Stable Intermediate State Research Articles

Sol-gel processing of an entirely new family of mixed valence glasses

Electro- and photochromic WO 3-based glasses have been prepared by conventional melting. In this case, high concentrations of WO 3 are required to induce the formation of larger complexes of H m W n O 3 n-m in the glasses and, therefore, the electro- or photochromic effect. The sol-gel process presents an alternative route for preparation of glasses, with low tungsten content. In low temperature syntheses, the greater kinetic control allows stabilization of intermediate states. The tungsten-doped silico-borate glasses obtained are monolithic, transparent and reversibly photochromic. The synthesis and characterization of these glasses are presented. The photochromic effect was investigated by absorption spectroscopy. The most attractive aspect of this method is the fact that the concentration of tungsten can be chosen and more importantly the size and the structure of the cluster, and therefore the optical properties, can be adjusted. Polyoxometalates as discrete oxides are isolated in a glass matrix and can be reduced.

Switches in species-specific codon preferences: The influence of mutation biases

A model of synonymous codon usage is developed in which the most frequent codons are selectively advantageous because of their coadaptation with tRNA abundances. Random drift opposes the progress of this coevolution by pushing codon frequencies in the direction of the frequency that would result from mutation in the absence of selection. It is predicted that, within a certain range, an increased mutation bias away from an advantageous codon has little influence on its usage in highly expressed genes. However, a subsequent small increase in mutation bias over a critical range leads to a large reduction in the frequency of the codon. The switch in preference from one synonym to another is a sharp transition, with no stable intermediate state in which neither codon is advantageous. Codon usage patterns were compared among three related bacterial species of differing genomic G & C contents, Escherichia coli, Serratia marcescens, and Proteus vulgaris. It was found that although changes in mutation biases do not always result in switches in codon preferences, some switches have occurred in the direction of species-specific mutation biases. Fluctuating mutation biases may therefore be the main cause of differences between species in their codon preferences.

Multistable states MIS transistor

Mathematical simulation and experimental studies of an MINpn (MISSS) metalconducting insulator-semiconductor bipolar transistor are described in the paper. Such devices generally have switching characteristics. The high-impedance state is associated with a reversebiased p-n junction which sustains high voltages. The breakover occurs when the sum of the small-signal current gains reaches unity. The low-impedance state is associated with an accumulation of the semiconductor surface which increases the electric field across the insulator. The energy bandshift may cause the valence-band edge of the semiconductor to be at a higher energy level than the metal-work function. The metal-insulator-semiconductor (MIS) acts as a minority diode and has a large flow of valence electrons. The second regenerative feedback may create the intermediate stable state, if the positive resistance appears prior to the second breakover. The simulation results show that this intermediate stable state may happen when the oxide thickness is within a certain (tunnelling) range. The larger barrier height device (majority diode) has a greater possibility of exhibiting the intermediate stable state. The narrower basewidth device is more significant in indicating the voltage collapse. The experimental result confirmed the existence of the intermediate stable state.

Novel solid state phase transitions in Na 4UO 2(SO 4) 3

The preparation of tetrasodium uranyl trisulfate Na 4UO 2(SO) 4) 3, in the glass state and its novel transformation via a stable intermediate state to the crystalline state, i.e. glass → intermediate → crystal is reported for the first time. The results from differential scanning calorimetry (DSC), infrared spectroscopy and X-ray powder diffraction show the intermediate as a pseudo-crystalline state, an incipient phase to its final crystal state. The intermediate → crystal transition does not show a measurable latent heat, ΔH t, thereby suggesting a non-first order transition type.

Detection and characterization by circular dichroism of a stable intermediate state formed in the thermal unfolding of papain.

The thermal unfolding of papain was studied at pH 2.6 by means of circular dichroism and difference spectroscopy. The transition curves obtained from ellipticity changes at 208 and 220 nm were biphasic, i.e., they showed two distinct successive steps, demonstrating the existence of an intermediate state of stable secondary conformation in the denaturation process. Difference-spectroscopy studies indicated that considerable exposure of aromatic side-chains is involved in both steps of the transition. Since papain has two domains in its molecular structure, our results suggest that they unfold in a successive way and rather independently. Furthermore, the structural characteristics of the intermediate state, obtained from its circular dichroism spectrum in the far-ultraviolet region, seem to point out that the second domain (residues 111-212) is the most stable part of the molecule.

A ‘molten globule’-like unfolding intermediate of a four domain protein, the Fc fragment of the IgG molecule

The Fc fragment of human IgG1 can be trapped in a stable intermediate state during thermal denaturation. In this conformation the molecule is compact with a native-like secondary structure, however, the tertiary structure is perturbed as revealed by intrinsic fluorescence measurements, the near-UV CD spectra and by mapping of antigenic sites with monoclonal antibodies. Similar phenomena were recently described for a few globular proteins of small size, and termed ‘the molten globule’ state. Our observation is a unique example of this phenomenon for a four domain protein.

Effects of vanadate on the rotational dynamics of spin-labeled calcium adenosinetriphosphatase in sarcoplasmic reticulum membranes.

We have studied the effects of vanadate on the rotational motion of the calcium adenosine-triphosphatase (Ca-ATPase) from sarcoplasmic reticulum (SR), using saturation-transfer electron paramagnetic resonance (ST-EPR). Vanadate has been proposed to act as a phosphate analogue and produce a stable intermediate state similar to the phosphoenzyme. This study provides evidence about the physical state of this intermediate. In particular, since ST-EPR provides a sensitive measure of microsecond protein rotational mobility, and hence of protein-protein association, these studies allowed us to ask (a) whether the vanadate-induced protein association observed in electron micrographs of SR vesicles also occurs under physiological (as opposed to fixed, stained, or frozen) conditions and (b) whether vanadate-induced changes in protein association also occur under conditions sufficient for enzyme inhibition but not for the production of large arrays detectable by electron microscopy (EM). At 5 mM decavanadate, a concentration sufficient to crystallize the ATPase on greater than 90% of the membrane surface area in EM, ST-EPR showed substantial immobilization of the spin-labeled protein, indicating protein-protein association in the unstained vesicles. Conventional EPR spectra of lipid probes showed that lipid hydrocarbon chain mobility is unaffected by decavanadate-induced protein crystallization in SR, suggesting that changes in protein-protein contacts do not involve the lipid hydrocarbon region. At 5 mM monovanadate, a concentration sufficient to inhibit the ATPase but not to form crystals detectable by EM, no changes were observed in ST-EPR or conventional EPR spectra of either protein or lipid.(ABSTRACT TRUNCATED AT 250 WORDS)

On the Concept of Intermediate One‐Particle States in Finite Chains. A Self‐Consistent Field Study

AbstractAb initio self‐consistent field calculations are performed on finite chains of hydrogen atoms and other model systems to test the prediction of a quantum‐size effect, namely the arising of intermediate one‐particle states. The calculations confirm earlier conjectures concerning the appearance of intermediate states, not only at the simple Hückel, but also at the self‐consistent field level of approximation. Furthermore, the stability of intermediate states with respect to perturbations is studied.

Nature of the 1-Methyladenine-Requiring Phase in Maturation of Starfish Oocytes: (1-methyladenine/oocyte maturation/oocyte stiffness/caffeine/starfish).

Reinitiation of meiosis in starfish oocytes requires the continuous presence of 1-methyladenine (1-MeAde) in the surrounding medium for a definite period. The length of the 'hormone-dependent phase' (HDP) in Asterina pectinifera, which was defined as the time necessary for induction of 50% germinal vesicle breakdown (GVBD), was found to be about 11 min at 17°C, and 8 min at 20°C. Repeated treatments for shorter periods with 1-MeAde revealed that the action of this agent was cumulative, and that stable intermediate states between the unstimulated and fully stimulated levels existed during the HDP. Measurement of the stiffness of oocytes also demonstrated this stable intermediate state. Thus, there may be a factor(s) in the cytoplasm that accumulates continuously during the HDP and triggers GVBD when it reaches a critical level(s). When dithiothreitol (DTT) was used as an artificial maturation-inducing agent, the intermediate state was far less stable, suggesting a difference in the modes of action of 1-MeAde and DTT. Isotonic CaCl2 , the Ca2+ ionophore (A 23187) and methylxanthines, which are known to cause increase in intracellular Ca2+ , had additive effects with 1-MeAde. These results suggest that part of the action of 1-MeAde is to release Ca2+ in the oocyte cytoplasm.

Involvement of DNA damage in hydroxyurea-mediated induction of endogenous murine retrovirus

Hydroxyurea (HU) induces AKR cells to produce endogenous murine retrovirus at a low frequency (approx. 1 x 10/sup -5/), and DNA synthesis is required soon after treatment with HU for induction to be observed (i.e., no stable induction intermediate is formed). Induction by HU can be enhanced by simultaneous treatment with halogenated pyrimidines, with the concomitant appearance of a stable induction intermediate state. The effects of the two compounds are synergistic, indicating an actual stimulation of HU-mediated induction by iodode-oxyuridine. Since HU inhibits semiconservative replication, and since (/sup 3/H)bromodeoxyuridine is incorporated into the cellular genome predominantly by unscheduled DNA synthesis (repair replication) under these conditions, this stimulation appears to be the result of insertion into DNA of the thymidine analogs during the repair of HU-induced alterations in the DNA. The nature of HU damage to DNA is not defined; if single-strand breaks are involved, they may occur at a frequency <10/sup -8/ and escape detection, but induction could also be due to other alterations in DNA. The characteristics of induction by HU, therefore, are similar to those of induction by other DNA-damaging treatments such as ..gamma.. or x irradiation or methylcholanthrene. This suggests that these agents may induce by similar,more » if not identical, mechanisms. Further, the ability of halogenated pyrimidines to form a stable induction intermediate when incorporated by repair synthesis, similar to the intermediate formed when the analogs are incorporated during semiconservative replication, suggests that the same sites are involved for induction by damaging agents or by halogenated pyrimidine incorporation.« less

Papain denaturation is not a two-state transition

. Even proteins such as lysozyme [2] which has a cleft in the middle and parvalbumin [3] which consists of two distinct domains are denatured without stable intermediate states. This led to a tempting conclusion that all small globular proteins built of one poly- peptide chain represent a single cooperative system. In this connection it was very interesting to examine papain in which two structural domains are separated by a deep cleft [4] . These parts of the molecule are linked by a number of secondary bonds and seem to be tightly fastened. However, consideration of the course of the chains in each part suggests that they fold independently [S] . Then the question arises whether these parts are indeed independent. Thermodynamic analysis of the calorimetric data on papain thermal denaturation carried out in this paper has shown that papain denaturation is not a two-state transition and the two parts of this macromolecule represent quasi-independent cooper- ative systems. Thus it follows that both parts of papain are folded independently. 2. Materials and methods A commercial preparation of papain (Fluka AG, Buchs SG, Switzerland) was twice recrystallized according to [6]. Papain was activated by reducing with 0.01 M dithiothreitol in 0.1 M Tris-HCl (PH 8.0) for 2 h at room temperature. Then the

Occurrence and characterization of stable intermediate state(s) in the unfolding of ovomucoid by guanidine hydrochloride.

Reversible unfolding of ovomucoid by guanidine hydrochloride, as followed by viscosity and difference-spectral measurements at 25 degrees C, pH6, occurred in two distinct steps involving at least three major conformational states, namely the native, intermediate and completely denatured states, occurring respectively in 60mm-sodium phosphate buffer, 3.5m-guanidine hydrochloride and 6m-guanidine hydrochloride. The overall native conformation of ovomucoid, as indicated by its intrinsic viscosity (5.24ml/g) and gel-filtration behaviour, differs significantly from that of a typical globular protein. Exposures of tyrosine residues in native ovomucoid measured by difference spectroscopy following perturbation with glycerol, ethylene glycol and dimethyl sulphoxide were, respectively, 0.42, 0.56 and 0.57. Of the exposed phenolic groups only one titrated normally (pK(int.), 9.91, electrostatic-interaction factor, w, 0.04). Results on difference spectra, solvent perturbation, phenolic titration and intrinsic viscosity (7.4ml/g) taken together showed that, although ovomucoid in 3.5m-guanidine hydrochloride was significantly unfolded, it retained a degree of native structure, removable with 6m-guanidine hydrochloride. In the latter, all the six tyrosine residues were available for titration, and the intrinsic viscosity of ovomucoid increased to 9.4ml/g. Furthermore, the characteristic fine structures in circular-dichrosim spectra of ovomucoid, associated with the elements of native structure, were abolished in 6m-guanidine hydrochloride, suggesting that the completely denatured state is structureless and presumably behaves as a cross-linked random coil. The latter state has been shown by analysis of the results on guanidine hydrochloride-dependence of the transition, intermediateright harpoon over left harpoondenatured, to be less stable than the intermediate state under native conditions by about 46kJ/mol at 25 degrees C. Attempts have been made to interpret the above results in the light of available information on the amino acid sequence of ovomucoid.

Multiple steady states in an isothermal, integral reactor: The catalytic oxidation of carbon monoxide over platinum‐alumina

AbstractStable isothermal multiplicities were observed during carbon monoxide oxidation in an integral reactor, filled with alumina supported platinum catalysts. The multiplicities were investigated in the conversion‐temperature, conversion‐inlet carbon monoxide concentration and conversion‐mass flow rate domains.The region of multiplicities was found to widen significantly upon catalyst aging which enhanced the pellets' diffusive resistances.Several intermediate stable steady states were found between the highest and lowest steady states, both experimentally and theoretically.All the above phenomena could be well interpreted by the interactions of the kinetics of carbon monoxide oxidation with intrapellet diffusion resistances.

ELECTRONIC CONFIGURATION AND LATTICE COLLAPSE IN Sm COMPOUNDS

A simple analytic model is presented which illustrates the physics of the configurational phase transition occuring in SmS under pressure and in the SmS-YS and SmS-SmAs systems with chemical substitution. The model includes only the largest interactions and is intented to demonstrate the requirements for a configurational phase transition to a stable intermediate valent state.

Magnetoresistance and field-induced phase transitions in the helical and conical states of holmium

Magnetoresistance measurements on single crystals of holmium are reported for the helical antiferromagnetic and conical ferromagnetic phases. Longitudinal and transverse measurements were made with the magnetic field applied in the $a$, $b$, and $c$ planes, including nine different field-current configurations. Data with the current parallel to the $c$ direction and the applied field parallel to the easy $b$ direction showed the magnetoresistance to be as large as 40%. Basal-plane resistance anomalies have been observed, which when compared to magnetostriction, magnetization, and neutron-diffraction data can be correlated with field-induced transitions, permitting the construction of schematic $H\ensuremath{-}T$ phase diagrams. The results of these measurements are in good general agreement with previous work, with the exception that evidence for an additional stable intermediate state has been obtained. The basal-plane data were isotropic with respect to the current direction, and highly anisotropic with respect to the direction of the applied magnetic field. In order to observe sharp resistance anomalies, it was essential to mount the samples in such a way as to provide for relief of thermal and magnetostrictive stresses. All samples studied were in the form of thin disks, with the magnetic field applied in the plane of the disk to minimize the demagnetizing effects.

Normal mode oscillations of the Williams domains in thin films of nematic liquid crystals

Very slow, time-dependent normal mode oscillations of the Williams domains in nematic liquid crystals subject to a low-frequency electric field are reported. These oscillations form a dynamically stable intermediate state between the Williams domain and the dynamic scattering regimes.

Electrochemical studies on rhenium in fused LiCl-KCl eutectic

Potentiometric and polarographic studies were carried out on Re(IV) and ReO 4 − in the LiCl-KCl eutectic at 450–550°C. The reversible apparent standard potential of the Re(IV)/Re(0) couple here is −0·389 + (5·6 x 10 −4) ( t − 450) V vs the standard Pt(II)/Pt(0) reference. Rhenium metal can be electrodeposited from these melts, but potentials exceeding about −1 V result in predeposition of Li(0) which partly dissolves in the rhenium. Anodic dissolution of rhenium metal produces Re(IV) and Re(III); the latter disproportionates at once to Re(IV) and Re(0). This reaction will support only low current densities. Re(IV) is stable indefinitely in the melt, but addition of K 2ReCl 6 to the melt involves some decomposition to metal during the dissolution process. ReO 4 − can be reduced to Re(0) in the eutectic at −1·2 V with high current efficiency. Stable intermediate oxidation states were not observed.

An analysis and experimental investigation of the binistor

This article is an analysis of a four-layer semiconductor device known as the binistor. An approximate equivalent of this device may be constructed from suitably connected NPN and PNP transistors. Analysis of the equivalent circuit configuration by means of the small-signal hybrid parameters enables a prediction of the circuit characteristics. From this analysis, it is shown that the device exhibits a voltage-stable negative-resistance characteristic in contrast with the usual current-stable negative resistance obtained from circuits employing a four-layer semiconductor device. This analysis indicates the manner in which the negative-resistance portion of the collector current-voltage characteristic is dependent upon the small-signal parameters of the NPN and PNP transistors and upon a certain resistance external to the device. A linear model of the device is proposed. Use of the model allows a prediction, within experimental accuracy, of the switching characteristics of the binistor used as a bistable device. Switching between the two states may be accomplished by three methods of control. This model suggests that the transfer characteristic between two particular ports should have the hysteresis characteristics of a mechanical relay. This analysis is born out by experiment. A circuit formed by a series combination of two binistors is shown. This circuit has two stable states with a stable output either at essentially the supply voltage, or at approximately ground potential. A modification with an intermediate stable state is also obtainable with the proper bias conditions. A logical extension of the binistor structure to a device that may have any desired number of stable states is proposed and a circuit of this type with three stable states is shown and discussed. Because of certain internal interaction phenomena, the device may be used as a modulator, and an experimental modulator circuit is developed and investigated.