Absence of reptation in highly confined polymers

We present results of mechanical stress relaxation measurements on polymers confined at the air-water interface in the form of a monolayer. Systematic measurements allow, to our knowledge, for the first time, observation of the scaling of the stress relaxation time of the highly confined polymers as a function of both surface concentration and molecular weight. The observed scaling is found to be very close to that expected for motion of unentangled polymer solutions with hydrodynamic interactions. Our experimental observations thus clearly rule out the possibility of entanglement and hence reptation as a mode of relaxation in such highly confined polymeric systems.

Isomerization Dynamics In Solution In The Absence Of An Activation Barrier - Evaluation Of The Potential Parameters

We analyze recent experimental results of Sundström and Gillbro by using the theory of Bagchi, Fleming and Oxtoby. The experimental results are in good agreement with this theory, but not with the earlier theory of Förster and Hoffmann. By fitting the new experimental results to the theory, we obtain approximate estimates of the frequency of the excited surface (assumed harmonic) and the width of the sink function.

Resistance Minimum in Dilute Magnetic Alloys in the Absence of Impurity Moments

A possible mechanism for the resistance minimum in dilute alloys in which the localized impurity states are non-magnetic is suggested. The fact is considered that what is essential to the Kondo-like behaviour is the interaction of the conduction electron spin s with the internal dynamical degrees of freedom of the impurity centre. The necessary internal dynamical degrees of freedom are provided by the dynamical Jahn-Teller effect associated with the degenerate 3d-orbitals of the transition-metal impurities interacting with the surrounding (octahedral) complex of the nearest-neighbour atoms. The fictitious spin I characterizing certain low-lying vibronic states of the system is shown to couple with the conduction electron spin s via s-d mixing and spin-orbit coupling, giving rise to a singular temperature-dependent exchange-like interaction. The resistivity so calculated is in fair agreement with the experimental results of Cape and Hake for Ti containing 0.2 at% of Fe.

Absence of parallelism between polyamine and nucleic acid contents during induced growth of cucumber cotyledons

The cytokinins (benzyladenine or benzyladenosine) decreased spermidine and spermine contents despite increasing putrescine content, when administered to isolated cotyledons of Cucumis sativus L. var. Guntur in organ culture. KCl decreased putrescine contents, although marginally increasing polyamine contents. The cytokinins and/or KCl augmented nucleic acid biosynthesis and accumulation, resulting in enhanced growth and differentiation of the isolated cotyledons. These observations show that polyamine accumulation and growth are not always coupled.

Solubilities of Some Chlorophenols in Supercritical CO2 in the Presence and Absence of Cosolvents

The solubilities of three chlorophenols, namely, 4-chlorophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol, in supercritical carbon dioxide were determined at temperatures from (308 to 3 18) K in the pressure range of (8.8 to 15.6) MPa. The Solubilities were determined both in the absence of cosolvents and in the presence of two cosolvents, methanol and acetone. The solubilities (in the absence of cosolvents) in mole fraction of 4-chlorophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol at 308 K were in the range of (0.0113 to 0.0215), (0.0312 to 0.0645), and (0.008 to 0.0173), respectively. The Solubilities of the chlorophenols followed the order 2,4-dichlorophenol & 4-chlorophenol & phenol & 2,4,6-trichlorophenol & pentachlorophenol. The solubility data were correlated with the Charstil model and with the Mendez-Santiago and Teja model. The overall deviation between the experimental data and the correlated results Was less than 6 % in averaged absolute relative deviation (AARD) for both of the models.

Proteomics and mass spectrometric studies reveal planktonic growth of Mycobacterium smegmatis in biofilm cultures in the absence of rpoZ

Mycobacterium smegmatis is known to form biofilms and many cell surface molecules like core glycopeptidolipids and short-chain mycolates appear to play important role in the process. However, the involvement of the cell surface molecules in mycobacteria towards complete maturation of biofilms is still not clear. This work demonstrates the importance of the glycopeptidolipid species with hydroxylated alkyl chain and the epoxylated mycolic acids, during the process of biofilm development. In our previous study, we reported the impairment of biofilm formation in rpoZ-deleted M. smegmatis, where rpoZ codes for the ω subunit of RNA polymerase (R. Mathew, R. Mukherjee, R. Balachandar, D. Chatterji, Microbiology 152 (2006) 1741). Here we report the occurrence of planktonic growth in a mc2155 strain which is devoid of rpoZ gene. This strain is deficient in selective incorporation of the hydroxylated glycopeptidolipids and the epoxy mycolates to their respective locations in the cell wall. Hence it forms a mutant biofilm defective in maturation, wherein the cells undertake various alternative metabolic pathways to survive in an environment where oxygen, the terminal electron acceptor, is limiting.

The key enzyme in galactose metabolism, UDP-galactose-4-epimerase, affects cell-wall integrity and morphology in Candida albicans even in the absence of galactose

The enzyme UDP-galactose-4-epimerase (GAL10) catalyzes a key step in galactose metabolism converting UDP-galactose to UDPglucose which then can get metabolized through glycolysis and TCA cycle thus allowing the cell to use galactose as a carbon and energy source. As in many fungi, a functional homolog of GAL10 exists in Candida albicans. The domainal organization of the homologs from Saccharomyces cerevisiae and C albicans show high degree of homology having both mutarotase and an epimerase domain. The former is responsible for the conversion of beta-D-galactose to alpha-D-galactose and the hitter for epimerization of UDP-galactose to UDP-glucose. Absence of C albicans GAL10 (CaGAL10) affects cell-wall organization, oxidative stress response, biofilm formation and filamentation. Cagal10 mutant cells tend to flocculate extensively as compared to the wild-type cells. The excessive filamentation in this mutant is reflected in its irregular and wrinkled colony morphology. Cagal10 strain is more susceptible to oxidative stress when tested in presence of H2O2. While the S. cerevsiae GAL10 (ScGAL10), essential for survival in the presence of galactose, has not been reported to have defects in the absence of galactose, the C albicans homolog shows these phenotypes during growth in the absence of galactose. Thus a functional CaGal10 is required not only for galactose metabolism but also for normal hyphal morphogenesis, colony morphology, maintenance of cell-wall integrity and for resistance to oxidative stress even in the absence of galactose. (c) 2006 Elsevier Inc. All rights reserved.

Hormones and Cuscuta development: IAA uptake transport and metabolism in relation to growth in the absence and presence of applied cytokinin

Transport of 1-14C-IAA in successive stem segments of Cuscuta was strictly basipetal in growing and non growing regions of the vine with a flux velocity of 10-12 mm/h (intercept method). This transport showed a distinct peaked profile, increasing from a low value at 10 mm from the apex to a maximum between 50 and 90 mm before declining to a low value again around 160 mm at which elongation growth ceased. The IAA transport profile paralleled the in vivo growth rate profile, though the latter peaked ahead of transport. A better correlation was observed between the profile of growth responsiveness of the vine to exogenous IAA application and the profile of IAA transport. Growth responsiveness was determined as the differential in growth rate of stem segments in vitro in the absence and presence of growth optimal concentration of IAA (10 μm). Retention of exogenous IAA in the stem was maximal where transport decreased, and this coincided with the region of maximal conjugation of applied 1-14C-IAA to aspartic acid to form indoleacetylaspartate (IAAsp). In addition to aspartate, IAA was conjugated to a small extent to an unidentified compound. IAA destruction by decarboxylation was greatest where transport was low, particularly in the nongrowing region, where lignification occurred (i.e., beyond 180 mm). At concentrations up to 20 μM, a pulse of 1-14C-IAA chased by "cold" IAA moved as a peak (with a peak displacement velocity of 12-18 mm/h) in the "growth" region of the vine, but became diffusionlike where growth either fell off steeply or ceased. At a higher (50 μM) IAA concentration, though uptake was not saturated, transport in the growth region became diffusionlike, indicating saturation of the system. Reduced IAA flux in the region where growth responsiveness to IAA declined coincided with the region of increased IAA conjugation. However, it cannot be concluded whether increased IAA conjugation was the cause or effect of decreased IAA flux. Application of benzyladenine to the vines in vivo, a treatment that elicited haustoria formation by 72 h, resulted in the inhibition of both IAA transport and elongation growth rate in the subapical region. In vitro treatment of vine segments with BA similarly increased IAA retention and decreased IAA transport. IAA loss was suppressed, and conjugation to IAAsp was enhanced. © 1989 Springer-Verlag New York Inc.

X-Ray structure of a ternary complex, copper(II)–lnosine 5-monophosphate–benzimidazole. The first example for the absence of direct metal–nucleotide interaction

The unprecedented absence of direct metal–nucleotide interaction has been observed in the X-ray structure of the ternary metal nucleotide system [Cu(bzim)(H2O)5]2+[IMP]2–·3H2O [IMP = inosine 5-monophosphate(2–), bzim = benzimidazole). The complex crystallizes in the space group P21 with a= 7.013(2), b= 13.179(9), c= 14.565(9)Å, = 94.82(4)°, and Z= 2. The structure was solved by the heavy-atom method and refined by full-matrix least squares on the basis of 1 761 observed (I? 3i) reflections to final R and R values of 0.034 and 0.036 respectively. The CuII has a distorted octahedral co-ordination with a nitrogen of the bzim ligand [Cu–N 1.947(5)Å] and three oxygens of water molecules in the basal plane [mean Cu–O 2.017(3)Å] and two more water oxygens at axial positions [Cu–O 2.194(6) and 2.732(5)Å]. The nucleotide base stacks with the bzim ligand at an average distance of 3.5 Å and an angle of 22°. In the lattice, N(7) of the base is linked to a lattice water through a hydrogen bond, while all the phosphate oxygens are involved in hydrogen bonds with co-ordinated as well as lattice water molecules. The co-ordination behaviour of IMP to CuII is compared in structures containing different -aromatic amines in order to assess the influence of the ternary ligand in complex formation. The present results indicate that, apart from the commonly observed phosphate binding, other modes of co-ordination are possible, these being influenced mainly by the -accepting properties of the ternary ligand.

Occurrence of 1-methyladenosine and absence of ribothymidine in transfer ribonucleic acid of Mycobacterium smegmatis

The minor base composition of Mycobacterium smegmatis tRNA has been studied. Thin-layer chromatographic patterns of a ribonuclease T2 digest of mycobacterial tRNA indicated the presence of appreciable amounts of 1-methyladenosine (which is commonly present only in eucaryotic tRNA), dihydrouridine, and 7-methylguanosine. Ribothymidine was absent. The S-adenosylmethionine-dependent tRNA methylases of M. smegmatis catalyzed the formation of 1-methyladenosine when Escherichia coli tRNA was used as acceptor. Similarly, E. coli extracts methylated the tRNA of M. smegmatis, forming ribothymidine.

Proposed role of w chromosome inactivation and the absence of dosage compensation in avian sex determination

Three features of avian sex chromosomes - female heterogamety (ZZ male, ZW female), the apparently inactive state of the W chromosome, and dose-dependent expression of Z-linked genes - are examined in regard to their possible relation to sex determination. It is proposed that the W chromosome is facultatively heterochromatic and that the Z and W chromosomes carry one or more homologous sex-determination genes. The absence of dosage compensation in ZZ embryos, and W inactivation in ZW embryos, would then bring about a 2n(ZZ)-n(ZW) inequality in the effective copy number of such genes. The absence of dosage compensation of Z-linked genes in ZZ embryos is viewed as a means by which two copies of Z-W homologous sex determination genes are kept active to meet the requirements of testis determination. W inactivation may promote ovarian development by reducing the effective copy number of these genes from 2n to n. If there is a W-specific gene for femaleness, spread of heterochromatization to this gene in cells forming the right gonadal primordium may explain the latter's normally undifferentiated state; reversal of heterochromatization may similarly explain the development of the right gonad into a testis following left ovariectomy.

The precision of regulation in Dictyostelium discoideum: implications for cell-type proportioning in the absence of spatial pattern

We have made careful counts of the exact number of spore, stalk and basal disc cells in small fruiting bodies of Dictyostelium discoideum (undifferentiated amoebae are found only rarely and on average their fraction is 4.96 x 10(-4)). (i) Within aggregates of a given size, the relative apportioning of amoebae to the main cell types occurs with a remarkable degree of precision. In most cases the coefficient of variation (c.v.) in the mean fraction of cells that form spores is within 4.86%. The contribution of stalk and basal disc cells is highly variable when considered separately (c.v.'s upto 25% and 100%, respectively), but markedly less so when considered together. Calculations based on theoretical models indicate that purely cell-autonomous specification of cell, fate cannot account for die observed accuracy of proportioning. Cell-autonomous determination to a prestalk or prespore condition followed by cell type interconversion, and stabilised by feedbacks, suffices to explain the measured accuracy. (ii) The fraction of amoebae that differentiates into spores increases monotonically with the total number of cells. This fraction rises from an average of 73.6% for total cell numbers below 30 and reaches 86.0% for cell numbers between 170 and 200 (it remains steady thereafter at around 86%). Correspondingly, the fraction of amoebae differentiating into stalk or basal disc decreases viith total size. These trends are in accordance with evolutionary expectations and imply that a mechanism for sensing the overall size of the aggregate also plays an essential role in the determination of cell-type proportions.

On the existence of hydrotalcite-like phases in the absence of trivalent cations

alpha-Hydroxides of nickel(II) and cobalt(II) are hydrotalcite-like phases, possessing a layered double hydroxide (LDH) structure even though there are no trivalent cations in the lattice. While the LDHs acquire a positive charge on the hydroxide layers by the incorporation of trivalent cations, we suggest that the alpha-hydroxides acquire a positive charge by partial protonation of the hydroxyl ions according to the equation M(OH)(2)+xH(+) --> [M(OH)(2-x)(H2O)(x)](x+). As in the LDHs, charge balance is restored by the incorporation of anions in the interlayer region. (C) 1997 Academic Press.