Complex Equilibrium Research Articles

A Renaissance of Atoll Ecology

The approximately 320 atolls of the world, scattered across the tropical oceanic basins, constitute a unique type of ecosystem in that they are each an integrated unit consisting of island, coral reef, and lagoon components. Atolls have a complex geology, ecology, and biogeography, which can be fully appreciated only by transcending the classic boundary thinking of marine and terrestrial realms. The atolls we observe today were shaped by Quaternary sea-level fluctuations, which imposed strong environmental filters on their communities. As entirely biogenic, reef-borne structures, the islands of atolls depend upon marine productivity, which catalyzes island community assembly. Island species communities exist in complex dynamic equilibria with the surrounding oceanographic conditions. Energy fluxes and element cycles of the atoll system readily cross habitat boundaries and create a productive, diverse, and biomass-rich ecosystem on land and underwater. Past human disturbances and future global change put atolls at the forefront of conservation and ecological restoration.

The interplay of Brown carbon (BrC) surrogates and copper: Implications for the oxidative potential of ambient particles

Atmospheric particulate matter (PM) poses adverse effects on human via producing reactive oxygen species (ROS). Oxidative potential (OP, ability to generate ROS) can be induced by various chemicals in PM, while their interplay remains poorly characterized. Here, we systematically assessed influences of Cu2+ on OP of Brown carbon (BrC) (e.g., imidazoles) using dithiothreitol (DTT) assay. Results showed DTT consumption rate exhibited an initial rise and later decline (0.25 −0.56 µM/min) along with increase of BrC concentration (0.1 − 2 µM), while no general trend was observed for •OH formation. Although Cu2+ showed either antagonism or synergism with BrC against DTT consumption, Cu2+ displayed antagonism with most BrC against •OH generation. Fluorescence quenching experiments provided evidence of complexation between Cu2+ and water-soluble organic compounds (WSOCs, from ambient PM2.5), which was influenced by Cu2+ concentration. Further parallel factor analysis of spectra showed that polycarboxylate-type humic acid-like substances (complexation site number (n): 0.46, complexation equilibrium constant (k): 0.51) and fulvic acid-like compounds (n: 0.42, k: 0.62) were the main components in WSOCs that complexed with Cu2+. Our results suggest the interactions of BrC and copper play a crucial role in PM OP and highlight complexation in evaluation of PM OP.

An automated Peak Group Analysis for vibrational spectra analysis

Peak Group Analysis (PGA) is a multivariate curve resolution technique that attempts to extract single pure component spectra from time series of spectral mixture data. It requires that the mixture spectra consist of relatively sharp peaks, as is typical in IR and Raman spectroscopy. PGA aims to construct from individual peaks the associated pure component spectra in the form of nonnegative linear combinations of the right singular vectors of the spectral data matrix.This work presents an automated PGA (autoPGA) that starts with upstream peak detection applied to time series of spectra, combining different window-based peak detection techniques with balanced peak acceptance criteria and peak grouping to deal with repeated detections. The next step is a single-spectrum-oriented PGA analysis. This is followed by a downstream correlation analysis to identify pure component spectra that occur multiple times. AutoPGA provides a complete pure component factorization of the matrix of measured data. The algorithm is applied to FT-IR data sets on various rhodium carbonyl complexes and from an equilibrium of iridium complexes.

Alkaline saline lakes: A chemical evolution experiment evaluating the stability of formaldehyde in an aqueous saline environment

Formaldehyde condensation in the presence of a mineral catalyst and under alkaline conditions is considered to be a "messy" chemical system due to its dependence on the complex chemical equilibrium between the reaction intermediates, which has a significant impact on the final products.This chemical system is extremely important in prebiotic chemistry and has been proposed as a potential pathway for carbohydrate formation in the early Earth. Saline and soda lakes are alkaline systems that could concentrate and accumulate a wide variety of ions (such as phosphate) and clay minerals, which can catalyze prebiotic chemical reactions. These geological environments have recently been suggested as ideal environments in which prebiotic chemical reactions could have occurred.This study uses Lake Alchichica in Mexico as a physicochemical analog of an early Archean saline lake to examine the stability of formaldehyde in these aqueous saline environments. Formaldehyde decomposes into sugar-like and CHO molecules in alkaline, high-salinity environments depending on the minerals phases present. As phosphate ion (HPO42−) is available in the aqueous medium, the results of our experiments also imply that phosphorylation processes may have occurred in these natural settings.

Intermolecular Interactions between Aldehydes and Alcohols: Conformational Equilibrium and Rotational Spectra of Acrolein-Methanol Complex.

The rotational spectra of the 1:1 complex formed by acrolein and methanol and its deuterated isotopologues have been analyzed. Two stable conformations in which two hydrogen bonds between the two moieties are formed were detected. The rotational lines show a hyperfine structure due to the methyl group internal rotation in the complex and the V3 barriers hindering the motion were determined as 2.629(5) kJ mol-1 and 2.722(5) kJ mol-1 for the two conformations, respectively. Quantum mechanical calculations at the MP2/aug-cc-pVTZ level and comprehensive analysis of the intermolecular interactions, utilizing NCI and SAPT approaches, highlight the driving forces of the interactions and allow the determination of the binding energies of complex formation.

The Effect of Mouthwash in Oral Microbiome: A Literature Review

The oral microbiome contains over seven hundred bacterial species as well as fungi, viruses, archaea, and protozoa. The complex equilibrium between resident species in the oral cavity is responsible for the maintenance of a healthy state or a state associated with disease. Mouthwash has also been shown to reduce plaque and gingivitis. The purpose of this article is to update our current knowledge of the effect of mouthwash in oral microbiome and to discuss the impact of mouthwash on changes in the oral microbiome. The article was conducted of two databases and were limited to period January 2019 to May 2024 with combination of the following keywords: “oral microbiome” associated by the Boolean operator AND. The results obtained were 11 articles found at the beginning of the search in both databases, and the 6 full text articles were selected for further review and discussion. Commensal, gingivitis and halitosis associated species were significantly reduced by twice daily use of LCM (Listerine Cool Mint) or ACPM (alcohol-containing prototype mouthrinse). The AFPM (alcohol-free prototype mouthrinse) group showed no statistically significant reductions. Its microbiological action is not due to selective killing of pathogenic bacteria but rather via a reset mechanism, in which the plaque microbiome composition is shifted to a healthier state after repeated use. CHX (Chlorhexidine) led to an increase in the abundance of some genera such as Neisseria, Streptococcus and Granulicatella, and lowered the abundance of Actinomyces, but did not affect the abundance of Veillonella. The effect of mouthwash in oral microbiome are short-term and long-term impacts on supragingival plaque microbiome, return from dysbiosis to healthier levels, increasing abundance of common oral opportunistic bacteria, reduce the oral pathogenic microbial load in healthy subjects.

Mechanisms of the Gewald Synthesis of 2-Aminothiophenes from Elemental Sulfur.

The Gewald reaction is a well-established one-pot method to access 2-aminothiophenes from carbonyl compounds, activated acetonitriles, and elemental sulfur. To elucidate the reaction's poorly understood mechanism, with regard to the decomposition of sulfur and polysulfide intermediates, we have performed a comprehensive computational study using density functional theory (DFT) calculations at the M06-2X (or ωB97X-D)/aug-cc-pV(T + d)Z/SMD(C2H5OH) level of theory. The results show that the reaction is initiated by a Knoevenagel-Cope condensation, followed by opening of the elemental sulfur, leading to polysulfide formation. The polysulfide intermediates can interconvert and decompose using various mechanisms including unimolecular cyclization, nucleophilic degradation, and scrambling. Protonation of the polysulfides changes their electrophilic behavior and provides a kinetically favorable pathway for their decomposition. This protonation-induced intermolecular degradation is feasible for polysulfides of all lengths, but unimolecular decomposition is kinetically favored for long polysulfides (≥6 sulfur atoms). None of the pathways provide any thermodynamic benefit due to the lack of resonance-stabilized leaving group, and a complex equilibrium of polysulfides of all lengths is expected in solution. Cyclization of the monosulfide with aromatization to the thiophene product is the only driving force behind the reaction, funneling all of the various intermediates into the observed product in a thermodynamically controlled process.

Investigating the Photophysical Aspects of a Naphthalene-Based Excited-State Proton Transfer Dye 1-(1H-Benzo[d]imidazol-2-yl)naphthalen-2-ol: pH-Dependent Modulation of Photodynamics.

The steady state and time-resolved photophysical behavior of a proton transfer dye 1-(1H-benzo[d]imidazol-2-yl)naphthalen-2-ol (H-BINO) was investigated. The excited state intramolecular proton transfer (ESIPT) reaction in H-BINO is predominant in nonpolar solutions (toluene and DCM) with a lifetime of ∼1.0 ns. However, in polar media (DMF and MeOH), the excited state photodynamics is characterized by a complex equilibrium of emission from the locally excited state (0.1-2.3 ns), the phototautomer (0.5-1.2 ns), and the anionic emission (2.1-5.4 ns). In the solid state, emission from the various aggregated states dictates the photobehavior. Interestingly, the photodynamics in aqueous solution changes starkly as a function of pH with the anionic (2.1 ns) and phototautomeric (0.5-1.0 ns) emissions guiding the photodynamics as the pH of the medium increases. Optimized structural parameters at the proton donor and acceptor sites for the enol and keto forms and the calculated potential energy curve along the proton transfer coordinate at the density functional theory (DFT) level with the B3LYP/6-311G++(d,p) theory support a favorable and barrierless ESIPT process. The current results will surely boost the ongoing research on small molecule emissive materials.

A Smartphone App to Support Self-Management for People Living With Sjögren's Syndrome: Qualitative Co-Design Workshops.

Sjögren's syndrome (SS) is the second most common autoimmune rheumatic disease, and the range of symptoms includes fatigue, dryness, sleep disturbances, and pain. Smartphone apps may help deliver a variety of cognitive and behavioral techniques to support self-management in SS. However, app-based interventions must be carefully designed to promote engagement and motivate behavior change. We aimed to explore self-management approaches and challenges experienced by people living with SS and produce a corresponding set of design recommendations that inform the design of an engaging, motivating, and evidence-based self-management app for those living with SS. We conducted a series of 8 co-design workshops and an additional 3 interviews with participants who were unable to attend a workshop. These were audio recorded, transcribed, and initially thematically analyzed using an inductive approach. Then, the themes were mapped to the Self-Determination Theory domains of competency, autonomy, and relatedness. Participants experienced a considerable demand in the daily work required in self-managing their SS. The condition demanded unrelenting, fluctuating, and unpredictable mental, physical, and social efforts. Participants used a wide variety of techniques to self-manage their symptoms; however, their sense of competency was undermined by the complexity and interconnected nature of their symptoms and affected by interactions with others. The daily contexts in which this labor was occurring revealed ample opportunities to use digital health aids. The lived experience of participants showed that the constructs of competency, autonomy, and relatedness existed in a complex equilibrium with each other. Sometimes, they were disrupted by tensions, whereas on other occasions, they worked together harmoniously. An SS self-management app needs to recognize the complexity and overlap of symptoms and the complexities of managing the condition in daily life. Identifying techniques that target several symptoms simultaneously may prevent users from becoming overwhelmed. Including techniques that support assertiveness and communication with others about the condition, its symptoms, and users' limitations may support users in their interactions with others and improve engagement in symptom management strategies.For digital health aids (such as self-management apps) to provide meaningful support, they should be designed according to human needs such as competence, autonomy, and relatedness. However, the complexities among the 3 Self-Determination Theory constructs should be carefully considered, as they present both design difficulties and opportunities.

Solid–Liquid Equilibrium and Thermodynamic Analysis of Transition Metal Complexes Supported by Bis(imino)pyridine in Different Solvents

Solid–Liquid Equilibrium and Thermodynamic Analysis of Transition Metal Complexes Supported by Bis(imino)pyridine in Different Solvents

Biofilm contamination in confined space stations: reduction, coexistence or an opportunity?

The prolonged human permanence in confined environments in space, such as in the case of the International Space Station, has inadvertently fostered conditions leading to uncontrolled microbial proliferation on surfaces, known as biofilm. Biofilm presence represents a challenge in critical spacecraft systems, that can lead to contamination issues and systems loss of function due to biofouling phenomena. This scenario is further complicated by microgravity that has a controversial role on biofilm growth and formation. Biocontamination can be a limiting factor in human long-term mission in outer Earth orbit and an economic and health issue on ISS. This study addresses the pressing need for effective antimicrobial strategies against such resilient biofilms in confined environments where the usage of biocidal chemical compounds is strictly controlled due to toxicity dangers. Traditional methods can be complemented by advanced antimicrobial coatings techniques. A promising approach is based on the oxygen plasma as coating platform. The technology can be potentially extended to a wide range of antibiofilm agents (e.g., peptides, bacteriophages, nanoparticles, quorum sensing disrupting agents, etc.) and substrates (e.g., metal, plastic, ceramic) showing an exceptional flexibility. An alternative vision of the biofilm challenge can be inspired by the dual nature of biofilms, addressed as “good” or “bad” depending on the specific application. Indeed, biofilm have a great potential in closed systems as small space habitat (e.g., ISS) that can be inspired by their role in “large space habitat” as planet Earth itself. The replication of such a complex biological equilibrium is an open challenge.

Prediction of Phase Equilibrium Conditions and Thermodynamic Stability of CO2-CH4 Gas Hydrate

With the large-scale promotion and application of CO2 flooding, more and more engineering problems have emerged. Due to the high CO2 mole fraction, the associated gas of CO2 flooding very easily forms solid hydrates, compared to conventional natural gas. This has resulted in production decline or shutdown. Understanding the phase equilibrium conditions for hydrate formation in production fluids is crucial for hydrate prevention and control. In this study, accurate predictions of CO2-CH4 mixed gas hydrate formation conditions were performed using theoretical models. The temperature and pressure ranges for hydrate formation were calculated for different CO2 mole fraction, ranging from −11.5 °C to 20.85 °C and from 0.81 MPa to −28.1 MPa, respectively. Based on the calculated phase equilibrium data, a multi-parameter empirical model was developed using polynomial fitting. The calculation errors for the multi-parameter empirical model were 3.09%. The multi-parameter empirical model established in this study can avoid complex thermodynamic equilibrium calculations and has the advantages of simplicity, high accuracy, and wide coverage of downhole conditions. Based on the calculated phase equilibrium data, the dissociation enthalpy of CO2-CH4 hydrate below and above the freezing point of water was calculated. The results showed that an increase in CO2 mole fraction led to an increase in hydrate dissociation enthalpy and enhanced thermodynamic stability, making hydrate prevention more challenging. Our work can contribute to the optimization of CO2 production fluid treatment processes and the development of hydrate prevention and control technologies.

Formation mechanism of n-octadecane @ calcium fluoride microencapsulated phase change material

Microencapsulating phase change materials (PCMs) with CaF2 as shell could obtain not only novel microencapsulated PCMs (MPCMs) but also potential luminescence materials with self-thermal regulation property. Prior to the preparation of good luminescent MPCMs with doped CaF2 as shell, the formation mechanism of the MPCMs should be well understood. In this work, n-octadecane (ODE) was selected as core to prepare CaF2 MPCMs and the formation mechanism was comprehensively investigated. The results revealed that the concentrations of the Ca2+ and the F− in the solution, which could be adjusted by the coordination equilibrium of Ca-citrate complex and the hydrolysis balance of NaBF4, played key roles in formation of the MPCMs. Moreover, the formation of the MPCMs was composed of five periods, including: formation of emulsion; formation of Ca-citrate intermediate microcapsules; induction of CaF2 shell; growth and aggregation of CaF2 shell and overgrowth of CaF2. Meanwhile, the results also revealed that prolonging the overgrowth period of CaF2 had significant effects on the morphology and properties of the prepared MPCMs. In addition, with the increase of the reaction temperature, the nucleation, growth and aggregation of CaF2 crystals could be accelerated, and the formation and growth periods of the CaF2 shell were shortened. This work is not only significant for the preparation and optimization of MPCMs with CaF2 as shell, but also can guide and promote the development of luminescent MPCMs.

The Effect of Thermal Residual Stress on the Stress State in a Short-Fiber Reinforced Thermoplastic

Upon their cooling and solidification, significant thermal residual stresses can develop in short-fiber reinforced thermoplastics due to the mismatch in coefficient of thermal expansion between fiber and matrix. In this study we set out to investigate this effect numerically. The build-up of thermal residual stresses is modeled by expanding a well-established constitutive model, the Eindhoven glassy polymer (EGP) model, with thermal expansion. The experimentally measured thermal residual stresses can be described using an effective glass-transition temperature and a constant coefficient of thermal expansion without the need for complex equilibrium kinetics associated with the glass transition itself. Subsequently, the influence of thermal residual stress on the deformation behavior for a short-fiber reinforced thermoplastic is studied employing multi-fiber representative volume elements (RVEs) for different fiber-weight fractions. The micromechanical models are evaluated on the importance of thermal residual stresses on the local and nominal stress state. From these analyses it can be concluded that the thermal residual stresses should be accounted for when assessing the quantitative local stress state and are therefore essential when local mechanisms are studied. In contrast, thermal residual stresses are not required to capture the nominal transient stress–strain response.

Introduction to the modeling of complex chemical reaction equilibrium using gPROMS® and GAMS®

AbstractIn the present paper several aspects of the simulation of complex chemical equilibrium are discussed, using two research and educational software: gPROMS® and GAMS®. All computations are performed to boost the understanding of chemical engineering students, undergraduate, and graduate, of the complex concepts behind both thermo‐chemical processes and optimization techniques. Four case studies with varying levels of difficulty illustrate the proposed methodology and robustness of the modeling systems: Catalytic steam reforming of bio‐ethanol at high temperatures. Partial oxidation of naphthalene using either air or pure oxygen. Supercritical water gasification of Microalga Spirulina. Dry and mixed reforming of glucose.Our results indicate that the use of optimization tools offered bygPROMS® and GAMS®software are useful and efficient tools to calculate the chemical and phase equilibrium by minimizing the Gibbs energy, provided that adequate initial guesses are used. Furthermore, the computational time spent in the calculations was generally quite short. The obtained equilibrium compositions are benchmarked using the ubiquitous process simulators: ASPEN‐Plus® and/or ASPEN‐Hysys® as well as data available from the open literature. We obtained excellent agreement between our results and their counterpart obtained using ASPEN‐Plus®. In the last part of this manuscript, authors share their experience in supervising senior term projects on the subject. A questionnaire was used to collect qualitative and quantitative feedback from the nine students involved in the projects. Their responses to a questionnaire focused on the chemical engineering thermodynamics theory as well as software usage during their investigations. This questionnaire demonstrates that students can overcome mathematical complexity by either using mathematical software or equivalent modeling systems (e.g., Matlab®, Mathematica©, gPROMS®, and GAMS®).

Interactions of CdSe Nanocrystals with Cationic Proteins Extracted from Moringa oleifera Seeds

Even with significant developments in nanoscience, relatively little is known about the interactions of nanocrystal semiconducting materials with bio-macromolecules. To investigate the interfacial phenomena of cadmium selenide quantum dot (CdSe QD) nanocrystals with proteins extracted from Moringa oleifera seeds, different concentrations of cadmium selenide quantum dots–Moringa oleifera seed protein (CdSe–MSP) complexes were prepared. Respective CdSe QDs with hexagonal phase and crystalline size in the range of 4–7 nm were synthesized and labelled with the purified mesoporous MSP having a surface area of 8.4 m2/g. The interaction mechanism between CdSe QDs and MSP was studied using UV–Vis absorption, fluorescence emission and Fourier Transform Infrared spectroscopies. The UV–Vis absorption spectra showed absorption bands of CdSe–MSP complexes at 546.5 nm. The fluorescence intensity of CdSe QDs was found to decrease with increasing concentration of MSP. The thermodynamic potentials ∆Hθ (−321.3 × 103 Jmol−1); ∆Sθ (156.0 JK−1mol−1) and ∆Gθ (−46.6 × 103 Jmol−1) were also calculated. The stability of the complex found is strongly influenced by electrostatics interaction and surface-bound complexation equilibrium attraction. This information can help to elucidate the surface characteristics of MSP and its potential interactions with other molecules or nanoparticles.

Quantification of peracetic acid (PAA) in the H2O2 + acetic acid reaction by the wavelength shift analysis in near-UV/visible absorption region.

In our study, we present an innovative method for the analysis and real-time monitoring of peracetic acid (PAA) formation within the near-UV/Vis (visible) wavelength region. PAA's absorption spectrum, influenced by its presence in a complex quaternary equilibrium mixture with hydrogen peroxide (H2O2), acetic acid, and water, lacks discernible peaks. This inherent complexity challenges conventional analytical techniques like Beer's law, which rely on absorption intensity as a foundation. To address this challenge, we introduce a novel approach that centers on the analysis of blue shifts in absorption wavelengths, particularly at an absorbance of 0.8 a.u. This method significantly enhances the precision of calibration curves for both diluted PAA and H2O2, unveiling an exponential correlation between wavelength and the logarithm of concentration for both components. Significantly, our approach allows for real-time and accurate measurements, especially during the dynamic PAA formation reaction. Our results exhibit excellent agreement with data obtained from Fourier-transform infrared (FT-IR) spectroscopy, validating the reliability of our method. It's noteworthy that under stable PAA concentration conditions (after 12h of solution interaction), both traditional absorption method and our approach closely align with the FT-IR method. However, in dynamic scenarios (0-12h), the absorption method exhibits higher error rates compared to our approach. Additionally, the increased concentration of a catalyst, sulfuric acid (H2SO4), significantly reduces the errors in both methods, a finding that warrants further exploration. In summary, our study not only advances our understanding of PAA and its spectral behavior but also introduces innovative and precise methods for determining PAA concentration in complex solutions. These advancements hold the potential to revolutionize the field of chemical analysis and spectroscopy.

A new instrumentation for simultaneous terahertz and mid-infrared spectroscopy in corrosive gaseous mixtures.

The correct interpretation of infrared (IR) observations of planetary atmospheres requires an accurate knowledge of temperature and partial and global pressures. Precise laboratory measurements of absorption intensities and line profiles, in the 200-350K temperature range, are, therefore, critical. However, for gases only existing in complex chemical equilibria, such as nitrous or hypobromous acids, it is not possible to rely on absolute pressure measurements to measure absolute integrated optical absorption cross sections or IR line intensities. To overcome this difficulty, a novel dual-beam terahertz (THz)/mid-IR experimental setup has been developed, relying on the simultaneous use of two instruments. The setup involves a newly constructed temperature-controlled (200-350K) cross-shaped absorption cell made of inert materials. The cell is traversed by the mid-IR beam from a high-resolution Fourier transform spectrometer using along a White-cell optical configuration providing absorption path lengths from 2.8 to 42m and by a THz radiation beam (82.5GHz to 1.1THz), probing simultaneously the same gaseous sample. The THz channel records pure rotational lines of molecules for which the dipole moment was previously measured with high precision using Stark spectroscopy. This allows for a determination of the partial pressure in the gaseous mixture and enables absolute line intensities to be retrieved for the mid-IR range. This new instrument opens a new possibility for the retrieval of spectroscopic parameters for unstable molecules of atmospheric interest. The design and performance of the equipment are presented and illustrated by an example of simultaneous THz and mid-IR measurement on nitrous acid (HONO) equilibrium.

Optimization of systems of industrial ventilation – case study

Industrial ventilation involves a deep knowledge of fluid dynamics, in the modern computerized version, three-dimensional heat propagation, complex fluid flow, equilibrium state and transient conditions, operating problems, contamination inside or outside the installations, etc. Industrial buildings generally comprise large spaces with varied sources of damage. The type of sources and their location depend on the technological process in each section. In order to dilute the harms, to ensure the environmental conditions necessary for the protection of the work and the realization of the microclimate required by the production process, through the industrial ventilation installations large air flows are carried. The design of the ventilation systems in the industrial sections requires a thorough knowledge of the technological process, of the machines and their location, the nature and quantity of the damages, the environmental conditions required from the technological point of view and of the labor protection.. In order to optimize the industrial ventilation systems, an industrial ventilation installation for exhausting and neutralizing VOC emissions was chosen. The optimization of the ventilation installation was possible with the help of the pressure loss balancing methodology.

Complexation and disproportionation of group 4 metal (alkoxy) halides with phosphine oxides.

Group 4 Lewis acids are well-known catalysts and precursors for (non-aqueous) sol-gel chemistry. Titanium, zirconium and hafnium halides, and alkoxy halides are precursors for the controlled synthesis of nanocrystals, often in the presence of Lewis base. Here, we investigate the interaction of Lewis bases with the tetrahalides (MX4, X = Cl, Br) and metal alkoxy halides (MXx(OR)4-x, x = 1-3, R = OiPr, OtBu). The tetrahalides yield the expected Lewis acid-base adducts MX4L2 (L = tetrahydrofuran or phosphine oxide). The mixed alkoxy halides react with Lewis bases in a more complex way. 31P NMR spectroscopy reveals that excess of phosphine oxide yields predominantly the complexation product, while a (sub)stoichiometric amount of phosphine oxide causes disproportionation of the MXx(OR)4-x species into MXx+1(OR)3-x and MXx-1(OR)5-x. The combination of complexation and disproportionation yields an atypical Job plot. In the case of zirconium isopropoxy chlorides, we fitted the concentration of all observed species and extracted thermodynamic descriptors from the Job plot. The complexation equilibrium constant decreases in the series: ZrCl3(OiPr) > ZrCl2(OiPr)2 ≫ ZrCl(OiPr)3, while the disproportionation equilibrium constant follows the opposite trend. Using calculations at the DFT level of theory, we show that disproportionation is driven by the more energetically favorable Lewis acid-base complex formed with the more acidic species. We also gain more insight into the isomerism of the complexes. The disproportionation reaction turns out to be a general phenomenon, for titanium, zirconium and hafnium, for chlorides and bromides, and for isopropoxides and tert-butoxides.