DNA condensation induced by metal complexes

Effects of particle size and pyrolytic temperature of biochar on the transformation behavior of antibiotic resistance genes

Rampant use of antibiotics has caused a rapid dissemination of antibiotic resistance genes (ARGs) in environment, posing great threats to ecosystems and human health. Applying biochar (BC) in natural systems to combat the spread of ARGs arises as an attention-grabbing solution. Unfortunately, the effectiveness of BC is still unmanageable due to the incomprehensive knowledge over correlations between BC properties and extracellular ARGs transformation. To pinpoint the crucial factors, we primarily explored transformation behaviors of plasmid-mediated ARGs exposed to BC (in suspensions or extraction solutions), adsorption capacities of ARGs on BC, and growth inhibition of E. coli imposed by BC. Specifically, the effects of BC properties including particle size (large-particulate 150 μm and colloidal 0.45-2 μm) and pyrolytic temperature (300, 400, 500, 600, and 700 °C) on the ARGs transformation were emphasized. Results showed that both large-particulate BC and colloidal BC, irrespective of their pyrolytic temperature, would induce significant inhibitory effects on the ARGs transformation, while the BC extraction solutions showed little effect except BC pyrolyzed at 300 °C. Correlation analysis uncovered that the inhibition effect of BC on ARGs transformation was tightly correlated with its adsorption capacity towards plasmid. Accordingly, greater inhibitory effects from those BCs with higher pyrolytic temperatures and smaller particle sizes mainly originated from their greater adsorption capacities. Intriguingly, E. coli was unable to ingest the plasmid adsorbed on BC, which led to ARGs blocked outside the cell membrane, although this inhibitory effect was partially affected by survival inhibition of BC on E. coli. Particularly, significant plasmid aggregation could occur in the extraction solution of large-particulate BC pyrolyzed at 300 °C, leading to a significant inhibition of ARGs transformation. Overall, our findings complete the insufficient understanding over the effects of BC on ARGs transformation behavior, and potentially provide new insights to scientific communities in mitigating ARGs spreading.

Soil minerals and organic matters affect ARGs transformation by changing the morphology of plasmid and bacterial responses

Soil environment is a vital place for the occurrence and spread of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs). Extracellular DNA-mediated transformation is an important pathway for ARGs horizontal transfer and widely exists in soil environment. However, little information is available on how common soil components affect ARGs transformation. Here, three minerals (quartz, kaolinite, and montmorillonite) and three organic matters (humic acid, biochar, and soot) were selected as typical soil components. A small amount in suspension (0.2 g/L) of most soil components (except for quartz and montmorillonite) promoted transformant production by 1.1-1.6 folds. For a high amount (8 g/L), biochar significantly promoted transformant production to 1.5 times, kaolinite exerted a 30 % inhibitory effect. From the perspective of plasmid, biochar induced a higher proportion of supercoiled plasmid than kaolinite; more dissolved organic matter and metal ions facilitated plasmid aggregation under the near-neutral pH, thus promoted transformation. As for the influence of materials on recipient, although biochar and kaolinite both increased reactive oxygen species (ROS) level and membrane permeability, biochar up-regulated more ROS related genes, resulting in intracellular ROS production and up-regulating the expression of carbohydrate metabolism and transformation related genes. While kaolinite inhibited transformation mainly by causing nutrient deficiency.

DNA recognition site of anticancer tinidazole copper(II) complexes

This paper describes the recognition process of tetrahedral [Cu^II(tnz)₂X₂] (X = Cl, Br) complexes by a DNA chain, analyzing the specific interaction between the DNA bases and backbone with the metal and the tinidazole (tnz) ligand. We identified the coordination of the copper metal center with one or two phosphates as the first recognition site for the tinidazole copper(II) complexes, while the ligands present partial intercalation into the minor groove. Also, we discuss a novel trigonal copper(I) tnz bromide complex, obtained by reducing the previously reported [Cu(tnz)₂Br₂]. This complex sheds light on the mechanism of action of tnz metal complexes as one of the most stable DNA-complex adducts depicts a trigonal geometry around the copper ion.

Ru(II) Complexes with Enaminone Structures for Rapid Sterilization of Staphylococcus aureus and MRSA with Little Accumulation of Drug Resistance

Drug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), pose a serious threat to human life. Therefore, there is urgent need to develop antibiotics with new chemical structures and antibacterial mechanisms, especially those that elicit little drug resistance after long-term use. Herein we synthesized three novel ruthenium complexes (Ru1-Ru3) containing the enaminone structures for the first time. At a concentration of 5 μM, Ru1-Ru3 can lead to a CFU reduction of about 5 log units towards S. aureus and MRSA. Interestingly, Ru3 displayed rapid bactericidal effects and could decrease the CFU numbers of both pathogens by 5 log units within 40 min. The control compounds (Ru4 and Ru5) without the enaminone structures displayed very poor antibacterial activity under the same conditions. Moreover, S. aureus did not show apparent drug resistance towards Ru3 after 20 passages incubation with a sublethal concentration. These results highlight the critical role of enaminone structures for antibacterial applications.

Synthesis, characterization, interactions with the DNA duplex dodecamer d(5'-CGCGAATTCGCG-3')2 and cytotoxicity of binuclear η6-arene-Ru(II) complexes

The novel binuclear η⁶-arene-Ru(II) complexes with the general formula {[(η⁶-cym)Ru(L)]₂(μ-BL)}(PF₆)₄, and their corresponding water soluble {[(η⁶-cym)Ru(L)]₂(μ-BL)}Cl₄, where cym = p-cymene, L = 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen), BL = 4,4'-bipyridine (BL-1), 1,2-bis(4-pyridyl)ethane (BL-2) and 1,3-bis(4-pyridyl)propane (BL-3), were synthesized and characterized. The structure of {[(η⁶-cym)Ru(phen)]₂(μ-BL-1)}(PF₆)₄ was determined by X-ray single crystal methods. The interaction of {[(η⁶-cym)Ru(phen)]₂(μ-BL-i)}Cl₄ (i = 1, 2, 3; (4), (5) and (6) correspondingly) with the DNA duplex d(5'-CGCGAATTCGCG-3')₂ was studied by means of NMR techniques and fluorescence titrations. The results show that complex (4) binds with a K_b = 12.133 × 10³ M^-1 through both intercalation and groove binding, while (5) and (6) are groove binders (K_b = 2.333 × 10³ M^-1 and K_b = 3.336 × 10³ M^-1 correspondingly). Comparison with the mononuclear complex [(η⁶-cym)Ru(phen)(py)]²⁺ reveals that it binds to the d(5'-CGCGAATTCGCG-3')₂ with a K_b value two orders of magnitude lower than (4) (K_b = 0.158 × 10³ M^-1), indicating that for the binuclear complexes both ruthenium moieties participate in the binding. The complexes were found to be cytotoxic against the A2780 and A2780 res. cancer cell line with a selectivity index (SI) in the range of 3.0-5.9.

Water soluble transition metal [Ni(II), Cu(II) and Zn(II)] complexes of N-phthaloylglycinate bis(1,2-diaminocyclohexane). DNA binding, pBR322 cleavage and cytotoxicity

To validate the effect of metal ions in analogous ligand scaffolds on DNA binding and cytotoxic response, we have synthesized a series of water-soluble ionic N-phthaloylglycinate conjugated bis(diaminocyclohexane)M²⁺ complexes where M = Ni(II), Cu(II) and Zn(II) (1-3). The structural characterization of the complexes (1-3) was achieved by spectroscopic {FT-IR, EPR, UV-vis absorption data, ¹H NMR, ESI-MS and elemental analysis} and single crystal X-ray diffraction studies, which revealed different topologies for the late 3d-transition metals. The Ni(II) and Zn(II) complexes exhibited an octahedral geometry with coordinated labile water molecules in the P1̄ space group while the Cu(II) complex revealed a square planar geometry with the P2₁/c space lattice. In vitro DNA-complexation studies were performed employing various complementary biophysical methods to quantify the intrinsic binding constant K_b and K_sv values and to envisage the binding modes and binding affinity of (1-3) at the therapeutic targets. The corroborative results of these experiments revealed a substantial geometric and electronic effect of (1-3) on DNA binding and the following inferences were observed, (i) high K_b and K_sv values, (ii) remarkable cleavage efficiency via an oxidative pathway, (iii) condensation behavior and (iv) good cytotoxic response to HepG2 and PTEN-caP8 cancer cell lines, with copper(II) complex 2 outperforming the other two complexes as a most promising anticancer drug candidate. Copper(II) complexes have been proven in the literature to be good anticancer drug entities, displaying inhibition of uncontrolled-cell growth by multiple pathways viz., anti-angiogenesis, inducing apoptosis and reactive oxygen species mediated cell death phenomena. Nickel(II) and zinc(II) ionic complexes 1 and 3 have also demonstrated good chemotherapeutic potential in vitro and the bioactive 1,2-diaminocyclohexane fragment in these complexes plays an instrumental role in anticancer activity.

Single Molecular Chelation Dynamics Reveals That DNA Has a Stronger Affinity toward Lead(II) than Cadmium(II)

Lead ions can bind to DNA via nonelectrostatic interactions and hence alter its structure, which may be related to their adverse effects. The dynamics of Pb²⁺-DNA interaction has not been well understood. In this study, we report the monomolecular dynamics of the Pb²⁺-DNA interaction using a magnetic tweezers (MT) setup. We found that lead cations could induce DNA compaction at ionic strengths above 1 μM, which was also confirmed by morphology characterization. The chelation behavior of the Pb²⁺-DNA and the Cd²⁺-DNA complex solutions after adding EDTA were compared. The results showed that EDTA chelated with the bound metal ions on DNA and consequently led to restoring the DNA to its original length but with different restoration speeds for the two solutions. The fast binding dynamics and the slower chelation dynamics of the Pb²⁺ scenario compared to that of Cd²⁺ suggested that Pb²⁺ was more capable to induce DNA conformational change and that the Pb²⁺-DNA complex was more stable than the Cd²⁺-DNA complex. The stronger affinities for DNA bases and the inner binding of lead cations were two possible causes of the dynamics differences. Three agents, including EDTA, sodium gluconate, and SDBS, were used to remove the bound lead ions on DNA. It was shown that EDTA was the most efficient, and sodium gluconate could not fully restore DNA from its compact state. We concluded that both EDTA and SDBS were good candidates to restore the Pb²⁺-bound DNA to its original state.

Biochar effectively inhibits the horizontal transfer of antibiotic resistance genes via transformation

The rapid spread of antibiotic resistance genes (ARGs) has posed a risk to human health. Here, the effects of biochar (BC) on the horizontal transfer of ARG-carrying plasmids to Escherichia coli via transformation were systematically investigated. BC could significantly inhibit the transformation of ARGs and the inhibition degree increased with pyrolysis temperature. Rice straw-derived BC showed a stronger inhibitory effect on the transformation of ARGs than that of peanut shell-derived BC from the same pyrolysis temperature. The inhibitory effect of BC from low pyrolysis temperature (300 ℃) was mainly caused by BC dissolutions, while it was mainly attributed to BC solids for high pyrolysis temperature (700 ℃) BC. BC dissolutions could induce intramolecular condensation and even agglomeration of plasmids, hindering their transformation into competent bacteria. The cell membrane permeability was slightly decreased in BC dissolutions, which might also contribute to the inhibitory effect. Plasmid can be adsorbed by BC solids and the adsorption increased with BC pyrolysis temperature. Meanwhile, BC-adsorbed plasmid could hardly be transformed into E. coli. BC solids could also deactivate E. coli and thereby inhibit their uptake of ARGs. These findings provide a way using BC to limit the spread of ARGs in the environment.

Metallohelix vectors for efficient gene delivery via cationic DNA nanoparticles

The design of efficient and safe gene delivery vehicles remains a major challenge for the application of gene therapy. Of the many reported gene delivery systems, metal complexes with high affinity for nucleic acids are emerging as an attractive option. We have discovered that certain metallohelices-optically pure, self-assembling triple-stranded arrays of fully encapsulated Fe-act as nonviral DNA delivery vectors capable of mediating efficient gene transfection. They induce formation of globular DNA particles which protect the DNA from degradation by various restriction endonucleases, are of suitable size and electrostatic potential for efficient membrane transport and are successfully processed by cells. The activity is highly structure-dependent-compact and shorter metallohelix enantiomers are far less efficient than less compact and longer enantiomers.

Covalent Conjugation of Carbon Dots with Plasmid and DNA Condensation Thereafter: Realistic Insights into the Condensate Morphology, Energetics, and Photophysics

The use of carbon quantum dots (CDs) as trackable nanocarriers for plasmid and gene as hybrid DNA condensates has gained momentum, as evident from the significant recent research efforts. However, the in-depth morphology of the condensates, the energetics of the condensation process, and the photophysical aspects of the CD are not well understood and often disregarded. Herein, for the first time, we covalently attached linearized pUC19 with citric acid and cysteamine-derived CD through the reaction of the surface amine groups of CDs with the 5'-phospho-methyl imidazolide derivative of the plasmid to obtain a 1:1 CD-pUC19 covalent conjugate. The CD-pUC19 conjugates were further transformed into DNA condensates with spermine that displayed a toroidal morphology with a diameter of ∼200 nm involving ∼2-5 CD-pUC19 conjugates in a single condensate. While the interaction of pristine CD to spermine was exothermic, the binding of the CD-pUC19 conjugate with spermine was endothermic and primarily entropy-driven. The condensed plasmid displayed severe conformational stress and deviation from the B-form due to the compact packing of the DNA but better transfection ability than the pristine CD. The CDs in the condensates tend to come close to each other at the core that results in their shielding from excitation. However, this does not prevent them from emanating reactive oxygen species on visible light exposure that compromises the decondensation process and cell viability at higher exposure times, calling for utmost caution in establishing them as nonviral transfecting agents universally.

Divalent metal ions and intermolecular interactions facilitate DNA network formation

The interactions between divalent metal ions and DNA are crucial for basic life processes. These interactions are also important in advanced technological products such as DNA-based ion sensors. Current polyelectrolyte theories cannot describe these interactions well and do not consider the corresponding dynamics. In this study, we report the single-molecule dynamics of the binding of divalent metal ions to a single DNA molecule and the morphology characterization of the complex. We found that most of the divalent metal ions (Mn²⁺, Zn²⁺, Co²⁺, Ni²⁺, and Cd²⁺), except Mg²⁺ and Ca²⁺, could cause monomolecular DNA condensation. For transition metal ions, different ionic strengths were required to induce the compaction, and different shortening speeds were displayed in the dynamics, indicating ionic specificity. Atomic force microscopy revealed that the morphologies of the metal ion-DNA complexes were affected by the ionic strength of the metal ion, DNA chain length, and DNA concentration. At low metal ion concentration, DNA tended to adopt a random coil conformation. Increasing the ionic strength led to network-like condensed structures, suggesting that divalent metal ions can induce attraction between DNA molecules. Furthermore, higher DNA concentration and longer chain length enhanced intermolecular interactions and consequently resulted in network structures with a higher degree of interconnectivity.

Zinc(ii)-cyclen coordinative amphiphiles for enhanced gene delivery

In this study, we developed coordinative amphiphiles for use as novel non-viral DNA vectors. As a modification of a conventional cationic lipid structure, we replaced the cationic head with a zinc(ii)-1,4,7,10-tetraazacyclododecane (Zn-cyclen) complex as a phosphate-directing group, and used biocompatible skeletons (α-tocopherol or cholesterol) as hydrophobic tails. The structure-activity relationship (SAR) was systematically investigated to study the effect of Zn-coordination on the gene transfection between cyclen-based traditional head-tail lipids and Zn(ii)-cyclen coordinative amphiphiles. The results reveal that both Zn-free lipids and Zn-containing amphiphiles could condense DNA into nano-sized particles with appropriate size and zeta-potentials. Agarose gel retardation assay and MTS-based cell viability assays demonstrated that the Zn(ii)-cyclen complex exhibited slightly lower DNA binding ability and much lower cytotoxicity compared to liposome analogues, respectively. Most importantly, in vitro transfection studies showed that the coordination of zinc(ii) to cyclen may dramatically increase the transfection efficiency of the conventional cationic lipid, and α-tocopherol-containing coordinative amphiphile Zn-Cyc-Toc gives the best transfection efficiency, which was enhanced 24.4 times after coordination and was 6.1 times higher than commercial transfection reagent lipofectamine 2000. Mechanism studies confirmed that the DNA complex formed from Zn-Cyc-Toc might induce higher cellular uptake and better endosomal escape ability than the lipoplexes formed from Zn-free lipid Cyc-Toc. This study not only demonstrates that these coordinative amphiphiles might be promising non-viral gene vectors, but also presents a novel strategy to enhance the gene transfection efficiency and biocompatibility of cyclen-based cationic lipids.

Zn-coordination could dramatically enhance the gene transfection efficiency and reduce the cytotoxicity of conventional cyclen-based cationic liposomes.

Synthesis, DNA/BSA binding studies and in vitro biological assay of nickel(II) complexes incorporating tridentate aroylhydrazone and triphenylphosphine ligands

Two new nickel (II) triphenylphosphine complexes derived from tridentate aroylhydrazone ligands [H2L1 = 2-hydroxy-3-methoxybenzylidene)benzohydrazone and H2L2 = N'-(2-hydroxy-3-methoxybenzylidene)-2-hydroxybenzoylhydrazone] and triphenylphosphine were prepared and their molecular structures were determined by single crystal X-ray diffraction analysis. Both nickel(II) complexes showed slightly distorted square planar geometry with one tridentate aroylhydrazone ligand coordinated through ONO donor atoms and one triphenylphosphine ligand coordinated to the nickel center through the phosphorus atom. DNA interaction studies indicated that both complexes possessed higher affinity to herring sperm DNA (HS-DNA) than the corresponding free aroylhydrazone ligand. Molecular docking investigations showed that both complexes could bind to DNA through intercalation of the phenyl rings between adjacent base pairs in the double helix. Meanwhile, bovine serum albumin (BSA) binding studies revealed the complexes could effectively interact with BSA and change the secondary structure of BSA. Further pharmacological evaluations of the synthesized complexes by in vitro antioxidant assays demonstrated high antioxidant activity against NO· and O2˙- radicals. The anticancer activity of each complex was assessed through in vitro cytotoxicity assays (CCK-8 kit) toward A549 and MCF-7 cancer cell and normal L-02 cell lines. Significantly, the Ni(II) complex derived from H2L1 ligand was found to be more effective cytotoxic toward MCF-7cancerous cell with the IC50 value equaled 9.7 μM, which showed potent cytotoxic activity over standard drug cisplatin. AbbreviationsA549human lung carcinoma cellBSAbovine serum albuminCCK-8Cell Counting Kit-8DFTdensity functional theoryDNAdeoxyribonucleic acidDPPH˙2,2-diphenyl-1-picrylhydrazylH2L12-hydroxy-3-methoxybenzylidene)benzohydrazone N'-(2-hydroxy-3-methoxybenzylidene)-2-hydroxybenzoylhydrazoneH2L2N'-(2-hydroxy-3-methoxybenzylidene)-2-hydroxybenzoylhydrazoneHOMOhighest occupied molecular orbitalIC50the 50% activityL-02human normal liver cellLOMOlowest unoccupied molecular orbital (LUMO)MCF-7human breast carcinoma cellNO˙nitric oxideO2˙-superoxide anionSODsuperoxide dismutaseCommunicated by Ramaswamy H. Sarma.

TAT-functionalized PEI-grafting rice bran polysaccharides for safe and efficient gene delivery

Polysaccharides are considered to be promising candidates for non-viral gene delivery because of their molecular diversity, which can be modified to fine-tune their physicochemical properties. In this work, transcriptional activator protein (TAT) functionalized PEI grafted polysaccharide polymer (PRBP) was prepared by using rice bran polysaccharide as the starting material, and characterized by various methods. The potential of TAT functionalized PRBP (PRBP-TAT) as gene vector was studied in vitro, including DNA loading capacity, DNA protection ability and biocompatibility. The cell uptake and transfection efficiency of the PRBP-TAT/pDNA polyplexes were studied. The results showed that PRBP-TAT could completely condense DNA at N/P 2. The PRBP-TAT/pDNA polyplexes could protect DNA from degrading by DNase and were efficiently internalized by cells. Biocompatibility result showed that PRBP-TAT had no significant cytotoxicity and effect on cell proliferation. At low N/P ratios of 1-3.5, PRBP-TAT showed higher transfection efficiency than PEI30k and PEI30k-grafted rice bran polysaccharide. PRBP-TAT and PEI showed the highest transfection efficiency of 42.8% and 28.1% when pDNA is 2 µg and N/P ratio is 1.5, respectively, while PRBP showed the highest transfection efficiency of 37.3% at N/P 2.5. These results indicate that PTA is a promising candidate vector for safe and efficient gene delivery.

The Development of Functional Non-Viral Vectors for Gene Delivery

Gene therapy is manipulation in/of gene expression in specific cells/tissue to treat diseases. This manipulation is carried out by introducing exogenous nucleic acids, such as DNA or RNA, into the cell. Because of their negative charge and considerable larger size, the delivery of these molecules, in general, should be mediated by gene vectors. Non-viral vectors, as promising delivery systems, have received considerable attention due to their low cytotoxicity and non-immunogenicity. As research continued, more and more functional non-viral vectors have emerged. They not only have the ability to deliver a gene into the cells but also have other functions, such as the performance of fluorescence imaging, which aids in monitoring their progress, targeted delivery, and biodegradation. Recently, many reviews related to non-viral vectors, such as polymers and cationic lipids, have been reported. However, there are few reviews regarding functional non-viral vectors. This review summarizes the common functional non-viral vectors developed in the last ten years and their potential applications in the future. The transfection efficiency and the transport mechanism of these materials were also discussed in detail. We hope that this review can help researchers design more new high-efficiency and low-toxicity multifunctional non-viral vectors, and further accelerate the progress of gene therapy.

Anomalous Elastic Properties of Attraction-Dominated DNA Self-Assembled 2D Films and the Resultant Dynamic Biodetection Signals of Microbeam Sensors

The condensation of DNA helices has been regularly found in cell nucleus, bacterial nucleoids, and viral capsids, and during its relevant biodetections the attractive interactions between DNA helices could not be neglected. In this letter, we theoretically characterize the elastic properties of double-stranded DNA (dsDNA) self-assembled 2D films and their multiscale correlations with the dynamic detection signals of DNA-microbeams. The comparison of attraction- and repulsion-dominated DNA films shows that the competition between attractive and repulsive micro-interactions endows dsDNA films in multivalent salt solutions with anomalous elastic properties such as tensile surface stresses and negative moduli; the occurrence of the tensile surface stress for the attraction-dominated DNA self-assembled film reveals the possible physical mechanism of the condensation found in organism. Furthermore, dynamic analyses of a hinged-hinged DNA-microbeam reveal non-monotonous frequency shifts due to attraction- or repulsion-dominated dsDNA adsorptions and dynamic instability occurrence during the detections of repulsion-dominated DNA films. This dynamic instability implies the existence of a sensitive interval of material parameters in which DNA adsorptions will induce a drastic natural frequency shift or a jump of vibration mode even with a tiny variation of the detection conditions. These new insights might provide us some potential guidance to achieve an ultra-highly sensitive biodetection method in the future.

Multistage dynamics of Hg2+-DNA interactions: a single-molecule study

The metal ion-DNA interaction is key to biochemical processes and has applications in areas such as metal ion sensors and DNA nanomachines. For example, the formation of the T-Hg2+-T structure has been used in technologies such as DNA-based mercuric ion sensors. Though the interaction is widely used for practical purposes, the underlying mechanism has not been fully understood. In the present study, we used magnetic tweezers to explore the interactions between λ-DNA and two metal ions, Hg2+ and Cd2+, at the single-molecule level. Both metal ions caused considerable DNA conformational changes. The resulting DNA compaction dynamics were related to the ion concentration and the exerted force. The increase in the ion concentration promoted DNA compaction, whereas exerting greater forces inhibited this process. Application of a high force generated two-stage dynamics of the Hg2+-DNA interaction. However, at a sufficiently high Hg2+ concentration, a lower force led to a three-stage process. In contrast, the curves of the binding of Cd2+ ions to DNA had a stepwise pattern. Both the AFM scanning results and the single-molecule measurements confirmed that Hg2+ influences the DNA conformation in a more pronounced manner than Cd2+. The multistage Hg2+-DNA interaction was considered to be a result of the different binding mechanisms, including the mismatched base-pair formation. A model was then proposed to explain the peculiar dynamics.

Small addition of Zn2+ in Ca2+@DNA results in elevated gene transfection by aminated PGMA-modified silicon nanowire arrays

Gene therapy, a promising and effective treatment, has ignited new hope in overcoming difficult-to-cure diseases. The key question in gene therapy is how to efficiently and safely deliver exogenous nucleic acids into the nuclei of target cells. To achieve stable, efficient and safe gene transfer and to ensure efficiency of gene transfer into cell nuclei, a zinc ion-assisted gene delivery nanosystem was proposed in the present study by loading a low concentration of Zn²⁺ in Ca²⁺@DNA nanoparticles on ethanolamine-functionalized poly(glycidyl methacrylate) (PGEA)-modified SiNWAs (Zn²⁺/Ca²⁺@DNA + SN-PGEA). The results showed that with the help of Zn ions, this composite nanosystem could promote more DNA in the cell nuclei and thus dramatically increased the transfection efficiency by as much as 7-fold. The nanosystem with 0.2 mM Zn²⁺, 100 mM Ca²⁺ and PGEA modification on SiNWAs displayed the highest transfection efficiency and good biocompatibility. This new composite nanosystem will have great potential in gene transfection for biomedical research.

DNA interaction of ruthenium(ii) complexes with imidazo[4,5-f][1,10]phenanthroline derivatives

The DNA interaction properties of four Ru(ii) complexes with imidazo[4,5-f][1,10]phenanthroline derivatives were investigated by spectral titration, gel electrophoresis (GAR), dynamic light scattering (DLS), zeta potential, atomic force microscopy (AFM), and transmission electron microscopy (TEM).

Reversible DNA compaction induced by partial intercalation of 16-Ph-16 gemini surfactants: evidence of triple helix formation

The interaction between calf thymus DNA and the gemini surfactants N,N'-[α,ω-phenylenebis(methylene)bis [N,N'-dimethyl-N-(1-hexadecyl)]-ammonium dibromide], p-16-Ph-16 (α = 1, ω = 3) and m-16-Ph-16 (α = 1, ω = 2), has been investigated via circular dichroism, fluorescence and UV-vis spectroscopy, zeta potential, dynamic light scattering, and AFM microscopy. Measurements were carried out in aqueous media at different molar ratios, R = (C16-Ph-16)/CDNA and C16-Ph-16 always below the critical micellar concentration (CMC) of the surfactant. Under these conditions, DNA undergoes two reversible conformational changes, compaction and decompaction, due to interaction with the surfactant molecules at low and high molar ratios, respectively. The extent of such conformational changes is correlated with both the degree of surfactant partial intercalation, and the size and charge of the surfactant aggregates formed, in each case. Comparison of the results shows that the para-form of the surfactant intercalates into the DNA to a major extent; therefore, the compaction/decompaction processes are more effective. Among these, the structure of the resulting 16-Ph-16/DNA decompacted complex is worthy of note. For the first time it can be demonstrated that the partial intercalation of the 16-Ph-16 gemini surfactants induces the formation of triplex DNA-like structures at a high R ratio.

A dinuclear Cu(i)-mediated complex: Theoretical studies of the G2Cu2 4+ cluster ion

Recently, the T-Hg(ii)₂-A base pair containing two equivalents of Hg(ii) has been prepared and characterized experimentally, which implies that there might exist considerable stable metal-mediated base pairs holding two neighbouring metal centers. Here we report a quantum chemical study on geometries, electronic structures, and bonding of various G₂Cu₂ ⁴⁺ (G = guanine) isomers including one di-copper(i) unit. Different density functional methods [Becke 3-parameter-Lee-Yang-Parr, Perdew-Becke-Ernzerhof, Becke-Perdew, Density Functional Theory with Dispersion Corrections (DFT-D)] assign ambiguous relative energies to these isomers with the singlet and triplet states. High-level ab initio [domain-based local pair natural orbital (DLPNO) coupled-cluster with single and double excitations and DLPNO-coupled-cluster with single, double, and perturbative triple excitations] calculations confirm that the lowest-lying isomer of the G₂Cu₂ ⁴⁺ ion has C _2h symmetry with the singlet state and is comparable to the singly and doubly charged homologues (G₂Cu₂ ⁺ and G₂Cu₂ ²⁺). The extended transition state (ETS)-natural orbitals for the chemical valence (ETS-NOCV) calculations point out that it has larger instantaneous interaction energy and bond dissociation energy than the corresponding singly and doubly charged complexes due to its relatively stronger attractive energies and weaker Pauli repulsion. The orbital interactions in the quadruply charged cluster chiefly come from Cu₂ ⁴⁺ ← G⋯G π donations. The results may help the understanding of the bonding properties of other potential metal-base pair complexes with the electron transfer.

Two-stage DNA compaction induced by silver ions suggests a cooperative binding mechanism

The interaction between silver ions and DNA plays an important role in the therapeutic use of silver ions and in related technologies such as DNA sensors. However, the underlying mechanism has not been fully understood. In this study, the dynamics of Ag⁺-DNA interaction at a single-molecule level was studied using magnetic tweezers. AgNO₃ solutions with concentrations ranging from 1 μM to 20 μM led to a 1.4-1.8 μm decrease in length of a single λ-DNA molecule, indicating that Ag⁺ has a strong binding with DNA, causing the DNA conformational change. The compaction process comprises one linear declining stage and another sigmoid-shaped stage, which can be attributed to the interaction mechanism. Considering the cooperative effect, the sigmoid trend was well explained using a phenomenological model. By contrast, addition of silver nanoparticle solution induced no detectable transition of DNA. The dependence of the interaction on ionic strength and DNA concentration was examined via morphology characterization and particle size distribution measurement. The size of the Ag⁺-DNA complex decreased with an increase in Ag⁺ ionic strength ranging from 1 μM to 1 mM. Morphology characterization confirmed that silver ions induced DNA to adopt a compacted globular conformation. At a fixed [AgNO₃]:[DNA base pairs] ratio, increasing DNA concentration led to increased sizes of the complexes. Intermolecular interaction is believed to affect the Ag⁺-DNA complex formation to a large extent.

Stability of Antibacterial Silver Carboxylate Complexes against Staphylococcus epidermidis and Their Cytotoxic Effects

The antibacterial effects against Staphylococcus epidermidis of five silver carboxylate complexes with anti-inflammatory ligands were studied in order to analyze and compare them in terms of stability (in solution and after exposure to UV light), and their antibacterial and morphological differences. Four effects of the Ag-complexes were evidenced by transmission electronic microscopy (TEM) and scanning electronic microscopy (SEM): DNA condensation, membrane disruption, shedding of cytoplasmic material and silver compound microcrystal penetration of bacteria. 5-Chlorosalicylic acid (5Cl) and sodium 4-aminosalicylate (4A) were the most effective ligands for synthesizing silver complexes with high levels of antibacterial activity. However, Ag-5Cl was the most stable against exposure UV light (365 nm). Cytotoxic effects were tested against two kinds of eukaryotic cells: murine fibroblast cells (T10 1/2) and human epithelial ovarian cancer cells (A2780). The main objective was to identify changes in their antibacterial properties associated with potential decomposition and the implications for clinical applications.

Enhanced DNA Binding and Photocleavage Abilities of β-Cyclodextrin Appended Ru(II) Complex through Supramolecular Strategy

Photosensitizers with high photocleavage ability are urgently needed to improve photodynamic therapy efficacy. Herein, a supramolecular complex was constructed through host-guest self-assembly using hexa-β-CD-appended ruthenium polypyridyl (6CD-Ru) and adamantane-modified anthracene (ADA-AN) in water. The targeted DNA-intercalation of peripheral anthracenes can remarkably enhance photocleavage ability and antitumor activity of the complex irradiated with visible light.

DNA Phase Transition in Charge Neutralization and Comformation Induced by Trivalent-Hydrolysed Metal Ions

It is well known that common trivalent counter ions can induce DNA compaction or condensation but are unable to invert DNA surface charge in a normal aqueous solution. In the present study, we found that trivalent-hydrolysed metal ions (Fe3+, Al3+) are not only capable of inducing DNA condensation, but they also invert the electrophoretic mobility of DNA by electrophoretic light scattering and single molecular techniques. In comparison with neutral trivalent cations, hydrolysed metal ions such as Fe3+ can induce DNA condensation at a much lower concentration of cations, and its corresponding morphology of condensed DNA was directly observed by atomic force microscopy (AFM). The condensing and unravelling forces of DNA condensates were measured by tethering DNA by magnetic tweezers (MT) measurements at various concentration of Fe3+ and Al3+. We found that a coil⁻globule transition of DNA by hydrolysed metal ions not only was observed in DNA-complex sizes, but also in the curve of electrophoretic mobility of DNA in solution. In contrast, the transition was not observed in the case of neutral trivalent cations such as La3+ and Co3+. We attribute the transition and charge inversion to the ion-specific interaction between hydrolysed metal ions and phosphates of DNA backbone.

Interfering with DNA High-Order Structures using Chiral Ruthenium(II) Complexes

In this work, it was found that DNA can undergo B-Z transformational changes and compaction in the presence of DNA intercalators such as ruthenium(II) polypyridyl complexes. The link between B-Z transition and condensation is weak but can be strengthened under certain circumstances with slight alterations to the structures of the ruthenium(II) complexes. Here, following on from previous research, this work reports a series of ruthenium(II) complexes with imidazophenanthroline ligands, which vary in size and planarity. The complexes exhibit distinct effects on DNA structures, ranging from little impact to the transformation of DNA secondary structures to the formation of higher-order DNA structures. Further studies on DNA morphological changes induced by chiral ruthenium(II) complexes are observed by atomic force microscopy and transmission electron microscopy.

Zn(II)-dipicolylamine-based metallo-lipids as novel non-viral gene vectors

In this study, a series of Zn(II)-dipicolylamine (Zn-DPA) based cationic lipids bearing different hydrophobic tails (long chains, α-tocopherol, cholesterol or diosgenin) were synthesized. Structure-activity relationship (SAR) of these lipids was studied in detail by investigating the effects of several structural aspects including the type of hydrophobic tails, the chain length and saturation degree. In addition, several assays were used to study their interactions with plasmid DNA, and results reveal that these lipids could condense DNA into nanosized particles with appropriate size and zeta-potentials. MTT-based cell viability assays showed that lipoplexes 5 had low cytotoxicity. The in vitro gene transfection studies showed the hydrophobic tails clearly affected the TE, and hexadecanol-containing lipid 5b gives the best TE, which was 2.2 times higher than bPEI 25k in the presence of 10% serum. The results not only demonstrate that these lipids might be promising non-viral gene vectors, but also afford us clues for further optimization of lipidic gene delivery materials.

Properties of polyplexes formed through interaction between hydrophobically-modified poly(ethylene imine)s and calf thymus DNA in aqueous solution

Polycationic polymers and DNA form soluble complexes in aqueous solution, which allows the transfer of genetic material into cells. Therefore, these chemically-modified polymers are of interest for use in studies aimed at better transfection efficiency and gene expression along with reduced cytotoxicity. In this study, branched poly(ethylene imine) (PEI) was modified by alkylation with n-alkyl groups (n = 4, 6, 8 and 12 carbons). The polyplexes formed through interaction of the modified PEIs and calf thymus DNA (ctDNA) were investigated using UV-Vis spectrophotometry, ethidium bromide fluorescence emission, circular dichroism spectroscopy, dynamic light scattering, and small-angle X-ray scattering techniques along with the determination of the zeta potential and viscosity. According to the results obtained, the formation of ctDNA-PEI polyplexes occurs in three steps. Firstly, when a small amount of polyelectrolyte is present the ctDNA chains are partially compacted. Subsequently, with the addition of more polyelectrolyte, the complexes have a null charge density and micrometric size. Lastly, with a higher concentration of PEI, the ctDNA is fully compacted by the PEI chains, leading to positively charged complexes with R_h values in the range of 52.0-86.0 nm. The viscosity and SAXS analysis suggested that the unmodified PEI exhibits the strongest interaction and promotes the best ctDNA condensation.