Synthesis, structural and physicochemical characterization of a new type Ti6-oxo cluster protected by a cyclic imide dioxime ligand

Reaction of the cyclic ligand (2Z,6Z)-piperidine-2,6-dione dioxime with TiCl4 and KOH yielded the hexanuclear cluster K6[TiIV6(μ3-O)2(μ2-O)3(CH3O)6(μ2–η1,η1,η2-Hpidiox-O,N,O′)4(μ2–η1,η1,η2-pidiox-O,N,O′)2]·7.5CH3OH possessing a new {Ti6O5} structural motif. The cluster core {Ti6O5} is wrapped by external tripodal imide dioxime ligands, showing good solubility and stability and thus, allowing its solution to be studied by means of electrospray ionization mass spectrometry, electrochemistry and 2D NMR, c. w. EPR and UV-vis spectroscopies. Density Functional Theory (DFT) calculations reveal that the cyclo-Ti3 metallic cores exhibit metallaromaticity which is expected to contribute to the stabilization of this system

Synthesis, structural and physicochemical characterization of a titanium(IV) compound with the hydroxamate ligand N,2-dihydroxybenzamide

The siderophore organic ligand N,2-dihydroxybenzamide (H2dihybe) incorporates the hydroxamate group, in addition to the phenoxy group in the ortho-position and reveals a very rich coordination chemistry with potential applications in medicine, materials, and physical sciences. The reaction of H2dihybe with TiCl4 in methyl alcohol and KOH yielded the tetranuclear titanium oxo-cluster (TOC) [TiIV4(μ-O)2(HOCH3)4(μ-Hdihybe)4(Hdihybe)4]Cl4∙10H2O∙12CH3OH (1). The titanium compound was characterized by single-crystal X-ray structure analysis, ESI-MS, 13C, and 1H NMR spectroscopy, solid-state and solution UV–Vis, IR vibrational, and luminescence spectroscopies and molecular orbital calculations. The inorganic core Ti4(μ-O)2 of 1 constitutes a rare structural motif for discrete TiIV4 oxo-clusters. High-resolution ESI-MS studies of 1 in methyl alcohol revealed the presence of isotopic distribution patterns which can be attributed to the tetranuclear clusters containing the inorganic core {Ti4(μ-O)2}. Solid-state IR spectroscopy of 1 showed the presence of an intense band at ~800 cm−1 which is absent in the spectrum of the H2dihybe and was attributed to the high-energy ν(Ti2–μ-O) stretching mode. The ν(C=O) in 1 is red-shifted by ~10 cm−1, while the ν(N-O) is blue-shifted by ~20 cm−1 in comparison to H2dihybe. Density Functional Theory (DFT) calculations reveal that in the experimental and theoretically predicted IR absorbance spectra of the ligand and Ti-complex, the main bands observed in the experimental spectra are also present in the calculated spectra supporting the proposed structural model. 1H and 13C NMR solution (CD3OD) studies of 1 reveal that it retains its integrity in CD3OD. The observed NMR changes upon addition of base to a CD3OD solution of 1, are due to an acid–base equilibrium and not a change in the TiIV coordination environment while the decrease in the complex’s lability is due to the improved electron-donating properties which arise from the ligand deprotonation. Luminescence spectroscopic studies of 1 in solution reveal a dual narrow luminescence at different excitation wavelengths. The TOC 1 exhibits a band-gap of 1.98 eV which renders it a promising candidate for photocatalytic investigations

Identification of Aggregation Processes in Hexamethylenetetramine Aqueous Solutions: A Comprehensive Raman and Acoustic Spectroscopic Study Combined with Density Functional Theory Calculations

Raman scattering has been employed to study in detail the concentration dependence of the vibrational modes for hexamethylenetetramine (HMTA) aqueous solutions. The formation of protonated and/or aggregated species has been clarified by comparing the experimental with the theoretically predicted vibrational spectra by means of quantum mechanical calculations. The analysis has shown that the vibrational modes of the solutions arise from a contribution of the vibrational modes of the HMTA self-aggregates and hetero-aggregates of HMTA with water molecules that are formed in the low- and intermediate-concentration regions, respectively. The protonation of HMTA is ruled out due to the large differences between the experimental and the theoretically calculated spectra of the protonated molecules of HTMA in the fingerprint region. In the low-concentration solutions, the hetero-aggregation reaction of HMTA with water is the dominant mechanism, while at higher concentrations, a self-aggregation mechanism occurs. Ultrasonic absorption and velocity measurements were carried out for hexamethylenetetramine aqueous solutions. The acoustic spectra reveal the presence of only one single Debye-type relaxation process that is assigned to the aggregation mechanism of HMTA. The sound absorption data follow two different dependencies on the HMTA mole fraction. The crossover 0.018 mole fraction signifies two separate regions with distinct structural characteristics. The relaxation mechanism observed in dilute solutions was attributed to hetero-association of HMTA with water molecules, while at higher concentrations, the observed relaxation process was assigned to the self-association reaction of HMTA molecules. This structural transformation is also reflected in several physicochemical properties of the system, including the kinematic viscosity, the mass density, the sound speed and the adiabatic compressibility of the HMTA aqueous solutions. The combination of vibrational and acoustic spectroscopies with molecular orbital calculations allowed us to disentangle the underlying processes and to elucidate the observed relaxation mechanism in the HMTA aqueous solutions

The Identification of Structural Changes in the Lithium Hexamethyldisilazide–Toluene System via Ultrasonic Relaxation Spectroscopy and Theoretical Calculations

Ultrasonic absorption measurements were carried out over a wide concentration and temperature range by means of a pulse technique to examine the structural mechanisms and the dynamical properties in lithium hexamethyldisilazide (LiHMDS)–toluene solutions. Acoustic spectra revealed two distinct Debye-type relaxational absorptions attributed to the formation of trimers from dimeric and monomer units and to the formation of aggregates between a LiHMDS dimer and one toluene molecule in low and high frequencies, respectively. The formation of aggregates was clarified by means of molecular docking and DFT methodologies. The aggregation number, the rate constants and the thermodynamic properties of these structural changes were determined by analyzing in detail the concentration-dependent relaxation parameters. The low-frequency relaxation mechanism dominates the acoustic spectra in the high LiHMDS mole fractions, while the high-frequency relaxation influences the spectra in the low LiHMDS mole fractions. In the intermediate mole fraction region (0.25 to 0.46), both relaxations prevail in the spectra. The adiabatic compressibility, the excess adiabatic compressibility and the theoretically estimated mean free length revealed a crossover in the 0.25 to 0.46 LiHMDS mole fractions that signified the transition from one structural mechanism related with the hetero-association of LiHMDS dimers with toluene molecules to the other structural mechanism assigned to the formation of LiHMDS trimers. The combined use of acoustic spectroscopy with theoretical calculations permitted us to disentangle the underlying structural mechanisms and evaluate the volume changes associated with each reaction. The results were compared with the corresponding theoretically predicted volume changes and discussed in the context of the concentration effect on intermolecular bonding

Raman spectra and microscopic dynamics of bulk and confined salol

In this paper we employ a new method, which enables one to calculate time correlation functions of vibrational relaxation by fits in the frequency domain, in the study of picosecond vibrational dynamics, that is, vibrational dephasing and vibrational frequency modulation. This method is applied to the molecular glass former salol in bulk, in a dilute CCl4 solution and in restricted geometries after confining it in nanoporous silica glasses of various pore sizes. The important finding is that the vibrational dynamics of the confined molecules becomes faster with decreasing the pore size. An attempt is made to rationalize this effect by invoking the cooperativity issue related to the sluggish dynamics as the glass transition is approached. The removal of many-body effects by trapping the molecules in less-crowded environments seems to be the key factor. The obtained results are described in the light of recent spectroscopic, X-ray diffraction and molecular dynamics studies performed on this liquid

Short-time dynamics of glass-forming liquids: Phenyl salicylate (salol) in bulk liquid, dilute solution, and confining geometries

Raman spectroscopy has been used to investigate picosecond vibrational dynamics of the molecular glass-former phenyl salicylate (salol). The study has concentrated on the elucidation and comparison of molecular dynamics of salol subjected to different local environments, namely in bulk, in a dilute CCl4 solution, and under spatial confinement in nanoporous sol-gel glasses. Contrary to most of the previous picosecond dynamics studies performed by means of Raman line profile analysis, we have employed in this paper a novel approach that enables the extraction of valuable short-time dynamics information through spectra fitting in the frequency domain. As a result, strongly overlapping vibrational lines can be put in focus. The analysis has shown a systematic dependence of vibrational relaxation on the local environment around a salol molecule. The magnitude of the vibrational relaxation time τV decreases in the sequence dilute solution-->bulk liquid-->confined liquid, indicating the modification of interactions when passing from the dilute solution to confined geometries. This fact has been rationalized by invoking the enhancement of the orientational order of salol molecules under spatial confinement. Similar conclusions can be drawn from the analysis of changes of the frequency modulation time τω upon confinement. The changes in second moments of vibrations as well as the observed blueshifts of the Raman peaks in confinement suggest the strengthening of repulsion between salol molecules in the restricted space. (C) 2003 American Institute of Physics

Thermal history of a low alkali borosilicate glass probed by infrared and Raman spectroscopy

Journal URL: http://www.ingentaconnect.com/content/sgt/gt; http://www.societyofglasstechnology.org.uk/cgi-bin/open.cgi?page=journal&sessionid=85597106; http://www.societyofglasstechnology.org.uk/cgi-bin/open.cgi?page=GlassTech/GT-00&sessionid=8559710

Synthesis, characterization and pharmacological evaluation of quinoline derivatives and their complexes with copper(ΙΙ) in in vitro cell models of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder of the central nervous system. The main pathophysiological mechanisms involve cholinergic neurotransmission, beta-amyloid (Αβ) and Tau proteins, several metal ions and oxidative stress, among others. Current drugs offer only relief of symptoms and not a cure of AD. Accumulating evidence suggests that multifunctional compounds, targeting multiple pathophysiological mechanisms, may have a great potential for the treatment of AD. In this study, we report on the synthesis and physicochemical characterization of four quinoline-based metal chelators and their respective copper(II) complexes. Most compounds were non-toxic at concentrations ≤5 μM. In neuroprotection studies employing undifferentiated and differentiated SH-SY5Y cells, the metal chelator N2,N6-di(quinolin-8-yl)pyridine-2,6-dicarboxamide (H2dqpyca) appeared to exert significant neuroprotection against both, Aβ peptide- and H2O2-induced toxicities. The copper(II) complex [CuII(H2bqch)Cl2].3H2O (H2bqch = N,N′-Bis(8-quinolyl)cyclohexane-1,2-diamine) also protected against H2O2-induced toxicity, with a half-maximal effective concentration of 80 nM. Molecular docking simulations, using the crystal structure of the acetylcholinesterase (AChE)-rivastigmine complex as a template, indicated a strong interaction of the metal chelator H2dqpyca, followed by H2bqch, with both the peripheral anionic site and the catalytic active site of AChE. In conclusion, the sufficient neuroprotection provided by the metal chelator H2dqpyca and the copper(II) complex [CuII(H2bqch)Cl2].3H2O along with the evidence for interaction between H2dqpyca and AChE, indicate that these compounds have the potential and should be further investigated in the framework of preclinical studies employing animal models of AD as candidate multifunctional lead compounds for the treatment of the disease