Order Of Reagent Addition Research Articles

Gold nanoparticles for photothermal therapy – Influence of experimental conditions on the properties of resulting AuNPs

Gold nanoparticles (AuNPs)-mediated Photothermal Therapy (PTT) is a minimally-invasive therapeutic approach that uses AuNPs to convert light into heat, leading to the thermal ablation of tumors. Thus, the efficacy of this strategy strongly relies on the photothermal conversion potential of AuNPs. The ability to convert light into heat can be enhanced by tuning the physicochemical and optical properties of AuNPs. This can be achieved by changing the conditions of AuNP's synthesis, such as the order of addition of reagents. The present work entails to explore how varying the order of reagents addition modulates the properties of AuNPs, particularly enhancing the photothermal conversion potential of the resulting AuNPs and consequently, improving PTT efficacy. For this, eleven different AuNPs' nanoformulations were synthetized following different sequences of addition of reagents. These nanoformulations were characterized regarding their physicochemical properties namely size, surface charge, gold concentration, surface morphology and maximum absorbance wavelength. In addition, their thermal activation profiles were determined in vitro. Furthermore, the biocompatibility of different nanoformulations was also assessed. Three nanoformulations, with the most favorable photothermal activation profiles (AuNPs 2, 3 and 7), were then selected for preliminary in vitro safety and efficacy assays using a panel of cell lines. These three nanoformulations were deemed safe in vitro at the tested concentrations. At 250 μM of gold content, and after an incubation period of 4 h, followed by 5 min irradiation with a laser emitting at 808 nm (7.96 W/cm2), AuNPs 7 significantly reduced the cell viability of all cancer cell lines tested (MCF-7, HCT-116 and A375) by ≥ 45 %. However, such cytotoxic effect was not observed for the human keratinocyte cell line (HaCat), thus demonstrating its specificity towards cancer cells. Overall, the results herein presented reinforce that the order of reagents addition is highly important for achieving adequate AuNPs for PTT.

Effect of Order of Reagents Addition on Optical and Structural Properties of CdS Quantum Dot Prepared by Chemical Bath Deposition Technique

Cadmium sulfide quantum dots were synthesized and deposited on glass substrates by chemical bath deposition (CBD) technique using cadmium sulfate and thiourea solutions in the presence of a 4,4’-(1,2-ethanediyldinitrilo)bis-(2-pentanone) (EDDBP) tetradentate ligand as a complexing agent. The order of reagents addition was varied to deposit films that were characterized for their surface morphological, optical, structural, and solid-state properties using a scanning electron microscope (SEM), a UV-visible spectrophotometer, an X-ray diffractometer (XRD), and Brunauer-Emmet-Teller (BET) analyses. The optimal condition for film deposition using the normal sequence of reagents addition was found at pH 8-12 and 298-353 ± 1K and gave films of 2.40-321.06 nm thickness, while the variation in the order of reagents addition gave improvements in the film properties. The optical properties and the observed direct band gaps (1.75-3.16 eV) of the films suggest usage in electroluminescent and solar cell devices since they have a first-order transition. The XRD patterns of the quantum dots indicated hexagonal wurzite structures, while the BET confirmed their mesoporous and nanonature.

Multimetallic post-synthetic modifications of copper selenide nanoparticles.

In this report, we investigate the addition of two metal cations, simultaneously and sequentially to Cu2-xSe nanoparticles. The metal combinations (Ag-Au, Ag-Pt, Hg-Au and Hg-Pt) are chosen such that one metal adds to the structure via cation exchange and the other adds to the structure via metal deposition when added individually to Cu2-xSe nanoparticles. Surprisingly, we find that for each metal combination, across all three synthesis routes, cation exchange and metal deposition products are obtained without deviation from the outcomes seen in the binary metal systems. However, within those outcomes the data show several types of heterogeneities in the morphologies formed including extent and composition of cation exchange products as well as the extent and composition of the metal deposited products. Taken together, these results suggest a hierarchical control for nanoheterostructure morphologies where the pathways of cation exchange or metal deposition in post-synthetic modification of Cu2-xSe exhibit relatively general outcomes as a function of metal, regardless of synthetic approach or metal combination. However, the detailed composition and interface populations of the resulting materials are more sensitive to both metal identities and synthetic procedure (e.g. order of reagent addition), suggesting that certain principles of metal chalcogenide post-synthetic modification are excitingly robust, while also revealing new avenues for both mechanistic discovery and structural control.

Assessing the influence of microwave-assisted synthesis parameters and stabilizing ligands on the optical properties of AIS/ZnS quantum dots

Luminescent semiconductor quantum dots (QDs) are frequently used in the life and material sciences as reporter for bioimaging studies and as active components in devices such as displays, light-emitting diodes, solar cells, and sensors. Increasing concerns regarding the use of toxic elements like cadmium and lead, and hazardous organic solvents during QD synthesis have meanwhile triggered the search for heavy-metal free QDs using green chemistry syntheses methods. Interesting candidates are ternary AgInS2 (AIS) QDs that exhibit broad photoluminescence (PL) bands, large effective Stokes shifts, high PL quantum yields (PL QYs), and long PL lifetimes, which are particularly beneficial for applications such as bioimaging, white light-emitting diodes, and solar concentrators. In addition, these nanomaterials can be prepared in high quality with a microwave-assisted (MW) synthesis in aqueous solution. The homogeneous heat diffusion and instant temperature rise of the MW synthesis enables a better control of QD nucleation and growth and thus increases the batch-to-batch reproducibility. In this study, we systematically explored the MW synthesis of AIS/ZnS QDs by varying parameters such as the order of reagent addition, precursor concentration, and type of stabilizing thiol ligand, and assessed their influence on the optical properties of the resulting AIS/ZnS QDs. Under optimized synthesis conditions, water-soluble AIS/ZnS QDs with a PL QY of 65% and excellent colloidal and long-term stability could be reproducible prepared.

The Formal Cross‐Coupling of Amines and Carboxylic Acids to Form sp3–sp3 Carbon–Carbon Bonds

AbstractWe have developed a deaminative–decarboxylative protocol to form new carbon(sp3)–carbon(sp3) bonds from activated amines and carboxylic acids. Amines and carboxylic acids are ubiquitous building blocks, available in broad chemical diversity and at lower cost than typical C−C coupling partners. To leverage amines and acids for C−C coupling, we developed a reductive nickel‐catalyzed cross‐coupling utilizing building block activation as pyridinium salts and redox‐active esters, respectively. Miniaturized high‐throughput experimentation studies were critical to our reaction optimization, with subtle experimental changes such as order of reagent addition, composition of a binary solvent system, and ligand identity having a significant impact on reaction performance. The developed protocol is used in the late‐stage diversification of pharmaceuticals while more than one thousand systematically captured and machine‐readable reaction datapoints are reposited.

The Formal Cross-Coupling of Amines and Carboxylic Acids to Form sp3 -sp3 Carbon-Carbon Bonds.

We have developed a deaminative-decarboxylative protocol to form new carbon(sp3 )-carbon(sp3 ) bonds from activated amines and carboxylic acids. Amines and carboxylic acids are ubiquitous building blocks, available in broad chemical diversity and at lower cost than typical C-C coupling partners. To leverage amines and acids for C-C coupling, we developed a reductive nickel-catalyzed cross-coupling utilizing building block activation as pyridinium salts and redox-active esters, respectively. Miniaturized high-throughput experimentation studies were critical to our reaction optimization, with subtle experimental changes such as order of reagent addition, composition of a binary solvent system, and ligand identity having a significant impact on reaction performance. The developed protocol is used in the late-stage diversification of pharmaceuticals while more than one thousand systematically captured and machine-readable reaction datapoints are reposited.

Remediation of real soil polluted with hexachlorocyclohexanes (α-HCH and β-HCH) using combined thermal and alkaline activation of persulfate: Optimization of the operating conditions

Contamination of organic pollutants such as hexachlorocyclohexane (HCH) isomers poses a significant threat to human health and the environment. The alkaline activation of persulfate (PS) intensified by temperature to remediate surface sediments contaminated with HCH-wastes dumped by a lindane producing company (mainly α-HCH = 254 mg kg−1 and β-HCH = 99 mg kg−1) has been optimized. The treatment leads to promising results at 40 °C. Batch experiments were carried out to evaluate the influence of reagent addition order (simultaneous or sequential), reaction temperature (40–60 °C), liquid/soil ratio (VL/WS = 1 and 2), PS concentration (20–60 g L−1) and stirring rate (10–100 rpm) on chlorinated compound abatement. The reagent addition order did not affect the efficiency of the process. Raising either temperature or PS concentration significantly accelerates the hydrolysis rate of β-HCH and the generated trichlorobenzenes (TCBs) oxidation rate. Increasing the VL/WS ratio also accelerated the pollutant oxidation rate. At the selected operating conditions (pH > 12, simultaneous addition of PS and NaOH, 50 °C, PS = 40 g L−1, VL/WS = 2, NaOH/PS = 2 and 100 rpm), a conversion of α-HCH and β-HCH of 100% and 81%, and a dechlorination degree of 94% were achieved in 3 days. PS consumption was 29%; thus, the aqueous solution could be reused in a new batch of soil remediation, the separation of the aqueous and the soil phases being a rapid sedimentation step.

Capped cadmium telluride quantum dots fluorescence enhancement by Se(IV) and its application to dietary supplements analysis

A thioglycolic capped CdTe probe for Se(IV) detection was optimised by nanocrystal size, pH, buffer composition and concentration, and the order of reagent addition. A large increase in fluorescence (>90%) was observed upon sequential addition of Se(IV), buffer, and CdTe probe, caused by surface passivation due to the presence of singly charged Se(IV) in ammoniacal buffer (0.01 mol L–1) at pH 8.4. This result indicated the possibility of inorganic Se speciation. The method presented a detection limit of 60.5 μg L–1 with RSD ≤ 3.5% (n = 8) and was successfully applied to dietary supplements analysis.

Dehydroabietylamine-based thiazolidin-4-ones and 2-thioxoimidazolidin-4-ones as novel tyrosyl-DNA phosphodiesterase 1 inhibitors.

Tyrosyl-DNA phosphodiesterase 1 (TDP1) is a DNA repair enzyme that plays a key role in repairing damage caused by various antitumor drugs. It is a promising target in medicinal chemistry for the creation of cancer adjuvant therapy. Inhibition of this enzyme together with the use of anticancer chemotherapy enhances the effect of the latter. The natural mutant of TDP1, TDP1(H493R), causes severe neurodegenerative disease spinocerebellar ataxia syndrome with axonal neuropathy (SCAN1). Inhibition of TDP1(H493R) appears to be useful in containment the progression of the disease. A library of compounds was synthesized starting from dehydroabietylamine including heterocyclic pharmacophore groups in the core. To obtain the desired products, the starting dehydroabietylamine was introduced sequentially in reaction with isothiocyanate and ethyl bromoacetate. Different classes of heterocyclic derivatives-2-iminothiazolidin-4-ons and 2-thioxoimidazolidin-4-ones-were obtained depending on the addition order of reagents. 2-Iminothiazolidin-4-thiones were obtained from 2-iminothiazolidin-4-ones under the action of the Lawesson's reagent. Effective TDP1 inhibitors were found among the obtained compounds that work in submicromolar concentrations. The inhibitor of TDP1(H493R) was also detected.

Enhanced separation of fluorite from calcite in acidic condition

In this study, the effects of reagent addition order on the flotation behavior of calcite and fluorite, as well as the influence of acid on the floatation behavior of the calcite, were investigated. Results showed that when the calcite surface had adsorbed the collector, the depression of calcite became increasingly difficult. The presence of acid significantly enhanced the selective depressing effect of depressants on calcite. Actual ore flotation and artificial mixed ore flotation experiments demonstrated that the addition of acid can significantly reduce the calcite content in the concentrate. This phenomenon can be explained by the exposure of the new calcite surface due to the surface dissolution, which facilitated the reaction of calcite with the depressor.

Manipulation of the Geometry and Modulation of the Optical Response of Surfactant-Free Gold Nanostars: A Systematic Bottom-Up Synthesis.

Among plasmonic nanoparticles, surfactant-free branched gold nanoparticles have exhibited exceptional properties as a nanoplatform for a wide variety of applications ranging from surface-enhanced Raman scattering sensing and imaging applications to photothermal treatment and photoimmunotherapy for cancer treatments. The effectiveness and reliability of branched gold nanoparticles in biomedical applications strongly rely on the consistency and reproducibility of physical, chemical, optical, and therapeutic properties of nanoparticles, which are mainly governed by their morphological features. Herein, we present an optimized bottom-up synthesis that improves the reproducibility and homogeneity of the gold-branched nanoparticles with desired morphological features and optical properties. We identified that the order of reagent addition is crucial for improved homogeneity of the branched nature of nanoparticles that enable a high batch-to-batch reproducibility and reliability. In addition, a different combination of the synthesis parameters, in particular, additive halides and concentration ratios of reactive Au to Ag and Au to Au seeds, which yield branched nanoparticle of similar localized surface plasmon resonances but with distinguishable changes in the dimensions of the branches, was realized. Overall, our study introduces the design parameters for the purpose-tailored manufacturing of surfactant-free gold nanostars in a reliable manner.

Ampholytic starch excipients for high loaded drug formulations: Mechanistic insights

Ampholytic starch derivatives are proposed as a new class of excipients carrying simultaneously anionic carboxymethyl (CM) and cationic aminoethyl (AE) groups on starch (St) polymeric chains. Three different types of derivatives were obtained by using the same reagents and varying only the order of their addition in the reaction medium: in one step method (OS) the two reactants were added simultaneously, whereas in two steps method (TS) either CMSt or AESt were prepared separately in the first step, followed by subsequent addition of the second reactant. It was found that all ampholytic derivatives were able to generate monolithic tablets by direct compression and allowed 60% loading of acidic (Acetylsalicylic acid), basic (Metformin), zwitterion (Mesalamine) or neutral (Acetaminophen) as drug models. The in vitro dissolution tests followed for 2 h in SGF and then in SIF, showed that the mentioned starch derivatives were stabilized by self-assembling and generated matrices able to control the release of drugs for about 24 h. The addition order of reagents has an impact on ampholytic starch properties offering thus a high versatility of this new class of starch excipients that can be tailored for challenging formulations with high dosages of several drugs.

Dearomatization Approach to 2-Trifluoromethylated Benzofuran and Dihydrobenzofuran Products.

A mild dearomatization enabled ortho-selective replacement of an aromatic C-H bond with a hexafluoroacetylacetone (hfacac) substituent has been developed. This reaction is dependent on a hypervalent iodine generated phenoxonium intermediate, a critical choice of solvent, and reagent addition order. The fluorinated dihydrobenzofuran product can be transformed into dihydrobenzofuran and benzofuran products decorated with a 2-trifluoromethyl group. The 3-trifluoromethylacyl substituted benzofurans rapidly form hydrates, which can be reduced to the corresponding alcohols.

Behaviour of ilmenite as a gangue mineral in the benzohydroxamic flotation of a complex pyrochlore-bearing ore

One challenge identified in the flotation of niobium bearing minerals with hydroxamates is the recovery of gangue minerals which can result in concentrate grade dilution. Micro-flotation of single and mixed minerals and bench scale flotation tests on a low-grade complex pyrochlore-bearing ore were conducted to assess the flotation behavior of ilmenite as a gangue mineral in the flotation of pyrochlore using benzohydroxamic acid (BHA) as a collector and sodium hexametaphosphate (SHMP) as a dispersant/depressant. In micro-flotation, high dosages of BHA resulted in high pyrochlore recovery and low ilmenite recovery at pH 8. It was observed that the order of addition of SHMP in relation to BHA had a strong effect on pyrochlore recovery, with high recovery maintained only when SHMP was added after BHA. When ilmenite and pyrochlore were floated in the same system, it was found that reagent addition order played an important role in selective flotation of pyrochlore. Flotation of pyrochlore was more selective over ilmenite when SHMP was added before BHA, similar to a cleaner flotation stage in real-ore flotation. Contrary to micro-flotation results titanium recovery was high (more than 60% TiO2 recovery in most cases) under similar pulp conditions in bench scale flotation, an indication that to some extent titanium minerals were recovered by a mechanism other than genuine flotation. Similarly, in mixed mineral micro-flotation, the recovery of ilmenite increased in the presence of pyrochlore. Two possible scenarios, one physical and the other chemical in nature, have been proposed to explain this observed phenomenon. First, it is possible that moderately floatable titanium mineral particles were recovered in the froth by association with highly floatable pyrochlore, particularly at starvation levels of a dispersant (SHMP) through the hydraulic entrainment of fines. The second possibility is that titanium minerals experienced inadvertent activation in multi-mineral systems, perhaps with metal-hydroxamates as the activating species, forming hydroxamate complexes involving ferric and/or niobium species. This research area is under further investigation.

How does the size of gold nanoparticles depend on citrate to gold ratio in Turkevich synthesis? Final answer to a debated question

The dependence between the size of gold nanoparticle (AuNP) and the citrate to gold molar ratio (X) is still a matter of debate 65years after the seminal work by Turkevich et al. for high X values. We assume that this dispersion of results is due to the variation of certain parameters that are often not mentioned in the protocols, and to the use of a single characterization technique (dynamic light scattering (DLS) or transmission electron microscopy (TEM)). To adress definitely the question of this dependence, we have synthesized AuNPs with very precise protocols ensuring that the only parameters to be modified are X and the sequence of reagent addition. We have then studied, for the first time, the dependence of the size with X quantitatively with a multimodal approach (UV–Visible spectroscopy, DLS and TEM) for 2 synthetic routes differing only by the sequence of reagent addition. We show unambiguously that AuNPs’ size decay monotonically, with X whatever the order of reagent addition. It allows us to exclude the occurrence of a measurable discontinuity for a peculiar value of X that prompted some authors to postulate the existence of two different reaction pathways when the citrate to gold molar ratio is around this value. In contrast, our result is in line with one reaction pathway, likely a “seed-mediated” growth mechanism, which should leads to monotonic size decrease. Also, we note that our result agrees with the sole available theoretical prediction (Kumar et al., 2007) on the whole range of X. Despite this apparent agreement, we point some contradictions between recent experimental results and basal hypothesis of this model.

Adsorption of copper sulphate on PGM-bearing ores and its influence on froth stability and flotation kinetics

Copper sulphate is used as an activator in the flotation of base metal sulphides as it promotes the interaction of collector molecules with mineral surfaces. It has been used as an activator in certain platinum group mineral (PGM) flotation operations in South Africa although the mechanisms by which improvements in flotation performance are achieved are not well understood. Some investigations have suggested these changes in flotation performance are due to changes in the froth phase rather than activation of minerals by true flotation in the pulp zone. In the present study, the effect of copper sulphate on froth stability was investigated on two PGM containing ores, namely Merensky and UG2 (Upper Group 2) ores from the Bushveld Complex of South Africa. Froth stability tests were conducted using a non-overflowing froth stability column. Zeta potential tests and ethylenediaminetetraacetic acid (EDTA) tests were used to confirm the adsorption of reagents onto pure minerals commonly found in the two ores. The results of full-scale UG2 concentrator on/off copper sulphate tests are also presented. The UG2 ore showed a substantial decrease in froth stability in the order of reagent addition: no reagents>copper>xanthate>copper+xanthate, while Merensky ore showed a slight decrease. It was shown through zeta potential measurements that copper species were to be found on plagioclase, chromite, talc and pyrrhotite surfaces and through EDTA extraction that this copper was in the form of almost equal amounts of Cu(OH)2 and chemically reacted copper ions on the Merensky and UG2 ore surfaces. In certain cases, the presence of copper sulphate and xanthate substantially increased the recovery, and therefore the implied hydrophobicity, of pure minerals in a frothless microflotation device. It was, therefore, proposed that increases in hydrophobicity beyond an optimum contact angle for froth stability, were the cause of instabilities in the froth phase and these were found to impact grade and recovery in a full-scale concentrator. Differences in the extent of froth phase effects between the different ores can be attributed to differences in mineralogy.

REMOVAL OF PHOSPHORUS FROM WASTE OF A BEVERAGE INDUSTRY BY STRUVITE PRECIPITATION

Waste from a cola beverage industry containing high concentration of phosphorus (P) was treated by the struvite precipitation method. The influence of excess of ammonia and order of reagent addition were evaluated as independent variables on the removal and recovery of phosphorus from cola beverage waste. It was removed about 95% of P of the sample in a short reaction time. The precipitated crystals were identified and analyzed by X-ray Diffraction (XRD), infra-red spectroscopy (IR) and surface area (BET), revealing that there was the formation of a pure and mesoporous crystalline phase.

Importance of reagent addition order in contaminant degradation in an Fe(ii)/PMS system

Reagent addition order has a significant effect on the contaminant degradation process in an Fe(II)/PMS system.

Coating process and stability of metal-polyphenol film

Supramolecular metal-organic thin films coated on material surfaces have attracted considerable interest in chemistry and materials science. Tannic acid (TA), a natural polyphenol product, has been recently demonstrated to be able to crosslink through coordination with Fe3+ ions, thus providing a novel metal-organic system to build nano-scale coating on various substrates. However, the coating process of Fe3+-TA film and the experimental parameters that influence the stability of the film are not well elucidated. In this study, we explored the effects of experimental parameters (order of reagents addition, addition of alkali and surface wettability of the substrates) on the stability of the Fe3+-TA film, and further inferred the mechanism of the coating process, using quartz and silicon as model substrates. The results showed that the Fe3+-TA films prepared in reverse order of reagent addition exhibited totally different growth profiles during the film formation process. The addition of alkali solution had very little impact on the film thickness, but changed the structure and morphology of the film and dramatically improved its stability. Moreover, low-wettable surface facilitates the formation of stable Fe3+-TA film. By the analysis of the chemical compositions, the mechanisms of the formation of these films were specified. This study provides a better understanding of the coating process of the Fe3+-TA film, which would benefit to develop the stable Fe3+-TA system with desirable properties for specific applications.

Regioselectivity in ligand substitution reactions on diiron complexes governed by nucleophilic and electrophilic ligand properties.

The discovery of a diiron organometallic site in nature within the diiron hydrogenase, [FeFe]-H2ase, active site has prompted revisits of the classic organometallic chemistry involving the Fe-Fe bond and bridging ligands, particularly of the (μ-SCH2XCH2S)[Fe(CO)3]2 and (μ-SCH2XCH2S)[Fe(CO)2L]2 (X = CH2, NH; L = PMe3, CN(-), and NHC's (NHC = N-heterocyclic carbene)), derived from CO/L exchange reactions. Through the synergy of synthetic chemistry and density functional theory computations, the regioselectivity of nucleophilic (PMe3 or CN(-)) and electrophilic (nitrosonium, NO(+)) ligand substitution on the diiron dithiolate framework of the (μ-pdt)[Fe(CO)2NHC][Fe(CO)3] complex (pdt = propanedithiolate) reveals the electron density shifts in the diiron core of such complexes that mimic the [FeFe]-H2ase active site. While CO substitution by PMe3, followed by reaction with NO(+), produces (μ-pdt)(μ-CO)[Fe(NHC)(NO)][Fe(CO)2PMe3](+), the alternate order of reagent addition produces the structural isomer (μ-pdt)[Fe(NHC)(NO)PMe3][Fe(CO)3](+), illustrating how the nucleophile and electrophile choose the electron-poor metal and the electron-rich metal, respectively. Theoretical explorations of simpler analogues, (μ-pdt)[Fe(CO)2CN][Fe(CO)3](-), (μ-pdt)[Fe(CO)3]2, and (μ-pdt)[Fe(CO)2NO][Fe(CO)3](+), provide an explanation for the role that the electron-rich iron moiety plays in inducing the rotation of the electron-poor iron moiety to produce a bridging CO ligand, a key factor in stabilizing the electron-rich iron moiety and for support of the rotated structure as found in the enzyme active site.