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Controllable and visible delivery of therapeutic agents is critical for tumor precise therapy. Tumor targeting and deep penetration of therapeutic agents are still challenging issues for controllable delivery. Visible drug delivery with imaging navigation can optimize the treatment window for personalized medicine. Herein, a biomimetic platelet intelligent vehicle with navigation (IRDNP-PLT) was developed to achieve controllable and visible delivery with a navigation system, a driving system, and a loading system. The platelets acted as engines and drug repositories to exert the target driving and delivery functions. The fluorescent photothermal agent IR-820 was introduced in the platform to offer an imaging navigation for the intelligent platelet vehicle in addition to photothermal therapy. The nanodrug-loaded platelets enabled efficient drug loading and controlled release of the therapeutic payload by encapsulating photothermal-/pH-sensitive chemotherapeutic nanoparticles (PDA@Dox NPs). In in vivo experiments on 4T1 tumor-bearing mice models, IRDNP-PLT performed well in tumor targeting and showed excellent therapeutic efficacy and tumor recurrence prevention ability. The intelligent platelet vehicle achieved the functions of tumor targeting and deep penetration, fluorescence imaging guidance, photocontrolled drug release, and chemo-photothermal combination therapy, suggesting the advancement for tumor precise delivery and efficient therapy.

Chemotherapy is the recommended treatment for patients with advanced pancreatic ductal adenocarcinoma (PDAC). However, efficacy of traditional chemotherapy is not satisfactory due to the presence of a dense dysplastic tumor stroma which prevents drug accumulation in and deep penetration into tumors. To overcome these obstacles, we designed and synthesized peptide dendrimers as potentiators of conventional chemotherapy. The dendrimers markedly promoted free doxorubicin accumulation and penetration deeply into 3D multicellular PDAC tumor cultures upon co-incubation. Co-administration of the dendrimer and doxorubicin into PDAC tumor xenograft-bearing mice greatly increased the doxorubicin concentration in the tumor. In addition, the dendrimer also promoted free doxorubicin internalization into PDAC cells upon co-incubation in media mimicking tumor microenvironment. Finally, a significant enhancement in the anticancer efficacy of doxorubicin and gemcitabine when either of the drugs was individually co-administered with the dendrimer into PDAC tumor xenograft-bearing mice was observed. This was especially pronounced for the combination treatment with the dendrimer and gemcitabine, resulting in a tumor weight decrease to 12.9% compared to the treatment with gemcitabine alone. This can be attributed to the combination of the multi-functionalities of the dendrimer, i.e., promoting free drug accumulation and penetration deeply into tumors and internalization into cancer cells., (Copyright © 2021 Elsevier B.V. All rights reserved.)

The severe side-effects and drug resistance development of conventional chemotherapy are mainly caused by poor tumor penetration as well as nonspecific biodistribution and insufficient cellular uptake of drugs. Herein a branched arginine-rich polymer was synthesized and co-administration of this polymer with doxorubicin, a model drug of chemotherapeutic agents, overcame simultaneously the three obstacles shown above. Co-incubation of the polymer promoted doxorubicin penetration deeply into multicellular tumor spheroids and internalization into cancer cells. Upon co-injection of the polymer with doxorubicin into tumor-bearing mice, the enhanced drug accumulation in and deep penetration into tumor tissue were observed compared to injection of doxorubicin alone. A combined therapy of doxorubicin and the polymer in the treatment of tumor-bearing mice showed a marked enhancement in anticancer efficacy compared to doxorubicin alone. Notably, the treatment with the combination regime reduced the doxorubicin dose to one fifth without reducing the antitumor efficacy compared to the treatment with doxorubicin alone. The possible mechanism of action of the polymer was postulated, in which the guanidinium groups of arginine residues in the polymer may play a pivotal role in the action., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Despite progress on DNA-assembled nanoparticle (NP) superstructures, their complicated synthesis procedures hamper their potential biomedical applications. Here, we present an exceptionally simple strategy for the synthesis of single-stranded DNA (ssDNA) assembled Fe 3 O 4 supraparticles (DFe-SPs) as magnetic resonance contrast agents. Unlike traditional approaches that assemble DNA-conjugated NPs via Watson-Crick hybridization, our DFe-SPs are formed with a high yield through one-step synthesis and assembly of ultrasmall Fe 3 O 4 NPs via ssDNA-metal coordination bridges. We demonstrate that the DFe-SPs can efficiently accumulate into tumors for sensitive MR imaging. By virtue of reversible DNA-metal coordination bridges, the DFe-SPs could be disassembled into isolated small NPs in vivo, facilitating their elimination from the body. This work opens a new avenue for the ssDNA-mediated synthesis of superstructures, which expands the repertoire of DNA-directed NP assembly for biomedical applications.

Conventional chemotherapy is a standard care for many cancers at present. However, their severe dose-dependent side effects are the major impediment for successful cancer therapy. Herein nanoparticles were used as a potentiator to enhance the uptake of free chemotherapeutic agents by cancer cells during chemotherapy. A pH-sensitive β-carboxylate amide group-containing polymer, bPEI-DMA, was obtained by a one-step chemical reaction of commercially available branched polyethyleneimine with 2,3-dimethylmaleic anhydride. The obtained single-macromolecule nanoparticles with a size of 6.4 nm possessed zwitterions and a slight net negative charge at neutral pH, and thereby showed low cytotoxicity. Incubation of MCF-7 cells with bPEI-DMA at tumor acidic pHs led to leakage of lactate dehydrogenase from the cells. Sequential incubation of bPEI-DMA and doxorubicin with MCF-7 cells at tumor acidic pHs caused enhanced uptake of doxorubicin by the cells. These results can be attributed to the tumor pH-triggered positive charge generation on the nanoparticles due to the hydrolysis of the β-carboxylate amide groups, and subsequently the positive charge caused an increase in cell membrane permeability. Sequential injection of bPEI-DMA and free doxorubicin or free cisplatin into nude mice bearing human tumors markedly inhibited the tumor growth, leading to a ~ 68% decrease in tumor volumes compared to injection of the free drugs alone. Sequential injection of bPEI-DMA and a half dose of free doxorubicin resulted in even greater tumor inhibition but less side effects than injection of a full dose of doxorubicin alone., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Antimicrobial peptides (AMPs) are regarded as next-generation antibiotics to replace conventional antibiotics due to their rapid and broad-spectrum antimicrobial properties and far less sensitivity to the development of pathogen resistance. However, they are susceptible to proteolysis in vivo by endogenous or bacterial proteases as well as induce the lysis of red blood cells, which prevent their intravenous applications. In this work, polyion complex (PIC) micelles of the cationic AMP MSI-78 and the anionic copolymer methoxy poly(ethylene glycol)-b-poly(α-glutamic acid) (mPEG-b-PGlu) were prepared to develop novel antimicrobial agents for potential application in vivo. With an increase in molar ratio of mPEG-b-PGlu to MSI-78, the complexation ability of the PIC micelles increased. FITC-labeled MSI-78 showed a sustained release from the PIC micelles. More importantly, these PIC micelles greatly decreased the hemolytic toxicity of MSI-78 to human red blood cells, without influencing its antimicrobial activity. Thus, this approach could be used as a suitable in vivo delivery method of AMPs in the future., (Copyright © 2018. Published by Elsevier B.V.)

Chlorambucil, a chemotherapeutic agent, is usually administered orally to treat chronic lymphocytic leukemia and some other types of cancers in regimens of conventional and metronomic chemotherapies. However, the hydrolytic instability of chlorambucil is a major limitation in achieving the optimum therapeutic performance. In this work, mesoporous polymeric microspheres were prepared by free radical suspension copolymerization of methyl acrylate and divinylbenzene in the presence of porogen. Chlorambucil was loaded into the mesoporous polymeric microspheres through adsorption of the drug in aqueous media with high loading capacity up to more than 350 mg/g. Chlorambucil-loaded mesoporous polymeric microspheres showed sustained release property in media simulating gastrointestinal fluids, with nearly zero order release kinetics. Furthermore, the mesoporous polymeric microspheres as carriers greatly stabilized chlorambucil against its hydrolysis. The hydrolyzation percentage of chlorambucil that was adsorbed on the microspheres after incubation for 36 h in media simulating gastrointestinal fluids was less than 10%, while more than 90% of free chlorambucil hydrolyzed after incubation in the same media for 4 h. The chlorambucil-loaded mesoporous polymeric microspheres may be used as oral sustained release formulations, especially as oral formulations for the application in metronomic chemotherapy., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Despite extensive investigations, the clinical translation of nanocarrier-based drug delivery systems (NDDS) for cancer therapy is hindered by inefficient delivery and poor tumor penetration. Conventional chemotherapy by administration of free small molecule anticancer drugs remains the standard of care for many cancers. Herein, other than for carrying and releasing drugs, small nanoparticles were used as a potentiator of conventional chemotherapy by co-administration with free chemotherapeutic agents. This strategy avoided the problems associated with drug loading and controlled release encountered in NDDS, and was also much simpler than NDDS. Negatively charged poly(amido amine)-2,3-dimethylmaleic monoamide (PAMAM-DMA) dendrimers were prepared, which possessed low toxicity and can be converted to positively charged PAMAM dendrimers responsive to tumor acidic pH. The in situ formed PAMAM in tumor tissue promoted cellular uptake of co-administered doxorubicin by increasing the cell membrane permeability, and subsequently enhanced the cytotoxicity of doxorubicin. The small size of the dendrimers was favorable for deep penetration in tumor. Co-injection of PAMAM-DMA with doxorubicin into nude mice bearing human tumors almost completely inhibited tumor growth, with a mean tumor weight reducing by 55.9% after the treatment compared with the treatment with doxorubicin alone., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Methotrexate as a model drug with poor aqueous solubility was adsorbed into porous polymeric adsorbents, which was used as oral sustained release formulations. In vitro release assay in simulated gastrointestinal fluids showed that the methotrexate-loaded adsorbents showed distinct sustained release performance. The release rate increased with increase in pore size of the adsorbents. In vivo pharmacokinetic study showed that the maximal plasma methotrexate concentrations after oral administration of free methotrexate and methotrexate-loaded DA201-H (a commercial porous polymeric adsorbent) to rats occurred at 40min and 5h post-dose, respectively; and the plasma concentrations decreased to 22% after 5h for free methotrexate and 44% after 24h for methotrexate-loaded DA201-H, respectively. The load of methotrexate into the porous polymeric adsorbents not only resulted in obvious sustained release, but also enhanced the oral bioavailability of methotrexate. The areas under the curve, AUC 0-24 and AUC 0-inf , for methotrexate-loaded DA201-H increased 3.3 and 7.7 times, respectively, compared to those for free methotrexate., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Addition polymerization usually results in polymers with long carbon-carbon main chains. Cyanoacrylate (CA) is arguably an important example of such polymerization and has gained widespread acceptance as an all-purpose adhesive. However, CA-based medical adhesives have never been approved by the U.S. Federal Drug Administration for use below the skin, mainly due to the low biodegradability and biocompatibility of their solid glue after polymerization. In this research, a cross-linking strategy involving the combination of alkyl-CA and the cross-linking agent poly(ethylene glycol)-di(cyanoacrylate) (CA-PEG-CA) to form a copolymeric network was used to synthesize a new generation of biodegradable CA medical adhesives. The degradability could be modulated by adjusting the ratio of CA-PEG-CA to alkyl-CA and the length of PEG. An optimal composite adhesive, LKJ11, was shown to have excellent biodegradability, adhesive capability, and biocompatibility. Importantly, the molecular weight of polycyanoacrylate chains in the polymerized LKJ11 was greatly reduced compared to those polymerized from pure butyl-CA. Thus, the degradation product could be readily extracted. The results showed that LKJ11 represents a new generation of CA-based biodegradable medical adhesives. This advance also provides a general strategy to facilitate the conversion of other polymers with long carbon-carbon main chains to a biodegradable form, thereby expanding the novel applications available for traditional polymeric materials.

Although PEG remains the gold standard for stealth functionalization in drug delivery field up to date, complete inhibition of protein corona formation on PEG-coated nanoparticles remains a challenge. To improve the stealth property of PEG, herein an α-glutamyl group was conjugated to the end of PEG and polymeric micelles with α-glutamyl-terminated PEG shells were prepared. After incubation with bovine serum albumin or in fetal calf serum, the size of the micelles changed slightly, while the size of the micelles of similar diblock copolymer but without α-glutamyl group increased markedly. These results indicated that the micelles with α-glutamyl-terminated PEG shells showed low non-specific protein adsorption. In vivo blood clearance kinetics assay showed that the micelles with α-glutamyl-terminated PEG shells exhibited a longer in vivo blood circulation time compared with similar micelles but without α-glutamyl groups. The better stealth property of the micelles with α-glutamyl-terminated PEG shells was presumably attributed to the zwitterionic property of the α-glutamyl groups., (Copyright © 2015 Elsevier B.V. All rights reserved.)

To overcome barriers associated with gene delivery, a series of peptides consisting of multifunctional fragments, including a cationic amphiphilic α-helical antimicrobial peptide (AMP), a cell penetrating peptide (CPP), TAT, a stearyl moiety, and cysteine residues, were designed and synthesized for evaluation as non-viral gene vectors. TAT and AMP segments were utilized to mediate cellular uptake and endosomal escape, respectively. Stearyl moieties provide an intramolecular hydrophobic environment to promote AMPs to form an α-helical conformation in PBS, and this is beneficial for DNA binding, cellular uptake, and endosomal escape. The α-helical content of the peptides, as well as the particle size, zeta potential, and morphology of the peptide/DNA complexes, was characterized. Fluorescence activated cell sorting (FACS) and confocal microscopy data showed that the peptides were able to efficiently translocate a pGL3 control plasmid across the plasma membrane via endocytosis, and then they successfully evaded endosomal entrapment and possible metabolic degradation. Moreover, one of the peptide vectors exhibited a high transfection efficiency similar to that of Lipofectamine 2000, concomitant with lower cytotoxicity. Overall, a combination of the four functional segments tested was used to generate a non-viral gene vector that synergistically promoted cellular uptake, endosomal escape, and gene expression.

A facile and highly efficient new approach (namely RAFT coupling chemistry) to obtain well-defined hydrophilic molecularly imprinted polymer (MIP) microspheres with excellent specific recognition ability toward small organic analytes in the real, undiluted biological samples is described. It involves the first synthesis of "living" MIP microspheres with surface-bound vinyl and dithioester groups via RAFT precipitation polymerization (RAFTPP) and their subsequent grafting of hydrophilic polymer brushes by the simple coupling reaction of hydrophilic macro-RAFT agents (i.e., hydrophilic polymers with a dithioester end group) with vinyl groups on the "living" MIP particles in the presence of a free radical initiator. The successful grafting of hydrophilic polymer brushes onto the obtained MIP particles was confirmed by SEM, FT-IR, static contact angle and water dispersion studies, elemental analyses, and template binding experiments. Well-defined MIP particles with densely grafted hydrophilic polymer brushes (∼1.8 chains/nm(2)) of desired chemical structures and molecular weights were readily obtained, which showed significantly improved surface hydrophilicity and could thus function properly in real biological media. The origin of the high grafting densities of the polymer brushes was clarified and the general applicability of the strategy was demonstrated. In particular, the well-defined characteristics of the resulting hydrophilic MIP particles allowed the first systematic study on the effects of various structural parameters of the grafted hydrophilic polymer brushes on their water-compatibility, which is of great importance for rationally designing more advanced real biological sample-compatible MIPs.

A facile and highly efficient approach to obtain narrowly dispersed hydrophilic and magnetic molecularly imprinted polymer microspheres with molecular recognition ability in a real biological sample as good as what they show in the organic solvent-based media is described for the first time.

Micelles with surface morpholino groups were stealthy at blood and normal tissue pH (7.4) due to the unprotonated hydrophilic morpholino groups on the surfaces. At tumor pH (<7), the micelle surfaces were positively charged because of the protonation of the morpholino groups, which promoted the cellular uptake of the micelles.

Magnetic nanoparticles (MNPs) functionalized with specific ligands are emerging as a highly integrated platform for cancer targeting, drug delivery, and magnetic resonance imaging applications. In this study, we describe a multifunctional magnetic nanoparticle system (FITC-Tat MNPs) consisting of a fluorescently labeled cell penetrating peptide (FITC-Tat peptide), a biocompatible block copolymer PEG(600)-b-poly(glycerol monoacrylate) (PEG(600)-b-PGA), and a superparamagnetic iron oxide (SPIO) nanoparticle core. The particles were prepared by direct chemisorption of PEG(600)-b-PGA conjugated with FITC-Tat peptide on the SPIO nanoparticles. FITC-MNPs without Tat were prepared for comparison. Flow cytometry assays revealed significantly higher uptake of FITC-Tat MNPs compared to FITC-MNPs in Caco-2 cells. These results were confirmed using confocal laser scanning microscopy (LSCM), which further demonstrated that the FITC-Tat MNPs accumulated in the cytoplasm and nucleus while the FITC-MNPs were localized in the cell membrane compartments. The FITC-Tat MNPs did not exhibit observable cytotoxicity in MTS assays., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Random and diblock copolymers of 2-(N,N-dimethylamino)ethyl methacrylate and butyl methacrylate are prepared by ATRP. As mimics of cationic antimicrobial peptides, the random and diblock copolymers show similar antimicrobial activities. In contrast, the diblock copolymers have much lower hemolytic activities than the random copolymers. The cell selectivity (HC(50)/MIC, where HC(50) is the concentration to lyse 50% of human red blood cells and MIC is the minimum concentration to inhibit bacterial growth) of the diblock copolymers are 150 to 27,500 times higher than that of random copolymers with similar compositions., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Multifunctional nanocarriers with multilayer core-shell architecture were prepared by coating superparamagnetic Fe(3)O(4) nanoparticle cores with a mixture of the triblock copolymer methoxy poly(ethylene glycol)-b-poly(methacrylic acid-co-n-butyl methacrylate)-b-poly(glycerol monomethacrylate) and the folate-conjugated block copolymer folate-poly(ethylene glycol)-b-poly(glycerol monomethacrylate). The model anticancer agent adriamycin (ADR), containing an amine group and a hydrophobic moiety, was loaded into the nanocarrier at pH 7.4 by ionic bonding and hydrophobic interactions. The release rate of the loaded drug molecules was slow at pH 7.4 (i.e. mimicking the blood environment) but increased significantly at acidic pH (i.e. mimicking endosome/lysosome conditions). Acid-triggered drug release resulted from the polycarboxylate protonation of poly(methacrylic acid), which broke the ionic bond between the carrier and ADR. Cellular uptake by folate receptor-overexpressing HeLa cells of the folate-conjugated ADR-loaded nanoparticles was higher than that of non-folated-conjugated nanoparticles. Thus, folate conjugation significantly increased nanoparticle cytotoxicity. These findings show the potential viability of a folate-targeting, pH-responsive nanocarrier for amine-containing anticancer drugs., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Nanocarriers with multilayer core-shell architecture were prepared by coating a superparamagnetic Fe(3)O(4) core with a triblock copolymer. The first block of the copolymer formed the biocompatible outermost shell of the nanocarrier. The second block that contains amino groups and hydrophobic moiety formed the inner shell. The third block bound tightly onto the Fe(3)O(4) core. Chlorambucil (an anticancer agent) and indomethacin (an anti-inflammation agent), each containing a carboxyl group and a hydrophobic moiety, were loaded into the amino-group-containing inner shell by a combination of ionic and hydrophobic interactions. The release rate of the loaded drugs was slow at pH 7.4, mimicking the blood environment, whereas the release rate increased significantly at acidic pH, mimicking the intracellular conditions in the endosome/lysosome. This can be attributed to the disruption of the ionic bond caused by protonation of the carboxylate anion of the drugs and the swelling of the inner shell caused by protonation of the amino groups.

A 9-residue peptide, CP-1 (GLRILLLKV-NH(2)), is synthesized by solid-phase synthesis method. CP-1 is a C-terminal amidated derivative of a hydrophobic transmembrane segment (CP) of the T-cell antigen receptor (TCR) alpha-chain. CP-1 shows broad-spectrum antimicrobial activities against Gram-positive and Gram-negative bacteria with the minimal inhibitory concentration (MIC) values between 3 and 77microM. Circular dichroism (CD) spectral data shows that CP-1 adopts a well-defined beta-sheet structure in membrane-mimicking environments. CP-1 kills E. coli without lysing the cell membrane or forming transmembrane pores. However, CP-1 can penetrate the bacterial cell membranes and accumulate in the cytoplasm in both Gram-positive S. aureus and Gram-negative E. coli. Moreover CP-1 shows binding affinity for plasmid DNA. These results indicate that the killing mechanism of CP-1 likely involves the penetration into the cytoplasm and binding to intracellular components such as DNA.

PEGylation of peptide drugs prolongs their circulating lifetimes in plasma. However, PEGylation can produce a decrease in the in vitro bioactivity. Longer poly(ethylene glycol) (PEG) chains are favourable for circulating lifetimes but unfavourable for in vitro bioactivities. In order to circumvent the conflicting effects of PEG length, a hydrophobic peptide, using an antimicrobial peptide as a model, was PEGylated with short PEG chains. The PEGylated peptides self-assembled in aqueous solution into micelles with PEG shell and peptide core. In these micelles, the core peptides were protected by the shell, thus reducing proteolytic degradation. Meanwhile, most of the in vitro antimicrobial activities still remained due to the short PEG chain attached. The stabilities of the PEGylated peptides were much higher than that of the unPEGylated peptides in the presence of chymotrypsin and serum. The antimicrobial activities of the PEGylated peptides in the presence of serum, an ex vivo assay, were much higher than that of the unPEGylated peptide.

Poly[(glycidyl methacrylate)-co-(glycerol monomethacrylate)]-grafted magnetic microspheres were prepared by graft random copolymerization via ATRP from polymer microspheres with dispersed Fe(3)O(4) nanoparticles. Penicillin G acylase (PGA) was immobilized onto the polymer brush-grafted magnetic microspheres. The immobilized PGA prepared with initial glycidyl methacrylate/glycerol monomethacrylate ratios of 40/60 to 60/40 possessed higher catalytic activity than that prepared with higher proportions of glycidyl methacrylate in the initial monomer mixture. The immobilized PGA showed high thermal stability and enhanced tolerability to the pH variance.

Methoxypoly(ethylene glycol)-oligo(aspartic acid) (MPEG-Asp(n)-NH(2), n = 2-5) hybrid block copolymers were synthesized and used as stabilizers to prepare superparamagnetic Fe(3)O(4) nanoparticles with magnetite as the inner core and and poly(ethylene glycol) as the hydrophilic outer shell. The aqueous dispersions of the nanoparticles were stable at pH 2-11 and in 1M NaCl solution, when repeat number, n, was 3 or more. Transmission electron microscopy showed that the nanoparticles, stabilized with MPEG-Asp(3)-NH(2), were about 14 nm in diameter. Magnetic measurements indicated that MPEG-Asp(3)-NH(2)-coated iron oxide nanoparticles showed superparamagnetic behavior. Cell adhesion assay and in vitro cell viability/cytotoxicity studies showed that MPEG-Asp(3)-NH(2)-coated iron oxide nanoparticles had less effect on cell adhesion/viability and morphology, and less cytotoxicity compared with uncoated, poly (acrylic acid)-coated, and MPEG-poly(acrylic acid)-coated iron oxide nanoparticles.

The goal of this work was to investigate the synergistic effect between the electrostatic and hydrophobic interactions upon the uptake of organic ions with hydrophobic moieties by ion-exchange resins with hydrophobic matrixes. The uptake of neutral amino acids by a macroporous polystyrene-based strongly acidic cation-exchange resin (D001) and two strongly acidic cation-exchange resins (poly(2-acrylamido-2-methyl propanesulfonic acid) and poly(vinylsulfonic acid)) with much less hydrophobic matrixes essentially follow an ion exchange stoichiometry. However, the thermodynamic parameters of the uptakes indicate that besides electrostatic interaction, hydrophobic interaction also contributes to the affinity of the amino acids with hydrophobic side chains for D001. No detectable uptake capacities for the amino acids by D001AM, which was obtained by amidation of the sulfonic acid groups of D001, can be determined. Thus, it is deduced that the hydrophobic interaction alone contributes little to the uptake of these amino acids by D001, of which hydrophobicity is the same with or lower than that of D001AM. These results indicate that synergistic effect exists between the electrostatic and hydrophobic interactions when the two interactions exist in a chelate manner and the hydrophobic interaction contributes to the uptake even if the hydrophobic interaction is so weak that it contributes little to the uptake when it acts alone.

In our previous paper it was shown that the two C-terminal Gln residues of a C-terminal 15-residue fragment, Mel(12-26) (GLPALISWIKRKRQQ-NH2), of melittin and a series of individual substituted analogues might not involved in the interaction with bacterial membranes. In this paper, peptides with one and two Gln residues deletion, respectively, Mel(12-25) and Mel(12-24), were synthesized and characterized. Both of the deletion peptides showed higher antimicrobial activities than the parent peptide, Mel(12-26). If both of the Gln residues of Mel(12-26) were respectively replaced by a hydrophilic amino acid Gly, the antimicrobial activity increased slightly. If the Gln residue of Mel(12-25) was replaced by a hydrophobic amino acid Leu, the antimicrobial activity changed little, although the substituted peptide possessed much higher hydrophobicity and higher alpha-helical conformation percentage in 1,1,1,3,3,3-hexafluoro-2-propanol/water determined by circular dichroism spectroscopy (CD) than the parent peptide. These results indicated that the two C-terminal residues might be indeed not involved in the binding to bacterial membranes. The antimicrobial activity increasing with the residue deletion may be caused by the decrease of the translational and rotational entropic cost of the binding of the peptides to bacterial membranes because of the lower molecular weights of the deletion peptides.

Residues 1-9 of M(12-26) (GLPALISWIKRKRQQ-NH2), the C-terminal 15-residue segment of melittin, were substituted individually to change the hydropathicities in these positions. Antimicrobial and hemolytic activities of these peptides were determined. The results showed increased antimicrobial activities with increased hydrophobicities at almost all the positions studied. The effects at positions 2, 5, 8 and 9 were significant while the effects at the other positions were small. These two groups of residues were located on the opposite faces of the alpha-helix. In other words, the hydrophobicities of the two faces were favorable, but one face (the more favorable face) contributed more to the antimicrobial activities than the other (the less favorable face). The hydrophobicity, not the amphipathicity, seems to be crucial for antimicrobial activity. In contrast, the hydrophobicity of one face was favorable but the other was unfavorable for the hemolytic activity, indicating that the amphipathicity may be important for hemolysis. Interestingly, the more favorable face for antimicrobial activity was located opposite to the favorable face for hemolytic activity, indicating the direction of the hydrophobic face for the antimicrobial activity and direction of the amphipathicity for the hemolytic activity were also important.

Cystine and tyrosine were used as model sorbates to illustrate the design of sorbents with high sorption selectivity using two types of weak interactions that act synergistically. When two types of weak interactions are the driving forces in a sorption and they act synergistically, the second interaction would be effectively intramolecular. The entropy lost for the second interaction should be lower than that for the same interaction that occurs alone, and thus a significant enhancement of sorption should result. We designed an N-acetyl aminomethyl polystyrene resin (N-acetyl HC-D309), which was expected to sorb tyrosine through hydrophobic interaction and hydrogen bonding but not cystine. The chromatographic results for tyrosine and cystine indicate that the separation efficiencies on the N-acetyl HC-D309 column are higher than those on a styrene-divinylbenzene copolymer column, on which sorption should be driven by hydrophobic interaction only, and on an acrylamide-N,N'-methylene bisacrylamide copolymer column, on which sorption should be driven by hydrogen bonding only. Tyrosine as well as cystine had no retention at all on the acrylamide-N,N'-methylene bisacrylamide copolymer column. indicating the hydrogen bonding had little contribution to the sorption when it acted alone. The above results further indicate that hydrophobic interaction and hydrogen bonding contributed to the sorption of tyrosine on N-acetyl HC-D309 and they also acted synergistically. One of the conclusions of this paper is that some weak interactions which contribute little to the sorption when they act alone may contribute to the sorption when they act synergistically with other interactions.