Calorimetric indication of the molten globule-like state of cytochrome c induced by n-alkyl sulfates at low concentrations

The molten globule state has been proposed as a major intermediate of protein folding. However it has proven difficult to obtain thermodynamic data characterizing this state. To explore an alternative approach for characterization of the molten globule state, n-alkyl sulfates induced formation of the molten globule state of horse cytochrome c at pH 2 was studied by isothermal titration calorimetry (ITC). Titration of the acid unfolded state of cytochrome c with sodium octyl sulfate, sodium dodecyl sulfate or sodium tetradecyl sulfate, generated an exothermic reaction for formation of the molten globule state. The effects of various n-alkyl sulfates on the acid unfolded state of cytochrome c demonstrated that the increased alkyl chain length enhanced the exothermic values of calorimetric enthalpy and induced a more compact molten globule states. The heat contents agreed well with the conformational transition measured by molar ellipticity at 222 nm ([θ]₂₂₂) and Stoke radius (Rs) values. These results emphasize that isothermal titration calorimetry provides a reasonable alternative method for characterization of the molten globule state.     

Unsymmetrical 1B2 (ππ1) state of ozone

Using ab initio SCF CI calculations it is shown that the ππ1 singlet state of ozone has an unsymmetrical equilibrium geometry with one long and one short OO bond. A similar behavior has been experimentally demonstrated on the parent SO₂ molecule. The double-minimum potential energy surface of this state results from an avoided crossing involving (1) the singlet ππ1 state itself which is stabilized by an unsymmetrical stretching of the two bonds and (2) a lower lying (nπ1)² doubly excited state which is destabilized by the same distortion.     

The Fourier transform and diode laser spectrum of the ν2 band of diazomethane

The infrared spectrum of the ν₂ band (NN stretching) of gaseous diazomethane at 2100 cm^?1 has been measured by means of an interferometer and a tunable diode laser spectrometer. For the first time the rotational J and K_a structure of this A-type parallel band has been resolved. Since the spectrum was found to be perturbed it was not possible to fit the upper state levels to an overall hamiltonian. Nine subbands have been analysed with the support of millimeter wave data for the ground vibrational state. Term values for the ν₂ = 1 vibrational state with K_a up to 5 have been obtained and subband origins, effective rotational constants B and centrifugal distortion constants D and H were determined for each K_a substate.     

The second-order stark effect on the 1B2u electronic origin of tetracene and pentacene in p-terphenyl

The electric field induced shift of the electronic origin of the lowest B_2u singlet state of tetracene and pentacene in p-terphenyl at 1.8°K has been measured. From this shift we calculate the difference in polarizability of this state and the ground state along the long molecular axis to be 4.5 ± 0.5 ų for tetracene and 19.8 ± 1.0 ų for pentacene (F_c′ = 0.505 F_eff). The ratio of these tensor elements (Δα)_zz for pentacene and tetracene is found to be 4.4 ± 0.6 and is independent of the local field approximation.     

Two photon excitation spectrum of benzene and benzene-d6 in the gas phase: Assignment of inducing modes by hot band analysis

The two-photon absorption spectrum for benzene-h₆ and -d₆ is reported and assigned, leading to the frequency assignment for hitherto unknown vibrations in the electronically excited state. In addition absorption has been measured from hot bands in the ground state. This latter technique has allowed us to make an unequivocal assignment of the vibrational modes responsible for inducing the otherwise forbidden two-photon process. The result is in disagreement with current theory, for this prototype two-photon spectrum in the gas phase.     

Differential scanning calorimetric study of the molten globule state of cytochrome c induced by sodium n-dodecyl sulfate

The molten globule (MG) state, a compact denatured state with a significantly native-like secondary structure but a largely flexible and disordered tertiary structure, has been proposed to be a major intermediate of protein folding. To explore another approach for characterizing the MG state, sodium dodecyl sulfate (SDS) induced formation of the MG state of horse cytochrome c at pH 2 was studied by circular dichroism, visible spectroscopy, isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC). These techniques confirmed that the addition of SDS to acid-unfolded state of cytochrome c induced the MG state. Although, the DSC thermal denaturation of cytochrome c was always calorimetrically irreversible, the MG state induced by SDS at low concentrations showed a reversible profile. The spectroscopic properties demonstrated that the hydrophobic tail of SDS utilized the hydrophobic contribution to stabilizing the heme conformation at MG state in cytochrome c. This would be the main reason of thermal profile reversibility of MG state in cytochrome c. The reversibility of DSC thermogram would allow its deconvolution and analysis of the energetic domains for this protein.     

Crystalline field effect on ESR parameters

The ground state wavefunction of the V⁴⁺ ion in different single crystals has been estimated using different spinhamiltonian constants obtained from ESR studies. The ground state wavefunction is the d_xy type with a slight admixture of the excited states d_x²–_y², d_xz and d_yz. The hyperfine interaction parameter has also been determined and the nature of the chemical binding in complexes has been explained on the basis of this parameter.     

Two-photon absorption spectroscopy of iodine monochloride in the 5 eV region

Two-photon high resolution sequential spectroscopy has been used to excite iodine monochloride from X¹Σ⁺ ground state to the intermediate A³Π₁ state and thence to a final electronic state at 4.82 eV. Vibrational and rotational analyses of this state have been carried out for both isotopic species. For I³⁵Cl, T_e = 38916.0 cm^?1 ω_e = 168.99 cm^?1, ω_ex_e = 0.357 cm^?1 and B_e = 0.05685 cm^?1. The state probably has Ω = 1 in case (c) coupling approximation. It is also shown how to two-photon technique enables rotational line structure of the A ← X transition to be selectively excited for either isotopic species at a resolution of 500000, from an absorption mixture containing natural iodine monochloride plus its iodine dissociation product at equilibrium vapour pressure.     

Photofragment spectroscopy of SO+ in the wavelength range from 308–514.5 nm

The direct photodissociation process SO⁺+hv→S⁺+O has been studied using the technique of ion photofragment spectroscopy. The kinetic energy distribution of the S⁺ photofragments has been measured for selected wavelengths in the range λ=308–514.5 nm. Transitions from the metastablea ⁴∏ state to the dissociative 1⁴∑⁺ state as well as from theX ²∏ ground state to a higher-lying²∏ state have been observed. From the vibrationally resolved kinetic energy spectra, the potential curve of the repulsive 1⁴∑⁺ state has been determined for the range of internuclear distancesR=3.0–4.5a ₀. In addition, the analysis gives the vibrational population of the SO⁺ (a ⁴∏) ions after dissociative electron-impact ionization of SO₂ in the low-pressure monoplasmatron ion source.     

Possible large magnetic moments in 4d transition metal clusters

The electronic structure and magnetism of 13 atom clusters of ruthenium, rhodium and palladium having face centered cubic(fcc) geometry has been studied using a Gaussian orbital basis and the local spin density approximation. Calculations were done for the lattice spacings relevant to the bulk crystal lattice. Using the fixed moment states as input potentials, as many as 3 self-consistent states were obtained for these clusters. The 3 converged states of Rh₁₃ cluster is found to have magnetic moments of 0.69 _μB , 1.00 _μB and 1.46 _μB . Out of these states, 0.69 _μB moment state is found to be the ground state. But the total energy difference between the 0.69 _μB and 1.00 _μB state is very small. The 1.46 _μB moment state coincides with the state reported previously by other authors which was obtained using the discrete variational method. The experimentally observed moment was around 0.47 _μB . Our calculated moment is closer to the experimentally observed moment than the previously reported moment, but is still a bit larger. Ru₁₃ cluster is also found to have large moments, and 3 self-consistent states are also obtained for this cluster. The 3 magnetic moments of the Ru₁₃ cluster are 0.46 _μB , 0.62 _μB and 1.08 _μB . Out of these states, 0.62 _μB moment state is found to be the ground state. For the Pd₁₃ cluster, in addition to the nonmagnetic state previously reported, a state with magnetic moment of 0.46 _μB is also found to exist indicating possible magnetism in cluster phase.     

First observation of intra-5f fluorescence from an actinyl center: Np(VI) near-IR emission in Cs2U(Np)O2Cl4

Fluorescence from an excited 5f state of Np(VI) has been observed in the doped impurity system Cs₂U(Np)O₂Cl₄. This is the first intra-5f fluorescence transition that has been detected at room temperature in a condensed-phase system with an actinyl (An(VI)O₂²⁺) core, and it is a rare example of fluorescence of any kind from non-uranyl ions of this type. The emission originates from an excited state approximately 6890 cm⁻¹ above the ground state. Its emission spectrum and fluorescence lifetime at 295 K will be discussed. Vibronic structure in the emission spectrum is assigned based on comparison with the detailed analysis of the absorption spectra published by Denning et al.     

Assignment and analysis of the absorption and emission spectra of the lowest nπ* triplet state in 9,10-anthraquinone

Polarized Zeeman absorption experiments on 9,10-anthraquinone crystals show the lowest triplet state in this molecule to be a g nπ^* state. The gap between this state and the higher u nπ^* state is found to be 410 cm^?1. The phosphorescence spectrum of an isotopically mixed crystal of AQ-h₈ in AQ-d₈ is analyzed in detail and confirms the orbitally forbidden nature of the emitting state. The results are compared with those previously obtained for p-benzoquinone.     

The millimeter wave spectrum of iodoethyne,HCCI

The rotational spectrum of iodoethyne, HCCI, has been observed in the frequency range from 105 to 305 GHz. A sensitive spectrometer system employing source modulation, a harmonic generator millimeter wave source and a liquid helium cooled InSb-detector has been used. The rotational constants and nuclear quadrupole coupling parameters of HCCI have been obtained for the ground state and the first and second excited vibrational states of ν₄. The rotational spectrum of the 2ν₅ state has also been identified. The very weak spectrum shows unusual relative intensities which are interpreted by assuming a dipole moment change with ν₄ excitation of 0.07 D. The ground state dipole moment is then estimated to be 0.020(10) D.     

Microwave spectrum of cyclohexanone

The rotational spectrum of cyclohexanone has been observed within the frequency region from 18.0 to 40.0 GHz. Transitions in the ground state and six excited states have been assigned. The ground state rotational constants are (in MHz) A = 4195.316 +- 0.059, B = 2502.627 ± 0.005 and C = 1754.443 ± 0.005.From information obtained from relative intensity measurements, these excited states are estimated to be ~ 100 cm^?1 above the ground state for the first excited state of the ring-bending mode and ~ 180 cm^?1 for the first excited state of the ring-twisting mode.     

Quantum mechanical law of corresponding states from ISM equation of state: compressed liquids

In this paper, we explore the theory of the equation of state from the view point of Ihm–Song–Mason (ISM) equation of state, which has been derived on the basis of statistical mechanical perturbation theory, and is characterized by three temperature dependent parameters, α, b, B₂, and a free parameter Γ. This equation is applied well to non-polar fluids in subcritical and supercritical regions and to molten alkali metals. We present results that show Γ varies slightly with temperature. Among the nobles group, Γ values are quite the same and are correlated except He, which deviates so much even no moderate correlation is seen. In the alkali metals group, Γ values are roughly the same for K, Rb, and Cs but are different for Li and Na. We have previously shown that Γ conforms to B₂, the second virial coefficient, and thus to the nature of the particular fluid system. These observations plus the discussion on quantum mechanical law of corresponding states suggest that the ISM equation of state stands as an analytical equation of state which explicitly incorporates quantum effects by the parameter Γ. Then, we suggest a law of corresponding states as p*=p*(v*, T*, Γ) where, asterisks stand for reduced pressure, volume, and temperature, respectively.     

Excited-state interaction of m-aminoacetophenone with t-amyl alchohol

Electronic interaction of m-aminoacetophenone (MAAP) with t-amyl alcohol in the excited state has been investigated by steady-state and nanosecond spectroscopies. It was shown that the MAAP molecules forms a complex with two t-amyl alcohol molecules in the ground state, and that the complex further associates with the alcohol molecules in the excited state.     

Energy transfer from a platinum—nickel excited state to platinum clusters in quasi-one-dimensional Ba(Pt,Ni)(CN)4·nH2O crystals

Laser-induced luminescence in quasi-one-dimensional Ba(Pt, Ni)(CN)₄·nH₂O crystals has been measured from 5 to 300 K. A well-defined luminescence peak is observed, corresponding to an excited electronic state of platinum and nickel. Energy transfer from this Pt—Ni excited state to Pt(CN)₄^2? clusters is found to be very much dependent on the temperature.     

Alignment of atomic autoionizing states created by slow Na++He collisions

Ejected-electron spectra have been measured for collisions of He-atoms with Na⁺-ions, whose impact energy ranged from 1.7 to 7.0 keV. The ion impact-energy dependence of the angular-differential cross-section of the ejected electrons has been investigated for an aligned autoionizing state Na**(2p ⁵ 3s ^{2 2} P), which has been created by charge transfer from the He-atoms. The alignment of the autoionizing state Na**(2p ⁵ 3s ^{2 2} P) is discussed in relation to the scattering angles of the Na⁺-ions. A complete longitudinal alignment has been observed with respect to the quasimolecular axis.     

Reaction Mechanism of the Exchange Reaction between CuCl and BaO Studied by Time-Resolved X-ray Absorption Spectroscopy

The solid state reaction 2CuCl+BaO→Cu₂O+BaCl₂ has been examined in situ using energy-dispersive X-ray absorption fine-structure spectroscopy (DXAFS). A high time resolution on the order of seconds between two Cu K-XANES spectra has been achieved by this experimental setup. The spectra suggest that the transformation of CuCl to Cu₂O is preceded by an unidentified, intermediate state. Fingerprint methods as well as principal component analysis have been applied, which confirm the formation of exactly one new intermediate phase. The nature of this phase remains unidentified and could not be elucidated by the experimental investigations.     

Multiphoton ionisation spectroscopy of H2S: a reinvestigation of the 1B1-1A1 band at 139.1 nm

The 3 + 1 multiphoton ionisation (MPI) spectrum of the ¹B₁-¹A₁ transition in H₂S at 139.1 nm has been recorded in both linearly and circularly polarised light. The rotational structure shows marked differences from that of the one-photon absorption spectrum. Properties of the excited state revealed through analysis of this structure include confirmation of its ¹B₁ character, refined values for its A, B and C rotational constants and the operation of an energy-dependent predissociation mechanism. It is shown that the third-rank tensor component of the transition operator dominates over the first-rank component in this MPI band. The orbital nature of this ¹B₁ excited state is considered.