Electrocatalytic Reduction of Nitrogen to Ammonia Using Tiara-like Phenylethanethiolated Nickel Cluster

The fixing of N₂ to NH₃ is challenging due to the inertness of the N≡N bond. Commercially, ammonia production depends on the energy-consuming Haber-Bosch (H−B) process, which emits CO₂ while using fossil fuels as the sources of hydrogen and energy. An alternative method for NH₃ production is the electrochemical nitrogen reduction reaction (NRR) process as it is powered by renewable energy sources. Here, we report a tiara-like nickel-thiolate cluster, [Ni₆(PET)₁₂] (where, PET=2-phenylethanethiol)] as an efficient electro-catalyst for the electrochemical NRR at ambient conditions. Ammonia (NH₃: 16.2±0.8 μg h⁻¹ cm⁻²) was the only nitrogenous product over the potential of −2.3 V vs. F_c⁺/F_c with a Faradaic efficiency of 25%±1.7. Based on theoretical calculations, NRR by [Ni₆(PET)₁₂] proceeds through both the distal and alternating pathways with an onset potential of −1.84 V vs. RHE (i.e., −2.46 V vs. F_c⁺/F_c) which corroborates with the experimental findings.     

Synthetic Matching of Complex Monoterpene Indole Alkaloid Chemical Space

Monoterpene indole alkaloids (MIAs) are endowed with high structural and spatial complexity and characterized by diverse biological activities. Given this complexity-activity combination in MIAs, rapid and efficient access to chemical matter related to and with complexity similar to these alkaloids would be highly desirable, since such compound classes might display novel bioactivity. We describe the design and synthesis of a pseudo-natural product (pseudo-NP) collection obtained by the unprecedented combination of MIA fragments through complexity-generating transformations, resulting in arrangements not currently accessible by biosynthetic pathways. Cheminformatic analyses revealed that both the pseudo-NPs and the MIAs reside in a unique and common area of chemical space with high spatial complexity-density that is only sparsely populated by other natural products and drugs. Investigation of bioactivity guided by morphological profiling identified pseudo-NPs that inhibit DNA synthesis and modulate tubulin. These results demonstrate that the pseudo-NP collection occupies similar biologically relevant chemical space that Nature has endowed MIAs with.     

Solving restricted open-shell equations in excited state molecular dynamics simulations

Different approaches to the solution of restricted open-shell equations are summarized and a general implementation for the first excited singlet state in the Car–Parrinello molecular dynamics code (CPMD) is presented. For molecular dynamics simulations where energy conservation is an important criterion, different choices of parameters are necessary depending on the particular chemical situation.     

Electrochemical behaviour of the LiF-(CaF2)-La2O3 system

The electrochemical behaviour of the LiF-La₂O₃ and LiF-CaF₂-La₂O₃ systems was investigated by means of cyclic voltammetry. Several types of working electrodes (spectrographic pure graphite, W, Mo, Ni, Cu) were used. It was found that chemical reactions take place in the system during the dissolution of lanthanum oxide. The reduction of lithium cations occurred at the most positive potential from the species formed in the melt on ‘inert’ cathodes (W, Mo). The reactive cathodes (Cu, Ni) allowed the lanthanum deposition with depolarisation.     

Thallium fractionation in polluted environmental samples using a modified BCR three-step sequential extraction procedure and its determination by electrothermal atomic absorption spectrometry

Determination of thallium in polluted environmental samples and their extracts obtained by a modified BCR three-step sequential extraction procedure was used to study thallium distribution and mobility in the monitored polluted area affected by acidification (Šobov, Central Slovakia). The results of fractionation applied to 5 soil certified reference materials and 14 environmental samples show that the vast majority of thallium occurred in the residual fraction. This means that highly toxic thallium is strongly entrapped in the parent rock materials remains immobile and its environmental toxicity is therefore reduced. The limit of detection for thallium in the studied fractions was lower than 0.050 mg kg⁻¹, the precision (RSD) of the ultratrace determination of thallium in the studied fractions was better than 17 % and the accuracy of the used method was verified by analyzing certified reference materials. Presented at the XVIIIth Slovak Spectroscopic Conference, Spišská Nová Ves, 15–18 October 2006.     

Controlled interparticle spacing for surface-modified gold nanoparticle aggregates

Aggregation of gold nanoparticles of increasing size has been studied as a consequence of adsorption of 2-aminothiophenol (ATP) on gold nanoparticle surfaces. The capping property of ATP in the acidic pH range has been accounted from UV-vis absorption spectroscopy and surface-enhanced Raman scattering (SERS) studies. The effect of nanoparticle size (8-55 nm) on the nature of aggregation as well as the variation in the optical response due to variable degree of interparticle coupling effects among the gold particles have been critically examined. Various techniques such as transmission electron microscopy, X-ray diffraction, zeta-potential, and average particle size measurement were undertaken to characterize the nanoparticle aggregates. The aggregate size, interparticle distances, and absorption band wavelengths were found to be highly dependent on the pH of the medium and the concentration of the capping agent, ATP. The acquired SERS spectra of ATP relate the interparticle spacing. It has been observed that the SERS signal intensities are different for different sized gold nanoparticles.     

Gram level synthesis of lead-free solder in the nanometer length scale obtained from tin and silver compounds using silicone oil

A straightforward route to gram level synthesis of a pure phase of the Sn-Ag nanoalloy in an eutectic composition (Sn/Ag 96.5:3.5) in silicone oil is reported. The composition, morphology, and microstructure of the alloy were fully characterized. In a mixture of ethylene glycol and silicone oil, direct reduction of Sn(II) acetate and Ag(I) nitrate gave the Sn-Ag nanoalloy. The nanoalloy disintegrates by sonication and reforms by heating, leading to smaller particles with a melting point as low as 128 degrees C.     

Synthesis of carbohydrate-conjugated nanoparticles and quantum dots

Nanoparticle-based probes are emerging as alternatives to molecular probes due to their various advantages, such as bright and tunable optical property, enhanced chemical and photochemical stability, and ease of introduction of multifunctionality. This work presents a simple and general approach for functionalizing various nanoparticle systems for use as glycobiological probes. Silica-coated nanoparticles of Ag, Fe3O4, and ZnS-CdSe were synthesized and functionalized with dextran. The resulting 10-40-nm-sized particles were robust, water-soluble, colloidally stable, and biochemically active.     

Fluorescence study of the solvation of fluorescent probes prodan and laurdan in poly(epsilon-caprolactone)-block-poly(ethylene oxide) vesicles in aqueous solutions with tetrahydrofurane

Steady-state and time-resolved fluorescence measurements were used to study the relaxation of the microenvironment of hydrophobic probes 6-propionyl-2-(dimethylamino)naphthalene (prodan) and 6-dodecanoyl-2-(dimethylamino)naphthalene (laurdan) in systems containing vesicles formed by the amphiphilic diblock copolymer poly(epsilon-caprolactone)-block-poly(ethylene oxide) (PCL-PEO) and water/tetrahydrofurane (THF) solvent mixtures. It was found that in case of prodan, both steady-state and time-resolved emission spectra were composed of two subspectra corresponding to the emission of prodan molecules located (i) in fairly rigid (effectively viscous) and hydrophobic domains of the vesicles close to the PCL/PEO interface and (ii) in a more polar and less viscous medium (in the bulk solution). The fraction of the emission from the more polar microenvironment increases with increasing content of THF in the system. Laurdan, in contrast to prodan, appeared to be solubilized preferentially in the hydrophobic domains up to 30 vol % of THF content, and its emission spectra changed only due to swelling of hydrophobic PCL domains by added THF. The study shows that the analysis of the time-resolved emission from a probe distributed in two media is, in principle, possible, but it is quite complex and appreciably less accurate, and the relaxation times are ill-defined averages of several processes. The bimodal or shoulder-containing time-resolved spectra have to be decomposed in pertinent time-resolved subspectra and treated separately. Another important result of the study is a piece of knowledge concerning the motion of the probe with respect to the vesicle. In the studied complex system, not only the relaxation of the solvent and reorganization of polymer segments around the fluorescent headgroup of the probe affect the emission but also a lateral motion of the probe with respect to the nanoparticle within the lifetime of the excited state contributes significantly to the relaxation and to the relatively slow time-resolved Stokes shift.     

The C-O stretch as an unprecedently large spectral marker for the electron transfer between Copper(II) and a phenolate anion

An unprecedented red shift of more than 200 cm(-1) in the vibrational frequency of the C-O bond in the [Cu(PhO)Ln]+ complex (PhO = phenoxy), dependent on the number n of additional ligands L, is reported. Upon change of n from 1 to 2, the spin density is shifted from the aromatic ring to the oxygen and copper atoms, which is reflected in the bond order and thus vibrational frequency of the C-O bond.