The crystal-engineering strategy was intended to produce a new crystalline phase of berberine, a natural-product medicine associated with antimicrobial properties. Hydrothermal screening experiments yielded the berberine–2-sulfobenzoate salt, and diffraction and thermal analysis supported successful formation of the intended material. The structural investigation found no classic hydrogen bonds within the reported salt system.

Instead, weak C–H···O contacts stabilize the interaction between berberine and 2-sulfobenzoate, while a strong dimeric intermolecular hydrogen bond forms between two 2-sulfobenzoate molecules. Spectroscopic observations showed that vibrational modes in the berberine–2-sulfobenzoate salt shifted relative to the modes of the individual components, with the change evident in the Raman spectra. The researchers interpreted these shifts in conjunction with the crystal structure and computational results, showing that salt formation alters the molecular environment experienced by berberine and 2-sulfobenzoate.

For the density functional calculations, they selected a 1:2 berberine–2-sulfobenzoate system so that the model would cover a larger number of intermolecular hydrogen bonds. The modeled system was examined with quantum theory of atoms in molecules and reduced-gradient density analysis to interpret the strength and type of the molecular interactions, while natural bond orbital analysis was used to assess the stability of the system. The calculations also produced molecular electrostatic potential surfaces for berberine, 2-sulfobenzoate and the salt system, identifying regions associated with electrophilic, nucleophilic and neutral behavior.

Frontier molecular orbital and global-descriptor calculations indicated that the modeled berberine–2-sulfobenzoate salt was more chemically reactive than berberine alone. Molar refractivity was used to characterize drug-likeness behavior, and the authors described the combined evidence as confirmation of a new berberine salt with improved physicochemical properties. These reactivity and drug-likeness results are properties predicted or modeled computationally; the study does not establish clinical advantages for the salt.

The research is a laboratory synthesis and solid-state characterization of a crystalline material rather than a clinical investigation of its effects in people.

Subject of Research: Experimental and quantum-chemical characterization of a crystalline berberine–2-sulfobenzoate salt

Article Title: Synthesis, crystal structure, and characterization of a new crystalline berberine–2-sulfobenzoate salt, integrating vibrational spectroscopy and quantum chemical investigation

Article References: Srivastava, D. A., Prajapati, P., Shimpi, M. R., & Tandon, P. (2026). Synthesis, Crystal Structure and Characterization of a New Crystalline Berberine-2-Sulfobenzoate Salt, Integrating Vibrational Spectroscopy and Quantum Chemical Investigation. Frontiers in Chemistry, 14, 1971429. https://doi.org/10.3389/fchem.2026.1971429

Image Credits: AI Generated

DOI: 10.3389/fchem.2026.1971429

Keywords: berberine, 2-sulfobenzoate, crystal synthesis, hydrogen bonding, vibrational spectroscopy, Raman spectroscopy, density functional theory, quantum chemistry, molecular reactivity, physicochemical properties, Synthesis, crystal

The study, published as a Perspective in Frontiers in Drug Discovery by Elier E. Abreu-Martínez, David Ramírez-Palma, Gabriel Merino, and Karina Martinez-Mayorga, takes a well-established idea from medicinal chemistry and asks whether it applies far beyond biology. In structure–activity relationship studies, researchers have documented so-called activity cliffs: pairs or groups of compounds that are structurally almost identical yet differ enormously in biological activity. These cliffs are not rare curiosities. Analyses of the ChEMBL repository covering 27,610 bioactive compounds tested against 414 targets showed that activity cliffs account for roughly five percent of molecular pairs satisfying common structural similarity criteria, and because individual compounds can participate in many pairs, between 22 and 34 percent of compounds are involved in at least one cliff. The authors now argue that an analogous phenomenon, which they call property cliffs, exists for physicochemical properties, and that it deserves independent conceptual status rather than being treated as a loose extension of the activity-cliff idea.

The technical case begins with an apparent paradox. Many molecular properties behave in an approximately additive fashion with respect to chemical structure, which is precisely why fragment-based models work so well. The Ghose–Crippen model and the Moriguchi method estimate logP, the octanol/water partition coefficient, as the sum of local contributions from specific structural fragments. Topological polar surface area can likewise be approximated by adding up the contributions of polar fragments. If properties are essentially additive, one might expect structure–property landscapes to be smooth, with gradual changes responding to gradual structural modifications, leaving no room for cliffs at all. The authors contend that this conclusion is not justified, because protonation state, electronic structure, conformational preferences, intermolecular interactions, and crystal packing can all produce large property variations from small structural perturbations.

The evidence spans classical chemistry and cutting-edge materials. A textbook example is the chlorine oxyacid series at 25 degrees Celsius: hypochlorous acid has a pKa of about 7.4, chlorous acid about 1.94, and chloric acid about minus 2.7. Each added oxygen atom enhances charge delocalization in the conjugate base, driving acidity down precipitously. In drug-like molecules, the effect can be just as striking. In propylpiperidine-derived antimigraine agents, introducing a single fluorine atom lowers the pKa by approximately one unit relative to the parent compound, and a second fluorine produces another substantial decrease. These stereoelectronic effects alter molecular basicity enough to influence receptor affinity and oral bioavailability, meaning a property cliff can cascade directly into pharmacological consequences.

Lipophilicity, often assumed to be strictly additive, also shows cliff-like behavior. Phenol has a logP of approximately 1.5, while p-methylphenol sits at about 2.0 and p-tert-butylphenol at about 3.3. Replacing the phenol hydrogen with a tert-butyl group therefore increases lipophilicity by roughly 1.8 logP units, corresponding to nearly two orders of magnitude in the actual octanol/water partition coefficient. This reflects the combined influence of hydrophobic effects, molecular volume, and solvent reorganization, showing that logP is not always the simple sum of its parts.

Chemical reactivity provides perhaps the most extreme examples. In computational studies of diarylamine formation through a Smiles rearrangement, researchers identified a base-catalyzed concerted 3-exo-trig pathway and found that small changes in the substitution pattern of the S-aryl ring produce dramatic changes in reactivity. Progressive introduction of nitro groups decreases the activation barrier from 29.0 kcal per mole in the monosubstituted system to 21.0 and 18.6 kcal per mole in the di- and trisubstituted derivatives, causing the rate constants at 298.15 K to climb from 2.0 times ten to the minus nine per second to 2.4 times ten to the minus three and then 1.9 times ten to the minus one per second. Trifluoromethanesulfonyl substituents are even more powerful, lowering barriers to as little as 9.9 and 8.4 kcal per mole and raising calculated rate constants by more than twelve orders of magnitude relative to the parent system. Mechanistically, these trends can be rationalized through well-established electronic effects, yet viewed within a structure–property framework they appear as an extreme discontinuity in the reactivity landscape, exhibiting the defining characteristics of a property cliff.

The phenomenon extends into the solid state, where subtle structural perturbations trigger abrupt changes in electronic properties. In blue phosphorene bilayers, small variations in stacking arrangement or interlayer distance can induce a transition between semiconducting and metallic behavior. Most reported stacking modes are semiconducting, but the A1B-minus-one arrangement is metallic and is also the most energetically stable configuration. Remarkably, increasing the interlayer distance within that same arrangement from 3.01 to 4.93 angstroms restores semiconducting behavior. Covalent organic frameworks show analogous sensitivity: in Tp-BTD frameworks, switching the interlayer stacking from eclipsed AA to offset AB to ABC polymorphs produces substantial functional differences without altering chemical composition. In the photoinduced oxidation of amines to imines, the ABC polymorph achieves 72 percent conversion of amines to imines while the AA and AB structures manage only about 20 percent, differences arising from stacking-dependent pore size, relative stability, and tautomeric equilibrium.

Antiaromaticity and electronic transport supply a final molecular-scale illustration. HDHA and ODHA are closely related 12-pi-electron macrocycles that formally satisfy Hückel’s 4n rule and are therefore antiaromatic, yet they differ markedly in the strength of their paratropic ring currents. HDHA sustains a paratropic current of minus 15.6 nanoamperes per tesla, while ODHA reaches minus 95 nanoamperes per tesla, an approximately sixfold increase in antiaromatic character. This enhancement is accompanied by a substantial change in electronic transport: near the Fermi level, HDHA exhibits moderate transmission values of roughly 0.03 to 0.17, whereas ODHA reaches 0.66 to 0.76. Changes in electron delocalization and antiaromatic stabilization explain the chemistry, but within a structure–property framework the pair represents a pronounced discontinuity in which a modest structural modification produces disproportionately large changes in both magnetic and transport properties.

Beyond existence, the analysis draws two further distinctions that shape how property cliffs should be studied. First, the authors propose that activity cliffs are probably more prevalent than property cliffs, a hypothesis grounded in mechanism rather than statistics. Biological activity depends on conformational effects, desolvation processes, specific ligand–receptor interactions, active-site reorganization, alternative binding modes, and the coexistence of orthosteric and allosteric sites, all of which are intrinsically nonlinear and context dependent. Many physicochemical properties, by contrast, are governed by local structural contributions and behave more additively. Second, property cliffs tend to be more mechanistically interpretable. Activity cliffs frequently reflect the combined action of multiple interacting factors that are difficult to disentangle; in crystallographic analyses of protein–ligand complexes, one category accounting for roughly 13 to 23 percent of analyzed cliffs involves several simultaneous contributions with no dominant factor, and another category of about ten percent involves structurally similar ligands with nearly indistinguishable binding modes yet activity differences of at least two orders of magnitude, with no obvious structural explanation. Property cliffs, by contrast, usually originate from identifiable phenomena such as nonlinear electronic effects, steric and volume effects, interaction coupling, conformational changes, changes in dominant state, solvation effects, switches in the dominant reaction pathway, or supramolecular organization effects.

The implications reach well beyond conceptual tidiness. The authors argue that recognizing property cliffs as a distinct class of structure–property discontinuities could improve QSPR modeling, computational chemistry, materials science, and data-driven molecular design, especially as modern predictive models are increasingly applied to electronic, optical, catalytic, spectroscopic, and transport properties far beyond their traditional medicinal-chemistry role. Because the significance of a property change is inherently property dependent, universal numerical thresholds are unlikely to work; a change of one pKa unit, a tenfold variation in a rate constant, a large conductivity shift, or a semiconducting-to-metallic transition may each represent a discontinuity of practical significance on different scales. Instead, the authors advocate property-specific criteria, molecular similarity metrics, matched molecular pair analysis, error quantification, and applicability domain assessment as a more robust foundation for identifying discontinuities. They also caution that apparent cliffs can arise from measurement error, data-quality issues, limitations of the molecular representation, or extrapolation beyond a model’s applicability domain, so identifying a discontinuity and interpreting its origin are conceptually distinct steps. Systematic characterization of property cliffs, the authors conclude, may reveal new insights into molecular function and materials performance while exposing exactly where machine-learning models for molecular properties are most likely to fail.

Subject of Research: The existence and nature of property cliffs, abrupt physicochemical property changes caused by small structural modifications, in structure–property relationships

Article Title: Do property cliffs exist? A conceptual analysis of structural changes and molecular properties

Article References: Abreu-Martínez, E. E., Ramírez-Palma, D., Merino, G., & Martinez-Mayorga, K. (2026). Do property cliffs exist? A conceptual analysis of structural changes and molecular properties. Frontiers in Drug Discovery, 6, Article 1899616. https://doi.org/10.3389/fddsv.2026.1899616

Image Credits: AI Generated

DOI: 10.3389/fddsv.2026.1899616

Keywords: property cliffs, activity cliffs, QSAR, QSPR, physicochemical properties, cheminformatics, molecular machine learning, materials discovery, chemical space, property, cliffs, exist

The research team, led by Jialiang Zou and Youping Liu of Chengdu University of Traditional Chinese Medicine, collected honey from beekeepers and commercial sources spanning Sichuan, Beijing, Shanghai, Heilongjiang, Zhejiang and Fujian. Three samples came from Sichuan alone, including one from Hongqi Village in Wenchuan County and two from Derong County in the Garzê Tibetan Autonomous Prefecture, one of which contained pieces of honeycomb. All samples were stored at 4 degrees Celsius and analyzed in triplicate, giving the team a robust dataset of fourteen physicochemical parameters per honey.

Those parameters included ash content, soluble solids measured in degrees Brix, water content, electrical conductivity, pH, alpha-amylase activity, hydrogen peroxide concentration, peroxidase activity, total protein, total phenolic content, total flavonoid content and three separate antioxidant assays. The results revealed dramatic variation. Electrical conductivity, for example, ranged from 501.70 microsiemens per centimeter in the Wenchuan honey to just 3.30 in the Fujian sample, a difference of several hundredfold. Ash content followed a similar pattern, with the Wenchuan honey highest at 0.48 percent and the Fujian honey lowest at 0.02 percent, reflecting the close relationship between minerals, ash and conductivity.

Water content proved to be a critical quality marker. Only the two Sichuan honeys and the Fujian honey fell below the 20 percent limit set by the Codex Alimentarius international food standard, while the Wenchuan sample exceeded it at 24.17 percent. Because excess water combined with honey’s naturally acidic environment can trigger fermentation, the authors argue that regulatory authorities should strengthen supervision and standardize production processes. Degrees Brix, which tracks sugar concentration, correlated inversely with water content, with the Derong honeys and the Fujian honey showing the highest values.

Enzyme activity told its own story. Alpha-amylase, secreted by the hypopharyngeal glands of bees, degrades with heat treatment or prolonged storage, making it a freshness indicator. The Wenchuan honey showed the highest activity at 4.39 milligrams per minute per gram, suggesting it had undergone neither high-temperature processing nor extended storage. The same sample also recorded high levels of hydrogen peroxide and peroxidase, two components of honey’s antimicrobial system. Hydrogen peroxide is generated when glucose oxidase is activated upon dilution, converting glucose into the antimicrobial compound, while peroxidase helps maintain redox balance.

To turn these measurements into a classification tool, the researchers built a random forest model, an ensemble machine learning method that aggregates the votes of many decision trees. The model’s out-of-bag error stabilized at roughly 10 to 12.5 percent once the number of trees reached 100 to 200, indicating sufficient training without overfitting. Six of the eight honeys, including the Wenchuan, Derong, Beijing, Shanghai, Fujian and Heilongjiang samples, were classified with zero error. Only the Zhejiang and honeycomb-containing Derong samples caused confusion, with two Zhejiang samples misclassified as Beijing honey. Crucially, the model identified total flavonoid content as the single most important discriminatory parameter, followed by electrical conductivity and DPPH radical scavenging activity, while pH and peroxidase contributed little.

Correlation analysis reinforced the chemical logic behind these distinctions. Electrical conductivity, ash content and total phenolic content were strongly positively correlated, consistent with the idea that minerals and organic acids from the nectar source drive all three. Total phenolics and total flavonoids also correlated significantly with antioxidant capacity, confirming that these compounds largely account for honey’s antioxidant power. Fourier transform infrared spectroscopy, which probes functional groups across the mid-infrared region, confirmed that all honeys were dominated by water, sugars and minor protein, but could not itself separate samples by origin, underscoring the need for finer analytical tools.

Those finer tools came in the form of volatile and non-volatile profiling. An electronic nose with eight metal-oxide sensors captured broad flavor differences, with all honeys responding most strongly to the sensor sensitive to nitrogen oxides, and the Wenchuan honey showing the strongest responses on five of eight sensors. Headspace solid-phase microextraction coupled to gas chromatography-mass spectrometry then annotated 696 volatile organic compounds, dominated by hydrocarbons, heterocyclic compounds and esters. Orthogonal partial least-squares discriminant analysis, validated by 200 permutation tests, cleanly separated all eight honeys and flagged 184 volatile markers with variable importance in projection scores above 1. Relative odor activity analysis identified 95 aroma-active compounds, led by a pyrazine contributing floral and green notes and beta-ionone, which adds floral, sweet and fruity character.

Untargeted metabolomics by ultra performance liquid chromatography-tandem mass spectrometry added a third layer, annotating 2246 non-volatile metabolites, with amino acids and derivatives the most numerous class at 573 compounds. Although saccharides made up only 4.72 percent of annotated compounds, they dominated by relative abundance, ranging from 21.72 to 29.43 percent. The comparison of representative sugars proved revealing: the Wenchuan honey had the highest gluconic acid content, suggesting stronger antibacterial activity, while both the Wenchuan and Fujian honeys showed low sucrose levels, indicating greater maturity. The Fujian honey stood out for its high glucose and fructose contents, implying greater sweetness and glycemic impact. Across all samples, fructose substantially exceeded glucose, suggesting a low crystallization tendency.

Metabolomic clustering mirrored the volatile results: the Wenchuan honey formed its own group, the two Derong samples clustered together, and the remaining five honeys were difficult to separate. Screening for differential metabolites yielded 1583 compounds significant in at least one comparison, with the largest contrast, 1059 differential metabolites, between the Wenchuan and Fujian honeys. Intriguingly, the artificial sweetener neotame, roughly 8000 times sweeter than sucrose, was among the metabolites upregulated in the Wenchuan sample, alongside rhapontigenin and N-phenylacetylphenylalanine. Shared differential metabolites were enriched in phenylalanine, tyrosine and tryptophan biosynthesis pathways, which feed the production of aromatic compounds and flavonoid precursors. The authors conclude that physicochemical properties provided the most effective basis for geographical discrimination, while volatile and non-volatile profiles allowed only partial separation, and they call for sampling from more regions to build a broader classification model. One unexpected bonus finding was that the honeycomb-containing sample showed the strongest antioxidant activity of all, hinting that the wax comb, routinely discarded by the apiculture industry, may harbor bioactive compounds worth recovering.

Subject of Research: Geographical origin discrimination of honey using physicochemical properties, volatile compounds and metabolomics

Article Title: Geographical origin discrimination of honey based on physicochemical properties and chemical composition

Article References: Zou, J., Xu, H., Wang, P., Zhang, L., Li, L., Chen, L., Chen, H., Wang, F., Hu, Y., & Liu, Y. (2026). Geographical origin discrimination of honey based on physicochemical properties and chemical composition. Food Chemistry: X, Article 104588. https://doi.org/10.1016/j.fochx.2026.104588

Image Credits: AI Generated

DOI: 10.1016/j.fochx.2026.104588

Keywords: honey, geographical origin, food authentication, physicochemical properties, random forest, volatile organic compounds, GC-MS, metabolomics, UPLC-MS/MS, antioxidant activity, flavonoids, electronic nose

Polysaccharides are long chains of sugar units that plants deploy for energy storage, structural support, and defense. When consumed, they act largely as dietary fiber: resistant to digestion in the upper gastrointestinal tract but accessible to the trillions of microbes that colonize the colon. There, gut bacteria ferment these chains into short-chain fatty acids such as acetate, propionate, and butyrate, compounds with well-documented roles in maintaining the intestinal barrier, modulating inflammation, and influencing metabolism. Because of this, the molecular architecture of a fruit polysaccharide—its monosaccharide composition, molecular weight, glycosidic linkages, and degree of branching—directly shapes its nutritional and functional value.

The research team set out to determine whether processing changes this architecture. Sun-drying, the most widespread low-cost preservation method in rural agricultural communities, exposes fruit to ultraviolet radiation, heat, oxygen, and enzymatic activity over days or weeks. Steaming, by contrast, is a rapid, moist-heat treatment typically used to soften tissue before consumption. These treatments impose very different chemical stresses, and the study investigated how each one propagates through to the final polysaccharide extract.

Using a suite of analytical techniques standard in carbohydrate chemistry, the researchers profiled polysaccharides extracted from fresh, sun-dried, and steamed fruit. Molecular weight distribution analyses revealed that processing measurably shifted the size of the polysaccharide populations, with thermal exposure capable of depolymerizing large chains into smaller fragments or, conversely, promoting associations among chains. Monosaccharide composition analysis and linkage determination indicated that the proportions of constituent sugars—typically including galacturonic acid, arabinose, galactose, rhamnose, and glucose in pectic and hemicellulosic fractions—were sensitive to the treatment applied. Spectroscopic characterization supported these observations, showing changes in functional group signatures consistent with altered branching or side-chain content.

These structural differences were not merely academic. The physicochemical properties of the polysaccharides—solubility, water-holding behavior, viscosity, and thermal characteristics—varied according to processing method. Such properties matter in practice: they govern mouthfeel and texture in foods, determine how fiber behaves during digestion and transit, and influence the accessibility of the polysaccharide backbone to bacterial enzymes in the gut. A highly branched, high-molecular-weight pectin does not interact with the intestinal environment in the same way as a degraded, low-molecular-weight fraction, and the study documented these divergences in detail.

The most consequential findings concerned gut-related function. In experiments simulating gastrointestinal conditions and gut microbial fermentation, polysaccharides from differently processed fruits displayed distinct fermentation profiles, with differences in the production of short-chain fatty acids and in the support of bacterial growth. This indicates that the health-relevant behavior of a fruit’s fiber fraction can be tuned—perhaps unintentionally—by the way the fruit is handled after harvest. For a crop like Ehretia macrophylla, whose fruit is consumed or used in folk preparations in processed form, the implication is that processing choices carry nutritional weight, not just sensory weight.

The work sits within a broader movement in food science to treat processing as a form of ingredient design. Previous studies have shown that drying, fermentation, extrusion, and heat treatments can each reshape the prebiotic potential of plant polysaccharides from sources as varied as apples, Goji berries, seaweeds, and medicinal mushrooms. What distinguishes the present study is its systematic side-by-side comparison of two traditional methods applied to the same raw material, allowing the authors to attribute differences specifically to the processing route rather than to raw material variability. This design strengthens the case that traditional knowledge and modern analytical chemistry can be productively combined.

For consumers and producers, the study offers practical perspective. Sun-drying remains indispensable in regions lacking cold chains, and steaming is deeply embedded in culinary practice; neither result suggests these methods should be abandoned. Instead, the research points toward optimizing conditions—drying duration, temperature, steam exposure time—to preserve or even enhance the structural features associated with beneficial fermentation. For food formulators, it suggests that process history should be considered when polysaccharide extracts are used as functional ingredients, since the same botanical source can yield extracts with different performance depending on pretreatment.

For scientists, the study raises productive questions. How do processing-induced structural changes translate to outcomes in vivo, in animal models or human trials? Can controlled thermal treatment be used deliberately to tailor prebiotic fibers? And how generalizable are these findings across other fruit polysaccharides, whose architectures differ substantially? Answering these questions will require coupling the kind of careful structural characterization demonstrated here with microbiome sequencing and metabolomic readouts. In the meantime, the message is clear: the road from orchard to gut microbiome is chemically long, and every step—including how the fruit is dried or cooked—leaves a trace on the fibers that feed our microbial partners.

Subject of Research: Effects of sun-drying and steaming on the structure, physicochemical properties, and gut-related functions of Ehretia macrophylla fruit polysaccharides

Article Title: Effects of sun-drying and steaming on Ehretia macrophylla Wall. (EMW) fruit polysaccharides: structure, physicochemical properties and gut-related functions

Article References: Mo, L., Li, H., Yu, Y., Li, J., Zhang, T., Zheng, S., Huang, D., & Zhao, C. (2026). Effects of sun-drying and steaming on Ehretia macrophylla Wall. (EMW) fruit polysaccharides: structure, physicochemical properties and gut-related functions. npj Science of Food. https://doi.org/10.1038/s41538-026-01144-4

Image Credits: AI Generated

DOI: 10.1038/s41538-026-01144-4

Keywords: Ehretia macrophylla, polysaccharides, sun-drying, steaming, food processing, dietary fiber, gut microbiota, short-chain fatty acids, prebiotics, food science, physicochemical properties, carbohydrate structure