Effect of vinylene and 1,4-phenylene spacers on efficiency of the ground-state intramolecular charge-transfer in enlarged 4-dimethylamino-1-methylpyridinium cations

¹⁵N NMR chemical shifts of the exo- and endocyclic nitrogen atoms show how efficient is the ground-state intramolecular charge transfer between these sites in 4-dimethylamino-1-methylpyridinium cation (increased contribution of the quinoid resonance form results in a shielding and deshielding effect of their NMR signals, respectively). As it was anticipated, insertion of vinylene and/or 1,4-phenylene spacers to the cation considerably hinders the ground-state charge transfer. This hypothesis is further supported by an analysis of the C–NMe₂ bond lengths (X-ray data show that spacers elongate this bond). The selected valence angles in the compounds studied are also linearly dependent on δ(¹⁵N_endo) and δ(¹⁵N_exo) values. Although the correlation coefficient for the δ(¹⁵N_endo) versus δ(¹⁵N_exo) dependence is equal to 0.983, decrease of the net charge on one nitrogen atom is not compensated entirely by its increase on another nitrogen atom. This shows that exocyclic nitrogen atom is not the only acceptor of the positive charge in the molecule. The natural population analysis shows that the positive charge is transferred not only to the exocyclic N but also to, e.g., 1- and N-methyl C as well as to C3 and C5 atoms in pyridine ring. Ground-state charge transfer through the p-phenylene moiety was found to be less effective than through the trans-vinylene bridge. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Conformational analysis of N-isopropylbenzohydroxamic acids: crystal structure, DFT, and NMR studies

X-ray crystal structure determinations together with density functional theory (DFT) calculations in vacuo and NMR studies in solution have been carried out for 4-MeOC₆H₄CONPrⁱOH 2a and 3,5-(NO₂)₂C₆H₃CONPrⁱOH 2b. The results were compared with that for the respective N-methyl benzohydroxamic acids. For crystal structures as well as for DFT-optimized geometries of 2 (both isomers) in vacuo, the effect of substituents in aromatic ring manifested by changing of charges is inconspicuous. Studies of potential energy surfaces showed that libration barrier around ω ₁ = 0° is low enough to make electron conjugation feasible, and that for 2b rotation barrier around C(O)N bond is higher by 6 kcal/mol and additionally, that rotation around N–C bond is hindered. A careful analysis of low-temperature ¹H NMR spectra confirmed the greater stability of Z-2a, the greater rigidity of E-2b and the influence of solvent on both isomers population. Despite solvent-dependent conformational alteration, both 2a and 2b crystallize exclusively as E isomers from ethyl acetate solution. Correlations of absolute ¹H, ¹³C, and ¹⁵N shielding calculations with experimental data were also analyzed. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The first naphthodiazaphosphorinane in the solid phase; syntheses, spectroscopic studies and X-ray crystallography of some new 1,3,2-diheterophosphorus compounds

New heterocyclic compounds of diazaphosphorinanes, diazaphospholes, and oxazaphospholes were synthesized and characterized by ¹H, ¹³C, ³¹P, NMR, IR spectroscopy, and CHN elemental analysis. The 3D structure of compound (5) was determined by X-ray crystallography. Since benzo- or naphthodiazaphospholes/diazaphosphorinanes containing aromatic rings are usually unstable in the solution state, their single crystal structures are rarely reported and, to the best of our knowledge, this structure is the first occasion of naphthodiazaphosphorinanes obtained here. It is noticeable that the P=O and C=O bonds are closer to syn than anti configuration and the P=O bond is placed in a pseudo-equatorial position. This structure produced a 3D polymeric chain via strong hydrogen bonds and electrostatic short contacts. Due to the ring strain of five-membered rings, for all diazaphospholes great ² J(PNH_endocyclic) coupling constants (about 18.0 Hz), as well as high ^2,3 J(P,C) coupling constants for the aromatic carbon atoms connected to the five-membered ring (about 14.5, 13.5 Hz, respectively) were measured. Replacement of one NH group in a diazaphosphole ring by an oxygen atom caused exceedingly decreased ring strain and hence highly diminished ² J(PNH_endocyclic) coupling constant. Furthermore, ³¹P NMR spectra of oxazaphospholes, like the spectra of diazaphosphorinanes, indicated highly shielded phosphorus atoms relative to those of their diazaphospholes analogs. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis and characterization of palladium(II) complexes of thioureas. X-ray structures of [Pd( N , N ′-dimethylthiourea)4]Cl2?·?2H2O and [Pd(tetramethylthiourea)4]Cl2

Palladium(II) complexes of thiones having the general formula [Pd(L)₄]Cl₂, where L = thiourea (Tu), methylthiourea (Metu), N,N′-dimethylthiourea (Dmtu), and tetramethylthiourea (Tmtu) were prepared by reacting K₂[PdCl₄] with the corresponding thiones. The complexes have been characterized by elemental analysis, IR and NMR spectroscopy, and two of these, [Pd(Dmtu)₄]Cl₂ · 2H₂O (1) and [Pd(Tmtu)₄]Cl₂ (2), by X-ray crystallography. An upfield shift in the >C=S resonance of thiones in ¹³C NMR and downfield shift in N–H resonance in ¹H NMR are consistent in showing sulfur coordination with palladium(II). The crystal structures of the complexes show a square-planar coordination environment around the Pd(II) ions with the average cis and trans S–Pd–S bond angles of 89.64° and 173.48°, respectively. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. An erratum to this article can be found at     

An NMR study of cyclodextrin complexes of the steroidal neuromuscular blocker drug Rocuronium Bromide

The interaction of Rocuronium Bromide, and a model steroid Org 7402, with three cyclodextrins (β‐cyclodextrin, γ‐cyclodextrin and Org 25969) was studied by solution state NMR experiments. Stoichiometries and binding constants were determined from ¹H chemical shift titrations. All of the systems formed 1 : 1 complexes. Most of the complexes were in fast exchange with unbound species on the NMR time scale, but the most tightly bound complex (Rocuronium Bromide–Org 25969) was in the slow exchange regime. The geometry of the complexes was inferred from ¹H and ¹³C NMR shift changes upon complexation and from intramolecular NOE correlations. Rocuronium Bromide forms a weak complex with β‐cyclodextrin (K_a = 3.3 ± 0.5 × 10³ M ^?1) and no clear picture of the structure of the complex emerges. The complexes with γ‐cyclodextrin (K_a = 1.8 ± 0.2 × 10⁴ M ^?1) and Org 25969 (K_a > 10⁵ M ^?1) are true inclusion complexes with the steroid located inside the central void of the cyclodextrin. Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis and assessment of molecular recognizability by RP-HPLC of an N-alkyl-β-Ala-L-Phe-derived organic phase with self-assembling ability

An N-alky-β-Ala-L-Phe derivative, N'-octadecyl-N ^α -[(N-acryloyl)-β-alanyl]-L-phenylalanineamide (1), with a polymerizable head group has been synthesized and telomerized with the silane coupling agent 3-mercaptopropyltrimethoxysilane (MPS). SEM and DSC observations indicated that both 1 and its telomer (T-1) could self-assemble into fibrillar forms with highly ordered structures in organic media such as benzene through complementary hydrogen bonding between the amide moieties. T-1 was grafted onto porous silica gels through the terminal trimethoxysilyl group and then packed into a stainless steel column. RP-HPLC results for polycyclic aromatic hydrocarbons (PAHs) demonstrated that significantly higher molecular shape recognition could be achieved by silica-supported T-1 (Sil-T-1). In this paper, the mechanism of the selectivity enhancement in HPLC by Sil-T-1 is discussed on the basis of comparing with the corresponding L-Phe derivative N'-octadecyl-N ^α -(acryloyl)-L-phenylalanineamide (2) without β -Ala and the stationary phase (Sil-T-2) obtained from it. The HPLC column materials Sil-T-1 and Sil-T-2 were characterized by DSC, TGA, DRIFT-IR, and ¹³C and ²⁹Si CP-MAS NMR spectroscopic measurements. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis, spectroscopic, and X-ray structural characterization of pharmacologically active substituted pyrazolyl-acetanilides

Five new pyrazole acetanilides were synthesized by N-alkylation of pyrazole and its derivatives with 4′-propionyl-2-iodoacetanilide. Compounds 1–5 were characterized by ¹H NMR, ¹³C NMR, IR, UV–Vis, MS, and elemental analysis. X-ray structures of representative compounds 1, 3, and 5 established their conformations and solid-state hydrogen bonding preferences. Acute toxicity, local anesthetic, and antiarrhythmic activities were assessed for compounds 1–5 using established protocols. Lower potencies and lower acute toxicities were recorded relative to lidocaine. Enhanced anesthetic activity of compound 3 was attributed to the presence of the propionyl group in the molecule. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis and crystal structures of two isostructural manganese(III) and iron(III) complexes derived from <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′-bis(3-ethoxysalicylidene)-1,2-propanediamine with cytochrome P450-like hydroxylation properties

Two isostructural mononuclear complexes with the formula [M^IIIL(N₃)(OH₂)] × 1/2N₂ (M = Mn for (1) and Fe for (2); H₂L = N,N′-bis(3-ethoxysalicylidene)-1,2-propanediamine) have been synthesized and characterized by physico-chemical and spectroscopic methods. Each compound consists of a mononuclear complex molecule and half of a nitrogen molecule of crystallization. Each metal atom in the complexes has a slightly distorted octahedral geometry, coordinated by two nitrogen and two phenolic donors of L, the oxygen atom of the water molecule, and the nitrogen atom of the azide group. Determination by GC/MS analysis indicated that complex (1) has no catalytic property for the dioxygen oxidization of cyclohexene, but complex (2) has good properties. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The use of MM/QM calculations of 13C and 15N chemical shifts in the conformational analysis of alkyl substituted anilines

The calculation of the ¹³C and ¹⁵N NMR chemical shifts by a combined molecular mechanics (Pcmodel 9.1/MMFF94) and ab initio (GIAO (B3LYP/DFT, 6-31 + G(d)) procedure is used to investigate the conformations of a variety of alkyl substituted anilines. The ¹³C shifts are obtained from the GIAO isotropic shielding (Ciso) with separate references for sp³ and sp² carbons (δc = δref − Ciso). The ¹⁵N shifts are obtained similarly from the GIAO isotropic shielding (Niso) with reference to the ¹⁵N chemical shift of aniline. Comparison of the observed and calculated shifts provides information on the molecular conformations. Aniline and the 2,6-dialkylanilines exist with a rapidly inverting symmetric pyramidal nitrogen atom. The 2-alkylanilines have similar conformations with the NH₂ group tilted away from the 2-alkyl substituent. The N,N-dialkylanilines show more varied conformations. N,N-dimethylaniline has a similar structure to aniline, but N-ethyl, N-methylaniline, N,N-diethylaniline, and N,N-diisopropylaniline are conformationally mobile with two rapidly interconverting conformers. In contrast, the anilines substituted at C₂ and the nitrogen atom exist as one conformer where the steric interaction between the C₂ substituent and the N substituent determines the conformation. In 2-methyl-N-methylaniline, the nitrogen atom is pyramidal as usual with the N-methyl opposite to the 2-methyl, but in 2-methyl-N,N-dimethyl aniline, the NMe₂ group is now almost orthogonal to the phenyl plane. This is also the case with 2-methyl-N,N-diethylaniline and 2,6-diisopropyl-N,N-dimethylaniline. The comparison of the observed and calculated ¹⁵N chemical shifts confirms the above findings, in particular the pyramidal conformation of aniline and the above observations with respect to the conformations of the N,N-dialkylanilines.     

Nucleophilicities of Para‐Substituted Phenoxide Ions in Water and Correlation Analysis

Second‐order rate constants for the reactions of 2‐aryl‐4,6‐dinitrobenzotriazole 1‐oxides 1a‐d with some 4‐X‐substituted phenoxide ions 2a‐d (X = OCH₃, H, Cl, and CN) have been measured in aqueous solution at 20°C. The pK_a values for the σ‐complexation processes of a series of benzotriazole 1a‐d measured in water have been used to determine their electrophilicity parameters E according to the correlation E = –3.20 – 0.662 pK_a (F. Terrier, S. Lakhdar, T. Boubaker, and R. Goumont, J Org Chem, 2005 , 70, 6242–6253). For these reactions, plots of log k versus the electrophilicity parameters E of the benzotriazoles 1a‐d were linear, allowing to derive the nucleophilicity parameters N and s for phenoxide ions as defined by the Mayr equation log k₁ (20°C) = s (E + N) (H. Mayr, M. Patz. Angew Chem, Int Ed Engl 1994 , 33, 938–957). The N values are found to cover a range of nucleophilicity from 6.85 to 10.22, going from 4‐cyanophenoxide 2d for the least reactive ion to 4‐methoxyphenoxide 2a for the most reactive nucleophile. Good linear correlations were found between the nucleophilicity parameters N of phenoxide ions 2a‐d and the pK_a values of their conjugate acids (N = –3.05 + 1.25 pK_a) and the constants of the substituents X (N = 9.21 – 2.51).     

Supramolecular self-assembly of two Cu(II) complexes with 1,2,4-triazole derivatives: syntheses,crystal structures and magnetic properties

Two two-dimensional coordination complexes, {[Cu₄(BTM)₆(OPA)₄] · 4DMF · 3H₂O} _n (1) and {[Cu(BDTM)(OH)](ClO₄) · 2H₂O} _n (2) (BTM = bis(1,2,4-triazol-1-yl)methane, BDTM = bis(3,5-dimethyl-1,2,4-triazol-1-yl)methane, OPA²⁻ = ortho-phthalic dianion, DMF = N,N-dimethylformamide), were synthesized and structurally characterized. Each Cu(II) ion locates in a distorted square pyramidal geometry in 1, in which OPA²⁻ ligands bridge Cu²⁺ ions along a axis to form a magnetic transmission chain and BTM ligands act as flexible spacers to construct the two-dimensional layer structure. In 2, each Cu²⁺ ion adopts tetra-coordination geometry to two hydroxyl groups and two triazolyl nitrogen atoms from two different BDTM ligands. Two hydroxyl groups bridge two Cu²⁺ ions to form a rhombic diamond, and four BDTM ligands connect four diamonds to form a 36-membered macrocyclic structure with large channels along a axis. Magnetic properties revealed that both OPA²⁻ and OH⁻ mediate anti-ferromagnetic interactions between Cu²⁺ ions with J = − 0.06(3) and −301.9(2) cm⁻¹ for 1 and 2, respectively. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Intermediate and ion-pair formation in the outer-sphere reactions between azido-pentacyanocobaltate(III) and iron(II) polypyridyl complexes in aqueous medium

The kinetics of the reactions between azido-pentacyanocobaltate(III), Co(CN)₅N₃ ³⁻, and iron(II) polypyridyl complexes, Fe(LL)₃ ²⁺ (LL = bipy, phen), have been studied in both neutral and acidic aqueous solutions at I = 0.1 mol dm⁻³ NaCl. The reactions were carried out under pseudo-first-order conditions in which the concentration of Fe(LL)₃ ²⁺ was kept constant, and the second-order rate constants obtained for the reactions at 35 °C were within the range of 0.156–0.219 dm³ mol⁻¹ s⁻¹ for LL = bipy and 0.090–0.118 dm³ mol⁻¹ s⁻¹ for LL = phen. Activation parameters were measured for these systems. The dependence of reaction rates on acid was studied in the range [H⁺] = 0.001–0.008 mol dm⁻³. The reaction in acid medium shows interesting kinetics. Two reactive species were identified in acid medium, namely, the protonated cobalt complex and the azido-bridged binuclear complex. The electron-transfer process is proposed to go by mixed outer- and inner-sphere mechanisms in acid medium, in which electron transfer through the bridged inner-sphere complex (k ₅) is slower than through the outer-sphere path (k ₄). Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

New functional triethoxysilanes as iodide sources for dye-sensitized solar cells

Three new triethoxysilanes bearing quaternary ammonium alkyl iodides are reported, N,N,N-triethyl-3-(triethoxysilyl)propan-1-aminium iodide 1, N,N,N-triheptyl-3-(triethoxysilyl)propan-1-aminium iodide 2 and N,N,N-tridodecyl-3-(triethoxysilyl)propan-1-aminium iodide 3. ¹H and ¹³C NMR spectroscopy and electrospray mass spectrometry were used to confirm the synthesis of pure products. Electrolytes based on these ionic liquids were developed and their performance in dye-sensitized solar cells (DSSCs) evaluated. The electrolytes incorporated 1 and 2 (in 30–60 wt%) as iodide sources together with I₂ (0.08 M), 0.1 M guanidinium thiocyanate and 0.5 M tert-butylpyridine in acetonitrile (AN); and I₂ (0.15 M) and N-methylbenzimidazole (0.5 M) for 2-methoxyproprionitrile (MPN) as co-solvent. Testing of DSSCs to analyze the influence of chain length (ethyl and heptyl) on cell efficiency revealed that, for silanes concentration of 1 M, electrolyte B (based on 2 in AN) and electrolyte C (based on 1 in MPN) gave the best cell efficiency at simulated full sunlight (AM 1.5, 1000 W m⁻²) illumination (5.0–5.3%). At 0.1 Sunlight (AM 1.5, 100 W m⁻²), electrolyte B gave the best performance of 8.0%. High open circuit voltages (V_OC) of 750–850 mV were achieved for a number of quite efficient cells (5–6%). For silane 2, variation of the I⁻/I₂ ratio and total silane content (1–2 M 2) on DSSC efficiency gave a consistent efficiency of 8.0% at 0.1 Sunlight. At full sunlight, the cell efficiency decreased as the silane concentration increased from 1 M (5.0%) to 2 M (3.7%), largely due to a drop in short circuit current.     

Pyrazole‐1‐carbothioamide as a Potent Precursor for Synthesis of Some New N‐heterocycles of Potential Biological Activity

Herein, we reported the efficient synthesis of new azoles as bio‐functional analogs, employing the easily obtainable N‐acetyl‐3,5‐diphenyl‐4,5‐dihydro‐1H‐pyrazole‐1‐carbothioamide ( 1 ), as a versatile precursor. The structures of the newly synthesized compounds were elucidated based on their IR, ¹H NMR, and ¹³C NMR mass spectral and elemental analysis. Furthermore, some selected compounds were evaluated in vitro for their antimicrobial activities. The preliminary bioassay results indicate that the majority of the tested compounds exhibited significant antimicrobial activity. Compounds 12 , 11 , 18 , 30 , 22 , 3 , and 2 were found to be the most potent against the tested microorganisms with minimum inhibitory concentration ≤ (12.25 μg/mL), indicating that conjugates bearing thiazole moiety, as well as those with N‐substituted electron‐withdrawing groups, exhibited higher potency than the rest of other compounds.     

Synthesis,structure, and electrochemistry of <Emphasis Type="Italic">trans</Emphasis>-[Co<Superscript>III</Superscript>{(BA)<Subscript>2</Subscript>pn}(L)<Subscript>2</Subscript>]ClO<Subscript>4</Subscript> complexes

The structure, spectroscopic, and electrochemical properties of [Co{(BA)₂pn}(L)₂]ClO₄ complexes, where (BA)₂pn = N,N′-bis(benzoylacetone)-1,3-propylenediimine dianion and the two ancillary ligands (L) are pyridine, py (1), and 4-methylpyridine, 4-Mepy (2), have been investigated. These complexes have been characterized by elemental analyses, IR, UV–Vis and ¹H-NMR spectroscopy. The crystal structure of [Co{(BA)₂pn}(py)₂]ClO₄ (1) has been determined by X-ray diffraction. The coordination geometry around cobalt(III) is best described as a distorted octahedron. The electrochemical reduction of these complexes at a glassy carbon electrode in acetonitrile solution indicates that the first reduction process corresponding to Co^III–Co^II is electrochemically irreversible, which is accompanied by the dissociation of the axial N(py)–cobalt bonds. This process becomes quasi-reversible upon the addition of excess py ligands. The second reduction step of Co^II/I shows reversible behavior and is not influenced by the nature of the axial ligands. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis and NMR elucidation of pentacyclo-undecane diamine derivatives as potential anti-tuberculosis drugs

The complete structural elucidation of six novel pentacycloundecane (PCU) derivatives is reported. The target molecules are potential anti-tuberculosis agents. The addition of side arms to the PCU cage skeleton at position C-8/C-11 results in major overlapping of the methine resonances of the ¹H NMR spectrum. The use of 2D NMR techniques proved to be a very useful tool in overcoming the difficulties encountered in the elucidation of cage compounds using ¹H and ¹³C spectra only. All compounds reported are meso compounds thereby simplifying the complexity of the NMR spectra. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Hole‐transporting host‐polymer series consisting of triphenylamine basic structures for phosphorescent polymer light‐emitting diodes

A series of novel styrene derived monomers with triphenylamine‐based units, and their polymers have been synthesized and compared with the well‐known structure of polymer of N,N′‐bis(3‐methylphenyl)‐N,N′‐diphenylbenzidine with respect to their hole‐transporting behavior in phosphorescent polymer light‐emitting diodes (PLEDs). A vinyltriphenylamine structure was selected as a basic unit, functionalized at the para positions with the following side groups: diphenylamine, 3‐methylphenyl‐aniline, 1‐ and 2‐naphthylamine, carbazole, and phenothiazine. The polymers are used in PLEDs as host polymers for blend systems with the following device configuration: glass/indium–tin–oxide/PEDOT:PSS/polymer‐blend/CsF/Ca/Ag. In addition to the hole‐transporting host polymer, the polymer blend includes a phosphorescent dopant [Ir(Me‐ppy)₃] and an electron‐transporting molecule (2‐(4‐biphenyl)‐5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole). We demonstrate that two polymers are excellent hole‐transporting matrix materials for these blend systems because of their good overall electroluminescent performances and their comparatively high glass transition temperatures. For the carbazole‐substituted polymer (T_g = 246 °C), a luminous efficiency of 35 cd A^?1 and a brightness of 6700 cd m^?2 at 10 V is accessible. The phenothiazine‐functionalized polymer (T_g = 220 °C) shows nearly the same outstanding PLED behavior. Hence, both these polymers outperform the well‐known polymer of N,N′‐bis(3‐methylphenyl)‐N,N′‐diphenylbenzidine, showing only a luminous efficiency of 7.9 cd A^?1 and a brightness of 2500 cd m^?2 (10 V). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3417–3430, 2010     

Living free‐radical polymerization of sterically hindered monomers: Improving the understanding of 1,1‐disubstituted monomer systems

The sterically hindered, 1,1‐disubstituted monomers di‐n‐butyl itaconate (DBI), dicyclohexyl itaconate (DCHI), and dimethyl itaconate (DMI) were polymerized with reversible addition–fragmentation chain transfer (RAFT) free‐radical polymerization and atom transfer radical polymerization (ATRP). Cumyl dithiobenzoate, cumyl phenyl dithioacetate, 2‐cyanoprop‐2‐yl dithiobenzoate, 4‐cyanopentanoic acid dithiobenzoate, and S‐methoxycarbonylphenylmethyl dithiobenzoate were employed as RAFT agents to mediate a series of polymerizations at 60 °C yielding polymers ranging in their number‐average molecular weight from 4500 to 60,000 g mol^?1. The RAFT polymerizations of these hindered monomers displayed hybrid living behavior (between conventional and living free‐radical polymerization) of various degrees depending on the molecular structure of the initial RAFT agent. In addition, DCHI was polymerized via ATRP with a CuCl/methyl benzoate/N,N,N′,N″,N″‐pentamethyldiethylenetriamine/cyclohexanone system at 60 °C. Both the ATRP and RAFT polymerization of the hindered monomers displayed living characteristics; however, broader than expected molecular weight distributions were observed for the RAFT systems (polydispersity index = 1.15–3.35). To assess the cause of this broadness, chain‐transfer‐to‐monomer constants for DMI, DBI, and DCHI were determined (1.4 × 10^?3, 1.3 × 10^?3, and 1.0 × 10^?3, respectively) at 60 °C. Simulations carried out with the PREDICI program package suggested that chain transfer to monomer contributed to the broadening process. In addition, the experimental results indicated that viscosity had a pronounced effect on the broadness of the molecular weight distributions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3692–3710, 2006     

Determination of tetracycline residues in soil by pressurized liquid extraction and liquid chromatography tandem mass spectrometry

An optimized extraction and cleanup method for the analysis of chlortetracycline (CTC), doxycycline (DC), oxytetracycline (OTC) and tetracycline (TC) in soil is presented. Soil extraction in a pressurized liquid extraction system, followed by extract clean up using solid-phase extraction (SPE) and tetracycline determination by liquid chromatography tandem mass spectrometry (LC-MS/MS) provided appropriate efficiency and reproducibility. Different dispersing agents and solvents for soil extraction and several SPE cartridges for cleanup were compared. The best extraction results were obtained using ethylenediamine tetraacetic acid-treated sand as dispersing agent, and water at 70 °C. The most effective cleanup was obtained using Strata-X^TM sorbent in combination with a strong anion exchange cartridge. Recoveries ranged from 71% to 96% and precision, as indicated by the relative standard deviations, was within the range of 8–15%. The limits of quantification (LOQs) by using LC-MS/MS, based on signal-to-noise ratio (S/N) of 10, ranged from 1 μg kg⁻¹ for TC to 5 μg kg⁻¹ for CTC. These results pointed out that this technique is appropriate to determine tetracyclines in soils. Analysis of 100 samples taken in the Valencian Community revealed that, in soil, up to 5 μg kg⁻¹ CTC, 15 μg kg⁻¹ OTC, 18 μg kg⁻¹ TC, and 12 μg kg⁻¹ DC could be detected. Detection of the analytes in several samples, which typify great part of the Spanish agricultural soils, should be outlined as most important result of this study. Electronic supplementary material  The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

Variations in the gross alpha and beta activity in surface waters at the Atomic Weapons Establishment Aldermaston (UK)

N,N,N′,N′-tetra-2-ethylhexyldiglycolamide (T2EHDGA) has been used for the preferential extraction of ⁹⁰Y from its mixture with ⁹⁰Sr from HNO₃ as well as HCl medium. The separation efficiencies have been found out under varying experimental conditions. The extracted species were determined from T2EHDGA concentration variation experiments carried out at 3 M nitric acid as well as HCl and were found out to be Y(X₃)₃·3(TEHDGA)_(o) for both the extraction systems, where X = NO₃ ⁻ and Cl⁻, respectively. Comparison of the T2EHDGA and TODGA based separation methods is also made. In order to avoid third phase formation, iso-decanol has been used as the modifier in all the studies. The modifier content was optimized to 30% for 4 M HCl and 20% for 6 M HNO₃ as the feed aqueous phases. Separation schemes were developed for the separation of carrier free ⁹⁰Y and the purity was checked by the half-life measurement method.