Spontaneous vesicle formation of mixtures of double-chain cationic surfactants with a different counterion

Aggregate formation of a didodecyldimethylammonium bromide (DDAB) and didodecyldimethylammonium chloride (DDAC) mixture in aqueous solution was investigated. The concentration vs composition diagram of aggregate formation was constructed by analyzing the surface tension, turbidity, and electrical conductivity data. The cryogenic transmission electron microscopy was applied to several representative points in the diagram and provided information of the morphology of aggregates. The sequence of monomer (m) - m + small aggregate (A) - m + A + vesicle (V) - m + V was concluded with increasing total concentration of surfactants at all mixing ratios. The compositions of counterions in A and V were estimated on the basis of thermodynamic consideration and examined from the viewpoint of asymmetry of constituents and uneven distribution between outer and inner monolayers of a vesicle bilayer. Vesicle surfaces were suggested to abound in chloride ions compared to bulk solution, which is opposite to spherical micelle surfaces.     

A strong bound on the integral of the central path curvature and its relationship with the iteration-complexity of primal-dual path-following LP algorithms

The main goals of this paper are to: i) relate two iteration-complexity bounds derived for the Mizuno-Todd-Ye predictor-corrector (MTY P-C) algorithm for linear programming (LP), and; ii) study the geometrical structure of the LP central path. The first iteration-complexity bound for the MTY P-C algorithm considered in this paper is expressed in terms of the integral of a certain curvature function over the traversed portion of the central path. The second iteration-complexity bound, derived recently by the authors using the notion of crossover events introduced by Vavasis and Ye, is expressed in terms of a scale-invariant condition number associated with m × n constraint matrix of the LP. In this paper, we establish a relationship between these bounds by showing that the first one can be majorized by the second one. We also establish a geometric result about the central path which gives a rigorous justification based on the curvature of the central path of a claim made by Vavasis and Ye, in view of the behavior of their layered least squares path following LP method, that the central path consists of long but straight continuous parts while the remaining curved part is relatively “short”. R. D. C. Monteiro was supported in part by NSF Grants CCR-0203113 and CCF-0430644 and ONR grant N00014-05-1-0183. T. Tsuchiya was supported in part by Japan-US Joint Research Projects of Japan Society for the Promotion of Science “Algorithms for linear programs over symmetric cones” and the Grants-in-Aid for Scientific Research (C) 15510144 of Japan Society for the Promotion of Science.     

Letter: correlation between phosphorylation ratios by matrix-assisted laser desorption/ionization time-of-flight mass spectrometric analysis and enzyme kinetics

To identify the correlation between the phosphorylation ratios by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-ToF MS) analysis and enzyme kinetics (K(m), V(max), and V(max)/K(m)) is important to understand whether MALDI-TOF MS can be applied for monitoring the properties of peptides that are substrates of protein kinases. The correlation between phosphorylation ratios and enzyme kinetics was examined using peptides for protein kinase C (PKC) and for 60 kDa phosphoprotein, encoded by the cellular sarcoma gene (c-Src). Phosphorylation ratios, analyzed by MALDI-ToF MS, showed higher correlation coefficient (r = > +0.7) for V(max)/K(m) compared with that (r = < -/+0.6) for K(m) or V(max). For ion modes, a higher correlation coefficient between phosphorylation ratios and V(max)/K(m) was identified in the positive mode (r = > +0.7) compared to that in the negative mode (r = < +0.5). These results suggest that MALDI-ToF MS is a useful tool to evaluate V(max)/K(m) of peptides for protein kinases.     

Adsorption and micellization behavior of novel gluconamide-type gemini surfactants

The adsorption and micellization behavior of novel sugar-based gemini surfactants (N,N(')-dialkyl-N,N(')-digluconamide ethylenediamine, Glu(n)-2-Glu(n), where n is the hydrocarbon chain length of 8, 10 and 12) has been studied on the basis of static/dynamic surface tension, fluorescence, dynamic light scattering (DLS) and cryogenic transmission electron microscope (cryo-TEM) data. The static surface tension of the aqueous Glu(n)-2-Glu(n) solutions measured at the critical micelle concentration (cmc) is observed to be significantly lower than that of the corresponding monomeric surfactants. This suggests that the gemini surfactants, newly synthesized in the current study, are able to form a closely packed monolayer film at the air/aqueous solution interface. The greater ability in the molecular association is supported by the remarkably (approximately 100-200 times) lower cmc of the gemini surfactants compared with the corresponding monomeric ones. With a combination of the fluorescence and DLS data, a structural transformation of the Glu(n)-2-Glu(n) micelles is suggested to occur with an increase in the concentration. The cryo-TEM measurements clearly confirm the formation of worm-like micelles of Glu(12)-2-Glu(12) at the concentration well above the cmc.     

Anti-Stokes Luminescence in Multi-Resonance-Type Thermally-Activated Delayed Fluorescence Molecules

Photon-upconversion in organic molecular systems is one of the promising technologies for future energy harvesting systems because these systems can generate excitons that possess higher energy than excitation energy. The photon-upconversion caused by absorbing ambient heat as additional energy is particularly interesting because it could ideally provide a light-driving cooling system. However, only a few organic molecular systems have been reported. Here, we report the anti-Stokes photoluminescence (ASPL) derived from hot-band absorption in a series of multi-resonance-type thermally-activated delayed fluorescence (MR-TADF) molecules. The MR-TADF molecules exhibited an anti-Stokes shift of approximately 0.1 eV with a high PL quantum yield in the solution state. The anti-Stokes shift corresponded well to the 1–0 vibration transition from the ground state to the excited singlet state, and we further evaluated a correlation between the activation energy for the ASPL intensity and the TADF process. Our demonstration underlines that MR-TADF molecules have become a novel class of ASPL materials for various future applications, such as light-driving cooling systems.     

Interaction between Divalent Copper Fluoride and Carboxamide Group Enabling Stereoretentive Fluorination of Tertiary Alkyl Halides

Herein, we report a copper-catalyzed stereospecific fluorination involving CsF and α-bromocarboxamides as tertiary alkyl sources that, unlike traditional stereospecific routes involving stereoinversive S_N2 reactions, proceeds with retention of stereochemistry. The developed stereospecific Cu-catalyzed reaction is among the most efficient methods for synthesizing fluorinated molecules that possess highly congested stereogenic carbon centers. Mechanistic studies revealed that the combined reactivity of CuF₂ and Cs salt is essential for completing the catalytic cycle. Our catalytic system underwent fluorination exclusively with tertiary alkyl bromides and did not react with primary alkyl bromides, indicating that this stereospecific fluorination methodology is suitable for synthesizing fluorinated building blocks possessing stereo-defined F-containing tertiary carbon stereogenic center.     

Direct measurement of interactions between stimulation-responsive drug delivery vehicles and artificial mucin layers by colloid probe atomic force microscopy

A novel thermo- and pH-sensitive nanogel particle, which is a core-shell structured particle with a poly(N-isopropylacrylamide) (p(NIPAAm)) hydrogel core and a poly(ethylene glycol) monomethacrylate grafted poly(methacrylic acid) (p(MMA-g-EG)) shell, is of interest as a vehicle for the controlled release of peptide drugs. The interactions between such nanogel particles and artificial mucin layers during both approach and separation were successfully measured by using colloid probe atomic force microscopy (AFM) under various compression forces, scan velocities, and pH values. While the magnitudes of the compression forces and scan velocities did not affect the interactions during the approach process, the adhesive force during the separation process increased with these parameters. The pH values significantly influenced the interactions between the nanogel particles and a mucin layer. A large steric repulsive force and a long-range adhesive force were measured at neutral pH due to the swollen p(MMA-g-EG) shell. On the other hand, at low pH values, the steric repulsive force disappeared and a short-range adhesive force was detected, which resulted from the collapse of the shell layer. The nanogel particles possessed a pH response that was sufficient to protect the incorporated peptide drug under the harsh acidic conditions in the stomach and to effectively adhere to the mucin layer of the small intestine, where the pH is neutral. The relationships among the nanogel particle-mucin layer interactions, pH conditions, scan velocities, and compression forces were systemically investigated and discussed.     

Papain‐Catalyzed Chemoenzymatic Synthesis of Telechelic Polypeptides Using Bis(Leucine Ethyl Ester) Initiator

In order to construct unique polypeptide architectures, a novel telechelic‐type initiator with two leucine ethyl ester units is designed for chemoenzymatic polymerization. Glycine or alanine ethyl ester is chemoenzymatically polymerized using papain in the presence of the initiator, and the propagation occurs at each leucine ethyl ester unit to produce the telechelic polypeptide. The formation of the telechelic polypeptides is confirmed by ¹H NMR and MALDI‐TOF mass spectroscopies. It is revealed by AFM observation that long nanofibrils are formed from the telechelic polyalanine, whereas a conventional linear polyalanine with a similar degree of polymerization shows granule‐like structures. The telechelic polyglycine and polyalanine show the crystalline structures of Polyglycine II and antiparallel β‐sheet, respectively. It is demonstrated that this method to synthesize telechelic‐type polypeptides potentially opens up a pathway to construct novel hierarchical structures by self‐assembly.