Structure of low-density nanoporous dielectrics revealed by low-vacuum electron microscopy and small-angle X-ray scattering

Aerogels (AGs) are ultralow-density nanoporous solids that have numerous potential applications. However, as most AGs are strong insulators with poor mechanical properties, direct studies of the complex nanoporous structure of AGs by methods such as atomic force and conventional scanning electron microscopy (SEM) have not proven feasible. Here, we use low-vacuum SEM to image directly the ligament and pore size and shape distributions of representative AGs over a wide range of length scales (approximately 100-105 nm). The structural information obtained is used for unambiguous, real-space interpretation of small-angle X-ray scattering curves for these complex nanoporous systems. Low-vacuum SEM permits imaging of both cross-sections and skin layers of AG monoliths. Images of skin layers reveal the presence of microcracks, which alter the properties of cast monolithic AGs.     

Effect of electron-donating and electron-withdrawing groups on peptide/single-walled carbon nanotube interactions

Nano-1, a designed peptide, has been demonstrated to efficiently disperse individual single-walled carbon nanotubes (SWNTs) by folding into an amphiphilic alpha-helix wherein the phenylalanine (Phe) residues on the hydrophobic face of the helix interact via pi-stacking with the aromatic surface of the SWNT. In this study, the ability of electron-donating (hydroxyl) and electron-withdrawing (nitro) groups on the phenyl ring of Phe to affect the interactions between the peptide and SWNTs is examined by substituting the Phe residues in the nano-1 sequence with tyrosine and p-nitro-phenylalanine, respectively. Atomic force microscopy measurements and optical absorption spectroscopy revealed that the ability to disperse individual SWNTs increases with increasing electron density of the aromatic residue on the hydrophobic face of the amphiphilic helical peptides. Scanning tunneling spectroscopy (STS) and Raman analyses were used to examine the effect of noncovalent protein functionalization on the electronic properties of SWNTs. Small shifts in the Raman G band peak for the peptide/SWNT composites, as well as weak features that appear near the Fermi energy (Ef) in the STS dI/dV spectra of the peptide-coated SWNTs, are suggestive of a weak charge-transfer interaction between the peptides and the SWNTs.     

Targeting SARS-CoV-2 Polymerase with New Nucleoside Analogues

Despite the fact that COVID-19 vaccines are already available on the market, there have not been any effective FDA-approved drugs to treat this disease. There are several already known drugs that through drug repositioning have shown an inhibitory activity against SARS-CoV-2 RNA-dependent RNA polymerase. These drugs are included in the family of nucleoside analogues. In our efforts, we synthesized a group of new nucleoside analogues, which are modified at the sugar moiety that is replaced by a quinazoline entity. Different nucleobase derivatives are used in order to increase the inhibition. Five new nucleoside analogues were evaluated with in vitro assays for targeting polymerase of SARS-CoV-2.     

Solid ink-printed filter paper as a green adsorbent material for the solid-phase extraction of UV filters from water samples

This work describes the development of a new green solid-phase extraction approach, which is based on the use of low-cost extraction discs composed of plain filter papers that are covered with a synthetic wax-like coating. The filter papers are printed in a commercial solid ink printer, which dispenses a synthetic wax-like ink on the surface of the paper, to cover the hydrophilic cellulose fibre matrix with an interface of lipophilic domains where non-polar analytes can partition through hydrophobic interactions. The modified paper filters were used to extract hydrophobic organic compounds from water samples following the customary procedure of solid-phase extraction without sorbent preconditioning and needless of high-vacuum sources. As a proof-of-concept application, a series of non-polar organic UV filters were used as model analytes to optimise the extraction parameters and evaluate the performance of the method in spiked water samples. Based on this principle, a new sample preparation platform with low environmental footprint has been developed that enables extraction to be carried out using low-cost, environmental benign and non-toxic conventional materials. The advantages and disadvantages of the method, alongside with its future prospects towards the development of custom-made ‘printed extraction kits’, are envisioned and discussed.     

Potassium Ion Induced Changes of Crystal Structure and Fluorescence of a Crown Ether

Luminescence properties and the x-ray structures of the fluorescent crown ether, 16-anthracen-ylmethyl-1,4,7,10,13-pentaoxa-16-aza-cyclooctadecane (CEA) and its complex with potassium hexafluorophosphate (CEAK) have been obtained. In the solid state CEAK gives a structured blue emission and CEA gives a broad structureless green emission. The differences in luminescence behavior are explained on the basis of crystal packing. X-ray analysis shows that every two adjacent anthracene moieties in CEA form a sandwich-like anti-parallel dimer; the green-structureless emission then arises from the π-π stack of the aromatic rings. In CEAK, disruption of the π-π stacking structure forces a large separation between the anthracene rings, which yields an anthracene monomer emission. Luminescence lifetime data support the assignments.     

Hexametallic manganese clusters with bulky derivatised salicylaldoximes

The reaction of Mn(ClO(4))(2)·6H(2)O with Ph-saoH(2) (Ph-saoH(2) = 2-hydroxybenzophenone oxime) in MeCN in the presence of sodium propionate forms the complex [Mn(III)(6)O(2)(Ph-sao)(6)(prop)(2)(MeCN)(2)]·5.27MeCN (1·5.27MeCN) (prop = propionate). Repeating the same reaction in EtOH produces the complex [Mn(III)(6)O(2)(Ph-sao)(6)(prop)(2)(EtOH)(4)] (2). Complexes 1 and 2 may be considered as structural isomers, since they display the same metallic core but different coordination modes of the propionate ligands; bridging in 1 and terminal in 2. Performing similar reactions and switching from sodium propionate to sodium adamantane-carboxylate (NaO(2)C-ada) and sodium pivalate (Napiv) in the presence of NEt(4)OH yields the complexes [Mn(III)(6)O(2)(Ph-sao)(6)(O(2)C-ada)(2)(MeOH)(4)] (3) and [Mn(III)(6)O(2)(Ph-sao)(6)(piv)(2)(EtOH)(4)]·0.5Et(2)O (4·0.5Et(2)O), respectively. All four complexes contain the same {Mn(III)(3)O(Ph-sao)(3)} building block. Variable temperature magnetic susceptibility and magnetization studies show that all complexes possess an S = 4 ground-state.     

Environmental sensitivity of Ru(II) complexes: the role of the accessory ligands

A suite of Ru(II) complexes in which one ligand is pH responsive and the other two are varied in an effort to achieve improved photophysics has been synthesized and their potential as pH reporters assessed. The more general purpose of the study was to examine the role of the accessory ligands in heteroleptic reporter complexes and the degree to which such ligands can affect the performance of luminescent reporters. For this suite of complexes, judicious choice of the accessory ligand can alter both the pK(a)* and the dynamic range of response. It was found that the emission color and brightness were influenced by pH, but the lifetimes were only weakly affected. Surprisingly, some accessory ligands which should have improved luminescent properties essentially turned off the pH response. Several possible reasons for this observation are explored. It is suggested, and density functional theory (DFT) calculations support, that the relative π* levels of the pH sensitive and the accessory ligands are critical.     

Photophysical and Analyte Sensing Properties of Cyclometalated Ir(III) Complexes

The synthesis of some heteroleptic, cyclometalated iridium(III) complexes is described. The utility of these [Ir(ppy)₂(N-N)]Cl (ppy = 2-phenylpyridine and N-N = substituted bipyridine, biquinoline, or phenanthroline) complexes as luminescence-based sensors is assessed. The emission intensity of an Ir(III) complex featuring the 3,3′-H_ndcbpy ligand (H_ndcbpy = dicarboxylic acid-2,2′-bipyridine; n = 0,1,2 to indicate deprotonated, mono- and diprotonated species, respectively) is seen to increase in the presence of Pb(II). Insight into the structure and analyte-sensing capability is achieved by X-ray crystallography in conjunction with computational modeling. Complexes incorporating carboxylic acid-functionalized bipyridine and biquinoline as the polypyridyl ligand show pH sensitivity while similar phenanthroline complexes do not.     

Luminescent Donor-Acceptor β-Diketones: Modulation of Emission by Solvent Polarity and Group II Metal Binding

A class of aryl trifluoromethyl-containing β-diketones were synthesized via one step Claisen condensation. These π-conjugated diketones exhibit strong solvatochromism from intramolecular donor-acceptor charge transfer (CT). In addition, fluorescence quantum yields (ϕ_f) and lifetimes (τ_f) were measured in different solvents. Diketones exhibit bathochromic shifts in emission spectra with increasing solvent polarity. Fluorescence changes upon Group II metal binding were also studied. Despite the relatively simple structure, the anthracene-CF₃ diketone, atm, has strong binding affinity for Mg²⁺. A 70 nm blue shift and sixfold increase in intensity were observed upon addition of only one equivalent MgCl₂ in ethanol solution. It also shows selectivity for Mg²⁺ binding even in the presence of excess Ca²⁺. Association constant (K_a) calculations suggest atm has two orders of magnitude stronger chelation for divalent magnesium than for calcium. These findings make atm an attractive starting point for molecular probe and light emitting material design.     

Electronic characterization of lithographically patterned microcoils for high sensitivity NMR detection

Nuclear magnetic resonance (NMR) offers a non-destructive, powerful, structure-specific analytical method for the identification of chemical and biological systems. The use of radio frequency (RF) microcoils has been shown to increase the sensitivity in mass-limited samples. Recent advances in micro-receiver technology have further demonstrated a substantial increase in mass sensitivity [D.L. Olson, T.L. Peck, A.G. Webb, R.L. Magin, J.V. Sweedler, High-resolution microcoil H-1-NMR for mass-limited, nanoliter-volume samples, Science 270 (5244) (1995) 1967–1970]. Lithographic methods for producing solenoid microcoils possess a level of flexibility and reproducibility that exceeds previous production methods, such as hand winding microcoils. This paper presents electrical characterizations of RF microcoils produced by a unique laser lithography system that can pattern three dimensional surfaces and compares calculated and experimental results to those for wire wound RF microcoils. We show that existing optimization conditions for RF coil design still hold true for RF microcoils produced by lithography. Current lithographic microcoils show somewhat inferior performance to wire wound RF microcoils due to limitations in the existing electroplating technique. In principle, however, when the pitch of the RF microcoil is less than 100 μm lithographic coils should show comparable performance to wire wound coils. In the cases of larger pitch, wire cross sections can be significantly larger and resistances lower than microfabricated conductors.