Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 26
Filtrar
2.
Artigo em Inglês | AIM | ID: biblio-1342262

RESUMO

A study to phenotypically characterize and determine the antibiogram of coagulase positive Staphylococci (CoPS) from the external surfaces of hospital cockroaches (Periplaneta americana) was conducted using standard microbiological methods. Out of the 50 cockroaches collected from various hospitals in Uyo, sixty-two percent (n = 31) had coagulase positive Staphylococci which consisted of Staphylococcus aureus (44.0 %; n = 22) and Staphylococcus intermedius (18.0 %; n = 9). The CoPS isolates showed 100% resistance to Penicillin, Tetracycline, Clindamycin and 80.6% sensitivity to Amoxicillin-clavulanate. The CoPS showed multiple antibiotic resistances to ≥ 3 antibiotics, with 60 % exhibiting resistance to 6 antibiotics. Out of the 80 % (n = 31) of the multidrug resistant CoPS that were sensitive to Amoxicillin-clavulanate, none of them showed production of beta lactamase. The cockroaches bore multiple antibiotic resistant CoPS on their external surfaces and their contact can initiate contamination of patients' food. Pest control measures in hospital are hereby recommended to minimize cockroach related infections


Assuntos
Humanos , Periplaneta , Clindamicina , beta-Lactamases , Staphylococcinum
5.
FEBS Lett ; 487(3): 390-6, 2001 Jan 05.
Artigo em Inglês | MEDLINE | ID: mdl-11163364

RESUMO

The solution structure of an apoA-I deletion mutant, apoA-I(1-186) was determined by the chemical shift index (CSI) method and the torsion angle likelihood obtained from shift and sequence similarity (TALOS) method, using heteronuclear multidimensional NMR spectra of [u-(13)C, u-(15)N, u-50% (2)H]apoA-I(1-186) in the presence of sodium dodecyl sulfate (SDS). The backbone resonances were assigned from a combination of triple-resonance data (HNCO, HNCA, HN(CO)CA, HN(CA)CO and HN(COCA)HA), and intraresidue and sequential NOEs (three-dimensional (3D) and four-dimensional (4D) 13C- and 15N-edited NOESY). Analysis of the NOEs, H(alpha), C(alpha) and C' chemical shifts shows that apoA-I(1-186) in lipid-mimetic solution is composed of alpha-helices (which include the residues 8-32, 45-64, 67-77, 83-87, 90-97, 100-140, 146-162, and 166-181), interrupted by short irregular segments. There is one relatively long, irregular and mostly flexible region (residues 33-44), that separates the N-terminal domain (residues 1-32) from the main body of protein. In addition, we report, for the first time, the structure of the N-terminal domain of apoA-I in a lipid-mimetic environment. Its structure (alpha-helix 8-32 and flexible linker 33-44) would suggest that this domain is structurally, and possibly functionally, separated from the other part of the molecule.


Assuntos
Apolipoproteína A-I/química , Apolipoproteína A-I/genética , Humanos , Técnicas In Vitro , Lipídeos , Espectroscopia de Ressonância Magnética , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/genética , Estrutura Secundária de Proteína , Deleção de Sequência , Soluções
6.
Fertil Steril ; 74(4): 771-9, 2000 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-11020522

RESUMO

OBJECTIVE: To test the hypothesis that androgens have a direct effect on the function of endometrial epithelial cells. DESIGN: In vitro study. SETTING: Academic research center. PATIENT(S): Endometrial epithelial cells were prepared from biopsy samples obtained from normal fertile women. INTERVENTIONS: Cells were incubated with androstenedione, testosterone, dihydrotestosterone, and DHEA. MAIN OUTCOME MEASURE(S): Secretion of glycodelin A into the culture fluid was used to assess secretory activity. Uptake of (3)H-thymidine and immunostaining for Ki67 was used to assess cell growth. The specific action of the androgens was confirmed by incubation with an antiandrogen, cyproterone acetate. RESULT(S): Androstenedione (10(-6) M and 10(-7) M) caused a dose-dependent decrease in glycodelin A secretion, uptake of (3)H-thymidine, and percentage of positive Ki67 cells in cultured human endometrial epithelial cells. Testosterone, dihydrotestosterone, and DHEA had no effect on glycodelin A secretion or (3)H-thymidine uptake. The direct effect of androgens on endometrial function were confirmed by demonstrating the presence of androgen receptors in cultured endometrial epithelial cells and showing that the direct effects of the androgens were not observed when cyproterone acetate was added to the cultures. CONCLUSION(S): The results suggest that androstenedione can inhibit human endometrial cell growth and secretory activity. Infertility and miscarriage associated with high androgen levels (e.g., that caused by the polycystic ovary syndrome) may be due to an adverse effect of high androgen levels on the endometrium.


Assuntos
Androgênios/fisiologia , Endométrio/fisiologia , Androstenodiona/fisiologia , Animais , Biomarcadores , Células Cultivadas , Acetato de Ciproterona/farmacologia , Desidroepiandrosterona/fisiologia , Di-Hidrotestosterona/farmacologia , Endométrio/efeitos dos fármacos , Células Epiteliais/fisiologia , Feminino , Glicodelina , Glicoproteínas/metabolismo , Humanos , Técnicas In Vitro , Antígeno Ki-67/análise , Camundongos , Avaliação de Resultados em Cuidados de Saúde , Proteínas da Gravidez/metabolismo , Radioimunoensaio , Testosterona/fisiologia , Timidina/metabolismo
7.
Fertil Steril ; 69(4): 682-90, 1998 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-9548158

RESUMO

OBJECTIVE: To compare plasma androgen concentrations in women who have recurrent miscarriages and in fertile women, and to correlate the results with concentrations of the endometrial protein PP14 in uterine flushings and plasma from women who have recurrent miscarriages. DESIGN: Retrospective study. SETTING: Hospital research unit. PATIENT(S): Women attending a recurrent miscarriage clinic and normal fertile volunteers. Ten of the women with recurrent miscarriages had polycystic ovary disease (PCOD) as assessed by ultrasonography or increased follicular LH levels. INTERVENTION(S): Plasma samples were obtained from the women on days LH-7, LH-4, LH+0, and LH+7 or LH+10 of a cycle. An endometrial flushing sample and a biopsy specimen were taken from women with recurrent miscarriages on day LH+7 or LH+10. MAIN OUTCOME MEASURE(S): Androstenedione, testosterone, and sex hormone-binding globulin (SHBG) were measured in the plasma samples. The endometrial protein PP14 was measured in the uterine flushings and in the LH+7 or LH+10 plasma samples from the women with recurrent miscarriages. RESULT(S): Testosterone concentrations were higher in the women with recurrent miscarriages both with and without PCOD on days LH-7 and LH-4 of the cycle. Concentrations of androstenedione also were higher in the women with recurrent miscarriages, but without PCOD on day LH-7. Testosterone SHBG ratios were higher in the women with recurrent miscarriages, without PCOD compared with the controls on days LH-7, LH+0, and LH+7. Mean follicular testosterone concentrations were correlated negatively with both uterine (r = -0.47) and plasma (r = -0.49) PP14 levels on day LH+10. Mean luteal phase testosterone SHBG ratios were correlated negatively with uterine PP14 concentrations on day LH+7 of the cycle (r = -0.674). CONCLUSION(S): Androgen levels are higher in women who have recurrent miscarriages than in normal fertile controls. These high levels of androgens may have a detrimental effect on endometrial function.


Assuntos
Aborto Habitual/sangue , Androstenodiona/sangue , Síndrome do Ovário Policístico/sangue , Globulina de Ligação a Hormônio Sexual/análise , Testosterona/análise , Aborto Habitual/patologia , Adulto , Androstenodiona/metabolismo , Biópsia , Colo do Útero/metabolismo , Colo do Útero/patologia , Estudos de Coortes , Endométrio/química , Feminino , Glicodelina , Glicoproteínas/análise , Glicoproteínas/sangue , Humanos , Hormônio Luteinizante/sangue , Hormônio Luteinizante/metabolismo , Ciclo Menstrual/sangue , Ciclo Menstrual/metabolismo , Ciclo Menstrual/fisiologia , Síndrome do Ovário Policístico/patologia , Gravidez , Proteínas da Gravidez/análise , Proteínas da Gravidez/sangue , Estudos Retrospectivos , Globulina de Ligação a Hormônio Sexual/metabolismo , Testosterona/sangue , Testosterona/metabolismo
8.
Br J Biomed Sci ; 56(1): 16-9, 1999.
Artigo em Inglês | MEDLINE | ID: mdl-10492910

RESUMO

Leptin is a protein, produced by adipose tissue, which has cytokine and hormonal properties. Serum leptin levels can be considered as a measure of body fat mass, and are involved in regulation of body weight. Previous studies suggest that leptin may have an additional role in reproduction, and there is also evidence for involvement in the hypothalamic-pituitary-gonadal axis. In this study, we investigate the possible changes in serum leptin concentration throughout the menstrual cycle. Samples were collected from apparently healthy, fertile women at different stages in their menstrual cycle, timed precisely according to the luteinising hormone (LH) surge. Mean serum leptin levels were significantly higher in the luteal phase (median 11.4 ng/mL) than in the follicular phase (median 10.0 ng/mL) (P < 0.001). In addition, mean serum leptin levels correlated with body mass index (r = 0.54, P < 0.05), but showed no correlation with luteal-phase progesterone levels. Results showed that levels of serum leptin vary during the menstrual cycle, and add to the mounting evidence that leptin has a role in reproduction. These fluctuations should be taken into account whenever studies are performed using female subjects.


Assuntos
Ciclo Menstrual/sangue , Proteínas/metabolismo , Adulto , Índice de Massa Corporal , Feminino , Fertilidade/fisiologia , Humanos , Leptina
9.
Mol Biol (Mosk) ; 22(4): 1026-32, 1988.
Artigo em Russo | MEDLINE | ID: mdl-3185529

RESUMO

Comparison has been made of the proton magnetic resonance (PMR) spectra of translating ribosomes in the pre-translocation and post-translocation states as well as of the complexes of translating ribosomes with elongation factors Tu (EF-Tu) or G (EF-G) in the presence of the uncleavable analogue of GTP--guanylyl-imidodiphosphate (GMP-PNP). It is shown that proteins L7/L12 within the translating ribosomes possess a high intramolecular mobility both in the pre-translocation and in the post-translocation states. The interaction of EF-G with translating ribosomes results in a decrease of the mobility of the L7/L12 proteins. The interaction of EF-Tu with translating ribosomes leads to slight changes in the PMR spectra different from the changes caused by EF-G.


Assuntos
Biossíntese de Proteínas , Proteínas Ribossômicas/análise , Ribossomos/análise , Espectroscopia de Ressonância Magnética , Fator G para Elongação de Peptídeos , Fator Tu de Elongação de Peptídeos/análise , Fatores de Alongamento de Peptídeos/análise
10.
Biofizika ; 27(1): 170-8, 1982.
Artigo em Russo | MEDLINE | ID: mdl-7066396

RESUMO

During the past few years new techniques have been developed in nuclear magnetic resonance (NMR) which make it possible to form two dimensional cross-sectional images related to the distribution of protons in biological structures. The methods are non-invasive and of low radiation hazard and could therefore have some clinical value in medical diagnosis. Several methods of producing NMR images are discussed and examples of biological application are given.


Assuntos
Células/ultraestrutura , Espectroscopia de Ressonância Magnética , Animais , Espectroscopia de Ressonância Magnética/instrumentação , Espectroscopia de Ressonância Magnética/métodos
11.
Biofizika ; 22(2): 201-6, 1977.
Artigo em Russo | MEDLINE | ID: mdl-193575

RESUMO

A comparison of the three known methods made it possible to work out methods of complex extraction of deutero amino acids, deutero sugars and deutero vitamins from algae Chlorella sp. K., grown autotrophically in heavy water. An analysis of the isotopic composition of deutero amino acids by PMR indicates that treatment with HCl introduces 1H into side chains of some amino acids by chemical exchange (C2, 6H of tyrosine, C2H of histidine, rho-H of phenylalanin, beta-CH2-aspartate and gamma-CH2-glutamate. These exchanges made the amino acids convenient to be used as the substrates for the growth of heterotrophic selective deuterated organisms as a source of selective deuterated proteins.


Assuntos
Chlorella/metabolismo , Deutério/metabolismo , Marcação por Isótopo/métodos , Aminoácidos/isolamento & purificação , Fenômenos Químicos , Química , Chlorella/análise , Espectroscopia de Ressonância de Spin Eletrônica , Monossacarídeos/isolamento & purificação
14.
Biochemistry ; 31(37): 8906-15, 1992 Sep 22.
Artigo em Inglês | MEDLINE | ID: mdl-1390678

RESUMO

Sequence-specific resonance assignments of human beta 2-microglobulin (M(r) 12,000) and its secondary structure are determined by 2D NMR techniques. The protein is found to contain two antiparallel beta-sheets each of four beta-strands with the beta-sheets being connected by a single disulfide linkage. No evidence for any regular helical structure is found. Amide proton-solvent-exchange rate constants and 3JHN alpha coupling constants are evaluated.


Assuntos
Microglobulina beta-2/ultraestrutura , Sequência de Aminoácidos , Humanos , Ligação de Hidrogênio , Concentração de Íons de Hidrogênio , Espectroscopia de Ressonância Magnética , Dados de Sequência Molecular , Movimento (Física) , Conformação Proteica , Soluções
15.
J Lipid Res ; 28(11): 1259-62, 1987 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-3430058

RESUMO

Interaction of homologous fatty acids (C3-C18) with sodium deoxycholate was investigated. From NMR and ultrasonic results it was found that short chain homologues (up to C9) do not participate in the formation of mixed micelles with sodium deoxycholate. Fatty acid homologues with longer chains (starting with C9) form mixed micelles by "burying" hydrophobic chains in hydrophobic environment of a sodium deoxycholate micelle.


Assuntos
Ácidos Graxos/análise , Fenômenos Químicos , Química , Ácido Desoxicólico/análise , Concentração de Íons de Hidrogênio , Espectroscopia de Ressonância Magnética , Micelas
16.
Am J Reprod Immunol ; 38(5): 339-42, 1997 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-9352025

RESUMO

PROBLEM: Menstrual cycle-associated variability in the circulating levels of several cytokines can be a confounding factor in measurements of in vivo cytokine levels in clinical studies. Since pregnancy-associated increases in interleukin-10 (IL-10) levels are well documented, we have investigated the variability in serum levels of IL-10 in healthy women at different stages of the menstrual cycle to ascertain whether this is a problem in comparative studies of circulating IL-10 levels. METHOD OF STUDY: We obtained fifty-four successive serum samples at points in the menstrual cycles of 12 healthy fertile women, precisely timed by measurement of the luteinizing hormone surge, and measured the interleukin-10 levels. RESULTS: Levels of IL-10 in successive serum samples from each woman taken on days LH - 7 (that is seven days prior to LH surge), LH - 4, LH + 1, LH + 7, and LH + 10 showed that IL-10 does not vary in a systematic way during the menstrual cycle. CONCLUSION: These results validate the sampling of women in studies of IL-10 levels in various clinical situations and establish that these levels are not dependent on menstrual cycle dates. They also suggest that menstrual cycle-related changes in IL-1 are not mediated by IL-10. The rise in progesterone in the luteal phase of the menstrual cycle is not mirrored by a rise in the circulating IL-10 level, which implies either that the pregnancy-associated rise is not related to progesterone or that it is only observed at the higher progesterone levels in pregnancy.


Assuntos
Interleucina-10/sangue , Ciclo Menstrual/sangue , Ciclo Menstrual/imunologia , Adulto , Feminino , Fase Folicular/sangue , Fase Folicular/imunologia , Humanos , Interleucina-1/sangue , Fase Luteal/sangue , Fase Luteal/imunologia , Gravidez , Progesterona/sangue , Fatores de Tempo
17.
Hum Reprod ; 13(8): 2261-5, 1998 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-9756307

RESUMO

Thirty postmenopausal women were randomized to receive either continuous combined (cc) 2 mg oestradiol valerate and 0.7 mg norethisterone acetate hormone replacement therapy (HRT) daily (15 women) or tibolone 2.5 mg daily (15 women) and were monitored to determine the relationship between the two biochemical markers placental protein 14 (PP14) and the glycoprotein CA125, endometrial histology and occurrence of irregular bleeding after 12 months of treatment. The concentrations of PP14 and CA125 in plasma and uterine flushings before and after therapy were measured and their concentrations were associated with the histology of endometrial biopsies obtained on the same day as venesection and endometrial flushing. The levels of PP14 in uterine flushings were significantly increased after the administration of both types of HRT (P < 0.05 for tibolone and P < 0.001 for ccHRT). However, the concentrations of PP14 found in flushings after ccHRT were considerably greater than those found in flushings after tibolone; levels were increased about 150-fold by ccHRT and 6-fold by tibolone (P < 0.001). Plasma concentration of PP14 after both types of HRT were also significantly raised to a similar degree (P < 0.01). In contrast, the concentration of plasma and uterine CA125 were unchanged by either treatment. Histological analysis of the endometrium from women after 12 months of HRT treatment showed that 86% (6/7) of women on ccHRT had secretory activity as compared to 44% (4/9) women on tibolone (P < 0.05). Women with higher post-HRT uterine PP14 concentration were more likely to have irregular bleeding (P < 0.05). Our studies have shown that endometrial PP14 but not CA125 concentrations are raised to a significant degree by two different forms of period-free HRT regimens. Increased PP14 concentrations in uterine flushing may suggest endometrial stimulation of some form and predict the predilection to irregular bleeding. Thus uterine PP14 concentrations may be used to monitor endometrial responses in women on HRT.


Assuntos
Endométrio/efeitos dos fármacos , Terapia de Reposição de Estrogênios/métodos , Antígeno Ca-125/sangue , Antígeno Ca-125/metabolismo , Endométrio/anatomia & histologia , Endométrio/metabolismo , Estradiol/administração & dosagem , Estradiol/análogos & derivados , Feminino , Glicodelina , Glicoproteínas/sangue , Glicoproteínas/metabolismo , Humanos , Menstruação/efeitos dos fármacos , Pessoa de Meia-Idade , Noretindrona/administração & dosagem , Noretindrona/análogos & derivados , Acetato de Noretindrona , Norpregnenos/administração & dosagem , Proteínas da Gravidez/sangue , Proteínas da Gravidez/metabolismo , Estudos Prospectivos
18.
Hum Reprod ; 13(1O): 2895-901, 1998 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-9804252

RESUMO

In this prospective study, we examined the possible diagnostic value of the measurement of two endometrial proteins, placental protein-14 (PP14) and CA-125, in the evaluation of pre- and post-menopausal bleeding. Concentrations of these two proteins were measured in plasma and uterine flushings obtained from 139 pre- and post-menopausal women with bleeding problems, and 26 normal post-menopausal control women without bleeding. Endometrial biopsy samples were also obtained for histological study. Concentrations of PP14 in both the plasma and uterine flushings in post-menopausal women were significantly lower (P < 0.001) than those of control pre-menopausal women. In post-menopausal women, the concentrations of PP14 (mean +/- SEM) in both plasma and flushing were significantly higher (P < 0.001) in women with endometrial adenocarcinoma (46.9+/-7.5 ng/ml plasma; 3350+/-1711 ng/ml flushing) than in the controls (7.6+/-1.3 ng/ml plasma; 125+/-27 ng/ml flushing) or in women with post-menopausal bleeding and atrophic endometrium (20.4+/-2.1 ng/ml plasma; 453+/-167 ng/ml flushing). In contrast CA-125 concentrations in plasma and flushings were similar in post-menopausal and pre-menopausal women. Plasma concentrations of CA-125 were higher in post-menopausal women with adenocarcinoma (29.1+/-7.4 IU/ml) than in those with post-menopausal bleeding and atrophic endometrium (21.8+/-2 IU/ml) (P < 0.05) or control post-menopausal subjects (16.1+/-2.1 IU/ml) (P < 0.01). CA-125 concentrations in uterine flushings were not significantly different in any group of post-menopausal women. The results show that concentrations of PP14 are correlated more strongly to endometrial histopathology than those of CA-125 in pre- and post-menopausal women. Elevated PP14 concentrations are also associated with the presence of endometrial adenocarcinoma and may have a potential to be used as a marker for this disease.


Assuntos
Antígeno Ca-125/sangue , Antígeno Ca-125/metabolismo , Glicoproteínas/sangue , Glicoproteínas/metabolismo , Proteínas da Gravidez/sangue , Proteínas da Gravidez/metabolismo , Hemorragia Uterina/etiologia , Hemorragia Uterina/metabolismo , Útero/metabolismo , Adenocarcinoma/sangue , Adenocarcinoma/diagnóstico , Adenocarcinoma/metabolismo , Adulto , Idoso , Atrofia , Biomarcadores Tumorais/sangue , Biomarcadores Tumorais/metabolismo , Neoplasias do Endométrio/sangue , Neoplasias do Endométrio/diagnóstico , Neoplasias do Endométrio/metabolismo , Endométrio/patologia , Feminino , Glicodelina , Humanos , Menopausa/imunologia , Menopausa/metabolismo , Pessoa de Meia-Idade , Estudos Prospectivos , Hemorragia Uterina/diagnóstico , Útero/imunologia , Útero/patologia
19.
Hum Reprod ; 16(6): 1244-50, 2001 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-11387299

RESUMO

Postmenopausal women taking oestradiol 17-beta 2 mg daily were randomized to receive either 25 or 50 microg gestodene from day 17 to 28 of the cycle in a double-blind study. Placental protein P14 (PP14) and CA 125 concentrations in uterine flushing, endometrial morphology and irregular bleeding after 12 cycles of study were observed. Eleven and 12 women in the 25 and 50 microg groups respectively completed the study. There were no significant differences in pre-treatment biochemical and morphological indices between the groups. The median PP14 concentration increased from 332 to 5800 ng/ml (P < 0.001) and from 145 to 27 160 ng/ml (P < 0.001) in the 25 and 50 microg gestodene groups respectively. No between-group significant rise of PP14 was observed. Similarly, no significant change was seen between the initial and post-treatment concentrations of CA 125 for either group. All biopsies were atrophic at inception of the study, and both regimens produced secretory endometrial transformation in the majority of biopsies. No between-group difference was observed in the morphometric indices measured, or any significant correlation between the concentrations of PP14 or CA 125 and morphology. The mean number of days of withdrawal bleeding (3.8 and 4.2 days for 25 and 50 microg respectively) were similar. In conclusion, both regimens produced a significant rise in uterine flushing concentrations of PP14, but not CA 125. PP14 is a sensitive biochemical marker in the assessment of endometrial response to hormone replacement therapy.


Assuntos
Endométrio/efeitos dos fármacos , Terapia de Reposição de Estrogênios , Norpregnenos/administração & dosagem , Congêneres da Progesterona/administração & dosagem , Adulto , Antígeno Ca-125/análise , Antígeno Ca-125/sangue , Método Duplo-Cego , Endométrio/fisiologia , Estradiol/administração & dosagem , Feminino , Glicodelina , Glicoproteínas/análise , Glicoproteínas/sangue , Humanos , Pessoa de Meia-Idade , Norpregnenos/efeitos adversos , Pós-Menopausa , Proteínas da Gravidez/análise , Proteínas da Gravidez/sangue , Congêneres da Progesterona/efeitos adversos , Estudos Prospectivos , Irrigação Terapêutica , Hemorragia Uterina/induzido quimicamente , Útero/metabolismo
20.
Biopolymers ; 28(2): 589-604, 1989 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-2713454

RESUMO

Formation and thermodynamic characteristics of C-H ... O hydrogen bonding of methylated uracils and caffeine have been studied by nmr along two lines. 1. The concentration and temperature dependencies of the PMR spectra of 1,3-dimethyluracil (m2 1,3Ura), 1,3-dimethylthymine (m2 1,3Thy), and 1,3,6-trimethyluracil (m3 1,3,6Ura) in chloroform at high concentrations of base analogs indicated the self-association of m2 1,3Ura and m2 1,3Thy via C(6)H ... O hydrogen bonding and the competitive formation of C-H ... O bonds between carbonyl oxygens and chloroform. The intermolecular interaction energy and the arrangement of molecules in the local minima of various m2 1,3Ura dimers were calculated by the method of atom-atom potentials. The deepest minimum for the m2 1,3Ura coplanar dimer corresponds to a C(6)-H ... O hydrogen-bond formation. 2. At low concentration of m2 1,3Ura and caffeine in CCl4, C(6)-H ... O bonding for m2 1,3Ura and C(8)-H ... O bonding for caffeine with oxygens of dimethyl sulfoxide (DMSO) and acetone were observed. The association constants of these complexes were obtained at different temperatures. The enthalpies delta H, of the m2 1,3Ura-DMSO, m2 1,3Ura-accetone, caffeine-DMSO, and caffeine-acetone complexes were -2 +/- 0.1 kcal/mol. The calculations showed that the deepest minimum of the caffeine-acetone coplanar complex corresponds to C(8)-H ... O bonding with energy of -3.5 kcal/mol and that of the m2 1,3Ura-acetone complexes corresponds to C(6)-H ... O bonding with energy of -3.4 kcal/mol. The approximate correction for the solvent effect provides good agreement of the experimental data with the calculations.


Assuntos
Timina/análogos & derivados , Uracila/análogos & derivados , Ligação de Hidrogênio , Espectroscopia de Ressonância Magnética , Estrutura Molecular , Termodinâmica
SELEÇÃO DE REFERÊNCIAS
Detalhe da pesquisa