Radiative lifetimes of the B1Π state of LiH and LiD

The lifetimes of the B¹Π vibrational levels of LiH and LiD were measured in a molecular beam apparatus using the method of delayed coincidences. The results for LiH are: τ(υ′ = 0) = 11.4 ns, τ(υ′ = 1) = 17.0 ns, τ(υ′ = 2) = 24 ns and for LiD τ(υ′ = 0) = 11.0 ns, τ(υ′ = 1) = 14.0 ns, τ(υ′ = 2) = 21 ns. These values are in good agreement with theoretical calculations. Three new brans of the A-X system were identified.     

Aggregation state and neurotoxic properties of alzheimer β-amyloid peptide

Alzheimer's disease (AD) represents the most common form of senile dementia and represents a tremendous health problem as the world population is aging. AD is characterized by the accumulation of amyloid β-peptide (Aβ) in the brain and the loss of cholinergic neurons in the basal forebrain. Accumulation of soluble and insoluble assemblies of Aβ in the brain is a crucial event in AD pathogenesis and the presence of amyloid plaques in the brain is required for definitive identification of AD. Yet, there is no correlation between amyloid plaques and the degree of dementia. In the past two decades researchers have devoted their effort to study and explain the mechanisms involved in the pathology of this devastating disease. Studies from different areas of the natural and medical sciences have provided important information towards the elucidation of some of the pathological processes that take place in AD. An aspect of crucial importance is the aggregation state of Aβ peptide and its role in neuropathology. Here, we discuss recent studies aimed at the identification of Aβ protein aggregates, the characterization of their toxic potential and the development of therapeutic strategies that target Aβ aggregation.     

Solid state amorphization and glass transition of tri-O-methyl-β-cyclodextrin

Amorphous solid of tri-O-methyl--cyclodextrin was formed by grinding the crystalline sample with a vibrating mill at room temperature. The amorphising process was examined by X-ray powder diffraction technique and differential scanning calorimetry (DSC). The Bragg peaks disappeared and the enthalpy of crystallization became constant for the sample ground for 25 min, indicating the apparent completion of the amorphization. A glass transition of the ground amorphous solid was found by DSC. The glass transition temperature T_g moved from 58°C to 79°C with grinding. The saturated T_g of the ground sample was the same as that of the liquid-quenched glass. No significant difference between the ground and liquid-quenched amorphous solids was found in the X-ray diffraction patterns. Infrared spectra of both amorphous solids, however, showed a definite difference for the band at 1194 cm^–1 assigned to the rocking of the CH₃ groups which are located at the molecular periphery.

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Zusammenfassung Amorphes festes Tri-O-methyl--cyclodextrin wurde bei Raumtemperatur durch Mahlen einer kristallinen Probe in einer Vibrationsmühle hergestellt. Der Amorphisierungsprozeß wurde mittels Röntgenpulverdiffraktion und DSC verfolgt. Die Braggschen Peaks verschwanden und die Kristallisierungsenthalpie nahm nach einem Mahldauer von 25 min einen konstanten Wert an, was auf die augenscheinliche Beendigung des Amorphisierungsprozesses hinweist. Mittels DSC wurde ein Glasumwandlungspunkt des gemahlenen amorphen Feststoffes gefunden. Die Glasumwandlungstemperatur T_g stieg durch das Mahlen von 58°C auf 79°C. Der Sättigungswert T_g der gemahlenen Probe war der gleiche wie für flüssigkeitsabgeschrecktes Glas. In den Röntgendiffraktogrammen konnte zwischen den gemahlenen und den flüssigkeitsabgeschreckten amorphen Feststoffen keinen Unterschied feststellen. Die IR-Spektren von beiden amorphen Feststoffen zeigen einen signifikanten Unterschied für die Bande bei 1194 cm^–1, der Nickschwingung der CH₃-Gruppen am Molekülrand.

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Dedicated to Professor Dr. H. J. Seifert on the occasion of his 60^th birthday

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Contribution No. 35 from the Microcalorimetry Research Centre.

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The authors thank the research group of Professor Yoshinobu Nakai, Faculty of Pharmaceutical Science, Chiba University, for their kind advice for the grinding-amorphization method. The authors are deeply indebted to Mr. Tetsuo Yamamoto for his X-ray diffraction experiments and Mr. Shin-ichi Ishikawa for his IR experiments.     

Ultrafast excited state dynamics and spectroscopy of 13,13'-diphenyl-β-carotene

Ultrafast transient broadband absorption spectroscopy based on the Pump-Supercontinuum Probe (PSCP) technique has been applied to characterize the excited state dynamics of the newly-synthesized artificial β-carotene derivative 13,13'-diphenyl-β-carotene in the wavelength range 340-770 nm with ca. 60 fs cross-correlation time after excitation to the S(2) state. The influence of phenyl substitution at the polyene backbone has been investigated in different solvents by comparing the dynamics of the internal conversion (IC) processes S(2)→ S(1) and S(1)→ S(0)* with results for β-carotene. Global analysis provides IC time constants and also time-dependent S(1) spectra demonstrating vibrational relaxation processes. Intramolecular vibrational redistribution processes are accelerated by phenyl substitution and are also solvent-dependent. DFT and TDDFT-TDA calculations suggest that both phenyl rings prefer an orientation where their ring planes are almost perpendicular to the plane of the carotene backbone, largely decoupling them electronically from the polyene system. This is consistent with several experimental observations: the up-field chemical shift of adjacent hydrogen atoms by a ring-current effect of the phenyl groups in the (1)H NMR spectrum, a small red-shift of the S(0)→ S(2)(0-0) transition energy in the steady-state absorption spectrum relative to β-carotene, and almost the same S(1)→ S(0)* IC time constant as in β-carotene, suggesting a similar S(1)-S(0) energy gap. The oscillator strength of the S(0)→ S(2) transition of the diphenyl derivative is reduced by ca. 20%. In addition, we observe a highly structured ground state bleach combined with excited state absorption at longer wavelengths, which is typical for an "S* state". Both features can be clearly assigned to absorption of vibrationally hot molecules in the ground electronic state S(0)* superimposed on the bleach of room temperature molecules S(0). The S(0)* population is formed by IC from S(1). These findings are discussed in detail with respect to alternative interpretations previously reported in the literature. Understanding the dynamics of this type of artificial phenyl-substituted carotene systems appears useful regarding their future structural optimization with respect to enhanced thermal stability while keeping the desired photophysical properties.     

Electronic state and photosensitivity of metal alkoxides chemically modified with β-diketones

Electronic state and optical absorption spectra of metal alkoxides stabilized with β-diketones (with a variety of substituents) were calculated using first-principle molecular orbital methods. The characteristics of the optical absorption and the mechanism of the photodissociation of alkoxides with irradiation of light are discussed. The position of the first peak observed in the near UV region in the theoretical spectra corresponded to that observed in the experimental spectra with a 25 nm shift toward shorter wavelengths. The first absorption peak observed in the visible range originated from electronic transitions to molecular orbitals, including the antibonding components of the C–O bonding in the chelate ring. The results suggested that the bonding of the chelate rings should be important in controlling the photosensitivity of chemically modified titanium alkoxides.     

Biophysical analysis of partially folded state of α-lactalbumin in the presence of cationic and anionic surfactants

The role of different types of interactions and their contribution in the stabilization of bovine α-lactalbumin (α-LA) molten globule in presence of cationic surfactant, hexadecyl trimethyl ammonium bromide (HTAB) and anionic surfactant, sodium dodecyl sulphate (SDS) have been examined using a combination of spectroscopic, light scattering and calorimetric techniques. The results correlated well with each other and were used to characterize the partially folded states of the protein both qualitatively and quantitatively. At lower concentration of the surfactants, the thermodynamic parameters obtained from UV-visible spectroscopy suggested an increased exposure of non-polar groups in HTAB while a possible restructuring of non-polar groups were indicated in SDS. The fluorescence and circular dichroism spectroscopy showed the formation of an intermediate state at various concentrations of HTAB and SDS while the lifetime measurements supported the assumption of protein-surfactant complex stability in HTAB as compared to SDS. The hydrodynamic diameter and the ζ-potential were analyzed by dynamic light scattering (DLS) which also implicated the combined influence of electrostatic and hydrophobic interactions in protein unfolding in HTAB and only hydrophobic interactions in SDS. The binding parameters for ANS obtained from isothermal titration calorimetric (ITC) measurements suggested a high stability of α-LA molten globule and the role of enthalpic and entropic contribution in the binding of ANS in HTAB. It also indicated the fragility of α-LA molten globule in SDS. The possible binding sites as well as the interactions of ANS with the partially folded protein were also studied from the thermodynamic parameters obtained from the ITC.     

Calculation of pVT and vapor–liquid equilibria of copolymer systems based on an equation of state

A molecular thermodynamic model for copolymers and their mixtures has been established by adopting the hard-sphere-chain fluid as a reference and a square-well (SW) term as well as an association term as a perturbation. The latter is introduced to consider various associating functions in a chain-like molecule based on the shield-sticky model of chemical association. The model adopts five molecular parameters, i.e. r_i, σ_ii ε_ii/k, δε_ii/k and ω_ii, for a polymer species i, where the last two are responsible for association. These parameters can be obtained from the pVT data of the corresponding molten homopolymer i. The model can be used to correlate pVT data for molten copolymers with an adjustable parameter describing the interaction between different polymer species. The model can also be used to calculate vapor–liquid equilibria (VLE) for copolymer solutions with three adjustable interaction parameters.     

Half-metallicity and spin-contamination of the electronic ground state of graphene nanoribbons and related systems: an impossible compromise?

An analysis using the formalism of crystalline orbitals for extended systems with periodicity in one dimension demonstrates that any antiferromagnetic and half-metallic spin-polarization of the edge states in n-acenes, and more generally in zigzag graphene nanoislands and nanoribbons of finite width, would imply a spin contamination S(2) that increases proportionally to system size, in sharp and clear contradiction with the implications of Lieb's theorem for compensated bipartite lattices and the expected value for a singlet (S = 0) electronic ground state. Verifications on naphthalene, larger n-acenes (n = 3-10) and rectangular nanographene islands of increasing size, as well as a comparison using unrestricted Hartree-Fock theory along with basis sets of improving quality against various many-body treatments demonstrate altogether that antiferromagnetism and half-metallicity in extended graphene nanoribbons will be quenched by an exact treatment of electron correlation, at the confines of non-relativistic many-body quantum mechanics. Indeed, for singlet states, symmetry-breakings in spin-densities are necessarily the outcome of a too approximate treatment of static and dynamic electron correlation in single-determinantal approaches, such as unrestricted Hartree-Fock or Density Functional Theory. In this context, such as the size-extensive spin-contamination to which it relates, half-metallicity is thus nothing else than a methodological artefact.     

Inclusion complexes of lamotrigine and hydroxy propyl β-cyclodextrin: solid state characterization and dissolution studies

Lamotrigine (LMN) is an antiepileptic drug, with poor aqueous solubility, which might lead to erratic bioavailability. The objective of the present work was to improve the dissolution characteristics of the LMN using Hydroxy propyl β-cyclodextrin (HP β-CD), which might offer reliable bioavailability. The phase solubility profile was classified as A _L -type, revealing 1:1 stoichiometric complexation, with a stability constant (Ks) of 573 M^?1. Binary systems of LMN and HP β-CD were prepared in different molar ratios (1:1, 1:2, 1:3 and 1:4) by kneading method. The binary systems were characterized by Fourier Transform Infrared (FT-IR) Spectroscopy, Differential Scanning Calorimetry (DSC) and Powder X-ray Diffraction Analysis (PXRD). Results revealed that in the kneaded products the entire drug was entrapped inside the HP β-CD cavity and reduction in drug crystallinity also took place, which may be responsible for improved dissolution characteristics as compared to that of the pure drug as depicted from the dissolution studies.     

High-resolution Fourier-transform infrared spectroscopy of the Coriolis coupled ground state and ν7 mode of ketenimine

High resolution FTIR spectra of the short lived species ketenimine have been recorded in the regions 390-1300 cm(-1) and 20-110 cm(-1) using synchrotron radiation. Two thousand six hundred sixty transitions of the ν(7) band centered at 693 cm(-1) and 126 far-IR rotational transitions have been assigned. Rotational and centrifugal distortion parameters for the ν(7) mode were determined and local Fermi and b-axis Coriolis interactions with 2ν(12) are treated. A further refinement of the ground state, ν(12) and ν(8) parameters was also achieved, including the treatment of previously unrecognized ac-axis and ab-axis second order perturbations to the ground state.     

A comparison of mixing rules for the combination of COSMO-RS and the Peng–Robinson equation of state

In this work, the COSMO-RS model is combined with a volume-translated Peng–Robinson equation of state (EOS) via a G^E$G^{\text{E}}$-based mixing rule. The performance of several mixing rules previously published for this purpose is compared and semi-empirical modifications to one of them are introduced to improve its performance in our application. The new mixing rule contains three internal parameters that are adjusted to achieve consistency between the mixing rule and COSMO-RS. No experimental binary data is needed for our EOS. The new COSMO-RS-based, predictive EOS introduces a density dependence into COSMO-RS and extends its applicability to higher pressures and to mixtures containing supercritical components.     

Solvent effects on the steady state photophysics of estrone and 17β-estradiol

Absorption and emission yields for estrone and 17β-estradiol were measured in a variety of room temperature solvents. Molar extinction coefficients were found to not vary as a function of solvent, while fluorescence yields were found to be significantly affected by the polarity and hydrogen-bond accepting ability of the solvent, with the yield for 17β-estradiol being highest in nonpolar, hydrogen-bond donating solvents, and lowest in the nonpolar, hydrogen-bond accepting solvent ethyl acetate. Estrone's emission yield was found to be a factor of ten smaller than 17β-estradiol's. Strong solvent and excitation wavelength dependences were found for the relative amounts of emission between estrone's two emission bands, with increased relative emission occurring in nonpolar aprotic solvents, and under higher excitation energies. These results are interpreted with the aid of vertical excitation energies from time-dependent density functional calculations using both explicit and implicit solvation models.     

Supramolecular helix and β-sheet through self-assembly of two isomeric tetrapeptides in crystals and formation of filaments and ribbons in the solid state

Single crystal X-ray diffraction studies show that the β-turn structure of tetrapeptide I, Boc-Gly-Phe-Aib-Leu-OMe (Aib: α-amino isobutyric acid) self-assembles to a supramolecular helix through intermolecular hydrogen bonding along the crystallographic a axis. By contrast the β-turn structure of an isomeric tetrapeptide II, Boc-Gly-Leu-Aib-Phe-OMe self-assembles to a supramolecular β-sheet-like structure via a two-dimensional (a, b axis) intermolecular hydrogen bonding network and π-π interactions. FT-IR studies of the peptides revealed that both of them form intermolecularly hydrogen bonded supramolecular structures in the solid state. Field emission scanning electron micrographs (FE-SEM) of the dried fibrous materials of the peptides show different morphologies, non-twisted filaments in case of peptide I and non-twisted filaments and ribbon-like structures in case of peptide II.     

The aromaticity and Möbius characteristics of carbeno[8]heteroannulenes and triplet state annulenes

Two types of annulene which may show significant M?bius aromatic character and bond and twist delocalisation are proposed; triplet states with 4n + 2 occupancy of the p pi array of atomic orbitals and a novel 8-pi carbeno[8]heteroannulene ring system 1 where the Hückel highly antiaromatic nature as a planar system can be attenuated or even reversed by the C2 symmetric M?bius distortion.     

A theoretical form of the Martin-Hou equation of state

A new equation of state is derived from the Barker-Henderson hard-sphere perturbation theory. It has the form similar to the Martin-Hou equation of state. The numerical values of the characteristic constants in the equation can be calculated by the method of Martin and Hou. The equation can be used to predict P-V-T properties accurately for fluids when the critical parameters (T_c, P_c and V_c) and one point on the vapor pressure cure are given. By using the functional relationships between the characteristic constants and the microscopic parameters, the molecular microscopic parameters of the substance can be obtained.     

The state energy and the displacements of the potential minima of the 2Ag− state in all-trans-β-carotene as determined by fluorescence spectroscopy

The fluorescence spectrum of all-trans-β-carotene was recorded at 170 K. The 1B_u⁺ → 1A_g⁻ fluorescence exhibited clear vibrational structures constituting a mirror image with those of the 1B_u⁺ ← 1A_g⁻ absorption, and the deconvolution of the entire spectrum identified the 2A_g⁻(0) → 1A_g⁻(0) transition at 14 500 cm⁻¹. The displacements of the 1B_u⁺ and 2A_g⁻ potential minima along ν₁ and ν₂ (the CC stretching and C–C stretching normal coordinates, respectively) were determined to be 1.2 and 0.9, and 1.6 and 1.5, respectively. Thus, much larger potential displacements in the 2A_g⁻ state than in the 1Bu⁺ state have been shown.     

P–V–T properties of polymer melts based on equation of state and neural network

An accurate and efficient analytical equation of state (EOS) and artificial neural network (ANN) methods are developed for the prediction of volumetric properties of polymer melts. To apply EOS, the second virial coefficients B₂(T), effective van der Waals co-volume, b(T) and correction factor, α(T) were determined. The second virial coefficient was calculated from a two-parameter corresponding states correlation, which is constructed with two constants as scaling parameters, i.e., temperature (T_f) and density at melting (ρ_f) point. The new correlations were used to predict the specific volumes of polypropylene glycol (PPG), polyethylene glycol (PEG), polypropylene (PP), polyvinylchloride (PVC), poly(1-butene)(PB1), poly (?-caprolactone) (PCL), polyethylene (PE) and polyvinylmethylether (PVME) at compressed state in the temperature range of 298.15–634.6 K. The obtained results show that the two models have good agreement with the experimental data with absolute average deviation of 0.28% and 0.39% for ANN and EOS, respectively. The Comparison of the results with ISM model shows that the proposed models represent an efficient method and are more accurate.     

Reactions of the OH adducts of cytosine and its derivatives with TEMPO and TEMPOL: A steady state γ-radiolysis and pulse radiolysis study

The reactions of the OH adducts of cytosine and its derivatives with nitroxides namely TEMPO and TEMPOL have been followed by steady state -radiolysis and pulse radiolysis. Pulse radiolysis studies show that the transient OH adducts of cytosine and its derivatives react with TEMPO and TEMPOL by electron transfer reaction and not by adduct formation as was observed in the case of thymine. The second order rate constants for these electron transfer reactions are of the order of 10⁷ - 10⁸ dm³ mol^-1 s^-1.     

Conformation of liquid crystalline state in interaction between chemical materials and biomembrane in terms of modern physics

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Pressure–volume–temperature measurements of phosphonium-based ionic liquids and analysis with simple equations of state

In spite of the great importance of the (P, V, T) data of phosphonium–based ionic liquids, only limited information on these data seems to be available in the open literature. In this work, we present the results for the density measurements of the trihexyltetradecylphosphonium chloride, [(C₆H₁₃)₃P(C₁₄H₂₉)][Cl] and trihexyltetradecylphosphonium dicyanamide, [(C₆H₁₃)₃P(C₁₄H₂₉)][N(CN₂)] with an estimated uncertainty of ±0.5 kg · m^?3. The ranges of temperature and pressure are T = (273.15 to 318.15) K and p = (0.1 to 25) MPa for [(C₆H₁₃)₃P(C₁₄H₂₉)][Cl] and T = (273.15 to 318.15) K and p = (0.1 to 35) MPa for [(C₆H₁₃)₃P(C₁₄H₂₉)][N(CN₂)]. The high consistency of our data for [(C₆H₁₃)₃P(C₁₄H₂₉)][Cl] compared with those measured by other authors allowed all the experimental data for this IL to be combined and correlated using the Goharshadi–Morsali–Abbaspour equation of state over a wide range of temperature and pressure. From this equation, thermomechanical coefficients as the isothermal compressibility, thermal expansivity, thermal pressure, and internal pressure were calculated for the two ILs. The Sanchez–Lacombe equation of state was used also for (P, V, T) correlation and the estimation of the free volume in these phosphonium ionic liquids. Finally ionic volumes for trihexyltetradecylphosphonium cation and several anions available in the literature made possible the calculation of the free (hole) volume.