Open Questions in Chemistry

Today, Communications Chemistry launches a series of Comment articles discussing key open questions in specific fields of fundamental chemical research. Here we outline the aims of this series and highlight each contribution within.

Liquid-liquid phase separation (LLPS) underlies the formation of intracellular membraneless compartments in biology and may have played a role in the formation of protocells that concentrate key chemicals during the origins of life. While LLPS of simple systems, such as oil and water, is well understood, many aspects of LLPS in complex, out-of-equilibrium molecular systems remain elusive. Here, the author discusses open questions and recent insights related to the formation, function and fate of such condensates both in cell biology and protocell research.

Interfacing ultrasmall metal nanoclusters (NCs) with proteins can present a dual opportunity: proteins can be used for protecting NCs, and the surface ligands of NCs may interact with proteins. Here, the authors identify and discuss remaining open questions surrounding the bio-NC interface that call for future research efforts.

The transfer of chiral information from optically pure reaction components to products can generate enantiomerically-enriched molecules, but the control of stereochemistry often proves challenging. Here, the author highlights how our fundamental understanding of stereocontrol has evolved and discusses possible approaches for the rational development of enantioselective catalysts.

The chemical space of prebiotic chemistry is extremely large, while extant biochemistry uses only a few thousand interconnected molecules. Here we discuss how the connection between these two regimes can be investigated, and explore major outstanding questions in the origin of life.

Molecular knots are evolving from academic curiosities to a practically useful class of mechanically interlocked molecules, capable of performing unique tasks at the nanoscale. In this comment, the author discusses the properties of molecular knots, and highlights future challenges for chemical topology.

Polymorphs, crystals with different structure and properties but the same molecular composition, arise from the subtle interplay between thermodynamics and kinetics during crystallisation. In this opinion piece, the authors review the latest developments in the field of polymorphism and discuss standing open questions.

Glycans are ubiquitous in biology, but their complex structure and biosynthesis have challenged research of their wide-ranging roles. Here, the authors comment on current trends on the role of chemical methodologies in the field of glycobiology.

In-depth understanding of the bonding characteristics of the lanthanide ions in contemporary lanthanide-based materials is mandatory for tailoring their properties for novel applications. Here, the authors elaborate on open questions regarding the bonding situation in mainly molecular lanthanide (4f) compounds, where, as compared to their actinide (5f) analogs in which covalency of the bonds is a common feature, this is still under discussion for the 4f compounds.

The Hückel rule defines that monocyclic and planar conjugated systems containing [4n + 2] π electrons are aromatic. Here, the authors highlight boron species that feature a globally 4n π system, defying the Hückel rule, but nonetheless exhibit aromaticity.

Superheavy elements are ideal for furthering our understanding of relativistic effects and how they affect physicochemical properties of heavy elements. In this comment, the author discusses the role of chemistry in the synthesis of new elements before addressing the future challenges concerning the chemical characterization of superheavy elements.

Nanoscience has progressed tremendously in the exploration of new phenomena not seen in bulk materials, however, the transition between nanoscale and bulk properties is not yet fully understood. Here the authors identify and discuss remaining open questions that call for future efforts.

Understanding the biogeochemistry of radionuclides in the environment is essential for effective isolation of nuclear waste in repositories, management of contaminated sites, ensuring long-term protection of our ecosystems, and limiting impacts on human health. Here the authors discuss the extreme complexity of this multidimensional chemistry problem, highlighting the outstanding open questions for the next generations of environmental radiochemists.

While sp²-hybridized carbon atoms in hydrocarbons typically contribute only one electron to their aromaticity, metals have more electrons from d or f orbitals available for participating in conjugation in organometallics, complicating the electron counting as well as analysis of their aromaticity. Here, the author comments on the challenges towards understanding aromaticity in organometallics and outlines several remaining questions that have yet to be answered.

The chemistry of stable low oxidation state group 2 metal compounds was initiated in 2007 and has since expanded rapidly, yielding many surprises. Here the author outlines advances in the field and discusses some of the open questions and challenges that remain to be answered in coming years.

First-row transition metals play several roles in biological processes and in medicine, but can be toxic in high concentrations. Here the authors comment on the sensitive biochemistry and speciation chemistry of the first-row transition metals, and outline some of the remaining questions that have yet to be answered.

Over the past decade, momentous progress has been made in the characterization of late actinide compounds. Here the authors highlight how advances in spectroscopic and computational tools have developed our understanding of fundamental transplutonium bonding interactions, and discuss whether covalency and heterogeneity changes in 5f-orbital bonding could be harnessed in environmentally and industrially relevant systems.

It has been a great joint achievement of astronomy, laboratory spectroscopy and quantum chemistry to identify interstellar molecules in various astronomical environments and piece together their origins story from the fragmented evidence. Here the authors provide a sketch of what we know and motivate the asking of open questions on carbon-based molecules in space.

Strong emergence is the main form of emergence that has been defended with respect to chemistry, and in particular molecular structure. Here, the author spells out this form of emergence, proposes new ways in which one can further explore the question of emergence, and explains why investigating emergence should be of interest not only to philosophers but to chemists as well.

Emerging experimental techniques combined with theoretical advances allow unprecedented studies of the dynamics of gas phase molecules and clusters induced in interactions with photons, electrons, or heavy particles. Here, the authors highlight recent advances, key open questions, and challenges in this field of research with focus on experimental studies of dynamics of ions stored on millisecond timescales and beyond, and its applications in astrochemistry and astronomy.

Recent high-pressure studies have uncovered many types of chemical bonds present in noble gas compounds. Here, by extrapolating what has been found so far, the authors discuss which future discoveries can be expected and recommend further avenues of exploration.

Transition metals are increasingly recognized as key drivers in the formation and aging of light-absorbing organic aerosols, known as brown carbon, which impact the energy flux in the atmosphere. Here the authors discuss somewhat overlooked condensed phase chemical processes and identify research needs to improve our fundamental understanding of atmospheric aerosols and ultimately reduce modelling uncertainties of the direct and indirect effects of aerosol particles on the climate.

Crystallization is observed in both nature and in the lab, and is critical to diverse areas of science and technology. Here, the author summarizes the theories that have been proposed to explain crystal growth from melts, and raises some open questions that remain.

Water adsorption in soft nanoporous materials can trigger large-scale structural transitions and introduce new properties in the confined water phase. Here, we look at some of the outstanding questions in this lively field of research.

The commercial use of natural methane hydrate is hampered by several open questions that remain regarding hydrate formation. Here the authors comment on past interpretations and aim to provide a roadmap for developing a predictive theory of methane hydrate nucleation.

The process of thermally activated delayed fluorescence (TADF) converts non-radiative triplet states into emissive singlet states. Herein we outline the fundamentals of TADF, some of the recent progress in understanding the key material properties responsible for promoting TADF and finally discuss some remaining challenges for the  potential applications of this phenomenon.

Ultrafast singlet fission has the potential to facilitate highly efficient photovoltaics through the multiplication of excitons in organic molecular architectures. Here, we consider the interplay of molecular structure and intermolecular coupling toward enabling ultrafast singlet fission and discuss open questions in the field.

Criegee intermediates are reactive intermediates formed in Earth’s atmosphere through ozonolysis of alkenes. Here the authors outline the fundamental chemistry that influences their highly conformer- and substituent-dependent unimolecular and bimolecular reactivity, and discuss open questions of fundamental and atmospheric interest.

Cloud droplets form in the atmosphere on aerosol particles, many of which result from nucleation of vapors. Here the authors comment on current knowledge and open questions regarding the condensational growth of nucleated particles to sizes where they influence cloud formation.

Airborne particles have significant impacts on health, visibility, and climate. Here, an overview of what is known about particle chemical composition is presented, along with open questions and challenges that are central to relating composition to life cycles and impacts.

Aerosols are highly dynamic, non-equilibrium systems exhibiting unique microphysical properties relative to bulk systems. Here the authors discuss the roles aerosols play in (bio)chemical transformations and identify open questions in aerosol-mediated reaction rate accelerations, aerosol optical properties, and microorganism survival.

Water can form a vast number of topological frameworks owing to its hydrogen-bonding ability, with 19 different forms of ice experimentally confirmed at present. Here, the authors comment on open questions and possible future discoveries, covering negative to ultrahigh pressures.

Chemical reaction networks (CRNs) are prototypical complex systems because reactions are nonlinear and connected in intricate ways, and they are also essential to understand living systems. Here, the author discusses how recent developments in nonequilibrium thermodynamics provide new insight on how CRNs process energy and perform sophisticated tasks, and describes open challenges in the field.