Physical–Chemical Properties and Transfection Activity of Cationic Lipid/DNA Complexes

Investigation of DNA interactions with cationic lipids is of particular importance for the fabrication of biosensors and nanodevices. Furthermore, lipid/DNA complexes can be applied for direct delivery of DNA‐based biopharmaceuticals to damaged cells as non‐viral vectors. To obtain more effective and safer DNA vectors, the new cationic lipids 2‐tetradecylhexadecanoic acid‐{2‐[(2‐aminoethyl)amino]ethyl}amide (C I ) and 2‐tetradecylhexadecanoic acid‐2‐[bis(2‐aminoethyl)amino]ethylamide (C II ) were synthesized and characterized. The synthesis, physical–chemical properties and first transfection and toxicity experiments are reported. Special attention was focused on the capability of C I and C II to complex DNA at low and high subphase pH values. Langmuir monolayers at the air/water interface represent a well‐defined model system to study the lipid/DNA complexes. Interactions and ordering of DNA under Langmuir monolayers of the new cationic lipids were studied using film balance measurements, grazing incidence X‐ray diffraction (GIXD) and X‐ray reflectivity (XR). The results obtained demonstrate the ability of these cationic lipids to couple with DNA at low as well as at high pH value. Moreover, the observed DNA structuring seems not to depend on subphase pH conditions. An influence of the chemical structure of the lipid head group on the DNA binding ability was clearly observed. Both compounds show good transfection efficacy and low toxicity in the in vitro experiments indicating that lipids with such structures are promising candidates for successful gene delivery systems.     

Lamellar versus Micellar Structures—Aggregation Behavior of a Three‐Chain Cationic Lipid Designed for Nonviral Polynucleotide Transfer

The aggregation behavior of a cationic lipid, N‐[6‐amino‐1‐oxo‐1‐(N‐tetradecylamino)hexan‐(2S)‐2‐yl]‐N′‐{2‐[N,N‐bis(2‐aminoethyl)amino]ethyl}‐2,2‐ditetradecylpropandiamide (DiTT4), is investigated in aqueous dispersions at different pH values (5, 7.3, and 10). An unusual aggregation behavior is observed whereby DiTT4 forms bilayer structures at pH 10 and 7.3. At pH 5, rod‐like micelles are the dominant aggregate form. The thermotropic and lyotropic behavior is studied using differential scanning calorimetry, small‐angle X‐ray scattering, and FTIR spectroscopy. In addition, investigations at the air–water interface are performed by recording area–pressure‐isotherms and infrared reflection–absorption (IRRA) spectra. Complementary dynamic light scattering experiments and transmission electron microscopy (TEM and cryoTEM) are also used. The ability of DiTT4 to complex plasmid DNA is investigated using fluorescence techniques and zeta potential measurements. Cell culture experiments demonstrate the ability of DiTT4 to enhance plasmid transfer in A549 cells.     

Structure–electrical property study of anisotropic polyaniline films

The relationships of the structure and electrical properties of anisotropic HCl‐doped polyaniline (PANI) films cast from N,N′‐dimethylpropylene urea (DMPU) solutions and stretched to different draw ratios were studied. The anisotropic structure of the stretched PANI films was examined by X‐ray diffraction, near‐infrared wave‐guide coupling, and polarized infrared measurements. The PANI emeraldine base (EB) films cast from DMPU solutions had a single‐phase noncrystalline structure, and stretching of the films did not cause crystallization to occur. The transition moment angles of two weakly absorbing infrared bands were determined, and the Hermans' orientation functions for the PANI EB films were calculated. The PANI films were then doped with HCl, and the electrical properties were determined by impedance spectroscopy. With a specially designed test fixture, the in‐plane and through‐plane impedance was obtained. The conductivity along the stretch direction increased with orientation. The in‐plane conductivity was significantly higher than the through‐plane conductivity. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 823–841, 2003     

Thermotropic Liquid Crystals Based on Extended 2,5‐Disubstituted‐1,3,4‐Oxadiazoles: Structure–Property Relationships,Variable‐Temperature Powder X‐ray Diffraction,and Small‐Angle X‐ray Scattering Studies

A class of extended 2,5‐disubstituted‐1,3,4‐oxadiazoles R¹‐C₆H₄‐{OC₂N₂}‐C₆H₄‐R² (R¹=R²=C₁₀H₂₁O 1 a , p‐C₁₀H₂₁O‐C₆H₄‐C?C 3 a , p‐CH₃O‐C₆H₄‐C?C 3 b ; R¹=C₁₀H₂₁O, R²=CH₃O 1 b , (CH₃)₂N 1 c ; F 1 d ; R¹=C₁₀H₂₁O‐C₆H₄‐C?C, R²=C₁₀H₂₁O 2 a , CH₃O 2 b , (CH₃)₂N 2 c , F 2 d ) were prepared, and their liquid‐crystalline properties were examined. In CH₂Cl₂ solution, these compounds displayed a room‐temperature emission with λ_max at 340–471 nm and quantum yields of 0.73–0.97. Compounds 1 d , 2 a – 2 d , and 3 a exhibited various thermotropic mesophases (monotropic, enantiotropic nematic/smectic), which were examined by polarized‐light optical microscopy and differential scanning calorimetry. Structure determination by a direct‐space approach using simulated annealing or parallel tempering of the powder X‐ray diffraction data revealed distinctive crystal‐packing arrangements for mesogenic molecules 2 b and 3 a , leading to different nematic mesophase behavior, with 2 b being monotropic and 3 a enantiotropic in the narrow temperature range of 200–210 °C. The structural transitions associated with these crystalline solids and their mesophases were studied by variable‐temperature X‐ray diffractometry. Nondestructive phase transitions (crystal‐to‐crystal, crystal‐to‐mesophase, mesophase‐to‐liquid) were observed in the diffractograms of 1 b, 1 d , 2 b, 2 d , and 3 a measured at 25–200 °C. Powder X‐ray diffraction and small‐angle X‐ray scattering data revealed that the structure of the annealed solid residue 2 b reverted to its original crystal/molecular packing when the isotropic liquid was cooled to room temperature. Structure–property relationships within these mesomorphic solids are discussed in the context of their molecular structures and intermolecular interactions.     

First‐Row Transition‐Metal–Diborane and –Borylene Complexes

A combined experimental and quantum chemical study of Group 7 borane, trimetallic triply bridged borylene and boride complexes has been undertaken. Treatment of [{Cp*CoCl}₂] (Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl) with LiBH₄ ? thf at ?78 °C, followed by room‐temperature reaction with three equivalents of [Mn₂(CO)₁₀] yielded a manganese hexahydridodiborate compound [{(OC)₄Mn}(η⁶‐B₂H₆){Mn(CO)₃}₂(μ‐H)] ( 1 ) and a triply bridged borylene complex [(μ₃‐BH)(Cp*Co)₂(μ‐CO)(μ‐H)₂MnH(CO)₃] ( 2 ). In a similar fashion, [Re₂(CO)₁₀] generated [(μ₃‐BH)(Cp*Co)₂(μ‐CO)(μ‐H)₂ReH(CO)₃] ( 3 ) and [(μ₃‐BH)(Cp*Co)₂(μ‐CO)₂(μ‐H)Co(CO)₃] ( 4 ) in modest yields. In contrast, [Ru₃(CO)₁₂] under similar reaction conditions yielded a heterometallic semi‐interstitial boride cluster [(Cp*Co)(μ‐H)₃Ru₃(CO)₉B] ( 5 ). The solid‐state X‐ray structure of compound 1 shows a significantly shorter boron–boron bond length. The detailed spectroscopic data of 1 and the unusual structural and bonding features have been described. All the complexes have been characterized by using ¹H, ¹¹B, ¹³C NMR spectroscopy, mass spectrometry, and X‐ray diffraction analysis. The DFT computations were used to shed light on the bonding and electronic structures of these new compounds. The study reveals a dominant B?H?Mn, a weak B?B?Mn interaction, and an enhanced B?B bonding in 1 .     

Racemic DNA Crystallography

Racemates increase the chances of crystallization by allowing molecular contacts to be formed in a greater number of ways. With the advent of protein synthesis, the production of protein racemates and racemic‐protein crystallography are now possible. Curiously, racemic DNA crystallography had not been investigated despite the commercial availability of L ‐ and D ‐deoxyribo‐oligonucleotides. Here, we report a study into racemic DNA crystallography showing the strong propensity of racemic DNA mixtures to form racemic crystals. We describe racemic crystal structures of various DNA sequences and folded conformations, including duplexes, quadruplexes, and a four‐way junction, showing that the advantages of racemic crystallography should extend to DNA.     

The Structures,Morphologies, and Photophysical Properties of Multiluminescent Layered Lanthanide–Phosphono–Carboxylate Nanoparticles

A new family of layered metal(III)–phosphono–carboxylate nanostructures (M=Y, Eu, Tb, Er, and Yb) was hydrothermally synthesized and their structures and morphologies were characterized by X‐ray powder diffraction and TEM. 4‐[Bis(phosphonomethyl)amino]caproic acid and 4‐ [bis(phosphonomethyl)amino]undecan‐ oic acid, with general formula (H₂O₃PCH₂)₂NR (R=C₅H₁₀COOH (P2CAPR) and C₁₀H₂₂COOH (P2UND), respectively) were used as building blocks for the preparation of novel layered hybrid materials in which the inorganic layers were composed of MO₇ or MO₈ polyhedra and PO₃C tetrahedra. The interlayer region was occupied by carboxyalkyl chains. These layered compounds were easily dispersed as stable solutions in alkylamine/water upon ultrasonication. These dispersions were constituted of rectangular elongated nanoparticles (NPs), which showed a distribution of sizes ranging from 20–500 nm. These new materials had interesting photophysical properties because they were multiluminescent compounds. These properties gave rise to several emission bands, which were spread over the broad spectroscopic region, from the near‐UV up to the near‐IR regions. Each emission band had a specific lifetime, which ranged from the sub‐ps to the ms scale.     

Nitrous‐Acid‐Mediated Synthesis of Iron–Nitrosyl–Porphyrin: pH‐Dependent Release of Nitric Oxide

Two iron–nitrosyl–porphyrins, nitrosyl[meso‐tetrakis(3,4,5‐trimethoxyphenylporphyrin]iron(II) acetic acid solvate ( 3 ) and nitrosyl[meso‐tetrakis(4‐methoxyphenylporphyrin]iron(II) CH₂Cl₂ solvate ( 4 ), were synthesized in quantitative yield by using a modified procedure with nitrous acid, followed by oxygen‐atom abstraction by triphenylphosphine under an argon atmosphere. These nitrosyl porphyrins are in the {FeNO}⁷ class. Under an argon atmosphere, these compounds are relatively stable over a broad range of pH values (4–8) but, under aerobic conditions, they release nitric oxide faster at high pH values than that at low pH values. The generated nitric‐oxide‐free iron(III)–porphyrin can be re‐nitrosylated by using nitrous acid and triphenylphosphine. The rapid release of NO from these Fe^II complexes at high pH values seems to be similar to that in nitrophorin, a nitric‐oxide‐transport protein, which formally possesses Fe^III. However, because the release of NO occurs from ferrous–nitrosyl–porphyrin under aerobic conditions, these compounds are more closely related to nitrobindin, a recently discovered heme protein.     

Opening a New Series of Calcium Boridecarbides with Heterographene Nets by Ca1–x(B,C)6 and Ca1–x(B,C)8 – Two Members of the (CaB2)Cn Compound Series

Ca_1–xB₂C₄ (x ~ 0.08) and Ca_1–xB₂C₆ (x ~ 0.04) are two compounds containing heterographene‐B,C nets which were prepared by solid state synthesis and structurally characterized by X‐ray powder diffraction data. Both compounds crystallize in the space group P6/ mmm (No. 191). The lattice constants are a = 4.55971(5) Å and c = 4.4020(1) Å for CaB₂C₄ and a = 2.58390(5) Å, c = 4.43597(8) Å for CaB₂C₆. The calcium atoms are intercalated between the heterographene (B,C) nets. The calcium atom distribution in Ca_1–xB₂C₆ is disordered, leading to diffuse scattering. A model for this disorder was developed that matches well the observed diffuse scattering observed in the electron diffraction pattern. For Ca_1–xB₂C₆ and its decomposition products magnetic and electric properties are being reported.     

Chlorine‐Induced Hydrogen‐Bonding Network of A Novel Dimer Based on Nickel and Tridentate Ligand: 3‐Hydrazine‐4‐amino‐1,2,4‐Triazole

The reaction of NiCl₂ and 3‐hydrazine‐4‐amino‐1,2,4‐triazole (Hatr) in the mixed solvent of EtOH and H₂O yielded a dimer compound ([Ni₂(Hatr)₂(H₂O)₂(EtOH)₂Cl₂]Cl₂·EtOH) with water and EtOH molecules coordinated to nickle ions. It crystallized in trigonal space group R‐3, a=b=29.67(1) Å, c=8.95(7) Å, β=120(1)°, as determined by single‐crystal X‐ray diffraction. Then, they were fully characterized by the IR spectroscopy, differential scanning calorimetry (DSC), thermogravimetry (TG), and elemental analysis.     

New Phases in the Lithiumnitridovanadate System — The Solid Solution Li7‐2xMgx[VN4] with 0 ≤ x ≤ 1

Solid solution phases Li_7‐2xMg_x[VN₄] (0 < x ≤ 1) with varying Mg‐content are obtained as yellow microcrystalline powders from heat treatment of mixtures of VN, Li₃N and Mg₃N₂ or from mixtures of Li₇[VN₄] and Mg₃N₂ at 1370 K in N₂ atmosphere at ambient pressure. At substitution parameter values of x > 0.5 a subsequent distortion from the ideal cubic unit cell to an orthorhombic unit cell is observed. The crystal structure of Li_7‐2xMg_x[VN₄] with x ≈ 1 was refined from neutron and X‐ray powder diffraction data (space group Pbca, No. 61, a = 963.03(3) pm, b = 958.44(3) pm, c = 951.93(2) pm, neutron pattern 14° — 156° 2θ, step non‐linear ≈ 0.0782° 2θ, No. of measured points 1816, R_p = 0.089, R_wp = 0.115, R_Bragg = 0.155, R_F = 0.114; X‐ray pattern 10° — 98° 2θ, step 0.005° 2θ, No. of measured points 17600, R_p = 0.028, R_wp = 0.045, R_Bragg = 0.113, R_F = 0.133, structure variables: 45). The crystal structure resembles a Li₂O type superstructure with the atomic arrangement of β‐Li₇[VN₄] and with two crystallographic Li‐sites each substituted by Mg with statistical occupation factors of 0.5. Chemical analyses prove the composition and XAS spectroscopy at the V K‐edge support the +5 oxidation state assignment for vanadium. XAS data also support the tetrahedral coordination of vanadium by N as indicated by the structure refinements.     

Dose‐, time‐and lipophilicity‐dependent silver(I)–N‐heterocyclic carbene complexes: Synthesis,characterization and interaction with plasmid and Aedes albopictus DNA

Four new Ag(I)–N‐heterocyclic carbene (NHC) complexes ( 5 – 8 ) bearing symmetrically substituted NHC ligands have been synthesized starting from the corresponding benzimidazolium bromide salts which are accessible in a single step from N ‐substituted benzimidazoles (N ‐alkyl and N ‐aryl) and subsequently reacted with the basic metal source Ag₂O in acetonitrile–methanol. These compounds were characterized using elemental analyses, ¹H NMR, ¹³C NMR, Fourier transform infrared and UV–visible spectroscopic techniques, and molar conductivity. Single‐crystal structural studies for complex 5 show that the Ag(I) centre has a perfectly linear C–Ag–C coordination, with quasi‐parallel pairs of aromatic benzimidazole planes. All the complexes interact with Aedes albopictus DNA via intercalation mode by a large hypochromicity of 22 and 27% and smaller hypochromicity of 16 and 19%. Furthermore, all complexes exhibit efficient DNA cleavage activity via a non‐oxidative mechanistic pathway. The DNase activities of the test compounds revealed a time‐ and concentration‐dependent activity pattern. The Ag(I)–NHC complexes showed considerably higher DNA cleavage activity compared to their respective benzimidazolium salts at a lower concentration. The DNA cleavage of these complexes changed from a moderate effect to a good one, corresponding to the increasing lipophilicity order of the complexes as 5  <  6  <  7  <  8 (1.02, 1.05, 1.78 and 2.06 for 5 – 8 , respectively). This order is further corroborated with the DNA binding study, but with the exception of complex 5 , which shows a better binding ability for DNA (K _b = 3.367 × 10⁶) than complexes 6 – 8 (6.982 × 10⁵, 8.376 × 10⁵ and 1.223 × 10⁶, respectively).     

Crystalline lipid domains: characterization by X-ray diffraction and their relation to biology

Biological membranes comprise thousands of different lipids, differing in their alkyl chains, headgroups, and degree of saturation. It is estimated that 5% of the genes in the human genome are responsible for regulating the lipid composition of cell membranes. Conceivably, the functional explanation for this diversity is found, at least in part, in the propensity of lipids to segregate into distinct domains, which are important for cell function. X-ray diffraction has been used increasingly to characterize the packing and phase behavior of lipids in membranes. Crystalline domains have been studied in synthetic membranes using wide- and small-angle X-ray scattering, and grazing incidence X-ray diffraction. Herein we summarize recent results obtained using the various X-ray methods, discuss the correlation between crystalline domains and liquid ordered domains studied with other techniques, and the relevance of crystalline domains to functional lipid domains in biological membranes.     

Die Kristallstrukturen der Cyanidofluoridoborate K[BFx(CN)4–x], x = 0–4

The crystal structure of K[BF₃(CN)] (Pbcn (Nr. 60) with a = 13.3486(15) b = 6.5239(7) c = 10.0085(11) Å, and eight formula units per unit cell) has been determined and the one of K[BF₂(CN)₂] was confirmed and improved. The different networks in the complete series of borates K[BF_x(CN)_4–x], x = 0–4 are compared and discussed.