In the design of new metal-organic frameworks, the constant challenges of framework stability and structural predictability continue to influence ligand choice in favour of well-studied ...dicarboxylates and similar ligands. However, a small subset of known MOF ligands contains suitable functionality for coordination sphere hydrogen bonding which can provide new opportunities in ligand design. Such interactions may serve to support and rigidity the coordination geometry of mononuclear coordination spheres, as well as providing extra thermodynamic and kinetic stabilisation to meet the challenge of hydrolytic stability in these materials. In this perspective, a collection of pyrazole, amine, amide and carboxylic acid containing species are examined through the lens of (primarily) inner-sphere hydrogen bonding. The influence of these interactions is then related to the overall structure, stability and function of these materials, to provide starting points for harnessing these interactions in future materials design.
Coordination sphere hydrogen bonding in coordination polymers and metal-organic frameworks (MOFs) is examined as a structurally and chemically stabilising influence, accessible through ligand design strategies.
Protein storage vacuoles (PSV) are the main repository of protein in dicotyledonous seeds, but little is known about the origins of these transient organelles. PSV are hypothesized to either arise de ...novo or originate from the preexisting embryonic vacuole (EV) during seed maturation. Here, we tested these hypotheses by studying PSV formation in Arabidopsis (Arabidopsis thaliana) embryos at different stages of seed maturation and recapitulated this process in Arabidopsis leaves reprogrammed to an embryogenic fate by inducing expression of the LEAFY COTYLEDON2 transcription factor. Confocal and immunoelectron microscopy indicated that both storage proteins and tonoplast proteins typical of PSV were delivered to the preexisting EV in embryos or to the lytic vacuole in reprogrammed leaf cells. In addition, sectioning through embryos at several developmental stages using serial block face scanning electron microscopy revealed the 3D architecture of forming PSV. Our results indicate that the preexisting EV is reprogrammed to become a PSV in Arabidopsis.
Ligands capable of simultaneous metal coordination and hydrogen bond donation provide useful structural features to enhance cooperativity and favour specific geometries within the coordination ...sphere. Here we present the first structurally characterised examples of coordination compounds containing protonated 7-azaindole- N -oxide HL , bearing a neutral oxo donor capable of terminal or bridging coordination modes adjacent to a convergent hydrogen bond donor. The ligand itself shows a strong tendency for dimeric assembly in the solid state, but is easily deprotonated to give the chelate complex Cu L 2 1. In the presence of lanthanide ions, however, four new complexes Eu(NO 3 ) 3 ( HL ) 3 2, Gd(NO 3 ) 3 ( HL ) 3 3, Eu 2 (μ 2 - HL ) 2 ( HL ) 4 Cl 6 4 and YbCl 3 ( HL ) 3 YbCl( HL ) 5 OH 2 2Cl 5 were prepared and crystallographically characterised. All four species show strong tendencies for hydrogen bonding from the ligand to impact their overall structures, including a C 3 propellor-like macrocyclic motif in 2 and 3 and a combination of intramolecular N–H⋯Cl contacts, and intermolecular tridentate anion binding in 5. Solution studies including HRMS and phosphorescence emission spectroscopy reveal persistence of the europium complex 2 in solution, despite the multiple possible binding modes of this ligand, hinting at a degree of cooperativity in these systems. These results show the utility of hydrogen bonding within the coordination sphere for influencing structural outcomes, relevant to the construction of stable higher-order crystalline assemblies.
Zn2+ plays an important role in the normal function of the endoplasmic reticulum (ER) and its deficiency can cause ER stress, which is related to a wide range of diseases. In order to provide tools ...to better understand the role of mobile Zn2+ in ER processes, the first custom designed ER-localised fluorescent Zn2+ probes have been developed through the introduction of a cyclohexyl sulfonylurea as an ER-targeting unit with different Zn2+ receptors. Experiments in vitro and in cellulo show that both probes have a good fluorescence switch on response to Zn2+, high selectivity over other cations, low toxicity, ER-specific targeting ability and are efficacious imaging agents for mobile Zn2+ in four different cell lines. Probe 9 has been used to detect mobile Zn2+ changes under ER stress induced by both tunicamycin or thapsigargin, which indicates that the new probes should allow a better understanding of the mechanisms cells use to respond to dysfunction of zinc homeostasis in the ER and its role in the initiation and progression of diseases to be developed.
The endoplasmic reticulum (ER) is a highly dynamic polygonal membrane network composed of interconnected tubules and sheets (cisternae) that forms the first compartment in the secretory pathway ...involved in protein translocation, folding, glycosylation, quality control, lipid synthesis, calcium signalling, and metabolon formation. Despite its central role in this plethora of biosynthetic, metabolic and physiological processes, there is little quantitative information on ER structure, morphology or dynamics. Here we describe a software package (AnalyzER) to automatically extract ER tubules and cisternae from multi-dimensional fluorescence images of plant ER. The structure, topology, protein-localisation patterns, and dynamics are automatically quantified using spatial, intensity and graph-theoretic metrics. We validate the method against manually-traced ground-truth networks, and calibrate the sub-resolution width estimates against ER profiles identified in serial block-face SEM images. We apply the approach to quantify the effects on ER morphology of drug treatments, abiotic stress and over-expression of ER tubule-shaping and cisternal-modifying proteins.
Zn
2+
plays an important role in the normal function of the endoplasmic reticulum (ER) and its deficiency can cause ER stress, which is related to a wide range of diseases. In order to provide tools ...to better understand the role of mobile Zn
2+
in ER processes, the first custom designed ER-localised fluorescent Zn
2+
probes have been developed through the introduction of a cyclohexyl sulfonylurea as an ER-targeting unit with different Zn
2+
receptors. Experiments
in vitro
and
in cellulo
show that both probes have a good fluorescence switch on response to Zn
2+
, high selectivity over other cations, low toxicity, ER-specific targeting ability and are efficacious imaging agents for mobile Zn
2+
in four different cell lines. Probe
9
has been used to detect mobile Zn
2+
changes under ER stress induced by both tunicamycin or thapsigargin, which indicates that the new probes should allow a better understanding of the mechanisms cells use to respond to dysfunction of zinc homeostasis in the ER and its role in the initiation and progression of diseases to be developed.
Two endoplasmic reticulum (ER) targeting probes were developed to image mobile Zn
2+
to help understand Zn
2+
related biological processes in the ER.
The endoplasmic reticulum forms the first compart- ment in a series of organelles which comprise the secretory pathway, it takes the form of an extremely dynamic and pleomorphic membrane-bounded ...network of tubules and cisternae which have numerous different cellular functions. In this review, we discuss the nature of endoplasmic reticulum structure and dynamics, its relationship with closely associated organelles, and its possible function as a highway for the distribution and delivery of a diverse range of structures from metabolic complexes to viral particles.
Azolate-containing ligands have played an important role in the development of water-stable metalorganic frameworks (MOFs) and related materials due to their particularly strong bonding with ...earth-abundant first row transition metal ions. Fused ring analogues of pyrazole, imidazole and triazole offer untapped potential to expand the scope of these systems as compact, robust anionic bridging ligands with much greater control over bridging geometries, pendant functionalities and electronic properties. The current design approaches in these systems have been directed by two separate methodologies. In one direction, the simple azoles imidazole, pyrazole and 1,2,4-triazole have been built up by adding fused ring functionality to increase complexity and allow new linker geometries. Meanwhile, in the search for biologically-compatible MOFs, purines such as adenine and hypoxanthine have been explored as linkers and their backbone functionalities optimised to prioritise stability and bridging geometry, leading independently to MOF linkers with similar key features. This highlight article surveys the convergence of these two approaches which both point to the benefits of fused 56 ring systems for their electronic and structural properties, and considers the key features that the ideal compact and stable heterocyclic linkers in functional metalorganic frameworks might contain.
Fused azolate ligands are hydrolytically-stable linkers for metalorganic frameworks. Their unique geometries and capacity for functionalisation have opened new pathways at the convergence of simple N-heterocycles and biologically relevant purines.
meta-Phenylene bis(phenylurea) receptors 1–4 were designed and synthesized to investigate the association between receptor shape, anion-selective binding and anion-directed self-assembly processes. ...Solution studies, performed through 1H NMR titrations with a variety of tetra-N-butylammonium salts, demonstrated strong binding of 2 equiv of H2PO4 –, AcO–, BzO– anions and comparatively weak binding of Cl–, HSO4 –, and SO4 2– anions. Binding modes and stability constants (log β) were determined by regression analysis of the obtained 1H NMR titration data in DMSO-d 6, and the cooperativities of the binding interactions were probed. Host–guest complexes of receptors 1 and 2 were studied in the crystalline phase to further probe the anion-binding behavior of this motif. This included a triple-stranded helicate consisting of three strands of receptor 2 arranged around a mixed-phosphate anionic core, which was characterized by using X-ray crystallography.
Spiro3.3heptane-2,6-dicarboxylic acid (Fecht's acid,
H
2
SHDC
) is examined as a non-aromatic terephthalic acid isostere for the first time. The rigid spirocyclic backbone provides greater steric ...bulk than conventional aromatic dicarboxylates with consequences for pore chemistry and control of interpenetration, presented here in the structures of two new MOFs. Complex
1
is a three-dimensional rod packed structure consisting of Yb-carboxylate chains bridged by
SHDC
linkers which, although non-porous, exhibits a surprisingly high thermal stability for a spirocyclic cyclobutane derivative. Complex
2
is a co-ligand complex of
SHDC
with
trans
-1,2-bis(4-pyridyl)ethene (
bpe
) which contains linear solvent channels despite fourfold interpenetration. Although the framework does not retain its structure following evacuation, a clear difference is observed in the extended structure compared to the structurally related terephthalate species. This observation suggests the non-aromatic backbone of Fecht's acid and other rigid aliphatic linkers may prove an effective means to disfavour deleterious close inter-framework contacts which prevail in interpenetrated aromatic MOFs.
The first of a new class of spiroalkane-derived MOF linkers shows aromaticity is not a prerequisite for ligand design in porous materials.
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