Temperature-dependent Aggregation Research Articles

Discovery of a dual pathway aggregation mechanism for a therapeutic constrained peptide.

Constrained peptides (CPs) have emerged as attractive candidates for drug discovery and development. To fully unlock the therapeutic potential of CPs, it is crucial to understand their physical stability and minimize the formation of aggregates that could induce immune responses. Although amyloid like aggregates have been researched extensively, few studies have focused on aggregates from other peptide scaffolds (e.g., CPs). In this work, a streamlined approach to effectively profile the nature and formation pathway of CP aggregates was demonstrated. Aggregates of various sizes were detected and shown to be amorphous. Though no major changes were found in peptide structure upon aggregation, these aggregates appeared to have mixed natures, consisting of primarily non-covalent aggregates with a low level of covalent species. This co-existence phenomenon was also supported by two kinetic pathways observed in time- and temperature-dependent aggregation studies. Furthermore, a stability study with 8 additional peptide variants exhibited good correlation between aggregation propensity and peptide hydrophobicity. Therefore, a dual aggregation pathway was proposed, with the non-covalent aggregates driven by hydrophobic interactions, whereas the covalent ones formed through disulfide scrambling. Overall, the workflow presented here provides a powerful strategy for comprehensive characterization of peptide aggregates and understanding their mechanisms of formation.

Organic Photovoltaics: Understanding the Preaggregation of Polymer Donors in Solution and Its Morphological Impact.

In bulk-heterojunction organic solar cells, it is well established that the active-layer morphology significantly impacts device performance. However, morphology control remains very challenging. An interesting step in that direction was recently provided by the development of polymer donors that display a temperature-dependent aggregation behavior in solution; the aggregation characteristics were found indeed to play a determining role in the eventual active-layer morphology. Here, a combination of thermodynamic analyses, molecular dynamics simulations, and long-range corrected density functional theory calculations enables us (i) to establish the Flory-Huggins interaction parameter, χ, as a useful figure of merit that allows us to integrate the contributions from all inter-related molecular interactions and to describe the extent of polymer preaggregation in solution at room temperature; (ii) to correlate the χ values for various polymer solutions to the extent of polymer aggregation and the morphological characteristics of the active layers; and (iii) to assess how polymer-polymer and polymer-solvent intermolecular interactions contribute to the variations in χ values among different polymer solutions. We have chosen to examine four representative polymer donors (PBT4T-2OD, PBTff4T-2OD, PffBT4T-2OD, and PffBTff4T-2DT) in solution in chlorobenzene or dichlorobenzene. With χ as a robust bridge, our results provide an unprecedented, detailed description of the relationships among intermolecular interactions, extent of polymer solution aggregation, and morphological features of the active layers.

Polymer Donors with Temperature-Insensitive, Strong Aggregation Properties Enabling Additive-Free, Processing Temperature-Tolerant High-Performance All-Polymer Solar Cells

In this work, the impact of temperature-dependent aggregation behaviors in benzodithiophene (BDT)-based polymer donors (PDs) on the electrical, morphological, and photovoltaic performances of all-p...

Temperature dependent aggregation mechanism and pathway of lysozyme: By all atom and coarse grained molecular dynamics simulation

Aggregation of protein causes various diseases including Alzheimer’s disease, Parkinson’s disease, and type II diabetes. It was found that aggregation of protein depends on many factors like temperature, pH, salt type, salt concentration, ionic strength, protein concentration, co solutes. Here we have tried to capture the aggregation mechanism and pathway of hen egg white lysozyme using molecular dynamics simulations at two different temperatures; 300 K and 340 K. Along with the all atom simulations to get the atomistic details of aggregation mechanism, we have used coarse grained simulation with MARTINI force field to monitor the aggregation for longer duration. Our results suggest that due to the aggregation, changes in the conformation of lysozyme are more at 340 K than at 300 K. The change in the conformation of the lysozyme at 300 K is mainly due to aggregation where at 340 K change in conformation of lysozyme is due to both aggregation and temperature. Also, a more compact aggregated system is formed at 340 K.

Temperature Induced Aggregation of Organic Semiconductors.

One important feature of organic semiconductors is their solution processability, which allows researchers to tune their aggregation states in solution and solid states and to control the processing conditions to reach desirable electronic and optoelectronic properties. Temperature is one of the most important processing parameters of organic semiconductors and has been studied extensively particularly for those conjugated small- and macro- molecules with strong temperature-dependent aggregation properties. This minireview summarizes the temperature-induced aggregation behaviors of organic semiconductors in solution, during solution casting and upon thermal annealing post-treatment of solid-state thin films. The influences of different aggregation states on the optoelectronic properties, in particular the photovoltaic properties, are discussed. The conclusions in this work will provide a rational guide to precisely control the aggregation states of organic semiconductors to fabricate high-performance optoelectronic devices.

Random terpolymer based on thiophene-thiazolothiazole unit enabling efficient non-fullerene organic solar cells

Developing a high-performance donor polymer is critical for achieving efficient non-fullerene organic solar cells (OSCs). Currently, most high-efficiency OSCs are based on a donor polymer named PM6, unfortunately, whose performance is highly sensitive to its molecular weight and thus has significant batch-to-batch variations. Here we report a donor polymer (named PM1) based on a random ternary polymerization strategy that enables highly efficient non-fullerene OSCs with efficiencies reaching 17.6%. Importantly, the PM1 polymer exhibits excellent batch-to-batch reproducibility. By including 20% of a weak electron-withdrawing thiophene-thiazolothiazole (TTz) into the PM6 polymer backbone, the resulting polymer (PM1) can maintain the positive effects (such as downshifted energy level and reduced miscibility) while minimize the negative ones (including reduced temperature-dependent aggregation property). With higher performance and greater synthesis reproducibility, the PM1 polymer has the promise to become the work-horse material for the non-fullerene OSC community.

Biophysical characterization of intrinsically disordered human Golgi matrix protein GRASP65

Golgi Reassembly and Stacking Proteins (GRASPs), including GRASP65/GRASP55, were firstly found as stacking factors of Golgi cisternae. Their involvement in other processes, such as unconventional protein secretion (UPS), have been demonstrated, suggesting GRASPs act as interaction hubs. However, structural details governing GRASP functions are not understood thoroughly. Here, we explored the structural features of human cis-Golgi GRASP65 in aqueous solution and compared them with those from trans-Golgi GRASP55. Besides their distinct Golgi localization, GRASP65/55 also seem to be selectively recruited to mitosis-related events or to UPS. Despite preserving the monomeric form in solution seen for GRASP55, as inferred from our SEC-MALS and DLS data, GRASP65 exhibited higher intrinsic disorder and susceptibility to denaturant than GRASP55 (disorder prediction, urea denaturation and circular dichroism data). Moreover, spectroscopic and microscopic studies showed for GRASP65 the same temperature-dependent amorphous aggregation and time-dependent amyloid fibrillation at 37 °C seen for GRASP55. In the latter case, however, GRASP65 presented a lower aggregation rate than GRASP55. The present and previous data evidenced that intrinsic disorder and formation of higher-order oligomers, such as amyloid fibrils, are common features within GRASP family potentially impacting the protein's participation in cell processes.

Reduced Nonradiative Recombination Energy Loss Enabled Efficient Polymer Solar Cells via Tuning Alkyl Chain Positions on Pendent Benzene Units of Polymers.

Nonradiative recombination energy loss (ΔE3) plays a key role in enhancing device efficiencies for polymer solar cells (PSCs). Until now, there is no clear resolution for reducing ΔE3 via molecular design. Herein, we report two conjugated polymers, PBDB-P-p and PBDB-P-m, which are integrated from benzo[1,2-b:4,5-b']dithiophene with alkylthio chain substituted at para- or meta-position on pendent benzene and benzo[1,2-c:4,5-c']dithiophene-4,8-dione. Both the polymers have different temperature-dependent aggregation properties but similar molecular energy levels. When BO-4Cl was used as an acceptor to fabricate PSCs, the device of PBDB-P-p:BO-4Cl displayed a maximal power conversion efficiency (PCE) of 13.83%, while the best device of PBDB-P-m:BO-4Cl exhibited a higher PCE of 14.12%. The close JSCs and fill factors in both PSCs are attributed to their formation of effective nanoscale phase separation as confirmed by atomic force microscopy measurements. We find that the PBDB-P-m-based device has 1 order of magnitude higher electroluminescence quantum efficiency (EQEEL) than in the PBDB-P-p-based one, which could arise from the relatively weak aggregation in the PBDB-P-m-based film. Thus, the PBDB-P-m-based device has a remarkably enhanced VOC of 0.86 V in contrast to 0.80 V in the PBDB-P-p-based device. This study offers a feasible structural optimization way on the alkylthio side chain substitute position on the conjugated polymer to enhance VOC by reducing nonradiative recombination energy loss in the resulting PSCs.

Novel molecular aspects of the CRISPR backbone protein ‘Cas7’ from cyanobacteria

The cyanobacterium Anabaena PCC 7120 shows the presence of Type I-D CRISPR system that can potentially confer adaptive immunity. The Cas7 protein (Alr1562), which forms the backbone of the type I-D surveillance complex, was characterized from Anabaena. Alr1562, showed the presence of the non-canonical RNA recognition motif and two intrinsically disordered regions (IDRs). When overexpressed in E. coli, the Alr1562 protein was soluble and could be purified by affinity chromatography, however, deletion of IDRs rendered Alr1562 completely insoluble. The purified Alr1562 was present in the dimeric or a RNA-associated higher oligomeric form, which appeared as spiral structures under electron microscope. With RNaseA and NaCl treatment, the higher oligomeric form converted to the lower oligomeric form, indicating that oligomerization occurred due to the association of Alr1562 with RNA. The secondary structure of both these forms was largely similar, resembling that of a partially folded protein. The dimeric Alr1562 was more prone to temperature-dependent aggregation than the higher oligomeric form. In vitro, the Alr1562 bound more specifically to a minimal CRISPR unit than to the non-specific RNA. Residues required for binding of Alr1562 to RNA, identified by protein modeling-based approaches, were mutated for functional validation. Interestingly, these mutant proteins, showing reduced ability to bind RNA were predominantly present in dimeric form. Alr1562 was detected with specific antiserum in Anabaena, suggesting that the type I-D system is expressed and may be functional in vivo. This is the first report that describes the characterization of a Cas protein from any photosynthetic organism.

Influence of Polymer Aggregation and Liquid Immiscibility on Morphology Tuning by Varying Composition in PffBT4T‐2DT/Nonfullerene Organic Solar Cells

The temperature dependent aggregation behavior of PffBT4T polymers used in organic solar cells plays a critical role in the formation of a favorable morphology in fullerene-based devices. However, there has been little investigation into the impact of donor/acceptor ratio on morphology tuning, especially for non-fullerene acceptors (NFAs). Herein, the influence of composition on morphology is reported for blends of PffBT4T-2DT with two NFAs, O-IDTBR and O-IDFBR. The monotectic phase behavior inferred from differential scanning calorimetry provides qualitative insight into the interplay between solid-liquid and liquid-liquid demixing. Transient absorption spectroscopy suggests that geminate recombination dominates charge decay and that the decay rate is insensitive to composition, corroborated by negligible changes in open-circuit voltage. Exciton lifetimes are also insensitive to composition, which is attributed to the signal being dominated by acceptor excitons which are formed and decay in domains of similar size and purity irrespective of composition. A hierarchical morphology is observed, where the composition dependence of size scales and scattering intensity from resonant soft X-ray scattering (R-SoXS) is dominated by variations in volume fractions of polymer/polymer rich domains. Results suggest an optimal morphology where polymer crystallite size and connectivity are balanced, ensuring a high probability of hole extraction via such domains.

Aggregation of β-crystallin through covalent binding to 1,2-naphthoquinone is rescued by α-crystallin chaperone.

Cataract induced by exposure to naphthalene is thought to mainly involve its metabolic activation, forming 1,2-naphthoquinone (1,2-NQ), which can modify proteins through chemical modifications. In the present study, we examined the effect of 1,2-NQ on aggregation of crystallins (cry) associated with cataract. Incubation of bovine β-cry with 1,2-NQ caused covalent modification of β-cry at Cys117 and Lys125 accompanied by reduction in its thiol content, resulting in a concentration- and temperature-dependent aggregation of β-cry, whereas only little aggregation of α-cry induced by 1,2-NQ was seen. Interestingly, addition of α-cry to the reaction mixture of β-cry and 1,2-NQ markedly blocked β-cry aggregation induced by 1,2-NQ in a concentration-dependent manner. These results suggest that β-cry predominantly undergoes chemical modification by 1,2-NQ, causing its aggregation, which is suppressed by the chaperone-like protein, α-cry. This β-cry aggregation may be, at least in part, involved in the induction of cataract caused by 1,2-NQ.

PCE11-based polymer solar cells with high efficiency over 13% achieved by room-temperature processing

Non-fullerene acceptors featuring excellent miscibility with temperature-dependent aggregation polymer PCE11 enable room-temperature processed polymer solar cells with high efficiency over 13%.

Control the interplay of crystallization and phase separation of conjugated polymer blends by the relative rate of nucleation and growth

In terms of the solution processing conjugated polymer blends, having a comprehensive understanding of the relationship between crystallization and phase separation is significant to optimize their performance. However, crystal nucleation and crystal growth are usually coupled during the process of the film formation process, and it is sometimes difficult to distinguish their respective effects on phase separation. We propose that apply the temperature-dependent aggregation (TDA) features of poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-di(2-octyldodecyl) 2,2′; 5′,2″; 5″,2‴-quaterthiophen-5,5‴-diyl)] (PffBT4T-2OD) to separate both nucleation and growth processes and conduct the investigation of their effects on phase separation of PffBT4T-2OD/N2200 (poly[[N,N′-bis(2-octyldodecyl)-napthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)]) blends. It can be discovered that the nucleation and growth of the blends system can be distinguished to three regions: Region I: dominated by the nucleation process (T is 25 °C–65 °C); Region II: dominated by both nucleation and growth processes (T is 65 °C–100 °C); and Region Ⅲ: dominated by the growth process (T is 100 °C–120 °C). In situ absorption spectroscopy and Urbach (Eu) are adopted to investigate the crystallization rate and crystal perfection in three regions. The different relative rates of nucleation and growth exert an impact on the interplay between crystallization and phase separation, which results in completely different morphology.

Aggregation of urea in water: Dynamic light scattering analyses

The aggregation behavior of urea in water is multifaceted; the urea-urea, urea-water, and water-water interactions lead to noteworthy characteristics with changes in condition. The concentration- and temperature-dependent aggregation of urea was studied using dynamic light scattering (DLS). The particle size analysis and polydispersity between 1.0 and 12.0 M aqueous urea revealed pronounced aggregation trends beginning at or above 6.0 M. A reversal of the observed trend in intensity correlation function was noticed above 10.0 M. Temperature-dependent intensity correlation functions between 20 and 70 °C corroborated the finding. An anomalous behavior at 60 °C was observed, supported by the polydispersity of the systems, throughout all concentrations of urea studied.

Double Acceptor Block-Containing Copolymers with Deep HOMO Levels for Organic Solar Cells: Adjusting Carboxylate Substituent Position for Planarity.

A deep highest occupied molecular orbital (HOMO) level is a prerequisite for polymer donor material to boost the organic solar cells (OSCs) performance by achieving high open circuit voltage ( Voc). Abandoning the traditional concept of donor-acceptor (D-A) structure, two copolymers PBTZ-4TC and PBTZ-C4T based on acceptor1-π-acceptor2 (A1-π-A2) architecture, where thiophene as the bridge, the difluorinated benzotriazole (BTZ) as A1 unit alternating copolymerized with 4,4'-dicarboxylate-substituted difluorotetrathiophene (4TC) and 3,3'-dicarboxylate-substituted difluorotetrathiophene (C4T) as A2, respectively, are developed. Because of the double acceptor blocks with high electron affinity, both A1-π-A2 type copolymers possess the lower HOMO levels of 5.52-5.56 eV, which are lower than most D-A type donors. Polymer PBTZ-4TC and PBTZ-C4T have the same backbone but only differ with the position of carboxylate substituent on the A2 unit. Intriguingly, subtle optimizing the position of the carboxylate-substitute causes a significantly difference on the properties of the A1-π-A2 type copolymers. PBTZ-C4T with more planar geometry is demonstrated with better light absorption, higher crystallinity, more pronounced temperature-dependent aggregation effect, and favorable bulk heterojunction morphology but with slightly higher HOMO level and more emission energy loss relative to the PBTZ-4TC. The PBTZ-C4T device exhibits the higher power conversion efficiency (PCE) of 9.34% than the PBTZ-4TC-based one (8.75%). These results reveal that concept of A1-π-A2 type copolymers not only can afford more flexibility in tuning the energy levels to achieve the deep HOMO levels but also can provide a facial strategy to greatly enrich the types of polymer donors for high-performance OSCs.

A rational comparison of the effects of halogen atoms incorporated into the polymer donors on the performance of polymer solar cells

Despite the high performance polymer solar cells obtained by the fluorinated or chlorinated polymer donors, there is no effective guideline for how to choose a reasonable halogen atom incorporated into copolymer donors when designing organic photovoltaic materials. Two polymers of PBDT-F-3T2C containing F atom and PBDT-Cl-3T2C containing Cl atom are designed and synthesized. A direct comparison of the effects of fluorine and chlorine atom on the properties of the copolymer and resulting device performance is systematically studied. It can be found that both of the chlorine and fluorine atoms can effectively reduce the HOMO and LUMO levels, but chlorine atom is revealed to possess stronger downshifting ability for energy levels than fluorine atom in the copolymers. On the other hand, compared with the chlorine atom with larger atomic radius, the smaller fluorine atom possess strong self-assembly feature and negligible steric hindrance, enable the PBDT-F-3T2C with higher crystallinity and solution temperature-dependent aggregation behavior than PBDT-Cl-3T2C. The higher absorption coefficient, more favorable morphology, higher and more balanced charge mobilies endow the PBDT-F-3T2C with higher device performance than PBDT-Cl-3T2C (11.67% vs 10.19%). In addition, the performance of the 1,2,4-trimethylbenzene (TMB) solvent processed devices is also sensitive to halogenate atoms. An expressive PCE of 10.04% is obtained for F-containing devices, which is almost double higher than the Cl-containing devices. These results would provide a guideline for rational incorporation of halogen atoms into the polymer donors for high performance polymer solar cells. • Two polymer donors of PBDT-F-3T2C and PBDT-Cl-3T2C are designed and synthesized. • The effects of F and Cl atom on the properties of the polymers and PSCs. • A PCE of 11.67% obtained for halogenated solvent processed device. • Non-halogenated solvent processed devices yield a PCE over 10%.

Conformational and aggregation properties of PffBT4T polymers: atomistic insight into the impact of alkyl-chain branching positions

The impact of the branching positions of alkyl chains on temperature dependent aggregation is rationalized by atomistic molecular dynamics simulations.

Wide bandgap donor-acceptor conjugated polymers with alkylthiophene as side chains for high-performance non-fullerene polymer solar cells

Abstract Four wide bandgap donor-acceptor (D-A) conjugated polymers, i.e. P-diF2T, P-TT, P-BDT and P-NDT, with bis(5-(2-decyltetradecyl)-[2,3′-bithiophen]-2′-yl)arylenes as D-units and 2-propyl-5,6-difluorobenzo[d][1,2,3]triazole (ffTAZ) as A unit were synthesized for photovoltaic applications. In P-diF2T, P-TT, P-BDT and P-NDT, 3,3′-difluoro-2,2′-bithiophene (diF2T), thieno[3,2-b]thiophene (TT), benzo[1,2-b:4,5-b']dithiophene (BDT) and naphtho[1,2-b:5,6-b']dithiophene (NDT) were used as aryl central units, respectively, to adjust the properties of the polymers. The optical bandgap is 1.83 eV for P-diF2T, 1.85 eV for P-TT, 1.90 eV for P-BDT and 2.04 eV for P-NDT. All four polymers show temperature-dependent aggregation behavior in solution, and their absorption spectra are complementary with that of non-fullerene acceptor (NFA) 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(5-hexylthiophen-2-yl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene (ITIC-Th). Polymer solar cells (PSCs) based on these polymers and ITIC-Th were fabricated and characterized. Power conversion efficiencies (PCEs) higher than 7% were demonstrated for all polymers. The devices based on P-diF2T exhibited the highest PCE up to 10.08% with a high fill factor (FF) of 0.741. The good photovoltaic performance of P-diF2T is attributed to the synergies of the low-lying highest occupied molecular orbital (HOMO) energy level of the polymer and the favorable microstructures and morphology and thereby high and balanced charge carrier mobilities of the blend films. This study suggested that adjusting aromatic D units together with using alkylthiophene as side chains is an effective approach to design donor polymers for high performance PSCs based on NFA.

Aggregation-phase diagrams of β2-microglobulin reveal temperature and salt effects on competitive formation of amyloids versus amorphous aggregates

Several serious diseases are associated with crystal-like amyloid fibrils or glass-like amorphous aggregates of denatured proteins. However, protein aggregation involving both types of aggregates has not yet been elucidated in much detail. Using a protein associated with dialysis-related amyloidosis, β2-microglobulin (β2m), we previously demonstrated that amyloid fibrils and amorphous aggregates form competitively depending on salt (NaCl) concentration. To examine the generality of the underlying competitive mechanisms, we herein investigated the effects of heat on acid-denatured β2m at pH 2. Using thioflavin fluorescence, CD, and light scattering analysis along with atomic force microscopy imaging, we found that the temperature-dependent aggregation of β2m markedly depends on NaCl concentration. Stepwise transitions from monomers to amyloids and then back to monomers were observed at low NaCl concentrations. Amorphous aggregates formed rapidly at ambient temperatures at high NaCl concentrations, but the transition from amorphous aggregates to amyloids occurred only as the temperature increased. Combining the data from the temperature- and NaCl-dependent transitions, we constructed a unified phase diagram of conformational states, indicating a parabolic solubility curve with a minimum NaCl concentration at ambient temperatures. Although amyloid fibrils formed above this solubility boundary, amorphous aggregates dominated in regions distant from this boundary. Kinetic competition between supersaturation-limited slow amyloid fibrillation and supersaturation-unlimited fast amorphous aggregation deformed the phase diagram, with amyloid regions disappearing with fast titration rates. We conclude that phase diagrams combining thermodynamics and kinetics data provide a comprehensive view of β2m aggregation exhibiting severe hysteresis depending on the heat- or salt-titration rates.

Importance of Nucleation during Morphology Evolution of the Blade-Cast PffBT4T-2OD-Based Organic Solar Cells

Different temperatures, solvents, and additives are used as influencing parameters to drive molecular packing and phase separation for the development of the controlled evolution of nanostructures for organic solar cells (OSCs). The temperature-dependent aggregation (TDA) features of polymers are explored by investigating aggregation in solution and solid thin-film states using solution small-angle neutron scattering (SANS), soft/hard X-ray scattering, and transmission electron microscopy (TEM) characterizations. In situ grazing incidence wide angle X-ray scattering (GIWAXS) reveals that the nucleation process is highly significant and responsible for the ultimate film morphology. Processing conditions such as temperatures, solvents, and additives were used to influence the nucleation and evolution of film morphology. The nucleation process may improve the polymer packing and phase separation. It may translate into optimized multilength scale domains and efficient charge percolation pathways, a strong imp...