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PubMed1988

Extraction of "deep" components from scalp EEG.

In an attempt to delineate the relative contribution of surface versus deep components in the EEG of patients with 3 per second generalized spike-wave discharges and clinical petit mal seizures, a mathematical method was devised which allows the splitting of the EEG into two major subsystems. It is based on the observation that broad electrical fields tend to represent activity at deeper structures while discrete narrow fields centered at one electrode position tend to be of more superficial origin. Since source derivation intentionally suppresses broad potential fields, a differentiation between superficial and deep activity can be achieved by subtracting the source density values from the corresponding electrode potential values. This will provide those aspects of the EEG which are contributed mainly by deep generators. The resultant data can then be subjected to eigenfunction analysis which yields few uncorrelated components. The percentage of contribution of each electrode to the total component thus derived can then be displayed as a topographic map. When this methodology was applied to ictal EEGs of three patients consistent results were obtained. The "deep" data yielded mainly two components with mutually perpendicular directions.

Cerebral Cortex↗
PubMed2005

A system for micro/nano fluidic flow diagnostics.

A system for flow measurement in micro/nano fluidic components is presented. Microfabricated arrays of straight channels with noncircular cross-sections were used for flow rate measurement. The calculated flow rates in these channels were determined using a finite difference approximation method. A pneumatic pumping system was utilized to control the pressure drop across the channels and flow rates were measured by collecting the fluids on a sensitive balance. The experimental setup was validated using long narrow circular tubes that mimic the range of flow resistances characteristic of micro/nano fluidic devices. Two types of channels cross-section were investigated. The first type contained an array of channels that were approximately trapezoidal (microchannels, approximately 6.5 microm deep) in cross-section and exhibited flow rates of 27.7--119.4 micro L/min within a pressure range of 64.1--277.1 kPa (9.3--40.2 psi). The second type contained an array of channels that were approximately arc-shaped (nanochannels, approximately 600 nm deep) and generated flow rates of 0.29--0.99 micro L/min within a pressure range of 137.2--334.4 kPa (19.9--48.5 psi). The flow rates calculated by the finite difference approximation method were within 5.5% and 19.68% of the average experimental flow rates in the microchannels and nanochannels, respectively.

Computer Simulation↗
PubMed1993

[Photoablation of the cornea with pulsed 2790 nm ErCr:YSGG laser irradiation. Basic studies].

The potential of 3 microns solid-state lasers as an alternative to excimer lasers for photoablative corneal surgery was investigated. A Q-switched ErCr:YSGG laser (2790 nm, 200 ns) was used for irradiation of porcine corneas and agar-agar samples. Mechanical tissue effects (stroma, endothelium) were documented by micromorphology. Laser-induced shock-waves were analyzed by piezo-electric transducers. No sharp ablation threshold, as in excimer laser photoablation, could be determined. Energy fluences < 2 J/cm2 led to dehydration of the irradiated samples. Higher fluences are necessary for the evaporation of tissue water to be so vigorous that the tissue matrix is expelled along with the organic matrix. At high fluences, the ablation rate exceeds the absorption depth of the laser radiation (up to 25 microns/pulse). At fluences between 2.5 and 28 J/cm2 the thermal necrosis zone adjacent to the crater was 7 +/- 3 microns. The intensity of the laser-induced acoustic shock waves can peak to some hundred bar. Small gas bubbles up to 1 mm were found in the surrounding area of the ablation crater. Apparently, they were pressed between the collagen lamellas by the explosive force of the ablative process. In deep excisions (> 75%) endothelial defects underneath the beam axis could be documented. Large-area tissue ablation, with a resolution in the range of 1 micron, as necessary in myopia correction, will not be possible with the present generation of ErCr:YSGG lasers. Its high ablation rate makes this laser suitable as a cutting (astigmatism, keratoplasty, vitreous surgery) and drilling (glaucoma) device.

Animals↗
PubMed2002

Uptake of transforming DNA in Gram-positive bacteria: a view from Streptococcus pneumoniae.

In a working model for the uptake of transforming DNA based on evidence taken from both Bacillus subtilis and Streptococcus pneumoniae, the ComG proteins are proposed to form a structure that provides access for DNA to the ComEA receptor through the peptidoglycan. DNA would then be delivered to the ComEC-ComFA transport complex. A DNA strand would be degraded by a nuclease, while its complement is pulled into the cell by ComFA through an aqueous pore formed by ComEC. The nuclease is known in S. pneumoniae only as EndA. We have examined the processing (i.e. binding, degradation and internalization) of DNA in S. pneumoniae strains lacking candidate uptake proteins. Mutants were generated by transposon insertion in endA, comEA/C, comFA/C, comGA and dprA. Processing of DNA was abolished only in a comGA mutant. As significant binding was measured in comEA mutants, we suggest the existence of two stages in binding: surface attachment (abolished in a comGA mutant) required for and preceding deep binding (by ComEA). Abolition of degradation in comGA and comEA mutants indicated that, despite its membrane location, EndA cannot access donor DNA by itself. We propose that ComEA is required to deliver DNA to EndA. DNA was still bound and degraded in comEC and comFA mutants. We conclude that recruitment of EndA can occur in the absence of ComEC or ComFA and that EndA is active even when the single strands it produces are not pulled into the cell. Finally, inactivation of dprA had no effect on the internalization of DNA, indicating that DprA is required at a later stage in transformation.

Bacterial Proteins↗
PubMed2004

Comparison of three different supercharging procedures in a rat skin flap model.

A significant clinical problem in reconstructive surgery is partial loss of a pedicled flap. To resolve this problem, various methods of vascular augmentation have been developed; "supercharging" is one of those techniques. A new rat flap model was developed for investigation of the supercharging procedure, and the efficacy of the arterial supercharging method was examined. The purpose of this study was to investigate how an arterial supercharging procedure could generate large flap survival areas with different supercharging positions in rats. On the basis of the vascular anatomical features of rats, a circumferential skin flap from the lower abdomen to the back, measuring 4 x 12 cm, was marked. The flap was divided along the dorsal midline. Forty rats were divided into four experimental groups, as follows: group 1 (control), flaps based only on the deep circumflex iliac artery and vein; group 2, flaps supercharged with the ipsilateral superficial inferior epigastric artery; group 3, flaps supercharged with the contralateral superficial inferior epigastric artery; group 4, flaps supercharged with the contralateral deep circumflex iliac artery. On the fourth postoperative day, the flaps were evaluated with measurements of necrosis and survival areas. Microfil (Flow Tech, Inc., Carver, Mass.) was then injected manually throughout the body, and the vascular changes produced by supercharging were angiographically evaluated. Compared with group 1 (control), the flap survival areas were significantly greater in distally supercharged flaps in groups 3 and 4 (mean flap survival, 91.2 +/- 5.2 percent and 90.5 +/- 10.6 percent, respectively; p < 0.001) and in proximally supercharged flaps in group 2 (45.9 +/- 4.1 percent, p < 0.05). Angiographic assessment of the flaps that survived completely revealed marked dilation of the choke veins among the territories and reorientation of dilated veins along the axes of the flaps. This study suggests that distal arterial supercharging (contralateral superficial inferior epigastric artery or contralateral deep circumflex iliac artery) is more effective than proximal arterial supercharging (ipsilateral superficial inferior epigastric artery) in increasing flap survival. Although the rat skin flap may not be analogous to human flaps, distal arterial supercharging might have useful therapeutic potential in increasing flap survival in clinical practice.

Angiography↗
PubMed2025

Efficient detection and characterization of targets of natural selection using transfer learning.

Natural selection leaves detectable patterns of altered spatial diversity within genomes, and identifying affected regions is crucial for understanding species evolution. Recently, machine learning approaches applied to raw population genomic data have been developed to uncover these adaptive signatures. Convolutional neural networks (CNNs) are particularly effective for this task, as they handle large data arrays while maintaining element correlations. However, shallow CNNs may miss complex patterns due to their limited capacity, while deep CNNs can capture these patterns but require extensive data and computational power. Transfer learning addresses these challenges by utilizing a deep CNN pre-trained on a large dataset as a feature extraction tool for downstream classification and evolutionary parameter prediction. This approach reduces extensive training data generation requirements and computational needs while maintaining high performance. In this study, we developed TrIdent, a tool that uses transfer learning to enhance detection of adaptive genomic regions from image representations of multilocus variation. We evaluated TrIdent across various genetic, demographic, and adaptive settings, in addition to unphased data and other confounding factors. TrIdent demonstrated improved detection of adaptive regions compared to recent methods using similar data representations. We further explored model interpretability through class activation maps and adapted TrIdent to infer selection parameters for identified adaptive candidates. Using whole-genome haplotype data from European and African populations, TrIdent effectively recapitulated known sweep candidates and identified novel cancer, and other disease-associated genes as potential sweeps.

Journal Article↗
PubMed1993

Laboratory evaluation of a low prime closed-circuit cardiopulmonary bypass system.

We have explored the potential advantages of a low prime closed-circuit cardiopulmonary bypass (CPB) system using a non-human primate model. Although manufacturers have reduced priming volumes in individual CPB components, the standard circuit volume remains high because of the tubing diameter and length necessary for gravity drainage. By replacing gravity drainage with the negative pressure generated by a centrifugal pump, we can realize significant tubing volume reduction. Closed-circuit bypass was conducted on 13 baboons ranging from 5-15 kg. The circuit consisted of a centrifugal pump, a hollow fiber oxygenator, and 1/4" arterial and venous tubing. The design of the circuit included the capacity to remove a limited amount of venous air. Circulatory arrest during deep hypothermia with volume displacement into a reservoir was also accomplished with this circuit. The potential benefits of this low prime closed-circuit bypass system include blood conservation and reduction in blood surface area contact. The future safe clinical use of this type of closed-circuit bypass for routine open heart surgery will depend upon the incorporation of a device in the venous line to remove air. This is the greatest threat to patient safety in a closed circuit system and its use for open chest surgery must wait until an efficient venous air elimination device is available.

Blood Transfusion, Autologous↗
PubMed2002

Ephrin-A5 restricts topographically specific arborization in the chick retinotectal projection in vivo.

The retinotectal map is the best characterized model system to study how axons respond to guidance cues during the formation of the nervous system. Recent studies have shown that the critical event in forming this map is topographic-specific axon branching. To elucidate the in vivo role of the repulsive cue ephrin-A5 in this event, we used chromophore-assisted laser inactivation (CALI) to generate acute loss of ephrin-A5 function in localized areas of the posterior tectum of chick embryos in ovo and analyzed the resulting changes of retinal projections during initial outgrowth (E11) and when retinal axons arborize in the deep layers in the tectum (E12). We confirmed that ephrin-A5 functions to restrict initial axon outgrowth at E11. At E12, CALI of ephrin-A5 did not affect the extent of axon outgrowth on the tectal surface but instead caused ectopic arborization posterior to the topographically correct site in deeper layers of the tectum. This shows that ephrin-A5 restricts arborization during this critical process for developing the retinotopic map. CALI provides an approach to inactivate in vivo function in higher vertebrates with high temporal and spatial specificity that may have wide application.

Animals↗
PubMed1976

Vitamin-A-induced mucous metaplasia. An in vitro system for modulating tight and gap junction differentiation.

Stratified squamous epithelia from 14-day chick embryo shank skin contain rare tight-junctional strands and only small gap junctions. Exposure of this tissue to retinoic acid (vitamin-A) (20 U/ml) in organ culture, however, induces mucous metaplasia, accompanied by tight-junction formation and gap-junction growth; untreated specimens continue to keratinize. To investigate sequential stages of junctional assembly and growth, we examined thin sections and freeze-fracture replicas at daily intervals for 3 days. During the metaplastic process, tight junctions assemble in midepidermal and upper regions, beginning on day 1 and becoming maximal on day 3. Two tight-junctional patterns could be tentatively identified as contributing to the emergence of fully formed zonulae occludentes: (a) the formation of individual ridges along the margins of gap junctions; (b) de novo generation of continuous ramifying strands by fusion of short strand segments and linear particulate aggregates near cellular apices. Gap junction enlargement, already maximal at day 1, occurs primarily three to four cell layers deep. Growth appears to occur by annexation of islands of 20-40 8.5-nm particles into larger lattices of islands separated by particle-free aisles. Eventually, a single gap junction may occupy much of the exposed membrane face in freeze-fractured tissue, but during apical migration of the cells such junctions disappear. The vitamin- A chick-skin system is presented as a responsive model for the controlled study of junction assembly.

Animals↗
PubMedDate not supplied

Estimates of the net excitatory currents evoked by visual stimulation of identified neurons in cat visual cortex.

The action potential discharge response of single neurons to both visual stimulation and injections of current were obtained during intracellular recordings in cat visual cortex in order to estimate the net excitatory current arriving at the soma during visual stimulation. Of 45 neurons recorded intracellularly, 19 pyramidal neurons and one basket cell were labelled with horseradish peroxidase. The discharge of all neurons adapted to constant current. For 40 neurons, a single exponential provided a good fit to the adapting discharge (r2 = 0.73 +/- 0.03) for all current intensities. Superficial layer neurons were significantly faster adapting [P < 0.001, mean (+/- SEM) time constant of adaptation = 11.5 +/- 1.3 ms; n = 20] than deep layer neurons (mean time constant of adaptation = 51.4 +/- 6.4 ms; n = 10). The percentage adaptation of the spike frequency, %(peak - adapted rate)/peak, was determined from the fitted exponential. Superficial layer neurons adapted significantly more strongly (P < 0.01, mean = 67 +/- 3%) than deep layer neurons (mean = 51 +/- 5%). The mean firing frequency in response to a current step of 320 ms duration had a linear relationship to the amplitude of the injected current (slope 66 spikes/s/nA; origin zero, mean r2 = 0.94; n = 33). This relationship provided a means of estimating the net peak excitatory current generated by visual stimuli. The estimated mean peak somatic current during the passage of a bar across the receptive field was 1.1 nA and the average current for the duration of the visually evoked discharge was 0.64 nA (n = 17). The transfer response of real and model neurons was obtained by differentiating the discharge response to a step input current and was then used to predict the output of the neuron following an arbitrary input. When these transfer responses were convolved with known input signals in model neurons, the predicted output was close to the simulated response of the model neuron to the same input waveforms. The transfer response was calculated for eight real neurons. Estimates of the net excitatory current arriving at the soma during visual stimulation was obtained by deconvolution. The mean peak somatic current for these neurons was 0.62 nA.

Action Potentials↗
PubMed2006

"Cricket singing means rain": semiotic meaning of insects in the district of Pedra Branca, Bahia State, northeastern Brazil.

This paper deals with the semiotic meanings which are given both to the appearance and/or behavior of insect species according to the ethnoentomological knowledge of the inhabitants of the village of Pedra Branca, Bahia State, Brazil. Data were collected from February to May 2001 by performing open-ended, recorded interviews with nine men and twenty-five women, whose ages ranged from 19 to 82 years old. Data were analyzed by using the union model, which involves considering all available information on the surveyed subject. Twelve kinds of insects were associated with both beneficial and harmful events, as well as with the indication of changing weather. The way local people perceive and interpret the appearance and/or behavior of certain species of insects depends on the cultural background of each inhabitant. The following semiotic meanings were recorded: fatal, funereal, auspicial, meteorological, societal, monetary, and of abundance or scarcity. The beliefs in the augural power of insects in the village of Pedra Branca are deep-rooted in the local tradition and are transmitted from generation to generation through oral culture. It is hoped that the data now available will be incorporated into a curriculum by those researchers interested in insect conservation and ethnobiology as well.

Adult↗
PubMed1991

Neuroblastoma grafts are noninvasively removed within mouse neocortex by selective laser activation of intracellular photolytic chromophore.

Studies of neural cell transplantation would be aided by the ability to damage or destroy, noninvasively and extremely selectively, grafted cells at defined times following their initial implantation. Mechanisms of graft integration and performance could be investigated, also providing insight into natural injury and repair mechanisms. At long wavelengths between 650 and 850 nm, laser energy can penetrate several millimeters of brain tissue without absorption or damage to the unpigmented tissue. However, targeted cells are selectively damaged by illumination at these long wavelengths if they contain latex nanospheres with incorporated cytolytic chromophores (e.g., chlorin e6). Light penetration allows many thousands of cells to be lesioned simultaneously, noninvasively, and deep within a surrounding matrix of other tissue. Such laser-activated damage has been termed laser photolysis (PL). We studied damage to C1300 neuroblastoma (NB) cells grafted into mouse neocortex in vivo by this process of PL. NB cells provided a simple and reproducible model of neural grafting, allowing direct histologic assessment of cellular growth and viability by distinct morphologic and mitotic criteria. Cells were cultured by standard methods, labeled in vitro by brief exposure to nanospheres containing chlorin e6, and grafted to sites within deep layers of mouse neocortex. Mice were exposed to transcranial, fractionated, unfocused pulses of 670-nm-wavelength energy totaling 90-120 J/cm2. We histologically assessed graft growth and cellular viability over a period from 2 d to 4 weeks, measured graft volumes quantitatively during the period of early rapid growth in controls (2 and 7 d), and generated 3-D reconstructions from serial sections to assist in visual analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

[Changes in the sleep-wakefulness cycle in experimental Parkinson's syndrome].

It was demonstrated in rat experiments that in modelling the akinetico-rigid parkinsonian syndrome by injecting kainic acid into the caudate nuclei the phases of wakefulness and light slow-wave sleep decreased while the phase of deep slow-wave sleep increased. In the tremorogenic from of the parkinsonian syndrome induced by reserpine the phases of wakefulness and deep slow-wave sleep decreased in the rats while the phases of light slow-wave and paradoxical sleep increased. In destruction of the substantia nigra with kainic acid the phase of paradoxical sleep reduced. The results of the study are discussed from the standpoint of the generator mechanisms of the development of neuropathological syndromes and the mechanisms of the interrelations of parkinsonism and epilepsy.

Animals↗
PubMed2005

Source analysis of interictal spikes in polymicrogyria: loss of relevant cortical fissures requires simultaneous EEG to avoid MEG misinterpretation.

PURPOSE: Multiple source analysis of interictal EEG and MEG spikes was used to identify irritative zones in polymicrogyria (PMG). Spike onset times and source localization were compared between both modalities. PMG is characterized by a marked loss of deep cortical fissures. Hence, differences between EEG and MEG were expected since MEG signals are predominantly generated from tangentially orientated neurons in fissures. PATIENTS: We studied 7 children and young adults (age 7.5 to 19 years) with localization-related epilepsy and unilateral polymicrogyria (PMG) as defined from anatomical MRI. METHODS: 122-channel whole-head MEG and 32-channel EEG were recorded simultaneously for 25 to 40 min. Using the BESA program, interictal spikes were identified visually and used as templates to search for similar spatio-temporal spike patterns throughout the recording. Detected similar spikes (r > 0.85) were averaged, high-pass filtered (5 Hz) to enhance spike onset, and subjected to multiple spatio-temporal source analysis. Source localization was visualized by superposition on T1-weighted MRI and compared to the lesion. RESULTS: Nine spike types were identified in seven patients (2 types in 2 patients). Eight out of nine EEG sources and seven MEG sources modeling spike onset were localized within the visible lesion. EEG spike onset preceded MEG significantly in two spike types by 19 and 25 ms. This was related to radial onset activity in EEG while MEG localized propagated activity. In one case, the earliest MEG spike activity was localized to the normal hemisphere while the preceding radial EEG onset activity was localized within the lesion. Distances between EEG and MEG onset sources varied markedly between 9 and 51 mm in the eight spike types with concordant lateralization. CONCLUSION: Interictal irritative zones were localized within the lesion in PMG comparable to other malformations, e.g., FCD. Discrepancies in MEG and EEG were related to the lack of deep fissures in PMG. In two cases, MEG was blind to the onset of radial interictal spike activity and localized propagated spike activity. In two other cases, MEG localized to the more peripheral parts of the irritative zone. Simultaneous EEG recordings with MEG and multiple source analysis are required to avoid problems of MEG interpretation.

Adolescent↗
PubMed2004

Sonodynamic therapy--a review of the synergistic effects of drugs and ultrasound.

Sonodynamic therapy, the ultrasound dependent enhancement of cytotoxic activities of certain compounds (sonosensitizers) in studies with cells in vitro and in tumor bearing animals, is reviewed. The attractive features of this modality for cancer treatment emerges from the ability to focus the ultrasound energy on malignancy sites buried deep in tissues and to locally activate a preloaded sonosensitizer. Possible mechanisms of sonodynamic therapy include generation of sonosensitizer derived radicals which initiate chain peroxidation of membrane lipids via peroxyl and/or alkoxyl radicals, the physical destabilization of the cell membrane by the sonosensitizer thereby rendering the cell more susceptible to shear forces or ultrasound enhanced drug transport across the cell membrane (sonoporation). Evidence against the role of singlet oxygen in sonodynamic therapy is discussed. The mechanism of sonodynamic therapy is probably not governed by a universal mechanism, but may be influenced by multiple factors including the nature of the biological model, the sonosensitizer and the ultrasound parameters. The current review emphasizes the effect of ultrasound induced free radicals in sonodynamic therapy.

Animals↗
PubMed1985

Infusion strategies to investigate the pharmacokinetics and pharmacodynamics of hypnotic drugs: etomidate as an example.

Etomidate was administered to six healthy volunteers by microprocessor controlled infusions, to generate three cycles of linearly increasing plasma levels, with an anticipated slope of 0.05 microgram ml-1 min-1. The infusions were stopped when a deep hypnotic state was obtained, as indicated by burst suppressions in the EEG. The infusions were restarted when the volunteers were fully orientated to person, place and time. The mean (+/-SD) doses of etomidate delivered by the first, second and third infusion were 165 +/- 30, 137 +/- 25 and 157 +/- 26 mg, respectively. Certain clinical signs were observed and related to the plasma concentrations of etomidate. Pharmacokinetic analysis was undertaken using an open two-compartment model. The therapeutic window was in a range of plasma concentrations between 0.3 and 1.0 microgram ml-1 of etomidate. Pharmacokinetic analysis gave a volume for the central compartment of 50 +/- 11 litre, an apparent volume of distribution of 252 +/- 51 litre and a total clearance of 1693 +/- 504 ml min-1. Microprocessor controlled infusions can serve as a powerful tool for research in clinical pharmacology. The achievement of linearly increasing plasma levels of etomidate allowed further pharmacokinetic and pharmacodynamic modelling concepts to be realized.

Adult↗
PubMed2006

The antithrombotic and anti-inflammatory effects of BCX-3607, a small molecule tissue factor/factor VIIa inhibitor.

Tissue factor (TF) is a transmembrane glycoprotein that binds its zymogen cofactor, Factor VIIa (FVIIa) on the cell surface. Together (TF/FVIIa) they activate Factor X (FX) and Factor IX (FIX) and start the extrinsic pathway of blood coagulation. As such, the TF/FVIIa complex plays an important role in normal physiology as well as in thrombotic diseases such as unstable angina (UA), disseminated intravascular coagulation (DIC), and deep vein thrombosis (DVT). In addition to its function as an initiator of coagulation, TF/FVIIa plays an important role in inflammation. Expression of TF on the cell surface and its appearance as a soluble molecule are characteristic features of acute and chronic inflammation in conditions such as sepsis and atherosclerosis. Here we demonstrate that BCX-3607, a small molecule potent inhibitor of TF/FVIIa, reduces thrombus weight in an animal model of DVT. BCX-3607 also decreases the level of interleukin-6 (IL-6) in a LPS-stimulated mouse model of endotoxemia. Additionally, in vitro studies indicate that BCX-3607 blocks the generation of TF/FVIIa-induced IL-8 mRNA in human keratinocytes and reduces the TF/FVIIa-mediated generation of IL-6 and IL-8 in human umbilical vein endothelial cells (HUVEC). Therefore, BCX-3607 might block the TF/FVIIa-mediated coagulation and inflammation associated with pathological conditions.

Animals↗
PubMed1997

Reaction of Nitrogen Chelates with the [Rh(2)](4+) Core: Bis-Chelate Products and Demonstration of Reversible, Chelate-Based Reduction Processes.

The preparations and properties are described of a series of [Rh(2)](4+) complexes possessing carboxylates and N-based chelates as ligands. Treatment of Rh(2)(O(2)CR)(4)(MeOH)(2) (R = Me (1), Et (2), Ph (3) or CF(3) (4)) with 2 equiv of 2,2'-bipyridine (bpy) in refluxing MeCN leads to the [Rh(2)(O(2)CR)(2)(bpy)(2)](2+) cation (in complexes 5-9). Reaction of 1 with 1,10-phenanthroline (phen), 4,4'-dimethyl-2,2'-bipyridine (Me(2)bpy), 4,4'-diphenyl-2,2'-bipyridine (Ph(2)bpy), and 4,7-diphenyl-1,10-phenanthroline (Ph(2)phen) leads to the analogous cations of complexes 10-13. Complex 6a, [Rh(2)(OAc)(2)(bpy)(2)(MeCN)(2)](PF(6))(2).2MeCN, crystallizes in monoclinic space group P2(1)/a with the following cell parameters at -172 degrees C: a = 14.433(2) Å, b = 12.810(1) Å, c = 22.78(3) Å, beta = 104.42(3) degrees, Z = 4, and V = 3971.2 Å(3). Complex 9, [Rh(2)(O(2)CCF(3))(4)(bpy)(2)].Me(2)CO, crystallizes in triclinic space group P&onemacr; with the following cell parameters at 20 degrees C: a = 14.260(4) Å, b = 15.375(4) Å, c = 9.709(2) Å, alpha = 105.98(2) degrees, beta = 97.49(2) degrees, gamma = 70.32(2) degrees, Z = 2, and V = 1925.2 Å(3). Both 6a and 9 contain a singly-bonded [Rh(2)](4+) unit with two cis bridging RCO(2)(-) groups and two syn-bpy chelate groups in a near-eclipsed conformation about the Rh-Rh vector. Reaction of [Rh(2)(tpy)(2)(MeCN)(4)](BF(4))(4) (15) (tpy = 2,2':6',2"-terpyridine) with NBu(n)(4)(O(2)CPh) gives [Rh(2)(O(2)CPh)(tpy)(2)(MeCN)(2)](BF(4))(3).MeCN (16). Complex 16 crystallizes in triclinic space group P&onemacr; with the following cell parameters at -168 degrees C: a = 11.684(4) Å, b = 20.373(8) Å, c = 10.451(3) Å, alpha = 93.47(2) degrees, beta = 110.53(1) degrees, gamma = 100.03(2) degrees, Z = 2, and V = 2274.1 Å(3). The cation of 16 consists of a [Rh(2)](4+) unit with a bridging PhCO(2)(-) group and two chelating tpy groups. The solution (1)H NMR properties of complexes 6-13 and 16 show the complexes to retain their solid-state structures on dissolution. The electrochemical properties of 6-13 and 16 were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in MeCN. The bis(bpy) and -(phen) complexes 6-8, 10, and 11 show a reversible, one-electron reduction in the range -0.83 to -0.91 V vs ferrocene and an additional, irreversible reduction and an irreversible oxidation; the Ph(2)bpy (12) and Ph(2)phen (13) complexes show a two-electron reversible reduction at -0.61 to -0.76 and a reversible one-electron oxidation at 0.68-0.89 V. Consideration of the potentials as a function of carboxylate and chelate identity leads to the conclusion that the reductions are ligand (chelate)-based. This is supported by an extended Hückel calculation on the model compound [Rh(2)(O(2)CH)(2)(bpy)(2)(HCN)(2)](2+), which shows the LUMO to be a bpy-based orbital comprising in-phase, sigma overlap of two bpy pi orbitals, one on each of the syn-bpy groups. In contrast, complex 16 shows no reversible reduction processes. Complex 6b, [Rh(2)(OAc)(2)(bpy)(2)(MeCN)(2)](BF(4))(2), in MeCN may be reduced with sodium acenaphthylenide in THF to give deep blue [Rh(2)(OAc)(2)(bpy)(2)(MeCN)(2)](BF(4)) (14) in high yield. The cation of 14 may also be generated by controlled potential electrolysis of 6a in MeCN at -0.99 V and by heating of a solution of 6a or 6b in alcohol.

Journal Article↗