Determination of ofloxacin in human serum by high-performance liquid chromatography with column switching.

The chromatographic behaviour of ofloxacin on various sorbents, including ODS, C8, C1, nitril, phenyl and tert,-butyl, as stationary phases was investigated and a high-performance liquid chromatography (HPLC) assay was developed for the determination of ofloxacin in serum. The serum samples were directly introduced onto an HPLC column after filtering through a Morcut II membrane filter to remove proteins. The filtrate was concentrated on a pre-column using a phenyl stationary phase and was then introduced to an analytical column with an ODS stationary phase by column switching. Ofloxacin and enoxacin as an internal standard were detected by ultraviolet absorbance at 300 nm. Determination was possible for ofloxacin over the concentration range 50-2000 ng/ml; the limit of detection was 20 ng/ml. The recovery of ofloxacin added to serum was 88.8-101.7% with a coefficient of variation of less than 5.2%. This method is applicable to pharmacokinetic studies of patients after treatment with ofloxacin.     

An atropisomeric M2L4 cage mixture displaying guest-induced convergence and strong guest emission in water

Introduction of atropisomeric axes into a bent bispyridine ligand leads to the quantitative formation of a complex mixture of atropisomeric M₂L₄ cages upon treatment with metal ions. Whereas the isomer ratio of the obtained cage mixture, consisting of up to 42 isomers, is insensitive to temperature and solvent, the quantitative convergence from the mixture to a single isomer is accomplished upon encapsulation of a large spherical guest, namely fullerene C₆₀. The observed isomerization with other guests depends largely on their size and shape (e.g., <10 and 82% convergence with planar triphenylene and bowl-shaped corannulene guests, respectively). Besides the unusual guest-induced convergence, the present cage mixture displays the strongest guest emission (Φ_F = 68%) among previously reported M_nL_m cages and capsules, upon encapsulation of a BODIPY dye in water.

A complex mixture of atropisomeric M₂L₄ cages is shown to undergo perfect convergence to a single isomer upon encapsulation of spherical C₆₀ in water. Moreover, the cage mixture displays very strong guest emission upon encapsulation of a BODIPY dye.     

Control of viscoelasticity using redox reaction

The viscoelasticity of a fluid was tuned with the Faradaic reaction of (11-ferrocenylundecyl)trimethylammonium bromide (FTMA), a "redox-switchable" surfactant. An aqueous solution of the reduced form of FTMA exhibited a remarkable viscoelasticity in the presence of sodium salicylate (NaSal) because of the formation of three-dimensional entanglement of wormlike micelles. Electrolytic oxidation of FTMA caused the viscosity of the system to dramatically decrease and the elasticity to disappear. This drastic decrease in viscoelasticity arose from the disruption of wormlike micelles. This novel electrorheological phenomenon is expected to be applicable to ink for inkjet printers, the electrochemically controlled release of substances entrapped in wormlike micelles of FTMA, and fluid flow rate control using electric signals.     

Voltammetric investigation of avidin-biotin complex formation using an electroactive bisbiotinyl compound

Formation of avidin-biotin complex was investigated using bisbiotinyl thionine (BBT) by means of voltammetric techniques. Thionine is an electroactive compound and has two amino groups that are necessary for the reaction with a biotinylation reagent. The biotinylation of thionine produces a new reagent with two biotin moieties at each end of thionine. Three BBTs of different lengths of the spacer that connects the biotin moiety to the thionine moiety were prepared. The avidin-biotin binding assay was achieved by measuring the electrode response of the thionine moiety in BBT. The binding affinity and the conformation of complex, which depended on the length of spacer, are discussed. BBT in which the spacer is shortest (BBT-S, distance between carbonyl group of the two biotin moieties: 11 Å) binds with only one avidin molecule. BBT with medium length of spacer (BBT-M, 28.8 Å) forms the complex with two avidin molecules. BBT with the longest spacer (BBT-L, 46.6 Å) allows binding with two avidin molecules as well as intramolecular binding within one avidin molecule. The affinity constants of BBT-S, BBT-M and BBT-L for avidin were estimated to be 7.0 × 10¹² M⁻¹, 3.2 × 10¹² M⁻¹ and 4.0 × 10¹² M⁻¹, respectively.     

Quantum dynamics driven by continuous laser fields under measurements: towards measurement-assisted quantum dynamics control

We study quantum system dynamics driven by continuous laser fields under the measurement process. In order to take into account the system transition due to the measurement, we define the superoperator which eliminates the coherence relevant to the measured quantum states. We clarify that the dynamics of the measured states is frozen in the frequent measurement limit, while the space spanned by unmeasured states is isolated from the original system. We also derive the effective Liouvillian which governs incoherent population dynamics under the condition, in which measurements are frequently applied. We apply the formulation to two-level and Lambda-type three-level systems and clarify how the quantum measurements hinder the coherent population dynamics driven by the continuous laser fields in practical examples. Analysis on the laser field amplitude dependency of the final distribution in the t-->infinity limit suggests the possibility of the measurement-assisted quantum control.     

Rapid and simple method for the determination of alpha 1-acid glycoprotein in serum by column liquid chromatography.

A rapid and simple method for the determination of alpha 1-acid glycoprotein (AAG) in serum was developed by using an anion-exchange column for clean-up of serum and a hydroxyapatite column for high-performance liquid chromatography (HPLC). A good correlation was observed between this HPLC method and the conventional radial immunodiffusion method. The method may also be used to determine the AAG concentration in the serum of experimental animals.     

Effect of mono-CDNP substitution of lysine residues on the redox reaction of cytochrome c electrostatically adsorbed on a mercaptoheptanoic acid modified Au(111) surface

The effect of charge-inverting modification of single surface lysine residue on the electron transfer (ET) reaction of horse heart cytochrome c (cyt c) is examined for 12 different types of mono-4-chloro-2,5-dinitrobenzoic acid substituted cyt c (mCDNPc) adsorbed on a Au(111) electrode modified with a self-assembled monolayer (SAM) of 7-mercapto-heptanoic acid (MHA). A negative shift in the redox potential by 10-35 mV as compared to that of native cyt c and a monolayer coverage in the range of 13-17 pmol cm(-2) are observed for electroactive mCDNPc's. The magnitude of the decrease in the ET rate constant (k(et)) of mCDNPc's compared with that of native cyt c depends on the position of the CDNP substitution. For mCDNPc's in which the modified lysine residue is outside of the interaction domain of cyt c with the SAM, the ratio of the k(et) of mCDNPc to that of native cyt c is correlated to the change in the dipole moment vector of cyt c due to the CDNP modification. This correlation suggests that the dipole moment of cyt c determines its orientation of adsorption on the SAM of MHA and significantly affects the rate of the ET. The CDNP modification of lysine residues at the interaction domain significantly decreases the rate, demonstrating the importance of the local charge environment in determining the rate of ET.     

Application of an automated synthesis suite to parallel solution-phase peptide synthesis

An in-house developed automated synthesis suite was used to prepare a library of 72 tetrapeptide derivatives, the starting materials for pharmaceutically attractive pentapeptides, employing a convergent strategy. An initial set of 18 dipeptides were synthesized on a large-scale (100-1000 g) using automated synthesis workstations, and then 72 tetrapeptides were synthesized on a medium scale (5-10 g) using an automated system. Each di- or tetrapeptide was prepared in a single operating cycle using a modified methanesulfonic acid method, then a sub-library of 56 pentapeptides were synthesized in parallel, on a small-scale (100 mg-1 g) using a robotic workstation.     

Ca0.8Y2.4Sn0.8O6, a quaternary oxide with mixed occupations of Ca/Y and Y/Sn

A new quaternary oxide, calcium yttrium stannate, Ca_0.8Y_2.4Sn_0.8O₆, is isostructural with Mg₃TeO₆ (trigonal, R). The empirical formula can be expressed as (Ca_0.2667Y_0.7333)₆(Y_0.4Sn_0.6)SnO₁₂. The Ca/Y site has a distorted coordination octa­hedron of O atoms, with Ca/Y—O distances ranging from 2.227 (3) to 2.350 (3) Å, while the octa­hedra of O atoms that coordinate to the Sn and Y/Sn sites are nearly regular, with an Sn—O distance of 2.066 (2) Å and a Y/Sn—O distance of 2.147 (3) Å.     

A stereochemical investigation of 2-methyl- and 2,5-dimethyl-3-phenyl-1,3-oxazolidines using NMR

The stereochemical properties of two 2-methyl-3-phenyl-1,3-oxazolidines and two of its 5-methyl substituted and four of its 2,5-dimethyl substituted derivatives have been investigated by pmr and cmr methods. The compounds of 2,5-dimethyl-3-phenyl-1,3-oxazolidines exist in isomeric cis and trans forms at the two methyl groups on the heterocyclic ring.