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Biomedical subjects

A J Schultz

Publications and source records attributed to A J Schultz.

At least 19 recordsLinked to original sources
PubMed2004

Box length search algorithm for molecular simulation of systems containing periodic structures.

We have developed a box length search algorithm to efficiently find the appropriate box dimensions for constant-volume molecular simulation of periodic structures. The algorithm works by finding the box lengths that equalize the pressure in each direction while maintaining constant total volume. Maintaining the volume at a fixed value ensures that quantitative comparisons can be made between simulation and experimental, theoretical or other simulation results for systems that are incompressible or nearly incompressible. We test the algorithm on a system of phase-separated block copolymers that has a preferred box length in one dimension. We also describe and test a Monte Carlo algorithm that allows the box lengths to change while maintaining constant volume. We find that the box length search algorithm converges at least two orders of magnitude more quickly than the variable box length Monte Carlo method. Although the box length search algorithm is not ergodic, it successfully finds the box length that minimizes the free energy of the system. We verify this by examining the free energy as determined by the Monte Carlo simulation.

Journal Article↗
PubMed2003

Gamma-ray and neutron diffraction studies of CoF2: magnetostriction, electron density and magnetic moments.

Accurate structure factors up to sin theta/lambda = 1.6 A(-1) have been measured with 316.5 keV gamma-rays from CoF(2), both at room temperature and in the antiferromagnetic state at 10 K. The same crystal was used to collect extended time-of-flight neutron diffraction data in the two magnetic states, which allowed an accurate determination of the fluorine positional parameter. For room temperature, the standard structural parameters are reported. At 10 K, a complete charge-density study has been carried out. The total number of 3d electrons on Co is found to be 6.95 (3). The experimental populations of the d orbitals agree with expectation from crystal field theory. The fluorine valence region exhibits a strong dipolar deformation. Electronic properties at the bond critical points and integrated atomic properties are derived from the static model electron density, revealing the Co-F interactions as purely ionic. On magnetic ordering, a shift of the fluorine ions of 1.5 (4) x 10(-3) A is found which confirms a prediction from theory of optical birefringence. The effect of magnetostriction on the distortion of the ligand coordination octahedra is compared for the late members of the 3d transition-metal difluorides. From neutron powder diffraction, an ordered magnetic moment of 2.60 (4) mu(B) per cobalt ion is found. Despite the strong deviation from the ideal spin value of 3 mu(B), there is still an appreciable orbital contribution to the local magnetic moment.

Journal Article↗
PubMed2001

Time-resolved in situ neutron diffraction studies of gas hydrate: transformation of structure II (sII) to structure I (sI).

We report the in situ observation from diffraction data of the conversion of a gas hydrate with the structure II (sII) lattice to one with the structure I (sI) lattice. Initially, the in situ formation, dissociation, and reactivity of argon gas clathrate hydrate was investigated by time-of-flight neutron powder diffraction at temperatures ranging from 230 to 263 K and pressures up to 5000 psi (34.5 MPa). These samples were prepared from deuterated ice crystals and transformed to hydrate by pressurizing the system with argon gas. Complete transformation from D(2)O ice to sII Ar hydrate was observed as the sample temperature was slowly increased through the D(2)O ice melting point. The transformation of sII argon hydrate to sI hydrate was achieved by removing excess Ar gas and exposing the hydrate to liquid CO(2) by pressurizing the Ar hydrate with CO(2). Results suggest the sI hydrate formed from CO(2) exchange in argon sII hydrate is a mixed Ar/CO(2) hydrate. The proposed exchange mechanism is consistent with clathrate hydrate being an equilibrium system in which guest molecules are exchanging between encapsulated molecules in the solid hydrate and free molecules in the surrounding gas or liquid phase.

Journal Article↗
PubMed2001

Tetrachlorobis(N1-phenylacetamidino-kappaN2)rhenium(IV) at 11 K by X-ray diffraction and at 20 K by neutron diffraction.

The crystal structure of the title compound, [ReCl(4)(C(8)H(10)N(2))(2)], has been determined by X-ray diffraction at 11 K and by neutron diffraction at 20 K. The accurate and extensive data sets lead to more precise determinations than are available from earlier work. The agreement in atomic positional and displacement parameters at these very low temperatures is good. The results will facilitate re-examination of the magnetic structure of the complex. The Re atom lies on a special position and the molecule has twofold crystallographic symmetry.

Journal Article↗
PubMed2001

Saccharinate as a versatile polyfunctional ligand. Four distinct coordination modes, misdirected valence, and a dominant aggregate structure from a single reaction system.

The reaction system consisting of copper, saccharinate, and the auxiliary ligands H(2)O, PPh(3), and NH(3) produces a sequence of compounds in which saccharinate is coordinated to copper in four distinct manners. The complex trans-[Cu(sacch)(2)(H(2)O)(4)] (2) (produced by thermal dehydration of trans-[Cu(sacch)(2)(H(2)O)(4)].2H(2)O (1)) reacts with triphenylphosphine in CH(2)Cl(2) to produce any or all of three Cu(I) complexes, depending upon conditions. The three Cu(I) compounds are Cu(sacch)(PPh(3))(3) (3), in which saccharinate binds to copper through the carbonyl group of the ligand, Cu(sacch)(PPh(3))(2) (4), in which sacch binds to Cu through its charge-bearing nitrogen atom; and [Cu(sacch)(PPh(3))](2) (5), a dinuclear complex in which saccharinate bridges two Cu centers through its imidate nitrogen and carbonyl oxygen atoms. Complexes 3-5 can be isolated individually, although in solution they exist in a complex equilibrium which has been examined by NMR spectroscopy. Each of the three Cu(I) products reacts with NH(3) in CH(2)Cl(2) solution to produce trans-[Cu(sacch)(2)(NH(3))(4)] (6), an unstable Cu(II) complex that exhibits misdirected valence at the Cu-N(sacch) bond. Complex 6 evolves spontaneously to [Cu(sacch)(NH(3))(4)](sacch).H(2)O (7), which in the solid state is dominated by a supramolecular aggregate of two formula units, linked by hydrogen bonding in which the water molecule plays a central role. Alternative pathways exist to several of the products. The X-ray crystal structure analyses of 3-7 are reported and establish the coordination modes of saccharinate, the misdirected valence in 6, and the supramolecular aggregation in 7. The structure analysis of 7 by single-crystal neutron diffraction is reported and together with the previously reported neutron structure analysis of 1 establishes the substitution of the auxiliary ligand H(2)O by NH(3) in the Cu(II) products.

Journal Article↗
PubMed2001

Cubic aluminum silicides RE8Ru12Al49Si9(Al(x)Si12-x) (RE = Pr, Sm) from liquid aluminum. Empty (Si,Al)12 cuboctahedral clusters and assignment of the Al/Si distribution with neutron diffraction.

Two new quaternary aluminum silicides, RE8Ru12Al49Si9(Al(x)Si12-x) (x approximately 4; RE = Pr, Sm), have been synthesized from Sm (or Sm2O3), Pr, Ru, and Si in molten aluminum between 800 and 1000 degrees C in sealed fused silica tubes. Both compounds form black shiny crystals that are stable in air and NaOH. The Nd analog is also stable. The compounds crystallize in a new structural type. The structure, determined by single-crystal X-ray diffraction, is cubic, space group Pm3m with Z = 1, and has lattice parameters of a = 11.510(1) A for Sm8Ru12Al49Si9(Al(x)Si12-x) and a = 11.553(2) A for Pr8Ru12Al49Si9(Al(x)Si12-x) (x approximately 4). The structure consists of octahedral units of AlSi6, at the cell center, Si2Ru4Al8 clusters, at each face center, SiAl8 cubes, at the middle of the cell edges, and unique (Al,Si)12 cuboctohedral clusters, at the cell corners. These different structural units are connected to each other either by shared atoms, Al-Al bonds, or Al-Ru bonds. The rare earth metal atoms fill the space between various structural units. The Al/Si distribution was verified by single-crystal neutron diffraction studies conducted on Pr8Ru12Al49Si9(Al(x)Si12-x). Sm8Ru12Al49Si9(Al(x)Si12-x) and Pr8Ru12Al49Si9(Al(x)Si12-x) show ferromagnetic ordering at Tc approximately 10 and approximately 20 K, respectively. A charge of 3+ can be assigned to the rare earth atoms while the Ru atoms are diamagnetic.

Journal Article↗
PubMed2001

Electrospray ionization with ambient pressure ion mobility separation and mass analysis by orthogonal time-of-flight mass spectrometry.

Rapid screening and identification of drug and other mixtures are possible using a novel ambient pressure high-resolution ion mobility (APIMS) orthogonal reflector time-of-flight mass spectrometer (TOFMS). Departing ions from the APIMS drift tube traversed a pressure interface between the APIMS and TOFMS where they were subjected to numerous gas collisions that could produce selective fragmentation. By increasing the accelerating field in the pressure interface region, the ions generated using water-cooled electrospray ionization (ESI) underwent collision-induced dissociation (CID). Mixtures of ESI ions were separated by APIMS based on their respective size-to-charge (s/z) ratios while CID and analysis of mass-to-charge (m/z) ratios occurred in the pressure interface and TOFMS. Product ions that were formed in this pressure interface region could be readily assigned to precursor ions by matching the mobility drift times. This process was demonstrated by the examination of a mixture of amphetamines and the resulting fragmentation patterns of the mobility-separated precursor ion species [M + H](+).

Amphetamines↗
PubMed2001

Structures of furanosides: geometrical analysis of low-temperature X-ray and neutron crystal structures of five crystalline methyl pentofuranosides.

Crystal structures of all five crystalline methyl D-pentofuranosides, methyl alpha-D-arabinofuranoside (1), methyl beta-D-arabinofuranoside (2), methyl alpha-D-lyxofuranoside (3), methyl beta-D-ribofuranoside (4) and methyl alpha-D-xylofuranoside (5) have been determined by means of cryogenic X-ray and neutron crystallography. The neutron diffraction experiments provide accurate, unbiased H-atom positions which are especially important because of the critical role of hydrogen bonding in these systems. This paper summarizes the geometrical and conformational parameters of the structures of all five crystalline methyl pentofuranosides, several of them reported here for the first time. The methyl pentofuranoside structures are compared with the structures of the five crystalline methyl hexopyranosides for which accurate X-ray and neutron structures have been determined. Unlike the methyl hexopyranosides, which crystallize exclusively in the C(1) chair conformation, the five crystalline methyl pentofuranosides represent a very wide range of ring conformations.

Journal Article↗
PubMed2000

Coupling high-pressure MALDI with ion mobility/orthogonal time-of-flight mass spectrometry.

A new ion mobility/time-of-flight mass spectrometer employing a high-pressure MALDI source has been designed and tested. The prototype instrument operates at a source/drift cell pressure of 1-10 Torr helium, resulting in a mobility resolution of approximately 25. A small time-of-flight mass spectrometer (20 cm) with a mass resolution of up to 200 has been attached to the drift cell to identify (in terms of mass-to-charge ratio) the separated ions. A simple tripeptide mixture has been separated in the drift tube and mass identified as singly protonated species. The ability to separate peptide mixtures, e.g., tryptic digest of a protein, is illustrated and compared to results obtained on a high-vacuum time-of-flight instrument.

Amino Acid Sequence↗
PubMed2000

Structural and EPR study of the dependence on deuteration of the Jahn-Teller distortion in ammonium hexaaquacopper(II) sulfate, (NH4).

The variation of the EPR spectra with degree of deuteration of the partially deuterated Tutton salt ammonium hexaaquacopper(II) sulfate, (NH4)2[Cu(H2O)6](SO4)2, has been measured at 293 K. The measurements indicate that the structure changes quite abruptly from that of the pure hydrogenous salt to that of the fully deuterated salt at approximately 50% deuteration. The structure of a crystal in which approximately 42% of the hydrogen atoms were replaced by deuterium was elucidated at 15 K by single-crystal time-of-flight neutron diffraction. The hexaaquacopper(II) complex exhibits an orthorhombically distorted, tetragonally elongated octahedral coordination geometry (Cu-O bond distances of 2.281(1), 2.007(1), and 1.975(1) A). The structure is very similar to that reported for the undeuterated salt at 9.6 K, and markedly different from that of the fully deuterated compound at 15 K, which has similar Cu-O bond lengths but with the directions of the long and intermediate bonds interchanged. There is no evidence for disorder or partial switching of the Cu-O bond directions. This is consistent with the temperature dependence of the EPR spectrum of the approximately 42% deuterated compound, which indicates a thermal equilibrium between the two structural forms close to room temperature similar to that reported for the undeuterated compound, but complete reversion to the low-temperature phase on cooling to 5 K. The possible influence of deuteration upon the hydrogen-bonding distances and the bearing of this upon the structural modifications of the compound are discussed.

Journal Article↗
PubMed2000

Use of the neisserial lipoprotein (Lip) for subtyping Neisseria gonorrhoeae.

The pathogenic Neisseria species N. meningitidis and N. gonorrhoeae possess an outer membrane lipoprotein, designated Lip, which is present in all strains tested. The predicted protein sequence of Lip consists of a consensus AAEAP amino acid repeat. The objective of this study was to determine the feasibility of using the Lip repeat number and sequence for subtyping of Neisseria gonorrhoeae. The lip genes of each isolate were amplified by PCR and sequenced to determine the repeat number and sequence. Among the 46 strains we examined, eight different Lip repeat numbers were identified, with lengths of 11 (1 strain), 12 (14 strains), 13 (2 strains), 14 (10 strains), 15 (5 strains), 16 (10 strains), 17 (3 strains), and 20 (1 strain) repeats. Analysis indicated differences in the sequences within the repeats that resulted in amino acid alterations in repeat classes that contained multiple strains. Among the 46 isolates examined, we were able to identify 17 unique Lip subtyping patterns.

Amino Acid Sequence↗
PubMed2000

Na2Fe(CN)5(NO).2D2O at 11 and 293 K by X-ray, and at 15 K by neutron diffraction.

The crystal structure of Na(2)Fe(CN)(5)(NO).2D(2)O, disodium pentacyanonitrosylferrate(III) bis(dideuterium oxide), has been determined by X-ray diffraction at 11 and 293 K, and by neutron diffraction at 15 K. The accurate and extensive data sets lead to more precise determinations than are available from earlier work. The agreement in atomic positional and displacement parameters between the determinations at low temperature is very good.

Journal Article↗
PubMed1998

Videotape increases parent knowledge about poliovirus vaccines and choices of polio vaccination schedules.

OBJECTIVE: To study the effect of an educational videotape about poliovirus vaccines and choices of schedules for parents/guardians of children starting the polio vaccination series. DESIGN: Prospective, randomized trial comparing two educational interventions. SETTING: Five pediatric offices (two university-based, two health maintenance organization staff models, and one private practice) and a local health department immunization clinic in the greater Lansing, MI, area. PARTICIPANTS: A total of 287 parents/guardians of 2- to 3-month-olds presenting for well-child care and due for the first set of immunizations including poliovirus vaccine. INTERVENTIONS: Parents/guardians were randomized to read the vaccine information statement (VIS) alone or to read the VIS and view a 15-minute videotape about polio vaccination and choices of schedules produced by Michigan State University. The intervention groups were similar by race/ethnicity, education, and relationship to the child. OUTCOME MEASURES: Change in knowledge about the risk of poliomyelitis in the United States, transmission of poliomyelitis, characteristics of the two poliovirus vaccines, and choices of polio vaccination schedules; and parent opinion on effectiveness of the interventions, as measured by pre- and postintervention questionnaires. RESULTS: Both interventions resulted in increased test scores of knowledge. However, videotape viewers scored significantly higher on their posttest compared with parents/guardians assigned to VIS only. This significant increase was noted across all practice types, two of three major racial/ethnic groups, and educational levels. (The increase for Hispanic parents/guardians approached significance). Reading the VIS did not improve posttest scores for videotape viewers. Reading the VIS did improve posttest scores for those assigned to VIS only, but these scores still were not as high as for videotape viewers who did not read the VIS. CONCLUSIONS: This study demonstrated that a complicated discussion of risks/benefits of two vaccines and their schedules of administration could be communicated effectively via a videotaped presentation. In addition, the videotape was more effective than VIS alone in increasing short-term knowledge, regardless of practice type, race/ethnicity, or educational level. As immunization schedules increase in complexity and parents are asked to make more choices, videotaped information may be a better method to achieve the goal of truly informed consent.

Adult↗
PubMed1993

Guided tissue regeneration (GTR) of nonsubmerged implants in immediate extraction sites.

The learning objective of this article is the placement of nonsubmerged implants immediately after extraction, with membrane barriers, according to the principles of guided tissue regeneration (GTR). Fixtures were immobilized by engaging bone beyond the apex and were exposed to the oral cavity during healing. The implants and cell-occlusive barriers were placed in 6 patients; all barriers were removed by week 10. Three patients received freeze-dried bone allografts. A systemic antibiotic, an oral antimicrobial rinse, and reinforced plaque removal were employed. Radiographic and attachment level measurements at 3 and 6 months indicated that osseous regeneration had taken place and was still ongoing. All fixtures were restored after each implant reached 6-month maturity.

Aged↗
PubMed1991

Treatment of periodontal defects with an absorbable membrane (polyglactin 910) with and without osseous grafting: case reports.

The purpose of these reports is to illustrate the possible use of polyglactin 910 as an absorbable membrane for periodontal healing. Eleven surgical sites in 10 patients are reported. Vicryl mesh was used on all sites, and osseous allograft material was used in 8 of these sites. Radiographic evaluation and sounding with anesthesia indicate improvement in the treated areas. Few adverse effects were seen at the treated sites. Therefore, polyglactin offers promise as a material for use in periodontal therapy, especially in deep infrabony pockets. Further controlled studies comparing polyglactin 910 and other resorbable materials as barrier membranes are needed to establish their safety and efficacy.

Adult↗
PubMed1989

Rural America. Unique opportunities for health care delivery and health services research.

A general deterioration is occurring in the quality of life of rural Americans, and it is affecting the quality of health and mental health service delivery. About 24% of the U.S. population lives in nonmetropolitan areas where the citizens are older, less well educated, have lower incomes, and are more homogeneous in terms of race and ethnicity. Medicare and private insurance discriminate against rural services in their reimbursement policies, and there is a shortage of health personnel in rural areas. However, there has been renewed congressional action to meet rural needs. Both the House and Senate have established rural caucuses, and an Office of Rural Health Policy has been established in the federal executive branch. Legislative successes were achieved between 1985 and 1988. Rural initiatives will provide psychology with unique opportunities in the next several years.

Delivery of Health Care↗
PubMed1988

DNA homology and immunological cross-reactivity between Aeromonas hydrophila cytotonic toxin and cholera toxin.

DNA colony hybridization with three 18- to 20-base-long synthetic oligonucleotide probes for cholera toxin (CT) was used to screen 12 clinical isolates of Aeromonas hydrophila. Under stringent hybridizing (overnight at 40 degrees C) and washing (1 h at 50 degrees C) conditions, nine strains reacted with the 32P-labeled CT probes. Concentrated (10x) cell-free supernatants or lysates from eight cultures, heated at 56 degrees C for 20 min, produced cytotonic effects in Y-1 mouse adrenal cells and Chinese hamster ovary (CHO) cells and caused a 1.5- to 22-fold increase in production of cyclic AMP in CHO cells. Preincubation with anti-CT reduced the CHO cell titer of cell lysates by 10-fold. In the GM1 ganglioside enzyme-linked immunosorbent assay, heated supernatants and lysates gave readings equivalent to 3.5 to 100 ng of CT. Three proteins with molecular weights of 89,900, 37,000, and 11,000 reacted with anti-CT on immunoblots of cell lysates from sodium dodecyl sulfate-polyacrylamide gels. These results suggest that there is DNA homology and immunological cross-reactivity between CT and the A. hydrophila cytotonic toxin.

Aeromonas↗