Trehalose Has a Protective Effect on Human Brain-Type Creatine Kinase During Thermal Denaturation

We investigated the effects of trehalose on thermal inactivation and aggregation of human brain-type creatine kinase (hBBCK) in this study. In the presence of 1.0 M trehalose, the midpoint temperature of thermal inactivation (T (m)) of hBBCK increased by 4.6 °C, and the activation energy (E (a)) for thermal inactivation increased from 29.7 to 41.1 kJ mol(-1). Intrinsic fluorescence spectra also showed an increase in the apparent transition temperature (T (1/2)) of hBBCK from 43.0 °C to 46.5 °C, 47.7 °C, and 49.9 °C in 0, 0.6, 0.8, and 1.2 M trehalose, respectively. In addition, trehalose significantly blocked the aggregation of hBBCK during thermal denaturation. Our results indicate that trehalose has potential applications as a thermal stabilizer and may aid in the folding of other enzymes in addition to hBBCK.     

Solvolyses of 2-Deoxy-alpha- and beta-D-Glucopyranosyl 4'-Bromoisoquinolinium Tetrafluoroborates

The solvolyses of 2-deoxy-alpha- and beta-D-glucopyranosyl 4'-bromoisoquinolinium tetrafluoroborates (1 and 2) were monitored in aqueous methanol, ethanol, trifluoroethanol, and binary mixtures of ethanol and trifluoroethanol. The observed rate constants are consistent with the solvolyses of 1 and 2 proceeding via dissociative (D(N) A(N)) transition states. In comparison to the alpha-anomer, solvolysis of the beta-compound gives a greater transition state charge delocalization onto the ring oxygen atom. Analysis of the solvolysis product ratios indicates that the 2-deoxyglucosyl oxacarbenium ion is not solvent-equilibrated in the solvent mixtures studied. In the solvolysis of compound 1, the solvent trifluoroethanol facilitates diffusional separation of the leaving group and, in so doing, promotes the formation of the retained trifluoroethyl glycoside.     

Characterization of the singlet and triplet excited states of 3-chloro-4-methylumbelliferone

An extensive photophysical characterization of 3-chloro-4-methylumbelliferone (3Cl4MU) in the ground-state, S(0), first excited singlet state, S(1), and lowest triplet state, T(1), was undertaken in water, neutral ethanol, acidified ethanol, and basified ethanol. Quantitative measurements of quantum yields (fluorescence, phosphorescence, intersystem crossing, internal conversion, and singlet oxygen formation) together with lifetimes were obtained at room and low temperature in water, dioxane/water mixtures, and alcohols. The different transient species were assigned and a general kinetic scheme is presented, summarizing the excited-state multiequilibria of 3Cl4MU. In water, the equilibrium is restricted to neutral (N*) and anionic (A*) species, both in the ground (pK(a) = 7.2) and first excited singlet states (pK(a)* = 0.5). In dioxane/water mixtures (pH ca. 6), substantial changes of the kinetics of the S(1) state were observed with the appearance of an additional tautomeric T* species. In low water content mixtures (mixture 9:1 v:v), only the neutral (N*) and tautomeric (T*) forms of 3Cl4MU are observed, whereas at higher water content mixtures (water mole fraction superior to 0.45), all three species N*, T*, and A* coexist in the excited state. In the triplet state, in the nonprotic and nonpolar solvent dioxane, the observed transient signals were assigned as the triplet-triplet transition of the neutral form, N*(T(1)) → N*(T(n)). In water, two transient species were observed and are assigned as the triplets of the neutral N*(T(1)) and the anionic form, A*(T(1)) (also obtained in basified ethanol). The phosphorescence spectra and decays of 3Cl4MU, in neutral, acidified, and basified solutions, demonstrate that only these two species N*(T(1)) and A*(T(1)) exist in the lowest lying triplet state, T(1). The radiative channel was found dominant for the deactivation of the anionic species, whereas with the neutral the S(1) ? S(0) internal conversion competes with fluorescence. For both N* and A* the intersystem crossing yield represents a minor deactivation channel for S(1).     

Magnitude of the CH/pi interaction in the gas phase: experimental and theoretical determination of the accurate interaction energy in benzene-methane

The accurate CH/pi interaction energy of the benzene-methane model system was experimentally and theoretically determined. In the experiment, mass analyzed threshold ionization spectroscopy was applied to the benzene-methane cluster in the gas phase, prepared in a supersonic molecular beam. The binding energy in the neutral ground state of the cluster, which is regarded as the CH/pi interaction energy for this model system, was evaluated from the dissociation threshold measurements of the cluster cation. The experimentally determined binding energy (D(0)) was 1.03-1.13 kcal/mol. The interaction energy of the model system was calculated by ab initio molecular orbital methods. The estimated CCSD(T) interaction energy at the basis set limit (D(e)) was -1.43 kcal/mol. The calculated binding energy (D(0)) after the vibrational zero-point energy correction (1.13 kcal/mol) agrees well with the experimental value. The effects of basis set and electron correlation correction procedure on the calculated CH/pi interaction energy were evaluated. Accuracy of the calculated interaction energies by DFT methods using BLYP, B3LYP, PW91 and PBE functionals was also discussed.     

Effects of sugars and polyols on the stability of azurin in ice

This study represents the first attempt to gain a quantitative estimate of the protective influence of sugars (sucrose and trehalose) and polyols (sorbitol and glycerol) on the thermodynamic stability (DeltaG degrees ) of a protein in low-temperature part-frozen aqueous solutions. The method, based on guanidinium chloride denaturation of the azurin mutant C112S from Pseudomonas aeruginosa, distinguishes between the effects of cooling to subfreezing temperatures from those induced specifically by the formation of a solid ice phase. The results point out that in the liquid state the generally stabilizing effect (at molar concentrations) of these polyhydric compounds is markedly attenuated on cooling to subfreezing temperatures such that at -15 degrees C, only sucrose still exerts a significant increase in DeltaG degrees . At this temperature, and in the absence of additives, the formation of ice caused a progressive destabilization of the native fold, DeltaG degrees decreasing up to 3-4 kcal/mol as the fraction of liquid water in equilibrium with ice (V(L) was reduced to less than 1%. Unexpectedly, denaturation profiles in ice at selected V(L) demonstrate that none of the above sugars and polyols counters effectively the decrease in protein stability at small V(L). Only trehalose was able to partly attenuate the ice perturbation, raising DeltaG degrees by a modest 0.6-0.8 kcal/mol relative to the salt reference. In all cases the reduction in DeltaG degrees caused by the solidification of water correlates with the decrease in m-value. The implication is that DeltaASA of unfolding is smaller in ice because protein-ice interactions either increase the solvent-accessible surface area (ASA) of the native fold (partial unfolding) or reduce the ASA of the denatured state (compaction), or both. Information on the protein tertiary structure in ice, in the absence and in the presence of sucrose or glycerol, suggests that these osmolytes play an important role in maintaining a compact native state that in their absence is expanded and partly unfolded. Thus, it appears that the prevailing mechanism by which these osmolytes act as cryoprotectants is through preservation of the native conformation in the liquidus rather than by increasing the thermodynamic stability of the native fold.     

Rotational dynamics of water and benzene controlled by anion field in ionic liquids: 1-butyl-3-methylimidazolium chloride and hexafluorophosphate

The rotational correlation time (tau(2R)) is determined for D(2)O (polar) and C(6)D(6) (apolar) in 1-butyl-3-methylimidazolium chloride ([bmim][Cl]) and hexafluorophosphate ([bmim][PF(6)]) by measuring (2)H (D) nuclear magnetic resonance spin-lattice relaxation time (T(1)) in the temperature range from -20 to 110 degrees C. The tau(2R) ratio of water to benzene (tau(WB)) was used as a measure of solute-solvent attraction. tau(WB) is 0.73 and 0.52 in [bmim][Cl] and [bmim][PF(6)], respectively, whereas the molecular volume ratio is as small as 0.11. The slowdown of the water dynamics compared to the benzene dynamics in ionic liquids is interpreted by the Coulombic attractive interaction between the polar water molecule and the anion. As for the anion effect, the rotational dynamics of water solvated by Cl(-) is slower than that solvated by PF(6) (-), whereas the rotational dynamics of benzene is similar in the two ionic liquids. This is interpreted as an indication of the stronger solvation by the anion with a larger surface charge density. The slowdown of the water dynamics via Coulombic solvation is actually significant only at water concentrations lower than approximately 9 mol dm(-3) at room temperature, and it is indistinguishable at temperatures above approximately 100 degrees C. The quadrupolar coupling constants determined for D(2)O and C(6)D(6) in the ionic liquids were smaller by a factor of 2-3 than those in the pure liquid state.     

Theoretical approaches to estimating homolytic bond dissociation energies of organocopper and organosilver compounds

Although organocopper and organosilver compounds are known to decompose by homolytic pathways among others, surprisingly little is known about their bond dissociation energies (BDEs). In order to address this deficiency, the performance of the DFT functionals BLYP, B3LYP, BP86, TPSSTPSS, BHandHLYP, M06L, M06, M06-2X, B97D, and PBEPBE, along with the double hybrids, mPW2-PLYP, B2-PLYP, and the ab initio methods, MP2 and CCSD(T), have been benchmarked against the thermochemistry for the M-C homolytic BDEs (D(0)) of Cu-CH(3) and Ag-CH(3), derived from guided ion beam experiments and CBS limit calculations (D(0)(Cu-CH(3)) = 223 kJ·mol(-1); D(0)(Ag-CH(3)) = 169 kJ·mol(-1)). Of the tested methods, in terms of chemical accuracy, error margin, and computational expense, M06 and BLYP were found to perform best for homolytic dissociation of methylcopper and methylsilver, compared with the CBS limit gold standard. Thus the M06 functional was used to evaluate the M-C homolytic bond dissociation energies of Cu-R and Ag-R, R = Et, Pr, iPr, tBu, allyl, CH(2)Ph, and Ph. It was found that D(0)(Ag-R) was always lower (～50 kJ·mol(-1)) than that of D(0)(Cu-R). The trends in BDE when changing the R ligand reflected the H-R bond energy trends for the alkyl ligands, while for R = allyl, CH(2)Ph, and Ph, some differences in bond energy trends arose. These trends in homolytic bond dissociation energy help rationalize the previously reported (Rijs, N. J.; O'Hair, R. A. J. Organometallics2010, 29, 2282-2291) fragmentation pathways of the organometallate anions, [CH(3)MR](-).     

New evidences of glass transitions and microstructures of soy protein plasticized with glycerol

Soy protein isolate (SPI) and glycerol were mixed under mild (L series) and severe (H series) mixing conditions, respectively, and then were compression-molded at 140 degrees C and 20 MPa to prepare the sheets (SL and SH series). The glass transition behaviors and microstructures of the soy protein plasticized with glycerol were investigated carefully by using differential scanning calorimetry and small-angle X-ray scattering. The results revealed that there were two glass transitions in the SPI/glycerol systems. When the glycerol contents ranged from 25 to 40 wt.-%, all of the SL- and SH-series sheets showed two glass transition temperatures (T(g1) and T(g2)) corresponding to glycerol-rich and protein-rich domains, respectively. The T(g1) values of the sheets decreased from -28.5 to -65.2 degrees C with an increase of glycerol content from 25 to 50 wt.-%, whereas the T(g2) values were almost invariable at about 44 degrees C. The results from wide-angle X-ray diffraction and small-angle X-ray scattering indicated that both protein-rich and glycerol-rich domains existed as amorphous morphologies, and the radii of gyration (R(g)) of the protein-rich domains were around 60 nm, a result suggesting the existence of stable protein domains. The results above suggest that protein-rich domains were composed of the compact chains of protein with relatively low compatibility to glycerol and glycerol-rich domains consisted of relative loose chains that possessed good compatibility with glycerol. The significant microphase separation occurred in the SPI sheets containing more than 25 wt.-% glycerol, with a rapid decrease of the tensile strength and Young's modulus. [illustration in text].     

Film Formation from Nanosized Copolymeric Latex Particles: A Photon Transmission Study

The photon transmission technique was used to monitor the evolution of transparency during film formation from nanosized copolymeric latex particles. The latex films were prepared from poly(methyl methacrylate-co-butyl methacrylate) (P(MMA-co-BMA)) particles which were produced by microemulsion polymerization. These films were annealed at elevated temperatures in various time intervals above the glass transition temperature (T(g)) of P(MMA-co-BMA). It is observed that the transmitted photon intensity (I(tr)) from these films increased as the annealing temperature increased. There are three different film formation stages. These stages are explained by the void closure, healing, and interdiffusion processes, respectively. The activation energies for viscous flow (DeltaH approximately 16 kcal/mol), minor chains (DeltaE(H) approximately 27 kcal/mol), and backbone motion (Delta E(b) approximately 132 kcal/mol) were obtained using various models. Void closure (tau(v), T(v)) and healing points (tau(H), T(H)) were determined. Using the time-temperature pairs, void closure and healing activation energies were measured and found to be 21 and 30 kcal/mol, respectively. Copyright 2001 Academic Press.     

Charge-transfer guest interactions in luminescent MOFs: implications for solid-state temperature and environmental sensing

One of the ongoing goals in the field of porous materials is the design and synthesis of materials that possess chemical structures amenable for use in sensing applications. We describe the preparation, luminescence characteristics, and environmental sensing properties of variants of the aluminum-based MOF [Al(OH)(O(2)C-C(10)H(6)-CO(2))](∞). Careful activation of the open framework complex, 1, yielded a dynamic structural transformation to a non-porous form, 2, that exhibited strong inter-linker interactions and red-shifted emission characteristics indicative of dimer formation. We also demonstrate the formation of highly luminescent ground-state charge-transfer (CT) complexes between 1 and the electron-donating amines dimethylamine (DMA) (1a), and N,N-diethylaniline (DEA) (1b), both of which exhibit dual-emission characteristics and a ratiometric luminescence response that is sensitive to temperature and solvent polarity. Steady-state and time-resolved measurements on 1a, 1b, and 2 indicate that the MOF structures stabilize ground-state CT interactions that are distinct from the weakly-bound exciplexes formed in comparable mixtures of purely organic components. The spectra for 1a and 1b also indicate different temperature dependencies that correspond to thermally-activated complex formation (ΔH(f) = +1.1 ± 0.2 kcal mol(-1)) in 1a and static quenching effects (ΔH(f) = -2.2 ± 0.3 kcal mol(-1)) in 1b. The addition of ethanol, isopropanol, toluene, or chloroform to suspensions of 1b indicate destabilization of the CT state with increasing solvent polarity, which suggests the generalized application of this or related materials in sensor applications.     

Accurate quantum chemical energies for the interaction of hydrocarbons with oxide surfaces: CH(4)/MgO(001)

We examine the adsorption of CH(4) on the MgO(001) surface by a hybrid approach. It combines MP2 calculations with extrapolation to the complete basis set limit for the adsorption site and the CH(4)-CH(4) pair interactions in the adsorbate layer, with DFT+dispersion calculations under periodic boundary conditions for the whole system. To the total binding energy of 10.7 kJ mol(-1), the DFT+D(ispersion) correction contributes 0.7 kJ mol(-1) only, showing that the Mg(9)O(9) two-layer surface model is an excellent choice and that the interaction between the CH(4) molecules in the adsorbate layer is dominated by pair interactions. Contributions due to relaxation of the atom positions of 0.6 kJ mol(-1) (evaluated at DFT+dispersion) and of higher order correlation effects of 2.0 kJ mol(-1) (evaluated by CCSD(T)) yield a final estimate of 13.3 kJ mol(-1). To this total adsorption energy, the lateral interactions between the CH(4) molecules in the adsorbate layer contribute substantially, 4.1 kJ mol(-1)."Observed" desorption energies of 15.3 and 16.0 kJ mol(-1) have been derived from the observed Arrhenius desorption barriers (12.6 and 13.1 kJ mol(-1)) using thermal enthalpy contributions and a substantial zero-point energy (4.2 kJ mol(-1)) calculated from DFT+D vibrational frequencies. The comparison shows that our final hybrid MP2?:?PBE+D+ΔCCSD(T) estimate has reached chemical accuracy. It misses 2-3 kJ mol(-1) of binding only, which is most likely due to missing higher order correlation effects.PBE+D(ispersion) itself yields an adsorption energy that agrees within 1 kJ mol(-1) with our final hybrid MP2?:?PBE+D+ΔCCSD(T) estimate.     

SFG study of the ethanol in an acidic medium--Pt(110) interface: effects of the alcohol concentration

Ethanol in an acidic solution-Pt(110) interface was studied by SFG spectroscopy (between 1820 and 2325 cm(-1)) to explore primarily the effects of the alcohol concentration. Stretching bands of H-Pt (ca. 1970 or 2050 cm(-1)) and CO (ca. 1980 and 2040 cm(-1)) species, produced by the ethanol oxidation, were detected during the adsorption and oxidation of 0-1 mol L(-1) ethanol in a 0.1 mol L(-1) HClO(4) solution on the electrode surface. Hydrogen and CO coadsorb stably on Pt(110) between 0.05 and 0.15 V in ethanol-containing solutions. In this potential range, the blue shift of the hydrogen resonance (ca. 80 cm(-1)) reveals a weakening of the hydrogen bonding between adsorbed hydrogen and water molecules in the double layer. After the hydrogen desorption (0.15 V), the formation of compact CO islands, depending on the ethanol concentration, lifts the Pt(110) surface reconstruction. In ethanol-free solution, the surface remains reconstructed. The lower-frequency CO band is assigned to the CO species adsorbed on (1 x 2) reconstructed Pt(110) domains, having smaller local coverages, while the higher-frequency CO band is attributed to the close-packed CO species adsorbed on (1 x 1) patches. The reaction pathway forming CO(2) is less favored with increasing ethanol concentration.     

Photoinduced C-N bond cleavage in 2-azido-1,3-diphenyl-propan-1-one derivatives: photorelease of hydrazoic acid

Photolysis of 3-azido-1,3-diphenyl-propan-1-one (1a) in toluene yields 1,3-diphenyl-propen-1-one (2), whereas irradiation of 3-azido-2,2-dimethyl-1,3-diphenyl-propan-1-one (1b) results in the formation of mainly 2,2-dimethyl-1,3-diphenyl-propan-1-one. Laser flash photolysis (308 nm) of 1a,b in acetonitrile reveals a transient absorption (lambda max = approximately 310 nm) due to the formation of radicals 4a and 4b, respectively, which have lifetimes of approximately 14 micros at ambient temperature. TD-DFT calculations (B3LYP/6-31+G(d)) reveal that the first and second excited states of the triplet ketone (T1K (n,pi*) and T2K (pi,pi*)) in azide 1a are almost degenerate, at approximately 74 and 76 kcal/mol above the ground state (S0), respectively. Similarly, azide 1b has T1K and T2K 75 and 82 kcal/mol above S0, respectively. The calculated transition state for cleaving the C-N bond is located 71 and 74 kcal/mol above S0 in azides 1a and 1b, respectively. The calculated bond dissociation energies for breaking the C-N bond are 55 and 58 kcal/mol for azides 1a and 1b, respectively, making C-N bond breakage accessible from T1K in azides 1 at ambient temperature. In comparison, the irradiation of azides 1 in argon matrices at 14 K lead to the formation of the corresponding triplet alkyl nitrenes (1-n), via intramolecular energy transfer from T2K. The characterization of 1-n was supported by isotope labeling, IR spectroscopy, and molecular modeling.     

The photophysical properties of a julolidene-based molecular rotor

The photophysical properties of 9-dicyanovinyljulolidine are sensitive to solvent viscosity but are little affected by changes in polarity. In fluid solution, the lifetime of the first-excited singlet state is very short and triplet state formation cannot be detected by laser flash photolysis. Decay of the excited singlet state is strongly activated and weak phosphorescence can be observed in a glassy matrix at 77 K. Temperature dependent 1H NMR studies indicate that the molecule undergoes slow internal rotation in solution, for which the activation energy has a value of ca. 35 kJ mol(-1). This process is unlikely to account for the poor fluorescence quantum yield found in fluid solution. Instead, it is considered that the target compound undergoes rapid rotation around the dicyanovinyl double bond from the excited singlet state. The rate of rotation depends weakly on the viscosity of the solvent in a range of linear alcohols at room temperature. This might represent the fact that the rotor is relatively small and can pack into cavities in the solvent structure. In glycerol, the rate of rotation is more sensitive to viscosity effects but a quite complex temperature dependence is observed in ethanol. Here, the rate is almost activationless in a glassy matrix and in fluid solution at high temperature but strongly activated at intermediate temperatures.     

Temperature dependence of the Landau-Placzek ratio in glass forming liquids

Here, we studied Rayleigh-Brillouin light scattering in ten different glass-forming liquids (α-picoline, toluene, o-toluidine, ethanol, salol, glycerol, dibutyl phthalate, o-terphenyl, propylene carbonate, and propylene glycol). For each of these liquids it was found that the Landau-Placzek ratio is in a good agreement with the theory at high temperatures and significantly exceeds the theoretical prediction below a certain temperature. Transition between the two temperature regimes occurs near T(A), where T(A) is crossover point from an Arrhenius-like to a non-Arrhenius behavior for the α-relaxation time dependence on temperature. Increase of the Landau-Placzek ratio relative to the theoretical prediction below T(A) seems to be the universal feature of glass-formers. We suggest that formation of locally favored structures in liquids below T(A) causes observed excess of the Landau-Placzek ratio.     

Simulations of concentrated suspensions of rigid fibers: relationship between short-time diffusivities and the long-time rotational diffusion

Brownian dynamics simulations of the behavior of suspensions of fibers demonstrate that the scaling of the rotational diffusivity with respect to the number density (nL3) is a sensitive function of the thickness and the parameter L2D(R0)/D(T0), where D(R0) is the rotational diffusivity at infinite dilution, D(T0) is the average center-of-mass diffusivity at infinite dilution, and L is the fiber length. Existing theories for the long-time rotational diffusivities of rigid fibers in the semidilute and concentrated regimes fail to accurately account for the relationship with the dilute values of the rotational and translational diffusivities of the various physical models used to simulate the fibers. The concentration regime studied in this work ranges from a number density of nL3 approximately 0-150, which is below the transition from an isotropic to nematic state. The effect of the fiber thickness was studied by performing simulations of rods with aspect ratios (fiber length over diameter) of 25, 50, and 500, as well as performing projections for infinitely thin fibers. The excluded volume of the rods was enforced through the use of short-range potentials. For a rod with an aspect ratio of 50 with a parameter of L2D(R0)/D(T0)=9, which corresponds to a slender-body model of the individual fibers, the rotational diffusivity (D(R)) scales as D(R)/D(R0) approximately (nL3)(-1.9) in the concentration regime of 70 < or = nL3 < or = 150. Similarly with a parameter of L2D(R0)/D(T0)=4, corresponding to a rigid-dumbbell model, the rotational diffusivity scales as D(R)/D(R0) approximately (nL3)(-1.1) over the same range of concentrations. For rods with aspect ratios of 25, it is observed that a difference in the scaling is seen for L2D(R0)/D(T0) approximately < 8, with higher values of this ratio exhibiting essentially the same scaling. Additional values of the ratio L2D(R0)/D(T0) were investigated to determine the overall behavior of the suspension dynamics with respect to this parameter. These findings resolve discrepancies between simulation results for rotational diffusivities reported by previous investigators and provide new insights for the development of an accurate theory for the diffusivity of rigid rods suspended in solution.     

Reversible pressure deformation of a thermophilic cytochrome P450 enzyme (CYP119) and its active-site mutants

The pressure stability of the thermophilic CYP119 from Sulfolobus solfataricus and its active-site Thr213 and Thr214 mutants was investigated. At 20 degrees C and pH 6.5, the protein undergoes a reversible P450-to-P420 inactivation with a midpoint at 380 MPa and a reaction volume change of -28 mL/mol. The volume of activation of the process was -9.5 mL/mol. The inactivation transition was retarded, and the absolute reaction volume was decreased by increasing temperature or by mutations that decrease the size of the active-site cavity. High pressure affected the tryptophan fluorescence yield, which decreased by about 37% at 480 MPa. The effect was reversible and suggested considerable contraction of the protein. Aerobic decomposition of iron-aryl complexes of the CYP119 T213A mutant under increasing hydrostatic pressure resulted in variation of the N-arylprotoporphyrin-IX regioisomer (N(B):N(A):N(C):N(D)) adduct pattern from 39:47:07:07 at 0.1 MPa to 23:36:14:27 at 400 MPa. Preincubation of the protein at 400 MPa followed by complex formation and decomposition gave the same regioisomer distribution as untreated protein. The results indicate that the protein is reversibly inactivated by pressure, in contrast to the irreversible inactivation of P450(cam) and other P450 enzymes, and that this inactivation process is modulated by changes in the active-site cavity dimensions.     

Effects of osmolytes on the helical conformation of model peptide: molecular dynamics simulation

Co-solvents such as glycerol and sorbitol are small organic molecules solvated in the cellular solutions that can have profound effects on the protein structures. Here, the molecular dynamics simulations and comparative structural analysis of magainin, as a peptide model, in pure water, 2,2,2-trifluoroethanol∕water, glycerol∕water, and sorbitol∕water are reported. Our results show that the peptide NMR structure is largely maintained its native structure in osmolytes-water mixtures. The simulation data indicates that the stabilizing effect of glycerol and sorbitol is induced by preferential accumulation of glycerol and sorbitol molecules around the nonpolar and aromatic residues. Thus, the presence of glycerol and sorbitol molecules decreases the interactions of water molecules with the hydrophobic residues of the peptide, and the alpha helical structure is stabilized.     

Peroxy radical isomerization in the oxidation of isoprene

We report experimental evidence for the formation of C(5)-hydroperoxyaldehydes (HPALDs) from 1,6-H-shift isomerizations in peroxy radicals formed from the hydroxyl radical (OH) oxidation of 2-methyl-1,3-butadiene (isoprene). At 295 K, the isomerization rate of isoprene peroxy radicals (ISO2?) relative to the rate of reaction of ISO2? + HO2 is k(isom)(295)/(k(ISO2?+HO2)(295)) = (1.2 ± 0.6) x 10(8) mol cm(-3), or k(isom)(295) ? 0.002 s(-1). The temperature dependence of this rate was determined through experiments conducted at 295, 310 and 318 K and is well described by k(isom)(T)/(k(ISO2?+HO2)(T)) = 2.0 x 10(21) exp(-9000/T) mol cm(-3). The overall uncertainty in the isomerization rate (relative to k(ISO2?+HO2)) is estimated to be 50%. Peroxy radicals from the oxidation of the fully deuterated isoprene analog isomerize at a rate ～15 times slower than non-deuterated isoprene. The fraction of isoprene peroxy radicals reacting by 1,6-H-shift isomerization is estimated to be 8-11% globally, with values up to 20% in tropical regions.     

Characterization of a shallow-bound 0g+ valence state of I2 using emission from the D 0u+(3P2) and F' 0u+(1D2) ion-pair states populated by amplified spontaneous emission

A range of vibrational levels of the D 0(u)(+)((3)P(2)) and F' 0(u)(+)((1)D(2)) ion-pair states of I(2) is shown to be easily generated by amplified spontaneous emission (ASE) from their more accessible partners, E 0(g)(+)((3)P(2)) and f' 0(g)(+)((1)D(2)), in sufficient concentration for dispersed fluorescence studies of the D 0(u)(+)((3)P(2)) --> 0(g)(+)(bb) and F' 0(u)(+)((1)D(2)) --> 0(g)(+)(bb) transitions to be carried out. T(0) (J = 49) of this shallow-bound 0(g)(+)(bb) valence state is unambiguously determined and an improved R(e) value of 3.952 +/- 0.005 A is obtained from optimizing the fit of the intensities of the vibrational progressions in the 0(g)(+)(bb) state, and T(e) is found to be 27311.3 +/- 2 cm(-1), leading to D(e) = 442.0 +/- 2 cm(-1).