Tertiary Amine Function Research Articles

Non‐Heme Iron Complexes for Stereoselective Oxidation: Tuning of the Selectivity in Dihydroxylation Using Different Solvents

AbstractA new class of functional models for non‐heme iron‐based dioxygenases, including [(N3Py‐Me)Fe(CH3CN)2](ClO4)2 and [(N3Py‐Bn)Fe(CH3CN)2](ClO4)2 {N3Py‐Me = [di(2‐pyridyl)methyl]methyl(2‐pyridyl)methylamine; N3Py‐Bn = [di(2‐pyridyl)methyl]benzyl(2‐pyridyl)methylamine}, is presented here. NMR, UV and X‐ray analyses revealed that six‐coordinate low‐spin FeII complexes with the pyridine N‐atoms and the tertiary amine functionality of the ligand bound to Fe are formed. The two remaining coordination sites located cis to each other are occupied by labile CH3CN groups that are easily exchanged by other ligands. We demonstrate that the reactivity and stereoselectivity of the complexes investigated depend on the choice of the solvent. The complexes have been examined as catalysts for the oxidation of both alkanes and olefins in CH3CN. In this solvent alkanes are oxidized to alcohols and ketones and olefins to the corresponding cis‐epoxides and cis‐diols. In acetone as solvent a different reactivity pattern was found, with, as the most striking example, the trans‐dihydroxylation of cis‐olefins. 18O‐labeling studies in CH3CN establish incorporation of 18O from H218O2 and H218O in both the epoxide and the diol implicating an HO‐FeV=18O active intermediate originating from an H218O‐FeIIIOOH species. These results are in full agreement with mechanistic schemes derived for other dioxygenase model systems. Based on labeling studies in acetone an additional oxidation mechanism is proposed for this solvent, in which the solvent acetone is involved. This is the first example of a catalyst that can give cis‐ or trans‐dihydroxylation products, just by changing the solvent. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Design and synthesis of new ethylenediamine or propylenediamine diacetic acid derivatives for Re(I) organometallic chemistry

A general synthetic approach for a novel range of bifunctional chelating agent (BCA) for the ‘ fac-[M(CO) 3] +‘ core (M= 99mTc, 99Tc or Re) has been developed. The strategy includes the facile preparation of these tridentate ligands possessing a tertiary amine bearing two carboxylic acid functions as coordinating site and an aromatic amino group for coupling to a biovector. First complexation study has shown that these compounds act exclusively as tridentate ligands (via the two acids and the tertiary amine functions). The convenient synthesis of these new ligands coupled with their high affinity for Re(I) make them quite promising for biomedical applications.

N,N-bis(2,3-Dihydroxypropyl) Octadecylamine for Liquid–Liquid Extraction of Boric Acid

N,N-bis(2,3-dihydroxypropyl) octadecylamine (BPO) has been synthesized by condensation of octadecylamine with 2 M of 1-chloro 2,3-propandiol (1-chloroglycerol) in alcohol, in high yields (88.0%). Its solution in 2-ethyl hexanol has been demonstrated to be very efficient in liquid–liquid extraction of boric acid from aqueous solutions. Two vicinal-diol functions of BPO make it versatile reagent for boron extraction. The long aliphatic chain involved provides solubility in organic solvents. At relatively low boric acid concentrations, i.e., 1.2% (w/w), about 98% of BPO involves boron chelation, in nonbuffered conditions. The role of the tertiary amine function is entrapping acidic proton resulting from possible anionic borate complexation. In the study, pH dependence of the boric acid extraction and regeneration conditions of the chelating agent has been investigated. Overall results indicate that the boron complex is stable above pH 4.7 and the presence of some common foreign ions such as Ca(II) and Mg(II) does not affect the extraction. The complexed boron can be recovered from organic phase by treating with 2 M H2SO4 solutions. Due to nonhydrolyzability of the linkages in BPO it can be recovered and may be of interest to use in continuous extraction systems.

Ticlopidine as a selective mechanism-based inhibitor of human cytochrome P450 2C19.

Experiments using recombinant yeast-expressed human liver cytochromes P450 confirmed previous literature data indicating that ticlopidine is an inhibitor of CYP 2C19. The present studies demonstrated that ticlopidine is selective for CYP 2C19 within the CYP 2C subfamily. UV-visible studies on the interaction of a series of ticlopidine derivatives with CYP 2C19 showed that ticlopidine binds to the CYP 2C19 active site with a K(s) value of 2.8 +/- 1 microM. Derivatives that do not involve either the o-chlorophenyl substituent, the free tertiary amine function, or the thiophene ring of ticlopidine did not lead to such spectral interactions and failed to inhibit CYP 2C19. Ticlopidine is oxidized by CYP 2C19 with formation of two major metabolites, the keto tautomer of 2-hydroxyticlopidine (1) and the dimers of ticlopidine S-oxide (TSOD) (V(max) = 13 +/- 2 and 0.4 +/- 0.1 min(-1)). During this oxidation, CYP 2C19 was inactivated; the rate of its inactivation was time and ticlopidine concentration dependent. This process meets the chemical and kinetic criteria generally accepted for mechanism-based enzyme inactivation. It occurs in parralel with CYP 2C19-catalyzed oxidation of ticlopidine, is inhibited by an alternative well-known substrate of CYP 2C19, omeprazole, and correlates with the covalent binding of ticlopidine metabolite(s) to proteins. Moreover, CYP 2C19 inactivation is not inhibited by the presence of 5 mM glutathione, suggesting that it is due to an alkylation occurring inside the CYP 2C19 active site. The effects of ticlopidine on CYP 2C19 are very analogous with those previously described for the inactivation of CYP 2C9 by tienilic acid. This suggests that a similar electrophilic intermediate, possibly a thiophene S-oxide, is involved in the inactivation of CYP 2C19 and CYP 2C9 by ticlopidine and tienilic acid, respectively. The kinetic parameters calculated for ticlopidine-dependent inactivation of CYP 2C19, i.e., t(1/2max) = 3.4 min, k(inact) = 3.2 10(-3) s(-1), K(I) = 87 microM, k(inact)/K(I) = 37 L.mol(-1).s(-1), and r (partition ratio) = 26 (in relation with formation of 1 + TSOD), classify ticlopidine as an efficient mechanism-based inhibitor although somewhat less efficient than tienilic acid for CYP 2C9. Importantly, ticlopidine is the first selective mechanism-based inhibitor of human liver CYP 2C19 and should be a new interesting tool for studying the topology of the active site of CYP 2C19.

Evaluation of a tertiary amine labeling protocol for peptides and proteins using Ru(bpy) 33+-based chemiluminescence detection

The properties of four ruthenium complexes and their efficiency as probes for chemiluminescent (CL) detection were evaluated, and a protocol for CL detection of a protein labeled with a tertiary amine was proposed. Of the four ruthenium complexes studied, Ru(bpy) 3 3+ proved to exhibit the characteristics necessary for optimum CL detection. Two biotin derivatives were synthesized containing a tertiary amine functionality and then incubated with the protein, avidin. The addition of the tertiary amine moiety to biotin made the derivative more sensitive to Ru(bpy) 3 3+-based CL. Quantitative data were obtained as a model of a labeling protocol by varying the number of biotins per avidin. Limit of detection (LOD) for either derivative were determined to be ∼50 nM, for the lowest concentration studied. The relative luminescence response increased with increasing number of tertiary amine labels per molecule of avidin. The results showed the potential of this approach for the detection of proteins using this tertiary amine labeling methodology.

Partitioning of a heterotelechelic polystyrene to separate interfaces of thin films

Heterotelechelic deuteropolystyrenes have been synthesised with a tertiary amine functionality at one end and a fluorocarbon group at the other end of the polymer chain. A layer of this polymer, circa 120 A thick, has been attached to the surface of a silicon substrate and subsequently covered with a much thicker layer of hydrogenous polystyrene. The combination has then been annealed at 413 K under vacuum for defined times and the subsequent distribution of the deutero heterotelechelic polymer determined using nuclear reaction analysis and neutron reflectometry. The influences of annealing time, molecular weight and thickness of the hydrogenous polymer have been examined. Nuclear reaction analysis showed that an excess of the heterotelechelic polymer formed at both interfaces with a larger excess remaining at the substrate-polymer interface. When the molecular weight of the hydrogenous polymer is lower than that of the deuteropolymer, the deutero layer is initially swollen by the hydrogenous polymer but the thickness then decreases as deutero polymer becomes detached from the silicon substrate and an additional excess layer is eventually formed at the vacuum-polymer surface. When the molecular weight of the hydrogenous polymer is higher, there is an initial shrinkage of the deuteropolymer layer, but the original thickness (∼ radius of gyration of the deuteropolymer) is regained on prolonged annealing. There is no evidence for bridging between the two interfaces by the heterotelechelic polymer. After five days annealing the volume fraction distribution of the deuteropolymer at the silicon substrate was well described by a self-consistent field model where the only adjustable parameter was the sticking energy of the tertiary amine group to the silicon substrate for which a value of 8kBT was obtained. Comparison of the dependence of the equilibrium layer thickness of the deuteropolymer on the equilibrium grafting density at the silicon surface with the predictions of scaling theory for brush-like polymer layers suggested that the grafted molecules were in the ideal, unperturbed brush region.

A multireceptorial binding reinvestigation on an extended class of σ ligands: N-[ω-(indan-1-yl and tetralin-1-yl)alkyl] derivatives of 3,3-dimethylpiperidine reveal high affinities towards σ 1 and EBP sites

New 1-[ω-(2,3-dihydro-1 H-inden-1-yl)- and (2,3-dihydro-5-methoxy-1 H-inden-1-yl)alkyl]- and 1-[ω-(1,2,3,4-tetrahydronaphthalen-1-yl)- and (6-methoxy- or 6-fluoro-1,2,3,4-tetrahydronaphthalen-1-yl)alkyl] derivatives of 3,3-dimethylpiperidine were synthesized, as homologous compounds of an existing series of σ ligands, in order to carry out σ receptor subtypes structure–affinity relationships. The new compounds and some of their related analogues, already reported, were tested in new multireceptorial radioligand binding assays. As reference compounds, the known σ 1 ligands SA 4503, BD 1008 and NE 100 were also prepared and tested. All reported compounds showed high σ 1 affinity assayed by (+)-[ 3H]-pentazocine on guinea-pig brain (apparent K i=1.75–72.2 nM) and moderate or low σ 2 affinity by [ 3H]-DTG on rat liver, in contrast with previous results. One tertiary amine function spaced by a five-membered chain from a phenyl group is the structural feature shared by the most active compounds 26 and 43 and some reference σ 1 ligands. The reported σ 1 ligands, including reference compounds, also demonstrated a high affinity towards EBP (Δ 8–Δ 7 sterol isomerase) site (apparent K i=0.48–14.8 nM) and some of them ( 37 and 44) were good ligands at L-type Ca ++ channel. 1-[4-(2,3-Dihydro-1 H-inden-1-yl)butyl]-3,3-dimethylpiperidine ( 26) was the best mixed σ 1 and EBP ligand (apparent K i=1.75 and 1.54 nM, respectively) with a good selectivity versus σ 2 receptor (138- and 157-fold, respectively).

Enantioseparation of dihydropyridine derivatives by means of neutral and negatively charged beta-cyclodextrin derivatives using capillary electrophoresis.

Employing capillary electrophoresis, the racemates of 29 acidic, neutral and basic dihydropyridines (DHPs) were separated by means of neutral and negatively charged cyclodextrins (CDs). Whereas the enantiomers of the acidic DHPs could be resolved with neutral CDs, mostly alpha- and beta-CD, the enantiomers of the neutral DHPs were only baseline-separated using the sulfobutyl ether-substituted beta-CD. Working in reversed polarity mode (detector at the anode) improved the peak shape and the resolution of the enantiomers. The racemates of the DHP bearing a secondary or tertiary amine function in the side chain at position 3 could be separated by using either the neutral gamma-CD or negatively charged CDs. The poor peak shape found with anionic CDs could be improved by the addition of methanol. The combination of gamma-CD and sulfated beta-CD allowed the detection of the minor enantiomer of lercanidipine (24) at less than 1% w/w.

Vanadium(IV) and -(V) complexes with O,N-chelating aminophenolate and pyridylalkoxide ligands.

Two different monoanionic O,N-chelating ligand systems, i.e., [OC6H2(CH2NMe2)-2-Me2-4,6]- (1) and [OCMe2([2]-Py)]- (2), have been applied in the synthesis of vanadium(V) complexes. The tertiary amine functionality in 1 caused reduction of the vanadium nucleus to the 4+ oxidation state with either [VOCl3], [V(=NR)Cl3], or [V(=NR)(NEt2)3] (R = Ph, (3a, 5a), R = p-Tol (3b, 5b)), and applying 1 as a reducing agent resulted in the synthesis of the vanadium(IV) complexes [VO(OC6H2(CH2NMe2)-2-Me2-4,6)2] (4) and [V(=NPh)(OC6H2(CH2NMe2)-2-Me2-4,6)2] (6). In the case of [V(=N-p-Tol)(NEt2)(OC6H2(CH2NMe2)-2-Me2-4,6)2] (7b), the reduction was sufficiently slow to allow its characterization by 1H NMR and variable-temperature studies showed it to be a five-coordinate species in solution. Although the reaction of 1 with [V(=N-p-Tol)(O-i-Pr)3] (9b) did not result in reduction of the vanadium nucleus, vanadium(V) compounds could not be isolated. Mixtures of the vanadium(V) (mono)phenolate, [V(=N-p-Tol)(O-i-Pr)2(OC6H2(CH2NMe2)-2-Me2-4,6)] (10), and the vanadium(V) (bis)phenolate, [V(=N-p-Tol)(O-i-Pr)(OC6H2(CH2NMe2)-2-Me2-4,6)2] (11), were obtained. With the pyridylalkoxide 2, no reduction was observed and the vanadium(V) compounds [VOCl2(OCMe2([2]-Py))] (12) and [V(=N-p-Tol)Cl2(OCMe2([2]-Py)] (13) were obtained. 51V NMR showed 7b and 12 to be five-coordinate in solution, whereas for 10, 11, and 13 a coordination number of 6 was found. Compounds 12 and 13 showed decreased activity compared to their nonchelated vanadium(V) analogues when applied as catalysts in ethene polymerization. Two polymorphic forms with a difference in the V-N-C angle of 12.5 degrees have been found for 6. Crystal data: 6.Et2O, triclinic, P1, a = 11.1557(6) A, b = 12.5744(12) A, c = 13.1051(14) A, alpha = 64.244(8) degrees, beta = 70.472(7) degrees, gamma = 87.950(6) degrees, V = 1547(3) A3, Z = 2; 6.C6H6, triclinic, P1, a = 8.6034(3) A, b = 13.3614(4) A, c = 15.1044(5) A, alpha = 98.182(3) degrees, beta = 105.618(2) degrees, gamma = 107.130(2) degrees, V = 1551.00(10) A3, Z = 2; 12, orthorhombic, Pbca, a = 11.8576(12) A, b = 12.6710(13) A, c = 14.722(2) A, V = 2211.9(4) A3, Z = 8.

A novel prodrug approach for tertiary amines. 2. Physicochemical and in vitro enzymatic evaluation of selected N‐phosphonooxymethyl prodrugs

Quaternary amine prodrugs resulting from N‐phosphonooxymethyl derivatization of the tertiary amine functionality of drugs represents a novel approach for improving their water solubility. Separate reports have demonstrated the synthetic feasibility and rapid and quantitative prodrug to parent drug conversion in rats and dogs. This work is a preliminary evaluation of the physicochemical and in vitro enzymatic reversion properties of selected prodrugs. The loxapine prodrug had over a 15 000‐fold increase in aqueous solubility relative to loxapine free base at pH 7.4. The loxapine prodrug was also shown to be quite stable at neutral pH values. The time for degradation product (parent drug) precipitation from an aqueous prodrug formulation would be expected to dictate the shelf life. Using this assumption, together with solubility and elevated temperature chemical stability studies, the shelf life of a parenteral formulation of the loxapine prodrug was projected to be close to 2 years at pH 7.4 and 25 °C. In addition, the prodrugs of cinnarizine and loxapine have been shown to be substrates for alkaline phosphatase, an enzyme found throughout the human body, and revert to the parent compound in its presence. The results from these evaluations demonstrate that the derivatives examined have many of the ideal properties required for potential clinical application.

Macrolide antibiotics, drug interactions and microsomal enzymes: implications for veterinary medicine

The macrolide group of antibiotics includes natural members, pro-drugs and semi-synthetic derivatives, thus named because they are composed of a large aglycone ring (from 14 to 16 carbon atoms), to which are attached several sugars. Some of them are amino-sugars, containing a diethylamino, tertiary amine function. A number of antibiotics, including erythromycin, oleandomycin, triacetyl-oleandomycin (troleandomycin), carbomycin, spiramycin, tylosin, rosamicin, azithromycin, clarithromycin, dirithromycin and others, are members of this group. On a comparative basis, erythromycin and oleandomycin are similar, with the same basic 14-carbon lactone ring and side chain sugars. The remaining compounds contain a basic 15- or 16-carbon lactone ring and one or two side-chain sugars. Most of the macrolides are produced by Streptomyces spp bacteria. An exception is rosamicin, which is produced by Micromonospora . Clarithromycin and azithromycin are new semi-synthetic derivatives of erythromycin.

Functionalized micelle-templated silicas (MTS) and their use as catalysts for fine chemicals

Functionalization of micelle-templated silica (MTS) was achieved by silanation of the MTS surface by 3-amino and 3-halogeno-propyl alkoxysilane in an apolar solvent. The grafted halogeno organic moieties were further modified by halogen substitution of other functions such as piperidine, tetraalkyl guanidine, (-)-ephedrine, 3-[N,N′-bis-3-salicyldenamino propylamine] (Salpr) and 3-[N,N′-bis-3-(3,5-di-tert-butylsalicyldenamino) propylamine] (tSalpr). During the modification procedure, the regular mesoporous structure of the MTS support was preserved. MTS-bound primary and tertiary amine functions were effective immobilized catalysts for Knoevenagel condensation and selective monoglyceride synthesis. MTS-bound 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) was an efficient base catalyst for performing transesterification reaction. Chiral β-aminoalcohols such as (-)-ephedrine grafted on MTS allowed the catalysed alkylation of benzaldehyde by diethylzinc with high conversion and selectivity in 1-phenyl-propanol and moderate enantioselectivity in the (1R) enantiomorph. Manganese (III) Salpr and tSalpr complexes linked to the MTS surface catalysed styrene epoxidation using iodosylbenzene. The efficiency of this latter catalysis should be improved by the use of other liganding molecules more resistant than salen-type ligands towards oxidation media.

Thiazole derivatives as inhibitors of purified bovine liver mitochondrial monoamine oxidase-B: structure-activity relationships and theoretical study.

Structure-activity relationships were performed on a new series of thiazole derivatives which selectively inactivate monoamine oxidase-B (MAO-B), purified from mitochondrial beef liver. All of the synthesized and tested compounds showed non-competitive inhibition, suggesting the formation of a stable adduct between the tertiary amine function, linked to the thiazolyl derivatives and the active site of the enzyme. The mechanism of MAO-B inhibition is discussed in terms of the Ionization Potential of the amine nitrogen atom and the conformational flexibility of the inhibitors.

An Amidinate Ligand with a Pendant Amine Functionality; Synthesis of a Vanadium(III) Complex and Ethene Polymerization Catalysis[#

A new type of amidinate ancillary ligand has been prepared, which incorporates a pendant tertiary amine functionality. The crystal structure of a vanadium(III) derivative, [SiMe3NC(Ph)NCH2CH2NMe2]VCl2(THF) (1), shows that the ligand can adopt a facial geometry, with an unusual distortion of the amidinate nitrogen bearing the pendant functionality. With AlEt2Cl cocatalyst the compound 1 produces a single-site catalytic system for the polymerization of ethene.

New super-hairy semi-rigid polymers

Living monofunctional poly(tetramethylene oxyde) (PTMO) (THF bulk polymerization initiated at 20°C by methyl triflate) was end capped by reaction with 3-(dimethylamino)propyl isocyanide. Selective and quantitative quaternization of the tertiary amine function results in the straightforward synthesis of PTMO macromonomers of the isocyanide type with a fairly good control of molecular weight and polydispersity (M n = 1800-4400, M w /M n = 1.2). Their homopolymerization at 40°C in highly concentrated methanol solution (macromonomer weight fraction =0.80) initiated by NiCl 2 quantitatively yields the corresponding poly(macromonomers) of high degrees of polymerization (DP w > 10 3 ) and of very unusual and maximum branching density: one graft chain per every backbone carbon atom. According to a semi-quantitative analysis of their radius of gyration, as derived from light scattering measurements (EtOAc-iPrOH 9: 1 by vol., Et 4 N + CF 3 SO 3 - 0.05 M), an increase of the intrinsic rigidity (persistence length) of the worm-like poly(isonitrile) backbone induced by the PTMO branches cannot be ruled out. These super-hairy polymers may be considered as exotic comb-shaped cationic poly(amphiphiles) of potential interest as new lyotropic and thermotropic materials.

New super-hairy semi-rigid polymers

Living monofunctional poly(tetramethylene oxyde) (PTMO) (THF bulk polymerization initiated at 20°C by methyl triflate) was end capped by reaction with 3-(dimethylamino)propyl isocyanide. Selective and quantitative quaternization of the tertiary amine function results in the straightforward synthesis of PTMO macromonomers of the isocyanide type with a fairly good control of molecular weight and polydispersity (M̄n ≈ 1800–4400, M̄w/M̄n ≈ 1.2). Their homopolymerization at 40°C in highly concentrated methanol solution (macromonomer weight fraction ≈0.80) initiated by NiCl2 quantitatively yields the corresponding poly(macromonomers) of high degrees of polymerization (DPw > 103) and of very unusual and maximum branching density: one graft chain per every backbone carbon atom. According to a semi-quantitative analysis of their radius of gyration, as derived from light scattering measurements (EtOAc-iPrOH 9 : 1 by vol., Et4N+CF3SO3−0.05 M), an increase of the intrinsic rigidity (persistence length) of the worm-like poly-(isonitrile) backbone induced by the PTMO branches cannot be ruled out. These super-hairy polymers may be considered as exotic comb-shaped cationic poly(amphiphiles) of potential interest as new lyotropic and thermotropic materials.

New super-hairy semi-rigid polymers

Living monofunctional poly(tetramethylene oxyde) (PTMO) (THF bulk polymerization initiated at 20°C by methyl triflate) was end capped by reaction with 3-(dimethylamino)propyl isocyanide. Selective and quantitative quaternization of the tertiary amine function results in the straightforward synthesis of PTMO macromonomers of the isocyanide type with a fairly good control of molecular weight and polydispersity (M̄n ≈ 1800–4400, M̄w/M̄n ≈ 1.2). Their homopolymerization at 40°C in highly concentrated methanol solution (macromonomer weight fraction ≈0.80) initiated by NiCl2 quantitatively yields the corresponding poly(macromonomers) of high degrees of polymerization (DPw > 103) and of very unusual and maximum branching density: one graft chain per every backbone carbon atom. According to a semi-quantitative analysis of their radius of gyration, as derived from light scattering measurements (EtOAc-iPrOH 9 : 1 by vol., Et4N+CF3SO3−0.05 M), an increase of the intrinsic rigidity (persistence length) of the worm-like poly-(isonitrile) backbone induced by the PTMO branches cannot be ruled out. These super-hairy polymers may be considered as exotic comb-shaped cationic poly(amphiphiles) of potential interest as new lyotropic and thermotropic materials.

STDS study for the identification of released compounds from commercial ion-exchange resins

Physical and chemical stability of polymeric sorbents, including ion-exchange resins, is among the main concern of both manufacturers and users. Different countries are gradually introducing regulations for the use of ion exchangers in water conditioning, food and beverage processing, separation of pharmaceutical products, and also for the use of reference materials as drugs and medical devices. Since all the applications mentioned may directly influence human health, the treated products must be free of any trace toxic compound potentially released by the polymeric matrix of the sorbent. The System for Thermal Diagnostic Studies (STDS) has recently been introduced commercially as a new versatile and powerful technique for the identification of the products evolved after thermal stress of solid phases. In this paper are presented the results of an STDS investigation to simulate the release of organic compounds from commercial weak and strong electrolyte anion and cation resins, differing for the type of polymeric matrix (polystyrene and polyacrylic based), porosity (gel and macroporous type), and functional groups, including sulfonic and carboxylate functionalities for the cation resins, and secondary, tertiary amine and quaternary ammonium functionalities for the anion resins. STDS determinations were carried out at 130, 200, 250 and 300°C by using a constant reaction time (10 min) and an inert (He) gas atmosphere. The thermally released compounds were cryofocused at −60°C and separated by temperature-programmed gas chromatography. The qualitative identification of the released compounds was made by searching the MS library NBS 54K. Thermogravimetric determinations were also carried out on a set of cation resins to complement STDS data.

Electron-Rich Oxoruthenium(IV) Cleavage Agents: A Zero-Order Rate Law for DNA Catalysis.

A new family of oxoruthenium(IV) complexes based on [(DAMP)(L)RuO](2+) have been prepared where DAMP = 2,6-bis((dimethylamino)methyl)pyridine and L = 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), or dipyridophenazine (dppz). The structures of [(DAMP)(bpy)RuO](2+) and [(DAMP)(phen)RuO](2+) were determined by X-ray crystallography. The Ru-O bond lengths (1.805(3) and 1.814(4) Å, respectively) are indicative of multiple bonding, as expected for oxoruthenium(IV), and clear steric protection of the Ru=O moiety is provided by the DAMP ligand. Cyclic voltammetry shows that the tertiary amine functionalities of the DAMP ligand stabilize both the Ru(IV)O(2+) and Ru(III)OH(2+) redox forms relative to other (polypyridyl)oxoruthenium(IV) complexes. As a result, the oxidations of both sec-phenylethanol and trans-stilbene are approximately 100 times slower for [(DAMP)(bpy)RuO](2+) than for [(bpy)(2)(py)RuO](2+). Accordingly, the reaction mechanisms involve oxidation of substrate only by the Ru(IV)O(2+) form with no contribution from direct oxidation by the Ru(III)OH(2+) intermediate, which greatly simplifies the kinetic analysis. The Ru(IV)O(2+) forms are not effective oxidants of the sugar moiety of mononucleotides; however, the base functionality of guanosine 5'-monophosphate is oxidized at detectable rates. In contrast, cleavage of a hairpin oligonucleotide is detected at both guanine and sugar functionalities, indicating that the oligomer promotes sugar oxidation by increasing the local concentration of the metal complex. The Ru(III)OH(2+) form of the DAMP complexes is stable in the absence of DNA but is reduced following a zero-order rate law in the presence of calf thymus DNA. Analysis using a model that resembles Michaelis-Menten kinetics indicates that the binding domain on DNA catalyzes the disproportionation of the complex. The model yields a binding constant and a calculated first-order rate constant that are in good agreement with independent measurements.

Adsorption and ion exchange of some groundwater anion contaminants in an amine modified coconut coir

The adsorption of nitrate, chromium (VI), arsenic (V) and selenium (VI) anions in an amine modified coconut coir (MCC-AE : with secondary and tertiary amine functionality) were studied to determine the capability of this easily prepared and low-cost material in removing typical groundwater anion contaminants. Batch adsorption-ion exchange experiments were conducted using 200 mg MCC-AE, initially containing chloride as the resident anion, and 50 ml of different anion-containing water of varying concentrations. It is presumed, at this low pH, that only SeO42− remained as a divalent anion, while monovalent species H2AsO4− and HCrO4− predominated in their respective exchanging ion solutions. The adsorption data were fitted using the Freundlich equation and maximum adsorption for each anion was estimated using their respective Freundlich equation constants. MCC-AE exhibited preference for divalent Cr (VI) and Se (VI) anions compared with the Cl− resident ion. Maximum As (V) adsorption was 0.086 mmol/g, while maximum adsorption of Cr (VI), NO3− and Se (VI) anions was 0.327 mmol/g, 0.459 mmol/g, and 0.222 mmol/g, respectively. The ion exchange capacity of MCC-AE is estimated, based on its exchange capacity for nitrate, to be within 0.46 mmol of positive charges per gram. Similar adsorption experiments were conducted for comparison using commercial chloride-form Amberlite IRA-900 strong base (quaternary amine functionality) anion exchanger, with an exchange capacity of 4.2 meq/g. Maximum adsorption of the different ions in IRA-900 was about 3 times higher for NO3−, 9 times higher for Se (VI), 10 times higher for As (V) and 9 times higher for Cr (VI), than that in MCC-AE. Differences in the ion exchange behavior of MCC-AE and IRA-900 were probably due to the different amine functionalities in the two exchangers. The results suggest that MCC-AE may be used as a low-cost alternative adsorbent/ion exchanger for treatment of anion contaminants in groundwater.