Can a catanionic surfactant mixture act as a drug delivery vehicle?

Surfactants can self-assemble in dilute aqueous solutions into a variety of microstructures, including micelles, vesicles, and bilayers. Recently, there has been an increasing interest in unilamellar vesicles, which are composed of a closed bilayer that separates an inner aqueous compartment from the outer aqueous environment. This interest is motivated by their potential to be applied as vehicles for active agents in drug delivery via several routes of administration. Active drug molecules can be encapsulated in the bilayer membrane if they are lipophilic or in the core of the vesicle if they are hydrophilic. Furthermore vesicles formed by mixing of cationic and anionic surfactants (so called ‘catanionic’ systems) can be used as models for biological membranes as they have low critical micelle concentration (cmc) and are highly biocompatible. In this work the formation of amino acid based mixed surfactant vesicles and their stabilization and biocompatibility were studied systematically using several instrumental techniques.     

Can azulene-like molecules function as substitution-free molecular rectifiers?

The feasibility of employing azulene-like molecules as a new type of high performance substitution-free molecular rectifier has been explored using NEGF-DFT calculation. The electronic transport behaviors of metal-molecule-metal junctions consisting of various azulene-like dithiol molecules are investigated, which reveals that the azulene-like molecules exhibit high conductance and bias-dependent rectification effects. Among all the substitution-free azulene-like structures, cyclohepta[b]cyclopenta[g]naphthalene exhibits the highest rectification ratio, revealing that the all fused aromatic ring structure and an appropriate separation between the pentagon and heptagon rings are essential for achieving both high conductance and high rectification ratio. The rectification ratio can be increased by substituting the pentagon ring with electron-withdrawing group and/or the heptagon ring with electron donating groups. Further increase of the rectification ratio may also be obtained by lithium adsorption on the pentagon ring. This work reveals that azulene-like molecules may be used as a new class of highly conductive unimolecular rectifiers.     

Can the peroxosuccinate complex in the catalytic cycle of taurine/alpha-ketoglutarate dioxygenase (TauD) act as an alternative oxidant?

Density functional theoretical studies on the catalytic properties of the peroxosuccinate intermediate in the catalytic cycle of taurine/alpha-ketoglutarate dioxygenase suggest that it cannot act as a second oxidant.     

Can a consecutive double turn conformation be considered as a peptide based molecular scaffold for supramolecular helix in the solid state?

Helices and sheets are ubiquitous in nature. However, there are also some examples of self-assembling molecules forming supramolecular helices and sheets in unnatural systems. Unlike supramolecular sheets there are a very few examples of peptide sub-units that can be used to construct supramolecular helical architectures using the backbone hydrogen bonding functionalities of peptides. In this report we describe the design and synthesis of two single turn/bend forming peptides (Boc-Phe-Aib-Ile-OMe 1 and Boc-Ala-Leu-Aib-OMe 2) (Aib: α-aminoisobutyric acid) and a series of double-turn forming peptides (Boc-Phe-Aib-Ile-Aib-OMe 3, Boc-Leu-Aib-Gly-Aib-OMe 4 and Boc-γ-Abu-Aib-Leu-Aib-OMe 5) (γ-Abu: γ-aminobutyric acid). It has been found that, in crystals, on self-assembly, single turn/bend forming peptides form either a supramolecular sheet (peptide 1) or a supramolecular helix (peptide 2), unlike self-associating double turn forming peptides, which have only the option of forming supramolecular helical assemblages.     

Molecular structures of carbonyl-linked bis(dioxolene) complexes: can a carbonyl group act as an effective ferromagnetic coupler?

Molecular structures of two bis(ZnIIdioxolene) complexes are described: (TpCum,MeZn)(2)1-H2 (C106H123.50B2N12O10Zn2), tetragonal, P4/ncc, a = 25.1810(2) A, b = 25.1810(2) A, c = 34.7744(2) A, alpha = 90 degrees, beta = 90 degrees, gamma = 90 degrees, Z = 8; (TpCum,MeZn)(2)1-H (C101H120B2N12O6Zn2), triclinic, P1, a = 13.6624(2) A, b = 13.80920(10) A, c = 26.62340(10) A, alpha = 96.6910(10) degrees, beta = 91.8560(10) degrees, gamma = 109.0190(10) degrees, Z = 2. One of the complexes, (TpCum,MeZn)(2)1-H2, has two protonated catecholate ligands, while the other complex, (TpCum,MeZn)(2)1-H, has one protonated catecholate and one semiquinone ligand. When reacted with PbO2, a labile S = 1, bis(ZnIIsemiquinone) complex is formed in which the two semiquinones are attached to a common carbonyl group.     

How Can a Carbene be Active in an Ionic Liquid?

The solvation of the carbene 1‐ethyl‐3‐methylimidazole‐2‐ylidene in the ionic liquid 1‐ethyl‐3‐methylimidazolium acetate was investigated by ab initio molecular dynamics simulations in order to reveal the interaction between these two highly important classes of materials: N‐heterocyclic carbenes with superb catalytic activity and ionic liquids with advantageous properties as solvents and reaction media. In contrast to previously published data on analogous systems, no hydrogen bond is observed between the hypovalent carbon atom and the most acidic ring hydrogen atoms, as these interaction sites of the imidazolium ring are predominantly occupied by the acetate ions. Keeping the carbene away from the ring hydrogen atoms prevents stabilization of this reactive species, and hence any retarding effect on subsequent reactions, which explains the observed high reactivity of the carbene in acetate‐based ionic liquids. Instead, the carbene exhibits a weaker interaction with the methyl group of the imidazolium cation by forming a hitherto unprecedented kind of C???H?C hydrogen bond. This unexpected finding not only indicates a novel kind of hydrogen bond for carbenes, but also shows that such interaction sites of the imidazolium cation are not limited to the ring hydrogen atoms. Thus, the results give the solute–solvent interactions within ionic liquids a new perspective, and provide a further, albeit weak, site of interaction to tune in order to achieve the desired environment for any dissolved active ingredient.     

Can coil-to-globule transition of a single chain be treated as a phase transition?

The effects of the concentration (C) and heating rate on the collapse and association of poly(N-isopropylacrylamide) chains in water have been investigated by use of ultrasensitive differential scanning calorimetry. In the dilute solutions, both the phase transition temperature (Tp) and enthalpy change (DeltaH) increase with the heating rate but decrease with concentration. By extrapolation to zero heating rate and zero concentration, Tp and DeltaH for coil-to-globule transition of a single chain in thermodynamic equilibrium can be obtained. In semidilute solutions, both Tp and DeltaH increase with the heating rate but slightly vary with the concentration. Tp and DeltaH for pure interchain association in equilibrium are obtained by extrapolation to zero heating rate. Our experiments reveal that only intrachain contraction occurs when the concentration is infinitely close to zero. When the concentration is above the overlap concentration (C*), only interchain association exists. In the range 0相似文献   

Synthetic hosts via molecular imprinting--are universal synthetic antibodies realistically possible?

Of the many ways to make synthetic hosts, one of the most appealing involves molecular imprinting. In the commonest approach monomer units assemble around or are attached to a template (imprint) molecule and then linked together using a cross-linking agent. Template removal ideally leaves cavities within the molecularly imprinted polymer (MIP) that possess a shape and functional group complementarity to the imprint molecule allowing its tight and selective uptake. This review highlights some recent advances in the synthesis of MIPs (often called "synthetic antibodies") and enumerates a "wish list" of properties for the perfect MIP that may guide future studies.     

β-Trifluoromethyl-α-functionalized-vinyl sulfides as a potential synthetic intermediate

The β-(trifluoromethyl)vinyl sulfides on treatment with n-BuLi/TMEDA at −78 °C were readily lithiated at an α-position of the sulfanyl group, and the generated β-trifluoromethyl-α-sulfanylvinyl anions were reacted with a variety of electrophiles to give the corresponding β-trifluoromethyl-α-functionalized-vinyl sulfides 4aa-4aq in good to excellent yields. The reactivity of some products has been examined. The palladium-catalyzed cross-coupling reaction as well as homo-coupling reaction of 4af provided the corresponding products in good yields, respectively. The Diels-Alder reaction of cyclic dienes and 14 derived from 4ao provided the desired six-membered cyclic products with high endo-trifluoromethyl group selectivity.     

Do biopolymers behave the same as synthetic high polymers?

The first measurements in our laboratory of some 55 years ago dealt with adiabatic calorimetry of linear, semicrystalline polyethylene. Quickly it became obvious that time needed to be controlled to study the metastable and unstable states. Shortly thereafter, my first students were building our own DTA, capable to give quantitative, time-dependent calorimetric data. Only few years later, we could present the quantitative link between molecular motion and heat capacity in the melting and glass-transition regions. One of these students involved in this study was Prof. Michael Jaffe. His study dealt with semicrystalline polyoxymethylene, a synthetic carbohydrate. He could use the first quantitative commercial equipment and modify it to heating with rates of 100 K min⁻¹ and more. Today, rates reaching up to 10⁷ K min⁻¹ and faster are available for the analysis of unstable and small phases. The key question of this beginning study on biopolymer-related materials is the title question of this presentation for this symposium.     

Dansyl-Modified γ-Cyclodextrin as a fluorescent sensor for molecular recognition

Dansyl-Modified -Cyclodextrin (1) has been prepared as a sensor for detecting organic compounds.1 shows pure monomer fluorescence whose intensity is decreased or enhanced upon addition of guest species. The value I/I ⁰, whereI andI ⁰ are fluorescence intensities in the presence and absence of a guest and I isI ⁰–I, was used as a parameter of sensitivity.1 exhibits highly sensitive and selective molecular recognition ability, particularly, for ursodeoxycholic acid, chenodeoxycholic acid, and lithocholic acid.     

Dansyl-Modified γ-Cyclodextrin as a fluorescent sensor for molecular recognition

The crystal structure of thiamine iodide sesquihydrate has been determined by X-ray diffraction methods as a host-guest model for coenzyme-substrate interactions. The asymmetric unit contains two chemical units. Both the thiamine molecules A and B, which are crystallographically independent, assume the usualF conformation and have a disordered hydroxyethyl side chain. An iodide anion (or a water molecule) bridges the pyrimidine and thiazolium rings of molecule A (or B) by forming a hydrogen bond with the amino group and an electrostatic contact with the thiazolium ring to stabilize the molecular conformation. In the crystal the thiamine molecules self-associate to form a pipe-like polymeric structure, in which four thiamine hosts surround an iodide guest and hold it through C(2)-H...I hydrogen bonds and thiazolium...I electrostatic interactions. Crystal data: C₁₂H₁₇N₄OS⁺·I^– · 1.5 H₂O, monoclinic,P2₁/c, a=12.585(2), b=25.303(5), c=12.030(2) Å, =115.15(1)°,V=3468(1) ų,Z=8,D _c=1.606 g cm^–3,R=0.045 for 3328 observed reflections. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP. 82156 (13 pages).     

A fluorescent molecular ruler as a selective probe for ω-aminoacids

A fluorescent probe for ω-aminoacids behaves as a molecular ruler, changing the yellow fluorescent emission into blue as a function of the distance between the terminal ammonium and the carboxylate groups, permitting the quantitative detection of ω-aminoacids, their metabolites and related drugs, such as pregabalin or gabapentin, from pharmaceutical formulations.     

Will water act as a photocatalyst for cluster phase chemical reactions? Vibrational overtone-induced dehydration reaction of methanediol

The possibility of water catalysis in the vibrational overtone-induced dehydration reaction of methanediol is investigated using ab initio dynamical simulations of small methanediol-water clusters. Quantum chemistry calculations employing clusters with one or two water molecules reveal that the barrier to dehydration is lowered by over 20 kcal/mol because of hydrogen-bonding at the transition state. Nevertheless, the simulations of the reaction dynamics following OH-stretch excitation show little catalytic effect of water and, in some cases, even show an anticatalytic effect. The quantum yield for the dehydration reaction exhibits a delayed threshold effect where reaction does not occur until the photon energy is far above the barrier energy. Unlike thermally induced reactions, it is argued that competition between reaction and the irreversible dissipation of photon energy may be expected to raise the dynamical threshold for the reaction above the transition state energy. It is concluded that quantum chemistry calculations showing barrier lowering are not sufficient to infer water catalysis in photochemical reactions, which instead require dynamical modeling.     

Eu3+ as an MCD probe?

On the basis of the selection rules for magnetic dipole and induced electric dipole transitions in rare earths, the sign of the A₁ term corresponding to the ⁷F₀ → ⁵D₂ transition in the Eu³⁺ spectrum is shown to be related to the site symmetry of the Eu³⁺ ion. The most favourable coordination polyhedra of the rare earth ions are considered and the predicted MCD signals discussed. It is suggested that the induced electric dipole transition ⁵D₂ → ⁷F₀ in Eu³⁺ be used as an MCD probe for the determination of the coordination symmetry, while the ⁵D₁ → ⁷F₀ can be used as a sign reference transition.     

Can glycans unveil the origin of glycoprotein hormones? - human chorionic gonadotrophin as an example -

Doping with (glyco)protein hormones represent an extremely challenging, analytical problem as nearly all are constitutively present at low concentrations that fluctuate according to circadian or alternative periodical, or external stimuli. Thus the mere concentration in a biological sample is only resolutive when this surpasses extreme values. As the vast majority of these molecules are produced by recombinant DNA technology it is believed that the exogenous molecules could bear the signature of the host cell. In particular, these could comprise structural differences originated from co or post-translational differences. In this study we have employed both proteomics and glycomics strategies to compare recombinant and urinary human chorionic gonadotrophin in order to evaluate this hypothesis. As anticipated the recombinant hormone could be shown to contain N-glycolyl neuraminic acid, a sialic acid that cannot be produced by humans. Furthermore, differences were observed in the overall glycosylation, in particular the presence of abundant hybrid-type glycans that were much less pronounced in the recombinant species. These differences were determined to occur predominantly in the alpha-subunit for which antidoping strategies focussed on these elements could be used for both chorionic gonadotrophin and lutrophin as they share the same alpha-subunit.