A first principles study of the electronic structure and optical response of heterobimetallic M-dicyanoaurate-based coordination polymers (M = Mn, Co, Ni, Zn and Cd).

The electronic structure and derived optical properties of five synthesized metal-dicyanoaurate(I), (K)M[Au(CN)2], (M = Mn, Co, Ni, Zn and Cd), coordination polymers are described from a combined experimental analysis and theoretical study based on density functional theory. In this sense, the topological features that influence the electronic structure, which in turn give rise to electronic transitions associated with the band gap energy, are studied from first principles calculations (with hybrid HSE06 and GGA-PBE density functionals) and electronic spectroscopy. The impact of gold (through spin-orbit coupling) and aurophilic interactions on the electronic transitions that gives rise to optical properties is described. The calculated projected density of states and band dispersion diagrams shed light on the molecular orbital distribution and the role of a dicyanoaurate(I) molecular block as the origin of the optical properties. Infrared, Raman and ultraviolet-visible spectroscopic analyses reveal the effect that charge transfer interactions, of a metal → ligand and metal → metal nature, have on the electronic behavior within the solids through association with the polarizing power of transition metals and gold atoms.

Vibrational Modes and Phonon and Thermodynamic Properties of the Metaboric Acid Polymorphs α-, ß-, and γ-(BOH)3O3 within a Density Functional Theory Framework.

A combined study of vibrational and thermodynamic properties of metaboric acid (BOH)3O3 crystal polymorphs α, ß, and γ were obtained through density functional theory (DFT) calculations in an attempt to resolve the conflicting assignments that currently exist in the literature for them. A complete correlation between the normal-mode assignment and vibrational signatures to distinguish particular features of each metaboric acid polymorph, in particular, those related to motions of the planar layers in α-(BOH)3O3, with a level of detail surpassing essays based on previous published experimental works has been achieved. Besides, no DFT-based research work was published early on the (BOH)3O3 polymorph vibrational properties, and our DFT-simulated infrared and Raman spectra for all metaboric acid polymorphs agree very well with experiment. Comparison of the previously published experimental IR and Raman spectroscopic results with predictions from higher levels DFT calculations allows identification of the in-plane and out-of-plane B-O bending modes. For example, the strongest measured (DFT-calculated) Raman modes of α-(BOH)3O3 at 591 and 797 cm-1 (599 and 810 cm-1) are identified as vibrational signatures of breathing B3O3/Ag in-plane modes, while the shoulder in the lattice modes region at 135 (143) cm-1 is the vibrational signature of the bending B3O3/B1g out-of-plane mode. Phonon-dispersion bands and their respective phonon densities of states were also evaluated for each system, as well as temperature-dependent curves for entropy, enthalpy, free energy, heat capacity, and Debye temperature. Phonon dispersion curves are singular for each (BOH)3O3 species, and a consistent gap decrease between the lowest and highest frequency vibrational bands was observed. The DFT-based calculations also revealed that the noncovalent interactions prevalent in the α and ß crystals lead to significant differences with respect to the thermodynamic properties in comparison with the γ phase.

Photo-induced charge transfer in Prussian blue analogues as detected by photoacoustic spectroscopy.

The photo-induced charge transfer in four series of Prussian blue (PB) analogues was studied from photoacoustic spectra. In cobalticyanides the observed signals were assigned to a metal-to-ligand charge transfer, which appears as a shoulder below 450 nm, and to d-d transitions for Co(II), Ni(II) and Cu(II) complex salts. No evidence of metal-to-metal charge transfer was observed for this series, which is probably due to the high stability of low spin cobalt(III) in the hexacyanide complex. Photoacoustic spectra for ferricyanides are broad bands, which result particularly intense up to 750 nm. Such features were attributed to the overlapping of contributions from metal-to-ligand (<600 nm) and metal-to-metal charge transfer transitions, with probably also a minor contribution from d-d transitions in the outer metal. The spectra for the ferrocyanides series are dominated by the metal-to-ligand charge transfer band below 550 nm, approximately 100 nm above this transition in cobalticyanides. Within the studied solids, the most intense and broad metal-to-metal charge transfer bands were found for a series of low spin Co(III) high spin Co(II) hexacyanoferrates(II,III) and with similar features also for ferric ferrocyanide (Prussian blue), assigned to Fe(II)-->Co(III) and Fe(II)-->Fe(III) photo-induced transition, respectively. The first of these transitions requires of more energetic photons to be observed, its maximum falls at 580 nm while for Prussian blue it is found at 670 nm. Prussian blue analogues are usually obtained as nanometric size particles and many of them have a microporous structure. The role of surface atoms on the observed charge transfer bands in the studied series of compounds is also discussed.

Postsynaptic antagonism by 4-aminopyridine of ketamine effect in frog (Hyla crepitans) neuromuscular junctions.

The action of ketamine (50 microM) and 4-aminopyridine (4-AP) (50 microM) on the frog (Hyla crepitans) neuromuscular junction using standard intracellular recording techniques was investigated. In our experiments the amplitude of evoked end plate potential was decreased by ketamine and increased by 4-AP, which is similar to the effects reported by other investigators. However, novel effects of the drugs on postsynaptic acetylcholine receptors were detected when miniature end plate potential (MEPP) amplitude and time-course were analyzed. The experiments were performed and registered in presence of 1% dimethylsulfoxide to augment frequency of MEPP's. When ketamine was added to the saline solution, MEPP amplitude control values were reduced from 226 (214, 240) microV (n = 529, median and its 95% confidence interval) to 140 (130, 151) microV (n = 143) by 50 microM ketamine. 4-AP alone also depressed MEPP amplitude to 129 (70, 152) microV (n = 91). The two drugs are partial antagonists, when they were applied together, MEPP amplitude was 180 (172, 188) microV (n = 207). The effect of ketamine on time course of MEPP's, expressed as time to peak, reduced the control values of 4.74 (4.61, 4.88) msec (n = 529) to 3.84 (3.72, 4.01) msec (n = 143) (P less than 0.001); the effect of 4-AP was to reduce the control values to 1.93 (1.79, 2.10) msec (n = 91). The time to peak after adding ketamine and 4-AP was 3.25 (3.12, 3.38) msec (n = 207), expressing an antagonistic effect of the drugs. All values are statistically distinct (P less than 0.001). Thus, our results show that a postsynaptic mechanism is responsible for a significant part of the antagonism of ketamine effects by 4-AP.