Turbidimetric Measurements Research Articles

Cationic curdlan: Synthesis, characterization and application of quaternary ammonium salts of curdlan

Water-soluble curdlan derivatives containing quaternary ammonium groups with a degree of substitution up to 0.15 were synthesized using different cationic agents in alkaline medium. The chemical structure of curdlan derivatives was confirmed by FTIR, 13C and 1H NMR spectroscopy. The influence of some reaction conditions (temperature, time, and molar ratio) on the degree of substitution and the viscosimetic behaviour were studied. The degree of substitution increased with the amount of the cationization agent per anhydroglucose unit and was higher when the glycidyl reagents were used, compared with the case when the reagents contained chloro-hydroxypropyl groups. The viscosity behaviour of these new derivatives of curdlan in aqueous solutions and the values of intrinsic viscosities calculated using different semi-empirical equations denote a high hydrodynamic dimension of the macromolecular coils. The interaction of these cationic curdlan derivatives with an anionic curdlan (monobasic curdlan phosphate) was studied in situ by turbidimetric measurements and after 24h by optical density and dynamic light scattering. The formation of polyelectrolyte complexes was influenced by the degree of substitution, the nature of the quaternary substituent, and by the ionic strength of the aqueous solution. The morphology of the polyelectrolyte complexes particles in dry state was examined by atomic force microscopy.

A Novel In Vitro Approach for Simultaneous Evaluation of CYP3A4 Inhibition and Kinetic Aqueous Solubility

In the early stages of the drug discovery process, evaluation of the drug metabolism and physicochemical properties of new chemical entities is crucial to prioritize those candidates displaying a better profile for further development. In terms of metabolism, drug–drug interactions mediated through CYP450 inhibition are a significant safety concern, and therefore the effect of new candidate drugs on CYP450 activity should be screened early. In the initial stages of drug discovery, when physicochemical properties such as aqueous solubility have not been optimized yet, there might be a large number of candidate compounds showing artificially low CYP450 inhibition, and consequently potential drug–drug interaction toxicity might be overlooked. In this work, we present a novel in vitro approach for simultaneous evaluation of CYP3A4 inhibition potential and kinetic aqueous solubility (NIVA-CYPI-KS). This new methodology is based on fluorogenic CYP450 activities and turbidimetric measurements for compound solubility, and it provides a significant improvement in the use of resources and a better understanding of CYP450 inhibition data.

Intercomparison of Numerical Inversion Algorithms for Particle Size Determination of Polystyrene Suspensions Using Spectral Turbidimetry

The continuous monitoring of the particle size distribution in particulate processes with suspensions or emulsions requires measurement techniques that can be used as in situ devices in contrast to ex situ or laboratory methods. In this context, for the evaluation of turbidimetric spectral measurements, the application of different numerical inversion algorithms is investigated with respect to the particle size distribution determination of polystyrene suspensions. A modified regularization concept consisting of a Twomey-Phillips-Regularization with an integrated nonnegative constraint and a modified L-curve criterion for the selection of the regularization parameter is used. The particle size (i.e., particle diameter) of polystyrene suspensions in the rangex=0.03–3 µm was validated via dynamic light scattering and differential centrifugal sedimentation and compared to the retrieved particle size distribution from the inverted turbidimetry measurements.

Core–shell hybrid nanocapsules for oral delivery of camptothecin: formulation development, in vitro and in vivo evaluation

The objective of this study was to design and in vitro–in vivo evaluate oral nanocapsules prepared from amphiphilic cyclodextrins (CDs) or poly-e-caprolactone (PCL) for the effective oral delivery of an anticancer agent, camptothecin (CPT). CPT-loaded anionic and Chitosan (CS)-coated cationic nanocapsules were prepared and characterized in vitro. Morphological analysis was performed by scanning electron microscope (SEM). CPT release profile was evaluated using dialysis method under sink conditions. To determine the protective effect and drug stability provided by nanocapsules, all the formulations were incubated in simulated gastrointestinal media. Measurement of mucoadhesive tendency of CPT-loaded nanocapsules was realized by turbidimetric method. Penetration of nanocapsules was performed through an artificial mucus model. The permeability of CPT in solution form and bound to nanocapsule formulations were demonstrated across Caco-2 cell line. Finally, the intestinal uptake of nanocapsules was evaluated in vivo, in a mouse model. Both anionic and cationic formulations were in the range of 180–220 nm with a narrow size distribution and desired zeta potential values. CPT-loaded nanocapsules were found to be stable in simulated gastrointestinal media. Turbidimetric measurements confirmed the interaction between nanoparticles and mucin. Penetration of CPT through an artificial mucus gel layer was higher with CS-coated nanocapsules in accordance with the results obtained from permeability studies across Caco-2 cell line. In vivo animal studies confirmed that the intestinal uptake of nanocapsules was significantly higher with cationic nanocapsules. CPT-loaded positively charged CD nanocapsules might be an attractive and promising treatment for oral chemotherapy.

Screening of Bacillus coagulans strains in lignin supplemented minimal medium with high throughput turbidity measurements

The aim of this study was to extend the options for screening and characterization of microorganism through kinetic growth parameters. In order to obtain data, automated turbidimetric measurements were accomplished to observe the response of strains of Bacillus coagulans. For the characterization, it was decided to examine the influence of varying concentrations of lignin with respect to bacterial growth. Different mathematical models are used for comparison: logistic, Gompertz, Baranyi and Richards and Stannard. The growth response was characterized by parameters like maximum growth rate, maximum population, and the lag time. In this short analysis we present a mathematical approach towards a comparison of different microorganisms. Furthermore, it can be demonstrated that lignin in low concentrations can have a positive influence on the growth of B. coagulans.

Complex formation between ovalbumin and strong polyanion PSSNa: Study of structure and properties

The mixture system of long-chain polyelectrolyte complexed with a globular protein was investigated based on dynamic light scattering and turbidimetric measurements. We have discussed at different pH values the influence of high salt concentration and mass ratio (protein:PSSNa) on the behavior of the mixture. In dilute concentration regime, the PSSNa chain contracts at pHc by patch binding. We found two critical values of mass ratio: The first corresponds to the maximum shrinking of PSSNa. The second indicates the system that became more stable where the number of proteins attached to the PSSNa chain was constant. The screen of electrostatic interaction shows a high contribution of hydrophobic interaction at large salt concentration to form the coacervates. By building phase diagram, the continuity of pHφ1 in over whole range of salt concentrations and the widening of pH window (pHφ1–pHφ2) were observed. At certain salt concentrations, we can obtain the coexistence of two types of complex particles formed by electrostatic and hydrophobic interactions.

Multicommutated flow analysis system for determination of total protein in cerebrospinal fluid

A fully mechanized, computer-controlled, multicommutated flow analysis (MCFA) system dedicated for total protein determination in cerebrospinal fluid samples has been developed. For the protein determination the Exton method has been applied. Dedicated turbidimetric and nephelometric flow-through detectors operating according to paired-emitter detector diode principle have been fabricated by integration of two or three respective light emitting diodes. The developed MCFA system is characterized by robust, compact design and low consumption of the sample (72μL). The limits of detection for turbidimetric and nephelometric detection mode are 65mgL−1 and 9mgL−1, respectively. For turbidimetric measurements the range of linear response offered by the MCFA system is 72–900mgL−1, whereas in the case of nephelometric detection 18–500mgL−1 linear range is obtained. The throughput of the MCFA system is over 30 injection per hour. The analytical system was optimized with bovine serum albumin standards and successfully validated with real samples of human cerebrospinal fluid.

Mucoadhesive Properties and Interaction with P-Glycoprotein (P-gp) of Thiolated-Chitosans and -Glycol Chitosans and Corresponding Parent Polymers: A Comparative Study

The aim of the present work was to compare the mucoadhesive and efflux pump P-glycoprotein (P-gp) interacting properties of chitosan (CS)- and glycolchitosan (GCS)-based thiomers and corresponding unmodified parent polymers. For this purpose, the glycol chitosan-N-acetyl-cysteine (GCS-NAC) and glycol chitosan-glutathione (GCS-GSH) thiomers were prepared under simple and mild conditions. Their mucoadhesive characteristics were studied by turbidimetric and zeta potential measurements. The P-gp interacting properties were evaluated measuring the effects of thiolated- and unmodified-polymers on the bidirectional transport (BA/AB) of rhodamine-123 across Caco-2 cells as well as in the calcein-AM and ATPase activity assays. Although all the thiomers and unmodified polymers showed optimal-excellent mucoadhesive properties, the best mucoadhesive performances have been obtained by CS and CS-based thiomers. Moreover, it was found that the pretreatment of Caco-2 cell monolayer with GCS-NAC or GCS restores Rho-123 cell entrance by inhibiting P-gp activity. Hence, GCS-NAC and GCS may constitute new biomaterials useful for improving the bioavailability of P-gp substrates.

A New Thermosensitive Poly(N‐propionyl‐aspartic acid/ethylene glycol) with No Cytotoxicity and Tunable UCST

A new thermosensitive poly(N‐propionyl‐aspartic acid/ethylene glycol) (PPAE) with no cytotoxicity and an upper critical solution temperature (UCST) is synthesized by polycondensation of l‐aspartic acid and ethylene glycol. The chemical structures of the monomer and polymer are confirmed by FTIR and 1H NMR spectroscopy, and by elemental analysis measurements. Turbidimetric measurements indicate that PPAE shows a reversible UCST phase transition at 1.5–37.6 °C in pure water or an alcohol/water mixture. The UCST can be facilely tuned via changing the content of alcohol in water or the normal saline. Moreover, the survival rate of HeLa cells to PPAE is close to 100% within 48 h, demonstrating no cytotoxicity. Such aspartic acid‐based polymers with tunable thermosensitivity could be useful in the biomedical field. image

Are ionic liquids extremophiles cell wall breakers? Esther Gutiérrez, M. Ángeles Sanromán, Ana Rodríguez, Francisco J. Deive * Department of Chemical Engineering, University of Vigo, 36310, Vigo, Spain * Corresponding author: Tel.: +34986818723; E-mail address: deive@uvigo.es

Are ionic liquids extremophiles cell wall breakers? Esther Gutiérrez, M. Ángeles Sanromán, Ana Rodríguez, Francisco J. Deive * Department of Chemical Engineering, University of Vigo, 36310, Vigo, Spain * Corresponding author: Tel.: +34986818723; E-mail address: deive@uvigo.es

Does Long-Term Administration of a Beta-Blocker (Timolol) Induce Fibril-Based Cataract Formation In-vivo?

Timolol is a non-selective beta-adrenergic receptor antagonist administered for treating glaucoma, heart attacks and hypertension. In the present study, we set out to determine whether or not timolol can provoke cataract formation, thus the influence of timolol on the amyloid-type aggregation of crystallin was investigated. We then provided experimental evidence of crystallin aggregation and its induction by timolol using different spectroscopic measurements. Turbidimetric measurements as well as ThT fluorescence data indicated that timolol induce extent of crystallin amyloid formation. The kinetic of protein aggregation was also changed in presence of increasing concentrations of the drug suggesting that long-term drug administration may contribute to the development of cataract. Since the consequence of timolol-crystallin interaction has yet to be identified, additional data on it may help us to postpone amyloid cataract formation.

Application of Single Angle Turbidimetry on Coag-Flocculation Effect of <i>Detarium microcarpum</i> Seed in Brewery Effluent

Coagulation-flocculation is a proven technique for the removal of suspended solids in wastewater, through the application of single angle turbidimetric measurement. Through this measurement, the coag-flocculation kinetics and functional parameters behavior of Detarium microcarpumin brewery effluent with respect to pH, dosage and time were followed at room temperature. Process parameters such as order of reaction α, rate constant (K), coagulation period τ1/2 etc were determined. Results indicated that reaction order, rate constant, period, pH and dosage recorded optimum values at 2, 1.8 × 10-2 L/mg.min, 0.152 min, 4 and 100 mg/L, respectively. Maximum efficiency recorded was 96.07% at 30 min. Detarium microcarpum has shown potential as an effective bio-coagulant for the removal of turbidity from brewery effluent.

Complex coacervation in gelatin/sodium caseinate mixtures

Gelatin is a protein widely used in food, pharmaceutical and cosmetic products as an emulsifier, peptizer, thickener, and binder. Polypeptide structure of gelatin molecule facilitates its interactions with other oppositely charged ingredients often present in such products. Sodium caseinate (NaCN) due to its excellent functional and nutritional properties, is also very often used as a hydrophilic emulsifier in a wide range of dispersed systems together with other proteins, like gelatin. Since both proteins are polyelectrolytes, different type of interactions in such systems may occur. In the present study, turbidimetric, viscosimetric, surface tension, zeta potential and rheological measurements were performed in order to investigate the interactions in the mixtures of those two proteins. All these measurements showed presence of interaction between gelatin and NaCN that resulted in insoluble complex coacervate formation at certain proteins ratio.

Turbidimetry for the stability evaluation of emulsions used in machining industry

Emulsified fluids are used in many industrial and consumer areas, for instance as products in the food or health industry as well as technical fluids in the machining industry. Metalworking fluids (MWF) are used as coolants and lubricants in metalworking processes. During their usage MWF emulsions may change their physical and chemical properties, which influences their performance and decrease the physical stability and therefore their lifetime. This article discusses results of turbidimetric spectra measurement of MWF emulsions to be used for process control, MWF quality monitoring and formulation purposes. Therefore, laboratory experiments have been carried out investigating the physical stability. Metal working emulsions have been treated and destabilised by different concentrations of salts. The destabilisation process was monitored by undiluted turbidity measurements and evaluated by the temporal change of the wavelength exponent. Thus, it was possible to determine specific conditions, for example a specific critical salt concentration for maintaining, stability of the MWF formulations.

Turbidimetric and intrinsic viscosity study of EVA copolymer–solvent systems

Both Hansen solubility parameter and Flory–Huggins interaction parameter of two EVA [Poly(ethylene-co-vinyl acetate)] copolymers with different vinyl acetate content have been obtained by means of intrinsic viscosity measurements. To calculate this last parameter it was also necessary to determine the theta solvent at different temperatures of the two EVA copolymers with turbidimetric measurements. The results indicate that the vinyl acetate content is a variable which influences the composition of the theta solvent and Flory–Huggins parameter (the higher the vinyl acetate content, the lower the Flory–Huggins parameter), although its influence over the Hansen solubility parameter is almost negligible.

Glycopolyoxazoline-lectin interactions. Effects of ligand structure on clustering kinetics

Turbidimetric measurements were used to examine the clustering of concanavalin A (Con A) with glucosylated polyoxazolines. For homopolymers, and also block copolymers, precipitation of Con Aoccured faster with longer glucoslyated chains and higher valency of the ligand. For statistical copolymers, the same trend was observed for increasing spacing between glucose residues or decreasing epitope density. Also the nature of the non-binding side chains appeared to have impact on the clustering kinetics.

Elaboration of Glycopolymer-Functionalized Micelles from anN-Vinylpyrrolidone/Lactide-Based Reactive Copolymer Platform

Glycopolymer-corona-based micelles are obtained in a one-pot procedure, through reaction of D-mannosamine or D-glucosamine with the N-succinimidyl (NS) esters of a poly(D,L-lactide)-block-poly(N-acryloxysuccinimide-co-N-vinylpyrrolidone) (PLA-b-P(NAS-co-NVP)) amphiphilic copolymer (presenting quasi-alternating NAS/NVP units) in dimethyl sulfoxide (DMSO), followed by nanoprecipitation and dialysis against water. The glycopolymer micelles exhibit a higher CMC and size than those obtained from unmodified copolymer, due to increased hydrophilicity of the external block as a result of sugar derivatization, and the availability of the sugars at the micelle surface is evidenced through interactions with Concanavalin A (Con A) lectin, as attested by turbidimetric measurements and enzyme-linked lectin assay (ELLA). Interestingly, the glycopolymer micelles can be further used for hydrophobic molecule encapsulation and release, as shown with imiquimod, while keeping their interactions with con A intact. It is concluded that the PLA-based amphiphilic/reactive copolymer represents a versatile platform for glycopolymer-based micelle constructs for drug/vaccine delivery.

Nephelometry and turbidimetry with paired emitter detector diodes and their application for determination of total urinary protein

Two miniature and compact optoelectronic devices fabricated by means of integration of light emitting diodes have been developed for turbidimetric and nephelometric measurements. These devices are operating according to paired-emitter-detector-diode (PEDD) principle. The detectors have been characterized using bovine serum albumin and Exton protein assay as a model analyte and a model analytical method, respectively. The developed detectors have been adapted for measurements under conditions of flow injection analysis (FIA). Under optimized conditions the turbidimetric flow system offers the range of linear response up to 400mgL−1 with the detection limit at 20mgL−1. The linear range and detection limit found for optimized nephelometric FIA system are 15–500mgL−1 and 8mgL−1, respectively. The PEDD-based FIA systems with the detector operating according to both modes of measurements have been successfully applied for urinalysis offering total protein determination at physiological and pathological levels with high throughput (over 60 injections per hour).

Formation and functionality of soluble and insoluble electrostatic complexes within mixtures of canola protein isolate and (κ-, ι- and λ-type) carrageenan

The formation of electrostatic complexes between a canola protein isolate (CPI) and (κ-, ι-, and λ-type) carrageenan (CG) was investigated as a function of pH (1.50–7.50) and biopolymer weight mixing ratio (1:1–75:1, CPI–CG) by turbidimetric measurements during an acid titration. The addition of CG to CPI suppressed CPI–CPI aggregation. Critical pHs designating structure forming events (pHc, pHϕ1 — soluble and insoluble complexes, respectively) shifted to more acidic pHs as the mixing ratio increased then plateaued at the 15–20:1 ratio. The functional properties (solubility, foaming capacity/stability, emulsion capacity, emulsion stability) of the complexes (20:1, CPI–CG) at pHc (6.75) and pHϕ1 (5.00) were compared to CPI alone. At both pHs, solubility, foaming capacity and emulsion capacity of CPI were reduced upon complexation with CG. Emulsion stability of the complexes was high at ~87–96% depending on pH and CG type. Differences in functionality based on CG type were related to the structure and charge of the CG molecules. The pH of net neutrality was reduced from pH5.78 for CPI alone to pH5.35 for CPI–κ-CG and pH4.95 for both CPI–κ-CG and CPI–ι-CG.

Analysis of the Stability of Metal Working Fluid Emulsions by Turbidity Spectra

AbstractThe physical stability of emulsions can be related to changes in the droplet size distribution over time. Stability control of emulsions used as metal working fluids is an important factor for the machining industry due to the decreased performance of aged and broken emulsions. Results of turbidimetric spectra measurements of metal working fluids for process control purposes and emulsion stability monitoring are discussed. Metal working emulsions were artificially destabilized by admixing salts which resulted in droplet coagulation. The destabilization process was investigated by measuring the droplet size distribution and the turbidity spectra over time. The results were evaluated based on quantitative criteria proposed in the literature. The applicability of these criteria to evaluate metal working fluids during machining operations is discussed.