Scopus İndeksli Yayınlar Koleksiyonu

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Citation - WoS: 21
Citation - Scopus: 31
Adoption of Mobile Health Apps in Dietetic Practice: Case Study of Diyetkolik
(Jmır Publıcatıons, Inc, 130 Queens Quay E, 2020) Akdur, Görkem; Aydın, Mehmet Nafiz; Akdur, Gizdem
Background: Dietetics mobile health apps provide lifestyle tracking and support on demand. Mobile health has become a new trend for health service providers through which they have been shifting their services from clinical consultations to online apps. These apps usually offer basic features at no cost and charge a premium for advanced features. Although diet apps are now more common and have a larger user base, in general, there is a gap in literature addressing why users intend to use diet apps. We used Diyetkolik, Turkey's most widely used online dietetics platform for 7 years, as a case study to understand the behavioral intentions of users. Objective: The aim of this study was to investigate the factors that influence the behavioral intentions of users to adopt and use mobile health apps. We used the Technology Acceptance Model and extended it by exploring other factors such as price-value, perceived risk, and trust factors in order to assess the technology acceptance of users. Methods: We conducted quantitative research on the Diyetkolik app users by using random sampling. Valid data samples gathered from 658 app users were analyzed statistically by applying structural equation modeling. Results: Statistical findings suggested that perceived usefulness (P<.001), perceived ease of use (P<.001), trust (P<.001), and price-value (P<.001) had significant relationships with behavioral intention to use. However, no relationship between perceived risk and behavioral intention was found (P=.99). Additionally, there was no statistical significance for age (P=.09), gender (P=.98), or previous app use experience (P=.14) on the intention to use the app. Conclusions: This research is an invaluable addition to Technology Acceptance Model literature. The results indicated that 2 external factors (trust and price-value) in addition to Technology Acceptance Model factors showed statistical relevance with behavioral intention to use and improved our understanding of user acceptance of a mobile health app. The third external factor (perceived risk) did not show any statistical relevance regarding behavioral intention to use. Most users of the Diyetkolik dietetics app were hesitant in purchasing dietitian services online. Users should be frequently reassured about the security of the platform and the authenticity of the platform's dietitians to ensure that users' interactions with the dietitians are based on trust for the platform and the brand.
Citation - WoS: 79
Citation - Scopus: 95
The association of the severity of obstructive sleep apnea with plasma leptin levels
(Amer Medical Assoc., 2003) Öztürk, Levent; Ünal, Murat; Tamer, Lülüfer; Çelikoğlu, Firuz
Objective: To examine whether circulating leptin levels correlate with the severity of disease in patients with obstructive sleep apnea. Design: Prospective nonrandomized study. Setting: Referral sleep laboratory for patients with sleep-disordered breathing and biochemistry laboratory. Patients: Thirty-two subjects (mean+/-SD age 47+/-12 years) who were referred for suspected sleep apnea underwent an overnight sleep study and fasting morning venous blood sampling. Patients were divided into 3 groups with respect to apnea-hypopnea index: (1) severe sleep apnea (n=8) apnea-hypopnea index greater than 20
Citation - WoS: 5
Citation - Scopus: 4
The Availability of Emergency Contraception From Family Health Centers in Turkey
(Elsevier Ireland Ltd, 2022) O'Neil, Mary Lou; Aldanmaz, Bahar; Altuntas, Deniz
Reproductive health care, including contraception, is a fundamental aspect of any public health care system and it is important to reduce barriers to access to all forms of contraception, including emergency contraception. In recent years, the rhetoric of pronatalism in Turkey has come to dominate and raises questions about the availability of reproductive health care services, in particular contraception, from state run facilities. This study aimed to determine the availability of dedicated emergency contraception (EC) from government run Family Health Centers (FHCs) in Turkey. In 2019, a team of trained researchers called a random sample of 583 FHCs located in the largest cities in twelve regions across Turkey asking for dedicated EC. Dedicated EC is largely unavailable from government supported FHCs. Only 6.1% stated that they provided EC while 53.8% stated that it was not available and that they could provide no alternative. A further 28.3% declared that they could provide an alternative to dedicated EC that almost always consisted of oral contraceptives. We found statistically significant variations in response rate and availability among cities as well as the rate of referral to pharmacies. There is little access to EC from government sponsored health clinics designated to provide family planning services, which hinders access to an essential reproductive health care service that should be available to women everywhere.
Citation - WoS: 71
Citation - Scopus: 88
Banking Sector Reactions To Covid-19: the Role of Bank-Specific Factors and Government Policy Responses
(Elsevier, 2021) Demir, Ender; Danisman, Gamze Ozturk
This paper examines the impact of bank-specific factors and variations in the context of stringency of government policy responses on bank stock returns because of the COVID-19 pandemic. A sample of 1,927 publicly listed banks from 110 countries is used for the period of the first major wave of COVID-19, that is, January to May 2020. Our findings indicate that stock returns of banks with higher capitalization and deposits, more diversification, lower non-performing loans, and larger size are more resilient to the pandemic. While banks' environment and governance scores do not have a significant impact, higher social and corporate social responsibility strategy scores intensify the negative stock price reaction to COVID-19. We further observe that the pandemic induced reduction in bank stock prices is mitigated as the strictness of government policy responses increases, mainly through economic responses such as income support, debt and contract relief, and fiscal measures from governments.
Citation - WoS: 3
Citation - Scopus: 3
Beliefs of Living Donors About Recipients' End-Stage Liver Failure and Surgery for Organ Donation
(Elsevier Science Inc, 2017) Krespi-Boothby, Margörit Rita; Tankurt, A.; Acarli, Koray; Kanmaz, Turan; Yankol, Yucel; Kalayoğlu, Murat
Background. The concept of beliefs could provide a basis for how donors may perceive recipients' end-stage liver failure (ESLF) and surgery for organ donation. However there is no such quantitative study. Therefore the objective of this study was to explore beliefs of living donors about recipients' ESLF and surgery for organ donation. Methods. The sample comprised 16 living donors who donated a part of their liver to a patient who had ESLF. The data were analyzed by following established procedures for inductive qualitative analysis. Results. Analysis showed that donors' beliefs can be viewed in a number of groups. Beliefs about recipients' ESLF included diverse explanations for ESLF (blaming oneself and physicians) and physical symptoms (developmental slowing down). Beliefs about being a donor included reasons for being a donor (performing a good deed being healed) barriers to being a donor (other people being ignorant and selfish) ways to manage these barriers (following one's gut feeling) and factors facilitating being a donor (the feeling that one does not have many people to leave behind). Beliefs about surgery for organ donation included physical effects (pain feeling stiff). Beliefs about organ donation included views that general organ donation should be encouraged and that people's awareness should be raised. Conclusions. Existing psychological perspectives could help to interpret some beliefs. Nevertheless other beliefs not previously reported could be considered as targets for individual consultations/psycho-educational programs for fostering emotional well-being.
Citation - WoS: 2
Citation - Scopus: 2
Biased Perceptions Against Female Scientists Affect Intentions To Get Vaccinated for Covid-19
(Sage Publications Ltd, 2022) Dogan, Isminaz; Baruh, Lemi; Cemalcilar, Zeynep; Kuru, Ozan; Yildirim, Kerem; Carkoglu, Ali
Based on role congruity theory, we investigated how gender bias may influence public attitudes toward the vaccine in Turkey. Using a between-subjects design, we tested whether an emphasis on the female versus the male scientist as the vaccine's inventor in a news story influenced attitudes about the BioNTech vaccine and vaccination intentions. Partly confirming role congruity theory, three-way interaction results from 665 participants demonstrated that among male participants with a stronger belief in traditional gender roles (compared to males with lower belief), the presence of the female inventor, either by herself or together with the male inventor, decreased the perceived efficacy and safety of the vaccine and reduced intentions to be vaccinated by the BioNTech vaccine. We did not observe such differences for women. These findings highlight how gender bias may influence individuals' information processing and decision making in a way that may have negative consequences for public health.
Citation - WoS: 1
Citation - Scopus: 2
Can Reflection Mitigate Covid-19 Vaccine Conspiracy Beliefs and Hesitancy
(Routledge, 2025) Bayrak, F.; Kayatepe, E.; Özman, N.; Yilmaz, O.; Isler, O.; Saribay, S.A.
Objective design: Periods of social turmoil, such as the COVID-19 pandemic, tend to amplify conspiracy beliefs, evidenced by increased vaccine hesitancy. Despite this trend, effective interventions targeting vaccine-related conspiracy beliefs remain scarce, partly due to underexplored cognitive processes. Three competing theoretical accounts offer differing predictions about the role of reflective thinking in supporting conspiracy beliefs: the Motivated Reasoning Account suggests reflection strengthens commitment to pre-existing attitudes; the Reflective Reasoning Account posits that reflection enhances belief accuracy; and the Reflective Doubt Account proposes reflection fosters general scepticism. Main outcome measures: Utilising open science practices and a validated technique to activate reflection, we conducted an experimental investigation with a diverse sample (N = 1483) segmented by vaccine attitudes. We investigated the impact of reflection on specific and generic COVID-19 conspiracy beliefs and vaccine-support behaviours across pro-vaccine, neutral, and vaccine-hesitant groups, while examining the moderating effects of scientific literacy, intellectual humility, and actively open-minded thinking. Results: The confirmatory analysis provided no direct support for the theoretical predictions. However, findings indicated that intellectual humility significantly moderated the effect of reflection, enhancing vaccine-support behaviour among participants with high intellectual humility, highlighting the complex interplay of cognitive style and prior attitudes in shaping responses to conspiracy beliefs and vaccine-support actions. Conclusion: The study highlights that while reflective thinking alone did not directly influence vaccine support behavior, its positive effect emerged among individuals with higher intellectual humility, emphasizing the importance of individual differences in shaping belief-related outcomes. © 2025 Informa UK Limited, trading as Taylor & Francis Group.
Citation - Scopus: 1
Children's Questions and Teachers' Responses About Covid-19 in Türkiye and the Us
(Public Library Science, 2024) Unlutabak, Burcu; Trujillo Hernandez, Graciela; Velioglu, Ilayda; Menendez, David; Rosengren, Karl S.
Question-asking is a crucial tool for acquiring information about unseen entities, such as viruses; thus, examining children's questions within the context of COVID-19 is particularly important for understanding children's learning about the coronavirus. The study examined 3-12-year-old children's questions and teachers' responses about the COVID-19 pandemic in T & uuml;rkiye, a non-Western developing context, and the United States, a Western cultural context. A total of 119 teachers from T & uuml;rkiye and 95 teachers from the US participated in the study. Teachers completed an online survey consisting of a demographic form and a questionnaire asking them to report three questions about COVID-19 asked by children in their classrooms and their responses to these questions. We analyzed children's questions and teachers' responses for their type and content and examined demographic factors associated with children's questions and teachers' responses. Consistent with the literature, children from T & uuml;rkiye asked fewer explanation-seeking (i.e., why/how) questions than children from the United States. Children asked questions about viruses and precautions. Teachers responded to children's questions realistically in both countries. The findings have important implications for how children gain knowledge from teachers when discussing health, disease, and virus topics in two countries.
Citation - WoS: 2
Citation - Scopus: 2
Correlated conformational dynamics of the human GluN1-GluN2A type N-methyl-D-aspartate (NMDA) receptor
(SPRINGER, 2021) Esşiz, Şebnem; Gencel, Melis; Aktolun, Muhammed; Demir, Ayhan; Carpenter, Timothy S.; Servili, Burak
N-Methyl-D-aspartate receptors (NMDARs) are glutamate-gated ion channels found in the nerve cell membranes. As a result of overexcitation of NMDARs, neuronal death occurs and may lead to diseases such as epilepsy, stroke, Alzheimer's disease, and Parkinson's disease. In this study, human GluN1- GluN2A type NMDAR structure is modeled based on the X-ray structure of the Xenopus laevis template and missing loops are added by ab-initio loop modeling. The final structure is chosen according to two different model assessment scores. To be able to observe the structural changes upon ligand binding, glycine and glutamate molecules are docked into the corresponding binding sites of the receptor. Subsequently, molecular dynamics simulations of 1.3 mu s are performed for both apo and ligand-bound structures. Structural parameters, which have been considered to show functionally important changes in previous NMDAR studies, are monitored as conformational rulers to understand the dynamics of the conformational changes. Moreover, principal component analysis (PCA) is performed for the equilibrated part of the simulations. From these analyses, the differences in between apo and ligand-bound simulations can be summarized as the following: The girdle right at the beginning of the pore loop, which connects M2 and M3 helices of the ion channel, partially opens. Ligands act like an adhesive for the ligand-binding domain (LBD) by keeping the bi-lobed structure together and consequently this is reflected to the overall dynamics of the protein as an increased correlation of the LBD with especially the amino-terminal domain (ATD) of the protein.
Citation - WoS: 1
Citation - Scopus: 1
Decision Making, Emotion Recognition and Childhood Traumatic Experiences in Murder Convicts Imprisoned With Aggravated Life Sentence: a Prison Study
(Turkish Neuropsychiatry Assoc-Turk Noropsikiyatri Derneği, 2025) Cikrikcili, Ugur; Yildirim, Elif; Buker, Seda; Ger, Can; Erozden, Ozan; Gurvit, Hakan; Saydam, Bilgin
Introduction: Decision-making and emotion recognition are two fundamental themes in social cognition. Disorders in these areas can lead to interpersonal, psychosocial, and legal problems for the individual and society. The likelihood of consequent aggression and crime makes them foci of forensic psychiatry over time. In this study, two developmental disorders that have a clear relationship with crime, that are antisocial personality disorder (ASPD), and psychopathy are investigated for their relationship with these social cognitive deficits. Methods: The present study involved 23 male prison inmates who were diagnosed with both antisocial personality disorder and psychopathy, as well as 23 control participants who were matched for age, gender, and level of education. Following the psychiatric interview, Reading the Mind in the Eyes Test (RMET), the Iowa Gambling Test (IGT), Toronto Alexithymia Scale (TAS), Defense Styles Questionnaire (DSQ), Childhood Psychic Trauma Scale (CTQ), Hare Psychopathy Checklist (PCL-R) were administered to all participants. Results: The results of the study showed that ASPD group performed statistically worse than healthy controls in TAS, CTQ, all items of DSQ, PCL-R Factor 1 and 2, and all the IGT scores (p<0.05). There were no statistically significant difference between in the RMETtest performances Conclusion: These results suggest that ASPD and psychopathy lead to impaired decision-making behaviors due to the inability to recognize one's own emotions and impulsivity, and that these characteristics play a critical role in the criminal behavior of individuals. In addition, contrary to expectations, the results of affective theory of mind assessed with the RMET showed similar characteristics in homicide convicts and healthy controls. These data indicate the need for further research in the field of forensic psychiatry.
Citation - WoS: 2
Citation - Scopus: 2
Design, Synthesis, Molecular Modeling, and Bioactivity Evaluation of 1,10-Phenanthroline and Prodigiosin (ps) Derivatives and Their Copper(i) Complexes Against Mtor and Hdac Enzymes as Highly Potent and Effective New Anticancer Therapeutic Drugs
(Frontiers Media Sa, 2022) Cetin, M. Mustafa; Peng, Wenjing; Unruh, Daniel; Mayer, Michael F.; Mechref, Yehia; Yelekci, Kemal
Breast cancer is the second type of cancer with a high probability of brain metastasis and has always been one of the main problems of breast cancer research due to the lack of effective treatment methods. Demand for developing an effective drug against breast cancer brain metastasis and finding molecular mechanisms that play a role in effective treatment are gradually increasing. However, there is no effective anticancer therapeutic drug or treatment method specific to breast cancer, in particular, for patients with a high risk of brain metastases. It is known that mTOR and HDAC enzymes play essential roles in the development of breast cancer brain metastasis. Therefore, it is vital to develop some new drugs and conduct studies toward the inhibition of these enzymes that might be a possible solution to treat breast cancer brain metastasis. In this study, a series of 1,10-phenanthroline and Prodigiosin derivatives consisting of their copper(I) complexes have been synthesized and characterized. Their biological activities were tested in vitro on six different cell lines (including the normal cell line). To obtain additional parallel validations of the experimental data, some in silico modeling studies were carried out with mTOR and HDAC1 enzymes, which are very crucial drug targets, to discover novel and potent drugs for breast cancer and related brain metastases disease.
Citation - WoS: 36
Citation - Scopus: 49
Does off-pump CAPG reduce gastrointestinal complications?
(Elsevier Science Inc, 2004) Sanisoğlu, İlhan; Güden, Mustafa; Bayramoğlu, Zehra; Sağbaş, Ertan; Dibekoğlu, Cengiz; Sanisoğlu, S. Yavuz; Akpınar, Belhhan
Background. The aim of this study was to compare gastrointestinal complications and associated risk factors among patients undergoing cardiac surgery using off- and on-pump revascularization techniques. Methods. A total of 1146 adult patients who underwent coronary artery surgery during a 6-year period were evaluated retrospectively. Group 1 consisted of 546 patients operated using off-pump techniques and group 2 consisted of 600 cases operated with cardiopulmonary bypass. Patients were compared and evaluated for gastrointestinal complications and possible associated risk factors using univariate and multivariate logistic regression analysis. Results. Overall mortality was 1.6% in group 1 and 2.2% in group 2 (p = 0.523). Mortality due to gastrointestinal complications was 38.5% and 35.7% respectively in group 1 and group 2. The mean EuroSCORE value was 5.1 +/- 2.8 in group 1 and 3.8 +/- 2.4 in group 2 (p < 0.001). The most common gastrointestinal complication in the off-pump group was gastrointestinal bleeding. The leading complication in group 2 was intestinal ischemia. Conclusions. The incidence rates of gastrointestinal complications were similar in the on- and off-pump coronary artery bypass groups the type of gastrointestinal complications however was different. Mortality rate due to these complications was also similar and remained high regardless of the type of surgery. Cardiopulmonary bypass did not emerge as a risk factor for gastrointestinal complications but prolonged cardiopulmonary bypass (longer than 98 minutes) resulted in a high incidence of such complications. Old age and advanced arteriosclerosis emerged as risk factors in both groups resulting in gastrointestinal complications suggesting the ischemic nature of the injury. (C) 2004 by The Society of Thoracic Surgeons.
Citation - WoS: 6
Citation - Scopus: 7
Drying of Polyacrylamide Composite Gels Formed With Various Kappa- Carrageenan Content
(Springer/Plenum Publishers, 2011) Evingür, Gülşen Akın; Pekcan, Önder
Drying of polyacrylamide (PAAm)-kappa-carrageenan (kappa C) composite gels were monitored by using steady-state fluorescence technique. Disc shaped gels were formed from acrylamide (AAm) and N N'- methylenebisacrylamide(Bis) with various kappa- carrageenan (kappa C) contents by free radical crosslinking copolymerization in water. Pyranine (P) was doped as a fluorescence probe and scattered light I (sc) and fluorescence intensities I were monitored during drying of these gels. It is observed that fluorescence intensity of pyranine increased as drying time is increased for all samples. The increase in I was modeled using Stern- Volmer equation and diffusion with moving boundary. It is found that desorption coefficient D decreased as kappa C contents were increased. Supporting gravimetrical and volumetric experiments were also carried out during drying of PAAm- kappa C composite gels.
Dynamics of Feline Coronavirus and Fip: a Compartmental Modeling Approach
(Hindawi Ltd, 2023) Dobie, Ayse Peker; Bayrakal, Alper; Or, Mehmet Erman; Bilge, Ayse Humeyra
The investigation of infectious agents invading human and nonhuman populations represents a rich research domain within the framework of mathematical biology, captivating the interest of scientists across various disciplines. In this work, we examine the endemic equilibrium of feline coronavirus and feline infectious peritonitis by using a modified susceptible-infected-susceptible epidemiological model. We incorporate the concept of mutations from FCoV to FIP to enrich our analysis. We establish that the model, when subjected to reasonable parameter ranges, supports an endemic equilibrium wherein the FCoV group dominates. To demonstrate the stability of the equilibria under typical parameters and initial conditions, we employ the model SCF presented by Dobie in 2022 (Dobie, 2022). We ascertain that the equilibrium values reside within the interior domains of stability. Additionally, we displayed perturbed solutions to enhance our understanding. Remarkably, our findings align qualitatively with existing literature, which reports the prevalence of seropositivity to FCoV among stray cats (Tekelioglu et al. 2015, Oguzoglu et al. 2010, Pratelli 2008, Arshad et al. 2004).
Citation - WoS: 11
Citation - Scopus: 11
Early Parental Causal Language Input Predicts Children's Later Causal Verb Understanding
(Cambridge Univ Press, 2023) Aktan-Erciyes, Asli; Goksun, Tilbe
How does parental causal input relate to children's later comprehension of causal verbs? Causal constructions in verbs differ across languages. Turkish has both lexical and morphological causatives. We asked whether (1) parental causal language input varied for different types of play (guided vs. free play), (2) early parental causal language input predicted children's causal verb understanding. Twenty-nine infants participated at three timepoints. Parents used lexical causatives more than morphological ones for guided-play for both timepoints, but for free-play, the same difference was only found at Time 2. For Time 3, children were tested on a verb comprehension and a vocabulary task. Morphological causative input, but not lexical causative input, during free-play predicted children's causal verb comprehension. For guided-play, the same relation did not hold. Findings suggest a role of specific types of causal input on children's understanding of causal verbs that are received in certain play contexts.
Citation - Scopus: 19
Effect of Glurenorm on Immunohistochemical Changes in Pancreatic ? Cells of Rats in Experimental Diabetes
(2005) Koyutürk, Meral; Özsoy-Saçan, Özlem; Bolkent, Şehnaz; Yanardağ, Refiye
Immunohistochemical localization of islets of Langerhans of streptozotocin (65 mg/kg ip) induced diabetic + glurenorm (10 mg/kg po) treated female albino rats revealed increase in number of ? cells and insulin immunoreactivity of cells. The results suggest that glurenorm can cause the stimulation of cells of endocrine pancreas in diabetic rats.
Citation - WoS: 32
Citation - Scopus: 37
Effect of low-dose methyl prednisolone on serum cytokine levels following extracorporeal circulation
(Arnold Hodder Headline Plc., 1999) Yılmaz, Mert; Ener, Serdar; Akalın, Halis; Sağdıç, Kadir; Serdar, O. Akin; Cengiz, Mete
The systemic inflammatory response to cardiopulmonary bypass (CPB) is associated with increased production of cytokines. This systemic inflammatory response characterized by the activation of interleukin-6 (IL-6) and interleukin-8 (IL-8) during and after CPB is well documented. A prospective randomized double-blind study was performed so as to understand the effects of low-dose methyl prednisolone sodium succinate (MPSS) on the circulating levels of serum cytokines and clinical outcome. Twenty patients were randomly divided into two groups on the basis of the administration of low-dose(1 mg/kg) MPSS in = 10) and placebo in = 10) into the pump prime solution. All patients were scheduled to undergo a primary
Citation - WoS: 4
Citation - Scopus: 4
Effect of the Treatment of Brucellosis on Leukocyte Superoxide Dismutase Activity and Plasma Nitric Oxide Level
(Sage Publications Inc, 2005) Karabulut, Aysun Bay; Sönmez, Emine; Bayındır, Yaşar
Background: The mechanisms by which brucellae evade intracellular killing by polymorphonuclear leukocytes are incompletely understood. In this study we evaluated changes of leukocyte superoxide dismutase (SOD) activity and plasma total nitrite as an indicator of nitric oxide (NO) levels during brucellosis therapy. Methods: Thirty-two patients with acute brucellosis 27 patients with chronic brucellosis and 30 healthy controls were included in the study. Patients with acute brucellosis were tested for leukocyte SOD activity and plasma total nitrite levels before during (21st day) and at the end (45th day) of the combined therapy of rifampicin and doxycycline. The same parameters were also investigated in chronic cases and controls. Results: The SOD activities were lower in patients with acute brucellosis before therapy compared with those 21 and 45 days after starting therapy (P < 0.001). In contrast total nitrite levels did not change significantly (P > 0.05). Conclusions: In the present study leukocyte SOD activity was found to be decreased in patients with acute brucellosis. Enzyme activity was increased by treatment finally reaching the activity of healthy controls. Using an antioxidant agent in addition to classical antimicrobial therapy for acute brucellosis might be a therapeutic approach.
Citation - WoS: 86
Citation - Scopus: 90
Electrical and Optical Percolations of Polystyrene Latex-Multiwalled Carbon Nanotube Composites
(Academic Press Inc Elsevier Science, 2010) Kara, Selim; Arda, Ertan; Dolastir, Fahrettin; Pekcan, Önder
Electrical conductivity and optical transmittance properties of polystyrene (PS)-multiwalled carbon nanotube (MWCNT) composite films were investigated. Composite films were prepared by mixing of various mass fractions of MWCNT in PS-water dispersions. After water evaporates powder composite films were annealed at 175 degrees C above the glass transition of PS for 20 min. Photon transmission and two point probe resistivity techniques were employed to determine the variations of the optical and the electrical properties of composites. Transmitted light intensity I(tr) and surface resistivity R(s) were monitored as a function of MWCNT mass fraction (M). It was observed that both the surface resistivity and the optical transparency were decreased by increasing the amount of MWCNT added to the polymeric system. Conductivity and optical results were interpreted according to the classical and site percolation theory respectively. The electrical (sigma) and the optical (op) percolation threshold values and critical exponents were calculated as M(sigma) = 1.8 wt.% M(op) = 0-0.13 wt.% and beta(sigma) = 2.25 beta(op) = 0.32 respectively. (C) 2010 Elsevier Inc. All rights reserved.
Engineering of Geobacillus Kaustophilus Lipase for Enhanced Catalytic Efficiency and Methanol Tolerance in Biodiesel Production from Sunflower Oil
(Elsevier, 2025) Tulek, Ahmet; Poyraz, Yagmur; Sukur, Gozde; Pacal, Nurettin; Ozdemir, F. Inci; Yildirim, Deniz; Essiz, Sebnem
Lipase-mediated biodiesel production offers a sustainable and environmentally friendly alternative to conventional chemical methods. However, enzyme limitations such as low activity, poor thermal stability, and limited solvent tolerance remain challenges. In this study, a lipase from Geobacillus kaustophilus (Gklip) was engineered for improved biodiesel production using molecular docking, molecular dynamics (MD) simulations, and molecular mechanics/generalized born surface area (MM/GBSA) free energy calculations. Five mutants (Y29S, Q114T, F289D, Q184M, and Q114F) were generated via site-directed mutagenesis and expressed in Escherichia coli. Biochemical characterization revealed that all mutants retained the wild-type's optimal temperature (50 degrees C) and pH (8.0), while showing varying pH ranges, with the broadest observed in Q184M. Thermal stability increased significantly in Q184M (32.86-fold) and Q114F (5.93-fold). Catalytic efficiencies improved by 2.07-, 2.05-, and 2.63-fold in Q184M, F289D, and Y29S, respectively, compared to the wild-type (0.57). In the presence of 60 % methanol, the wild-type retained only 30.4 % activity, while Q184M maintained 67.5 %, highlighting superior solvent tolerance. Biodiesel conversion assays using sunflower oil showed no product formation by the wild-type, whereas Q184M, Q114F, and F289D achieved yields of 58.7 %, 56.3 %, and 49.2 %, respectively. These findings identify Q184M and Q114F as promising enzyme candidates for enzymatic biodiesel production.

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