Mass spectrometry of dinucleotide analogues containing 6-azauracil moiety

The mass fragmentation of three dinucleotide analogues in which D -ribose phosphodiester linkages were replaced by a three methylene unit chain has been investigated. The fragmentation pathways were proposed on the basis of high resolution data and metastable transitions. These compounds demonstrated a unique fragmentation with the formation of the fragment ion containing nitrogen at the end of the C₃H₆ chain.     

Role of polyaniline morphology in Pd particles dispersion. Hydrogenation of alkynes in the presence of Pd-polyaniline catalysts

Two polyaniline (PANI) samples of various molecular masses were used for the preparation of palladium catalysts (with 2 mass % of Pd). The physicochemical features of starting polyanilines were found to substantially affect the size and extent of palladium nanoparticles aggregation. Strongly aggregated large palladium particles appeared in the PANI sample of more compact morphology (PANI-H), higher crystallinity and lower specific surface area. Pd nanoparticles of a definitively smaller size were formed in the more amorphous PANI sample of looser morphology (PANI-L) and the extent of particles aggregation was markedly lower. The catalytic properties of Pd/PANI samples were studied in a liquid phase hydrogenation of unsaturated triple bond (C≡C) in alkynes reactants, phenylacetylene, and cyclohexylacetylene. The 2 mass % Pd/PANI-L catalyst prepared using polymer of less compact texture exhibited much higher activity in both reactions. In the presence of the 2 mass % Pd/PANI-L catalyst, alkene products were formed with a high selectivity (approximately 90 %) attained at the almost complete conversion of alkynes. This highly selective hydrogenation of the C≡C to the C=C bond was related to the presence of an electroactive polymer, PANI, in close proximity with Pd active sites. Polyaniline could have a role in a steric effect as well as in a modification of adsorptive properties of Pd centres.     

(Co)polymers of oligo(ethylene glycol) methacrylates—temperature‐induced aggregation in aqueous solution

The synthesis and aggregation behavior of well‐defined thermosensitive (co)polymers of oligo(ethylene glycol) methacrylates (POEGMA) in aqueous solutions were investigated. The cloud points of the POEGMAs solutions were determined by turbidimetry and dynamic light scattering. For POEGMA (co)polymers the cloud point temperature (T_CP) increased linearly with increasing content of more hydrophilic comonomer. The mesoglobules formed by POEGMAs in dilute aqueous solutions above T_CP were studied by light scattering. The size of mesoglobules depended on the concentration and the heating procedures. The aggregates became smaller with decreasing initial concentration of polymer and increasing rates of temperature change. By selecting the proper heating and dilution procedures, the influence of the (co)polymer structure on the size of the mesoglobules could be determined. The size of the mesoglobules decreased with the length of the OEG side chains and increased with increasing content of more hydrophilic comonomer. The light scattering parameters of the mesoglobules—A₂ values and shape factors ${R_{\rm g}\over R_{\rm h}}$ —suggested that the hydrophilic OEG side chains placed at the periphery of the mesoglobules in direct contact with the surrounding water controlled the size of mesoglobules and their stability. Shape factors for all POEGMA mesoglobules indicated that the mesoglobules remained highly hydrated after formation. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Geometric changes around an N atom due to a urethane‐type bis(tert‐butoxycarbonyl) substituent

Two crystal structures of urethane‐protected derivatives of aspartic acid dimethyl ester are presented, namely dimethyl (2S)‐2‐[(tert‐butoxycarbonyl)amino]butanedioate, C₁₁H₁₉NO₆, and dimethyl (2S)‐2‐{bis[(tert‐butoxycarbonyl]amino}butanedioate, C₁₆H₂₇NO₈. The geometry at the N atom is discussed and compared with similar structures. The analysis of singly and doubly N‐substituted derivatives reveals an elongation of all bonds involving the N atom and conformational changes of the amino acid side chain due to steric interactions with two bulky substituents on the amino group.     

An Approach to Transfer Methods from HPLC to UHPLC Techniques in Some Carbapenems

Stability-indicating LC methods were developed and validated for the quantitative determination of doripenem, meropenem and tebipenem in the presence of their degradation products formed during forced degradation studies. Isocratic HPLC and UHPLC separations were performed with a core–shell Kinetex 1.7, 2.6 and 5 µm, all C18, 100A, 100 × 2.1 mm columns and the mobile phase composed of acetonitrile and 12 mmol L^?1 ammonium acetate in different ratios. The flow rates of the mobile phase were: 0.5 mL min^?1 for 1.7 µm column, and 1.0 mL min^?1 for 2.6 and 5 µm ones. Detection wavelength was 298 nm and temperature was set at 30 °C. All analysed drugs were exposed to stress conditions which caused their hydrolysis and thermal degradation. The methods were validated by evaluation of linearity, accuracy, precision, selectivity and robustness. Proposed methods were successfully applied for the determination of investigated antibiotics during kinetic studies in aqueous solutions and in the solid state. The advantages of chromatographic procedures which are based on the use of C18 stationary phases with different particle sizes in the analysis of selected carbapenems were discussed.     

Improved Gram–Schmidt Type Downdating Methods

The problem of deleting a row from a Q–R factorization (called downdating) using Gram–Schmidt orthogonalization is intimately connected to using classical iterative methods to solve a least squares problem with the orthogonal factor as the coefficient matrix. Past approaches to downdating have focused upon accurate computation of the residual of that least squares problem, then finding a unit vector in the direction of the residual that becomes a new column for the orthogonal factor. It is also important to compute the solution vector of the related least squares problem accurately, as that vector must be used in the downdating process to maintain good backward error in the new factorization. Using this observation, new algorithms are proposed. One of the new algorithms proposed is a modification of one due to Yoo and Park [BIT, 36:161–181, 1996]. That algorithm is shown to be a Gram–Schmidt procedure. Also presented are new results that bound the loss of orthogonality after downdating. An error analysis shows that the proposed algorithms’ behavior in floating point arithmetic is close to their behavior in exact arithmetic. Experiments show that the changes proposed in this paper can have a dramatic impact upon the accuracy of the downdated Q–R decomposition. AMS subject classification (2000) 65F20, 65F25