Biomedical subjects

Paul S Weiss

Publications and source records attributed to Paul S Weiss.

At least 19 recordsLinked to original sources

PubMed2006

Tuning interactions between ligands in self-assembled double-decker phthalocyanine arrays.

Lanthanide double-decker (DD) complexes represent an interesting system to engineer intermolecular interactions at different distances from the surface. Such atomic-level understanding and control are crucial for the development of molecular devices with three-dimensional complexity. We herein demonstrate an example of how the surface arrangements of DD molecules are influenced by varying intermolecular interactions. By varying the size of a ligand, we observed significant expansion of the lattice even though the top ligands of DD molecules remain too small to interact directly with each other. We also demonstrate that DD molecules in different local environments adopt significantly different structures. Such structures suggest that subtle interactions exist between the top ligand of one molecule and the bottom ligands of its neighbors.

Journal Article↗

PubMed2006

Directed assembly and separation of self-assembled monolayers via electrochemical processing.

Separated domains of 1-dodecanethiolate were fabricated via solution displacement of preformed 1-adamantanethiolate self-assembled monolayers on Au{111}. Subsequently, the 1-adamantanethiolate domains were desorbed selectively, and the substrate was exposed to a 1-octanethiol solution, creating artificially separated self-assembled monolayers of 1-dodecanethiolate and 1-octanethiolate. The molecular order of each lattice type and the apparent height differences imaged with scanning tunneling microscopy and the two distinct cathodic peaks observed with cyclic voltammetry indicated distinct separated domains of each lattice type in the separated self-assembled monolayers. By manipulating the intermolecular interaction strengths of the patterned molecules, we are able to control the structure and properties of the separated self-assembled monolayers via the exploitation of competitive adsorption and the utilization of electrochemical processing, which can be extended to other self-assembly patterning techniques such as microdisplacement printing.

Adamantane↗

PubMed2006

Spectral diffusion in the tunneling spectra of ligand-stabilized undecagold clusters.

We report diffusion in the tunneling spectra of isolated, ligand-stabilized undecagold (Au11) clusters immobilized by attachment to alpha,omega-alkanedithiolate tethers inserted into alkanethiolate self-assembled monolayers. We use scanning tunneling microscopy and spectroscopy at cryogenic (UHV, 4 K) conditions to measure these clusters' conductance with complete control of their chemical and physical environment; additionally, thermal broadening of their electronic states as well as their mobility is minimized. At low temperature, the Au11 clusters demonstrate Coulomb blockade behavior, with zero-conductance gaps resulting from quantum size effects. Surprisingly, chemically identical and even single particles produced different families of tunneling spectra, comparable to previous results for heterogeneous distributions of particles. We hypothesize that, while these particles are chemically attached to the surface of the SAM for measurement, these assemblies may still be sufficiently dynamic to affect their transport properties significantly.

Journal Article↗

PubMed2006

Associations between olfactory identification and verbal memory in patients with schizophrenia, first-degree relatives, and non-psychiatric controls.

OBJECTIVE: Olfactory identification deficits and verbal memory impairments may represent trait markers for schizophrenia. The aims of this study were to: (1) assess olfactory identification in patients, first-degree relatives, and non-psychiatric controls, (2) determine differences in verbal memory functioning in these three groups, and (3) study correlations between olfactory identification and three specific verbal memory domains. METHOD: A total of 106 participants-41 patients with schizophrenia or related disorders, 27 relatives, and 38 controls-were assessed with the University of Pennsylvania Smell Identification Test (UPSIT) and the Wechsler Memory Scale-Third Edition. Linear mixed models, accounting for clustering within families and relevant covariates, were used to compare scores across groups and to examine associations between olfactory identification ability and the three verbal memory domains. RESULTS: A group effect was apparent for all four measures, and relatives scored midway between patients and controls on all three memory domains. UPSIT scores were significantly correlated with all three forms of verbal memory. Age, verbal working memory, and auditory recognition delayed memory were independently predictive of UPSIT scores. CONCLUSIONS: Impairments in olfactory identification and verbal memory appear to represent two correlated risk markers for schizophrenia, and frontal-temporal deficits likely account for both impairments.

Adult↗

PubMed2006

Dynamics and spectroscopy of hydrogen atoms on Pd{111}.

Chemisorption of hydrogen on Pd{111} is a relatively simple, yet important surface chemical process. By using low-temperature scanning tunneling microscopy, tip-induced motion of adsorbed atomic hydrogen at 4 K has been observed at low coverage. The motion has been ascribed to excitation of vibrational modes that decay into translational modes; vibrational spectroscopy via inelastic electron tunneling corroborates this assignment, and the barrier to hydrogen atom motion has been determined. At higher coverages, tip-induced motion of vacancies in the hydrogen overlayer is observed, and the associated barrier has also been determined.

Journal Article↗

PubMed2006

A physical model of axonal damage due to oxidative stress.

Oxidative damage is implicated in the pathogenesis of neurodegenerative disorders, including Alzheimer's, Parkinson's, and Huntington's diseases, and in normal aging. Here, we model oxidative stress in neurons using photogenerated radicals in a simplified membrane-encapsulated microtubule system. Using fluorescence and differential interference contrast microscopies, we monitor photochemically induced microtubule breakdown on the supported region of membrane in encapsulating synthetic liposomes as a function of lipid composition and environment. Degradation of vesicle-encapsulated microtubules is caused by attack from free radicals formed upon UV excitation of the lipid-soluble fluorescent probe, 6-(9-anthroyloxy)stearic acid. Probe concentration was typically limited to a regime in which microtubule degradation was slow, and microtubule degradation was monitored by changes in the observed protrusion of the membrane surface. The kinetics of microtubule degradation are influenced by lipid saturation level, fluorescent probe concentration, and the presence of free-radical scavengers. This system is sufficient to reproduce some degenerative morphologies found in vivo.

Axons↗

PubMed2006

Molecular engineering and measurements to test hypothesized mechanisms in single molecule conductance switching.

Six customized phenylene-ethynylene-based oligomers have been studied for their electronic properties using scanning tunneling microscopy to test hypothesized mechanisms of stochastic conductance switching. Previously suggested mechanisms include functional group reduction, functional group rotation, backbone ring rotation, neighboring molecule interactions, bond fluctuations, and hybridization changes. Here, we test these hypotheses experimentally by varying the molecular designs of the switches; the ability of the molecules to switch via each hypothetical mechanism is selectively engineered into or out of each molecule. We conclude that hybridization changes at the molecule-surface interface are responsible for the switching we observe.

Journal Article↗

PubMed2006

Double-ink dip-pen nanolithography studies elucidate molecular transport.

We have investigated the transport mechanism of the inks most typically used in dip-pen nanolithography by patterning both 16-mercaptohexadecanoic acid (MHDA) and 1-octadecanethiol (ODT) on the same Au{111} substrate. Several pattern geometries were used to probe ink transport from the tip to the sample during patterning of both dots (stationary tip) and lines (moving tip). When ODT was written on top of a pre-existing MHDA structure, the ODT was observed at the outsides of the MHDA structure, and the transport rate increased. In the reverse case, the MHDA was also observed on the outsides of the previously patterned ODT features; however, the transport rate was reduced. Furthermore, the shapes of pre-existing patterns of one ink were not changed by deposition of the other ink. These results highlight the important role hydrophobicity plays, both of the substrate as well as of the inks, in determining transport properties and thereby patterns produced in dip-pen nanolithography.

Journal Article↗

PubMed2006

Two-dimensional crystal growth and stacking of bis(phthalocyaninato) rare earth sandwich complexes at the 1-phenyloctane/graphite interface.

Initial stages of two-dimensional crystal growth of the double-decker sandwich complex Lu(Pc*)2 [Pc* = 2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyaninato] have been studied by scanning tunneling microscopy at the liquid/solid interface between 1-phenyloctane and highly oriented pyrolytic graphite. High-resolution images strongly suggest alignment of the double-decker molecules into monolayers with the phthalocyanine rings parallel to the surface. Domains were observed with either hexagonal or quadrate packing motifs, and the growing interface of the layer was imaged. Molecular resolution was achieved, and the face of the phthalocyanine rings appeared as somewhat diffuse circular features. The alkyl chains are proposed to be interdigitating to maintain planar side-by-side packing.

Journal Article↗

PubMed2006

Determinants of health plan membership among patients in routine U.S. psychiatric practice.

This study utilized a large clinical dataset of patients representative of those in routine U.S. psychiatric practice to assess the influence of sociodemographic variables and diagnostic class on health plan membership (public or private). Data on patients with schizophrenia or other psychotic disorders (n=288) and patients with mood or anxiety disorders (n=1304) were obtained from a cross-sectional practice-based survey conducted by the American Psychiatric Institute for Research and Education. The likelihood of health plan membership was lower among males and among those from a minority race/ethnicity. Health plan membership was also affected by educational attainment and employment status. Even after controlling for these sociodemographic determinants of health plan membership, individuals with schizophrenia/other psychotic disorders were significantly less likely to belong to a health plan than those with mood/anxiety disorders.

Adult↗

PubMed2006

Pilot normative database for the Wolf Motor Function Test.

OBJECTIVE: To gather initial data on the Wolf Motor Function Test (WMFT) from able-bodied participants. DESIGN: Cross-sectional cohort study. SETTING: Clinical research laboratory. PARTICIPANTS: A convenience sample of 51 healthy able-bodied, right-hand dominant, adult participants, between the ages of 40 and 79 years. INTERVENTION: One-time administration of the WMFT. MAIN OUTCOME MEASURE: The WMFT. RESULTS: Mean data are presented for all timed and strength tasks. For timed tasks on the WMFT, there were no significant differences among subjects for hand or sex nor was there a hand by sex interaction. Men were significantly stronger than women on the 2 strength tasks, however. CONCLUSIONS: We provide preliminary normative data for the WMFT. More data are needed to produce precise estimates of norms and to explore relations among sex, age, and hand dominance.

Adult↗

PubMed2005

Transport rates vary with deposition time in dip-pen nanolithography.

By patterning with dip-pen nanolithography using tip dwell times ranging from 15 s to 2 h over a period of 19 h, we show that the transport rate for smaller patterns is different than for larger ones. This transport behavior is found for both 1-octadecanethiol (ODT) and 16-mercaptohexadecanoic acid (MHDA) inks on gold substrates. Additionally, MHDA shows an overall decrease in transport rate as a function of total writing time during such experiments. These results indicate that measurements with short dwell times are insufficient to determine transport rates for larger features.

Journal Article↗

PubMed2005

Molecular engineering of the polarity and interactions of molecular electronic switches.

We have investigated and learned to control switching of oligo(phenylene ethynylene)s embedded in amide-containing alkanethiol self-assembled monolayers on Au{111}. We demonstrate bias-dependent switching of the oligo(phenylene ethynylene)s as a function of the interaction between the dipole moment of the oligo(phenylene ethynylene)s and the electric field applied between the scanning tunneling microscope tip and the substrate. We are able to invert the polarity of the switches by altering their design-inverting their dipole moments. For appropriately designed switches and matrix molecules, the conductance states are stabilized by intermolecular hydrogen bonding. These results further support the hypothesis that conductance switching in these molecules is due to hybridization changes at the molecule-substrate bonds due to tilting of the switch molecules.

Journal Article↗

PubMed2005

Observation and manipulation of subsurface hydride in Pd[111] and its effect on surface chemical, physical, and electronic properties.

We report the observation and manipulation of hydrogen atoms beneath the surface of a Pd[111] crystal by using low-temperature scanning tunneling microscopy. These subsurface hydride sites have been postulated to have critical roles in hydrogen storage, metal embrittlement, fuel cells, and catalytic reactions, but they have been neither observed directly nor selectively populated previously. We demonstrate that the subsurface region of Pd can be populated with hydrogen atoms from the bulk by applying voltage pulses from a scanning tunneling microscope tip. This phenomenon is explained with an inelastic excitation mechanism, whereby hydrogen atoms in the bulk are excited by tunneling electrons and are promoted to more stable sites in the subsurface region. We show that this selectively placed subsurface hydride affects the electronic, geometric, and chemical properties of the surface. Specifically, we observed the effects of hydride formation on surface deformation and charge and on adsorbed hydrogen on the surface. Hydrogen segregation and overlayer vacancy ordering on the Pd[111] have been characterized and explained in terms of the surface changes attributable to selective hydrogen occupation of subsurface hydride sites in Pd[111].

Journal Article↗

PubMed2005

Heat-stabilized phospholipid films: film characterization and the production of protein-resistant surfaces.

Phospholipid films have been shown in a number of studies to exhibit potential as nonfouling surfaces for biomaterial applications. However, the practical application of such films has been hindered by instability in aqueous solutions and significant detachment under mild shear stresses. Methods for stabilizing lipid films have been investigated, but to date require the presence of specific functional groups or chemical modification of the lipid molecule. In contrast to these methods, we present a process for heat-stabilization of lipid films. These heat-stabilized films have been shown to be able to withstand repeated rinsing without significant detachment. Phosphatidylcholine monolayers were formed on hydrophobic self-assembled monolayers using the liposome fusion method and stabilized at 80 degrees C. The films were characterized using Fourier transform infrared spectroscopy, ellipsometry, and atomic force microscopy and were shown to be defect free after repeated rinsing. Further experiments using a quartz crystal microbalance showed that the heat-stabilized lipid films were highly resistant to nonspecific protein adhesion and compared very favorably with poly(ethylene glycol)-coated surfaces under identical exposure conditions.

Adsorption↗

PubMed2005

Relative conductances of alkaneselenolate and alkanethiolate monolayers on Au{111}.

The electronic properties of alkanethiolate [CH3(CH2)nS-, n = 9 and 11] and alkaneselenolate [CH3(CH2)nSe-, n = 9 and 11] self-assembled monolayers on Au{111} have been quantitatively compared. Simultaneously acquired apparent tunneling barrier height (ATBH) and scanning tunneling microscopy (STM) images reveal that alkanethiolate molecules have a lower barrier to tunneling, and therefore a higher conductance than alkaneselenolates of the same alkyl chain length. Molecular and contact conductance differences were elucidated by using observed STM topographic tunneling height differences between the analogous species. This apparent topographic difference combined with comparative ATBH data indicate that the observed decrease in conductance for alkaneselenolates compared to alkanethiolates originates exclusively from the Au-chalcogenide physical, chemical, and electronic contact.

Journal Article↗

PubMed2005

The associations between substance use disorders, schizophrenia-spectrum disorders, and Axis IV psychosocial problems.

BACKGROUND: Substance abuse among individuals with schizophrenia-spectrum disorders (SSDs) is associated with a range of adverse psychosocial outcomes in the areas of occupational functioning, housing stability, economic independence, access to health care, and involvement with the legal system. The aim of this study was to estimate the effects of substance use disorders (SUDs), SSDS, and dual diagnosis with both disorders on the risk for six important Axis IV psychosocial problems. This was accomplished using a large dataset of patients who are representative of individuals in routine US psychiatric practice. METHOD: Weighted data from the 1999 Study of Psychiatric Patients and Treatments from a practice-based research network of the American Psychiatric Institute for Research and Education were analyzed. Some 615 US psychiatrists provided detailed clinical, psychosocial, and health services information on 1,843 patients, including 285 patients with one or more SUDs without an SSD, 180 patients with a diagnosis of an SSD without substance abuse comorbidity, and 68 dually diagnosed patients. Logistic regression models were used to determine effect estimates (adjusted odds ratios), and corresponding 95% confidence intervals were calculated. RESULTS: After adjusting for sociodemographic variables and for SSD diagnosis, SUD diagnosis was independently associated with increased risk for five of the Axis IV psychosocial problems of interest (occupational problems, housing problems, economic problems, problems with access to health care services, and problems related to interaction with the legal system/crime) when compared to all other psychiatric patients (n=1,310). After adjusting for the sociodemographic variables and for SUD diagnosis, SSD diagnosis (compared to all other psychiatric diagnoses) was associated with Axis IV economic problems, but not with the other five psychosocial problems of interest. The presence of both an SUD and an SSD diagnosis (dual diagnosis) was associated with a greater risk for four of the six Axis IV psychosocial problems studied, compared to the risks associated with either diagnosis alone. Limiting the substance of abuse to alcohol resulted in similar findings. CONCLUSIONS: Although SUDs are associated with increased risk for poor social adjustment, the comorbidity of SUDs and SSDs is associated with greatly compounded psychosocial burdens. These findings, from a large sample of representative US psychiatric patients, demonstrate the ongoing need for improved services and policies for those specially burdened patients with the dual diagnosis of both an SSD and substance abuse or dependence.

Adult↗

PubMed2005

Predictors of psychiatrist-reported treatment-compliance problems among patients in routine U.S. psychiatric care.

Characteristics associated with psychiatrist-reported treatment-compliance problems were investigated using the 1999 Study of Psychiatric Patients and Treatments from the Practice Research Network of the American Psychiatric Institute for Research and Education (n=1,843). Logistic regression was used to study characteristics associated with compliance problems as perceived by treating psychiatrists. Among the 22 potential predictors of interest, all but three (age, gender, and problems with primary support group) were found to be significantly associated with treatment-compliance problems in bivariate analyses. A predictive model was developed consisting of eight independently significant predictors from diagnostic, clinical, psychosocial, and treatment-history domains. These predictors included substance use disorder diagnosis, medication side effects, moderate to severe psychotic symptoms, personality disorder diagnosis, economic problems, prior hospitalization, current Global Assessment of Functioning scale score, and duration of treatment with current psychiatrist. This predictive model correctly identified the presence or absence of treatment-compliance problems in 91% of patients in a sample randomly drawn from the dataset before model construction. These findings may be useful to clinicians, researchers, and program planners interested in addressing the important issue of treatment-compliance problems in psychiatric care settings.

Adult↗