Liquid water is one of the most important media and solvent for chemical reactions, which is also the main object in scholarly investigation of the chemical reactions occurring in condensed (liquid) matter. The composition, structure, and characteristics of water may vary significantly under different conditions, especially under extreme conditions, which may change both the rates (kinetics) and favorability (thermodynamics) of individual chemical reactions in solution. Thus, the condensed matter chemistry under (normal) mild conditions, hydrothermal conditions, and supercritical water conditions may differ considerably. In this review, we discuss the influences of the composition, structure, and characteristics of liquid water and solution on the chemical reactions within, which includes the state and reactivity of the reactants, processes and mechanisms of reactions, compositions and structures of the intermediate and final products. Examples of these reactions are dissolution and crystallization, double decomposition reaction of salts, acid-base reaction, precipitation, gelation and crystallization, hydrolysis, redox reaction, and coordination reactions. In our discussions, we emphasize that it is essential to consider the chemical reactions occurring in aqueous solutions at the level of condensed matter physical science; and similarly it is also essential to investigate chemical reactions occurring in other types of liquids such as organic solvents, ionic liquids, and molecular substances in molten state. We well understand that this review will result in more in-depth discussions and possibly criticisms about the topics of condensed matter chemistry as well as our perspectives among our peer researchers, which will definitely advance this emerging science in liquids and possibly serve as a base for establishing the new discipline of condensed matter chemistry.

Water is a clean, safe, environmentally benign chemical reaction medium. Understanding the properties of water and the chemical processes in hydrothermal systems is of vital significance in the research of condensed matter chemistry. The physicochemical features of water under hydrothermal conditions greatly differ from that under normal conditions, and thus the hydrothermal technique has been extended to much broader systems. In this review article, we introduce the structures of water and its clusters, the variation of their properties along with conditions, and relevant condensed matters in hydrothermal systems. We also illustrate hydrothermal chemistry by discussing the preparation of typical materials through hydrothermal methods, hydrothermal organic reactions, and bio-hydrothermal chemistry. By relating condensed matter and hydrothermal chemistry, we hope this review will offer new ideas for comprehending hydrothermal reaction systems from the angle of condensed matter chemistry.

Ionic liquids are new solvents that can replace traditional solvents to achieve efficient, low-carbon, clean, recycling, novel processes and technologies, and have important application values in completing the “double carbon” goal. Meanwhile, ionic liquids are a kind of typical “soft condensed matter (soft matter)”, and their fundamental understandings and applications strongly depend on the study of their inner multi-scale microstructures, which requires the idea of “condensed matter chemistry” as the future research direction, that is, performing multi-level studies on the composition, structures, properties, functions and their relationships, and thus to regulate the transport and reaction processes in the real application systems. In this paper, we briefly review the research on ionic liquids from the perspective of “condensed matter chemistry”. At first, we introduce the chemical structures and physicochemical properties of ionic liquids, pointing out that it is necessary to study their inner structures to understand the changes in these properties. We then introduce the structures of ionic liquids from the molecular level to the nano-/micro-scale, including ion pairs, hydrogen bonds, hydrogen bond networks, clusters, interfacial structures, and nano-confined structures. Finally, the future of “condensed matter chemistry” research on ionic liquids is discussed.

Hydrated cation-π interaction, as a kind of non-covalent interaction, is essential to the study of soft condensed matter. This paper reviews the recent progress in the two-dimensional crystals of unconventional stoichiometries induced by the hydrated cation-π interaction, and their distinguished features. These crystals include Na₂Cl, Na₃Cl and CaCl at ambient conditions. These crystals have abnormal cation-anion ratios different from those of normal three-dimensional crystals and unique electronic structures. Consequently, their physical and chemical properties are usually different from those of normal three-dimensional crystals, including the room temperature ferromagnetism. These ferromagnetic materials of unconventional stoichiometries may provide new insight into biomagnetism, medicine-related magnetism and the design of low-dimensional ferromagnetic materials.

Condensed matter chemistry, as a science of studying condensed matter in chemical reactions, has attracted extensive attention recently. In this review, condensed matter chemistry related to asymmetric catalysis and synthesis are briefly summarized, and different condensed matter phenomena in asymmetric catalytic reactions were classified. Besides, relative works were discussed in detail to illustrate the effects of the multi-level structures and composition of condensed matter on the catalytic activity, enantio- and regioselective control. It is hoped that the system of condensed matter science would be well developed by attracting more attention and bringing more thoughts to the essence of reaction from the perspective of condensed matter chemistry.

Glycans are the most abundant organic polymers in nature, and vital biomaterials for structural support and energy storage in living organisms. Meanwhile, glycans play an important role in cell recognition, differentiation, development, carcinogenesis and immunity. Compared with nucleic acid and protein, the specific role of glycans in many biological processes is still unknown, which is related to the difficulty of accessing well-defined glycans and the lack of precise tools for manipulating glycans in vivo. Synthetic methods in carbohydrate chemistry have been developed rapidly in recent decades, providing a powerful weapon for the study of synthetic glycans, especially oligosaccharides. Nevertheless, compared with the synthesis of nucleic acids and proteins, the synthesis of structurally well-defined glycans remains an unsolved chemical challenge with many unexpected problems. There are various factors that may affect the efficiency and stereoselectivity of glycosylation profile. Furthermore, glycans could be assembled into ordered aggregates through intermolecular non-covalent forces, then affecting the synthesis. For instance, in the process of removal protecting groups, the great change of solubility of glycan has a decisive effect on the reaction. The effect of aggregation formation on reactivity has not been thoroughly studied. Therefore, it is still necessary to complete the synthesis of well-defined glycan through trial-and-error experiments. In addition, glycans and glycoconjugates play an important role in living organisms by forming supramolecular structures. In conclusion, it is of great significance to study the condensed matter chemistry in glycans and their synthesis.

The opto-electronic properties of organic materials are not only dependent on the molecular structures, but also the aggregated states. In many cases, the cooperativity of intermolecular interactions can generate the new functions beyond those as single molecules. Thus, our recognition should not only limit on the level of single molecule, but pay much attention to molecular aggregates with the Molecular Uniting Set Identified Characteristic (MUSIC). Among them, organic room temperature phosphorescence (RTP) as the unique emission of organic molecules at aggregate state, demonstrating the high sensitivity and responsiveness to their aggregation behaviors in most cases. Thus, in this review, RTP property was selected as the typical optoelectronic property of molecular aggregates, and the formation processes and crucial factors have been systematical investigated and discussed. Furthermore, the related strategies can be applied into various fields, including mechano-luminescence, second-order non-linear optics, mechanochromism and OLEDS, in which the opto-electronic properties can be the static performance and/or dynamic response stimulated by force, light, heat and electric field. Finally, the controllability and predictability of molecular design of optoelectronic materials are effectively demonstrated by the established relationship between molecular structures-stacking modes and intermolecular interactions, together with the proposed effective strategies for the adjustment of molecular aggregation behaviors.

The interaction between the changes of polymer condensed states and chemical reactions becomes more directly in the solvent-free polymer polymerizations. Melt polymerization (MP), reactive extrusion (REX) and solid phase polymerization (SPP) are classical solvent-free polymerization production technologies. The solvent-free polymerization production technology is a new science and technologies integrating polymer resin synthesis, material processing and preparation and engineering. It is the frontier field of contemporary material science, and represents the inevitable trend of the development of the resin production technology. In this paper, the three typical resin industrial synthesis technologies and their corresponding mechanisms are briefly introduced, and the actual productions of polyethylene terephthalate (PET) and polylactic acid (PLA) were shown, and the relationship between the three production technologies were also exhibited. In here, the basic problems of polymer condensed state changes and related chemical reactions were revealed by these three solvent-free polymerization technologies, and some valuable references for scientific researcher were provided.

Photosynthesis in nature stores solar energy in chemical bonds through a green and efficient way. Mimicking the structure and function of the active center of natural photosynthesis, inert chemical bonds of small molecules (H₂O, CO₂ and N₂ etc.) can be activated and converted for energy conversion. Herein, we summarize the important progress of artificial photosynthesis in water splitting into oxygen and hydrogen, carbon dioxide and nitrogen reduction. Meanwhile, we analyze the design ideas and working principles of related photochemical conversion systems, and discuss the challenges and future development of artificial photosynthesis.

Condensed matter chemistry is a new research field that studies the multi-level structures of condensed matter constructed by intermolecular interactions for realizing functionalities and chemical reactions. Compared with solid-state condensed matter chemistry, the study of liquid condensed matter chemistry involves multiphase states, such as how liquid condensed matter affects the state and functional properties of dispersoids. It is important to understand the aggregation behaviors of dispersoids from the perspective of condensed matter chemistry, which is not only beneficial to the preparation of the expected structures, but also can deepen the understanding of the formation process of the assembled structure. In this paper, based on a brief overview of the physical and chemical properties of liquid condensed matter, especially those related to dispersion and dissolution, typical examples are selected to illustrate the assembly process, assembly and disassembly, and structural transformation of dispersoids in the liquid condensed matter. In terms of the influence of the liquid condensed state on properties of dispersoids, the UV-vis absorption, electron transfer, chirality regulation and catalysis are discussed. In these processes, as the continuous phase, the properties of the liquid condensed state, such as dielectric constant, polarity and viscosity, play key roles in the existing states and properties of the dispersoids. However, due to the limitation of the detection range of the present instruments, it is difficult to accurately measure the fast, variable and subtle forces between liquid condensed matter and dispersoids in time and space. Therefore, it is an important and effective strategy to perform mutual fitting from both experimental and theoretical aspects to illustrate the role of liquid condensed matter.

Biomolecular condensates form various cellular membraneless organelles and play diverse biological functions as a result of their specific physicochemical properties. For example, biomolecular condensates are able to perceive changes in the external environment, regulate the cellular concentration of proteins, modulate different signaling pathways and selectively partition hub proteins as well as nucleic acids. Abnormal formation and changes of biomolecular condensates are closely related to human diseases, especially neurodegenerative diseases, cancers and viral diseases such as COVID-19. Intrinsically disordered proteins (IDPs) play key roles in the formation and regulation of biomolecular condensates. In this review, we analyze the roles that IDPs and small molecules play in biomolecular condensates formation and regulation, propose the possibility of rationally regulating biomolecular condensates through ligand design targeting IDPs, and discuss the challenges of understanding biomolecular condensate formation and regulation mechanisms and for discovering novel chemical compounds to modulate biomolecular condensates.

Protein and RNA molecules tend to form supramolecular assemblies called membrane-less organelles via liquid-liquid phase separation of proteins in cells. These organelles have fusion properties similar to liquid droplets formed by biological macromolecules when their concentrations are higher than saturation concentrations. Upon aging, these dynamic droplets change their material properties and transform into gels, followed by formation of solid condensates. It is well known that proteins with low-complexity domains undergo liquid-liquid phase separation. The common pathological feature of neurodegenerative diseases such as transmissible spongiform encephalopathy, amyotrophic lateral sclerosis, and Alzheimer’s disease is toxic oligomers or amyloid aggregates formed by misfolded proteins including prion protein, DNA- and RNA-binding protein TDP-43, and Tau protein. A large number of studies have shown that prion protein, TDP-43, and Tau protein all undergo liquid-liquid phase separation and form protein condensates. This review summarizes the role of protein phase separation and condensation in neurodegenerative diseases, elaborates the mechanism of protein condensation modulating transmissible spongiform encephalopathies, TDP-43 proteinopathies, and tauopathies, and focuses on the initiation effect of phase separation on aggregation and toxicity of misfolded proteins in neurodegenerative diseases. Finally, we discuss and prospect the challenges and opportunities of association study between protein condensation and neurodegenerative diseases.

For the study of paleontology, we must start from the direction of paleontological "changes," go deep inside the fossil bones and cells, and explore what changes had taken place in terms of chemical composition, the structural and morphological changes of the ancient organisms over a very long time ago. What does it change into? What remains and preserved as fossils do we have in our hands today? Then the most important question: what is the chemical mechanism for preserving these organic residues? What is the critical role of condensed matter chemistry in these complex geological events? From the perspective of condensed matter chemistry in this paper, the author tries his best to explore the most fundamental mysteries related to PaleoChemistry in paleontology. Three examples are given to illustrate possible condensed matter chemical reactions, which must have played a critical primary mechanism in PaleoChemistry, waiting for us to uncover. For example, fossils are generally believed to be ancient organisms that changed into stone/rock, from once-living organisms to lifeless inorganic minerals. It is commonly believed that organic matters cannot be preserved for millions or billions of years. However, our team found preserved native collagen Type I in the 195 million years ago Lufengosaurus embryonic bones. Many amino acids were found in the 2.2 billion-year-old fossils. The evidence of steranes proved these organisms were the oldest multicellular eukaryotes. This is one of the most significant discoveries in the life evolution of the Earth. From the examples of these paleontological fossils, it can be seen that condensed matter chemistry is not only a bystander of theoretical chemistry but a key role. Its importance is worthy of our investment in the in-depth study to uncover the mysteries of the fundamental chemistry of countless chemical reactions from ancient organisms to fossils in our hands.