A Synthetic Block Copolymer Regulates S1 Nuclease Fragmentation of Supercoiled Plasmid DNA

pH-Responsive Biomaterials for the Treatment of Dental Caries-A Focussed and Critical Review

Dental caries is a common and costly multifactorial biofilm disease caused by cariogenic bacteria that ferment carbohydrates to lactic acid, demineralizing the inorganic component of teeth. Therefore, low pH (pH 4.5) is a characteristic signal of the localised carious environment, compared to a healthy oral pH range (6.8 to 7.4). The development of pH-responsive delivery systems that release antibacterial agents in response to low pH has gained attention as a targeted therapy for dental caries. Release is triggered by high levels of acidogenic species and their reduction may select for the establishment of health-associated biofilm communities. Moreover, drug efficacy can be amplified by the modification of the delivery system to target adhesion to the plaque biofilm to extend the retention time of antimicrobial agents in the oral cavity. In this review, recent developments of different pH-responsive nanocarriers and their biofilm targeting mechanisms are discussed. This review critically discusses the current state of the art and innovations in the development and use of smart delivery materials for dental caries treatment. The authors' views for the future of the field are also presented.

pH-activated antibiofilm strategies for controlling dental caries

Dental biofilms are highly assembled microbial communities surrounded by an extracellular matrix, which protects the resident microbes. The microbes, including commensal bacteria and opportunistic pathogens, coexist with each other to maintain relative balance under healthy conditions. However, under hostile conditions such as sugar intake and poor oral care, biofilms can generate excessive acids. Prolonged low pH in biofilm increases proportions of acidogenic and aciduric microbes, which breaks the ecological equilibrium and finally causes dental caries. Given the complexity of oral microenvironment, controlling the acidic biofilms using antimicrobials that are activated at low pH could be a desirable approach to control dental caries. Therefore, recent researches have focused on designing novel kinds of pH-activated strategies, including pH-responsive antimicrobial agents and pH-sensitive drug delivery systems. These agents exert antibacterial properties only under low pH conditions, so they are able to disrupt acidic biofilms without breaking the neutral microenvironment and biodiversity in the mouth. The mechanisms of low pH activation are mainly based on protonation and deprotonation reactions, acids labile linkages, and H⁺-triggered reactive oxygen species production. This review summarized pH-activated antibiofilm strategies to control dental caries, concentrating on their effect, mechanisms of action, and biocompatibility, as well as the limitation of current research and the prospects for future study.

Structural Polymorphism of Single pDNA Condensates Elicited by Cationic Block Polyelectrolytes

DNA folding is a core phenomenon in genome packaging within a nucleus. Such a phenomenon is induced by polyelectrolyte complexation between anionic DNA and cationic proteins of histones. In this regard, complexes formed between DNA and cationic polyelectrolytes have been investigated as models to gain insight into genome packaging. Upon complexation, DNA undergoes folding to reduce its occupied volume, which often results in multi-complex associated aggregates. However, when cationic copolymers comprising a polycation block and a neutral hydrophilic polymer block are used instead, DNA undergoes folding as a single molecule within a spontaneously formed polyplex micelle (PM), thereby allowing the observation of the higher-order structures that DNA forms. The DNA complex forms polymorphic structures, including globular, rod-shaped, and ring-shaped (toroidal) structures. This review focuses on the polymorphism of DNA, particularly, to elucidate when, how, and why DNA organizes into these structures with cationic copolymers. The interactions between DNA and the copolymers, and the specific nature of DNA in rigidity; i.e., rigid but foldable, play significant roles in the observed polymorphism. Moreover, PMs serve as potential gene vectors for systemic application. The significance of the controlled DNA folding for such an application is addressed briefly in the last part.

pH-Responsive polymeric nanocarriers for efficient killing of cariogenic bacteria in biofilms

Traditional antibacterial treatments, such as chlorhexidine (CHX), destroy cariogenic biofilms. However, they exert negative effects in clinical applications, for example, teeth staining, taste disturbance and harm to oral tissue after a long-term exposure. Therefore, biocompatible strategies for efficient antibacterial drug delivery are in high demand. In this study, aimed at dental caries therapy enhancement, we designed a pH-responsive nanocarrier system, capable of releasing CHX in an acidic environment within cariogenic biofilms. Cationic poly(ethylene glycol)-block-poly(2-(((2-aminoethyl)carbamoyl)oxy)ethyl methacrylate) (PEG-b-PAECOEMA) was synthesized first. Modification of PAECOEMA by citraconic anhydride (CA) forms negatively charged PEG-b-PAECOEMA/CA, which could assemble into core-shell polyionic complex micelles (PICMs) when mixed with cationic CHX via electrostatic interactions. PICMs are stable in healthy neutral oral microenvironments with CHX encapsulated in the core and PEG shell exposed. Once in acidic milieu within caries-producing biofilms, they rapidly disassemble and release CHX cargo owing to degradation of citraconic amide groups. Molecular structures of the above copolymers were confirmed using 1H NMR and gel permeation chromatography (GPC) analysis. The pH-dependent degradation rates of citraconic amide in PEG-b-PAECOEMA/CA copolymer were measured by fluorescamine method. Atomic force microscopy (AFM) studies confirmed successful assembly of well-defined spherical PICMs in aqueous solution. The disassembly of PICMs in acidic microenvironment was observed using dynamic light scattering (DLS). PICMs showed an obvious pH-dependent drug release profile when the pH changed from 7.4 to 5.5. More importantly, the micellar system could reduce drug toxicity of CHX and exhibited outstanding antibacterial capability in the biofilm of Streptococcus mutans. Micelles constructed from pH-sensitive PEG-b-PAECOEMA/CA are highly promising for dental caries therapy and provide guidelines for drug-delivery system design in other acidic pathologic systems.

Block Copolymer Micelles in Nanomedicine Applications

Polymeric micelles are demonstrating high potential as nanomedicines capable of controlling the distribution and function of loaded bioactive agents in the body, effectively overcoming biological barriers, and various formulations are engaged in intensive preclinical and clinical testing. This Review focuses on polymeric micelles assembled through multimolecular interactions between block copolymers and the loaded drugs, proteins, or nucleic acids as translationable nanomedicines. The aspects involved in the design of successful micellar carriers are described in detail on the basis of the type of polymer/payload interaction, as well as the interplay of micelles with the biological interface, emphasizing on the chemistry and engineering of the block copolymers. By shaping these features, polymeric micelles have been propitious for delivering a wide range of therapeutics through effective sensing of targets in the body and adjustment of their properties in response to particular stimuli, modulating the activity of the loaded drugs at the targeted sites, even at the subcellular level. Finally, the future perspectives and imminent challenges for polymeric micelles as nanomedicines are discussed, anticipating to spur further innovations.

PEG-peptide conjugates

The remarkable diversity of the self-assembly behavior of PEG-peptides is reviewed, including self-assemblies formed by PEG-peptides with β-sheet and α-helical (coiled-coil) peptide sequences. The modes of self-assembly in solution and in the solid state are discussed. Additionally, applications in bionanotechnology and synthetic materials science are summarized.

Alkylimidazolium end-modified poly(ethylene glycol) to form the mono-ion complex with plasmid DNA for in vivo gene delivery

In this study, we consider that the decrease in the transfection activity of polycations in vivo, compared with that in vitro, results from their polyion complex formation. Namely, owing to cross-linking between polycations and plasmid DNAs (pDNAs), the disadvantage of in vivo gene delivery mainly stems from the difficulty in controlling the properties of the resulting polyion complex at the nanoscale size. To avoid the cross-linking by polycations, we have establish the concept of "mono-ion complex" formation between pDNA and a monocationic biocompatible polymer. Here we have synthesized alkylimidazolium end-modified poly(ethylene glycol), that is, R-Im-PEG, and have tuned the electrostatic interaction between the resulting alkylimidazolium group and the phosphate group of pDNA by the length of the alkyl chain to achieve "mono-ion complex" formation with pDNA for in vivo gene delivery. Instead of a polyion complex, our original concept of the "mono-ion complex" consisting of the Bu-Im-PEG and pDNA is expected to offer unique tools to break through the barriers of in vivo gene delivery. As well as the field of gene delivery, this study is considered to have exploded the common sense that it is impossible to form not a polyion complex but a "mono-ion complex" under aqueous conditions for all fields of the modification of biomacromolecules.

Coating of single DNA molecules by genetically engineered protein diblock copolymers

Coating DNA is an effective way to modulate its physical properties and interactions. Current chemosynthetic polymers form DNA aggregates with random size and shape. In this study, monodisperse protein diblock copolymers are produced at high yield in recombinant yeast. They carry a large hydrophilic colloidal block (≈400 amino acids) linked to a short binding block (≈12 basic amino acids). It is demonstrated that these protein polymers complex single DNA molecules as highly stable nanorods, reminiscent of cylindrical viruses. It is proposed that inter- and intramolecular bridging of DNA molecules are prevented completely by the small size of the binding block attached to the large colloidal stability block. These protein diblocks serve as a scaffold that can be tuned for application in DNA-based nanotechnology.

Silk-based gene carriers with cell membrane destabilizing peptides

Complexes of recombinant silk-polylysine molecules with ppTG1 peptide, a lysine-rich cell membrane destabilizing peptide to bind plasmid DNA (pDNA), are designed as less-cytotoxic and highly efficient gene carriers. The peptide destabilizes the cell membrane and promotes gene transfer. Our particular interest is in how ppTG1 enhances transfection efficiency of the silk-based delivery system into human cells. Genetically engineered silk proteins containing polylysine and the monomeric and dimeric ppTG1 sequences are synthesized in Escherichia coli , followed by transfection experiments. The pDNA complexes of silk-polylysine-ppTG1 dimer recombinant proteins prepared at an N/P 2 (the ratio of number of amines/phosphates from pDNA) shows the highest transfection efficiency into human embryonic kidney (HEK) cells, the level of which is comparable to the transfection reagent Lipofectamine 2000. The assemblies show a globular morphology with an average hydrodynamic diameter of 99 nm and almost no β-sheet structure. Additionally, the silk-based pDNA complexes demonstrate excellent DNase resistance as well as efficient release of the pDNA by enzymes that degrade silk proteins. Also, comparison with β-sheet induced silk-based pDNA complexes indicates that the β-sheet structure content of the silk sequence of the pDNA complexes controls the enzymatic degradation rate of the complexes and, hence, can regulate the release profile of genes from the complexes. The bioengineered silk-based gene delivery vehicles containing cell membrane destabilizing peptides are therefore concluded to have potential for a less-toxic and controlled-release gene delivery system.

Characterizing DNA condensation and conformational changes in organic solvents

Organic solvents offer a new approach to formulate DNA into novel structures suitable for gene delivery. In this study, we examined the in situ behavior of DNA in N, N-dimethylformamide (DMF) at low concentration via laser light scattering (LLS), TEM, UV absorbance and Zeta potential analysis. Results revealed that, in DMF, a 21bp oligonucleotide remained intact, while calf thymus DNA and supercoiled plasmid DNA were condensed and denatured. During condensation and denaturation, the size was decreased by a factor of 8–10, with calf thymus DNA forming spherical globules while plasmid DNA exhibited a toroid-like conformation. In the condensed state, DNA molecules were still able to release the counterions to be negatively charged, indicating that the condensation was mainly driven by the excluded volume interactions. The condensation induced by DMF was reversible for plasmid DNA but not for calf thymus DNA. When plasmid DNA was removed from DMF and resuspended in an aqueous solution, the DNA was quickly regained a double stranded configuration. These findings provide further insight into the behavior and condensation mechanism of DNA in an organic solvent and may aid in developing more efficient non-viral gene delivery systems.

Polymeric micelles from poly(ethylene glycol)-poly(amino acid) block copolymer for drug and gene delivery

Dramatic advances in biological research have revealed the mechanisms underlying many diseases at the molecular level. However, conventional techniques may be inadequate for direct application of this new knowledge to medical treatments. Nanobiotechnology, which integrates biology with the rapidly growing field of nanotechnology, has great potential to overcome many technical problems and lead to the development of effective therapies. The use of nanobiotechnology in drug delivery systems (DDS) is attractive for advanced treatment of conditions such as cancer and genetic diseases. In this review paper for a special issue on biomaterial research in Japan, we discuss the development of DDS based on polymeric micelles mainly in our group for anti-cancer drug and gene delivery, and also address our challenges associated with developing polymeric micelles as super-functionalized nanodevices with intelligent performance.

Synthesis and Reactivity of the Methoxozirconium Pentatungstate (nBu4N)6[{(μ-MeO)ZrW5O18}2]: Insights into Proton-Transfer Reactions, Solution Dynamics, and Assembly of {ZrW5O18}2- Building Blocks

The methoxo-bridged, dimeric, ZrIV-substituted Lindqvist-type polyoxometalate (POM) (nBu4N)6[{(mu-MeO)ZrW5O18}2], (TBA)61, has been synthesized by stoichiometric hydrolysis of Zr(OnPr)4, [{Zr(OiPr)3(mu-OnPr)(iPrOH)}2], or [{Zr(OiPr)4(iPrOH)}2] and [{WO(OMe)4}2] in the presence of (nBu4N)2WO4, providing access to the systematic nonaqueous chemistry of ZrW5 POMs for the first time and an efficient route to 17O-enriched samples for 17O NMR studies. 1H NMR provided no evidence for dissociation of 1 in solution, although exchange with MeOH was shown to be slow by an EXSY study. Reactions with HX at elevated temperatures gave a range of anions [{XZrW5O18}n]3n- (X = OH, 3; OPh, 4; OC6H4Me-4, 5; OC6H4(CHO)-2, 6; acac, 7; OAc, 8), where n = 2 for 3 and n = 1 for 4-8, while 1H and 17O NMR studies of hydrolysis of 1 revealed the formation of an intermediate [(mu-MeO)(mu-HO)(ZrW5O18)2]6-. Electrospray ionization mass spectrometry of 1 and 3 illustrated the robust nature of the ZrW5O18 framework, and X-ray crystal structure determinations showed that steric interactions between ligands X and the ZrW5O18 surface are important. The coordination number of Zr is restricted to six in aryloxides 4 and 5, while seven-coordination is achieved in the chelate complexes 6-8. Given the inert nature of the methoxo bridges in 1, protonation of ZrOW sites is proposed as a possible step in reactions with HX. The diphenylphosphinate ligand in [(Ph2PO2)ZrW5O18]3- was found to be labile and upon attempted recrystallization the aggregate [(mu3-HO)2(ZrW5O18)3H]7- 9 was formed, which was found to be protonated at ZrOZr and ZrOW sites. This work demonstrates the flexibility of the {ZrW5O18}2- core as a molecular platform for modeling catalysis by tungstated zirconia surfaces.

Biological Soft Materials

With one or two exceptions, biological materials are "soft", meaning that they combine viscous and elastic elements. This mechanical behavior results from self-assembled supramolecular structures that are stabilized by noncovalent interactions. It is an ongoing and profound challenge to understand the self-organization of biological materials. In many cases, concepts can be imported from soft-matter physics and chemistry, which have traditionally focused on materials such as colloids, polymers, surfactants, and liquid crystals. Using these ideas, it is possible to gain a new perspective on phenomena as diverse as DNA condensation, protein and peptide fibrillization, lipid partitioning in rafts, vesicle fusion and budding, and others, as discussed in this selective review of recent highlights from the literature.

Zr(IV)-monosubstituted Keggin-type dimeric polyoxometalates: synthesis, characterization, catalysis of H2O2-based oxidations, and theoretical study

The previously unknown Zr(IV)-monosubstituted Keggin-type polyoxometalates (Zr-POMs), (n-Bu4N)7H[{PW11O39Zr(mu-OH)}2] (1), (n-Bu4N)8[{PW11O39Zr(mu-OH)}2] (2), and (n-Bu4N)9[{PW11O39Zr}2(mu-OH)(mu-O)] (3) differing in their protonation state, have been prepared starting from heteropolyacid H5PW11ZrO40.14H2O. The compounds were characterized by elemental analysis, potentiometric titration, X-ray single-crystal structure, and IR, Raman, and 31P and 183W NMR spectroscopy. The single-crystal X-ray analysis of 2 reveals that two Keggin structural units [PW11O39Zr]3- are linked through two hydroxo bridges Zr-(OH)-Zr with Zr(IV) in 7-fold coordination. The IR spectra of 1 and 2 show a characteristic band at 772 cm(-1), which moves to 767 cm(-1) for 3, reflecting deprotonation of the Zr-(OH)-Zr bond. Potentiometric titration with methanolic Bu4NOH indicates that 1-3 contain 2, 1, and 0 acid protons, respectively. (83W NMR reveals Cs symmetry of 2 and 3 in dry MeCN, while for 1, it discovers nonequivalence of its two subunits and their distortion resulting from localization of the acidic proton on one of the Zr-O-W bridging O atoms. The (31)P NMR spectra of 2 and 3 differ insignificantly in dry MeCN, showing only signals at delta -12.46 and -12.44 ppm, respectively, while the spectrum of 1 displays two resonances at delta -12.3 (narrow) and -13.2 (broad) ppm, indicating slow proton exchange on the (31)P NMR time scale. The theoretical calculations carried out at the density functional theory level on the dimeric species 1-3 propose that protonation at the Zr-O-Zr bridging site is more favorable than protonation at Zr-O-W sites. Calculations also revealed that the doubly bridged hydroxo structure is thermodynamically more stable than the singly bridged oxo structure, in marked contrast with analogous Ti- and Nb-monosubstituted polyoxometalates. The interaction of 1-3 with H(2)O and H(2)O(2) in MeCN has been studied by both (31)P and (183)W NMR. The stability of the [PW(11)O(39)ZrOH](4-) structural unit toward at least 100-fold excess of H2O2 in MeCN was confirmed by both NMR and Raman spectroscopy. The interaction of 1 and 2 with H2O in MeCN produces most likely monomeric species (n-Bu4N)3+n[PW11O39Zr(OH)(n(H2O)(3-n)] (n = 0 and 1) showing a broad 31P NMR signal at delta -13.2 ppm, while interaction with H2O2 leads to the formation of an unstable peroxo species (delta -12.3 ppm), which reacts rapidly with cyclohexene, producing 2-cyclohexen-1-one and trans-cyclohexane-1,2-diol. Both 1 and 2 show a pronounced catalytic activity in H2O2 decomposition and H2O2-based oxidation of organic substrates, including cyclohexene, alpha-pinene, and 2,3,6-trimethylphenol. The oxidation products are consistent with those of a homolytic oxidation mechanism. On the contrary, 3 containing no acid protons reacts with neither H2O nor H2O2 and shows negligible catalytic activity. The Zr-monosubstituted polyoxometalates can be used as tractable homogeneous probes of Zr single-site heterogeneous catalysts in studying mechanisms of H2O2-based oxidations.

From Chain to Network: Design and Analysis of Novel Organic−Inorganic Assemblies from Organically Functionalized Zinc-Substituted Polyoxovanadates and Zinc Organoamine Subunits

A series of novel organic-inorganic assemblies, [Zn(Meen)2]2[(4,4'-bipy)Zn2As8V12O40(H2O)] (1), [Zn(en)2(H2O)][Zn(en)2(4,4'-bipy)Zn2As8V12O40(H2O)].3H2O (2), [[Zn(en)3]2[Zn2As8V12O40(H2O)]].4H2O.0.25bipy (3) and [Zn2(en)5][[Zn(en)2][(bpe)HZn2As8V12O40(H2O)]2].7H2O (4) [en = ethylenediamine, Meen = 1,2-diaminopropane, 4,4'-bipy = 4,4'-bipyridine, and bpe = 1,2-bis(4-pyridyl)ethane] constructed from organically modified Zn-substituted polyoxovanadates and zinc organoamine subunits have been synthesized. Each anion cluster of compound 1 is directly linked by the 4,4'-bipy ligand into a one-dimensional (1D) straight chain. The secondary metal complex [Zn(Meen)2]2+ acts as an isolated countercation. The 1D chain structure of 2 is similar to that of 1 but sinuate because of the secondary metal complex [Zn(en)2]2+ decorated on the anion cluster. The en ligands covalently bonding to the surface anion of 3 not only support the secondary metal complex [Zn(en)2]2+ but also coordinate to another anion through the secondary metal complex [Zn(en)2]2+ bridge to form an "eight-shaped" chiral helix. The unprecedented 2D layer of compound 4 with large nanosized inner rectangular cavities [33.669(6) x 14.720(8) A] is successfully achieved through the anion clusters polymerized first into chains by flexible organic ligands and then secondary metal complexes bridged between the chains. The different coordination abilities and geometries of the bidentate organodiamine ligands used in the four-reaction systems play important roles in the formation of the final structures: from straight chains to sinuate chains, to helical chiral chains, and finally to a 2D layer with helices.

Syntheses and X-ray Crystal Structures of Zirconium(IV) and Hafnium(IV) Complexes Containing Monovacant Wells−Dawson and Keggin Polyoxotungstates

The syntheses and crystal structures of a series of zirconium(IV) and hafnium(IV) complexes with Dawson monovacant phosphotungstate [alpha2-P2W17O61](10-) and in situ-generated Keggin monovacant phosphotungstate [alpha-PW11O39](7-), which was obtained by a reaction of [alpha-PW12O40](3-) with Na2CO3, are described. K15H[Zr(alpha2-P2W17O61)2].25H2O (K-1), K16[Hf(alpha2-P2W17O61)2].19H2O (K-2), (Et2NH2)10[Zr(alpha-PW11O39)2].7H2O (Et2NH2-3), and (Et2NH2)10[Hf(alpha-PW11O39)2].2H2O (Et2NH2-4), being afforded by reactions in aqueous solutions of monolacunary Dawson and Keggin polyoxotungstates with ZrCl2O.8H2O and HfCl2O.8H2O followed by exchanging countercations, were obtained as analytically pure, homogeneous colorless crystals. Single-crystal X-ray structure analyses revealed that the Zr(IV) and Hf(IV) ions are in a square antiprismatic coordination environment with eight oxygen atoms, four of them being provided from each of the two monovacant polyanion ligands. Although the total molecular shapes and the 8-coordinate zirconium and hafnium centers of complexes 1-4 are identical, the bonding modes (bond lengths and bond angles) around the zirconium(IV) and hafnium(IV) centers were dependent on the monovacant structures of the polyanion ligands. Additionally, the characterization of complexes 1-4 was accomplished by elemental analysis, TG/DTA, FTIR, and solution (31P and 183W) NMR spectroscopy.

Action of apoptotic endonuclease DNase γ on naked DNA and chromatin substrates

The internucleosomal cleavage of genomic DNA is a biochemical hallmark of apoptosis. DNase gamma, a Mg2+/Ca2+-dependent endonuclease, has been suggested to be one of the apoptotic endonucleases, but its biochemical characteristic has not been fully elucidated. Here, using recombinant DNase gamma, we showed that DNase gamma is a Mg2+/Ca2+-dependent single-stranded DNA nickase and has a high activity at low ionic strength. Under higher ionic strength, such as physiological buffer conditions, the endonuclease activity of DNase gamma is restricted, but its activity is enhanced in the presence of linker histone H1, which explains DNA cleavage at linker regions of apoptotic nuclei.

Facile Synthesis of Enantiopure Chiral Molecular Rectangles Exhibiting Induced Circular Dichroism

[structure: see text] The facile syntheses of enantiopure molecular rectangles using 1,8-bis(trans-Pt(PEt(3))(2)(NO(3)))anthracene and optically pure d- or l-tartrate are reported in high yields. These self-assembled macrocycles are unique examples where the phenomenon of induced chiral dichroism (ICD) has been observed in chiral metallosupramolecular assemblies.