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PubMed2003

Solution and solid-state spin-crossover behavior in a pseudotetrahedral d7 ion.

This Communication describes a pseudotetrahedral d7 complex, [PhBP3]Co(OSiPh3), that exhibits thermally induced spin-crossover both in solution and in the solid state. Magnetic crossover behavior is achieved by confluence of the X-type ligand and the tripodal auxiliary employed. Four-coordinate platforms of the present geometry type may offer a new approach to magnetic spin-crossover behavior distinct from their electronically related pseudooctahedral counterparts.

Journal Article↗

PubMed2005

Self-assembly of DNA double-double crossover complexes into high-density, doubly connected, planar structures.

We designed a molecular complex, the double-double crossover, consisting of four DNA double helices connected by six reciprocal exchanges. Atomic force micrographs suggest that double-double crossover complexes self-assemble into high-density, doubly connected, two-dimensional, planar structures. Such structures may be suitable as substrates for the deposition of nanomaterials in the creation of high-density electrical and quantum devices. We speculate about a modified double-double crossover complex that might self-assemble into high-density, doubly connected, three-dimensional structures.

DNA↗

PubMed2006

Global fluid phase equilibria and critical phenomena of selected mixtures using the crossover soft-SAFT equation.

We present here the extension of the crossover soft-statistical associating fluid theory (soft-SAFT) equation of state to mixtures, as well as some illustrative applications of the methodology to mixtures of particular scientific and technological interest. The procedure is based on White's work (White, J. A. Fluid Phase Equilib. 1992, 75, 53) from the renormalization group theory, as for the pure fluids, with the isomorphism assumption applied to the mixtures. The equation is applied to three groups of mixtures: selected mixtures of n-alkanes, the CO2/n-alkane homologous series, and the CO2/1-alkanol homologous series. The crossover equation is first applied to the pure components of the mixtures, CO2 and the 1-alkanol family, while an available correlation is used for the molecular parameters of the n-alkane series (Llovell et al. J. Chem. Phys 2004, 121, 10715). A set of transferable molecular parameters is provided for the 1-alkanols series; these are accurate for the whole range of thermodynamic conditions. The crossover soft-SAFT equation is able to accurately describe these compounds near to and far from the critical point. The theory is then used to represent the phase behavior and the critical phenomena of the selected mixtures. We use binary interaction parameters xi and eta for dissimilar mixtures. These parameters are fitted at some particular conditions (one subcritical temperature or binary critical data) and used to predict the behavior of the mixture at different conditions (other subcritical conditions and/or critical conditions). The equation is able to capture the continuous change in the critical behavior of the CO2/n-alkane and the CO2/1-alkanol homologous series as the chain length of the second compound increases. Excellent agreement with experimental data is obtained, even in the most nonideal cases. The new equation is proved to be a powerful tool to study the global phase behavior of complex systems, as well as other thermodynamic properties of very challenging mixtures.

Journal Article↗

PubMed2002

An examination of crossover and spillover effects of spousal and expatriate cross-cultural adjustment on expatriate outcomes.

Integrating work-family and cross-cultural adjustment literatures, the researchers proposed and tested a spillover and crossover model of expatriates' cross-cultural adjustment with reciprocal relationships. Spillover effects refer to the influence that expatriate attitudes in a particular domain (e.g., work) have on attitudes in other domains (e.g., nonwork), whereas crossover effects refer to the influence of expatriate attitudes on the spouse's attitudes (and vice versa). Data collected from Japanese expatriates, their spouses, and their superiors strongly supported both spillover and crossover effects between expatriate and spousal cross-cultural adjustment. In addition, expatriates' cross-cultural adjustment was found to be related to satisfaction, which, in turn, was found to be negatively related to expatriates' intention to return to their homeland early.

Adaptation, Psychological↗

PubMed2026

ZEP1 orchestrates template choice and crossover pathways to ensure meiotic genome integrity in rice.

Meiotic crossovers (COs) are tightly regulated to ensure chromosome segregation while limiting aberrant recombination. Transverse filament (TF) proteins of the synaptonemal complex (SC) regulate class I crossoverts, yet how the SC coordinates homologous recombination (HR) to maintain faithful recombination remains unclear. Here, we show that loss of rice TF protein ZEP1 does not uniformly enhance HEI10-marked class I COs; instead, ZEP1 null mutants display asynapsis, multivalent formation, and chromosome fragmentation. These defects depend on double-strand breaks (DSBs) and genetically place ZEP1 function after strand invasion. ZEP1 interacts with anti-crossover factors MEICA1, FIGNL1, and RMI1, and is required for their enrichment at the synaptonemal complex; its loss causes persistent DMC1/RAD51 signals, indicating dysregulated strand invasion. Genetic interactions further support impaired recombination intermediate homeostasis, with ZMM removal partially alleviating chromosome abnormalities, while MUS81 becomes increasingly essential. We propose that the synaptonemal complex functions as a structural hub, where ZEP1 concentrates anti-crossover modules that restrain invasion and coordinate recombination intermediate processing to promote HR repair. Furthermore, ZEP1 dosage may provide a constrained lever to tune CO outcomes in a background-dependent manner.

Journal Article↗

PubMed2006

A DFT computational study of spin crossover in iron(III) and iron(II) tripodal imidazole complexes. A comparison of experiment with calculations.

B3LYP* functionals were used to model the sixteen iron(II) (1A, LS and 5T, HS) and iron(III) (2T, LS and 6A, HS) complexes of the 1:3 Schiff base condensate of tris(2-aminoethyl)amine and imidazole-4-carboxaldehyde, H3L1, and its deprotonated forms, [H2L1]1-, [HL1]2-, and [L1]3-. This ligand system is unusual in that [FeH3L1]3+, [FeH3L1]2+ and [FeL1]- all exhibit a spin crossover between 100-300 K. This makes these complexes ideal for a hybrid DFT computational approach and provides an opportunity to refine the value of the exact exchange admixture parameter, c3, and to predict properties of partially protonated complexes that are not experimentally available. The accepted value of 0.20 is larger than the value of approximately 0.13 that was found to best reproduce experimental data in terms of spin state predictions. With iron(III) B3LYP calculations showed that all of the complexes were low spin at 298 K with the exception of [FeH3L1]3+ which is spin crossover in agreement with experimental results. It was also shown for iron(III) that the ligand field increased as the number of protons decreased. In contrast all of the iron(II) complexes were close to the spin crossover region regardless of protonation state. Experimental structures are fairly well modeled by this system in regard to the key structural indicators of spin state, which are the bite and trans angles. The calculated iron to nitrogen atom distances are always larger in the high spin form than the low spin form but all iron to nitrogen bond distances are larger than the experimental values. In general non-bonded interactions are not well modeled by this methodology.

Journal Article↗

PubMed2005

Making crossovers during meiosis.

Homologous recombination (HR) is required to promote both correct chromosome segregation and genetic variation during meiosis. For this to be successful recombination intermediates must be resolved to generate reciprocal exchanges or 'crossovers' between the homologous chromosomes (homologues) during the first meiotic division. Crossover recombination promotes faithful chromosome segregation by establishing connections (chiasmata) between the homologues, which help guide their proper bipolar alignment on the meiotic spindle. Recent studies of meiotic recombination in both the budding and fission yeasts have established that there are at least two pathways for generating crossovers. One pathway involves the resolution of fully ligated four-way DNA junctions [HJs (Holliday junctions)] by an as yet unidentified endonuclease. The second pathway appears to involve the cleavage of the precursors of ligated HJs, namely displacement (D) loops and unligated/nicked HJs, by the Mus81-Eme1/Mms4 endonuclease.

Chromosome Segregation↗

PubMed1999

A double-blind, randomized, multicentre, crossover study to prove equivalence of pancreatin minimicrospheres versus microspheres in exocrine pancreatic insufficiency.

BACKGROUND: Modern pancreatin preparations consist of enteric-coated microspheres to protect the enzymes from gastric acid. There are, however, no clinical trials comparing different sizes of pancreatin microspheres with regard to fat excretion and fat intake. AIM: To prove both equivalent efficacy and safety of conventional pancreatin microspheres and smaller pancreatin minimicrospheres in patients with exocrine insufficiency due to chronic pancreatitis. METHODS: In this prospective, randomized, double-blind, multicentre, crossover trial, patients with a stool fat excretion of > 7.5 g/day during a placebo period were randomly assigned either to the minimicrosphere/microsphere treatment sequence or vice versa. The primary end-point was the coefficient of fat absorption, which was calculated from fat excretion and fat intake during the course of a standardized diet. Stool weight, clinical symptoms and the safety of the preparations were also evaluated. RESULTS: Thirty-seven patients entered the study, of whom 23 fulfilled the criteria for the crossover period. In the per protocol analysis (n=18), the 90% confidence intervals for the coefficient of fat absorption of both crossover periods lay entirely within the equivalence range (P=0.02). The intention-to-treat analysis revealed similar results, but the equivalence range was slightly missed (P=0.07). Similar results were obtained for the secondary parameters and the reported adverse events. CONCLUSIONS: Pancreatin minimicrospheres have been shown to be equally effective as microspheres in improving the coefficient of fat absorption in patients with exocrine insufficiency due to chronic pancreatitis.

Adult↗

PubMed1997

Involvement of the MRE2 gene of yeast in formation of meiosis-specific double-strand breaks and crossover recombination through RNA splicing.

BACKGROUND: The mre2 mutant of Saccharomyces cerevisiae is defective in meiotic recombination and produces inviable spores, but the sensitivities to DNA damaging agents, methyl methanesulphonate and ultraviolet light are not altered by the mutation. Mre2 has two copies of RNA recognition motif (RRM), suggesting its participation in RNA metabolism in meiosis. RESULTS: An amino acid substitution in the N-terminal RRM of Mre2 confers a meiotic recombination defect. Using this mre2N strain, the MER2 gene was isolated as a multi-copy suppressor of the recombination defect. Meiosis-specific splicing of MER2 pre-mRNA was impaired in the mre2 deletion (mre2delta) mutant. The mre2delta mutant was defective in the formation of meiosis-specific double-strand breaks (DSBs) and crossover and noncrossover recombinants. When the chromosomal MER2 gene was replaced with the intronless derivative of MER2 gene, cMER2, the formation of DSBs and of noncrossover recombinants were restored in the mre2delta mutant. However, the amount of crossover recombinants produced in the mre2delta cMER2 strain was approximately 30% that in the wild-type. In addition, the mre2delta cMER2 mutant was defective in chromosome segregation and in viable spore formation. CONCLUSIONS: Mre2 participates in the formation of DSBs through meiosis-specific splicing of MER2 pre-mRNA. Besides, Mre2 is also involved in crossover recombination, possibly through splicing of RNA from another gene(s).

Binding Sites↗

PubMed2002

Online hemodiafiltration versus acetate-free biofiltration: a prospective crossover study.

Online hemodiafiltration (online HDF) and acetate-free biofiltration (AFB) are 2 innovative renal replacement therapies. Convincing evidence has shown that both techniques are superior to conventional hemodialysis in many aspects. The aim of the present investigation was to compare online HDF and AFB in 12 stable maintenance hemodialysis patients in a prospective, randomized crossover trial. Twelve stable dialysis patients, age 49.7 +/- 11.3 years and on dialysis for 83.5 +/- 76.7 months, were treated prospectively and randomly by either AFB, predilution HDF (pre-HDF), or postdilution HDF (post-HDF) for a total of 36 weeks using exclusively F60S high-flux dialyzers. Routine blood biochemical tests, bone metabolism parameters, and clearance for both small and larger molecular weight substances were measured at defined intervals. During the trial period inter- and intradialysis symptoms, e.g., hypotensive episodes and intradialysis arterial blood gas analyses, were recorded. Both online HDF and AFB were well accepted by the overwhelming majority of patients and also by the dialysis staff. Pretreatment sodium, total and ionized calcium, chloride, bicarbonate, and urea did not differ within or between the 3 treatment groups. Potassium increased slightly in HDF patients while phosphate and beta2-microglobulin (beta2-M) decreased in all groups. After dialysis, AFB patients exhibited a significantly higher bicarbonate concentration and lower potassium level when identical potassium concentrations in dialysate were used. Patients receiving AFB manifested less intradialysis partial pressure of oxygen drop and partial pressure of carbon dioxide rise than those on HDF treatments. HDF treatments could afford higher single-pool and double-pool Kt/V, higher effective urea and beta2M clearance, and lower total interdialysis symptom scores than the AFB treatment method. While bone metabolism parameters did not differ between the 3 dialysis modalities, some parameters such as deoxypyridinoline in HDF and osteocalcin, pyridinoline, and deoxypyridinoline in AFB deteriorated at the end of the crossover study. Aluminum concentration decreased progressively to about one-third of prestudy values at the end of the study with all 3 treatments. AFB was associated with a lower predialysis mean arterial pressure (MAP), a smaller drop in MAP during treatment, and similar hypotension episodes compared with the 2 HDF treatments. Albumin concentration showed a trend to decrease during the first 2 months of the trial period followed by a slight increase thereafter but still significantly lower than initial value at the end of crossover. Both online HDF and AFB share most of the features of optimal renal replacement therapy. Online HDF is superior to AFB in such aspects as increased delivered dialysis dose both for small and larger molecular weight toxins and less interdialysis symptoms. On the other hand, AFB is associated with a smaller effect on arterial blood gas values and improved intradialysis hemodynamic tolerance. Some dialysis-related symptoms and complications in the case of our AFB practice could be attributable, at least in part, to low dialysate calcium level.

Adult↗

PubMed2006

A randomized crossover trial comparing sevelamer with calcium acetate in children with CKD.

BACKGROUND: A multicenter, randomized, open-label, crossover study was performed to compare the efficacy and safety of sevelamer, a calcium-free phosphate binder, with calcium acetate in pediatric patients with chronic kidney disease (CKD). METHODS: Children (age, 0.9 to 18 years) with CKD undergoing hemodialysis or peritoneal dialysis or with a glomerular filtration rate of 20 or greater and less than 60 mL/min/1.73 m2 (> or = 0.33 and < 1.00 mL/s/1.73 m2) were randomly assigned to the following treatment scheme: 2 weeks of washout followed by 8 weeks of treatment with either sevelamer or calcium acetate in a crossover fashion. Phosphorus, calcium, and intact parathyroid hormone in serum were measured every 2 weeks, and phosphate binder dosages were adjusted, if needed. Serum lipid and vitamin concentrations were measured at the beginning and end of each treatment period. The primary end point was the decrease in serum phosphorus levels after 8 weeks of treatment. RESULTS: Forty-four patients were screened. Altogether, data for 18 patients (5 girls) aged 12.4 +/- 4.1 years were used for the crossover analysis. There was no significant difference in serum phosphorus levels at 8 weeks after the start of treatment in both groups. Total cholesterol (-27%) and low-density lipoprotein cholesterol (-34%) levels decreased significantly with sevelamer treatment (P < 0.02 and P < 0.005). An increased incidence of hypercalcemia (P < 0.0005) was observed with calcium acetate treatment, whereas metabolic acidosis was more frequent with sevelamer treatment (P < 0.005). CONCLUSION: Treatment of children with CKD with sevelamer and calcium acetate provides similar phosphorus level control. The marked decrease in lipid levels and lower rate of hypercalcemia may augment the long-term benefit of sevelamer.

Acetates↗

PubMed2002

Hypoglossal-facial crossover in facial-nerve palsy: pure end-to-sideanastomosis technique.

Hypoglossal-facial crossover is the most popular method of reconstructing the facial nerve in facial palsy resulting from proximal facial-nerve injury near the brainstem. Conventional hypoglossal-facial crossover involves performing a partial hypoglossal-nerve section or incision and an interpositional nerve graft to bridge the gap between the two nerves, which sometimes results in hemiglossal atrophy and its sequelae. Furthermore, the nerve graft may delay recovery and make facial reanimation weak. To solve these problems, we attempted to perform 'pure end-to-side anastomosis' (without section of the hypoglossal nerve) between the hypoglossal and facial nerves in four patients with facial palsy. In two patients (group I) a sural-nerve graft was used to bridge the gap between the two nerves. In the other two patients (group II) the intratemporal facial nerve was mobilised to the neck and one tension-free end-to-side anastomosis was performed. Facial symmetry and tone at rest were restored in all cases. Facial reanimation was achieved in group II after 8 months. Despite the small number of cases, we believe that the technique of hypoglossal-facial crossover with 'pure end-to-side anastomosis' and mobilisation of the intratemporal facial nerve can decrease donor-nerve morbidity in facial-nerve rehabilitation.

Adult↗

PubMed2004

Simplified crossover droplet model for adsorption of pure fluids in slit pores.

We present a generalized crossover (GC) model for the excess adsorption of pure fluids at a flat solid-liquid interface, which reproduces scaling behavior of the excess adsorption in the critical region and is reduced to the classical, van der Waals-type analytical model far away from the bulk critical point. In developing this model, we used the density-functional theory (DFT) approach for the order parameter profile calculations with a generalized corresponding states model for the local free-energy density. The GC DFT model well represents the available experimental adsorption data for Kr/graphite, C2H4/graphite, C3H8/graphite, CO2/silica, and SF6/graphite systems in the entire density range 0 < rho < or = 3rhoc and temperatures up to 1.7Tc. In the critical region 0.5 rhoc < r < or = 1.5rhoc and T < or = 1.15Tc, the GC DFT model is consistent with the predictions of the asymptotic renormalization-group crossover model for the critical adsorption in a semi-infinite system developed earlier. For the excess adsorption on the critical isochore, both theories predict a scaling-law behavior Gamma proportional tau(-nu+beta), but fail to reproduce a "critical depletion" of the excess adsorption along the critical isochore of the SF6/graphite system near Tc. We show that an anomalous decrease of adsorption observed in this system at tau = T/Tc - 1 < 10(-2) can be explained by finite-size effect and develop a simplified crossover droplet (SCD) model for the excess adsorption in a slit pore. With the effective size of the pore of L = 50 nm, the SCD model reproduces all available experimental data for SF6/graphite, including the critical isochore data where tau-->0, within experimental accuracy. At L >> xib (where xib is a bulk correlation length) the SCD model is transformed into the GC DFT model for semi-infinite systems. Application of the SCD model to the excess adsorption of carbon dioxide on the silica gel is also discussed.

Journal Article↗

PubMed2004

Decay of correlation functions in hard-sphere mixtures: structural crossover.

We investigate the decay of pair correlation functions in a homogeneous (bulk) binary mixture of hard spheres. At a given state point the asymptotic decay r-->infinity of all three correlation functions is governed by a common exponential decay length and a common wavelength of oscillations. Provided the mixture is sufficiently asymmetric, size ratios q less than or approximately 0.7, we find that the common wavelength reflects either the size of the small or that of the big spheres. By analyzing the (complex) poles of the partial structure factors we find a sharp structural crossover line in the phase diagram. On one side of this line the common wavelength is approximately the diameter of the smaller sized spheres whereas on the other side it is approximately the diameter of the bigger ones; the wavelength of the longest ranged oscillations changes discontinuously at the structural crossover line. Using density functional theory and Monte Carlo simulations we show that structural crossover also manifests itself in the intermediate range behavior of the pair correlation functions and we comment on the relevance of this observation for real (colloidal) mixtures. In highly asymmetric mixtures, q< or =0.1, where there is metastable fluid-fluid transition, we find a Fisher-Widom line with two branches. This line separates a region of the phase diagram where the decay of pair correlations is oscillatory from one in which it is monotonic.

Journal Article↗

PubMed1985

Response of patients in classes III and IV of cardiomyopathy to therapy in a blind and crossover trial with coenzyme Q10.

Coenzyme Q10 (CoQ10), a biochemically established redox component of respiration including the coupled mechanisms of electron transfer and oxidative phosphorylation, is naturally present in the human myocardium. A double-blind and double-crossover trial has been conducted by administering CoQ10 and a matching placebo orally to two groups of patients having class III or IV cardiomyopathy (classification according to criteria of the New York Heart Association). Group A received CoQ10 and then placebo; group B received placebo and then CoQ10. Blood levels of CoQ10 and cardiac function were determined at 0 and 4 weeks (control stabilization period) and at 16 and 28 weeks (after the 12-week CoQ/placebo-treatment periods). For group A, significant increases in CoQ10 blood levels and cardiac function occurred during CoQ10 treatment and then decreased during crossover to placebo. For group B, there was no change in CoQ10 blood levels and cardiac function during placebo treatment, but increases in both parameters occurred in crossover to CoQ10. These patients, steadily worsening and expected to die within 2 years under conventional therapy, generally showed an extraordinary clinical improvement, indicating that CoQ10 therapy might extend the lives of such patients. This improvement could be due to correction of a myocardial deficiency of CoQ10 and to enhanced synthesis of CoQ10-requiring enzymes.

Adult↗

PubMed1999

Chromosome regions between centromeres and proximal crossovers are the physical sites of major effect loci for yield in potato: genetic analysis employing meiotic mutants.

Meiotic mutant (2n) gametes formed by first-division restitution without crossover (FDR-NCO) are expected to be superior to FDR with crossover (FDR-CO) because they transmit to the progeny, without disruption by recombination, almost 100% of the parental genotype. FDR-CO transfers approximately 80% of the parental heterozygosity and a large fraction of the epistatic interactions. Another genetic expectation associated with both FDR gametes is their equivalence for the phenotypic expression of traits controlled by genes residing between centromeres and proximal crossover sites. This set of unique cytogenetic features of FDR mutants was employed here as a tool to infer physical location of quantitative trait loci controlling total tuber yield (TTY) in potato. Two assays were conducted to verify the superiority of FDR-NCO over FDR-CO gametes for TTY by using progenies from 4x-2x factorial crosses. Male clones were 2n-pollen producers by either FDR-CO or FDR-NCO mechanisms. Compared with the 4x parents, TTY of the progenies ranged from 41% to 175% (i.e., high-parent heterosis). However, no significant TTY differences were observed between FDR-CO and FDR-NCO families. In addition, the size of variance components of males was smaller than females and near zero. Our results reinforce the hypothesis that genes controlling yielding ability have a predominant physical location between centromeres and proximal chiasmata. Quantitative trait loci in chromosome regions with reduced levels of recombination may provide a partial explanation for the slow progress in increasing TTY through conventional 4x-4x crosses and for the often high degree of heterosis obtained by introgressing genetic diversity via 4x-2x crosses in potato.

Journal Article↗

PubMed1999

Left-handed DNA crossovers. Implications for DNA-DNA recognition and structural alterations.

The close approach of DNA segments participates in many biological functions including DNA condensation and DNA processing. Previous crystallographic studies have shown that B-DNA self-fitting by mutual groove-backbone interaction produces right-handed DNA crossovers. These structures have opened new perspectives on the role of close DNA-DNA interactions in the architecture and activity the DNA molecule. In the present study, the analysis of the crystal packing of two B-DNA decamer duplexes d(CCIIICCCGG) and d(CCGCCGGCGG) reveals the existence of new modes of DNA crossing. Symmetric left-handed crossovers are produced by mutual fitting of DNA grooves at the crossing point. New sequence patterns contribute to stabilize longitudinal fitting of the sugar-phosphate backbone into the major groove. In addition, the close approach of DNA segments greatly influences the DNA conformation in a sequence dependent manner. This study provides new insights into the role of DNA sequence and structure in DNA-DNA recognition. In providing detailed molecular views of DNA crossovers of opposite chirality, this study can also help to elucidate the role of symmetry and chirality in the recognition of complex DNA structures by protein dimers or tetramers, such as topoisomerase II and recombinase enzymes. These results are discussed in the context of the possible relationships between DNA condensation and DNA processing.

Crystallography↗

PubMed1998

Crossover designs with correlated observations.

Crossover designs are widely used in different medical investigations where a number of treatments have to be compared. Sequences of treatments are given to subjects, and in practice the observations within each subject are likely to be correlated. This paper is concerned with the construction of crossover designs for such cases. The design problem is nonlinear in the parameters, and design optimality depends on the parameters defining the correlation structure. When the correlation structure is known, local optimum designs are obtained. When the distribution of its parameters is known, optimum Bayesian crossover designs are constructed. The optimum sizes of the groups of subjects receiving the same sequence of treatments are also determined.

Algorithms↗