Factors affecting extubating time of postoperative patients who underwent congenital cardiac surgery: a randomized prospective study.

OBJECTIVE: Anesthesia management in pediatric cardiac surgery using health resources sparingly focuses on reducing morbidity and mortality and increasing patients' quality of life. The duration of postoperative mechanical ventilation (MV) heavily influences pediatric cardiac surgery recovery. Thus, in this study we aimed to determine factors influencing extubation times after pediatric cardiac surgery. PATIENTS AND METHODS: A total of 72 pediatric patients with an ASA score of III or above undergoing cardiac surgery were included in the study. As a result of their extubation time, the patients were divided into three groups as follows: those who were extubated immediately after surgery or in the operating room (OR) were recorded as Immediate Extubators (IE); those who were extubated within 6 to 48 hours of entering the intensive care unit were recorded as Early Extubators (EE), and those who were extubated after 48 hours or not extubated were recorded as Delayed Extubators (DE). RESULTS: A logistic regression analysis showed that anomalies and need of MV before surgery, airway difficulty, and prolonged cross-clamp (CC) time were observed as factors affecting DE. The risk of DE was significantly correlated with the presence of abnormality [Odds ratio (OR): 20.3, 95% Confident interval (CI): 2.8-142.7], with the need of MV before surgery (OR: 1,844, 95% CI: 1.8-1,790,461.9), and with the presence of airway difficulty (OR: 44.7, 95% CI: 4.4-445.0). In addition, it was determined that CC time increased the probability of DE 1.038 times per minute (95% CI: 1.004-1.072). CONCLUSIONS: Early and immediate extubation in children who underwent congenital heart surgery was successfully performed in our clinic. Early and immediate extubation in pediatric cardiac surgery can be completed safely and successfully when suitable conditions are provided.

Indomethacin co-amorphous drug-drug systems with improved solubility, supersaturation, dissolution rate and physical stability.

In this study, new co-amorphous drug systems were designed using a pharmacologically relevant combination to improve the solubility and dissolution of indomethacin. Combinations of indomethacin-paracetamol (IND-PAR) as an anti-inflammatory/pain killer, and indomethacin-nicotinamide (IND-NCT) for prevention of gastric ulcers caused by IND, were developed for co-amorphization. The effect of PAR and NCT on the solubility, supersaturation, and dissolution of the poorly soluble counterpart, IND, was investigated. PAR and NCT were found to enhance the solubility and supersaturation of IND in biorelevant medium (FaSSIF) and in FaSSIF blank. Differential scanning calorimetry (DSC) showed capability of IND-PAR and IND-NCT binary mixtures to form eutectic mixture. Powder X-ray diffraction and DSC indicated the formation of a homogenous co-amorphous system with single Tg value. Hydrogen bonding between IND and each of PAR and NCT were found to stabilize the co-amorphous systems as supported by FTIR studies. The intrinsic dissolution rate under sink conditions was improved over that of plain amorphous IND both in FaSSIF and FaSSIF blank. IND-PAR 2:1 and IND-NCT 1:1 were extremely stable and remained amorphous for 7 months at 25 °C, while all co-amorphous formulations were stable at least up to one month at 40 °C under dry condition. The present work demonstrates an improved approach to combine IND-PAR and IND-NCT as promising co-amorphous systems for potential therapeutical applications.

Total Occlusion of the Left Descending and circumflex Coronary Artery without ST Elevation: the De Winter electrocardiographic pattern.

de Winter syndrome, or anterior ST segment elevation myocardial infarction (STEMI), constitutes 2% of acute myocardial infarctions. In contrast to classic ST segment elevation as seen with STEMI, it involves ST depression with precordial derivations and sharp waves. de Winter syndrome indicates critical narrowing of the left ascending coronary artery (LAD). Recognizing this presentation is important in terms of both mortality and morbidity. We present the case of a 71-year old patient presenting at the Emergency Department with chest pain, who had findings of de Winter syndrome on their ECG. Coronary angiography confirmed occlusions in the LAD and circumflex (CX) coronary arteries.

Moderate disability has negative effect on spatiotemporal parameters in patients with chronic low back pain.

BACKGROUND: It is known that the patients with chronic low back pain (CLBP) has different spatiotemporal characteristics than healthy controls such as average speed, cadence, step and stride length parameters. CLBP is a heterogeneous phenomenon in terms of causing various level of disability. RESEARCH QUESTION: Does disability levels make a difference on spatiotemporal characteristics of patients with CLBP? METHODS: 66 patients with CLBP and 32 healthy controls between the ages of 25 and 65 years participated to study. The patients who had neurological, orthopedic, cardiovascular, metastatic history excluded from study. Resting, activity and night pain and functional disability were evaluated with Visual Analog Scale (VAS), Oswestry Disability Index (ODI) respectively. The patients were divided into two groups according to their disability level: moderate and severe. Gait analyses were performed with Optogait treadmill-based photocell system (Version 1.6.4.0, Microgate, Bolzano, Italy). After two trials were done, the spatiotemporal characteristics recorded for one minute while patients walked their preferred speed on the treadmill. One-way ANOVA was used to compare these parameters among the perceived disability level (moderate, severe) and healthy controls.The level of significance was accepted as 0.05. RESULTS: Step length, stride length, and preferred walking speed were the parameters that differentiate the gait between healthy controls and patients with CLBP (p < 0.05). According to post-hoc analyses, moderate CLBP was identified as the group most different from the healthy controls (p < 0.05). SIGNIFICANCE: Results of this study describe how compensating mechanism were seen in CLBP subgroups. As opposed to expectations, an increase in disability would not create higher difference in spatiotemporal characteristics between healthy controls and patients with severe disability. We propose that patients with severe and moderate disability had different ways to normalize their gait.

Tannic acid as a co-former in co-amorphous systems: Enhancing their physical stability, solubility and dissolution behavior.

Co-amorphous systems have been increasingly investigated to improve the solubility and dissolution rate of poorly soluble drugs. Considering the ability of tannic acid (TA), a polyphenolic compound, to form hydrogen bonds with compounds that contain carbonyl groups, we hypothesized that tannic acid will also be effective in stabilizing amorphous form of drugs in co-amorphous systems. Co-amorphization by TA of two poorly soluble model drugs, carbamazepine (CBZ) and indomethacin (IND) was investigated. Tannic acid facilitated the amorphization of studied drugs and successful co-amorphous systems were obtained as proved by powder X-Ray diffraction (PXRD). Differential scanning calorimetry (DSC) confirmed the homogeneous structure as indicated by the existence of a single Tg for each co-amorphous product. The expected molecular interactions between phenolic groups in TA and carbonyl groups in the studied drugs (CBZ and IND) were confirmed by analyzing their infrared spectra. Drug-TA co-amorphous formulations showed an enhanced equilibrium solubility over the individual drugs. Powder dissolution test under sink conditions showed improved dissolution profiles of drug-TA co-amorphous formulations compared to the corresponding crystalline drugs and physical mixtures. Tannic acid also showed a superior stabilizing effect. CBZ-TA co-amorphous system was physically stable at dry conditions (up to 6 months at 40 °C), under 60% relative humidity (up to one month at 20 °C), and in solution (after 48 h of solubility measurements), as revealed by PXRD examination of the remaining solid after solubility measurement. However, IND-TA co-amorphous formulation remained stable at dry conditions up to 6 months at 4 °C and up to one month at 60% relative humidity at 20 °C. These findings demonstrate the potential of tannic acid as a promising co-former in co-amorphous systems of poorly soluble drugs.

Nisin/polyanion layer-by-layer films exhibiting different mechanisms in antimicrobial efficacy.

Nisin/polyanion Layer-by-Layer (LbL) films are reported to exhibit different mechanisms in antimicrobial efficacy depending on the type of polyanion. LbL films consisting of nisin as the polycationic component were prepared using two different polyanionic constituents: poly acrylic acid (PAA) and dextran sulfate (DX). Due to the weaker interaction strength of carboxylate groups with nisin compared to sulfate/nisin, a larger molecular weight of PAA was needed to achieve LbL assembly. PAA-100K/nisin and DX-15K/nisin multilayer films exhibited significantly different properties. PAA-nisin films grew faster compared to DX-nisin films and showed, for 60 bilayer films, an average bilayer thickness of 21.6 nm compared to that of 6.1 nm in DX-nisin films. The total amount of nisin was found to be 17.1 ± 2.2 µg cm-2 in (PAA-nisin)60 and 6.8 ± 0.4 µg cm-2 in (DX-nisin)60 films. The stability of the films was investigated at three different pH values of 6.0, 7.4 and 9.5. (PAA-nisin)60 films exhibited the release of nisin into the solution which resulted in the disintegration of the film over several hours. A burst release was observed in the first hour followed by a slower release and disintegration over 24 hours with a complete release at pH 9.5. The bacterial growth inhibition test against Staphylococcus epidermidis confirmed the antimicrobial activity of nisin released from PAA-nisin films. PAA was found to stabilize nisin and the film-released nisin retained its antimicrobial activity in the neutral and alkaline pH values. Unlike PAA-nisin films, (DX-nisin)60 films were stable at the physiological conditions up to 14 days with no release of nisin. DX-nisin films were found to inhibit the attachment of Staphylococcus epidermidis and prevent biofilm formation. These results clearly demonstrate the effect of different polyanions on nisin LbL films to achieve different mechanisms in antimicrobial efficacy and show the potential of PAA-nisin multilayer films as promising local delivery systems for treatment of burns and wounds, while DX-nisin multilayer films can be employed as stable coatings against bacterial attachment and biofilm formation.

Successful intravenous lipid emulsion therapy: Olanzapine intoxication.

Olanzapine is an antipsychotic drug used in psychiatric diseases. At high doses it exhibits cardiovascular and neurological sideeffects in particular. Lipid emulsion therapy for the removal of medication from plasma in high-dose lipophilic drug use has recently become very widespread. In the light of current literature, this report discusses the successful treatment of a patient within 4 hrs of olanzapine overdose as an attempted suicide, who presented with agitation and clouded consciousness.

Poly(2-Ethyl-2-Oxazoline) as an Alternative to Poly(Vinylpyrrolidone) in Solid Dispersions for Solubility and Dissolution Rate Enhancement of Drugs.

Poly(2-ethyl-2-oxazoline) (PEOX), a biocompatible polymer considered as pseudopolypeptide, was introduced as a potential alternative to the commonly used polymer, poly(vinylpyrrolidone) (PVP) for the preparation of solid dispersion with a poorly soluble drug. Glipizide (GPZ), a Biopharmaceutical Classification System class II model drug, was selected for solubility and dissolution rate study. GPZ-polymer solid dispersions and physical mixtures were characterized and investigated by X-ray diffractometry, differential scanning calorimetry, scanning electron microscopy, and FTIR spectroscopy. The impact of polymers on crystal nucleation kinetics was studied, and PEOX exhibited strong inhibitory effect compared with PVP. Solubility and dissolution behavior of the prepared solid dispersions and their physical blends were in vitro examined and evaluated. A significant enhancement in GPZ solubility was obtained with PEOX compared with the pure drug and solid dispersion with PVP. A big improvement in the intrinsic dissolution rate (45 times) and dissolved amount of GPZ (58 times) was achieved with PEOX in fasted state simulated intestinal fluid, against comparable enhancement observed with PEOX and PVP in phosphate buffer at pH 6.8. Lower molecular weight of PEOX-5K (5000 g/mol) was found to be superior to higher molecular weight PEOX-50K (50,000 g/mol) in the improvement of dissolution behavior. The findings of this study with GPZ as a model drug introduce lower molecular weight PEOX as a promising polymeric carrier toward better oral bioavailability of poorly soluble drugs.

Restructuring of poly(2-ethyl-2-oxazoline)/tannic acid multilayers into fibers.

H-Bonded, pH-responsive poly(2-ethyl-2-oxazoline) (PEOX) and tannic acid (TA) multilayers were prepared by layer-by-layer deposition. Free-floating PEOX/TA multilayers were shown to restructure in a pH3 phosphate buffer solution to H-bonded, pH-responsive PEOX/TA fibers. This restructuring was also evident during the growth of multilayers thicker than 15 bilayers (BL). The growth profile of 30 BL-thick films showed a significant decrease in the film thickness from 118 nm to 85 nm between 15 BL and 20 BL, after which the growth trend was regained with some small fluctuations. This decrease was associated with the detachment of film patches from the top surface of the film. The rinse solutions consisted of fibrous aggregates, which were formed by the restructuring of the detached multilayer patches. These fibers were characterized by TGA, XPS, FTIR and SEM measurements which showed that the fibers consisted of H-bonded PEOX and TA molecules. As such, the fibers were pH-responsive and disintegrated at pH > 8.5. Scanning electron microscopy images indicated that the fibers might have been formed by the curling of planar LbL film patches and the dried fibers looked like collapsed hollow tubes on solid substrates. These results contribute to our understanding of the stability of LbL films in various chemical conditions and the ways to modify the morphology of self-assembled structures. pH-responsive fibrous aggregates are important in a variety of biomedical applications, from controlled release to sensors.

Effect of Vasoactive Therapy Used for Brain-Dead Donors on Graft Survival After Kidney Transplantation.

Serum catecholamine levels and peripheral vascular resistance decrease after brain death. Vasoactive drugs are used to control these hemodynamic changes and to improve perfusion of the organs. These drugs might have a role in rejection or loss of the graft organ. We aimed to investigate the effects of vasoactive drugs used in the cadaveric donor care on post-transplant renal graft functions. In this retrospective study, medical records of 135 cadaveric donors (270 kidneys) and recipients of these kidneys were evaluated. Correlation analysis was done to assess the data for factors that may cause rejection and graft loss. Vasoactive drug (noradrenaline 49%, dopamine 60%, adrenaline 3%, dobutamine 11%) consumption ratio was 85.8% in donor care. Increased number of noradrenaline infusion days was associated with decreased rates of graft rejection and graft loss. This correlation was not found for dopamine. Results of the Pearson correlation analysis test showed a relation between noradrenaline use and decrease in graft loss and graft rejection. Noradrenaline but not dopamine used in cadaveric donor care decreased the graft rejection rate and graft loss, presumably by improving hemodynamic stability and organ perfusion, although we found no special reason.

The optical characterization of metal-mediated aggregation behaviour of amphiphilic Zn(ii) phthalocyanines.

Ag(+) mediated aggregation behaviour of two different amphiphilic zinc phthalocyanines (Zn-Pcs) (symmetric and asymmetric) has been investigated in solution, at the air-water interface and in Langmuir-Blodgett (LB) films transferred onto glass substrates. A 4 : 1 ([Ag(+)]/[Pc]) complexation was observed for both symmetric and asymmetric Zn-Pcs at high [Ag(+)] concentrations which led to the formation of H-aggregates in solution. At the air-water interface, both symmetric and asymmetric Zn-Pcs showed a tilted, edge-on orientation in columnar stacks. Addition of Ag(+) to the subphase enhanced the order in the monolayers. LB films on glass substrates showed a split Q-band indicating the presence of "herring-bone" type aggregation consisting of both H- and J-aggregates. For LB films deposited from a Ag(+) containing subphase, a shoulder appeared in the absorption spectra at longer wavelengths which indicates that the fraction of J-aggregates was enhanced by Ag(+) in LB films. The molecular orientation in LB films was investigated by polarized absorption spectroscopy and a tilt angle was calculated to be 49° with the substrate normal for symmetric and 74.6° for the asymmetric Zn-Pc. The presence of Ag(+) cations in the subphase decreased the tilt angles slightly by 4-5°. These results indicate that Ag(+) induced the aggregation of Zn-Pcs and acted as a linker between Pc molecules in the ultrathin films of both symmetric and asymmetric Zn-Pcs. These results are important in inducing J-aggregates for the fabrication of molecular devices based on phthalocyanine thin films.

Pre-exercise arginine supplementation increases time to exhaustion in elite male wrestlers.

Dietary supplements containing arginine are among the most popular ergogenics intended to enhance strength, power and muscle recovery associated with both anaerobic and aerobic exercise. The aim of the present study was to evaluate the possible effect of pre-exercise acute intake of arginine on performance and exercise metabolism during incremental exhaustive exercise in elite male wrestlers. Nine volunteer elite male wrestlers (24.7±3.8 years) participated in this study. The test-retest protocol was used on the same subjects. The study was conducted using a cross-over design. A single dose of arginine (1.5 g · 10 kg(-1) body weight) or placebo was given to the subjects after 12 hours fasting (during the night) for both test and retest. Subjects were allowed to drink water but not allowed to eat anything between arginine or placebo ingestion and the exercise protocol. An incremental exercise protocol was applied and oxygen consumption was measured during the exercise. Heart rate and plasma lactate levels were measured during the exercise and recovery. Results showed that in the same working loads there was no significant difference for the mean lactate levels and no difference in maximum oxygen consumption (arginine 52.47±4.01 mL · kg(-1) · min(-1), placebo 52.07±5.21 mL · kg(-1) · min(-1)) or in maximum heart rates (arginine 181.09±13.57 bpm, placebo 185.89±7.38 bpm) between arginine and placebo trials. Time to exhaustion was longer with arginine supplementation (1386.8±69.8 s) compared to placebo (1313±90.8 s) (p < 0.05). These results suggest that L-arginine supplementation can have beneficial effects on exercise performance in elite male wrestlers but cannot explain the metabolic pathways which are responsible from these effects.

Association of genetic polymorphisms with endothelial dysfunction in chronic heart failure.

OBJECTIVES: Endothelial dysfunction can be shown very early in the cardiovascular disease. In the present study the association between congestive heart failure (CHF), endothelial function and 3 gene polymorphisms was investigated. PATIENTS AND METHODS: In 104 healthy controls and 104 CHF patients, endothelial constitutive nitric oxide synthase (ecNOS), angiotensin converting enzyme (ACE) and angiotensin II type 1 receptor (AT1R) gene polymorphisms were assessed. The cause of CHF was ischemic in 68 patients and dilated cardiomyopathy (DCMP) in 36 patients. High resolution brachial artery ultrasound was used in 37 CHF patients and 37 healthy controls to assess the endothelial function. Endothelium-dependent vasodilation (EDD) and endothelium-independent vasodilation (EID) were determined. RESULTS: There no was difference between controls and CHF patients for the ACE, ecNOS, and AT1R genotype frequencies. Compared to controls CHF patients had significantly impaired EDD (9.0+5% vs 16±7%, p < 0.001) and EID (13±6% vs 19+8%, p = 0.001). EDD (7±4% vs 12+6%, p = 0.005), but not EID, was significantly impaired in ischemic CHF as compared to DCMP patients. In the CHF group ecNOS a allele and AT1R C allele influence the EDD. CONCLUSIONS: Endothelial dysfunction was present in CHF group and the presence of ecNOS a allele and AT1R C allele further impaired EDD.

Nanoparticle and gelation stabilized functional composites of an ionic salt in a hydrophobic polymer matrix.

Polymer composites consisted of small hydrophilic pockets homogeneously dispersed in a hydrophobic polymer matrix are important in many applications where controlled release of the functional agent from the hydrophilic phase is needed. As an example, a release of biomolecules or drugs from therapeutic formulations or release of salt in anti-icing application can be mentioned. Here, we report a method for preparation of such a composite material consisted of small KCOOH salt pockets distributed in the styrene-butadiene-styrene (SBS) polymer matrix and demonstrate its effectiveness in anti-icing coatings. The mixtures of the aqueous KCOOH and SBS-cyclohexane solutions were firstly stabilized by adding silica nanoparticles to the emulsions and, even more, by gelation of the aqueous phase by agarose. The emulsions were observed in optical microscope to check its stability in time and characterized by rheological measurements. The dry composite materials were obtained via casting the emulsions onto the glass substrates and evaporations of the organic solvent. Composite polymer films were characterized by water contact angle (WCA) measurements. The release of KCOOH salt into water and the freezing delay experiments of water droplets on dry composite films demonstrated their anti-icing properties. It has been concluded that hydrophobic and thermoplastic SBS polymer allows incorporation of the hydrophilic pockets/phases through our technique that opens the possibility for controlled delivering of anti-icing agents from the composite.

Endothelial constitutive nitric oxide synthase, angiotensin converting enzyme, angiotensin II type 1 receptor gene polymorphisms and endothelial functions in healthy individuals.

INTRODUCTION: Endothelial dysfunction is recognized as an early and initiating event in the pathogenesis of coronary artery disease. Gene polymorphisms of endothelial constitutive nitric oxide synthase (ecNOS), angiotensin converting enzyme (ACE) and angiotensin II type 1 receptor (AT1R) have been found to be associated with atherosclerosis.  We aimed to investigate the possible effects of ecNOS, ACE and AT1R gene polymorphisms on endothelial functions in healthy population. MATERIALS AND METHODS: In 255 healthy subjects (male/female: 119/136 mean age 35.1±2.3 years)  ecNOS, ACE and AT1R gene polymorphisms were assessed by polymerase chain reaction (PCR). Endothelium dependent (EDD, flow-mediated) and endothelium independent vasodilation (EID) were measured by high resolution brachial artery ultrasound and 0.5 mg sublingual nitroglycerine respectively. RESULTS: ecNOS and ACE genes had no significant effect on EDD and EID. However, subjects with AT1RAC+CC genotypes had lower EDD compared to subjects with AT1RAA genotype in females (19.4 ± 6.6% vs 21.5 ± 7.8%, p = 0.041). EDD and EID were significantly negatively associated with  age, body mass index, serum creatinine, glucose, uric acid and hemoglobin levels. When the data on age, uric acid, BMI, glucose, creatinine, and hemoglobin were split into 3 as low-1/3, mid-1/3 and  high 1/3, there was significant graded decrease in EDD and EID with these parameters. In multiple regression analysis, age and presence of AT1RAC+CC genotype  retained as significant independent factors predicting endothelial functions. CONCLUSIONS: Gene polymorphisms of endothelial constitutive nitric oxide synthase and  angiotensin converting enzyme had no effect on endothelial functions. However, the presence of angiotensin II type 1 receptor polymorhism (AT1RAC+CC genotype) seemed to adversely affect the endothelial functions as reflected by impaired endothelium dependent and independent vasodilatation in healthy individuals.

Effects of diosmine-hesperidine on experimental colonic anastomosis.

AIM: Our goal was to determine the effects of a diosmine-hesperidine combination on wound healing in a rat model of colonic anastomosis. MATERIALS AND METHODS: In this study, 20 Wistar Albino female rats were randomized into four experimental groups containing five rats in each group. A segment of 1 cm of colon was excised 4 cm proximally to the peritoneal reflection in all rats without carrying out any mechanical or antibacterial bowel preparation. Colonic anastomosis was performed with interrupted, inverting sutures of 6/0 polypropylene. Beginning from the first postoperative day, the rats in Groups II and IV received 100 mg/kg per day of diosmine-hesperidine via orogastic route by 4F fine feeding catheter. RESULTS: A significant difference was detected between groups in terms of their hydroxyproline levels (p<0.05); the hydroxyproline level of Group I was significantly lower than that of the other groups while no significant difference was noted between Groups II and III. CONCLUSION: The administration of diosmine-hesperidine increased the amount of collagen and bursting pressures at the anastomotic site and thus had favorable influences on the healing of colonic anastomosis (Tab. 1, Fig. 3, Ref. 33).

Effect of anions on the cloud point temperature of aqueous poly(2-ethyl-2-oxazoline) solutions.

Poly(2-alkyl-2-oxazoline)s have recently gained attention in especially biological applications due to their lower critical solution temperature being close to the body temperature and their biocompatibility. The understanding of how cloud point temperature (T(c)) depends on the salt concentration and the molecular mechanisms responsible for such behavior are important to tune T(c) as desired by the applications. In this paper, we report the effect of a series of sodium salts on T(c) of aqueous poly(2-ethyl-2-oxazoline) (PEOX) solutions by dynamic light scattering. PEOX samples having four different molecular weights were investigated, and the results were compared with those of poly(N-isopropylacrylamide) (PNIPAM), the mostly investigated and used thermoresponsive polymer. Kosmotropic anions decreased T(c) linearly while chaotropic anions increased T(c) nonlinearly with salt concentration. The contributions of different mechanisms to T(c) change have been discussed. Our results indicate that the dominant mechanism is the dehydration of PEOX for divalent kosmotropic anions (CO(3)(2-), SO(4)(2-), S(2)O(3)(2-)) and direct binding for chaotropic anions (NO(3)(-), I(-), ClO(4)(-), SCN(-)). For the remaining monovalent kosmotropic anions (H(2)PO(4)(-), F(-), Cl(-), Br(-)), a combination of dehydration and surface tension mechanisms was in effect. The additional contribution of the surface tension mechanism for the monovalent kosmotropic anions was inferred for different molecular weight PEOX samples and also for PNIPAM. With PEOX molecular weight decreasing from 500,000 to 5000 g/mol, T(c) decreased less with salt concentration which was attributed to the contribution of the surface tension mechanism. For PEOX samples, the decrease of T(c) with kosmotropic anion concentration was faster compared to PNIPAM due to differences in their chemical structure. Our results show that the molecular mechanisms of interactions between PEOX chains and specific anions can simply be inferred from determination of T(c) by a common technique-dynamic light scattering.

Effect of structural isomerism and polymer end group on the pH-stability of hydrogen-bonded multilayers.

Association of tannic acid (TA) with structurally isomeric poly(N-isopropylacrylamide) (PNIPAM) and poly(2-isopropyl-2-oxazoline) (PIPOX) has been examined at surfaces to understand the effect of different molecular arrangements in a polymer repeating unit of structural isomers on the construction and pH-stability of hydrogen-bonded multilayers. Films were fabricated using layer-by-layer (LbL) technique through hydrogen-bonding interactions primarily between carbonyl groups of neutral polymers and hydroxyl groups of TA molecules at pH 2. PIPOX and TA formed thinner and more stable films in the pH scale with a critical dissolution pH of 9 when compared to films of PNIPAM and TA with a critical pH of 8. The differences in the thickness and pH-stability were due to different conformational behavior of PNIPAM and PIPOX in water which affects the accessibility of carbonyl groups for participation in the hydrogen bonding and the number of binding sites between the polymer pairs. Addition of electrostatic interactions by introducing amino groups only at the PIPOX chain end shifted the critical dissolution pH to higher values and resulted in gradual dissolution of the films in a wide pH range of 9-12. Such films hold promise for use in biomedical field due to biocompatibility and lower critical solution temperature (LCST) behavior at near physiological temperature of PNIPAM and PIPOX together with the pH-response of the hydrogen-bonded films.