Validation gaps in Chemistry

Representative open questions

Showing 30 of 63 — one per source paper, highest-quality first.

• Mechanistic investigations of the formation of multifunctional products from the multi-generation ●OH oxidation of styrene (2026) · doi

  The structures of some specific multi-generation oxidation products of styrene remain uncharacterized in laboratory chamber experiments and are merely inferred from exact mass and fragmentation data rather than definitively identified through experimental spectroscopic techniques.

• Donor-length engineering in directly linked covalent heptazine frameworks for photocatalytic H2O2 Production (2026) · doi

  The EPR spin-trapping experiments for ·OH detection using DMPO were conducted in purely aqueous solution under Ar-bubbling conditions; the detection and quantification of ·OH radicals in the presence of competing solutes (e.g., humic acids, inorganic ions) and at varying dissolved oxygen concentrations for H2O2 photosynthesis on heptazine catalysts have not been systematically studied.

• High-Entropy Catalysts for Biomass-Derived Chemicals Valorization: Mechanisms, Applications, and Opportunities (2026) · doi

  While particle size engineering has been identified as critical for tuning active site exposure, lattice distortion degree, and mass transfer efficiency in high-entropy catalysts, the specific size ranges (nanometer scale thresholds) that optimize configurational diversity and entropy effects for individual biomass valorization reactions (HMF, furfural, glucose, glycerol transformations) have not been systematically characterized.

• QM/MM hybrid simulation of enzyme-Mn synergistic catalysis for quinazolinones: computational determination of activation energy and transition state (2026) · doi

  While infrared vibrational frequency predictions showed ≤8 cm⁻¹ deviation from experimental values, the study was limited to eight spectral modes (C-N stretching, Mn-O stretching, etc.); comprehensive vibrational spectrum simulation across the full 400-4000 cm⁻¹ range for enzyme-Mn quinazolinone complexes would validate frequency prediction reliability for mechanistic characterization.

• Olympian colour chemistry (2012) · doi

  The paper identifies that additives intended to stabilise photochromic dyes can produce undesired consequences such as altering photocolouration kinetics or generating residual colour in the non-activated state, but does not quantify the threshold concentrations or structural modifications of spirooxazines and naphthopyrans at which these side effects become problematic versus acceptable for commercial lens applications.

• WITHDRAWN: Combinatorial Chemistry Online Volume 15, Issue 11, November 2013 (2013) · doi

  The dynamic combinatorial chemistry protocol described by Fang et al. for isolating ligand-target adducts from dynamic combinatorial libraries has only been demonstrated via a single case study identifying competitive inhibitors of lysozyme; systematic evaluation of this acceleration protocol across structurally diverse protein targets and varying library compositions remains unexplored.

• Transmetallation Reaction of Alkali and Alkaline-earth Metal Ions in Supramolecular Complex of [{Au6Cd3(tdme)2(D-pen)6}Cd4Na4](NO3)12 (2026) · doi

  The transmetallation reactions were investigated exclusively under solid-state single-crystal-to-single-crystal conditions. Whether the selectivity patterns and mechanistic insights (metal-linker exchange but not metal-center exchange) hold in solution-phase transmetallation or under different synthetic conditions (temperature, solvent, reaction time variations) remains unexamined.

• Synthesis of Tetravalent Boron Complexes with Pyrazolone-Based Ligand and their Drug-Likeness (2026) · doi

  The study evaluated drug-likeness of tetravalent boron complexes (MPAP-1 to MPAP-6) using computational physicochemical properties against five rule sets (Lipinski, Ghose, Veber, Egan, Muegge), but did not conduct in vitro absorption, distribution, metabolism, and excretion (ADME) studies or cell-based bioavailability assays to experimentally validate the predicted oral bioavailability of these pyrazolone-based boron coordination compounds.

• The advent of macrocyclic chemistry (2012) · doi

  The resistance to acid demetallation in cyclic diamines is attributed to absence of terminal amine functions and rate-determining second protonation, but systematic kinetic studies varying pH, temperature, and solvent conditions across different macrocyclic diazirine architectures are not detailed.

• Analytical Techniques in Chemistry (2019) · doi

  The pH metry standardization procedure uses buffer solutions at pH 4, 7, and 9.2, but the paper does not address the accuracy and stability of pH meter calibration across extended temperature ranges or in solutions with extreme ionic strength, which are common in industrial analytical applications of potentiometric titrations.

• Basic Organometallic Chemistry (2016) · doi

  The paper demonstrates that Zeise's salt undergoes hydrolysis and nucleophilic displacement reactions, but does not systematically compare reactivity patterns or substitution rates with other metal-alkene complexes containing different transition metals or different alkene ligands.

• The Basis of a Greener Analytical Chemistry (2011) · doi

  The paper mentions solid phase extraction units, capillary microextraction, and solid phase spectrophotometry for reducing solvent consumption in greener analytical chemistry, but provides no comparative quantitative data on solvent and reagent consumption reduction achieved by each technique when applied to the same analytical problem.

• Bis (N-Heterocyclic Carbene) Palladium Complex Immobilized Onto Fe3o4@Sio2 as a Catalyst for Sonogashira (Amine/Copper Free) and Hiyama Coupling of Arbr/Cl in Green Media (2026) · doi

  Catalyst loading optimization (entries 14-17 in Table 1) shows that reducing catalyst from 20 mg drastically decreases yield, but the specific minimum active site concentration required for efficient Sonogashira coupling and the relationship between Fe3O4@SiO2 support particle size and catalytic turnover frequency are not reported. Characterization of active site density and heterogeneity across catalyst batches would validate reproducibility.

• Coordination chemistry of poly(thioether)borate ligands (2010) · doi

  The side-on [PhTtAd]Ni(O2) complex is described as potentially lying on the superoxo-to-peroxo continuum based on DFT-derived O–O distances, but experimental methods to definitively distinguish between nickel(II)-superoxo versus more activated peroxo character through spectroscopic techniques beyond EPR and computational modeling have not been demonstrated.

• My journey in the CO2-chemistry wonderland (2017) · doi

  Metal oxide catalysts for selective epoxidation of olefins show unpredictable performance dependent on the 'mode of being' of the oxide on the catalyst surface, which varies with synthetic procedure and uncontrolled factors. Systematic characterization studies are needed to identify and control the surface oxide structure parameters that determine whether the catalyst produces selective epoxidation (100% propene oxide) versus combustion or aldehyde/ketone formation.

• Resonance-enhanced multiphoton ionization time-of-flight mass spectrometry for the real-time analysis of a retronasal aroma compound from a cumin sandwich (2026) · doi

  The proposed logistic function fitting approach for extracting quantitative release times (γ1, γ2) from time profiles exhibiting breath-synchronized fluctuations has not been validated against independent methods or on other aroma compound classes beyond p-cymene in cumin sandwiches using REMPI-TOFMS.

• Multicomponent reactions in crop protection chemistry (2020) · doi

  Multicomponent syntheses of mandipropamid-related mandelamides and oomyceticides using alkyne chemistry have been reported, but systematic comparison of different multicomponent reaction pathways (Kabachnik-Fields vs. isocyanide-based approaches) for generating these fungicide scaffolds has not been conducted.

• Shilov alkane platinum chemistry: 45 years (2015) · doi

  The catalyst recycling stability and separation efficiency of heterogenized PtII triazine-based systems requires quantitative testing across multiple reaction cycles to establish maximum recyclability limits and activity retention profiles for direct industrial alkane oxidation processes.

• Developments in Heterocyclic Microwave Chemistry (2016) · doi

  The transition metal-free Ullmann-type O-arylation for xanthone and azaxanthone synthesis shows that electron-donating groups ortho or para to the halogen cause prolonged microwave reaction times, but no detailed kinetic studies or mechanistic analysis of this electronic rate effect have been conducted under microwave heating versus conventional thermal conditions.

• Flow Chemistry as a Drug Discovery Tool: A Medicinal Chemistry Perspective (2018) · doi

  The three-step functionalization–Boc deprotection–functionalization sequence (Scheme 21) generates >180 mg of final material without intermediate purifications, but no data are provided on whether this inline processing strategy introduces detectable byproduct accumulation, how product purity compares to batch-purified analogs, or what impurity thresholds trigger need for inline purification between steps.

• Self-Assembly of Complementary Components Using a Tripodal Bismuth Compound: Pnictogen Bonding or Coordination Chemistry? (2021) · doi

  The discrepancy between hydrodynamic volumes (VH) calculated from diffusion coefficients and van der Waals volumes (VvdW) from crystallographic data was attributed to temperature differences (100 K vs. solution conditions) and solvent sphere effects, but this relationship has not been systematically validated across the series of compounds (2, 2·Py3, 2·TPA, 2²·4) at multiple temperatures.

• Atmospheric oxidation chemistry of hexafluoroisobutylene initiated by OH radical: Kinetics and mechanism (2021) · doi

  Secondary oxidation products IM4 and IM9 are predicted to undergo further atmospheric reactions with O₂/NO, but experimental detection and quantification of these intermediates remain absent; direct laboratory measurements using spectroscopic or chromatographic techniques are required to validate the proposed oxidation mechanism.

• Preparation and Biological Activity of Molecular Complexes Based on Secondary Metabolites of Glycyrrhiza Glabra L. and Sophora Japonica L. (2026) · doi

  Biological evaluation of GA:Rutin complexes was restricted to a single capillary permeability model in mice; cytokine profiling, histopathology, and broader pharmacological tests characterizing the in vivo mechanisms of the supramolecular complex were not performed.

• Flow Chemistry in Drug Discovery: Challenges and Opportunities (2021) · doi

  The paper describes integration of AI algorithms with continuous flow platforms for synthetic route selection and parameter optimization, but does not specify what types of chemical reaction databases are required, how complete these databases must be, or validation metrics for AI-predicted synthetic routes when translated from small-scale microfluidic screening to larger manufacturing scale.

• Water extract rice husk as an efficient catalyst to synthesis of p-thymol tailored 1,2,4-triazole sulfanyls as potential antidiabetic candidates (2026) · doi

  The BOILED-Egg model predicts that compounds 7a, 7g, 7f, and 7L are P-glycoprotein substrates (PGP+), indicating potential active efflux from the gastrointestinal tract and brain, but the paper does not experimentally validate blood-brain barrier permeability or investigate whether BBB penetration is desirable or problematic for antidiabetic efficacy of these sulfanyl compounds.

• The Burgeoning of Mechanically Interlocked Molecules in Chemistry (2019) · doi

  The integration of mechanical bonds into macroscopic gel materials has been demonstrated with [c2]daisy chains and cyclodextrin-based artificial muscles in hydrogels, but the quantitative effect of mechanical bonds on the elastic and mechanical properties of bulk gel objects remains incompletely characterized across different gel compositions and environmental conditions.

• Dynamic Chemistry of Anion Recognition (2011) · doi

  The de novo structure-based design approach for self-assembled anion receptors (implemented via HostDesigner software) has been demonstrated for sulfate coordination cage design, but the method's transferability to other divalent oxoanions (carbonate, selenate) or alternative cage geometries beyond M4L6 tetrahedral architectures remains unexplored and requires systematic validation.

• Supramolecular polymer chemistry meets computational chemistry: theoretical simulations on advanced self-assembling chiral materials (2018) · doi

  The ROESY-derived intermolecular contact data for pyreneimidazoles 7a and 7b were successfully matched to dimer F geometry, but multi-scale molecular dynamics simulations accounting for solvent effects (MCH vs CHCl₃) have not been performed to explain why the same compounds form helical structures in one solvent versus non-helical aggregates in another.

• A universal atomically dispersed cobalt catalyst for alkylation of ketones alcohols and lignin-derived compounds (2026) · doi

  While the catalyst demonstrates reusability over multiple cycles, the specific number of consecutive reaction cycles tested and the quantitative deactivation profile of Co@NC-PPDA under repetitive alkylation conditions have not been explicitly reported. Long-term catalyst stability data under industrial operating conditions (>10 cycles with varying substrate types) are absent.

• Redox chemistry of aquatitanium(II), Ti2+(aq) (2011) · doi

  The Ti(III)–Ti(IV) binuclear complex formation in the Mo(V) decomposition pathway shows a stability constant near 200 M⁻¹ estimated from kinetic saturation, but the structural features and coordination environment of this Ti(III)–Ti(IV) intermediate remain uncharacterized. Direct spectroscopic or crystallographic evidence is needed to confirm the proposed binuclear successor complex mechanism.