Molecular Ellipticity Research Articles

Comparison study on atomic and molecular ellipticity dependence of high-order harmonic generation

We systematically investigate ellipticity dependence of high-order harmonic generation of Ar and ${\mathrm{N}}_{2}$ in intense elliptically polarized laser fields. The experimental normalized ratios of low-order harmonic intensity to high-order harmonic intensity increase with ellipticity for both Ar and ${\mathrm{N}}_{2}$, and quantitatively depend on targets and trajectory paths. The experimental results are well reproduced by a nonadiabatic semiclassical simulation and explained by trajectory-based analysis. In addition, the influence of nuclear distance on the ratios is theoretically investigated. Our work reveals that the difference between atoms and molecules can be attributed to the influence of different ionic potentials, which depends on the molecular structure (internuclear distance) and alignment, on the evolution of the photoelectron.

Molecular Ellipticity of Circulating Albumin-Bilirubin Complex Associates With Mortality in Patients With Severe Alcoholic Hepatitis

Hyperbilirubinemia and hypoalbuminemia are features of hepatic dysfunction that associate with disease severity. This is because hepatic insufficiency causes hypoalbuminemia, which indirectly increases the circulating levels of free bilirubin. Circular dichroism (CD) spectroscopy can be used to quantify the molecular ellipticity (ME) of the albumin-bilirubin complex, and might associate with the severity or outcome of severe alcoholic hepatitis (SAH). We performed a cross-sectional study of 265 patients with SAH admitted in the Department of Hepatology, Institute of Liver and Biliary Sciences in New Delhi, India from January 2014 through January 2016. Blood samples were collected and patients were followed for 12 months or death. The molar ratios of bilirubin: albumin and albumin-bilirubin complexes were determined for a discovery cohort (30 patients who survived the study period and 60 patients who did not survive) and compared with those of 60 patients with alcoholic cirrhosis and 30 healthy individuals (controls). Optical activities of albumin-bilirubin complexes in blood samples were determined by CD spectroscopy and compared among groups. Findings were validated in a separate cohort of 150 patients with SAH from the same institute. We studied the correlation between ME and albumin binding capacity (ABiC). The molar ratio of bilirubin: albumin was higher in patients with SAH than with alcoholic cirrhosis or controls (P < .05). Patients with SAH had different CD spectra and higher ME than the other groups (P < .01); ME correlated with model for end-stage liver disease score (with and without Na) and discriminant function (r2 > .3; P < .01). ME values above a cut off of 1.84 mdeg predicted 3-month mortality in patients with SAH with an area under receiver operating characteristic curve of 0.87 (95% CI, 0.79-0.95), a 77% positive predictive value, and a 90% negative predictive value. The hazard ratio and concordance index of ME values for 3-month mortality in patients with SAH was 10% higher than the hazard ratio and concordance index of model for end-stage liver disease score. In patients with SAH, there was an inverse correlation between ME and ABiC (r2 > 0.7; P < .01). We observed a significant reduction in ABiC with increasing levels of bilirubin invitro prepared albumin-bilirubin complex. In a cross-sectional study of patients with SAH, we associated ME of the albumin-bilirubin complex, measured by CD spectroscopy, with outcomes of patients with SAH. Increased loading of bilirubin on albumin could explain reduced albumin function. Bilirubin removal by albumin dialysis might benefit patients with SAH.

Directed Evolution of Recombinant C-Terminal Truncated Staphylococcus epidermidis Lipase AT2 for the Enhancement of Thermostability.

In the industrial processes, lipases are expected to operate at temperatures above 45 °C and could retain activity in organic solvents. Hence, a C-terminal truncated lipase from Staphylococcus epidermis AT2 (rT-M386) was engineered by directed evolution. A mutant with glycine-to-cysteine substitution (G210C) demonstrated a remarkable improvement of thermostability, whereby the mutation enhanced the activity five-fold when compared to the rT-M386 at 50 °C. The rT-M386 and G210C lipases were purified concurrently using GST-affinity chromatography. The biochemical and biophysical properties of both enzymes were investigated. The G210C lipase showed a higher optimum temperature (45 °C) and displayed a more prolonged half-life in the range of 40–60 °C as compared to rT-M386. Both lipases exhibited optimal activity and stability at pH 8. The G210C showed the highest stability in the presence of polar organic solvents at 50 °C compared to the rT-M386. Denatured protein analysis presented a significant change in the molecular ellipticity value above 60 °C, which verified the experimental result on the temperature and thermostability profile of G210C.

207 - Redox Activity Induced by Metal Coordination with Prion Peptide

Background Physiological function of prion protein (PrP) is still unknown, however its redox and metal-reservoir potentials are viewed as meaningful. We also showed the conformational change of the human PrP binding to Cu2+ [1]. In this report, we have examined the redox ability and the stability of metals at binding site using octarepeat peptide, which is a primary site for Cu2+ uptake in the N-terminal region of PrP. Materials and Methods An eight-residue peptide (PHGGGWGQ) of prion protein was used for the spectroscopic affinity assay for metal ions (Cu2+, Ni2+, Co2+, Zn2+, and Mn2+). For electron spin resonance (ESR), the peptide and Cu2+ were prepared as 0.1 mM in 10 mM HEPES buffer (pH 7.6) containing 30% glycerol. The ESR spectrum was acquired at 20 K. For circular dichroism (CD), the peptide and Cu2+ were prepared as 0.8 mM in 15 mM HEPES buffer. To verify competitive metal binding, octapeptide-Cu2+ was titrated with other divalent metal ions such as Ni2+, Co2+, Zn2+, and Mn2+. The reactivity of metal-containing peptide with ROS was analyzed by ESR spin trapping with CYPMPO. Results The ESR at 20K showed two types of coordination modes for the binding of octapeptide-Cu2+. The CD spectrum of octapepide-Cu2+ indicated the characteristic positive peak of molecular ellipticity at visible wavelengths, which was also assigned to Cu2+ coordination complexes. The CD peak of octapeptide-Cu2+was reduced by titrating with other divalent metal ions, such as Ni2+, Co2+, Zn2+, and Mn2+. ESR spin trapping showed that the copper-peptide complex converted superoxide into hydroxyl radical.

THU-319 - Molecular Ellipticity of Circulating Albumin-Bilirubin Complex is a Reliable Prognostic Measure of Severity of Acute on Chronic Liver Failure (ACLF)

THU-319 - Molecular Ellipticity of Circulating Albumin-Bilirubin Complex is a Reliable Prognostic Measure of Severity of Acute on Chronic Liver Failure (ACLF)

Comparative In Vitro Binding Studies of TiCl2(dpme)2, Ti(ada)2(bzac)2, and TiCl2(bzac)(bpme) Titanium Complexes with Calf-Thymus DNA.

The binding of TiCl2(dpme)2 (1), (dpme = 6,6′-dimethyl-2,2′-bipyridine), Ti(ada)2(bzac)2 (2), (ada = adamantylamine; bzac = benzoylacetone), and TiCl2(bzac)(bpme) (3), (bpme = 4,4′-dimethyl-2,2′-bipyrdine) with calf thymus (ct) DNA has been studied by UV-visible spectroscopy, thermal denaturation, and circular dichroism spectroscopy. In UV-visible study complexes 1, 2, and 3 showed red, blue, and red shifts, respectively, upon the addition of ct-DNA along with a significant hyperchromism. The intrinsic binding constants (K b) calculated from UV-visible absorption studies were 2.3 × 103 M−1, 3.3 × 103 M−1 and, 7.1 × 103 M−1 for complexes 1, 2, and 3, respectively. The change in melting temperature (ΔT m) was calculated to be 2-3°C for each complex. Circular dichroism (CD) study showed blue shift for complex 2 and red shift for complexes 1 and 3 along with rise in molecular ellipticity upon the addition of complexes. Results suggest a binding mode of complex 2 different than 1 and 3.

Stereochemical assignments of 22-isoxazolinylsteroids using circular dichroism

Circular dichroism (CD) spectra of 22-hydroxy- and 22-acetoxy-22-isoxazolinylsteroids were studied. The configuration of the C-5′ center of the heterocycle was established from the sign of the n-π*-transition band of the azomethine chromophore. The band molecular ellipticity was shown to depend on the mutual placement of the isoxazoline ring and the steroid skeleton of the studied compounds.

Pre-gel solution properties of gellan polysaccharides: Effect of potassium and calcium ions on chain associations

Abstract The effect of added ions (0.5 mM K+ or 0.25 mM Ca2+) and temperature (25 or 60 °C) on the solution properties of gellan polysaccharides (0.15% w/w) were investigated using static light scattering, circular dichroism (CD) and viscometry. At 60 °C (coil), the addition of salts caused an increase in the radius of gyration (Rg) and a decrease in peak area within the CD spectrum. As temperatures declined (60–25 °C), gellan appeared to undergo an intramolecular coil–helix transition, which was accompanied by a 15–36% reduction in Rg, depending upon the ionic conditions. Temperature dependence of the molecular ellipticity at 200 nm during heating, described by the van’t Hoff relationship, estimated enthalpic changes for double helix unraveling to range between 7.9 and 11.7 kJ/mole depending on the ionic conditions. At 25 °C (double helix), Rg decreased with the added salts and intrinsic viscosity decreased as a function of increasing Ca2+ (0.1–0.25 mM) or K+ (0.2–0.5 mM) levels.

Alkaloids from Nerine filifolia

The novel compounds N-demethylbelladine, 6α-methoxybuphanidrine and filifoline, in addition to five known alkaloids, and phenol have been isolated from fresh bulbs of Nerine filifolia (Amaryllidaceae). The structure and stereochemistry of the compounds were determined by physical and spectroscopic methods, including 1D and 2D NMR and mass spectroscopic techniques. An unusual circular dichroism response from filifoline has required a semi-synthetic derivatisation strategy towards key C-11 endo analogues of the β-crinane representative ambelline in which the nature of substituents was observed to have a profound effect on molecular ellipticity. Filifoline was not cytotoxic to myoblast (L6) cells and exhibited no anti-protozoal activity in an in vitro screen against four different parasitic protozoa.

Dilute solution properties of κ-carrageenan polysaccharides: effect of potassium and calcium ions on chain conformation

The effect of added ions (0.5 mM K + or 0.25 mM Ca 2+) and temperature (25 or 60 °C) on the solution properties of κ-carrageenan (0.2%, w/w) were investigated using static light scattering, circular dichroism and viscometry. At 60 °C (coil conformation), added salts caused a decrease in the radius of gyration ( R g), as chains became less spatially extended. As temperatures declined (60–25 °C), κ-carrageenan underwent a temperature-induced transition whereby R g decreased by ∼18% with or without added K +, and 2.7% with added Ca 2+. Temperature dependence of the molecular ellipticity [ θ] at 620 nm, described by the van't Hoff relationship, estimated enthalpic changes for the unraveling of the ordered conformation of 2.3–4.1 kJ/mole depending on the ionic conditions. At 25 °C (ordered conformation), R g decreased and [ θ] increased with added salts. No significant effect of ionic strength on intrinsic viscosity was found.

A circular dichroism study of the interaction between n-decanoyl-N-methylglucamide and surface active agents in mixed micelles

The interaction between MEGA-10 and surface active agents was studied by means of circular dichroism. The molecular ellipticity of MEGA-10 varied with the addition of surface active agents, but its peak wavelength did not. The carbonyl group of MEGA-10 did not interact with the nonionic surface active agents nor the catanionic surfactant (of which the anionic and cationic portions were decanesulfonate and decyltrimethylammonium, respectively). It did, however, interact with the ionic surfactants, and also strongly with the ammonium group and the benzene ring. The interaction between MEGA-10 and ionic surfactant charges did not differ according to the sign of the charge. Circular dichroism spectra are a useful tool for performing research into the interaction between an optically active carbonyl group and an additive.

Kinetics of the salt-induced B- to Z-DNA transition

The salt-induced B- to Z-DNA conformational transition is a cooperative- and time-dependent process. From a modified form of the logistic equation which describes an equilibrium between two states we have deduced a kinetic function to quantify the degree of the B to Z transition of a synthetic (dG-dC) ⋅ (dG-dC) polynucleotide. This function was obtained by introduction of time as a variable in the logistic function so that the equilibrium constant, K, is replaced by a new constant Ks, characteristic of the type of salt used. This constant is defined as the salt concentration needed to reach the B-Z transition-midpoint in the time unit. The equation fits the data obtained by circular dichroism (CD) for changes in molecular ellipticity of poly(dG-m5dC) ⋅ poly(dG-m5dC) and poly(dG-dC) ⋅ poly(dG-dC) incubated with various concentrations of mono-, di-, and trivalent salts at a constant temperature. The derived expression may be a very useful tool for studying the kinetics of the B- to Z-DNA transition.

Ultrasonic velocity and circular dichroism in aqueous gellan solutions

Circular dichroism spectra and ultrasonic velocities of aqueous gellan solutions with and without added salts were measured at various temperatures. At higher temperatures the molecular ellipticity at 204 nm [ θ] 204 is almost independent of the temperature but decreases steeply at a given temperature ( T c) with further lowering temperature. With decreasing temperature, the difference in velocities between aqueous gellan solution and solvent ( ΔV) increases in the same manner as that of most aqueous systems, followed by a slight maximum or shoulder at T c, and then increases again. These abrupt changes in sound velocity and circular dichroism at T c may be caused by a thermally induced conformational change of gellan molecule in aqueous solutions. The decrease in the ultrasonic velocity was explained in terms of the dehydration of the water molecules. Effects of addition of some monovalent cations on the ultrasonic velocities were also studied.

Synthesis, molecular structure, and properties of in-phosphaphanes with substituted basal aromatic rings

A series of nitro-substituted phosphine-containing cyclophanes (2-4) was prepared by base-promoted condensation of various nitrated derivatives of 1,3,5-tris(bromomethyl)benzene with tris(2-mercaptophenyl)phosphine under conditions of high dilution. The mononitro cyclophane 2 was reduced with TiCl 3 in THF-EtOH to give the corresponding amino derivative 5. The 13 C NMR spectra of these compounds exhibit «through-space» spin-spin coupling between the phosphorus and the substituted banal aromatic ring, and in their 31 P NMR spectra the phosphorus resonances are anomalously far downfield.The X-ray crystal structures of cyclophanes 4 and 5 reveal a pronouced inward pyramidalization of the phosphines such that the phosphorous atoms are 2.98 and 2.92 A, respectively, from the centers of the basal rings.These cyclophanes are rigid, molecular propellers, and compound 2 was chromatographically resolved on a chiral HPLC column.The circular dichroism spectra of the pure enantiomers showed a very high molecular ellipticity at 332nm of 120 000 deg;cm 2 .dmol -1

9-(Dicyanovinyl)Julolidine Binding to Bovine Brain Calmodulin

A molecular rotor, 9-(dicyanovinyl)julolidine (DCVJ), is a fluorescent dye whose intramolecular rotation determines its fluorescence yield [Kung, C.E. & Reed, J.K. (1989) Biochemistry 28, 6678-6686]. DCVJ binds to bovine brain calmodulin and emits strong fluorescence. In fluorescence titration experiments, the dissociation constant and the number of binding sites were determined to be 20 +/- 10 microM and 0.7 +/- 0.5 in the presence of Ca2+, and 22 +/- 10 microM and 0.6 +/- 0.5 in the absence of Ca2+, respectively. The fluorescence intensity of bound DCVJ increased 10-fold in the presence of Ca2+ compared to that in the absence of Ca2+. The fluorescence titration curve of DCVJ-calmodulin showed a transition at pCa 6.5. Over the same Ca2+ range, a decrease in molecular ellipticity at 222 nm and an increase in tyrosine fluorescence of calmodulin were observed. These results mean that the conformational change of calmodulin due to the Ca2+ binding induces the microenvironmental change of the DCVJ binding site from the flexible to the rigid state, resulting in inhibition of the intramolecular rotation of DCVJ and an increase in its fluorescence.

The conformational change of DNA in aqueous alcohol solutions containing metallic ions determined by using differential scanning calorimeter

In order to obtain information about the conformational change of DNA by changing the environment surrounding DNA molecule, we measured the helix-coil transition of DNA solutions with various concentrations of ethanol at a given concentration of various kinds of metallic ion by means of an adiabatic differential scanning calorimeter. The observed heat of transition, ΔH increases, but the transition temperature, T 1 decreases with increasing the concentration of ethanol, demonstrating that the conformation of DNA may considerably change by environment surrounding DNA. In order to confirm the conformational change of DNA, we also measured the CD spectra at room temperature under the same experimental conditions as the DSC measurement. The concentration range of ethanol where molecular ellipticity ratio, [θ] max/[θ] min of positive maximum, [θ] max to negative minimum, [θ] min changes is in good agreement with that obtained from DSC measurements. We will discuss the conformational change of DNA in solutions with various proportions of ethanol and a definite concentration of metallic ion by combining the results obtained by the calorimetric and spectral measurements.

The cyclodextrin inclusion complexes of acylferrocenes: their preparation, and the induced Cotton effects in their circular dichroism spectra

Complexes of α-, β, γ-cyclodextrins (CyD's) with acylferrocenes (C 5H 5FeC 5H 4-COR, R  H, CH 3, CF 3; XC 5H 4FeC 5H 4Y, X  Y  COCH 3, X, Y  COCH 2CH 2, COCH 2CO), prepared in situ in ethylene glycol or by dissolution of the 1 1 solid complexes have been investigated by use of circular dichroism (CD). Wavelengths for extrema, signs, molecular ellipticity [θ], and the rotatory strenghts, R k, of the induced Cotton effects (ICE) have been determined, and were found to correspond to the metallocene chromophores.

The interaction of δ-hemolysin with calmodulin

δ-Hemolysin forms a 1 : 1 complex with Ca 2+-liganded calmodulin. Probably because of the pronounced tendency of δ-hemolysin to self-associate, the apparent binding affinity is much less than that for melittin. Complex formation is reflected by an increase in quantum yield of Trp-15 of δ-hemolysin and by increased shielding from acrylamide quenching. There is, however, no indication of a change in peptide molecular ellipticity. The binding of 2-toluidinyl-naphthalene-6-sulfonate is reduced by complex formation, suggesting the involvement of a hydrophobic region. Complex formation also blocks the proteolysis by trypsin of the bond between residues 77 and 78. The time decays of fluorescence intensity and anisotropy for tryptophan are multiexponential for both free and complexed δ-hemolysin; the average decay time for intensity is substantially increased for the complex. The localized mobility of tryptophan is greatly reduced in the complex. Complex formation appears to involve both the C-terminlobe and the connecting strand of calmodulin.

Improved oscillating buoy viscometer

An improved design of the vertically oscillating buoy viscometer with real-time computer control, evaluation, and plotting is presented. In this method, the optically observed phase lag of the buoy relative to a sinusoidal driving force is a direct and absolute measure of viscosity. Construction features of the new version improve reassembly precision and give three-axis positioning of the sphere, as well as an 80-fold improvement in the signal-to-noise ratio for small amplitudes of the buoy motion. Design of the ‘‘crossed coil’’ system is discussed and the magnetic and mechanical faults which lead to various kinds of motional instability are considered. Boundary layer corrections are now computer corrected as are temperature variations. The evaluation of ‘‘intrinsic viscosity’’ as a measure of molecular ellipticity is discussed and one measurement set is presented.

Circular dichroism of copoly(γ‐stearyl‐L‐glutamate–γ‐methyl‐L‐glutamate)

AbstractCopoly(γ‐stearly‐L‐glutamate‐γ‐methyl‐L‐glutamate)s with various compositions were synthesized by the ester exchange reaction of poly(γ‐methyl‐L‐glutamate). Circular dichroism studies were carried out for solution and solid film as a function of the degree of stearylation and temperature. The slight and gradual temperature dependence of molecular ellipticity was observed for solution of all the copolyglutamates studied here and for the solid film of the copolyglutamate with the degree of stearylation of 16%, indicative of no reversal in the helix sense. However the remarkable change in negative molecular ellipticity with temperature was detected for the solid film of the copolyglutamate with a low degree of stearylation, e.g., 52%, whereas the drastic change in molecular ellipticity from a negative to positive value appeared for that with a higher degree of stearylation. This is discussed in terms of the reversal in the helix sense from a right‐ to left‐handed α helix with the increase of temperature occurring at the melting temperature of the ordered side chain region.