Biomedical subjects

Dennis W Smith

Publications and source records attributed to Dennis W Smith.

14 recordsLinked to original sources

PubMed2006

Synthesis and electronic factors in thermal cyclodimerization of functionalized aromatic trifluorovinyl ethers.

A series of 19 p-substituted aromatic trifluorovinyl ether compounds were prepared from versatile intermediate p-Br-C(6)H(4)-O-CF=CF(2) and underwent thermal radical mediated cyclodimerization to new difunctional compounds containing the 1,2-disubstituted perfluorocyclobutyl (PFCB) linkage. The synthetic scope demonstrates the functional group transformation tolerance of the fluorovinyl ether, and the dimers are useful as monomers for traditional step-growth polymerization methods. (19)F NMR spectra confirmed that p-substitution affects the trifluorovinyl ether group chemical shifts. The first kinetic studies and substituent effects on thermal cyclodimerization were performed, and the results indicated that electron-withdrawing groups slow the rate of cyclodimerization. The data were further analyzed using the Hammett equation, and reaction constants (rho) of -0.46 at 120 degrees C and -0.59 at 130 degrees C were calculated. This study presents the first liner free energy relationship reported for the cyclodimerization of aromatic trifluorovinyl ethers to PFCB compounds.

Journal Article↗

PubMed2006

Seasonal variations in the initiation of smoking among adolescents.

Numerous studies have identified a variety of reasons that youths give for starting smoking. Few efforts have been made, however, to identify seasonal variations in initiation. This study was an attempt to fill that void. We examined data from 342 youths participating in a mandated smoking education and cessation program in Texas. Data were collected based on responses to questions in participant workbooks, including an item asking participants about the month in which they started smoking. A total of 47% of the participants indicated that they started smoking in May through August (chi2 = 91.42, df = 3). Post-hoc analyses indicated that significantly more youths than expected began smoking in May and June, whereas significantly fewer youths than expected began smoking in September and November. Unsupervised time out of school during the first months of summer vacation is a period of increased danger for smoking initiation. The significantly lower rates during September seem to be related to the beginning of school.

Activities of Daily Living↗

PubMed2005

An exploration of self-reported negative affect by adolescents as a reason for smoking: implications for tobacco prevention and intervention programs.

BACKGROUND: Negative affect is related to initiation and maintenance of smoking among youth and understanding its role is important when developing effective prevention and cessation programs. This study investigates the relationship between adolescent negative affect and smoking dependence, behaviors, attitudes, and self-efficacy in order to shed light on differences in adolescent smoking maintenance and cessation. METHODS: 721 smoking youth participated in a cognitive-behavioral smoking cessation program. Reasons for smoking were categorized (alpha = 0.87) and youth were placed into one of two groups based on presence or absence of negative affect. One-way repeated measures ANOVA determined if differences existed between the groups on smoking behaviors, attitudes, and self-efficacy. One-way ANOVA determined if differences existed on Fagerström Nicotine Tolerance Dependence (FTND) scores. RESULTS: Adolescents indicating negative affect for smoking were significantly more likely to have future smoking intentions and had significantly less self-efficacy to quit smoking than adolescent reporting other reasons. CONCLUSIONS: This study supports the need to address negative affect among adolescents participating in prevention and cessation programs. An examination of negative affect will provide program developers and facilitators with information to improve their interventions, assist with cessation, and provide an avenue to access other needed health services.

Adolescent↗

PubMed2004

Perfluorocyclobutyl-linked hexa-peri-hexabenzocoronene networks.

Hexa-peri-hexabenzocoronene (HBC) derivatives possess many interesting properties ranging from liquid crystallinity, to hole transport, to variable emission behavior, yet are plagued by insolubility and general accessibility of polymerizable substituents. The first synthesis of trifluorovinyl ether-substituted hexabenzocoronene and its polymerization to perfluorocyclobutyl (PFCB) polymers and copolymers is shown. Unlike hydrocarbon ethers, fluoro vinyl ethers are stable under HBC oxidation conditions. Discrete HBC units in PFCB polymers provide access to potentially processable HBC optical materials.

Journal Article↗

PubMed2004

In situ EPR spectroscopy of aromatic diyne cyclopolymerization.

Electron paramagnetic resonance (EPR) spectroscopy was successfully used for the first time to follow the Bergman cyclization of bis-ortho-diynyl arene (BODA) compounds. Five BODA monomers with different spacer (X) and terminal groups (R) were compared. In situ polymerization via EPR spectroscopy yielded first-order rate expressions. Monomers with spacer -O- or -C(CF(3))(2) and terminal group R = Ph exhibited similar kinetic behavior upon thermal polymerization, whereas monomers with pyridine and thiophene terminal groups gave significantly higher rates of polymerization over phenyl-terminated derivatives. A model compound, 1,2-bis(phenylethynyl)benzene, was used to probe the polymerization mechanism, and radical intermediates were found to be stable indefinitely at room temperature.

Journal Article↗

PubMed2004

Amido-modified polylactide for potential tissue engineering applications.

Poly(ester amide) copolymers based on L-lactide (2) and a new depsipeptide (1) were prepared by ring opening polymerization in the presence of Sn(Oct)2 as the catalyst. Variable monomer feed ratios up to 2.3 mol% 1 afforded copolymers containing ester and amido functional groups in the backbone. Lower glass transition temperatures and reduced crystallization kinetics and crystallinity compared to homo-polylactide (PLA) was achieved with low levels of amido incorporation. A reactivity comparison between enchainment of 2 and 1 was determined using in situ infrared spectroscopy. An increase in shear viscosity was observed with the increase of 1 content as determined by rheology studies. Cellular compatibility of the co-polymers was investigated by seeding D1 mouse stem cells onto films and characterizing cell morphology by optical microscopy. Preliminary results indicate that these novel materials exhibit reduced cell attachment compared to PLA and, pending further exploration, may have potential use in biomedical applications.

Animals↗

PubMed2004

Novel fluoropolymer functionalized silsesquioxanes for nanoscale architecture of hybrid composites.

Condensation of octa(aminophenyl)silsesquioxane with 4-(trifluorovinyloxy)benzoyl chloride affords new fluoroolefin functionalized silsesquioxanes in good yield. The new octa-trifluorovinyl functionalized monomer undergoes thermal copolymerization with established trifluorovinyl aryl ether terminated perfluorocyclobutyl (PFCB) oligomers, giving the first example of silsesquioxane functionalized PFCB materials. The new hybrid polymers offer a versatile building block toward a variety of nanocomposite applications including low loss photonics.

Aniline Compounds↗

PubMed2004

Importance of tobacco cessation services at higher education public institutions in Texas.

While rates of tobacco use on university campuses rose over the past decade, little is known about what institutions are doing to address this rising concern. Health center directors at public institutions of higher education across the state of Texas were surveyed (n = 42) regarding the perceived importance of smoking cessation, prevalence of interventions on their campuses, and perceived success of intervening efforts. While most health center directors regarded smoking cessation as important, over half of the directors indicated that their sites did not offer tobacco cessation services of any kind. Furthermore, of those offering smoking cessation, most believed that their smoking cessation programs were only somewhat or not at all effective. Findings revealed that there is a noticeable gap between perceived importance and actual implementation of smoking cessation programs within university-based health centers. Recommendations include implementing innovative cessation methods, such as those that are Web-based and highly accessible to students.

Adolescent↗

PubMed2003

Use of sol-gels as solid matrixes for simultaneous multielement determination by radio frequency glow discharge optical emission spectrometry: determinations of suspended particulate matter.

A new approach for the analysis of particulate matter by radio frequency glow discharge optical emission spectrometry (rf-GD-OES) is described. Dispersion of the particles in a sol-gel sample matrix provides a convenient means of generating a thin film suitable for sputter-sampling into the discharge. Acid-catalyzed sol-gel glasses synthesized from tetramethyl orthosilicate were prepared and spun-cast on glass substrates. The resultant thin films on glass substrates were analyzed to determine the discharge operating conditions and resultant sputtering characteristics while a number of optical emission lines of the film components were monitored. Slurries of powdered standard reference materials NIST SRM 1884a (Portland Cement) and NIST SRM 2690 (Coal Fly Ash) dispersed in the sols were cast into films in the same manner. Use of the sol-gels as sample matrixes allows for background subtraction through the use of analytical blanks and may facilitate the generation of calibration curves via readily synthesized, matrix-matched analytical standards in solids analysis. Detection limits were determined for minor elements via the RSDB method to be in the range of 1-10 microg/g in Portland Cement and Coal Fly Ash samples for the elements Al, Fe, Mg, S, and Si. Values for Ca were in the range of 15-35 microg/g. This preliminary study demonstrates the possibility of incorporating various insoluble species, including ceramics and geological specimens in powder form, into a solid matrix for further analysis by either rf-GD-OES or MS.

Journal Article↗

PubMed2003

Three bis-ortho-diynylarenes (BODA).

The molecule of 3,3',4,4'-tetrakis(phenylethynyl)biphenyl, C(44)H(26), is approximately planar and is located on a crystallographic inversion center. Bis[3,4-bis(phenylethynyl)phenyl] ether, C(44)H(26)O, has molecules located on twofold symmetry axes, whereas the molecule of 2,2-bis[3,4-bis(phenylethynyl)phenyl]propane, C(47)H(32), does not exhibit any molecular symmetry.

Journal Article↗

PubMed2003

Differences in evaluations of a tobacco awareness and cessation program by adolescents in four stages of change.

This study determined whether adolescents in four stages of change provided significantly different ratings on evaluations of a tobacco awareness and cessation program and the program facilitators. A systematic sample of 639 adolescents in four stages of change (precontemplation, contemplation, preparation, and action) was used for analysis. Analysis of variance revealed significant differences in ratings on 'Cessation Skills,' 'Situation Management,' 'Overall Facilitator,' and 'Facilitator Likeability' evaluations between the groups. Follow-up analysis revealed that adolescent precontemplators provided significantly lower ratings than those in preparation and action, and adolescents in action provided significantly higher ratings than precontemplators and contemplators. This study suggests a need to assess the stage of the adolescent at the beginning of the program in order to provide the facilitator the opportunity to engage and motivate adolescents who are in the precontemplation and contemplation stage of change. This study also provides important information for facilitator training, program planning, and program delivery.

Adolescent↗

PubMed2002

Tobacco use and quit behaviors among delinquent youth: a pilot study.

With rates of adolescent tobacco use steadily increasing over the past 20 years, assisting youth to quit, particularly those youth most susceptible to tobacco use, has become a national focus. The purpose of this pilot study was to examine and profile the smoking patterns of a small sample (n = 37) of juvenile offenders in Texas. In contrast to anecdotal reports, the sample group from this study did not differ clinically from the general population of adolescent tobacco users. Importantly, the study participants indicated previous attempts to stop smoking. The authors conclude that delinquent youth may be responsive to cognitive behavioral smoking cessation programs that also address the management of peer networks.

Adolescent↗

PubMedDate not supplied

Keeping all children healthy: challenges to leading an active lifestyle for preschool children qualifying for at-risk programs.

This study examined contextual factors associated with physical activity of urban African American preschoolers (N = 59). Qualitative research methodologies utilized data from home visits, caregiver and child interviews, field notes, and document collection. The primary finding suggested, "In underserved communities fundamental barriers exist that obstruct young children's ability to be physically active." Four themes were developed revealing that outside environments limited opportunities for physical activity, home environments resulted in sedentary behaviors, and communities had limited physical activity role models. Despite this, young children enjoyed being physically active.

Black or African American↗

PubMedDate not supplied

Theory-based development and testing of an adolescent tobacco-use awareness program.

OBJECTIVE: To develop and disseminate an effective tobacco awareness and cessation program. METHODS: Self-report data from youth (n=1,601) and implementation data from site facilitators (n=16) provided the basis for the trial program evaluation. RESULTS: Approximately 146 total classes and 1,601 youth were served. Significantly (p<.01) more participants were in the action stage of change at the end of the program. At follow-up, 40% of the participants indicated they were tobacco free. CONCLUSION: The multiple iterative steps in program development were described. A theoretically based program, like the ATCP, is well worth exploring as a public health intervention.

Adolescent↗