Substituent Functional Groups Research Articles

Mercury photolytic transformation affected by low-molecular-weight natural organics in water

Mechanisms by which dissolved organic matter (DOM) mediates the photochemical reduction of Hg(II) in aquatic ecosystems are not fully understood, owing to the heterogeneous nature and complex structural properties of DOM. In this work, naturally occurring aromatic compounds including salicylic, 4-hydrobenzoic, anthranilic, 4-aminobenzoic, and phthalic acid were systematically studied as surrogates for DOM in order to gain an improved mechanistic understanding of these compounds in the photoreduction of Hg(II) in water. We show that the photoreduction rates of Hg(II) are influenced not only by the substituent functional groups such as –OH, –NH2 and –COOH on the benzene ring, but also the positioning of these functional groups on the ring structure. The Hg(II) photoreduction rate decreases in the order anthranilic acid>salicylic acid>phthalic acid according to the presence of the –NH2, –OH, –COOH functional groups on benzoic acid. The substitution position of the functional groups affects reduction rates in the order anthranilic acid>4-aminobenzoic acid and salicylic acid>4-hydroxybenzoic acid. Reduction rates correlate strongly with ultraviolet (UV) absorption of these compounds and their concentrations, suggesting that the formation of organic free radicals during photolysis of these compounds is responsible for Hg(II) photoreduction. These results provide insight into the role of low-molecular-weight organic compounds and possibly DOM in Hg photoredox transformation and may thus have important implications for understanding Hg geochemical cycling in the environment.

Synthesis and selection of hindered new amine absorbents for CO2 capture

This work focuses on synthesizing and selecting hindered new amine absorbents to reduce the regeneration energy cost for CO2 capture. To achieve this target we synthesized seven secondary and two tertiary amine based CO2 absorbents with systematic modification of their chemical structures by an appropriate placement of substituent functional groups especially the alkyl functions (e.g. methyl, isopropyl, isobutyl, secondary butyl etc.), relative to the position of the amino group. Performances evaluations of these new absorbents in aqueous solutions were carried out based on their CO2 absorption rate, absorption capacity and heat of reaction measurements. Particular attention was paid to absorbents with a potential for high absorption rate and low heats of reaction. The results for the synthesized amino alcohols were then compared with conventional absorbents AMP and MDEA which were chosen as the base case for all comparisons. We found three high performance absorbents with advantages of high absorption rate and low heats of reaction compared with AMP and MDEA. Absorbents higher CO2 absorption rate and lower heat energy consumption characteristics will reduce the regeneration energy cost of CO2 during stripping.

Electrical, optical and hole transport mechanism in thin films of poly(3-octylthiophene-co-3-hexylthiophene): Synthesis and characterization

The present study demonstrates the designing of copolymer poly(3-octylthiophene-co-3-hexylthiophene) (P3OT-HT) and study of the hole transport mechanism in it. Detailed structural, optical and thermal studies of P3OT-HT discuss its synthesis aspects. Current density–voltage characteristics have been studied at different temperatures (290–110 K) to understand the mechanism of hole transport in P3OT-HT. It has been established that current density in P3OT-HT thin films is governed by space charge limited conduction with traps distributed exponentially in energy and space. Hole mobility is both temperature and electric field dependent arising due to substituent functional groups attached the polymer backbone.

How does each substituent functional group of oseltamivir lose its activity against virulent H5N1 influenza mutants?

To reveal the source of oseltamivir-resistance in influenza (A/H5N1) mutants, the drug-target interactions at each functional group were investigated using MD/LIE simulations. Oseltamivir in the H274Y mutation primarily loses the electrostatic and the vdW interaction energies at the –NH 3 + and –OCHEt 2 moieties corresponding to the weakened hydrogen-bonds and changed distances to N1 residues. Differentially, the N294S mutation showed small changes of binding energies and intermolecular interactions. Interestingly, the presence of different conformations of E276 positioned between the –OCHEt 2 group and the mutated residue is likely to play an important role in oseltamivir-resistant identification. In the H274Y mutant, it moves towards the –OCHEt 2 group leading to a reduction in hydrophobicity and pocket size, whilst in the N294S mutant it acts as the hydrogen network center bridging with R224 and the mutated residue S294. The molecular details have answered a question of how the H274Y and N294S mutations confer the high- and medium-level of oseltamivir-resistance to H5N1.

Synthesis, solubilities, and cyclic capacities of amino alcohols for CO2 capture from flue gas streams

Abstract Amines that have been widely used in post combustion CO 2 capture processes are monoethanolamine (MEA), diethanolamine (DEA) and N-methyldiethanolamine (MDEA). If used individually, these solvents have their limitations, and efforts to resolve these have produced formulated solvents consisting of blends of amines and some chemical additives. The advantages derivable from amine blends are also limited to commercially available individual amines. It is therefore desirable to synthesize new amines or amino alcohols that could incorporate the advantages of amine blends in the same molecule or provide new materials for blending in a formulated solvent. Recently, such amino alcohols have been synthesized based on an approach of rational molecular design and synthesis. This involved a systematic modification of the structure of amino alcohols by an appropriate placement of substituent functional groups, especially the hydroxyl function, relative to the position of the amino group. Some of the resulting amino alcohols were 4-(diethylamino)-2-butanol (Reg 1); 4-(piperidino)-2-butanol (Reg 2); 4- propylamino-2-butanol (Reg 3) and 4-(ethyl-methyl-amino)-2-butanol (Reg 4). The performance of these amino alcohols in aqueous solutions in terms of solubility of CO 2 and cyclic capacity were compared with those of aqueous MEA using tests conducted at temperatures of 40, 60 and 80 ∘ C at CO 2 partial pressures of 15 and 100 kPa. All the listed amino alcohols provided a much higher CO 2 absorption capacity than MEA with Reg 3 showing the highest absorption capacities at all the temperature considered. The cyclic capacity (derived as the difference between the solubilities at 40 and 80 ∘ C) of the listed solvents were also much higher than that for MEA with Reg 4 showing the highest cyclic capacity. These characteristics result in a much higher CO 2 absorption and a much less energy consumption for absorbent regeneration, such as in CO 2 stripping, compared to conventional amines.

Acylguanidine inhibitors of β-secretase: Optimization of the pyrrole ring substituents extending into the [formula omitted] substrate binding pocket

The proteolytic enzyme β-secretase (BACE-1) produces amyloid β (Aβ) peptide, the primary constituent of neurofibrillary plaques, implicated in Alzheimer’s disease, by cleavage of the amyloid precursor protein. A small molecule inhibitor of BACE-1, (diaminomethylene)-2,5-diphenyl-1H-pyrrole-1-acetamide ( 1, BACE-1 IC 50 = 3.7 μM), was recently described, representing a new small molecule lead. Initial SAR investigation demonstrated the potential of accessing the nearby S 3 and S 1 ′ substrate binding pockets of the BACE-1 enzyme by building substituents off one of the phenyl substituents and guanidinyl functional group. We report here the optimization of guanidinyl functional group substituents on 1, leading to potent submicromolar BACE-1 inhibitors.

Characterization of gem-difluoropropargyl synthons through HF loss from protonated molecules in methane chemical ionization mass spectra

Electron impact and methane chemical ionization mass spectra were obtained following gas chromatography/mass spectrometry for several gem-difluoropropargyl compounds, which had been synthesized as potential intermediates for synthesis of gem-difluoromethylene-containing C-3 acetylenes. EI spectra were variable with respect to the presentation of molecular ions, depending on substituent functional groups present. Methane-CI spectra were characterized by loss of 19 mass units from molecular weight with all compounds examined. These [ M − 19] + ions often presented as base peaks of the CI spectra, and were more reliably present and abundant than [ M + 1] + ions for these compounds. These ions could have been formed by elimination of HF from the protonated molecules under conditions of methane chemical ionization.

Electrochemical properties of aryladamantanes as new overcharge protection compounds for lithium cells

The development of new overcharge protection compounds for 4 V-class lithium cells with LiCoO 2 cathodes was attempted in order to protect the cells from the hazards of ignition and/or explosion when overcharged. At least two requirements must be met as regards overcharge protection compounds. They must have an oxidation potential ( E ox) in the 4.6–4.8 V range versus Li/Li + and they must not adversely influence the lithium cycling efficiency (Eff). The overcharge protection compounds were used by adding them to the electrolyte solution, which was LiClO 4/propylene carbonate. First, this study involved a basic examination of the relationships among the E ox values of arenes including polyacenes, naphthalene derivatives and methylbenzenes, their chemical structure, the aromatic ring size and the effects of substituent functional groups. Next, the E ox and Eff values of cycloalkanes including cyclohexane, decaline, adamantane and norbornane were examined. Based on these examination results, various adamantane derivatives were synthesized and their electrochemical properties were investigated. Finally, four aryladamantanes (1-( p-tolyl)adamantane, 1-( m-tolyl)adamantane, 1-( o-tolyl)adamantane, 1-(4-ethylphenyl)adamantane) were found to exhibit better E ox and Eff values than those of biphenyl, which is already used in commercial cells as an overcharge protection additive.

New Functional Hexahelicenes — Synthesis, Chiroptical Properties, X‐Ray Crystal Structures, and Comparative Data Bank Analysis of Hexahelicenes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

New Functional Hexahelicenes − Synthesis, Chiroptical Properties, X‐ray Crystal Structures, and Comparative Data Bank Analysis of Hexahelicenes

AbstractSeven new hexahelicenes (3−7, 9, 10) containing different functional group substituents have been synthesized and, in three cases (4, 8, 10), optically resolved. Optical rotations were measured and CD spectra are reported. X‐ray crystal structures of the helicenes 1, 3, 4, 8, and 9 have been determined, of which 4 represents a 1:1 clathrate with acetone. These show a concerted interplay of C−H···O, C−H···π, and π···π supramolecular interactions in the packings, mostly yielding stacks of molecules (1, 3, 4, 8). Statistical analysis of the molecular dimensions in these and related crystal structures was carried out in order to identify potential parameters relevant to macroscopic phenomena, including optical rotation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Resonant Tunneling and the Substituent Effect on Negative Differential Resistance in a Molecular Junction

ABSTRACTRecently there has been an explosion of interest in the potential use of individual molecules as electronic device elements. The electrical characteristics of molecular junctions, individual molecules spanning the gap between two metal electrodes, have been reported and certain molecular species have been found to exhibit highly nonlinear current versus applied-voltage (I/V) properties. Intriguingly, these nonlinearities (pronounced peaks) in the I/V behavior are extremely sensitive to the functionalization of the molecule forming the junction. The substitution of a single functional group can completely eliminate the nonlinear behavior. Many have suggested that resonant tunneling could lead to the observed nonlinearities. Resonant tunneling requires a double potential barrier along the electron transfer coordinate. We propose a possible physical origin for such a double potential barrier and support the model with first principles electronic structure calculations. Next we discuss a quantum mechanical tunneling model for electron transport through the double potential barrier. The model gives insight into the origin of nonlinear I/V behavior in molecular junctions and the effect of substituent functional groups on the junction molecule.

Pharmacokinetic Analysis of Free Radicals by in vivo BCM (Blood Circulation Monitoring)-ESR Method

In pharmacokinetic studies, a variety of analytical method including radioisotopic detection and HPLC (high performance liquid chromatography) has been used. In the present investigation, we developed in vivo BCM (Blood Circulation Monitoring)-ESR method, which is a new technique with a conventional X-band ESR spectrometer for observing stable free radicals in the circulating blood of living rats under anaesthesia. Both 5–(PROXYL derivatives) and 6–(TEMPO derivatives) membered nitroxide spin probes with various types of substituent functional group were used. After physicochemical properties of the spin probes such as hyperfine coupling constant (A-value), g-value and partition coefficient as well as chemical stability of the compounds in the fresh blood were obtained, the in vivo BCM-ESR method was performed in normal rats. Several pharmacokinetic parameters such as half-life of the probes, distribution volume, total body clearance and mean residence time were obtained and discussed in terms of their chemical structures. In addition, clearance of a spin probe was related to the urine concentration. The BCM-ESR method was found to be very useful to observe free radicals at the real time. By time-dependent ESR signal decay of spin probes, pharmacokinetic parameters were obtained.

Molecular aspects of design of immunoassays for drugs.

An understanding of the molecular structure of the antibody binding site, the epitope complementary to the antibody, and the intermolecular forces that determine the affinity and specificity of the interaction of antibody and epitope is fundamental to the design of immunoassays. This is particularly important for haptens because their small size results in small changes in substituent functional groups, e.g., optical rotation and carboxyl substitution for amide resulting in large changes in binding affinity. It should be possible to predict the effect of haptenic structure on binding affinity by considering the resulting changes in balance between the different intermolecular forces. This information can be used in designing immunogens and modifying the reaction conditions used during assay optimization, such as pH or ionic strength, that enhance the predominant intermolecular forces to increase the binding affinity but leave minimal matrix effects. Improved understanding of the molecular aspects of the immunological interaction can facilitate more rapid and economic immunoassay development.

Molecular Cocrystals of Carboxylic Acids. XIX. The Crystal Structures of Two Adducts of 3-Aminobenzoic Acid With 3,5-Dinitrobenzoic Acid: the 1:1 and the 2:2 Hydrate Cocrystals

Two cocrystalline molecular adducts of 3-aminobenzoic acid (3-aba) with the aromatic carboxylic acid 3,5-dinitrobenzoic acid (dnba), [(3-aba)(dnba)](1) and [(3-aba)2(dnba)2(H2O)] (2), have been prepared and their hydrogen-bonding associations determined by means of single-crystal X-ray diffraction. Complex (1) is similar to known 1:1 complexes of 4-aminobenzoic acid with other aromatic acids, with protonation of the amine group and carboxylic acid-carboxylate hydrogen-bonding associations. However, the 2:2 hydrate complex (2) has only one hetero-pair involved in proton transfer, the other remaining neutral. With both compounds there is an extensive hydrogen-bonding network involving all substituent functional groups as well as the lattice water in compound (2).

ChemInform Abstract: Effect of Substituent Functional Groups on Nucleophilic Reaction Velocity: Determination of Quaternization Rates with Methyl Iodide (II) for Poly‐Substituted Pyridines

ChemInform Abstract: Effect of Substituent Functional Groups on Nucleophilic Reaction Velocity: Determination of Quaternization Rates with Methyl Iodide (II) for Poly‐Substituted Pyridines

Effect of Substituent Functional Groups on Nucleophilic Reaction Velocity: Determination of Quaternization Rates with Methyl Iodide for Poly-Substituted Pyridines

Effect of Substituent Functional Groups on Nucleophilic Reaction Velocity: Determination of Quaternization Rates with Methyl Iodide for Poly-Substituted Pyridines

Electrical properties of electrochemically prepared thin polyphenylene oxide films on a platinum surface: The role of ionic impurities in electroforming and conduction

Thin films of polyphenylene oxide with alkyl radical substituents (type A) or with hydroxy- or carboxymethylated functional group substituents (type B) form on the surface of a platinum electrode subjected to anodic polarization in a methanol-NaOH medium containing different types of phenolic monomers such as 2,6- or 3,5-xylenol, ortho- or meta-hydroxylbenzyl alcohol or ortho-hydroxyphenylacetic acid. The current-voltage characteristics of MIM capacitors with type A dielectrics exhibit a strictly capacitive behaviour when they are subject to an electric field; those of capacitors with type B dielectrics indicate that negative resistance and electron emission occur. These different types of conduction are closely related to the presence or absence of impurities in the films. X-ray photoelectron spectroscopy analysis shows that the type A polymers are “pure” and that the type B polymers are doped with sodium ions.

Kinetic and Thermodynamic Aspects of In Vitro Interphase Transfer of Tetracyclines II: Influence of Divalent Metal Salts

With a two-phase in vitro model composed of an aqueous pH 5.5 buffer and 1-octanol, the kinetics of the interphase transfer of tetracycline derivatives were examined in the presence and absence of calcium and magnesium salts, and the contribution of some functional group substituents to the “apparent” free energy changes for partitioning of tetracyclines was evaluated. Only small changes were observed in kf, kb, Kω0, and apparent functional group free energy changes, ΔFG ΔF, m the presence of divalent metals as compared to values observed in the absence of these metals. Introduction of the C-6β hydroxyl group on the tetracycline nucleus decreased the apparent Kω0 because of a positive apparent ΔFG ΔF contribution, whereas introduction of C-5 hydroxyl, C-6α methyl, or C-7 chloro groups increased the apparent Kω0 through negative apparent ΔFG ΔF contributions.

Effect of functional group substituents on the paper chromatography of purines and pyrimidines

Curves relating the R f of purines and pyrimidines on paper to the water content of acetonitrile-water mobile phases are used to predict the relative polarity of the solutes and the relative effect of functional groups in establishing these relative polarities. The water content of the mobile phase necessary to cause the solute to migrate to a given R f value is a measure of the polarity of the solute. Oxygen and amino groups enhance the polarity of purine, while methyl groups strongly decrease the polarity. At pH 10, oxygen is 2.5 times as effective as the amino group in establishing differences in polarity among the solutes.