Chemical Engineering of Photoactivity in Heterometallic Titanium–Organic Frameworks by Metal Doping

We report a new family of titanium–organic frameworks that enlarges the limited number of crystalline, porous materials available for this metal. They are chemically robust and can be prepared as single crystals at multi‐gram scale from multiple precursors. Their heterometallic structure enables engineering of their photoactivity by metal doping rather than by linker functionalization. Compared to other methodologies based on the post‐synthetic metallation of MOFs, our approach is well‐fitted for controlling the positioning of dopants at an atomic level to gain more precise control over the band‐gap and electronic properties of the porous solid. Changes in the band‐gap are also rationalized with computational modelling and experimentally confirmed by photocatalytic H₂ production.     

Selective Functionalization of Aminoheterocycles by a Pyrylium Salt

The functionalization of aminoheterocycles by using a pyrylium tetrafluoroborate reagent (Pyry‐BF₄) is presented. This reagent efficiently condenses with a great variety of heterocyclic amines and primes the C?N bond for nucleophilic aromatic substitution. More than 60 examples for the formation of C?O, C?N, C?S, or C?SO₂R bonds are disclosed herein. In contrast to C?N activation through diazotization and polyalkylation, this method is characterized by its mild conditions and impressive functional‐group tolerance. In addition to small‐molecule derivatization, Pyry‐BF₄ allows the introduction of functional groups in a late‐stage fashion to furnish highly functionalized structures.     

Twisting Behaviour of Conformal Maps

This paper is devoted to the study of different types of twistingpoints of conformal maps. We define the sets of gyration, spiraland oscillation points and we prove, in the case that f is conformalalmost nowhere, that the above sets have Hausdorff dimensionone. Also we define points of bounded radial oscillation. Itis proved that there are always points of -bounded radial oscillationbut there exists a conformal map without points of small boundedradial oscillation.     

Photometric and fluorimetric study of the acid-base behavior of 2,2′-diquinolyl and 2,2′,2″-terpyridyl

A photometric and fluorimetric study of the acid-base behavior of 2,2-diquinolyl and 2,2,2-terpyridyl was performed. In sulfuric acid medium, the doubly charged 2,2-diquinolynium ion undergoes the first dissociation atH ₀=0.20±0.09, as determined by fluorimetry (_ex=336 nm, _em=424 nm). Photometric titration is less accurate because of the overlapping of the absorption spectra. The second dissociation constant of 2,2-diquinolyl was determined by fluorimetric titration (_ex=336 nm, _em=420 nm), obtaining a value of 3.67±0.03. The triply charged 2,2,2-terpyridyl molecule was found to undergo the first dissociation atH ₀=–7.17±0.04, as determined by fluorimetric titration (_ex=316 nm, _em=350 nm), in aqueous sulfuric acid medium. Photometric titration (=335 nm) was performed in the presence of 6.5% ethanol because of the low solubility of the compound in water. In this ethanolicwater medium, a value of the dissociation constant atH ₀=–7.39±0.03 was calculated. The second dissociation constant was determined to be 2.81±0.12 by photometric titration at 285 nm, and values of 4.03±0.26 and 4.16±0.20 were found for the third dissociation constant by photometric titrations at 320 and 295 nm, in 10% ethanol, in close agreement with previously reported values. The fluorimetric titration profile obtained by exciting at 274 nm and measuring the fluorescence emission at 350 nm, in the zone betweenH ₀=–3 and pH=10, is complicated by the several equilibria involved.     

Estimate of foil thickness by stereomicroscopy technique

The determination of foil thickness by stereomicroscopy technique is discussed. The calculation of the foil thickness is performed in a general position of the foil in an electron microscope for a general choice of the marker position. In this case the crystallographic orientation of the foil normal has to be known. But there exists a special case (markers lie in the diffraction plane) where it is not necessary to know the orientation of the foil normal. The relative error in determining the foil thickness is about 10%.List of symbols B direction in the foil parallel with the primary beam in the first micrograph - d vector describing a common straight line of and ₁ ( ₁) - F direction in the foil parallel with the primary beam in the second micrograph - g diffraction vector - M magnification - n foil normal - o vector defined byn ×B - p ₁ first coordinate ofX in the first micrograph - p ₂ first coordinate ofX in the second micrograph - p _1i ,P _2i quantitiesP ₁,P ₂ corresponding to thei-th markers on the top surface - t _B foil thickness measured in theB direction - auxiliary quantity - corresponding to thei-th markers on the top surface - t _d foil thickness measured in thed direction - t _F foil thickness in general - t _n foil thickness measured in then direction - X ₁ point in _B characterizing one of the markers - X ₂ point in _T characterizing one of the markers - X _2i X ₂ corresponding to thei-th markers on the top surface - X _g magnitude ofX _g - X _gi magnitude ofX _gi - X magnitude ofX - X vector connecting pointX ₁ withX ₂ (X X ₂–X ₁ - X _g component ofX perpendicular to the plane ₁ - X _gi X _gi corresponding to thei-th markers on the top surface - X component ofX lying in the plane ₁ - z distance between _{1 T} and the end point ofX divided by cos Greek symbols angle between ₁ and _{1 B} - angle betweeng and _T - ₁, ₂ reflection planes - plane containingn andg - m measure error - p difference betweenp ₂ andp ₁ (p=p ₂–p ₁) - P accuracy of length measurement - (t _B )_max maximum error oft _B - maximum error of - accuracy of angle measurement - angle characterizing the deviation from the foil position when symmetrical tilting is achieved - angle of tilt betweenB andF (between stereomicrographs) - _T plane describing approximately the top surface of the foil - _b plane describing approximately the bottom surface of the foil - screen plane - angle between ₁ andX - plane containingn andB - angle of tilting from starting (after inserting the foil into the microscope) to working position (position during image observation) Special symbol intersection of two planes (common straight line)     

Crystal structures and magnetic properties of bipyridine copper(II) complexes

The synthesis, structure and magnetic properties of [Cu(diMe-bipy)Br₂] are reported (diMe-bipy=4,4-dimethyl 2,2-bipyridine). The complex has a polymeric structure composed of [Cu(diMebipy)Br₂] subunits linked via bridging bromine atoms. Each copper atom is hexacoordinated in a distorted octahedral coordination environment. Crystallographic data: monoclinic, space groupC2/c,Z=4, unit cell of dimensionsa=18.312(7),b=9.818(2),c=7.486(2)Å,=107.750(0)° at 293 K. The best fit of the magnetic susceptibility data by the uniform Heisenberg chain model forS=1/2 ions yields values for the exchange coupling constant of –0.46 cm^–1. The magnetic susceptibility of the dimeric [Cu(diMe-bipy)Cl₂]₂·0.5H₂O exhibits a maximum near 12 K that is indicative of an antiferromagnetic interaction between the two metal centers. The best fit of the experimental data by the Bleaney-Bowers equation was obtained withg=1.95 andJ=–6.99 cm^–1.     

Shape preserving representations and optimality of the Bernstein basis

This paper gives an affirmative answer to a conjecture given in [10]: the Bernstein basis has optimal shape preserving properties among all normalized totally positive bases for the space of polynomials of degree less than or equal ton over a compact interval. There is also a simple test to recognize normalized totally positive bases (which have good shape preserving properties), and the corresponding corner cutting algorithm to generate the Bézier polygon is also included. Among other properties, it is also proved that the Wronskian matrix of a totally positive basis on an interval [a, ) is also totally positive.Both authors were partially supported by DGICYT PS90-0121.     

Effective Hamiltonians from first principles

The equations of motion for a quantum system of the electromagnetic field interacting with matter are derived from the first principle Hamiltonian (two-level atomic systems are assumed) and from the effective Hamiltonian. The derivation is based on the memoryfunction theory of Mori and on the theory of random frequency modulation of Tokuyama and Mori. On the ground of comparison of the equations of motion from the first principle Hamiltonian with those from the effective Hamiltonian a justification of the use of effective Hamiltonians is discussed.     

Synthesis,crystal and molecular structure and spectroscopic studies (i.r., electronic,13C-n.m.r. and Mössbauer) of the perchlorate of nitrosyltetracyanoiron(II)-μ-cyano-pentaamminecobalt(III)trihydrate and its chromium(III) analogue

Summary The two new title compounds have been synthesized and characterized by x-ray crystal structure and spectroscopic measurements. Both compounds are air-stable and isomorphous. The crystal system, space group and Z for both compounds are: hexagonal, p6₁ and 6. Lattice constants for the Co^III and Cr^III complexes are as follows:a = 9.674(3) Å,c = 37.196(6) Å anda = 9.786(3) Å,c = 37.852(6) A, respectively. The molecular structure shows a great distortion in the Fe-C-N-M torsion angle [–46.8(7)° and –51.3(7)°, respectively] which has been interpreted as due to the presence of the NO ligand. The spectral studies confirm the presence of the -cyano ligand by the clear splitting of the (CN) stretching vibration atca. 2200 cm^–1 and the shift of 15–20 nm towards higher frequencies in the first d-d transition of M^III. The¹³C-n.m.r. spectrum of the diamagnetic Co^III complex confirms the presence of the -cyano ligand in solution and, as in the solid phase, the bridging group iscis to the NO of the nitroprusside. The Mössbauer spectra show that the principal axis component of electric field gradient tensor will most likely be directed in the Fe-NO direction (as in the nitroprusside ion) and not towards the CN bridge.     

Micellar liquid chromatography determination of B vitamins with direct injection and ultraviolet absorbance detection

A micellar reversed-phase liquid chromatographic procedure was developed for the control of five water-soluble vitamins, B (nicotinamide), B1 (thiamine), B2 (riboflavin), B6 (pyridoxine and pyridoxamine), in multivitamin pharmaceutical formulations (capsules, pills and syrups). Optimization procedure includes studies about the composition of the mobile phase (sodium dodecyl sulphate and the modifiers propanol, butanol or pentanol), flow-rate and temperature. Chromatographic analysis of all vitamins was carried out using a single mobile phase of 0.1 M SDS-4% (v/v) pentanol at pH 3, in a C18 column in isocratic mode, and UV-detection at 270, 290 and 325 nm. The flow-rates selected were 1.0 ml/min in the interval 0 to 6 min, and 2.0 ml/min until the end of the chromatogram and temperature was 45 degrees C. In the micellar liquid chromatographic system, the samples were injected without pretreatment, and the analysis time was below 12 min. Repeatabilities and intermediate precision were achieved according to ICH, and were below 5%. When the method is applied to real samples, the amount found with respect to the declared compositions were within the 91-105% range. These results were similar to those obtained with a conventional 60:40 (v/v) methanol-water mixture for some of the vitamins, but with the advantage of use a single mobile phase for the analyses of the five vitamins, with direct injection of the samples and reduced toxicity, flammability, environmental impact and cost of the micellar-pentanol solutions.