Determination of the intrinsic site pK(a) value and cooperativity of the symmetrical hexadentate chelator N,N',N'-tris[2-(3-hydroxy-2-oxo-1,2-dihydropyridin-1-yl)acetamido]ethylamine

The three overlapping pK(a) values of N,N',N'-tris[2-(3-hydroxy-2-oxo-1,2-dihydropyridin-1-yl)acetamido]ethylamine, a tripodal hexadentate chelator formed from three 3-hydroxy-2(1H)-pyridinone moieties amide linked to tris-(2-aminoethyl)amine, were determined by simultaneous spectrophotometric and potentiometric titration. The data was analysed by non-linear regression with constraints to deal with (a) the highly correlated absorptivities and (b) the highly correlated pK(a) values. The three pK(a) values were optimized first from the spectrophotometric data (absorbance vs. pH) by non-linear regression to a model in which the molar absorptivity of the ith species ((i)) was constrained by the correlation equation (i) = epsilon (0) + (epsilon (3) - epsilon (0))i 3 with i = 0, 1, 2, 3, where (3) and (0) represent the molar absorptivities of the most protonated and least protonated species, respectively. The molar absorbitivity of the four species defined by three pK(a) values is, therefore, linearly related to proton stoichiometry. The pK(a) values were then optimized from the potentiometric data (pH vs. titrant volume) by non-linear regression to a model in which the three pK(a) values were constrained by the correlation equation pK(a(i)) = pK(a(int)) + b(i - 1) + (i - 2)log(3) where i = 1, 2 or 3. This expresses the three pK(a) values in terms of only two optimizable parameters, the intrinsic site pK(a) (pK(a(int))) and the interaction energy between sites (b). The fixed term (i - 2)log(3) accounts for the statistical effect on the pK(a) values of three equivalent ionizable sites. The modified analytical derivatives required for optimization of these parameters by the Gauss-Newton-Marquardt algorithm and the merits of optimizing pK(a) values with these two correlation equations are discussed. The optimized pK(a) values were 9.31 +/- 0.01, 8.75 +/- 0.01 and 8.19 +/- 0.01. The separation between pK(a) values is 0.58 comprising 0.477 for the statistical effect and 0.081 for the interaction energy while the intrinsic site pK(a) is 8.672 +/- 0.005. The tertiary amine at the centre of the tripodal backbone has a pK(a) of 5.88 +/- 0.03.     

Structural and variable-temperature NMR studies of 9-diisopropylphosphanylanthracenes and 9,10-bis(diisopropylphosphanyl)anthracenes and their oxidation products

The diisopropylphosphanyl-substituted anthracenes i-Pr2P(C14H9) (1a), i-Pr2P(C14H8)Br (2a), and (i-Pr2P)2(C14H8) (3a) and some of their oxidation products were prepared from 9-bromoanthracene and 9,10-dibromoanthracene, respectively. Low-temperature (1)H NMR spectra of the 9-monophosphanyl-substituted anthracenes 1a and 2a are in accordance with a staggered conformer, while above room temperature dynamic processes occur. The low-temperature NMR spectrum of the 9,10-diphosphanylanthracene 3a indicates the presence of two different rotational isomers. The rotational barrier for 1a was determined from variable-temperature (1)H NMR spectra to be 56 kJ mol(-1) (DeltaG(298K)). The crystal structure determinations show the solid-state conformers to be consistent with the prevailing conformer at low temperature.     

Transfer rate and separation of Cd(II) and Zn(II) chloride species by a trilaurylammonium chloride—triethylbenzene supported liquid membrane

The transfer rate of Cd(II) and Zn(II) from aqueous feed chloride solutions to ammonium acetate strip solutions through a supported liquid membrane consisting of a trilaurylammonium chloride (TLAHCl) solution in triethylbenzene (t-e-b), adsorbed on a polypropylene microporous film, was studied. The influence of the stirring speed, feed chloride concentration, and TLAHCI carrier concentration was investigated. The data were explained by a previously derived equation in terms of membrane diffusion, aqueous film diffusion, and aqueous complex formation chemistry. The best experimental conditions to perform a Cd(II)Zn(II) separation were identified. The separation of Zn(II) and Cd(II) was experimentally studied.     

Kinetic investigation of the reactions of S-4-nitrophenyl 4-substituted thiobenzoates with secondary alicyclic amines in aqueous ethanol

The reactions of S-4-nitrophenyl 4-X-substituted thiobenzoates (X = H, Cl, and NO(2): 1, 2, and 3, respectively) with a series of secondary alicyclic amines (SAA) were subjected to a kinetic investigation in 44 wt % ethanol-water, at 25.0 degrees C and an ionic strength of 0.2 M (KCl). The reactions were followed spectrophotometrically by monitoring the release of 4-nitrobenzenethiolate anion at 420-425 nm. Under excess amine, pseudo-first-order rate constants (k(obsd)) are obtained for all reactions. The plots of k(obsd) vs [SAA] at constant pH are linear with the slope (k(N)) independent of pH. The statistically corrected Br?nsted-type plots (log k(N)/q vs pK(a) + log p/q) for the reactions of 1 and 2 are nonlinear with slopes at high pK(a), beta(1) = 0.27 and 0.10, respectively, and slopes at low pK(a), beta(2) = 0.86 and 0.84, respectively. The Br?nsted curvature is centered at pK(a) (pK(a)(0)) 10.0 and 10.4, respectively. The reactions of SAA with 3 exhibit a linear Br?nsted-type plot of slope 0.81. These results are consistent with a stepwise mechanism, through a zwitterionic tetrahedral intermediate (T(+/-)). For the reactions of 1 and 2, there is a change in rate-determining step with amine basicity, from T(+/-) breakdown to products at low pK(a), to T(+/-) formation at high pK(a). For the reactions of 3, breakdown to products of T(+/-) is rate limiting for all the SAA series (pK(a)(0) > 11). The increasing pK(a)(0) value as the substituent in the acyl group becomes more electron withdrawing is attributed to an increasing nucleofugality of SAA from T(+/-). The greater pK(a)(0) value for the reactions of SAA with 1, relative to that found in the pyridinolysis of 2,4-dinitrophenyl benzoate (pK(a)(0) = 9.5), is explained by the greater nucleofugality from T(+/-) of the former amines, compared to isobasic pyridines, and the greater leaving ability from T(+/-) of 2,4-dinitrophenoxide relative to 4-nitrobenzenethiolate.     

Metal-Metal Multiply Bonded Complexes of Technetium. 5.(1) Tris and Tetrakis(formamidinato) Complexes of Ditechnetium

Compounds of the type Tc(2)Cl(4)(PR(3))(4) (PR(3) = PEt(3), PMe(2)Ph, PMePh(2)) react with the molten formamidines HDPhF (HDPhF = diphenylformamidine) and HDTolF (HDTolF = di-p-tolylformamidine) to produce mixtures of tris- and tetrakis-bridged formamidinate complexes of ditechnetium. The displacement of chloride and phosphine by [DPhF](-) was accompanied by the oxidation of the dimetal core to produce the mixed-valent complexes Tc(2)(DPhF)(3)Cl(2) (1) and Tc(2)(DPhF)(4)Cl (2) in modest yield. The solid-state structures of the di-p-tolyl analog of 1, Tc(2)(DTolF)(3)Cl(2) (1a), and Tc(2)(DPhF)(4)Cl.C(7)H(8) (2.C(7)H(8)) have been determined by single crystal X-ray diffraction studies and are described in detail. The structure of 1a consists of three formamidinate ligands spanning the two technetium atoms. The two chloride ligands, which complete the coordination sphere, are bound equatorially at distances of 2.357(1) and 2.346(2) ? from the metals. Though possessing no crystallographic symmetry, 1a approximates C(2)(v)() symmetry. The metal-metal bond length of 2.0937(6) ? ranks among the shortest reported for technetium and is indicative of a Tc-Tc multiple bond. Compound 2 crystallizes with the Tc atoms colinear with a crystallographic 4-fold axis. The four bridging formamidinate ligands are arranged in a lantern geometry about the dimetal unit. The chloride is bonded in an axial position at a distance of 2.450(4) ?. The Tc-Tc bond length of 2.119(2) ? is also consistent with the presence of a high order Tc-Tc bond. The electronic structures of 1 and 2 were investigated by means of SCF-Xalpha-SW molecular orbital calculations using the model compounds Tc(2)(HNCHNH)(3)Cl(2) and Tc(2)(HNCHNH)(4)Cl. The results support the presence of a sigma(2)pi(4)delta(2)delta ground state configuration giving rise to a formal bond order of 3.5. The LUMO in both cases is a low-lying pi orbital. The formamidinate complexes 1 and 2 have been further characterized by IR spectroscopy and cyclic voltammetry. The crystallographic parameters for 1a and 2.C(7)H(8) are as follows: Tc(2)(DTolF)(3)Cl(2) (1a), monoclinic space group P2(1)/n (No. 14) with a = 16.185(2) ?, b = 15.637(2) ?, c = 17.812(1) ?, beta = 110.142(5) degrees, V = 4232.3(6) ?(3) and Z = 4; Tc(2)(DPhF)(4)Cl.C(7)H(8) (2.C(7)H(8)), tetragonal space group P4/ncc (No. 130) with a = 15.245(2) ?, c = 21.832(3) ?, V = 5074.1(9) ?(3) and Z = 4.     

Crystal structure of a partly self-complementary peptide nucleic acid (PNA) oligomer showing a duplex-triplex network

The X-ray structure of a partly self-complementary peptide nucleic acid (PNA) decamer (H-GTAGATCACT-l-Lys-NH(2)) to 2.60 A resolution is reported. The structure is mainly controlled by the canonical Watson-Crick base pairs formed by the self-complementary stretch of four bases in the middle of the decamer (G(4)A(5)T(6)C(7)). One right- and one left-handed Watson-Crick duplex are formed. The two PNA units C(9)T(10) change helical handedness, so that each PNA strand contains both a right- and a left-handed section. The changed handedness in C(9)T(10) allows formation of Hoogsteen hydrogen bonding between C(9)T(10) and G(4)A(5) of a PNA strand in an adjacent Watson-Crick double helix of the same handedness. Thereby, a PNA-PNA-PNA triplex is formed. The PNA unit A(3) forms a noncanonical base pair with A(8) in a symmetry-related strand of opposite handedness; the base pair is of the A-A reverse Hoogsteen type. The structural diversity of this PNA demonstrates how the PNA backbone is able to adapt to structures governed by the stacking and hydrogen-bonding interactions between the nucleobases. The crystal structure further shows how PNA oligomers containing limited sequence complementarity may form complex hydrogen-bonding networks.     

Nucleophilic epoxidation of alpha'-hydroxy vinyl sulfoxides

The nucleophilic epoxidation of a variety of alpha'-(1-hydroxyalkyl) vinyl sulfones and sulfoxides has been studied. The sulfones give rise to anti oxiranes with modest (E) or excellent (Z) selectivities and in good yields. The (E)-sulfoxides display low reactivity within a reinforcing/nonreinforcing scenario. The use of t-BuOOLi in Et(2)O allows for a highly syn-selective epoxidation-oxidation. The (Z)-sulfoxides display a remarkably high reactivity under these conditions. The reinforcing (S,S(S)) diastereomers (3e-g) yield hydroxy sulfinyl oxiranes with high yields and selectivities. In contrast, the (R,S(S)) diastereomers (4e-g) show diminished reactivities and a very substrate-dependent stereochemical outcome. The structure of these oxiranes has been secured by chemical correlations and an X-ray crystal structure.     

A surface fit approach with a disposable optical tongue for alkaline ion analysis

A disposable optical tongue for the alkaline ions Na(I) and K(I) is described. The two-sensor layout prepared on a transparent support consists of non-specific polymeric membranes working by ionophore-chromoionophore chemistry. The non-specific behavior of the membranes was controlled by means of the crown ether-type ionophore present. The imaging of the tongue, after reaction for 3 min with the unknown solution, by means of a conventional flatbed scanner working by transmission mode, makes it possible to calculate the H (hue) value of the hue, saturation, value (HSV) color space used as a robust and precise analytical parameter. The modelling of the response of the two-sensor tongue as a sigmoidal surface is used to characterize the behavior of the tongue and as a basis to infer the concentration values. To compute the concentration of two analytes from the two hue values obtained using the optical tongue, a surface fit approach was used. The tongue works over a wide dynamic range (1.0×10(-4)-0.1 M both in Na(I) and K(I)). The sensing membranes show good intramembrane (1.4% RSD) and intermembrane precision (0.71% RSD) and lifetime (around 45 days in darkness). The procedure was used to analyze Na(I) and K(I) in different types of natural waters (tap and mineral), validating the results against a reference procedure.     

Construction of a dimethyl sulfoxide sensor based on dimethyl sulfoxide reductase immobilized on a au film electrode.

A novel dimethyl sulfoxide (DMSO) sensor using DMSO reductase and film electrodes was constructed. The Au and Ag electrodes were fabricated on slide glass by vacuum deposition and the application of a photolithographic technique. The micro-chamber (4 x 50 x 1 mm, volume 200 microl) was fabricated on a poly(dimethylsiloxane) (PDMS) polymer. The Pt electrode was implanted in a PDMS polymer. DMSO reductase was immobilized on a Au film electrode with bovine serum albumin (BSA)-glutaraldehyde. This sensor could determine DMSO in an unpurged aqueous solution with glucose oxidase (GOD) and catalase (CAT) for oxygen removal. The DMSO sensor showed a linear response within 1 mM DMSO with a correlation coefficient of 0.999. The detection limit was 200 microM (3sigma), and the sensitivity was 23.8 mA M(-1) cm(-2). The relative standard deviations at each concentration were within 3.6%.     

Extension of the self-consistent spectrophotometric basicity scale in acetonitrile to a full span of 28 pKa units: unification of different basicity scales

The earlier compiled self-consistent spectrophotometric basicity scale in acetonitrile (AN) was expanded to range from 3.8 to 32.0 pK(a) units, that is 28 orders of magnitude. Altogether 54 new relative basicity measurements (DeltapK(a) measurements) were carried out and 37 new compounds were introduced to the scale (it now includes altogether 89 bases). The relative basicity of any two bases in the scale can be obtained by combining at least two independent sets of measurements. Multiple overlapping measurements make the results more reliable. The overall consistency (as defined earlier) of the measurements is s = 0.03 pK(a) units. Thorough analysis of all of our experimental data (DeltapK(a) values of this and earlier works) and experimental pK(a) data in AN available in the literature (works from the groups of Coetzee and Padmanabhan, Kolthoff and Chantooni, Jr., the Schwesinger group, Bren' et al. and some others, altogether 19 papers) was carried out. On the basis of this analysis the anchor point of the scale-pyridine-was shifted upward by 0.20 pK(a) units thereby also revising the absolute pK(a) values of all the bases on the scale. This way very good agreement between our relative data and the absolute pK(a) values of the abovementioned authors was obtained. The revised basicity scale was interconnected with the earlier published self-consistent acidity scale by DeltapK(a) measurements between acids and bases. The rms deviation between the directly measured DeltapK(a) values and the absolute pK(a) values of the compounds was 0.10 pK(a) units.     

Experimental studies of the dynamics of the bond-forming reactions of CF2(2+) with H2O using position-sensitive coincidence spectroscopy

The dynamics of the product channels forming OCF(+)+H(+)+HF and HCF(2) (+)+H(+)+O following the collisions of CF(2) (2+) with H(2)O have been investigated with a new position-sensitive coincidence experiment at a center-of-mass collision energy of 5.6 eV. The results show the formation of OCF(+) occurs via the formation of a doubly charged collision complex [H(2)O-CF(2)](2+) which subsequently undergoes a charge separating dissociation to form H(+) and HOCF(2) (+). The HOCF(2) (+) monocation subsequently fragments to form HF+OCF(+). The lifetimes of the collision complex and the HOCF(2) (+) ion are at least of the order of their rotational period. The kinetic energy release in this reaction indicates that it involves the ground state of CF(2) (2+) and forms the ground electronic states of OCF(+) and HF. The mechanism for forming HCF(2) (+) involves the direct and rapid abstraction of a hydride ion from H(2)O by CF(2) (2+). The resulting OH(+) ion subsequently fragments to H(+)+O, on a time scale at least comparable with its rotational period.     

Application of a stepwise flow ratiometry without phase separation to the determination of the chloroform/water distribution coefficients of volatile diazines

The chloroform/water distribution coefficients (K(D)) of sixteen diazine compounds were determined by a stepwise flow ratiometry. An aqueous solution of analyte was delivered and merged with chloroform. The flow rate ratio of both the phases was varied stepwise under a constant total (chloroform+aqueous) flow rate. The analyte was extracted to chloroform while both the phases, which were segmented by each other, were passing through an extraction coil. The segmented stream was then led to a UV/Vis detector directly without phase-separation. The absorbance of the chloroform and aqueous phases (A(o) and A(a), respectively) was each measured at the maximum absorption wavelength of the analyte. The plots of A(-1) against R(f), (AR(f))(-1) against R(f)(-1), and AR(f) against A gave straight lines, where A was A(o), A(a) or the sum of them (A(S)). The K(D) of the analyte was calculated from the slopes and intercepts of the plots. The log K(D) values obtained for the analytes (-0.5-1.4) were agreed well with the values measured by a shake-flask method. The present method is simple, rapid (5 min/determination) and applicable to the volatile compounds with reasonable precision (standard deviation of log K(D)<0.07).     

A tightly coupled linear array of perylene, bis(porphyrin), and phthalocyanine units that functions as a photoinduced energy-transfer cascade

We have prepared a linear array of chromophores consisting of a perylene input unit, a bis(free base porphyrin) transmission unit, and a free base phthalocyanine output unit for studies in artificial photosynthesis and molecular photonics. The synthesis involved four stages: (1) a rational synthesis of trans-AB2C-porphyrin building blocks each bearing one meso-unsubstituted position, (2) oxidative, meso,meso coupling of the zinc porphyrin monomers to afford a bis(zinc porphyrin) bearing one phthalonitrile group and one iodophenyl group, (3) preparation of a bis(porphyrin)-phthalocyanine array via a mixed cyclization involving the bis(free base porphyrin) and 4-tert-butylphthalonitrile, and (4) Pd-mediated coupling of an ethynylperylene to afford a perylene-bis(porphyrin)-phthalocyanine linear array. The perylene-bis(porphyrin)-phthalocyanine array absorbs strongly across the visible spectrum. Excitation at 490 nm, where the perylene absorbs preferentially, results in fluorescence almost exclusively from the phthalocyanine (phi(f) = 0.78). The excited phthalocyanine forms with time constants of 2 ps (90%) and 13 ps (10%). The observed time constants resemble those of corresponding phenylethyne-linked dyads, including a perylene-porphyrin (< or = 0.5 ps) and a porphyrin-phthalocyanine (1.1 ps (70%) and 8 ps (30%)). The perylene-bis(porphyrin)-phthalocyanine architecture exhibits efficient light-harvesting properties and rapid funneling of energy in a cascade from perylene to bis(porphyrin) to phthalocyanine.     

Acid-base equilibria in gamma-butyrolactone studied by use of pH-ISFETs

pH-ISFETs were used in the study of acid-base equilibria in gamma-butyrolactone (GBL). After the spectrophotometric determination of the pK(a) value of 3,5-dichloropicric acid, the pK(a) values and homo-conjugation constants of various acids (including the conjugate acids of bases) were determined potentiometrically using a Ta(2)O(5)-type pH-ISFET. The values of pK(a) in GBL were in a linear relation with those in propylene carbonate (PC) and 1.0 units smaller on average. The difference in pK(a) between GBL and PC was mainly attributable to the difference in proton solvation. The autoprotolysis constant of GBL, roughly estimated by a rapid titration with a Si(3)N(4)-ISFET, was about 30 on the pK(SH) scale. A comparative study was made of the response speeds of the Ta(2)O(5)- and Si(3)N(4)-type pH-ISFETs and a conventional pH-glass electrode. The result was Si(3)N(4)-ISFET > Ta(2)O(5)-ISFET > glass electrode. Because GBL is not stable against acids and bases, the use of pH-ISFETs was much more convenient than the use of the conventional glass electrode.     

Adsorption characteristics of as(III) and as(V) with titanium dioxide loaded Amberlite XAD-7 resin.

The adsorption characteristics of As(V) and As(III) on titanium dioxide loaded Amberlite XAD-7 resin have been studied. The resin was prepared by impregnation of Ti(OC2H5)4 followed by hydrolysis with ammonium hydroxide. Batch adsorption experiments were carried out as a function of the pH, shaking time and the concentration of As(V) and As(III) ions. The resin showed a strong adsorption for As(V) from pH 1 to 5 and for As(III) from pH 5 to 10. The adsorption isotherm data for As(V) at pH 4 fitted well to a Langmuir equation with a binding constant of 59 dm3 mol(-1) and a capacity constant of 0.063 mmol g(-1). The data for As(III) at pH 7 also fitted well to a Langmuir equation with a binding constant of 5.4 dm3 mol(-1) and a capacity constant of 0.13 mmol g(-1). The effect of diverse ions on the adsorption of arsenic was also studied. Column adsorption experiments showed that the adsorption of As(III) is more favorable compared to As(V), due to both the faster adsorption and larger capacity for As(III) than As(V).     

Ferromagnetism in an extended three-dimensional, diamond-like copper(II) network: a new copper(II)/1-hydroxybenzotriazolato complex exhibiting soft-magnet properties and two transitions at 6.4 and 4.4 K

The use of the substituted benzotriazole ligand btaOH (1-hydroxybenzotriazole) in copper(II) chemistry has yielded a structurally and magnetically very interesting complex. The [Cu2(O2CMe)4(H2O)2]/btaOH.H2O/aqueous NH3 (1:4:4, 1:3:3, 1:2:2) reaction system in MeOH gives dark brown-green [Cu(btaO)2(MeOH)]n (4) in approximately 80% yield. 4 crystallizes in the tetragonal space group P4(3)2(1)2 with (at 25 degrees C) a = 9.915(1) A, b = 9.915(1) A, c = 14.715(2) A, and Z = 4. The structure consists of a 3D, diamond-like copper(II) lattice. The CuII atom has a square pyramidal geometry with four btaO- ligands at the basal plane. The btaO- ion functions as a bidentate bridging ligand, with N(3) and the deprotonated oxygen being the ligating atoms. Dc and ac magnetic susceptibility measurements, together with low-field (10 G) and high-field (up to 5000 G) magnetization data, are consistent with ferromagnetic interactions on the scale of the crystal lattice with two critical temperatures: 6.4 and 4.4 K. The former critical temperature could correspond to a transition from a paramagnetic to a ferromagnetic state; the latter one, to a transition from a ferromagnetically ordered state to its 3D ordering. The magnetic data, along with the field dependence of the magnetization and the EPR data, are also in line with a soft magnet. Moreover, the EPR studies performed on 4 reveal unique features reported for the first time in the field of molecular magnetism.     

Synthesis and characterization of (octaaryltetraazaporphyrinato)indium(III) complexes for optical limiting

The preparation of (octaaryltetraazaporphyrinato)indium(III) chlorides [aryl = phenyl (5a), p-tert-butylphenyl (6a), p-(trifluoromethyl)phenyl (7a), m-(trifluoromethyl)phenyl (8a)] and their reactions with aryl Grignard reagents XMgBr to give 5b-8b [X = p-(trifluoromethyl)phenyl] and 5c (R = 3,5-difluorophenyl) are described. The characterization of all compounds by UV-vis, FT-IR, and (1)H and (13)C NMR spectroscopy was performed. The hypsochromic shift of all bands in the absorption spectra of complexes 5a-8a is observed in the sequence 6a < 5a < 7a approximately 8a. This is associated with the increasing electron-withdrawing character of the aryl substituents in the periphery of the tetraazaporphyrin macrocycle. Compounds 8a,b are very good soluble in organic solvents with 8a exhibiting the higher photochemical stability among the various synthesized species. The optical limiting (OL) properties of the complexes have been studied and correlated with the structure of the (tetraazaporphyrinato)indium(III) complexes and the electronic nature of the different substituents. In particular, the OL effect at 532 nm increases on going from the series of compounds 5 to the series 8.     

Development of micromarkers with various photoluminescence colors as tracers for shadowing pursuits.

Micromarkers with five photoluminescence colors were developed as tracers for shadowing pursuits. The markers are colorless powders with particle diameters of several tens to several hundreds of micrometers, prepared using a cryogenic sample crusher. They were visualized using red, green, yellow, magenta or cyan photoluminescence under ultraviolet light at approximately 365 nm. The markers were composed of photoluminescent compounds dispersed in polyvinyl butyral. The photoluminescent compounds in the polyvinyl butyral were stable under ambient conditions for more than one year after application. The compounds with the red, green, yellow, magenta and cyan photoluminescence contained a europium (Eu(3+)) complex, a terbium (Tb(3+)) complex, a mixture of Tb(3+) and Eu(3+) complexes, a mixture of Eu(3+) complex and o-coumaric acid, and a mixture of Tb(3+) complex and 7-hydroxycoumarin along with a few drops of a sodium bicarbonate aqueous solution, respectively. Neodymium (Nd(3+)) and ytterbium (Yb(3+)) complexes with photoluminescence in the near-IR wavelength region can also be added to these visible photoluminescent compounds as secret markers for discrimination. The markers were non-destructively identified using a microscopic FT-IR spectrometer and a microscopic spectrometer equipped with a fluorescence detector.     

Chemiluminescent determination of the pesticide bromoxynil by on-line photodegradation in a flow-injection system.

A new, robust and simple method is proposed for the chemiluminescent determination of the pesticide Bromoxynil. The empirical procedure is performed with the aid of a flow-injection manifold provided with an on-line photo-reactor to obtain chemiluminescent photofragments. After a period of 12 s of irradiation with an 8 W low-pressure mercury lamp, a chemiluminescent oxidation was performed with the system potassium permanganate in a polyphosphoric acid medium. The photolysis required a basic medium (KOH 0.014 mol l(-1)) with ethanol (1%) as a sensitizer. The method allowed the determination of 134 samples (h-1) of Bromoxynil in a wide interval of concentrations, over the range 5 x 10(-3) - 1 mg l(-1); the detection limit was 5 x 10(-3) mg l(-1). The RSD (n=24) at 0.25 mg l(-1) of the pesticide level was 2.3%. The method was applied to a water sample and to a formulation.     

Synthesis, Characterization, and Bonding of Two New Heteropolychalcogenides: alpha-CsCu(S(x)()Se(4-x)) and CsCu(S(x)()Se(6-x))

The Cs-Cu-Q (Q = S, Se) system has been investigated using copper metal, cesium chloride, and alkali-metal polychalcogenide salts under mild hydrothermal reaction conditions. Heteropolychalcogenide salts and mixtures of known polysulfide and polyselenide salts have been used as reagents. The reaction products contain the alpha-CsCuQ(4) and CsCuQ(6) structures. The alpha-CsCuQ(4) phase exhibits a smooth transition in lattice parameters from the pure sulfur to the pure selenium phases, based on Vegard's law. The CsCuQ(6) phase has been prepared as the pure sulfur analog and a selenium rich analog. The single-crystal structures of the disordered compounds alpha-CsCuS(2)Se(2) (P2(1)2(1)2(1), Z = 4, a = 5.439(1) ?, b = 8.878(2) ?, c = 13.762(4) ?) and CsCuS(1.6)Se(4.4) (P&onemacr;, Z = 2, a = 11.253(4) ?, b = 11.585(2) ?, c = 7.211(2) ?, alpha = 92.93 degrees, beta = 100.94 degrees, gamma = 74.51 degrees ) have been solved using a correlated-site occupancy model. These disordered structures display a polychalcogenide geometry in which the sulfur atoms prefer positions that are bound to copper. The optical absorption spectra of these materials have been investigated. The optical band gap varies as a function of the sulfur-selenium ratio. Extended Hückel crystal orbital calculations have been performed to investigate the electronic structure and bonding in these compounds in an attempt to explain the site distribution of sulfur and selenium.