MPA Molecules Research Articles

Adsorption mechanism of 3-mercaptopropionic acid as a chalcopyrite depressant in chalcopyrite and galena separation flotation

3-mercaptopropionic acid (MPA) is an ideal depressant in chalcopyrite-galena separation due to the advantages of high efficiency, environmental friendliness, and low dosage. However, its inhibition mechanism for chalcopyrite was unclear. In this study, the adsorption mechanism of MPA on the chalcopyrite surface was investigated in detail to understand its excellent inhibition effect on the flotability of chalcopyrite. The flotation and surface variation of chalcopyrite and galena were examined by micro-flotation experiments, Fourier transform infrared spectroscopy (FT-IR) analysis, X-ray photoelectron spectroscopy (XPS) studies, and atonic force microscopy (AFM) observation. The micro-flotation experiments results indicated that MPA exhibited a superior selective inhibition ability than that of thioglycolic acid (TGA) even under a relatively lower concentration. The surface analysis revealed a significant decrease of SBX adsorption on the chalcopyrite surface after pre-treatment with MPA. While the pre-treated galena surface still kept strong interaction with SBX. Moreover, the AFM observation clearly demonstrated that the adsorbed MPA molecules formed a network structure on the chalcopyrite surface due to the hydrogen-bond interaction, which could dramatically enhance the adsorption stability of MPA on the chalcopyrite surface, depressing the subsequent SBX chemosorption. These results shed light on the characteristic inhibition mechanism of MPA, which promotes its practical application on chalcopyrite and galena separation flotation.

A Highly Sensitive Mercury Ion Sensor Based on Solid-Liquid Contact Electrification

In recent years, triboelectric nanogenerators (TENGs) are proved to be as the prime backbone for developing a self-powered sensing system. However, solid-solid contact electrification based nanogenerators suffer mostly due to inefficient contact which poses a major bottleneck for the development of long term durable and stable nanosensors. In this regard, we have reported a strategic methodology to develop a highly sensitive mercury ion sensor based on solid-liquid contact electrification, which has prime importance for the self-powered monitoring of mercury ion due to its high health risk and environmental pollution toxicity. In this work, 3-mercaptopropionic acid (MPA) capped Au nanoparticles (NPs) are employed as the solid friction layer as well as the recognition element for mercury ion detection. In addition, volatile organic solvent acetone is utilized as the contact liquid instead of water. The developed nanosensor exhibits long term stability and contact frequency independent sensing performance compared to previously reported solid-solid triboelectric nanosensors (TENS) for mercury ion detection. The large binding affinity of Hg2+ and the carboxylic groups results in the increase of transferred charges and enhanced surface potential. It is interesting to observe that the work function reduces after the binding of Hg2+ ions onto MPA molecules, which is also favorable for electron transfer during the contact electrification process. The developed nanosensor can provide a wide linear detection range from 10 nM to 1 μM as well as a low detection limit of 10 nM. As a whole, this work demonstrates a novel paradigm for designing a rapid, low-cost, and portable self-powered sensing system for real time highly selective monitoring of mercury ion from complex environmental samples.

Selective polymorphic crystal growth on self-assembled monolayer using molecular modeling as an assistant method

A screening method for selective polymorphic crystal growth was proposed using molecular modeling as an assistant tool in this work. Three typical pharmaceutical polymorphic crystals which are theophylline, l-serine and fumaric acid were chosen as case studies to investigate their selective growth on self-assembled monolayer (SAM) prepared by depositing 3-mercaptopropionic acid (MPA) on gold. Molecular modeling was applied to analyze the arrangement of MPA molecules on the surface, as well as to value the binding energy between these three crystal faces with MPA SAM. The simulation results were used to predict the effect of SAM on the two dimensional selective growth of the polymorphic crystals, and crystallization experiments were carried out to verify the modeling prediction. The results indicate that MPA SAM can directionally induce the nucleation of polymorphic crystals by geometric and chemical interactions matching. Molecular modeling can be as an effective assistant tool to reveal the matching degree, which can give valuable suggestions on the polymorphic drug design.

Exploring the enhancement of electron tunneling induced by intermolecular interactions on surface of self-assembled monolayer

The topic of intermolecular interactions enhancing electron tunneling between protein residues on biofilm surface has been investigated by some theoretical studies. However, few of experimental studies could confirm this viewpoint. In this work, the Mercaptopropionic acid self-assembled monolayer (MPA SAM) with terminal carboxyl groups was constructed, as a simplified model for functionalized biomimic membrane. The electron tunneling rate constant of ferrocenylmethanol redox process on SAM was obtained from experimental results of scanning electrochemical microscopy. It is found that the electron tunneling across MPA SAM is faster than that of contrastive Methyl mercaptopropionate SAM. This result is attributed to the intermolecular interactions between the redox and MPA molecules. The conditions of lower pH and weaker ion pair effect all benefit the formation of the intermolecular interactions, resulting the enhancement of electron tunneling more obvious. Based on this, this kind of intermolecular interaction is inferred to be intermolecular hydrogen bond. Our work may have contributions to exploring electron tunneling between protein residues on biofilm surface.

Ligand Exchange Functionalization of CIS Quantum Dots for CIS/ZnO Film Heterojunctions

Colloidal quantum dots (QD) are rapidly making their way into several optoelectronic applications. While Cd- and Pb-based QDs are promising for high-performance devices, toxicity remains a concern. In this regard, Cu-In-S (CIS) QDs provide an alternative option for scalable, commercial production. A low-temperature, high-throughput process was used to synthesize CIS QDs with 1-dodecanethiol (DDT) ligands. While QD synthesis with a DDT ligand is facile, there are drawbacks when it comes to device implementation and interfacing with electron transport films such as ZnO. A ligand exchange process was employed to replace the DDT ligands in the as-synthesized QDs with 3-mercaptopropionic acid (MPA); owing to the short and bifunctional nature of the MPA molecules, this process improved the surface adhesion and carrier transport to ZnO. I-V measurements on planar structures showed the significance of ligand exchange in CIS QDs for heterojunction device implementation.

3-Mercaptopropionic acid functionalization of titanium dioxide thin films

Abstract Nanostructured titanium dioxide (TiO2) films are commonly employed as surface modifiers on medical and dental metallic implants, presenting promising results related to interactions with living tissues, promoting improvements in the in vivo biocorrosion resistance and increased bioactivity when compared to non-coated metallic materials. In addition to these properties, titanium dioxide is also well recognized for its biocompatibility. However, considering the necessary integration with surrounding tissues when this oxide is applied as implant coatings, there are many aspects of the adhesion mechanisms located at the interface between the biological environment and the oxide surface that still need to be addressed. Specifically regarding the surface chemistry, these oxides are mainly terminated by hydroxyl groups (-OH) that are readily functionalized by different molecules, such as the 3-mercaptopropionic acid (MPA). In this contribution, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were used to examine the adsorption of MPA on anatase- and rutile-phase forms of TiO2 thin film surfaces grown by RF magnetron sputtering. According to the obtained results, both anatase and rutile TiO2 films present similarities in roughness and thickness. However, different responses to interaction with the MPA molecules were observed, wherein the functionalization was seen to occur only for the rutile phase.

Molecular Dynamics Study of the Solution Structure, Clustering, and Diffusion of Four Aqueous Alkanolamines.

CO2 sequestration from anthropogenic resources is a challenge to the design of environmental processes at a large scale. Reversible chemical absorption by amine-based solvents is one of the most efficient methods of CO2 removal. Molecular simulation techniques are very useful tools to investigate CO2 binding by aqueous alkanolamine molecules for further technological application. In the present work, we have performed detailed atomistic molecular dynamics simulations of aqueous solutions of three prototype amines: monoethanolamine (MEA) as a standard, 3-aminopropanol (MPA), 2-methylaminoethanol (MMEA), and 4-diethylamino-2-butanol (DEAB) as potential novel CO2 absorptive solvents. Solvent densities, radial distribution functions, cluster size distributions, hydrogen-bonding statistics, and diffusion coefficients for a full range of mixture compositions have been obtained. The solvent densities and diffusion coefficients from simulations are in good agreement with those in the experiment. In aqueous solution, MEA, MPA, and MMEA molecules prefer to be fully solvated by water molecules, whereas DEAB molecules tend to self-aggregate. In a range from 30/70-50/50 (w/w) alkanolamine/water mixtures, they form a bicontinuous phase (both alkanolamine and water are organized in two mutually percolating clusters). Among the studied aqueous alkanolamine solutions, the diffusion coefficients decrease in the following order MEA > MPA = MMEA > DEAB. With an increase of water content, the diffusion coefficients increase for all studied alkanolamines. The presented results are a first step for process-scale simulation and provide important qualitative and quantitative information for the design and engineering of efficient new CO2 removal processes.

On the temperature dependency and reversibility of sheet resistance of silver nanoparticles covered by 3-mercaptopropionic acid

The temperature dependency and reversibility of the sheet resistance of silver nanoparticles covered by 3-mercaptopropionic acid (Ag-MPA) molecules, used in the printed temperature sensor, has been investigated. The microstructural evaluation, the FTIR spectra and thermal property analyses of the Ag-MPA films suggest co-existence of both weakly adsorbed as well as firmly adsorbed MPA molecules on the surface of Ag nanoparticles. The weakly adsorbed MPA molecules was to a great extent be desorbed and removed from the surfaces of silver nanoparticles when heated up to 180 °C for the first time. While the firmly adsorbed MPA molecules remain on the surfaces of silver nanoparticles even at higher temperature. Yet the firmly adsorbed MPA molecules are likely having gone through a transformation circle from/to the gauche and trans conformations in correspondence to a heating and cooling cycle, which results in temperature dependent and reversible sheet resistance. The MPA molecules in the gauche conformation are more densely packed on the surface of silver nanoparticles and can hinder the electron’s movability within the Ag-MPA film. While in the trans conformation with lower ‘surface space’ coverage by the MPA molecules, electrons move more freely within the film. Based on the temperature dependent nature, the fully printed temperature sensor using the Ag-MPA nanoparticles as the functional layer was made, of which the highest sensitivity is 5.12% °C−1 at 200 °C.

Photodegradation of Mercaptopropionic Acid- and Thioglycollic Acid-Capped CdTe Quantum Dots in Buffer Solutions.

CdTe quantum dots (QDs) were synthesized by 3-mercaptopropionic acid (MPA) and thioglycollic acid (TGA) as capping agents. It is confirmed that TGA and MPA molecules were attached on the surface of the QDs using Fourier transform infrared (FT-IR) spectra. The movement of the QDs in agarose gel electrophoresis indicated that MPA-capped CdTe QDs had small hydrodynamic diameter. The photoluminescence (PL) intensity of TGA-capped QDs is higher than that of MPA-capped QDs at same QD concentration because of the surface passivation of TGA. To systemically investigate the photodegradation, CdTe QDs with various PL peak wavelengths were dispersed in phosphate buffered saline (PBS) and Tris-borate-ethylenediaminetetraacetic acid (TBE) buffer solutions. It was found that the PL intensity of the QDs in PBS decreased with time. The PL peak wavelengths of the QDs in PBS solutions remained unchanged. As for TGA-capped CdTe QDs, the results of PL peak wavelengths in TBE buffer solutions indicated that S(2-) released by TGA attached to Cd(2+) and formed CdS-like clusters layer on the surface of aqueous CdTe QDs. In addition, the number of TGA on the CdTe QDs surface was more than that of MPA. When the QDs were added to buffer solutions, agents were removed from the surface of CdTe QDs, which decreased the passivation of agents thus resulted in photodegradation of CdTe QDs in buffer solutions.

Folic acid-conjugated core/shell ZnS:Mn/ZnS quantum dots as targeted probes for two photon fluorescence imaging of cancer cells

This work presents a novel approach to producing water soluble manganese-doped core/shell ZnS/ZnS quantum dots (ZnS:Mn/ZnS). The Mn-doped ZnS core was prepared through a nucleation doping strategy and a ZnS shell was grown on ZnS:Mn d-dots by decomposition of Zn2+–3-mercaptopropionic acid (MPA) complexes at 100°C. It was found that the Mn2+4T1→6A1 fluorescence emission at ∼590nm significantly increased after growth of the shell when the Mn2+ doping content was 4.0at.%. A photoluminescence quantum yield of ∼22% was obtained for core/shell nanocrystals. The nanoparticles were structurally and compositionally characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and dynamic light scattering. The surface MPA molecules favor the dispersion of ZnS:Mn/ZnS QDs in aqueous media and make possible conjugation with targeting folic acid molecules. The folate receptor-mediated delivery of folic acid-conjugated ZnS:Mn/ZnS QDs was demonstrated using confocal microscopy with biphotonic excitation. Bare and folate-conjugated QDs exhibit only weak cytotoxicity towards folate receptor-positive T47D cancer cells and MCF-7 cells, used as a reference, at high concentrations (mmolar range) after 72h incubation.

A calorimetric investigation of the assembly of gold nanorods to form necklaces

Interaction of gold nanorods with cysteine as well as 3-mercaptopropionic acid (MPA) has been investigated by isothermal titration calorimetry (ITC), in combination with electronic absorption spectroscopy and electron microscopy. The assembly process with MPA shows two steps, the first due to the binding of MPA to gold nanorods through the sulfur atom, and the second due to assembly of the MPA capped gold nanorods through the formation of cyclic hydrogen bonded dimers between the MPA molecules. In the case of cysteine only a single step is observed in ITC, due to the binding of the molecules to gold nanorods.

In situ SERS studies on the adsorption of tyrosinase on bare and alkanethiol-modified silver substrates

Copper-containing phenols oxidase enzyme tyrosinase (TY) from mushroom was adsorbed on bare silver substrates and on silver substrates modified with monolayers formed from various ω-functionalised alkanethiols: HS–(CH 2) 2–NH 2 (CYS), HS–(CH 2) 2–SO 3Na (MES), HS–(CH 2) 2–COOH (MPA), HS–(CH 2) 10–COOH (MUA) and HS–(CH 2) 15–COOH (MHA). Structures of formed adlayers have been determined by means of surface-enhanced Raman scattering (SERS) measurements. The results of our experiments suggest that bonding of TY to the silver surface takes place, to a large extent, via the aromatic rings oriented parallel to the metal surface. The integrity of monolayers formed from all studied thiols is not destroyed after immersion in a TY aqueous solution. Previous measurements carried out for laccase (other widely used copper-containing polyphenol oxidase enzyme) revealed that linkage monolayers formed from short-chain alkanethiols (CYS, MES, MPA) do not prevent direct interaction of this enzyme with the metal surface. It means that the structure of the linkage monolayer is significantly different when covered with various enzymes. We found that for the Ag/MPA/TY system a significant part of MPA molecules interact with the silver surface via both sulphur moiety and the carboxylic group. The other TY-induced changes of the thiolates linkage monolayer structure are very similar to the previously reported changes of the structure of these monolayers induced by the adsorption of bovine serum albumin [see A. Kudelski, Vib. Spectrosc. 41 (2006) 83].

Structure of Mixed Carboxylic Acid Terminated Self-Assembled Monolayers: Experimental and Theoretical Investigation

The structure and stability of mixed self-assembled monolayers (SAMs) of 3-mercaptopropionic acid (MPA) and 11-mercaptoundecanoic acid (MUA) prepared by immersion in ethanolic solutions were studied by cyclic voltammetry, electrochemical impedance spectroscopy, ellipsometry, and STM as a function of the thiol composition of the forming solution. The presence of a single reductive desorption peak in the voltammograms of the mixed SAMs and the lack of phase segregation observed by STM support the formation of homogeneous SAMs despite the large chain length difference between MPA and MUA. To explain the driving force leading to the formation of a homogeneous mixture, intermolecular interactions within the SAM were investigated using density functional theory. The carboxyl groups of adjacent MPA and MUA molecules in a compact monolayer can form a stable head to head cyclic dimer with a hydrogen bond strength of 16.2 kcal/mol. The flexibility of the alkyl chain of MUA allows the carboxyl groups of adjacent MPA and MUA molecules to be located on the same plane. However, the carboxyls of adjacent MPA−MPA and MUA−MUA pairs form much weaker hydrogen bonds because steric constraints avoid the formation of the stable cyclic dimer. Therefore, the prevalence of MPA−MUA interactions over MPA−MPA and MUA−MUA interactions explains the homogeneous mixing of MPA and MUA. The potential chemical switchability properties of mixed monolayers of mercaptoalcanoic acids of different chain lengths as a function of the solution pH are discussed.

Novel material concepts of transducers for chemical and biosensors

The objectives of this work are to contribute to the knowledge about physical and chemical properties of WBG semiconductors, such as ZnO and GaN towards development of advanced bio- and chemical sensors. For the semiconductors, growth techniques typically yielding single crystal material are applied. Thin epitaxial quality films of ZnO and GaN are fabricated on SiC or sapphire substrates. An emphasis is given to ZnO due to the interesting combination of the semiconductor and oxide properties. Surface bio-functionalization of ZnO is performed by APTES, MPA or MP-TMS molecules. We have compared some of the results to (hydroxylated) GaN surfaces functionalized by MP-TMS. The covalent attachment of the self-assembled biomolecular layers has been proven by XPS analysis. For complementary electrical characterization impedance spectroscopy measurements were performed. The results are intended to serve the realization of bioelectronic transducer devices based on SiC or GaN transistors with a ZnO gate layer.To take advantage of the catalytic properties of ZnO, initial prototypes of chemical sensors for gas sensing are processed on ZnO deposited either on SiC or on sapphire and they are further tested for the response to reducing or oxidizing gas ambient. The sensor devices show sensitivity to oxygen in the surface resistivity mode while a Pt Schottky contact ZnO/SiC device responds to reducing gases. These results are compared to published results on Pt/GaN Schottky diodes.

Assembly of Au colloids into linear and spherical aggregates and effect of ultrasound irradiation on structure

In this work, we aimed to tune the aggregation state of Au colloids by judicious regulation of their surface charges and by introduction of ultrasound irradiation. Au colloids were prepared by reduction of HAuCl4 with NaBH4 in the presence of 3-mercaptopropionic acid (MPA) as the stabilizing ligand. The Au colloids capped with MPA molecules possessing a single –SH terminal group, can form either linear or spherical Au colloid aggregates depending on the MPA ∶ Au ratio, solution pH and Au colloid concentration. Adjustment of these parameters provides a convenient means of regulating surface charge on the Au colloid surface and, thus, the state and degree of aggregation. The spherical aggregates appeared to be thermodynamically stable, and ultrasound irradiation could promote their formation. Intense ultrasound irradiation resulted in the formation of well-crystallized nanospheres whilst mild irradiation tended to produce a more amorphous product. This is the first observation of a sonication effect on the crystallization state in freely suspended Au colloids in aqueous solution.

Raman study on the structure of adlayers formed on silver from mixtures of 2-aminoethanethiol and 3-mercaptopropionic acid

Silver surfaces were covered with adlayers formed from mixtures of 2-aminoethanethiol (cysteamine, CYS) and 3-mercaptopropionic acid (MPA). The composition and structure of adlayers thus formed were investigated by surface-enhanced Raman scattering (SERS). SERS measurements revealed that the layer formed from the 1:1 mixture of 10-mM aqueous solutions of CYS and MPA is composed of co-adsorbed CYS and MPA molecules. From the SERS spectrum of such an adlayer, one can also deduce that practically all MPA molecules are dissociated. pH-controlled experiments showed that MPA is also dissociated when mixed MPA + CYS adlayer is soaked in the solution buffered to pH = 5.0, whereas in the case of one-component adlayer, almost all MPA molecules are protonated at the same pH value. It means that the presence of CYS molecules induces dissociation of neighbouring MPA molecules and that co-adsorbed MPA and CYS probably form mixed salt-like structures under these conditions. At lower pH values (3.2), the layer is mainly composed of non-dissociated MPA molecules, while at slightly alkaline solution (pH = 9) strong preference of CYS molecules at the surface adlayer is observed. This phenomenon may be ascribed to strong stabilization of the adlayer structure by the network of hydrogen bonds between COOH (at lower pH) or NH2(at higher pH) groups of adjacent molecules. Formation of mixed adlayer is possible in the limited range of pH values that enable protonation of NH2 groups with simultaneous deprotonation of the COOH groups. Our results also demonstrate that the mixed salt-like MPA + CYS adlayers could be formed from the MPA + CYS solutions only if the concentrations of both compounds are of the same order of magnitude. This suggests no strong thermodynamic preference for such adlayers. Copyright © 2005 John Wiley & Sons, Ltd.

Hydrothermal synthesis and structure of a new layered zincophosphate intercalated with 3-methylaminopropylamine cations

A novel layered zincophosphate (ZnPO?MPA) was prepared by hydrothermal crystallization using 3-methylaminopropylamine (MPA) as a structure-directing agent. The structure consists of macroanion [Zn2P3O8(OH)3]2- layers which are built up of 4-membered ring channels. The channels (of about 3.7 ? diameter) arise through the connection of the neighbouring rings by two oxygen bridges. The negative charge of the layers is compensated by diprotonated MPA molecules which are stacked parallel to the ring channels. ZnPO?MPA is stable up to 300 ?C. At higher temperatures MPA decomposition begins followed by a dehydration, which occurs through condensation of the framework hydroxyl groups. The activation energy of the MPA decomposition is high due to the fact that the layers and MPA cations are held together by strong hydrogen bonds.

Exploring the use of the tripeptide Gly–Gly–His as a selective recognition element for the fabrication of electrochemical copper sensors

The modification of electrodes with the tripeptide Gly-Gly-His for the detection of copper in water samples is described in detail. The tripeptide modified electrode was prepared by first self-assembling 3-mercaptopropionic acid (MPA) onto the gold electrode followed by covalent attachment of the tripeptide to the self-assembled monolayer using carbodiimide coupling. The electrodes were characterized using electrochemistry, a newly developed mass-spectrometry method and quantum mechanical calculations. The mass spectrometry confirmed the modification to proceed as expected with peptide bonds formed between the carboxylic acids of the MPA and the terminal amine of the peptide. Electrochemical measurements indicated that approximately half the MPA molecules in a SAM are modified with the peptide. The peptide modified electrodes exhibited high sensitivity to copper which is attributed to the stable 4N coordinate complex the peptide formed around the metal ion to give copper the preferred tetragonal coordination. The formation of a 4 coordinate complex was predicted using quantum mechanical calculation and confirmed using mass spectrometry. The adsorption of the copper to the peptide modified electrode was consistent with a Langmuir isotherm with a binding constant of (8.1 +/- 0.4) 10(10) M(-1) at 25 degrees C.

Raman study on the structure of 3-mercaptopropionic acid monolayers on silver

The influence of pH on the structure of 3-mercaptopropionic acid (MPA) monolayers on silver, and the changes in the structure of monolayers during adsorption and desorption of MPA molecules were investigated by surface-enhanced Raman scattering. The measurements were carried out in aqueous solutions. It was demonstrated that during the self-assembling of the monolayer there was a significant increase in the portion of a trans conformer of S–C–C chains of adsorbed MPA molecules, and a large portion of the COO − groups of the adsorbed MPA molecules was protonated. The strength of adsorbed acid clearly depends on its surface concentration. Desorption of MPA progressed at a slow rate and significant changes (reverse to the changes during adsorption) were observed after more than 1 h.

Crystallization behaviour of poly(N-methyldodecano-12-lactam) Part 2. Recrystallization

The recrystallization process of poly(N-methyldodecano-12-lactam) MPA has been studied by differential scanning calorimetry (DSC), wide- and small-angle X-ray scattering (WAXS, SAXS) and Raman spectroscopy. During this irreversible process, the primary crystalline structure with a melting temperature of about 324K is transformed to the higher-ordered final structure melting at 335K. Isothermal recrystallization has an optimum at 327–329K. During recrystallization, no change in crystalline modification takes place; however, crystallinity is increased from 30 to 35% (by WAXS) and the long period rises from 10.0 to 11.2nm. The MPA sample recrystallized at 327K and relaxed at laboratory temperature shows the melting point of 338.8K. Crystallization/recrystallization of MPA is a diffusion-controlled kinetic process dependent on molecular weight and the rate of temperature changes. On the molecular level, the crystallization/recrystallization processes taking place in MPA can be interpreted as being directed by two conformational transitions in MPA molecules, namely the trans/cis transition on the C–N bond and the gauche/trans transition of the C–C sequences.