Spectroscopic studies of the intermolecular interactions of Congo red and tinopal CBS with modified cellulose fibers

Synthesis of porous calcium-guar gum benzoate nano-biohybrids for sorptive removal of congo red and phosphates from water

This work aims to develop an eco-sound nano-bio-hybrid sorbent using sustainable materials for sorptive elimination of congo red and phosphates from aquatic environment. An amphipathic biopolymer derivative, high DS guar gum benzoate (GGBN) was used for entrapment of as synthesized calcium carbonate nanoparticles using solvent diffusion nano-precipitation technique. Designer nano-biohybrids were developed upon experimenting with various materials stoichiometry. SEM, XRD and EDX studies confirmed near-uniform impregnation of rhombohedral calcium carbonate crystals throughout the biopolymer matrix. Average pore size distribution and surface area of final product Ca-GGBNC, were estimated from NDLFT and BET methods respectively. Analysis of adsorption findings acquired at study temperature 27 ± 2 °C showed that the maximum adsorption capacity of Ca-GGBNC recorded qmax, 333.33 mg/g for congo red azo dye and that for phosphate was at 500 mg/g. Adsorptive removal was noted and both components followed pseudo second order kinetics. Intra-particle diffusion kinetics investigation disclosed that the boundary layer effect was prominent and the adsorption rates were not solely directed by the diffusion stage. Activation energy, Ea was to be estimated using Arrhenius equation at 56.136 and 47.015 KJ/mol for congo red and phosphates respectively. The calculated thermodynamic parameters(ΔG°, ΔH°, and ΔS°) revealed the spontaneous, feasible and endothermic sorption process. Owing to active surface area, spherical size, functional moiety and porous network, antibacterial properties of nanobiohybrid were persistent and MIC against E. coli and S. aureus were recorded at 200 μg/mL and 350 μg/mL respectively.

Unveiling the interactions between biomaterials and heterocyclic dyes: A sustainable approach for wastewater treatment

The present Review investigates the interactions between biomaterials and heterocyclic dyes, focusing on their potential application in sustainable wastewater treatment. Heterocyclic dyes are widely used in various industries, resulting in their widespread presence in wastewater, posing environmental challenges. This review explores the utilization of biomaterials as adsorbents for the removal of heterocyclic dyes from contaminated water sources. The interactions between biomaterials, such as cellulose, microfibrilated cellulose and lignin and different heterocyclic dyes are examined through reported experimental analysis and characterization techniques. The study evaluates the adsorption capacity, kinetics, and thermodynamics of the biomaterial-dye systems to elucidate the underlying mechanisms and optimize the treatment process. The review highlight the promising potential of biomaterial-based approaches for sustainable wastewater treatment, providing insights for the development of efficient and environmentally friendly dye removal technologies.

pH-dependent effect of Congo Red on the growth of Aspergillus nidulans and Aspergillus niger

The azo dye Congo Red (CR) is frequently used as an agent to elicit cell wall integrity stress in fungi. This highly toxic aromatic, heterocyclic compound contains two azo bonds as chromophore, which are responsible for protonation under acidic conditions, leading to changes in the molecular structure of the dye and the color of the solution. The investigation of how CR affects the growth of Aspergillus nidulans and Aspergillus niger on surface cultures provided us with evidence about its pH-dependent toxicity. Reducing the starting pH of the media from 7 to 3 decreased both the toxicity of CR and the dose-dependence of its toxicity substantially. These changes can be explained by the pH-dependent structural changes of CR and its precipitation at low pH. The pH also depended on the fungi; they could induce a decrease or even an increase, which could be important in the loss of dose-dependence. Our experiments led to the conclusion that in studies to evaluate the antifungal effect of CR, properly buffered solutions with pH values adjusted to above 5 are highly recommended to achieve a well-detectable and dose-dependent antifungal effect. However, for decolorization of CR solutions, lower pH is suggested where the decreased toxicity and solubility of CR could help this process.

Comparative Analysis of Bacterial Cellulose Membranes Synthesized by Chosen Komagataeibacter Strains and Their Application Potential

This article presents a comparative analysis of bacterial cellulose membranes synthesized by several strains of the Komagataeibacter genus in terms of their specific physical, physico-chemical, and mechanical properties. Herein, the aim was to choose the most suitable microorganisms producing cellulosic materials with the greatest potential for the fabrication of bio-inspired nanocomposites. The selection was based on three main steps, starting from the evaluation of BNC biosynthetic efficiency with and without the addition of ethanol, followed by the assessment of mechanical breaking strength, and the physical parameters (compactness, structural integrity, appearance, and thickness) of the obtained biological materials. Ultimately, based on the performed screening procedure, three efficiently growing strains (K. hansenii H3 (6Et), K. rhaeticus K4 (8Et), and Komagataeibacter sp. isolated from balsamic vinegar (12Et)) were chosen for further modifications, enabling additional cellulose functionalization. Here, supplementation of the growth medium with five representative polymeric compounds (citrus/apple pectin, wheat starch, polyvinyl alcohol, polyethylene glycol) led to significant changes in BNC properties, especially dye loading abilities, mechanical strength, and water adsorption/retention capacities. The resulting nanocomposites can be potentially useful in various fields of medicine and industry, and in the future, they may become a practical and cost-effective competitor against commercial biomaterials currently available on the market.

Application of biodegradable cellulose-based biomass materials in wastewater treatment

Water bodies contain a large number of harmful environmental pollutants, including oil, heavy metal ions and dyes, which has become a major global problem. The current work focusses on the development and future prospect of sustainable application of biodegradable cellulose-biomass materials in water treatment, considering that they show an important prospect in wastewater treatment. This paper summarizes the advantages and disadvantages of cellulose-biomass materials in removing harmful substances and pollutants from water and the key problems the technology faces. Cellulose-biomass material has unique structure, is environment friendly, degradable, renewable and provides low energy cost benefits, among other advantages. In this paper, the research progress of wastewater treatment in recent years is reviewed from the following three aspects: oil-water separation, heavy metal ions in water, and dye adsorption. The future research direction is also discussed.

Real-time adsorption of optical brightening agents on cellulose thin films

Optical brightening agents (OBAs) are commonly used in textile and paper industry to adjust product brightness and color appearence. Continuous production processes lead to short residence time of the dyes in the fiber suspension, making it necessary to understand the kinetics of adsorption. The interaction mechanisms of OBAs with cellulose are challenging to establish as the fibrous nature of cellulosic substrates complicates acquisition of real-time data. Here, we explore the real-time adsorption of different OBAs (di, tetra- and hexasulfonated compounds) onto different cellulose surfaces using surface plasmon resonance spectroscopy. Ionic strength, surface topography and polarity were varied and yielded 0.76-11.35 mg m^-2 OBA on cellulose. We identified four independent mechanisms governing OBA-cellulose interactions. These involve the polarity of the cellulose surface, the solubility of the OBA, the ionic strength during adsorption and presence of bivalent cations such as Ca²⁺. These results can be exploited for process optimization in related industries as they allow for a simple adjustment and experimental testing procedures including performance assessment of novel OBAs.

Adsorption Performance for Reactive Blue 221 Dye of β-Chitosan/Polyamine Functionalized Graphene Oxide Hybrid Adsorbent with High Acid-Alkali Resistance Stability in Different Acid-Alkaline Environments

A hybrid material obtained by blending β-chitosan (CS) with triethylenetetramine-functionalized graphene oxide (TFGO) (CSGO), was used as an adsorbent for a reactive dye (C.I. Reactive Blue 221 Dye, RB221), and the adsorption and removal performances of unmodified CS and mix-modified CSGO were investigated and compared systematically at different pH values (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12). The adsorption capacities of CS and CSGO were 45.5 and 56.1 mg/g, respectively, at a pH of 2 and 5.4 and 37.2 mg/g, respectively, at a pH of 12. This indicates that TFGO was successfully introduced into CSGO, enabling π-π interactions and electrostatic attraction with the dye molecules. Additionally, benzene ring-shaped GO exhibited a high surface chemical stability, which was conducive to maintaining the stability of the acid and alkali resistance of the CSGO adsorbent. The RB221 adsorption performance of CS and CSGO at acidic condition (pH 3) and alkaline condition (pH 12) and different temperatures was investigated by calculating the adsorption kinetics and isotherms of adsorbents. Overall, the adsorption efficiency of CSGO was superior to that of CS; thus, CSGO is promising for the treatment of dye effluents in a wide pH range.

Isothermal Adsorption Properties for the Adsorption and Removal of Reactive Blue 221 Dye from Aqueous Solutions by Cross-Linked β-Chitosan Glycan as Acid-Resistant Adsorbent

Dye effluent causes serious pollution and damage to the environment and needs a series of treatments before it can be discharged. Among the numerous effluent treatment methods, adsorption is the simplest and does not cause secondary pollution. Bio-adsorbents are especially advantageous in the treatment of low-concentration dye effluent. In this study, the adsorption and removal capacities of unmodified α- and β-chitosan and modified β-chitosan (β-chitosan cross-linked with triethylenetetramine, BCCT) on C.I. Reactive Blue 221 (RB221) dye were compared. The experiments were performed on the adsorption of the RB221 dye by unmodified α- and β-chitosan and cross-linkage⁻modified BCCT at different temperatures and for different durations, which are presented along with the relevant adsorption kinetics calculations. According to the results, as the temperature increased from 303 to 333 K, the initial adsorption rates of the adsorbents, α-chitosan, β-chitosan, and BCCT, for the RB221 dye, changed from 1.01 × 10², 4.74 × 10², and 1.48 × 10⁶ mg/g min to 5.98 × 10⁴, 4.23 × 10⁸, and 1.52 × 1013 mg/g min, respectively. BCCT thus showed the best adsorption for the dye at all temperatures from the Elovich model. These results confirmed the successful introduction of a polyaminated and cross-linked extended structure as a modification for the BCCT adsorbent, which makes it resistant to acid hydrolysis and gives it the functional amine group for dye adsorption, thereby promoting the ability of BCCT to adsorb dyes under strongly acidic conditions. The compound synthesized in this study is expected to be a good choice in the future for purifying strongly acidic effluent containing anionic organic dyes.

Basic Dye Removal with Sorption onto Low-Cost Natural Textile Fibers

Over the last several years, the trend of researchers has been to use some very low-cost materials as adsorbents. For this purpose, some already commercially used bast fibers were selected as potential adsorbent materials to remove basic dye from synthetic effluents. The adsorption of basic yellow 37 dye was studied using three different bast fibers under the names of flax, ramie, and kenaf. Their morphological structure was examined using several techniques such as scanning electron microscopy (SEM), crystallinity, X-Ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), as well as those characterizations being a useful tool to propose a mechanism of the whole adsorption process. The adsorption evaluation was achieved by studying at first the pH (12) and temperature effects (25–55 °C). Two isotherm models (Langmuir and Freundlich) were also applied to the experimental equilibrium data revealing the superiority of ramie fibers (327, 435, and 460 mg·g−1 (25 °C) for kenaf, flax, and ramie, respectively). The crucial adsorbent’s dosage was found to be 0.1 g per litre for all fibers, while the completed desorption study (eluant’s pH and reuse cycles) also confirmed the strong potential of these kinds of fibers as adsorbents. The latter may be attributed to the cellulosic content.

Current characterization methods for cellulose nanomaterials

A new family of materials comprised of cellulose, cellulose nanomaterials (CNMs), having properties and functionalities distinct from molecular cellulose and wood pulp, is being developed for applications that were once thought impossible for cellulosic materials. Commercialization, paralleled by research in this field, is fueled by the unique combination of characteristics, such as high on-axis stiffness, sustainability, scalability, and mechanical reinforcement of a wide variety of materials, leading to their utility across a broad spectrum of high-performance material applications. However, with this exponential growth in interest/activity, the development of measurement protocols necessary for consistent, reliable and accurate materials characterization has been outpaced. These protocols, developed in the broader research community, are critical for the advancement in understanding, process optimization, and utilization of CNMs in materials development. This review establishes detailed best practices, methods and techniques for characterizing CNM particle morphology, surface chemistry, surface charge, purity, crystallinity, rheological properties, mechanical properties, and toxicity for two distinct forms of CNMs: cellulose nanocrystals and cellulose nanofibrils.

Adsorptive amputation of hazardous azo dye Congo red from wastewater: a critical review

Increasing amount of dyes in an ecosystem has propelled the search of various methods for dye removal. Amongst all the methods, adsorption occupies a prominent place in dye removal. Keeping this in mind, many adsorbents used for the removal of hazardous anionic azo dye Congo red (CR) from aqueous medium were reviewed by the authors. The main objectives behind this review article are to assemble the information on scattered adsorbents and enlighten the wide range of potentially effective adsorbents for CR removal. Thus, CR sorption by various adsorbents such as activated carbon, non-conventional low-cost materials, nanomaterials, composites and nanocomposites are surveyed and critically reviewed as well as their sorption capacities are also compared. This review also explores the grey areas of the adsorption performance of various adsorbents with reference to the effects of pH, contact time, initial dye concentration and adsorbent dosage. The equilibrium adsorption isotherm, kinetic and thermodynamic data of different adsorbents used for CR removal were also analysed. It is evident from a literature survey of more than 290 published papers that nanoparticle and nanocomposite adsorbents have demonstrated outstanding adsorption capabilities for CR. Graphical abstract ᅟ.

Aggregation of Congo red with surfactants and Ag-nanoparticles in an aqueous solution

Self aggregation, sorption, and interaction of Congo red, with cetyltrimethylammonium bromide (CTAB), sodium dodecylsulfate (SDS), Ag(+) ions and silver nanoparticles have been determined spectrophotometrically. Congo red self-aggregation was identified from UV-visible spectra due to the shrinkage in an absorption band at 495 nm. The shape of the absorbance spectrum changed entirely with increasing [Congo red] but wavelength maxima remain unchanged. The molar absorptivity was found to be 9804 mol(-1) dm(3) cm(-1) at 495 nm. Absorption spectra of Congo red with Ag(+) ions show an isosbestic point. The complex formation constant and difference in absorption coefficients were found to be 8.5 × 10(4) mol(-1) dm(3) and 11,764 mol(-1) dm(3) cm(-1), respectively. Silver nano-particles could not be used for the catalytic degradation of Congo red because it results in the formation of a strong complex with them. Sodium dodecylsulfate did not show any significant interaction with this dye. Congo red was also used as a probe to determine the critical micellar concentration of CTAB.

Decolorization of organic dyes by gold nanoflowers prepared on reduced graphene oxide by tea polyphenols

The green approaches for chemical syntheses are becoming important in various fields comprising chemical synthesis.

Development and application of methodology for rapid screening of potential amyloid probes

Herein, we demonstrate that it is possible to rapidly screen hydrophobic fluorescent aromatic molecules with regards to their properties as amyloid probes. By grinding the hydrophobic molecule with the amyloidogenic protein insulin, we obtained a water-soluble composite material. When this material is dissolved and exposed to conditions promoting amyloid formation, the protein aggregates into amyloid fibrils incorporating the hydrophobic molecule. As a result, changes in the fluorescence spectra of the hydrophobic molecule can be correlated to the formation of amyloid fibrils, and the suitability of the hydrophobic molecular skeleton as an amyloid probe can thus be assessed. As a result, we discovered two new amyloid probes, of which one is the well-known laser dye DCM. The grinding method can also be used for rapid preparation of novel composite materials between dyes and proteins, which can be used in materials science applications such as organic electronics and photonics.

Determination of Tinopal CBS-X in rice papers and rice noodles using HPLC with fluorescence detection and LC-MS/MS

To date there have been no reports of methods to determine Tinopal CBS-X. We developed a rapid and simple method to determine the Tinopal CBS-X content in rice noodles and rice papers using HPLC equipped with fluorescence detection. Heating the rice noodles and rice papers to 80°C after adding 75% methanol solution induced the release of Tinopal CBS-X from processed rice products. Tinopal CBS-X was separated using an isocratic mobile phase comprising 50% acetonitrile/water containing 0.4% tetrabutyl ammonium hydrogen sulphate at pH 8.0. The samples suspected to be positive by HPLC analysis were then confirmed by LC-MS/MS analysis. This study also investigated the Tinopal CBS-X content of three rice noodle products and two rice papers. The limits of quantification for rice papers and rice noodles were 1.58 and 1.51 µg kg(-1), respectively, and their correlation curves showed good linearity with r(2) ≥ 0.9997 and ≥ 0.9998, respectively. Moreover, rice papers had recoveries of 70.3-83.3% with precision ranging from 5.0% to 7.9%, whereas rice noodles had slightly lower recoveries of 63.4-78.7% and precisions of 8.5-11.5%. Only one rice noodle product contained Tinopal CBS-X, at around 2.1 mg kg(-1), whereas it was not detected in four other samples. Consequently, Tinopal CBS-X from rice noodles and rice papers can be successfully detected using the developed pre-treatment and ion-pairing HPLC system coupled with fluorescence detection.

A rapid, inexpensive, and semi-quantitative method for determining pollen tube extension using fluorescence

BACKGROUND

Pollen tubes extend rapidly when pollen grains are incubated in defined media. Tube extension requires many critical functions of plant cells including molecular signaling, cytoskeleton remodeling, secretion, and cell wall synthesis. Consequently, pollen tube growth has been established as a way to conduct primary screens of chemical libraries to identify compounds that perturb key cellular processes in plants.

RESULTS

Here we report a simple, inexpensive, rapid and semi-quantitative method for measurement of pollen tube growth in microtiter plates. The method relies on Congo Red binding to pollen tubes and correlates dye fluorescence to tube length.

CONCLUSIONS

This method can be used in any laboratory without specialized equipment, and has the potential to enable larger screens as chemical libraries grow and to make chemical screening accessible to researchers building specialized libraries designed to probe pathways in plant biology.

Enzymatic activity of cholesterol oxidase immobilized onto polymer nanoparticles mediated by Congo red

Poly(ethylene glycol), PEG, decorated polystyrene (PS) nanoparticles were synthesized and characterized by means of dynamic light scattering (DLS), zeta (ζ) potential measurements, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The adsorption of Congo red (CR) onto PS/PEG particles was evidenced by the decrease of ζ potential values and increase in the particles mean diameter in comparison to bare particles. Cholesterol oxidase (ChOx), the main enzyme in the oxidation of cholesterol, adsorbed onto PS/PEG and PS/PEG/CR particles, as revealed by the increase in the particles mean size and spectrophotometry. The enzymatic activity of free and immobilized ChOx was determined as a function of time by means of a coupled reaction with horseradish peroxidase. The activity of free ChOx decreased with time, while the activity of immobilized ChOx increased with time; after 1h reaction the latter was half of the former. Freeze-drying the ChOx covered PS/PEG/CR particles allowed their storage for at least one month under room conditions without loss of enzymatic activity. Conjugation effects between CR and ChOx or cholesterol evidenced by circular dichroism and spectrophotometry rendered a conformational state of ChOx, such that the enzymatic action was favored. ChOx adsorbed onto PS/PEG presents no enzymatic activity, probably due to ChOx denaturation or unfavorable orientation. Freeze-dried and freshly prepared dispersions of ChOx immobilized onto PS/PEG/CR particles yielded linear response in the cholesterol concentration range of 100mgdL(-1) (lowest limit of normal blood concentration) to 300mgdL(-1) (high risk level).

Behaviors and mechanism of acid dyes sorption onto diethylenetriamine-modified native and enzymatic hydrolysis starch

In this paper, different starches were modified by diethylenetriamine. The native starch reacted with diethylenetriamine giving CAS, whereas the enzymatic hydrolysis starch was modified by diethylenetriamine producing CAES. Adsorption capacities of CAES for four acid dyes, namely, Acid orange 7 (AO7), Acid orange 10 (AO10), Acid green 25 (AG25) and Acid red 18 (AR18) have been determined to be 2.521, 1.242, 1.798 and 1.570 mmol g(-1), respectively. In all cases, CAES has exhibited higher sorption ability than CAS, and the increment for these dyes took the sequence of AO7 (0.944 mmol g(-1))>AO10 (0.592 mmol g(-1))>AR18 (0.411 mmol g(-1))>AG25 (0.047 mmol g(-1)). Sorption kinetics and isotherms analysis showed that these sorption processes were better fitted to pseudo-second-order equation and Langmuir equation. Chemical sorption mechanisms were confirmed by studying the effects of pH, ionic strength and hydrogen bonding. Thermodynamic parameters of these dyes onto CAES and CAS were also observed and it indicated that these sorption processes were exothermic and spontaneous in nature.

Removal of methylene blue from aqueous solution with silica nano-sheets derived from vermiculite

The adsorption kinetics of a cationic dye, methylene blue (MB), onto the silica nano-sheets derived from vermiculite via acid leaching was investigated in aqueous solution in a batch system with respect to contact time, initial dye concentration, pH, and temperature. Experimental results have shown that increasing initial dye concentration favors the adsorption while the acidic pH and temperature go against the adsorption. Experimental data related to the adsorption of MB on the silica nano-sheets under different conditions were applied to the pseudo-first-order equation, the pseudo-second-order equation and the intraparticle diffusion equation, and the rate constants of first-order adsorption (k(1)), the rate constants of second-order adsorption (k(2)) and intraparticle diffusion rate constants (k(int)) were calculated, respectively. The experimental data fitted very well the pseudo-second-order kinetic model. The activation energy of system (E(a)) was calculated as 3.42 kJ/mol. The thermodynamics parameters of activation such as Gibbs free energy, enthalpy, entropy were also evaluated and found that DeltaG*, DeltaH*, and DeltaS* are 65.95 (71.63, 77.45)kJ/mol, 0.984 (0.776, 0.568)kJ/mol, and -0.222 (-0.223, -0.224)kJ/(Kmol) at 20 (45, 70) degrees C, respectively. The desorption of the dye on the silica nano-sheets using ethanol was also investigated primarily.

Sorption of a fluorescent whitening agent (Tinopal CBS) onto modified cellulose fibers in the presence of surfactants and salt

The combined effect of salt (10 mmol L(-1)) and surfactants on the sorption of the fluorescent brightener 4,4'-distyrylbiphenyl sodium sulfonate (Tinopal CBS) onto modified cellulose fibers was studied. Sorption efficiencies with both cationic and anionic surfactants were evaluated. Emission spectroscopy was used for quantitative analysis since Tinopal has an intense fluorescence. The sorption efficiency of the brightener is greater for solutions containing a cationic surfactant (DTAC) below the critical micelle concentration (cmc), while for an anionic surfactant (SDS) above its cmc the efficiency is greater. The profile of the sorption isotherms were interpreted in terms of the evolution of surfactant aggregation at the fiber/solution interface. Salt influences the efficiency of the Tinopal sorption on the modified cellulose fibers either because it decreases the cmc of the surfactants or because the ions screen the surface charges of the fiber which decreases the electrostatic interaction among the charged headgroup of the surfactant and the charged fiber surface.

Role of surfactants in the sorption of the whitening agent Tinopal CBS onto viscose fibers: a fluorescence spectroscopy study

In the present work, we studied the role of an anionic surfactant, sodium dodecyl sulfate, and a cationic surfactant, dodecyltrimethylammonium chloride, in the sorption of 4,4'-distyrylbiphenyl sodium sulfonate (Tinopal CBS) onto modified cellulose fibers. Fluorescence spectroscopy was used to quantify the amount of sorbed Tinopal CBS on the fiber surface. Differences in the spectral properties and the efficiency of sorption of the whitener/surfactant/fiber system are explained in terms of electrostatic interactions. Our results also show that the sorption efficiency is greater for solutions containing cationic surfactants only below the critical micelle concentration, while anionic surfactants show a smooth influence on the sorption process.

Microstructural imaging of early gel layer formation in HPMC matrices

A real-time confocal fluorescence imaging method has been developed which allows the critical early stages of gel layer formation in hydroxypropylmethylcellulose (HPMC) matrices to be examined. Congo Red, a fluorophore whose fluorescence is selectively intensified when bound to beta-D-glucopyranosyl sequences, has allowed mapping of hydrated polymer regions within the emerging gel layer, and revealed for the first time, the microstructural sequence of polymer hydration during development of the early gel layer. Liquid penetration and swelling can be examined in unprecedented detail. The earliest images revealed an initial phase of liquid ingress into the tablet pore network, followed by the progressive formation of a coherent gel layer by outward columnar swelling and coalescence of hydrated HPMC particles. Salts can markedly affect HPMC matrix behaviour. Gel layer growth in 0.1-0.5 M NaCl was progressively suppressed until at 0.75 M, particles clearly failed to coalesce into a gel layer, although with considerable polymer swelling. The failure to form a limiting diffusion barrier resulted in enhanced liquid penetration of the core, and the swelling of particles that did not coalesce culminated in surface disintegration. This provides direct evidence of physical mechanisms that contribute to salts accelerating drug release from HPMC matrices.