Bilateral Mature Ovarian Teratoma with Torsion in a Premenarchal Girl.

Mature cystic teratoma is the most common type of ovarian tumor in children. Adnexal torsion is the main complication of mature ovarian teratoma. The synchronous bilateral incidence of mature cystic teratoma in premenarchal girls is known to be rare. However, the incidence of adnexal torsion is higher in young girls. A 10-year-old girl presenting with acute abdomen was managed by emergency laparotomy. Bilateral mature ovarian teratoma with adnexal torsion of the right ovary was found. The right ovarian tissue was not viable due to torsion and an oophorectomy was necessary. Cystectomy with preservation of the ovarian tissue of the left ovary was performed. Histopathological diagnosis was bilateral synchronous mature teratoma with necrosis of the right adnexa. Although the risk of malignancy of torsed ovaries and mature teratomas in premenarchal girls is low, their removal is recommended to prevent adnexal torsion. Decision between ovarian tissue sparing surgery or oophorectomy depends on the risk of malignancy, fertility preservation and the avoidance of early menopause.

Quarter of a century of work of the Intersectoral Commission on Iodine Deficiency Solution.

World Summit for Children held in 1990 in its final declaration called for removal of iodine deficiency to the year 2000. Urgency of iodine deficiency in the Czech Republic was highlighted by the studies of the Institute of Endocrinology in Prague in the early 90's. The Intersectoral Commission on Iodine Deficiency Solution arising from the initiative of endocrinologists, hygienists and paediatricians was then established in 1995. Representants from selected ministries, non-governmental organizations and food and pharmaceutical industry also participated in its work. Activities initiated by the Intersectoral Commission succeeded significantly improve the iodine status of population and supressed the deficit until 2000. In next years the Intersectoral Commission continuously evaluated results of monitoring of iodine status of population, held national conferences and annual Iodine Days that gave the opportunity to revive public interest in iodine. This Intersectoral Commission although deserved for the reduction of excessive levels of iodine in cows milk after 2000 and will address iodine deficiency in pregnant and breastfeeding women. The Intersectoral Commission will pay attention on expected decrease of kitchen salt consumption and subsequent reduction of iodine offer, will deal food supplements containing an excessive amount of iodine and will constantly monitor iodine status of the population.

[Iodine supply and iodinuria among the Czech population between the years 1995 and 2016]. / Zásobení jodem a jodurie obyvatel v Ceské republice v letech 1995-2016.

Monitoring of Ioduria and Iodine saturation are essential tools for evaluation of effectivness of measures aimed at elimination of diseases caused by iodine deficiency. Between 1995 and 2016 monitoring of ioduria was udertaken in various population groups in Czech Republic. The most recent study (2015) found only 37 % of pregnant women in optimal range of ioduria (150-300 mcg/l), in iodopenic range 27 %, while 6 % of these had severe iodopenia below 50 mcg/l. In a group of 3y old children investigated in the same year, 57 % were found to have Ioduria within the recommended range (90-299 mcg/l), 24 % had higher than recommended Ioduria (300-499 mcg/l) and 8 % excessive saturation (over 500 mcg/l). Observed group of seniors (60-75 years) satisfied criteria for maintenance of elimination of iodine deficit of International Council for Control of Iodine Deficiency Disorders (ICCIDD), the advisory institution to World Health Organisation (WHO), as only 9 % of participants were found to have Ioduria less than 100 mcg/l and no participant had Ioduria below 50 mcg/l. Main challenges are currently stabilisation of Iodine content in milk and ensuring optimal saturation of pregnant and breast feeding women with Iodine. On-going ambition of the Inter-resort Commission for Solution of Iodine Deficit (MKJD) affiliated to the National Health Institute in Prague is to reduce and eventually eliminate diseases caused by Iodine deficiency or excess. Also, to achieve Ioduria between 100-300 mcg/l in majority of population, which would indicate adequate Iodine supply, while median of Iodurias should remain below 300 mcg/l.Key words: iodine deficiency - iodine supply - ioduria.

[Solution of Iodine deficiency in the Czech Republic - history and current situation20 years of work of prof. Václav Zamrazil for Commission for the solution of Iodine deficiency]. / Resení jodového deficitu v Ceské republice - historie a soucasný stav20 let práce prof. MUDr. Václava Zamrazila v Meziresortní komisi pro resení jodového deficitu.

Diseases caused by Iodine deficit are preventable. Inter resort Commission for the solution of Iodine deficiency (MKJD) at State Institute for Health (SZU) in Prague has been taking effective measures which satisfied requirements of the Principles for sustainable elimination of diseases caused by Iodine deficiency ICCD WHO: 96 % of households is using iodized salt, average Iodine content is 25 mg/1 kg of salt. Data from studies show ioduria less 100 mcg/l in only 9 per cent of seniors, 5 % of children 7-10 years, 3 % of children 10-12 years. Under 50 mcg only 1 % of children 10-12 years. Median of iodurias is below 300 mcg/l (seniors 185 mcg/l, children 7-10 years 277 mcg/l, children 10-12 years 252 mcg/l). We satisfy 8 of 10 indicators of Principles for Sustainable elimination of diseases caused by Iodine deficiency. Results of screening for congenital hypothyroidism are in keeping with sufficient iodine intake in newborns. Unsatisfactory situation however persist in expectant and breast feeding mothers 16 % [11] 6 % [10] of women included in the respective studies had ioduria below 50 mpg/l. Milk and dairy produce became a rich dietary source of Iodine as cattle feeds are fortified with Iodine. No part of observed human population is exposed Iodine doses higher than 17 mcg/kg. Next target for prevention will be achieving optimal iodine concentration in milk and improvement of iodine saturation of expectant and nursing mothers. Integral part is the monitoring of iodine saturation of population.Key words: dietary exposition - dietary sources of iodine - Inter resort commission for elimination of iodine deficit - iodine deficiency - iodine supply - iodized salt - ioduria.

Premicellar interaction of PEO-PPO-PEO triblock copolymers with partially hydrophobic alcohols: NMR study.

The interactions of three alcohols, namely, 2-butanol (BuOH), 3-methyl-2-butanol (MeBuOH), and 3,3-dimethyl-2-butanol (Me2BuOH) with propylene oxide octamer (PO8) and the copolymers (EO)8(PO)13(EO)8(L35) and (EO)13(PO)30(EO)13(L64) in D2O were studied using (13)C NMR spectra and relaxations and (1)H PFG NMR diffusion measurements. For L64, it was shown that the temperature at which the PO chain starts to change its conformation under dehydration decreases by 6 K for each additional methyl group in the alcohol molecule (i.e. with increasing its hydrophobicity), and the analogous conformation states are attained at temperatures approximately 10 K lower compared using ketonic analogs of the alcohols under the same conditions. Also, the first signs of L64 aggregation, according to the normalized diffusion coefficients, are at temperatures 7, 10, and 13 K lower for BuOH, MeBuOH, and Me2BuOH, respectively. These effects are much weaker for (PO)13 in L35 or nonexistent for (PO)8 in PO8, thus showing the role of cooperativity in dehydration and aggregation processes. According to diffusion measurements, the molar fraction of the alcohol hydrogen bonded to L64 increases with its hydrophobicity and, in an apparent conflict with thermodynamics, with increasing temperature at which also higher NOE can be observed. Strong hydrogen bond interaction, which is in cooperation with hydrophobic interaction, does not preclude the exchange between bound and free states of the alcohol, however. Using (13)C transverse relaxation, its correlation time is shown to be of the order of 10 ms.

Scavenger receptor for hemoglobin in preterm prelabor rupture of membranes pregnancies complicated by histological chorioamnionitis.

OBJECTIVE: We sought to evaluate the distribution of scavenger receptor for hemoglobin positive (CD163(+)) cells in the placenta and fetal membranes from pregnancies complicated by preterm prelabor rupture of membranes with respect to the presence and absence of histological chorioamnionitis. METHODS: Sixty-two women with singleton pregnancies with a gestational age between 24+0 and 36+6 weeks were included in a prospective cohort study. CD163 was evaluated by immunohistochemistry in the placenta and fetal membranes. The number of CD163(+) cells and neutrophils was counted in the following locations: fetal membranes' amnion, chorion, and decidua, as well as the placenta's amnion, chorionic plate, subchorionic fibrin, stem villi, terminal villi, and decidua. RESULTS: CD163(+) cells were found in all compartments of the placenta and the fetal membranes regardless of the inflammatory status. A positive correlation between the number of CD163(+) cells and neutrophils in the subchorionic fibrin and the chorionic plate was found. The number of CD163(+) cells was higher in the placental subchorionic fibrin and chorionic plate when histological chorioamnionitis was present. CONCLUSION: The presence of histological chorioamnionitis affected the number of CD163(+) cells in the placental chorionic plate and in the subchorionic fibrin but not in the fetal membranes.

Interaction of premicellar states of a PEO-PPO-PEO triblock copolymer with partially hydrophobic substances: NMR study.

According to (1)H and (13)C NMR spectra, relaxations, and PFG NMR self-diffusion measurements, partially hydrophobic additives methyl-ethyl ketone (MEK), methyl-isopropyl ketone (MIPK), and methyl-t-butyl ketone (MTBK) facilitate the conformation change and subsequent self-association of the copolymer Pluronic L64. The correlation time (4-9 ms) and activation energy (43-52 kJ/mol) of transition between its conformation states decrease with the increasing hydrophobicity and bulkiness of the additive. The temperature of the first PPO self-association decreases in the same order (by 4 K for MTBK). The interaction of the additives was indirectly proved by the decrease of their rotational and translational mobility in the presence of L64. The rotational correlation time τ(c) is between 3 and 6 × 10(-11) s, whereas that of the same molecules in the absence of L64 is lower than 6 × 10(-12) s. The normalized self-diffusion coefficient decreases to about 0.7 of its original value in the presence of L64. The interaction of the additive with the PPO block is transient but effective enough to facilitate its conformational change and self-association. Its mediation by a water molecule bound to PPO as a possible mechanism is suggested.

Interaction of hydrated protons with octyl-phenyl-N,N-diisobutylcarbamoylmethyl phosphine oxide (CMPO): NMR and theoretical study.

Interaction of octyl-phenyl-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO, the 'classical' rare metal extraction agent) with fully ionized hydrated protons (HP) was studied in acetonitrile-d(3) using (1)H, (13)C, (31)P NMR, PFG NMR and magnetic relaxation. The experimental results were confronted with high-precision ab initio DFT calculations. Relative chemical shifts of NMR signals of CMPO (0.01 mol/L) under the presence of HP in the molar ratio ß = 0-2.0 mol/mol show binding between CMPO and HP. Self-diffusion measurements using (1)H PFG NMR demonstrate that larger complexes with higher content of CMPO are generally formed at ß < 0.75. Analyzing the collective dependence of (13)C and (31)P NMR chemical shifts on ß by the use of program LETAGROP, we obtained very good fitting for the assumed coexistence of two complexes (CMPO)(2)·HP (C(2)) and CMPO.HP (C(1)). The logarithms of the respective stabilization constants log K(i) were found to be 7.518 (C(2)) and 4.581 (C(1)). The system dynamics was studied by measuring the transverse (1)H NMR relaxation using CPMG sequence with varying delays t(p) between the π pulses in the mixtures with ß = 0.4-0.8. The following exchange correlation times were obtained: τ(10) = 2.35 × 10(-5), τ(20) = 0.82 × 10(-4), τ(21) = 0.45 × 10(-3) s. The DFT calculations support the conclusion that the complexes C(1) and C(2) are the main species in the mixtures of CMPO with HP. They also agree with the NMR and FTIR observation that the main site to which H(3) O(+) is bound is the P=O group, whereas the amide group does not form a strong bond with the ion when excess water molecules are present.

Interaction of cesium ions with calix[4]arene-bis(t-octylbenzo-18-crown-6): NMR and theoretical study.

Using (1)H, (13)C, and (133)Cs NMR spectra, it is shown that calix[4]arene-bis(t-octylbenzo-18-crown-6) (L) forms complexes with one (L·Cs(+)) and two (L·2Cs(+)) Cs(+) ions offered by cesium bis(1,2-dicarbollide) cobaltate (CsDCC) in nitrobenzene-d(5). The ions interact with all six oxygen atoms in the crown-ether ring and the π electrons of the calixarene aromatic moieties. According to extraction technique, the stability constant of the first complex is log ß(nb)(L·Cs(+)) = 8.8 ± 0.1. According to (133)Cs NMR spectra, the value of the equilibrium constant of the second complex is log K(nb)((2))(L·2Cs(+)) = 6.3 ± 0.2, i.e., its stabilization constant is log ß(nb)(L·2Cs(+)) = 15.1 ± 0.3. Self-diffusion measurements by (1)H pulsed-field gradient (PFG) NMR combined with density functional theory (DFT) calculations suggest that one DCC(­) ion is tightly associated with L·Cs(+), decreasing its positive charge and consequently stabilizing the second complex, L·2Cs(+). Using a saturation-transfer (133)Cs NMR technique, the correlation times τ(ex) of chemical exchange between L·Cs(+) and L·2Cs(+) as well as between L·2Cs(+) and free Cs(+) ions were determined as 33.6 and 29.2 ms, respectively.

N-(2-Hydroxypropyl)methacrylamide-based polymer conjugates with pH-controlled activation of doxorubicin for cell-specific or passive tumour targeting. Synthesis by RAFT polymerisation and physicochemical characterisation.

Controlled radical reversible addition-fragmentation chain transfer (RAFT) polymerisation was used to prepare water-soluble polymer-drug carriers based on copolymers of N-(2-hydroxypropyl)methacrylamide (HPMA) with a hydrazide group-containing monomer, showing well-defined structure with narrow molecular weight distribution (approx. 1.1-1.2). The anticancer therapeutic doxorubicin was bound to the polymeric carrier by a hydrazone bond, enabling pH-controlled release under mildly acid conditions that mimics the environment in endosomes/lysosomes of tumour cells. RAFT polymerisation facilitated the synthesis of semitelechelic copolymers, which were used in the synthesis of monoclonal anti-CD20 antibody-polymer-drug conjugate designed for cell-specific tumour targeting. They were also used for producing a biodegradable high-molecular-weight graft polymer-drug conjugate that degrade in the presence of glutathione, which is designed for passive targeting to solid tumours. The conjugates exhibited well-defined structures with narrow molecular weight distributions of approx. 1.3 and pH-controlled drug release.

Cooperative interaction of hydronium ion with an ethereally fenced hexaarylbenzene-based receptor: an NMR and theoretical study.

Using (1)H and (13)C NMR and DFT calculations, the structure and interactions of the symmetric ethereally fenced hexaarylbenzene receptor 1 with hydronium ions were studied. Both 1 and its equimolecular complex 1.H(3)O(+) exhibit C(3v) symmetry. According to DFT, two similar optimal structures of the complex exist, the more stable one being 15.4 kJ/mol lower in energy. The equilibrium between 1 and 1.H(3)O(+) complexes is characterized by the stabilization constant K = 1.97 x 10(6) (i.e., the binding constant eta = 6.3) according to both proton and carbon NMR spectra. The exchange dynamics between 1 and the complex measured by the delay-varied CPMG sequence had to be corrected for the internal exchange processes in both 1 (conformation change) and the complex (vacillation between the two minima). After this correction, the correlation time of exchange was found to be 4.76 x 10(-5) s. Such relatively fast exchange can be explained only by it being mediated by the excess water molecules present in the system.

Cooperative preassociation stages of PEO-PPO-PEO triblock copolymers: NMR and theoretical study.

Using (1)H and (13)C 1D and 2D NMR spectra, pulsed field-gradient (PFG) diffusion measurements, and (13)C relaxations supported by density functional theory (DFT) calculations, the temperature-dependent behavior of (EO)(m)(PO)(n)(EO)(m) block copolymers (m/n = 31/14, 31/72, and 17/1) in D(2)O below and at the critical micellar temperature (CMT) was investigated in order to understand the nature of primary self-association acts and their true driving force. It was shown that a conformation change of the PO block followed by mild and reversible association with other PO blocks and eventually with the inner parts of EO blocks starts at temperatures 10-12 K below the CMT. The primary process is the entropy-driven disintegration of the PPO hydration envelope based on cooperation of hydrophobic hydration and hydrogen bonding. The partial dehydration of PPO is followed by its conformation change. Both processes are cooperative and reversible with a correlation time of the order 0.01 s and an activation energy of 51.3 kJ/mol. The PPO chain in a staggered conformation is prone to self-association starting at temperatures 5-6 K below CMT. In (EO)(m)(PO)(n)(EO)(m) block copolymers, this process is complicated by the stripping of PEO chains of a part of hydrogen-bound water and entwining them with PPO. It is shown that only inner (PPO-near) parts of PEO take part in the process, the end-groups remaining free.

Hydration modes of an amphiphilic molecule: NMR, FTIR, and theoretical study of the interactions in the water-lutidine system.

Using (1)H and (13)C NMR spectra and relaxations, PFG NMR diffusion measurements, FTIR spectra, and quantum-chemical structure predictions and optimizations on the MP2/6-31G(d) level, we have studied interactions between water (W) and lutidine (2,6-dimethylpyridine, L) in a wide range of ratios. At low W content up to 35%, W was found to bind to L by an O-H***N hydrogen bond and form transient L-W aggregates containing two to four L molecules in cooperation with two to three other W molecules. At higher W content, these aggregates are gradually cleaved to single L molecules enwrapped by a hydration shell anchored in an O-H***N hydrogen bond. At all compositions of the mixture, the various hydrate forms are in fast mutual exchange with a correlation time on the order of 1 x 10(-5) s.

NMR investigation of aniline oligomers produced in the early stages of oxidative polymerization of aniline.

The products obtained within early stages of the oxidative polymerization of aniline in solutions of various weak organic acids or in water, and aniline oligomers produced by the oxidation of aniline and aniline-(15)N in acetic acid (0.4 M) with a limited amount of oxidant were analyzed using 1H, 13C, and 15N 1D and 2D NMR spectroscopy and 1H PFG NMR. Such products are virtually identical in all cases, according to 1H NMR. They are always a mixture of products, among which one of them is prominent. Both native and neutralized forms of the products were examined. As shown by a combination of 1H DQF COSY, 1H NOESY, 1H-(13)C and 1H-(15)N HSQC, and 1H-(13)C and 1H-(15)N HMBC spectra, both forms of this product contain an oligoaniline moiety ended mostly by phenylamino groups. In a significant amount, the chains contain--either as an inner or terminal group--an unexpected six-member ring with an oxygen-containing substituted quinoneimine structure. The most probable structure of the major product is given. The difference between the native and neutralized forms of the product was examined. It is shown that the oligomeric chains, in particular quinoneimine units of the former one, are protonated. Both forms of the product exhibit a slight paramagnetism, and contain about 2x10(-9) mol g(-1) of unpaired electron spins.

Interaction of hydrated protons with trioctylphosphine oxide: NMR and theoretical study.

Interaction of trioctylphosphine oxide (TOPO) with fully ionized hydrated protons (HP) was studied in acetonitrile-d(3) and nitrobenzene-d(5) using (1)H, (13)C, and (31)P NMR, PFG NMR, and magnetic relaxation, and the experimental results were confronted with high-precision ab initio DFT calculations. Relative chemical shifts of NMR signals of TOPO (0.02 mol/L) under the presence of HP in the molar ratio beta = 0-2.0 mol/mol show binding between TOPO and HP. Self-diffusion measurements using (1)H PFG NMR demonstrate that larger complexes with higher content of TOPO are generally formed at beta < 0.75. Analyzing the dependence of (31)P NMR chemical shifts on beta by the use of program LETAGROP, we obtained very good fitting for the assumed coexistence of three complexes (TOPO)(i).HP (named C(i)), where i = 1, 2, 3. The logarithms of the respective stabilization constants log K(i) were found to be 3.63, 4.67, and 7.23 in acetonitrile and 3.91, 6.04, and 7.92 in nitrobenzene. The (31)P NMR chemical shifts Deltadelta(i) corresponding to these complexes are 39.35, 29.51, and 19.72 ppm in acetonitrile and 38.37, 28.47, and 18.63 ppm in nitrobenzene. These values and the calculated values of alpha(i) =[C(i)]/[TOPO](0) were utilized in the analysis of the system dynamics. This was done by measuring the transverse (31)P NMR relaxation by the CPMG sequence with varying delays t(p) between the pi pulses in the mixtures with beta = 0.5, 1.25, and 1.5. Calculating the probabilities of imaginable exchange processes shows that only three of them can have significant influence on relaxation rate R(2), namely C(1) <--> TOPO, C(2) <--> C(1), and C(3) <--> C(2). Using the slopes of the R(2)-t(p)(-1) dependences in the above three mixtures, the following correlation times were obtained: tau(10) = 2.5 x 10(-6), tau(21) = 7.4 x 10(-5), tau(32) = 11.3 x 10(-5) s. The DFT calculations support the hypothesis that complexes C(1) to C(3) are the main species in the mixtures of TOPO with HP, with the only exception that additional water molecules are bound to the complexes in the case of C(1) and C(2). Schematically, the compositions of the three stable complexes is [3TOPO.H(3)O](+), [2TOPO.H(3)O.H(2)O](+), and [TOPO.H(3)O.2H(2)O](+). The relative (31)P NMR shifts calculated for the optimized structures of C(1), C(2), and C(3) are in very good agreement with the experimentally observed values.

NMR and theoretical study of the cooperative interaction of hydrated proton with dibenzo-24-crown-8.

Interaction of hydrated protons (HPs) with dibenzo-24-crown-8 (DBC in nitrobenzene-d(5) was studied by (1)H and (13)C NMR under assistance of ab initio-density functional theory (DFT) quantum calculations. HPs were afforded by hydrogen bis(1,2-dicarbollyl) cobaltate (HDCC) with 3.5 M excess of H(2)O. The forming of a complex between HP and DBC leads to marked and additive relative shifts of both (1)H and (13)C signals. This was utilized for the estimation of the stabilization constant K of the complex. Its value is at least 10(6) l/mol, which agrees with the result of independent extraction method (log K = 6.3). Using absolute integral intensities of the HP signal in a water-saturated system, it was shown that the form of HP present in the complex must be H(5)O(2)(+), in accord with formerly published structure of the complex in crystalline form. The investigation of the dynamics of exchange between bound and free DBC by transverse relaxation using variably spaced pulses in the Carr-Purcell-Meiboom-Gill (CPMG) sequence or on-resonance rotating-frame relaxation with variable spin-lock field intensity was partly hampered by the fast relaxation of some signals in the complex because of relative immobilization of its internal motions. In order to remove these effects, a pulse sequence dipolar interaction-free transverse relaxation (DIFTRE) for static DIFTRE was devised and the MLEV17 pulse sequence with high intensity of electromagnetic field was used in a separate series of experiments. Using the results of these latter experiments, the correlation time of exchange was established to be about 0.8 ms, which complied with the shape of the spectra. The accompanying ab initio DFT calculations showed that the apparent symmetry of the molecules of both DBC and its complex with H(5)O(2)(+) was probably the result of averaging of energetically close conformations (five for DBC and four for the complex). Both NMR and the calculations show that the basic mode of binding of the ion in the complex is analogous to that found in crystal but the most pronounced conformation is slightly different.

Interaction of hydronium ion with dibenzo-18-crown-6: NMR, IR, and theoretical study.

Interaction of dibenzo-18-crown-6 (DBC) with H 3O (+) (HP) in nitrobenzene- d 5 and dichloromethane- d 2 was studied by using (1)H and (13)C NMR spectra and relaxations, FTIR spectra, and quantum chemical DFT calculations. NMR shows that the DBC*HP complex is in a dynamic equilibrium with the reactants, the equilibrium constant K being 0.66 x 10 (3), 1.16 x 10 (4), and 1.03 x 10 (4) L x mol (-1) in CD 2Cl 2, nitrobenzene, and acetonitrile, respectively. The complex appears to have a C 2 v symmetry in NMR, but FTIR combined with DFT normal mode calculations suggest that such high symmetry is only apparent and due to exchange averaging of the structure. FTIR spectra as well as energy-optimized DFT calculations show that the most stable state of the complex in solution is that with three linear hydrogen bonds of HP with one CH 2-O-CH 2 and two Ar-O-Ar oxygen atoms. The structure is similar to that found in solid state but adopts a somewhat different conformation in solution. The dynamics of exchange between bound and free DBC was studied by NMR transverse relaxation. It was found to be too fast to give reproducible results when measured with the ordinary CPMG sequence or its variant DIFTRE removing residual static dipolar interaction, but it could be established by rotating-frame measurements with high intensity of the spin-lock field. The correlation time of exchange was found to be 5.6 x 10 (-6) and 3.8 x 10 (-6) s in dichloromethane and nitrobenzene, respectively. Such fast exchange can be explained by cooperative assistance of present water molecules.

Cooperative interaction of n-butylammonium ion with 1,3-alternate tetrapropoxycalix [4]arene: NMR and theoretical study.

The interaction of 1,3-alternate tetrapropoxycalix[4]arene (1) with n-butylammonium ion (2) in CD(2)Cl(2) was examined using (1)H, (13)C and (14)N NMR spectroscopy and DFT (density functional theory) calculations. NMR shows that 1 forms with 2 an equimolecular hydrogen-bonded complex with the equilibrium constant 5.91 x 10(3) l/mol at 296 K. The structure of the complex can be shown to be asymmetric at 203 K, with 2 interacting by hydrogen bonds with the two ethereal oxygen atoms of one half of 1 and with the pi system of the other half, but is rapidly averaged to an apparent C(4h) symmetry by chemical exchange at higher temperatures. Using two related but independent techniques based on transverse and rotating-frame proton relaxation, it is shown that only an intermolecular exchange of 2 between the bound and free states takes place, in contrast to previously studied interaction of 1 with H(3)O(+). Its correlation time is 0.169 ms. It is shown by DFT calculations that such swift exchange is not possible without a cooperative interaction of both 2 and 1 with several molecules of water present. Similarities and contrasts between the exchange processes of 2 and H(3)O(+) bound to 1 are discussed, in particular with respect to the apparent quantum tunneling of the latter inside the molecule of the complex.

Cooperative interaction of H3O+ with 1,3-alternate tetrapropoxycalix[4]arene: NMR and theoretical study.

Interaction of H3O+ or H5O2+ with 1,3-alternate tetrapropoxycalix[4]arene (1) was studied in nitrobenzene and dichloromethane using 1H and 13C NMR including transverse and rotating-frame relaxations and density functional level of theory (DFT) quantum calculations. According to NMR, the ion forms an equimolecular complex with 1 with the equilibrium constant K being 3.97 x 10(3) L.mol(-1) at 296 K. The ions are bound by strong hydrogen bonds to the phenoxy-oxygen atoms of one half of 1 and by a medium-strong hydrogen bond to the pi system of the aromatic rings of the other half. The complex appears to have C(4h) symmetry in NMR even when cooling its solution down to 213 K, which could be due either to a genuine symmetry of the complex (if the ion is H5O2+) or to fast structure averaging by ion exchange processes (if the ion is H3O+). Therefore, the dynamics of the system was studied. Using two independent NMR methods (transverse and rotating-frame relaxation), two different exchange processes were discerned with correlation times 25 x 10(-6) and 5 x 10(-6) s, the first being clearly intermolecular and the other being apparently intramolecular. The energetic aspects of the possible exchange processes were examined by DFT quantum calculations. Rotation of H3O+ ion within one binding site with the energy barrier 8.13 kcal/mol is easily possible. Intermolecular exchange by freeing the ion from the complex has too high a barrier but cooperative interaction of the ion with additional water molecules makes it viable. The intramolecular exchange (or hopping) of the H3O+ ion between the two sites of the molecule is not viable in the classical manner, the barrier being 25.6 kcal/mol. Quantum tunneling of the ion is highly improbable, too. Alternative mechanisms including concerted two-ion intermolecular exchange and cooperative interaction with another bound water molecule including complexation with proton dihydrate H5O2+ are discussed.

Cooperative hydrogen bonds of macromolecules. 3. A model study of the proximity effect.

Experimental and theoretical evidence for the proximity effect as a basic mechanism of the hydrogen bond cooperativity was obtained in a model system. Hydrogen bond (HB) interaction between poly(4-vinylpyridine) (PVP) and selected acids as HB donors was studied using PFG NMR self-diffusion measurements, 1H NMR longitudinal relaxation and quantum-mechanical DFT calculations. Bivalent HB donors, such as glutaric (GA) and adipic acid (AA), were compared to univalent donors 4-chlorobutyric acid, 4-acetylbutyric acid and 5-chlorovaleric acid. PFG NMR established substantially larger HB equilibrium constants for AA and, in particular, GA than for univalent donors, thus indicating cooperativity of COOH groups in bivalent donors. According to the values of these constants, the fraction of the transiently bound GA and AA molecules, which are bound by two hydrogen bonds, is 0.70 and 0.63, respectively. This result, which means substantial cooperativity in particular in GA, was then independently verified by a relaxation study comparing longitudinal relaxation rates of univalent and bivalent donors. Analysis of relaxation led to the same probabilities that HB of one COOH group of a bivalent donor will be accompanied by HB of another COOH group of the same molecule, namely 0.70 for GA and 0.63 for AA. Such cooperativity must be due to the proximity effect, i.e., the lowering of the entropy demand of the next binding by the motional restriction imposed by the already existing bonds. This conclusion is in excellent agreement with DFT calculations on the interaction of GA with a model vinylpyridine dimer, which predict preference of double binding of the same GA molecule over that of two GA molecules and show that this preference is due to a substantially lower entropy demand.