Hyperfine structure and core polarization in Nd I 4f 4f 4 5d6s

The high resolution laser-atomic-beam technique was used to investigate the hyperfine structure in Nd I 4f ⁴ 5d6s ⁷ L, ⁷ K, ⁷ I, ⁷ H, ⁷ G, ⁵ L, ⁵ K, and ⁵ I for both of the stable odd isotopes. The metastable states were populated by an arc discharge burning in the atomic beam, and 31 transitions to higher odd levels have been studied. Knowledge of the hyperfine constants of 34 levels of 4f ⁴ 5d6s allowed a comprehensive parametric analysis to be performed, using the effective tensor operator formalism. Compared to earlier analyses, a significant reduction of errors has been achieved for all the parameters. The contact parameter a _4f ¹⁰ has been fitted freely, thus providing an experimental value for the core-polarization effects. They are about six times larger than the relativistic effects.     

Extraction-photometric determination of vanadium(V) with N-hydroxy-N-m-tolyl-N′-(2-methyl-5-chloro)phenyl-p-toluamidine hydrochloride in the presence of acetic,monochloroacetic, and phenylacetic acids

N-Hydroxy-N-m-tolyl-N′-(2-methyl-5-chloro)phenyl-p-toluamidine hydrochloride (HTMCPTH), a monobasic and bidentate chelating agent which reacts with vanadium(V) in carboxylic acid media to develop a blue-violet complex, has been employed as a highly selective reagent for extraction and direct photometric determination of the metal. Solvent extraction experiments indicate that from aqueous acetic acid (1.0–10.0 M), monochloroacetic acid (0.1–10.0 M), and phenylacetic acid (at pH 0.5–6.0) vanadium(V) is quantitatively extracted into chloroform. Almost all common ions including Fe³⁺, Cu²⁺, Ni²⁺, Co²⁺, Mn²⁺, Cr³⁺, Ti⁴⁺, Zr⁴⁺, and Mo⁶⁺ do not interfere with the proposed method. The procedure has been utilized for accurate determination of vanadium in standard steels.     

Benzimidazole-based optical probe for selective detection of multiple-cations via dual-channel analysis

A benzimidazole-based optical probe having pendant carboxyl, amine, and imine groups as ionophore has been prepared for screening various metal ions. The 4-(1H-benzo[d]imidazol-2-yl)-1H-imidazole-5-carboxylic acid (1) has been obtained in good yield and characterized by full battery of complementary physico-chemical techniques including ¹H NMR, UV-Vis, fluorescence spectroscopy, and single crystal X-ray crystallography. Metal ion-binding properties of 1 have been studied using ppm level concentration of representative alkali metal (Na⁺, K⁺), alkaline earth metal (Mg²⁺, Ca²⁺), and transition metal (Zn²⁺, Co²⁺, Fe³⁺, Cd²⁺, Hg²⁺, Pb²⁺, Cu²⁺, Ag⁺) ions and the output signal was monitored via two different channels viz chromogenically and fluorogenically. Selective recognition of Hg²⁺ has been explored with absorption spectra whereas emission spectra of 1 display differential response for multiple cations at parts-per-million (ppm) level concentration that allow selective detection of Ca²⁺, Mg²⁺, and Na⁺ ions. The results have been discussed in light of selectivity, sensitivity, response time, mode of binding/interactions, and sensing properties.     

A study on the reaction between N-substituted p-phenylenediamines and ozone: experimental results and theoretical aspects in relation to their antiozonant activity

The following p-phenylenediamines (PPD): N,N,N^′,N^′-tetramethyl-p-phenylenediamine (TMPPD), N,N^′-dimethylbutyl-p-phenylenediamine (6PPD), N,N^′-diaryl-p-phenylenediamine (DPPD), tris-(N-dimethylpentyl-p-phenylenediamine)-N^′,N^′,N^′-1,3,5-triazine (6PPDTZ), have been oxidized under the action of O₃ in diluted solutions. In all cases the radical cation or semiquinone radical was the first derivative formed by monoelectronic oxidation of the substrate. The radical cation has been studied by electronic spectroscopy and the electronic spectral changes of all mentioned PPD has been followed as function of the ozonation time. The results have been discussed in the frame of the antiozonant properties of these PPD which are used as antiozonant agents in diene rubber protection. It is shown that the antiozonant activity of each PPD considered correlates with the free enthalpy of formation of the respective radical cation. The lowest is the free energy of formation of a PPD radical cation and the highest is the antiozonant activity in a diene rubber compound.     

First generation poly(propyleneimine) dendrimers functionalised with 1,8-naphthalimide units as fluorescence sensors for metal cations and protons

The synthesis of two new green fluorescent poly(propyleneimine) dendrimers from first generation has been described. The new materials are comprised of a 1,8-naphthalimide fluorophore having a substituent at C-4 position. The substituent in the first case is a N,N-dimethylaminoethylamino group while in the second one it is N-methylpiperazine. The spectroscopic and photophysical characteristics of the new dendrimers determined in organic solvent of different polarity have been presented. Both dendrimers show substantial increases in their fluorescence intensity in the presence of metal cations (Zn²⁺, Co²⁺, Ni²⁺, Pb²⁺, Mn²⁺, Cu²⁺, Fe³⁺ and Ag⁺) and protons. The influence of the photoinduced electron transfer on their sensing properties has been discussed.     

Classification of 3-3 transitions in neonlike germanium in laser-produced plasma

Classification of 3-3 transitions in neonlike germanium in laser-produced plasma has been made. The spectra have been observed in the range of 185–290 Å using a high resolving power (λ/Δλ ～ 13000) grazing-incidence spectrometer in XUV laser experiment. A total of 21 lines (including five lasing lines) have been classified as transitions between the 2s ²2p ⁵3s, 3p, 3d or 2s2p ⁶3p, 3d and sodiumlike germanium configurations. The identified transitions have been used to derive energy levels of 2s ²2p ⁵3l in neonlike germanium. The experimental results have been compared with theoretical predictions from Dirac-Fock (MCDF) calculations.     

The effects of biologically important divalent and trivalent metal cations on the cyclization step of dopamine autoxidation reaction: A quantum chemical study

Dopamine is the most essential monoaminergic neurotransmitter involved in the pathophysiology of neurodegenerative disorders, and its autoxidation has been recognized as one of the potential trigger factors for dopaminergic neuron loss. The cyclization of dopamine o-quinone was shown to be the irreversible and rate-limiting step of the autoxidation reaction at physiologic pH values. Furthermore, various metal ions such as Al³⁺, Fe³⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, and Mn²⁺ have been clinically associated with neurodegeneration, especially Parkinsonism and dementia. It has been proposed that these metal ions could increase the rate of the dopamine autoxidation reaction; however, the exact mechanism has not yet been fully understood. Using advanced quantum chemical calculations with the inclusion of solvent effects we showed that except for Mn²⁺, the studied metal cations could form complexes with dopamine o-quinone and significantly increase the dopamine o-quinone cyclization rate in aqueous solution; first, by enabling the cyclization to proceed spontaneously without the attack of the unprotonated amino group by hydroxide ion; second, by decreasing the intrinsic activation energy; and third, by decreasing the free energy of protonated amino group deprotonation. The latter also decreases the protective effect of acidic pH on dopamine autoxidation found in synaptic vesicles. The results are fully consistent with experimental data and provide deeper understanding of the effects of metal cations on the dopamine autoxidation reaction at physiologic pH values.     

LC Determination and Pharmacokinetic Study of Sinomenine in Dog Plasma

A simple HPLC method has been developed for determination of sinomenine in dog plasma and has been used to evaluate the pharmacokinetics of sinomenine tablets in dogs. Chromatographic separation was performed on a reversed-phase column with 0.78% (w/v) NaH₂PO₄-acetonitrile, 88:12 (v/v), as mobile phase, delivered at a flow rate of 1.5 mL min^?1. Detection was performed at 265 nm. The limit of quantification was 5.0 ng mL^?1. The calibration range was from 5.0 to 1000 ng mL^?1. The developed method was applied to pharmacokinetic studies of sinomenine sustained-release tablets (test preparation) and sinomenine conventional tablets (reference preparation) in six dogs. Pharmacokinetic data t _max, C _max, AUC _0-t , AUC _0-∞, and t _1/2 for both preparations were determined from plasma concentration-time profiles. The method was sufficiently sensitive, simple, and repeatable for use in pharmacokinetic studies.     

Cyclam as a Structure-Directing Agent in the Crystallization of Aluminophosphate Open Framework Materials from Fluoride Media

Two aluminofluorophosphates have been synthesized using 1,4,8,11-tetraazacyclotetradecane (cyclam) as a structure-directing agent (SDA). The two materials were synthesized hydrothermally and their structures solved by microcrystal diffraction using synchrotron radiation. In both cases, the SDA has been located crystallographically. The first material, [F, Cyclam]-AlPO-CHA, has the molecular formula Al₆P₆O₂₄F₂.C₁₀N₄H₂₆ and has a framework structure related to the mineral chabazite, with the cyclam molecules occluded within chabazite-like cages (space group P-1, a=9.0993(4) Å, b=9.2232(5) Å, c=9.3929(4) Å, α=77.881(2)^o, β=87.205(1)^o, γ=87.777(1)^o, Z=1, wR(F²)=0.1354, R(F)=0.0487). The second material, [F, Cu-Cyclam]-AlPO-SAS, has the molecular formula Al₈P₈O₃₂F₂.[CuC₁₀N₄H₂₄.2H₂O] and has a framework structure closely related to STA-6 (SAS) zeolite structure type, although the usual tetragonal symmetry has been reduced to monoclinic by the presence of the fluoride ions (space group P2₁/n, a=10.3738(4) Å, b=14.8060(5) Å, c=13.4494(5) Å, β=90.275(1)^o, Z=2, wR(F²)=0.1484, R(F)=0.0524). The cyclam is occluded as a copper complex ordered within the cages of the structure.     

Synthesis of a lactone natural product found in Greek tobacco

A short and stereoselective synthesis of (3R^∗,4R^∗,7R^∗)-3,7-epoxy-4,8-dimethyl-8-nonen-4-olide, a natural product isolated from cured tobacco leaves, has been completed in six steps and 22% overall yield. A samarium(II) iodide mediated reductive cyclisation has been used to construct the functionalised tetrahydropyranol core and subsequent sequential stereoselective addition of methyllithium and lactonisation furnished the natural product.     

Chemical studies of marine invertebrates—XLIII: Novel sesquiterpenes from clavularia inflata and clavularia koellikeri (Coelenterata,Octocorallia,Stolonifera)

Two novel sesquiterpenes, 12-acetoxycyclosinularane (1) and 12-acetoxysinularene(2),have been isolated from Clavularia inftata. Their structures have been determined by X-ray diffraction analysis and chemical correlation respectively. Moreover, the new aromadendrane sesquiterpene(1R^*, 1aS^*, 4R^*, 7R^*, 7aS^*, 7bS^*, 5Z)-4,4a,7-trihydroxyaromadendr-5-en-8-oic acid methyl ester (19) has been isolated from the related species C. koellikeri. Its structure has been established by X-ray diffraction analysis. These compounds are the first sesquiterpenes isolated from Octocorallia of the order Stolonifera.     

Carbon monoxide molecules in an argon matrix: empirical evaluation of the Ar·Ar,C·Ar and O·Ar potential parameters

A potential force field has been evaluated for the calculation of the properties of the solid CO-Ar system. The CO·Ar potential energy has been expressed as a sum of the C·Ar and O·Ar interatomic interactions. The (6-exp) Buckingham form of the atom—atom potential, ? = ?Ar^?6 + B exp (?αr), has been used (r is the interatomic distance). The values of the A, B and α numerical parameters for the C·Ar and O·Ar potential have been obtained from those for the C·C, O·O, and Ar·Ar potentials using known combining rules. These values are the following: A_C·Ar = 3379 kJ/mol A⁶, B_C·Ar = 3.12 × 10⁵ kJ/mol, α_C·Ar = 3.493 A^?1, A_O·Ar = 2737 kJ/mol A⁶, B_O·Ar = 3.28 × 10⁵ kJ/mol, α_O·Ar = 3.706 A^?1. The three parameters of the Ar·Ar potential function (A_Ar·Ar = 6554 kJ/mol A⁶, B_Ar·Ar = 3.27 × 10⁵ kJ/mol, α_Ar·Ar = 3.305 A^?1) have been fitted to a set of experimental data for the Ar crystal (zero-temperature lattice spacing and energy, and the value of the isothermal compressibility). The CO·Ar potential surface has been calculated showing the most favourable position of an Ar atom near the CO molecule and the orientational dependence of the CO·Ar interactions. The CO·Ar separation distance at the potential minimum and the depth of the potential well are equal to 3.63 A and ?1.321 kJ/mol, respectively. Comparison has been made of the derived Ar·Ar and Co·Ar potential functions with other such functions available in the literature.     

Pulse radiolysis study of redox reactions of safranine T in aqueous solutions: One electron oxidation

One electron oxidation of safranine T by specific oxidizing radicals such as Cl^-₂, Tl²⁺, Tl(OH)⁺, N^.₃, Br^-₂ etc. has been studied using the nanosecond pulse radiolysis technique. Reaction of free Br^. atom has also been investigated at neutral pH. The semioxidized safranine species formed by these reactions have been shown to exist in two conjugate acid-base forms with pK_a=4.0. Their spectral and kinetic parameters have been evaluated. Using N^.₃/N^-₃ and I^-₂/2I^- as reference couples, the one electron reduction potential of the semioxidized safranine has been determined to be 1.13±0.02 V vs NHE. The absorption spectra, second order decay rate constant and the pK_a of the OH-reaction product revealed features quite different from that of the semioxidized species suggesting that the mode of OH reaction is not via electron abstraction.     

Thermodynamics of molecular interactions in binary mixtures of non-electrolytes. Molar excess volumes

Molar excess volumes, V^E, for pyridine (A) + α-picoline (B), + β-picoline (B) and + γ-picoline (B) and benzene (A) + toluene (B), + o-xylene (B) and + p-xylene (B) and carbon tetrachloride (A) + n-heptane (B) have been measured dilatometrically as a function of temperature and composition and have been utilized to study B—B and B—B—B interactions in the presence of A via the Mayer—McMillan approach. A model has also been presented to account for these B—B and B—B—B interactions. The V^E data at 308.15 K have also been analysed in terms of the “graph theoretical” approach which describes the V^E data well for all these mixtures at 308.15 K. The “graph theoretical” approach has further been extended to successfully evaluate V^E data for a mixture at any temperature, T₂, when the V^E data at T₁ are known.     

Synthesis of new benzimidazolium salts with tunable emission intensities and their application as fluorescent probes for Fe in pure aqueous media

A series of novel, water-soluble benzimidazolium salts with common ‘fluorophore–spacer–receptor’ PET design has been synthesized. Despite the common PET scaffold these benzimidazolium salts displayed diverse emission intensities in pure aqueous solutions. The observed emission intensities were found to be influenced by the functionalized alkyl side arms present on the benzimidazolium ring. These benzimidazolium salts were also found to act as selective sensors for Fe³⁺ ions over other metal ions like Na⁺, K⁺, Ca²⁺, Mg²⁺, Ba²⁺, Al³⁺, Cr³⁺, Co²⁺, Ni²⁺, Mn²⁺, Zn²⁺, Pb²⁺, Ag⁺, Cu²⁺ and Hg²⁺ in pure aqueous media.     

Topological aspects of the thermodynamics of binary mixtures of non-electrolytes

An approach based on the “graph” theory has been evolved to predict molar excess enthalpies, H^E, and molar excess volumes, V^E, for a number of binary mixtures of non-electrolytes. The calculated H^E and V^E values compare reasonably well with their corresponding experimental values. The limitations of this approach have also been discussed.     

Stabilization of unusual electronic configurations of transition elements in elongated six-coordinated oxygen sites of a K2NiF4 structure

The A′_xA_2?xLi_0.5M_0.5O₄ matrix deriving from the K₂NiF₄ structure has an elongated MO₆ octahedron; it has been used to stabilize anisotropic electronic configurations such as high-spin Fe⁴⁺, low-spin Co⁴⁺, medium-spin Co³⁺, low-spin Ni³⁺, or low-spin Cu³⁺. The choice of ions to be stabilized was based on a simple model for predicting the electronic configuration of a dⁿ ion in a tetragonally distorted octahedral environment.     

Ab initio calculations of electron-spin magnetic moments for Li,Be and B hydrides inX 2∑+ states

Electron-spin magnetic moments, in the form ofg-shifts, have been computed at the ROHF level for theX ²∑⁺ states of LiH⁺, BeH²⁺, LiH^?, BeH and BH⁺. A perturbative approach, complete to second-order in appropriate Breit-Pauli operators, has been used. Retention of two-centre integrals has proven vital. First-order terms are important, especially in describing the negativeg _∥ shifts observed experimentally in²∑⁺ molecules. The relativistic mass correction dominates in first-order, except for LiH^? where the two-electron spin-Zeeman gauge correction supersedes. Second-order terms contribute negatively, and only to the Δg _⊥ component. Along the isoelectronic series LiH^? → BeH → BH⁺, the magnitude of Δg _⊥ increases due to the dependence of spin-orbit coupling on nuclear charge. The relation ofg-shifts to electronic structure and bonding is explored.     

A new mode of formation of the phosphorus—phosphorus bond: Synthesis and crystal structure determination of 1,5-dichloro-2,4-dimethyl-2,4- diaza-1,5-diphospha-1,5-diphenylpentan-3-one and of 1,4-dimethyl-2,3-diphenyl-1,4,3,2- diazadiphospholidin-5-one-2-oxide and its oxidation with tetrachloroorthobenzoquinone

Reaction of phenyldichlorophosphine, 2b, with N,N′-dimethyl-N,N′-bis(trimethylsilyl)urea, 1, leads to a symmetrical diphosphorylation product, 3b. A mechanism for the formation of 3b, on the basis of ³¹P NMR-data, is proposed. 3b reacts with oxalic acid bis(trimethylsilyl)ester, 5, with intramolecular P—P-coupling and formation of the λ³P–λ⁴P-mixed-valence diphosphorus compound, 1,4-dimethyl-2,3-diphenyl-1,4,3,2- diazadiphospholidin-5-one-2-oxide, 6, which has been oxidized by means of tetrachloroorthobenzoquinone (TOB), 7, to the λ⁴P–λ⁵P-compound, 8. The structures of 3b, 6 and 8 have been elucidated by ¹H- and ³¹P-NMR-spectroscopy; single crystal X-ray diffraction studies of 3b and of 6 have been conducted. The identity of both compounds has been confirmed. In the acyclic diphosphorus compound, 3b, a remarkably short non-bonding PP distance of 280.6 pm has been found while the PP bond length in the cyclic compound 6 is of the usual order of magnitude (221.1 and 221.8 pm, respectively).     

Population transfer between the fine-structure levels 5s5p 3 P 1 and 5s5p 3 P 0 of114Cd atoms by collisions with molecular gases

Fine-structure mixing of excited¹¹⁴Cd 5³ P _J atoms induced by collisions with various molecular gases (N₂, H₂, D₂, CO, CH₄, C₂H₆) has been investigated by a combined method of absorption and fluorescence spectroscopy. After pulsed optical excitation of the Cd(5³ P ₁) level, the time dependence of the population densities has been measured simultaneously both for the 5³ P ₁ state and for the collisionally populated 5³ P ₀ state. By analyzing the signal curves at different molecular gas pressures cross sections for collisional transfer between the¹¹⁴Cd 5³ P ₁ and 5³ P ₀ levels as well as the quenching cross sections for the 5³ P levels have been obtained.