LY3041658/ interleukin-8 complex structure as targets for IL-8 small molecule inhibitors discovery using a combination of in silico methods

Since interleukin-8 (IL-8/CXCL8) and its receptor, CXCR1 and CXCR2, were known in the early 1990s, biological pathways related to these proteins were proven to have high clinical value in cancer and inflammatory/autoimmune conditions treatment. Recently, IL-8 has been identified as biomarker for severe COVID-19 patients and COVID-19 prognosis. Boyles et al. (mAbs 12 (2020), pp. 1831880) have published a high-resolution X-ray crystal structure of the LY3041658 Fab in a complex human CXCL8. They described the ability to bind to IL-8 and the blocking of IL-8/its receptors interaction by the LY3041658 monoclonal antibody. Therefore, the study has been designed to identify potential small molecules inhibiting interleukin-8 by targeting LY3041658/IL-8 complex structure using an in silico approach. A structure‑based pharmacophore and molecular docking models of the protein active site cavity were generated to identify possible candidates, followed by virtual screening with the ZINC database. ADME analysis of hit compounds was also conducted. Molecular dynamics simulations were then performed to survey the behaviour and stability of the ligand-protein complexes. Furthermore, the MM/PBSA technique has been utilized to evaluate the free binding energy. The final data confirmed that one newly obtained compound, ZINC21882765, may serve as the best potential inhibitor for IL-8.

Discovery of superconductivity in AlB2-type hexagonal YGa2

A crystalline sample YGa₂with the AlB₂-type hexagonal structure has been synthesized using the self-flux method. We measured electrical resistivity and specific heat down to 0.4 K and in fields up to 200 mT. The obtained data reveal type-II superconductivity. Unusual behaviour of the temperature dependence of upper critical fieldH_c2(T_c) was attributed to the crystal twinning of two phases possessing close lattice parameters. We determined thermodynamic parameters in the superconducting and normal states of YGa₂. DFT calculations indicated a large change in the Fermi velocity of carriers nearby cylinder-like structured Fermi surface along the Γ -Aline.

Magnetic interactions in graphene decorated with iron oxide nanoparticles

We present the studies of structural and magnetic properties of graphene composites prepared with several quantities ofα-Fe₂O₃dopant of 5%, 25% and 50% made with either ethanol or acetone. Our studies showed the presence of a weak magnetic order up to room temperature and saturation magnetization close to 0.2 emu g^-1in pure commercial graphene. With regard to magnetic properties of our graphene + iron oxide samples, the solvent used during the preparation of the composite had a significant influence on them. For graphene + Fe₂O₃samples made with acetone the magnetic properties of pure graphene played a major role in the overall magnetic susceptibility and magnetization. On the other hand, for graphene + iron oxide samples made with ethanol we observed the presence of superparamagnetic blocking atT < 110 K which was due to the additional appearance ofγ-Fe₃O₄nanoparticles. Changes in the synthesis solvent played a major role in the magnetic properties of our graphene + Fe₂O₃nanocomposite samples resulting in much higher saturation magnetization for the samples made with ethanol. Both the shape and the parameters characterizing magnetization hysteresis loops depend strongly on the amount of iron oxide and changes in the preparation method.

Physical properties of the layered oxypnictide Sr2ScFeAsO3: a Mössbauer study down to 1.7 K

A polycrystalline sample of Sr2ScFeAsO3was studied by57Fe Mössbauer spectroscopy down to 1.7 K. In contrast to the earlier Mössbauer data, the obtained in this work results indicate that Sr2ScFeAsO3is in paramagnetic state down to 10 K, while the spectra recorded at 4.6 K and 1.7 K show a weak magnetic order of Fe moments in the Fe2As2layers. Temperature dependences of isomer shift and quadrupole splitting/shift are compared with specific heat and electrical resistivity data from earlier investigations revealing different local Debye temperatures for the Fe2As2and perovskite-related Sr2ScO3layers. Finally, a fast decrease of the carrier density was observed below 80 K and this effect seems to be responsible for the absence of superconductivity in the studied compound.

57Fe Mössbauer and magnetic studies of Th7Co2.5 57Fe0.5 and Th7Ni2.5 57Fe0.5 superconductors

The noncentrosymmetric Th₇Co_2.5 ⁵⁷Fe_0.5 and Th₇Ni_2.5 ⁵⁷Fe_0.5 superconductors were studied by means of ⁵⁷Fe transmission Mössbauer spectroscopy (TMS), ac-magnetic susceptibility and magnetization measurements. The low-temperature data showed that both compounds are type-II superconductors with transition temperature close to [Formula: see text] K. The collected Mössbauer spectra of the studied samples consist of one well-resolved doublet over the temperature range measured. Neither abnormal behaviour of the hyperfine parameters at or near [Formula: see text] nor phonon softening were found. A comparison of ⁵⁷Fe Mössbauer data of Ni- and Co-based superconductors with those of Th₇Fe₃ indicated that with decreasing 3d-electron numbers across the series Th₇Ni_2.5 ⁵⁷Fe_0.5 [Formula: see text] Th₇Co_2.5 ⁵⁷Fe_0.5 [Formula: see text] Th₇Fe₃, the s-electron density around the Fe nucleus and as well as the electric field gradient strength increases. The latter finding is associated with increasing asymmetricity of 3d-electron distribution and this fact presumably gives arise to an exotic superconductivity in the Co- and Fe-based compounds.

Superconducting-state properties and electronic band structure calculations of a noncentrosymmetric Th7Ni3 compound

Superconducting-state properties of a noncentrosymmetric Th₇Ni₃ compound have been investigated using magnetic, electrical resistivity and specific heat measurements as well as by electronic band structure calculations. The study reveals that the studied compound is a dirty type-II superconductor with [Formula: see text] K and a weak electron-phonon coupling [Formula: see text]. Moreover, in contrast to an exotic superconductivity observed previously in Th₇Fe₃ and Th₇Co₃, data reported in this paper give clear evidence that Th₇Ni₃ is a conventional single-gap superconductor. The experimental results are supported by DFT calculations of the electronic band structure, density of states, electron localization functions and Fermi surfaces which were performed using the full-potential linear muffin-tin-orbital and full-potential linearized augmented plane wave methods. Theoretical data show that asymmetric spin-orbit coupling in Th₇Ni₃ is quite small; hence the electronic band structure of this compound is weakly affected by the spin-orbit effects. We have determined fundamental parameters of Th₇Ni₃ and compared the superconducting properties with other Th₇T₃ (T  =  Fe, Co and Ru) compounds.

Specific heat and Hall effect of the ferromagnetic Kondo lattice UCu0.9Sb2

We have investigated the electrical resistivity ρ, specific heat C _p and Hall coefficient R _H on a single crystal of a ferromagnetic Kondo lattice UCu_0.9Sb₂. The experimental [Formula: see text], C _p (T) and [Formula: see text] data evidence a bulk magnetic phase transition at [Formula: see text] K, and additionally exhibit an unexpected bump located in the temperature range T _C/10-T _C/3. UCu_0.9Sb₂ has an enhanced electronic specific heat coefficient [Formula: see text] mJ molK^-2, corresponding to Kondo temperature [Formula: see text] K. An analysis of the Hall effect data for j//(a, b)-plane and H// c-axis reveals that the low-temperature ordinary Hall coefficient R ₀ is positive, suggesting that p-type electrical conductivity is dominant. The density of the carriers at 2 K is about 0.6 holes f.u.^-1, which may categorize the studied compound into class of low carrier density compounds. Combined γ and R ₀ data divulge an effective mass of charge carriers [Formula: see text] 27 m _e . This finding together with quite low Hall mobility [Formula: see text] cm² Vs^-1 and Kadowaki-Woods ratio [Formula: see text] [Formula: see text] cm (mol K² mJ^-1)², manifest the development of heavy-fermion state in the ferromagnetic UCu_0.9Sb₂ compound at low temperatures.

The influence of temperature, pressure and Ag doping on the physical properties of TiO2 nanoceramics

Undoped and Ag-doped TiO₂ ceramics have been prepared at temperatures between 500-1000 °C and under pressures up to 8 GPa. Their crystal structures and physical properties were investigated by means of EDX, SEM, TEM, X-ray powder diffraction, and magnetization M, specific heat C_p and electrical resistance ρ measurements. It is found that the anatase-structured As-cast powder transforms into rutile and columbite-type at 500 °C and 5.5 GPa. The stabilization of the latter phase is fulfilled under a pressure of 8 GPa and at temperatures above 800 °C. On the basis of experimental results, we conclude that the physical properties of TiO₂ can be tailored along with its crystal structure. In particular, magnetic properties change from paramagnetic in anatase and rutile to magnetic correlations and in all likelihood magnetic-field-induced antiferromagnetic short-range order in columbite-structured TiO₂. Contrasting behaviour in the temperature dependences of specific heat between anatase/rutile and columbite-type TiO₂ is obvious. Differently from anatase/rutile, the C_p of columbite-type TiO₂ exhibits a low-temperature excess, being interpreted as due to magnetic correlations, or else the prevalence of soft modes. An analysis of ρ(T) for columbite-type TiO₂ in the temperature range of 280-400 K reveals the presence of a new trapping state at an energy level of ∼28 meV within the originally forbidden gap. Furthermore, thermal fluctuation-induced tunnelling and hopping conductivities are suggested to govern in a lower temperature range. We recognize that the Ag-doped contents do not alter the crystal structure but considerably enhance magnetic correlations, compared to undoped samples.

Physical properties and electronic band structure of noncentrosymmetric Th7Co3 superconductor

The physical properties of the noncentrosymmetric superconductor Th7Co3 have been investigated by means of ac-magnetic susceptibility, magnetization, specific heat, electrical resistivity, magnetoresistance and Hall effect measurements. From these data it is established that Th7Co3 is a dirty type-II superconductor with [Formula: see text] K, [Formula: see text] and moderate electron-phonon coupling [Formula: see text]. Some evidences for anisotropic superconducting gap are found, including e.g. reduced specific heat jump ([Formula: see text]) at T c, diminished superconducting energy gap ([Formula: see text]) as compared to the BCS values, power law field dependence of the Sommerfeld coefficient at 0.4 K ([Formula: see text]), and a concave curvature of the [Formula: see text] line. The magnitudes of the thermodynamic critical field and the energy gap are consistent with mean-squared anisotropy parameter [Formula: see text]. The electronic specific heat in the superconducting state is reasonably fitted to an oblate spheroidal gap model. Calculations of scalar relativistic and fully relativistic electronic band structures reveal considerable differences in the degenerate structure, resulting from asymmetric spin-orbit coupling (ASOC). A large splitting energy of spin-up spin-down bands at the Fermi level E F, [Formula: see text] meV is observed and a sizeable ratio [Formula: see text] could classify the studied compound into the class of noncentrosymmetric superconductors with strong ASOC. The noncentrosymmetry of the crystal structure and the atomic relativistic effects are both responsible for an importance of ASOC in Th7Co3. The calculated results for the density of states show a Van Hove singularity just below E F and dominant role of the 6d electrons of Th to the superconductivity.

Dielectric properties of Co(CO3)(H2O)2(C3H4N2)2 and [Co(C3H3N2)2]n

Dielectric relaxation phenomenon with non-Debye dynamics in Co(CO₃)(H₂O)₂(C₃H₄N₂)₂ and [Co(C₃H₃N₂)₂]_n, resembling the behaviour of ferroelectric relaxors is presumably connected with the charge carriers.

Muon spin rotation and relaxation studies of the filled skutterudite superconductor ThPt4Ge12

Longitudinal and transverse field muon spin rotation/relaxation measurements have been carried out on a polycrystalline sample of ThPt(4)Ge(12). The zero-field measurements in the longitudinal geometry do not reveal any signature of a spontaneous internal magnetic field below the superconducting transition temperature, indicating the preservation of time-reversal symmetry in the superconducting state of ThPt(4)Ge(12). From the transverse field data, the zero field magnetic penetration depth, λ(0), was estimated to be 110(15) nm, and then we have estimated the effective mass of the quasiparticles, m*≈4.5m(e), and the superfluid carrier density, n(s)≈1.06 × 10(28) carriers m(-3). We found a marked difference between the zero-field cooling and field-cooled vortex state muon spin relaxation rates, σ(s)(T), below the irreversibility temperature, T(ir) ∼ 2.5 K. A linear field dependence of σ(s)(H) and power law behaviour of σ(s)(T) exhibit a significant deviation from those expected for isotropic BCS-superconductors. The analysis of correlation between the superconducting transition temperature and the effective Fermi temperature within the Uemura classification scheme reveals that the condensation energy in ThPt(4)Ge(12) is comparable to those of exotic superconductors.

Evidence for a spin pseudogap in the normal state of superconducting Mo(3)Sb(7)

Using muon spin relaxation (μSR) and inelastic neutron scattering (INS) we have investigated the normal state of the superconductor Mo(3)Sb(7) and the reference compound Ru(3)Sn(7). The μSR experiments on Ru(3)Sn(7) reveal static and relatively slow dynamic relaxations, which are ascribed to a random static nuclear dipole field and thermally activated muon motion, respectively. INS experiments on Ru(3)Sn(7), on the other hand, reveal three phononic excitations at 11, 18 and 23 meV, substantiating the assertion of Einstein and Debye oscillations derived from the specific heat and electrical resistivity data. The distinct difference in the μSR as well as INS spectra between Ru(3)Sn(7) and Mo(3)Sb(7) provides strong evidence for a magnetic/electronic nature of the phase transition at T(*) = 50 K in the Mo-based compound. On the basis of the μSR and INS data, the energy spin pseudogap of 150(10) K was estimated. The observed weak magnetism in the dynamic susceptibility χ('')(Q,ω) and residual longitudinal field relaxation at 5 K imply a static ordering or quantum fluctuations.

Emergence of a superconducting state from an antiferromagnetic phase in single crystals of the heavy fermion compound Ce2PdIn8

Single crystals of Ce2PdIn8 were studied by means of magnetic susceptibility, electrical resistivity, and specific heat measurements. The compound was found to be a heavy fermion clean-limit superconductor with Tc=0.68 K. Most remarkably, the superconductivity in this system emerges out of the antiferromagnetic state that sets in at TN=10 K, and both cooperative phenomena coexist in a bulk at ambient pressure conditions.

Specific reversal of multidrug resistance to colchicine in CEM/VLB(100) cells by Gynostemma pentaphyllum extract

P-glycoprotein (P-gp)-mediated multiple drug resistance (MDR) is perhaps the most thoroughly studied cellular mechanism of cytotoxic drug resistance. Its efflux function can be circumvented by a wide range of pharmacological agents in vitro and in vivo. Most of these agents are pharmaceuticals used clinically for conditions other than cancer. However, their use in alleviating MDR is limited because the concentrations required for inhibition of the pump surpass their dose-limiting toxicity. The aim of this research is to study the role of gypenosides, isolated from Gynostemma pentaphyllum, as modulators of P-gp-mediated MDR in tumor cells, at both cellular and plasma membrane level. In the presence of total gypenoside preparation (0.1 mg/ml), an approximately 15-fold reversal of colchicine (COL) resistance was observed in P-gp-overexpressed CEM/VLB(100) cells. However, the gypenoside sample showed no reversal effect in cells treated with vinblastine and taxol. A purified gypenoside sample (gypenoside fraction 100) exhibited even more significant reversal of COL resistance (approximately 42-fold) in the CEM/VLB(100) cells. Further examination of the reversal effect of fraction 100 in membrane vesicles derived from CEM/VLB(100) cells using the continuous fluorescence method found that gypenoside fraction 100 at 0.1 mg/ml completely abolished the transport of fluorescein-COL.

Intermediate valence behaviour of Yb in a new intermetallic compound YbNi(0.8)Al(4.2)

We report on the valence band electronic structure as well as structural, magnetic and electronic transport properties of a novel intermetallic YbNi(0.8)Al(4.2). The compound crystallizes in the orthorhombic YNiAl(4)-type structure (a = 4.049(2),b = 15.305(5) and c = 6.586(3) Å) with space group Cmcm. The valence band spectrum and magnetic data indicate an intermediate valency of Yb ions in the studied compound with a valence of about 2.66 at room temperature. The temperature dependences of electrical resistivity, Hall effect and thermoelectric power display characteristic features of Kondo lattice with a large Kondo temperature (∼1300 K), being consistent with the intermediate valence scenario. An analysis of magnetic data suggests the presence of strong ferromagnetic correlations in the investigated compound at low temperatures. In order to obtain information about the electron-hole analogy between the Ce and Yb compounds, we have compared the observed behaviour with that of the dense Kondo compound CeNiAl(4).

Photoemission studies and electronic structure of U(2)T(2)In (T = Ni, Rh, Pt) compounds

The electronic structure of the tetragonal U(2)T(2)In (T = Ni, Rh, Pt) compounds in the paramagnetic phase were studied by x-ray photoelectron spectroscopy (XPS). Both valence band and core level spectra were analysed. The experimental data are compared with the calculations of the density of states using the tight-binding linear muffin-tin orbital method (TB-LMTO) and full-potential local-orbital full-relativistic method (FPLO). The calculated data reveal a dominant U 5f electron character for the states near the Fermi level E(F) with a small contribution from U 5d, Ni 3d, Rh 4d, Pt 5d and In 5p states. The XPS valence bands of these compounds are characterized by a sharp peak of the U 5f states near the Fermi level (E(F)) and broad peaks of the Ni 3d, Rh 4d and Pt 5d states at about 2.6, 3.2 and 4.0 eV below E(F), respectively. The small change in the position of the U 5f peak with respect to E(F) is -0.35 eV for T = Ni and -0.15 eV for T = Rh and Pt. A satellite between the Ni 2p(1/2) and Ni 2p(3/2) peaks is visible, suggesting that the Ni 3d band is not completely filled, and the existence of a small induced magnetic moment on the Ni atoms cannot be ruled out.

Performance measurements of a depth-encoding PET detector module based on position-sensitive avalanche photodiode read-out

We are developing a high-resolution, high-efficiency positron emission tomography (PET) detector module with depth of interaction (DOI) capability based on a lutetium oxyorthosilicate (LSO) scintillator array coupled at both ends to position-sensitive avalanche photodiodes (PSAPDs). In this paper we present the DOI resolution, energy resolution and timing resolution results for complete detector modules. The detector module consists of a 7 x 7 matrix of LSO scintillator crystals (1 x 1 x 20 mm3 in dimension) coupled to 8 x 8 mm2 PSAPDs at both ends. Flood histograms were acquired and used to generate crystal look-up tables. The DOI resolution was measured for individual crystals within the array by using the ratio of the signal amplitudes from the two PSAPDs on an event-by-event basis. A measure of the total scintillation light produced was obtained by summing the signal amplitudes from the two PSAPDs. This summed signal was used to measure the energy resolution. The DOI resolution was measured to be 3-4 mm FWHM irrespective of the position of the crystal within the array, or the interaction location along the length of the crystal. The total light signal and energy resolution was almost independent of the depth of interaction. The measured energy resolution averaged 14% FWHM. The coincidence timing resolution measured using a pair of identical detector modules was 4.5 ns FWHM. These results are consistent with the design goals and the performance required of a compact, high-resolution and high-efficiency PET detector module for small animal and breast imaging applications.

Fascioliasis in Vietnam

A confirmed diagnosis of human fascioliasis was rare in Vietnam until 1978 when two cases were reported in humans. Since 1997, we have confirmed 500 cases of human fascioliasis. The majority of cases come from the central provinces of Vietnam: Da Nang, Quang Ngai, Binh Dinh, Phu Yen and Khanh Hoa. Patients were treated in hospitals in Ho Chi Minh City. All had high peripheral blood eosinophilic counts (16-70%) and positive serology with Fasciola gigantica antigen with positive titers of 1/1,600 to 1/12,800. We are unsure whether this represents an endemic pattern of disease or whether improved specific laboratory tools now facilitate better diagnosis. It is also possible that with changes in environmental factors and in the number and breeds of herbivorous domestic animals, Fasciola is increasing in frequency and easily contaminates the food.

The stability of gingerol and shogaol in aqueous solutions

Gingerols, pungent principles of ginger (the rhizome of Zingiber officinale), are biologically active components that may make a significant contribution towards medicinal applications of ginger and some products derived from ginger. Gingerols, however, are thermally labile due to the presence of a beta-hydroxy keto group in the structure, and undergo dehydration readily to form the corresponding shogaols. This study investigated the stability of [6]-gingerol [5-hydroxy-1-(4-hydroxy-3-methoxyphenyl)decan-3-one] at temperatures ranging from 37 to 100 degrees C in aqueous solutions, at pH 1, 4, and 7. Quantitative measurements of [6]-gingerol and its major degradation product [6]-shogaol [1-(4-hydroxy-3-methoxyphenyl)decan-4-ene-3-one] were performed by HPLC. Kinetics of [6]-gingerol degradation was characterized by least square fitting of a rate equation. It was found that gingerol exhibited novel reversible kinetics, in which it undergoes dehydration-hydration transformations with shogaol, the major degradation product. Degradation rates were found to be pH dependent with greatest stability observed at pH 4. The reversible degradation of [6]-gingerol at 100 degrees C and pH 1 was relatively fast and reached equilibrium within 2 h. Activation energies for the forward and reverse reactions for [6]-gingerol were calculated from the Arrhenius equation using reaction rates obtained at temperatures ranging from 37 to 100 degrees C.

Architecture of the pulmonary veins: relevance to radiofrequency ablation

BACKGROUND

Radiofrequency ablation of tissues in pulmonary veins can eliminate paroxysmal atrial fibrillation.

OBJECTIVE

To explore the characteristics of normal pulmonary veins so as to provide more information relevant to radiofrequency ablation.

METHODS

20 structurally normal heart specimens were examined grossly. Histological sections were made from 65 pulmonary veins.

RESULTS

The longest myocardial sleeves were found in the superior veins. The sleeves were thickest at the venoatrial junction in the left superior pulmonary veins. For the superior veins, the sleeves were thickest along the inferior walls and thinnest superiorly. The sleeves were composed mainly of circularly or spirally oriented bundles of myocytes with additional bundles that were longitudinally or obliquely oriented, sometimes forming mesh-like arrangements. Fibrotic changes estimated at between 5% and 70% across three transverse sections were seen in 17 veins that were from individuals aged 30 to 72 years.

CONCLUSIONS

The myocardial architecture in normal pulmonary veins is highly variable. The complex arrangement, stretch, and increase in fibrosis may produce greater non-uniform anisotropic properties.

Gingerols and related analogues inhibit arachidonic acid-induced human platelet serotonin release and aggregation

Gingerols, the active components of ginger (the rhizome of Zingiber officinale, Roscoe), represent a potential new class of platelet activation inhibitors. In this study, we examined the ability of a series of synthetic gingerols and related phenylalkanol analogues (G1-G7) to inhibit human platelet activation, compared to aspirin, by measuring their effects on arachidonic acid (AA)-induced platelet serotonin release and aggregation in vitro. The IC(50) for inhibition of AA-induced (at EC(50)=0.75 mM) serotonin release by aspirin was 23.4+/-3.6 microM. Gingerols and related analogues (G1-G7) inhibited the AA-induced platelet release reaction in a similar dose range as aspirin, with IC(50) values between 45.3 and 82.6 microM. G1-G7 were also effective inhibitors of AA-induced human platelet aggregation. Maximum inhibitory (IC(max)) values of 10.5+/-3.9 and 10.4+/-3.2 microM for G3 and G4, respectively, were approximately 2-fold greater than aspirin (IC(max)=6.0+/-1.0 microM). The remaining gingerols and related analogues maximally inhibited AA-induced platelet aggregation at approximately 20-25 microM. The mechanism underlying inhibition of the AA-induced platelet release reaction and aggregation by G1-G7 may be via an effect on cyclooxygenase (COX) activity in platelets because representative gingerols and related analogues (G3-G6) potently inhibited COX activity in rat basophilic leukemia (RBL-2H3) cells. These results provide a basis for the design of more potent synthetic gingerol analogues, with similar potencies to aspirin, as platelet activation inhibitors with potential value in cardiovascular disease.

Effect of ginger constituents and synthetic analogues on cyclooxygenase-2 enzyme in intact cells

Seventeen pungent oleoresin principles of ginger (Zingiber officinale, Roscoe) and synthetic analogues were evaluated for inhibition of cyclooxygenase-2 (COX-2) enzyme activity in the intact cell. These compounds exhibited a concentration and structure dependent inhibition of the enzyme, with IC(50) values in the range of 1-25 microM. Ginger constituents, [8]-paradol and [8]-shogaol, as well as two synthetic analogues, 3-hydroxy-1-(4-hydroxy-3-methoxyphenyl)decane and 5-hydroxy-1-(4-hydroxy-3-methoxyphenyl)dodecane, showed strong inhibitory effects on COX-2 enzyme activity. The SAR analysis of these phenolic compounds revealed three important structural features that affect COX-2 inhibition: (i) lipophilicity of the alkyl side chain, (ii) substitution pattern of hydroxy and carbonyl groups on the side chain, and (iii) substitution pattern of hydroxy and methoxy groups on the aromatic moiety.

Disaccharide conformational flexibility. I. An adiabatic potential energy map for sucrose

Constrained conformational energy minimizations have been used to calculate an adiabatic (phi, psi) potential energy surface for the disaccharide sucrose. The inclusion of molecular flexibility in the conformational energy analysis of this disaccharide was found to have a significant effect upon the allowed conformational space of the molecule. Three low-energy regions were identified on the adiabatic energy surface, and two of these regions were found to contain two related local minimum-energy conformations, with similar energies, differing only in the directionality of the intra-residue hydrogen bonds of the glucose portion of the molecule. The known crystal structures of seven molecules containing the sucrose moiety all fall within the region of the primary allowed minimum and are consistent with the relaxed energy map, while these crystal conformations could not be rationalized using energy maps for rigid residue geometries. The greater flexibility of the furanoid ring relative to that of the pyranoid ring contributed significantly to the enlargement of the low-energy region on the adiabatic map. However, in spite of the importance of limited flexibility in understanding the conformation and fluctuations of sucrose, this molecule was found to be considerably more rigid that some other disaccharides, such as maltose and cellobiose, in accord with experimental studies.

Disaccharide conformational flexibility. II. Molecular dynamics simulations of sucrose

Molecular dynamics simulations have been used to study the motions in vacuum of the disaccharide sucrose. Ensembles of trajectories were calculated for each of the five local minimum energy conformations identified in the adiabatic conformational energy mapping of this molecule. The model sucrose molecules were found to exhibit a variety of motions, although the global minimum energy conformation was found to be dynamically stable, and no transitions away from this structure were observed to occur spontaneously. In all but one of these vacuum trajectories, the intramolecular hydrogen bond between residues was maintained, in accord with recent nmr studies of this molecule in aqueous solution. Considerable flexibility of the furanoid ring was found in the trajectories. No "flips" to the opposite puckering for this ring were found in the simulations starting from the global minimum, although such a transition was observed for a trajectory initiated with one of the higher local minimum energy conformations. Overall, the observed structural fluctuations were consistent with the experimental picture of sucrose as a relatively rigid molecule.