Urea Linkages Research Articles

One-step hydroxylation of rubber seed oil and synthesis of green polyurethane networks thereof

The unsaturation in Rubber seed oil (RSO) was converted to polyhydroxy compound (HY-RSO) in a single step reaction using potassium permanganate solution under carefully controlled conditions. The HY-RSO polyol so formed was reacted with methylene diisocyanate (MDI) to synthesize polyurethane prepolymer (PU) containing terminal isocyanate groups. Moisture aided curing of the prepolymer led to crosslinked polyurethanes bearing additional urea linkages. The cross-linked poly(urethane-urea)‘s mechanical, thermal and thermo-physical properties increased with increase in the isocyanate-content in the precursor. These properties were better than those of a PU network derived from castor oil as a reference polyol. It was demonstrated for the first time that RSO could effectively be converted to a value-added hydroxyl derivative for eventual conversion to many useful materials including polyurethanes for related applications.

Biomimetic hybrid membranes with covalently anchored chitosan – Material design, transport and separation

New hybrid membrane was inspired by biomimicking the water harvesting system in the back of fogstand beetle. Therefore, efficient hydrophobic material with hydrophilic chitosan (CS) islands was produced by the covalent attachment of chitosan to the hydrophobic surface of PVDF membranes. The attachment of CS molecules allows upgrading the membrane permeability and antifouling properties. Employing the “grafting to” approach, CS was anchored to pre-activated PVDF-membranes by urea linker via silanization. Materials were used for different separation processes, including membrane distillation (MD) for the removal of hazardous volatile organic compounds, desalination, and concentration of raw juices. Material physiochemical features, wettability, stability, tribology, and morphology, were assessed with respect to transport and separation. The hybrid-material possessed improved thermal stability and water resistance. The process separation index increased from ~6.8 kg m−2 h−1 to 90 kg m−2 h−1 for pristine and hybrid-material, respectively. During the juice concentration, the normalized flux decline for pristine was ~50%, whereas for hybrid material below 10%. On the pristine material, a visible layer of foulant was found after the separation, whereas the hybrid membrane shows a relatively clean surface. The developed strategy offers several distinct advantages for generating new materials having potential applications in water oil separation and wastewater treatment.

Squaramides and Ureas: A Flexible Approach to Polymerase-Compatible Nucleic Acid Assembly.

Joining oligonucleotides together (ligation) is a powerful means of retrieving information from the nanoscale. To recover this information, the linkages created must be compatible with polymerases. However, enzymatic ligation is restrictive and current chemical ligation methods lack flexibility. Herein, a versatile ligation platform based on the formation of urea and squaramide artificial backbones from minimally modified 3′‐ and 5′‐amino oligonucleotides is described. One‐pot ligation gives a urea linkage with excellent read‐through speed, or a squaramide linkage that is read‐through under selective conditions. The squaramide linkage can be broken and reformed on demand, while stable pre‐activated precursor oligonucleotides expand the scope of the ligation reaction to reagent‐free, mild conditions. The utility of our system is demonstrated by replacing the enzymatically biased RNA‐to‐DNA reverse transcription step of RT‐qPCR with a rapid nucleic‐acid‐template‐dependent DNA chemical ligation system, that allows direct RNA detection.

Squaramides and Ureas: A Flexible Approach to Polymerase‐Compatible Nucleic Acid Assembly

AbstractJoining oligonucleotides together (ligation) is a powerful means of retrieving information from the nanoscale. To recover this information, the linkages created must be compatible with polymerases. However, enzymatic ligation is restrictive and current chemical ligation methods lack flexibility. Herein, a versatile ligation platform based on the formation of urea and squaramide artificial backbones from minimally modified 3′‐ and 5′‐amino oligonucleotides is described. One‐pot ligation gives a urea linkage with excellent read‐through speed, or a squaramide linkage that is read‐through under selective conditions. The squaramide linkage can be broken and reformed on demand, while stable pre‐activated precursor oligonucleotides expand the scope of the ligation reaction to reagent‐free, mild conditions. The utility of our system is demonstrated by replacing the enzymatically biased RNA‐to‐DNA reverse transcription step of RT‐qPCR with a rapid nucleic‐acid‐template‐dependent DNA chemical ligation system, that allows direct RNA detection.

Modular 4D Printing Assisted by Dynamic Chemical Bonds

Modular 4D printing is achieved by assembling and welding the modules of printed self-folding structures containing dynamic chemical bonds, enabling multifunctional shape-shifting structures and devices.

Benzothiazolyl Ureas are Low Micromolar and Uncompetitive Inhibitors of 17β-HSD10 with Implications to Alzheimer's Disease Treatment.

Human 17β-hydroxysteroid dehydrogenase type 10 is a multifunctional protein involved in many enzymatic and structural processes within mitochondria. This enzyme was suggested to be involved in several neurological diseases, e.g., mental retardation, Parkinson’s disease, or Alzheimer’s disease, in which it was shown to interact with the amyloid-beta peptide. We prepared approximately 60 new compounds based on a benzothiazolyl scaffold and evaluated their inhibitory ability and mechanism of action. The most potent inhibitors contained 3-chloro and 4-hydroxy substitution on the phenyl ring moiety, a small substituent at position 6 on the benzothiazole moiety, and the two moieties were connected via a urea linker (4at, 4bb, and 4bg). These compounds exhibited IC50 values of 1–2 μM and showed an uncompetitive mechanism of action with respect to the substrate, acetoacetyl-CoA. These uncompetitive benzothiazolyl inhibitors of 17β-hydroxysteroid dehydrogenase type 10 are promising compounds for potential drugs for neurodegenerative diseases that warrant further research and development.

Strain rate sensitivity of polyurea coatings: Viscous and elastic contributions

Polyurea, a reaction product of isocyanates and an amine blend has been reported to be highly strain rate sensitive, which responds in its own unique way when subjected to increasing strain rates. The amine blend comprise of a long chain amine, forming the soft segments, chain extender, which brings the urea linkages closer and a crosslinker, which serves as a chemical bond between the chains. In this work, we attempt to tune the viscous contribution in polyurea, by increasing crosslinking density, while keeping the amount of chain extender more or less constant. The viscoelastic behavior and its effect on the time dependant behavior was established by extensive dynamic studies. Quasi-static tests and Split Hopkinson testing was performed over large deformation rates (10−4 to 103 s−1). It was observed that polyureas with larger viscous contribution (tan δ), were capable of exhibiting larger strain rate sensitivity.

Spectroscopic study of the morphology development of closed-cell polyurethane foam using bio-based malonic acid as chain extender

In this study the advantages of using bio-based multi-functional malonic acid salt as chain extender in preparing closed cell polyurethane foams is demonstrated. We found that the presence of malonic acid salt can alter the reaction kinetics, segmental mobility and hence the relative kinetics of polyurethane and polyurea formation. By analyzing the infrared active vibrations, it is demonstrated that the formation of urethane and urea linkages is accelerated at the initial stage of reaction, resulting in enhanced viscosity build-up attributed to the catalytic activity of the triethylamine complexed with malonic acid. The relative kinetics in formation of different morphological features thus can be used to control the cell opening process. These results, combining information on polymerization kinetics, gas evolution and phase separation, illustrate the capability of using malonic acid salt as the chain extender to manipulate polyurethane foam morphology and its potential application in polyurethane closed cell foam systems.

Ionically Tagged Magnetic Nanoparticles with Urea Linkers: Application for Preparation of 2-Aryl-quinoline-4-carboxylic Acids via an Anomeric-Based Oxidation Mechanism.

In this exploration, we reported the design and synthesis of a novel ionically tagged magnetic nanoparticles bearing urea linkers, namely, Fe3O4@SiO2@(CH2)3–urea–thiazole sulfonic acid chloride. The structure of the mentioned compound was fully characterized by using several techniques including Fourier transform infrared spectroscopy, energy-dispersive X-ray analysis, elemental mapping analysis, thermogravimetric analysis/differential thermal analysis, scanning electron microscopy, transmission electron microscopy, and vibrating sample magnetometer. In the presence of the novel reusable catalyst, applied starting materials including aryl aldehydes, pyruvic acid, and 1-naphthylamine condensed to afford the desired 2-aryl-quinoline-4-carboxylic acid derivatives via an anomeric-based oxidation pathway under solvent-free conditions.

In vitro Degradation Analysis of 3D-architectured Gelatin-based Hydrogels

ABSTRACT:Multifunctional biopolymer-based materials are promising candidates for next generation regenerative biomaterials. Understanding the degradation behavior of biomaterials is vital for ensuring biological safety, as well as for better control of degradation properties based on rational design of a material’s physical and chemical characteristics. In this study, we decipher the degradation of a hydrogel prepared from gelatin and lysine diisocyanate ethyl ester (LDI) using in vitro models, which simulate hydrolytic, oxidative and enzymatic degradation (collagenase). Gravimetrical, morphological, mechanical and chemical properties were evaluated. Notably, the hydrogels were relatively resistant to hydrolytic degradation, but degraded rapidly within 21 days (>95% mass loss) under oxidative and collagenase degradation. Oxidative and collagenase degradation rapidly decreased the storage and loss modulus of the hydrogels, and slightly increased their viscous component (tan δ). For each degradation condition, the results suggest different possible degradation pathways associated to the gelatin polypeptide backbone, urea linkages and ester groups. The primary degradation mechanisms for the investigated gelatin based hydrogels are oxidative and enzymatic in nature. The relative hydrolytic stability of the hydrogels should ensure minimal degradation during storage and handling prior to application in surgical theatres.

Synthesis of novel 6-piperidin-1-ylpyrimidine-2,4-diamine 3-oxide substituted calix[4]arene as a highly selective and sensitive fluorescent sensor for Cu2+ in aqueous samples

In this study, we designed and synthesized a novel sensitive fluorescent sensor for Cu2+ cation by attaching two minoxidil molecules at the lower-rim of calix[4]arene annulus via the formation of two urea linkages. This chemosensor can selectively recognize Cu2+ in EtOH containing 5% H2O through a significant decline in fluorescence emission. The structure of the target molecule was determined by HRMS, 1H NMR, 13C NMR and FT-IR.

Enhancing doxorubicin anticancer activity with a novel polymeric platform photoreleasing nitric oxide.

Combinations of conventional chemotherapeutics with unconventional anticancer agents such as reactive oxygen and nitrogen species may offer treatment benefits for cancer therapies. Here we report a novel polymeric platform combining the delivery of Doxorubicin (DOXO) with the light-regulated release of nitric oxide (NO). An amphiphilic block-copolymer (P1) was designed and synthesized as the drug carrier, with pendant amine groups to attach DOXO via a urea linkage and a NO photodonor (NOPD) activable by visible light. The two grafted-copolymers (P1-DOXO and P1-NOPD) self-assembled via solvent displacement methods into nanoparticles (NPs), containing both therapeutic components (NP1) and, for comparison, the individual NOPD (NP2) and DOXO (NP3). All the NPs were fully characterized in terms of physicochemical, photochemical and photophysical properties. These experiments demonstrated that integration of the NOPD within the polymeric scaffold enhanced the NO photoreleasing efficiency when compared with the free NOPD, and that the proximity to DOXO on the polymer chains did not significantly affect the enhanced photochemical performance. Internalization of the NPs into lung, intestine, and skin cancer cell lines was investigated after co-formulation with Cy5 fluorescent tagged polymers, and cytotoxicity of the NPs against the same panel of cell lines was assessed under dark and light conditions. The overall results demonstrate effective cell internalization of the NPs and a notable enhancement in killing activity of the dual-action therapeutic NP1 when compared with NP2, NP3 and the free DOXO, respectively. This suggests that the combination of DOXO with photoregulated NO release, achieved through the mixed formulation strategy of tailored polymer conjugate NPs, may open new treatment modalities based on the use of NO to improve cancer therapies.

Tetrahydroquinoline units in flexible heteroarotinoids (Flex-Hets) convey anti-cancer properties in A2780 ovarian cancer cells

SHetA2 (NSC 721689), our lead Flex-Het anti-cancer agent, consists of a thiochroman (Ring A) and a 4-nitrophenyl (Ring B) linked by a thiourea bridge. In this work, several series of new analogs having a tetrahydroquinoline (THQ, Ring A) unit connected by a urea or thiourea linker to a 4-substituted phenyl (Ring B) have been prepared and evaluated relative to SHetA2 in terms of binding affinity with mortalin and inhibition of A2780 ovarian cancer cells. Six of the derivatives equaled or exceeded the efficacy shown by SHetA2. Compounds 1a-d (series 1), lacking a methyl on the Ring A nitrogen and the gem-dimethyls on the adjacent carbon, showed only weak activity. Salt 2, the quaternized N,N-dimethyl iodide salt analog of 1a, also possessed very modest growth inhibition in the cell line studied. Series 3 compounds, which had a C3 ketone and an N-methyl replacing the sulfur in Ring A, were most successful. Compound 3a [Ring A = 1,2,2,4,4-pentamethyl-3-oxo-1,2,3,4-tetrahydroquinolin-6-yl; urea linker; Ring B = 4-nitrophenyl] had slightly lower potency (IC50 3.8 μM), but better efficacy (94.8%) than SHetA2 (IC50 3.17 μM, efficacy 84.3%). In addition, 3c and 3d [urea and thiourea linkers, respectively; Ring B = 4-(trifluoromethyl)phenyl] and 3e and 3f [urea and thiourea linkers, respectively; Ring B = 4-(trifluoromethoxy)phenyl] were also evaluated since these agents possessed electron-withdrawing groups with H-bonding capability. All displayed good activity. Compounds 3c and 3e showed improvement in both potency and efficacy compared to SHetA2. In general, when the linker group between Rings A and B was a urea, efficacy values slightly exceeded those with a thiourea linker in the carbonyl-containing THQ systems 3a-g. In contrast, when Ring A possessed the 1,2,2,4,4-pentamethyl-3-hydroxytetrahydroquinolin-6-yl unit (4a-f, series 4), very modest potency and efficacy was observed. Model compound 5, an exact N-methyl THQ analog of SHetA2, demonstrated less potency (IC50 4.5 μM), but improved efficacy (91.7%). Modeling studies were performed to rationalize the observed results.

Use of a Thermally Degradable Chemical Vapor Deposited Polymer Film for Low Damage Plasma Processing of Highly Porous Dielectrics

Nanoporous materials show a large surface area and co-continuous topology, leading to a high sensitivity to chemically active components over macroscopic length scales. The processing of nanoporous systems can be complex, causing modifications of the original material, or appearance of unwanted contaminants. The present work report on a protection method based on temporary filling by a sacrificial template polymer, forming in-situ a reversible urea linkage. Microporous organo-silicate low-k dielectric thin films are used as demonstrators, exposed to aggressive plasma discharges. Depending on the studied material, the fraction of filled pore volume varies between 29 and 66 %, with a homogeneous spatial distribution. The filling component is formed by a blend of urea-linked polymer and isocyanate-terminated monomers, is stable during plasma processing and can be fully removed by annealing above 300°C. This sacrificial filler protect the internal structure of the porous dielectric from the plasma, leading to...

Spray processable polyurea formulations: Effect of chain extender length on material properties of polyurea coatings

ABSTRACTThe increasing usage of polyurea coatings has attracted the attention of researchers worldwide. Commercial polyurea formulations contain chain extenders as an essential ingredient, which increases the possibility of intermolecular H‐bonding by bringing the urea linkages closer. In this work, we establish the effect of increasing chain length of chain extender on the material properties of the polymer. Different types of chain extender were blended with a long chain diamine and subsequently reacted with an MDI‐based isocyanate prepolymer through a reactive spray processing technique. Polyurea coatings containing aromatic chain extenders were found to exhibit higher tensile strength as compared to their aliphatic analogues. Increasing the chain length of the aliphatic chain extender led to a reduction in the mechanical strength. A suitable combination of aromatic and aliphatic chain extender of short length was found to force the macromolecule to orient in such a fashion so as to result in optimal H‐bonding. This manifested in terms of improved processability, as confirmed by chemorheological investigations. Fourier transform infrared spectroscopy was used to understand the H‐bonded internal structure of the polymer. Optimum H‐bonding resulted in improved mechanical properties of the spray‐coated polyurea. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48573.

Influencing the properties of LigninPU films by changing copolyol chain length, lignin content and NCO/OH mol ratio

The polyurethane films with chemical incorporation of lignin (ligninPU) films were synthesized using kraft lignin (KL), 4,4′-Methylene diphenyl diisocyanate (MDI) and polypropylene glycol (PPG) copolyols and characterized. The effect of PPG chain lengths, lignin content, and NCO/OH mol ratio on crosslink density, thermal and mechanical properties of solution casted LigninPU films were studied. In general, homogenous and good quality films were obtained, irrespective of poor miscibility between PPG and KL. FTIR established the formation of urethane as well as urea linkages and covalent incorporation of lignin macromers within the PU network. The crosslink density (CD) values were between 0.2 and 1.2 × 10−3 mol cm−3. They were mainly influenced by lignin W% and increased with lignin content. A complex effect of change in NCO/OH ratio at constant lignin content and PPG copolyol on the CD values was observed. The thermal stability was higher for the films prepared with longer PPG copolyols at constant NCO/OH mol ratio and lignin content. The char yield for the ligninPU films increased as the NCO/OH ratio was increased from 1.1 to 1.5. The glass transition temperatures of the films were mainly influenced by the PPG chain length. PPG 425 based films were brittle at room temperature and exhibited Tg above 40 °C. Whereas the longer PPG derived ligninPU displayed more flexibility and featured Tg near or below room temperature. The mechanical properties of the films were found to deteriorate with increasing PPG chain length. The ultimate tensile strength and Young’s modulus increased with increasing lignin content, however % elongation at break decreased.

Design, synthesis, biological evaluation and molecular docking study of arylcarboxamido piperidine and piperazine-based hydroxamates as potential HDAC8 inhibitors with promising anticancer activity

HDAC8 has been established as one of the vital targets as far as the cancer is concerned. Different compounds having potential HDAC inhibitory activity have been approved by USFDA. However, none of these compounds are selective towards specific HDAC isoform. In this current study, some new hydroxamate derivatives with alkylpiperidine and alkylpiperazine linker moieties have been designed, synthesized and biologically evaluated. All these compounds are effective HDAC8 inhibitors comprising more or less similar cytotoxic potential against different cancer cell lines. It is observed that the piperazine scaffold containing compound is more active than the compound with piperidine scaffold for exerting HDAC8 inhibitory activity. Moreover, the 4-quinolyl cap group is better than the biphenyl group which is better than the benzyl group for producing higher HDAC8 inhibition as well as cytotoxicity. These compounds displayed selective HDAC8 inhibition over HDAC3. Moreover, these compounds showed an increased caspase3/7 activity suggesting their anticancer potential through modulation of apoptotic pathways. Molecular docking study with three potent compounds was performed with both HDAC3 and HDAC8 enzymes to understand the selectivity profile of these compounds. Compound containing 4-quinolyl cap group with alkyl piperazinyl urea linker moiety has been emerged out as the lead molecule that may be further modified to design more effective and selective HDAC8 inhibitors in future.

Thermomechanical characterization of thermoplastic polyimide–polyurea to improve the chain interaction via internal hydrogen bonds

Recently, we have studied polyimides (PIs) synthesized by incorporating an aromatic diamine monomer with a methylene linker, 4,4′‐methylenebis(2,6‐dimethylaniline), to make a robust main chain along with aliphatic polyetherdiamine backbone linkers to reduce rigidity. In this report, we incorporate a urea linkage into these materials in order to observe the effect of additional hydrogen bonding. The polymers are designed to exhibit thermal properties in between those of conventional aromatic PIs and polymers with wholly aliphatic ether diamine links. Herein, we demonstrate that the addition of 1,6 hexamethylene diisocyanate and the increase of hydrogen bonds at the urea linkage can be used to improve the thermal and mechanical properties of the PI. Furthermore, the imide ring is an important component to maintain the thermal stability characteristics in polyimide–polyurea hybrids. The polymers were characterized by FTIR, thermomechanical and calorimetric analysis, microhardness, and tensile testing. POLYM. ENG. SCI., 59:1948–1959, 2019. © 2019 Society of Plastics Engineers

Research on the interfacial reaction between amine group in urea and the coating materials of polyurethane coated urea

In this work, the polyurethane coated urea (PCU) and PE coated urea (PECU) were prepared by spraying the coating material. The isocyanates coatings on the surface of urea and granule inorganic compound fertilizer (NPK) were prepared and their infrared spectra were compared. The polyurethane coatings of PCU was analyzed by IR. The interface morphology between the PU coating and PE coating PECU and the surface of urea was compared by scanning electron microscope. The inner and outer surfaces morphology of polyurethane coatings was studied. The results showed that the peak of -NCO groups in the infrared spectrum of the coating on urea was weaker than of the coating on NPK, while the peaks of N-H, C-N and C = O were all relatively stronger, which proved that -NH2 in urea reacted with -NCO during the coating formation. SEM images showed that there was an obvious gap between PE coating and its urea core, while PU coating was tightly bonded with the surface of urea core, and the inner surface of PU coating had something undissolved after fully dissolved in water, which further illustrated that urea participate in the reaction of isocyanates with polyols. All of this results demonstrated that the amine group (-NH2) in urea reacted with the -NCO group in isocyanates and urea linkage (-NH-CO-NH-) was formed in the polyurethane coating.

Synthesis and CO2 separation of novel polyurethane membranes containing urea linkages

ABSTRACTWe synthesized novel polyurethane (PU) membranes from isophorone diisocyanate (IPDI), poly(ethylene glycol) (PEG) with a molecular weight of 2000, aminopropyl‐terminated poly(dimethyl siloxane) (PDMS) with a molecular weight of 2000, and 1,4‐butanediol (BDO) via a two‐step polymerization. The structure of each synthesized membrane was studied through Fourier transform infrared spectroscopy and gel permeation chromatography. The effect of the thermal behavior was determined by differential scanning calorimetry and thermogravimetric analysis. The gas‐permeability characteristics of the PU membranes were then tested for a single gas. The results show that the permeability of CO2 (PCO2) gradually increased with PDMS content. Among these PU membranes, PU‐d (PEG/PDMS = 1:1, PEG/PDMS/IPDI/BDO = 1:3:2) showed the best PCO2 (132.6 Barrer) at 25°C and 1 bar pressure. The gas‐permeability coefficients of each PU membrane at different operating temperatures were investigated, and the results show that PCO2 reached 302.6 Barrer at 65°C and 1 bar. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47723.