Side Reaction Products Research Articles

Mechanochemical synthesis of colloidal silver chloride particles in the NH4Cl–AgNO3–NH4NO3 system

Silver chloride nanoparticles prepared by exchange mechanochemical reaction NH4Cl + AgNO3 + zNH4NO3 = (z + 1)NH4NO3 + AgCl in ammonium nitrate matrix (diluent and side reaction product) at dilution parameters z = 7.22 and 3.64 are studied by X-ray diffraction and thermal analysis, electron microscopy, and dynamic light scattering. It is shown that free-form AgCl nanoparticles can be obtained after removal of ammonium nitrate by washing-out with water or thermal annealing at 300°C.

Contaminants in water: non-target UHPLC/MS analysis

Contamination of water resources is one of the major problems to be faced for environment preservation and sustainability. The monitoring of target compounds based on mass spectrometry and selected reaction monitoring mode is often insufficient to definitely assess the quality of surface water. Also potentially harmful non-target pollutants simultaneously present must be taken into account. Liquid chromatography coupled with tandem mass spectrometry is suitable to obtain complete information on water composition. Hybrid mass spectrometers such as triple quadrupole/linear ion trap, hybrid quadrupole/time-of-flight and linear ion trap/orbitrap analyzers should be used. Here, we review ultra-high performance liquid chromatography coupled with mass spectrometry methods developed for post-target and non-target screening analysis of water emerging contaminants, such as pesticides and their degradation products, pharmaceuticals and drug side-reaction products, surfactants and illicit drugs. The major points are the following: (1) the possibility of performing retrospective analysis only by high-resolution mass analyzer; (2) the compatibility of mass analyzer with ultra-high performance liquid chromatography; (3) the use of deconvolution software to detect unknowns; and (4) the limited availability of library database.

Quantitative I n Operando Spectroscopic Measurements of Species Concentrations in a Sodium-Halide Cell

Introduction In order to meet the increasing demand for energy storage, new battery technologies are needed to fulfill the needs of a world where electricity is of increasing importance (1, 2). One of the difficulties of developing new battery technologies is characterizing the electrochemical reactions that occur within the battery electrolyte. In this work, the authors present a novel approach for quantitative in-operando optical measurements of electrochemistry in battery electrolytes. An optically accessible cell was fabricated using a ceramic ion exchange membrane made from NASICON (Na Ion Super Conductor), a promising alternative to β-alumina for molten sodium batteries for stationary storage applications (3, 4, 5)­­. Optical access was achieved by sandwiching the battery between two UV-transparent windows (Figure 1). The battery chemistry utilized a copper cathode contained in an aqueous sodium iodide catholyte solution. During charging, copper is stripped from the cathode to form aqueous CuI2 -. The full cell reaction is Na+ + 2I- +Cu(s) ↔ Na + CuI2 - The aim of this work was to monitor the species present in the catholyte solution spectroscopically. Species concentrations were determined from UV absorption spectra using absorption cross-sections measured through fundamental experiments and calculated through ab initio simulations. Experimental Figure 1: Conceptual drawing of the optically accessible sodium halide cell. Optical access allows for in-operando measurements of electrochemical species concentrations via spectroscopic methods. The channels for the anode and cathode are each 2 mm wide. The cathode is spaced 1 mm from the NASICON separator. The separator is 1 mm thick. A molten sodium battery was constructed inside the optical cell by machining a NASICON wafer to accommodate a molten sodium anode and an aqueous catholyte. The front window of the cell was machined to allow electrodes and plumbing to be passed into the cell. Viton gaskets were used to seal around the NASICON, separating the aqueous solution from the sodium. UV absorption spectroscopy was used to measure changes in CuI2 -concentration as the cell was operated. Fundamental spectroscopic experiments were carried out to isolate the spectra of relevant electrochemical species. Measurements of the absorption cross-sections of the electrochemical species were then used to make quantitative measurements of species concentration in operando. Ab initio calculations of the UV-visible absorption spectra of relevant electrochemical species and possible products of side reactions (Na+, I-, I3 -, I2, and CuI2 -) were performed at the TD-B3LYP//aug-ccpv5z-pp, TD-M062X//aug-ccpv5z-pp, and EOM-CCSD//aug-ccpv5z-pp levels of theory. Calculations were carried out in Gaussian 09. Results of the calculations were compared to experimental results to verify assignment of absorption features to species present in the electrolyte. Conclusions A fully functional, optically accessible cell based on molten sodium-halide chemistry with a NASICON ion exchange membrane has been demonstrated. Furthermore, quantitative measurements of relevant electrochemical species concentrations have been demonstrated. UV absorption cross-sections of the electrochemical species and possible side reaction products have also been measured experimentally and calculated through ab initio methods. Acknowledgements The authors would like to thank Dr. Imre Gyuk at the Department of Energy Office of Electricity for providing the funding for this work. The authors also thank Dr. David Ingersoll from Sandia National Laboratories for overseeing the project, Dr. Sai Bhavaraju and Matt Robins from Ceramatec for their battery expertise and advice, Dr. Huayang Zhu and Dr. Robert Kee at CSM for support in computational battery modeling, and Dr. C. Mark Maupin for supporting the ab initio calculations. References Farhangi, H. The path of the smart grid – IEEE Power and Energy Magazine. 2010 , 8 (1), 18-28.Yang, Z.; Zhang, J.; Kinter-Meyer, M.C.; Lu, X.; Choi, D.; Lemmon, J.P.; and Liu, J. Electrochemical energy storage for green grid. Chemical Reviews. 2011, 111(5), 3577-3613.Hueso, K.B.; Armand, M.; and Rojo, T. High temperature sodium batteries: status, challenges and future trends. Energy Environmental Sci. 2013, 6(3), 734-749.Bhavarju, S.; Robins, M.; and Boxley, C. Battery charge transfer mechanisms. US20140030571 A1, January 30, 2014Zhu, H.; Bhavarju, S.; and Kee, R.J. Computational model of a sodium–copper–iodide rechargeable battery. Electrochimica Acta. 2013 112, 629-639. Figure 1

Three-Dimensional Au Microlattices as Positive Electrodes for Li-O2 Batteries.

We demonstrate the feasibility of using a 3-dimensional gold microlattice with a periodic porous structure and independently tunable surface composition as a Li-O2 battery cathode. The structure provides a platform for studying electrochemical reactions in architected Li-O2 electrodes with large (300 μm) pore sizes. The lack of carbon and chemical binders in these Au microlattices enabled the investigation of chemical and morphological processes that occur on the surfaces of the microlattice during cycling. Li-O2 cells with Au microlattice cathodes were discharged in 0.5 M lithium-bis(trifluoromethane)sulfonamide (LiTFSI) in a 1,2-dimethoxyethane (DME) electrolyte, with lithium metal foil as the anode. SEM analysis of microlattice cathodes after first discharge revealed the presence of toroidal-shaped 500-700 nm particles covering the surface of the electrode, which disappeared upon subsequent charging. Raman and FTIR spectroscopy analysis determined these particulates to be Li2O2. The morphology of discharge products evolved with cycling into micrometer-sized clusters of arranged "platelets", with a higher amount of side reaction products such as Li2CO3 and LiOH. This work shows that properly designed 3-dimensional architected materials may provide a useful foundation for investigating fundamental surface electrochemistry while simultaneously enabling mechanical robustness and enhancing the surface area over a factor of 30 compared with a thin film with the same foot print.

A Self-Promotion Effect during ORR Process in Lithium Oxygen Battery

Rechargeable lithium oxygen batteries have attracted enormous attention due to its high theoretical energy density which could fulfill the ever increased energy requirement for electrification of road transport. There are numerous significant problems hinder it moving from theory to practice, especially the fundamental understanding of ORR and OER processes. Great efforts have been paid on the fundamental mechanism of O2 reduction in nonaqueous electrolyte. In this study, by combining cyclic voltammetry (CV) with in-situ surface enhanced Raman spectroscopy (SERS), we show a self-promotion effect during ORR process in aprotic lithium oxygen battery, that is the residual lithium peroxide after charge can act as an effective nucleation site for subsequent discharge process, promoting the lithium peroxide precipitation. The promotion effect becomes more obvious as cycles continue, then recedes after dozens of cycles since the electrode surface is blocked by side reaction products. This self-promotion effect is strongly affected by the solvent, as reported previously, the pathway of O2 reduction to form Li2O2 is related to the solvent donor number (DN). We proved here the self-promotion effect of lithium peroxide is obviously observed in intermediate DN solvents in which lithium peroxide precipitation undergoes electrode surface and solution pathways simultaneously. As a result of the self-promotion effect, the discharge capacity increases as cycles continue during first dozens of cycles. In summary, this work provide more insights into the ORR process for further fundamental understanding of lithium oxygen battery.

Adaptation and transcriptome analysis of Aureobasidium pullulans in corncob hydrolysate for increased inhibitor tolerance to malic acid production.

Malic acid is a dicarboxylic acid widely used in the food industry, and is also a potential C4 platform chemical. Corncob is a low-cost renewable feedstock from agricultural industry. However, side-reaction products (furfural, 5-hydroxymethylfurfural (HMF), formic acid, and acetic acid) that severely hinder fermentation are formed during corncob pretreatment. The process for producing malic acid from a hydrolysate of corncob was investigated with a polymalic acid (PMA)-producing Aureobasidium pullulans strain. Under the optimal hydrolysate sugar concentration 110 g/L, A. pullulans was further adapted in an aerobic fibrous bed bioreactor (AFBB) by gradually increasing the sugar concentration of hydrolysate. After nine batches of fermentation, the production and productivity of malic acid reached 38.6 g/L and 0.4 g/L h, respectively, which was higher than that in the first batch (27.6 g/L and 0.29 g/L h, respectively). The adapted strain could grow under the stress of 0.5 g/L furfural, 3 g/L HMF, 2g/L acetic acid, and 0.5 g/L formic acid, whereas the wild type did not. Transcriptome analysis revealed that the differentially expressed genes were related to carbohydrate transport and metabolism, lipid transport and metabolism, signal transduction mechanism, redox metabolism, and energy production and conversion under 0.5 g/L furfural and 3 g/L HMF stress conditions. In total, 42 genes in the adapted strain were upregulated by 15-fold or more, and qRT-PCR also confirmed that the expression levels of key genes (i.e. SIR, GSS, CYS, and GSR) involved in sulfur assimilation pathway were upregulated by over 10-fold in adapted strain for cellular protection against oxidative stress.

Ultrathin Europium Oxide Nanoplatelets: “Hidden” Parameters and Controlled Synthesis, Unusual Crystal Structure, and Photoluminescence Properties

A good understanding of the relationship between the atomic scale structure of ultrasmall europium oxide nanocrystals (NCs) and their photoluminescence properties is of major interest in the design and development of innovative europium-based nanophosphors. As a consequence, the preparation of reliable (controlled size and shape distributions) and structurally well characterized ultrasmall europium oxide NCs is an essential prerequisite to understand the size effects on their photoluminescence properties. First, we reveal that nonaqueous approaches used to synthesize ultrasmall europium oxide NCs are deeply affected by “hidden” parameters that are directly related to the preparation of the reactive mixture. Indeed, trace amounts of products of side reactions and byproducts, such as acetic acid and water, act as growth-directing agents. Second, the challenging problem related to the structural characterization of ultrasmall europium oxide NCs is addressed for the first time by coupling high-resolution transmission electron microscopy and X-ray atomic pair distribution function. The ultrasmall thickness of the as-prepared NCs apparently dictates the crystalline structure, which can no longer be described by the crystal phases of their bulk counterparts. The induced distortions due to the ultrasmall thickness as well as the bonding of the stabilizing organic ligand are strong enough to break down the symmetry and, hence, prevent the europium oxide NCs from accommodating the usual bulk crystal phase. Finally, the formation of such unusual polymorphs of europium oxide has a profound impact on the resulting crystal field, with direct effects on the photoluminescence properties.

Electrochemical Effects of Silicon/Diamond-Like Carbon Layered Composite on Oxygen Cathodes in Lithium–Oxygen Batteries

Lithium–oxygen batteries are one of the most promising energy storage systems because of their high energy density. However, lithium carbonate (Li2CO3) and lithium carboxylates (HCO2Li, CH3CO2Li) are formed on cycling, which results in high charging over-potential and limited cycle life. In this study, a silicon/diamond-like carbon (Si–DLC) coating film was deposited onto an O2 electrode uniformly by plasma-enhanced chemical vapor deposition to improve the electrochemical properties of lithium–oxygen batteries. The coated layer prevented the direct contact of carbon with both the Li2O2 and the electrolyte, resulting in suppression of side-reaction product formation. For this reason, the coated cell showed better cycle life and round-trip efficiency than the pristine cell. When the charge was terminated, the potentials of the coated cell were 4.15V for both the 1st and 5th cycles, whereas those of a pristine cell were 4.34V for the 1st cycle and 4.51V for the 5th cycle at a current density of 100mAg−1 with a limited duration of 10h for a single charge and discharge cycle. The coated cell was able to stably reach 50 cycles, whereas the pristine cell only lasted 7 cycles.

Investigation of Naturally Occurring Fumonisin B1 and Glycated Fumonisin B1 in Korean Feedstuffs

Mycotoxins are potentially dangerous contaminants of livestock feeds. In this study, we measured the levels of fumonisin B1 and glycated fumonisin B1 in feedstuffs and then investigated the ability of the extrusion heating regimen to convert the most prevalent mycotoxin contaminant, fumonisin B1, to a less toxic glycated form. All feed samples were analyzed with fully validated methods. All measured concentrations of fumonisin B1 were below harmful thresholds, including European Union-recommended levels or US Food and Drug Administration action levels. Because fumonisin B1 was highly contaminated mycotoxin in our present investigation and fumonisin B1 has been shown to be less toxic following Maillard type reaction with reducing sugar, we examined the formation of fumonisin B1 derivatives by Maillard reaction under extrusion process conditions. We employed a variety of tandem mass spectrometric methodologies to selectively detect fumonisin B1 derivatives and to elucidate their structures partially. We found that compounds of m/z 736 were more likely artifacts or side reaction products rather than glycation products. N-(carboxymethyl) fumonisin B1 of m/z 780 and other major glycation products of m/z 794 and 810 were not detected, and only negligible amounts of methylene fumonisin B1 was found in 10 extruded feed samples. Therefore, either the tested extrusion conditions did not induce fumonisin B1 glycation or the glycation products simply could not be detected by the method employed in this study.

Discovery of a heparan sulfate 3-O-sulfation specific peeling reaction.

Heparan sulfate (HS) 3-O-sulfation determines the binding specificity of HS/heparin for antithrombin III and plays a key role in herpes simplex virus (HSV) infection. However, the low natural abundance of HS 3-O-sulfation poses a serious challenge for functional studies other than the two cases mentioned above. By contrast, multiple distinct isoforms of 3-O-sulfotranserases exist in mammals (up to seven isoenzymes). Here we describe a novel peeling reaction that specifically degrades HS chains with 3-O-sulfated glucosamine at the reducing-end. When HS/heparin is enzymatically depolymerized for compositional analysis, 3-O-sulfated glucosamine at the reducing ends appears to be susceptible to degradation under mildly basic conditions. We propose a 3-O-desulfation initiated peeling reaction mechanism based on the intermediate and side-reaction products observed. Our discovery calls for the re-evaluation of the natural abundance and functions of HS 3-O-sulfation by taking into consideration the negative impact of this novel peeling reaction.

Thermal decomposition of FOX-7 studied by ab initio molecular dynamics simulations

Ab initio molecular dynamics simulations were conducted to study the thermal decomposition mechanisms of solid FOX-7. We found that the initial decomposition of FOX-7 has three main reaction routes. The C–NO2 bond fission as reported previously is indeed the most common route. However, the inter- and intramolecular hydrogen transfers are also found to be valid, which is contradictory to previous energy minimization calculation results. The simulations agree well with known experimental data in terms of activation energy and reaction side products. A complete reaction network that describes how the main products, H2O, CO2 and N2 form in FOX-7 decomposition, is constructed from the simulation trajectories.

Metal-free Reductive Cyclization and Isomerization of Sulfanyl-1,6-diynes Using Sodium Borohydride

Abstract In this study, we demonstrated the metal-free reductive cyclization of sulfanyl-1,6-diynes with sodium borohydride in ethanol in the presence of diazabicyclo[5.4.0]undec-7-ene. 1,6-Diynes 1 and 5a–5h bearing hydrogen or phenyl as the R2 group afforded pyrroles 2 and 6a–6e in high yields without any side reaction products such as enynyl sulfides. 1,6-Diyne (R2 = Et) produced both pyrrole and enynyl sulfides; however, the use of cesium fluoride succeeded in the selective formation of pyrrole 6f.

Wisdom from the Human Eye: A Synthetic Melanin Radical Scavenger for Improved Cycle Life of Li–O2 Battery

Li–O2 batteries are attractive systems because they can deliver much higher energy densities than those of conventional lithium-ion batteries by engaging light gas-phase oxygen as a cathode active material. However, the inevitable generation of residual superoxide radicals gives rise to irreversible side reactions and consequently causes severe capacity degradation over cycling. To address this chronic issue, herein, we have taken a lesson from the human eye. Analogous to Li–O2 batteries, the human eye is liable to attack by reactive oxygen species (ROS), from its lifetime exposure to sunlight. However, it protects itself from the ROS attack by using melanin as a radical scavenger. To mimic such a defense mechanism against radical attack, we included polydopamine (pD), which is one of the most common synthetic melanins, in the ether-based electrolyte. As an outcome of the superoxide radical scavenging by the pD additive, the irreversible side reaction products were alleviated significantly, resulting in superior cycling performance. The present investigation provides a message that simple treatments inspired by the human body or nature could be effective solutions to the problems in various energy devices.

Sonochemical synthesis of lithium fluoride nano cubic as an active and simple catalyst for thia-Michael addition process: synthesis and structural characterization of β-aryl-β-mercapto ketones

LiF nano cubic, with an average particle size of 21.6 nm, was synthesized sonochemically, using tetrabutylammonium fluoride as the fluoride source and characterized by SEM-EDX and XRD. This was applied, as a heterogeneous nano-catalyst, to synthesize some β-aryl-β-mercapto ketone derivatives via thia-Michael addition reactions with excellent yields at room temperature. In this catalytic system, the products of undesirable side reactions resulting from 1,2-addition, polymerization, bis-addition and oxidative coupling of thiols were not observed. The products were characterized by elemental analysis, IR, NMR and mass, and also single crystal X-ray determination for 3-(4-chlorophenylthio)-1,3-diphenylpropan-1-one, 1-phenyl-3-(phenylthio)-3-p-tolylpropan-1-one, 3-(p-tolylthio)-1-phenyl-3-p-tolylpropan-1-one and 3-(4-chlorophenylthio)-1-phenyl-3-p-tolylpropan-1-one. Following the recent search on the CSD, it is found that there is no report on the structure determination of [R1]C[H][CH2C(O)R2][S-Ar] β-aryl-β-mercapto ketones with the S-C6H5, S-C6H4-p-CH3 and S-C6H4-p-Cl segments (as S-Ar).

Shape-selected nanocrystals for in situ spectro-electrochemistry studies on structurally well defined surfaces under controlled electrolyte transport: A combined in situ ATR-FTIR/online DEMS investigation of CO electrooxidation on Pt.

The suitability and potential of shape selected nanocrystals for in situ spectro-electrochemical and in particular spectro-electrocatalytic studies on structurally well defined electrodes under enforced and controlled electrolyte mass transport will be demonstrated, using Pt nanocrystals prepared by colloidal synthesis procedures and a flow cell set-up allowing simultaneous measurements of the Faradaic current, FTIR spectroscopy of adsorbed reaction intermediates and side products in an attenuated total reflection configuration (ATR-FTIRS) and differential electrochemical mass spectrometry (DEMS) measurements of volatile reaction products. Batches of shape-selected Pt nanocrystals with different shapes and hence different surface structures were prepared and structurally characterized by transmission electron microscopy (TEM) and electrochemical methods. The potential for in situ spectro-electrocatalytic studies is illustrated for COad oxidation on Pt nanocrystal surfaces, where we could separate contributions from two processes occurring simultaneously, oxidative COad removal and re-adsorption of (bi)sulfate anions, and reveal a distinct structure sensitivity in these processes and also in the structural implications of (bi)sulfate re-adsorption on the CO adlayer.

Synthesis of bis(2-haloethyl) selenides by reaction of selenium dihalides with ethylene

Introduction in the organic synthesis of new electrophilic reagents, selenium dichloride and dibromide, made it possible to develop effi cient methods of preparation of new organoselenium compounds [1–4]. Based on reactions of selenium dihalides with acetylene a new stereoselective method was developed for the synthesis of (Е,Е)-bis(2-halovinyl) selenides [2]. The reaction of selenium dihalides with alkenes proceeds stereoselectively leading to the formation of substituted bis-(2-haloethyl) selenides, products of addition by Markovnikoff rule or against it depending on the substituent at the double bond (electron-donor [3] or electron-acceptor [4]). Reactions of selenium dihalides with ethylene were not described in the literature. They would be applied to the direct atom economy synthesis of bis(2-haloethyl)selenides (I, II). Note that 2-haloethyl selenides are used in organic synthesis [5] and exhibit antitumor activity [6]. The published information exists on a reaction of selenium monochloride (Se2Cl2) with ethylene that results in bis(2-chloroethyl)selenium dichloride [7]. The reaction with ethylene of selenium tetrahalides afforded bis(2-haloethyl)selenium dihalides [8]. Therefore the preparation of selenides I, II in one stage from ethylene and selenium monohalides or tetrahalides failed [7, 8]. We investigated the reactions of selenium dihalides with ethylene and found the conditions ensuring the preparation of selenides I, II in up to 90–94% yield and minimum of side reaction products. SeX2 + 20_25°C X Se X

PEMFC Cathode Contamination Mechanisms for Several VOCs - Acetonitrile, Acetylene, Bromomethane, Iso-Propanol, Methyl Methacrylate, Naphthalene and Propene

The behavior of PEMFCs exposed to airborne contaminants was characterized in 2 stages. In the first stage, impedance spectroscopy was used to identify resistance loss types. In the second stage, other ex situ and in situ characterization methods were employed to obtain more detailed information about observed resistance loss types: rotating ring/disc electrode, membrane conductivity cell, tracer based method for residence time distribution measurements, segmented cell, and fuel cell coupled with a gas chromatograph/mass spectrograph. All 7 VOCs led to kinetic and mass transfer resistance changes. Only acetonitrile led to an ohmic resistance change. A decrease in catalyst active area (7 to >90 %) and increase in H2O2 side reaction product (18 to 1027 %) accounts for the smaller oxygen reduction current (12 to 100 %). An acetonitrile decomposition product is presumed to be responsible for the observed in situ ohmic loss because acetonitrile did not show an effect in the conductivity cell. Modest current redistributions were noted (<19 % on an absolute and dimensionless basis) but acetylene also initially showed a strong transient effect (≤100 % on an absolute and dimensionless basis) attributed to a gradual contamination along the flow field length. Only the unaffected contaminant species, CO2 and CO were detected at the cathode outlet. Contaminant conversion increased at higher cell voltages (62 to 332 % V-1) indicative of electrochemical oxidation. An acetylene contamination mechanism is proposed.

A Highly Productive, Whole-Cell DERA Chemoenzymatic Process for Production of Key Lactonized Side-Chain Intermediates in Statin Synthesis

Employing DERA (2-deoxyribose-5-phosphate aldolase), we developed the first whole-cell biotransformation process for production of chiral lactol intermediates useful for synthesis of optically pure super-statins such as rosuvastatin and pitavastatin. Herein, we report the development of a fed-batch, high-density fermentation with Escherichia coli BL21 (DE3) overexpressing the native E. coli deoC gene. High activity of this biomass allows direct utilization of the fermentation broth as a whole-cell DERA biocatalyst. We further show a highly productive bioconversion processes with this biocatalyst for conversion of 2-substituted acetaldehydes to the corresponding lactols. The process is evaluated in detail for conversion of acetyloxy-acetaldehyde with the first insight into the dynamics of reaction intermediates, side products and enzyme activity, allowing optimization of the feeding strategy of the aldehyde substrates for improved productivities, yields and purities. The resulting process for production of ((2S,4R)-4,6-dihydroxytetrahydro-2H-pyran-2-yl)methyl acetate (acetyloxymethylene-lactol) has a volumetric productivity exceeding 40 g L−1 h−1 (up to 50 g L−1 h−1) with >80% yield and >80% chromatographic purity with titers reaching 100 g L−1. Stereochemical selectivity of DERA allows excellent enantiomeric purities (ee >99.9%), which were demonstrated on downstream advanced intermediates. The presented process is highly cost effective and environmentally friendly. To our knowledge, this is the first asymmetric aldol condensation process achieved with whole-cell DERA catalysis and it simplifies and extends previously developed DERA-catalyzed approaches based on the isolated enzyme. Finally, applicability of the presented process is demonstrated by efficient preparation of a key lactol precursor, which fits directly into the lactone pathway to optically pure super-statins.

Facile and Stabile Linkages through Tyrosine: Bioconjugation Strategies with the Tyrosine-Click Reaction

The scope, chemoselectivity, and utility of the click-like tyrosine labeling reaction with 4-phenyl-3H-1,2,4-triazoline-3,5(4H)-diones (PTADs) is reported. To study the utility and chemoselectivity of PTAD derivatives in peptide and protein chemistry, we synthesized PTAD derivatives possessing azide, alkyne, and ketone groups and studied their reactions with amino acid derivatives and peptides of increasing complexity. With proteins we studied the compatibility of the tyrosine click reaction with cysteine and lysine-targeted labeling approaches and demonstrate that chemoselective trifunctionalization of proteins is readily achieved. In particular cases, we noted that PTAD decomposition resulted in formation of a putative isocyanate byproduct that was promiscuous in labeling. This side reaction product, however, was readily scavenged by the addition of a small amount of 2-amino-2-hydroxymethyl-propane-1,3-diol (Tris) to the reaction medium. To study the potential of the tyrosine click reaction to introduce poly(ethylene glycol) chains onto proteins (PEGylation), we demonstrate that this novel reagent provides for the selective PEGylation of chymotrypsinogen, whereas traditional succinimide-based PEGylation targeting lysine residues provided a more diverse range of PEGylated products. Finally, we applied the tyrosine click reaction to create a novel antibody-drug conjugate. For this purpose, we synthesized a PTAD derivative linked to the HIV entry inhibitor aplaviroc. Labeling of the antibody trastuzumab with this reagent provided a labeled antibody conjugate that demonstrated potent HIV-1 neutralization activity demonstrating the potential of this reaction in creating protein conjugates with small molecules. The tyrosine click linkage demonstrated stability to extremes of pH, temperature, and exposure to human blood plasma indicating that this linkage is significantly more robust than maleimide-type linkages that are commonly employed in bioconjugations. These studies support the broad utility of this reaction in the chemoselective modification of small molecules, peptides, and proteins under mild aqueous conditions over a broad pH range using a wide variety of biologically acceptable buffers such as phosphate buffered saline (PBS) and 2-amino-2-hydroxymethyl-propane-1,3-diol (Tris) buffers as well as others and mixed buffered compositions.

New range of natural products for pre-treatment of water desalination plants

Water desalination plants performance and time evolution of its main operational parameters may be influenced by the presence of certain substances both in solution and in suspension in natural waters. Within these substances, humic acids, which percentage may rise up to 50% of total organic matter, could lead to film formation on membranes surface if removal treatments are not properly implemented. Moreover, contact with disinfectant agents such as chlorine can cause the formation of trihalomethanes (THMs) as undesirable reaction side products. Synthetic coagulant and flocculant dosing programs are included as pre-treatments in water desalination plants as a first stage on water processing in order to remove colloidal matter, from both organic and inorganic sources. However, coagulant and flocculant overdosing not only may be null from the treatment effectiveness point of view but also might lead to recalcitrant fouling phenomena. ADIC GR102, a natural polymer, was used as a flocculant agent in natural organic matter removal processes leading to similar organic matter removal yields and Flocculation Index values to those obtained with currently marketed products. Several assays performed at 80% of coagulant requirement to destabilize the suspension and relatively low dosage of ADIC GR102 opened the doors to a promising future water treatment strategies.