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1.
2.
A physico-chemical investigation on the binding of some nonsteroidal anti-inflammatory drugs, Naproxen (NP) and Ketoprofen
(KP) and a drug model compound, salicylic acid (SA) to poly(N-vinyl-2-pyrrolidone) (PVP, molecular weight = 360,000), was
performed at pH 7.1 by the fluorescence competition method employing 1-anilinonaphthalene-8-sulphonate (ANS) as the fluorescent
probe. The binding affinities of these substrates to PVP are in the order KP < SA < NP which has been explained on the basis
of their structural features and the consequent effect on the interacting forces. Theπ-π interaction between the carbonyl group of PVP and theπ-ring system of the substrate molecule seems to be crucial in deciding the binding affinities of the substrates 相似文献
3.
B. Janković B. Adnađević J. Jovanović 《Journal of Thermal Analysis and Calorimetry》2008,92(3):821-827
An isothermal dehydration of equilibrium swollen poly(acrylic acid) hydrogel in the temperature range from 306 to 361 K was
investigated. The specific parameters connected with shape of the conversion curves were defined. The activation parameters
(E, lnA) of the isothermal dehydration of equilibrium swollen poly(acrylic acid) hydrogel were calculated, using Johnson-Mehl-Avrami
(JMA), ‘initial rate’ and ’stationary point’ methods. The reaction models for the investigated dehydration are determined
using the ‘model-fitting’ method. It was established that both, the reaction model and activation parameters of the hydrogel
dehydration were completely different for the isothermal process than for the non-isothermal one. It was found that the increase
in dehydration temperature lead to the changes in isothermal kinetic model for the investigated hydrogel dehydration. It was
established that the apparent activation energy (E) of hydrogel dehydration is similar to the value of the molar enthalpy
of water evaporation. 相似文献
4.
The binding of 1-anilinonaphthalene-8-sulphonate (ANS) to poly(N-vinyl-2-pyrrolidone) (PVP) of molecular weight grades k30
(molecular weight 40,000) and k90 (360,000) was studied by a dialysis technique in 0·05 M phosphate buffer, pH 7·1, at different
temperatures. The intrinsic binding constant,K, was determined. The binding was favoured by negative enthalpy and positive entropy in both the systems indicating respectively
that energetic forces and hydrophobic interactions were contributing to the binding affinity. The effects of addition of urea
and palmitic acid on binding were investigated by dialysis and fluorescence techniques. The results showed that the binding
of ANS to PVP was dependent on the nature and microenvironment of the binding sites and thereby pointed out the importance
of the iceberg structure of water in the binding system. 相似文献
5.
M.D Eddy 《Foundations of Chemistry》2004,6(2):161-175
In the 18th century, the concept of ‘affinity’, ‘principle’ and ‘element’ dominated chemical discourse, both inside and outside
the laboratory. Although much work has been done on these terms and the methodological commitments which guided their usage,
most studies over the past two centuries have concentrated on their application as relevant to Lavoisier's oxygen theory and
the new nomenclature. Kim's affinity challenges this historiographical trajectory by looking at several French chemists in the light of their private thoughts,
public disputations and communal networks. In doing so, she tells a complex story which points to the methodological and practical
importance of industrial and medical chemistry. The following review highlights the advantages and snares of such an approach
and makes a few historiographical points along the way.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
Shashi B. Kalia Priyanka Sankhyan R. Puri J. Christopher 《Journal of Thermal Analysis and Calorimetry》2012,107(2):597-605
Non-isothermal techniques, i.e. thermogravimetry (TG) and differential scanning calorimetry (DSC), have been applied to investigate
the thermal behaviour of carbaryl (1-naphthyl-N-methylcarbamate = 1-Naph-N-Mecbm) and its complexes, M(1-Naph-N-Mecbm)4X2, where M = Cu, X = Cl, NO3 and CH3COO and M = Zn, X = Cl. Carbaryl and Zn(1-Naph-N-Mecbm)4Cl2 complex exhibit two-stage thermal decomposition while the copper(II) complexes exhibit three and four-stage decomposition
in their TG curves. The nature of the metal ion has been found to play highly influential role on the nature of thermal decomposition
products as well as energy of activation ‘E*’. The presence of different anions does not seem to alter the thermal decomposition patterns. The complexes display weak
to medium intensity exothermic and endothermic DSC curves, while the free ligand exhibits two endothermic peaks. The kinetic
and thermodynamic parameters namely, the energy of activation ‘E*’, the frequency factor ‘A’ and the entropy of activation ‘S*’ etc. have been rationalized in relation to the bonding aspect of the carbaryl ligand. The nature and chemical composition
of the residues of the decomposition steps have been studied by elemental analysis and FTIR data. 相似文献
7.
M. Angiuli C. Ferrari L. Lepori E. Matteoli G. Salvetti E. Tombari A. Banti N. Minnaja 《Journal of Thermal Analysis and Calorimetry》2006,84(1):105-112
Extra Virgin olive oils
(7 samples) originating from different areas of Tuscany, defective olive oils
(5 samples), commercial edible seed oils (4 samples) and two commercial samples
of olive oil (one declared ‘extra virgin olive oil’ and one ‘olive
oil’) were studied by different calorimetric techniques: high sensitivity
isothermal, differential scanning, and modulated scanning calorimetry. The
temperature interval (–60) – (+30)°C was explored for monitoring: i) the main features of the liquid↔solid phase
transitions, ii) the nucleation and growth
rate of the polymorphous crystalline phases of the triacylglicerols, and iii) the melting process. This investigation was
planned for verifying the utility and effectiveness of calorimetry for screening
quality and origin of olive oil. To this end, the main calorimetric operation
modes have been applied, the experimental results reported and their utility
for developing an effective and reliable screening protocol discussed. 相似文献
8.
A new methodology for understanding the construction of polyhedral links has been developed on the basis of the Platonic solids
by using our method of the ‘n-branched curves and m-twisted double-lines covering’. There are five classes of platonic polyhedral links we can construct: the tetrahedral links;
the hexahedral links; the octahedral links; the dodecahedral links; the icosahedral links. The tetrahedral links, hexahedral
links, and dodecahedral links are, respectively, assembled by using the method of the ‘3-branched curves and m-twisted double-lines covering’, whereas the octahedral links and dodecahedral links are, respectively, made by using the
method of the ‘4-branched curves’ and ‘5-branched curves’, as well as ‘m-twisted double-lines covering’. Moreover, the analysis relating topological properties and link invariants is of considerable
importance. Link invariants are powerful tools to classify and measure the complexity of polyhedral catenanes. This study
provides further insight into the molecular design, as well as theoretical characterization, of the DNA polyhedral catenanes. 相似文献
9.
P. S. Fedotov M. S. Ermolin E. Yu. Savonina V. A. Kronrod B. Ya. Spivakov 《Journal of Analytical Chemistry》2010,65(12):1209-1214
A method for the continuous-flow fractionation of particles in a transverse centrifugal field in a rotating conoidal coiled
(RCC) column has been developed. A model of a planetary centrifuge with a conoidal drum of a special construction has been tested.
The effects of the rotation and revolution speed of the conoidal RCC, as well as the direction and pumping rate of the mobile
phase on the behavior of particles smaller than 1 μm have been studied. The conditions have been selected and optimized for
the retention and elution of spherical particles of the ‘150 nm’, ‘400 nm’, and ‘900 nm’ standard samples of silica gel (Polyscience Inc.). The possibility of using RCC for the analysis and production of monodisperse standard particle samples has been demonstrated.
In particular, the ‘900 nm’ particles have been separated from admixtures of small (100–200 nm) particles and nonspherical
1–2 μm particles present in the sample. The separated fractions have been characterized by electron microscopy. 相似文献
10.
As amyloid β (Aβ) is at the centre of pathogenesis of Alzheimer's disease (AD), Aβ aggregate-specific probes for in vivo studies of Aβ are potentially important for the early diagnosis and the assessment of new treatment strategies in the AD brain by noninvasive imaging. Several series of compounds derived from Congo red (CR) and Thioflavin T (ThT) have been evaluated as potential probes for the Aβ imaging. They include a diversity of core structures contributing to their affinities to Aβ. Small-molecule inhibi- tors were known to inhibit the formation of Aβ oligomers and fibrils. This inhibition has to be performed in such a way that these inhibitors bind to Aβ in the binding channel where Aβ-binding probes should sit. Therefore, several of them were used as novel core structures to develop Aβ probes, with their de- rivatives exhibiting good Aβ affinities. This approach will facilitate the design of a variety of candidates for Aβ probe molecules and anti-aggregation-therapeutic drugs. Moreover, the finding of Aβ probes with diverse core structures recognized by binding sites on Aβs will likely provide a promising per- spective for the design of 99mTc-labeled probe-derived molecules. 相似文献
11.
Summary The stability of emulsion of Toluene in water stabilized by partially flocculated ferric hydroxide sol has been studied. The
size of the emulsion droplets as determined by size frequency analysis is found to be of 1.1 μ radius. The flocculation studies were carried out haemocytometrically at different amount of electrolytes and at different
pH values. The electrokinetic potential ‘ζ’ was determined micro-electrophoretically at different amounts of electrolytes and
also at different pH's. In the case of tri and tetra valent anions the charge reversal was observed. In the light of the D.V.O. theory the interaction
energy profiles were drawn and 2–6 kT deep secondary minima obtained showing thereby the occurrence of reversible flocculation. Degree of aggregation has been
calculated theoretically at different values of ‘A’ and the value of A was found to be 1.0×10−12 erg to fit the value of degree of aggregation obtained haemocytometrically. The charge densities and binding parameters have
also been calculated. 相似文献
12.
The ‘characteristic function’ with two empirically determined parameters α and β, is proposed as a general purpose function to describe the variation of
precision (in terms of standard deviation σ), or uncertainty, with analyte concentration c (here denoting any compositional quantity), for specific analytical methods applied to a defined type of test material. In
this study it is applied to examples of analytical data collected under ‘instrumental’ conditions for estimating precision.
The function fitted the data well, with no systematic lack of fit. The study therefore extends the range of applications of
this function. 相似文献
13.
Many recent experimental studies have reported a surprising ultraslow component (even >10 ns) in the solvation dynamics of
a polar probe in an organized assembly, the origin of which is not understood at present. Here we propose two molecular mechanisms
in explanation. The first one involves the motion of the ‘buried water’ molecules (both translation and rotation), accompanied
by cooperative relaxation (‘local melting’) of several surfactant chains. An estimate of the time is obtained by using an
effective Rouse chain model of chain dynamics, coupled with a mean first passage time calculation. The second explanation
invokes self-diffusion of the (di)polar probe itself from a less polar to a more polar region. This may also involve cooperative motion of the surfactant chains in the hydrophobic
core, if the probe has a sizeable distribution inside the core prior to excitation, or escape of the probe to the bulk from
the surface of the self-assembly. The second mechanism should result in the narrowing of the full width of the emission spectrum with time, which has indeed been observed in recent experiments. It is argued that both the mechanisms may give rise to an ultraslow
time constant and may be applicable to different experimental situations. The effectiveness of solvation as a dynamical probe
in such complex systems has been discussed. 相似文献
14.
Complexation reactions of bivalent metal ions and ethyl-2,3-dioxobutyrate-2p-bromophenylhydrazone (EDOB-2p-BPH) have been studied potentiometrically in 50% (v/v) ethanol/water medium at different ionic strengths with respect to
NaClO4 and at different temperatures and their stability constants determined. The method of Bjerrum and Calvin as modified by Irving
and Rossotti has been used to determine then andpL values. Smin values which have the same significance as ‘T2’ have also been calculated. The thermodynamic stability constants and standard free energy change (ΔG) have also been calculated.
ΔG values are negative in all cases indicating that the reactions are spontaneous. The ligand field stabilization energy (δH)
has also been calculated for the 3d transition metals. 相似文献
15.
We have investigated the effect of ‘Graham’s salt’ as a phosphorous containing flame-retardant applied onto cotton fabric.
The optimum loading of this salt to impart flameretardancy has been determined to be about 36.78-41-31 g salt per 100 g cotton
woven fabric (plain 144 g m−2). Thermogravimetry of pure cotton, treated cotton fabric and the pure salt were accomplished. The curves were then compared
and commented. They reveal that this salt thermosensibilized combustion of the treated substrate as a dehydrating agent. The
results obtained fortified the ‘Chemical Theory’ and ‘Coating Theory’ evidenced the formation of carbonaceous residue upon
the cellulosic substrate during the combustion. 相似文献
16.
D. M. Price 《Journal of Thermal Analysis and Calorimetry》1998,51(1):231-236
By employing a ‘modulated-temperature’ heating programme composed of a series of heat-isotherm stages, it is possible to separate
the change in dimensions of an oriented material during heating into two contributions: a thermally ‘reversing’ component
which is due to linear thermal expansion and a ‘non-reversing’ part arising from relaxation to the disordered state on heating
aboveT
g. Some preliminary results for biaxially drawn poly(ethylene terephthalate) film are presented.
These experiments were carried out at the Thermal Methods & Conservation Science Laboratory, Department of Chemistry, Birkbeck
College, University of London. 相似文献
17.
R. Willink 《Accreditation and quality assurance》2010,15(9):521-527
This article discusses the measurement of the sum of small positive quantities each estimated in separate analyses. It extends
criticism recently given of ‘objective Bayesian’ methodology (Accred Qual Assur 15:181–188, 2010) and identifies two troublesome
effects: the inherent bias in an analysis for a single quantity is compounded when the measurand is the sum of such quantities,
and the precaution of overestimating measurement variability can actually make the resulting interval of measurement uncertainty
less reliable! Unacceptable results are obtained. A cause of this behavior is identified, and a distinction between ‘objective’
and ‘subjective’ Bayesian statistics is discussed. 相似文献
18.
Sgrignani J Magistrato A Dal Peraro M Vila AJ Carloni P Pierattelli R 《Journal of computer-aided molecular design》2012,26(4):425-435
Metallo-β-lactamases (MβLs) are Zn(II)-based bacterial enzymes that hydrolyze β-lactam antibiotics, hampering their beneficial
effects. In the most relevant subclass (B1), X-ray crystallography studies on the enzyme from Bacillus Cereus point to either two zinc ions in two metal sites (the so-called ‘3H’ and ‘DCH’ sites) or a single Zn(II) ion in the 3H site,
where the ion is coordinated by Asp120, Cys221 and His263 residues. However, spectroscopic studies on the B1 enzyme from B. Cereus in the mono-zinc form suggested the presence of the Zn(II) ion also in the DCH site, where it is bound to an aspartate, a
cysteine, a histidine and a water molecule. A structural model of this enzyme in its DCH mononuclear form, so far lacking,
is therefore required for inhibitor design and mechanistic studies. By using force field based and mixed quantum–classical
(QM/MM) molecular dynamics (MD) simulations of the protein in aqueous solution we constructed such structural model. The geometry
and the H-bond network at the catalytic site of this model, in the free form and in complex with two common β-lactam drugs,
is compared with experimental and theoretical findings of CphA and the recently solved crystal structure of new B2 MβL from
Serratia fonticola (Sfh-I). These are MβLs from the B2 subclass, which features an experimentally well established mono-zinc form, in which
the Zn(II) is located in the DCH site. From our simulations the εεδ and δεδ protomers emerge as possible DCH mono-zinc reactive
species, giving a novel contribution to the discussion on the MβL reactivity and to the drug design process. 相似文献
19.
Petra A W Van Den Berg Koert Grever Arie Van Hoek Willem J H Van Berkel Antonie J W G Visser 《Journal of Chemical Sciences》2007,119(2):123-133
Conformational heterogeneity of the FAD cofactor in p-hydroxybenzoate hydroxylase (PHBH) was investigated with time-resolved polarized flavin fluorescence. For binary enzyme/substrate
(analogue) complexes of wild-type PHBH and Tyr222 mutants, crystallographic studies have revealed two distinct flavin conformations;
the ‘in’ conformation with the isoalloxazine ring located in the active site, and the ‘out’ conformation with the isoalloxazine
ring disposed towards the protein surface. Fluorescence-lifetime analysis of these complexes revealed similar lifetime distributions
for the ‘in’ and ‘out’ conformations. The reason for this is twofold. First, the active site of PHBH contains various potential
fluorescence-quenching sites close to the flavin. Fluorescence analysis of uncomplexed PHBH Y222V and Y222A showed that Tyr222
is responsible for picosecond fluorescence quenching free enzyme. In addition, other potential quenching sites, including
a tryptophan and two tyrosines involved in substrate binding, are located nearby. Since the shortest distance between these
quenching sites and the isoalloxazine ring differs only little on average, these aromatic residues are likely to contribute
to fluorescence quenching. Second, the effect of flavin conformation on the fluorescence lifetime distribution is blurred
by binding of the aromatic substrates: saturation with aromatic substrates induces highly efficient fluorescence quenching.
The flavin conformation is therefore only reflected in the small relative contributions of the longer lifetimes. 相似文献
20.
Thermal analysis techniques were performed to reveal ‘crystalline solvate’ behavior between organic compounds and polar solvents.
Diimide-dicarboxylic acid (DIDA) was formed by reacting 3,3'-diaminodiphenylsulfone (3,3'-DPS) or 4,4'-diaminodiphenylsulfone
(4,4'-DPS) with trimellitic anhydride (TMA) in some polar solvents (PSv). The products could crystallize upon cooling in a
polar solvent media to form a solvate containing a finite quantity of solvents, leading to what can be termed as ‘crystalline
solvates’ (CS). This study has demonstrated that sampling techniques in TG and DSC must be kept to be as similar as possible,
which is a critical point in practices of thermal analysis techniques. DSC analysis revealed that there are two endothermic
peaks in the CS, with the lower one being the de-solvate temperature of CS (T
d) at which the solvated solvent molecules were removed, and the higher peak being the melting point of the de-solvated DIDA
(T
m). T
d was found to vary with the types of polar solvents and structures of DIDA. The TG result indicated that most of the sulfone-based
DIDA-CS contained 2 moles of solvent per mole of solvate. X-ray analysis revealed that different crystalline structures were
found for DIDA-CS solvated with different solvent molecules, but all de-solvated DIDA possessed the same crystal unit.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献