Silver nanoparticles as potential antiviral agents

Virus infections pose significant global health challenges, especially in view of the fact that the emergence of resistant viral strains and the adverse side effects associated with prolonged use continue to slow down the application of effective antiviral therapies. This makes imperative the need for the development of safe and potent alternatives to conventional antiviral drugs. In the present scenario, nanoscale materials have emerged as novel antiviral agents for the possibilities offered by their unique chemical and physical properties. Silver nanoparticles have mainly been studied for their antimicrobial potential against bacteria, but have also proven to be active against several types of viruses including human imunodeficiency virus, hepatitis B virus, herpes simplex virus, respiratory syncytial virus, and monkey pox virus. The use of metal nanoparticles provides an interesting opportunity for novel antiviral therapies. Since metals may attack a broad range of targets in the virus there is a lower possibility to develop resistance as compared to conventional antivirals. The present review focuses on the development of methods for the production of silver nanoparticles and on their use as antiviral therapeutics against pathogenic viruses.     

Planar hydrocarbons more optically active than their isomeric helicenes

Comparisons are made of the calculated optical rotation tensors of C(2v)-symmetric, polyaromatic hydrocarbons and their [5]helicene, [6]helicene, and [7]helicene isomers. Seven ∩-shaped, planar compounds had, in each case, larger computed tensor elements than the chiral helicenes. Merely obviating the condition of solution averaging wholly changes expectations of the magnitudes and etiologies of optical activity. Symmetries of achiral compounds facilitate semiquantitative correlations between structure and optical rotation.     

Synthesis of polysiloxane xerogels with fluorine-containing groups in the surface layer and their sorption properties

Hydrolysis and polycondensation reactions of tetraethoxysilane (TEOS) with 3,3,3-trifluoropropyl-trimethoxysilane (TFMS) or 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFES) were used to synthesize xerogels functionalized with fluorine-containing groups. According to transmission electron microscopy, the skeletons of synthesized polysiloxane xerogels have globular structures and consist of agglomerates of particles with fluorinated groups on their surfaces. FTIR spectroscopy showed that primary xerogel particles possess spatial polysiloxane networks, with fluorinated groups along with silanol groups and water in the surface layer. According to thermal analyses, the water content was 3–8 wt.%, and it decreased with increasing length of the fluorinated chain. Thermal destruction of the surface layer starts above 300 °C. The sorbents that were obtained were predominantly mesoporous materials with well-developed porous structures (S_BET = 400–960 m² g⁻¹, V_s = 0.66–0.93 cm³ g⁻¹). The influence of the TEOS/functional silane ratio and the natures of the functional groups on the structural and adsorptive properties were shown. The samples synthesized are organophilic. The affinity for n-hexane increases with increasing length of the fluorine-containing chain (PFES) and the content of fluorinated groups in the surface layer. The hybrid organic–inorganic materials that were obtained can be used for adsorption of hydrocarbons, including oil, from water.     

Hexaphenylbenzene-based polymers of intrinsic microporosity

Microporous polymers derived from the 1,2- and 1,4-regioisomers of di(3',4'-dihydroxyphenyl)tetraphenylbenzene have very different properties with the former being composed predominantly of cyclic oligomers whereas the latter is of high molar mass suitable for the formation of robust solvent-cast films of high gas permeability.     

Correlation of the EPR properties of perchlorotriphenylmethyl radicals and their efficiency as DNP polarizers

Water soluble perchlorinated trityl (PTM) radicals were found to be effective 95 GHz DNP (dynamic nuclear polarization) polarizers in ex situ (dissolution) (13)C DNP (Gabellieri et al., Angew Chem., Int. Ed. 2010, 49, 3360). The degree of the nuclear polarization obtained was reported to be dependent on the position of the chlorine substituents on the trityl skeleton. In addition, on the basis of the DNP frequency sweeps it was suggested that the (13)C NMR signal enhancement is mediated by the Cl nuclei. To understand the DNP mechanism of the PTM radicals we have explored the 95 GHz EPR characteristics of these radicals that are relevant to their performance as DNP polarizers. The EPR spectra of the radicals revealed axially symmetric g-tensors. A comparison of the spectra with the (13)C DNP frequency sweeps showed that although the solid effect mechanism is operational the DNP frequency sweeps reveal some extra width suggesting that contributions from EPR forbidden transitions involving (35,37)Cl nuclear flips are likely. This was substantiated experimentally by ELDOR (electron-electron double resonance) detected NMR measurements, which map the EPR forbidden transitions, and ELDOR experiments that follow the depolarization of the electron spin upon irradiation of the forbidden EPR transitions. DFT (density functional theory) calculations helped to assign the observed transitions and provided the relevant spin Hamiltonian parameters. These results show that the (35,37)Cl hyperfine and nuclear quadrupolar interactions cause a considerable nuclear state mixing at 95 GHz thus facilitating the polarization of the Cl nuclei upon microwave irradiation. Overlap of Cl nuclear frequencies and the (13)C Larmor frequency further facilitates the polarization of the (13)C nuclei by spin diffusion. Calculation of the (13)C DNP frequency sweep based on the Cl nuclear polarization showed that it does lead to an increase in the width of the spectra, improving the agreement with the experimental sweeps, thus supporting the existence of a new heteronuclear assisted DNP mechanism.     

Self-assembling of multi-jets by pyro-electrohydrodynamic effect for high throughput liquid nanodrops transfer

Destabilization of liquid film by electro-hydro-dynamics (EHD) pressure is achieved through the pyroelectric effect on a polar dielectric crystal. We show that by destabilizing the liquid film, periodical self-assembled multi-jets are obtained. The multi-jets operate simultaneously and could be exploited to dispense liquids with nanolitre drops. Such multiple self-assembled liquid jets have significant potential applicability for high-throughput liquid transfer by this novel pyro-EHD ink-jet approach. Since the method avoids the use of nozzles and electrodes, it is especially suitable for highly viscous liquids. Here we present and discuss the new multi-jet process and the results obtained with a liquid polymer (PDMS).     

Drimenol: A versatile synthon for compounds with trans-drimane skeleton

Several reviews have been published on sesquiterpenes, and on drimane-type sesquiterpenes, going through drimenol and related compounds among others. However, to our knowledge, this is the first review exclusively on drimenol. Although, the main focus is on drimenol as a synthon for other drimane-type compounds, synthetic routes to obtain racemic and (-)-drimenol are summarized, as well as its isolation and determination of its configuration, in the early fifties. The reviewed synthetic routes start from natural (-)-drimenol as chiral synthon in most of cases, nevertheless total syntheses are considered as well. The strategies where racemic drimenol is involved begin with biomimetic cyclization of trans-farnesol. Microbiological procedures to functionalize the A ring of drimenol are also commented. The revision is classified according to the chemical structure of the final product, which mainly correspond to structures of natural occurrence, although other related derivatives are also analyzed.     

The Influence of Nd and Sm on the Structure and Properties of Sol-Gel-Derived TiO2 Powders

TiO₂ nanopowders modified by Nd and Sm were prepared using the sol-gel technique. It was found by XRD analysis that the samples containing Sm are amorphous up to 300 °C, while those with Nd preserve a mixed organic-inorganic amorphous structure at higher temperatures (400 °C). The TiO₂ (rutile) was not detected up to 700 °C in the presence of both modified oxides. TiO₂ (anatase) crystals found at about 400 °C in the Sm-modified sample exhibited an average crystallite size of about 25–30 nm, while doping with Nd resulted in particles of a lower size—5–10 nm. It was established by DTA that organic decomposition is accompanied by significant weight loss occurring in the temperature range 240–350 °C. Photocatalytic tests showed that the samples heated at 500 °C possess photocatalytic activity under UV irradiation toward Malachite green organic dye. Selected compositions exhibited good antimicrobial activity against E. coli K12 and B. subtilis.     

Local structure and triplet energy migration in p-dichlorobenzene-p-dibromobenzene solid solutions

Studies of the first triplet absorption and emission spectra of p-dichlorobenzene-p-dibromobenzene (DCB-DBB) mixed crystals agree generally with the data, indicating that this system forms solid solutions. However, the spectral properties are found to be very different from that of isotopically mixed crystals of comparable concentrations. The singlet-triplet absorption spectra of the DCB-DBB mixtures are generally broad and not amenable to detailed analysis indicating significant site dependent perturbations of the DCB and DBB triplet energies. Energy migration enhances emission from the lower energy sites and in consequence a red shift in the position of the emission (0,0) is observed, which is a maximum at equimolar concentrations. The emission bands are generally much broader than found for isotopically mixed crystals, indicating that the many types of sites in the DCB-DBB system remained uncoupled. This is a direct consequence of exciton trapping by inhomogeneous energy broadening caused by the site energy disorder being greater than the triplet exciton band width. Long-range triplet energy migration is not observed at DCB concentrations less than 99 per cent. This high limit is only expected for near one-dimension energy migration topologies. New structure observed at low DCB concentrations is tentatively interpreted as being due to the formation of DCB n-mers. The observed splittings indicate that the gas-to-crystal shift of the DCB T ₁ state increases (becomes more negative) by 11 cm^-1 when a neighbouring DBB molecule is replaced by DCB.     

Noncovalent paramagnetic complexes: detection of halogen bonding in solution by ESR spectroscopy

Halogen-bonded complexes between aliphatic and aromatic iodoperfluorocarbons and persistent nitroxide radicals have been detected by ESR spectroscopy in solution. Quantitative data indicate that nitroxides behave as strong electron donors in halogen bonding, giving rise to interactions whose strength is close to that of strong hydrogen bonds. These results point to a novel design of supramolecular paramagnetic species.