Intramolecular Conformation Research Articles

Significant Electromechanical Characteristic Enhancement of Coaxial Electrospinning Core-Shell Fibers.

Electrospinning is a low-cost and straightforward method for producing various types of polymers in micro/nanofiber form. Among the various types of polymers, electrospun piezoelectric polymers have many potential applications. In this study, a new type of functional microfiber composed of poly(γ-benzyl-α,L-glutamate) (PBLG) and poly(vinylidene fluoride) (PVDF) with significantly enhanced electromechanical properties has been reported. Recently reported electrospun PBLG fibers exhibit polarity along the axial direction, while electrospun PVDF fibers have the highest net dipole moment in the transverse direction. Hence, a combination of PBLG and PVDF as a core–shell structure has been investigated in the present work. On polarization under a high voltage, enhancement in the net dipole moment in each material and the intramolecular conformation was observed. The piezoelectric coefficient of the electrospun PBLG/PVDF core–shell fibers was measured to be up to 68 pC N−1 (d33), and the voltage generation under longitudinal extension was 400 mVpp (peak-to-peak) at a frequency of 60 Hz, which is better than that of the electrospun homopolymer fibers. Such new types of functional materials can be used in various applications, such as sensors, actuators, smart materials, implantable biosensors, biomedical engineering devices, and energy harvesting devices.

A transposon-introduced G-quadruplex motif is selectively retained and constrained to downregulate CYP321A1.

Insects utilize xenobiotic compounds to up- and downregulate cytochrome P450 monooxygenases (P450s) involved in detoxification of toxic xenobiotics including phytochemicals and pesticides. G-quadruplexes (G4)-forming DNA motifs are enriched in the promoter regions of transcription factors and function as cis-acting elements to regulate these genes. Whether and how P450s gain and keep G4 DNA motifs to regulate their expression still remain unexplored. Here, we show that CYP321A1, a xenobiotic-metabolizing P450 from Helicoverpa zea, a polyphagous insect of economic importance, has acquired and preserved a G4 DNA motif by selectively retaining a transposon known as HzIS1-3 that carries this G4 DNA motif in its promoter region. The HzIS1-3 G4 DNA motif acts as a silencer to suppress the constitutive and induced expression of CYP321A1 by plant allelochemicals flavone and xanthotoxin through folding into an intramolecular parallel or hybrid-1 conformation in the absence or presence of K+ . The G4 ligand N-methylmesoporphyrin IX (NMM) strengthens the silencing effect of HzIS1-3 G4 DNA motif by switching its structure from hybrid-1 to hybrid-2. The enrichment of transposons in P450s and other environment-adaptation genes implies that selective retention of G4 DNA motif-carrying transposons may be the main evolutionary route for these genes to obtain G4 DNA motifs.

Structure dynamics of HIV-1 Env trimers on native virions engaged with living T cells

The HIV-1 envelope glycoprotein (Env) mediates viral entry into the host cell. Although the highly dynamic nature of Env intramolecular conformations has been shown with single molecule spectroscopy in vitro, the bona fide Env intra- and intermolecular mechanics when engaged with live T cells remains unknown. We used two photon fast fluorescence lifetime imaging detection of single-molecule Förster Resonance Energy Transfer occurring between fluorescent labels on HIV-1 Env on native virions. Our observations reveal Env dynamics at two levels: transitions between different intramolecular conformations and intermolecular interactions between Env within the viral membrane. Furthermore, we show that three broad neutralizing anti-Env antibodies directed to different epitopes restrict Env intramolecular dynamics and interactions between adjacent Env molecules when engaged with living T cells. Importantly, our results show that Env-Env interactions depend on efficient virus maturation, and that is disrupted upon binding of Env to CD4 or by neutralizing antibodies. Thus, this study illuminates how different intramolecular conformations and distribution of Env molecules mediate HIV-1 Env–T cell interactions in real time and therefore might control immune evasion.

Enthalpy–Entropy Compensation Effect for Triplet Pair Dissociation of Intramolecular Singlet Fission in Phenylene Spacer-Bridged Hexacene Dimers

Hexacene (Hc) is highly promising for singlet fission (SF). However, the number of SFs in Hc is extremely limited. As far as Hc dimers in solution are concerned, there is no report on the observation of the dissociation process from a correlated triplet pair (TT) to an individual one. The emphasis in this study is on the first observation of the quantitative TT generation together with the orientation-dependent photophysical discussions for TT dissociation using para- and meta-phenyl-bridged Hc dimers. Moreover, the activation enthalpies of Hc dimers in TT dissociation are smaller than those of pentacene (Pc) dimers, whereas the relative entropic contributions for Gibbs free energy of activation are much larger than the enthalpic ones in both Hc and Pc dimers. This implies that the vibrational motions are responsible for the intramolecular conformation changes associated with the TT dissociation. Consequently, "enthalpy-entropy compensation" has a large impact on the rate constants and quantum yields.

Optimizing the self‐assembly of conjugated polymers and small molecules through structurally programmed non‐covalent control

AbstractOrganic conjugated polymers and oligomers are key electronic materials for applications such as transistors, photovoltaics, and light emitting devices due to their potential for solution processability, mechanical flexibility, and precise structure‐based tuning compared to inorganic materials. In dilute environments, the optoelectronic properties of conjugated polymers are largely governed by their constitutional structure and, to a lesser degree, their solution‐state intramolecular configuration. In the solid state, intramolecular conformation and intermolecular electronic coupling impact these properties substantially, especially in relation to device performance. Therefore, an increasingly important area of research concerning conjugated materials is developing design strategies aimed at optimizing the solid‐state packing for electronic applications. Programming solid‐state packing arrangements through discrete non‐covalent interactions is an emerging strategy within the context of conjugated polymers. This review focuses on the use of the two most prevalent discrete and directional interactions used to dictate the self‐assembly of conjugated polymers and oligomers—hydrogen bonds and chalcogen bonds. We also discuss how these design motifs can imbue conjugated materials with appealing physical properties while simultaneously retaining or improving electronic capabilities.

ABEL-FRET: tether-free single-molecule FRET with hydrodynamic profiling.

Single-molecule Förster resonance energy transfer (smFRET) has become a versatile and widespread method to probe nanoscale conformation and dynamics. However, current experimental modalities often resort to molecule immobilization for long observation times and do not always approach the resolution limit of FRET-based nanoscale metrology. Here we present ABEL-FRET, an immobilization-free platform for smFRET measurements with ultrahigh resolving power in FRET efficiency. Importantly, single-molecule diffusivity is used to provide additional size and shape information for hydrodynamic profiling of individual molecules, which, together with the concurrently measured intramolecular conformation through FRET, enables a holistic and dynamic view of biomolecules and their complexes.

Insights into Regional Wetting Behaviors of Amphiphilic Collagen for Dual Separation of Emulsions.

Industrial manufacture generates a huge quantity of emulsion wastewater, which causes serious threats to the aquatic ecosystems. Water-in-oil (W/O) and oil-in-water (O/W) emulsions are two major types of emulsions discharged by industries. However, dual separation of W/O and O/W emulsions remains a challenging issue due to the contradictory permselectivity for separating the two emulsions. In the present investigation, the amphiphilicity-derived regional wetting mechanism of water and oil on the amphiphilic collagen fibers was revealed based on the combination of numerous experiments and molecular dynamics (MD) simulations. Electrostatic interactions and van der Waals force were manifested to be the driving forces of regional wetting in the hydrophilic and hydrophobic regions, respectively. The regional wetting endowed amphiphilic collagen fibers with underwater oleophobicity and underoil hydrophilicity, which enabled dual separation of emulsions by selectively retaining the dispersed water phase of W/O emulsions in the hydrophilic regions while the dispersed oil phase of O/W emulsions in the hydrophobic regions. The achieved separation efficiency was higher than 99.98%, and the flux reached 3337.6 L m-2 h-1. Initial wetting status significantly affects the regional wetting-enabled dual separation. Based on the MD simulations, amphiphilic intramolecular conformations of tropocollagen were suggested to be the origins of regional wetting on collagen fibers. Our findings may pave the way for developing high-performance dual separation materials that are promising to be utilized for the practical treatment of emulsion wastewater.

Spectroscopic and Theoretical Study of the Intramolecular π-Type Hydrogen Bonding and Conformations of 2-Cyclopenten-1-ol.

The conformations of 2-cyclopenten-1-ol (2CPOL) have been investigated by high-level theoretical computations and infrared spectroscopy. The six conformational minima correspond to specific values of the ring-puckering and OH internal rotation coordinates. The conformation with the lowest energy possesses intramolecular π-type hydrogen bonding. A second conformer with weaker hydrogen bonding has somewhat higher energy. Ab initio coupled-cluster theory with single and double excitations (CCSD) was used with the cc-pVTZ (triple-ζ) basis set to calculate the two-dimensional potential energy surface (PES) governing the conformational dynamics along the ring-puckering and internal rotation coordinates. The two conformers with the hydrogen bonding lie about 300 cm−1 (0.8 kcal/mole) lower in energy than the other four conformers. The lowest energy conformation has a calculated distance of 2.68 Å from the hydrogen atom on the OH group to the middle of the C=C double bond. For the other conformers, this distance is at least 0.3 Å longer. The infrared spectrum in the O-H stretching region agrees well with the predicted frequency differences between the conformers and shows the conformers with the hydrogen bonding to have the lowest values. The infrared spectra in other regions arise mostly from the two hydrogen-bonded species.

Recent Advances in Mechanism of AIE Mechanochromic Materials

Organic mechanochromic materials(also known as piezochromic materials), whose color or emission changes under mechanical force, have attracted great interest owing to their potential applications in pressure sensors, rewritable materials, optical storage, and security ink. Organic mechanochromic materials with aggregation-induced emission(AIE) features have better development prospects and research value owing to their excellent optical properties. To date, mechanochromism has mostly been realized by means of mechanical grinding. Nevertheless, the magnitude of the grinding force is usually uncontrollable and its direction is anisotropic, making it awkward to study the mechanism of mechanochromic materials. On the contrary, hydrostatic pressure, whose magnitude and direction are controllable, is a more valid and governable method to investigate the mechanism of mechanochromic materials, which can help us to construct a meaningful structure-property relationship and understand the latent origin of the mechanochromism. Furthermore, it is conducive to developing other mechanochromic material systems with desired chemical and physical properties. In this review, we focus on the recent progress in the mechanism of organic mechanochromic materials with AIE features under hydrostatic pressure. Four types of mechanisms are included: intermolecular interaction change, intramolecular conformation change, transformation from locally excited state to intramolecular charge-transfer state, and intra- and inter-molecular effects induced by hydrostatic pressure, respectively.

What Is the Assembly Pathway of a Conjugated Polymer From Solution to Thin Films?

The hierarchical assembly of conjugated polymers has gained much attention due to its critical role in determining optical/electrical/mechanical properties. The hierarchical morphology encompasses molecular-scale intramolecular conformation (torsion angle, chain folds) and intermolecular ordering (π–π stacking), mesoscale domain size, orientation and connectivity, and macroscale alignment and (para)crystallinity. Such complex morphology in the solid state is fully determined by the polymer assembly pathway in the solution state, which, in turn, is sensitively modulated by molecular structure and processing conditions. However, molecular pictures of polymer assembly pathways remain elusive due to the lack of detailed structural characterizations in the solution state and the lack of understanding on how various factors impact the assembly pathways. In this mini-review, we present possible assembly pathways of conjugated polymers and their characteristics across length scales. Recent advances in understanding and controlling of assembly pathways are highlighted. We also discuss the current gap in our knowledge of assembly pathways, with future perspectives on research needed on this topic.

Fluorescence in "Nonfluorescent" Polymers.

Recently, a great deal of research has been started on generating fairly strong photoluminescence from organic molecules without having any conjugated π-system or fluorophore. Discrete chromophores or auxochromophores termed as “subfluorophores” may undergo “space conjugation” via co-operative intramolecular conformation followed by intermolecular aggregation to generate fluorescence or sometimes phosphorescence emission. Polymeric materials are important in this regard as nonconjugated polymers self-assemble/aggregate in a moderately concentrated solution and also in the solid state, producing membranes, films, and so forth with good physical and mechanical properties. Therefore, promoting fluorescence in these commodity polymers is very much useful for sensing, organic light emitting diodes (OLED), and biological applications. In this perspective, we have discussed the aggregation-induced emission from four different types of architectures, for example, (i) dendrimers or hyperbranched polymers, (ii) entrapped polymeric micellar self-assembly, (iii) cluster formation, and (iv) stretching-induced aggregation, begining with the genesis of fluorescence from aggregation of propeller-shaped small organic molecules. The mechanism of induced fluorescence of polymers with subfluorophoric groups is also discussed from the theoretical calculations of the energy bands in the aggregated state. Also, an attempt has been made to highlight some useful applications in the sensing of surfactants, bacteria, cell imaging, drug delivery, gene delivery, OLED, and so forth.

Rotational Dynamics of Nitroxide Biradical in Room-Temperature Ionic Liquids Measured by Quantitative Simulation of EPR Spectra.

Temperature dependences of electron paramagnetic resonance (EPR) spectra of an imidazoline nitroxide biradical spin probe in a series of room-temperature ionic liquids in the temperature range 124-390 K have been quantitatively simulated. The unusual asymmetric EPR spectrum shape previously observed in these systems [Kokorin et al., Appl. Magn. Res. 48 (2016) 287] is shown to originate from anisotropic rotational diffusion of the probe molecule. All experimental spectra were quantitatively reproduced in simulation using a unified set of geometrical and magnetic parameters of the spin probe, which were found to be fully consistent with the biradical geometry obtained from density functional theory calculations. Temperature dependences of rotation diffusion coefficient of the probe characterize the molecular mobility of the ionic liquid, whereas the temperature dependences of the spin-exchange integral J and of the isotropic hyperfine interaction constant, aN, are shown to reflect the intramolecular conformation motions of the biradical probe.

Immobilization of dipyrenylphosphinic acid to boehmite: Fluorescent hybrid with weakened pyrene-aggregation

Ethyldipyrenylphosphate (DPyPOOEt) was designed and synthesized by utilizing ethyldichlorophosphate as the core and 1-bromopyrene as substituting groups, and afterwards dipyrenylphosphinic acid (DPyPOOH) was synthesized by the hydrolysis reaction of DPyPOOEt by using bromotrimethylsilane (TMSBr). Fluorescent hybrid was finally prepared by the dehydration condensation between DPyPOOH and hydroxyl groups on the surface of boehmite. The chemical structure of DPyPOOEt and DPyPOOH were characterized by 1H NMR and 13C NMR. Crystal structure, chemical structure and microtopography of hybrid were characterized by X-ray diffraction spectra (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM), respectively. The results demonstrate that the incorporation of two pyrene substituent groups into phosphine oxide can be successfully immobilized on the surface without any change of crystal structure of boehmite. Fluorescence spectra in solution and powder further demonstrated the occurrence of shape-changed and red-shifted emission peaks of DPyPOOEt and DPyPOOH than that of pyrene. In particular, compared to DPyPOOEt and DPyPOOH in solid, the hybrid shows blue-shifted fluorescence. Optimized molecular conformation, ground electronic structure of DPyPOOEt has been investigated in detail by quantum chemistry method. The introduction of phosphine oxide tunes the conjugated structure of pyrene-ring and spatial conformation between the pyrene-ring. In addition, intramolecular V-shanped conformation when DPyPOOH confined to boehmite surface reduce π-π aggregation between pyrene rings. Therefore, these results indicate that the hybrid is expected to highly efficient blue light-emitting material.

Structure and Dynamics of HIV-1 Env Trimers on Native Virions Engaged in Living T Cells

The HIV-1 envelope glycoprotein (Env) mediates viral entry into the host cell. Although the highly dynamic nature of Env intramolecular conformations has been shown with single molecule spectroscopy in vitro, the bona fide Env intra and intermolecular mechanics when engaged in live T cells remains unknown. We used two photon fast fluorescence lifetime imaging detection of single-molecule Forster Resonance Energy Transfer occurring between fluorescent labels on HIV-1 Env. Our observations of Env dynamics reveal transitions between four intramolecular conformations of Env trimer and two additional intermolecular conformations that mediate Env clustering. Furthermore, we show that three broadly neutralizing anti-Env antibodies directed to different epitopes destabilise Env intermolecular dynamics and their clusters engaged to living T cells. Thus, this study illuminates how different conformations and clusters of Env mediate HIV-1 Env–T cell interactions in real time and therefore might control immune evasion.

Structural studies of human Fis1 reveals a dynamic region important for Drp1 recruitment and mitochondrial fission

Fission protein 1 (Fis1) and dynamin‐related protein 1 (Drp1) were initially described as being evolutionarily conserved for mitochondrial fission, yet the role of Fis1 in human fission is unclear and disputed by many. In budding yeast where Fis1 helps to recruit Drp1 from the cytoplasm to mitochondria for fission, an N‐terminal “arm” of Fis1 is required for function. The yeast Fis1 arm interacts intramolecularly with a conserved surface that governs in vitro interactions with yeast Drp1. In human Fis1, NMR and x‐ray structures show a different arm conformation and its importance for human Drp1 recruitment is unknown. Here, we use MD simulations and comparisons to experimental NMR chemical shifts to show the human Fis1 arm can adopt an intramolecular conformation akin to that observed with the yeast molecule. This finding is further supported through intrinsic tryptophan fluorescence and NMR experiments on human Fis1 with and without the arm. Using NMR, the human Fis1 arm is also observed to be sensitive to environmental changes. The importance of these findings are revealed in cellular studies where the removal of the hFis1 arm reduces Drp1 recruitment and mitochondrial fission suggesting an important role for Fis1 in human mitochondrial fission.Support or Funding InformationThis project was supported by the following National Institutes of Health grants: R01GM067180 (to RBH), and R01HL128240 (to MEW).

Topology-Controlled Selective Fe3+ Binding in Water by δ-Peptides with a Dihydropyrimidinone-Containing Amino Acid

The effect of topology on the structure, self-assembly, and selective Fe3+ binding of δ-peptides has been investigated. A series of δ-peptides with an amino acid containing dihydropyrimidinone and o-, m-, and p-aminobenzoic acids have been designed to study the structure–function relationship. A new amino acid containing dihydropyrimidinone was synthesized by the Biginelli reaction of ethyl acetoacetate, urea, and o-nitrobenzaldehyde followed by reduction with iron powder and acetic acid. X-ray crystallography sheds some light on the conformations, self-assembly, and the diverse degrees of π–π stacking of adjacent δ-peptide molecules. Peptides with o- or m-aminobenzoic acid form eight-membered intramolecular hydrogen-bonded turn conformations and self-assemble through intermolecular hydrogen bonds between dihydropyrimidinone units to form a butterfly-like structure. However, the δ-peptide containing p-aminobenzoic acid forms a water-mediated cage-like structure. Irrespective of the presence of the same functional groups, only the δ-peptide with o-aminobenzoic acid can selectively bind Fe3+ in methanol as well as in water. The topology plays a crucial role in the selective Fe3+ ion binding by the δ-peptide.

Overcoming the difficulties of predicting conformational polymorph energetics in molecular crystals via correlated wavefunction methods.

Molecular crystal structure prediction is increasingly being applied to study the solid form landscapes of larger, more flexible pharmaceutical molecules. Despite many successes in crystal structure prediction, van der Waals-inclusive density functional theory (DFT) methods exhibit serious failures predicting the polymorph stabilities for a number of systems exhibiting conformational polymorphism, where changes in intramolecular conformation lead to different intermolecular crystal packings. Here, the stabilities of the conformational polymorphs of o-acetamidobenzamide, ROY, and oxalyl dihydrazide are examined in detail. DFT functionals that have previously been very successful in crystal structure prediction perform poorly in all three systems, due primarily to the poor intramolecular conformational energies, but also due to the intermolecular description in oxalyl dihydrazide. In all three cases, a fragment-based dispersion-corrected second-order Møller-Plesset perturbation theory (MP2D) treatment of the crystals overcomes these difficulties and predicts conformational polymorph stabilities in good agreement with experiment. These results highlight the need for methods which go beyond current-generation DFT functionals to make crystal polymorph stability predictions truly reliable.

Polymorphic mechanoresponsive luminescent material based on a fluorene–phenanthroimidazole hybrid by modulation of intramolecular conformation and intermolecular interaction

This study examined the multiple energetic pathways in solid-state photophysics, which are of increasing importance in solid-state lighting applications.

High cyclic stability of electrocaloric effect in relaxor poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymers in the absence of ferroelectric phase transition

The incorporation of bulky defects into ferroelectric poly(vinylidene fluoride-trifluoroethylene) copolymers can result in a relaxor behavior, accompanied by outstanding electrocaloric properties near room temperature. However, it remains elusive whether ferroelectric transition occurs in relaxor terpolymers, which is critical for the design of electrocaloric cooling devices. In this work, we study the electrocaloric fatigue in poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (61.8/30.4/7.8 mol. %) terpolymer, in which we revisit its controversial issue of the phase transition. We observe that the electrocaloric response of the terpolymers remains nearly constant (ΔS = 25.5 J K−1 kg−1, ΔT = 5.1 K at 100 MV m−1) within 50 cycles at different temperatures around room temperature. Moreover, we conduct temperature-dependent X-ray diffraction and Fourier-transform infrared spectroscopy measurements on the terpolymer to provide insights into the evolution in intermolecular lattice spacing and intramolecular conformation. We find no clear evidence of the ferroelectric-to-paraelectric phase transition near the temperature range, where differential scanning calorimeter measurement displays an endothermic peak.

Tuning Intramolecular Conformation and Packing Mode of Host Materials through Noncovalent Interactions for High-Efficiency Blue Electrophosphorescence.

Molecular conformation plays an important role in tuning the packing modes of organic optoelectronic materials to achieve enhanced and/or balanced charge transport. Here, we introduce the noncovalent intramolecular interactions to the host materials of phosphorescent organic light-emitting diodes (PhOLEDs). Different numbers and/or positions of intramolecular CH···N noncovalent interactions were constructed by using different N-heterocycles of pyridine, pyrimidine, and pyrazine as acceptor units and carbazole as the donor unit in a donor-acceptor-donor (D-A-D) motif. Thus, designed D-A-D molecules were synthesized facilely through a one-step Ullmann reaction in high yields, showing varied intramolecular interactions to regulate the molecular conformation significantly. Impressively, owing to the quasi-parallel molecular conformation, which is beneficial for forming facile transporting channels of both holes and electrons, the newly designed host material of 9,9′-(pyridine-2,5-diyl)bis(9H-carbazole) exhibits good device performance of blue PhOLEDs with current, power, and external quantum efficiencies up to 33.0 cd A–1, 32.1 lm W–1, and 16.3%, respectively. This work highlights the significant importance of the noncovalent interactions in designing advanced organic semiconductors for high-performance optoelectronic devices.