221,445 research outputs found
Tight Binding of a Dimeric Derivative of Vancomycin with Dimeric l-Lys-d-Ala-d-Ala
No full textThe ligand/receptor pair consisting of a synthetic
dimeric derivative of vancomycin (V), linked at the
C
terminus by p-xylylenediamine
(V-CONHCH2C6H4CH2NHCO-V),
and a dimeric derivative of
l-Lys-d-Ala-d-Ala,
[CH2CONεH(Nα-Ac)-l-Lys-d-Ala-d-Ala-CO2-]2,
provides a new system with which to study the influence of
divalency
on the strength of binding. A competitive assay using affinity
capillary electrophoresis (ACE) has been developed
and used to estimate the dissociation constant of the divalent complex
(≈ 1.1 nM) and the enhancement in
binding (∼103) relative to the corresponding monomeric
interaction between unmodified monomeric vancomycin
and
diacetyl-l-Lys-d-Ala-d-Ala
Design, Synthesis, and Characterization of a High-Affinity Trivalent System Derived from Vancomycin and l-Lys-d-Ala-d-Ala
No full textA trivalent derivative of vancomycin, tris(vancomycin carboxamide), [C6H3-1,3,5-(CONHC6H4-4-CH2NHCOV)3 (RtV3; V = vancomycin)], binds an analogous trivalent derivative of d-Ala-d-Ala, R‘tL‘3, (C6H3-1,3,5-[CONεH(Nα-Ac)-l-Lys-d-Ala-d-Ala]3) in water with a dissociation constant that is approximately 4 ×
10-17 M, as estimated by HPLC using a competitive assay against Nα,ε-diacetyl-l-Lys-d-Ala-d-Ala (L). This
binding is one of the tightest known for low molecular weight organic species. The dissociation of RtV3·R‘tL‘3
in the presence of an excess of L could be followed by HPLC. The kinetics of dissociation are quite different
from those of monovalent tight-binding systems such as avidin and biotin. In particular, the rate of dissociation
of the aggregate RtV3·R‘tL‘3 is rapid in the presence of monovalent L at concentrations greater than the value
of the dissociation constant for the complex of L with V; by contrast, the rate of dissociation of biotin·avidin
is independent of the concentration of biotin. Two mechanisms by which the dissociation may occur are
postulated and discussed. Calorimetric measurements for the trivalent system indicate that the enthalpy of
association is ∼−40 kcal/mol, about three times that of V + L, and thus the entropy of association is ∼−18
kcal/mol, approximately 4.5 times that of V + L
Ala Shearer Vickery Interview (Wayne County)
No full textAn interview with Ala Shearer Vickery of Monticello, Kentucky by Robert M. Rennick on the origin and history of place names and communities in Wayne County, Kentucky. The audio quality of the tape is substandard
A model for the M/M/1 queue and its applications in communication networks
No full textTypescript (photocopy).In this work, a continuous differential equation model describing the evolution of the mean number in an M/M/1 queue has been developed. The validity of this approximation has been established by comparisons with work by Stern {23} and with the results of extensive simulation studies. In an effort to extend the model to the prediction of the behavior of a network of queues, such as found in a packet switched communication network, the technique was successfully applied to a series of queues in tandem. This approximation scheme was next applied to a simple network which incorporated alternate routes between the source and destination. The existance of alternate routes necessitated, of course, the use of a control mechanism for choosing which route to use for a particular customer. In view of recent trends towards control based on averages, it was decided to implement a scheme based on such. It was found that the model accurately predicted the behavior of the network under this form of control. Finally, the model was used to describe a general N node ring network with distributed control
Il metodo delle soluzioni fondamentali per la soluzione del problema diretto M/EEG
No full textThe research already started on the mesh-free solution of the M / EEG direct problem has led to the development of a solver based on the method of fundamental solutions (MFS, method of fundamental solutions) able to manage the physical-geometric complexity of realistic models of the head more efficiently than traditional
ALA and m-ALA in bicontinuous lipid formulations: -Characterization and Transdermal Delivery
No full textδ-Aminolevulinic acid (ALA) and its methyl ester (m-ALA) are both used in photodynamic therapy (PDT) of certain non melanoma skin cancers as the basal cell carcinoma (BCC). In PDT the cancer cells are destroyed by a photochemical reaction that occurs when a photosensitive molecule is irradiated with light of a certain wavelength. The topically delivered ALA or m-ALA is, through the heme biosynthesis, transformed into the photosensitizer and accumulated in the chosen area.
In this thesis ALA and m-ALA (as hydrochloride salts) were incorporated in the monoolein/propylene glycol/water (MO/PG/water) sponge phase. The addition of up to 16% of the methyl ester made the samples more or less anisotropic dependent on the amount added. Isotropic liquids were reformed when water was added and the samples were characterized with nuclear magnetic resonance diffusometry (NMRD) and small angle X-ray scattering (SAXS) in order to confirm the reformation of the bicontinuous sponge phase. Highly obstructed self-diffusion coefficients were found for every component, which is a clear signal of the presence of a bicontinuous structure such as the sponge phase. Moreover, the diffusion coefficients of MO were evidently slower than for the other components indicating that the lipid by itself constitutes the structural skeleton, the bilayer of the phase. Small angle X-ray scattering confirmed the presence of the sponge phase by the presence of diffuse Bragg peak in the diffractograms.
The passive and iontophoretic transdermal delivery from sponge phases with added ALA and m-ALA were also studied. The sponge phase might have an optimal composition of the three components revealed from iontophoresis with 0.25% (w/w) ALA. The resulting fluxes from the two techniques with sponge phases incorporated with 16% m-ALA were comparable to fluxes received from clinically used formulations in both cases. Therefore, the MO/PG/water sponge phase can be regarded as a potential drug delivery vehicle for both passive diffusion and iontophoresis
ALA and m-ALA in bicontinuous lipid formulations: -Characterization and Transdermal Delivery
No full textδ-Aminolevulinic acid (ALA) and its methyl ester (m-ALA) are both used in photodynamic therapy (PDT) of certain non melanoma skin cancers as the basal cell carcinoma (BCC). In PDT the cancer cells are destroyed by a photochemical reaction that occurs when a photosensitive molecule is irradiated with light of a certain wavelength. The topically delivered ALA or m-ALA is, through the heme biosynthesis, transformed into the photosensitizer and accumulated in the chosen area.In this thesis ALA and m-ALA (as hydrochloride salts) were incorporated in the monoolein/propylene glycol/water (MO/PG/water) sponge phase. The addition of up to 16% of the methyl ester made the samples more or less anisotropic dependent on the amount added. Isotropic liquids were reformed when water was added and the samples were characterized with nuclear magnetic resonance diffusometry (NMRD) and small angle X-ray scattering (SAXS) in order to confirm the reformation of the bicontinuous sponge phase. Highly obstructed self-diffusion coefficients were found for every component, which is a clear signal of the presence of a bicontinuous structure such as the sponge phase. Moreover, the diffusion coefficients of MO were evidently slower than for the other components indicating that the lipid by itself constitutes the structural skeleton, the bilayer of the phase. Small angle X-ray scattering confirmed the presence of the sponge phase by the presence of diffuse Bragg peak in the diffractograms. The passive and iontophoretic transdermal delivery from sponge phases with added ALA and m-ALA were also studied. The sponge phase might have an optimal composition of the three components revealed from iontophoresis with 0.25% (w/w) ALA. The resulting fluxes from the two techniques with sponge phases incorporated with 16% m-ALA were comparable to fluxes received from clinically used formulations in both cases. Therefore, the MO/PG/water sponge phase can be regarded as a potential drug delivery vehicle for both passive diffusion and iontophoresis
The method of fundamental solutions in solving coupled boundary value problems for M/EEG
No full textThe estimation of neuronal activity in the human brain from electroencephalography (EEG) and magnetoencephalography (MEG) signals is a typical inverse problem whose solution pro- cess requires an accurate and fast forward solver. In this paper the method of fundamental solutions is, for the first time, proposed as a meshfree, boundary-type, and easy-to-implement alternative to the boundary element method (BEM) for solving the M/EEG forward problem. The solution of the forward problem is obtained by numerically solving a set of coupled boundary value problems for the three-dimensional Laplace equation. Numerical accuracy, convergence, and computational load are investigated. The proposed method is shown to be a competitive alternative to the state-of-the-art BEM for M/EEG forward solving
Low-temperature heat capacities and standard molar enthalpy of formation of the solid-state coordination compound trans-Cu(Ala)2(s) (Ala = l-α-alanine)
No full textLow-temperature heat capacities of the solid coordination compound trans-Cu(Ala)(2)(s) have been measured by a precision automated adiabatic calorimeter over the temperature range from T = 78 K to 390 K. The experimental values of the molar heat capacities in the temperature region were fitted to a polynomial equation of heat capacities (C-p,C-m) with the reduced temperatures (X), [X=f(T)], by a least square method. The smoothed molar heat capacities and thermodynamic functions of the complex trans-Cu(Ala)(2)(s) were calculated based on the fitted polynomial. The smoothed values of the molar heat capacities and fundamental thermodynamic functions of the sample relative to the standard reference temperature 298.15 K were tabulated with an interval of 5 K. Enthalpies of dissolution of {Cu(Ac)(2)center dot H2O(s) + 2Ala (s)} and 2:1 HAc (aq) in 100 ml of 2 mol dm(-3) HCl, respectively, and trans-Cu(Ala)(2)(s) in the solvent [2:1 HAc (aq) + 2 mol dm(-3) HCl] at T = 298.15 K were determined to be Delta H-s(m)degrees[Cu(Ac)(2)center dot H2O(s) + 2Ala(s)] = (6.75 +/- 0.04) kJ mol(-1), Delta H-s(m)degrees[2 : 1 HAc(aq)] = -(1.63 +/- 0.01) kJ mol(-1), and Delta H-s(m)degrees[trans-Cu(Ala)(2)(s)] = -(10.24 +/- 0.08) kJ mol(-1) by means of an isoperibol solution-reaction calorimeter. The standard molar enthalpy of formation of the compound was determined as Delta H-f(m)degrees(trans-Cu(Ala)(2)(s), 298.15 K) = -(1038.6 +/- 3.5) kJ mol(-1) from the enthalpies of dissolution and other auxiliary thermodynamic data using a Hess thermochemical cycle. (C) 2008 Elsevier B.V. All rights reserved
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