A modular approach for the synthesis of Kekulé diradicaloids is reported. The key step is the insertion of a carbene, namely, a cyclic (alkyl)(amino)carbene (CAAC), into the C–H bonds of two ...terminal alkynes linked by a spacer. Subsequent hydride abstraction, followed by two-electron reduction of the corresponding bis(iminium) salts, affords the desired diradicaloids. This synthetic route readily allows for the installation of communicating spacers, featuring different degrees of aromaticity and lengths, and gives the possibility of generating unsymmetrical compounds with two different CAACs. Electron paramagnetic resonance (EPR), NMR, UV–vis, and X-ray studies in combination with quantum-chemical calculations give insight into the electronic nature of the deeply colored Kekulé diradicaloids. They feature a singlet ground state with varying degrees of diradical character in combination with small singlet/triplet gaps. Upon lengthening of the spacer, the properties of the compounds approach those of monoradicals in which steric protection of the propargyl radical moiety is necessary to inhibit decomposition pathways. Most of these diradicaloids are stable at room temperature, both in solution and in the solid state, but are highly oxygen-sensitive. They represent the first diradicaloids derived from iminium salts.
In systemic amyloidosis, serum amyloid A (SAA) fibril deposits cause widespread damages to tissues and organs that eventually may lead to death. A therapeutically intervention therefore has either to ...dissolve these fibrils or inhibit their formation. However, only recently has the human SAA fibril structure been resolved at a resolution that is sufficient for development of drug candidates. Here, we use molecular dynamic simulations to probe the factors that modulate the stability of this fibril model. Our simulations suggest that fibril formation starts with the stacking of two misfolded monomers into metastable dimers, with the stacking depending on the N-terminal amyloidogenic regions of different chains forming anchors. The resulting dimers pack in a second step into a 2-fold two-layer tetramer that is stable enough to nucleate fibril formation. The stability of the initial dimers is enhanced under acidic conditions by a strong salt bridge and side-chain hydrogen bond network in the C-terminal cavity (residues 23–51) but is not affected by the presence of the disordered C-terminal tail.
Parkinson's disease is accompanied by the presence of amyloids in the brain that are formed of α-synuclein chains. The correlation between COVID-19 and the onset of Parkinson's disease led to the ...idea that amyloidogenic segments in SARS-COV-2 proteins can induce aggregation of α-synuclein. Using molecular dynamic simulations, we show that the fragment FKNIDGYFKI of the spike protein, which is unique for SARS-COV-2, preferentially shifts the ensemble of α-synuclein monomer toward rod-like fibril seeding conformations and, at the same time, differentially stabilizes this polymorph over the competing twister-like structure. Our results are compared with earlier work relying on a different protein fragment that is not specific for SARS-COV-2.
It is believed that amyloid-beta (Aβ) aggregates play a role in the pathogenesis of Alzheimer's disease. Aβ molecules form β-sheet structures with multiple interaction sites. This polymorphism gives ...rise to differences in morphology, physico-chemical property and level of cellular toxicity. We have investigated the conformational stability of various segmental polymorphisms using molecular dynamics simulations and find that the segmental polymorphic models of Aβ retain a U-shaped architecture. Our results demonstrate the importance of inter-sheet side chain-side chain contacts, hydrophobic contacts among the strands (β1 and β2) and of salt bridges in stabilizing the aggregates. Residues in β-sheet regions have smaller fluctuation while those at the edge and loop region are more mobile. The inter-peptide salt bridges between Asp23 and Lys28 are strong compared to intra-chain salt bridge and there is an exchange of the inter-chain salt-bridge with intra-chain salt bridge. As our results suggest that Aβ exists under physiological conditions as an ensemble of distinct segmental polymorphs, it may be necessary to account in the development of therapeutics for Alzheimer's disease the differences in structural stability and aggregation behavior of the various Aβ polymorphic forms.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Over decades diazoalkenes (R2C=C=N2) were postulated as reactive intermediates in organic chemistry even though their direct spectroscopic detection proved very challenging. In the 1970/80ies several ...groups probed their existence mainly indirectly by trapping experiments or directly by matrix‐isolation studies. In 2021, our group and the Severin group reported independently the synthesis and characterization of the first room‐temperature stable diazoalkenes, which initiated a rapidly expanding research field. Up to now four different classes of N‐heterocyclic substituted room‐temperature stable diazoalkenes have been reported. Their properties and unique reactivity, such as N2/CO exchange or utilization as vinylidene precursors in organic and transition metal chemistry are presented. This review summarizes the early discoveries of diazoalkenes from their initial postulation as transient, elusive species up to the recent findings of the room‐temperature stable derivatives.
Early discoveries of diazoalkenes (R2C=C=N2) in organic synthesis and the identification of room‐temperature‐stable diazoalkenes since 2021 are summarized in this Minireview. The synthesis, properties, and reactivity of this novel molecule class are presented, and its use in organic synthesis, main‐group, and transition‐metal chemistry highlighted.
Various diseases cause overexpression of the serum amyloid A (SAA) protein, which in some cases, but not in all cases, leads to amyloidosis as a secondary disease. Response to the overexpression ...involves dissociation of the SAA hexamer and subsequent cleavage of the released monomers, most commonly yielding fragments SAA1–76 of the full-sized SAA1–104. We report results from molecular dynamic simulations that probe the role of this cleavage for downregulating the activity and concentration of SAA. We propose a mechanism that relies on two elements. First, the probability to assemble into hexamers is lower for the fragments than it is for the full-sized protein. Second, unlike other fragments, SAA1–76 can switch between two distinct configurations. The first kind is easy to proteolyse (allowing a fast reduction of the SAA concentration) but prone to aggregation, whereas the situation is opposite for the second kind. If the time scale for amyloid formation is longer than the one for proteolysis, the aggregation-prone species dominates. However, if environmental conditions such as low pH increases the risk of amyloid formation, the ensemble shifts toward the more protected form. We speculate that SAA amyloidosis is a failure of this switching mechanism leading to accumulation of the aggregation-prone species and subsequent amyloid formation.
This paper is concerned with an Actor-Network Theory approach to museum space. It builds upon qualitative research at the Sainsbury Centre for Visual Arts, a museum and educational building in ...Norwich, England. Following the people who work with the building in the process of dismantling an exhibition, I examine the negotiations that emerge when a problem occurs with the handling of a specific artwork. Drawing on the concept of spacing by Bruno Latour, this paper highlights the multiplicity and complexity inherent in museum practices. I argue that space is not contained inside the building but is done with the building, exhibition objects, handling instructions, surfaces, and people. Analyzing this process of spacing, then, the work towardsand negotiation of stability and flux, of homogeneity and heterogeneity inherent to museum spaces become visible which allows for a rich and nuanced understanding of the relationship between people and physical stuff.
Nodular lymphocyte predominant Hodgkin lymphoma (NLPHL) is a subtype of Hodgkin lymphoma with a preserved B‐cell phenotype and follicular T helper (TFH) cells rosetting around the tumor cells, the ...lymphocyte‐predominant (LP) cells. As we recently described reactivity of the B‐cell receptors of LP cells of some NLPHL cases with Moraxella spp. proteins, we hypothesized that LP cells could present peptides to rosetting T cells in a major histocompatibility complex class II (MHCII)‐bound manner. Rosetting PD1+ T cells were present in the majority of NLPHL cases, both in typical (17/20) and variant patterns (16/19). In most cases, T‐cell rosettes were CD69+ (typical NLPHL, 17/20; NLPHL variant, 14/19). Furthermore, both MHCII alpha and beta chains were expressed in the LP cells in 23/39 NLPHL. Proximity ligation assay and confocal laser imaging demonstrated interaction of the MHCII beta chain expressed by the LP cells and the T‐cell receptor alpha chain expressed by rosetting T cells. We thus conclude that rosetting T cells in NLPHL express markers that are encountered after antigenic exposure, that MHCII is expressed by the LP cells, and that LP cells interact with rosetting T cells in an immunological synapse in a subset of cases. As they likely receive growth stimulatory signals in this way, blockade of this interaction, for example, by PD1‐directed checkpoint inhibitors, could be a treatment option in a subset of cases in the future.
Self-Assembly of Phenylalanine-Based Molecules German, Helen W; Uyaver, Sahin; Hansmann, Ulrich H. E
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory,
03/2015, Letnik:
119, Številka:
9
Journal Article
Recenzirano
Using molecular dynamics, we study the self-assembly of phenylalanine with charged end-groups at various temperatures and concentrations. As in the case of diphenylalanine, we observe the formation ...of nanotubes; however, phenylalanine aggregates in layers of four, not six, molecules. The observed aggregates are consistent with recent experimental measurements of fibrils obtained from mice with phenylketonuria. We investigate the stability and the mechanism by which these tubular structures form and discuss potential toxicity mechanisms.
Peptides build from D-amino acids resist enzymatic degradation. The resulting extended time of biological activity makes them prime candidates for the development of pharmaceuticals. Of special ...interest are D-retro-inverso (DRI) peptides where a reversed sequence of D-amino acids leads to molecules with almost the same structure, stability, and bioactivity as the parent L-peptides but increased resistance to proteolytic degradation. Here, we study the effect of DRI-Aβ
and DRI-Aβ
peptides on fibril formation. Using molecular dynamics simulations, we compare the stability of typical amyloid fibril models with such where the L-peptides are replaced by DRI-Aβ
and DRI-Aβ
peptides. We then explore the likelihood for cross fibrilization of Aβ L- and DRI-peptides by investigating how the presence of DRI peptides alters the elongation and stability of L-Aβ-fibrils. Our data suggest that full-length DRI-peptides may enhance the fibril formation and decrease the ratio of soluble toxic Aβ oligomers, pointing out potential for D-amino-acid-based drug design targeting Alzheimer's disease.
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