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At least 397 records · Page 22Linked to original sources
PubMed2000

Sodium cholate sorption on cationic dextran hydrogel microspheres. 1. Influence of the chemical structure of functional groups.

New hydrogel microspheres based on crosslinked dextran, containing pendant quaternary ammonium groups with different chemical structures have been synthesized and tested as possible bile acid sorbents The in vitro sodium cholate sorption by these hydrogels has been followed in the absence or in the presence of competing anions The sorption results have indicated a strong influence of the chemical structure of functional groups on both the affinity and selectivity towards cholate ions. The best sorption performances were obtained with hydrogels having in the structure of functional groups an alkyl substituent with the length higher than C(8).

Adsorption↗
PubMed2003

Auracyanin B structure in space group P6(5).

The structure of auracyanin B, a 'blue' copper protein produced by Chloroflexus aurantiacus, has previously been solved and refined in the hexagonal space group P6(4)22 with a single molecule in the asymmetric unit. The protein has now been crystallized in space group P6(5), with unit-cell parameters a = b = 115.9, c = 108.2 A. In the new crystal form, the asymmetric unit contains four protein molecules. The structure has been solved by molecular replacement and refined at 1.9 A resolution. The final residuals are R = 19.2% and R(free) = 21.9%. In relation to the earlier crystal structure, the doubling of the unit-cell volume and the lower symmetry are explained by small rotations of the molecules with respect to one another.

Bacterial Proteins↗
PubMed1997

Role of sialyloligosaccharide binding in Theiler's virus persistence.

Theiler's murine encephalomyelitis viruses (TMEVs) belong to the Picornaviridae family and are divided into two groups, typified by strain GDVII virus and members of the TO (Theiler's original) group. The highly virulent GDVII group causes acute encephalitis in mice, while the TO group is less virulent and causes a chronic demyelinating disease which is associated with viral persistence in mice. This persistent central nervous system infection with demyelination resembles multiple sclerosis (MS) in humans and has thus become an important model for studying MS. It has been shown that some of the determinants associated with viral persistence are located on the capsid proteins of the TO group. Structural comparisons of two persistent strains (BeAn and DA) and a highly virulent strain (GDVII) showed that the most significant structural variations between these two groups of viruses are located on the sites that may influence virus binding to cellular receptors. Most animal viruses attach to specific cellular receptors that, in part, determine host range and tissue tropism. In this study, atomic models of TMEV chimeras were built with the known structures of GDVII, BeAn, and DA viruses. Comparisons among the known GDVII, BeAn, and DA structures as well as the predicted models for the TMEV chimeras suggested that a gap on the capsid surface next to the putative receptor binding site, composed of residues from VP1 and VP2, may be important in determining viral persistence by influencing virus attachment to cellular receptors, such as sialyloligosaccharides. Our results showed that sialyllactose, the first three sugar molecules of common oligosaccharides on the surface of mammalian cells, inhibits virus binding to the host cell and infection with the persistent BeAn virus but not the nonpersistent GDVII and chimera 39 viruses.

Amino Acid Sequence↗
PubMed2003

The metallo-beta-lactamases fall into two distinct phylogenetic groups.

The Ambler Class B metallo-beta-lactamases fall into two distinct phylogenetic groups based on the observation that there is no significant sequence homology between the sequences of members of different groups. Structural alignments confirm that those groups are no more closely related to each other than are the three classes of serine beta-lactamases, Classes A, C, and D. We present phylogenies of these two groups and suggest a new classification scheme for the beta-lactamases.

Bacteria↗
PubMed2002

Multigroup discrete ordinates modeling of 125I 6702 seed dose distributions using a broad energy-group cross section representation.

Our purpose in this work is to demonstrate that the efficiency of dose-rate computations in 125I brachytherapy, using multigroup discrete ordinates radiation transport simulations, can be significantly enhanced using broad energy group cross sections without a loss of accuracy. To this end, the DANTSYS multigroup discrete ordinates neutral particle transport code was used to estimate the absorbed dose-rate distributions around an 125I-model 6702 seed in two-dimensional (2-D) cylindrical R-Z geometry for four different problems spanning the geometries found in clinical practice. First, simulations with a high resolution 210 energy groups library were used to analyze the photon flux spectral distribution throughout this set of problems. These distributions were used to design an energy group structure consisting of three broad groups along with suitable weighting functions from which the three-group cross sections were derived. The accuracy of 2-D DANTSYS dose-rate calculations was benchmarked against parallel Monte Carlo simulations. Ray effects were remedied by using the DANTSYS internal first collision source algorithm. It is demonstrated that the 125I primary photon spectrum leads to inappropriate weighting functions. An accuracy of +/-5% is achieved in the four problem geometries considered using geometry-independent three-group libraries derived from either material-specific weighting functions or a single material-independent weighting function. Agreement between Monte Carlo and the three-group DANTSYS calculations, within three standard Monte Carlo deviations, is observed everywhere except for a limited region along the Z axis of rotational symmetry, where ray effects are difficult to mitigate. The three-group DANTSYS calculations are 10-13 times faster than ones with a 210-group cross section library for 125I dosimetry problems. Compared to 2-D EGS4 Monte Carlo calculations, the 3-group DANTSYS simulations are a 100-fold more efficient. Provided that these efficiency gains can be sustained in three-dimensional geometries, the results suggest that discrete ordinates simulations may have the potential to serve as an efficient and accurate dose-calculation algorithm for low-energy brachytherapy treatment planning.

Brachytherapy↗
PubMed1990

[Group psychotherapy in borderline psychoneurotic diseases in adolescents: the basic principles and experience with its use].

An attempt is made to theoretically validate some principles of carrying out group psychotherapy in adolescents with borderline neuropsychic diseases, bearing in mind their psychological characteristics. After summarizing the experience gained with carrying out psychotherapy of 32 adolescents 3 principles were formulated: theoretical validation, clinico-psychological evidence for completing groups, structuring of the process of group psychotherapy. The suggested method of group psychotherapy is guided by the solution of problems in the "here and now" situation, provides special methods of introducing information, makes specific demands of the psychotherapist (emotional participation in the happening, the ability of being understood by the members of the group), training in different methods of information retrieval and giving. During group psychotherapy, the adolescents manifest formation of the feeling of responsibility for their behavior, the growth of social competence, destruction of egocentric aims and improvement of contacts in the families.

Adaptation, Psychological↗
PubMed1992

A group additivity model for analyzing absorption spectra of organic compounds: applications to partial structural analysis and molecular weight determinations of polymers, nucleotides, and peptides.

A new method for the analysis of organic structural groups from absorption spectra is described. The method is based on the integrated intensity of absorption. It requires only micrograms of analyzed compound, which may be fully recovered after analysis from its solution. The method can be used for different kinds of structural and/or kinetic studies. For example, the reaction kinetics and tautomeric equilibria can be easily studied by this method. The method can also be used for the determination of molecular weight and quantitative composition of polymers, nucleotides, and/or peptides. Hydrolysis or derivatization of the studied compounds is not necessary. On the basis of this method, automatic molecular weight, nucleotide, and peptide analyzers can be constructed.

Hydrogen-Ion Concentration↗
PubMed1980

Social climates in community groups: toward a taxonomy.

While community groups have often helped people cope with stress, little empirical research has been available to guide their use in prevention or treatment. To partly fill this gap, an empirical taxonomy of community groups was derived from ratings of 41 randomly selected groups on 35 dimensions of Group Structure, Function, and Membership Characteristics. Cluster analysis defined five types. By comparison with other associations, Self-Interest (e.g., liberation and minority) groups rated lower in regulations and had members who were newer to the community. Self-Help groups were highly regulated settings providing support, integration, and developmental aids. Their members had few social relations apart from the family. Social Communion groups rated high on the provision of support for members often living without family. Civic Development groups rated highest on dimensions emphasizing personal development for persons with external sources of support and status. Finally, Recreation groups were casual and briefly attended groups. Their members were younger and less often married than those in other associations. Strategies for group referrals may be implied.

California↗
PubMed1975

[Operon of riboflavin biosynthesis in Bacillus subtilis. VIII. Localization of group ribC markers in relation to the structural gene cluster group].

Regulatory markers of ribC group were located on the chromosome of Bacillus subtilis by means of genetic transformation using DNA isolated by the phenol-benzoate method of Kelly. Markers of this group controlling the regulation of riboflavin biosynthesis were mapped in the terminal region of the chromosome between phe and lys markers. A maximal value of contransfer index between ribC 1 and lys42 markers was found to be 3.5%.

Bacillus subtilis↗
PubMedDate not supplied

Helping early adolescents tell: a guided exercise for trauma-focused sexual abuse treatment groups.

This article discusses the telling of the personal stories of sexual abuse within the context of trauma-focused group therapy for early adolescent girls. It examines the general benefits of group therapy for early adolescents, and describes the trauma-focused structured group therapy model. It also includes a guided exercise that facilitates the telling of the stories by the girls, offers cues to the therapists about each girl's unique sexual abuse experience, and structures feedback from group members.

Adaptation, Psychological↗
PubMed1988

Structure of the group G streptococcal polysaccharide.

The structure of the group-specific polysaccharide of group G Streptococcus was determined by means of methylation analysis and selective chemical degradations. The anomeric configurations and conformations of the sugar residues were studied by 1H- and 13C-n.m.r. spectroscopy. The tetrasaccharide repeating unit, ----3)-alpha-D-Galp-(1----2)-[alpha-L-Rhap-(1----3)-beta-D-GalpNAc - (1----4)]-alpha-L-Rhap-(1----, was determined.

Carbohydrate Conformation↗
PubMed2002

Nonparametric discriminant analysis of phytoplankton species using data from analytical flow cytometry.

BACKGROUND: Analytical flow cytometry (AFC) provides rapid and accurate measurement of particles from heterogeneous populations. AFC has been used to classify and identify phytoplankton species, but most methods of discriminant analysis of resulting data have depended on normality assumptions and outcomes have been disappointing. METHODS AND RESULTS: In this study, we consider nonparametric methods based on density estimation. In addition to the familiar kernel method, methods based on wavelets are also implemented. Full five-dimensional wavelet estimation proves to be computationally prohibitive with current workstation power, so we employ projection pursuit for reduction of dimensionality. AFC typically produces very large samples, so we also investigate data simplification through binning. Further modifications to the discrimination strategy are suggested by specific features of phytoplankton data, namely, a hierarchical group structure, the possible presence of many groups, and the likelihood of encountering an aberrant group in a test sample. CONCLUSIONS: We apply all the resultant procedures to appropriate subsets of a very large data set, demonstrate their efficacy, and compare their error rates with those of more conventional methods. We further show that incorporation of the specific features of phytoplankton data into the analysis leads to improved results and provides a general framework for analysis of such data.

Animals↗
PubMed1996

The water adsorption characteristics of charged phospholipids.

The hydration isotherms of the negatively charged phospholipids, egg phosphatidic acid, bovine heart cardiolipin and two phosphatidylserines as well as one positively charged phospholipid, 1,2-dioleoyl-sn-glycero-3-ethylphosphocholine, have been obtained gravimetrically. The presence of an electrical charge on these phospholipids does not, in itself, determine whether the water binding to the phospholipids is 'strong' or 'weak'. Interestingly, hysteresis effects were present for certain charged phospholipids suggesting some rearrangement of the lipid molecular organization upon hydration and dehydration, perhaps due to the presence of the ionizable moiety. The hydration isotherms of the charged phospholipids have been analyzed by BET theory, although, of the charged lipids studied, all may not be amenable to the application of BET theory. The hydration isotherms and the resulting parameters obtained from the BET analysis are compared to those found previously for zwitterionic phospholipids, especially egg phosphatidylcholine. The water adsorption characteristics of phospholipids are found to depend mainly on the total head-group structure including the presence of hydrophobic groups as well as electrical charge on the head group.

Adsorption↗
PubMed1992

A new nursing medium: computer networks for group intervention.

The PLWAs and the caregivers of persons with AD were similar in their adaptation to this new technology as a communication medium with nurses. Both groups availed themselves of the resources, both technological and personal, on the computer network. Although different in demographics, they also were similar in their ability to form and work in a traditional group structure. Nurses have historically intervened with groups, and this article demonstrates that nurses can intervene on a computer network with groups. Yalom's therapeutic factors exist in both non-face-to-face groups and traditional groups. The benefits of this technology to nurses are numerous: they can access clients in an efficient yet supportive manner; they can respond to multiple levels of need in multiple clients; and they can attend to emotional as well as more concrete needs of clients. The benefits to clients are also numerous: they can use the system at a time, frequency, and duration of their choice; they have the opportunity to be supported in self-care efforts versus being in a more dependent role; and they can engage in a normalization of their experiences. Computer networks can enhance nursing's ability to intervene with clients experiencing clinical problems.

Acquired Immunodeficiency Syndrome↗
PubMed2001

Structural versatility of oxalamide-based compounds: a computational study on the isomerization of the oxalamide group and the structural preferences of the polyoxalamides.

The conformational properties of the oxalamide group and crystal structure of several polyoxalamides have been investigated by computational methods. First, a detailed quantum mechanical study of the conformational preferences of N,N'-dimethyloxalamide is reported. Results, which were obtained at the MP2/6-31G(d) level, provide not only the minimum energy conformations but also a description of the energetics and structural changes associated to the isomerization process of the oxalamide group. These quantum mechanical results together with those obtained from additional calculations have been used to develop a set of force-field parameters for the oxalamide group. Molecular mechanics calculations have been performed to test the parameters and to provide new information in terms of energy contributions about the isomerization of the oxalamide group. On the other hand, the new set of parameters has been used to investigate the structural preferences of polyoxalamides (-[NH-CO-CO-NH-(CH(2))(n)]-) by PCSP calculations. Results indicated that polyoxalamides with an even number of methylene groups adopt a structure with one hydrogen bonding direction, whereas polymers with an odd number of methylene groups prefer a structure with two hydrogen bonding directions. The latter crystal structure is completely different from that observed in conventional polyamides and has been investigated in detail through Monte Carlo simulations.

Crystallization↗
PubMed2002

A simulated annealing approach to define the genetic structure of populations.

We present a new approach for defining groups of populations that are geographically homogeneous and maximally differentiated from each other. As a by-product, it also leads to the identification of genetic barriers between these groups. The method is based on a simulated annealing procedure that aims to maximize the proportion of total genetic variance due to differences between groups of populations (spatial analysis of molecular variance; samova). Monte Carlo simulations were used to study the performance of our approach and, for comparison, the behaviour of the Monmonier algorithm, a procedure commonly used to identify zones of sharp genetic changes in a geographical area. Simulations showed that the samova algorithm indeed finds maximally differentiated groups, which do not always correspond to the simulated group structure in the presence of isolation by distance, especially when data from a single locus are available. In this case, the Monmonier algorithm seems slightly better at finding predefined genetic barriers, but can often lead to the definition of groups of populations not differentiated genetically. The samova algorithm was then applied to a set of European roe deer populations examined for their mitochondrial DNA (mtDNA) HVRI diversity. The inferred genetic structure seemed to confirm the hypothesis that some Italian populations were recently reintroduced from a Balkanic stock, as well as the differentiation of groups of populations possibly due to the postglacial recolonization of Europe or the action of a specific barrier to gene flow.

Algorithms↗