Wyniki wyszukiwania - Biblioteka Nauki

1

Determination of micelle aggregation numbers of alkyltrimethylammonium bromide and sodium dodecyl sulfate surfactants using time-resolved fluorescence quenching

100%

Pisárčik M. , Devínsky F. , Pupák M.

Open Chemistry

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2015

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tom 13

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nr 1

EN

The time-resolved fluorescence quenching method was applied to determine the micelle aggregation number of cationic single-chain surfactants dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB) and anionic surfactant sodium dodecyl sulfate (SDS). The concentration dependence of micelle aggregation number was found to be linear for all investigated surfactants in the concentration range 2‒15 × the value of critical micelle concentration of the respective surfactant. The values of micelle aggregation number were found in the range 30‒77. Different trends in the linear concentration dependence of micelle aggregation number were observed for cationic surfactants and for the anionic surfactant SDS. A small slope value was found for cationic surfactants, while the SDS micelle aggregation number concentration dependence showed significantly a larger slope value. The aggregation number increase with the increasing SDS concentration results in the micellar growth. Results from a simple analysis based on computer models of cationic and anionic surfactant molecules with dodecyl chains supports, the formation of intramicellar hydrogen bonding between surfactant molecules in SDS micelle shell.

2

Investigations of hydrogen bonding in the poly(urethane-urea)-based membrane materials by using FTIR spectroscopy

100%

Wolińska-Grabczyk A. , Kaczmarczyk B. , Jankowski A.

Polish Journal of Chemical Technology

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2008

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tom 10

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nr 4

53-56

EN

FTIR analysis was used to study the hydrogen bonding in 4,4'-diaminodiphenylmethane-based segmented poly(urethane-urea)s varying in the length of the poly(tetramethylene oxide) (PTMO)-based soft segments. Experiments were designed to follow the IR absorption of both the NH and carbonyl regions as a function of temperature in order to directly investigate the extent and strength of the hydrogen bonds, and thereby to gain some information about the possible alteration of the initial phase-segregated morphology as a result of the applied thermal treatment.

3

Raman spectroscopic study of the hydration of short-chain poly(oxyethylene)s C 1EnC 1 (n=1−4)

100%

Georgiev M. , Popova T. , Nickolov Z. , Goutev N. , Georgiev G. , Matsuura H.

Open Chemistry

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2004

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tom 2

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nr 4

617-626

EN

The hypothesis that the degree of hydration of poly(oxyethylene) (POE) in aqueous solution depends on the mole ratio of water molecules to ether oxygen atoms in the molecule has been verified by studying the isotropic Raman spectra in the O−H stretching region for four short-chain POEs (C 1EnC 1 withn=1−4). Excellent coincidence of the O−H stretching Raman band for all four POEs studied in the range of mole ratio H2O/Oether from 25 to 0.6 was observed, thus confirming the assumption stated above. A conclusion that all ether oxygen atoms in the POE molecule participate in hydrogen bonding with water molecules has been made.

4

Infrared and Raman Intensities in Proper and Improper Hydrogen-Bonded Systems

100%

Jabłoński M. , Sadlej A.

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2007

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tom Vol. 81, nr 5-6

767-782

EN

The IR intensities and Raman activities of the C–H stretchingmode as well as some other spectroscopic and structural features of NCHźźźNCH and F3CHźźźNCH are calculated in the MP2 approximation with a variety of correlation consistent basis sets. In agreement with earlier studies the traditional hydrogen bond in NCHźźźNCH results in the elongation of the C–H bond distance in the proton donor and the red shift of the corresponding vibration frequency. The opposite changes are found in F3CHźźźNCH. The IR intensity of the C–H stretching band in the NCHźźźNCH dimer markedly increases whereas for the blue-shifting F3CHźźźNCH complex the IR intensity of the corresponding band is significantly reduced. The Raman activity of the C–H stretching band in both investigated complexes increases upon the hydrogen bond formation. These results are analysed in terms of the interaction induced dipolemoments and polarizabilities, and their derivatives with respect to the C–H bond distance. The difference between IR intensities of the C–H stretching band calculated for NCHźźźNCH and F3CHźźźNCH is, however, a particular feature of the F3CHźźźNCH complex and cannot be used to distinguish between traditional and improper hydrogen bonds. Neither the Raman activities offer such a possibility. The present study of interaction induced properties shows that the blue shift of the X–H frequency in systems with improper hydrogen bonds is primarily due to particular features of the electronic structure of the proton donor.

5

Synthesis, Structures, and Antibacterial Activities of 3-Methoxy-N'-(3-bromo-5-chloro-2-hydroxybenzylidene) benzohydrazide Dimethanol Solvates and 3-Hydroxy-N'-(3-bromo-5-chloro-2-hydroxybenzylidene) benzohydrazide Methanol Solvate

100%

Zhu Q. Y. , Wei Y. J. , Wang F. W.

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tom Vol. 83, nr 7

1233-1240

EN

Two Schiff base com pounds, C15H12BrClN2O3×2CH3OH (1) and C14H10BrClN2O3×CH3OH (2), have been synthesized by the condensation reactions of equimolar quantities of 3-bromo-5-chlorosalicylaldehyde with 3-methoxy benzohydrazide and 3-hydroxy - benzohydrazide, respectively, in methanol solutions. Compound (1) consists of a Schiff base molecule and two metha ol molecules of crystallization, while compound (2) con - sists of a Schiff base molecule and one methanol molecule of crystallization. Both com - pounds were characterized by elemental analysis, IR spectra and single-crystal X-ray diffractions. As expected, each Schiff base molecule adopts an E-configuration about the C=N double bond. In both crystal structures, molecules are linked through intermolecular hydrogen bonds and weak Br×××O or Br×××Br interactions, forming layers. Both compounds possess potent antibacterial activities.

6

Principal Components Analysis of Infrared Spectra of Liquid Acetylacetone

100%

Czarnik-Matusewicz B. , Matusiak-Kucharska M. , Hawranek J. P.

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tom Vol. 83, nr 5

999-1011

EN

The spectrum of the absorption index in the Mid-Infrared (MIR) region was determined for intramolecularly hydrogen-bonded liquid acetylacetone from transmission studies. In the MIR region very thin layers with thick nesses of a few micrometers had to be used to obtain reliable data. The keto-enol tautomeric equilibrium in the pure liquid was studied by Principal Components Analysis (PCA) of a set of temperature dependent MIR spectra in the range from 25 to 75 graduate C. Identifications for numerous bands observed in the liquid phase were proposed basing on the results obtained by means of the separation obtained in the loadings plot.

7

Time-Resolved Infrared Spectroscopy of Water. Relation between the OH Stretching Frequency and the OO Distance

100%

Bratos S. , Leicknam J. C. , Pommeret S.

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tom Vol. 83, nr 5

737-745

EN

It is shown how infrared pump-probe spectroscopy can be used to measure subpico second variations of the oxygen-oxygen distribution function in liquid water. A diluted solution HDO/D2O rather than pure H2O is considered to switch off resonant vibrational interactions between water molecules; the local structure remains unchanged in this substitution. The present study is limited to times superior to 100–200 fs. This permits to avoid problems generated by hard sphere type collisions between water mole ules, as well as the interference between ultrafast pump and probe pulses. It is then shown that the Novak-Mikenda type relations between the OH stretching frequency and the OO distance largely sur vive when going from standard to ultrafast infrared spectroscopy. More over, the infrared pump-probe profiles of OH stretching bands closely parallel the oxygen-oxygen distribution functions in this time do main. Infrared pump-probe spectroscopy is thus a use ful substitute of time-resolved X-ray diffraction in this exceptional case.

8

Wiązanie wodorowe : wybrane zagadnienia

100%

Sobczyk L.

Wiadomości Chemiczne

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2001

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tom [Z] 55, 7-8

593-627

EN

In a short introduction the importance of hydrogen bonding is emphasized in life sciences and its role in molecular recognition and creation of living molecular systems. Then an attempt to define this specific molecular interaction is undertaken. Among most important features one should distinguish a particular repulsion potential which enables to approach directly interacting atoms on a distance markedly less than the sum of van der Waals radii. An important feature of hydrogen bonds is also the appearance of a double minimum potential for the proton motion. Among the main physical properties of hydrogen bonds there are analyzed dipole moments, nuclear magnetic resonance, quadrupole magnetic resonance, infra-red spectra and isotope effects. Most important isotope effects are related to infra-red spectra, geometry of bridges, phase transitions in hydrogen bonded ferroelectrics and fractionation factor. The evolution of the main characteristics is discussed depending on the acid-base properties expressed by means of the DpKa value of interacting components. A separate chapter is devoted to a dualistic nature of the interaction i.e. the structure creating and dynamical ones. The structure creating character is shown taking into account the induction of liquid crystalline properties while the dynamical properties are examplified on enzymic and photobiological processes and phase transitions in hydrogen bonded crystals. Current aspects of hydrogen bond interaction are limited to photoinduced proton transfer processes, the time resolved infra-red spectroscopy, low barrier hydrogen bonds (LBHB) and quantum molecular dynamics. In final remarks the importance of hydrogen bonding in searching for new materials of practical importance and crystal design are underlined.

9

Hydrogen-bonded assembly and binding affinity of the multi-point acceptor and isophthalic acid

100%

Xu L. , Zhu L. , Wu S. , Chen X. , Teng Q.

Open Chemistry

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2006

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tom 4

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nr 4

732-742

EN

Supermolecular complexes formed by oligophenyleneethynylene derivatives and isophthalic acid were studied using AM1 method to obtain binding energy. Electronic spectra and IR spectra of the complexes were calculated by INDO/CIS and AM1 methods based on AM1 geometries. Results indicated that the dimer could be formed by the monomers via hydrogen bonding because of the negative binding energy. Binding energy of the complexes was affected by electronegativity and steric effects of the substituents. The first UV absorptions and IR frequencies of N-H bonds of the complexes were both red-shifted compared with those of the monomers. The complexes could bind small molecules via hydrogen bonds, resulting in the change in UV absorptions and an increase in IR frequencies of N-H bonds.

10

Excited-state Solvation of Rhodamines: Dielectric and Specific Contributions

100%

Ferreira J. A. B. , Costa S. M. B.

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2008

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tom Vol. 82, nr 4

893-899

EN

Primary to tertiary amine based compounds of the form 9'-(2-ester-carbonyl)-phenyl- 3',6'-bis-(amino)-xanthylium) are studied as models for this class of compounds as regards the S1S0 shifts in solution. The magnitude of the solvatochromic shift decreases from primary amine to tertiary amine rhodamine chromophore. Primary aminoxanthylium spectral energy at maximum absorption decreases with the solvent electronic polarization whilst it increases with the orientational polarization function, suggesting extensive reorientation in the dipolar moment upon S1S0 excitation. By contrast, upon electronic excitation smaller dipolar moment variations are found in N-alkyl rhodamines, respectively with secondary and tertiary amine groups. Primary and secondary amine rhodamines' NH groups establish strong interactions with electron rich atomic centers of solvent molecules increasing the electronic stabilization energy.

11

Crystal and molecular structure of 2-(N,N-diethylamino)-methyl-4-bromo-6-formylphenol

100%

Woźniak K. , Anulewicz R. , Grech E. , Szady A.

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1998

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tom Vol. 72, nr 2

460-469

EN

Structural and spectroscopic properties of solid 2-(N,N-diethylamino)-methyl-4-bromo-6-formylphenol have been investigated. There are two molecules of the title compound in the independent part of the unit cell with only minor structural differences. This is an example of a Mannich base containing a neutral [O-H...N] intramolecular hydrogen bonding. Single crystal X-ray diffraction shows that the title molecule is dominated by neutral Kekule structures. Being involved in a strong intramolecular [O-H...N] hydrogen bonding, 2-(N,N-diethylamino)-methyl-4-bromo-6-formylphenol forms its crystal lattice by means of different types of weak intermolecular [C-H...O], and C-H...Br hydrogen bonds.

12

Studies on the Deamination of the Ethyl Ester of 5-Amino-3-methylisoxazole-4-carboxylic Acid

88%

Ryng S. , Szostak M.

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tom Vol. 83, nr 5

887-893

EN

The unusual behavior of the ethyl ester of 5-amino-3-methylisoxazole-4-carboxylic acid (1) during deamination is described. Possible explanations for the anomalies of the diazotization reaction are proposed. Deamination methods leading to ethyl ester of 3-methylisoxazole-4-carboxylic acid (5) are presented. 5 will serve as a lead compound for a new series of immunomodulatory agents.

13

A theoretical forecast of the hydrogen bond changes in the electronic excited state for BN and its derivatives

88%

Wang D. , Hao C. , Wang S. , Dong H. , Qiu J.

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2012

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tom 10

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nr 1

116-123

EN

The relationship between electronic spectral shifts and hydrogen-bonding dynamics in electronically excited states of the hydrogen-bonded complex is put forward. Hydrogen bond strengthening will induce a redshift of the corresponding electronic spectra, while hydrogen bond weakening will cause a blueshift. Time-dependent density function theory (TDDFT) was used to study the excitation energies in both singlet and triplet electronically excited states of Benzonitrile (BN), 4-aminobenzonitrile (ABN), and 4-dimethylaminobenzonitrile (DMABN) in methanol solvents. Only the intermolecular hydrogen bond C≡N...H-O was involved in our system. A fairly accurate forecast of the hydrogen bond changes in lowlying electronically excited states were presented in light of a very thorough consideration of their related electronic spectra. The deduction we used to depict the trend of the hydrogen bond changes in excited states could help others understand hydrogen-bonding dynamics more effectively.

14

Research on the Mechanical Properties and Curing Networks of Energetic GAP/TDI Binders

88%

Ma S. , Li Y. , Li Y. , Li G. , Luo Y.

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tom Vol. 14, no. 3

708--725

EN

This research focused on correlations between the macroscopic mechanical performance and microstructures of energetic binders. Initially a series of glycidyl azide polymer (GAP)/toluene diisocyanate (TDI) binders, catalyzed by a mixture of dibutyltin dilaurate (DBTDL) and triphenyl bismuth (TPB), was prepared. Uniaxial tensile testing, and low-field nuclear magnetic resonance and infrared spectroscopy were then used to investigate the mechanical properties, curing networks, and hydrogen bonding (H-bonds) of these binders. Additionally, a novel method based on the molecular theory of elasticity and the statistical theory of rubber elasticity was used to analyze the integrity of the networks. The results showed that the curing parameter R strongly influences the mechanical properties and toughness of the binders, and that a tensile stress (σm) of 1.6 MPa and an elongation (εm) of 1041% was observed with an R value of 1.6. The cross-linking density increased sharply with the curing parameter, but only modestly with an R value ≥ 1.8. The proportion of H-bonds formed by the imino groups increased with the R value and reached 72.61% at an R value of 1.6, indicating a positive correlation between the H-bonds and σm. Molecular entanglement was demonstrated to increase with R and to contribute dramatically to the mechanical performance. The integrity of these networks, evaluated by a correction factor (A), varies with R, and a network of the GAP/TDI binder with an R value of 1.6 is desirable.

15

Co-crystals of 2,4,6-Trihydroxybenzoic Acid with Aromatic Diazaheterocycles – Crystallographic Studies

75%

Jankowski W. , Kadzewski A. , Gdaniec M.

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2007

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tom Vol. 81, nr 5-6

1095-1108

EN

Binary co-crystals of 2,4,6-trihydroxybenzoic acid with pyrazine (1:1), quinoxaline (1:1) and phenazine (1:2) were prepared and their structure determined by X-ray crystallography. In the complex with pyrazine the carboxylic group of the acid is in the syn configuration and is connected via strong hydrogen bond to the N atom of the heterocyclic base. In the complex with phenazine the carboxylic group adopts the anti form and the acid molecule binds, via the phenolic groups, to two molecules of the base, in a manner typical for interaction of resorcinol with azaheterocycles. In the complex with quinoxaline the asymmetric part of the unit cell consists of two pairs of acid-base hydrogen- bonded units. In the first pair, 2,4,6-trihydroxybenzoic acid binds to quinoxaline via the carboxylic group, which is in the syn form. In the second pair, proton is transferred from the carboxylic group to the heterocyclic base, and the ions join via N-H+źźźO–(carboxylate) interaction. In both units acidic hydrogen atom is significantly shifted towards the center of hydrogen bond. Hydrogen bonds between the carboxyl group and the pyrazine and quinoxaline N-atoms are linear and short [OźźźN distances in the range 2.570(2)–2.630(2) capital A, ring].

16

Investigations of hydrogen bonding in the poly(urethane-urea)-based membrane materials by using FTIR spectroscopy

75%

Wolińska-Grabczyk A. , Kaczmarczyk B. , Jankowski A.

Polish Journal of Chemical Technology

|

2008

|

tom Vol. 10, nr 4

53-56

EN

FTIR analysis was used to study the hydrogen bonding in 4,4'-diaminodiphenylmethane-based segmented poly(urethane-urea)s varying in the length of the poly(tetramethylene oxide) (PTMO)-based soft segments. Experiments were designed to follow the IR absorption of both the NH and carbonyl regions as a function of temperature in order to directly investigate the extent and strength of the hydrogen bonds, and thereby to gain some information about the possible alteration of the initial phase-segregated morphology as a result of the applied thermal treatment.

17

Molecular Interactions and Structure of H-Bonded Complexes of Bifunctional Nitrogen-Containing Molecules

75%

Bureiko S. F. , Kucherov S. Y. , Schreiber V. M.

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tom Vol. 83, nr 5

771-785

EN

The results of experimental studies and quantum chemical calculations of vibrational spectra and struc ture of H-bonded complexes formed by N-containing bases 3,5-dimethylpyrazole, diphenyltriazene and diphenylformamidine with carboxylic acids and HHal are discussed. The IR spectra of solutions in CH2Cl2 and CCl4 and low temperature NMR spectra show the existence of equilibrium between monomers and cyclic selfassociates of the mole ules studied. Under the interaction with weak carboxylic acids the complexes have molecular structure with two H-bonds NH…O=C and OH…N, and the interaction with strong acids results information of cyclic H-bonded ionic pairs with proton transfer to the N atom of the base. The proton transfer in solution was observed also for open complexes with HHal. The quantum chemical DFT calulations in harmonic and an harmonic approximations confirm the formation of cyclic complexes, while the proton transfer along the OH…N bridge was supported for the complexes with strongest ac ids. It was shown that the use of variational multidimensional an harmonic approach is the most preferable for calculations of the high-frequency XH stretch in systems where the corresponding normal mode is less characteristic and involves motions of many atoms.

18

Predominance of Amino-Sulfonyl Hydrogen Bonding in (Z)-2-Benzene-sulfonyl-1-phenyl-2-(phenylhydrazono)ethanones in Crystals adn in Solution: An Experimental NMR and X-ray Crystallographic and Theoretical Ab initio and DFT/GIAO Studies

75%

Kolehmainen E. , Zakrzewski A. , Zakrzewska A. , Nissinen M. , Ośmiałowski B. , Gawinecki R.

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tom Vol. 77 / nr 1

31-45

EN

1H, 13C, and 15N NMR spectra show that (Z)-2-benzenesulfonyl-1-phenyl-2-(phenylhydrazono) ethanone is the only tautomeric form detected in chloroform solution. Substituent in the phenylhydrazone moiety does not affect this tautomeric preference. Ab initio calculations show that (Z)-2-benzenesulfonyl-1-phenyl-2-(phenylhydrazono)ethanone is really favoured over its proton transfer products in chloroform solution. This shows that N-H...OS(O) interaction is much stronger than the hydrogen bonds in other tautomeric forms. The (Z)-2-benzene-sulfonyl-1-phenyl-2-(phenylhydrazono)ethanone tautomer was also detected in the crystal state.

19

1H, 13C and 15N NMR Spectral and X-ray Structural Studies of 2-Arylsulfonylamino-5-chlorobenzophenones

75%

Kolehmainen E. , Nissinen M. , Janota H. , Gawinecki R. , Ośmiałowski B.

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tom Vol. 77 / nr 7

889-894

EN

Six 2-(4-R-phenylsulfonylamino)-5-chlorobenzophenones were prepared and their 1H, 13Cand 15NNMRspectra recorded and assigned. The dependence between the chemical shift of the amide proton and Hammett _ substituent constants is of the V type. Substituent effect on the chemical shift of the amide nitrogen atom was found insignificant. X-ray analysis shows that the terminal benzene rings in 2-(4-nitrophenylsulfonylamino)-5-chlorobenzophenone are located close to each other. They are not, however, parallel, dihedral angle between them being equal to 10.86 deg (MP2/6-31G**//HF/6-31G** ab initio calculations show this to be 20.44 deg). This shows that the mutual orientation of two benzene rings in the molecule of this compound is caused by the _-_ stacking. It is additionally reinforced by the intramolecular NH…O=C hydrogen bond. Except the dihedral angle between the benzene rings, X-ray determined structure of 2-(4-nitrophenylsulfonylamino)-5-chlorobenzophenone is very similar to this optimized by the ab initio calculations.

20

Effect of oxidation on the wetting of coal surfaces by water: experimental and molecular dynamics simulation studies

75%

Li E. , Lu Y. , Cheng F. , Wang X. , Miller J. D.

Physicochemical Problems of Mineral Processing

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2018

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tom Vol. 54, iss. 4

1039--1051

EN

The wettability of coal surfaces by water continues to be one of the key factors which determines the success of coal flotation. Consequently, oxidation of coal surfaces is a fundamental issue of interest. In this work, the effect of oxidation on the wetting of coal surfaces and the interaction between water molecules and oxygen-containing sites at the coal surface was investigated based on advancing/receding contact angle measurements and molecular dynamics simulations. For the simulation studies, a flat coal surface was constructed with the assistance of the molecular repulsion between graphite surfaces and the assembly of Wiser coal molecules. Our results indicated that the simulated advancing and receding contact angles were very similar, and both of them decreased, as expected, with an increase of hydroxyl sites at the coal surface. The good agreement between the simulated advancing/receding contact angles and the experimental receding contact angle values suggested that the configuration of the systems and the set of parameters for the simulation were appropriate. The spreading of water is mainly due to the hydrogen bonds formed between the interfacial water molecules and the hydroxyl sites at the coal surface. The hydroxyl groups show stronger hydration capacity than other oxygen-containing groups according to the calculated hydrogen bonds and interaction energies.