Design and synthesis of a new class of nonmacrocyclic alkali metal host compounds

A new class of nonmacrocyclic metal ion hosts has been examined that features a polyspirocyclic framework that offers a 1,3,5-triaxial presentation of ligating centers. These compounds are easily synthesized and exploit stereoelectronic influences to preorganize the metal ion binding site. While compounds bearing oxygen substituents (X = OH, OMe) failed to show appreciable binding of alkali metals, the aminated host (X = NHBn) exhibitied strong binding with association constants (K(a)) greater than 10(7)-10(8) as measured by picrate extraction analysis.     

Archetypical modeling and amphiphilic behavior of cobalt(II)-containing soft-materials with asymmetric tridentate ligands

The stabilization of a bivalent oxidation state in cobalt complexes of phenolate-based asymmetric tridentate ligands with iodo and bromo substituents is studied. The complexes [CoII(LIA)2].2CH3OH (1) and [CoII(LBrA)2].CH3OH (2) were characterized by means of several spectroscopic and spectrometric techniques. The molecular structure of 1 was determined by diffractometric analysis and reveals the cobalt(II) ion in a distorted-octahedral geometry. The centrosymmetric metal ion adopts a local D2h symmetry and is surrounded by facially coordinated ligands. Equivalent donor sets in both ligands are trans to each other, and DFT calculations suggest that the fac-trans configuration is favored by a small margin when compared to the fac-cis isomers. Both DFT calculations and EPR spectroscopy agree with a high-spin S=3/2 electronic configuration given by [ag1, b1g1, ag1, b2g2, b3g2]. This oxidation state was indirectly observed by the lack of a ppiphenolate-->dsigma*cobalt(III) charge-transfer band, which is found between 430 and 470 nm for similar cobalt(III) species. On the basis of the geometrical preferences and the oxidation state of archetypical 1 and 2, two metallosurfactants [CoII(LI-ODA)2] (3) and [CoII(LI-NOBA)2].CH2Cl2 (4) were obtained. The redox chemistry of 1-4 is marked by metal- and ligand-centered activity with several follow up processes and film formation on the electrode. Both metallosurfactants exhibit amphiphilic properties and organization, as shown by compression isotherms and Brewster angle microscopy but exhibit dissimilar collapse mechanisms; whereas 3 collapses at constant pressure, 4 exhibits a constant-area collapse. Langmuir-Blodgett films are readily obtained and were characterized by equilibrium contact angle and atomic force microscopy.     

4,4'-dithiodipyridine as a bridging ligand in osmium and ruthenium complexes: the electron conductor ability of the -S-S- bridge

The compounds [Ru(NH(3))(5)(dtdp)](TFMS)(3), [Os(NH(3))(5)(dtdp)](TFMS)(3), [(NH(3))(5)Os(dtdp)Os(NH(3))(5)](TFMS)(6), [(NH(3))(5)Os(dtdp)Ru(NH(3))(5)](TFMS)(3)(PF(6))(2), and [(NH(3))(5)Os(dtdp)Fe(CN)(5)] (dtdp = 4,4'-dithiodipyridine, TFMS = trifluoromethanesulfonate) have been synthesized and characterized by elemental analysis, cyclic voltammetry, electronic, vibrational, EPR, and (1)H NMR spectroscopies. Changes in the electronic and voltammetric spectra of the ion complex [Os(NH(3))(5)(dtdp)](3+) as a function of the solution pH enable us to calculate the pK(a) for the [Os(NH(3))(5)(dtdpH)](4+) and [Os(NH(3))(5)(dtdpH)](3+) acids as 3.5 and 5.5, respectively. The comparison of the above pK(a) data with that for the free ligand (pK(1) = 4.8) provides evidence for the -S-S- bridge efficiency as an electron conductor between the two pyridine rings. The symmetric complex, [(NH(3))(5)Os(dtdp)Os(NH(3))(5)](6+), is found to exist in two geometric forms, and the most abundant form (most probably trans) has a strong conductivity through the -S-S- bridge, as is shown by EPR, which finds it to have an S = 1 spin state with a spin-spin interaction parameter of 150-200 G both in the solid sate and in frozen solution. Further the NMR of the same complex shows a large displacement of unpaired spin into the pi orbitals of the dttp ligand relative to that found in [Os(NH(3))(5)(dtdp)](3+). The comproportionation constant, K(c) = 2.0 x 10(5), for the equilibrium equation [Os(II)Os(II)] + [Os(III)Os(III)] right harpoon over left harpoon 2[Os(II)Os(III)] and the near-infrared band energy for the mixed-valence species (MMCT), [(NH(3))(5)Os(dtdp)Os(NH(3))(5)](5+) (lambda(MMCT) = 1665 nm, epsilon = 3.5 x 10(3) M(-)(1) cm(-)(1), deltanu(1/2) = 3.7 x 10(3) cm(-)(1), alpha = 0.13, and H(AB) = 7.8 x 10(2) cm(-)(1)), are quite indicative of strong electron delocalization between the two osmium centers. The electrochemical and spectroscopic data for the unsymmetrical binuclear complexes [(NH(3))(5)Os(III)(dtdp)Ru(II)(NH(3))(5)](5+) (lambda(MMCT) = 965 nm, epsilon = 2.2 x 10(2) M(-)(1) cm(-)(1), deltanu(1/2) = 3.0 x 10(3) cm(-)(1), and H(AB) = 2.2 x 10(2) cm(-)(1)) and [(NH(3))(5)Os(III)(dtdp)Fe(II)(CN)(5)] (lambda(MMCT) = 790 nm, epsilon = 7.5 x 10 M(-)(1) cm(-)(1), deltanu(1/2) = 5.4 x 10(3) cm(-)(1), and H(AB) = 2.0 x 10(2) cm(-)(1)) also suggest a considerable electron delocalization through the S-S bridge. As indicated by a comparison of K(c) and energy of the MMCT process in the iron, ruthenium, and osmium complexes, the electron delocalization between the two metal centers increases in the following order: Fe < Ru < Os.     

Vibrational spectrum of the spin crossover complex [Fe(phen)(2)(NCS)(2)] studied by IR and Raman spectroscopy, nuclear inelastic scattering and DFT calculations

The vibrational modes of the low-spin and high-spin isomers of the spin crossover complex [Fe(phen)(2)(NCS)(2)] (phen = 1,10-phenanthroline) have been measured by IR and Raman spectroscopy and by nuclear inelastic scattering. The vibrational frequencies and normal modes and the IR and Raman intensities have been calculated by density functional methods. The vibrational entropy difference between the two isomers, DeltaS(vib), which is--together with the electronic entropy difference DeltaS(el)--the driving force for the spin-transition, has been determined from the measured and from the calculated frequencies. The calculated difference (DeltaS(vib) = 57-70 J mol(-1) K(-1), depending on the method) is in qualitative agreement with experimental values (20-36 J mol(-1) K(-1)). Only the low energy vibrational modes (20% of the 147 modes of the free molecule) contribute to the entropy difference and about three quarters of the vibrational entropy difference are due to the 15 modes of the central FeN(6) octahedron.     

Total flowtime and makespan for a no-wait <Emphasis Type="Italic">m</Emphasis>-machine flowshop with set-up times separated

This paper addresses the m-machine no-wait flowshop problem where the set-up time of a job is separated from its processing time. The performance measures considered are the total flowtime and makespan. The scheduling problem for makespan reduces to the travelling salesman problem (TSP), and the scheduling problem for total flowtime reduces to the time-dependent travelling salesman problem (TDTSP). Non-polynomial time solution methods are presented, along with a polynomial heuristic.     

Isotope effects on the picosecond time-resolved emission spectroscopy of tris(2,2'-bipyridine)ruthenium (II)

The excited-state properties of the transition metal complexes tris(2,2'-bipyridine) ruthenium(II) and tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) are examined using picosecond time-resolved luminescence spectroscopy. For both complexes, direct observation of a short-lived high-energy emission with a lifetime of less than 4 ps is reported. Upon deuteriation of the complexes the lifetime of the high-energy emission shows a marked increase with a biexponential decay (20 and approximately 300 ps components). Examination by time-resolved excited-state resonance Raman shows that for the perprotio complexes features attributable to the 3MLCT excited state are formed within 4 ps, while for the perdeuterio a rise time of approximately 20 ps is observed in the 3MLCT features. The results indicate that the emission in both cases may be 1MLCT in origin and are discussed with respect to heterogeneous electron transfer.     

Study of molecular motion in polysilastyrene by pulsed 1H nuclear magnetic resonance

Pulsed NMR spectra of protons in polysilastyrene, $ \rlap{--} [{\rm Si(CH}_{\rm 3} {\rm )}_{\rm 2} {\rm  Si(CH}_{\rm 3} )({\rm C}_6 {\rm H}_5 )\rlap{--} ]_n $, with n ≈ 60, have been measured in the temperature range 80–450 K. The linewidth is constant at 7.4 G up to 200 K and narrows considerably above 250 K to a constant value of 0.3 G above 360 K. The motion responsible for this effect has an activation energy of 43.7 kJ/mol and is identified with the large-scale motion occurring in the vicinity of the glass transition temperature. The spin-lattice relaxation time T₁ was measured by the π-t-½π pulse sequence as a function of temperature. Two motional minima in T₁ were observed. The low-temperature motion has an activation energy of 3.7 kJ/mol and is identified with methyl group reorientation. The high-temperature motion has an activation energy of 29.1 kJ/mol and might be due to segmental motion.     

QUANTUM YIELD VALUES FOR THE DECOMPOSITION OF SEVERAL SURFACE-ACTIVE PHOTOREACTIVE AMPHIPHILES

The quantum yield values for the decomposition of 12-azido-1-diazo-2-dodecanone, 1-diazo-11-dodecanone, 1-diazo-17-octadecen-2-one, stearoyl azide and 10-undecenyl azidoformate in hexane were determined. It was found that the compounds decomposed with relatively high quantum yields, suggesting their use in biological applications, especially for binding phospholipids to membrane proteins.     

Photoactivity tests of TiO2-based inorganic sunscreens. Part 1: Non-aqueous dispersions

A new method of measuring photoactivity of a major group of inorganic sunscreens (coated titanium dioxide) is presented based on the photobleaching of the radical 1,1-diphenyl-2-picrylhydrazyl.