Aqueous Buffer Medium Research Articles

Assessing the Quality of Solvent-Assisted Lipid Bilayers Formed at Different Phases and Aqueous Buffer Media: A QCM-D Study.

Supported lipid bilayers (SLBs) are low-complexity biomimetic membranes, serving as popular experimental platforms to study membrane organization and lipid transfer, membrane uptake of nanoparticles and biomolecules, and many other processes. Quartz crystal microbalance with dissipation monitoring has been utilized to probe the influence of several parameters on the quality of SLBs formed on Au- and SiO2-coated sensors. The influence of the aqueous medium (i.e., buffer type) and the adsorption temperature, above and below the lipid melting point, is neatly explored for SLBs of 1,2-dimyristoyl-sn-glycero-3-phosphocholine and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine formed by a solvent exchange. Below the lipid melting temperature, quality variations are observed upon the formation on Au and SiO2 surfaces, with the SLBs being more homogeneous for the latter. We further investigate how the buffer affects the detection of lipid melting in SLBs, a transition that necessitates high-sensitivity and time-consuming surface-sensitive techniques to be detected.

Pyrene-Appended Boronic Acids on Graphene Foam Electrodes Provide Quantum Capacitance-Based Molecular Sensors for Lactate.

Molecular recognition and sensing can be coupled to interfacial capacitance changes on graphene foam surfaces linked to double layer effects and coupled to enhanced quantum capacitance. 3D graphene foam film electrodes (Gii-Sens; thickness approximately 40 μm; roughness factor approximately 100) immersed in aqueous buffer media exhibit an order of magnitude jump in electrochemical capacitance upon adsorption of a charged molecular receptor based on pyrene-appended boronic acids (here, 4-borono-1-(pyren-2-ylmethyl)pyridin-1-ium bromide, or abbreviated T1). This pyrene-appended pyridinium boronic acid receptor is employed here as a molecular receptor for lactate. In the presence of lactate and at pH 4.0 (after pH optimization), the electrochemical capacitance (determined by impedance spectroscopy) doubles again. Lactic acid binding is expressed with a Hillian binding constant (Klactate = 75 mol-1 dm3 and α = 0.8 in aqueous buffer, Klactate = 460 mol-1 dm3 and α = 0.8 in artificial sweat, and Klactate = 340 mol-1 dm3 and α = 0.65 in human serum). The result is a selective molecular probe response for lactic acid with LoD = 1.3, 1.4, and 1.8 mM in aqueous buffer media (pH 4.0), in artificial sweat (adjusted to pH 4.7), and in human serum (pH adjusted to 4.0), respectively. The role of the pyrene-appended boronic acid is discussed based on the double layer structure and quantum capacitance changes. In the future, this new type of molecular capacitance sensor could provide selective enzyme-free analysis without analyte consumption for a wider range of analytes and complex environments.

Endoplasmic reticulum-targeted fluorescent probes for metal-free tracking of carbon monoxide in living cells

Endoplasmic Reticulum (ER) targetable fluorescent probes, ER-NapNO2 and ER-NapAllyl, have been designed and synthesized based on 1,8-naphthalimide fluorophore, for the selective and targeted detection of carbon monoxide (CO) in aqueous buffer medium of pH 7.4 at 37 °C. ER-targetable moiety, methyl sulfonamide unit, was attached with the one part with the fluorophore and another part was connected with CO reactive zone i.e. 4-nitrobenzyle and allyl group. Very weak fluorescence signals were observed with both the probes due to the possible PET process operating from naphthalimide moiety to electron withdrawing units i.e. -NO2 and allyl group. Interestingly, both of the probes exhibited their selective detection behavior towards CO in aqueous reaction buffer in absence of any metal ions e.g., palladium, rhodium, iron etc. The possible expulsion of highly fluorescent naphthalimide-derivative was identified from the reaction mixture during the reaction of both the probes and CO. The detection technique is found to highly selective towards CO over various reactive oxygen, nitrogen, sulfur, and other biological species with low detection limit, 0.080 µM and 0.161 µM of ER-NapNO2 and ER-NapAllyl respectively. Theoretical study using time dependent density functional theory (TDDFT) optimized the end-products formed after the reaction with CO and probes which excellently corroborate with the experimental observation. Also, the sensing reactions are exothermic with computed free energy changes for ER-NapNO2 and ER-NapAllyl are − 158.74 kcal/mol and − 28.51 kcal/mol respectively. Cellular confocal fluorescence microscopic experiments showed that these probes are also efficient to detect CO in ER specific regions in living cells.

Molecular Recognition of Imidazole-Based Drug Molecules by Cobalt(III)- and Zinc(II)-Coproporphyrins in Aqueous Media.

The methods of 1H NMR, spectrophotometric titration, mass spectrometry and elemental analysis are applied to determine the selective binding ability of Co(III)- and Zn(II)-coproporphyrins I towards a series of imidazole-based drug molecules with a wide spectrum of pharmacological activity (metronidazole, histamine, histidine, tinidazole, mercazolil, and pilocarpine) in phosphate buffer (pH 7.4) simulating the blood plasma environment. It is shown that in aqueous buffer media, Co(III)-coproporphyrin I, unlike Zn(II)-coproporphyrin I, binds two imidazole derivatives, and the stability of mono-axial Co-coproporphyrin imidazole complexes is two to three orders of magnitude higher than that of similar complexes of Zn-coproporphyrin I. The studied porphyrinates are found to have the highest binding ability to histamine and histidine due to the formation of two additional hydrogen bonds between the carboxyl groups of the porphyrinate side chains and the binding sites of the ligands in the case of histidine and a hydrogen bond between the amino group of the ligand and the carbonyl oxygen atom of the carboxyl group of the porphyrinate in the case of histamine. The structures of the resulting complexes are optimized by DFT quantum chemical calculations. The results of these studies may be of use in the design of biosensors, including those for the detection, control and verification of various veterinary drug residues in human food samples.

A new injectable quick hardening anti-collapse bone cement allows for improving biodegradation and bone repair.

The development of injectable cement-like biomaterials via a minimally invasive approach has always attracted considerable clinical interest for modern bone regeneration and repair. Although α-tricalcium phosphate (α-TCP) powders may readily react with water to form hydraulic calcium-deficient hydroxyapatite (CDHA) cement, its long setting time, poor anti-collapse properties, and low biodegradability are suboptimal for a variety of clinical applications. This study aimed to develop new injectable α-TCP-based bone cements via strontium doping, α-calcium sulfate hemihydrate (CSH) addition and liquid phase optimization. A combination of citric acid and chitosan was identified to facilitate the injectable and anti-washout properties, enabling higher resistance to structure collapse. Furthermore, CSH addition (5%-15%) was favorable for shortening the setting time (5-20min) and maintaining the compressive strength (10-14MPa) during incubation in an aqueous buffer medium. These α-TCP-based composites could also accelerate the biodegradation rate and new bone regeneration in rabbit lateral femoral bone defect models in vivo. Our studies demonstrate that foreign ion doping, secondary phase addition and liquid medium optimization could synergistically improve the physicochemical properties and biological performance of α-TCP-based bone cements, which will be promising biomaterials for repairing bone defects in situations of trauma and diseased bone.

Design of Ascorbic Acid Eutectic Mixtures With Sugars to Inhibit Oxidative Degradation.

L-Ascorbic acid (ASC), commonly known as vitamin C, acts as an anti-oxidant in the biological system. It is extensively used as an excipient in pharmaceutical industry, food supplements in fruit juices, and food materials due to its free radicals scavenging activity. Main drawback of ASC is its poor aqueous stability owing to the presence of lactone moiety that is easily oxidized to dehydroascorbic acid and further degraded. To improve aqueous stability and inhibit oxidative degradation, ASC was co-crystallized to constitute binary eutectic compositions with mono and di-saccharides such as glucose, sucrose, lactose, and mannitol. The eutectics were confirmed by their (single) lower melting endotherm compared to ASC and sugars, although Powder X-ray diffraction (PXRD) and Fourier transform Infrared spectroscopy (FT-IR) data confirmed the characteristics of their physical mixture. Scanning electron microscope (SEM) images of the binary eutectics confirmed their irregular morphology. The ASC eutectics exhibited improved shelf-life by 2–5-fold in weakly acidic (pH 5) and neutral (pH 7) aqueous buffer medium, whereas the eutectic with glucose enhanced shelf-life only by 1.1–1.2-fold in acidic medium (pH 3.3 and 4). Notably, stabilizing effect of the sugar eutectics decreased with increasing acidity of the medium. In addition, higher binding energy of the disaccharide eutectics partially supports the aqueous stability order of ASC in the neutral pH medium due to more number of non-bonded interactions than that of monosaccharides.

Co(III)-tetra(4-sulfonatophenyl)porphyrin complexes with bidentate ligands in aqueous buffer media

The processes of hydrophilic Co(III)-tetra(4-sulfonatophenyl)porphyrin supramolecular assembly with 4,4-bipyridyl in aqueous buffer media have been studied by UV-vis, 1D and 2D 1H NMR-spectroscopy. In the case of 1,4-diazabicyclo[2.2.2]octane, pyrazine and piperazine in aqueous solutions, no assembly was observed. Interactions of the hydrophilic Co(III)-tetraarylporphyrin with ionic micelles (cationic surfactants with different alkyl tail lengths) in buffer media were investigated. These studies were performed by the UV-vis, 1D NOESY-spectroscopy and dynamic lightscattering (DLS) methods. The metalloporphyrins were incorporated into the hydrophobic part of micelles, which led to Co(III) reduction to Co(II) in the Co-porphyrinate composition. The rate of Co(III) reduction accompanied by detachment of additional ligands coordinated on Co(III)-porphyrins or disruption of supramolecular dimers and depends on the surfactant concentration and nature. The results obtained indicate the possibility of creating supramolecular porphyrin-based assemblies with the preprogrammed lifetime (from several hours to several days) and could be used in the creation of host-guest systems for recognition, selective binding and the prolonged release of bioactive substrates as the means in the designing of biomimetic systems with effective binding affinities to heterocycles, DNA base pairs and RNA.

Supramolecular assembly of hydrophilic Co(III)-porphyrin with bidentate ligands in aqueous buffer media

The processes of hydrophilic Co(III)-tetra(4-sulfonatophenyl)porphyrin supramolecular assembly with 4,4-bipyridyl in aqueous buffer media have been studied by UV–vis, 1D and 2D 1H NMR-spectroscopy. In the case of 1,4-diazabicyclo[2.2.2]octane, pyrazine and piperazine in aqueous solutions, no assembly was observed. Interactions of the hydrophilic Co(III)-tetraarylporphyrin with ionic micelles (cationic surfactants with different alkyl tail lengths) in buffer media were investigated. These studies were performed by the UV–vis, 1D NOESY-spectroscopy and dynamic lightscattering (DLS) methods. The metalloporphyrins were incorporated into the hydrophobic part of micelles, which led to Co(III) reduction to Co(II) in the Co-porphyrinate composition. The rate of Co(III) reduction accompanied by detachment of additional ligands coordinated on Co(III)-porphyrins or disruption of supramolecular dimers and depends on the surfactant concentration and nature. The results obtained indicate the possibility of creating of supramolecular porphyrin-based assembles with the preprogrammed lifetime (from several hours to several days) and could be used in the creation of host–guest systems for recognition, selective binding and prolonged release of bioactive substrates as the means in the designing of biomimetic systems with effective binding affinities to heterocycles, DNA base pairs and RNA.

An Expeditious Approach towards the Synthesis and Application of Water-Soluble and Photostable Fluorogenic Chromones for DNA Detection.

The intensive research for hybridization probes based on organic molecules with fluorogenic properties is currently attracting particular attention due to their potential to efficiently recognize different DNA conformations and the local environment. However, most established organic chromophores do not meet the requirements of this task, as they do not exhibit good brightness in aqueous buffer media, develop aggregation and/or are not easily conjugated to oligodeoxynucleotides (ODNs) while keeping their photophysics intact. Herein, an important modification strategy was employed for a well-known fluorophore, 2-(4-(diethylamino)phenyl)-3-hydroxychromone (dEAF). Although this push–pull dye absorbs intensively in the visible range and shows emission with large Stokes shifts in all organic solvents, it is strongly quenched in water. This Achilles’ heel prompted us to implement a new strategy to obtain a series of dyes that retain all the photophysical features of dEAF in water, conjugate readily with oligonucleotides, and furthermore demonstrate sensitivity to hydration, thus paving the way for a high-performance fluorogenic DNA hybridization probe.

Supramolecular Assembly of Hydrophilic Co(Iii)-Porphyrin with Bidentate Ligands in Aqueous Buffer Media

Supramolecular Assembly of Hydrophilic Co(Iii)-Porphyrin with Bidentate Ligands in Aqueous Buffer Media

Follicular-targeted delivery of spironolactone provided by polymeric nanoparticles

This study proposes developing a topical formulation based on poly-ε-caprolactone (PCL) or methacrylic acid/methyl methacrylate copolymer (EL100) nanoparticles to enable a safer and more effective therapy of alopecia and acne with spironolactone. The effect of the size of the nanoparticle on follicular-targeted drug delivery is also verified. Compatibility studies based on thermal analyses and complementary techniques showed a small interaction of the drug with excipients, which may not compromise the drug stability. PCL nanoparticles of 180.0 ± 1.6 and 126.8 ± 1.0 nm, and EL100 nanoparticles of 102.7 ± 7.1 nm were then prepared. All nanoparticles entrapped more than 75 % of spironolactone, were physically stable, and stabilized the drug for at least 90 days. They were also non-irritant according to HET-CAM tests. Drug release from the nanoparticles was reduced in aqueous buffer media but fast when in contact with oil. Finally, in vitro skin penetration experiments revealed the largest nanoparticles (of 180 nm) targeted drug delivery to the hair follicles 5-fold (p < 0.05) more than the control solution, 2.1-fold (p < 0.05) more than nanoparticles produced with the same polymer (PCL) but with smaller size (123 nm), and 4.9-fold (p < 0.05) more than the 102-nm E100 nanoparticles. In conclusion, follicular targeting can be adjusted according to nanoparticle size, and this work succeeded in obtaining polymeric nanoparticles adequate to enable topical treatment of acne and alopecia with spironolactone.

In vitro kinetic release study of ketoprofen enantiomers from alginate metal complexes

BackgroundTo explore the release behavior of ketoprofen enantiomers from alginate-metal-complexes. Five mathematical models of drug release kinetics were investigated.ResultsBeads of alginate-metal complexes, loaded with racemic ketoprofen, were prepared by the ionotropic method. Divalent (Ca, Ba, Zn) and trivalent (Fe, Al) metals were used in the preparation of single-metal and mixed-metal alginate complexes. In vitro release experiments were carried out in an aqueous phosphate buffer medium at pH = 7.4. The concentrations of ketoprofen released enantiomers were determined using chiral HPLC technique. The obtained data were used to simulate the release kinetic of ketoprofen enantiomers using various mathematical models. The Korsmeyer-Peppas model was the best fit for Ca, Al, and Fe beads. Moreover, alginate-iron beads tend to release the drug faster than all other cases. In contrast, the drug release for alginate-barium complex was the slowest. The presence of barium in alginate mixed-metal complexes reduced ketoprofen release in the case of Fe and Zn, while it increased the release in the case of Al complex.ConclusionIn all the studied cases, ketoprofen showed very slow release for both enantiomers over a period exceeded 5 h (10 days in some cases). The release rate modification is possible using different multivalent metals, and it is also feasible by using two different metals for congealing either consecutively or simultaneously.

A new naphthalimide-Pd(II) complex as a light-up fluorescent chemosensor for selective detection of carbon monoxide in aqueous medium

A fluorescent light-up probe, MENap-Pd, was designed and synthesized to detect CO in aqueous buffer medium (pH 7.2, 37 °C). This detection was highly selective and sensitive towards CO. The probe prompted a more than 9-fold ‘turn-on’ fluorescence response to CO through the demetallation of the nonfluorescent Pd(II) complex, MENap-Pd to generate free fluorescent ligand, MENap in the reaction medium. The fluorescence response is highly selective towards relevant reactive oxygen, nitrogen, and sulfur species and also various cationic, anionic, and neutral species present in biological system. The limit of detection (LOD) of this probe for CO sensing (CORM-2) is calculated as 1.4 μM with a linear range of 0–60 μM concentration of CORM-2.

Electrical impedance spectroscopy of plant cells in aqueous buffer media over a wide frequency range of 4 Hz to 20 GHz

Electrical impedance spectroscopy was performed on suspensions of plant cells in aqueous buffer media over a wide frequency range of 4 Hz to 20 GHz. Custom probes were designed, manufactured, and used for these investigations. Experiments were performed with a custom-made parallel plate probe and impedance analysers in the low-frequency range (4 Hz to 5 MHz), with a custom-made coaxial airline probe and a vector network analyser in the mid-frequency range (100 kHz to 3 GHz), and with a commercial open-ended probe and a vector network analyser in the high-frequency range (200 MHz to 20 GHz). The impedance data acquired were processed in order to eliminate the effects of parasitics and compensate for geometrical differences between the three probes. Following this, the data were fitted to a unified model consisting of the Randles and Debye models. The data were also normalized to a reference measurement, in order to accentuate the effects of cell concentration on the impedance of the suspensions.•The methodology allows for impedance spectroscopy of cell suspensions over a wide frequency range spanning 10 orders of magnitude.•It allows for compensation of parasitics and of geometrical variations between probes, using mathematical techniques

Biocatalyzed Redox Processes Employing Green Reaction Media.

The application of biocatalysts to perform reductive/oxidative chemical processes has attracted great interest in recent years, due to their environmentally friendly conditions combined with high selectivities. In some circumstances, the aqueous buffer medium normally employed in biocatalytic procedures is not the best option to develop these processes, due to solubility and/or inhibition issues, requiring biocatalyzed redox procedures to circumvent these drawbacks, by developing novel green non-conventional media, including the use of biobased solvents, reactions conducted in neat conditions and the application of neoteric solvents such as deep eutectic solvents.

A spectroscopic deciphering of the differential interaction behavior of alkaloid drugs with native B-DNA and protonated DNA

The present study demonstrates a detailed spectroscopic investigation on the differential extent and modes of interaction of two alkaloid drugs, Sanguinarine (SG) and Berberine (BR), with biologically significant protonated and B-forms of herring sperm DNA in aqueous buffer medium of pH 3.5 and 7.4 respectively. The steady-state spectroscopic results substantiate the binding interaction of either drug molecule with protonated as well as B-form of DNA. The drug:DNA binding strength obtained employing the Benesi-Hildebrand equation reveals a significantly higher binding affinity of BR with B-DNA at pH 7.4 compared to that with protonated DNA at pH 3.5. However, the binding constant obtained for interaction of iminium form of SG with protonated DNA is found to be an order of magnitude higher compared to that in case of interaction with B-DNA. Moreover, the steady-state emission results validate the role of preferential electrostatic interaction between the cationic forms of the drugs (cationic BR and the iminium form of SG) and the negatively charged phosphate backbone of B-DNA under physiological conditions at pH 7.4 which has been further corroborated by monitoring the effect of a strong electrolyte on drug:DNA interaction under the various experimental conditions. The circular dichroic (CD) spectroscopic studies reveal the probable intercalative binding of the drug molecules within DNA at either pH. The time-resolved fluorescence decay measurements along with the time-resolved fluorescence anisotropy studies further substantiate the binding interaction of the drugs with protonated as well as B-form of herring sperm DNA.

In vitro Lipolysis as a Tool for the Establishment of IVIVC for Lipid-Based Drug Delivery Systems.

In vitro lipolysis has emerged as a powerful tool in the development of in vitro in vivo correlation for Lipid-based Drug Delivery System (LbDDS). In vitro lipolysis possesses the ability to mimic the assimilation of LbDDS in the human biological system. The digestion medium for in vitro lipolysis commonly contains an aqueous buffer media, bile salts, phospholipids and sodium chloride. The concentrations of these compounds are defined by the physiological conditions prevailing in the fasted or fed state. The pH of the medium is monitored by a pH-sensitive electrode connected to a computercontrolled pH-stat device capable of maintaining a predefined pH value via titration with sodium hydroxide. Copenhagen, Monash and Jerusalem are used as different models for in vitro lipolysis studies. The most common approach used in evaluating the kinetics of lipolysis of emulsion-based encapsulation systems is the pH-stat titration technique. This is widely used in both the nutritional and the pharmacological research fields as a rapid screening tool. Analytical tools for the assessment of in vitro lipolysis include HPLC, GC, HPTLC, SEM, Cryo TEM, Electron paramagnetic resonance spectroscopy, Raman spectroscopy and Nanoparticle Tracking Analysis (NTA) for the characterization of the lipids and colloidal phases after digestion of lipids. Various researches have been carried out for the establishment of IVIVC by using in vitro lipolysis models. The current publication also presents an updated review of various researches in the field of in vitro lipolysis.

Modulation of Semiconducting Behavior and a Change in Morphology upon Gelation of a Peptide Appended Naphthalenediimide

A dipeptide-appended naphthalenediimide (NDI) is self-assembled in an aqueous phosphate buffer medium of pH 7.5 to form nanovesicular structures. Interestingly, these molecules are assembled to for...

A Lysosome-Targetable Fluorescence Sensor for Ultrasensitive Detection of Hg2+ in Living Cells and Real Samples.

A new lysosome-targetable fluorescence sensor, Lyso-HGP, was designed and synthesized based on 4-methyl-2,6-diformylphenol as a fluorophore. Lyso-HGP displays highly sensitive fluorescent detection of Hg2+ in HEPES buffer solution (10 mM, DMSO 1%) of pH 7.0 at 37 °C due to the formation of highly fluorescent formyl-functionalized derivative Lyso-HGP-CHO. The sensor triggered a "turn-on" fluorescence response to Hg2+ with a simultaneous increase of fluorescence intensity by 180-fold just after 10 min. The response is very selective over a variety of biologically relevant cations, anions, molecules, and competitive toxic heavy metal cations. The limit of detection (LOD) was calculated as low as 6.82 nM. So, it can be utilized to detect this toxic heavy metal in biology and environmental samples in an aqueous buffer medium. Also, the sensor is able to monitor the subcellular distribution of Hg2+ specifically localized in the lysosome's compartment in the MCF7 human breast cancer cell line by fluorescence microscopy.

Rational design of a boron-dipyrromethene-based fluorescent probe for detecting Pd2+ sensitively and selectively in aqueous media.

A novel fluorescent probe for Pd2+ based on the BODIPY fluorophore exploiting the PET (Photoinduced Electron Transfer) mechanism was designed and successfully synthesized. The fluorescent probe 1 was prepared by introducing m-bisimidazolylbenzene which was connected by phenyl acetylene to the BODIPY dye at the meso position. It exhibited a rapid response and high sensitivity and selectivity toward Pd2+. Probe 1 presented a rapid quenched fluorescence response in aqueous buffer media (pH 5.5) and the detection limit estimated from the titration results was 2.9 × 10-7 M. Meanwhile, other common metal ions did not interfere with the recognition process. The DFT calculation proved that coordination of bisimidazole ligands with Pd2+ effectively decreases the LUMO energy of m-bisimidazolylbenzene which was located between the HOMO and LUMO energies of the BODIPY dye leading to fluorescence quenching via the d-PET mechanism.