Incorporation Of Hydrophobic Groups Research Articles

Mussel‐Inspired Polyesters with Aliphatic Pendant Groups Demonstrate the Importance of Hydrophobicity in Underwater Adhesion

AbstractRecognizing the potential for synthetic adhesives that can function in wet environments, elements of mussel foot proteins such as L‐3,4‐dihydroxyphenylalanine (DOPA) and phosphoserine have been incorporated into synthetic adhesives. Such adhesives have corroborated the advantage of surface active groups like DOPA, but have not yet demonstrated superior performance in wet or underwater environments, without using organic solvents. What has been conspicuously absent from such designs is the effect of hydrophobic components in the performance of underwater adhesives. Herein it is shown that incorporation of hydrophobic groups in low modulus polyester adhesives provides very high lap‐shear strength and resistance to water penetration. In addition to the excellent performance in wet conditions, the designed adhesive can be applied underwater without any solvent, is biodegradable, and is designed from soybean oil, which is a readily available and renewable resource.

Synthesis and rheological properties of hydrophobically modified poly(vinyl alcohol)

A novel series of water-soluble hydrophobically modified poly(vinyl alcohol) (HMPVA) with various hydrophobe contents was prepared by grafting poly(vinyl alcohol) (PVA) using 1-dodecanol and toluene-2,4-diisocyanate as hydrophobic monomer and coupling agent, respectively. The chemical structure of HMPVA was analyzed by Fourier Transform Infrared Spectrometer (FTIR) and 1H NMR. Rheological properties of the aqueous solutions also confirmed the incorporation of hydrophobic groups into PVA. In dilute concentration regime, HMPVAs exhibited lower intrinsic viscosity than PVA, suggesting that HMPVA molecules were more shrunken. While the aqueous solution viscosity was enhanced due to hydrophobic modification at a high concentration, and HMPVAs with higher hydrophobe contents exhibited lager values of apparent viscosities. Over a frequency range of 1 to102 rad/s, the dynamic storage modulus of PVA solution was smaller than the dynamic loss modulus whereas the dynamic storage modulus of HMPVAs solutions was greater than the dynamic loss modulus, indicating the evolution of viscoelastic solid properties in HMPVAs solutions. The yield stress of PVA was nearly zero whereas that of HMPVAs represented positive values, implying that networks were present in HMPVAs solutions.

Cationic amphipathic peptides accumulate sialylated proteins and lipids in the plasma membrane of eukaryotic host cells

Cationic antimicrobial peptides (CAMPs) selectively target bacterial membranes by electrostatic interactions with negatively charged lipids. It turned out that for inhibition of microbial growth a high CAMP membrane concentration is required, which can be realized by the incorporation of hydrophobic groups within the peptide. Increasing hydrophobicity, however, reduces the CAMP selectivity for bacterial over eukaryotic host membranes, thereby causing the risk of detrimental side-effects. In this study we addressed how cationic amphipathic peptides—in particular a CAMP with Lysine–Leucine–Lysine repeats (termed KLK)—affect the localization and dynamics of molecules in eukaryotic membranes. We found KLK to selectively inhibit the endocytosis of a subgroup of membrane proteins and lipids by electrostatically interacting with negatively charged sialic acid moieties. Ultrastructural characterization revealed the formation of membrane invaginations representing fission or fusion intermediates, in which the sialylated proteins and lipids were immobilized. Experiments on structurally different cationic amphipathic peptides (KLK, 6-MO-LF11-322 and NK14-2) indicated a cooperation of electrostatic and hydrophobic forces that selectively arrest sialylated membrane constituents.

Ultrabright Fluorescent Mesoporous Silica Nanoparticles

The first successful approach to synthesizing ultrabright fluorescent mesoporous silica nanoparticles is reported. Fluorescent dye is physically entrapped inside nanochannels of a silica matrix created during templated sol-gel self-assembly. The problem of dye leakage from open channels is solved by incorporation of hydrophobic groups in the silica matrix. This makes the approach compatible with virtually any dye that can withstand the synthesis. The method is demonstrated using the dye Rhodamine 6G. The obtained 40-nm silica particles are about 30 times brighter than 30-nm coated water-soluble quantum dots. The particles are substantially more photostable than the encapsulated organic dye itself.

Copolymers for Hepatocyte‐Specific Targeting Carrying Galactose and Hydrophobic Alkyl Groups

Core-forming hydrophobic alkyl groups were incorporated into amphiphilic PVLA to enhance the stability and inclusion ability of the homopolymeric micelles in water. The CAC and hepatocyte targeting in the synthesized P(VLA-co-VBH) were investigated in vitro. The CAC of the copolymers decreased and the stability of the copolymeric micelles increased with the incorporation of hydrophobic groups into the homopolymer. The galactose moieties in the copolymer could be recognized by the ASGP-R of the hepatocytes through a receptor-mediated mechanism. The copolymers efficiently delivered a water-insoluble drug to the hepatocytes. Hence, they be used to deliver hydrophobic drugs to cure various liver diseases.

Mannose Glycoconjugates Functionalized at Positions 1 and 6. Binding Analysis to DC-SIGN Using Biosensors

The design of glycoconjugates to allow the generation of multivalent ligands capable of interacting with the receptor DC-SIGN is a topic of high interest due to the role played by this lectin in pathogen infections. Mannose, a ligand of this lectin, could be conjugated at two different positions, 1 and 6, not implicated in the binding process. We have prepared mannose conjugates at these two positions with a long spacer to allow their attachment to a biosensor chip surface. Analysis of the interaction between these surfaces and the tetravalent extracellular domain (ECD) of DC-SIGN by SPR biosensor has demonstrated that both positions are available for this conjugation without affecting the protein binding process. These results emphasize the possibility to conjugate mannose at position 6, allowing the incorporation of hydrophobic groups at the anomeric position to interact with hydrophobic residues in the carbohydrate recognition domain of DC-SIGN, increasing binding affinities. This fact is relevant for the future design of new ligands and the corresponding multivalent systems for DC-SIGN.

Effect of Hydrophobic Modification on Rheological and Swelling Features during Chemical Gelation of Aqueous Polysaccharides

Rheological characteristics during chemical gelation with the cross-linker ethylene glycol diglycidyl ether (EGDE) of semidilute aqueous solutions of hydroxyethylcellulose (HEC) and of two hydrophobically modified analogues (HM-1-HEC and HM-2-HEC) are reported. In addition, rheological features of gelling samples (dextran and its hydrophobically modified analogue (HM-dextran)) of a different structure have been examined. Some swelling experiments on these gels in the postgel region are also reported. The gelation time of the hydroxyethylcellulose systems decreased with increasing cross-linker concentration, and incorporation of hydrophobic units of HEC resulted in a slower gelation. The time of gelation for the dextran system was only slightly affected by the incorporation of hydrophobic groups (HM-dextran). At the gel point, a power law frequency dependence of the dynamic storage modulus (G' proportional to omegan') and loss modulus (G'' proportional to omegan'') was observed for all gelling systems with n' = n'' = n. The attachment of hydrophobic moieties on the dextran chains had virtually no impact on the value of n (n = 0.77), and the percolation model describes the incipient dextran gels. By increasing the number of hydrophobic groups of the HEC polymer, the value of n for the corresponding incipient gel drops significantly, and the value of the gel strength parameter increases strongly. Incorporation of hydrophobic units in the HEC chains promotes the formation of stronger incipient gels because of the contribution from the hydrophobic association effect. The frequency dependence of the complex viscosity reveals that all the investigated gels become more solidlike in the postgel domain. Far into the postgel region, the hydrophobicity of HEC plays a minor role for the strength of the gel network, whereas the values of the complex viscosity are significantly higher for HM-dextran than for the corresponding dextran gel. The swelling experiments on HEC, HM-1-HEC, and HM-2-HEC systems disclose that the degree of swelling of the postgels in water is quite different, depending on the relative distance from the gel point at which the cross-linker reaction is quenched. At a given distance from the gel point, the swelling of the HEC gel is less pronounced than for the corresponding hydrophobically modified samples. At this stage, the swelling of the HM-dextran gel is stronger than for the dextran gel.