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The charge-transfer transition energies and the electronic-coupling matrix element, |H(DA)|, for electron transfer from aminopyridine (ap) to the 4-carbonyl-2,2'-bipyridine (cbpy) in cbpy-(gly)(n)-ap (gly = glycine, n = 0-6) molecules were calculated using the Zerner's INDO/S, together with the Cave and Newton methods. The oligopeptide linkages used were those of the idealized protein secondary structures, the alpha-helix, 3(10)-helix, beta-strand, and polyproline I- and II-helices. The charge-transfer transition energies are influenced by the magnitude and direction of the dipole generated by the peptide secondary structure. The electronic coupling |H(DA)| between (cbpy) and (ap) is also dependent on the nature of the secondary structure of the peptide. A plot of 2.ln|H(DA)| versus the charge-transfer distance (assumed to be the dipole moment change between the ground state and the charge-transfer states) showed that the polyproline II structure is a more efficient bridge for long-distance electron-transfer reactions (beta = 0.7 A(-1)) than the other secondary structures (beta approximately 1.3 A(-1)). Similar calculations on charged dipeptide derivatives, [CH(3)CONHCH(2)CONHCH(3)](+/)(-), showed that peptide-peptide interaction is more dependent on conformation in the cationic than in the anionic dipeptides. The alpha-helix and polyproline II-helix both have large peptide-peptide interactions (|H(DA)|800 cm(-1)) which arise from the angular dependence of their pi-orbitals. Such an interaction is much weaker than in the beta-strand peptides. These combined results were found to be consistent with electron-transfer rates experimentally observed across short peptide bridges in polyproline II (n = 1-3). These results can also account for directional electron transfer observed in an alpha-helical structure (different ET rates versus the direction of the molecular dipole).

The Rion Device E-type (RDE) has been applied to 39 patients with severe mixed deafness that could not be rehabilitated by surgical means or the conventional hearing aid. Careful follow-up studies have been conducted on all of them to assess clinical and audiologic results. The device could function more than 10 years, affording natural quality of hearing without howling and wearing discomforts. Functional principles of the device, indications, and surgical methods of implantation are described. The failures and delayed problems were also presented together with the preventive measures.

The binding of the host H1 (N,N‘-bis(6-pivalamidopyrid-2-yl)-3,5-pyridinedicarboxamide) to three different ruthenium polypyridine complexes with an attached barbituric acid and barbital moieties (RuG1, RuG2, RuG3) (where G1 = 5-[4-(4‘-methyl)-2,2‘-bipyridylidene]-2,4,6-(1H,3H,5H)-pyrimidinetrione, G2 = 5-[4-(4‘-methyl)-2,2‘-bipyridyl]methyl-2,4,6-(1H,3H,5H)-pyrimidinetrione, and G3 = 5-ethyl, 5-[4-(4‘-methyl)-2,2‘-bipyridyl]methyl-2,4,6-(1H,3H,5H)-pyrimidinetrione) and Ru = (4,4‘-di-tert-butyl-bpy)2Ru (bpy = 2,2‘-bipyridine) has been studied in chlorinated solvents by NMR and fluorescence titrations. Significant binding was only observed between H1 and the RuG2 series, while steric hindrance significantly diminished binding between H1 and RuG1 or RuG3. The high binding constant for RuG2 was related to the presence of the enolate form of the barbituric acid guest which forms strong H-bonds with the complementary host H1. For the organic barbituric acid and barbital guests, the keto and enol bind only weakl...

Dear Editor, Tympanic membrane perforation is frequently encountered in outpatient otorhinolaryngology practice. We have introduced a treatment procedure to promote regeneration of the tympanic membrane and closure of perforations using an atelocollagen sponge/silicone membrane combined with human basic fibroblast growth factor that promotes wound healing.1,2 This report describes epithelial pearl formation following our outpatient-based tympanic membrane regeneration therapy.

The excited state properties of a series of singly bonded dirhodium compounds, consisting of Rh(0)(2), Rh(0)Rh(II)X(2), and Rh(II)(2)X(4) (X = Cl and Br) cores coordinated by three bis(difluorophosphino)methylamine ligands, have been investigated. The newly synthesized complexes with X = Br have been structurally characterized. The mixed-valence complex Rh(2)[mgr;-CH(3)N(PF(2))(2)](3)Br(2)[(PF(2))CH(3)N(PF(2))] crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a = 13.868(7) Å, b = 16.090(5) Å, c = 11.614(5) Å, V = 1591(3) Å(3), and Z = 4; the structure was refined to values of R = 0.052 and R(w) = 0.062. Orange crystals of Rh(2)[mgr;-CH(3)N(PF(2))(2)](3)Br(4) are monoclinic with a C2/c space group: a = 14.62(6) Å, b = 12.20(2) Å, c = 14.33(1) Å; beta = 106.0(2) degrees; V = 2457(11) Å(3); Z = 4; and R = 0.058 and R(w) = 0.056. Crystalline solids and low-temperature glasses of each member of the chloride and bromide series exhibit long-lived red luminescence. Excitation profiles and temperature dependencies of the emission bandwidths and lifetimes for all complexes are characteristic of luminescence originating from a dsigma excited state. Efficient nonradiative decay is observed upon the thermal population of an excited state proximate to the lowest energy emissive excited state of these complexes. The nonradiative decay rate constant of the upper excited state is 10(2)-10(3) and 10(3)-10(4) greater than that of the emissive excited state for complexes with X = Cl and Br, respectively.

The absorption spectra of RuII(NH3)5L and RuIII(NH3)5L (L is an aromatic N-heterocycle or nitrile) complexes in 50:50 glycerol−water glasses at 77 K (Ds = 3.9) are a function of the applied field in the 106−107 V/m range. Analysis of the spectra in terms of the Liptay equations yields ground−excited state dipole-moment differences ranging from 4 to 37 D, depending upon the nature of L. The measured dipole moment differences, particularly those for the MLCT transitions, are much smaller than the values estimated from a simple consideration of the electron-transfer distances. The discrepancy between the observed and naive dipole-moment estimates arises mainly from the multielectron nature of the response to excitation. Good agreement is obtained with the predictions of a model which includes refinement of the effective electron-transfer distance, the shift in the valence electron distribution in the excited state, and the effects of electron delocalization (π-backbonding for Ru(II) and π-bonding for the Ru(...

Both metal-to-ligand charge transfer (MLCT) and oxidation (ionization) processes have been investigated for (NH3)5RuL2+ complexes with L = pyridine, pyrazine, and protonated pyrazine. Calculations ...

The spectroscopic and magnetic properties of a quadruply bonded dimolybdenum core intercalated into the layered metal phosphates (LMPs) of vanadium and niobium have been examined. Layer modification of the LMPs was achieved by redox intercalation of the Mo{sub 2}{sup 4+} core solvated by acetonitrile and by its ion-exchange reaction following reduction of the phosphate host layers with NaBH{sub 4}. Regardless of the reaction pathway, a similiar product is obtained. The reacted layers display a contraction of the d-spacing with concomitant insertion of up to 0.2 molybdenum atoms per layer unit cell. Structural characterization and absorption spectroscopy of these materials reveal that the bimetallic core residing in the gallery interlayer region is the mixed-valence Mo{sub 2}{sup 5+} center in a transverse orientation. In this arrangement the ubiquitous D{sub 4h} coordination environment of multiply bonded {open_quotes}Mo{sub 2}O{sub 8}{close_quotes} complexes is achieved with the dimolybdenum core keyed into tetragonal oxygen cavities of the layer. Magnetic susceptibility and EPRR studies reveal that electrons in the layers are antiferromagnetically coupled and that the exchange interaction is in a weak coupling regime. This exchange interaction is enhanced by the presence of the paramagnetic Mo{sub 2}{sup 5+} center within the interlayer region of the LMP. 95 refs.,more » 8 fig.« less

Solids and low-temperature solution glasses of the diplatinum(III) tetraphosphates Pt 2 (HPO 4 ) 4 L 2 n− (L=H 2 O, n=2; L=Cl or Br, n=4) exhibit red luminescence upon irradiation with near-ultraviolet light. Emission lifetimes and quantum yields of crystalline potassium salts were measured over a wide temperature range (10-300 K)

The surgical results of ossicular chain reconstruction using a hydroxyapatite prosthesis were evaluated in 106 ears of 101 patients who were followed up for > 5 years. Successful reconstruction was defined as: (1) postoperative air-bone gap of

The chemistry of two-electron mixed valence dimers Mn-1—Mn+1 provides a unique foundation for the design of multielectron photochemical activation schemes. We have recently prepared a homologous Rh2 fluorophosphine series that is based on a Rh0RhII two-electron mixed valence complex, which features a trigonal bipyramidal coordination geometry about a Rh0 center, an octahedral coordination about a RhII center and a Rh···Rh separation characteristic of a single metal-metal bond. This novel compound exhibits long-lived luminescence, and steady state and time-resolved spectroscopic studies reveal a metal localized excited state of dσ* character. The reactivity of the Rh0RhII compound provides a benchmark for two-electron mixed valence bimetallic cores in that two-electron oxidations are promoted at the Rh0 center and two-electron reductions are effected at the RhII center. Within this framework, the strategy for the development of parallel reactivity of electronically excited binuclear complexes can be elaborated. Transient absorption spectroscopy of the quadruply bonded M2X4(PBu3)4 complexes (M = Mo(II), W(II); X = Cl) provides strong evidence for the generation of a two-electron mixed valence MIMIII excited state complex upon δ2 → δδ* excitation. The smooth reaction of electronically excited W2Cl4(dppm)4 with methyl iodide to a W2Cl4(dppm)4(CH3)(I) photoproduct with direct addition of the organic substrate to the metal-metal core is consistent with the reactivity pattern established by the mixed valence Rh0RhII dimer.

This paper reports results for metal-to-ligand charge transfer (MLCT) and ligand-to-metal charge transfer (LMCT) absorption bands of Ru(II) and Ru(III) complexes and shows that the dipole-moment changes can be understood in terms of a two-state model which considers polarization, induced-dipole, and delocalization effects. In summary, the change in the charge of the metal center produced by charge-transfer excitation results in a change in ligand polarization which reduces the expected dipole-moment change. It is shown that including this effect, together with the effect of the permanent dipoles of the NH{sub 3} ligands, results in encouragingly good agreement with the predictions of a two-state model for MLCT and LMCT transitions. 22 refs.