Adjacent Functional Groups Research Articles

Adsorption behavior of antimony(III) oxyanions on magnetite surface in aqueous organic acid environment

Antimony(III) adsorption is observed on magnetite (Fe3O4) surface under acidic and reducing condition through surface hydroxyl (SOH) groups bonding on Fe3O4 surface. Desorption of adsorbed Sb(III) is observed from Fe3O4 surface along with iron release in organic acid at 85°C after 5h of experiment. Tartaric acid (TA) shows minimum Sb(III) adsorption on Fe3O4 among the organic acid studied. The reason is TA having two sets of adjacent functional groups viz. OCOH and COH which are responsible for the formation of five-membered bidendate chelate with Sb(III). Other oxyanions, cations or complexing agents along with TA influences the Sb(III) adsorption on Fe3O4. The surface of magnetite is modified by the addition of fatty acids viz. Lauric acid, benzoic acid to bind the SOH groups present on the surface. This results in delaying the process of adsorption without changing the quantity of saturation adsorption of Sb(III) on Fe3O4 surface.

Computational Design of Effective, Bioinspired HOCl Antioxidants: The Role of Intramolecular Cl+ and H+ Shifts

The enzyme myeloperoxidase generates significant amounts of hypochlorous acid (HOCl) at sites of inflammation to inflict oxidative damage upon invading pathogens. However, excessive production of this potent oxidant is associated with numerous inflammatory diseases. Recent kinetic measurements suggest that the endogenous antioxidant carnosine is an effective HOCl scavenger. On the basis of computational modeling, we suggest a possible mechanism for this antioxidant activity. We find that a unique structural relationship between three adjacent functional groups (imidazole, carboxylic acid, and terminal amine) enables an intramolecular chlorine transfer to occur. In particular, two sequential proton shifts are coupled with a Cl(+) shift converting the kinetically favored product (chlorinated at the imidazole nitrogen) into the thermodynamically favored product (chlorinated at the terminal amine) effectively trapping the chlorine. We proceed to design systems that share similar structural features to those of carnosine but with even greater HOCl-scavenging capabilities.

N′-Cyclododecylidenepyridine-4-carbohydrazide

The title compound, C18H27N3O, is a derivative of the anti­tuberculosis drug isoniazid (systematic name: pyridine-4-carbohydrazidei). The crystal structure consists of repeating C(4) chains along the b axis, formed by N—H⋯O hydrogen bonds with adjacent amide functional groups that are related by a b-glide plane. The cyclo­dodecyl ring has the same approximately ‘square’ conformation, as seen in the parent hydro­carbon cyclo­dodecane.

Ultrasonic-assisted sodium hypochlorite oxidation of activated carbons for enhanced removal of Co(II) from aqueous solutions

Ultrasonic irradiation was employed to assist the modification of activated carbons (AC) by sodium hypochlorite, and tested for their ability to remove Co(II) from aqueous solutions. Modification of the activated carbon significantly enhanced their Co(II) adsorption capacity, which increased with the increasing NaOCl impregnating concentration. Ultrasonic-assisted impregnation can enhance the oxidation ability of the NaOCl solution, thus gave a higher adsorption capacity of Co(II) compared with the use of impregnation only. The Co(II) removal was a combination of adsorption and chemical precipitation. The optimal adsorption pH range for the native and modified AC was pH 7.0–8.5 and 4.5–8.5 respectively, above which precipitation of copper hydroxide became the main contributor to the cobalt removal. Cation exchange, electrostatic interaction, and surface complexation were demonstrated as the major mechanisms for the adsorption. Based on the XPS and FTIR analyses, Co(II) irons were considered to form monodentate charged complexes with the oxygen functionalities on the native AC, while they primarily formed multidentate coordination complexes within the modified carbon. The enhanced Co(II) removal by the ultrasonic-assisted NaOCl modified carbons was probably derived from their improved cation exchange capacity and higher content of adjacent aliphatic functional groups, which provided more complexation sites for cobalt.

Regioselective synthesis and biological evaluation of some novel thiophene-containing heterocyclic scaffolds as potential chemotherapeutic agents

In the reaction of 2-amino-3-carbethoxythiophene derivative 2b with hydrazine hydrate the respective aminocarbohydrazide 3 was isolated. Treatment of the latter product with carbon disulfide in alkaline medium caused a heterocyclization to give 1,3,4-oxadiazole-2-thione 5 rather than 3-amino-2-thioxothieno[2,3- d ]pyrimidin-4-one 4 , which could be obtained on treatment of carbohydrazide 3 with thiourea. The structure of products 4 and 5 was proved by spectroscopic methods and chemical transformations. Derivatization led to two novel series of condensed and uncondensed thiophenes, which were of significant interest for biological study. Since compound 4 contains two adjacent reactive functional groups, it reacted readily with different electrophilic reagents to provide a series of thieno[2,3-d]pyrimidin-4-one derivatives with annelated bridgehead nitrogen heterocycles 8 - 11 , whereas a second series of 3-heteroaryl-substituted thiophenes 13 - 17 was obtained by thioamide functionalization in 1,3,4-oxadiazole derivative 5 using various chemical reagents. The new thiophene-based derivatives were evaluated for their preliminary antimicrobial activity against a representative panel of Gram-positive and Gram-negative bacteria as well as fungi strains. The compounds tested displayed different levels of inhibitory effects, with the assays carried out on two pathogenic bacteria and two pathogenic fungi. Of these compounds, the monocyclic aminothiophene derivative 15 showed the highest effect on pathogenic bacteria, while the tricyclic condensed thiophene derivative 8 was observed to have the same inhibitory effect against pathogenic mould ( Aspergillus flavus ) as the reference drug Amphotericin B. For those derivatives belonging to first series of condensed thiophenes with annelated bridgehead nitrogen heterocycles, it has been observed that the antibacterial effect was in general found to be significantly higher than the corresponding uncondensed analogues. Although most of the condensed and uncondensed thiophenes under investigation showed generally remarkable in vitro antibacterial activity, unfortunately, no significant antifungal activity was observed with any of the compounds tested except for 8. Surprisingly, compound 8 displayed an excellent effect on fungus ( A. flavus ) on the one hand, whereas the lowest effect on bacteria on the other. The attachment of a triazolothiadiazine moiety to a thiophene ring could be considered as a promising strategy for the development of new therapeutic antibacterial agents related to the aminothiophene system.

Oxygen-independent decarbonylation of aldehydes by cyanobacterial aldehyde decarbonylase: a new reaction of diiron enzymes.

The search for new biofuels has generated increased interest in biochemical pathways that produce hydrocarbons.[1] Although hydrocarbons are simple molecules, the biosynthesis of molecules that lack any chemical functional groups is surprisingly challenging.[2] Biochemical reactions that remove functionality, such as decarboxylations, dehydrations and reduction of double bonds, invariably rely on the presence of adjacent functional groups to stabilize unfavorable transition states. Enzymes involved in hydrocarbon biosynthesis are therefore of interest both for applications in biofuels production and because of the unusual and chemically difficult reactions they catalyze.[3] One enzyme that has attracted particular interest, is aldehyde decarbonylase (AD), which catalyzes the decarbonylation of long-chain fatty aldehydes, to the corresponding alkanes.[4]

TBAF-Promoted Dehydrobrominations of Vicinal Dibromides Having an Adjacent O-Functional Group

Regioselective HBr elimination of vicinal dibromides having an adjacent oxygen functional group to give the corresponding 2-bromoalk-1-enes was controlled using 1.1 equivalents of TBAF. Two-step elimination to give the corresponding alkynes was controlled using 5.0 equivalents of TBAF. High yield and high selectivity require the presence of an oxygen functional group at the neighboring position of the elimination site.

Direct Assignment of the Relative Configuration in 1,3,n-Methyl-Branched Carbon Chains by 1H NMR Spectroscopy

On the basis of the assignment of methylene proton signals in (1)H NMR and determination of the chemical shift difference (Deltadelta), the relative configuration of 1,3,n-methyl-branched deoxypropionates can be determined directly. Comparison of the chemical shifts in the corresponding syn- and anti-configured compound pairs shows remarkable differences, while the absolute values depend on the presence and nature of adjacent functional groups. The determination of the Deltadelta values provides a reliable assessment of the relative configuration in 1,3,n-methyl-branched polypropionate chains and is even valid for macrocycles.

Effects of natural organic matter model compounds on the transformation of carbon tetrachloride by chloride green rust

Interest has grown in the use of reactive minerals for natural and engineered transformation of ground water contaminants. This study investigated how the structural properties of 10 model compounds representing natural organic matter (NOM) influenced their adsorption to chloride green rust (GR-Cl), and how this adsorption affected rate constants for transformation of carbon tetrachloride (CT) by GR-Cl. The affinity of benzoic acid, phthalic acid, trimesic acid, pyromellitic acid, and mellitic acid for the GR-Cl surface generally increased in the order of increasing number of carboxylic acid functional groups, increasing acidity of these functional groups, and increasing charge density. For NOM model compounds that had phenolic functional groups ( p-hydroxybenzoic acid, α-resorcylic acid, and caffeic acid), the affinity for the GR-Cl surface was greatest for caffeic acid, which had two adjacent phenolic functional groups. Some NOM model compounds had experimentally determined Langmuir maximum adsorption capacities ( q max−Langmuir) greater than those calculated based on external surface area measurements and the size of the NOM model compound, suggesting adsorption to internal as well as external sites at the GR-Cl surface for these compounds. Rate constants for CT transformation by GR-Cl generally decreased as the affinity of the NOM model compounds (estimated by Langmuir K values) increased, but there was no statistically significant correlation between Langmuir parameters (i.e., K and q max−Langmuir) and rate constants, perhaps due to significant adsorption of some NOM model compounds to sites that were not accessible to CT, such as interlayer sites. Unlike the other NOM model compounds, caffeic acid, which adsorbed to a significant extent to the GR-Cl surface, increased the rate constant for CT transformation. The influence of NOM on rate constants for CT transformation by green rusts should be considered in ground water remediation planning.

On‐column titration and investigation of metal complex formation for aminopolycarboxylate functionalised monoliths using scanning contactless conductivity detection

The application of scanning capacitively coupled contactless conductivity detection (SC(4)D) for the determination of pH dependant behaviour of two aminopolycarboxylates immobilised onto the surface of a monolithic capillary column is described. The use of SC(4)D to visualise changes in conductivity of the discrete zones of functional groups within monolithic capillary columns allows for the effects of immobilisation on the physicochemical properties of zones to be compared to that of the functional group in solution. The perturbation of the pK(a) values of the functional groups can be attributed to the change in chemical environment experienced by the functional group through the presence of local hydrogen bonding and surface induced effects. These bonds, both between adjacent functional groups and with the monolithic polymethacrylate scaffold, result in a modification of the electron density on the functional group and therefore a change in pK(a). Changes in the pK(a) of N-(2-acetamido)iminodiacetic acid (ADA) from 2.48 to 5.2 for one of the acidic protons, with little change in the pK(a) of the amine group, were observed, which correlates to similar changes in aggregated systems of aminopolycarboxylates. Similar results were obtained for the iminodiacetic acid (IDA) once immobilised onto the surface of the monolith. Furthermore, the ability to measure changes in the charge of such discrete zones of functional groups allows for the visualisation of complexation events occurring directly on-column, where such complexes result in a change in charge of the functional group. This potentially useful technique is illustrated within for the formation of aminopolycarboxylate complexes with a selection of metal ions.

Antimony(V) complexing with O-bearing organic ligands in aqueous solution: an X-ray absorption fine structure spectroscopy and potentiometric study

AbstractThe stabilityand structure of aqueous complexes formed by pentavalent antimony (SbV) with simple organic ligands (acetic, adipic, oxalic, citric acids, catechol and xylitol) having O-functional groups (carboxyl, alcoholic hydroxyl, aliphatic and aromatic hydroxyl) typical of natural organic matter (NOM), were determined at 25°C from potentiometric and X-ray absorption fine structure spectroscopy (XAFS) measurements. In organic-free aqueous solutions, spectroscopic data are consistent with the dominant formation of SbV hydroxide species, Sb(OH)5 and Sb(OH)6-, at acid and near-neutral to basic pH, respectively. Potentiometric measurements demonstrate negligible complexing with mono-functional organic ligands (acetic) or those having non-adjacent carboxylic groups (adipic). In contrast, in the presence of poly-functional carboxylic, hydroxyl carboxylic acids and aliphatic and phenolic hydroxyl, SbV forms stable 1:1 or 1:3 complexes in coordination 6 with the studied organic ligands, over a wide pH range pertinent to natural waters (3 ≤ pH ≤ 9). The XAFS measurements show that in these species the central SbV atom has an octahedral geometry with 6 oxygen atoms from hydroxyl moieties and adjacent functional groups (O = C—OH and/or C—OH) of the ligand, forming bidendate chelate cycles. Stability constants for SbV-oxalate complexes generated from potentiometric experiments were used to model SbV complexing with di-carboxylic functional groups of natural humic acids. Our predictions show that in an aqueous solution of pH between 1 and 4 containing 1 μg/l of Sb and 5 mg/l of dissolved organic carbon (DOC), up to 15% of total dissolved Sb maybe bound to aqueous organic matter via di-carboxylic groups.

Hydration of strongly basic anionites: Ab initio calculations

For the hydration of isolated and adjacent functional groups of strongly basic anionites, ab initio quantum-chemical calculations have been performed via the molecular fragment method. As counterions, OH−, F−, Cl−, Br−, and I− ions have been tested. It has been shown that Cl−, Br−, and I− ions are strongly bonded to the functional groups. The hydration of the functional groups in all cases leads to the removal of anions from a cation at a distance that is markedly larger than the sum of their ionic radii. This effect makes itself evident even in the case of addition of two water molecules. During interaction of adjacent functional groups, no appreciable change in the mutual arrangement of ions takes place.

Elucidation of the in vitro metabolic profile of stable isotope labeled BAL19403 by accurate mass capillary liquid chromatography/quadrupole time‐of‐flight mass spectrometry and isotope exchange

The in vitro metabolic pattern of BAL19403, a novel macrolide antibiotic, was investigated by capillary liquid chromatography/quadrupole time-of-flight mass spectrometry (LC/QTOF-MS) in incubations with human microsomes. For the elucidation of the metabolic pathway, BAL19403 labeled with four deuterium atoms (D4) was used, and detection of metabolites performed using mixtures of the unlabeled (H4) BAL19403 and its D4 analogue (1:1) as substrate. All metabolites appeared with similar chromatographic behavior. MS/MS spectra of BAL19403 and its metabolites are dominated by non-informative fragment ions. Therefore, the structure of the metabolites was elucidated mainly by accurate mass measurements with subsequent proposals of elemental compositions. Main biotransformations were N-demethylation, lactone ring hydrolysis, and oxidation. Additionally, N-dealkylation of the aromatic moiety was identified. This dealkylation results not only in formation of an aldehyde, according to the classical pathway, but also in formation of the corresponding alcohol and carboxylic acid. Final elucidation of their structures was possible, since this dealkylation takes place vicinal to the deuterium-labeled part of BAL19403 and interferes with D/H exchange. The degree of D/H exchange, determined by analysis of the metabolite isotopic pattern, was used to elucidate the adjacent functional group.

Studying aromatic compounds in infrared spectra based on support vector machine

In this work, a support vector machine (SVM)-based model was successfully developed to study the aromatic compounds in the form of infrared spectra. At first, the support vector machine and artificial neural networks (ANN) methods were applied to construct classifier system for aromatic compounds based on entire spectra. The results showed that both approaches performed well in identifying the adjacent functional group of aromatic compounds and SVM behaved appreciably better than ANN in distinguishing the substituted types of benzene. Hence, SVM was selected to further study the spectra–structure correlation based on segmental spectra. The experiment suggested that some segmental spectra may represent significant information concealed in entire spectra and C–H and C–C wagging out-of-plane vibration was the most important among the characteristic absorptions of benzene. A cross-validation procedure was used in all experiments.

Hydrogen Bond Directed Palladium‐Catalyzed Allylic Substitution of Cyclic Substrates.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Hydrogen-bond directed palladium-catalyzed allylic substitution of cyclic substrates

The regioselectivity of the Pd-catalyzed allylic substitution of cyclic substrates possessing an adjacent amide functional group was investigated. With imide-like nucleophiles, six-membered ring substrates were found to proceed with a high level of regiodirection whereas hydrogen-bond directed addition was not a significant factor in the five-membered ring substrates.

Optimal Chain Architectures for the Molecular Design of Functional Polymer Surfaces

The Scheutjens−Fleer self-consistent mean-field theory is used to calculate the surface segregation of various chemical functional moieties located on functional polymers of different architectures. Our results demonstrate the importance of the number and location of functional groups and their surface preference relative to polymer backbone segments in determining surface segregation. In general, we conclude that adjacency of similar functional groups is the most effective means for enhancing surface segregation of functional groups and that having two functional groups of similar character is always preferable to having two functional groups of opposite character, the Pushmi-Pullyu architecture, where one group prefers the surface while the other is repelled from it. The calculations demonstrate that the optimal architecture for producing a low-energy release surface is a functional polymer with adjacent low-energy functional groups located at one chain end. In this situation, both enthalpic and entropi...

Carbohydrate Hydrogen-Bonding Cooperativity − Intramolecular Hydrogen Bonds and Their Cooperative Effect on Intermolecular Processes − Binding to a Hydrogen-Bond Acceptor Molecule

The high hydroxy (OH) group content in carbohydrates makes the study of carbohydrate OH···XH and OH···X H-bond energetics fundamental to understanding of carbohydrate recognition. There is, however, a relative lack of knowledge concerning the factors that allow a carbohydrate to participate in recognition events stabilised by intermolecular H bonds. We therefore present here a systematic study on the factors that determine the formation of a well-defined intramolecular H-bonding network between carbohydrate hydroxy groups, and its cooperative or anti-cooperative influence on selected intermolecular processes mediated by H bonds. With this in mind, we first determined the H-bonding networks of a series of carbohydrate derivatives − monoalcohols, 1,2- and 1,3-diols and amidoalcohols − by 1H NMR and FT-IR spectroscopy. The hydroxy groups of these compounds showed different abilities to form intramolecular H bonds, depending on their relative positions and configurations on the pyranose ring, and on the nature of the adjacent functional groups. It has also been shown that both the directionality and strength of the intramolecular H-bonding network of a carbohydrate govern the formation of cooperative or anti-cooperative H-bond centres, with consequent repercussions on the thermodynamics of the intermolecular H-bonding interactions of the carbohydrate in question. From this study, some general rules for the prediction of the intramolecular H-bonding network characteristics of a given carbohydrate and its influence on the energetics of intended intermolecular recognition processes have been inferred. The results presented here give a new perspective over understanding of the role of the H-bonding interactions in carbohydrate recognition and have fundamental implications for the rational design of glycoconjugates incorporating H-bonding motifs with geometrical and electronic complementarity to given receptor molecules.

Neutral Ligands for Selective Chloride Anion Complexation: (α,α,α,α)-5,10,15,20-Tetrakis(2-(arylurea)phenyl)porphyrins

A series of neutral, urea-appended, free-base porphyrins and their Zn(II) complexes have been synthesized and characterized. The (α,α,α,α)-5,10,15,20-tetrakis(2-(arylurea)phenyl)porphyrins bind strongly (K (M-1) > 103−105) to chloride anion in DMSO-d6 and also in the more competitive solvent system DMSO-d6/D2O (88:12, v/v) and bromide anion in DMSO-d6, as revealed by 1H NMR titration studies. The porphyrin derivatives exhibited significant binding selectivity since they complexed with the spherical Cl- and Br- to a much greater extent than with the tetrahedral H2PO4- and HSO4- and the trigonal NO3- anions in DMSO-d6. Indeed, the selectivity trend Cl- > Br- ≫ H2PO4- > HSO4- > NO3- is novel for any neutral urea-anion binding system. On the other hand, the corresponding metalloporphyrins exhibited a decrease in binding strength and selectivity in DMSO-d6. The stoichiometry of binding for the anions and porphyrins was determined to be 1:1. The enthalpy of complexation was determined to be highly favorable and the entropy of complexation determined to be unfavorable from a variable-temperature 1H NMR experiment with a 1:1 tetrabutylammonium bromide/porphyrin complex. X-ray crystallography revealed (α,α,α,α)-5,10,15,20-tetrakis(2-(4-chlorophenylurea)phenyl)porphyrin to be the first coordination complex of an anion (chloride and bromide) bound by a neutral free-base porphyrin. The binding motif consisted of the halide, buried deep within the porphyrin pocket, bound by two adjacent urea functional groups via four hydrogen bonds, with the two remaining urea functional groups involved in hydrogen bonding to solvent molecules. The crystal structure of the tetrabutylammonium halide−porphyrin complex showed additional Coulombic interaction between the electron-poor sulfur of a pocket-bound, hydrogen-bonded DMSO and halide anion.

Fragmentation of Protonated Amides Through Intermediate Ion–Neutral Complexes: Neighboring Group Participation

It has been shown that neighboring group participation plays an important role in the fragmentation of protonated amides; the attachment of an adjacent functional group capable of accepting a proton provides alternative pathways of low energy for the formation of the inevitable N-protonated species in the fragmentation of the amide bond. Under methane chemical ionization (CI) conditions, protonated aniline ( m/ z 94) is only 1.6% of the base peak MH + ion for acetanilide; the abundance of the m/ z 94 ion is increased to 15% for acetoacetanilide and protonated o-methoxyaniline reaches a relative intensity of 49% for N-acetyl- o-methoxyaniline. A more striking difference in ease of the formation of protonated anilines is found for acetanilides bearing a nitro group at different positions. Protonated nitroaniline ( m/ z 139) is the base peak in the methane CI spectrum of N-acetyl- o-nitroaniline; the m/ z 139 ion drops to only 0.7% for the para isomer, and this ion is increased to 31.5% in the spectrum of N-acetoaceto- p-nitroaniline. By employing low energy collision-induced dissociation, it has been found that the fragmentation of protonated amides proceeds by way of ion–neutral complexes. In the case of acetanilide, for example, the cleavage of the amide bond gives rise to an acetylium ion and neutral aniline, which are bound together as a complex. An α-hydrogen of the acetylium ion, which is activated by the positive charge, is captured by aniline due to its higher proton affinity as compared with ketene. For those compounds having mobile protons other than the amidic hydrogen, it is indicated that such proton has the priority to be transferred in the reaction. Thus, the proton on the free carboxyl group of N-phenyl succinic and maleic monoamides is transferred in the fragmentation, leading to anhydrides as the neutral species in the formation of protonated aniline.