RESUMEN

KEY POINTS: Muscle fibre cross sectional area is enhanced with massage in the form of cyclic compressive loading during regrowth after atrophy. Massage enhances protein synthesis of the myofibrillar and cytosolic, but not the mitochondrial fraction, in muscle during regrowth. Focal adhesion kinase activation and satellite cell number are elevated in muscles undergoing massage during regrowth. Muscle fibre cross sectional area and protein synthesis of the myofibrillar fraction, but not DNA synthesis, are elevated in muscle of the contralateral non-massaged limb. Massage in the form of cyclic compressive loading is a potential anabolic intervention during muscle regrowth after atrophy. ABSTRACT: Massage, in the form of cyclic compressive loading (CCL), is associated with multiple health benefits, but its potential anabolic effect on atrophied muscle has not been investigated. We hypothesized that the mechanical activity associated with CCL induces an anabolic effect in skeletal muscle undergoing regrowth after a period of atrophy. Fischer-Brown Norway rats at 10 months of age were hindlimb unloaded for a period of 2 weeks. The rats were then allowed reambulation with CCL applied at a 4.5 N load at 0.5 Hz frequency for 30 min every other day for four bouts during a regrowth period of 8 days. Muscle fibre cross sectional area was enhanced by 18% with massage during regrowth compared to reloading alone, and this was accompanied by elevated myofibrillar and cytosolic protein as well as DNA synthesis. Focal adhesion kinase phosphorylation indicated that CCL increased mechanical stimulation, while a higher number of Pax7+ cells likely explains the elevated DNA synthesis. Surprisingly, the contralateral non-massaged limb exhibited a comparable 17% higher muscle fibre size compared to reloading alone, and myofibrillar protein synthesis, but not DNA synthesis, was also elevated. We conclude that massage in the form of CCL induces an anabolic response in muscles regrowing after an atrophy-inducing event. We suggest that massage can be used as an intervention to aid in the regrowth of muscle lost during immobilization.

Asunto(s)

Miembro Posterior/fisiología , Masaje/métodos , Músculo Esquelético/crecimiento & desarrollo , Atrofia Muscular/terapia , Células Satélite del Músculo Esquelético/citología , Animales , Células Cultivadas , Masculino , Ratas , Ratas Endogámicas BN , Ratas Endogámicas F344

RESUMEN

Novel therapies have turned to delivering compounds to the brain using nasal sprays, bypassing the blood brain barrier, and enriching treatment options for brain aging and/or Alzheimer's disease. We conducted a series of in vivo experiments to test the impact of intranasal Apidra, a zinc-free insulin formulation, on the brain of young and aged F344 rats. Both single acute and repeated daily doses were compared to test the hypothesis that insulin could improve memory recall in aged memory-deficient animals. We quantified insulin signaling in different brain regions and at different times following delivery. We measured cerebral blood flow (CBF) using MRI and also characterized several brain metabolite levels using MR spectroscopy. We show that neither acute nor chronic Apidra improved memory or recall in young or aged animals. Within 2 hours of a single dose, increased insulin signaling was seen in ventral areas of the aged brains only. Although chronic Apidra was able to offset reduced CBF with aging, it also caused significant reductions in markers of neuronal integrity. Our data suggest that this zinc-free insulin formulation may actually hasten cognitive decline with age when used chronically.

Asunto(s)

Encéfalo/efectos de los fármacos , Encéfalo/metabolismo , Cognición/efectos de los fármacos , Insulina/análogos & derivados , Transducción de Señal/efectos de los fármacos , Administración Intranasal , Factores de Edad , Animales , Circulación Cerebrovascular , Insulina/administración & dosificación , Insulina/farmacología , Masculino , Ratas , Ratas Endogámicas F344 , Zinc

RESUMEN

Serotonin modulates various physiological processes and behaviors. This study investigates the role of 5-HT in locomotion and feeding behaviors as well as in modulation of sensory-motor circuits. The 5-HT biosynthesis was dysregulated by feeding Drosophila larvae 5-HT, a 5-HT precursor, or an inhibitor of tryptophan hydroxylase during early stages of development. The effects of feeding fluoxetine, a selective serotonin reuptake inhibitor, during early second instars were also examined. 5-HT receptor subtypes were manipulated using RNA interference mediated knockdown and 5-HT receptor insertional mutations. Moreover, synaptic transmission at 5-HT neurons was blocked or enhanced in both larvae and adult flies. The results demonstrate that disruption of components within the 5-HT system significantly impairs locomotion and feeding behaviors in larvae. Acute activation of 5-HT neurons disrupts normal locomotion activity in adult flies. To determine which 5-HT receptor subtype modulates the evoked sensory-motor activity, pharmacological agents were used. In addition, the activity of 5-HT neurons was enhanced by expressing and activating TrpA1 channels or channelrhodopsin-2 while recording the evoked excitatory postsynaptic potentials (EPSPs) in muscle fibers. 5-HT2 receptor activation mediates a modulatory role in a sensory-motor circuit, and the activation of 5-HT neurons can suppress the neural circuit activity, while fluoxetine can significantly decrease the sensory-motor activity.

Asunto(s)

Encéfalo/fisiología , Conducta Alimentaria/fisiología , Locomoción , Neuronas Serotoninérgicas/fisiología , Serotonina/fisiología , 5-Hidroxitriptófano/administración & dosificación , Animales , Proteínas de Drosophila/metabolismo , Drosophila melanogaster , Inhibidores Enzimáticos/administración & dosificación , Potenciales Postsinápticos Excitadores , Conducta Alimentaria/efectos de los fármacos , Fenclonina/administración & dosificación , Locomoción/efectos de los fármacos , Subunidades de Proteína/metabolismo , Receptores de Serotonina/fisiología , Células Receptoras Sensoriales/fisiología , Serotonina/administración & dosificación , Triptófano Hidroxilasa/metabolismo

RESUMEN

Optogenetics is a revolutionary technique that enables noninvasive activation of electrically excitable cells. In mammals, heart rate has traditionally been modulated with pharmacological agents or direct stimulation of cardiac tissue with electrodes. However, implanted wires have been known to cause physical damage and damage from electrical currents. Here, we describe a proof of concept to optically drive cardiac function in a model organism, Drosophila melanogaster. We expressed the light sensitive channelrhodopsin protein ChR2.XXL in larval Drosophila hearts and examined light-induced activation of cardiac tissue. After demonstrating optical stimulation of larval heart rate, the approach was tested at low temperature and low calcium levels to simulate mammalian heart transplant conditions. Optical activation of ChR2.XXL substantially increased heart rate in all conditions. We have developed a system that can be instrumental in characterizing the physiology of optogenetically controlled cardiac function with an intact heart.

Asunto(s)

Calcio/metabolismo , Frecuencia Cardíaca/fisiología , Optogenética/métodos , Animales , Drosophila melanogaster , Rodopsina/genética , Temperatura

RESUMEN

The commonly used mood altering drug fluoxetine (Prozac) in humans has a low occurrence in reports of harmful effects from overdose; however, individuals with altered metabolism of the drug and accidental overdose have led to critical conditions and even death. We addressed direct actions of high concentrations on synaptic transmission at neuromuscular junctions (NMJs), neural properties, and cardiac function unrelated to fluoxetine's action as a selective 5-HT reuptake inhibitor. There appears to be action in blocking action potentials in crayfish axons, enhanced occurrences of spontaneous synaptic vesicle fusion events in the presynaptic terminals at NMJs of both Drosophila and crayfish. In rodent neurons, cytoplasmic Ca(2+) rises by fluoxetine and is thapsigargin dependent. The Drosophila larval heart showed a dose dependent effect in cardiac arrest. Acute paralytic behavior in crayfish occurred at a systemic concentration of 2mM. A high percentage of death as well as slowed development occurred in Drosophila larvae consuming food containing 100µM fluoxetine. The release of Ca(2+) from the endoplasmic reticulum in neurons and the cardiac tissue as well as blockage of voltage-gated Na(+) channels in neurons could explain the effects on the whole animal as well as the isolated tissues. The use of various animal models in demonstrating the potential mechanisms for the toxic effects with high doses of fluoxetine maybe beneficial for acute treatments in humans. Future studies in determining how fluoxetine is internalized in cells and if there are subtle effects of these mentioned mechanisms presented with chronic therapeutic doses are of general interest.

Asunto(s)

Astacoidea/efectos de los fármacos , Drosophila melanogaster/efectos de los fármacos , Fluoxetina/toxicidad , Miocitos Cardíacos/efectos de los fármacos , Unión Neuromuscular/efectos de los fármacos , Neuronas/efectos de los fármacos , Inhibidores Selectivos de la Recaptación de Serotonina/toxicidad , Animales , Astacoidea/metabolismo , Conducta Animal/efectos de los fármacos , Señalización del Calcio/efectos de los fármacos , Células Cultivadas , Relación Dosis-Respuesta a Droga , Drosophila melanogaster/metabolismo , Potenciales Postsinápticos Excitadores/efectos de los fármacos , Paro Cardíaco/inducido químicamente , Paro Cardíaco/metabolismo , Ratones , Modelos Animales , Miocitos Cardíacos/metabolismo , Miocitos Cardíacos/patología , Unión Neuromuscular/metabolismo , Unión Neuromuscular/patología , Neuronas/metabolismo , Neuronas/patología , Terminales Presinápticos/efectos de los fármacos , Terminales Presinápticos/metabolismo , Medición de Riesgo , Especificidad de la Especie , Factores de Tiempo

RESUMEN

Afferent neurons commonly exhibit a somatotopic arrangement in the central nervous system that organizes spatially discrete sensory input. We are interested in how that spatial input gets integrated into motor commands. With resources for screening genes and neural circuits, and given that the cells and ion channels that transduce tactile stimuli in Drosophila larvae are remarkably well-characterized, larval mechanosensation is an ideal system for investigating how specific behaviors emerge from localized sensory input. We observed that crawling larvae are more reactive to a 20mN tactile stimulus on the head than on the tail or abdomen. Behavioral responses that were evoked by the stimuli also depended on where the stimulus was delivered. Differences in relative sensitivity were observed in different genotypes, e.g., a null white mutant and hypomorphic smn mutant are significantly more reactive to tail touches than Canton-S larvae. Responses were inhibited by silencing chemical transmission in a combination of multidendritic and chordotonal neurons, but not by inhibiting any specific subset of neurons. Extracellular recordings from segmental nerves revealed that sensory-evoked responses exhibit spike-timing dependence at the neural circuit level. Tactile stimuli reduced endogenous firing frequency and increased bursting periods when applied during periods of motor activity. The same stimulus initiated bursts of activity when applied during inactive periods. Together, these data depict the spatial and temporal complexity of mechanosensation as it applies to action selection, and provide a foundation for addressing how neural circuits in the CNS adjust their activity to afferent input.

Asunto(s)

Drosophila melanogaster/fisiología , Mecanotransducción Celular/fisiología , Vías Nerviosas/fisiología , Transportadoras de Casetes de Unión a ATP/genética , Animales , Conducta Animal/fisiología , Proteínas de Drosophila/genética , Electrofisiología , Proteínas del Ojo/genética , Técnicas de Inactivación de Genes , Genotipo , Larva , Neuronas Aferentes/fisiología , Proteínas de Unión al ARN/genética , Tacto/fisiología

RESUMEN

Serotonin, 5-hydroxytryptamine (5-HT), plays various roles in the fruit fly, Drosophila melanogaster. Previous studies have shown that 5-HT modulates the heart rate in third instar larvae. However, the receptor subtypes that mediate 5-HT action in larval cardiac tissue had yet to be determined. In this study, various 5-HT agonists and antagonists were employed to determine which 5-HT receptor subtypes are responsible for the positive chronotropic effect by 5-HT. The pharmacological results demonstrate that a 5-HT2B agonist significantly increases the heart rate; however, 5-HT1A, 5-HT1B, and 5-HT7 agonists do not have a significant effect on the heart rate. Furthermore, 5-HT2 antagonist, ketanserin, markedly reduces the positive chronotropic effect of 5-HT in a dose-response manner. Furthermore, we employed genetic approaches to confirm the pharmacological results. For this purpose, we used RNA interference line to knock down 5-HT2ADro and also used 5-HT2ADro and 5-HT2BDro insertional mutation lines. The results show that 5-HT2ADro or 5-HT2BDro receptor mutations reduce the response of the heart to 5-HT. Given these results, we conclude that these 5-HT2 receptor subtypes are involved in the action of 5-HT on the heart rate in the larval stage.

Asunto(s)

Drosophila/genética , Frecuencia Cardíaca/efectos de los fármacos , Receptores de Serotonina/genética , Receptores de Serotonina/metabolismo , Animales , Aorta/efectos de los fármacos , Aorta/metabolismo , Relación Dosis-Respuesta a Droga , Drosophila/efectos de los fármacos , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Frecuencia Cardíaca/fisiología , Ketanserina/farmacología , Larva/efectos de los fármacos , Mutación , Miocardio/metabolismo , Interferencia de ARN , Receptor de Serotonina 5-HT2A/genética , Receptor de Serotonina 5-HT2A/metabolismo , Receptor de Serotonina 5-HT2B/metabolismo , Serotonina/análogos & derivados , Serotonina/farmacología , Antagonistas de la Serotonina/farmacología , Agonistas de Receptores de Serotonina/farmacología

RESUMEN

Drosophila serves as a playground for examining the effects of genetic mutations on development, physiological function and behavior. Many physiological measures that address the effects of mutations require semi-intact or cultured preparations. To obtain consistent physiological recordings, cellular function needs to remain viable. Numerous physiological salines have been developed for fly preparations, with emphasis on nervous system viability. The commonly used saline drifts in pH and will cause an alteration in the heart rate. We identify a saline that maintains a stable pH and physiological function in the larval heart, skeletal neuromuscular junction, and ventral nerve cord preparations. Using these common assays, we screened various pH buffers of differing concentrations to identify optimum conditions. Buffers at 25 mM produce a stable heart rate with minimal variation in pH. Excitatory junction potentials evoked directly on larval muscles or through sensory-CNS-motor circuits were unaffected by at buffers at 25 mM. The salines examined did not impede the modulatory effect of serotonin on heart rate or neural activity. Together, our results indicate that the higher buffer concentrations needed to stabilize pH in HL3 hemolymph-like saline do not interfere with the acute function of neurons or cardiac myocytes.

Asunto(s)

Drosophila melanogaster/fisiología , Unión Neuromuscular/efectos de los fármacos , Cloruro de Sodio/farmacología , Transmisión Sináptica/efectos de los fármacos , Animales , Tampones (Química) , Sistema Nervioso Central/efectos de los fármacos , Sistema Nervioso Central/fisiología , Drosophila melanogaster/efectos de los fármacos , Potenciales Evocados/efectos de los fármacos , Corazón/efectos de los fármacos , Corazón/fisiología , Frecuencia Cardíaca/efectos de los fármacos , Hemolinfa , Concentración de Iones de Hidrógeno , Larva/efectos de los fármacos , Larva/fisiología , Músculos/efectos de los fármacos , Músculos/fisiología , Unión Neuromuscular/fisiología , Células Receptoras Sensoriales/efectos de los fármacos , Células Receptoras Sensoriales/fisiología , Serotonina/metabolismo , Cloruro de Sodio/química , Transmisión Sináptica/fisiología

RESUMEN

The cockroach ventral nerve cord preparation is a tractable system for neuroethology experiments, neural network modeling, and testing the physiological effects of insecticides. This article describes the scope of cockroach sensory modalities that can be used to assay how an insect nervous system responds to environmental perturbations. Emphasis here is on the escape behavior mediated by cerci to giant fiber transmission in Periplaneta americana. This in situ preparation requires only moderate dissecting skill and electrophysiological expertise to generate reproducible recordings of neuronal activity. Peptides or other chemical reagents can then be applied directly to the nervous system in solution with the physiological saline. Insecticides could also be administered prior to dissection and the escape circuit can serve as a proxy for the excitable state of the central nervous system. In this context the assays described herein would also be useful to researchers interested in limb regeneration and the evolution of nervous system development for which P. americana is an established model organism.

Asunto(s)

Sistema Nervioso Central/fisiología , Sistema Nervioso Central/cirugía , Red Nerviosa/fisiología , Periplaneta/fisiología , Animales , Disección/métodos , Estimulación Eléctrica , Masculino , Modelos Animales , Células Receptoras Sensoriales/fisiología

RESUMEN

The freshwater leech, Hirudo medicinalis, is a versatile model organism that has been used to address scientific questions in the fields of neurophysiology, neuroethology, and developmental biology. The goal of this report is to consolidate experimental techniques from the leech system into a single article that will be of use to physiologists with expertise in other nervous system preparations, or to biology students with little or no electrophysiology experience. We demonstrate how to dissect the leech for recording intracellularly from identified neural circuits in the ganglion. Next we show how individual cells of known function can be removed from the ganglion to be cultured in a Petri dish, and how to record from those neurons in culture. Then we demonstrate how to prepare a patch of innervated skin to be used for mapping sensory or motor fields. These leech preparations are still widely used to address basic electrical properties of neural networks, behavior, synaptogenesis, and development. They are also an appropriate training module for neuroscience or physiology teaching laboratories.

Asunto(s)

Técnicas de Cultivo de Célula/métodos , Sanguijuelas/fisiología , Fenómenos Fisiológicos del Sistema Nervioso , Neuronas/fisiología , Animales , Fenómenos Electrofisiológicos , Ganglios/citología , Ganglios/fisiología , Sanguijuelas/citología , Modelos Animales , Red Nerviosa/citología , Red Nerviosa/fisiología , Sistema Nervioso/citología , Neuronas/citología , Piel/inervación

RESUMEN

The primary purpose of these procedures is to demonstrate for teaching and research purposes how to record the activity of living primary sensory neurons responsible for proprioception as they are detecting joint position and movement, and muscle tension. Electrical activity from crustacean proprioceptors and tension receptors is recorded by basic neurophysiological instrumentation, and a transducer is used to simultaneously measure force that is generated by stimulating a motor nerve. In addition, we demonstrate how to stain the neurons for a quick assessment of their anatomical arrangement or for permanent fixation. Staining reveals anatomical organization that is representative of chordotonal organs in most crustaceans. Comparing the tension nerve responses to the proprioceptive responses is an effective teaching tool in determining how these sensory neurons are defined functionally and how the anatomy is correlated to the function. Three staining techniques are presented allowing researchers and instructors to choose a method that is ideal for their laboratory.

Asunto(s)

Extremidades/inervación , Neurofisiología/educación , Propiocepción/fisiología , Células Receptoras Sensoriales/fisiología , Animales , Crustáceos

RESUMEN

The fruit fly, Drosophila melanogaster, is a good experimental organism to study the underlying mechanism of heart rate (HR) regulation. It is already known that many neuromodulators (serotonin, dopamine, octopamine, acetylcholine) change the HR in Drosophila melanogaster larvae. In this study, we investigated the role of cAMP-PKA signaling pathway in HR regulation and 5-HT positive chronotropic action. In order to obtain insight into the 5-HT mechanism of action in larvae cardiomyocytes, genetic and pharmacological approaches were used. We used transgenic flies that expressed the hM4Di receptor [designer receptors exclusively activated by designer drugs (DREADDs)] as one tool. Our previous results showed that activation of hM4Di receptors (modified muscarinic acetylcholine receptors) decreases or arrests the heart from beating. In this study, it was hypothesized that the positive chronotropic effect of serotonin [5-hydroxytryptamine (5-HT)] are mediated by serotonin receptors coupled to the adenylyl cyclase pathway and downstream cAMP and PKA activity. Activation of hM4Di by clozapine-N-oxide (CNO) was predicted to block the effects of serotonin by inhibiting adenylyl cyclase activity through Gαi pathway activation. Interestingly, we found here that manipulation of adenylyl cyclase activity and cAMP levels had no significant effect on HR. The ability of hM4Di receptor activation to slow or stop the heart is therefore likely mediated by activation of GIRK channels to produce hyperpolarization of cardiomyocytes, and not through inhibition of adenylyl cyclase.

Asunto(s)

AMP Cíclico/metabolismo , Frecuencia Cardíaca/efectos de los fármacos , Serotonina/farmacología , Adenilil Ciclasas/metabolismo , Animales , Animales Modificados Genéticamente , Clozapina/análogos & derivados , Clozapina/farmacología , Proteínas Quinasas Dependientes de AMP Cíclico/metabolismo , Drosophila , Larva/efectos de los fármacos , Larva/metabolismo , Miocitos Cardíacos/efectos de los fármacos , Miocitos Cardíacos/metabolismo , Neurotransmisores/farmacología , Farmacogenética/métodos , Receptores Muscarínicos/metabolismo , Receptores de Serotonina/metabolismo , Transducción de Señal/efectos de los fármacos

RESUMEN

We have translated a powerful genetic tool, designer receptors exclusively activated by designer drugs (DREADDs), from mammalian systems to Drosophila melanogaster to selectively, rapidly, reversibly, and dose-dependently control behaviors and physiological processes in the fly. DREADDs are muscarinic acetylcholine G protein-coupled receptors evolved for loss of affinity to acetylcholine and for the ability to be fully activated by an otherwise biologically inert chemical, clozapine-N-oxide. We demonstrate its ability to control a variety of behaviors and processes in larvae and adults, including heart rate, sensory processing, diurnal behavior, learning and memory, and courtship. The advantages of this particular technology include the dose-responsive control of behaviors, the lack of a need for specialized equipment, and the capacity to remotely control signaling in essentially all neuronal and nonneuronal fly tissues.

Asunto(s)

Conducta Animal/efectos de los fármacos , Drogas de Diseño/farmacología , Drosophila/efectos de los fármacos , Drosophila/fisiología , Neuronas/efectos de los fármacos , Animales , Conducta Animal/fisiología , Técnicas Biosensibles , Drogas de Diseño/química , Diseño de Fármacos , Femenino , Masculino , Neuronas/fisiología , Transducción de Señal

RESUMEN

Community and student demand for relevant nursing leadership graduate programs provided the impetus for this study. The aims were to identify components of highly competent nursing leadership, and strategies to integrate those components into education and practice. Nursing leaders gathered in five focus groups. A semi-structured interview guide was used to elicit narratives about nursing leadership. Interpretive analysis proceeded from identification of themes to uncovering of paradigm cases. Essential nursing leadership competencies comprised communication skills such as listening, conflict resolution, the ability to communicate a vision, motivate, and inspire. Additionally, leaders needed technological adroitness, fiscal dexterity, and the courage to be proactive during rapid change. Implications included a revision in the leadership focus of the nursing masters program, and the necessity that nurse retention should be enhanced by better educated nurse leaders who are grounded in practice and ready to provide a vision for the future.

Asunto(s)

Actitud del Personal de Salud , Educación de Postgrado en Enfermería/organización & administración , Liderazgo , Enfermeras Administradoras , Competencia Profesional , Comunicación , Curriculum , Enfermería Basada en la Evidencia/educación , Enfermería Basada en la Evidencia/organización & administración , Grupos Focales , Predicción , Conocimientos, Actitudes y Práctica en Salud , Humanos , Relaciones Interprofesionales , Motivación , Evaluación de Necesidades , Noroeste de Estados Unidos , Enfermeras Administradoras/educación , Enfermeras Administradoras/organización & administración , Enfermeras Administradoras/psicología , Rol de la Enfermera/psicología , Investigación Metodológica en Enfermería , Innovación Organizacional , Reorganización del Personal , Competencia Profesional/normas , Investigación Cualitativa , Encuestas y Cuestionarios

RESUMEN

Micellar solutions of tetramethylammonium dodecyl sulfate have been studied to determine the degree of counterion binding. Tetramethylammonium chloride was added over a wide range of surfactant concentrations such that the total concentration of tetramethylammonium ions in solution remained constant. Small angle neutron scattering experiments showed a constancy in aggregation number across this series, consistent with the constant C(aq) concept of Bales et al. (J. Phys. Chem. B 2001, 105, 6798). Pulsed-field gradient and electrophoretic NMR experiments were used to determine the degree of counterion dissociation, alpha, which was found to be 0.33. This value is in contrast to the value from conductivity measurements (alpha = 0.2), but supports the concept of an aggregation number based definition of alpha.

Asunto(s)

Espectroscopía de Resonancia Magnética , Neutrones , Compuestos de Amonio Cuaternario/química , Dodecil Sulfato de Sodio/química , Tensoactivos/química , Dispersión de Radiación

RESUMEN

The enthalpies of dilution of micellar solutions of several 12-s-12 dimeric surfactants of the alkanediyl-alpha,omega-bis(dodecyldi-methylammonium bromide) type, differing by the carbon number s of the alkanediyl spacer, and of dodecyltrimethylammonium bromide (DTAB) have been measured calorimetrically, in a range of concentrations extending from well below to well above the critical micelle concentration (cmc). The results permitted the determination of the enthalpy of micellization, DeltaH degrees (M), of the investigated surfactants at 25 and 35 degrees C. The values of DeltaH degrees (M) were always negative and became more negative as the temperature was increased. The plot of -DeltaH degrees (M) against s showed a shallow minimum at about s=5 and a large decrease of -DeltaH degrees (M) going from 12-2-12 to 12- 4-12. This effect has been attributed to the contribution to DeltaH degrees (M) of the hindered rotation of the dodecyl chains around the spacer C-C bond for 12-2-12. This hindrance is shown to rapidly disappear when s is increased from 2 to above 4. The specific heats of micellization, the free energies of micellization, and the entropies of micellization (DeltaS degrees (M)) have been calculated using the DeltaH degrees (M) values and the reported cmc and micelle ionization degree data for 12-s-12 surfactants and DTAB. For all surfactants the results show that TDeltaS degrees (M)>-DeltaH degrees (M), indicating an entropy-driven micellization.

RESUMEN

The aqueous solutions of mixtures of various conventional surfactants and dimeric anionic and cationic surfactants have been investigated by electrical conductivity, spectrofluorometry, and time-resolved fluorescence quenching to determine the critical micelle concentrations and the micelle aggregation numbers in these mixtures. The following systems have been investigated: 12-2-12/DTAB, 12-2-12/C(12)E(6), 12-2-12/C(12)E(8), 12-3-12/C(12)E(8), Dim3/C(12)E(8), and Dim4/C(12)E(8) (12-2-12 and 12-3-12=dimethylene-1,2- and trimethylene-1,3-bis(dodecyldimethylammonium bromide), respectively; C(12)E(6) and C(12)E(8)=hexa- and octaethyleneglycol monododecylethers, respectively; Dim3 and Dim4=anionic dimeric surfactants of the disodium sulfonate type, Scheme 1; DTAB=dodecyltrimethylammonium bromide). For the sake of comparison the conventional surfactant mixtures DTAB/C(12)E(8) and SDS/C(12)E(8) (SDS=sodium dodecylsulfate) have also been investigated (reference systems). Synergism in micelle formation (presence of a minimum in the cmc vs composition plot) has been observed for the Dim4/C(12)E(8) mixture but not for other dimeric surfactant/nonionic surfactant mixtures investigated. The aggregation numbers of the mixed reference systems DTAB/C(12)E(8) and SDS/C(12)E(8) vary monotonously with composition from the value of the aggregation number of the pure C(12)E(8) to that of the pure ionic component. In contrast, the aggregation number of the dimeric surfactant/C(12)E(8) mixtures goes through a minimum at a low value of the dimeric surfactant mole fraction. This minimum does not appear to be correlated to the existence of synergism in micelle formation. The initial decrease of the aggregation number of the nonionic surfactant upon addition of ionic surfactant, up to a mole fraction of ionic surfactant of about 0.2 (in equivalent per total equivalent), depends little on the nature the surfactant, whether conventional or dimeric. The results also show that the microviscosity of the systems containing dimeric surfactants is larger than that of the reference systems. Copyright 2001 Academic Press.

RESUMEN

A novel fluorescent gemini surfactant, 1,4-bis-(2'-(N-dodecyl pyridinio-4"-yl)ethenyl)benzene dibromide, abbreviated BDPEBB, has been synthesized and its photophysical properties have been studied in different environments. BDPEBB has a limited solubility in alcohols where it is found in aggregate form at concentrations>/=1 mM. In other solvents, e.g., water, it is only found in aggregate form, even at much lower concentrations. Solvent polarity has a small and insignificant solvatochromic effect but alcohols give a specific interaction with BDPEBB, causing a significant hypsochromic shift in absorption maxima and a large increase in relative fluorescence efficiency. Pyrene fluorescence is effectively quenched by BDPEBB. Pyrene also forms associative complexes with BDPEBB in water. These complexes are partly dissociated in the presence of surfactant micelles. Triton X-100 micelles provide a favorable environment for BDPEBB solubilization well distinguished from the behavior of ionic surfactants. Small quantities of BDPEBB have a large influence on the behavior of aqueous sodium dodecylsulfate (SDS) and sodium decylsulfate (SDeS) micelles, inducing the formation of large aggregates, visible by the naked eye. These large aggregates are most probably microcrystals of BDPEBB(2+)/2DS(-) or BDPEBB(2+)/2DeS(-). The aggregation number of SDS and SDeS micelles in the absence and in the presence of BDPEBB has been calculated by exploitation of the static luminescence quenching kinetics of Ru(bpy)(3)(2+) by 9-methylanthracene, both solubilized in the micellar phase. It has been observed that Ru(bpy)(3)(2+) inhibits the precipitation of SDeS micelles in the presence of BDPEBB. Our results suggest that double-chain surfactant chromophores should be employed with particular care if they are to be used as probes of the micellar phase. Copyright 2000 Academic Press.

RESUMEN

The interaction between hydroxypropylguar (HPG) and its dodecyl-modified derivative (HMHPG) and cationic surfactant oligomers has been investigated by measurements of the solution viscosity at constant shear rate, microviscosity of the aggregates (dipyrenylpropane fluorescence emission spectra), and aggregation number of the polymer hydrophobe and of the surfactant (time-resolved fluorescence quenching). The surfactants are dodecyltrimethylammonium bromide (DTAB, monomeric surfactant) and some of its dimers and trimers which differed by the carbon number s of the polymethylene spacer connecting the surfactant moieties (2

RESUMEN

The effect of dissolved gas (nitrogen, argon) on the properties of the droplets in water-in-oil and oil-in-water microemulsions (surfactant aggregation number, microviscosity, and micropolarity) has been investigated by means of time-resolved fluorescence quenching and spectrofluorometry. This study extends a similar one on aqueous micellar solutions (R. G. Alargova et al., Langmuir 14, 1575, 1998). The selected microemulsions were characterized by droplets of fairly large size and high volume fraction, in order to minimize the effect of the curvature of the surfactant layer and maximize the amount of gas that can be solubilized in the system. Within the experimental error, the investigated properties (surfactant aggregation number, intradroplet quenching rate constant which is related to the droplet microviscosity, and fluorescent probe lifetime and micropolarity) were found to be independent on whether the system was degassed, nitrogen-saturated, or argon-saturated, in the temperature range between 10 and 35 degrees C. The results confirm the conclusion reached in the above study; i.e., the effect of solubilized gases on the hydrophobic interaction which controls the formation of surfactant assemblies is extremely small and well below the sensitivity of the fluorescence probing techniques used in this investigation. Copyright 1999 Academic Press.