Discrete Molecules Research Articles

Modulation of the magnetic dynamics in two air-stable sulfur-ligated dysprosium complexes via polymerization.

Two air-stable sulfur-ligated dysprosium(III) complexes [HN(Et)3][Dy2NaL8] (1) and [DyNaL4(MeOH)x(H2O)2-x]n (2) based on 2-pyridinethiol 1-oxide (HL) were synthesized and structurally characterized. Discrete 1 and polymeric 2 share the same anionic unit of [DyL4]- with the O4S4 coordination environment, but differ in the precise geometry with triangular dodecahedron geometry in 1 and biaugmented trigonal prism geometry in 2. The subtle change leads to observable temperature-independent relaxation for 2 while a faster relaxation with invisible peak for 1 at zero dc field. Under an optimal dc field, both display the typical Raman process with a smaller pre-factor and higher exponent for 2. Ab initio calculations reveal that the predicted energy barriers are 287 cm-1 for 1 and 303 cm-1 for 2. These results demonstrate the construction and magnetic modulation of air-stable sulfur-ligated Dy-SMM architectures.

Filling the gap with a bulky diaryl boron group: fluorinated and non-fluorinated copper pyrazolates fitted with a dimesityl boron moiety on the backbone.

Successful synthesis has been reported of 4-Mes2B-3,5-(CF3)2PzH and 4-Mes2B-3,5-(CF3)2PzH bearing sterically demanding diarylboron moieties at the pyrazole ring 4-position, and their corresponding copper(I) pyrazolate complexes. They show visible blue photoluminescence in solution. The X-ray crystal structures revealed that the fluorinated {[4-BMes2-3,5-(CF3)2Pz]Cu}3 crystallizes as discrete trinuclear molecules whereas as the non-fluorinated {[4-BMes2-3,5-(CH3)2Pz]Cu}3 forms dimers of trimers with two close inter-trimer Cu⋯Cu separations. The solid {[4-BMes2-3,5-(CF3)2Pz]Cu}3 featuring a sterically confined Cu3N6 core displays bright blue phosphorescence while {[4-BMes2-3,5-(CH3)2Pz]Cu}3, which is a dimer of a trimer, is a red phosphor at room temperature. This work illustrates the modulation of photo-physical properties of metal pyrazolates by adjusting the supporting ligand steric features and introducing secondary diarylboron luminophores. Computational analysis of the structures and photophysical properties of copper complexes are also presented.

Instantaneous degradation of nerve agent simulants using zirconium-based metal–organic polyhedra

Metal–organic polyhedra (MOPs) are discrete molecules made of metal ions/clusters and organic ligands, and their crystal packing leads to the generation of intrinsic and extrinsic porosity.

Crystal structure of bis{3-(3,5-dichlorophenyl)-5-[6-(1H-pyrazol-1-yl)pyridin-2-yl]-4H-1,2,4-triazol-4-ido}iron(II) methanol disolvate

The asymmetric unit of the title compound, [FeII(C16H9Cl2N6)2]·2CH3OH, consists of half of a charge-neutral complex molecule and a discrete methanol molecule. The planar anionic tridentate ligand 2-[5-(3,5-dichlorophenyl)-4H-1,2,4-triazol-3-ato]-6-(1H-pyrazol-1-yl)pyridine coordinates to the FeII ion through the N atoms of the pyrazole, pyridine and triazole groups, forming a coordination sphere of the central ion that deviates moderately from an octahedral geometry. The average Fe—N bond distance is 1.953 Å, indicating the low-spin state of the FeII ion. The cone-like-shaped molecules, nested into each other, are linked through double weak C—H(pz)...π(ph) interactions into mono-periodic columns, which are further linked through weak C—H...N′/C′ interactions into di-periodic layers. The layers interact through double weak C–H(ph)...Cl bonds with neighbouring molecules. Energy framework analysis at the B3LYP/6–31 G(d,p) theory level reproduces the strong interaction within the layers and the weaker interlayer interactions. Intermolecular contacts were quantified using Hirshfeld surface analysis and two-dimensional fingerprint plots, the relative contributions of the contacts to the crystal packing being H...H 26.1%, H...C/C...H 24.4%, H...Cl/Cl...H 18.9% and H...N/N...H 12.1%.

Metal-to-ligand ratio-controlled assembly of two Ca(II) complexes: Synthesis, structures, reactant-induced reversible transformation, and catalytic properties

Hydrothermal reactions of Ca(NO3)2·4H2O and topiroxostat with different metal-to-ligand ratios yielded two new complexes {[Ca2(L)2(H2O)6]·H2O}n (1) and Ca(HL)2(H2O)4 (2) [H2L = 4-(3-(pyridine-4-yl)-1H-1,2,4-triazol-5-yl)picolinic acid], involving ligand in situ formation by hydrolysis of topiroxostat. X-ray structural analysis revealed that complex 1 has a 1D coordination polymeric structure while complex 2 displays a 0D discrete molecule. Both complexes exhibit interesting reactant-induced reversible structural transformation properties. Thermogravimetric analysis and temperature-dependent PXRD patterns indicated that the network of 1 keep high thermal stability up to 400 °C. The catalytic performance of the complexes for the solvent-free ring-opening polymerization of ε-caprolactone has been investigated.

Crystal structure of bis-{3-(3,4-di-methyl-phen-yl)-5-[6-(1H-pyrazol-1-yl)pyridin-2-yl]-4H-1,2,4-triazol-4-ido}iron(II) methanol disolvate.

As a result of the high symmetry of the Aea2 structure, the asymmetric unit of the title compound, [FeII(C18H15N6)2]·2MeOH, consists of half of a charge-neutral complex mol-ecule and a discrete methanol mol-ecule. The planar anionic tridentate ligand 2-[5-(3,4-di-methyl-phen-yl)-4H-1,2,4-triazol-3-ato]-6-(1H-pyrazol-1-yl)pyridine coordinates the FeII ion meridionally through the N atoms of the pyrazole, pyridine and triazole groups, forming a pseudo-octa-hedral coordination sphere of the central ion. The average Fe-N bond distance is 1.955 Å, indicating a low-spin state of the FeII ion. Neighbouring cone-shaped mol-ecules, nested into each other, are linked through double weak C-H(pz)⋯π(ph') inter-actions into mono-periodic columns, which are further linked through weak C-H⋯N'/C' inter-actions into di-periodic layers. No inter-actions shorter than the sum of the van der Waals radii of the neighbouring layers are observed. Energy framework analysis at the B3LYP/6-31 G(d,p) theory level, performed to qu-antify the inter-molecular inter-action energies, reproduces the weak inter-layer inter-actions in contrast to the strong inter-action within the layers. Inter-molecular contacts were qu-anti-fied using Hirshfeld surface analysis and two-dimensional fingerprint plots, showing the relative contributions of the contacts to the crystal packing to be H⋯H 48.5%, H⋯C/C⋯H 28.9%, H⋯N/N⋯H 16.2% and C⋯C 2.4%.

Carbon dioxide adsorption and conversion to methane and ethane on hydrogen boride sheets

Hydrogen boride (HB) sheets are metal-free two-dimensional materials comprising boron and hydrogen in a 1:1 stoichiometric ratio. In spite of the several advancements, the fundamental interactions between HB sheets and discrete molecules remain unclear. Here, we report the adsorption of CO2 and its conversion to CH4 and C2H6 using hydrogen-deficient HB sheets. Although fresh HB sheets did not adsorb CO2, hydrogen-deficient HB sheets reproducibly physisorbed CO2 at 297 K. The adsorption followed the Langmuir model with a saturation coverage of 2.4 × 10−4 mol g−1 and a heat of adsorption of approximately 20 kJ mol−1, which was supported by density functional theory calculations. When heated in a CO2 atmosphere, hydrogen-deficient HB began reacting with CO2 at 423 K. The detection of CH4 and C2H6 as CO2 reaction products in a moist atmosphere indicated that hydrogen-deficient HB promotes C–C coupling and CO2 conversion reactions. Our findings highlight the application potential of HB sheets as catalysts for CO2 conversion.

Crystal structure of haloxon, C14H14Cl3O6P

The crystal structure of haloxon has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional theory techniques. Haloxon crystallizes in space group P21/n (#14) with a = 19.60382(6), b = 10.05473(3), c = 8.73591(2) Å, β = 92.6617(2)°, V = 1720.088(11) Å3, and Z = 4. The structure consists of discrete molecules. The mean planes of the fused ring systems are approximately 0–11 and 011. The rings form staggered stacks perpendicular to these planes. There are no traditional hydrogen bonds in the structure, but several C–H⋯O and C–H⋯Cl hydrogen bonds contribute to the crystal energy. The powder pattern has been submitted to ICDD for inclusion in the Powder Diffraction File™ (PDF®).

Thickness-dependent spin bistable transitions in single-crystalline molecular 2D material

The advent of two-dimensional (2D) crystals has led to numerous scientific breakthroughs. Conventional 2D systems have in-plane covalent bonds and a weak out-of-plane van-der-Waals bond. Here we report a new type of 2D material composed of discrete magnetic molecules, where anisotropic van-der-Waals interactions bond the molecules into a 2D packing. Through mechanical exfoliation, we can obtain single-crystalline molecular monolayers, which can be readily integrated into other 2D systems. Optical spectroscopy suggests the few-layered molecules preserve the temperature-induced spin-crossover switching observed in the bulk form but show a drastic increase in thermal hysteresis unique to these thin 2D molecule assemblies. The trapping of spin bistability with decreasing layer number can arise from domain wall dynamics in reduced dimensions. Our results establish molecular solids with strong anisotropy of intermolecular interactions as precursors to a new class of 2D materials, affording possibilities to control molecular functionalities through substrate and interlayer interactions.

Crossing the Boundaries between Analogue and Digital

Given that they do not benefit from CMOS technology scaling, analogue integrated circuits are soon becoming a constraint in terms of the cost and performance of nanoscale integrated systems. This has led to some debate about whether analogue circuits are still useful in the era of digital technology. The usual reaction is that analogue circuitry will always be needed, if not everywhere, then at least in interface circuits that exchange data with physically analogue environments. The fact that matter is made up of discrete atoms and molecules, that basic physical quantities like electromagnetic radiation and electric charge are quantized, and even that information is transmitted as discrete pulses in biological systems all make the physical world less "intrinsically analog" than it first appears. In other words, it appears more and more plausible that the foundation for our regular analogue experiences is a distinct or digital one.

Solvation Thermodynamics of Solutes in Water and Ionic Liquids Using the Multiscale Solvation-Layer Interface Condition Continuum Model.

Molecular assembly processes are generally driven by thermodynamic properties in solutions. Atomistic modeling can be very helpful in designing and understanding complex systems, except that bulk solvent is very inefficient to treat explicitly as discrete molecules. In this work, we develop and assess two multiscale solvation models for computing solvation thermodynamic properties. The new SLIC/CDC model combines continuum solvent electrostatics based on the solvent layer interface condition (SLIC) with new statistical thermodynamic models for hydrogen bonding and nonpolar modes: cavity formation, dispersion interactions, combinatorial mixing (CDC). Given the structures of 500 solutes, the SLIC/CDC model predicts Gibbs energies of solvation in water with an average accuracy better than 1 kcal/mol, when compared to experimental measurements, and better than 0.8 kcal/mol, when compared to explicit-solvent molecular dynamics simulations. The individual SLIC/CDC energy mode values agree quantitatively with those computed from explicit-solvent molecular dynamics. The previously published SLIC/SASA multiscale model combines the SLIC continuum electrostatic model with the solvent-accessible surface area (SASA) nonpolar energy mode. With our new, improved parametrization method, the SLIC/SASA model now predicts Gibbs energies of solvation with better than 1.4 kcal/mol average accuracy in aqueous systems, compared to experimental and explicit-solvent molecular dynamics, and better than 1.6 kcal/mol average accuracy in ionic liquids, compared to explicit-solvent molecular dynamics. Both models predict solvation entropies, and are the first implicit-solvation models capable of predicting solvation heat capacities.

(Invited, Digital Presentation) Synthesis of Multi-Metallic Clusters Using a Dendrimer Reactor

Dendrimers are highly branched organic macromolecules with successive layers or “generations” of branch units surrounding a central core. Organic inorganic hybrid versions have also been produced, by trapping metal ions or metal clusters within the voids of the dendrimers. Their unusual, tree-like topology endows these nanometer-sized macromolecules with a gradient in branch density from the interior to the exterior, which can be exploited to direct the transfer of charge and energy from the dendrimer periphery to its core.We show that tinchloride, SnCl2 and FeCl3 complexes to the imines groups of a spherical polyphenylazomethine dendrimer in a stepwise fashion according to an electron gradient, with complexation in a more peripheral generation proceeding only after complexation in generations closer to the core has been completed. By attaching an electron-withdrawing group to the dendrimer core, we are able to change the complexation pattern, so that the core imines are complexed last. By further extending this strategy, it should be possible to control the number and location of metal ions incorporated into dendrimer structures, which might and uses as tailored catalysts, building blocks, or fine-controlled clusters for advanced materials. The metal-assembly in a discrete molecule can be converted to a size-regulated metal particle with a size smaller than 1 nm as a molecular reactor. Due to the well-defined number of metal clusters in the subnanometer size region, its property is much different from that of bulk or general metal nanoparticles. The chemistry of metal clusters on the sub-nanometer scale is not yet well understood because metal clusters, especially multi-metallic clusters, are difficult to synthesize with control over size and composition. The template synthesis of multi-metallic sub-nanoclusters is achieved using a phenylazomethine dendrimer as a macromolecular template.

Microwave Irradiation as a Powerful Tool for the Preparation of n-Type Benzotriazole Semiconductors with Applications in Organic Field-Effect Transistors.

In this work, as an equivocal proof of the potential of microwave irradiation in organic synthesis, a complex pyrazine-decorated benzotriazole derivative that is challenging to prepare under conventional conditions has been obtained upon microwave irradiation, thus efficiently improving the process and yields, dramatically decreasing the reaction times and resulting in an environmentally friendly synthetic procedure. In addition, this useful derivative could be applied in organic electronics, specifically in organic field-effect transistors (OFETs), exhibiting the highest electron mobilities reported to date for benzotriazole discrete molecules, of around 10−2 cm2V−1s−1.

Highly Ordered Supramolecular Assembled Networks Tailored by Bioinspired H-Bonding Confinement for Recyclable Ion-Transport Materials

Highly Ordered Supramolecular Assembled Networks Tailored by Bioinspired H-Bonding Confinement for Recyclable Ion-Transport Materials

Investigation on Oil Physical States of Hybrid Shale Oil System: A Case Study on Cretaceous Second White Speckled Shale Formation from Highwood River Outcrop, Southern Alberta

Nine samples collected from the Upper Cretaceous Second White Speckled Shale Formation at the Highwood River outcrop in southern Alberta were geochemically characterized for their oil contents, physical states, and chemical compositions. Cold extraction was performed on 8–10 mm and 2–5 mm chips sequentially to obtain the first and second extractable organic matter (EOM-1 and EOM-2), while Soxhlet extraction was performed on powder from previously extracted chips to obtain the third extract (EOM-3). EOM-1 can be roughly regarded as free oil and EOM-2 is weakly adsorbed on mineral surfaces, while EOM-3 may represent the oil strongly adsorbed on kerogen. While both extraction yields and Rock-Eval pyrolysates differed from their original values due to the evaporative loss during outcropping, there was a generally positive correlation between the total EOM and total oil derived from Rock-Eval pyrolysis. EOM-1 was linearly correlated with Rock-Eval S1, while the extractable S2 content was well correlated with the loss of TOC, suggesting that TOC content was the main constraint for adsorbed oils. A bulk composition analysis illustrated that EOM-1 contained more saturated hydrocarbons, while EOM-3 was enriched in resins and asphaltenes. More detailed fractionation between the free and adsorbed oils was demonstrated by molecular compositions of each extract using quantitative GC-MS analysis. Lower-molecular-weight n-alkanes and smaller-ring-number aromatic compounds were preferentially concentrated in EOM-1 as compared to their higher-molecular or greater-ring-number counterparts and vice versa for EOM-3. Fractionation between isoprenoids and adjacent eluted n-alkanes, isomers of steranes, hopanes, alkylnaphthalenes, alkylphenanthrenes and alkyldibenzothiophenes was insignificant, suggesting no allogenic charge from deep strata. Strong chemical fractionation between saturated and aromatic hydrocarbon fractions was observed with EOM-1 apparently enriched in n-alkanes, while EOM-3 retained more aromatic hydrocarbons. However, the difference between free and adsorbed state oils was less dramatic than the variation from shales and siltstones. Lithological heterogeneities controlled both the amount and composition of retained fluids. Oil that resided in shales (source rock) behaved more similar to the EOM-3, with diffusive expulsion leading to the release of discrete molecules from a more adsorbed or occluded phase to a more free phase in siltstones with more connected pores and/or fractures (reservoir). Under current technical conditions, only the free oil can flow and will be the recoverable resource. Therefore, the highest potential can be expected from intervals adjacent to organic-rich beds. The compositional variations due to expulsion and primary migration from source rocks to reservoirs illustrated in the present study will contribute to a better understanding of the distribution of hydrocarbons generated and stored within the shale plays.

STUDY OF THE ROLE OF RNA-INTERFERENCE IN THE REGULATION OF DISCRETE FRAGMENTATION OF 18S RRNA IN PLANTS

Under stressful conditions, cells must rapidly reduce the level of total mRNA translation, while maintaining the synthesis of some special proteins that help resist stress. In animals and yeast, the inhibition of protein synthesis is mainly associated with the modification of the translation initiation and elongation factors. In plant cells, many of these regulatory mechanisms are not realized. We hypothesize that plants have an alternative mechanism for suppressing mRNA translation associated with site-specific fragmentation of 18S rRNA molecules within 40S ribosomal subunits. Understanding the molecular mechanisms of plant response to stress is the basis for increasing the efficiency of the breeding process in order to develop stress-resistant varieties of economically important plant species. We found that during a heat shock, discrete RNA molecules accumulate in the cells of various plant species, which are 5'-terminal fragments of 18S rRNA that remain bound in the composition of ribosomal subunits. In this work, the method of nucleic acid hybridization was used to study RNA-interference as a possible mechanism mediating the phenomenon of discrete fragmentation of 18S rRNA in plants in response to heat shock. MicroRNA molecules complementary to the target regions of 18S rRNA, through which its rupture was carried out with the formation of stress-induced 5'-terminal RNA fragments, were not found. The small 5'-terminal fragments of 18S rRNA revealed during the work are proposed to be used as a new type of stress biomarkers in plant cells. The optimized nucleic acid hybridization technique using a DIG-labeled probe complementary to the highly conserved 1-35 5'-end region of plant 18S rRNA can be used to efficiently detect these stress RNA markers.

Novel Gels: An Emerging Approach for Delivering of Therapeutic Molecules and Recent Trends.

Gels are semisolid, homogeneous systems with continuous or discrete therapeutic molecules in a suitable lipophilic or hydrophilic three-dimensional network base. Innovative gel systems possess multipurpose applications in cosmetics, food, pharmaceuticals, biotechnology, and so forth. Formulating a gel-based delivery system is simple and the delivery system enables the release of loaded therapeutic molecules. Furthermore, it facilitates the delivery of molecules via various routes as these gel-based systems offer proximal surface contact between a loaded therapeutic molecule and an absorption site. In the past decade, researchers have potentially explored and established a significant understanding of gel-based delivery systems for drug delivery. Subsequently, they have enabled the prospects of developing novel gel-based systems that illicit drug release by specific biological or external stimuli, such as temperature, pH, enzymes, ultrasound, antigens, etc. These systems are considered smart gels for their broad applications. This review reflects the significant role of advanced gel-based delivery systems for various therapeutic benefits. This detailed discussion is focused on strategies for the formulation of different novel gel-based systems, as well as it highlights the current research trends of these systems and patented technologies.

Mechanistic Analysis of the VirA Sensor Kinase in Agrobacterium tumefaciens Using Structural Models.

Agrobacterium tumefaciens pathogenesis of plants is initiated with signal reception and culminates with transforming the genomic DNA of its host. The histidine sensor kinase VirA receives and reacts to discrete signaling molecules for the full induction of the genes necessary for this process. Though many of the components of this process have been identified, the precise mechanism of how VirA coordinates the response to host signals, namely phenols and sugars, is unknown. Recent advances of molecular modeling have allowed us to test structure/function predictions and contextualize previous experiments with VirA. In particular, the deep mind software AlphaFold has generated a structural model for the entire protein, allowing us to construct a model that addresses the mechanism of VirA signal reception. Here, we deepen our analysis of the region of VirA that is critical for phenol reception, model and probe potential phenol-binding sites of VirA, and refine its mechanism to strengthen our understanding of A. tumefaciens signal perception.

Transition Metal Nanoparticles‐Catalyzed Organic Reactions within Porous Organic Cages

AbstractTransition metal catalysis has played an important role in modern organic chemistry. In order to develop highly efficient and sustainable methodologies, considerable efforts have been devoted to combining the benefits of homogeneous catalysis and heterogeneous catalysis. Porous organic cages (POCs) are a relatively new type of discrete molecules with permanent cavities and good solubilities. These intrinsic properties make POCs expedient catalyst support for the homogenization of heterogeneous transition metal nanoparticles (MNPs). This review mainly focuses on the recent progress of MNPs‐catalyzed reductions and coupling reactions within POCs. In most cases, the MNPs@POC complexes have exhibited outstanding reactivity, dispersibility, stability, and reusability. These pioneering contributions have enriched the methodology toolbox for advanced organic synthesis.

Optimizing therapeutic outcomes of immune checkpoint blockade by a microbial tryptophan metabolite

BackgroundDespite the great success, the therapeutic benefits of immune checkpoint inhibitors (ICIs) in cancer immunotherapy are limited by either various resistance mechanisms or ICI-associated toxic effects including gastrointestinal toxicity. Thus,...