Accurate Gain Flattening Filters Manufactured by Optical Compensation Monitoring Method

GFFs with less than 0.4 dB peak-to-peak error functions are routinely fabricated using commercially available coating machines by utilizing the natural error compensation mechanism of wavelength variable turning point optical monitoring method.     

Synthesis, crystal structure, and nonlinear optical behavior of beta-unsubstituted meso-meso E-vinylene-linked porphyrin dimers

[structure: see text] A vinylene-linked porphyrin dimer, with no substituents at the beta-positions, has been synthesized by CuI/CsF promoted Stille coupling. In the crystal structure of this dimer, the C(2)H(2) bridge is twisted by 45 degrees relative to the plane of the porphyrins. The absorption, emission spectra, and electrochemistry reveal substantial porphyrin-porphyrin pi-conjugation. The triplet excited-state absorption spectrum of this dimer makes it suitable for reverse saturable absorption at 710-900 nm.     

A twenty-four membered mixed-metal macrocycle; synthesis and structure of cyclo-[(3-Me-1,2-C6H3O2)2SbNa(THF)2]6

The first example of a twenty-four membered mixed p-/s-block macrocycle, cyclo-[(3-Me-1,2-C6H3O2)2SbNa(THF)2]6 1 has been synthesised and structurally characterised from the reaction between 3-Me-1,2-C6H3(OH)(ONa) and (Me2N)2Sb(CH2)3Sb(NMe2)2.     

Enhancing the Photo and Thermal Stability of Nicotine through Crystal Engineering with Gentisic Acid

The use of crystal engineering to convert liquids into crystalline solids remains a powerful method for inhibiting undesired degradation pathways. When nicotine, a liquid sensitive to both light and air, is combined with the GRAS-listed compound, gentisic acid, the resulting crystalline solid, exhibits enhanced photo and thermal stability. Despite a modest ΔT_m of 42.7 °C, the melting point of 155.9 °C for the nicotinium gentisate salt is the highest reported for nicotine-containing crystalline solids. An analysis of the crystal packing and thermodynamic properties provides context for the observed properties.     

Quantitative Raman Analysis of Carotenoid Protein Complexes in Aqueous Solution

Carotenoids are naturally abundant, fat-soluble pigmented compounds with dietary, antioxidant and vision protection advantages. The dietary carotenoids, Beta Carotene, Lutein, and Zeaxanthin, complexed with in bovine serum albumin (BSA) in aqueous solution, were explored using Raman spectroscopy to differentiate and quantify their spectral signatures. UV visible absorption spectroscopy was employed to confirm the linearity of responses over the concentration range employed (0.05–1 mg/mL) and, of the 4 Raman source wavelengths (785 nm, 660 nm, 532 nm, 473 nm), 532 nm was chosen to provide the optimal response. After preprocessing to remove water and BSA contributions, and correct for self-absorption, a partial least squares model with R² of 0.9995, resulted in an accuracy of the Root Mean Squared Error of Prediction for Beta Carotene of 0.0032 mg/mL and Limit of Detection 0.0106 mg/mL. Principal Components Analysis clearly differentiated solutions of the three carotenoids, based primarily on small shifts of the main peak at ~1520 cm⁻¹. Least squares fitting analysis of the spectra of admixtures of the carotenoid:protein complexes showed reasonable correlation between norminal% and fitted%, yielding 100% contribution when fitted with individual carotenoid complexes and variable contributions with multiple ratios of admixtures. The results indicate the technique can potentially be used to quantify the carotenoid content of human serum and to identify their differential contributions for application in clinical analysis.     

Characterisation and cryomagnetic study of a hydrothermally synthesised hydrogen bonded L–M–L type co-ordination polymer

A ligand–metal–ligand type co-ordination polymer [Ni (C₆H₁₂N₄)(NCS)₂(H₂O)₂] _n has been synthesised under controlled hydrothermal conditions. Here 1,3,5,7-tetraazatricyclo[3.3.1]decane [or hexamethylenetetramine (hmt)] has been used as a μ-(N,N′) bidentate spacer molecule. The prepared polymeric complex has been characterised by elemental and spectral analyses. The structure has been confirmed by a single crystal X-ray diffraction study. Magneto-structural correlation has been drawn from cryomagnetic susceptibility measurements (2–300 K) which unequivocally reflects very weak magnetic spin interactions among the long distant octahedral Ni(II) metal centres mediated by hmt and weak hydrogen bonding interactions between the adjacent zigzag one-dimensional polymeric chains carrying into a two-dimensional infinite polymeric framework.     

Heterologous expression, purification, refolding, and structural-functional characterization of EP-B2, a self-activating barley cysteine endoprotease

We describe the heterologous expression in Escherichia coli of the proenzyme precursor to EP-B2, a cysteine endoprotease from germinating barley seeds. High yields (50 mg/l) of recombinant proEP-B2 were obtained from E. coli inclusion bodies in shake flask cultures following purification and refolding. The zymogen was rapidly autoactivated to its mature form under acidic conditions at a rate independent of proEP-B2 concentration, suggesting a cis mechanism of autoactivation. Mature EP-B2 was stable and active over a wide pH range and efficiently hydrolyzed a recombinant wheat gluten protein, alpha2-gliadin, at sequences with known immunotoxicity in celiac sprue patients. The X-ray crystal structure of mature EP-B2 bound to leupeptin was solved to 2.2 A resolution and provided atomic insights into the observed subsite specificity of the endoprotease. Our findings suggest that orally administered proEP-B2 may be especially well suited for treatment of celiac sprue.     

Insight into the nonlinear absorbance of two related series of two-photon absorbing chromophores

A comprehensive photophysical study of the linear and nonlinear absorption properties has been carried out on two series of two-photon absorbing dyes to gain insight into how structure-property relationships influence observed nonlinear absorption. The materials studied consist of an electron accepting benzothiazole group connected to an electron donating diphenylamine via a fluorene bridging group. Two series differ from each other by the addition of one phenyl group and for each series one-arm (dipolar, AF240 and AF270), two-arm (quadrupolar, AF287 and AF295), and three-arm (octupolar, AF350 and AF380) versions were studied. Overall the AF240 series exhibits higher intrinsic two-photon absorption (TPA) cross-sections than the AF270 series as well as enhanced nanosecond nonlinear absorption, with an increase with number of branches. The enhanced nanosecond nonlinearity is understood by taking into account the contribution from the singlet and triplet excited states and was verified by a two-photon assisted excited-state absorption model that satisfactorily predicts the nonlinear absorption of the chromophores.     

New Cu(II) complexes with polydentate chelating Schiff base ligands: Synthesis, structures, characterisations and biochemical activity studies

We have reported herein the synthesis of three new Cu(II) complexes of tri- and tetradentate Schiff base ligands containing N₃ or N₄ donor set along with terminal NNN⁻ or SCN⁻ ligands: [L¹Cu(NCS)]ClO₄ (1), [L²Cu(NCS)₂] (2) and [L³Cu(NNN)]ClO₄ (3) [L¹ = NC₅H₄C(CH₃)=N(CH₂)₃N=C(CH₃)C₅H₄N, L²= Me₂N–(CH₂)₃–N=C(CH₃)C₅H₄N and L³ = NC₅H₄CH=N–(CH₂)₄–N=CHC₅H₄N]. The complexes have been systematically characterised by elemental, spectroscopic and electrochemical techniques. Antimicrobial activities of the Schiff base ligands and their metal complexes have been studied using the disc diffusion method on the strains of Candida tropicalis and Bacillus megaterium. Structures of all the complexes have been unequivocally established from single crystal X-ray diffraction analyses that show the monomeric units containing a five-coordinated copper center in highly distorted square pyramidal geometry with thiocyanate or azide anion coordinated as terminal ligand. The complexes 1 and 3 crystallise in monoclinic (P2₁/c) and 2 in triclinic (P-1) space group, respectively.