Encapsulation efficiency measured on single small unilamellar vesicles

In this communication we present a fluorescent based method to measure the encapsulation efficiency in single small unilamellar vesicles. The single small unilamellar vesicles are loaded with a dye in the membrane and a dye in the lumen. They are immobilized on a surface and then imaged with a fluorescent microscope. The dye in the membrane is used to determine the vesicle size, and the lumen dye is used to determine the absolute amount of encapsulant. The correlation of the two signals allows us to calculate the encapsulation efficiency in a single vesicle as a function of size. We discovered that the encapsulation efficiency is inversely proportional to the vesicle radius and that a significant number of vesicles are empty. Both observations would be averaged out in bulk experiments. They pertain for vesicles prepared through the rehydration technique but may be relevant for other formulations as well.     

Electroactive self-assembled monolayers: Laviron's interaction model extended to non-random distribution of redox centers

The Laviron's interaction model, dedicated to randomly distributed electroactive adsorbed species, was extended to a non-random distribution in order to extract the current–voltage characteristics from any surface distribution of electroactive centers on self-assembled monolayer (SAM). Confronted to electrochemical behaviour of nitroxyl radical SAMs, the agreement observed between theory and experiments provides evidence of a distribution independence of the interaction parameters.     

Tailoring the properties of thermoplastic starch by blending with cinnamyl alcohol and radiation processing: An insight into the competitive grafting and scission reactions

The present paper focuses on the effects of electron beam (EB) irradiation on thermoplastic materials based on destructurized starch including glycerol and water as plasticizers to assess the potentiality of cinnamyl alcohol as reactive additive capable of counterbalancing the degradation of the polysaccharide by inducing interchain covalent linkages. The tensile properties at break of test specimens of controlled composition submitted to EB irradiation at doses ranging from 50 to 200 kGy revealed the presence of competitive chain scission and bridging in samples containing cinnamyl alcohol at a relative concentration of 2.5% with regard to dry starch. The occurrence of crosslinking under particular conditions was evidenced by gel fraction measurements. The treatment under radiation was also applied to model blends including maltodextrin as a model for starch and the other ingredients to gain an insight into the radiation induced mechanisms at the molecular level. The presence of cinnamyl alcohol is found to limit degradation. Size exclusion chromatography and gel fraction allowed to monitor the effects and confirmed unambiguously the attachment of UV-absorbing chromophores onto the maltodextrin main chain. The combination of the obtained results demonstrates the possibility of altering in a favorable way the tensile properties of plasticized starch by applying high energy radiation to properly formulated blends including aromatic compounds like cinnamyl alcohol.     

Comparison of Vibrational Spectroscopic Techniques for Quantification of Water in Natural Deep Eutectic Solvents

Vibrational spectroscopic techniques, i.e., attenuated total reflectance infrared (ATR-IR), near infrared spectroscopy (NIRS) and Raman spectroscopy (RS), coupled with Partial Least Squares Regression (PLSR), were evaluated as cost-effective label-free and reagent-free tools to monitor water content in Levulinic Acid/L-Proline (LALP) (2:1, mol/mol) Natural Deep Eutectic Solvent (NADES). ATR-IR delivered the best outcome of Root Mean Squared Error (RMSE) of Cross-Validation (CV) = 0.27% added water concentration, RMSE of Prediction (P) = 0.27% added water concentration and mean % relative error = 2.59%. Two NIRS instruments (benchtop and handheld) were also compared during the study, respectively yielding RMSECV = 0.35% added water concentration, RMSEP = 0.56% added water concentration and mean % relative error = 5.13% added water concentration, and RMECV = 0.36% added water concentration, RMSEP = 0.68% added water concentration and mean % relative error = 6.23%. RS analysis performed in quartz cuvettes enabled accurate water quantification with RMECV = 0.43% added water concentration, RMSEP = 0.67% added water concentration and mean % relative error = 6.75%. While the vibrational spectroscopic techniques studied have shown high performance in relation to reliable determination of water concentration, their accuracy is most likely related to their sensitivity to detect the LALP compounds in the NADES. For instance, whereas ATR-IR spectra display strong features from water, Levulinic Acid and L-Proline that contribute to the PLSR predictive models constructed, NIRS and RS spectra are respectively dominated by either water or LALP compounds, representing partial molecular information and moderate accuracy compared to ATR-IR. However, while ATR-IR instruments are common in chemistry and physics laboratories, making the technique readily transferable to water quantification in NADES, Raman spectroscopy offers promising potential for future development for in situ, sample withdrawal-free analysis for high throughput and online monitoring.     

A New Alternative Tool to Analyse Glycosylation in Monoclonal Antibodies Based on Drop-Coating Deposition Raman imaging: A Proof of Concept

Glycosylation is considered a critical quality attribute of therapeutic proteins as it affects their stability, bioactivity, and safety. Hence, the development of analytical methods able to characterize the composition and structure of glycoproteins is crucial. Existing methods are time consuming, expensive, and require significant sample preparation, which can alter the robustness of the analyses. In this context, we developed a fast, direct, and simple drop-coating deposition Raman imaging (DCDR) method combined with multivariate curve resolution alternating least square (MCR-ALS) to analyze glycosylation in monoclonal antibodies (mAbs). A database of hyperspectral Raman imaging data of glycoproteins was built, and the glycoproteins were characterized by LC-FLR-MS as a reference method to determine the composition in glycans and monosaccharides. The DCDR method was used and allowed the separation of excipient and protein by forming a “coffee ring”. MCR-ALS analysis was performed to visualize the distribution of the compounds in the drop and to extract the pure spectral components. Further, the strategy of SVD-truncation was used to select the number of components to resolve by MCR-ALS. Raman spectra were processed by support vector regression (SVR). SVR models showed good predictive performance in terms of RMSECV, R²_CV.     

Reinvestigation of the synthesis of “covalent-assembly” type probes for fluoride ion detection. Identification of novel 7-(diethylamino)coumarins with aggregation-induced emission properties

An unprecedented C-3 functionalization of 4-(diethylamino)salicylaldehyde through a Friedel-Crafts type alkylation reaction has been discovered during the synthesis of “covalent-assembly”-based fluorescent probes for detection of fluoride ions. The resulting Friedel-Crafts adduct was successfully used for the preparation of two novel 8-substituted 7-(diethylamino)coumarin dyes. The photophysical study of these fluorophores has enabled us to highlight their remarkable aggregation-induced emission (AIE) properties characterized by a yellow-orange emission of aggregates in water. Therefore, 4-(tert-butyldimethylsilyloxy)benzyl substituent was identified as a novel AIE-active moiety which could be seen as a possible alternative to popular tetraphenylethylene (TPE).     

A micromechanics-based model for sand-silt mixtures

Experimental observations have shown the significant impact of fines or coarse grains on the behavior of sand-silt mixtures. To describe the behavior of sand-silt mixtures under both drained and undrained conditions, this paper presents a mathematical model based on a micromechanical approach. The novelty of this model is the introduction of the equivalent mean size and the evolution of the position of the critical state line with fines content for various sand-silt mixtures. The predictive capability of the model was evaluated by comparing the model simulations with experimental results on undrained triaxial tests of Foundry sand-silt mixtures with fines content, f_c = 0–100% and Ottawa sand-silt mixtures with fines content f_c = 0–50%, and on drained triaxial tests of Hong Kong Completely Decomposed Granite (HK-CDG) mixtures before and after erosion. The predicted local behavior in the contact planes has also been examined. It shows that all local contact planes are mobilized to different degrees in terms of local stress and strain and that a few active contact planes contribute dominantly to the deformation of the assembly, leading to an anisotropic global behavior when the soil is subjected to external loading.     

Characterization of the mechanical properties of cross-linked serum albumin microcapsules: effect of size and protein concentration

A microfluidic technique is used to characterize the mechanical behavior of capsules that are produced in a two-step process: first, an emulsification step to form droplets, followed by a cross-linking step to encapsulate the droplets within a thin membrane composed of cross-linked proteins. The objective is to study the influence of the capsule size and protein concentration on the membrane mechanical properties. The microcapsules are fabricated by cross-linking of human serum albumin (HSA) with concentrations from 15 to 35 % (w/v). A wide range of capsule radii (～40–450 μm) is obtained by varying the stirring speed in the emulsification step. For each stirring speed, a low threshold value in protein concentration is found, below which no coherent capsules could be produced. The smaller the stirring speed, the lower the concentration can be. Increasing the concentration from the threshold value and considering capsules of a given size, we show that the surface shear modulus of the membrane increases with the concentration following a sigmoidal curve. The increase in mechanical resistance reveals a higher degree of cross-linking in the membrane. Varying the stirring speed, we find that the surface shear modulus strongly increases with the capsule radius: its increase is two orders of magnitude larger than the increase in size for the capsules under consideration. It demonstrates that the cross-linking reaction is a function of the emulsion size distribution and that capsules produced in batch through emulsification processes inherently have a distribution in mechanical resistance.