pH-dependent Morphology Research Articles

PH-Dependent Morphology of Copper (II) Oxide in Hydrothermal Process and Their Photoelectrochemical Application for Non-Enzymatic Glucose Biosensor

In this study, we investigated the influence of pH on the hydrothermal synthesis of copper (II) oxide CuO nanostructures with the aim of tuning their morphology. By varying the pH of the reaction medium, we successfully produced CuO nanostructures with three distinct morphologies including nanoparticles, nanorods, and nanosheets according to the pH levels of 4, 7, and 12, respectively. The observed variations in surface morphology are attributed to fluctuations in growth rates across different crystal facets, which are influenced by the presence of intermediate species within the reaction. This report also compared the structural and optical properties of the synthesized CuO nanostructures and explored their potential for photoelectrochemical glucose sensing. Notably, CuO nanoparticles and nanorods displayed exceptional performance with calculated limits of detection of 0.69 nM and 0.61 nM, respectively. Both of these morphologies exhibited a linear response to glucose within their corresponding concentration ranges (3–20 nM and 20–150 nM). As a result, CuO nanorods appear to be a more favorable photoelectrochemical sensing method because of the large surface area as well as the lowest solution resistance in electroimpedance analysis compared to CuO nanoparticles and nanosheets forms. These findings strongly suggest the promising application of hydrothermal-synthesized CuO nanostructures for ultrasensitive photoelectrochemical glucose biosensors.

On the assembly of zwitterionic block copolymers with phospholipids

Materials containing zwitterionic polymers are interesting candidates for diverse applications due to their versatile properties. The assembly of the amphiphilic block copolymer poly(cholesteryl methacrylate)-block-poly(2-methacryloyloxyethyl phosphorylcholine) with three different phospholipids (1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1,2-dioleoyl-sn-glycero-3-phospho-l-serine (DOPS) and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE)) into small and giant vesicles is reported focusing on their morphology, size, and membrane properties. Giant hybrid vesicles were obtained for all types of lipids, but DOPC was more suitable to assemble small hybrid vesicles without a large fraction of hybrid micelles present. Further, the permeability of the small vesicle membranes towards 5(6)-carboxyfluorescein is very similar to comparable sized liposomes. In contrast, the permeability of the giant hybrid vesicle membranes towards 5(6)-carboxy-X-rhodamine is higher compared to only cholesterol-containing lipid giant vesicles. DOPS-containing vesicles showed pH-dependent morphology changes. Hybrid vesicles containing DOPS and DOPE in addition to the block copolymer have the highest association with HepG2 cells. In contrast, only DOPC-containing hybrid vesicles can be incorporated into alginate beads. Taken together, using these block copolymer with a zwitterionic hydrophilic extension of the chosen architecture offers fundamental insight into the possibility to assemble hybrid vesicles and their potential in bottom-up synthetic biology.

PH dependent morphology and texture evolution of ZnO nanoparticles fabricated by microwave-assisted chemical synthesis and their photocatalytic dye degradation activities

ZnO nanostructures are well-known photocatalysts for the degradation of toxic organic dyes and their morphology, size, and other physicochemical properties play important roles in their photocatalytic performance. To study the effect of size, morphology, and synthesis conditions in photocatalytic performance, we synthesized ZnO nanoparticles of different morphologies through a simple microwave-assisted chemical process at different pH values of the reaction mixture. Different pH values of the reaction mixture produced ZnO nanoparticles of different morphologies and sizes. The nature of the pH controlling agent and final pH of the reaction mixture were seen to have considerable effects on the lattice parameters and microstrain of the ZnO nanocrystals, along with their photocatalytic performance. We observed that while the ZnO nanostructures synthesized at very high pH values of the reaction mixture have a high specific surface area, their photocatalytic activity is higher when they are synthesized at acidic pH or pH near the isoelectric point of ZnO. The results demonstrate that the photocatalytic activity of ZnO nanostructures not only depends on their size or specific surface area but also strongly depends on the concentration of catalytic sites at their surface.

Effect of pH dependent morphology on room temperature NH3 sensing performances of β-Ga2O3

— β-Ga2O3 powders were synthesized by hydrothermal method at different pH values ranging from 5 to 14. Obtained powder samples, showed polycrystalline nature and monoclinic crystalline structure upon investigation through XRD. The micrographs of powder samples resulted from SEM investigations showed different morphologies ranging from basic to hierarchical structures as pH value changes. Extremely alkaline solution (with pH = 14) caused to yield hierarchical morphologies whereas the acidic solution (with pH = 5) ensued basic rod-like morphologies. Cocoon shaped morphology was maintained from neutral (pH = 7) to moderately basic (pH = 11) conditions. Optical band gaps of the samples were calculated from Kubelka-Munk plot resulted from the data obtained by UV–Visible spectroscopic analysis. Synthesized β-Ga2O3 powder samples were drop casted on glass substrate which was pre-printed with Inter Digitated Electrode pattern (IDE) of Silver (Ag) ink. These drop coated thick films are then used for the different concentrations of NH3 vapor detection at room temperature. Morphology based model proposed for room temperature NH3 sensing. It has been observed that β-Ga2O3 prepared under pH = 14 showed higher response and sensitivity due to its hierarchy in morphology and relatively lower band gap of 4.61 eV.

PH-Dependent morphology and optical properties of lysine-derived molecular biodynamers

The spherical micelles of the carbazole monomer transformed into nanorods in the course of the polymerization. The polymeric nanorods show pH-dependent changes in fluorescence emission and size.

Improvement of the Photocatalytic Activity of ZnO/Burkeite Heterostructure Prepared by Combustion Method

In this work, a novel route is discussed to produce in one step ZnO/Burkeite powders by the modified solution combustion method. The ZnO particles enhance the photocatalytic activity in the degradation of Rhodamine B, in which Burkeite mineral acts as a support due to the pH-dependent morphology of the particle aggregates of the as-synthesized powders. The X-ray diffraction (XRD) characterization shows the presence of a heterostructure: ZnO/Burkeite. The Scanning Electron Microscopy (SEM) image shows a morphological dependence with the pH of the solution used for the synthesis. The results show that the system with the highest degradation (92.4%) corresponds to the case in which ZnO/Burkeite heterostructure was synthesized with a pH 11.

PH-Responsive Polypeptide-Based Smart Nano-Carriers for Theranostic Applications.

Smart nano-carriers have attained great significance in the biomedical field due to their versatile and interesting designs with different functionalities. The initial stages of the development of nanocarriers mainly focused on the guest loading efficiency, biocompatibility of the host and the circulation time. Later the requirements of less side effects with more efficacy arose by attributing targetability and stimuli-responsive characteristics to nano-carriers along with their bio- compatibility. Researchers are utilizing many stimuli-responsive polymers for the better release of the guest molecules at the targeted sites. Among these, pH-triggered release achieves increasing importance because of the pH variation in different organ and cancer cells of acidic pH. This specific feature is utilized to release the guest molecules more precisely in the targeted site by designing polymers having specific functionality with the pH dependent morphology change characteristics. In this review, we mainly concert on the pH-responsive polypeptides and some interesting nano-carrier designs for the effective theranostic applications. Also, emphasis is made on pharmaceutical application of the different nano-carriers with respect to the organ, tissue and cellular level pH environment.

Self-assembly pH-sensitive chitosan/alginate coated polyelectrolyte complexes for oral delivery of insulin

Polyelectrolyte complexes (PEC) provide new opportunities for controlled release system of drugs, and have potentials to address challenges on the way to effective oral insulin delivery. Here, an innovative pH-sensitive PEC for insulin oral administration was developed, which was formed by self-assembly of two oppositely charged nanoparticles (chitosan-coated nanoparticles and alginate-coated nanoparticles) through electrostatic interaction via optimised double emulsion method. The encapsulation efficiency of insulin-loaded alginate-coated and chitosan-coated nanoparticles were 81.5 ± 7.4% and 55.2 ± 7.0%, respectively, and the particle size of these nanoparticles were in 200–300 nm range. The pH-dependent morphology of PEC was observed by transmission electron microscopy. The PEC exhibited insulin release profile triggered by pH in vitro and was non-cytotoxicity against Caco-2 cell. The insulin-loaded PEC could decrease blood glucose levels effectively and prolong insulin release after oral administration to diabetic rats. The results illustrated that the as-prepared PEC may be employed as a potential oral insulin delivery system.

PH-dependent morphology and its effect on the optical properties of LaF3:Nd nanocrystals

Nd3+-doped LaF3 nanocrystals with different morphologies have been produced via solvothermal method at various pH values (1–6). Their morphologies and optical properties were characterized by TEM, fluorescence spectra and decay curves. A possible formation mechanism including burst-nucleation and growth process was proposed. The results reveal that when the pH increases from 1 to 2 to 4–6, the nanocrystals' mean size reduces slightly and the morphologies transform from the hollow sphere to the packed hexagon. The fluorescence lifetime and quantum efficiency achieved maximum for the samples synthesized at pH = 2. These nanocrystals with small size (<30 nm) and bright photoluminescence are promising phosphors in the applications of biological, optical amplifiers and liquid laser fields.

Mesoporous silica SBA-15 sheet with perpendicular nanochannels

Free-standing thin sheet form of mesoporous silica materials with perpendicular orientation is a much desired materials for its possible applications in catalysis, mask, and separation. A three component amphiphile system of sodium dodecyl sulfate/hexadecyltrimethylammonium bromide/pluronic-123(C16TMAB/SDS/P123) was employed to template the condensation of sodium silicates for the formation of SBA(⊥), a thin sheet of SBA-15 with perpendicular nanochannels. SBA(⊥) can be synthesized at SDS/C16TMAB=1.5 and T⩾40°C and shows pH-dependent morphology. It has uniform pore size ∼9nm, homogeneous sheet thickness in the range of 60–300nm and dimension of several microns. We studied in details the structure and morphology of the SBA(⊥) with variation of three experimental parameters: the SDS/C16TMAB ratio, the temperature, and the pH condition in the synthetic gel. It is proposed that the mixed surfactants of SDS and C16TMAB form catanionic vesicle in which the P123 and silicates are condensed. The balanced interaction of P123/silicate with the narrow confinement under surfactant bi-layers of C16TMAB/SDS promoted the formation of perpendicular nanochannels. Low temperature and pH conditions favor stronger segregation of the PPO and PEO–oligosilicate segments in the SBA(⊥) structure which gives the basis of thickness control of the sheet. The control of structure and morphology are discussed with modern theory of microphase separation in block copolymers under confinement.

Effect of Molecular Weight and Arm Number on the Growth and pH-Dependent Morphology of Star Poly[2-(dimethylamino)ethyl methacrylate]/Poly(styrenesulfonate) Multilayer Films

The influence of molecular weight and arm number of star polymers on the buildup and pH-dependent morphology changes of multilayer films assembled from star poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) and linear poly(styrenesulfonate) (PSS) was systematically investigated. Well-defined star PDMAEMA, consisting of β-cyclodextrin (CD) core and different arm number (21, 14, and 7) were successfully synthesized via atom transfer radical polymerization (ATRP). It is found that star polymers with certain arm number deposit more mass with the increase of molecular weight. As for the star polymers with almost the same arm length but different arm number, film assembled from 14-arm star PDMAEMA exhibits the fastest growth and the most significant morphology changes upon the pH 2.75 treatment. It is assumed that the interdiffusion of PSS controlled by star PDMAEMA with different structures should be responsible for the different buildup and pH-dependent morphology changes of the multilayer films.

Morphology controllable synthesis of ZnO crystals—pH-dependent growth

ZnO crystals were grown through a solution-based chemical route at ambient pressure and low temperature. It was found that the solution pH is a dominative factor in determining the morphology of crystals: Rod-like ZnO crystals are apt to be formed at near neutral condition, whereas flower-like structured ZnO crystals are preferred to be formed at higher solution pH. By monitoring the reaction intermediates during the ZnO growth process, it was realized that the crucial role of solution pH in determining the morphology of ZnO crystals is to control the structure of the primary reaction intermediates at the early stage of ZnO growth. Moreover, by appreciate controlling the solution pH together with Zn 2+ concentration, various ZnO crystals of rod-like, dumbbell-like and even more complex flower-like structures were obtained without any template, and a pH-dependent morphology controllable growth mechanism is suggested.

Hydrogen-Bond-Induced Microstructural Transition of Ionic Micelles in the Presence of Neutral Naphthols: pH Dependent Morphology and Location of Surface Activity

The effect of naphthols and methoxynaphthalenes on the microstructure transition of cetyltrimethylammonium bromide (CTAB) micelles is studied. Although the surface activities of these two types of organic dopants are strong, methoxynaphthalenes failed to promote spherical to worm-like micellar transition and to impart viscoelasticity to the aqueous CTAB solution, presumably due to their inability to form unique H-bonds with interfacial water. The micropolarity of OH sites of micelle-embedded naphthols is measured by observing the pK(a) shift at the micellar surface relative to bulk water. On the basis of spectroscopic and other data, the microstructures formed by both classes of dopants at the micellar surface are predicted. On the basis of hydroxyaromatic dopants, a simple and effective route to design pH-responsive viscoelastic worm-like micelles and the vesicles of single tail cationic surfactant (CTAB) is reported. Results are confirmed by observing cryogenic transmission electron microscopy (cryo-TEM) images.

Identification and Characterization of the Slowly Exchanging pH-dependent Conformational Rearrangement in KcsA

Gating of ion channels is strictly regulated by physiological conditions as well as intra/extracellular ligands. To understand the underlying structures mediating ion channel gating, we investigated the pH-dependent gating of the K(+) channel KcsA under near-physiological conditions, using solution-state NMR. In a series of (1)H(15)N-TROSY HSQC (transverse relaxation optimized spectroscopy-heteronuclear single quantum coherence) spectra measured at various pH values, significant chemical shift changes were detected between pH 3.9 and 5.2, reflecting a conformational rearrangement associated with the gating. The pH-dependent chemical shift changes were mainly observed for the resonances from the residues near the intracellular helix bundle, which has been considered to form the primary gate in the K(+) channel, as well as the intracellular extension of the inner helix. The substitution of His-25 by Ala abolished this pH-dependent conformational rearrangement, indicating that the residue serves as a "pH-sensor" for the channel. Although the electrophysiological open probability of KcsA is less than 10%, the conformations of the intracellular helix bundle between the acidic and neutral conditions seem to be remarkably different. This supports the recently proposed "dual gating" properties of the K(+) channel, in which the activation-coupled inactivation at the selectivity filter determines the channel open probability of the channel. Indeed, a pH-dependent chemical shift change was also observed for the signal from the Trp-67 indole, which is involved in a hydrogen bond network related to the activation-coupled inactivation. The slow kinetic parameter obtained for the intracellular bundle seems to fit better into the time scale for burst duration than very fast fluctuations within a burst period, indicating the existence of another gating element with faster kinetic properties.

Morphology evolution of GaPO4 mesocrystals in a nonionic triblock copolymer system by pH-dependent control

In the synthesis of gallium phosphate, GaPO4, crystals via a hydrothermal route, using amphiphilic triblock copolymer F127, [(EO)106(PO)70(EO)106]–OH, as a surfactant-template, a pH-dependent morphology evolution is observed in the progress of crystal growth. By altering the initial pH level from 7.34 to 11.54, the morphology of crystals is varied from the mesoscale assembly of nanoparticles with porosity, so-called porous mesocrystals, to colloidal crystalline nanoparticles. Thus far, the porous GaPO4 mesocrystals created by self-assembled nanoparticles, is reported for the first time. The typical pore size distribution of porous GaPO4 mesocrystals derived from the adsorption branch by the Barrett–Joyner–Halenda (BJH) model ranges from 1.0 to 3.5 nm with a major distribution peak centered at 2.5 nm.

A facile route for preparing rhabdophane rare earth phosphate nanorods

Lanthanum orthophosphate nanorods with typical dimensions of 8 nm in diameter and 80 nm in length were prepared simply by mixing NaH2PO4 and LaCl3 aqueous solutions in an oil bath of 100 °C. Eu3+- and Ce3+-doped nanorods were also be prepared in a similar way by introducing Eu3+ and Ce3+ ions, respectively, into the reaction systems. TEM (transmission electron microscope) and XRD (X-ray diffraction) results revealed that the above-mentioned lanthanide orthophosphate nanorods possessed a rhabdophane-type structure. Compositional analysis by X-ray photoelectron spectroscopy demonstrated that LaPO4 nanorods had an anion-rich surface, which might be the main reason for their colloidal stabilities. The appearance of radiating aggregates during the early stage of the precipitation reactions and their pH dependent morphologies indicated that the formation of lanthanide orthophosphate nanorods was mainly governed by the growth nature of hexagonal LaPO4. The optical measurements indicated that LaPO4 ∶ Ce3+ with the rhabdophane structure has stronger electron–phonon coupling than monazite-type. The fluorescence quantum yield of LaPO4 ∶ Ce3+ nanorods was estimated to be 35%. In comparison with rhabdophane nanoparticles, the strongest emission of the Eu3+-doped nanorods originates from the 5D0 to 7F1 transition rather than 5D0 to 7F2. This may be attributed to the nature of the 1D structure as well as the lattice distortions in the nanorods.

PH-dependent multiple morphologies of novel aggregates of carboxyl-terminated polymide in water

Rigid low-molecular-weight polyimide with two carboxyl ends (CPI) formed pH-dependent multiple morphologies including dimpled-beads, porous aggregates and vesicles via self-assembly in aqueous media. This is a rapid and conventional approach to a series of pH-dependent morphologies of mono-component aggregates based on a readily attainable rigid homopolymer.

Characterization of a conditional mutant with altered envelope showing pH-dependent morphology and temperature-dependent division.

SUMMARY: The properties of a conditional mutant of Klebsiella pneumoniae (Mir M7) are described. The mutant has a pH-dependent disturbance of morphology and a temperature-dependent disturbance of division. At pH 7 the mutant grows as cocci and at 41 °C (restrictive temperature) division is inhibited. At acid pH and restrictive temperature, filaments are formed. At pH 7 and permissive temperature, polymorphous cocci are obtained. At pH 7 and 41 °C, giant polymorphous cells are formed. The inhibition of division is phenotypically reverted by 0.05 M-Mg2+, 0.1 M-Na+ or 0.4 M-sucrose. Seventeen revertants were isolated having exactly the same characteristics as the wild-type Klebsiella, so it seems that only one mutation is responsible for the different disturbances of the mutant. The possibility of membrane damage on which the morphology and division disturbances may depend is discussed.