Pairing Phenomena Research Articles

Hydrophobic ion pairing: altering the solubility properties of biomolecules.

The high aqueous solubility of ionic compounds can be attributed to the ease of solvation of the counter ions. Replacement of the counter ions with ionic detergents dramatically alters the solubility properties of the molecule. Not only does the aqueous solubility drop precipitously, but the solubility in organic phases increases as well. Consequently, the partition coefficient changes by orders of magnitude. This ion pairing phenomenon, which we term hydrophobic ion pairing (HIP), has been extended to polyelectrolytes, such as proteins and polynucleotides. These materials form HIP complexes that dissolve in a range of organic solvents, often with retention of native structure and enzymatic activity. The HIP process has been used to purify protein mixtures, conduct enzymatic reactions in nonaqueous environments, increase structural stability, enhance bioavailability, and prepare new dosage forms.

Enhanced electron pairing in a lattice of Berry-phase molecules.

We show that electron hopping in a lattice of molecules possessing a Berry phase naturally leads to pairing. Our building block is a simple molecular site model inspired by ${\mathrm{C}}_{60}$, but realized in closer similarity with ${\mathrm{Na}}_{3}$. In the resulting model electron hopping must be accompanied by orbital operators, whose function is to switch on and off the Berry phase as the electron number changes. The effective Hamiltonians (electron-rotor and electron-pseudospin) obtained in this way are then shown to exhibit a strong pairing phenomenon, by means of one-dimensional linear-chain case studies. This emerges naturally from numerical studies of small-N-site rings, as well as from a BCS-like mean-field theory formulation. The pairing may be explained as resulting from the exchange of singlet pairs of orbital excitations, and is intimately connected with the extra degeneracy implied by the Berry phase when the electron number is odd. The relevance of this model to fullerides, to other molecular superconductors, as well as to present and future experiments, is discussed.

Pseudopotential plane-wave study of alpha -YHx.

The solid-solution phase of hydrogen in hexagonal close-packed yttrium (\ensuremath{\alpha}-${\mathrm{YH}}_{\mathit{x}}$) is studied using the pseudopotential method within the local-density-functional approximation with a plane-wave basis. The binding energies associated with different interstitial sites are evaluated for several ordered structures: ${\mathrm{YH}}_{0.5}$, ${\mathrm{YH}}_{0.25}$, and ${\mathrm{YH}}_{0.167}$. It is found that the occupation of the tetrahedral site is always energetically favorable. The hydrogen potential-energy curves around the tetrahedral sites along the c axis and along the path connecting the adjacent octahedral sites are also calculated for ${\mathrm{YH}}_{0.25}$. In particular, the local vibrational mode along the c axis is estimated to be 100 meV, in excellent agreement with that measured in neutron-scattering experiments. Finally, the intriguing pairing phenomenon is investigated by calculating the total energy for various pairing configurations. The possibility of pairing between nearest-neighbor tetrahedral sites is excluded due to the high energy. It is found that the pairing of hydrogen across a metal atom is indeed energetically favorable compared with other kinds of pairs considered and also with isolated tetrahedral hydrogen atoms. The connection with the electronic structure of the system is also examined.

Observation expérimentale de la morphologie "en algue" et d'états asymétriques appariés en solidification directionnelle de films minces d'alliages CBr4-C2Cl6

The morphology of the growth in the thin-film directional solidification of a CBr4 - 8 mol% C2Cl6 alloy is studied for a particular crystalline orientation, namely, where a axis is perpendicular to the plane of the film. In this case, the effective surface tension as well as attachment kinetics anisotropies are very weak, and a disordered, seaweed structure is observed. In good agreement with recent numerical studies by Ihle and Muller-Krumbhaar (Phys. Rev. E 49 2972 (1994)), we show that this disordered structure is mainly composed of pairs of asymmetric fingers. This pairing phenomenon is in fact generic of all crystal orientations and is as well observed in standard, highly anisotropic grains, for higher velocities and thus higher undercoolings, as predicted numerically. In addition to the pulling velocity and the effective anisotropy in the plane of the experiment, we point out the relevance of the cellular spacing as a determinant parameter for the generation of symmetric or paired asymmetric structures. We also discuss the differences between the periodic patterns found numerically and the disordered morphologies observed experimentally.

Survival bonding: a response to stress and work with AIDS.

There is ample literature describing the ongoing stressors and tremendous emotional impact on health care professionals caring for patients with AIDS. This paper is a report of a research study which explored collegial relationships and staff retention to determine factors that reduced staff burnout. The study explored an observed phenomenon of pairing among staff members of various disciplines, working with patients with AIDS, in a tertiary care hospital. The authors called this phenomenon "survival bonding." These informal but intense relationships offered staff a mutually supportive environment which reduced their anxiety, stress, and helped prevent burnout. Given the growing volume of HIV infected persons, and the increased work load of many health care professionals in the aids field, it is important to understand the complex emotional and social support needs of staff to prevent burnout and to improve staff recruitment and retention.

Radical Pair Phenomena in Exciplex and Excited Radical Systems*

Radical Pair Phenomena in Exciplex and Excited Radical Systems*

A marsupial for a new approach to studies in reproductive biology

The phytogeny of marsupials is outlined, and a description is given of the New World family, the Didelphidae. The discovery mat the didelphid Monodelphis domestica, (Grey, short-tailed opossum), will breed readily in standard laboratory conditions has made possible the study of aspects of the reproductive biology of marsupials, that until now have involved lengthy and painstaking fieldwork. This article illustrates some unusual aspects of the gamete biology of Monodelphis; for example, the phenomenon of epididymal sperm pairing, and compares the marsupial mode of fertilization with that of eutherian mammals. A basic and as yet unresolved question in developmental biology is that of how a recently fertilized egg undergoes differentiation into a mulMcellular organism. Evidence to date, outlined in this article, and described in Monodelphis, suggests that the mechanisms involved in the differentiation of a marsupial embryo may be essentially different from those of eutherian species. The importance of this f...

Scanning tunneling microscopy study of the adsorption and recombinative desorption of hydrogen from the Si(100)-2×1 surface

A scanning tunneling microscopy and spectroscopy study of the adsorption and recombinative desorption of hydrogen from the Si(100)-2×1 surface is presented. Initially at room temperature, hydrogen atoms singly occupy the Si dimer units resulting in the formation of isolated Si–H bonds and unpaired dangling bonds. At higher temperatures (∼630 K) these hydrogen atoms tend to pair up on the dimer units. Thus there is a thermodynamic preference for the hydrogen atoms to occupy the dimers in pairs. This pairing phenomenon is due to a π interaction between the dangling bonds on the Si(100)-2×1 surface which favors pairing the unpaired dangling bonds on the dimer units. This pairing of dangling bonds in turn forces the hydrogen atoms to pair. Following desorption from the saturated surface, pairs of dangling bonds are found localized on the Si dimer units, suggesting that desorption involves the direct recombination of hydrogen atoms from the dimers units of the monohydride surface. The implications of this desorption mechanism are discussed and compared to earlier models.

Radical Pair Phenomena in Exciplex and Excited Radical Systems*

Radical Pair Phenomena in Exciplex and Excited Radical Systems*

Immunofluorescent localization of triplex DNA in polytene chromosomes of Chironomus and Drosophila

Purine.pyrimidine (pur.pyr) DNA tracts are prevalent in eukaryotic genomes. They can adopt a triplex conformation in vitro under conditions that may exist in vivo, suggesting that triplex (H-) DNA may exist naturally in chromosomes. To explore this possibility and gain insight concerning potential functions, the distribution of triplex DNA was studied in fixed polytene chromosomes of Chironomus tentans and Drosophila melanogaster by indirect immunofluorescence microscopy using an anti-triplex DNA monoclonal antibody (Jel 318). Chromosomes stained with this antibody exhibited immunopositive regions corresponding to condensed chromatin bands; interbands were less immunofluorescent. These results imply that there is more triplex DNA in bands than in interbands. In Chironomus, nucleolar organizer regions and Balbiani rings were immunonegative, indicating that triplex DNA is not present in decondensed, transcriptionally active chromatin. A few specific bands in both Chironomus and Drosophila were intensely immunofluorescent. In Drosophila, one such region was 81F on chromosome 3R. Competition during staining with exogenously added sequences corresponding to a constituent 1.672 g/cm3 satellite DNA in region 81F failed to abolish the immunofluorescence, suggesting that the satellite DNA does not fortuitously react with Jel 318 and implying that unidentified pur.pyr sequences forming triplex DNA are also present at this location. Region 81F exhibits ectopic pairing with nonrelated chromosome regions that have also proven to be intensely immunopositive; this suggests that the formation of triplex DNA between common, shared pur.pyr sequences in these otherwise nonhomologous bands might account for the ectopic pairing phenomenon. Together with our previous results, these data are consistent with the hypothesis that triplex DNA may play a role in chromosome organization by participating in regional chromatin condensation.

Evidence of pairing and its role in the recombinative desorption of hydrogen from the Si(100)-2 x 1 surface.

A scanning tunneling microscopy and spectroscopy study of the recombinative desorption of hydrogen from the Si(100)-2\ifmmode\times\else\texttimes\fi{}1 surface is presented. Initially at room temperature, hydrogen atoms singly occupy the Si dimer units while at higher temperatures (\ensuremath{\sim}630 K) these atoms tend to pair up. This pairing phenomenon is due to a \ensuremath{\pi}-bonding interaction which favors pairing individual dangling bonds on the dimer units. Following desorption from the saturated surface, pairs of dangling bonds are found loaalized on the Si dimer units. The significance of these paired-dangling-bond sites is d)scussed in ligh* of the desorption model recently proposed by Sinniah et al.

Ectopic pairing responsible for a constantly found «loop» configuration in polytene chromosomes ofDrosophila

SUMMARYIn homosequential members of the Drosophila nasuta subgroup, division 53 at the proximal end of polytene chromosome arm 2R always displays a «loop» configuration of 55 chromosome bands. Homologous configurations are constantly found in the high polytenized salivary gland chromosomes as well as in the low polytenized gut chromosomes. Light and electron microscopic studies of Surface Spread Polytene (SSP) chromosomes in Drosophila nasuta albomicans revealed that the loop configuration is formed by multiple ectopic pairing among bands of subdivisions 53A, 53E, 54A and 55A. The constant presence at homologous loci in different tissues of D. n. albomicans and its conservation in the members of the D. nasuta subgroup distinguish this configuration from other occasionally found ectopic pairing configurations in Drosophila. By this, division 53 offers an unique material for cytogenetic and molecular genetic studies of this special phenomenon of somatic pairing.

Observations on the structure of the ion pair formed between tris(ethylenediamine)cobalt(3+) and (1,2-diaminoethane-N,N,N',N'-tetraacetato)cobalt(1-)

Ion pairing phenomena in solutions involving the metal-ion complexes [Co(en) 3 ] 3+ (en=1,2-diaminoethane) and [Co(edta)] − (edta 4− =1,2-diaminoethane-N,N,N',N'-tetraacetate(4−)) are investigated by using nuclear magnetic resonance techniques. In agreement with earlier results from stereoselectivity studies, the interaction of [Co(edta)] − in the ion pair is well-defined, presenting a pseudo-C 3 carboxylate face to its cationic partner

Structural and energetic aspects of spin pairing in lanthanides

Numerical Hartree-Fock calculations on the lanthanide ions confirm the earlier results of Marcantonatos and coworkers, by showing that the excitation from the ground state of a given f n - configuration to a state with lower spin multiplicity is accompanied by a change in size and shape of the orbitals. This orbital change is also shown to be at the basis of a new interpretation of the spin pairing phenomenon in lanthanides. This interpretation is significantly different from the picture offered by conventional multiplet theory; indeed, the spin pairing energy, calculated on the basis of Hartree- Fock theory is accompanied by a decrease in interelectronic repulsion. Although the relevant energetic (repulsion) effects are obviously quite large, the underlying size effects are very much smaller. Therefore, it seems highly unlikely that they are responsible for the change in coordination number of Gd(H 2O) 8 3+ upon excitation, as suggested by Marcantonatos.

Phase transitions in electron systems with short-range pairing interactions: Ground state

We propose a real-space, tight-binding model of electrons with short-range pairing interactions. The model involves a competition between the ordinary single particle hoppingt and an attractive interactionV between the singlet electronic pairs formed on neighboring lattice sites. The Hamiltonian effectively describes a mechanism for pair formation. We study the ground-state properties of its onedimensional version using numerically exact finite chain calculations for up toN= 10 sites. The ground-state wave functions, the energy spectrum, and various ground-state correlation functions are calculated with the help of an exactly equivalent system of two coupledS=1/2 spin chains. The results indicate the existence of a transition between the band and the localized pairs situation. The transition takes place forV/t= 1.4−0.1 and appears to be of essential singularity type. Comparison with other models used for pairing phenomena, like the negativeU-Hubbard model is made.

Models and methods for pairing data

AbstractThis paper deals with models and methods for count data derived from observations on pairing phenomena. Pairs formed from “similar” members are excluded. Various models are considered and analyzed. Particular emphasis is on developing methods for testing whether particular pairs are prone to occur more or less often than expected by chance.

Unit activity of the septum and hippocampus transplanted alone or together into the anterior chamber of the rat eye

Unit activity of grafts of the septum and hippocampus, developing for 3–6 months in the anterior chamber of the eye was investigated in acute experiments on curarized orcerveau isole rats. Whereas neurons in the transplanted septum had spontaneous activity of irregular, regular, or rhythmic bursting type, activity was absent in hippocampal grafts or consisted of very infrequent synchronized population sites. If grafts of the septum and hippocampus developed together and contact was established between them, the same types of activity developed in the hippocampus as in the septum. In many paired grafts spontaneous epileptic phenomena were observed; they were easily provoked also by electrical stimulation of one of the grafts. Superfusion with medium with a high Mg++ concentration and low Ca++ concentration abolished spontaneous activity in most neurons of hippocampal but not septal grafts, and also suppressed some of the epileptic phenomena, evidence of the leading role of the septum in the organization of spontaneous hippocampal unit activity.

On the modification of the estimated masses of the six-quark states due to pairing effect

This note discusses the pairing effect in relation to the six-quark (q6) states composed of the light quarks u, d and s. In particular, the bearing of this effect on the binding energies and as such on the masses of those states has been emphsized. This point is clearly reflected in the modification, as shown in this note, of the bagmodel-estimated masses of the light strange q6-states due to pairing phenomenon which occurs in these states.

Simple three-dimensional vortex motions in coflowing jets and wakes

The vortex patterns which occur in coflowing jets and wakes at moderate Reynolds numbers (of order 500) are examined in detail. Flow visualization is used in conjunction with a flying hot-wire system which allows instantaneous velocity vector fields to be rapidly measured and related to the smoke patterns. The structures were made perfectly periodic in time by artificial stimulation. The experiments were therefore completely deterministic. This newly developed data-acquisition technique does not require the use of Taylor's hypothesis for inferring patterns from a fixed streamwise position. It therefore allows the vector fields of rapidly evolving patterns to be produced. It also allows the phenomenon of three-dimensional vortex pairing to be studied. The classification of patterns and conjectured topologies made by Perry & Lim (1978a, b) and the interpretations of Perry, Lim & Chong (1980) and Perry & Watmuff (1981) are examined. In the light of more-detailed measurements, it is found that some of these interpretations require modification.Vortex ‘skeleton’ models of the patterns are constructed and it is found that the Biot-Savart law gives vector fields which are in reasonable agreement with the experiments. It is also found that the power-spectral density of a periodic array of eddies can be explained in terms of potential flow vortices.

A Comparison of Perfluorinated Carboxylate and Sulfonate Ion Exchange Polymers: II . Sorption and Transport Properties in Concentrated Solution Environments

Various properties of a perfluorinated carboxylate polymer film have been studied in concentrated and solution environments at elevated temperatures. Electrolyte and water sorption measurements reveal relatively constant electrolyte uptake but decreasing water sorption with increasing solution concentration. The apparent of the carboxylate exchange sites was found to be 1.9. Sodium ion self‐diffusion in the polymer was measured as a function of solution pH and concentration. Several differences in the diffusional properties of the carboxylate vs. Nafion sulfonate polymer films were found and are discussed in terms of ion pairing phenomena. Transport numbers for Na+ and in these polymers at high current densities were measured and are discussed in terms of the nature of ion transport in these polymers.