Novel designs for sampled grating-based multiplexers demultiplexers

Novel multiplexers-demultiplexers for dense wavelength-division multiplexing systems that use interleaved sampled gratings are presented. It is shown that, with the appropriate design, configurations ranging from hybrid to add-drop as well as all-grating-based multiplexers can easily be realized.     

Simple and accurate candidate reference measurement procedure for total testosterone in human serum by one-step liquid-liquid extraction coupled with isotope dilution mass spectrometry

Testosterone in human serum is commonly tested in clinical laboratories using immunoassay methods as well as liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods. To standardize and ensure the accuracy of the measurement results, reference procedures with higher metrological order are required. A simple measurement procedure based on one-step liquid-liquid extraction (LLE) and liquid chromatography-isotope dilution tandem mass spectrometry (LC-IDMS/MS) was developed for total testosterone in human serum. The procedure involved serum spiked with ¹³C₃-testosterone, equilibration for 2 h, and extraction with an organic solvent. Testosterone certified reference material (CRM) was used as the calibration standard to ensure the traceability to the International System of Units (SI). Testosterone in serum CRMs from the National Institute for Standards and Technology (NIST) and LGC were used to validate the accuracy of the newly developed method. The deviations of the obtained values from the NIST and LGC certified values ranged from −0.55% to 0.45%. Similarly, the coefficient of variations (CVs) of the replicate measurements were in the range of 0.55% and 0.78%, respectively. The relative expanded uncertainties were comparable with those of the certified materials. The newly developed LC-IDMS/MS procedure demonstrated adequate trueness and precision, and was simple to perform. The method can be used for value assignment of testosterone in external quality assessment (EQA) materials as well as certification of CRMs in the future.

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Structural,spectroscopic, and reactivity comparison of xanthene- and dibenzofuran-bridged cofacial bisporphyrins

A comparison of the structure, spectroscopy, and oxygen atom-transfer reactivity of cofacial bisporphyrins anchored by xanthene (DPX) and dibenzofuran (DPD) pillars is presented. The synthesis and characterization of dicopper(II) and dinickel(II) complexes of DPD completes a homologous series of homobimetallic zinc(II), copper(II), and nickel(II) complexes for both cofacial platforms. X-ray crystallographic analysis of the parent free-base porphyrins H(4)DPX (1) and H(4)DPD (5) confirms the face-to-face arrangement of the two porphyrin macrocycles with a large available range of vertical pocket sizes: 1 (C(80)H(92)Cl(2)N(8)O), triclinic, space group P1 macro, a = 13.5167(12) A, b = 21.7008(18) A, c = 23.808(2) A, alpha = 80.116(2) degrees, beta = 76.832(2) degrees, gamma = 80.4070(10) degrees, Z = 4; 5 (C(80)H(83)N(8)O(2)), monoclinic, space group C2/c, a = 22.666(2) A, b = 13.6749(14) A, c = 42.084(4) A, beta = 94.554(2) degrees, Z = 8. EPR spectroscopy of dicopper(II) derivatives Cu(2)DPX (3) and Cu(2)DPD (7) complements the crystallographic studies by probing intramolecular metal-metal arrangements in frozen solution. Exciton interactions between the porphyrin subunits in fluid solution are revealed by steady-state and time-resolved electronic absorption and emission spectroscopy. The resulting compilation of structural and spectroscopic data provides a benchmark for the use of these and related platforms for the activation of small-molecule substrates. A structure-function relation is developed for the photoinduced oxygen atom-transfer reactions of bisiron(III) mu-oxo derivatives of DPX and DPD. The efficiency of the photochemical process is markedly dependent (approximately 10(4)-fold) on the vertical flexibility of cofacial architecture provided by the spacer.     

Targeted proton delivery in the catalyzed reduction of oxygen to water by bimetallic pacman porphyrins

A combined experimental and theoretical investigation of the role of proton delivery in determining O2 reduction pathways catalyzed by cofacial bisporphyrins is presented. A homologous family of dicobalt(II) Pacman porphyrins anchored by xanthene [Co2(DPX) (1) and Co2(DPXM) (3)] and dibenzofuran [Co2(DPD) (2) and Co2(DPDM) (4)] have been synthesized, characterized, and evaluated as catalysts for the direct four-proton, four-electron reduction of O2 to H2O. Structural analysis of the intramolecular diiron(III) mu-oxo complex Fe2O(DPXM) (5) and electrochemical measurements of 1-4 establish that Pacman derivatives bearing an aryl group trans to the spacer possess structural flexibilities and redox properties similar to those of their parent counterparts; however, these trans-aryl catalysts exhibit markedly reduced selectivities for the direct reduction of O2 to H2O over the two-proton, two-electron pathway to H2O2. Density functional theory calculations reveal that trans-aryl substitution results in inefficient proton delivery to O2-bound catalysts compared to unsubstituted congeners. In particular, the HOMO of [Co2(DPXM)(O2)]+ disfavors proton transfer to the bound oxygen species, funneling the O-O activation pathway to single-electron chemistry and the production of H2O2, whereas the HOMO of [Co2(DPX)(O2)]+ directs protonation to the [Co2O2] core to facilitate subsequent multielectron O-O bond activation to generate two molecules of H2O. Our findings highlight the importance of controlling both proton and electron inventories for specific O-O bond activation and offer a unified model for O-O bond activation within the clefts of bimetallic porphyrins.     

Thermodynamics of micellization of cationic surfactants in aqueous solutions: consequences of the presence of the 2-acylaminoethyl moiety in the surfactant head group

The enthalpies of micellization of the following surfactant series have been determined by calorimetry: benzyl (2-acylaminoethyl)dimethylammonium chlorides, RABzMe₂Cl, and alkyldimethylbenzylammonium chlorides, RBzMe₂Cl, where A, Bz and Me refer to amide, benzyl, and methyl groups, respectively and the acyl (for RABzMe₂Cl) and/or the alkyl (for RBzMe₂Cl) groups C₁₀, C₁₂, C₁₄, and C₁₆, respectively. For both series, the shapes of the calorimetric titration curves (enthalpograms) depend on the following micellar parameters: critical micelle concentration, aggregation number, and degree of counterion binding. The calorimetric-based critical micelle concentrations are in excellent agreement with those determined by conductivity. The Gibbs free energy, the enthalpy and the entropy of micellization were calculated, and divided into contributions from the CH₂ groups of the hydrophobic tail, and the terminal CH₃ plus head group of the surfactant. For both surfactant series, all thermodynamic parameters per CH₂ group were found to be similar, since their transfer (from bulk solution to the micelle) is independent of the surfactant head-group structure. The Gibbs free energy, the enthalpy, and the entropy of transfer of the head group of RABzMe₂Cl are more favorable than their counterparts for RBzMe₂Cl, because of direct and/or water mediated hygrogen bonding of the amide groups in the micelle.     

Comparison of algorithms and databases for matching unknown mass spectra

The most used algorithms for the identification of electron-ionization mass spectra are INCOS and probability based matching (PBM). For unknown spectra of high purity, ～75% of rank 1 answers are correct for both algorithms, matched against the National Institute of Standards and Technology 62,235 spectrum database. With matching criteria that retrieve 50% of the possible correct answers from the Wiley 228,998 spectrum database, 54% of the PBM and 42% of the INCOS answers are correct; for 85% purity unknowns, 48% and 27% are correct. For an unknown spectrum of two compounds, neither was reported in the first three INCOS answers; eight of the first ten PBM answers identify both components.     

Flexibility of the triblock copolymers modulating their penetration and expulsion mechanism in Langmuir monolayers of dihexadecyl phosphoric acid

The surface activity of the poly–[block (ethylene oxide)]–poly [block (propylene oxide)]–poly [block (ethylene oxide)] copolymers (EO)_x–(PO)_y–(EO)_x adsorbed together with dihexadecyl phosphoric acid (DHP), a synthetic phospholipid, is analyzed from their surface pressure and surface potential isotherms. The block copolymers of (EO)_x–(PO)_y–(EO)_x with variable molecular weight (1100–14 000) were dissolved in the subphase for DHP monolayers. The concentration of the copolymers within the aqueous subphase were selected to render an initial surface tension of 60 mN/m. The simultaneous adsorption of the copolymer and DHP is attested by the observation of a liquid expanded state at large areas, absent for pure DHP monolayers. Above some critical surface pressure all copolymers cited above are expelled from the interface. The surface potential isotherms, which give information on the component of the molecular dipole moment normal to the plane of the monolayer, are interpreted in terms of changes in the copolymer conformation as well as in terms of the copolymer desorption from the air–liquid interface. For an equal hydrophobic/hydrophilic ratio, the size of the chains or molecular weight is decisive in the mechanism of the copolymer expulsion from the air–liquid interface.     

Bounds on the Size of the Likelihood Ratio Test of Independence in a Contingency Table

Bounds are obtained on the limiting size of the nominal level-α likelihood ratio test of independence in a r × c contingency table. The situations considered include sampling with both marginal totals random and with one margin fixed. Upper and lower bounds are obtained. The limiting size is greater than α when some marginal probabilities are small. As the degrees of freedom increase, the limiting size tends to 1 for all α-values.