The two faces of chemistry: can they be reconciled?

Shortly before his death, Richard Bader commented in this Journal on the dichotomy that exists within chemistry and between chemists. We believe that the dichotomy results from different goals and objectives inherent in the chemical disciplines. At one extreme are designers who synthesize new molecules with interesting properties. For these chemists, the rationale underpinning molecular synthesis is far less important than the end product—the molecules themselves. At the other extreme are the chemists who seek a fundamental understanding of molecular properties. We suggest that the Quantum Theory of Atoms in Molecules, by virtue of the rich hierarchical structure inherent in the theory, offers a bridge through which to unite these two groups. However, if there is to be reconciliation, it falls to the theorists to develop “quantum mechanically” correct tools and concepts useful to the synthetic and applied chemist.     

Fluorine in the Earth and the solar system,where does it come from and can it be found?

This review (1) presents a summary of the distribution of fluorine in different fluid (surficial, subterranean, metamorphic, and magmatic–hydrothermal–geothermal) and solid (oceanic and continental crust, mantle, and core) domains of the Earth, and various extraterrestrial materials and bodies (meteorites, planets and moons, and the Sun); (2) it provides an estimate of the total fluorine abundance for the Earth and in its dominant reservoirs contributing to the Earth's fluorine endowment; and (3) it discusses key observations that could further improve our understanding of fluorine abundances and geochemical systematics.     

Singlet fission for dye-sensitized solar cells: can a suitable sensitizer be found?

We discuss possible improvements in the efficiency of dye-sensitized photovoltaic cells using dyes capable of singlet fission into two triplets, thus producing two electron-hole pairs from a single photon. It is pointed out that, in addition to derivatives of large alternant hydrocarbons, those of biradicals are also likely candidates for a favorable ordering of excited-state energy levels, E(T2), E(S1) > 2E(T1). A large number of potentially favorable structures has been examined by the semiempirical Pariser-Parr-Pople method and some also by the time-dependent density functional theory method. Several likely candidates have been identified for experimental examination.     

Improving the intrinsic activity of electrocatalysts for sustainable energy conversion: where are we and where can we go?

As we are in the midst of a climate crisis, there is an urgent need to transition to the sustainable production of fuels and chemicals. A promising strategy towards this transition is to use renewable energy for the electrochemical conversion of abundant molecules present in the earth''s atmosphere such as H₂O, O₂, N₂ and CO₂, to synthetic fuels and chemicals. A cornerstone to this strategy is the development of earth abundant electrocatalysts with high intrinsic activity towards the desired products. In this perspective, we discuss the importance and challenges involved in the estimation of intrinsic activity both from the experimental and theoretical front. Through a thorough analysis of published data, we find that only modest improvements in intrinsic activity of electrocatalysts have been achieved in the past two decades which necessitates the need for a paradigm shift in electrocatalyst design. To this end, we highlight opportunities offered by tuning three components of the electrochemical environment: cations, buffering anions and the electrolyte pH. These components can significantly alter catalytic activity as demonstrated using several examples, and bring us a step closer towards complete system level optimization of electrochemical routes to sustainable energy conversion.

We evaluate the improvements over the past two decades in intrinsic activity of electrocatalysts for sustainable energy conversion, and highlight opportunities from tuning the electrolyte.     

Synthesis,characterization, and biocide activity of new dithiocarbamate-based complexes of In(III), Ga(III), and Bi(III) – Part III

In this work, we describe the syntheses, characterization, and antifungal activity of [In{S₂CNR(R¹)}₃] (1), [Ga{S₂CNR(R¹)}₃] (2), [Bi{S₂CNR(R¹)}₃] (3), [In{S₂CNR(R²)}₃] (4), [Ga{S₂CNR(R²)}₃] (5), and [Bi{S₂CNR(R²)}₃] (6) {R?=?Me; R¹?=?CH₂CH(OMe)₂; and R²?=?2-methyl-1,3-dioxolane}. All complexes have been characterized using infrared and ¹H and ¹³C spectroscopy, and the structures of 1, 3, 4, and 6 have been authenticated by X-ray diffraction. The In(III)–dithiocarbamate bonding scheme depicts a distorted octahedral with asymmetric In(III)–S bonds and S–In–S angles. A pentagonal bipyramid is observed for the corresponding Bi(III) complexes with intermolecular Bi–S associations through the lone pair of electrons. The antifungal activities of 1–6 have been screened against Aspergillus niger, Aspergillus parasiticus, and Penicillium citrinum, and the results have been compared with those of nystatin and miconazole nitrate, as control drugs.     

Versatile and efficient functionalisation of multiallylic dendronised polymers: can dense packing be reached?

Surface modification of a multiallylic dendronised polymer was performed using hydrosilylation, hydroboration or radical addition of thiols to cover the polymer with various functional moieties; surface congestion is expected to occur when bulky groups are grafted.     

Phase behaviour of fluorocarbon and hydrocarbon mixtures: interpretation of type II and type III behaviour in terms of a ‘hard-sphere + attractive force’ equation of state

Christou, G., Morrow, T., Sadus, R.J. and Young, C.L., 1986. Phase behaviour of fluoro-carbon and hydrocarbon mixtures: interpretation of type II and type III behaviour in terms of a ‘hard-sphere + attractive force’ equation of state. Fluid Phase Equilibria, 25: 263–272.Experimental measurements of the upper critical solution temperature of octadecafluorooctane + n-alkanes are reported. These measurements and those discussed by Schneider (1983) on the phase behaviour of tetrafluoromethane + alkanes are compared with results obtained from the one-fluid model using a ‘hard sphere + attractive term’ equation of state.Interaction parameters, ξ, obtained from the comparison together with values from the literature on other fluorocarbon + hydrocarbon mixtures show trends which are briefly discussed.     

Hybrid electron cyclotron resonance-radio-frequency plasma etching of III–V semiconductors in Cl2-based discharges. Part II: InP and related compounds

Electron Cyclotron Resonance (ECR) discharges of CCl₂F₂ or PCl₃ have been used to etch InP, InAs, InSb, InGaAs and AlInAs. The etch rates of these materials increase linearly with additional RF power level applied to the cathode and are in the range 50–180 Å · min^–1 for 50 W (DC bias 308 V), 10 mTorr, 38 CCl₂F₂/2 O₂ plasmas. The etch rates fall rapidly with increasing pressure or increasing O₂-to-CCl₂F₂ ratio. Polymeric surface residues up to 40 Å thick are found on all of these semiconductors when using Freon-based gas mixtures. Etching at practical rates is possible with only 100 V self-bias when using PCl₃ discharges, and the addition of microwave excitation under these conditions enhances the etch rates by factors of 2–9. At higher self-biases (300 V) etch rates of 3500–8000 Å · min^–1 are possible with PCl₃ although the surface morphologies are significantly rougher and the etching less anisotropic than with CCl₂F₂-based mixtures.     

Hybrid electron cyclotron resonance-radio-frequency plasma etching of III–V semiconductors in Cl2-based discharges. Part I: GaAs and related compounds

A systematic study has been performed of the dry etching characteristics of GaAs, Al_0.3Ga_0.7As, and GaSb in chlorine-based electron cyclotron resonance (ECR) discharges. The gas mixtures investigated were CCl₂F₂/O₂, CHCl₂F/O₂, and PCl₃. The etching rates of all three materials increase rapidly with applied RF power, while the addition of the microwave power at moderate levels (150 W) increases the etch rates by 20–80%. In the microwave discharges, the etch rates decrease with increasing pressure, but at 1 m Torr it is possible to obtain usable rates for self-bias voltages 100 V. Of the Freon-based mixtures, CHCl₂F provides the least degradation of optical (photoluminescence) and electrical (diode ideality factors and Schottky barrier heights) properties of GaAs as a result of dry etching. Smooth surface morphologies are obtained on all three materials provided the microwave power is limited to 200 W. Above this power, there is surface roughening evident with all of the gas mixtures investigated.     

Glass transition kinetics and fragility index of chalcogenides from Ag–As–S–Se system

Journal of Thermal Analysis and Calorimetry - The glass transition temperature dependence on a heating rate was investigated by differential scanning calorimetry for chalcogenide glasses from the...     

Vanillin based polymers: III. Electrochemical dimerization of vanillin revisited and synthesis of hydrovanilloin–formaldehyde polymer

Electrochemical dimerization of vanillin in basic medium produced mixtures of meso/DL-hydrovanilloins, in contrary to earlier claims of the formation of meso-hydrovanilloin as the sole product. In the reinvestigation we have found that meso-percentage depends on the current density and the highest meso-percentage of 94% is achieved under 64 mA/cm² current density, using Pb electrodes and 1.25 M aqueous NaOH as the electrolyte. Condensation of the renewable resources based monomer hydrovanilloin with formaldehyde in aqueous NaOH gives hydrovanilloin–formaldehyde polymer in 91% yield. The linear polymer is shown to contain hydrovanilloin units with methylene bridges connecting C-6 positions of the aromatic rings.     

The Graovac–Pisanski index of zig-zag tubulenes and the generalized cut method

The Graovac–Pisanski index, which is also called the modified Wiener index, was introduced in 1991 by Graovac and Pisanski. This variation of the classical Wiener index takes into account the symmetries of a graph. In 2016 Ghorbani and Klav?ar calculated this index by using the cut method, which we generalize in this paper. Moreover, we prove that in some cases the automorphism group of a zig-zag tubulene is isomorphic to the direct product of a dihedral group and a cyclic group. Finally, the closed formulas for the Graovac–Pisanski index of zig-zag tubulenes are calculated.     

Swelling and Dissolution of Cellulose Part 1: Free Floating Cotton and Wood Fibres in N-Methylmorpholine-N-oxide–Water Mixtures

Summary: Five modes describing the behaviour of cellulose fibres dipped in a chemical have been identified:

• Mode 1: Fast dissolution by disintegration into fragments
• Mode 2: Large swelling by ballooning, and dissolution
• Mode 3: Large swelling by ballooning, and no dissolution
• Mode 4: Homogeneous swelling, and no dissolution
• Mode 5: No swelling and no dissolution

In the case of the behaviour of wood and cotton cellulose fibres in N-methylmorpholine-N-oxide (NMMO) and water mixtures, four domains of water content have been identified. Below 17% of water up to monohydrate (13%), the fibres are disintegrated into rod-like fragments and dissolve (mode 1). In NMMO – water mixtures containing 19–24% water, the cellulose fibres exhibit a heterogeneous swelling by forming balloons (composed of dissolved cellulose holds inside a membrane) separated with non-swollen sections. The whole fibre will completely dissolve (mode 2) in four successive steps (growth of the balloons, burst of the balloons, dissolution of the non-swollen sections and finally dissolution of the membrane). With still greater water contents (25–30%), only the ballooning phenomenon is observed, with a partial dissolution inside the balloon (mode 3). Above 35% of water, the fibres swell homogeneously and are not dissolving (mode 4).     

The mechanism of chemical degradation of polymers: Part III—The anomaly in the hydrolysis of glycolide copolymers

The data published on the chemical and enzymatic degradation of polyesters and some other polymers is analysed. Earlier studies on copolymers have shown that chemical stability changes monotonously with change in composition if the corresponding homopolymers differ in their sensitivity to the action of a degrading agent. The present work shows that anomalous dependence of chemical stability on copolymer composition is observed for a copolymer based on the isomeric monomers, glycolide and ethylene glycol oxalate. In this case the minimum in the chemical stability versus copolymer composition curve corresponds to the minimum in the copolymer melting temperature versus copolymer composition curve. A possible interpretation of the observed phenomenon is given.     

Antioxidants and stabilizers: Part CVI—Mechanism of antioxidant action of dithiobisphenols

A disulfidic bridge connecting two alkylated phenolic moieties is considered to be a decisive structural factor in the high antioxidant efficiency of dithiobisphenols in polypropylene (PP) autoxidation and tert-butylhydro-peroxide (TBH) decomposition. Strong retardation of the later phases of the autoxidation of PP doped with two dithiobisphenols (I(d), II(d)) is a consequence of the stepwise accumulation of antioxidant-active S-oxidation products. Thermolabile thiosulfonate and sulfoxide are formed (among other transformation products) and are considered to be sources of peroxidolytic species. The latter are involved, as very efficient agents after depletion of the originally present dithiobisphenols, in the overstoichiometric phase of hydroperoxide decomposition. Calcium (II) salts may partially reduce the overall hydroperoxide decomposition efficiency of dithiobisphenols.