Study of p-(3-carboxy-1-adamantyl)-calix[4]arene with hydrogen bonds along the upper and lower rim by IR spectroscopy and DFT.

The IR spectra of p-(3-carboxy-1-adamantyl)-calix[4]arene (AdC4A) were studied. Using IR spectroscopy, it has been shown that in calixarene in dilute solution in CCl4, there was no free hydroxyl absorption band. The hydroxyl group band was characterized by a very low frequency, which indicates a strong intramolecular hydrogen bond on the lower rim of the calixarene molecules. On the upper rim of the calixarene, the carboxyl groups form cyclic dimer or tetramer complexes via intermolecular hydrogen bonds. The cone conformation persists, but there is a mutual influence of the hydrogen bonds along the top and bottom rims of the calixarene molecule. The structure with dimeric hydrogen bonds between the carboxyl groups is 16.5 KJ/mol more preferable than the structure with tetrameric cyclic hydrogen bonds for AdC4A. The reactivity depends on the type of association on the upper rim, whether these are hydrogen-bonded dimers or cyclic tetrameric association. Graphical abstract .

Vibrational spectroscopic investigation of the gold complexation within the cascade structure of phosphorus-containing dendrimer.

The interaction of the phosphoric dendrimer with gold was performed by means of vibrational spectroscopy and quantum chemistry. Stable complexes are formed with a PN-PS linkage, whereas with an isolated PS bond this does not occur. The change in geometric parameters and delocalization of electric charge under the influence of gold was discovered. The classification of bands in the experimental vibrational spectra of the dendrimer and its complex was carried out. HOMO of molecule of the dendrimer is localized on the SPNP linkage, whereas the LUMO is located on the terminal group. In the SPNP linkage there is a noticeable delocalization of the charge which leads to a change in the reactivity of this group. Interaction energy was estimated as the difference between the energies of the complex and the energies of the molecules of the dendrimer G'0 and two molecules AuCl and is equal to 25.2 eV. The ionization energy IE and electron affinity EA for AuCl are higher than for dendrimer, therefore, when the complex is formed, these quantities increases. Chemical potential and the electrophilicity index in the complex also increases.

Vibrational spectroscopic study of cationic phosphorus dendrimers with aminoethylpiperidine terminal groups.

Two generations of phosphoric dendrimers with piperidine functional groups were synthesized for use in biology and medicine. Neutral samples are soluble in organic solvents but after protonation these dendrimers become water soluble and can be used for biological experiments. The FTIR and FT Raman spectra of two generations of dendrimers Gi constructed from the cyclotriphosphazene core, repeating units OC6H4CHNN(CH3)P(S)< and aminoethylpiperidine end groups NH(CH2)2C5NH11 were recorded. The study of the IR spectra shows that the NH groups form hydrogen bonds. The calculation of the molecular structure and vibrational spectra of the first generation dendrimer was performed by the method of DFT. This molecule has flat, repeating units and a plane of symmetry passing through the core. The calculation of the distribution of potential energy made it possible to classify the bands in the experimental spectra of dendrimers. Amine groups are manifested in the form of a band of NH stretching vibrations at 3389 cm-1 in the IR spectrum of G1. NH+ stretching bands located at 2646 and 2540 cm-1 in the IR spectrum of G2. The stretching vibrations of NH+ groups are noticeably shifted to low frequencies due to the formation of a hydrogen bond with the chlorine atom. The line at 1575 cm-1 in the Raman spectrum of G1 is characteristic for repeating units.

Cyclic cooperative intramolecular hydrogen bond in p-tert-butylcalix[6]arene according to FTIR spectroscopy and DFT studies.

This article describes a comparative research of IR spectra and H-bonds in the p-tert-butylcalix[6]arene (TB6) and calix[6]arene (C6). IR spectra were computed for compressed cone conformation by DFT method. The assignment of the bands in the IR spectra of the TB6 and C6 was made. The effect of the bulky tert-butyl substituents on the structure and H-bonding in TB6 was established. Our research has shown that in TB6 and C6 the cyclic H-bond is realized, which ensures the existence of a compressed cone conformation. Introduction of tert-butyl substituents in TB6 leads to hardening of H-bonds. Examination of IR spectra showed that when heated TB6 remains in a compressed cone conformation. In a molecule of TB6 and C6 oxygen atoms are in a "boat" conformation.

Structure, IR and Raman spectra of phosphotrihydrazide studied by DFT.

The FTIR and FT Raman measurements of the phosphotrihydrazide (S)P[N(Me)-NH2]3 have been performed. This compound is a zero generation dendrimer G0 with terminal amine groups. Structural optimization and normal mode analysis were obtained for G0 by the density functional theory (DFT). Optimized geometric bond length and angles obtained by DFT show good agreement with experiment. The amine terminal groups are characterized by the well-defined bands at 3321, 3238, 1614cm(-1) in the experimental IR spectrum and by bands at 3327, 3241cm(-1) in the Raman spectrum of G0. The experimental frequencies of asymmetric and symmetric NH2 stretching vibrations of amine group are lower than theoretical values due to intramolecular NH⋯S hydrogen bond. This hydrogen bond is also responsible for higher experimental infrared intensity of these bands as compared with theoretical values. Relying on DFT calculations a complete vibrational assignment is proposed for the studied dendrimer.

Spectroscopic and molecular structure investigation of the phosphorus-containing G'2 dendrimer with terminal aldehyde groups using DFT method.

The FTIR and FT Raman spectra of the second generation dendrimer G'2 built from thiophosphoryl core with terminal aldehyde groups have been recorded. The structural optimization and normal mode analysis were performed for model compound C, consisting of thiophosphoryl core, one branch with three repeated units, and four 4-oxybenzaldehyde terminal groups on the basis of the density functional theory (DFT) at the PBE/TZ2P level. The vibrational frequencies, infrared and Raman intensities for the t,g,g- and t,-g,g-conformers of the terminal groups were calculated. The t,g,g-conformer is 2.0 kcal/mol less stable compared to t,-g,g-conformer. A reliable assignment of the fundamental bands observed in the experimental IR and Raman spectra of dendrimer was achieved. For the low generations (G'1 to G'3) the disk form of studied dendrimer molecules is the most probable. For higher generations, the shape of dendrimer molecules will be that of a cauliflower.

DFT study of Raman spectra of hexakis(4-N'(-di(4-oxyphenethylamino)-(thio)phosphonyl)-N'-methyl-diazobenzene)cyclotriphosphazene.

The FT-Raman spectrum of the hexakis(4-N'(-di(4-oxyphenethylamino)-(thio)phosphonyl)-N'-methyl-diazobenzene)cyclotriphosphazene which is the first generation dendrimer G1 built from the cyclotriphosphazene core, six arms -O-C6H4-CH=N-N(CH3)-P(S)< and twelve 4-oxyphenethylamino terminal groups -O-C6H4-(CH2)2-NH2 G1 has been recorded. The structural optimization and normal mode analysis were performed for model compound C, consisting of cyclotriphosphazene core, one arm -O-C6H4-CH=N-N(CH3)-P(S)< and two 4-oxyphenethylamino terminal groups -O-C6H4-(CH2)2-NH2 on the basis of the density functional theory (DFT) at the PBE/TZ2P level. The calculated geometrical parameters and harmonic vibrational frequencies are predicted in good agreement with the experimental data. It was found that G1 has a concave lens structure with planar -O-C6H4-CH=N-N(CH3)-P(S)< fragments and slightly non-planar cyclotriphosphazene core. The 4-oxyphenethylamino groups attached to different arms show significant deviations from a symmetrical arrangement relative to the local planes of repeating units. The experimental Raman spectra of G1 dendron was interpreted by means of potential energy distribution. Relying on DFT calculations, as well as on experimental information, a spectral interpretation was proposed.

DFT study of Raman spectra of phosphorus-containing dendrons built from cyclotriphosphazene core with terminal carbamate and ester groups.

The FT Raman spectra of the zero (Gv0) and first generations (Gv1) of phosphorus-containing dendrons with terminal carbamate groups and one ester function and [2-(4-hydroxyphenyl)ethyl]-carbamic acid tert-butyl ester (C) have been recorded and analyzed. The lines of free ν(C=O) bonds are not observed in the experimental Raman spectrum of C and thus association of carbamate groups by hydrogen bonds occur. The frequencies of ν(C=O) lines in the experimental Raman spectrum reveal the presence of the different types of H-bonds in the amorphous state of Gv0. Density functional theory (DFT) calculations of C gave geometrical parameters for the t-g-, g-g-, tg-, gg-conformers. The most stable is the gg-conformer. The structural optimization and normal mode analysis were performed for dendrons on the basis of the DFT. The calculated geometrical parameters, harmonic vibrational frequencies and Raman intensities are predicted in a good agreement with the experimental data. The experimental Raman spectra of dendrons were interpreted by means of potential energy distribution. Relying on DFT calculations the lines of a core, repeating units and terminal groups of dendrons were assigned. The polarizabilities and lipophilicity of dendrons were estimated.

Structural and spectroscopic properties of the second generation phosphorus-viologen "molecular asterisk".

The FTIR and FT Raman spectra of the second generation phosphorus-viologen "molecular asterisk" G2 built from cyclotriphosphazene core with 12 viologen units and 6 terminal phosphonate groups have been recorded and analyzed. The experimental X-ray data of 1,1-bis(4-formylbenzyl)-4,4'-bipyridinium bis(hexaflurophosphate) was used in molecular modeling studies. The optimization of isolated 1,1-bis(4-formylbenzyl)-4,4'-bipyridinium (BFBP) molecule without counter ions PF6(-) does not lead to significant changes of dihedral angles, thus the molecular conformation does not depend on interactions with the counter ions. The structural optimization and normal mode analysis were performed for G2 on the basis of the density functional theory (DFT). The calculated geometrical parameters and harmonic vibrational frequencies are predicted in a good agreement with the experimental data. It was found that G2 has a kind of "egg timer" structure with planar OC6H4CHNN(CH3) fragments and slightly non-planar cyclotriphosphazene core. The experimental IR and Raman spectra of G2 were interpreted by means of potential energy distribution.

DFT study of structure, IR and Raman spectra of the first generation dendron built from cyclotriphosphazene core with terminal carbamate and ester groups.

The FTIR and FT-Raman spectra of the first generation dendron built from the cyclotriphosphazene core, five arms -O-C(6)H(4)-CH=N-N(CH(3))-P(S) 2 bonds on the righthand side with ten carbamate terminal groups and one ester function G(v1) have been recorded. The IR and Raman spectra of the zero generation dendron G(v0) and first generation dendrimer G(1) with the same core and terminal groups were also examined. The structural optimization and normal mode analysis were performed for dendron G(v1) on the basis of the density functional theory (DFT). The calculated geometrical parameters and harmonic vibrational frequencies are predicted in a good agreement with the experimental data. It was found that G(v1) has a concave lens structure with planar -O-C(6)H(4)-CH=N-N(CH(3))-P(S) 2 bonds on the righhand side fragments and slightly non-planar cyclotriphosphazene core. The carbamate groups attached to different arms show significant deviations from a symmetrical arrangement relative to the local planes of repeating units. The experimental IR spectrum of G(v1) dendron was interpreted by means of potential energy distributions. The strong band 1604 cm(-1) shows marked changes of the optical density in dependence of the carbamate, ester or azomethyne substituents in the aromatic ring. The frequencies of ν(N-H) and ν(C=O) bands in the IR spectra reveal the presence of the different types of H-bonds in the studied dendrimers.

Vibrational spectra study of fluorescent dendrimers built from the cyclotriphosphazene core with terminal dansyl and carbamate groups.

The FTIR and FT Raman spectra of the "Janus"-type dendrimers, possessing five carbamate groups on one side and five fluorescent dansyl derivatives on the other side, with amide G(1) and hydrazone G(2) central linkages were studied. These surface-block dendrimers are obtained by the coupling of two different dendrons. The FTIR and FT-Raman spectra of the zero generation dendrons, built from the hexafunctional cyclotriphosphazene core, with five dansyl terminal groups and one carbamate G(0v) and one oxybenzaldehyde function G(0v)' have been recorded. The structural optimization and normal mode analysis were performed for dendron G(0v)' on the basis of the density functional theory (DFT). The calculated geometrical parameters and harmonic vibrational frequencies are predicted in a good agreement with the experimental data. It was found that dendron molecule G(0v)' has a concave lens structure with planar -O-C(6)H(4)-CHO fragments and slightly non-planar cyclotriphosphazene core. The experimental IR and Raman spectra of dendron G(0v)' were interpreted by means of potential energy distributions. Relying on DFT calculations a complete vibrational assignment is proposed. The strong band 1597 cm(-1) show marked changes of the optical density in dependence of substituents in the aromatic ring. The frequencies of ν(N-H) bands in the IR spectra reveal the presence of the different types of H-bonds in the dendrimers.

Raman spectroscopy study of phosphorus-containing dendrimers built from thiophosphoryl core.

The FT-Raman spectra of 10 generations of phosphorus-containing dendrimers containing P=S and P=O bonds with terminal benzaldehyde and P-Cl groups have been recorded and analyzed. The Raman spectra of dendrimers are determined by the ratio T(n)/R(n) (T(n)--number of terminal groups, R(n)--number of repeating units). This ratio trends to r-1 (r--branching functionality of repeating unit), and becomes constant, when the generation number is higher than 3. The lines full width at half height in Raman spectra of 10 generations was measured. The possibility appears to separate the lines assigned to the core, repeating units and terminal groups of dendrimers by difference spectroscopy method. The influence of the encirclement on the line frequencies and intensities was studied and due to the predictable, controlled and reproducible structure of dendrimers the information, usually inaccessible is obtained. Some lines in the Raman difference spectra have characteristic EPR-like form. The strong line at 1600 cm(-1) show marked changes of intensity in dependence of aldehyde (-CH=O) or azomethyne (-CH=N) substituents in the aromatic ring.

IR spectroscopy investigation using DFT analysis on the structure of P(1) phosphorus dendrimer built from octasubstituted metal-free phthalocyanine core.

The IR spectra of P(1) phosphorus dendrimer built from an octasubstituted metal-free phthalocyanine core have been recorded in the region 4000-400cm(-1). Besides the phthalocyanine core, P(1) possess also eight C(6)H(4)-CHN-N(CH(3))-P(S) arms and terminal P-Cl groups. The optimized molecular geometry, frequency and intensity of the IR bands have been calculated using density functional theory (DFT). The P(1) molecules exist in a stable conformation with planar C(6)H(4)-CHN-N(CH(3))- fragments and phthalocyanine core. The calculated geometrical parameters and harmonic vibrational frequencies are predicted in a good agreement with the experimental data. The experimental IR spectrum of P(1) dendrimer was interpreted by means of potential energy distributions. Relying on DFT calculations a complete vibrational assignment is proposed. The difference IR spectra of molecules built from the thiophosphoryl, cyclotriphosphazene, and phthalocyanine cores with the same repeated units and terminal groups were studied in order to undermine the role of the core functionality on the dendrimer architecture.

FTIR and FT-Raman spectra and DFT vibrational analysis of phosphorus-containing dendrons.

FTIR and FT-Raman spectra of four generations of phosphorus-containing dendrons with terminal aldehyde or PCl groups have been recorded and analyzed. Their spectral patterns are determined by the ratio T/R (T, the number of terminal groups; R, the number of repeated units). Bands assigned to the core, repeated units and terminal groups were separated by the difference spectroscopy method. The optimized geometry, frequencies and intensity of IR bands of G(1v) generation dendron with terminal aldehyde groups were obtained by the density functional theory (DFT). It was found that the internal skeleton of molecules exists in a single stable conformation with planar O-C(6)H(4)-CHN-N(CH(3))-P(S) fragments, but terminal groups may adopt the t,g,g- and t,-g,g-rotational isomers. The t,-g,g-conformer is 0.74 kcal/mol less stable compared to the t,g,g-conformer. The bond length and bond angles obtained by DFT show the best agreement with experimental data. Relying on DFT calculations a complete assignment of vibrations is proposed for different parts of the studied dendrons. The calculated frequencies and intensity of IR bands of the t,g,g- and t,-g,g-conformers of G(1v) are found to be in reasonable agreement with the experimental results. The most reactive site in dendron is the core function and vinyl group is preferred for nucleophilic attack. In dendrimer the most reactive are the terminal groups.

FTIR spectroscopy and DFT studies of carbosilane dendrimers.

The FTIR spectra of G(3), G(4), and G(9) generations of polybutylcarbosilane dendrimers have been recorded and analyzed. The structural optimization and normal mode analysis were performed for G(1) generation on the basis of density functional theory (DFT). This calculation gave vibrational frequencies and infrared intensities for the t,t- and g,-g-conformers of the butyl terminal groups, attached to the same silicon atom. The g,-g-conformer is 5.83 kcal/mol less stable compared to t,t-conformer. Relying on DFT calculations a complete vibrational assignment is proposed for different parts of the studied dendrimers. The dependence of band full width at half height in the IR spectra on generation number is established. The IR spectra of carbosilane dendrimers at higher temperatures at the ambient air and isolated from atmosphere air were studied. At temperature 180 degrees C all studied carbosilane dendrimers are stable when contact with atmosphere is absent, in the air they oxidize and thus CO and SiO groups appear.

DFT analysis of structure and IR spectra of phosphorus G1v generation dendron.

FT-IR spectra of phosphorus dendron G(1v) generation with terminal P-Cl groups have been recorded. Density functional theory is used for analyzing the properties of each structural part (core, branches, surface). It is found that the repeating branching units of G(1v) exist in a single stable conformation with planar -O-C(6)H(4)-CH=N-N(CH(3))-P fragments. DFT results for the structure of G(1v) are in good agreement with recent X-ray diffraction measurements. A complete vibrational assignment is proposed for different parts of G(1v). The global and local reactivity descriptors have been used to characterize the reactivity pattern of the core function and terminal group. Our study reveals that the most reactive site of G(1v) is the core function and =CH(2) side of vinyl group is preferred for nucleophilic attack. In the dendrimer G(1) the most reactive are the terminal groups. IR spectroscopy combined with ab initio DFT computation provides unique detailed information about the structure and reactivity of the technologically relevant materials, which could not be obtained before with any other technique.

DFT calculations of structure and IR spectra of the phoshorus-containing G'0v generation dendron.

FT-IR spectra of the phosphorus-containing dendron G'(0v) generation with terminal aldehyde groups have been recorded. The structural optimization and normal mode analysis are performed for the G'(0v) on the basis of the ab initio density functional theory. This calculations gave vibrational frequencies and infrared intensities for the t,g,g- and t,-g,g-conformers of the G'(0v). The t,-g,g-conformer is 0.71 kcal/mol less stable compared to t,g,g-conformer. Relying on DFT calculations a complete vibrational assignment is proposed for different parts of the dendron. The influence of encirclement on band frequencies and intensity is studied and the information usually inaccessible is obtained. The global and local reactivity descriptors have been used to characterize the reactivity pattern of the core function and terminal groups. Our study reveals that the most reactive site in the dendron is the core function and the CH(2) side of the vinyl group is preferred for nucleophilic attack. In the dendrimer the most reactive are the terminal groups.

DFT and IR spectroscopic analysis of p-tert-butylthiacalix[4]arene.

Vibrational analysis of p-tert-butylthiacalix[4]arene based on an experimental mid and far IR spectra is described here. Density functional calculations of a most stable cone conformer related to crystalline solid FT-IR spectra in the temperature range up to 180 degrees C as well spectra of dilute solution have been used to obtain a better understanding of conformational state and a hydrogen bonding of p-tert-butylthiacalix[4]arene. Complete assignments were made for experimental FT-IR spectra of the cone conformer. Heating (up to 180 degrees C) of crystalline p-tert-butylthiacalix[4]arene did not change both conformational and cooperative H-bonding state of its molecules. A temperature spectral effect seems to be due to some relaxation of crystal packing mostly viewed on the OH bands.

The hydrogen bonding and conformations of p-tert-butylcalix[4]arene as studied by IR spectroscopy and by DFT calculations.

IR and far IR spectra of p-tert-butylcalix[4]arene were recorded at various temperatures between 16 and 180 degrees C and spectra of solutions and crystalline solids were obtained. Ab initio density functional calculations gave vibrational frequencies and infrared intensities for four conformers: cone, partial cone, 1,2- and 1,3-alternate. Complete assignments were made for experimental IR spectra of the cone conformer. The bands characteristic for each conformation were defined. It was revealed that O--H stretching low-frequency shift Deltanu in the cone conformation exceeds Deltanu shifts for other conformers. The effect was stipulated by a cooperative interaction of cyclic hydrogen bonds. The obtained spectra-structure correlation can be used for characteristic of calixarenes conformation.

Band intensity in the IR spectra and conformations of calix[4]arene and thiacalix[4]arene.

The experimental IR and Far IR spectra of the calix[4]arene, p-tert-butylcalix[4]arene, thialcalix[4]arene and p-tert-butylthiacalix[4]arene were examined at different temperatures and interpreted. The band frequencies and intensities in the IR spectra of the calix[4]arene and thialcalix[4]arene were calculated. The absorption curves of the four possible calix[4]arene conformations: cone, partial cone, 1,2- and 1,3-alternate were computed. The bands characteristic for each conformation are defined and assigned. The obtained spectra-structure correlation can be used for the characteristic of calixarenes conformation.