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PubMed2006

Evaluation of sexual function in young men with spina bifida and myelomeningocele using the International Index of Erectile Function.

OBJECTIVES: To assess sexual function in young men with spina bifida and myelomeningocele. METHODS: Between November 2003 and February 2004, a cross-sectional study was performed in 55 men older than 18 years of age who had been regularly followed up for myelomeningocele since childhood, between 1961 and 1985, in the Pediatric Internal Surgery Department. The International Index of Erectile Function (IIEF) questionnaire was mailed to each man. RESULTS: The response rate was 72.7%. Of the 40 men who replied, 16 (40%) had had sexual intercourse at least once during the previous month. These were the older men (age 31.9 +/- 5.7 years versus 27.7 +/- 5.5 years, P = 0.027). The IIEF scores for the whole group were erectile function 11.61 +/- 9.44, orgasmic function 3.53 +/- 3.86, sexual desire 6.94 +/- 2.4, intercourse satisfaction 3.7 +/- 4.81, and overall satisfaction 4.7 +/- 3.34. According to the classification of Cappelleri, of the 16 men who had had sexual intercourse during the previous month, 4 had no erectile dysfunction, 3 had mild, 4 mild to moderate, and 5 severe dysfunction. Erectile function was statistically related to the ability to maintain erections (mean IIEF score 4 and 5 for men with no erectile dysfunction versus a mean IIEF score of 4 and 5 for men with erectile dysfunction: 4.75 +/- 0.5 versus 2.00 +/- 1.32, P = 0.011 for IIEF score of 4 and 4.50 +/- 1.5 versus 3 +/- 2, P = 0.040 for IIEF score of 5). CONCLUSIONS: Young adult men with spina bifida and myelomeningocele begin sexual activity late. Moreover, 75% have erectile dysfunction that is related to difficulty in maintaining erections.

Adult↗

PubMed2003

Abnormal prefrontal cortex function during response inhibition in Turner syndrome: functional magnetic resonance imaging evidence.

BACKGROUND: Turner syndrome (TuS) arises from the partial or complete absence of one X chromosome. Although neuropsychological studies report impaired attentional function and response inhibition in TuS, the neural correlates of these cognitive problems are unknown. METHODS: Eleven female subjects with TuS and 11 individually matched normal control subjects were imaged using functional magnetic resonance imaging while performing a Go/NoGo task. RESULTS: Groups did not differ on accuracy or reaction time; however, the TuS group activated more in the bilateral superior and middle frontal gyri than control subjects. Control subjects did not activate more than the TuS group in any region. CONCLUSION: These findings suggest that female subjects with TuS compensate for executive dysfunction via recruitment of additional prefrontal cortex regions involved in inhibition, attention, and working memory, functions necessary for successful performance of Go/NoGo tasks. Elucidating brain function in TuS will advance our understanding of the influence of X-chromosome genes on neurodevelopment and brain function and contribute to planning future intervention strategies.

Adolescent↗

PubMed2002

One fold with many functions: the evolutionary relationships between TIM barrel families based on their sequences, structures and functions.

The eightfold (betaalpha) barrel structure, first observed in triose-phosphate isomerase, occurs ubiquitously in nature. It is nearly always an enzyme and most often involved in molecular or energy metabolism within the cell. In this review we bring together data on the sequence, structure and function of the proteins known to adopt this fold. We highlight the sequence and functional diversity in the 21 homologous superfamilies, which include 76 different sequence families. In many structures, the barrels are "mixed and matched" with other domains generating additional variety. Global and local structure-based alignments are used to explore the distribution of the associated functional residues on this common structural scaffold. Many of the substrates/co-factors include a phosphate moiety, which is usually but not always bound towards the C-terminal end of the sequence. Some, but not all, of these structures, exhibit a structurally conserved "phosphate binding motif". In contrast metal-ligating residues and catalytic residues are distributed along the sequence. However, we also found striking structural superposition of some of these residues. Lastly we consider the possible evolutionary relationships between these proteins, whose sequences are so diverse that even the most powerful approaches find few relationships, yet whose active sites all cluster at one end of the barrel. This extreme example of the "one fold-many functions" paradigm illustrates the difficulty of assigning function through a structural genomics approach for some folds.

Aldose-Ketose Isomerases↗

PubMed1992

Function of the conus medullaris and cauda equina in the early period following spinal cord injury and the relationship to recovery of detrusor function.

A total of 26 patients with an early suprasacral spinal cord injury underwent comprehensive neurourological evaluation to determine if there was any correlation between the return of detrusor function and neural function of the sacral cord. In addition, the incidence of a subclinical sacral neural dysfunction early after spinal cord injury was assessed. Lumbosacral evoked potentials to tibial nerve stimulation were used to assess the sensory root and cord gray matter of the L5 to S2 segments, while urodynamic evaluation was performed to assess detrusor function. Of those patients with normal lumbosacral evoked potentials 82% recovered detrusor contractility as opposed to 66% with abnormal evoked potentials. Four patients (23.5%) had persistent detrusor areflexia when studied 9 to 20 months following the acute injury. The potential problems attempting to correlate the neurophysiological and urodynamic studies are multiple and are extensively discussed. Despite these potential problems the return of detrusor function correlated well with associated normal lumbosacral evoked potentials suggesting that this test can be used in the early phase following spinal cord injury to predict return of bladder function, since it is independent of the level of spinal cord excitability. Of the patients studied 38% had coexistence of an occult lumbosacral dysfunction. This rate is higher than that found in the chronic stabilized spinal cord injury population (20.5%), since the cases in our study may represent a more severe lesion.

Adolescent↗

PubMed2005

Functional cell classes and functional architecture in the early visual system of a highly visual rodent.

Over the last 50 years, studies of receptive field properties in mammalian visual brain structures such as lateral geniculate nucleus (LGN) and primary visual cortex (V1) have suggested the existence of cell classes with unique functional response properties, and in visual cortex of many mammals these functional response properties show considerable spatial organization termed functional architecture. In recent years, there has been considerable interest in understanding the cellular mechanisms that underlie visual responses and plasticity in intact animals, and studies of individual neurons in brain slices have identified distinct cell classes on the basis of anatomical features, synaptic connectivity, or gene expression. However, the relationships between cell classes identified in studies of brain slices and those in the intact animal remain largely unclear. Rodents offer many advantages for investigating these relationships, as they are appropriate for a wide variety of experimental techniques and genetically modified mice are relatively easy to obtain or produce. Unfortunately, a barrier to using these animals in vision research is a lack of understanding of the relationship of rodent visual systems to the visual systems in more commonly studied mammals such as carnivores and non-human primates. Here we review recent comparative studies of functional response properties in LGN and V1 of a highly visual diurnal rodent, the gray squirrel. In the LGN, our data are consistent with the idea that all mammals have a class of LGN neurons that is sustained, another class that is transient, and a third class of more heterogeneous cells, but some response properties such as linearity of spatial summation, contrast gain, and dependence of receptive field size on eccentricity vary from species to species. In V1, the squirrel has many orientation-selective neurons, and these orientation-selective cells can be further subdivided into simple and complex cells. Despite the fact that squirrel has greater visual acuity and a physically larger V1 than some mammals that have orientation maps in V1, we do not find orientation maps in V1 of squirrel, which is similar to results in other less visual rodents. We suggest that orientation maps are not necessary for high acuity vision or orientation selectivity and that cortical functional architecture can vary greatly from species to species.

Animals↗

PubMed2000

Evaluation of male sexual function after pelvic trauma by the International Index of Erectile Function.

OBJECTIVES: To assess the multifaceted male sexual function after pelvic ring fracture. METHODS: A cross-sectional study of male sexual function after pelvic ring fractures was conducted, using the International Index of Erectile Function (IIEF). The department of traumatology database was scanned (June 1996 to April 1999) for 30 to 70-year-old male patients with pelvic fracture. Seventy-six consecutive, literate patients were then contacted by mail. IIEF domain scores were calculated for all responders. Cappelleri's method for identification and grading of erectile dysfunction was applied for patients sexually active within the past 4 weeks. Student's t test was used to compare the domain scorings of patients with those of the control population used for the IIEF psychometric validation. Relationships between IIEF results and patient characteristics were sought by Spearman's rank correlation coefficient for quantitative variables and Student's t test for classes. RESULTS: Forty-six patients answered (60.1% response rate). Thirty-seven patients had experienced sexual intercourse in the past 4 weeks during which 11 patients (29.7%) had exhibited various degrees of impaired erection. As a whole, compared with the published controls a significant decrease in overall satisfaction (P <0.05) was demonstrated. Pubic diastasis was further related to impaired erectile function and overall satisfaction; we suggest that cavernosal nerves might be damaged at the time of diastasis. CONCLUSIONS: This study evidenced the impairment of sexual overall satisfaction after pelvic trauma and the specific decrease in erectile function and erection firmness and confidence associated with pubic diastasis. The IIEF questionnaire might be considered at the time of rehabilitation to identify those patients that could benefit from supportive treatments.

Adult↗

PubMed2001

Morphological and functional characteristics of the dominant follicle and corpus luteum in cattle and their influence on ovarian function.

Predicting the functional activity of a dominant follicle (DF) and corpus luteum (CL) might be important before starting a superovulation regime or a synchronization program. The DF and CL were characterized morphologically by using ultrasonography and were characterized functionally by estimating the estradiol-17beta/progesterone (E2/P4) ratio. Their influence on ovarian function was estimated through their ability to ovulate at different stages of development in response to PGF2alpha-application. A total of 47 Holstein Friesian (35 cows and 12 heifers) were used in two experiments. In Experiment 1, 25 animals were examined by daily transrectal palpation and ultrasonography to follow the morphological development of the DF. The status of the DF was categorized into 3 groups (A1, B1, C1). The A1 group (n=7) contained animals with DF in the growing phase or in early static growth phase for less than 3 days. Group B1 (n=13) included animals with DF in static growth phase for 3 to 4 days, while Group C1 (n=5) comprised animals with DF keeping a plateau for more than 4 days or animals with DF in the regression phase. The DF were aspirated transvaginally and the follicular fluid (FF) was analyzed for E2 and P4. In Experiment 2, 22 animals were included. As in Experiment 1, the animals were classified into three groups (A2, n=10; B2, n=5; C2, n=7). They were treated by a single dose of PGF2alpha (25 mg, i.m.) between Days 8 and 12 of the cycle. Results showed that luteolyses occurred in all animals. The DF, which were in growing or in early static growth phase < 3 days were always E2-dominant (E2 > P4) and ovulated after PGF2alpha-application in 6/8 of cases and persisted in 2 (Group A2). The DF persisting > 4 days or that had been in regression were always P4-dominant. This type of DF regressed after PGF2alpha-application (Group C2). The DF in early static growth phase for 3 to 4 days in 5/13 cases were E2-dominant and in 8/13 cases were P4-dominant. This type of DF ovulated in 3/5 cases and regressed in 2/5 cases after PGF2alpha-application (Group B2). These results suggest that the DF is morphologically and functionally defined as long as the DF is in the growing or early static growth phase (A1, A2) for at least 2 days or if the DF is in regression (C1, C2). However, when the DF is in the static growth phase for 3 or 4 days (B1, B2), their morphological and functional characteristics are different. The CL controlls ovulation in the A and C groups and plays an abettor's roll in the B-group.

Animals↗

PubMed1997

Highest level automatisms in the nervous system: a theory of functional principles underlying the highest forms of brain function.

A concept that all hierarchical levels of the nervous system are built according to the same functional principles is proposed. Each level is responsible for a discrete type or set of automatisms, is a learning system, and contains two distinct functional subdivisions: (1) a controller, a subsystem providing a governing set of rules or commands-a control law-that directs the action of the recipient of these rules-the controlled object; and (2) a model, a subsystem that generates a model of object behavior, i.e. afferent information flow expected from the controlled object. A control system such as this receives two types of afferent signals-initiating and informational. The difference between these signals is that a control system minimizes initiating signals during the realization of an automatism, i.e. a control neural network utilizes informational signals to compute the proper output that minimizes the initiating input signal. A mismatch or error signal, a type of initiating signal, is responsible for learning. Both the control law and the model can be adjusted during learning. The learning process starts when the error signal increases and stops when it is minimized. A network hierarchy is structurally and functionally organized in such a way that a lower control system in the nervous system becomes the controlled object for a higher one. This hierarchy leads to a generalization of encoded functional parameters and, consequently, the working space for each higher level control system becomes more abstracted. This is the reason why each hierarchical level within the control nervous system uses detectors specific for feature of the controlled object and the environment that match the control needs in order to obtain information about the current state of the object in the environment. Movement of information toward higher hierarchical levels also is accompanied by an increase in the duration of initiating signals within each control system. The ability to store a long prehistory of preceding events is considered as the mechanism that necessitated the invention of more complex and more rapid forms of learning such as operant learning, and made possible more complex multistep computational algorithms that require memorization of the results of previous intermediate computations. The functions of the cerebellum, the limbic system and the cortico-basal ganglia-thalamocortical loops are analyzed to illustrate the utility and applicability of this theoretical concept. Basal ganglia-thalamocortical loops are described as modeling, predictive loops, and their dopaminergic innervation as an error distribution system.

Automatism↗

PubMed2003

Rate dependency of the human cortical network subserving executive functions during generation of random number series--a functional magnetic resonance imaging study.

In a random number generation (RNG) task subjects are instructed to generate the numbers 1-10 in a random fashion. RNG performance is assumed to involve executive functions, as it requires controlled response generation and suppression of habitual responses. To investigate cerebral structures involved in RNG associated executive functions we investigated functional magnetic resonance imaging in eight healthy subjects while performing an RNG task at two different response rates (1 and 2 Hz). During the 1 Hz condition an activation was detected bilaterally in the dorsolateral prefrontal cortex (BA 9/46), the lateral premotor cortex (BA 6), the anterior cingulate (BA 32), the inferior and superior parietal cortex (BA 7/40) and the cerebellar hemispheres. In the 2 Hz condition behavioural data showed higher counting tendencies reflecting poorer executive control. In parallel, a homogenous diminution of the activity in the involved cortical areas was obtained. This finding would support the theory of a cortical network involved in executive functions consisting of distinct brain regions working together rather than a distinct fronto-cortical functional localisation.

Adult↗

PubMed1986

Characterization of the functional border zone around regionally ischemic myocardium using circumferential flow-function maps.

Previous studies have suggested that there exists a functional border zone in myocardium at the lateral margins of an ischemic area. The functional border zone is normally perfused but is characterized by abnormal contractile function. To define the spatial characteristics of this border zone, circumferential maps of left ventricular function by two-dimensional echocardiography and of coronary flow using radioactive microspheres were generated in 18 dogs at baseline and after circumflex coronary occlusion. Circumferential left ventricular wall thickening was measured in all dogs at 22.5 degrees intervals over 360 degrees. In seven dogs, the pathologic slice corresponding to the two-dimensional echocardiographic image was circumferentially dissected into 16 segments corresponding to 22.5 degrees intervals and a subendocardial myocardial blood flow map was derived. In the other 11 dogs, autoradiography was performed of the pathologic slice corresponding to the two-dimensional echocardiographic image, and the hypoperfusion zone was directly measured. There was no difference between the circumferential extent of hypoperfusion zones by either perfusion measurement technique in the five dogs that had both techniques performed (140 +/- 12 versus 124 +/- 7 degrees, p = NS). The hypofunctional zone by two-dimensional echocardiography was significantly larger than the hypoperfusion zone (174 +/- 4 versus 125 +/- 26 degrees, p less than 0.0005), indicating that a zone of normally perfused but abnormally contracting muscle surrounds the ischemic area. However, this border zone in our model was small, measuring 49 +/- 34 degrees (approximately 8 to 9 mm on either lateral border). This suggests that the functional border zone lateral to ischemic myocardium exists, but is relatively discrete.

Animals↗

PubMedDate not supplied

Within-session patterns of responding during functional analyses: the role of establishing operations in clarifying behavioral function.

Functional analysis procedures have been demonstrated to be effective for identifying the operant mechanisms underlying problem behavior. However, functional analyses sometimes yield results that are undifferentiated (i.e., show similar levels of responding across test conditions). Within-session (i.e., minute-by-minute) analyses of response patterns during undifferentiated functional analyses have proven useful in clarifying behavioral function. This study extends previous research by examining within-session changes in responding associated with variations in relevant establishing operations. Levels of problem behavior during the presentation and removal of reinforcement were compared when responding occurred in test conditions associated with sources of social reinforcement (i.e., access to attention, materials, escape). Results showed that changes in responding associated with changes in relevant establishing operations could be examined to clarify behavioral function.

Child↗

PubMedDate not supplied

An evaluation of functional variables affecting severe problem behaviors in adults with mental retardation by using the Questions about Behavioral Function Scale (QABF).

We examined the functions of five severe problem behaviors in a sample of 417 institutionalized persons with mental retardation by using the Questions About Behavior Function Scale. The behaviors we examined included self-injurious behavior, aggression, stereotypies, pica, and rumination. The most common function for all behaviors except aggression was nonsocial. Aggression, however, was maintained by external environmental contingencies. Particular items of the Questions About Behavior Function Scale were identified as more frequently occurring and critical in ascertaining behavioral function. Implications of these results for developing more effective treatment plans are discussed.

Adult↗

PubMed1997

The functional significance of symptomatology and cognitive function in schizophrenia.

The relationships between positive and negative symptomatology, cognitive function, and the ability to perform basic activities of daily living in patients with schizophrenia were examined in two studies. In study 1, 112 medicated patients were assessed utilizing the Brief Psychiatric Rating Scale (positive symptoms), the Negative Symptom Assessment (negative symptoms and cognitive function), and the Functional Needs Assessment (activities of daily living). Study 2 (n = 41), utilized the same measures of symptomatology and added a comprehensive neuropsychological test battery. Regression analyses in both studies determined that symptomatology predicts a relatively small amount of the variance in the ability to perform basic activities of daily living. Cognitive function, whether assessed with the Cognition subscale of the Negative Symptom Assessment or a comprehensive neuropsychological test battery, predicted over 40% of the variance in scores on the Functional Needs Assessment. A path model in which cognition predicted both concurrent symptomatology and activities of daily living and where symptomatology had little direct impact upon activities of daily living fit the data. The importance of addressing cognitive deficits in psychosocial intervention programs is discussed.

Activities of Daily Living↗

PubMed2004

Everyday functioning in relation to cognitive functioning and neuroimaging in community-dwelling Hispanic and non-Hispanic older adults.

The purpose of this study was to examine how a specific informant-based measure of everyday functioning, the Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE; Jorm & Korten, 1988) relates to cognition and structural neuroimaging in a large multicultural, multilingual sample of Caucasians and Hispanics. Cognitive variables included selected subtests from the Spanish and English Neuropsychological Assessment Scales (SENAS; Mungas et al., 2000): Verbal Memory, Object Naming, Verbal Attention Span, Verbal Conceptual Thinking, and Pattern Recognition. The association between the IQCODE and selected neuroimaging variables, hippocampal volume and white matter hyperintensity, was evaluated in a subsample of English- and Spanish-speaking Hispanic individuals. The cognitive variables showed strong bivariate relationships with the IQCODE, although only Verbal Memory and Object Naming independently predicted level of functional ability. Verbal Memory was the strongest predictor of functional status, accounting for 23% of the variance in the IQCODE. White matter hyperintensity was also independently related to the IQCODE, accounting for 18% of the variance. Hippocampal volume was related to the IQCODE in a simple bivariate analysis, but was not an independent predictor of reported functional status after controlling for age. The relationships between cognitive variables and functional status, as well as between the imaging variables and the IQCODE, did not differ across language-ethnic groups.

Activities of Daily Living↗

PubMed1999

Structural analysis of phospholipase A2 from functional perspective. 1. Functionally relevant solution structure and roles of the hydrogen-bonding network.

Bovine pancreatic phospholipase A2 (PLA2), a small (13.8 kDa) Ca2+-dependent lipolytic enzyme, is rich in functional and structural character. In an effort to examine its detailed structure-function relationship, we determined its solution structure by multidimensional nuclear magnetic resonance (NMR) spectroscopy at a functionally relevant pH. An ensemble of 20 structures generated has an average root-mean-square deviation (RMSD) of 0.62 +/- 0.08 A for backbone (N, Calpha, C) atoms and 0.98 +/- 0.09 A for all heavy atoms. The overall structure shows several notable differences from the crystal structure: the first three residues at the N-terminus, the calcium-binding loop (Y25-T36), and the surface loop (V63-N72) appear to be flexible; the alpha-helical conformation of helix B (E17-F22) is absent; helix D appears to be shorter (D59-V63 instead of D59-D66); and the hydrogen-bonding network is less defined. These differences were analyzed in relation to the function of PLA2. We then further examined the H-bonding network, because its functional role or even its existence in solution has been in dispute recently. Our results show that part of the H-bonding network (the portion away from N-terminus) clearly exists in solution, as evidenced by direct observation (at 11.1 ppm) of a strong H-bond between Y73 and D99 and an implicated interaction between D99 and H48. Analyses of a series of mutants indicated that the existence of the Y73.D99 H-bond correlates directly with the conformational stability of the mutant. Loss of this H-bond results in a loss of 2-3 kcal/mol in the conformational stability of PLA2. The unequivocal identification and demonstration of the structural importance of a specific hydrogen bond, and the magnitude of its contribution to conformational stability, are uncommon to the best of our knowledge. Our results also suggest that, while the D99.H48 catalytic diad is the key catalytic machinery of PLA2, it also helps to maintain conformational integrity.

Animals↗

PubMed2005

Nitrogen activation via three-coordinate molybdenum complexes: comparison of density functional theory performance with wave function based methods.

Obtaining an accurate theoretical model for the activation of dinitrogen by three-coordinate molybdenum amide complexes (e.g. Mo(NH2)3) is difficult due to the interaction of various high- and low-spin open-shell complexes along the reaction coordinate which must be treated with comparable levels of accuracy in order to obtain reasonable potential energy surfaces. Density functional theory with present-day functionals is a popular choice in this situation; however, the dinitrogen activation reaction energetics vary substantially with the choice of functional. An assessment of the reaction using specialized wave function based methods indicates that although current density functionals in general agree qualitatively on the mechanistic details of the reaction, a variety of high-level electron correlation methods (including CCSD(T), OD(T), CCSD(2), KS-CCSD(T), and spin-flip CCSD) provide a consistent but slightly different representation of the system.

Journal Article↗

PubMed2005

Comprehensive study of density functional theory based properties for group 14 atoms and functional groups, -XY3 (X = C, Si, Ge, Sn, Pb, Element 114; Y = CH3, H, F, Cl, Br, I, At).

All electron nonrelativistic and relativistic density functional theory calculations at the BP86/QZ4P (Slater type) level are reported for a set of fundamentally useful DFT based reactivity descriptors for group 14 elements (C, Si, Ge, Sn, Pb, Element 114 (abbreviated as Uuq)) and functional groups, -XY3 (X = C, Si, Ge, Sn, Pb, Element 114 (Uuq); Y = CH3, H, F, Cl, Br, I, At); these include electronegativity (chi), chemical hardness (eta), global softness (S), and electrophilicity index (omega). This approach permits an evaluation of the discrepancies in electronegativity scales and associated properties at uniform levels affording a nonempirical analysis for the first time. The vital importance of the spin-orbit interaction, in addition to the scalar relativistic terms, is demonstrated in reproducing the experimental trends on going from top to bottom of the group. The order for isolated atoms is altered when passing to -XY3 groups for all of the properties studied. For example, the calculated atomic electronegativities show a uniform decrease from C to Pb increasing again to Uuq as verified in the experimental data for C-Pb but at variance with several other scales. The sequence for functional groups is different and in accordance with experimental NMR data where available. The experimental hardness sequence for the isolated atoms (C > Pb > Si > Ge > Sn) is opposed to the trends of decreasing hardness on going down the periodic table as is found, e.g., in the halogen group and confirmed by this study. The -XY3 functional groups however follow the C > Si > Ge > Sn > Pb sequence. The recently developed electrophilicity index (omega) has been shown to be highly correlated with the electron affinity rather than the electronegativity. Finally, regression analyses that discriminate between the properties are carried out to investigate the nature of additivity of atomic contributions in functional group properties.

Journal Article↗

PubMed2006

Interactions of hydrogen with Pd and Pd/Ni alloy chain-functionalized single walled carbon nanotubes from density functional theory.

Density functional theory is employed to study Pd and Pd/Ni alloy monatomic chain-functionalized metallic single walled carbon nanotubes (SWNT(6,6)) and semiconducting SWNT(10,0), and their interactions with hydrogen molecules. The stable geometries and binding energies have been determined for both isolated chains and chains on SWNT surfaces. We found that continuous Pd and Pd/Ni chains form on SWNTs with geometries close to stable geometries in the isolated chains. Ni alloying improves stability of the chains owing to a higher binding energy to both Pd and C atoms. The physical properties of SWNTs are significantly modified by chain functionalization. SWNT(10,0) is transformed to metal by either Pd or alloy chains, or to a smaller band gap semiconductor, depending on the Pd binding site. From calculations for H(2) interactions with the optimized chain-SWNT systems, the adsorption energy per H atom is found to be about 2.6 times larger for Pd/Ni chain-functionalized SWNTs than for pure Pd chain-functionalized SWNTs. Band structure calculations show that the SWNT(10,0) reverts back to semiconductor and SWNT(6,6) has reduced density of states at the Fermi level upon H(2) adsorption. This result is consistent with the experimentally observed increase of electrical resistance when Pd-coated SWNTs are used as H(2) sensing materials. Finally, our results suggest that Pd/Ni-SWNT materials are potentially good H(2)-sensing materials.

Journal Article↗