Academic literature on the topic 'Organic carbon binding'

Binding organic liquids are a strong base of amidine have been used for CO2 capture. Up to now, there is no known datum on the reaction kinetics of CO2 with 1,5-Diazabicyclo[4.3.0]non-5-ene (DBN). In this paper, Kinetics of reaction between CO2 and DBN/MDEA in 1-Pentanol were performed utilizing the stirred cell reactor with DBN concentration (2 – 2.9 M) and at room temperature. The reaction path was qualified using zwitterion and the termolecular mechanism. From the kinetic datum with DBN concentrations (2 – 2.9 M), it was found that the capturing process happen in a fast reaction system with a second-order reaction kinetics of DBN/MDEA and first order with CO2. In addition, CO2 absorption was achieved using gas – liquid contact system. CO2 absorption rate was (2×10^(-5)-2.8 × 10^(-5) kmol⁄m^2 .sec) at DBN concentration (2 – 2.9 M). Finally, it is known that DBN/MDEA/1-Pentanol/CO2 system is easily switchable and can be used both CO2 capture and for other applications that require rapid change of medium from nonionic to ionic liquid.

Atrazine is still widely used in China. Atrazine residue (1.86–1 100 mg/kg) in the soil has exceeded the allowable limit (1.0 mg/kg), affecting soil structure and soil aggregate composition. To understand the long-term application of atrazine on soil aggregates and the binding agent, four treatments were established in cornfield planted since 1998, including without atrazine applied (AT₀), atrazine applied (28% atrazine, 1 200–1 350 mL/ha/year) once a year from 2012 to 2018 (AT₆, 167 mg/kg), from 2008 to 2018 (AT₁₀, 127.64 mg/kg) as well as from 2002 to 2018 (AT₁₆, 102 mg/kg) with three replications. Along with the increase of atrazine application time, the mass fraction of soil aggregates > 5 mm and 2–5 mm decreased significantly while the mass fraction of soil aggregates 0.5–2 mm and < 0.5 mm increased gradually, and the change of aggregate binding agents contents were the same as that of aggregates. The contents of soil organic carbon (SOC) and glomalin-related soil protein (GRSP) in the aggregates > 5 mm and 2–5 mm were significantly negatively correlated with the years of atrazine application. Our results show that although atrazine residue in the soil does not increase with the increased yearly application, its concentration is still markedly higher than the permitted limit value and seriously affected the content of SOC and GRSP of aggregates > 2 mm, which can lead to a decrease of soil aggregate stability and soil quality.

Abstract Recalcitrant organic matter (ROM) in combined kraft mill effluents is that organic matter remaining in the effluents after primary and secondary treatment. Recalcitrant organic matter comprises of both high molecular weight (HMW) and low molecular weight (LMW) components and is of interest, since environmental regulators are considering placing limits on final effluent COD and colour. Biologically treated pulp mill effluent was fractionated by ultrafiltration to study the contributions of the high and low molecular weight recalcitrant organics towards final effluent COD and AOX. Batch biodegradation tests were carried out on lab-generated biotreated effluent from lab scale sequencing batch reactors operating at 35, 45, 55 and 60°C, to investigate if the residual recalcitrant fraction could be further degraded. Biodegradation tests involved the optimization of the microbiological medium by the addition of either an alternate carbon source (glucose) or a carbon-nitrogen substrate (yeast extract). Treatment temperatures and nutrient levels were varied and the effect of each of these four factors on the biodegradability of the recalcitrant fractions was studied. The recalcitrant portion was found to be resistant to further biodegradation, even under optimized microbiological conditions. The HMW fraction of the ROM obtained from final biotreated effluent from a bleached kraft pulp mill (HMW ROMMill) was studied for its ability to bind other organic model pollutants in an aqueous environment. Pentachlorophenol (PCP) was tested for its binding onto the HMW ROMMill, using toxicity as a surrogate parameter for binding, in the Microtox™ test. Equilibrium dialysis studies were carried out to investigate the ability of HMW ROMMill to bind 14C-Benzopyrene (BaP) and 3H-dehydroabietic acid (DHA). Microtox™ studies failed to indicate the binding of PCP onto HMW ROMMill. BaP and DHA however did bind onto HMW ROMMill. BaP binding onto HMW ROMMill was higher than DHA binding, possibly due to its hydrophobicity. Also, increasing the dissolved organic carbon concentration of HMW ROMMill led to a decrease in the partition coefficient values for both BaP and DHA.

Carbon dioxide (CO2) capture has been the most crucial research issue due to the dangerous impact of carbon dioxide emissions on global warming and climate change. In recent decades, a new absorption technology has been used to get rid of carbon dioxide. This procedure is getting tremendous attention being applied to improve CO2 uptake by using nanofluids. However, other studies are needed to enhance the nanofluid absorption/desorption rate and decrease the requirements of energy through the desorption process. This research aimed to study the influence of addition nanoparticles by determining the enhancement factor of the absorption/desorption rate of carbon dioxide. All nanofluids used in this study prepared by adding nanoparticles with ultrasound treatment without surfactants. The influence of adding nanoparticles to the binding organic liquids (BOL) of monoethanolamine (MEA) and ethanol on the absorption/desorption of CO2 was studied experimentally in a stirring reactor. The nanoparticles of Al2O3, Fe2O3, and SiO2 were selected, which showed different properties for the investigation. The effect of volume percentage of nanoparticles, type of nanoparticles, and stirring speed on the rate of CO2 absorption and the impact of volume percentage of nanoparticles and type of nanoparticles on the CO2 desorption rate were studied. It has been found that nanoparticles suspended in BOL are a good absorbent in the current MEA infrastructure due to their less corrosive nature and lower energy requirements for regeneration than the current MEA. In this work, carbon dioxide absorption was improved by 11% and carbon dioxide absorption increased by 8.5% from BOL alone. The alumina nanofluid at a concentration of 0.05 absorbed the highest carbon dioxide by 0.061 g/s. In contrast, the iron oxide nano particles at a concentration of 0.01 volume% absorbed the most elevated carbon dioxide of 0.0077 g/s.

AbstractStrained aromatic macrocycles based on cycloparaphenylenes (CPPs) are the shortest repeating units of armchair single-walled carbon nanotubes. Since the development of several new synthetic methodologies for accessing these structures, their properties have been extensively studied. Besides the fundamental interest in these novel molecular scaffolds, their application in the field of materials science is an ongoing topic of research. Most of the reported CPP-type macrocycles display strong binding toward fullerenes, due to the perfect match between the convex and concave π-surfaces of fullerenes and CPPs, respectively. Highly functionalized CPP derivatives capable of supramolecular binding with other molecules are rarely reported. The synthesis of highly functionalized [n]cyclo-2,7-pyrenylenes leads to CPP-type macrocycles with a defined cavity capable of binding non-fullerene guests with high association constants.

Uncontaminated stream waters in the vicinity of a Co mine in Idaho were titrated with Cu to determine the Cu-binding characteristics of natural dissolved organic matter (DOM) and suspended particles. Nonlinear regressions of bound versus free Cu concentrations were consistent with a two-ligand model for DOM complexation of Cu, in which the conditional stability constants (log K) and complexation capacities (CC) were log K1 = 7.26, CC1 = 0.21 µmol Cu·mg dissolved organic carbon (DOC)-1 and log K2 = 5.13, CC2 = 2.89 µmol Cu·mg DOC-1. Copper-binding constants were similar in filtered (0.45 µm) and unfiltered water samples. Calcium, Mg, and Co did not compete appreciably with Cu for DOM complexation at concentrations present in site waters. Copper binding to amorphous iron oxide flocs also was not important at the Fe concentrations present in the stream waters. We selected a mixture of three organic acids, dipicolinic, oxalic, and malonic, to mimic the Cu-binding properties of this DOM. Geochemical models were developed to estimate Cu speciation and evaluate its bioavailability in companion fish toxicity tests using the DOM analogue (Marr et al. 1999. Can. J. Fish. Aquat. Sci. 56: 1471-1483).

The direct conversion of carbon–hydrogen bonds into valuable carbon-carbon and carbon-heteroatom bonds is a significant challenge to synthetic organic chemists. More than ever, chemists are employing Rh(III)-catalysts bearing cyclopentadienyl (Cp) ligands to transform otherwise inert C–H bonds. Furthermore, manipulating the sterics and electronics of the Cp ligand show significant impact on catalytic transformations. Our group has developed a library of CpˣRh(III)-precatalysts in hopes of enhancing known reactivity as well as discovering new C–H bond functionalizations. We have previously reported that N-enoxyphthalimides are a unique one-carbon component for the cyclopropanation of activated alkenes. In an effort to expand the scope to accessible alkenes, we have found a number of symmetrical unactivated alkenes undergo [2+1] annulation to afford intriguing spirocyclic cyclopropanes. Additionally, we have developed a Rh(III)-catalyzed diastereoselective [2+1] annulation onto allylic alcohols to furnish substituted cyclopropyl ketones. Notably, the traceless oxyphthalimide handle serves three functions: directing C–H activation, oxidation of Rh(III), and, collectively with the allylic alcohol, in directing cyclopropanation to control diastereoselectivity. Allylic alcohols are shown to be highly reactive olefin coupling partners leading to a directed diastereoselective cyclopropanation reaction, providing products not accessible by other routes. Next, an artifact of previous cyclopropanation reactions leads to the formation of a Rh-π-allyl complex. Attempts at 1,1-carboamination of alkenes are made using alkenes and nitrenoid precursors toward the 3-component synthesis of allylic amines. Stoichiometric studies help elucidate the mechanism and challenges. Lastly, efforts toward 1,2-carboamination of alkenes initiated by sp³ C–H bond activation are made with two different reactivity manifolds. Isolation of reaction intermediates are discussed as well as providing viable paths toward valuable products.

Sandy soils have low water and nutrient holding capacity which limit crop growth. In the short-term, these constraints can be overcome by increased fertiliser application or irrigation. However, long-term solutions are needed to improve farm productivity and sustainability. Clay added to sandy soils may be such a solution. Compared to sandy soils, clay soils have smaller pores and higher cation exchange capacity and therefore greater water and nutrient holding capacity. Clay can also bind organic matter via cation bridges and thereby reduce its accessibility to decomposing microbes. In sandy soils with clay subsoil, the clay can be mixed into the sandy top soil by delving or spading. However, the clay subsoil is not uniformly distributed in the sandy top soil. It forms clay peds of varying size which creates a highly non-uniform soil environment with patches of sandy soil with clay peds next to sandy soil with little or no clay. The clay-rich patches can hold more water and nutrients compared to the surrounding sandy soil that could influence nutrient availability and organic C binding. Little is known about the influence of ped size and rate of clay added to sandy soil on nutrient availability and organic C binding after residue addition. The aims of the study were i) to determine the effect of clay addition rate and ped size in residue amended sandy soil on soil respiration, nutrient availability and organic C retention ii) to assess the effect of clay soil particle size and clay soil properties on nutrient availability and organic C binding after addition of residues with low or high C/N ratio iii) to determine the effect of clay addition rate and ped size on nutrient leaching after mineral fertilizer addition. A series of incubation experiments were carried out to assess the effect of clay addition rate and ped size on nutrient availability and organic C retention on < 53 μm fraction after mixing with low and high C/N ratio residue. In the first study, clay peds of 1, 2 or 3 mm size derived from a clay-rich Vertosol (73% clay) were added to a sandy soil (3% clay) at clay addition rates of 10% and 20% w/w. After addition of ground mature faba bean residue (C/N 37) at 10 g kg-1, the soils were incubated for 45 days at 80% of water holding capacity. Clay addition to sandy soil influenced nutrient availability after plant residue addition, particularly when small peds are added at higher rates. Sandy soil with clay peds had a greater maximum NH4 and P sorption capacity than sandy soil alone, sorption capacity was higher at 20% compared to 10% clay addition and greater with 1 mm than 3 mm peds. Retrieval of clay peds at the end of the experiment showed ped breakdown during the experiment but also formation of larger peds. Compared to the < 53 μm fraction added at the start of the experiment, total organic carbon (TOC) content of the < 53 μm fraction was up to two-fold higher, particularly in the smaller peds (1 and 2 mm). The study confirmed that claying can increase organic C sequestration, but also showed that organic C sequestration is likely to be greatest when the added clay peds are small. The capacity to bind organic C and nutrients may depend on clay soil properties such as mineralogy, clay concentration and exchangeable Fe and Al. A 45-day experiment was carried out to investigate the effect of clay type on nutrient availability and organic carbon retention with residues differing in C/N ratio (20 or 47). Two clay soils with smectite as a dominant mineral were used. They differed in smectite percentage [high (40%) or low (5-10%)], clay content (73 or 42%) and exchangeable Fe and Al concentration (low or high). The clay soils were added to sandy soil at rate of 20% w/w either finely ground or as 2 mm peds. Over 45 days, available N and P, microbial biomass N and P concentrations and cumulative respiration were greater with low C/N than high C/N residue. With low C/N residue, compared to sandy soil alone clay addition increased available N concentration and initial microbial biomass C and N, but decreased cumulative respiration and P availability. This study showed that addition of clay soil to sandy soil influences nutrient availability, but there were no clear differences between clay soils or sizes. The lack of differences between high and low smectite clay soil suggests that a high concentration of Fe and Al oxides can compensate for a lower clay concentration and proportion of smectite with respect to binding of organic matter and nutrients. In the previous studies, we found that clay addition had no consistent effect on cumulative respiration and ped size effect was variable. Secondly, low C/N ratio residue had stronger effect on nutrient availability due to its high decomposition rate and nutrient release compared to high C/N ratio residue. The third experiment was conducted to investigate that if clay addition has a different effect on respiration and nutrient availability when added as peds with a greater range of sizes (1, 3 and 5 mm) in presence of plant residue with lower C/N ratio. The aims of this experiment were to (i) determine the effect of clay addition rate and ped size in residue amended sandy soil on nutrient availability, and (ii) assess breakdown of peds during the experiment and organic C retention by the < 53 μm fraction of the peds. Clay soil addition to sandy soil amended with plant residue reduced respiration rate and available P concentration. Ped size had little effect on respiration and nutrient availability. Clay soil addition increased soil organic carbon retention compared to sandy soil alone. With respect to ped size, the experiment showed substantial ped breakdown and but also formation of larger peds over 45 days. The first three experiments were conducted over 45 days. But longer term studies are needed to better evaluate the effect of claying in the field. To investigate the effect of repeated addition of residue (finely ground wheat mature shoots added every 2 months) in clay amended sandy soil, a longer term (8 months) study was conducted with clay soil added as finely ground soil, 1 and 3 mm peds. The organic C content of the whole soil increased during the experiment with a greater increase in clay amended soils. The organic C content of the > 53 μm fraction was very low and changed little over time. With finely ground clay soil and 1 mm peds, the organic C content of the < 53 μm fraction increased mainly in the first 2 months while in 3 mm peds it increased over 6 months to reach similar concentrations as with finely ground clay soil and 1 mm peds. Excessive use of fertilizer in sandy soils can cause leaching of nutrient elements N and P into water ways and cause eutrophication. In the fifth experiment, clay soil was added in sandy soil at 10% or 20% clay soil w/w finely ground or as 2 and 5 mm peds with and without N and P fertiliser (27 mg N kg-1 and 7 mg P kg-1). The clay sand mixture (30 g) was placed in cores with nylon mesh at the bottom. The soils were incubated at 80% water holding capacity and leachate was collected weekly for 50 days. Clay addition significantly reduced leaching of N and P as compared to sandy soil alone. In sandy soil alone, the highest N (68%) leaching occurred after the first week whereas the highest amount (41%) of P was leached after two weeks. It can be concluded that clay addition to sandy soil can reduce the risk of nutrient leaching and enhance carbon sequestration in sandy soils by decreasing C loss via respiration and leaching. This effect will be greatest with finely ground clay soil or small peds.
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food & Wine, 2017

碩士
國立臺北科技大學
化學工程研究所
101
Part I： A bifunctional nicotinamide adenine dinucleotide (NADH) and hydrogen peroxide (H2O2) biosensor has been successfully fabricated using poly(neutral red) (PNR), flavin adenine dinucleotide (FAD) and multi-walled carbon nanotubes (MWCNT). The electro-codeposition of PNR and FAD on MWCNT electrode can be easily carried out involving the positively charged PNR formation which induces the negatively charged FAD to codeposit on electrode surface. The PNR-FAD-MWCNT hybrid composite can effectively lower over-potential to 0.05 V and -0.1 V for NADH oxidation and H2O2 reduction, respectively. The kinetic constant, kkin, evaluated by voltammetry using a PNR-FAD-MWCNT rotating disk electrode (RDE), provided values of 1.6×104 M-1 s-1 and 2×105 M-1 s-1 for the electrocatalytic reaction of NADH and H2O2, respectively. Amperometric measurements presented that the active composite exhibited good performance with linear concentration ranges of 1.3 – 933.3 μM and 1 – 2555 μM, sensitivity of 457.2 μA mM-1 cm-2 and 10.1 μA mM-1 cm-2, and detection limits of 1.3 μM and 0.1 μM (S/N = 3), for NADH and H2O2, respectively. It allows the possibility that a bifunctional biosensor can be easily prepared and used for switchable determination of NADH and H2O2. Part II： Poly(brilliant cresyl blue) (PBCB) has been successfully electrodeposited on multi-walled carbon nanotubes (MWCNT) to form PBCB-MWCNT modified electrode by repeatedly cyclic voltammetry. MWCNT enables the higher current response in the hybrid composite when compared to the PBCB formation without using MWCNT. Well redox peak current development in the film formation indicates that MWCNT provides more electroactive surface areas for PBCB deposition and reduces the disorder situation of polymer chains. It is stable in various scan rates and different pH conditions. The surface coverage of BCB and PBCB was estimated in 7.4×10-11 and 7.6×10-11 mol cm-2 at PBCB-MWCNT/GCE higher than that at PBCB/GCE. More deposition amount indicates that MWCNT can provide more space for both BCB and PBCB. It shows lower over-potential and higher current response to persulfate when compared to the bare and PBCB electrodes. More obvious reduction currents are found using LSV technique. Applied potential at -0.03 V, it shows the sensitivity of 124.5 and 21.2 μA mM-1 cm-2 for the linear concentration range of 10-5 – 10-4 and 3.1×10-3 – 1.01×10-1 M, and detection limit of 1 μM (S/N = 3). Part III： This work presents that electrocatalytic oxidation of methanol can be enhanced by the hybrid nanocomposites of amino-functionalized multi-walled carbon nanotubes (MWCNT) decorated with nickel and copper nanoparticles (NPs). This active hybrid composite can be simply prepared by the electrodeposition of nickel and copper on the MWCNT-modified electrode. It effectively catalyzes methanol in the alkaline solution (pH 13) with high current response and low overpotential at about 0.6 V. As a methanol electrochemical sensor, it provides two specific linear response ranges of 1 – 10 μM and 24.7 – 74.1 mM, with sensitivity of 5×104 μA mM-1 cm-2 and 115 μA mM-1 cm-2, respectively. Particularly, it shows a superior detection limit of 1 μM (S/N = 3) with no interference of ethanol. It is an efficient promising methanol sensor in food industry due to high selectivity, high sensitivity, low detection limit, simplicity, and low cost.

Significant developments have been made in the field of C–H activation. However, various disadvantages, mainly low reactivity and selectivity, limit their usage in large-scale synthesis. It is crucial to understand the mechanisms and the nature of the transient species involved in the C–H activation paths to develop effective catalytic routes for homogeneous C–H functionalization reactions. Computational techniques are employed in this study to throw light on these processes. Chapter 1 briefly introduces C–H activation and functionalization reactions. After classifying the reactions on the basis of mechanisms, computational studies on the mechanisms of C–H activation reactions are described. The challenges involved in the discovery of efficient homogeneous C–H functionalization catalysts and progress made in the field are discussed. The insights provided to overcome the problems associated with the catalytic C–H functionalization reactions in a few examples are highlighted. In Chapter 2, DFT model studies are carried out to estimate the affinity and selectivity of 16-electron half-sandwich d6-metal fragments (η5–C5H5)Re(CO)2 and (η6–C6H6)W(CO)2 for binding with alkane C–H bonds. Different C–H binding sites of pentane, at the M06 level of theory have been evaluated. The effects of ancillary ligand variations on the metal–pentane binding strength are studied by substituting different ligands such as N-heterocyclic carbene (NHC), PF3 and NO+ for one of the carbonyl ligands. Isomers of the metal-pentane C–H σ-complexes studied in this chapter are shown in Scheme 1. Binding energies of the terminal methyl C–H bonds (C1 and C5) are significantly lower than those of the methylene C–H bonds (C2, C3 and C4) in all the cases. The metal–pentane binding interactions of the rhenium complexes are significantly stronger than those of the corresponding tungsten analogs. The PF3 complexes have slightly greater binding energies compared to the CO complexes, in both Re(I) and W(0) analogs. These results are in conformity with the experimental results. The electron-deficient nitrosyl complexes have the highest binding energies. These results illustrate that by proper tuning of the electronic factors of the transition-metal fragments with different ancillary ligands, the alkane C–H binding affinity can be controlled. Energy decomposition analyses (EDA) are carried out to determine the nature of the interaction between the metal fragments and pentane C–H bonds. Scheme 1. Formation of pentane C–H σ-complexes Chapter 3 addresses the energetics of various intramolecular site-exchange (chain walking) processes and C–H oxidative addition reactions (Scheme 2) of the pentane C–H σ-complexes studied in Chapter 2. Four possible site-exchange processes such as 1,2-, 1,3-, 1,4- and 1,5-migration processes are studied using DFT/M06 level of theory. η2-(H,H)···M type transition states are located for these migrations (Scheme 2). The 1,3-migration is the most favorable process. Two different pentyl hydride isomers, as shown in Scheme 2, are obtained for oxidative addition of methyl and methylene C–H bonds of pentane for all systems, at same level of theory. Oxidative insertion of metal into the methyl C–H bonds is more favorable than insertion into the methylene C–H bonds for all complexes. The activation energies of all site-exchange and C–H oxidative addition processes of the Re(I) complexes are significantly greater than those of the corresponding W(0) complexes. For all these processes, the activation barriers of the electron-deficient NO+ complexes are the greatest among all ligand systems studied, in both Re(I) and W(0) systems. These results are consistent with the experimental results and suggest that the experimentally observed pentyl hydride isomer [(η5–C5H5)Re(CO)(PF3)H(C5H11)] might be Isomer B and not Isomer A (Scheme 2). The C–H oxidative addition reactions are less favorable than dynamic site-exchange processes in all complexes. These results imply that the metal fragments migrate along the pentane chain more easily than insert into the pentane C–H bonds. Scheme 2. Alkane chain walking and C–H oxidative addition reactions Chapter 4 deals with the mechanisms and energetics of a unique metal migration process of an olefin complex that proceeds via olefinic (C–H)···Metal interaction. Migration of the Re(I) fragment from one π face of the olefin to the opposite π face in [(η5–C5H5)Re(NO)(PPh3)(PhCH═CH2)]+ has been documented experimentally by Gladysz and coworkers. The experimental results provide evidences for an intramolecular mechanism for this process (i.e., without styrene dissociation from Re(I)) and based on kinetic isotope effects (KIE), the involvement of a trans C–H bond is indicated. Either oxidative addition or a vinylic (C–H)···Re interaction could account for the experimentally observed kinetic isotope effect. In this study, the free energy of activation for the migration of Re from one enantioface of the olefin to the other through various pathways is computed using DFT calculations at the B3LYP and M06 levels. Two pathways, one that involves migration of Re through a trans (C–H)···Re interaction and another that involves oxidative addition of Re into the trans C–H bond, are identified as possible paths (Scheme 3) at the B3LYP level. Surprisingly, at the M06 level, DFT computes a lower energy path for the conducted tour mechanism that is not consistent with the experimental KIE. But the computed energy profiles for the reaction are consistent with the experiment when computations are carried out at the B3LYP level. Scheme 3. Mechanisms of olefin π face exchange reaction In Chapter 5, the mechanistic studies of C–H metathesis of d6 half-sandwich complex [(η5–C5Me5)Ru(CH3)(CO)(C6H6)] are discussed. A 1-step mechanism that proceeds via a four-center transition state and a 2-step Oxidative Addition and Reductive Coupling mechanism (OA/RC) are identified as possible mechanisms (Scheme 4) using DFT/M06 level of theory. The 1-step mechanism is more favorable than the 2-step mechanism. As in the oxidative addition intermediate, metal–hydrogen bond is observed in the four-center transition state of the 1-step mechanism. This mechanism is referred to as Oxidative Hydrogen Migration (OHM) rather than σ-Bond Metathesis (σ-BM) which proceeds via a transition state without M−H bonding. The effects of metal (M = Fe(II), Ru(II) or Os(II)) and ancillary ligand (L = H–, NHC, CO or NO+) variations on the mechanisms and energetics of the model Cp complex [(η5–C5H5)M(CH3)(L)(C6H6)] are also studied (Scheme 4). Scheme 4. Oxidative hydrogen migration vs Oxidative addition/reductive coupling Increase in the electron-density on the metal center, using electron-donating ligands such as H−, favors the formation of the oxidative species (intermediate or transition state) and reduces the activation barriers of the C–H metathesis reaction. Similarly, the electron-withdrawing NO+ ligand, which reduces the electron density on the metal center, increases the activation energies of the C–H metathesis reaction or disfavors the formation of the oxidative species. Factor affecting the choice of the mechanism of the C–H metathesis reaction is found to be the net charge transfer between the two fragments [(η5–C5H5)M(CH3)(L)] and benzene in [(η5–C5H5)M(CH3)(L)(C6H6)]. The computational studies reported in this thesis provide valuable insight into the mechanisms and energetics of C–H binding, activation and fluxional processes of the (C–H)···Metal σ alkane and alkene complexes. These studies will be helpful in solving problems associated with the C–H activation reactions. Reference Thenraj, M.; Samuelson, A. G. Organometallics 2013, 32, 7141. (For structural formula and figures pl see the abstract pdf file.)

AbstractThe interstellar medium is extremely heterogeneous in terms of physical environments and chemical composition. Spectroscopic observations in the recent decades have revealed the presence of gaseous material and dust grains covered in ices predominantly of water in interstellar clouds, the interplay of which may elucidate the existence of more than 250 molecular species. Of these species of varied complexity, several terrestrial carbon-containing compounds have been discovered, known as interstellar complex organic molecules (iCOMs) in the astrochemical argot. In order to investigate the formation of iCOMs, it is crucial to explore gas-grain chemistry and in this regard, one of the fundamental parameters is the binding energy (BE), which is an essential input in astrochemical models. In this work, the BEs of 13 iCOMs on a crystalline H2O-ice surface have been computed by means of quantum chemical periodic calculations. The hybrid B3LYP-D3 DFT method was used for the geometry optimizations of the adsorbate/ice systems and for computing the BEs. Furthermore, to refine the BE values, an ONIOM2-like approximation has been employed to obtain them at CCSD(T), which correlate well with those obtained at B3LYP-D3. Additionally, aiming to lower the computational cost, structural optimizations were carried out using the HF-3c level of theory, followed by single point energy calculations at B3LYP-D3 in order to obtain BE values comparable to the full DFT treatment.

Organic carbon sequestration is delineated from the different mechanisms underlying the storage of organic matter in mineral soils. The scene is set with definitions of the major terms within the complex of organic matter formation in soils, followed by describing the types of organic matter entering the soil and the major processes during turnover and the protective mechanisms leading to organic matter storage in soils. Detritusphere and rhizosphere are identified as soil compartments with high and specific organic matter input. From the process complex of OM degradation and binding, the potential of different soils for sequestering organic carbon is delineated and its limitations discussed with regard to the possibility of C saturation of mineral soils. In the light of these considerations, soil management options are deduced either by increasing organic carbon inputs to the soil by improved land use/management practices or by decreasing organic carbon outputs.

Carbon nanostructures such as carbon nanotubes, graphene, graphene oxide and their derivatives, have been recognized in biomedicine and drug delivery, due to their outstanding optical, mechanical, thermal, and electrical characteristics. Carbon nanostructures/ polymer composites with various active and functional groups provide many binding sites for inorganic/organic species and biomolecules and are described as favorable candidates to label and drag different drugs, genes, proteins and therapeutic molecules. This chapter focuses on studies about the deployment of nanostructures/ polymer composites, for efficient drug delivery, especially localized controlled drug/gene delivery systems (LCDDS). Effects of various parameters and features, including composite microstructures, hydrophobicity and hydrophilicity of composites, glass transition and polymer matrix molecular weight, on LCDDS are fully examined and discussed.

Natural organic matter (NOM) is a major intermediate in the global carbon, nitrogen, sulfur, and phosphorus cycles. NOM is also the environmental matrix that frequently controls binding, transport, degradation, and toxicity of many organic and inorganic contaminants. Despite its importance, NOM is poorly understood at the structural chemistry level because of its molecular complexity and heterogeniety. Nuclear magnetic resonance (NMR) spectroscopy is one of the most useful spectrometric methods used to investigate NOM structure because qualitative and quantitative organic structure information for certain organic elements can be generated by NMR for NOM in both the solution and solid states under nondegradative conditions. However, NMR spectroscopy is not as sensitive as infrared or ultraviolet-visible spectroscopy; it is not at present applicable to organic oxygen and sulfur, and quantification of NMR spectra is difficult under certain conditions. The purpose of this overview is to present briefly the “state of the art” of NMR characterization of NOM, and to suggest future directions for NMR research into NOM. More comprehensive texts concerning the practice of NMR spectroscopy and its application to NOM in various environments have been produced by Wilson and by Wershaw and Mikita. Carbon, hydrogen, and oxygen are the major elements of NOM; together they comprise about 90% of the mass. The minor elements that constitute the remainder are nitrogen, sulfur, phosphorus, and trace amounts of the various halogen elements. With the exception of coal, in which carbon is the most abundant element, the order of relative abundance in NOM on an atomic basis is H > C > O > N > S > P = halogens. The optimum NMR-active nuclei for these elements are 1H, 13C, 17O, 15N, 33S, 31P, and 19F. The natural abundances and receptivities of these nuclei relative to 1H are given in Table 12.1. Quadrupolar effects for 17O, 33S, and halogen elements other than 19F lead to line broadening that greatly limits resolution in NMR studies of these elements in NOM.

Semiconductor and magnetic nanoparticles hold unique optical and magnetic properties, and great promise for bio-imaging and therapeutic applications. As part of their stable synthesis, the nanocrystal surfaces are usually capped by long chain organic moieties such as trioctylphosphine oxide. This capping serves two purposes: it saturates dangling bonds at the exposed crystalline lattice, and it prevents irreversible aggregation by stabilizing the colloid through entropic repulsion. These nanocrystals can be rendered water-soluble by either ligand exchange or overcoating, which hampers their widespread use in biological imaging and biomedical therapeutics. Here, we report a novel scheme of synthesizing fluorescent PbS and magnetic Fe3O4 nanoparticles using DNA oligonucleotides. Our method of PbS synthesis includes addition of Na2S to the mixture solution of DNA sequence and Pb acetate (at a fixed molar ratio of DNA/S2−/Pb2+ of 1:2:4) in a standard TAE buffer at room temperature in the open air. In the case of Fe3O4 particle synthesis, ferric and ferrous chloride were mixed with DNA in DI water at a molar ratio of DNA/Fe2+/Fe3+ = 1:4:8 and the particles were formed via reductive precipitation, induced by increasing pH to ∼11 with addition of ammonium hydroxide. These nanocrystals are highly stable and water-soluble immediately after the synthesis, due to DNA termination. We examined the surface chemistry between oligonucleotides and nanocrystals using FTIR spectroscopy, and found that the different chemical moieties of nucleobases passivate the particle surface. Strong coordination of primary amine and carbonyl groups provides the chemical and colloidal stabilities, leading to high particle yields (Figure 1). The resulting PbS nanocrystals have a distribution of 3–6 nm in diameter, while a broader size distribution is observed with Fe3O4 nanoparticles as shown in Figure 1b and c, respectively. A similar observation was reported with the pH change-induced Fe3O4 particles of a bimodal size distribution where superparamagnetic and ferrimagnetic magnetites co-exist. In spite of the differences, FTIR measurements suggest that the chemical nature of the oligonucleotide stabilization in this case is identical to the PbS system. As a particular application, we demonstrate that aptamer-capped PbS QD can detect a target protein based on selective charge transfer, since the oligonucleotide-templated synthesis can also serve the additional purpose of providing selective binding to a molecular target. Here, we use thrombin and a thrombin-binding aptamer as a model system. These QD have diameters of 3∼6 nm and fluoresce around 1050 nm. We find that a DNA aptamer can passivate near IR fluorescent PbS nanocrystals, rendering them water-soluble and stable against aggregation, and retain the secondary conformation needed to selectively bind to its target, thrombin, as shown in Figure 2. Importantly, we find that when the aptamer-functionalized nanoparticles binds to its target (only the target), there is a highly systematic and selective quenching of the PL, even in high concentrations of interfering proteins as shown in Figure 3a and b. Thrombin is detected within one minute with a detection limit of ∼1 nM. This PL quenching is attributed to charge transfer from functional groups on the protein to the nanocrystals. A charge transfer can suppress optical transition mechanisms as we observe a significant decrease in QD absorption with target addition (Figure 3c). Here, we rule out other possibilities including Forster resonance energy transfer (FRET) and particle aggregation, because thrombin absorb only in the UV, and we did not observe any significant change in the diffusion coefficient of the particles with the target analyte, respectively. The charge transfer-induced photobleaching of QD and carbon nanotubes was observed with amine groups, Ru-based complexes, and azobenzene compounds. This selective detection of an unlabeled protein is distinct from previously reported schemes utilizing electrochemistry, absorption, and FRET. In this scheme, the target detection by a unique, direct PL transduction is observed even in the presence of high background concentrations of interfering negatively or positively charged proteins. This mechanism is the first to selectively modulate the QD PL directly, enabling new types of label free assays and detection schemes. This direct optical transduction is possible due to oligonucleotidetemplated surface passivation and molecular recognition. This chemistry may lead to more nanoparticle-based optical and magnetic probes that can be activated in a highly chemoselective manner.

Background: Engineered carbon nanotubes (CNTs) are expected to be increasingly released into the environment with the rapid increase in their production and use. The discharged CNTs may interact with coexisting contaminants and subsequently change environmental behaviors and ecological effects of both the CNTs themselves and the contaminants. Dissolved organic matter (DOM) plays a critical role in the transport of CNTs in the aquatic environment, affecting both CNT's surface properties through adsorption, and its colloidal stability in solution. Therefore, CNT-bound DOM complexes may interact with coexisting contaminants, thus affecting their environmental fate. With increasing production and use of CNTs, there is an increasing risk that humans could be exposed to CNTs mainly through ingestion and inhalation. Since CNTs can be carriers of contaminants due to their high adsorption affinity and capacity, the distribution of these nanoparticles in the environment holds a potential environmental and health risk. Project objectives: The overall goal of this project was to gain a better understanding of the environmental behavior of engineered nanoparticles with DOM and organic pollutant in aqueous systems. The scope of this study includes: characterizing various types of engineered nanoparticles and their interaction with DOM; binding studies of organic contaminants by nanoparticles and DOM-nanoparticle complexes; and examining interactions in DOM-nanoparticles-contaminant systems. Major conclusions, solutions and achievements: DOM has a pronounced effect on colloidal stability of CNTs in solution and on their surface chemistry and reactivity toward associated contaminants. The structure and chemical makeup of both CNTs and DOM determine their interactions and nature of formed complexes. CNTs, contaminants and DOM can co-occur in the aquatic environment. The occurrence of co-contaminants, as well as of co-introduction of DOM, was found to suppress the adsorption of organic contaminants to CNTs through both competition over adsorption sites and direct interactions in solution. Furthermore, the release of residual contaminants from CNTs could be enhanced by biomolecules found in the digestive as well as the respiratory tracts, thus increasing the bioaccessibility of adsorbed contaminants and possibly the overall toxicity of contaminant-associated CNTs. Contaminant desorption could be promoted by both solubilization and sorptive competition by biological surfactants. Scientific and agricultural implications: The information gained in the current project may assist in predicting the transport and fate of both CNTs and associated contaminants in the natural environment. Furthermore, the results imply a serious health risk from contaminant-associated CNTs.

Ethylene is a plant hormone that controls many plant responses, such as growth, senescence, ripening, abscission and seed germination. Recently, 1-methy- cyclopropene (1-MCP), was shown to bind to ethylene receptor for a certain period of time and prevent ethylene action. The objectives of this research were to synthesize analogues of 1-MCP and test their potency to block the ethylene receptor and inhibit ethylene action. During the course of this project, procedures for synthesis and shipment of the cyclopropene compounds were developed as well assay procedures for each compound were worked out. Thirteen new compounds were synthesized. All of them are structural analogues of 1-MCP, with substitution in the 1-position and a side chain containing 2 to 10 carbons. After preliminary studies, nine promising compounds were selected for in-depth study. The potency of the compounds to inhibit ethylene action was tested on a wide scope of systems like: climacteric fruits (banana, avocado and tomato), the triple response (etiolated peas), and leaf abscission (citrus). As the putative inhibitors are suspected to compete for the site of binding and a competitive type of inhibition could be considered, a high concentration of ethylene (300 m1.L-1) was used to induce ripening and other physiological processes. The tests were conducted under extreme conditions which hasten ripening like treatment and storage at 22 to 25oC. There were fluctuations in the responses as related to the concentrations of the inhibitors. Some required much higher concentration to exert the same effect, while some, when applied at the same concentration, blocked the receptor for a longer period of time than the others. Some fruits and other plant organs responded differently to the same inhibitor, indicating differences in characteristics and availability of the ethylene receptors in the various tissues. The potency of the putative inhibitors was found to be greatly affected by their molecular structural and size. In addition, it was found that treatment with the inhibitor should be given before the onset of ethylene action In the case of fruit, treatment should be carried out before the pre-climacteric stage. Simultaneous treatment with ethylene and the inhibitors reduced the inhibitors' effect. The relationship between ethylene and the inhibitors is of a non-competitive nature. All the fruits treated with the putative inhibitors resumed normal ripening after recovery from the inhibition. This fact is of great importance when considering the inhibitors for practical use. The advantage of using inhibitors of ethylene action over inhibitors of ethylene production lies in the ability of the inhibitors of ethylene action to protect the tissue against both endogenous and exogenous ethylene, thus providing better overall protection. Our findings indicate that 1-MCP and its structural analogues are potent inhibitors of ethylene action capable of providing good protection against endogenous and exogenous ethylene. The fact that the compounds are in a gas phase and are non-phytotoxic, odorless and effective at minute concentrations, renders them promising candidates for commercial use. However, the development of water-soluble inhibitors will expand the potential use of the inhibitors in agriculture.