Ground subsidence caused by permafrost thawing causes the formation of thermokarst ponds, where organic compounds from eroding permafrost accumulate. We photolyzed water samples from two such ponds ...in Northern Quebec and discovered the emission of volatile organic compounds (VOCs) using mass spectrometry. One pond near peat-covered permafrost mounds was organic-rich, while the other near sandy mounds was organic-poor. Compounds up to C10 were detected, comprising the atoms of O, N, and S. The main compounds were methanol, acetaldehyde, and acetone. Hourly VOC fluxes under actinic fluxes similar to local solar fluxes might reach up to 1.7 nmol C m–2 s–1. Unexpectedly, the fluxes of VOCs from the organic-poor pond were greater than those from the organic-rich pond. We suggest that different segregations of organics at the air/water interface may partly explain this observation. This study indicates that sunlit thermokarst ponds are a significant source of atmospheric VOCs, which may affect the environment and climate via ozone and aerosol formation. Further work is required for understanding the relationship between the pond’s organic composition and VOC emission fluxes.
A new methodology has been developed for preparing α-functional polymers in a one-pot simultaneous polymerization/isocyanate “click” reaction. Our original synthetic strategy is based on the ...preparation of a carbonyl-azide chain transfer agent (CTA) precursor that undergoes the Curtius rearrangement in situ during reversible addition–fragmentation chain transfer (RAFT) polymerization yielding well-controlled α-isocyanate modified polymers. This strategy overcomes numerous difficulties associated with the synthesis of a polymerization mediator bearing an isocyanate at the R group and with the handling of such a reactive functionality. This new carbonyl-azide CTA can control the polymerization of a wide range of monomers, including (meth)acrylates, acrylamides, and styrenes (M n = 2–30 kDa; Đ = 1.16–1.38). We also show that this carbonyl-azide CTA can be used as a universal platform for the synthesis of α-end-functionalized polymers in a one-pot RAFT polymerization/isocyanate “click” procedure.
β-Sheet forming self assembling cyclic peptides offer a versatile scaffold for the construction and control of hydrogen-bonded nanotube assemblies. These structures have major advantages over other ...nanoscale tubular structures, including sub-nanometer control over the internal diameter, and the ability to control internal and external chemical functionality. This Tutorial Review presents an overview of nanotubes derived from this class of cyclic peptides. The design rationale for functional nanotubes based on cyclic peptide ring size and chemical functionality is discussed. Additionally, we highlight the recent expansion of the nanotube toolbox through conjugation of (macro)molecules to the cyclic peptides. These provide additional functionality and control nanotube dimensions that could potentially prove beneficial in future applications.
Here, we report a simple approach for end group functionalization of linear polymers and graft copolymers via an interchange process of reversible addition–fragmentation chain transfer (RAFT) ...polymerization chain transfer agents (CTAs). The high functional group tolerance of the RAFT process allows a library of functionalities to be introduced. Moreover, this approach allows multiple functional groups to be installed simultaneously. Furthermore, as an alternative to end group analysis, we report the utility of the supernatant of the reaction mixture to determine the degree of functionalization.
A supramolecular strategy of switching the self-assembly of cyclic peptide-polymer conjugates using host-guest chemistry is proposed. The formation of tubular supramolecular polymers based on cyclic ...peptide-polymer conjugates can be controlled by reversibly attaching cucurbit7uril onto the cyclic peptide via host-guest interactions.
The present study examines the behavior of cyclic peptide polymer conjugates that have been designed to combine their self-assembling ability via H-bonding with the properties of amphiphilic diblock ...copolymers. Using a combination of asymmetric flow-field flow fractionation (AF4) and small-angle neutron scattering (SANS), we have uncovered unique insight based on the population of structures established at a 24 h equilibrium profile. Our results determine that by introducing a small quantity of hydrophobicity into the conjugated polymer corona, the resulting nanotube structures exhibit low unimer dissociation which signifies enhanced stability. Furthermore, as the hydrophobicity of the polymer corona is increased, the elongation of the nanotubes is observed due to an increase in the association of unimers. This encompasses not only the H-bonding of unimers into nanotubes but also the self-assembly of single nanotubes into segmented-nanotube structures with high aspect ratios. However, this influence relies on a subtle balance between the hydrophobicity and hydrophilicity of the polymer corona. This balance is proposed to determine the solvent entropic penalty of hydrating the system, whereby the cost scales with the hydrophobic quantity. Consequently, it has been suggested that at a critical hydrophobic quantity, the solvation penalty becomes high enough such that the self-assembly of the system deviates from ordered hydrogen bonding. The association behavior is instead dominated by the hydrophobic effect which results in the undesirable formation of disordered aggregates.
Organic peroxy radicals (RO
) play a pivotal role in the degradation of hydrocarbons. The autoxidation of atmospheric RO
radicals produces highly oxygenated organic molecules (HOMs), including ...low-volatility ROOR dimers formed by bimolecular RO
+ RO
reactions. HOMs can initiate and greatly contribute to the formation and growth of atmospheric particles. As a result, HOMs have far-reaching health and climate implications. Nevertheless, the structures and formation mechanism of RO
radicals and HOMs remain elusive. Here, we present the in-situ characterization of RO
and dimer structure in the gas-phase, using online tandem mass spectrometry analyses. In this study, we constrain the structures and formation pathway of several HOM-RO
radicals and dimers produced from monoterpene ozonolysis, a prominent atmospheric oxidation process. In addition to providing insights into atmospheric HOM chemistry, this study debuts online tandem MS analyses as a unique approach for the chemical characterization of reactive compounds, e.g., organic radicals.
The partition and self-assembly of a new generation of cyclic peptide–polymer conjugates into well-defined phospholipid trans-bilayer channels is presented. By varying the structural parameters of ...the cyclic peptide–polymer conjugates through the ligation of hydrophobic and hydrophilic polymers, both the structure of the artificial channels using large unilamellar vesicle assays and the structural parameters required for phospholipid bilayer partitioning are elucidated. In addition, temperature was used as an external stimulus for the modulation of transbilayer channel formation without requiring the redesign and synthesis of the cyclic peptide core. The thermoresponsive character of the cyclic peptide–polymer conjugates lays the foundation for on-demand control over phospholipid transmembrane transport, which could lead to viable alternatives to current transport systems that traditionally rely on endocytic pathways.
Poly(styrene-co-maleic anhydride) copolymers (PSMA) with controlled number and distribution of maleic anhydride (MAnh) units were synthesized by reversible addition–fragmentation chain transfer ...polymerization using chain-transfer agents (CTA) suitable for industrial scale processes. Linear- and star-shaped alternating PSMA polymers were prepared in a single-step synthesis, while a one-pot sequential chain-extension strategy was utilized to prepare diblock, multiblock, and multisite copolymer architectures. A library of grafted PSMAs with controlled density and distribution of side chains was achieved by the subsequent grafting of long aliphatic alcohol chains (C22) to the MAnh units. The influence of structure, composition, and long alkyl chain addition on PSMAs behavior in solution was studied with triple-detection size exclusion chromatography, while their thermal properties were examined by thermogravimetric analysis and differential scanning calorimetry. Overall, the side chain density and distribution did not impact the polymer conformations in solution (random coil); however, an effect on the molecular size (R h) and structure density (intrinsic viscosity) were observed. The materials density was shown to be dependent on polymer architectures as lower intrinsic viscosity was observed for the star copolymer. All the materials had similar degradation points (400 °C), while the rate of degradation showed a dependence on the MAnh content and polymeric architecture. Ultimately, the grafting of long aliphatic side chains (crystalline) onto the PSMA backbone, even at low density, was shown to drastically change the microphase ordering, as all the grafted copolymers became semicrystalline. The difference of the crystallization temperature between low density multisite materials (T c ≈ 8 °C) and the high density alternating material (T c ≈ 40 °C) highlights the major importance of controlling copolymer composition and structure to tune material properties.
This Viewpoint highlights the design principles and development of peptide-based supramolecular polymers. Here we delve deep into the practicalities of synthesizing and characterizing these ...macromolecular structures and provide a thorough overview of the benefits and challenges that come with these systems. This Viewpoint emphasizes to beginners and experts alike the importance of understanding the fundamental behavior and self-assembly processes when designing these complex and dynamic functional materials.
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