Spectroscopic and structural studies on metal halide complexes of 4-vinylpyridine

Fourier transform infrared spectra (4000–400 cm⁻¹) are reported for metal(II) halide 4-vinlypridine complexes of the following stoichiometries: [MX₂(4-vipy]_n (n=4, M=Ni, X=Cl or Br; n=2, M=Cd, X=Cl, Br or I) and assignment are given for all the observed bands. These spectra were compared with X-ray powder diffraction patterns of complexes. It is shown that the proposed structures for these complexes derived from FTIR spectra are consistent with the X-ray powder diffraction measurements and the elemental analysis results. Coordination effect on 4-vinylpyridine has also been investigated.     

Spectroscopic and structural investigations reveal the signaling mechanism of a luminescent molybdate sensor

A heteroditopic ligand H(2)-L consisting of a dihydroxybenzene (catechol)-unit linked via an amide bond to a pyridyl-unit and its methyl-protected precursor Me(2)-L were synthesized, characterized, and their photophysical properties investigated. The three accessible protonation states of the ligand, H(3)-L(+), H(2)-L, and H-L(-), showed distinct (1)H NMR, absorption and emission spectroscopic characteristics that allow pH-sensing. The spectroscopic signatures obtained act as a guide to understand the signaling mechanism of the luminescent pH and molybdate sensor [Re(bpy)(CO)(3)(H(2)-L)](+). It was found that upon deprotonation of the 2-hydroxy group of H(2)-L, a ligand-based absorption band emerges that overlaps with the Re(dπ)→bpy metal-to-ligand charge transfer (MLCT) band of the sensor, reducing the quantum yield for emission on excitation in the 370 nm region. In addition, deprotonation of the catechol-unit leads to quenching of the emission from the Re(dπ)→bpy (3)MLCT state, consistent with photoinduced electron transfer from the electron-rich, deprotonated catecholate to the Re-based luminophore. Finally, reaction of 2 equiv of [Re(bpy)(CO)(3)(H(2)-L)](+) with molybdate was shown to give the zwitterionic Mo(VI) complex [MoO(2){Re(CO)(3)(bpy)(L)}(2)], as confirmed by electrospray ionization (ESI) mass spectrometry and X-ray crystallography. The crystal structure determination revealed that two fully deprotonated sensor molecules are bound via their oxygen-donors to a cis-dioxo-MoO(2) center.     

Spiroleucettadine: synthetic studies and investigations towards structural revision

Synthetic efforts towards spiroleucettadine are described, including the enantioselective synthesis of the presumed biosynthetic precursor. High level density functional theory calculations were used to predict the ¹³C NMR shifts of possible alternative structures and, along with a re-evaluation of the available NMR data, allow the proposal of revised structures for this spirocyclic alkaloid.     

Spectroscopic structural studies of salicylic acid,salicylamide and aspirin

The electronic absorption spectra of the salicylic acid and the salicylamide molecules have been studied using SCF—CL calculations. The singlet and the triplet electronic transition energies have been calculated. The state functions of eight excited states for these molecules have been calculated in addition to the oscillator strengths, charge densities, ionization potentials and electron affinities. Our calculations lead to the presence of salicylic acid and salicylamide in the β-forms in which the carboxylic hydroxyl group or the amino group is directed toward the enolic hydroxyl group. The salicylic acid and the salicylamide molecules have the C_s point group symmetry, but the aspirin molecule has the C₁ point group symmetry, in which the acetyl group does not lie in the plane of the salicylic acid molecule.     

Spectroscopic studies on the irreversible heat-induced structural transition of Pin1

Previously, the mechanism of the thermal unfolding of Pin1 (on-line measurements) was studied, revealing that Pin1 has a relatively high thermal stability. However, it is still questionable whether the unfolding of Pin1 is reversible. In the present work, intrinsic tryptophan fluorescence, ANS fluorescence, RLS, FTIR and CD spectroscopies are used to evaluate the reversibility of the thermal unfolding of Pin1. Intrinsic tryptophan fluorescence studies indicate that structural changes around tryptophan motifs in Pin1 are possibly reversible after heat treatment (even above 98°C), for no significant change in the intensity or λ(max) of the spectra was observed. ANS fluorescence measurements indicate the irreversible exposure of the hydrophobic clusters in Pin1 after heat treatment at 98°C, with increase in the fluorescence intensity and blue shift in λmax. Also, RLS signals of the Pin1-ANS system increased after heat treatment, possibly implying both the unfolding and the aggregation of Pin1. In addition, FTIR and CD results confirmed the irreversible unfolding of the secondary structure in Pin1 after heat treatment above 90°C, showing decreases in both α-helix and β-sheet. In summary, the present work mainly suggests that heat treatment, especially above 90°C, has an important impact on the structural stability of Pin1, and the structural unfolding induced by heat was proved to be irreversible.     

Spectroscopic and structural studies on polyfluorophenyl tellurides and tellurium(IV) dihalides

Bis(fluorophenyl) tellurides R2Te (R = C6F2H3 (1), CF3C6F4 (2), CF3C6F4OC6F4 (3), and C6F5 (4)) are synthesized by the facile reaction of Na2Te with bromo-fluorobenzenes, RBr. The corresponding bis(fluorophenyl)tellurium(IV) dihalides, R2TeHal2 (Hal = F, Cl, and Br) (5-16), are obtained by the oxidation of 1-4 with mild halogenating agents (XeF2, SO2Cl2, and Br2). The dihalides show temperature-dependent NMR spectra. On the basis of the 19F NMR spectra of the two series, (C6F2H3)2TeHal2 (Hal = F (5), Cl (9), and Br (13)) and R2TeCl2 (R = C6F2H3 (9), CF3C6F4 (10), CF3C6F4OC6F4 (11), and C6F5 (12)), the coalescence temperatures, T(c), and free enthalpies, DeltaG, of rotation of the TeC bonds are determined. The activation enthalpies for the dichlorides/dibromide 9-13 are in the range of 14.4-15.2 kcal mol(-1) and that for the difluoride 5 is considerably lower at 10.7 kcal mol(-1). In addition to thorough spectroscopic characterization of 1-16, the crystal structures of the monotellurides 2 and 4 as well as of the tellurium(IV) dihalides 5, 6, 9, 10, and 13 were determined. The dihalides show interesting intermolecular Te...Hal contacts, significantly shorter than the sum of the van der Waals radii, leading to different networks of association.     

Spectroscopic and structural studies on dichlorobis(nicotinamide)zinc(II)

ZnCl₂(C₆H₆N₂O)₂ complex was prepared and investigated. The stoichiometry of this complex was derived from the results of elemental analysis and infrared spectroscopic studies. The crystal and molecular structure of the complex was also crystallographically characterized, to obtain a certain structure. The Zn(II) atom is coordinated by two chloride ligands and two N atoms from the nicotinamide ligands, in a distorted tetrahedral coordination environment, with Zn-N distances 2.058(3) and 2.057(4) Å, Zn-Cl distances of 2.221(1) and 2.209(1) Å and N-Zn-N and Cl-Zn-Cl angles of 101.8(1) and 121.81(5)°, respectively.     

Spectroscopic studies of structural changes in irradiated LDPE and its blends

The low temperature glass transition occurring at low temperature in polyethylene samples was studied using Fourier transform infrared, FT‐Raman spectroscopic techniques, which are known to be sensitive to any structural changes in the investigated samples. Anomalous behavior was obtained in the temperature range (98 K → 383 K) indicating the existence of phase transition occurring at about 98 K and disappearing at about 323 K while heating for unirradiated virgin low density polyethylene (VPE) sample with or without crosslinking agent (trimethylol propane triacrylate, TMPTA). Addition of TMPTA monomer caused severe changes in the temperature dependence of both unirradiated and irradiated polyethylene samples. The results given indicated the occurrence of abnormal temperature dependence, which is thought to be related with low temperature structural change resulting from local crosslinking in scrapped polyethylene (SPE) sample already suffering from high degree of crosslinking. Differential scanning calorimetry (DSC) thermograms confirmed the observed new phase transition observed in both unirradiated and irradiated TMPTA loaded VPE/SPE (50/50 wt %) blend. Irradiation, addition of TMPTA as a crosslinking agent, and blending VPE with SPE were found to affect remarkably the variation of the vibration spectrum of LDPE and consequently the resulting structural changes. The experimental results obtained were discussed and correlated with reorientational disorders of the molecular segments (local crosslinking). © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 850–859, 2007     

Thermochemical and structural investigations

The phase diagrams of the systems ABr/SmBr₃ were reinvestigated. The findings of Blachnik for the systems withA=Cs, Rb, K were confirmed; however, the dimorphic compound K₃SmBr₆ is stable only above 572 K. The equilibrium temperature, found bye.m.f.-measurements in a solid state galvanic cell for the reaction KBr+K₂SmBr₅=L-K₃SmBr₆, is smaller (522 K). The formation temperature for Rb₃SmBr₆ is 279 K (DTA) and 256 K (e.m.f.) resp. By solution calorimetry was proved that the compounds Cs₂SmBr₅ and KSm₂Br₇ don't exist at 0 K. In the system NaBr/SmBr₃ only one hitherto unknown dimorphic compound Na₃SmBr₃ exists above 473 K. L-Na₃SmBr crystallizes in the hexagonal space groupR¯3, above 519 K H-Na₃SmBr₆ has the monoclinic cryolite-structure. Powder patterns of other compounds not yet investigated — H-/L-A₃ SmBr₆, ASm₂Br₇ (A=Cs, Rb, K) and Cs₂SmBr₅ — were indexed analogously to known structure families. The structure parameters of SmBr₃·6H₂O were determined by single-crystal measurements.This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industry. Michael Alsmann is grateful for a grant of the University Gh Kassel.     

Novel synthetic aromatic thiourea derivatives and investigations on their cytotoxic potential efficacy

Aromatic thiourea derivatives were synthesized by standard reactions from isothiocyanates in high yield. An efficient one-pot synthesis of primary amine with carbon disulfide involving the intermediate dithiocarbamate conversion using T₃P (propane phosphonic anhydride) to isothiocyanate is reported. Newly synthesized compounds showed excellent luminescence property. Cytotoxic investigation with different human cancer cell lines showed IC₅₀ values varying from of 17 to 40 μM for N-phenethyl-3,4-dihydroisoquinoline-2(1H)-carbothioamide (SCR172) among other molecules. Increase in Sub G1 population and increased depolarisation of mitochondria were evident in cells treated with SCR172, suggesting its role as a cancer therapeutic agent. This provides a lead structure for further synthetic modifications.     

Spectroscopic investigations of solvent effect on chiral interactions

The spectrophotometric method was used to determine the mechanism of chiral interactions between a known chiral selector, tert-butyl carbamoylated quinine (t-BuCQN), and N-derivative amino acids (DNB-Leu). Results obtained on binding constants, free energy of binding (DeltaG), and difference in free energy of binding (DeltaDeltaG) values seem to suggest that there are three possible types of interactions between DNB-Leu and t-BuCQN: electrostatic interaction between the carboxylate group of the DNB-Leu and the ammonium group of the t-BuCQN, the donor-acceptor charge-transfer type of interaction between the (acceptor) aromatic group of the amino acid and the (donor) aromatic group of the t-BuCQN, and the hydrogen-bonding interaction between the amide group of the DNB-Leu and the carbonyl group of t-BuCQN. The strongest interaction will be observed if all of three interactions are in operation as in the case of DNB-Leu. The electrostatic interaction seems to play the dominant role in the interactions. While the charge-transfer interaction is relatively weaker, it seems, however, to be responsible for enantiomeric selectivity, namely, the closer the electron acceptor dinitrophenyl group is to the electron donor quinoline group, the higher is the enantiomeric selectivity. Specifically, in solvent with high polarity, both donor and acceptor are solvated by solvent molecules, thereby preventing them from being close. As a consequence, the interaction will be weaker and, hence, lower enantiomeric selectivity. Solvation will be less in less polar solvent which, in turn, leads to stronger interaction and higher enantiomeric selectivity.     

Spectroscopic investigations of ThF and ThF+

The electronic spectra of ThF and ThF(+) have been examined using laser induced fluorescence and resonant two-photon ionization techniques. The results from high-level ab initio calculations have been used to guide the assignment of these data. Spectra for ThF show that the molecule has an X (2)Δ(3/2) ground state. The upper spin-orbit component, X (2)Δ(5/2) was found at an energy of 2575(15) cm(-1). The low-lying states of ThF(+) were probed using dispersed fluorescence and pulsed field ionization-zero kinetic energy (PFI-ZEKE) photoelectron spectroscopy. Vibronic progressions belonging to four electronic states were identified. The lowest energy states were clearly (1)Σ(+) and (3)Δ(1). Although the energy ordering could not be rigorously determined, the evidence favors assignment of (1)Σ(+) as the ground state. The (3)Δ(1) state, of interest for investigation of the electron electric dipole moment, is just 315.0(5) cm(-1) above the ground state. The PFI-ZEKE measurements for ThF yielded an ionization energy of 51 581(3) cm(-1). Molecular constants show that the vibrational constant increases and the bond length shortens on ionization. This is consistent with removal of a non-bonding Th-centered 6d or 7s electron. Laser excitation of ThF(+) was used to probe electronically excited states in the range of 19,000-21,500 cm(-1).     

Spectroscopic studies on caffeine and isocaffeine

UV and NMR spectra of caffeine and Isocaffeine were measured in three solvents of different polarity. The Information so obtained revealed unique differences in the electronic structure of 7- and 9- alkyl substituted xanthines. 9-Methyl derivatives bear a “soft” nitrogen at position 3; in 7-methylxanthines this nitrogen is rather “hard”. This characteristic distinction is explained on the basis of orbital interactions, which are also responsible for self-association. In the process of self-association. isocaffeine and caffeine share a hydrophobic effect, but in caffeine water bridges play a decisive rote in molecular aggregation. In contrast, in isocaffeine high polarisability makes the most important contribution to self-association. Steric interference between 3- and 9-alkyl substituents or between a 9-methy1 and a 3-NH group, proposed earlier, does not explain satisfactorily the properties of these xanthines.     

Spectroscopic investigations on II–VI-semiconductor nanocrystals and their assemblies

This review points out that (magneto-)optical measurements may help to shine light on the recombination processes taking place in semiconductor nanocrystals. The surface capping with thiols creates a CdS shell around CdTe cores and forms a Cd site that is not fourfold-coordinated at the surface. It is pointed out how specific cappings such as thio-amines and thio-acids assist in coupling NCs and how we may distinguish between NC–NC interactions via electrostatic and covalent linking with the aid of the optical measurements. Furthermore, with static and time-resolved ODMR studies on IR-active core-shell HgTe/Hg _x Cd_1−x Te(S) particles it is demonstrated how the nature of the recombination emission being associated with a Cd–Hg mixed site is elucidated and by this yielding structural information on the NC core-shell interface. With these examples we show that and how nanomaterials of probable technological interest are studied beneficially with advanced spectroscopic techniques.     

Spectroscopic investigations on Naphthol and Tetrahydronaphthol. A theoretical approach

The computational efficiencies of the semi-empirical method have been compared with those of different ab-initio methods for positional isomers of Naphthol and Tetrahydro-naphthol type molecules. The efficiencies for computations in case of optimized structure, electronic absorption and emission properties are investigated. For that semi-empirical approach ZINDO and two different nature of ab-initio approaches such as TD-HF/6-311G(d,p) and TD-DFT/B3LYP/6-311G(d,p) were considered. The three main approaches are studied here to give the right direction of simulation. Semi-empirical AM1/ZINDO function itself can detect the trend of molecular transitions and the values obtained by simulations are more realistic than ab-initio methods. Ab-initio methods can reproduce exact values of first transitional energy with some scaling factor both in ground and in excited states of Tetrahydro-naphthol positional isomers whereas no solution or prediction could be inferred for Naphthol isomers.     

Spectroscopic investigations of polyacrylonitrile thermal degradation

PAN undergoes chemical decomposition in stages on thermal treatment. In the literature, several mechanisms were proposed for the degradation process. However, the decomposition pathway and the structural rearrangement of solid residue in relation to the loss of volatile products are not fully understood. The degradation process has therefore received further attention in this work by employing a combination of FT-IR, high-resolution solid-state ¹³C-NMR, pyrolysis GC-MS, and microelemental analysis. These investigations have established that PAN decomposes to gaseous and volatile products over a range of temperatures (150–590°C) with concurrent stabilization of the structure of residual matter occurring on a parallel course. While linear polymerization of nitrile group is the principal reaction in the decomposition process, cyclization followed by extended conjugation is the notable exothermic process. No evidence has been obtained for the formation of oxygen-containing chromophores either as intermediates or as part of the chemical structure of the residue. Temperature sensitivity of oligomer formation has been established through pyrolysis–GC-MS studies. The overall decomposition profile of PAN has thus been established. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2503–2512, 1998     

Spectroscopic,structural, electrochemical,and cytotoxicity studies on dithiocarbamato-chelated ruthenium organometallics incorporating imine-phenol function

The heterogeneous phase reaction of [Ru(η²-RL)(PPh₃)₂(CO)Cl] (1) with the sodium salts of dimethyl dithiocarbamate (^MeDTC), diethyl dithiocarbamate (^EtDTC), and pyrrolidine dithiocarbamate (^PyrDTC) ligands led to the isolation of bright-yellow crystalline solids of type [Ru(η¹-RL)(PPh₃)₂(CO)(^R′DTC)] (2(R)(^R′DTC)) where η²-RL is C₆H₂O-2-CHNHC₆H₄R(p)-3-Me-5, η¹-RL is C₆H₂OH-2-CHNC₆H₄R(p)-3-Me-5, R is Me, OMe, Cl, and R^′ = Me, Et, Pyr. The binding of dithiocarbamate ligand is accompanied by the dissociation of Ru-O and Ru-Cl bonds along with concomitant prototropic shift from iminium–phenolato to imine–phenol motif. The reaction also involves a sterically controlled change in rotational conformation in going to the products. The X-ray crystal structure of [Ru(η¹-ClL)(PPh₃)₂(CO)(^EtDTC)] (2(Cl)(^EtDTC)) has been described here. An account of different spectral (UV–Vis, IR, NMR) and electrochemical data of the complexes are also asserted. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) analyses were performed to scrutinize the electronic structure and the absorption spectra of the complexes. One of the dithiocarbamato complexes has also been found to have in vitro antiproliferative properties against MDA-MB-231 breast cancer cell line which was determined by MTT assay. Cell death occurs mainly through apoptosis and flow cytometric analysis indicates that the complex induces cell cycle arrest in the sub G0/G1 phase.