共查询到20条相似文献,搜索用时 31 毫秒
1.
G. V. Kotelnikov S. P. Moiseyeva E. V. Mezhburd V. P. Krayev 《Journal of Thermal Analysis and Calorimetry》2002,68(3):803-818
A new isothermal titration calorimeter with 78.5 μL volume capillary chambers has been developed. It is based on the theory
of mixing reagents in a capillary chamber of a titration calorimeter and separation of the sensitive volume of chambers in
a differential calorimeter. The evaluation of the efficiency of diffusion mixing is described by means of an oscillating dispensing
needle. The calorimeter was tested by the reactions: Ba2+– 18-Crown-6 and Rnase-2’CMP. The main advantages of the new titration calorimeter are the use of very small amounts of reagents,
the high accuracy of separating the sensitive volume of calorimetric chambers and the minimization of power input while mixing
reagents in a horizontally located capillary chamber.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
2.
Debasis Jana Barun Bandyopadhyay Debashis Mukherjee 《Theoretical chemistry accounts》1999,102(1-6):317-327
We present in this paper a multi-reference coupled cluster (MRCC) formulation for energy differences which treats orbital
relaxation and correlation effects on the same footing, by invoking a novel cluster ansatz of the valence portion of the wave
operator Ωv. Unlike in the traditional normal-ordered exponential representation of Ωv, our new relaxation-inducing ansatz, represented symbolically as E
r(S), allows contractions between the spectator lines and also certain other special contractions. By an extensive theoretical
analysis, taking as an example the case of one-hole model space (the IP problem), we demonstrate that our ansatz incorporates
in a manifestly spin-free form the orbital relaxation to all orders. The traditional Thouless-type of exponential transformation
via one-body excitations can induce the same effect, as is done in the valence-specific or the quasi-valence-specific MRCC
formalisms, but they have to be done in the spin-orbital basis – making the spin adaptation of the problem a complicated exercise.
In contrast, we use a spin-free representation of the cluster operators right from start, but expand the rank of the cluster
operators by involving spectator orbitals to distinguish the various spin possibilities. The combinatorial factors entering
the contracted power series in E
r(S) are chosen in such a way that they correspond to what we would have obtained if we had used a Thouless-like transformation
to induce the orbital relaxation. Our working equations generally have only finite powers of the cluster operators S, resulting in a very compact formulation of the relaxation problem. Pilot numerical applications for the IP computations
of HF and H2O in the core, the inner valence and the outer valence regions show very good performance of the method vis-a-vis those obtained
using the traditional normal ordered ansatz for Ωv. The improvement in the core IP value is particularly impressive, although even for the valence regions there is an overall
improvement of the IP values.
Received: 3 August 1998 / Accepted: 30 September 1998 / Published online: 15 February 1999 相似文献
3.
A. A. Korolev V. E. Shiryaeva T. P. Popova A. A. Kurganov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(9):1617-1622
The influence of the conditions of the synthesis of polymer monoliths based on ethylene glycol dimethacrylate on the properties
of monolithic capillary columns for gas chromatography was investigated. It was established that the time of polymerization,
the temperature of synthesis, and the composition of the polymerization mixture have a strong effect on the dynamic and chromatographic
properties of the columns. It was concluded that monolithic capillary columns synthesized under optimum conditions are characterized
by a height equivalent to a theoretical plate of 30–40 μm, which is considerably less than that for traditional hollow capillary
columns of the same diameter. 相似文献
4.
Nuclear magnetic resonance (NMR) spectroscopy is one of the most important and powerful instrumental analytical techniques
for structural elucidation of unknown small and large (complex) isolated and synthesized compounds in organic and inorganic
chemistry. X-ray crystallography, neutron scattering (neutron diffraction), and NMR spectroscopy are the only suitable methods
for three-dimensional structure determination at atomic resolution. Moreover, these methods are complementary. However, by
means of NMR spectroscopy, reaction dynamics and interaction processes can also be investigated. Unfortunately, this technique
is very insensitive in comparison with other spectrometric (e.g., mass spectrometry) and spectroscopic (e.g., infrared spectroscopy)
methods. Mainly through the development of stronger magnets and more sensitive solenoidal microcoil flow probes, this drawback
has been successfully counteracted. Capillary NMR spectroscopy increases the mass-based sensitivity of the NMR spectroscopic
analysis up to 100-fold compared with conventional 5-mm NMR probes, and thus can be coupled online and off-line with other
microseparation and detection techniques. It offers not only higher sensitivity, but in many cases provides better quality
spectra than traditional methods. Owing to the immense number of compounds (e.g., of natural product extracts and compound
libraries) to be examined, single microcoil flow probe NMR spectroscopy will soon be far from being sufficiently effective
as a screening method. For this reason, an inevitable trend towards coupled microseparation–multiple microcoil flow probe
NMR techniques, which allow simultaneous online and off-line detection of several compounds, will occur. In this review we
describe the current status and possible future developments of single and multiple microcoil capillary flow probe NMR spectroscopy
and its application as a high-throughput tool for the analysis of a large number of mass-limited samples. The advantages and
drawbacks of different coupled microseparation–capillary NMR spectroscopy techniques, such as capillary high-performance liquid
chromatography–NMR spectroscopy, capillary electrophoresis–NMR spectroscopy, and capillary gas chromatography–NMR spectroscopy,
are discussed and demonstrated by specific applications. Another subject of discussion is the progress in parallel NMR detection
techniques. Furthermore, the applicability and mixing capability of tiny reactor systems, termed “microreactors” or “micromixers,”
implemented in NMR probes is demonstrated by carbamate- and imine-forming reactions. 相似文献
5.
A new interface for combining capillary electrophoresis with inductively coupled plasma-mass spectrometry 总被引:1,自引:0,他引:1
This paper describes the development and design of a new, efficient, simple and robust interface for coupling capillary electrophoresis
(CE) with inductively coupled plasma-mass spectrometry. The interface is based on a modified microconcentric nebulizer which permits a low flow rate of about 6 μL/min in the free aspiration mode. This interface construction
provides an electrical connection for stable electrophoretic separations and adapts the flow rate of the electro-osmotic flow
inside the CE capillary to the flow rate of the nebulizer for efficient transport of the analytes into the plasma. By optimization
of the fluid mechanical properties the interface prevents the nebulizer from causing any laminar flow in the CE capillary
and thus the high resolution power of CE can be preserved. Furthermore, this new device permits independent optimization of
the nebulization from the CE whereby exact positioning of the CE capillary is not necessary, thus enabling fast exchange.
A low dead volume spraychamber has been constructed which circumvents any band broadening of the sharp CE signals. Peak widths
down to 3.5 s comparable to CE with UV detection are possible.
Received: 5 February 1999 / Revised: 21 April 1999 / Accepted: 23 April 1999 相似文献
6.
This paper describes the development and design of a new, efficient, simple and robust interface for coupling capillary electrophoresis
(CE) with inductively coupled plasma-mass spectrometry. The interface is based on a modified microconcentric nebulizer which permits a low flow rate of about 6 μL/min in the free aspiration mode. This interface construction
provides an electrical connection for stable electrophoretic separations and adapts the flow rate of the electro-osmotic flow
inside the CE capillary to the flow rate of the nebulizer for efficient transport of the analytes into the plasma. By optimization
of the fluid mechanical properties the interface prevents the nebulizer from causing any laminar flow in the CE capillary
and thus the high resolution power of CE can be preserved. Furthermore, this new device permits independent optimization of
the nebulization from the CE whereby exact positioning of the CE capillary is not necessary, thus enabling fast exchange.
A low dead volume spraychamber has been constructed which circumvents any band broadening of the sharp CE signals. Peak widths
down to 3.5 s comparable to CE with UV detection are possible.
Received: 5 February 1999 / Revised: 21 April 1999 / Accepted: 23 April 1999 相似文献
7.
Carrillo CA Saloni D Lucia LA Hubbe MA Rojas OJ 《Journal of colloid and interface science》2012,381(1):171-179
A new approach based on microemulsions formulated with at least 85% water and minority components consisting of oil (limonene) and surfactant (anionic and nonionic) is demonstrated for the first time to be effective for flooding wood's complex capillary structure. The formulation of the microemulsion was based on phase behavior scans of Surfactant-Oil-Water systems (SOWs) and the construction of pseudo-ternary diagrams to localize thermodynamically stable one-phase emulsion systems with different composition, salinity and water-to-oil ratios. Wicking and fluid penetration isotherms followed different kinetic regimes and indicated enhanced performance relative to that of the base fluids (water, oil or surfactant solutions). The key properties of microemulsions to effectively penetrate the solid structure are discussed; microemulsion formulation and resultant viscosity are found to have a determining effect in the extent of fluid uptake. The solubilization of cell wall components is observed after microemulsion impregnation. Thus, the microemulsion can be tuned not only to effectively penetrate the void spaces but also to solubilize hydrophobic and hydrophilic components. The concept proposed in this research is expected to open opportunities in fluid sorption in fiber systems for biomass pretreatment, and delivery of hydrophilic or lipophilic moieties in porous, lignocellulosics. 相似文献
8.
Marco Häser 《Theoretical chemistry accounts》1993,87(1-2):147-173
Summary A novel formulation of MP2 theory is presented which starts from the Laplace transform MP2 ansatz, and subsequently moves from a molecular orbital (MO) representation to an atomic orbital (AO) representation. Consequently, the new formulation is denoted AO-MP2. As in traditional MP2 approaches electron repulsion integrals still need to be transformed. Strict bounds on the individual MP2 energy contribution of each intermediate four-index quantity allow to screen off numerically insignificant integrals with a single threshold parameter. Implicit in our formulation is a bound to two-particle density matrix elements. For small molecules the computational cost for AO-MP2 calculations is about a factor of 100 higher than for traditional MO-based approaches, but due to screening the computational effort in larger systems will only grow with the fourth power of the size of the system (or less) as is demonstrated both in theory and in application. MP2 calculations on (non-metallic) crystalline systems seem to be a feasible extension of the Laplace transform approach. In large molecules the AO-MP2 ansatz allows massively parallel MP2 calculations without input/output of four-index quantities provided that each processor has in-core memory for a limited number of two-index quantities. Energy gradient formulas for the AO-MP2 approach are derived.Dedicated to Prof. W. Kutzelnigg whose books on theoretical chemistry aroused my interest in this field 相似文献
9.
The second-order correlation energy of M?ller–Plesset perturbation theory is computed for the neon atom using a wave function
that depends explicitly on the interelectronic coordinates (MP2-R12). The resolution-of-identity (RI) approximation, which
is invoked in the standard formulation of MP2-R12 theory, is largely avoided by rigorously computing the necessary three-electron
integrals. The basis-set limit for the second-order correlation energy is reached to within 0.1 mE
h. A comparison with the conventional RI-based MP2-R12 method shows that only three-electron integrals over s and p orbitals need to be computed exactly, indicating that the RI approximation can be safely used for integrals involving orbitals
of higher angular momentum.
Received: 9 May 2001 / Accepted: 31 October 2001 / Published online: 9 January 2002 相似文献
10.
11.
The work analyzes the existing ambiguity in the ways of application of theoretical relationships derived for infinite numeric
series to real experiments of finite duration. A new calculation technique based on constructing a two-dimensional discrete
time grid is used as a research tool. The described technique allows simplifying drastically without loss of stringency the
derivation of the key relationships of the theory of spectral analysis of random time series of finite duration and formulating
the main correlation identity lying in the basis of the Wiener—Khintchine theorem. It is shown that only a biased estimate
of the correlation function, as opposed to an unbiased one, satisfies the main correlation identity and therefore it is the
only basis for the possibility of correct application of the Wiener—Khintchine theorem to the real data of finite duration.
It is also shown that the appearing undesirable increase in the number of spectral lines in the case of using biased correlation
estimates is manifested only inside the subsystem of odd spectrum harmonics and the transition to the even harmonic subsystem
eliminates this effect completely. In the case of the general theory of spectra, it is of importance that all the even harmonics
coincide with the result of the spectrum direct calculation using the Schuster method, which proves the theoretical equivalence
of the direct and indirect methods of the energy spectrum calculation. 相似文献
12.
Determination of baicalin, chlorogenic acid and caffeic acid in traditional chinese medicinal preparations by capillary zone electrophoresis 总被引:3,自引:0,他引:3
Summary A capillary zone electrophoresis (CZE) method was developed for the simultaneous assay of three bioactive components—baicalin,
chlorogenic acid and caffeic acid—in seven traditional Chinese medicinal preparations. The analytes were separated successfully
within 3.5 min using 10 mM borate buffer (pH8.6). Regression equations revealed linear relationships (correlation coefficients
0.9942–0.9996) between the peak area and concentration of the three analytes. The relative standard deviations of the migration
times and the peak areas of the three constituents were 1.12–2.68% and 1.62–5.73%, respectively. Recovery of the three constituents
ranged from 89 to 107%. The extraction efficiencies of different extraction solutions are also discussed. The contents of
the three components in seven different Chinese medicinal preparations containing Honeysuckle flower and/orScutellariae radix were determined by the CZE method with satisfactory results. 相似文献
13.
S Chandrasekhar 《Research on Chemical Intermediates》1997,23(1):55-62
By the temporal Uncertainty principle, chemical systems may be described in terms of ‘kinetic’ or ‘thermodynamic’ complementary
formulations, based on rate or equilibrium constants, and free energy changes respectively. Thereby, the paradox of the dichotomous
formulations of the Curtin-Hammett principle is resolved. A new formulation of the principle is suggested, and a fundamental
conflict with transition state theory is indicated. 相似文献
14.
《Current Opinion in Colloid & Interface Science》2014,19(6):575-584
The addition of small amounts of a secondary fluid to a suspension can, through the attractive capillary force, lead to particle bridging and network formation. The capillary bridging phenomenon can be used to stabilize particle suspensions and precisely tune their rheological properties. This effect can even occur when the secondary fluid wets the particles less well than the bulk fluid. These materials, so-called capillary suspensions, have been the subject of recent research studying the mechanism for network formation, the properties of these suspensions, and how the material properties can be modified. Recent work in colloidal clusters is summarized and the relationship to capillary suspensions is discussed. Capillary suspensions can also be used as a pathway for new material design and some of these applications are highlighted. Results obtained to date are summarized and central questions that remain to be answered are proposed in this review. 相似文献
15.
Organic/inorganic hybrid materials prepared by the sol–gel approach have rapidly become a fascinating new field of research
in materials science. The explosion of activity in this area in the past decade has made tremendous progress in both the fundamental
understanding of the sol–gel process and the development and applications of new organic/inorganic hybrid materials. Polymer-inorganic
nanocomposite present an interesting approach to improve the separation properties of polymer material because they possess
properties of both organic and inorganic such as good permeability, selectivity, mechanical strength, and thermal and chemical
stability. Composite material derived by combining the sol–gel approach and organic polymers synthesis of hybrid material
were the focus area of review It has also been demonstrated in this review that a more complete understanding of their structure–property
behavior can be gained by employing many of the standard tools that are utilized for developing similar structure–property
relationships of organic polymers. This review article is introductory in nature and gives introduction to composite materials/nanocomposite,
their applications and the methods commonly employed for their synthesis and characterization. A brief literature survey on
the polysaccharide templated and polysaccharide/protein dual templated synthesis of silica composite materials is also presented
in this review article. 相似文献
16.
电负性是分子中一个原子把电子拉向它自身的能力,是化学理论的基本概念之一。继Pauling建立第一个电负性标度后,提出了众多的电负性标度。只是在密度泛函理论的基础上,电负性概念和电负性均衡原理,才被精密地论证。近二十多年来,电负性理论的重要发展是:应用电负性均衡模型或方法,可以快速地计算分子体系的电荷分布,从而确定分子的其他性质,甚至包括分子的结构和反应性指标。通常的电负性均衡方法只把分子划分到原子区域,虽然简单直观,但其精度和应用范围受到限制。原子与键电负性均衡方法,把分子划分到包括原子区域、化学键区域和孤对电子区域,能够较快速精密地计算分子的电荷分布和其他性质,并被应用到构建新一代可极化或浮动电荷力场的探索中,有广阔的应用前景。 相似文献
17.
Paul W. Ayers 《Theoretical chemistry accounts》2007,118(2):371-381
The electronegativity equalization principle states that, in its ground state, the electronegativity of every component in
a system is the same. A paradox then arises: molecular fragments that are very far apart must still have the same electronegativity,
which seems to contradict the common assumption that spatially separated molecular species can be described independently.
Density-functional theory provides the tools needed to analyze this paradox at a fundamental level, and a resolution is found
from the properties of the exact Hohenberg–Kohn functional. Specifically, there is no paradox because the electronegativity
is not uniquely defined for separated systems. Instead, there is an “apparent electronegativity” that preserves locality.
This may have implications for the treatment of charge-transfer excited states. A model for the energy as a function of the
number of electrons is also presented. This model gives some insight into the utility of the grand canonical ensemble formulation
(at nonzero temperature) and, unlike most previous models, this model recovers the appropriate behavior in the limits of infinitely
separated and/or weakly interacting subsystems. 相似文献
18.
Summary Permethyl monoamino β-cyclodextrin, a new chiral selector, has been synthesized and tested as a chiral discriminating agent
in capillary electrophoresis. This agent is suitable for separation of both negatively and positively charged as well as neutral
enantiomers. At various concentrations of permethyl monoamino β-cyclodextrin, stable electroosmotic flow was measured in a
cathodic direction. Due to the high solubilizing power and low conductivity of permethyl monoamino β-cyclodextrin efficiencies
of up to 600 000 theoretical plates efficiency could be obtained. This high efficiency resulted in baseline separations of
enantiomers resolved by a separation factor of only 1.009.
This paper is dedicated to the memory of Dr. Tibor Tóth.
Presented at Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 1–3, 1999. 相似文献
19.
This study investigates the use of thread as a flexible and low-cost substrate for the rapid grouping of blood. The use of
a capillary substrate such as thread for blood grouping utilises the sensitivity of the flow resistance of large particles
in narrow capillary channels to separate agglutinated red blood cells (RBCs) from plasma. Large and discrete particles formed
in a continuous liquid phase do not provide capillary wicking driving force and fall behind the capillary wicking front, leading
to their separation from the wicking liquid. The capillary substrate therefore provides a very promising but different mechanism
for the separation of the agglutinated RBCs and the blood serum phase compared to most existing blood grouping methods. The
principle of chromatographic separation is also exploited in this study via the use of suitable dyes to enhance the visual
detection of the agglutinated RBCs and the serum phase; surprising and encouraging outcomes are obtained. Using a thread-based
device, the ABO and Rh groups can be successfully determined with only 2 μL of whole blood from a pricked finger tip within
1 min and without pre-treatment of the blood sample. It is hoped that a new, inexpensive, rapid and simple method may provide
an easy-to-use blood grouping platform well suited to those in developing or remote regions of the world. 相似文献
20.
Capillary pressure curves are widely used in materials, soil, and environmental sciences, and especially in the petroleum industry. The traditional (Hassler-Brunner) interpretation of centrifugal capillary pressure data is based on several assumptions. These assumptions are known to lead to significant errors in the measurement of capillary pressure curves. In this work, we propose a new "single-shot" method to measure the capillary pressure curve of a long sedimentary rock core using a single-speed centrifuge experiment and magnetic-resonance imaging to directly determine the water saturation distribution along the length of the sample. Since only a single moderate centrifuge speed is employed, the effect of gravity can be ignored and the outlet boundary condition of the core plug was maintained. The capillary pressure curve obtained by the single-shot method is remarkably consistent with results determined with conventional mercury-intrusion methods. The proposed method is much faster and more precise than traditional centrifuge methods. 相似文献