Manifestation of intramolecular hydrogen bonds in the IR spectra of bioactive aminophenols

The intermolecular interactions in solutions of aminophenols in CCl₄ are studied by the methods of IR Fourier spectroscopy. If the hydroxyl groups of aminophenol molecules occupy the ortho positions with respect to the amino groups of the molecules, the hydroxyl and amino groups are involved in intramolecular interactions with the formation of hydrogen bonds O-H...N and N-H...O. The introduction of two additional tert-butyl groups into the structure of the aminophenol molecule facilitates the formation of O-H...N bonds and impedes the formation of N-H...O bonds. The occurrence of the carbonyl group in the structure of aminophenols leads to the formation of intramolecular hydrogen bonds O-H...O=C. The introduction of the methyl groups into carbonyl-containing aminophenols transforms the O-H...O=C bond into the hydrogen bond N-H...O=C.     

Intramolecular and intermolecular hydrogen bonds in aminophenols

IR-Fourier spectroscopy methods are adopted to study intramolecular and intermolecular hydrogen bonds that form in CCl₄ solutions of aminophenol derivatives and in a solid phase of these compounds pressed in KBr. If a hydroxyl group is present in the molecule in the ortho-position to an amino group, then intramolecular interactions between OH and NH groups will take place in aminophenol solutions. Intramolecular O–H⋅⋅⋅O=S=O and N–H⋅⋅⋅O=S=O hydrogen bonds are found in solutions of compounds containing a sulfonamide fragment. Additional acylation of the amino group causes an intramolecular O–H⋅⋅⋅O=C hydrogen bond to form in solutions. Functional groups OH, NH, SO₂, and C=O interact with one another in various ways in the solid phase to form intermolecular hydrogen bonds in aminophenols.     

Manifestation of intramolecular and intermolecular interactions in infrared absorption spectra of biologically active aminophenols

FTIR methods were used to study intramolecular and intermolecular interactions in solutions and the solid state of the biologically active aminophenols 2-anilino-4,6-di-tert-butylphenol, N-(3,5-di-tert-butyl-2-methoxyphenyl)aniline, and 2,4-di-tert-butyl-10H-1-phenothiazinol. An analysis of the IR spectra has shown that intramolecular interactions between the OH and NH groups occur in solutions of 2-anilino-4,6-di-tertbutylphenol in CCl₄ to form O-H⋯N hydrogen bonds. The NH groups in solutions of N-(3,5-di-tert-butyl-2-methoxyphenyl)aniline in CCl₄ are present in the non-associated state because of the absence of hydroxyl groups in the molecular structure. The OH and NH groups in solutions of 2,4-di-tert-butyl-10H-1-phenothiazinol in CCl₄ do not interact within the molecule due to a decrease in the conformational mobility of the molecular fragments due to the presence of the rigid C_Ar-S-C_Ar molecular bond in this compound. Intermolecular interactions involving the NH groups occur in the solid state of these compounds. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 1, pp. 68–73, January–February, 2008.     

Spectroscopic properties of pharmacologically active phenols

The IR Fourier-transform spectra of pharmacologically active phenol molecules in solutions in CCl₄ and in the crystalline state have been studied. Phenol derivatives with different directivities and different levels of pharmacological efficiency have been examined. Based on analysis of the IR spectra of screened phenols, the antimicrobial activity of phenols with free hydroxyl groups has been shown to be highest. The high antimicrobial activity of aminophenols is related to the formation of intramolecular hydrogen bonds. For aminophenols that are active against herpesviruses, O-H...N hydrogen bonds are formed in molecules. The main characteristic of the high antiviral activity against A-type influenza is predominance of intramolecular hydrogen bonds of the O-H...O=C type in molecules. Sulfur-containing aminophenols, which manifest activity against HIV infection, are characterized by the occurrence of hydrogen bonds that involve the participation of the OH, NH, and SO₂ groups.     

Hydrogen bonds of anti-HIV active aminophenols

Analysis of IR-Fourier spectra from solutions and crystals of antiviral sulfo-containing aminophenols has shown that various types of intramolecular and intermolecular interactions can occur in molecules of these compounds. Three types of intramolecular hydrogen bonds (O–H⋅⋅⋅N, O–H⋅⋅⋅O=S=O, and N–H⋅⋅⋅O=S=O) are formed in CCl₄ solutions of the sulfo-containing aminophenols. The formation of intermolecular H-bonds involving the NH- and OH-groups and the preservation of the intramolecular O–H⋅⋅⋅O=S=O H-bond are characteristic of the anti-HIV active aminophenol crystals. Spectral attributes are determined in order to distinguish between the anti-HIV active and inactive sulfo-containing aminophenols.     

Hydrogen bonds and antiviral activity of benzaldehyde derivatives

We have obtained the Fourier transform IR spectra of solutions of benzaldehyde derivatives having different antiviral activities against a herpes virus. We observe a correlation between the presence of hydrogen bonds in the benzaldehyde molecules and the appearance of antiviral properties in the compounds. For compounds having antiviral activity, we have obtained spectral data suggesting the existence of hydrogen bonds of the type C=O⋅⋅⋅H–O and O–H⋅⋅⋅O in the molecules. When the hydrogen atom in the hydroxyl groups are replaced by a methyl group, no intramolecular hydrogen bonds are formed and the compounds lose their antiviral activity.     

Intramolecular interactions in antiviral derivatives of 4,6-di-<Emphasis Type="Italic">tert</Emphasis>-butyl-2-aminophenol

We have used Fourier transform IR (FTIR) spectroscopy to study intramolecular interactions in solutions of 4,6-di-tert-butyl-2-aminophenol in n-hexane. When the hydroxyl group in the molecule is ortho to the amino group, an O―H⋅⋅⋅N intramolecular hydrogen bond is formed in the 4-6-di-tert-butyl-2-aminophenol derivatives, where the strength of the hydrogen bond depends on the type of substituent at the para position of the phenyl ring. If there are electron-donor groups on the phenyl ring, then a stronger O―H⋅⋅⋅N bond is formed in the 4,6-di-tert-butyl-2-aminophenol derivatives than in molecules containing electron-acceptor Cl and Br atoms. Formation of the above-indicated intramolecular hydrogen bond affects the course of radiation-induced reactions occurring in n-hexane with participation of these compounds and also affects their antiviral activity. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 434–439, May–June, 2009.     

Electronic structure, spectral-luminescent, and proton acceptor properties of biologically active aminophenols

The absorption and fluorescence spectra and fluorescence quantum yields of a number of biologically active derivatives of o-aminophenol are measured in an inert solvent, hexane. The IR spectrum of a solution of 2-amino-4,6-di-tert-butylphenol is studied in CCI₄ and IR bands are found that indicate the presence of two conformers in this solution with intramolecular hydrogen bonds O-H…N and N-H…O. Using methods of IR Fourier transform spectroscopy, the structural features of a number of biologically active o-aminophenols with different substituents are considered. The absorption and fluorescence spectra of o-aminophenols are calculated and interpreted by the method of intermediate neglect of differential overlap with spectroscopic parameterization. Calculation data are compared with the results of the experiment. Proton acceptor properties of o-aminophenol molecules are theoretically evaluated using the method of molecular electrostatic potential. The role played by various substituents in the formation of the proton acceptor properties of o-aminophenols is experimentally studied.     

Intramolecular hydrogen bonds in sulfur-containing aminophenols

IR Fourier spectroscopy methods have been adopted to study intramolecular interactions that occur in CCl₄ solutions of antiviral derivatives of aminophenol. Analysis of the IR spectra showed that intramolecular bonds O–H···N, O–H···O=C, N–H···O=S=O, and O–H···O=S=O can occur in these compounds depending on the substituent on the amino group. Not only the presence of intramolecular O–H···N, O–H···O=S=O, and N– H···O=S=O hydrogen bonds in 2-amino-4,6-di-tert-butylphenol derivatives containing a sulfonamide fragment but also conformational equilibrium among these types of intramolecular interactions are essential for the manifestation of high efficiency in suppressing HIV-infection in cell culture.     

Ramsey terms for two-, three-, and four-bond coupling involving 15N and 17O in hydrogen-bonded and nonhydrogen-bonded systems: are coupling constants sensitive to RAHBs?

Ab initio EOM-CCSD/(qzp,qz2p) calculations have been performed on complexes with intermolecular hydrogen bonds involving ¹⁵N and ¹⁷O, and molecules with and without intramolecular hydrogen bonds involving these nuclei. Coupling constants across intermolecular hydrogen bonds are well approximated by the Fermi-contact (FC) term. In general, ^2hJ(X–Y) for intramolecular coupling across X–H^…Y hydrogen bonds are not sensitive to the presence of resonance-assisted hydrogen bonds (RAHBs). However, ^2hJ(O–O) for coupling across the intramolecular hydrogen bond in malonaldehyde is greater than ^2hJ(O–O) for its saturated counterpart, so that ^2hJ(O–O) is sensitive to the presence of the RAHB. This is also the case for the sulphur analogues of malonaldehyde. For these unsaturated hydrogen-bonded molecules, molecules with carboxyl groups, and trans-glyoxal, J is dominated by the paramagnetic spin orbit (PSO) term. For these systems, the primary mode of coupling transmission is through the conjugated chain. For complexes with intermolecular hydrogen bonds, saturated molecules with intramolecular hydrogen bonds, unsaturated and saturated molecules in which the hydrogen bond has been broken, and unsaturated molecules with intramolecular N–H^…N or O–H^…N hydrogen bonds, J is dominated by the FC term. FC domination in hydrogen-bonded systems indicates that the primary transmission mode is across the hydrogen bond.     

Fourier transform IR spectroscopic study of substituent effect in aromatic amino acids on the zwitterion–neutral molecule tautomeric equilibrium

Four aromatic amino acids (p-aminobenzoic, 4,6-diaminoisophthalic, o-aminobenzoic, and methylene-bis-anthranilic) were studied by FTIR spectroscopy. The first two molecules were found to exist in the solid phase exclusively in neutral form and the latter two in coexisting neutral and ionic forms. The shift of the tautomeric equilibrium from neutral molecule to zwitterion is determined by the character of substitution, molecular conformation, and the possibility of noncovalent bonds formed between the functional groups. The separation of charges becomes possible only if the conformers of the molecule include a structure with an OH….N intramolecular hydrogen bond. The proton is completely transferred from the acid group to the amino group when the strong intermolecular hydrogen bonds can stabilize the formed zwitterion. Otherwise, uncharged complexes with different degrees of proton transfer to the amino group are formed.     

IR Spectroscopic Investigation and Conformational Analysis of Unsaturated C<Superscript>20</Superscript> and C<Superscript>22</Superscript> Steroid Alcohols

With the IR-spectroscopy method and the quantum-chemical AM1 method, the Δ²² and Δ²³ steroids containing a hydroxyl group at C²⁰ or C²² have been studied in order to elucidate the mutual arrangement in space of the hydroxyl group and of the double bond in the side chain of the molecules. The conformational analysis of steroid alcohols has been performed and the population of their stable conformers has been calculated. The frequencies of the bands in the IR spectra of alcohols in the region of the stretching vibration of OH groups have been assigned to certain conformers and the possibility of formation of the intramolecular hydrogen bond of the OH groups with the π-electron cloud of C=C bonds has been analyzed. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 3, pp. 317–324, May–June, 2005.     

Calculation of electronic spectra for intermolecular complexes of 3-aminophthalimide by a modified Hückel molecular orbital method

Calculation of the spectra of intermolecular complexes of 3-aminophthalimide is used as an example to show that when hydrogen bonds are present, the resonance integrals for the proton donor and acceptor atoms are different from zero. Theoretical analysis of strained 3-aminophthalimide complexes allowed us to establish the determining role of hydrogen bonds in their formation. Using an intramolecular peptide hydrogen bond as an example, we studied the effect of the solvent on its parameters. In particular, we showed that hydrogen bond formation with a proton-acceptor group of the chelate ring leads to a decrease in the resonance integral, and consequently a decrease in the enthalpy of formation of the intramolecular hydrogen bond, to a significantly greater degree than formation of a hydrogen bond at a proton-donor group. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 735–740, November–December, 2006.     

Time-dependent density functional theory study on excited state intramolecular proton transfer of 3-hydroxy-2-(pyridin-2-yl)-4H-chromen-4-one

The time-dependent density functional theory (TDDFT) method was carried out to investigate the excited state intramolecular proton transfer (ESIPT) process of 3-hydroxy-2-(pyridin-2-yl)-4H-chromen-4-one (1a). 1a has two tautomeric forms: one is 1a(O), which is induced by intramolecular hydrogen bond O-H?O=C, and the other one is 1a(N), which is caused by intramolecular hydrogen bond O-H?N. From excited state to tautomer excited state coming from ESIPT, the hydroxyl hydrogen breaks away and the dissociated hydrogen adsorbed on pyridinic nitrogen or carbonyl oxygen formed new intramolecular HB and the corresponding bond length and bond angle varied greatly. In comparison, a similar process of proton transfer for 1a(N)H⁺ protonated 1a(N) from ground state to excited state was obtained. This detailed proton transfer mechanism was provided by molecular orbitals analysis and it may be applied to molecular switch and organic Lewis acid/base. We investigated the excited state proton transfer mechanism of the four molecules through the theoretical method for the first time and gave unambiguous geometry of excited state.     

How universal are hydrogen bond correlations? A density functional study of intramolecular hydrogen bonding in low-energy conformers of α-amino acids

Hydrogen bonding is one of the most important and ubiquitous interactions present in Nature. Several studies have attempted to characterise and understand the nature of this very basic interaction. These include both experimental and theoretical investigations of different types of chemical compounds, as well as systems subjected to high pressure. The O–H..O bond is of course the best studied hydrogen bond, and most studies have concentrated on intermolecular hydrogen bonding in solids and liquids. In this paper, we analyse and characterise normal hydrogen bonding of the general type, D–H...A, in intramolecular hydrogen bonding interactions. Using a first-principles density functional theory approach, we investigate low energy conformers of the twenty α-amino acids. Within these conformers, several different types of intramolecular hydrogen bonds are identified. The hydrogen bond within a given conformer occurs between two molecular groups, either both within the backbone itself, or one in the backbone and one in the side chain. In a few conformers, more than one (type of) hydrogen bond is seen to occur.

Interestingly, the strength of the hydrogen bonds in the amino acids spans quite a large range, from weak to strong. The signature of hydrogen bonding in these molecules, as reflected in their theoretical vibrational spectra, is analysed. With the new first-principles data from 51 hydrogen bonds, various parameters relating to the hydrogen bond, such as hydrogen bond length, hydrogen bond angle, bond length and vibrational frequencies are studied. Interestingly, the correlation between these parameters in these bonds is found to be in consonance with those obtained in earlier experimental studies of normal hydrogen bonds on vastly different systems. Our study provides some of the most detailed first-principles support, and the first involving vibrational frequencies, for the universality of hydrogen bond correlations in materials.     

Rapidly progressing photophysical and photochemical relaxation processes in complex organic molecules

Using methods of high-speed kinetic laser spectroscopy, we investigated the dynamics and mechanisms of rapidly progressing relaxation processes in multiatomic molecules. We separated intra- and intermolecular channels of relaxation of the vibrational energy of excitation by the rate of transformation of nonstationary absorption spectra in a picosecond range of times. The role of highly excited electronic states in the process of electronic-vibrational relaxation in molecules of the class of phenazines was ascertained. Applying femtosecond light pulses in a real time scale, we recorded the dynamics of the decay of optically induced anisotropy in rarefied vapors of organic compounds. Several mechanisms of transfer of a hydrogen atom in the process of formation of free radicals in photoreduction of ketones were established. The dynamics of formation of inter- and intramolecular exciplexes in binary gas-phase systems was investigated. We determined the mechanisms of intramolecular dissociation of a C–O chemical bond in spiropyrans and xanthene dyes. Photodissociation of S–S bonds in molecules of disulfides was studied. The possibility of the existence of states with intramolecular charge transport with a twisted configuration for organic free radicals is shown. To whom correspondence should be addressed. Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 5, pp. 635–661, September–October, 1998.     

Molecular mechanism of gelation upon the addition of water to a solution of poly(acrylonitrile) in dimethylsulfoxide

The solidification of a solution of poly(acrylonitrile) (PAN) in dimethylsulfoxide (DMSO) upon introduction of water into the solution is studied by Raman spectroscopy. In the absence of water, DMSO molecules are found to produce dipole-dipole bonds with PAN molecules. Upon the introduction of water, DMSO molecules produce hydrogen bonds with it and bands at 1005 and 1015 cm⁻¹ appear in the Raman spectrum, which are assigned to the valence vibrations of S=O bonds involved in the hydrogen bonds. Simultaneously, water molecules produce hydrogen bonds with PAN molecules: R-C≡N...H-O-H...N≡C-R, where R is the carbon skeleton of a PAN molecule. Accordingly, a band at 2250 cm⁻¹ arises in the Raman spectrum, which is assigned to the valence vibrations of C≡N bonds producing hydrogen bonds with a water molecule. When the water content is low and the DMSO concentration is high, the length of the hydrogen bonds varies in wide limits and the band at 2250 cm⁻¹ is wide. As the water content rises, DMSO molecules come out of PAN, the variation of the hydrogen bond length in it decreases (the band at 2250 cm⁻¹ narrows), and a high-viscosity system (gel) arises that consists of PAN molecules bonded to water molecules via “equally strong” hydrogen bonds.     

Hydrogen bonding in oxalic acid and its complexes: A database study of neutron structures

The basic result of carboxylic group that the oxygen atom of the -OH never seems to be a hydrogen bond acceptor is violated in the cases, namely urea oxalic acid and bis urea oxalic acid complexes, where the hydroxyl oxygen atom is an acceptor of a weak N—H… O hydrogen bond. The parameters of this hydrogen bond, respectively in these structures are: hydrogen acceptor distance 2.110 Å and 2.127 Å and the bending angle at hydrogen, 165.6° and 165.8°. The bond strength around the hydroxyl oxygen is close to 1.91 valence units, indicating that it has hardly any strength left to form hydrogen bonds. These two structures being highly planar, force the formation of this hydrogen bond. As oxalic acid is the common moiety, the structures of the two polymorphs, α-oxalic acid and β-oxalic acid, also were looked into in terms of hydrogen bonding and packing.     

脉冲升温纳秒时间分辨中红外光谱研究氨基酸重水溶液的分子间氢键

应用变温傅立叶变换红外光谱和脉冲升温纳秒时间分辨红外差谱研究了组氨酸和甘氨酸的重水溶液的羧基负离子的振动．结果表明不仅氨基酸分子之间形成氢键，而且氨基酸分子和溶剂分子之间也形成氢键．当温度升高时，羧基负离子在1600?1610 cm?1 附近的反对称伸缩振动发生蓝移，说明高温使氢键减弱．温度从10℃突然升高到20℃，组氨酸的时间分辨瞬态光谱出现两个漂白峰，一个在1604 cm?1，指认为形成氨基酸分子间氢键的羧基负离子的峰；另一个在1612 cm?1，指认为氨基酸分子和溶剂分子形成氢键的羧基负离子的峰．前     

A theoretical study on the ESPT mechanism for a novel Bis‐HPBT fluorophore

In this work, based on the density functional theory and time‐dependent density functional theory methods, the properties of the 2 intramolecular hydrogen bonds (O1‐H2···N3 and O4‐H5···N6) of a new photochemical sensor 4‐(3‐(benzo[d]thiazol‐2‐yl)‐5‐tert‐butyl‐4‐hydroxybenzyl)‐2‐(benzo[d]thiazol‐2‐yl)‐6‐tert‐butyl phenol (Bis‐HPBT) have been investigated in detail. The calculated dominating bond lengths and bond angles about these 2 hydrogen bonds (O1‐H2···N3 and O4‐H5···N6) demonstrate that the intramolecular hydrogen bonds should be strengthened in the S₁ state. In addition, the variations of hydrogen bonds of Bis‐HPBT have been also testified based on infrared vibrational spectra. Our theoretical results reproduced absorption and emission spectra of the experiment, which verifies that the theoretical level we used is reasonable and effective in this work. Further, hydrogen bonding strengthening manifests the tendency of excited state intramolecular proton transfer (ESIPT) process. Frontier molecular orbitals depict the nature of electronically excited state and support the ESIPT reaction. According to the calculated results of potential energy curves along stepwise and synergetic O1‐H2 and O4‐H5 coordinates, the potential energy barrier of approximately 1.399 kcal/mol is discovered in the S₁ state, which supports the single ESIPT process along with 1 hydrogen bond of Bis‐HPBT. In other words, the proton transfer reaction can be facilitated based on the electronic excitation effectively. In turn, through the process of radiative transition, the proton‐transfer Bis‐HPBT‐SPT form regresses to the ground state with the fluorescence of 539 nm.