Presence Of Monomer Research Articles

Detection of Coconut cadang‐cadang viroid sequences in oil and coconut palm by ribonuclease protection assay

AbstractA ribonuclease protection assay (RPA) has been developed for detecting Coconut cadang‐cadang viroid (CCCVd) sequences. An RNA probe complementary to full‐length CCCVd246 was used, terminating at nucleotide 65 in the upper conserved region, and linked to a non‐viroid 5′ sequence, which acted as an internal control for ribonuclease activity. Extracts from CCCVd‐infected coconut (Cocos nucifera) and African oil (Elaeis guineensis) palms protected three major fragments of approximately 250, 125 and 50 nt and a variable number of minor fragments. Extracts of healthy coconut palms, Potato spindle tuber viroid‐infected tomato and transfer RNA did not protect the probe. The approximately 250 nt fragment is predicted to indicate the presence of monomers and dimers of circular CCCVd246, linear CCCVd246 with the same termini as the probe and point mutants of these forms. The origin of smaller protected fragments is discussed. RPA‐detected CCCVd sequences in 13 of 18 oil palms surveyed in a commercial plantation in Malaysia. Signal intensity varied between the positive oil palms and was generally lower than in coconut palms infected with CCCVd. An infection phenotype was implied but not confirmed by the observation that in a group of 10 oil palms with orange leaf spotting, 9 contained CCCVd, whereas in a group of 8 palms without orange spotting, the viroid was detected in 4. Of four coconut palms in Sri Lanka shown by dot‐blot assay to contain CCCVd‐related RNA, one was shown by RPA to be positive for the CCCVd246 sequence. RPA is therefore a robust and sensitive test for CCCVd sequences, and our results show that sequences closely related to CCCVd246 are not confined to the Philippines.

Preparation of Langmuir–Blodgett films of aligned sepiolite fibers and orientation of methylene blue molecules adsorbed on the film

Sepiolite is a clay mineral with a fibrous morphology; the fibers possess rectangular channels along the fiber direction, and have cation-exchange ability. Amphiphilic octadecylammonium cations (ODAH(+)) spread at an interface between the air and a dispersion of sepiolite fibers have hybridized with the fibers to form a floating monolayer. Surface pressure-molecular area isotherms did not indicate clear collapse points of the hybrid monolayers. Observation of the hybrid films on glass plates by atomic force microscopy revealed that the sepiolite fibers preferred to be aligned perpendicularly to the compression direction, and that some fibers overlapped upon compression or even before compression. Out-of-plane and in-plane X-ray diffraction patterns of the hybrid film showed that the fibers were not only aligned by the compression but oriented around the fiber direction. Electronic spectra of methylene blue cations (MB(+)) adsorbed on the hybrid film indicated the presence of monomers and dimers of MB(+). The absorption intensity due to the monomer was dependent on the polarization direction of the incident beam; interestingly, the monomers were spontaneously oriented along the sepiolite fiber direction but the dimers were not oriented. By comparison with the results of rhodamine 6G adsorbed on the film, the monomers of MB(+) would probably be present in the channels of sepiolite fibers, while the dimers would be adsorbed on the external surface of the fibers.

Do equilibrium clusters exist in concentrated lysozyme solutions?

In contrast to our previous findings (1), Shukla et al. (2) claim the absence of clusters in concentrated lysozyme solutions. This claim is based on scattering data that show no significant differences from our data, where conditions are similar. Our sample preparation and measurements are thus comparable and both our conclusions based on virtually identical data. Nevertheless, the existence of clusters is refuted because, first, “the interference peak … displays a clear trend toward higher q-values with increasing protein concentration” and, second, “is adequately and consistently described by the form and structure factors of individual lysozyme particles using an interaction potential involving short-range attraction and long-range repulsion” (conclusions in ref. 2). However, we both observe the usual shift in peak position at low concentrations, where the well separated molecules experience the long-range repulsion, and, crucially, we both also find an essentially concentration-independent position for concentrated solutions (1, 2) where the closer molecules overcome the repulsive barrier and the short-range attraction induces clusters. [Note that they do not compare data from concentrated solutions in their article (2) but only in supporting information (SI) Fig. S9.] Furthermore, fits of form and structure factors result in values for the pair potential but cannot provide direct information on the presence of monomers and/or clusters. Nonetheless, for a potential with similar values as determined by Shukla et al. (2), MD simulations have confirmed the presence of clusters (3). Therefore, their data (2) actually confirm our earlier data and interpretation (1) that the peak position is concentration-independent and clusters are present in lysozyme solutions, which, as stated in both of our titles, are concentrated.

Removal of uranium from mining industry feed simulant solutions using trapped amidoxime functionality within a mesoporous imprinted polymer material

Ion imprinted polymer (IIP) material of mesoporous nature was prepared in two steps: (i) by forming binary/ternary complexes of uranyl imprint ion with a suitable non-vinylated uranophile, formamidoxime and/or vinylated ligand, 4-vinyl pyridine (VP) and (ii) by thermally copolymerizing them with 2-hydroxy ethyl methacrylate (HEMA) as the functional monomer and ethylene glycol dimethacrylate (EGDMA) as the cross-linking monomer in presence of 2,2′-azobisisobutyronitrile as initiator and 2-methoxy ethanol as porogen. The IIP material formed was subsequently leached with 50% (v/v) HCl to obtain leached materials which then rebind uranyl ions selectively from aqueous solutions. Corresponding non-imprinted polymer (NIP) materials were also prepared under the same conditions exactly as the IIP but in the absence of the uranyl ion template. Extensive characterization of IIP (both unleached and leached) and NIP materials were done using SEM, XPS, EDS, IR and BET-surface area and pore size analysis. The optimal pH for quantitative removal is 8.0–9.0 and the IIP materials offered either higher or comparable retention capacity 80.0 μmol of uranyl ion per g of polymer with respect to most of the hitherto prepared uranyl IIP materials. In addition, the imprinting effect was noticed in all the experimental variables and selectivity characteristics. The applicability of IIP material for the removal of emerging toxic pollutant uranium from uranium mining industry feed simulant solution is successfully demonstrated.

Studies of the Polydiacetylene Bis-p-chlorocinnamate of 10,12-Docosadiyn-1,22-diol

The bis-p-chlorocinnamate of 10,12-docosadiyn-1,22-diol polymerized with 60Co gamma radiation to give a soluble polydiacetylene (PDA), PDA-ClCIN-22. We have studied PDA-ClCIN-22 in both crystallographic powder and solution coated films. Thin films of solution coated PDA-ClCIN-22 exhibit an absorption maximum of 544 nm, similar to the concentrated solution in chlorobenzene. Irradiation of these films with 254 nm UV light in air leads to loss of intensity in the visible spectrum. The thin films of PDA-ClCIN-22 are amorphous by X-ray powder diffraction. Irradiation of both PDA-ClCIN-22 powder and film with 254 nm light did not result in photochemical reactivity of the chlorocinnamate group as recorded by FTIR spectra. Differential scanning calorimetry (DSC) studies of PDA-ClCIN-22 reveal that presence of monomer and endothermic transitions near 116°C and 134°C on a first heating. On a second heating of a sample of PDA-ClCIN-22 taken to 150°C on first heating, the 116°C and 134°C endotherms are absent. These endotherms are also lost by monomer extraction with boiling cyclohexane. One possible source of the endotherms would be conformational transitions in the side chain.

Kinetics study of the UV-initiated cationic polymerization of cycloaliphatic diepoxide resins

Photo-differential scanning calorimetry (photo-DSC) was used to study the cure kinetics of UV-initiated cationic photo-polymerization of epoxy resin monomers in presence of different photoinitiators and to investigate the photo-reactivity with respect to their chemical structure. Two cycloaliphatic diepoxy monomers – 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate and bis-(3,4-epoxycyclohexyl) adipate – were studied. Both monomers have two terminal epoxy functional groups and differ only in the number of, so-called, “space” carboxylate group and thus the overall length of the molecule. Different kinetics analysis results, including enthalpy of the reaction, induction time, peak maximum, percentage conversion were obtained for both epoxy systems for different amounts of added photoinitiator and at different isothermal temperatures (30–70 °C). Two kinetic parameters – rate coefficient ( k) and the order of the initiating reaction ( m) – were determined, using an autocatalytic kinetics model. Activation energy for the two epoxies curing process using the Arrhenius equation was calculated as well. Results show that photochemical reactivity is influenced by the chemical structures of monomers.

ISA Channel Complexes Include Four Subunits Each of DPP6 and Kv4.2

Kv4 potassium channels produce rapidly inactivating currents that regulate excitability of muscles and nerves. To reconstitute the neuronal A-type current I(SA), Kv4 subunits assemble with DPP6, a single transmembrane domain accessory subunit. DPP6 alters function-accelerating activation, inactivation, and recovery from inactivation-and increases surface expression. We sought here to determine the stoichiometry of Kv4 and DPP6 in complexes using functional and biochemical methods. First, wild type channels formed from subunit monomers were compared with channels carrying subunits linked in tandem to enforce 4:4 and 4:2 assemblies (Kv4.2-DPP6 and Kv4.2-Kv4.2-DPP6). Next, channels were overexpressed and purified so that the molar ratio of subunits in complexes could be assessed by direct amino acid analysis. Both biophysical and biochemical methods indicate that I(SA) channels carry four subunits each of Kv4.2 and DPP6.

Living carbocationic polymerization. IV. Living polymerization of isobutylene

Truly living polymerization of isobutylene (IB) has been achieved for the first time by the use of new initiating systems comprising organic acetate-BCl3 complexes under conventional laboratory conditions in various solvents from −10 to −50°C. The overall rates of polymerization are very high, which necessitated the development of the incremental monomer addition (IMA) technique to demonstrate living systems. The living nature of the polymerizations was demonstrated by linear $\[\bar M_n \]$ versus grams polyisobutylene (PIB) formed plots starting at the origin and horizontal number of polymer molecules formed versus amount of polymer formed plots. $\[\overline {DP_n } \]$ obeys [IB]/[CH3COORt · BCl3]. Molecular weight distributions (MWD) are very narrow in homogeneous systems $\[\left( {{{\bar M_w } \mathord{\left/ {\vphantom {{\bar M_w } {\bar M_n = 1.2 - 1.3}}} \right. \kern-\nulldelimiterspace} {\bar M_n = 1.2 - 1.3}}} \right)\]$ whereas somewhat broader values are obtained when the polymer precipitates out of solution $\[\left( {{{\bar M_w } \mathord{\left/ {\vphantom {{\bar M_w } {\bar M_n = 1.4 - 3.0}}} \right. \kern-\nulldelimiterspace} {\bar M_n = 1.4 - 3.0}}} \right)\]$. The MWDs tend to narrow with increasing molecular weights, i.e., with the accumulation of precipitated polymer in the reactor. Traces of moisture do not affect the outcome of living polymerizations. In the presence of monomer both first and second order chain transfer to monomer are avoided even at −10°C. The diagnosis of first and second order chain transfer has been accomplished, and the first order process seems to dominate. Forced termination can be effected either by thermally decomposing the propagating complexes or by nucleophiles. In either case the end groups will be tertiary chlorides. The living polymerization of isobutylene initiated by ester · BCl3 complexes most likely proceeds by a two-component group transfer polymerization.

Studies of electrical moment and thermodynamic properties of water in organic solvents at 298.15 K

We report in this paper on measurements of static dielectric constant ( ε) at 1 kHz for solutions of water dissolved in organic solvents (benzene and 1,4-dioxane) of low dielectric constant at 298.15 K. The solutions having different water activities and hence concentrations were prepared by isopiestic technique. The solubility data indicate validity of Henry's law only near solutions of unit water activity. The variation of ε with concentration of water is subjected to analysis using the Kirkwood–Fröhlich equation. The calculated dipole moment values ( μ) for water molecules indicate presence of monomers in 1, 4-dioxane solutions while μ values in case of the H 2O–benzene system reveal change of monomer to cyclic-trimer species. Also, an attempt is made to apply McMillan–Meyer theory to the data of the H 2O–benzene system. The results of these indicate presence of pair and triplet interactions (osmotic virial coefficients) for water molecules in the condensed phase.

Electrochemical synthesis of new conducting copolymers containing pseudo-polyether cages with pyrrole

Abstract Conducting copolymers have been synthesized via electrochemical oxidation of pyrrole (Py) in the presence of monomer 1,11-bis(1,1-pyrrole)-3,6,9-trioxaundecane ( I ) in an electrolytic solution containing 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF 6 ) dissolved in acetonitrile. It is observed that reversible redox behavior of poly( I - co -Py)s shifts to more positive potentials with the increasing amount of I in the comonomer mixture, indicating formation of a copolymer. It is also found that increasing the ratio of I in the comonomer mixture decreases the conductivity of the obtained polymer films. The dark electrical conductivity measurements in the temperature range of 300–100 K revealed the extrinsic type of conduction with activation energy values being in the range of 82.3–16.9 meV.

Proton NMR assignments for R,S‐1,1′‐binaphthol (BN) and R,S‐1,1′‐binaphthyl‐2,2′‐diyl hydrogen phosphate (BNDHP) interacting with bile salt micelles

We report proton chemical shifts for two model chiral analytes that are commonly used in the study of micellar electrokinetic capillary chromatography (MEKC), R,S-1,1'-binaphthol (1, BN) and R,S-1,1'-binaphthyl-2,2'-diyl hydrogen phosphate (2, BNDHP), in the absence and presence of monomers and micelles of sodium cholate and sodium deoxycholate. The analytes undergo fast exchange in and out of the micelles, which perturbs the analytes' chemical shifts, and which we use to resolve some resonances that are degenerate at both 300 and 600 MHz. Although BN and BNDHP are simple molecules, the proton assignments are only unambiguously established with the aid of the exchange with micelles, an attractive alternative to other methodologies such as the use of paramagnetic shift reagents which may also cause spectral distortions. We rely also upon 2D-NOE spectra of samples in the presence of micelles to perform these assignments. Recently published assignments, which were based upon 2D-COSY spectroscopy, appear to be in error and are corrected here. Finally, we note that these shifts are information-rich reporters on the nature of the interactions of these model analytes with the micelles.

Synthesis and Evaluation of Semiconductive Polymer Compositions

A semiconductive polymer composition was prepared in which micronized particulate conductive filler, such as copper or graphite, is dispersed in a polymeric component that is of an essentially amorphous thermoplastic resin (such as polymethylmethacrylate). These molding powders of polymethylmethacrylate were prepared by suspension polymerization of methylmethacrylate monomer in presence of these conductors. The prepared molding powder contains 4.8% and 40.44% by volume (with respect to polymethylmethacrylate (PMMA)) of copper and graphite, respectively. The effect of blending copper and graphite at different vol % to the prepared molding powder on the specific resistance of the product was studied. It was concluded that the specific resistance of molding powder was decreased from 2.1 × 1011 to 3.05 × 106 ohm.cm at 70% volume copper and from 2.3 × 104 to 2 × 102 ohm cm at 80% volume graphite.

Zero-temperature Kosterlitz–Thouless transition in a two-dimensional quantum system

We construct a local interacting quantum dimer model on the square lattice, whose zero-temperature phase diagram is characterized by a line of critical points separating two ordered phases of the valence bond crystal type. On one side, the line of critical points terminates in a quantum transition inherited from a Kosterlitz–Thouless transition in an associated classical model. We also discuss the effect of a longer-range dimer interaction that can be used to suppress the line of critical points by gradually shrinking it to a single point. Finally, we propose a way to generalize the quantum Hamiltonian to a dilute dimer model in presence of monomers and we qualitatively discuss the phase diagram.

Ethylene Polymerization Using Discrete Nickel(II) Iminophosphonamide Complexes

The syntheses and structures of the discrete (π-allyl)nickel iminophosphonamide (PN2) complexes 2a−d from the reaction of (π-allyl)nickel bromide and the corresponding PN2 ligands 3a,b or from the reaction of (π-allyl)2Ni and phosphorane 1 are reported. Complexes 2a,b are characterized by having long Ni−N distances coupled with an acute bite angle for the PN2 ligand. The π-allyl ligands in complexes 2a−d are not fluxional on the NMR time scale at room temperature, although chemical exchange between the isomeric complexes 2c,d occurs via PN2 ligand reorientation. Purified complexes 2a−d are not active for ethylene polymerization; it is only when complexes 2c,d are generated in situ in the presence of monomer that high-Mw branched poly(ethylene) is formed. A variety of indirect evidence suggests that the active catalyst arises from the reaction of Ni(0)−alkene complexes with phosphorane 1, either preformed or generated in situ through decomposition of (π-allyl)2Ni. A bona fide PN2NiPh(PPh3) complex, 5, was prepared from NiPh(PPh3)2Br and the PN2 ligand 3a and was structurally characterized. This complex is active for 1-hexene isomerization in the absence of an activator. During hexene isomerization, variable amounts of the paramagnetic bis(PN2) complex 4 are produced along with ligand 3a. In addition, the fluxional intermediate 6, containing both a PN2 ligand and coordinated PPh3, is present during catalysis. Reaction of 5 with an equimolar amount of propene provides α-methylstyrene, the product of 1,2-insertion followed by β-H elimination. Complex 5 is not effective for polymerization or oligomerization of ethylene under a variety of conditions. The reactions of complex 5 with various phosphine scavengers were studied, and of these only Rh(acac)(C2H4)2 is both effective and selective for PPh3. Hard Lewis acids, including AlMe3, B(C6F5)3, and PMAO, have a pronounced tendency toward abstraction of the PN2 or other anionic ligands in these unhindered complexes. All of the complexes reported in this paper are extremely active for ethylene dimerization in the presence of PMAO. In the presence of stoichiometric Rh(I), complex 5 rapidly isomerizes 1-hexene and in the presence of ethylene produces branched PE oligomers at modest activity.

Cytological analysis of Saccharomyces cerevisiae cells supporting cymbidium ringspot virus defective interfering RNA replication

The replicase proteins p33 and p92 of Cymbidium ringspot virus (CymRSV) were found to support the replication of defective interfering (DI) RNA in Saccharomyces cerevisiae cells. Two yeast strains were used, differing in the biogenesis of peroxisomes, the organelles supplying the membranous vesicular environment in which CymRSV RNA replication takes place in infected plant cells. Double-labelled immunofluorescence showed that both p33 and p92 replicase proteins localized to peroxisomes, independently of one another and of the presence of the replication template. It is suggested that these proteins are sorted initially from the cytosol to the endoplasmic reticulum and then to peroxisomes. However, only the expression of p33, but not p92, increased the number of peroxisomes and induced membrane proliferation. DI RNA replication occurred in yeast cells, as demonstrated by the presence of monomers and dimers of positive and negative polarities. Labelling with BrUTP showed that peroxisomes were the sites of nascent viral synthesis, whereas in situ hybridization indicated that DI RNA progeny were diffused throughout the cytoplasm. DI RNA replication also took place in yeast cells devoid of peroxisomes. It is suggested that replication in these cells was targeted to the endoplasmic reticulum.

Protein stability in the presence of polymer degradation products: Consequences for controlled release formulations

When encapsulating proteins in polymer microspheres for sustained drug delivery there are three stages during which the stability of the protein must be maintained: (1) the fabrication of the microspheres, (2) the storage of the microspheres, and (3) the release of the encapsulated protein. This study focuses on the effects of polymer degradation products on the primary, secondary, and tertiary structure of tetanus toxoid, ovalbumin (Ova), and lysozyme after incubation for 0 or 20 days in the presence of ester (lactic acid and glycolic acid) and anhydride (sebacic acid and 1,6-bis( p-carboxyphenoxy)hexane) monomers. The structure and antigenicity or enzymatic activity of each protein in the presence of each monomer was quantified. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis, circular dichroism, and fluorescence spectroscopy were used to assess/evaluate the primary, secondary, and tertiary structures of the proteins, respectively. Enzyme-linked immunosorbent assay was used to measure changes in the antigenicity of tetanus toxoid and Ova and a fluorescence-based assay was used to determine the enzymatic activity of lysozyme. Tetanus toxoid was found to be the most stable in the presence of anhydride monomers, while Ova was most stable in the presence of sebacic acid, and lysozyme was stable when incubated with all of the monomers studied.

Study of correlation factors and dipolar excess free energies of esters in benzene

The dielectric properties of ethyl acrylate, ethyl benzoate and ethyl butyrate in benzene were studied. The dielectric constants of the binary mixtures of the above three esters at various concentrations in benzene were measured at 298 K, 308 K and 318 K. The possible short-range interaction between the ester molecules were studied using Kirkwood–Frohlich correlation factor ( g'). The long-range interaction between the solute molecules was studied by dipolar excess free energies (Δ F 0 E). The Eyring correlation parameters G and G ⁎ were also determined. The fluid structure of these systems is analyzed in the light of the theory. The presence of monomers and the existence of dipole–dipole interactions are identified.

Impaired dimerization of von Willebrand factor subunit due to mutation A2801D in the CK domain results in a recessive type 2A subtype IID von Willebrand disease

The CK domain of von Willebrand factor (VWF) is involved in the dimerization of the protein. We identified the homozygous substitution A2801D of the CK domain in two siblings. Patients had low levels of VWF in plasma, abnormal ristocetin-induced binding to platelets and abnormal multimeric pattern with a lack of high molecular weight (HMW) forms and the presence of intervening bands between normal multimers. Accordingly, they were classified in type 2A, subtype IID, von Willebrand disease (VWD). Both asymptomatic parents carried the mutation at the heterozygous state. Their plasmaVWF exhibited the full range of multimers found in normal plasma. When analyzed by high resolution gel electrophoresis, very faint bands corresponding to the position of intervening bands of the propositus can be observed. The mutated recombinant (r)VWF-D2801, the hybrid rVWF-A/D2801 and the mutated C-terminal VWF fragment rSPII-D2801 were expressed in COS-7 cells. rVWF-D2801 showed an abnormal multimeric distribution similar to that of the propositus'VWF with intervening bands and a lack of HMW species. rVWF-A/D2801 exhibited the full range of multimers and the aberrant sized forms observed both in propositus'VWF and in rVWF-D2801. rSPII-WT assembled correctly into a dimer of 220 kDa. rSPII-D2801 appeared as a mixture of monomeric and dimeric forms which may be related to the abnormal multimeric pattern of the propositus and both mutated rVWF. We concluded that mutation A2801D disturbs the folding of the CK domain, which may result in a mixture of monomers and dimers of VWF. Multimers containing either an odd or even number of mature subunits are produced, and the presence of monomers appears to limit the degree of multimerization. In the heterozygousVWF, the presence of normal dimers improves the multimerization process. In conclusion, the mutation A2801D appears to be responsible for a recessive type 2A, subtype IID, VWD.

Simultaneous emulsification and interfacial polycondensation for the preparation of colloidal suspensions of nanocapsules

Sub-micrometric particles having an oil core and a polymer shell (nanocapsules) have been prepared by combining in a single stage the emulsification process and an interfacial polymerization reaction. The spontaneous emulsification produced very fast a dispersion of oil droplets of 100–400 nm mean diameter at the surface of which the subsequent polycondensation reaction took place. The process has been optimized with respect to the choice of α-tocopherol as the oil and made robust regarding the presence of monomers in the aqueous and oil phases and their conversion into polymers. The major cause of troubles was the large concentration of diol or diamine monomers in the aqueous phase that made the oil droplets unstable with respect to aggregation immediately after their formation. Once the emulsifier has adsorbed and the polymerization has completed, the final suspensions of nanocapsules were quite stable over long periods. A secondary population of micrometric particles that coexisted with the nanocapsules was present in several cases, which was unfavourable regarding their application as a drug delivery system for cosmetic applications.

Isolation and Characterization of a Satellite DNA Family in Achirus lineatus (Teleostei: Pleuronectiformes: Achiridae)

Agarose gels stained with Ethidium bromide and Southern blot experiments of HindIII-digested genomic DNA of Achirus lineatus evidenced the presence of monomers and multimers of a DNA segment of about 200 bp, named here Al-HindIII sequence. No signals were observed in Southern blot experiments with genomic DNA of other flatfish species. The DNA sequencing of four recombinant clones showed that Al-HindIII sequences had 204 bp and were 63.72% AT-rich. FISH experiments using a Al-HindIII sequence as probe showed bright signals in the centromeric position of all chromosomes of A. lineatus.