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1.
Molecular dynamics with design is used to calculate the electric potentials of isolated water clusters containing Na+ or Cl−. The number of water molecules in the clusters is from 4 to 14. It is noted that electrostatic interaction plays a dominant
role in the clusters; the dependence of the dielectric constant of the cluster on the size of the latter is determined.
Institute of Thermal Physics, Ural Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 1, pp. 66–73, January–February, 1998. 相似文献
2.
O. I. Arillo-Flores M. F. Ruiz-López M. I. Bernal-Uruchurtu 《Theoretical chemistry accounts》2007,118(2):425-435
We discuss the failure of commonly used AM1 and PM3 semiempirical methods to correctly describe acid dissociation. We focus
our analysis on HCl because of its physicochemical importance and its relevance in atmospheric chemistry. The structure of
non-dissociated and dissociated HCl – (H2O)
n
clusters is accounted for. The very bad results obtained with PM3 (and also with AM1) are related to large errors in gas-phase
proton affinity of water and gas-phase acidity of HCl. Indeed, estimation of pKa values shows that neither AM1 nor PM3 are able to predict HCl dissociation in liquid water since HCl is found to be a weaker
acid than H3O+. We have proposed in previous works a modified PM3 approach (PM3-MAIS) adapted to intermolecular calculations. It is derived
from PM3 by reparameterization of the core–core functions using ab initio data. Since parameters for H–Cl and O–Cl core–core
interactions were not yet available, we have carried out the corresponding optimization. Application of the PM3-MAIS method
to HCl dissociation in HCl–(H2O)
n
clusters leads to a huge improvement over PM3 results. Though the method predicts a slightly overestimated HCl acidity in
water environment, the overall agreement with ab initio calculations is very satisfying and justifies efforts to develop new
semiempirical methods. 相似文献
3.
V. P. Koropchanu F. G. Paladii S. I. Boldyrev V. Ya. Gamurar' 《Journal of Structural Chemistry》1996,37(5):707-712
The tunnel states of square-planar bielectron transfer dn-dn-dn+1-dn+1 (n=0–4) clusters are considered. The nature of the ground spin state is revealed in the limiting case of a strong double
exchange. It is shown that the magnetic properties of these systems radically differ from those of clusters with one migrating
electron (hole) and tetrameric tetrahedral bielectron transfer clusters.
Moldova State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 5, pp. 826–833, September–October, 1996.
Translated by I. Izvekova 相似文献
4.
Lang SM Claes P Neukermans S Janssens E 《Journal of the American Society for Mass Spectrometry》2011,22(9):1508-1514
Structural information on free transition metal doped aluminum clusters, Al
n
TM
+ (TM = Ti, V, Cr), was obtained by studying their ability for argon physisorption. Systematic size (n = 5 – 35) and temperature (T = 145 – 300 K) dependent investigations reveal that bare Al
n
+ clusters are inert toward argon, while Al
n
TM
+ clusters attach one argon atom up to a critical cluster size. This size is interpreted as the geometrical transition from
surface-located dopant atoms to endohedrally doped aluminum clusters with the transition metal atom residing in an aluminum
cage. The critical size, n
crit
, is found to be surprisingly large, namely n
crit = 16 and n
crit = 19 – 21 for TM = V, Cr, and TM = Ti, respectively. Experimental cluster–argon bond dissociation energies have been derived as function of cluster size from
equilibrium mass spectra and are in the 0.1–0.3 eV range. 相似文献
5.
K. Fujii Y. Matsumoto Y. Kaieda D. Kobayashi Y. Umebayashi S. Ishiguro 《Journal of Thermal Analysis and Calorimetry》2006,85(3):567-573
Cobalt(II)
chloro complexation has been studied by titration calorimetry and spectrophotometry
in solvent mixtures of N-methylformamide
(NMF) and N,N-dimethylformamide
(DMF). It revealed that a series of mononuclear CoClnn
(2–n)+
(n=1–4) complexes are formed in the
mixtures of NMF mole fraction x
NMF=0.05
and 0.25, and the CoCl+, CoCl3
–
and CoCl4
2– complexes
in the mixture of x
NMF=0.5,
and their formation constants, enthalpies and entropies were obtained. As
compared with DMF, the complexation is markedly suppressed in the mixtures,
as well as in NMF. The decreasing formation constant of CoCl+
with the NMF content is mainly ascribed to the decreasing formation entropy.
DMF is aprotic and thus less-structured, whereas NMF is protic to form hydrogen-
bonded clusters. In DMF-NMF mixtures, solvent clusters in neat NMF are ruptured
to yield new clusters involving DMF, the structure of which depends on the
solvent composition. The entropy of formation of CoCl+
will be discussed in relation to the liquid structure of DMF, NMF and their
mixtures. 相似文献
6.
A potential function is suggested to describe the interaction of the calcium ion with the water molecule using the tetrahedral
model of the water molecule. Monte Carlo simulations of small clusters Ca(H2O)n (n≤20) and analyses of the resulting F-structures showed that the coordination number of Ca is 8. The structure of water
adsorbed in the α-cavity of zeolite CaA depends predominantly on interactions with Ca2+ ions. The water molecule forms one hydrogen bond with an oxygen atom of the framework; the molecules are not hydrogen-bonded
with each other. In this respect the structure of water in the Ca form of zeolite A resembles that in the Na form but differs
from that in the K form.
Institute of Physical Chemistry, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 1, pp. 88–97, January–February, 1996
Translated by L. Smolina 相似文献
7.
This paper studies the formation of a stable anion pair as a result of cluster interactions with water molecules (the number
of molecules n=4, 6, 8, and 14). The hydration shells of the clusters obtained in a preliminary calculation are destructed
to form closed chains of properly oriented water molecules in the space between the anions. The type of the resulting structure
depends on the number of shared water molecules. The character of stabilization of the anion pair, determined by calculating
different energy terms, also changes as n increases. The cyclic structures obtained in the region of the anion pair differ
considerably from the structure of isolated Cl− (H2O)n clusters and that of the aqueous solution of NaCl. The capture of water molecules by the anion pair is manifested in the
nucleation of industrial steam.
Institute of Thermal Physics, Ural Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 2, pp. 289–298, March–April, 1996.
Translated by L. Smolina 相似文献
8.
Fragmentation of sputtered vanadium and niobium cluster ions,kinetic release and dissociation energy
N. Kh. Dzhemilev V. M. Rotshtein O. F. Tukfatullin Sh. T. Khozhiev 《Journal of Analytical Chemistry》2011,66(14):1404-1410
The generation and unimolecular fragmentation of V
n
+ and Nb
n
+ clusters formed in sputtering vanadium and niobium surfaces by Xe+ ions has been studied. The method of measuring the kinetic energy of fragment ions (kinetic energy release distribution)
has been used to determine the dissociation energy. Kinetic energy spectra have been measured in the field-free zone (corresponding
to a time window of 10−5–10−4 sec after emission) of an ion microanalyzer with double focusing in reverse geometry. The results of spectra measurement
were treated using the Rice-Ramsperge-Kassel theory of unimolecular reactions and the “evaporative ensemble”, which allowed
us to calculate the dissociation energies of homonuclear V
n
1 (n= 5–11) and Nb
n
1 (n = 3–8) clusters. 相似文献
9.
Petrek J Vítecek J Vlasínová H Kizek R Kramer KJ Adam V Klejdus B Havel L 《Analytical and bioanalytical chemistry》2005,383(4):576-586
Image analysis (IA) was used to determine the areas and circumferences of clusters of early somatic embryos (ESEs) of the
Norway spruce (Picea abies /L./Karst.). Results obtained from IA were compared with the fresh weights of the ESE clusters and their esterase activities.
The areas of the ESE clusters correlated well with both the increases in fresh weight (R
2=0.99) of the ESEs and their esterase activities (R
2=0.99). In addition, we studied the viability of the ESEs, which was determined by (a) double staining with fluorescein diacetate
and propidium iodide (the resulting fluorescence was quantified by IA) and (b) determining esterase activity using a spectrofluorimetric
detector. The results obtained with IA and esterase assay were comparable (the deviation between the tangents of the bisectors
was 6.4%). IA was also used to study the effect of Pb–EDTA chelate (50, 250 and 500 μM) on the viability of the ESEs and on
the growth of clusters. The presence of Pb–EDTA markedly slowed the growth of ESEs clusters (by more than 65% with 250 μM
of Pb–EDTA after 288 h of cultivation) and decreased the viability of ESEs (by more than 30% with 500 μM of Pb–EDTA after
288 h of cultivation). The lead concentration in the ESEs was determined by differential pulse anodic stripping voltammetry
and increased with the external lead concentration and the time of treatment from 100 to 600 pg Pb/100 mg of fresh weight
of ESEs. Glutathione is a diagnostic marker of the influence of Pb–EDTA on ESEs and its content was determined by high–performance
liquid chromatography coupled with mass spectrometry. The glutathione content changed linearly with treatment time and the
applied external lead concentration. The highest glutathione content was obtained at 250 μM of Pb–EDTA after 192 h of cultivation. 相似文献
10.
Geometry optimizations were performed on monoanionic and dianionic clusters of sulfate anions with carbon dioxide, SO4−1/−2(CO2)
n
, for n = 1–4, using the B3PW91 density functional method with the 6-311 + G(3df) basis set. Limited calculations were carried out with the CCSD(T) and MP2 methods. Binding energies, as well as adiabatic
and vertical electron detachment energies, were calculated. No covalent bonding is seen for monoanionic clusters, with O3SO–CO2 bond distances between 2.8 and 3.0 ?. Dianionic clusters show covalent bonding of type [O3S–O–CO2]−2, [O3S–O–C(O)O–CO2]−2, and [O2C–O–S(O2)–O–CO2]−2, where one or two oxygens of SO4−2 are shared with CO2. Starting with n = 2, the dianionic clusters become adiabatically more stable than the corresponding monoanionic ones. Comparison with SO4−1/−2(SO2)
n
and CO3−1/−2(SO2)
n
clusters, the binding energies are smaller for the present SO4−1/−2(CO2)
n
systems, while stabilization of the dianion occurs at n = 2 for both SO4−2(CO2)
n
and SO4−2(SO2)
n
, but only at n = 3 for CO3−2(SO2)
n
. 相似文献
11.
We present the first-principle calculations on the electronic excitations and second-order properties in solution phase of
two typical inorganic trinuclear anionic clusters, [MoCu2S4(SPh)2]2− and [Mo2CuS4]1−(edt)2(PPh3) (edt=1,2-ethanedithiolato) in the framework of density functional theory (DFT). The computed excitation energies are in good agreement
with the outcome of the measurements. The predicted values of the molecular quadratic hyperpolarizabilities are of the comparable
order of those of the typical organometallic chromophores. We demonstrate the significant contributions to the second-order
responses from the charge transfers between the metal centers (MMCT) which are ascribed to the direct metal–metal bonding interactions in these two charged clusters. This meaningful ligand-independent mechanism for the second-order response largely relates to metal–metal bonding strength, and the understanding will benefit
to the future design of the new-generation molecular based nonlinear optical materials and optoelectronic devices by means
of the conscious tuning of metal–metal interactions and metal-core structures of inorganic polynuclear clusters. 相似文献
12.
V. P. Koropchanu F. G. Paladii S. I. Boldyrev V. Ya. Gamurar' 《Journal of Structural Chemistry》1996,37(3):398-408
Tunnel-exchange states of tetrahedral tetrameric clusters dn-dn-dn+1-dn+1 with double transfer are considered to calculate the energy levels and wave functions. A method based on the second quantization
technique and group-theoretical approach is developed. The nature of the ground spin state of the above systems is determined.
It is shown that the structures have magnetic properties that radically differ from the properties of clusters with one migrating
electron (hole).
Moldova State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 3, pp. 458–470, May–June, 1996. 相似文献
13.
Thesensitivityofsilverhalideemulsionscouldbeimprovedgreatlyafterbeingchemicallysensitized.Thematterwhichplaysanimportantroleisthesocalledsensitizationcentersformedduringthechemicalsensitizationprocess.Thestudyontheformatin,natureandfunctionofthesecent… 相似文献
14.
Tunnel states of dimeric mixed-valence clusters with dn-dn+2 type two-electron transfer are considered. General expressions for the matrix elements of the double exchange operator are
obtained taking into account the contributions of the excited states. The energy spectrum of the clusters is calculated and
the magnetic properties are studied. Allowance for the dn+1-dn+1 excited states considerably affects the energy spectrum and the magnetic properties of the systems.
Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 6, pp. 1038–1045, November–December, 1997. 相似文献
15.
Distributions of argon clusters (Ar
n
+
wheren=1–27) obtained in a molecular beam/time-of-flight system were analyzed in order to assess the influence of fragmentation.
The results from rudimentary pseudopotential molecular calculations were calculated to predict the most stable structures
and stabilities for the smaller argon ion sized clusters (Ar
n
+
wheren=3−9). 相似文献
16.
Density functional calculations are performed to study the structures and electronic properties of Al
n
Co
m
clusters with n = 1–7 and m = 1–2. Frequency analysis is also performed after structural optimization to make sure that the calculated ground states
are real minima. The corresponding total and binding energies, adiabatic electron affinities and ionization potentials are
presented and discussed to aid the identification of our calculations. The BSSE correction is also considered in our calculation.
Among Al
n
Co
m
, Al
n
Co
m
−, and Al
n
Co
m
= clusters (n = 1–7 and m = 1–2), Al4Co−, Al6Co−, Al2Co2, and Al6Co2 are predicted to be more stable. Our results are consistent with the available experimental data. 相似文献
17.
Possible geometrical structures and relative stabilities of (F2AlN3)
n
(n = 1–4) clusters were studied using density functional theory at the B3LYP/6-311+G* level. The optimized clusters (F2AlN3)
n
(n = 2–4) possess cyclic structure containing Al–Nα–Al linkages, and azido in azides has linear structure. The IR spectra of the optimized (F2AlN3)
n
(n = 1–4) clusters have three vibrational sections, the whole strongest vibrational peaks lie in 2218–2246 cm−1, and the vibrational modes are N3 asymmetric stretching vibrations. Trends in thermodynamic properties with temperature and oligomerization degree n are discussed, respectively. A study of their thermodynamic properties suggests that monomer 1A forms the most stable clusters
(2A, 3A, and 4B) can occur spontaneously in the gas phase at temperatures up to 800 K. 相似文献
18.
Y. S. Murillo L. Giraldo J. C. Moreno-Piraján 《Journal of Thermal Analysis and Calorimetry》2011,104(2):555-559
A way to calculate the enthalpic contributions of each component of the mixture of activated carbon and water to the immersion
enthalpy using the concepts of the solution enthalpies is presented. By determining the immersion enthalpies of a microporous
activated carbon in water, with values that are between –18.97 and −27.21 Jg−1, from these and the mass ratio of activated carbon and water, differential enthalpies for the activated carbon,
ΔHDIFacH_{{\rm DIF}_{\rm ac}} and water, ΔHDIFwH_{{\rm DIF}_{\rm w}} are calculated, and values between –15.95 and –26.81 Jg−1 and between –19.14 and –42.45 Jg−1, respectively are obtained. For low ratios of the mixture, the components’ contributions to the immersion enthalpy of activated
carbon and water differ by 3.20 Jg−1. 相似文献
19.
Dalia Nayak Devdeep Mukherjee Aparna Banerjee Jhumpa Mukherjee 《Journal of Radioanalytical and Nuclear Chemistry》2010,283(2):477-480
The present work discusses the complexation behavior of bioligand cysteine with cobalt and the immobilization of this complex
(Co–Cys) onto a biocompatible ligand and common drug base, polyvinylpyrrolidone (PVP). The complexation behavior has been
studied by radiometric method and UV–Vis spectrophotometry. The radiometric method involves dialysis of 60Co–Cys–PVP complex against triple distilled water which subsequently gives the dynamic dissociation constant (k
d) of the complex. The half life of 60Co–Cys–PVP complex calculated from k
d value is 22.6 h against triple distilled water at pH 8.5. The UV–Vis spectra analysis confirms the complexation of Co with
cysteine at this pH and also indicates that the cysteine ligated Co(II) centers easily get oxidised to Co(III) centers (low
spin, d6) in the presence of air at alkaline pH showing no d–d transitions. 相似文献
20.
Kazushige Yokoyama Bradley E. Johnson Jonathan W. Bourne 《Journal of Sol-Gel Science and Technology》2007,43(2):259-268
The [Ru(bpy)3]2+ ion was encapsulated in a silica based sol–gel thin film, and the luminescence decay time constant of the photo-excited 3MLCT (metal-ligand-charge-transfer) was examined when this thin film was immersed in water, methanol, ethanol, 2-propanol,
and glycerol. The luminescence decays of the films in the methanol, 2-propanol, and glycerol were better explained by a KWW
model, while the luminescence decay of film immersed in water and ethanol were both well explained by a single exponential
decay. Intriguingly, the dynamics of the dopants immersed in water, ethanol as well as in sol–gel bulk deviated from a single
exponential fit and began to better explained by the the KWW model as temperature increased. The energy gap, ΔE(sol–gel film) and ΔE(solution), between the lowest 3MLCT state and atom localized 3
dd state for dopants under the presence of all solvents tested in this study were extracted from the temperature dependence
study of the luminescence decay time constant. Generally, the ΔE(sol–gel film) values of ethanol and water were reduced from ΔE(solution), and ΔE(sol–gel film) value in all solvents matched the value of ΔE for sol–gel bulk. The effect on the dynamics in solvent over three weeks was investigated, and the films immersed in water
presented the most remarkable monotonic increase in relaxation rates finally approaching the asymptotic value observed in
the water solution. This phenomenon was considered to correspond to a trapping environment change due to a hydrophilic interaction
through sequential intrusion of water or ethanol solvent into sol–gel pores. 相似文献