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1.
Disabil Rehabil ; : 1-9, 2023 Nov 10.
Artículo en Inglés | MEDLINE | ID: mdl-37950406

RESUMEN

PURPOSE: This focus group study aimed to explore experiences and perceptions on post-stroke fatigue guidance in Dutch rehabilitation and follow-up care among people/patients with stroke and health professionals. METHODS: Ten persons with stroke and twelve health professionals with different professions within stroke rehabilitation or follow-up care in the Netherlands were purposively sampled and included. Eight online focus group interviews were conducted. We analysed the data using reflexive thematic analysis. RESULTS: Three themes were identified. Guidance in fatigue management did not always match the needs of people/patients with stroke. Professionals were positive about the provided fatigue guidance (e.g. advice on activity pacing), but found it could be better tailored to the situation of people/patients with stroke. Professionals believe the right time for post-stroke fatigue guidance is when people/patients with stroke are motivated to change physical activity behaviour to manage fatigue - mostly several months after stroke - while people/patients with stroke preferred information on post-stroke fatigue well before discharge. Follow-up care and suggestions for improvement described that follow-up support after rehabilitation by a stroke coach is not implemented nationwide, while people/patients with stroke and professionals expressed a need for it. CONCLUSIONS: The study findings will help guide improvement of fatigue guidance in stroke rehabilitation programmes and stroke follow-up care aiming to improve physical activity, functioning, participation, and health.


We recommend fatigue guidance, including peer support, to be accessible to all people after stroke and for health professionals to pay attention to acceptance of the stroke.To improve fatigue guidance, we suggest providing information on post-stroke fatigue to people after stroke and their relatives well before discharge from stroke rehabilitation.Tailored advice on activity pacing during and after stroke rehabilitation is important to fill the current unmet need of people after stroke to manage fatigue and to gradually improve participation, physical activity behaviour and health.We recommend to health professionals working in stroke rehabilitation to tailor the rehabilitation schedule to their patients' energy level and perception of fatigue levels.

2.
N Z Vet J ; 71(6): 295-305, 2023 Nov.
Artículo en Inglés | MEDLINE | ID: mdl-37492960

RESUMEN

AIMS: To evaluate, in a pasture-based dairy herd, the response to a three-time point hoof trimming regime on lameness incidence and time from calving to observation of an elevated locomotion score (LS). METHODS: This study was conducted on a 940-cow spring-calving herd in New Zealand's North Island between May 2018 and May 2019. Cows (n = 250) were randomly allocated to the hoof trimming group, with the remainder assigned to the non-trim cohort. One trained professional hoof trimmer used the five-step Dutch method to trim the hind feet of the trimming group. Throughout the subsequent production season, the whole herd was locomotion-scored fortnightly using the 4-point (0-3) Dairy NZ lameness score. Kaplan-Meier survival curves were used to assess the univariable effect of trimming on the interval between calving and first LS of ≥ 2 and first LS ≥ 1. A multivariable Cox proportional hazards regression was used to further evaluate the effect of trimming on time to elevated LS. RESULTS: Mean lameness (LS ≥ 2) prevalence was 2.6%, with 30% of cows having ≥ 4 observations during the study period when at least one LS was ≥ 2. For LS ≥ 1, mean prevalence was 40%, with 98.6% of cows having ≥ 4 observations during the study period when at least one LS was ≥ 1 during lactation. Hoof trimming had no apparent effect on the incidence of clinical lameness (LS ≥ 2) (trimmed vs. non-trimmed: 33.2% vs. 28.8%, respectively), but for LS ≥ 1, there was a small decrease in the incidence of LS ≥ 1 (trimmed vs. non-trimmed: 96.9% vs. 99.3%, respectively). The hazard of a cow having a first observed LS ≥ 2 in the control group was 0.87 (95% CI = 0.66-1.14) times that of the trimmed group; however, the hazard of a cow having a first LS ≥ 1 was 1.60 (95% CI = 1.37-1.88) times higher in the control than in the trimmed group. CONCLUSION AND CLINICAL RELEVANCE: On this farm, prophylactic hoof trimming had no clinically relevant impact on the incidence of clinical lameness and was not associated with clinically beneficial reductions in time to first observed LS ≥ 2. This may be because claw horn imbalance was not pronounced on this farm, with 53% of cows needing no trim on either hind limb on the first trimming occasion. Further research on the response to prophylactic trimming in pasture-based dairy cattle is required.


Asunto(s)
Enfermedades de los Bovinos , Enfermedades del Pie , Cojera Animal , Animales , Bovinos , Femenino , Enfermedades de los Bovinos/epidemiología , Enfermedades de los Bovinos/prevención & control , Industria Lechera/métodos , Enfermedades del Pie/epidemiología , Enfermedades del Pie/prevención & control , Enfermedades del Pie/veterinaria , Lactancia , Cojera Animal/epidemiología , Cojera Animal/prevención & control , Locomoción
4.
Qual Life Res ; 30(1): 67-80, 2021 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-32986126

RESUMEN

PURPOSE: To identify Health-related Quality of Life (HR-QoL) trajectories in a large heterogeneous cohort of people with a physical disability and/or chronic disease during and after rehabilitation and to determine which factors before discharge are associated with longitudinal trajectory membership. METHODS: A total of 1100 people with a physical disability and/or chronic disease were included from the longitudinal cohort study Rehabilitation, Sports and Active lifestyle. All participants participated in a physical activity promotion programme in Dutch rehabilitation care. HR-QoL was assessed using the RAND-12 Health Status Inventory questionnaire at baseline (T0: 3-6 weeks before discharge) and at 14 (T1), 33 (T2) and 52 (T3) weeks after discharge from rehabilitation. A data-driven approach using Latent Class Growth Mixture modelling was used to determine HR-QoL trajectories. Multiple binomial multivariable logistic regression analyses were used to determine person-, disease- and lifestyle-related factors associated with trajectory membership. RESULTS: Three HR-QoL trajectories were identified: moderate (N = 635), high (N = 429) and recovery (N = 36). Trajectory membership was associated with person-related factors (age and body mass index), disease-related factors (perceived fatigue, perceived pain and acceptance of the disease) and one lifestyle-related factor (alcohol consumption) before discharge from rehabilitation. CONCLUSIONS: Most of the people who participated in a physical activity promotion programme obtained a relatively stable but moderate HR-QoL. The identified HR-QoL trajectories among our heterogeneous cohort are disease-overarching. Our findings suggest that people in rehabilitation may benefit from person-centred advice on management of fatigue and pain (e.g. activity pacing) and the acceptance of the disability.


Asunto(s)
Personas con Discapacidad/psicología , Promoción de la Salud/métodos , Calidad de Vida/psicología , Enfermedad Crónica , Estudios de Cohortes , Ejercicio Físico , Femenino , Humanos , Estilo de Vida , Estudios Longitudinales , Masculino , Persona de Mediana Edad , Encuestas y Cuestionarios
5.
Health Res Policy Syst ; 18(1): 51, 2020 May 25.
Artículo en Inglés | MEDLINE | ID: mdl-32450919

RESUMEN

BACKGROUND: Conducting research in partnership with stakeholders (e.g. policy-makers, practitioners, organisations, patients) is a promising and popular approach to improving the implementation of research findings in policy and practice. This study aimed to identify the principles, strategies, outcomes and impacts reported in different types of reviews of research partnerships in order to obtain a better understanding of the scope of the research partnership literature. METHODS: This review of reviews is part of a Coordinated Multicenter Team approach to synthesise the research partnership literature with five conceptually linked literature reviews. The main research question was 'What principles, strategies, outcomes and impacts are reported in different types of research partnership approaches?'. We included articles describing a literature review of research partnerships using a systematic search strategy. We used an adapted version of the Revised Assessment of Multiple Systematic Reviews tool to assess quality. Nine electronic databases were searched from inception to April 2018. Principles, strategies, outcomes and impacts were extracted from the included reviews and analysed using direct content analysis. RESULTS: We included 86 reviews using terms describing several research partnership approaches (e.g. community-based participatory research, participatory research, integrated knowledge translation). After the analyses, we synthesised 17 overarching principles and 11 overarching strategies and grouped them into one of the following subcategories: relationship between partners; co-production of knowledge; meaningful stakeholder engagement; capacity-building, support and resources; communication process; and ethical issues related to the collaborative research activities. Similarly, we synthesised 20 overarching outcomes and impacts on researchers, stakeholders, the community or society, and the research process. CONCLUSIONS: This review of reviews is the first that presents overarching principles, strategies, outcomes and impacts of research partnerships. This review is unique in scope as we synthesised literature across multiple research areas, involving different stakeholder groups. Our findings can be used as a first step to guide the initiation and maintenance of research partnerships and to create a classification system of the key domains of research partnerships, which may improve reporting consistency in the research partnership literature. TRIAL REGISTRATION: This study is registered via Open Science Framework: https://doi.org/10.17605/OSF.IO/GVR7Y.


Asunto(s)
Conducta Cooperativa , Proyectos de Investigación , Literatura de Revisión como Asunto , Participación de los Interesados , Personal Administrativo , Creación de Capacidad , Comunicación , Investigación Participativa Basada en la Comunidad/métodos , Ética en Investigación , Personal de Salud , Investigación sobre Servicios de Salud , Humanos , Organizaciones , Participación del Paciente , Investigadores , Revisiones Sistemáticas como Asunto , Investigación Biomédica Traslacional
6.
Neth Heart J ; 20(12): 509-12, 2012 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-23100093

RESUMEN

Communication between the aortic sinus and a cardiac chamber is a rare anomaly that can be diagnosed in children and young adults. We describe two cases with a tunnel between the aortic sinus and right atrium, discuss diagnostic modalities, and review the literature on this anomaly.

7.
N Z Vet J ; 60(6): 349-55, 2012 Nov.
Artículo en Inglés | MEDLINE | ID: mdl-22943738

RESUMEN

AIMS: To determine if inequality in height between claws within each hindlimb of dairy cattle is a risk factor for the development of lameness and to determine the effect of preventive trimming of these claws on the subsequent risk of lameness. METHODS: Cows (n=2,695) on three dairy farms in Canterbury, New Zealand, were examined and the height differential between their hind claws on each limb was measured. Cows were blocked by age, then breed and grouped by height differential, before being randomly assigned to either treatment or control groups. Cows in the control group were not trimmed, whilst cows in the treatment group were all trimmed according to the 'Dutch Trimming' method by an experienced foot trimmer. All subsequent clinical incidences of lameness were identified, recorded and classified according to five categories. The overall incidence of lameness, the effect of claw height differential on the incidence of lameness and the effect of trimming on the incidence of lameness were assessed using both GEE modelling and survival analysis. RESULTS: The incidence of lameness identified in any untrimmed hindlimb irrespective of diagnosis, measured at a limb level and assessing the first incidence of lameness only, was 10.0% for a 6-month period from November to drying off. The predominant lesion identified was white line disease (WLD; 7.9% incidence and 78.6% of all lameness). The overall incidence of hindlimb lameness measured at cow level for the same period was 14.5%. The risk of lameness was influenced by breed (p=0.016), age (p=0.002) and claw height differential (p=0.026). There were no significant interactions. The risk of lameness was lowest where the claw height differential was 0-2 mm. The incidence of lameness in the first 70 days following trimming was higher in older cows than in younger cows (p<0.001). Trimming did not affect lameness incidence (p=0.185). The Cox proportional hazard model demonstrated that farm (p<0.001), trimming group (p=0.021); and age (p=0.021) significantly affected the median days to lameness in the first 70 days following trimming. CONCLUSIONS AND CLINICAL RELEVANCE: Hind feet with lower height differentials between claws had a lower incidence of lameness. Trimming of these feet to remove the height differential did not reduce their overall incidence of lameness, but did increase days to first lameness.


Asunto(s)
Crianza de Animales Domésticos/métodos , Enfermedades de los Bovinos/prevención & control , Enfermedades del Pie/veterinaria , Pezuñas y Garras , Cojera Animal/prevención & control , Animales , Bovinos , Enfermedades de los Bovinos/epidemiología , Industria Lechera , Femenino , Enfermedades del Pie/prevención & control , Cojera Animal/epidemiología , Nueva Zelanda/epidemiología
9.
Langmuir ; 26(13): 11118-26, 2010 Jul 06.
Artículo en Inglés | MEDLINE | ID: mdl-20550154

RESUMEN

We present molecular dynamics (MD) simulations to study the plausibility of the water replacement hypothesis (WRH) from the viewpoint of structural chemistry. A total of 256 2-oleoyl-1-palmitoyl-sn-glycero-3-phosphocholine (POPC) lipids were modeled for 400 ns at 11.7 or 5.4 waters/lipid. To obtain a single dehydrated bilayer relevant to the WRH, simulations were performed in the NP(xy)h(z)T ensemble with h(z) > 8 nm, allowing interactions between lipids in the membrane plane and preventing interactions between neighboring membranes via periodic boundary conditions. This setup resulted in a stable single bilayer in (or near) the gel state. Trehalose caused a concentration-dependent increase of the area per lipid (APL) accompanied by fluidizing the bilayer core. This mechanism has been suggested by the WRH. However, dehydrated bilayers in the presence of trehalose were not structurally identical to fully hydrated bilayers. The headgroup vector was in a more parallel orientation in dehydrated bilayers with respect to the bilayer plane and maintained this orientation in the presence of trehalose in spite of APL increase. The total dipole potential changed sign in dehydrated bilayers and remained slightly positive in the presence of trehalose. The model of a dehydrated bilayer presented here allows the study of the mechanisms of membrane protection against desiccation by different compounds.


Asunto(s)
Membrana Dobles de Lípidos/química , Fosfatidilcolinas/química , Trehalosa/química , Agua/química , Simulación de Dinámica Molecular
10.
Pediatr Neurosurg ; 45(4): 281-90, 2009.
Artículo en Inglés | MEDLINE | ID: mdl-19690444

RESUMEN

Intraspinal dermoid and epidermoid tumors are two histopathological subtypes of cutaneous inclusion tumors of the spine. This classification is based on obsolete embryological knowledge. In fact, according to current embryology, both tumor types consist of ectodermal derivatives. Therefore, we hypothesized that dermoid and epidermoid tumors do not differ in clinical practice. To explore this hypothesis, we studied the clinical, radiological and intraoperative findings of 18 patients, and related these findings to the histopathological characteristics of the tumor. No differences were found between dermoid and epidermoid tumors regarding clinical presentation, radiological examination and outcome, while intraoperative diagnosis by the surgeon correlated with the histopathological diagnosis in only 8 of 18 cases. Therefore, the histopathological difference between intraspinal dermoid and epidermoid tumors is not important in clinical practice and should be avoided. A new nomenclature is proposed in which both tumor types are referred to as 'spinal cutaneous inclusion tumors'.


Asunto(s)
Quiste Dermoide/diagnóstico , Quiste Dermoide/cirugía , Quiste Epidérmico/diagnóstico , Quiste Epidérmico/cirugía , Neoplasias de la Columna Vertebral/diagnóstico , Neoplasias de la Columna Vertebral/cirugía , Adulto , Niño , Preescolar , Estudios de Cohortes , Femenino , Estudios de Seguimiento , Humanos , Lactante , Masculino , Persona de Mediana Edad , Estudios Retrospectivos
11.
Biochim Biophys Acta ; 1778(4): 890-5, 2008 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-18291092

RESUMEN

The osmotic shrinkage of giant unilamellar dioleoylphosphatidylglycerol (DOPG) vesicles in a hypertonic osmotic solution is investigated. The volume reduction for given membrane area leads to a vesiculation of the bilayer into the interior of the giant. The size of the daughter vesicles that appear inside the giant is uniform and an increasing function of the cholesterol content, but independent of the osmotic gradient applied. The radius of the daughter vesicles increases from 0.2 microm to 3.0 microm when the cholesterol content is changed from 0 to 40%. It is argued that the size of the daughter vesicles is regulated by the membrane persistence length, which is an exponential function of the mean bending modulus. From the kinetics of shrinkage it follows that approximately 14% of the daughter vesicles remain attached to the mother giant. This is in reasonable agreement with osmotic swelling experiments which show that approximately 11% of the daughter vesicles is available for area expansion.


Asunto(s)
1,2-Dipalmitoilfosfatidilcolina/metabolismo , Colesterol/metabolismo , Liposomas Unilamelares/metabolismo , Ósmosis
12.
Phys Rev E Stat Nonlin Soft Matter Phys ; 76(1 Pt 1): 011903, 2007 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-17677490

RESUMEN

In spite of the large mean bending moduli observed for phospholipid bilayers, stable vesicle phases were recently observed for dilute solutions of charged phospholipids. A correspondingly large negative Gaussian bending modulus associated with charged membranes results in an overall curvature energy that is so low that entropic stabilization is possible. The mean bending modulus determines the membrane persistence length and therefore it is reasonable that there is a correlation between the membrane rigidity and the size of the lipid vesicles. Here we show that in mixtures of the anionic phospholipid dioleoylphosphatidylglycerol and the zwitterionic phospholipid dioleoylphosphatidylcholine the radius of vesicles produced by repetitive freeze-thaw cycles is considerably smaller than expected from the rigidities of the corresponding pure lipid bilayers. Self-consistent field calculations indicate that the changes in the equilibrium radius of mixed bilayers can be attributed to the dependences of the mean bending modulus k(c) on lipid mixing and the average surface charge density.


Asunto(s)
Membrana Dobles de Lípidos/química , Liposomas/química , Fluidez de la Membrana , Modelos Químicos , Modelos Moleculares , Fosfolípidos/química , Simulación por Computador , Elasticidad , Conformación Molecular , Estrés Mecánico
13.
J Phys Chem B ; 111(25): 7127-32, 2007 Jun 28.
Artículo en Inglés | MEDLINE | ID: mdl-17530881

RESUMEN

We correlate the molecularly realistic self-consistent field predictions for the mean bending modulus kc of charged lipid vesicles with experimental observations of the size R of corresponding vesicles that are produced by the freeze-thaw method. We elaborate on the Ansatz that the bending modulus is related to the membrane persistence length and that this length scale sets the radius of the vesicles. Alkali cations have a remarkable effect on the mean bending modulus and thus on the equilibrium radius of negatively charged entropically stabilized dioleoylphosphatidylglycerol (DOPG) vesicles. Where cation hydration typically results in thicker and thus stiffer membranes, specific adsorption to the bilayer surface results in a decrease of the surface charge density and the thickness of the membrane-associated electric double layer. As a result of these opposing effects on kc and R, the largest DOPG vesicles are found in the presence of K+, which combines an intermediate hydration enthalpy and PG-binding affinity.


Asunto(s)
Aniones/química , Cationes/química , Membrana Dobles de Lípidos/química , Fosfatidilgliceroles/química , Agua/química , Metales Alcalinos/química , Concentración Osmolar
14.
Langmuir ; 23(11): 6315-20, 2007 May 22.
Artículo en Inglés | MEDLINE | ID: mdl-17461604

RESUMEN

We have studied the phase behavior of zwitterionic phospholipid dioleoylphosphatidylcholine (DOPC) vesicles (membranes) and interpreted our results using scaling arguments in combination with molecular realistic self-consistent field (SCF) calculations. DOPC membranes acquire a partial negative charge per lipid molecule at intermediate NaBr concentrations. As a result of this, dilute DOPC solutions form stable unilamellar vesicles. Both at low and high salt concentrations phase separation into a lamellar and a vesicular phase is observed. The vesicle radius decreases as a power law with decreasing lipid concentration. This power-law concentration dependence indicates that the vesicle phase is entropically stabilized; the size of the DOPC vesicles result from a competition between the bending energy and translation and undulation entropy. This scaling behavior breaks down for very small vesicles. This appears to be consistent with SCF predictions that point to the fact that in this regime the mean bending modulus kc increases with curvature. The SCF theory predicts that, at low ionic strength, the membrane stability improves when there is more charge on the lipids. Upon a decrease of the ionic strength, lipids with a full negative charge form vesicles that grow exponentially in size because the mean bending modulus increases with decreasing ionic strength. At the same time the Gaussian bending modulus becomes increasingly negative such that the overall bending energy tends to zero. This indicates that small micelles become the dominant species. The SCF theory thus predicts a catastrophic break down of giant vesicles in favor of small micelles at sufficiently low ionic strength and high charge density on the lipids.


Asunto(s)
Liposomas/química , Bromuros , Electroquímica , Entropía , Concentración Osmolar , Tamaño de la Partícula , Fosfatidilcolinas/química , Compuestos de Sodio , Soluciones
15.
Eukaryot Cell ; 6(2): 157-70, 2007 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-17099083

RESUMEN

Ascospores of the fungus Talaromyces macrosporus are dormant and extremely stress resistant, whereas fungal conidia--the main airborne vehicles of distribution--are not. Here, physical parameters of the cytoplasm of these types of spores were compared. Cytoplasmic viscosity and level of anisotropy as judged by spin probe studies (electron spin resonance) were extremely high in dormant ascospores and during early germination and decreased only partly after trehalose degradation and glucose efflux. Upon prosilition (ejection of the spore), these parameters fell sharply to values characteristic of vegetative cells. These changes occurred without major volume changes that suggest dramatic changes in cytoplasmic organization. Azide reversibly inhibited prosilition as well as the decline in cytoplasmic parameters. No organelle structures were observed in etched, cryoplaned specimens of ascospores by low-temperature scanning electron microscopy (LTSEM), confirming the high cytoplasmic viscosity. However, cell structures became visible upon prosilition, indicating reduced viscosity. The viscosity of fresh conidia of different Penicillium species was lower, namely, 3.5 to 4.8 cP, than that of ascospores, near 15 cP. In addition the level of anisotropic motion was markedly lower in these cells (h(0)/h(+1) = 1.16 versus 1.4). This was confirmed by LTSEM images showing cell structures. The decline of cytoplasmic viscosity in conidia during germination was linked with a gradual increase in cell volume. These data show that mechanisms of cytoplasm conservation during germination differ markedly between ascospores and conidia.


Asunto(s)
Citoplasma/metabolismo , Esporas Fúngicas/crecimiento & desarrollo , Talaromyces/crecimiento & desarrollo , Anisotropía , Espectroscopía de Resonancia por Spin del Electrón , Esporas Fúngicas/ultraestructura , Estrés Mecánico , Talaromyces/ultraestructura , Temperatura , Viscosidad
16.
Vaccine ; 24(5): 644-51, 2006 Jan 30.
Artículo en Inglés | MEDLINE | ID: mdl-16157423

RESUMEN

This study examines the factors that influence parents' decisions to have their children vaccinated under the Dutch National Immunisation Programme. A computer questionnaire was sent to 500 parents in 1999 (the response rate was 98.2%). The intention to vaccinate was most strongly determined by attitudes. The belief that vaccination is safe and the best way to protect children against infectious diseases positively influenced parents' attitudes. The idea that children receive too many vaccines simultaneously and that vaccination interferes with natural development had a negative effect on attitudes. Dutch parents believe that doctors only inform them about the benefits of vaccination and disregard possible drawbacks. Since attitudes did not appear to be the result of thorough deliberation, parents could easily be influenced by negative publicity about vaccination. Educational campaigns and practitioners' advice should provide complete information about all aspects of the question, enabling parents to make well-considered and therefore enduring decisions.


Asunto(s)
Padres/psicología , Aceptación de la Atención de Salud/estadística & datos numéricos , Vacunación/estadística & datos numéricos , Adulto , Actitud , Niño , Interpretación Estadística de Datos , Encuestas de Atención de la Salud , Educación en Salud , Humanos , Programas de Inmunización/estadística & datos numéricos , Modelos Logísticos , Países Bajos/epidemiología , Encuestas y Cuestionarios , Vacunación/efectos adversos , Vacunación/psicología
17.
Biophys J ; 87(6): 3882-93, 2004 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-15377511

RESUMEN

The swelling behavior of charged phospholipids in pure water is completely different from that of neutral or isoelectric phospholipids. It was therefore suggested in the past that, instead of multilamellar phases, vesicles represent the stable structures of charged lipids in excess water. In this article, we show that this might indeed be the case for dioleoylphosphatidylglycerol and even for dioleoylphosphatidylcholine in certain salts. The size of the vesicles formed by these lipids depends on the phospholipid concentration in a way that has been predicted in the literature for vesicles of which the curvature energy is compensated for by translational entropy and a renormalization of the bending moduli (entropic stabilization). Self-consistent field calculations on charged bilayers show that the mean bending modulus kc and the Gaussian bending modulus k have opposite sign and /k/>kc, especially at low ionic strength. This has the implication that the energy needed to curve the bilayer into a closed vesicle Eves=4pi(2kc+k) is much less than one would expect based on the value of kc alone. As a result, Eves can relatively easily be entropically compensated. The radii of vesicles that are stabilized by entropy are expected to depend on the membrane persistence length and thus on kc. Experiments in which the vesicle size is studied as a function of the salt and the salt concentration correlate well with self-consistent field predictions of kc as a function of ionic strength.


Asunto(s)
Membrana Dobles de Lípidos/química , Liposomas/química , Fluidez de la Membrana , Modelos Químicos , Modelos Moleculares , Fosfatidilgliceroles/química , Cloruro de Sodio/química , Simulación por Computador , Elasticidad , Conformación Molecular , Tamaño de la Partícula , Electricidad Estática , Estrés Mecánico , Propiedades de Superficie , Temperatura
18.
Cryobiology ; 48(1): 46-54, 2004 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-14969681

RESUMEN

The aim of this study was to investigate the effect of sodium citrate on the properties of dried amorphous sucrose glasses. Addition of sodium citrate to a sucrose solution followed by freeze-drying or convective drying resulted in a glass transition temperature (Tg) that was higher than the well-studied sucrose Tg. This result was obtained either at reduced water content of the analysed sample or by removal of water during Modulated DSC analysis. After removal of the remaining water ( < 3.5% w/w), a Tg of approximately 105 degrees C was obtained at a mass ratio of sodium citrate to sucrose of 0.3. FTIR analysis showed a similar increase in Tg as was found with Modulated DSC analysis. The Tg values were derived from breaks in the vibrational frequency vs. temperature plots in the OH stretching and bending regions. Elevated average strength of hydrogen bonding in the sucrose/citrate glass was concluded from the downshift of the OH stretching band of 25 cm(-1) and from the reduced wavenumber temperature coefficient (WTC). The antisymmetric carboxylate stretch of citrate sensed the glass transition of the mixture, from which we conclude that citrate interacts with the sucrose OH via its carboxylate groups.


Asunto(s)
Citratos , Liofilización/métodos , Sacarosa , Rastreo Diferencial de Calorimetría , Citratos/química , Citrato de Sodio , Soluciones , Espectroscopía Infrarroja por Transformada de Fourier , Sacarosa/química , Termodinámica
19.
Trends Plant Sci ; 6(9): 431-8, 2001 Sep.
Artículo en Inglés | MEDLINE | ID: mdl-11544133

RESUMEN

Anhydrobiosis ("life without water") is the remarkable ability of certain organisms to survive almost total dehydration. It requires a coordinated series of events during dehydration that are associated with preventing oxidative damage and maintaining the native structure of macromolecules and membranes. The preferential hydration of macromolecules is essential when there is still bulk water present, but replacement by sugars becomes important upon further drying. Recent advances in our understanding of the mechanism of anhydrobiosis include the downregulation of metabolism, dehydration-induced partitioning of amphiphilic compounds into membranes and immobilization of the cytoplasm in a stable multicomponent glassy matrix.


Asunto(s)
Fenómenos Fisiológicos de las Plantas , Agua , Adaptación Fisiológica , Metabolismo de los Hidratos de Carbono , Membrana Celular/metabolismo , Sustancias Macromoleculares , Presión Osmótica , Estrés Oxidativo , Proteínas de Plantas/fisiología , Prolina/metabolismo , Conformación Proteica
20.
J Exp Bot ; 52(358): 919-31, 2001 May.
Artículo en Inglés | MEDLINE | ID: mdl-11432909

RESUMEN

Storage of neem (Azadirachta indica) seeds is difficult because of their sensitivity to chilling stress at moisture contents (MC) > or =10% or imbibitional stress below 10% MC. The hypothesis was tested that an elevated gel-to-liquid crystalline phase transition temperature (Tm) of membranes is responsible for this storage behaviour. To this end a spin probe technique, Fourier transform infrared microspectroscopy, and electron microscopy were used. The in situ Tm of hydrated membranes was between 10 degrees C and 15 degrees C, coinciding with the critical minimum temperature for germination. During storage, viability of fresh embryos was lost within two weeks at 5 degrees C, but remained high at 25 degrees C. The loss of viability coincided with an increased leakage of K+ from the embryos upon imbibition and with an increased proportion of cells with injured plasma membranes. Freeze-fracture replicas of plasma membranes from chilled, hydrated axes showed lateral phase separation and signs of the inverted hexagonal phase. Dehydrated embryos were sensitive to soaking in water, particularly at low temperatures, but fresh embryos were not. After soaking dry embryos at 5 degrees C (4 h) plus 1 d of further incubation at 25 degrees C, the axis cells were structurally disorganized and did not become turgid. In contrast, cells had a healthy appearance and were turgid after soaking at 35 degrees C. Imbibitional stress was associated with the loss of plasma membrane integrity in a limited number of cells, which expanded during further incubation of the embryos at 25 degrees C. It is suggested that the injuries brought about by storage or imbibition at sub-optimal temperatures in tropical seeds whose membranes have a high intrinsic Tm (10-15 degrees C), are caused by gel phase formation.


Asunto(s)
Rosales/fisiología , Semillas , Membrana Celular/fisiología , Membrana Celular/ultraestructura , Frío , Fertilidad , Germinación , Preservación Biológica , Rosales/ultraestructura , Espectroscopía Infrarroja por Transformada de Fourier , Marcadores de Spin , Agua
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