs operating in aqueous electrolytes. Poly(3‐hexylthiophene) (P3HT)‐ and poly[3‐(5‐carboxypentyl)thiophene)] (P3CPT)‐based transistors are studied under the application of a bias in the continuous and pulse mode. Combining electrical and spectroscopic characterizations, it is possible to ascribe the performance variation of P3HT devices to backbone rearrangements induced by side chain oxidation, hydration, and interfacial electrochemical doping at the semiconductor/electrolyte interface, while the presence of polar side chains in P3CPT enhances the oxidative degradation of the polymer throughout the bulk of the film. The charge‐trapping model based on a stretched exponential is commonly exploited for the description of EBS in solid dielectric organic field‐effect transistors (OFETs). The same model is here applied to fit liquid dielectric EGOT behavior. The extracted material parameters are in good agreement with those found in the literature for P3HT‐based OFETs. Finally, a novel improvement of the model is proposed to allow reproducing P3CPT data by accounting for its different degradation process.

Hydrogen‐Deuterium Exchange Identifies the Structural Basis of Phase Separation of the Chromosome Passenger Complex

The centromere is the locus that directs accurate chromosome segregation, and a master regulatory complex, the chromosome passenger complex (CPC) is enriched in a region of the mitotic centromere termed the inner centromere. In mitosis, the CPC monitors the connections of the centromere to the mitotic spindle, acting to destabilize incorrect attachments but permitting correct attachments to persist. The CPC contains the Aurora‐B kinase and three regulatory subunits: INCENP, Survivin and Borealin. Recent findings support a role for CPC phase separation in its localization and function in mitotic error correction (Trivedi et al., 2019, Nat. Cell Biol. 21:1127‐1137). Liquid‐liquid phase separation is emerging as a central regulatory principle of cell biology. This form of phase separation is often driven by multivalency of adhesive domains and/or linear motifs. The sequences of these domains are often found in unstructured regions where they are enriched in uncharged polar side chains, charged amino acids, or aromatic residues; additionally, structural plasticity allows them to generate multiple, weakly‐adhesive, inter‐ and intramolecular interactions. Currently there are no techniques to globally map the motifs on proteins that drive the multivalent interactions. In this context, we now employ hydrogen/deuterium exchange coupled to mass spectrometry (HXMS) to study dynamics of CPC phase separation. We have identified four regions within the regulatory CPC subunits that upon phase separation exhibit differential HX (three slower and one faster). Importantly, three of these regions map to structured regions of proteins while one maps to the expected intrinsically disordered regions. Each of the four regions is enriched with charged amino acids. Mutation of key residues in one of the differential HX regions within the INCENP subunit diminish droplet size and quantity, suggesting that we have successfully mapped a key surface for the phase separation properties of the CPC. In broader context we have shown for the first time how HXMS coupled with structural data and bioinformatic analysis can be applied to study molecular basics of protein liquid‐liquid phase separation.

Substitutability of metal-binding sites in an alcohol dehydrogenase

Covalently anchoring of a ligand/metal via polar amino acid side chain(s) is often observed in metalloenzyme, while the substitutability of metal-binding sites remains elusive. In this study, we utilized a zinc-dependent alcohol dehydrogenase from Thermoanaerobacter brockii (TbSADH) as a model enzyme, analyzed the sequence conservation of the three residues Cys37, His59, and Asp150 that bind the zinc ion, and constructed the mutant library. After experimental validation, three out of 224 clones, which showed comparative conversion and ee values as the wild-type enzyme in the asymmetric reduction of the model substrate tetrahydrofuran-3-one, were screened out. The results reveal that the metal-binding sites in TbSADH are substitutable without tradeoff in activity and stereoselectivity, which lay a foundation for designing ADH-catalyzed new reactions via metal ion replacement.

MptpA Kinetics Enhanced by Allosteric Control of an Active Conformation

Understanding allostery in the Mycobacterium tuberculosis low molecular weight protein tyrosine phosphatase (MptpA) is a subject of great interest since MptpA is one of two protein tyrosine phosphatases (PTPs) from the pathogenic organism Mycobacterium tuberculosis expressed during host cell infection. Here, we combine computational modeling with solution NMR spectroscopy and we find that Q75 is an allosteric site. Removal of the polar side chain of Q75 by mutation to leucine results in a cascade of events that reposition the acid loop over the active site and relocates the catalytic aspartic acid (D126) at an optimal position for proton donation to the leaving aryl group of the substrate and for subsequent hydrolysis of the thiophosphoryl intermediate. The computational analysis is consistent with kinetic data, and NMR spectroscopy, showing that the Q75L mutant exhibits enhanced reaction kinetics with similar substrate binding affinity. We anticipate that our findings will motivate further studies on the possibility that MptpA remains passivated during the chronic state of infection and increases its activity as part of the pathogenic life cycle of M. tuberculosis possibly via allosteric means.