Total intensity light scattering from short,optically anisotropic wormlike chains

Simple exact equations are derived for intensity light scattering from optically anisotropic wormlike chains in the absence of excluded volume. The results are valid at low scattering angles (q² 〈R²_G〉 ? 1) for all sormilke chains from rigid rods to random couils. The present work and an earlier theory [Nagai, K. (1972) Polym. J. 3 , 67–83] appear to be equivalent, although they were both derived using different methods. The present work is primarily concerned with short wormlike chains, since intensity light scattering from short fragments may provide valuable information about DNA flexibility. By using the results of this work to reanalyze some older light-scattering studies [Godfrey, J. E. & Eisenberg, H. (1976) Biophys. Chem. 5 , 301–318], it is shown that anisotropy corrections to polarized light-scattering measurements have been overcorrected in the past. It can be anticipated that future light-scattering experiments will determine the base-pair anisotropy.     

Steady-state and transient electric birefringence of solutions of bent-rod macromolecules

We first calculate the steady-state birefringence, expressed in the form of specific Kerr constant, K_sp, of rigid, bent-rod macromolecules. Equations are derived for K_sp as a function of the geometric and electro-optical parameters. We also consider flexibly hinged rods and evaluate K_sp for them by averaging over the angle between the two arms, ?. Next, we turn to the time decay of the electric birefringence. The decay function for rigid bent rods is a sum of three exponential terms, and a procedure for their calculation is indicated. We observe that single-exponential decays can be found for ? > 90° or ? < 60°, in spite of the high electro-optical and hydrodynamic anisotropy of the macromolecule. Special attention is paid to the case of rods with equal arms.     

Light scattering from wormlike chains with excluded volume effects

This paper reports a calculation of the angular dependence of light scattering from wormlike chains with excluded volume effects. The Daniels distribution function, modified for excluded volume effects, is used to compute averages for scattering elements separated by contour lengths which are long with respect to the persistence length of the chain. An expansion in terms of exactly known moments of the distribution for the wormlike coil without excluded volume is used for short contour lengths. The results are applied to scattering from calf thymus (M = 18.1 × 10⁶) and T7 (M = 25.4 × 10⁶) DNA. It is demonstrated that the same values of excluded volume parameter (ε = 0.11) and statistical segment length (1/λ′ = 900 Å) which explain the sedimentation and viscosity behavior of DNA also account satisfactorily for the scattering behavior. Molecular weights and root-mean-square radii estimated by extrapolation from scattering data obtained in the angular region from 10° to 25° will be 5–10% too large for DNA of molecular weight 20 × 10⁶–30 × 10⁶.     

Superoxide-mediated lysis of erythrocytes: The role of colloid-osmotic forces

Although superoxide anions are a well-known mediator of cytotoxicity, their mechanism of target cell lysis is not clearly understood. In the present study we have used an exogenous source of superoxide to study erythrocyte cytolysis. RBC lysis was studied in buffers containing the cations Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺; superoxide anions were produced and available in these buffers. During this model superoxide-dependent cytolytic process, erythrocytes underwent a shape change from biconcave disk to sphere as shown by scanning electron microscopy. Soret band transmitted light microscopy has confirmed this shape change and shown that it precedes cytosolic oxidation. This evidence is consistent with a colloid-osmotic type lytic mechanism. Erythrocyte lysis was studied by ⁵¹Crrelease and light scattering methods. Superoxide-mediated target cytolysis was characterized by: (1) a sigmoidal dose-response curve and (2) a lag time in cytolysis after superoxide addition in kinetic light scattering experiments. The efficacy of cytolysis followed the rank order Cs⁺ > Rb⁺ > Na⁺, Li⁺ > sucrose = raffinose, which provides additional support for a colloid-osmotic lytic mechanism. Furthermore, the rank order potency correlates with the cations' hydration numbers. We suggest that oxidative events trigger the formation of colloid-osmotic pores ～I nm in diameter. © 1993 Wiley-Liss, Inc.     

Clathrin triskelia show evidence of molecular flexibility

The clathrin triskelion, which is a three-legged pinwheel-shaped heteropolymer, is a major component in the protein coats of certain post-Golgi and endocytic vesicles. At low pH, or at physiological pH in the presence of assembly proteins, triskelia will self-assemble to form a closed clathrin cage, or “basket”. Recent static light scattering and dynamic light scattering studies of triskelia in solution showed that an individual triskelion has an intrinsic pucker similar to, but differing from, that inferred from a high resolution cryoEM structure of a triskelion in a clathrin basket. We extend the earlier solution studies by performing small-angle neutron scattering (SANS) experiments on isolated triskelia, allowing us to examine a higher q range than that probed by static light scattering. Results of the SANS measurements are consistent with the light scattering measurements, but show a shoulder in the scattering function at intermediate q values (0.016 Å⁻¹), just beyond the Guinier regime. This feature can be accounted for by Brownian dynamics simulations based on flexible bead-spring models of a triskelion, which generate time-averaged scattering functions. Calculated scattering profiles are in good agreement with the experimental SANS profiles when the persistence length of the assumed semiflexible triskelion is close to that previously estimated from the analysis of electron micrographs.     

Quasi-elastic light scattering from fibrinogen and fibrin intermediate structures

Quasi-elastic light scattering measurements have been carried out for (i) human and bovine fibrinogens under identical conditions, (ii) for a large number of fractionated and unfractionated fibrin intermediates at various pH (10.0 to 10.5), (iii) for three intermediates polymerized at pH 7.4 and stabilized at pH 10.5 and (iv) for a gelled clot. Human and bovine fibrinogen proved to have noticeably different diffusion coefficients (same M_w) indicating a longer rod on the average for the human than for the bovine fibrinogen. This finding is in agreement with measurements of the integrated light scattering from these fibrinogens where a mass per unit length $\text{M}{}_{\mathrm{w}}\text{L}{}_{\mathrm{w}}$ of 3860 and 5460 g mol^?1 nm^?1 were found, respectively. No angular dependence of the apparent diffusion coefficient D_app = Γ/q² was found for the monomers and the fibrin clot; all other samples from (ii) showed an angular dependence if M_w ? 1.76 × 10⁶, were Γ is the first cumulant of the time correlation function and q = (4π/λ) sin?/2. A plot of D_app/D versus q²〈S²〉 gave curves which, for the low molecular weight samples, correspond to ellipsoids. For the longer fibrils a dynamic behaviour in between that of a long rigid rod and random coil was found and indicates a certain flexibility of the fibrils. The diffusion coefficients from (ii) decay with increasing molecular weight and can be described by Perrin's theory for ellipsoids when M₂ < 2 × 10⁶ while a beter agreement with Kirkwood's theory of long rods is obtained for the longer fibrils. The hydrodynamic behaviour of (iii) indicates short and unbranched rods of considerable thickness.     

DEPRESSION OF MASTIGOCLADUS LAMINOSUS (CYANOPHYTA) NITROGENASE ACTIVITY UNDER NORMAL SUNLIGHT INTENSITIES1

The effect of light intensity (PAR) on the nitrogenase activity of Mastigocladus laminosus Cohn was studied by the acetylene reduction technique. Benthic mat from a thermal stream, Hot River, in Yellowstone National Park was used in both experimental and in situ incubations. This hot spring maintained a mean pH of 7.0, was essentially isothermal (ca. 50°C), and had virtually no upstream to downstream physicochemical gradients (P > 0.05). Two surveys of the stream showed that nitrogenase of the M. laminosus mat was significantly more active (P > 0.02) under low light intensities than under high intensities, 252 and 712 μE · m^?2· s^?1, respectively. Maximum activity of Hot River Mastigocladus (268 nmol C₂H₄· mg Chl a^?1· h^?1) occurred at 50% full midday light intensities; the rates at low light (mean = 247 nmol C₂H₄· mg Chl a^?1· h^?1) were significantly (P > 0.001) greater than those at high light (mean = 106). The results indicate that M. laminosus nitrogenase activity is low light adapted and suggest that the temporal pattern for nitrogen fixation might be significantly different from that of thermophilic Calothrix.     

Eco-fingerprinting of the dinoflagellate <Emphasis Type="Italic">Borghiella dodgei</Emphasis>: experimental evidence of a specific environmental niche

In Lake Tovel, an oligotrophic and weakly stratified lake, the dinoflagellate Borghiella dodgei Moestrup, Hansen et Daugbjerg, showed a peculiar spatial–temporal pattern with highest abundances in the bottom of the shallow side bay (4 m) along with remarkable abundance variations from year to year. We investigated B. dodgei’s growth in laboratory cultures and related results to their implication for bloom formation. B. dodgei was cultivated under different temperature, nutrient and light conditions. Growth rates, cell biovolume, cyst formation and pigment and mycosporine-like amino acids (MAAs) concentrations were determined. Experiments showed that this alga (i) had higher growth rates at low temperatures (<7°C) and high irradiance levels (~250 μmol m⁻² s⁻¹), (ii) produced higher yields with organic supplements such as peptone, (iii) did not grow in the dark even with organic supplements, (iv) survived for long periods without a light source, (v) synthesised MAAs, (vi) showed an increase in cell volume with nutrient shortage and increasing temperatures (>7°C) and (vii) had high encystment rates with temperatures >7°C. These laboratory fingerprints allowed us to construct a theoretical model defining the species’ niche. Borghiella needed a mixture of low temperatures, high irradiance levels and sufficient quantities of dissolved organic nitrogen to form blooms. Such a strict combination was probably a transient situation and occurred in oligotrophic Lake Tovel only in early summers followed by heavy spring rains.     

Physico-chemical Property of Rare Earths—Effects on the Energy Regulation of Photosystem II in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Photosystem II (PSII) from Arabidopsis thaliana treated by lanthanum (La³⁺), cerium (Ce³⁺), and neodymium (Nd³⁺) were isolated to investigate the effects of 4f electron characteristics and alternation valence of rare earth elements (REEs) on PSII function regulation comparatively. Results showed that REE treatment could induce the generous expression of LhcII b in A. thaliana and increase the content of light-harvesting complex II and its trimer on the thylakoid membrane significantly. Meanwhile, the light absorption in the red and blue region and fluorescence quantum yield near 683 nm were obviously increased; oxygen evolution rate was greatly improved too, suggesting that REEs could enhance the efficiency of light absorption, regulate excitation energy distribution from photosystem I (PSI) to PSII, and thus increase the activity of photochemical reaction and oxygen evolution accordingly. The efficiency order of the four treatments was Ce³⁺ > Nd³⁺ > La³⁺ > control.     

Light scattering study of natural DNAs over a wide range of molecular weights: Evidence for compaction of the large molecules

This work reports light scattering measurements on DNA in aqueous solutions (100 mM NaCl, 1 mM EDTA and 10 mM Tris–HCl buffer, pH 7.8) over a wide range of molecular weights (10²–10⁵ base pairs) and shows that, in the above standard solvent, shorter chains (<10⁴ base pairs) behave as a “wormlike chain” and their diffusion coefficients as obtained by dynamic light scattering measurements, confirm the prediction of standard wormlike model, whilst longer chains (>10⁴ base pairs) behave in a different manner. Dynamic and static light scattering and SEM analysis indicate that DNA molecules 10⁵ base pairs long, condense into compact structures in our solvent conditions. Calculations done using a wormlike model are also presented and discussed in comparison both to our experimental data and to other data reported in the literature.     

A novel Ca2+-feedback mechanism extends the operating range of mammalian rods to brighter light

Sensory cells adjust their sensitivity to incoming signals, such as odor or light, in response to changes in background stimulation, thereby extending the range over which they operate. For instance, rod photoreceptors are extremely sensitive in darkness, so that they are able to detect individual photons, but remain responsive to visual stimuli under conditions of bright ambient light, which would be expected to saturate their response given the high gain of the rod transduction cascade in darkness. These photoreceptors regulate their sensitivity to light rapidly and reversibly in response to changes in ambient illumination, thereby avoiding saturation. Calcium ions (Ca²⁺) play a major role in mediating the rapid, subsecond adaptation to light, and the Ca²⁺-binding proteins GCAP1 and GCAP2 (or guanylyl cyclase–activating proteins [GCAPs]) have been identified as important mediators of the photoreceptor response to changes in intracellular Ca²⁺. However, mouse rods lacking both GCAP1 and GCAP2 (GCAP^−/−) still show substantial light adaptation. Here, we determined the Ca²⁺ dependency of this residual light adaptation and, by combining pharmacological, genetic, and electrophysiological tools, showed that an unknown Ca²⁺-dependent mechanism contributes to light adaptation in GCAP^−/− mouse rods. We found that mimicking the light-induced decrease in intracellular [Ca²⁺] accelerated recovery of the response to visual stimuli and caused a fourfold decrease of sensitivity in GCAP^−/− rods. About half of this Ca²⁺-dependent regulation of sensitivity could be attributed to the recoverin-mediated pathway, whereas half of it was caused by the unknown mechanism. Furthermore, our data demonstrate that the feedback mechanisms regulating the sensitivity of mammalian rods on the second and subsecond time scales are all Ca²⁺ dependent and that, unlike salamander rods, Ca²⁺-independent background-induced acceleration of flash response kinetics is rather weak in mouse rods.     

Blue Light Reception in Phycomyces: Red Light Sensitization in madC Mutants

Sporangiophores of the zygomycete fungus Phycomyces blakesleeanus are sensitive to near UV and blue light. The quantum effectiveness of yellow and red light is more than 6 orders of magnitude below that of near UV or blue light. Phototropism mutants with a defect in the gene madC are about 10⁶ times less sensitive to blue light than the wild type. These mutants respond, however, to yellow and red light when the long wavelength light is given simultaneously with actinic blue light. In the presence of yellow or red light the photogravitropic threshold of madC mutants is lowered about 100-fold though the yellow and the red light alone are phototropically ineffective. A step-up of the fluence rate of broad-band red light (> 600 nm) from 6 × 10^?3 to 6W m^?2 elicits, in mutant C 148 madC, a transient deceleration of the growth rate. The growth rate of the wild type is not affected by the same treatment. The results are interpreted in terms of a red light absorbing intermediate of the blue light photoreceptor of Phycomyces. The intermediate should be short-lived in the wild type and should accumulate in madC mutants.     

Magnetic resonance Raman activity: Inverse Faraday effect in hemoglobin

A complete polarization study of human oxy- and carbonmonoxyhemoglobin (carbonylhemoglobin) A and S is reported for backscattered light in the resonance Raman light-scattering situation with excitations in the long-wavelength region, =5682 Å and 5815 Å, and in the short-wavelength region, =4579 Å and 4880 Å, as comparison. All four polarization components of the scattered light with respect to the two conditions of linear and circular polarization of the incident light were measured. These were: (1) parallel; (2) perpendicular; (3) corotating; and (4) contrarotating.This method has been used to characterize the three invariants of the nonsymmetric Raman tensor for randomly oriented molecules. These invariants are based on a model in which the scattered light is dependent on only an induced electric dipole. With no higher moments involved in the scattering process, the amplitude of any band measured under the four conditions should satisfy the relation: (1)+(2)=(3)+(4).The experiments reported here demonstrate that although this relation is satisfied for short-wavelength (4579 Å and 4880 Å) excitation, it does not apply for long-wavelength (5682 Å and 5815 Å) excitation, for which (1)+(2)<(3)+(4) holds.There are larged-d metal-electron influences on the long, but not the short, wavelength absorption region of hemoproteins. A large metal-electron magnetic dipole moment can thus be induced with circularly polarized light of long wavelength, owing to the availability of a transition involving charge transfer interaction coupling between metal orbitals and the porphyrin ^* orbitals.The increase in light scattering is due to aninverse Faraday effect, resulting in magnetic resonance Raman activity. Owing to large crystal field influences and Jahn-Teller instability, the critical zero-field splitting energy is also large. The incident circularly polarized radiation at =5700 Å (=17,544 cm^–1) is approximately the critical cubic splitting parameter, _C , the calculated value for which is 18,500 cm^–1. This incident light equalizes or mixes the energy levels of the¹ A ₁ and⁵ T ₂ states; i.e., it populates magnetic substates. An induced electric dipole-magnetic dipole transition, besides an induced electric dipole transition, is then permitted for circularly polarized light at the Larmor precession frequency, but not permitted for linearly polarized light, as thed-d metal transition is electric dipole disallowed.The hemoglobin S solution and gel scatter longwavelength light in a similar fashion; i.e., a large induced magnetic dipole moment is implicated for the circularly polarized conditions. In addition, there are bands at 750 and 1050 cm^–1 for the hemoglobin S gel not present in dissolved hemoglobin S nor in hemoglobin A. The presence of these bands is attributed to changes in theB _1g mode of porphyrin ring vibrations.     

Physicochemical studies on xylinan (acetan). III. Hydrodynamic characterization by analytical ultracentrifugation and dynamic light scattering

A laboratory-made sample of the polysaccharide xylinan (acetan) has been further characterized with respect to (i) purity, (ii) molar mass and polydispersity, and (iii) gross conformation by a combination of hydrodynamic measurements (sedimentation velocity and equilibrium analytical ultracentrifugation, viscometry, and dynamic light scattering) in aqueous NaCl (I = 0.10 mol·L⁻¹). Sedimentation velocity diagrams recorded using Schlieren optics revealed highly pure material sedimenting as a single boundary [s^o_20.w = 9.5 ± 0.7) S; k_s = (273 ± 112) mL/g]. The hypersharp nature of these boundaries is symptomatic of a polydisperse and highly nonideal (in the thermodynamic sense) system. Low speed sedimentation equilibrium in the analytical ultracentrifuge using Rayleigh interference optics and two different types of extrapolation procedure (involving point and whole-cell molar masses) gave a weight average molar mass M_w of (2.5 ± 0.5) × 10⁻⁶ g·mol⁻¹ and also a second virial coefficient, B = (2.8 ± 0.7) × 10⁻⁴ mL·mol·g⁻², both values in good agreement with those from light scattering-based procedures (Part II of this series). A dynamic Zimm plot from dynamic light scattering measurements gave a z-average translational diffusion coefficient D^o_20.w = (3.02 ± 0.05) × 10⁻⁸ cm²·s⁻¹ and the concentration-dependence parameter k_D = (370 ± 15) mL/g. Combination of s^o_20.w with D^o_20.w via the Svedberg equation gave another estimate for M_w of ≅ 2.4 × 10⁶ g/mol, again in good agreement. Both the Wales-van Holde ratio (k_s/[η]) ≅ 0.4 (with [η] = (760 ± 77) mL/g) and the ρ-parameter (ratio of the radius of gyration from static light scattering to the hydrodynamic radius from dynamic light scattering) as ρ > 2.0 all indicate an extended conformation for the macromolecules in solution. These findings, plus Rinde-type simulations of the sedimentation equilibrium data are all consistent with the interpretation in terms of a unimodal wormlike coil model performed earlier. © 1996 John Wiley & Sons, Inc.     

RdgB2 is required for dim-light input into intrinsically photosensitive retinal ganglion cells

A subset of retinal ganglion cells is intrinsically photosensitive (ipRGCs) and contributes directly to the pupillary light reflex and circadian photoentrainment under bright-light conditions. ipRGCs are also indirectly activated by light through cellular circuits initiated in rods and cones. A mammalian homologue (RdgB2) of a phosphoinositide transfer/exchange protein that functions in Drosophila phototransduction is expressed in the retinal ganglion cell layer. This raised the possibility that RdgB2 might function in the intrinsic light response in ipRGCs, which depends on a cascade reminiscent of Drosophila phototransduction. Here we found that under high light intensities, RdgB2^−/− mutant mice showed normal pupillary light responses and circadian photoentrainment. Consistent with this behavioral phenotype, the intrinsic light responses of ipRGCs in RdgB2^−/− were indistinguishable from wild-type. In contrast, under low-light conditions, RdgB2^−/− mutants displayed defects in both circadian photoentrainment and the pupillary light response. The RdgB2 protein was not expressed in ipRGCs but was in GABAergic amacrine cells, which provided inhibitory feedback onto bipolar cells. We propose that RdgB2 is required in a cellular circuit that transduces light input from rods to bipolar cells that are coupled to GABAergic amacrine cells and ultimately to ipRGCs, thereby enabling ipRGCs to respond to dim light.     

Adaptive potentiation in rod photoreceptors after light exposure

Photoreceptors adapt to changes in illumination by altering transduction kinetics and sensitivity, thereby extending their working range. We describe a previously unknown form of rod photoreceptor adaptation in wild-type (WT) mice that manifests as a potentiation of the light response after periods of conditioning light exposure. We characterize the stimulus conditions that evoke this graded hypersensitivity and examine the molecular mechanisms of adaptation underlying the phenomenon. After exposure to periods of saturating illumination, rods show a 10–35% increase in circulating dark current, an adaptive potentiation (AP) to light exposure. This potentiation grows as exposure to light is extended up to 3 min and decreases with longer exposures. Cells return to their initial dark-adapted sensitivity with a time constant of recovery of ∼7 s. Halving the extracellular Mg concentration prolongs the adaptation, increasing the time constant of recovery to 13.3 s, but does not affect the magnitude of potentiation. In rods lacking guanylate cyclase activating proteins 1 and 2 (GCAP^−/−), AP is more than doubled compared with WT rods, and halving the extracellular Mg concentration does not affect the recovery time constant. Rods from a mouse expressing cyclic nucleotide–gated channels incapable of binding calmodulin also showed a marked increase in the amplitude of AP. Application of an insulin-like growth factor-1 receptor (IGF-1R) kinase inhibitor (Tyrphostin AG1024) blocked AP, whereas application of an insulin receptor kinase inhibitor (HNMPA(AM)₃) failed to do so. A broad-acting tyrosine phosphatase inhibitor (orthovanadate) also blocked AP. Our findings identify a unique form of adaptation in photoreceptors, so that they show transient hypersensitivity to light, and are consistent with a model in which light history, acting via the IGF-1R, can increase the sensitivity of rod photoreceptors, whereas the photocurrent overshoot is regulated by Ca-calmodulin and Ca²⁺/Mg²⁺-sensitive GCAPs.     

Dégradation du DNA par H2O2 en présence d'ions Cu++, Fe++ et Fe+++

The mechanism of degradation of calf thymus DNA by H₂O₂ in dark and light, and in the presence of either Cu⁺⁺, Fe⁺⁺, or Fe⁺⁺⁺ ions has been investigated by following the decrease of molecular weight M?_w by light scattering. Both in the dark and in light, the rate of degradation decreases in the following order: Cu⁺⁺>Fe⁺⁺>Fe⁺⁺⁺. In order to exploit quantitatively the variation of M?_w with time, we calculated the probability p(t) of rupture in a double stranded polymer as a function of the occurence at random of both breaks of the “first kind” (single hits) and of the “second kind” (double hits), when there are caused by any degrading agent. The value of p(t) can then be related to M?_w(t) for the present case of a randomly polydisperse sample of DNA molecules. In the dark, and in the presence of Cu⁺⁺ ions, a degradation of the first kind (which takes place through the simultaneous or successive splitting of both strands of DNA at the same level) is the only one so far observed. The number of degradation sites of the first kind is equivalent to the number of bound Cu⁺⁺ ions in inner sites of DNA. A model is set up to explain the successive breaks of the two strands of the DNA molecule through the formation of a complex (DNA site–Cu⁺⁺-H₂O₂) which exhibits peroxidative properties. The comparison of the degradation induced under these conditions in a native and a sonicated DNA, shows that the specific sites of attack of ultrasonic waves are not specific sites of H₂O₂ action in the presence of Cu⁺⁺ ions. In the dark and in the presence of Fe⁺⁺ or Fe⁺⁺⁺ ions, breaks of the first kind and second kind are superimposed, but the last are predominant. This is ascribed to the low binding of iron ions in inner sites of DNA under these conditions. A large increase in degradation rate of the second kind occurred in the presence of light (with or without added metallic ions and) is ascribed to the action of the free radicals HO^· (and HO₂^·) which arise from the photolysis of H₂O₂. These results are discussed in relation to those obtained by the action of ionizing radiations on aqueous solutions of DNA.     

Alcohol induced structural and dynamic changes in β-lactoglobulin in aqueous solution: A neutron scattering study

Structural and dynamic properties of β-lactoglobulin (β-LG) were revealed as a function of alcohol concentration in ethanol- and trifluoroethanol(TFE)-water mixtures with circular dichroism (CD), small-angle neutron scattering (SANS) and quasi-elastic neutron scattering (QENS). The CD spectra showed that an increase in TFE concentration promotes the formation of the β-sheet structure of β-LG. The SANS-intensities were fitted using form factors for two attached spheres for the native and native-like states of the protein. At higher alcohol concentrations, where aggregation takes place, a form factor modelling diffusion limited colloidal aggregation (DLCA) was employed. The QENS-data were analyzed in terms of internal motions for all alcohol concentrations. While low concentrations of TFE (10% (v/v)) lead to an increase of the mean square amplitudes of vibrations < u²> and a retention of a native-like structure — but not to an increase of the characteristic radius of proton diffusion processes a. Addition of 20% (v/v) of TFE induces aggregation, going along with a further increase of < u²>. Further increase of TFE concentration to 30% (v/v) changes the nanoscale structure of the oligomeric nucleate, but induces no further significant changes in < u²>. The present study underlines the necessity of methods sensitive to the dynamics of a system to obtain a complete picture of a molecular process.     

Partitioning particulate scattering and absorption into contributions of phytoplankton and non-algal particles in winter in Lake Taihu (China)

Light scattering, backscattering, and absorption coefficients of particles were observed at 62 locations in Lake Taihu (China) in November 2008. A method using a priori knowledge and the measured data was proposed to partition particulate scattering and absorption into contributions of phytoplankton and non-algal particles. The results showed that phytoplankton weakly contributed to the particulate scattering and backscattering with the mean b _ph/b _p values usually below 10% and b _bph/b _bt values of 0.3–3.9% in the whole visible light spectrum, and an approximate relationship of b _bt ≈ b _bp ≈ b _bnap was regarded as reasonable in Lake Taihu. In contrast with scattering and backscattering, phytoplankton made more contributions to the particulate absorption with the mean a _ph/a _p values varying in a wide range of about 20–70%. Both the scattering and absorption spectra of non-algal particles can be modeled well by corresponding methods. A power function model was used to simulate the scattering spectra, which presented high predictive accuracies with MAPE values usually below 5% and RMSE values below 1.5 m⁻¹, while the spectral absorption model also performed well with mean S _nap being 0.0052 nm⁻¹ (standard deviation, SD = 0.0010 nm⁻¹). As to the phytoplankton absorption, a quadratic function model used was considered to have a good performance with corresponding parameters being supported at each wavelength in the spectral range of 400–700 nm. Additionally, two basic bio-optical parameters were determined, that is, b _nap^*(550) = 0.604 m² g⁻¹ and a _ph^*(675) = 0.0288 m² mg⁻¹. Overall, these results obtained in the present study supply us with new knowledge about optical properties of suspended particulates in an inland and highly turbid lake (Lake Taihu), which are beneficial to the development of analytical models of water color remote sensing.