Role Of Different Functional Groups Research Articles

Effect of Dissolved Organic Matter on the Photodegradation of Decachlorobiphenyl (PCB-209) in Heterogeneous Systems: Experimental Analysis and Excited-State Theory Calculations.

Dissolved organic matter (DOM) can affect the transformation of pollutants through photosensitization, but most current research focuses on hydrophilic pollutants, making it such that less attention is paid to hydrophobic pollutants. In this paper, the effect and action mechanism of coexisting DOM on the photodegradation of decachlorobiphenyl (PCB-209) on suspended particles collected from the Yellow River were systematically investigated in a heterogeneous system using DOM standards and model compounds. Through molecular probe experiments, mass spectrometry analysis and theoretical calculations, we found that the excited triplet state of DOM (3DOM*) could excite PCB-209 to undergo dechlorination reaction. Due to the different modes of electron transition, the presence of carbonyl groups decreased the energy of 3DOM*, whereas the electron-donating groups made the energy of 3DOM* higher. DOM containing phenolic hydroxyl groups led to a higher steady-state concentration of •OH, and DOM containing phenyl ketone structures had a stronger ability to produce •O2-. Compared with aqueous •OH, •O2- produced from hydrophobic microregions could react more readily with PCB-209. This study deepens the understanding of the role of different functional groups of DOM in the photosensitized transformation of hydrophobic compounds.

Defect Passivation and Crystallization Regulation for Efficient and Stable Formamidinium Lead Iodide Solar Cells with Multifunctional Amidino Additive.

Amidino-based additives show great potential in high-performance perovskite solar cells (PSCs). However, the role of different functional groups in amidino-based additives have not been well elucidated. Herein, two multifunctional amidino additives 4-amidinobenzoic acid hydrochloride (ABAc) and 4-amidinobenzamide hydrochloride (ABAm) are employed to improve the film quality of formamidinium lead iodide (FAPbI3) perovskites. Compared with ABAc, the amide group imparts ABAm with larger dipole moment and thus stronger interactions with the perovskite components, i.e., the hydrogen bonds between N…H and I- anion and coordination bonds between C = O and Pb2+ cation. It strengthens the passivation effect of iodine vacancy defect and slows down the crystallization process of α-FAPbI3, resulting in the significantly reduced non-radiative recombination, long carrier lifetime of 1.7 µs, uniformly large crystalline grains, and enhances hydrophobicity. Profiting from the improved film quality, the ABAm-treated PSC achieves a high efficiency of 24.60%, and maintains 93% of the initial efficiency after storage in ambient environment for 1200 hours. This work provides new insights for rational design of multifunctional additives regarding of defect passivation and crystallization control toward highly efficient and stable PSCs.

Comprehensive evaluation of spontaneous combustion phenomenon from asphaltite perspective: Comparison with coal and clues of a universal process

Asphaltite holds importance as an energy raw material for Turkey. This study explores the potential for spontaneous combustion during underground mining production of Şırnak Üçkardeşler vein asphaltites and describes a generalized process by highlighting similarities and differences with self-heating of coal. Incubation tests, gas composition analysis, and infrared spectroscopy were conducted. Additionally, thermal analysis, surface area measurements, pore diameter analysis, mechanical testing, proximate analysis, and ultimate analysis were performed on the samples. The results reveal key differences in the spontaneous combustion behavior of asphaltites compared to low-rank coals. Melting, occurring between 60 and 80 °C, replaces the moisture-related stagnation observed in coals. The role of different functional groups, such as OH, CH, and CH2, in fueling the initial oxidation processes and other radicals initiating thermal runaway is identified. The reduction in surface area and pore diameters of asphaltites at higher temperatures limit their oxidation capacity. The compressive and tensile strengths of asphaltites significantly decrease with temperature. Similar to coals, carbon dioxide and carbon monoxide are indicative of spontaneous combustion, with carbon monoxide exhibiting a regular increase in temperature. The Arrhenius form confirms the occurrence of homogeneous reactions in asphaltite spontaneous combustion after 75 °C. These findings provide valuable insights into a universal mechanisms and warning signs of spontaneous combustion, aiding in the development of effective prevention strategies.

Accurate molecular dynamics modeling of Pseudomonas aeruginosa outer membrane interaction with signaling molecules.

Pseudomonas aeruginosa is an opportunistic pathogen responsible for lungs, urinary tract, and surgical wound infections. This gram-negative bacterium releases outer membrane vesicles (OMV) derived from the cell's outer membrane (OM), serving diverse functions in bacterial survival, including nutrient acquisition, signaling, antibiotic resistance, delivery vehicle, and host-immune response modulation. This work aims to develop an accurate in silico model of P. aeruginosa outer membrane using all-atom molecular dynamics (MD) to understand OMV biogenesis formation based on the prediction of the bilayer-couple model. This model predicts the intercalation of a signaling molecule name Pseudomonas Quinolone Signal (PQS) to the OM as the main driver for the vesicle formation. In this study, the asymmetric model OM is composed of PA14 Lipid A in the outer leaflet and a mixture of POPE and POPG phospholipids in the inner leaflet. Due to the use of periodic boundary conditions in MD simulations, the compositional asymmetry imposes a fixed ratio of lipid numbers between the two leaflets, which needs to be set with caution. It has been shown that many widely used methods of defining this ratio lack control over the stress state of the membrane. As a result, the generated membrane could have a non-zero per leaflet tension. We investigate the role of the initial stress state on the intercalation of PQS to the OM. Free energy calculation shows that the favorable position of PQS within the membrane would shift significantly by variation of per leaflet tension, which could have important implications on the bilayer-couple model of OMV biogenesis. In addition, we model various PQS analogs to probe the role of different functional groups of PQS on the spontaneous intercalation of this signaling molecule to the membrane.

Mechanistic understanding of lithium-anode protection by organosulfide-based solid-electrolyte interphases and its implications

The mechanism by which organosulfide-rich solid-electrolyte interphase (SEI) protects the Li-metal anode (LMA) is shown. By examining the role of different functional groups, design rules to engender favorable SEIs for stable LMAs were formulated.

Mixed-Functionalized Sc2CTx ( T=O, OH, F ) MXene for Electrocatalytic CO2 Reduction: Insight from First-Principles Calculations

A microscopic understanding of the mixed-functionalized MXenes (${M}_{2}{X\ensuremath{-}T}_{x}$; ${T}_{x}=\text{O, OH,}$ and $\mathrm{F}$) are extremely important to the design of efficient ${\mathrm{CO}}_{2}$ catalytic activity. Here, we report a first-principles study of the ${\mathrm{CO}}_{2}$ activation on pure $\mathrm{O}$, $\mathrm{OH}$, and $\mathrm{F}$ and mixed-functionalized ${\mathrm{Sc}}_{2}\mathrm{C}$ MXene surfaces. We find that ${\mathrm{CO}}_{2}$ adsorption energy can be tuned by changing the coverage of $\mathrm{O}$, $\mathrm{OH}$, and $\mathrm{F}$ functional groups on the surface. Fully terminated $\mathrm{O}$ and $\mathrm{F}$ ${\mathrm{Sc}}_{2}\mathrm{C}$ forms weak interactions with ${\mathrm{CO}}_{2}$ molecules (binding energy $\ensuremath{-}0.136$ and $\ensuremath{-}0.168\phantom{\rule{0.2em}{0ex}}\mathrm{eV}$) whereas mixed-functionalized ${\mathrm{Sc}}_{2}\mathrm{C}$ surface exhibits higher binding energy($\ensuremath{-}0.364\phantom{\rule{0.2em}{0ex}}\mathrm{eV}$). In the mixed-functionalized ${\mathrm{Sc}}_{2}\mathrm{C}$ case, only $\mathrm{O}$ sites allow ${\mathrm{CO}}_{2}$ reduction ($\mathrm{F}$ and $\mathrm{OH}$ are inactive) and finally converts into methane (${\mathrm{CH}}_{4}$). Ab-initio-based Bader charge analysis and projected density of state calculations reveal strong bonding between the C atom of ${\mathrm{CO}}_{2}$ and $\mathrm{O}$ functional group. The Gibbs free-energy calculation confirms the conversion of $\mathrm{HCO}$ into ${\mathrm{H}}_{2}\mathrm{CO}$ to be a rate-limiting step with the limiting potential 1.387 eV. In the mixed-functionalized surface, as we increase the number of $\mathrm{OH}$ groups in the vicinity of $\mathrm{O}$ sites, the binding energy increases (transiting from a physisorption to a chemisorption regime). However, increasing the amount of O coverage turns out to be detrimental to the catalytic activity. Our study highlights the role of different functional groups in achieving efficient ${\mathrm{CO}}_{2}$ catalytic activity on ${\mathrm{Sc}}_{2}\mathrm{C}$ MXene, which can further help us to design experiments accordingly.

Functional Groups Assisted Tunable Dielectric Permittivity of Guest-Free Zn-Based Coordination Polymers for Gate Dielectrics.

The dielectric properties of coordination polymers has been a topic of recent interest, but the role of different functional groups on the dielectric properties of these polymers has not yet been fully addressed. Herein, the effects of electron-donating (R=NH2 ) and electron-withdrawing (R=NO2 ) groups on the dielectric behavior of such materials were investigated for two thermally stable and guest-free Zn-based coordination polymers, [Zn(L1 )(L2 )]n (1) and [Zn(L1 )(L3 )]n (2) [L1 =2-(2-pyridyl) benzimidazole (Pbim), L2 =5-aminoisophthalate (Aip), and L3 =5-nitroisophthalate (Nip)]. The results of dielectric studies of 1 revealed that it possesses a high dielectric constant (κ=65.5 at 1 kHz), while compound 2 displayed an even higher dielectric constant (κ=110.3 at 1 kHz). The electron donating and withdrawing effects of the NH2 and NO2 substituents induce changes in the polarity of the polymers, which is due to the inductive effect from the aryl ring for both NO2 and NH2 . Theoretical results from density functional theory (DFT) calculations, which also support the experimental findings, show that both compounds have a distinct electronic behavior with diverse wide bandgaps. The significance of the current work is to provide information about the structure-dielectric property relationships. So, this study promises to pave the way for further research on the effects of different functional groups on coordination polymers on their dielectric properties.

Contribution of legume and non-legume trees to litter dynamics and C-N-P inputs in a secondary seasonally dry tropical forest

Many studies have investigated nutrient cycling in seasonally dry tropical forests, but few have assessed the contribution of different functional groups to these processes. Here, we investigated general litter dynamics patterns and the contribution of legume and non-legume trees to litter dynamics and carbon (C), nitrogen (N), and phosphorus (P) inputs in a fragment of secondary seasonally dry tropical forest after half a century of forest succession in the Atlantic Forest biome in Brazil. Between 2016 and 2017, we quantified litterfall production, canopy cover, forest floor, and soil C and N storage in 11 permanent plots distributed in the fragment. Vegetation identity and structure had been previously assessed. We quantified the seasonal inputs of leaf litter and C, N, and P separately for each functional group (legume and non-legume tree species). We also analyzed the correlations between the variables measured for each functional group with the variables measured at the plot level. Litter dynamics and nutrient input were affected by climate and functional group. Litterfall production during the two driest months was three times higher than during the other periods of the year, suggesting that species synchronicity is likely to minimize drought-related damage on trees. Legume trees had twice the basal area attained by non-legume trees, but while legumes were larger, non-legumes were more abundant and dominant in the smaller diameter class. Legumes deposited twice as much N during the driest period of the year as non-legumes. Although leaf litter, C, and P inputs by legumes were generally higher than those of non-legumes, these differences during the dry season were not statistically significant. We also found that the legume variables correlated better with the plot-level variables, compared to the non-legume functional group. Our results also indicated potential effects of the leaf litter and nutrient inputs by the legume functional group on the decomposition constant and, consequently, on the time of forest floor decomposition. Further studies should assess the role of different functional groups in litter dynamics and nutrient inputs in seasonally dry tropical forests.

Interaction mechanism between lead species and activated carbon in MSW incineration flue gas: Role of different functional groups

Lead (Pb) pollution is of great public concern from an ecological environment perspective, and one of its main sources is municipal solid waste (MSW) incineration. Among various flue gas purification technologies, the activated carbon (AC) injection is undoubtedly the most mature and simple one. ACs prepared by various raw materials and manufacturing methods lead to different functional groups, which significantly modulate the surface chemistry and interaction behaviors with Pb species. Herein, the density functional theory (DFT) was employed to study the interaction mechanism between Pb species and surface functional groups (CH3–, OH–, COOH–, and Cl-). The results indicate that the trapping strengths of Cl-graphene and COOH-graphene surfaces are strong due to the lower electrostatic potential and the more intense orbital hybridization with Pb atom, while those of CH3-graphene and OH-graphene surfaces are relatively fragile. In addition, HCl exerts an inhibitory effect on the adsorption of Pb species and converts the easy-trapped Pb0 into the tough-trapped PbCl2. Since only the COOH-graphene surface can effectively resist the negative function of HCl and the Pb0 chlorination, the COOH– group is screened as the optimal functional group on the ACs to alleviate the Pb pollutant through promoting adsorption, tolerating HCl, and inhibiting chlorination.

One ring is sufficient to inhibit α-synuclein aggregation.

Parkinson’s disease, the second most prevalent neurodegenerative disorder worldwide, is characterized by a progressive loss of dopaminergic neurons in substantia nigra pars compacta, causing motor symptoms. This disorder’s main hallmark is the formation of intraneuronal protein inclusions, named Lewy bodies and neurites. The major component of these arrangements is α-synuclein, an intrinsically disordered and soluble protein that, in pathological conditions, can form toxic and cell-to-cell transmissible amyloid structures. Preventing α-synuclein aggregation has attracted significant effort in the search for a disease-modifying therapy for Parkinson’s disease. Small molecules like SynuClean-D, epigallocatechin gallate, trodusquemine, or anle138b exemplify this therapeutic potential. Here, we describe a subset of compounds containing a single aromatic ring, like dopamine, ZPDm, gallic acid, or entacapone, which act as molecular chaperones against α-synuclein aggregation. The simplicity of their structures contrasts with the complexity of the aggregation process, yet the block efficiently α-synuclein assembly into amyloid fibrils, in many cases, redirecting the reaction towards the formation of non-toxic off-pathway oligomers. Moreover, some of these compounds can disentangle mature α-synuclein amyloid fibrils. Their simple structures allow structure-activity relationship analysis to elucidate the role of different functional groups in the inhibition of α-synuclein aggregation and fibril dismantling, making them informative lead scaffolds for the rational development of efficient drugs.

Synthesis and characterization of a new class of phenothiazine molecules with 10H-substituted morpholine & piperidine derivatives: A structural insight

A series of 10H-substituted phenothiazine-based molecules were prepared by the base-catalyzed reactions. The synthesized compounds are characterized by Mass spectroscopy, NMR, and SCXRD to examine the role of different functional groups involved in the intermolecular interactions and conformational geometries. The crystal packing of the compounds is governed by O–H⋯O, C–H⋯O, and π–π interactions. A complete understanding of the intermolecular interactions is studied employing the Hirshfeld analysis, 2D Fingerprint plot. Furthermore, the density functional theory (DFT/B3LYP) method at the 6–311++G(d,p) basis set was performed to support and compare experimental & theoretical geometrical parameters of phenothiazine derivatives.

Time-Domain Terahertz Spectroscopy and Density Functional Theory Studies of Nitro/Nitrogen-Rich Aryl-Tetrazole Derivatives.

The paper reports the time-domain THz spectroscopy studies of noncentrosymmetric energetic nitro/nitrogen-rich aryl-tetrazole high-energy molecules. The fingerprint spectra in the THz domain reveal the role of different functional groups attached to position “1” of the tetrazole moiety, which controls the energetic properties. These responses are deliberated through density functional theory (DFT) calculations. The synthesized aryl-tetrazoles exhibit high positive heat of formation (369–744 kJ/mol), high detonation velocities, and pressures (Dv: 7734–8298 m·s–1; Dp: 24–28 GPa) in comparison to the noncentrosymmetric 2,4,6-trinitrotoluene (TNT). These compounds exhibit variation in the refractive indices and absorption between 0.1 and 2.2 THz range. The DFT studies at the molecular and single-crystal level (using plane wave pseudo potential method) endorse in detecting these bands (with ∼1% deviation). The calculated vibrational frequencies and linear optical properties are found to have good agreement with the experimental data in UV–visible and THz regions.

Expression Analysis of the <i>Candida albicans KEX2, SAP1, CDR1</i> and <i>LIP1</i>genes Influenced by Biosynthesized Silver Nanoparticles

Present investigation deals with the synthesis of silver nanoparticles (AgNPs) from <i>Lycopersicon esculentum</i> L. through simple and eco-friendly method and validation the capacity of nanoparticles to inhibit the virulence gene expression in <i>Candida albicans</i>. The nanoparticles thus obtained from <i>Lycopersicon esculentum</i> L. have been analysed and characterised by Scanning Electron Microscopy (SEM), UV-Vis spectrophotometer, X-ray diffraction (XRD) and Fourier Transform Infra-red Spectroscopy (FTIR) techniques. The average diameter of the AgNPs, whose morphology has been determined by SEM, was found to be 9.58 to 72.69 nm. The UV-vis spectrophotometer show peak located of silver nanoparticles at 340 nm. X-ray diffraction analysis also showed functional structure and pattern of silver nanoparticles. The FT-IR spectra indicated the role of different functional groups of reducing agent and silver nanoparticles. AgNPs at concentrations of 15 and 25% significantly downed expression of <i>Sap1, LIP1</i> and <i>Kex2</i>, but had no effect on the expression of <i>CDR1</i> gene. The findings of current study showed that tomato extract could be used as a green chemistry approach to produce AgNPs. It downed expression of <i>Sap1, LIP1</i> and <i>Kex2</i> genes, whereas had no effect on the expression of <i>CDR1</i> gene, that it appears needs higher concentrations of AgNPs to inhibit its gene expression.

Role of donor‐acceptor functional groups in N3P3 cyclic‐triphosphazene backbone. Unraveling bonding characteristics from natural orbitals within an extended transition state‐natural orbital for the chemical valence scheme

AbstractThe formation of cyclophosphazenes containing several ligands or substituent groups gives rise to an attractive derivative set, for development of novel applications, with variable properties. Here, it is possible to unravel the role of different functional groups attached to the N3P3 backbone, to reach a better understanding of the bonding character in the cyclic [─P─N─] skeleton. We employed the extended transition state‐natural orbital for the chemical valence scheme to unravel the σ and π orbital kernels that are involved in the assembling of such structures, by varying the acceptor‐donor characteristics of the ─CF3, ─NO2, ─COOH, ─CN, ─NH2, ─OH, and ─OCH3 groups, where ─NO2 behaves as a stronger electron‐withdrawing substituent rather than ─CF3, ─COOH, and ─CN, denoting that the nature of the ligand‐phosphazene interaction contributes to some degree to the bond strength of the cyclic [─P─N─] backbone. Our results reveal that the electron‐withdrawing ─NO2 group leads to higher σ and π [─P─N─] orbital‐energy contributions, which is reflected in a shortening of the [─P─N─] distance, contrasting with the case of electron‐donating groups such as ─NH2, ─OH, and ─OCH3 within the phosphazene set. These insights allow further variation and modulation of the bonding in the [─P─N─] ring.

Stronger dung removal in forests compared with grassland is driven by trait composition and biomass of dung beetles

1. Ecosystem processes depend on the biomass of the involved organisms, but their functional diversity may play an additional role. In particular, the exclusion of key functional groups through habitat disturbance may lead to the breakdown of ecosystem functions. Dung removal is an important process contributing to nutrient cycling and thus productivity in grazed ecosystems.2. This study investigated the role of different functional groups of dung beetles in dung removal in different habitats within a wood‐pasture in two different seasons. An experimental setting with 12 blocks and 108 dung pads was used to investigate short‐term dung removal over 1 week of exposure.3. Dung removal was most strongly affected by habitat type, with almost 40% lower levels in grassland than in adjacent forest and forest gaps. Of all assemblage characteristics, total biomass of tunneller species was the strongest predictor of dung removal, whereas functional diversity showed no significant effect. In accordance with the dung removal pattern at habitat type level, densities of large tunnellers were suppressed in grassland compared with forest.4. It is concluded that dung removal is habitat‐specific and large tunnellers play a disproportionate role in this important ecosystem function in temperate forests.

P-Sulphonatocalix[8]arene functionalized silica resin for the enhanced removal of methylene blue from wastewater: equilibrium and kinetic study

ABSTRACTThe present investigation represents the synthesis of new p-sulphonatocalix[8]arene-based silica resin, p-SC8SR (5) and its application for the enhanced removal of methylene blue (MB) dye from contaminated water. The new p-SC8SR (5) resin was characterized by FT-IR, SEM, and EDX spectroscopy. The adsorption of MB on p-SC8SR (5) was investigated systematically by evaluating the effects of adsorbent dosage, initial pH, contact time, dye concentration, and ionic strength. Excellent adsorption (94%) of MB on p-SC8SR (5) was achieved at pH 9.5, contact time 10 min by using 0.2 mol L−1 ionic strength and 2 × 10−5 M initial MB dye concentration. Kinetic behavior of MB dye adsorption process on the newly synthesized p-SC8SR (5) adsorbent follows the pseudo-second-order rate model (R2 = 0.998 and 0.999 for 2 × 10−5 M and 1 × 10−4 M, respectively). Adsorption isotherms were fitted well by the Freundlich model with excellent value of coefficient of determination (R2) = 0.995 which demonstrated that the adsorption of MB follows multilayer mechanism. Wastewater samples contaminated with MB were used to assess efficiency of the p-SC8SR (5) adsorbent. Results indicated that newly synthesized p-SC8SR (5) was found to be efficient adsorbent. During the removal process, the role of different functional groups’ cyclic structure was scrutinized and found that the ionic property as well as π–π interaction of host molecules played imperative role in the extent of adsorption.

Understanding the Role of Functional Groups in Polymeric Binder for Electrochemical Carbon Dioxide Reduction on Gold Nanoparticles

AbstractElectrochemical CO2 reduction reaction (CO2RR) is one of the promising strategies for converting CO2 to value‐added chemicals. Gold (Au) catalysts are considered to be the best benchmarking materials for CO2RR to produce CO. In this work, the role of different functional groups of polymeric binders on CO2RR over Au catalysts is systematically investigated by combined experimental measurements and density functional theory (DFT) calculations. Especially, it is revealed that the functional groups can play a role in suppressing the undesired hydrogen evolution reaction, the main competing reaction against CO2RR, thus enabling more catalytic active sites to be available for CO2RR and enhancing the CO2RR activity. Consistent with the DFT prediction, fluorine (F)‐containing functional groups in the F‐rich polytetrafluoroethylene binder lead to a high Faradaic efficiency (≈94.7%) of CO production. This study suggests a new strategy by optimizing polymeric binders for the selective CO2RR.

Qualitative and quantitative analysis of intermolecular interactions in xanthenedione derivatives.

The existence of intermolecular interactions and the conformational geometry adopted by molecules are related to biological activity. Xanthenedione molecules are promising and emerging antioxidants and acetylcholinesterase inhibitors. To examine the role of different functional groups involved in the intermolecular interactions and conformational geometries adopted in xanthenediones, a series of three substituted xanthenediones have been crystallized [9-(3-hydroxyphenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione, C23H26O4, 9-(5-bromo-2-methoxyphenyl)-3,3,6,6-tetramethyl-3,4,6,7-tetrahydro-2H-xanthene-1,8(5H,9H)-dione, C24H27BrO4, and 3,3,6,6-tetramethyl-9-(pyridin-2-yl)-3,4,6,7-tetrahydro-2H-xanthene-1,8(5H,9H)-dione, C22H25NO3] and their intermolecular interactions analyzed via Hirshfeld analysis. The results show that all the derivatives adopt the same structural conformation, where the central ring has a shallow boat conformation and the outer rings have a twisted boat conformation. The intermolecular interactions in the molecules are predominantly O-H...O, C-H...O and π-π interactions. The optimized structures of the derivatives from theoretical B3LYP/6-311G** calculations show a good correlation with the experimental structures. The lattice energy involved in the intermolecular interactions has been explored using PIXELC.

Self-assembling behavior of pyrimidine analogues: Unveiling the factors behind morphological diversity

Studying the self-assembly of uracil derivatives has great importance in biochemistry and nanotechnology. Now, in order to architect unique and interesting nucleobase nanostructures, herein, we report a simple, yet robust uracil moiety based platform which is potentially capable to self-assemble into fibrils.The system is validated using eight uracil moiety derivatives and the effect is examined via fluorescence lifetime imaging microscopy (FLIM), field emission scanning electron microscopy (FESEM), steady state DCM fluorescence and fluorescence correlation spectroscopy (FCS).FLIM and FESEM give qualitative information regarding the fibril formation of different morphologies including string, rod, flower, needles etc. Steady state DCM fluorescence and FCS establish a quantitative estimation of the extent of fibril formation. The involvement of hydrogen bonding interaction between NH and CO groups in the fibrillar growth of 5-IU is evoked from the crystallographic study. Again, the key role of different functional groups behind the formation of fibrillar network is investigated through blocking the COO− group of orotic acid with lanthanides. Finally, esterification and N,N′-dimethylation exquisitely explore the role and priority of different groups in the fibril formation of pyrimidine analogues. The results may be useful for understanding the processes of self-assembly of the uracil derivatives and the rationalized design of the uracil based supramolecular structures with specific properties.

The role of different functional groups in a novel adsorption-complexation-reduction multi-step kinetic model for hexavalent chromium retention by undissolved humic acid

Undissolved humic acid (HA) has a great retention effect on the migration of hexavalent chromium [Cr(VI)] in soil, and HA functional groups play a predominant role in this process. However, the coupled mode between Cr(VI) retention and HA functional groups reaction is still unclear. In this study, it was found that a fair amount of Cr on HA existed in the forms of ion exchangeable and binding Cr(VI) during the reaction resulting from the ion exchange adsorption and complexation of Cr(VI). According to the results of two-dimensional correlation spectroscopic analysis (2DCOS), HA functional groups participated in the reaction with Cr(VI) in the order of carboxyl ≈ chelated carboxyl > phenol > polysaccharide > methyl, and all the functional groups were more likely to be located at aromatic domains. Based on the results of XPS spectra, rather than to be oxidized by Cr(VI), carboxyl more tended to be complexed by chromium, which is regarded as the precondition for Cr(VI) reduction. Phenol, polysaccharide and methyl with distinct reaction activities successively acted as major electron donors for Cr(VI) reduction in different reaction stages. Consequently, it was determined that the retention of Cr(VI) by undissolved HA followed an adsorption-complexation-reduction mechanism, and based on this, a multi-step kinetic model with multiple types of complexation/reduction sites was developed to simulate the retention processes resulting in a much better fitting effect (R2 > 0.99) compared with traditional first-order and second-order kinetic models (R2 < 0.95). This demonstrated that the multi-step kinetic model is of great potential in accurately simulating the migration and transformation of Cr(VI) in soil environment.