The Increased Release Kinetics of Quercetin from Superparamagnetic Nanocarriers in Dialysis.

The actual cumulative mass of released quercetin from nanoparticles within the dialysis membrane was determined under the influence of external stationary and alternating magnetic fields. We have shown that the control of the release kinetics of quercetin from MNPs, i.e., the distribution of quercetin between the nanoparticles and the suspension within the membrane, can be tuned by the simple combination of stationary and alternating magnetic fields. Under non-sink conditions, the proportion of quercetin in the suspension inside the membrane is increased toward the nanoparticles, resulting in the increased release of quercetin. The results obtained could be applied to the release of insoluble flavonoids in aqueous suspensions in general.

The Fine-Tuned Release of Antioxidant from Superparamagnetic Nanocarriers under the Combination of Stationary and Alternating Magnetic Fields.

Superparamagnetic magnetite nanoparticles (MNPs) with excellent biocompatibility and negligible toxicity were prepared by solvothermal method and stabilized by widely used and biocompatible polymer poly(ethylene glycol) PEG-4000 Da. The unique properties of the synthesized MNPs enable them to host the unstable and water-insoluble quercetin as well as deliver and localize quercetin directly to the desired site. The chemical and physical properties were validated by X-ray powder diffraction (XRPD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), superconducting quantum interference device (SQUID) magnetometer, FTIR spectroscopy and dynamic light scattering (DLS). The kinetics of in vitro quercetin release from MNPs followed by UV/VIS spectroscopy was controlled by employing combined stationary and alternating magnetic fields. The obtained results have shown an increased response of quercetin from superparamagnetic MNPs under a lower stationary magnetic field and s higher frequency of alternating magnetic field. The achieved findings suggested that we designed promising targeted quercetin delivery with fine-tuning drug release from magnetic MNPs.

Flavonol clustering in model lipid membranes: DSC, AFM, force spectroscopy and MD simulations study.

We here report on flavonols (myricetin (MCE) and its glycoside myricitrin (MCI)) - 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) membrane interactions focusing on the effects of flavonol clustering on the membrane thermotropic and nanomechanical properties. Atomic force microscopy (AFM), force spectroscopy (FS) and differential scanning calorimetry (DSC) together with molecular dynamics (MD) simulations provided a consistent picture of flavonol - DMPC membrane interactions. DMPC membrane as a supported lipid bilayer preserved its integrity even at higher flavonol molar fraction x. When present at x = 0.1 - 0.3, MCE and MCI both slightly improve DMPC bilayer fluidity which is evidenced by the decrease in the main phase transition temperature Tm. MCE is found within the interior of the bilayer, while MCI incorporates in the head group-water interface region. AFM and FS confirmed clusters as protrusions with an average height of 0.012 µm and average diameters of 0.60 and 0.24 µm for MCE and MCI clusters, respectively. The average membrane thickness in DMPC fluid phase decreases for 7% at xMCE = 0.30, while only 4% at xMCI = 0.27. The induced membrane changes are dependent on the chemical and physical properties of inserted flavonols. The hypothesis regarding the tendency of flavonol to clustering in membranes by increasing flavonol molar fraction has been confirmed.

The Structural Integrity of the Model Lipid Membrane during Induced Lipid Peroxidation: The Role of Flavonols in the Inhibition of Lipid Peroxidation.

The structural integrity, elasticity, and fluidity of lipid membranes are critical for cellular activities such as communication between cells, exocytosis, and endocytosis. Unsaturated lipids, the main components of biological membranes, are particularly susceptible to the oxidative attack of reactive oxygen species. The peroxidation of unsaturated lipids, in our case 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), induces the structural reorganization of the membrane. We have employed a multi-technique approach to analyze typical properties of lipid bilayers, i.e., roughness, thickness, elasticity, and fluidity. We compared the alteration of the membrane properties upon initiated lipid peroxidation and examined the ability of flavonols, namely quercetin (QUE), myricetin (MCE), and myricitrin (MCI) at different molar fractions, to inhibit this change. Using Mass Spectrometry (MS) and Fourier Transform Infrared Spectroscopy (FTIR), we identified various carbonyl products and examined the extent of the reaction. From Atomic Force Microscopy (AFM), Force Spectroscopy (FS), Small Angle X-Ray Scattering (SAXS), and Electron Paramagnetic Resonance (EPR) experiments, we concluded that the membranes with inserted flavonols exhibit resistance against the structural changes induced by the oxidative attack, which is a finding with multiple biological implications. Our approach reveals the interplay between the flavonol molecular structure and the crucial membrane properties under oxidative attack and provides insight into the pathophysiology of cellular oxidative injury.

Comparative study of the effects of ortho-, meta- and para-carboranes (C2B10H12) on the physicochemical properties, cytotoxicity and antiviral activity of uridine and 2'-deoxyuridine boron cluster conjugates.

In this study, a series of uridine (U) and 2'-deoxyuridine (dU) conjugates containing an isomeric ortho-, meta- or para-carborane cluster (C2B10H12) attached at C-5 through an ethynyl linker were synthesized. The effect of carborane cluster isomerism on the conjugate syn/anti conformation, molar extinction coefficient, lipophilicity, susceptibility to phosphorylation (by TK1, TK2 and dCK), cytotoxicity and antiviral activity was evaluated. A strong effect of the boron cluster modification on the syn/anti equilibrium of the modified nucleosides was observed. An increase in lipophilicity compared with unmodified U and dU, especially for conjugates bearing a para-carborane cluster, was detected. Furthermore a pronounced and differential influence of the boron cluster modification on the electronic properties of the nucleobase chromophore was observed. The obtained conjugates have low or medium toxicity toward several cell lines, are phosphorylated fairly well by TK1 and are poor or not substrates for dCK. Furthermore, the conjugates preferentially inhibit HCMV replication with an SI index as high as 22 for the ortho-carborane derivative of U and more than 180 for the para-carborane derivative of dU.

Enhanced Protection of Biological Membranes during Lipid Peroxidation: Study of the Interactions between Flavonoid Loaded Mesoporous Silica Nanoparticles and Model Cell Membranes.

Flavonoids, polyphenols with anti-oxidative activity have high potential as novel therapeutics for neurodegenerative disease, but their applicability is rendered by their poor water solubility and chemical instability under physiological conditions. In this study, this is overcome by delivering flavonoids to model cell membranes (unsaturated DOPC) using prepared and characterized biodegradable mesoporous silica nanoparticles, MSNs. Quercetin, myricetin and myricitrin have been investigated in order to determine the relationship between flavonoid structure and protective activity towards oxidative stress, i.e., lipid peroxidation induced by the addition of hydrogen peroxide and/or Cu2+ ions. Among investigated flavonoids, quercetin showed the most enhanced and prolonged protective anti-oxidative activity. The nanomechanical (Young modulus) measurement of the MSNs treated DOPC membranes during lipid peroxidation confirmed attenuated membrane damage. By applying a combination of experimental techniques (atomic force microscopy-AFM, force spectroscopy, electrophoretic light scattering-ES and dynamic light scattering-DLS), this work generated detailed knowledge about the effects of flavonoid loaded MSNs on the elasticity of model membranes, especially under oxidative stress conditions. Results from this study will pave the way towards the development of innovative and improved markers for oxidative stress-associated neurological disorders. In addition, the obtained could be extended to designing effective delivery systems of other high potential bioactive molecules with an aim to improve human health in general.

Neurotoxic Effect of Ethanolic Extract of Propolis in the Presence of Copper Ions is Mediated through Enhanced Production of ROS and Stimulation of caspase-3/7 Activity.

Elevated amounts of copper are considered to be contributing factor in the progression of neurodegenerative diseases as they promote oxidative stress conditions. The aim of our study was to examine the effects of ethanolic extract of propolis (EEP) against copper-induced neuronal damage. In cultured P19 neuronal cells, EEP exacerbated copper-provoked neuronal cell death by increasing the generation of reactive oxygen species (ROS) and through the activation of caspase-3/7 activity. EEP augmented copper-induced up-regulation of p53 and Bax mRNA expressions. Neurotoxic effects of EEP were accompanied by a strong induction of glyceraldehyde 3-phosphate dehydrogenase (GAPDH) expression and decrease in the expression of c-fos mRNA. SB203580, an inhibitor of p38 mitogen-activated protein kinase (MAPK) prevented detrimental effects of EEP, whereas SP600125, an inhibitor of c-Jun N-terminal kinase (JNK), exacerbated EEP-induced neuronal cell death. Quercetin, a polyphenolic nutraceutical, which is usually present in propolis, was also able to exacerbate copper-induced neuronal death. Our data indicates a pro-oxidative and apoptotic mode of EEP action in the presence of excess copper, wherein ROS/p53/p38 interactions play an important role in death cascades. Our study also pointed out that detailed pharmacological and toxicological studies must be carried out for propolis and other dietary supplements in order to fully recognize the potential adverse effects in specific conditions.

Infrared spectroscopy of flavones and flavonols. Reexamination of the hydroxyl and carbonyl vibrations in relation to the interactions of flavonoids with membrane lipids.

Detailed vibrational assignments for twelve flavonoids (seven flavones (flavone, 3- and 5-hydroxyflavone, chrysin, apigenin, fisetin and luteolin) and five flavonols (galangin, kaempferol, quercetin, morin and myricetin)) have been made based on own and reported experimental data and calculations at the B3LYP/6-31+G(d,p) level of theory. All the molecules are treated in a uniform way by using the same set of redundancy-free set of internal coordinates. A generalized harmonic mode mixing is used to corroborate the vibrational characteristics of this important class of molecules. Each flavonoid molecule can be treated from the vibrational point of view as made of relatively weakly coupled chromone and phenyl part. It has been shown that the strongest band around 1600cm-1 need not be attributable to the CO stretching. The way the vibrations of any of the hydroxyl groups are mixed with ring vibrations and vibrations of other neighboring hydroxyl groups is rather involved. This imposes severe limitations on any attempt to describe normal modes of a flavonol in terms of hydroxyl or carbonyl group vibrations. The role of water molecules in the appearance of flavonoid IR spectra is emphasized. Knowing for the great affinity of phosphate groups in lipids towards water, the immediate consequence is a reasonable assumption that flavonoid lipid interactions is mediated by water.

Refractive Index Mixing Rules and Excess Infrared Spectra of Binary Mixtures.

Three refractive index mixing rules, Arago-Biot, Lorentz-Lorenz, and Newton, are generalized to complex refractive index and used to define infrared (IR) spectra of the corresponding ideal liquid mixtures. Using the measured optical constants n and k for acetonitrile-water mixtures (Bertie and Lan, 1997) the excess absorbances, AE = Aobs - Aideal, are calculated. Relying upon the well-established properties of the acetonitrile-water mixtures, the interpretation of the excess absorbances is established that is essentially based on the understanding of a liquid as a set of oscillators. The set depends on the composition of the mixture and comprises oscillators as present in the pure components and oscillators perturbed by hydrogen bonding between unlike molecules. The main features of an excess spectrum can be established assuming chemical equilibria among various oscillators. The most informative parts of the spectrum of a yet unstudied binary system can well be observed and even qualitatively explained from the excess absorbance provided: first, a detailed vibrational study of the components has been done; and, second, it is well understood what actually is subtracted from Aobs. As examples, the binary mixtures of ethynylbenzene and tetrachloroethylene and 2-ethynylpyridine and tetrachloroethylene are considered.

Ligand-Dependent Nanoparticle Clustering within Lipid Membranes Induced by Surrounding Medium.

The interactions between hydrophobic or semihydrophobic gold and silver nanoparticles (NPs) and a dimyristoylphosphatidylcholine (DMPC) bilayer as a model cell membrane in two ionic solutions result in the structural reorganization within the bilayer manifested as locally increased nanomechanical compaction in the vicinity of NP clusters as well as changed overall thermotropic properties. The effects of NP surface charge and hydrophobicity were examined using AFM imaging, force spectroscopy and IR spectroscopy. The NP clustering occurred during hydration process of dry films containing both the DMPC molecules and the NPs by the mechanism in which the number of bilayer deformations was reduced by NP clustering. The force spectroscopy showed increased bilayer density around (semi)hydrophobic NP clusters and thus locally increased lateral compaction of the bilayer. The strengthening effect was observed for both the silver and the gold NPs in a high ionic strength solution such as seawater, while it was absent under physiological conditions. The local lipid rearrangement induces the long-range lipid reorganization resulting in the bilayer phase transition shifting toward lower or higher temperatures depending on the solution ionic strength (at the most by -1.0 °C in phosphate buffered saline and at the most by +0.5 °C in seawater).

Ionic strength and composition govern the elasticity of biological membranes. A study of model DMPC bilayers by force- and transmission IR spectroscopy.

Infrared (IR) spectroscopy was used to quantify the ion mixture effect of seawater (SW), particularly the contribution of Mg(2+) and Ca(2+) as dominant divalent cations, on the thermotropic phase behaviour of 1,2-dimyristoyl-sn-glycero-3-posphocholine (DMPC) bilayers. The changed character of the main transition at 24 °C from sharp to gradual in films and the 1 °C shift of the main transition temperature in dispersions reflect the interactions of lipid headgroups with the ions in SW. Force spectroscopy was used to quantify the nanomechanical hardness of a DMPC supported lipid bilayer (SLB). Considering the electrostatic and ion binding equilibrium contributions while systematically probing the SLB in various salt solutions, we showed that ionic strength had a decisive influence on its nanomechanics. The mechanical hardness of DMPC SLBs in the liquid crystalline phase linearly increases with the increasing fraction of all ion-bound lipids in a series of monovalent salt solutions. It also linearly increases in the gel phase but almost three times faster (the corresponding slopes are 4.9 nN/100 mM and 13.32 nN/100 mM, respectively). We also showed that in the presence of divalent ions (Ca(2+) and Mg(2+)) the bilayer mechanical hardness was unproportionally increased, and that was accompanied with the decrease of Na(+) ion and increase of Cl(-) ion bound lipids. The underlying process is a cooperative and competitive ion binding in both the gel and the liquid crystalline phase. Bilayer hardness thus turned out to be very sensitive to ionic strength as well as to ionic composition of the surrounding medium. In particular, the indicated correlation helped us to emphasize the colligative properties of SW as a naturally occurring complex ion mixture.

Experimental and theoretical study of the cation binding properties of macrocyclic dehydrodibenzopyrido[15]annulenes.

The UV/Vis titration measurements, vibrational and NMR spectroscopy of isomeric dehydrodibenzopyrido[15]annulenes (DBPA) 1 and 2 clearly show that under proper conditions these macrocycles can achieve fast, quantitative and unselective binding of metal ions. The macrocycle 1 is an example of a hindered amine 2,6-bis(R)pyridine and its isomer 2 of a non-hindered amine 3,5-bis(R)pyridine. The protonation stoichiometry for both 1 and 2 was assumed to be DBPA:H(+)=1:1 and the formation constants logK=4.77±0.02 for 1, and logK=6.78±0.08 for 2 were obtained that well agree with those obtained under similar conditions for a macrocycle containing bipyridine units. The protonation of 2 gave the estimated stoichiometry of 2:H(+)=1:1 while the stoichiometric protonation of macrocycle 1 could not be achieved and the lower stability of the ion pair containing 1H(+) is most likely due to the inaccessibility of the nitrogen atom of 1 to the counterions and solvent molecules. The structures and electronic absorption spectra of 1 and 2, as well as the structures and spectra of 1H(+) and 2H(+), i.e. the species formed by protonation of the pyridine nitrogen, were calculated with the time-dependent DFT method with a B3LYP functional and a 6-31+G(d) basis set. The solvent effects were incorporated by means of the polarizable continuum model (PCM). The agreement of the calculated absorption data for the parent and protonated species with the observed spectra is rather satisfactory. Vibrational IR and Raman spectra of 1, 2, 1H(+) and 2H(+) in vacuo were calculated at the B3LYP/cc-pVTZ level of theory. Macrocycles 1 and 2, and their products protonated by trifluoromethanesulfonic acid (1HOTf and 2HOTf) were also characterized by temperature-dependent FTIR technique known as two dimensional IR correlation analysis. Quite large difference in degradation temperature between macrocycle 1 and 2 and their protonated complexes was measured, indicating that inclusion of proton leads to significant thermal stabilization of dehydroannulene ring.

The study of secondary effects in vibrational and hydrogen bonding properties of 2- and 3-ethynylpyridine and ethynylbenzene by IR spectroscopy.

Weak hydrogen bonds formed by 2- and 3-ethynylpyridine and ethynylbenzene with trimethylphosphate and phenol were characterized by IR spectroscopy and DFT calculations (B3LYP/6-311++G(d, p)). The structure and stability of ethynylpyridines and ethynylbenzene in the gas phase and in the complexes with trimethylphosphate and phenol are discussed in terms of geometry and electronic charge redistribution. Anharmonic effects are taken into account when calculating vibrational wavenumbers of these systems what lead to partial improvement of agreement with experiment. The changes in the electronic charge distribution are behind the frequency shifts of the CC stretching in opposite direction depending on the role the ethyne molecule has in a hydrogen bonded complex (Δν̃=+9 cm(-1) in trimethylphosphate complexes, Δν̃=-3 cm(-1) in phenol complexes). The association constants were determined by keeping the concentrations of proton donors approximately constant and low enough to avoid self-association and the proton acceptors were present in excess. The values obtained for the association constants and enthalpy changes in C2Cl4 (for trimethylphosphate complexes K≈0.5-1.0 mol(-1)dm(3) and -ΔrH≈6-8 kJ mol(-1), for phenol complexes K≈20-40 mol(-1) dm3-ΔrH≈17-22 kJ mol(-1)) are in good agreement with literature data.

Intramolecular resonance-assisted hydrogen bonds: a theoretical description by means of atomic charges and charge fluxes.

The characterization of intramolecular H-bonds in terms of atomic charges and charge fluxes (at the B3LYP/cc-pVTZ level of theory) has been extended to the case of the so called resonance-assisted (RA) H-bonds. A quadratic correlation between the charge fluxes φH and the molecular IR absorption coefficients E that includes the entire family of the studied systems (31 of them) containing both intra- and intermolecular hydrogen bonds (O-H···O/N) confirmed the critical importance of the charge fluxes on the IR intensity enhancements. Since they reflect changing of the atomic charge distribution during the normal modes of vibrations, the dynamic nature of hydrogen bonding properties has been re-emphasized. The changes of the charge flux of the hydroxyl hydrogen in an RA intramolecular H-bond are between those for "free" OH bonds and the values calculated for intermolecular H-bonds. The transition "free"→intramolecular→intermolecular is gradual and therefore the hydrogen charge flux can be considered as practically sufficient to give quantitative measure to the intuitively obvious statement that "intramolecular H-bonding is somehow in between no H-bonding situation and intermolecular H-bonding" and thus provide a quantitative and yet simple parameterization of H-bond strength. In strictly planar molecules, the difference of the sums of charges of atoms participating in the 6-membered H-bond ring ΔΣ can serve as a measure of the charge delocalization after the H-bond is formed. The electronic charge is withdrawn from the group of six atoms when the H-bond is formed in nitrophenol (ΔΣ=-0.07), while the opposite is true (ΔΣ=+0.03) for 2-hydroxy benzylidene amine. The corresponding values of the geometrical resonance parameter Δ are 0.39 and 0.37, respectively, similar to those found for 2-hydroxy acetophenone and 2-hydroxy benzaldehyde. The extent of the π-electron delocalization as measured by the resonance parameter Δ does not follow the strength of H-bond as measured by the charge flux φH.

Characterization of intramolecular hydrogen bonds by atomic charges and charge fluxes.

The electronic charge redistribution and the infrared intensities of the two types of intramolecular hydrogen bonds, O-H···O and O-H···π, of o-hydroxy- and o-ethynylphenol, respectively, together with a set of related intermolecular hydrogen bond complexes are described in terms of atomic charges and charge fluxes derived from atomic polar tensors calculated at the B3LYP/cc-pVTZ level of theory. The polarizable continuum model shows that both the atomic charges and charge fluxes are strongly dependent on solvent. It is shown that their values for the OH bond in an intramolecular hydrogen bond are not much different from those for the "free" OH bond, but the changes are toward the values found for an intermolecular hydrogen bond. The intermolecular hydrogen bond is characterized not only by the decreased atomic charge but also by the enlarged charge flux term of the same sign producing thus an enormous increase in IR intensity. The overall behavior of the charges and fluxes of the hydrogen atom in OH and ≡CH bonds agree well with the observed spectroscopic characteristics of inter- and intramolecular hydrogen bonding. The main reason for the differences between the two types of the hydrogen bond lies in the molecular structure because favorable linear proton donor-acceptor arrangement is not possible to achieve within a small molecule. The calculated intensities (in vacuo and in polarizable continuum) are only in qualitative agreement with the measured data.

Thermal analysis of paracetamol polymorphs by FT-IR spectroscopies.

A simple IR spectroscopy based methodology in routine screening studies of polymorphism is proposed. Reflectance and transmittance temperature-dependent IR measurements (coupled with the 2D-IR data presentation and the baseline analysis) offer a positive identification of each polymorphic phase, therefore allowing simple and rapid monitoring of the measured system. Applicability and flexibility of the methodology was demonstrated on the measurement of the model polymorphic compound paracetamol under various conditions (including geometric constraints and elevated pressure). The thermal behavior of paracetamol strongly depends on slight variations in experimental conditions that can result in formation of various phases (three polymorphs and the amorphous form). The amorphous phase can crystallize during heating into either Form II or Form III within almost identical temperature range. Likewise, the crystal transformations II→I and III→II also can proceed within almost identical temperature range. Furthermore, the thermal behavior is even more diverse than that, and includes the crystallizations of Forms I, II and III from the melt, and the high temperature II→I transition. The variety of the temperatures of the transformations is a major obstacle for unambiguous identification of a particular phase by DSC and a major reason for the implementation of these IR methods.

Determination of phase transition temperatures by the analysis of baseline variations in transmittance infrared spectroscopy.

A simple method for obtaining phase transition temperatures is proposed. It is based on absolute variations of a baseline in a temperature-dependent mid-infrared transmittance spectral data set recorded for a sample KBr pellet. The method is rapid, inexpensive, and completely free of any personal bias. The method efficiency was corroborated by measuring the phase transitions of mesomorphic (trans-4-heptyl cyclohexanecarboxylic acid) and polymorphic compounds (polycyclic aromatic hydrocarbons and phenylacetylenes). In addition, the exothermic decomposition of phenylacetylenes was also monitored, thereby opening the possibility for simple and rapid monitoring of chemical reactions in solid and liquid phase. A great prospect of the method as an economical way of establishing critical temperature regions for analytical and quality control purposes is foreseen.

Hydrogen bonding in 1,1'-Bi-2-naphthol within the polarizable continuum model.

Intra- and intermolecular hydrogen bonding of 1,1'-bi-2-naphthol in a series of solvents and in solid phase has been investigated by means of mid-IR spectroscopy and DFT reaction field calculations. The polarizable continuum model has been used to estimate the relative stability of isomers differing in the positions of the hydroxyl groups. The height of the potential barriers between them was also calculated and the corresponding transition states characterized. In hydrogen bond nonaccepting solvents, the isomer preference does not change relative to the gas phase, although the less stable isomers are more probable in solvents of higher relative permittivity. In hydrogen bond forming solvents, the least stable isomer is most probably prevalent due to the additional stabilization through intermolecular hydrogen bonds with solvent molecules. A detailed vibrational analysis revealed the spectral regions specific to the OH vibrations with the observed solvent effects concerning the redistribution of vibrational intensities rather than wavenumber shifts.

ESI-MS studies of mixed-ligand Fe(II) complexes containing 1,10-phenanthroline and 1,10-phenanthroline-5,6-dione as ligands.

In order to monitor the progression of the synthesis and the separation of novel mixed-ligand iron complexes containing 1,10-phenanthroline, 1,10-phenanthroline-5,6-dione, and NCS- as ligands all products were mass analyzed by electrospray ionization ion trap MS/MS. The spectra of methanol (MeOH), acetonitrile (ACN), water, and ethanol (EtOH) solutions were collected and the results were compared. It was detected under applied electrospray ionization mass spectrometry (ESI-MS) conditions that MeOH, water, and EtOH formed solvent clusters around the free or complexed 1,10-phenanthroline-5,6-dione. Owing to the solvent-ligand hydrogen-bond formation, the solvent-ligand clusters were formed in the polar protic solvents. The number of protic solvent molecules per complex ion in cluster depended on the number of 1,10-phenanthroline-5,6-dione ligands in the complex ion. Unlike MeOH, EtOH, or water, ACN was not involved in the formation of the solvent clusters with the iron complexes containing 1,10-phenanthroline-5,6-dione as ligand. We also showed that the NCS- group under certain solvent conditions served as a bidentate ligand.

Raman study of structural relaxation and boson peak in amorphous films of adamantane.

Low-frequency Raman scattering was used to study amorphous solid films of adamantane, a globular non-polar hydrocarbon molecule. As evidenced by its spectral characteristics this type of disorder is different from the orientational disorder found in the room temperature plastic phase by the absence of the translational order as well. This gives rise to the boson peak related to acoustic phonons which gradually disappears upon heating with simultaneous emerging of the phonon line at 50 cm-1 which characterizes the low-temperature ordered phase of adamantane. Adamantane dynamics resembles that of C60 fullerene although not in the same temperature range. All this makes adamantane an attractive system that could serve as a practical reference in molecular simulation studies of the glassy phase of model fluids.