RESUMEN

We report an extensive computational and spectroscopic study of several fluoropyridine-HCl complexes, and the parent, pyridine-HCl system. Matrix-IR spectra for pentafluoropyridine-HCl, 2,6-difluororpyridine-HCl, and 3,5-difluororpyridine-HCl in solid neon exhibit shifts for the H-Cl stretching band that parallel the effects of fluorination on hydrogen-bond strength. Analogous spectral shifts observed across various host environments (solid neon, argon, and nitrogen) for pentafluoropyridine-HCl and 2,6-difluororpyridine-HCl convey a systematically varying degree of matrix stabilization on the hydrogen bonds in these complexes. An extended quantum-chemical study of pyridine-HCl and eight fluorinated analogs, including 2-, 3-, and 4-fluoropyridine-HCl, 2,6- and 3,5-difluororpyridine-HCl, 2,4,6- and 3,4,5-trifluropyridine-HCl, as well as pentafluoropyridine-HCl, was also performed. Equilibrium structures and binding energies for the gas-phase complexes illustrate two clear trends in how fluorine substitution affects hydrogen bond strength; increasing fluorination weakens these interactions, yet substitution at the 2- and 6-positions has the most pronounced effect. Bonding analyses for a select subset of these systems reveal shifts in electron density that accompany hydrogen bonding, and most notably, the values of the electron density at the N-H bond critical points among the stronger systems in this subset significantly exceed those typical for moderately strong hydrogen-bonds. We also explored the effects of dielectric media on the structural and bonding properties of these systems. For pyridine-HCl, 3-fluoropyridine-HCl, and 3,5-difluororpyridine-HCl, a transition to proton transfer-type structures is observed at ε-values of 1.2, 1.5, and 2.0, respectively. This is signaled by key structural changes, as well as an increase in the negative charge on the chorine, and dramatic shifts in topological properties of the H-Cl and N-H bonds. In the case of pentafluoropyridine-HCl, and 2,6-difluororpyridine-HCl, we do not predict proton transfer in dielectric media up to ε = 20.0. However, there are clear indications that the media enhance hydrogen-bond strength, and moreover, these observations are completely consistent with the experimental IR spectra.

RESUMEN

We have explored the structural and energetic properties of OC-BX3 (X = F, Cl, or Br) complexes using computations and low-temperature infrared spectroscopy. Quantum-chemical calculations have provided equilibrium structures, binding energies, vibrational frequencies, and B-C potential energy curves. The OC-BF3 system is a weak, long-bonded complex with a single minimum on the B-C potential (R(B-C) = 2.865 Å). For the remaining two complexes, OC-BCl3 and OC-BBr3, computations predict two stable minima on their B-C potential curves. The BCl3 system is a weak complex with a long bond (R(B-C) = 3.358 Å), but it exhibits a secondary, meta-stable minimum with a short bond length of 1.659 Å. For OC-BBr3, the system is a weak complex with a relatively short bond of 1.604 Å (according to wB97X-D/aug-cc-pVTZ), but also has a secondary minimum at R(B-C) = 3.483 Å. This long-bond structure is the global minimum according to CCSD/aug-cc-pVTZ. In addition, the long-bond forms of both OC-BCl3 and OC-BBr3 were observed in matrix-isolation IR experiments. The measured CO stretching frequencies were 2145 cm-1 and 2143 cm-1, respectively. No signals due to the short-bond forms of OC-BCl3 and OC-BBr3 were observed.

RESUMEN

The FCH2CN-BCl3 and ClCH2CN-BCl3 complexes were investigated by quantum-chemical computations and low-temperature, matrix-isolation-IR spectroscopy. Theory predicts two stable equilibrium structures, with distinctly different B-N distances, for both complexes. One set of structures, which correspond to the global energy minima, exhibit B-N distances of 1.610 and 1.604 Å for FCH2CN-BCl3 and ClCH2CN-BCl3, respectively (via M06-2X/aug-cc-pVTZ). The corresponding binding energies are 5.3 and 6.3 kcal/mol. For the metastable structures, the B-N distances are 2.870 and 2.865 Å for FCH2CN-BCl3 and ClCH2CN-BCl3, respectively, and the corresponding binding energies are 3.2 and 3.3 kcal/mol. Also, the barriers between these structures on the B-N distance potentials are 2.5 and 2.8 kcal/mol, respectively, relative to the secondary, long-bond minima. In addition, several IR bands of both FCH2CN-BCl3 and ClCH2CN-BCl3 were observed in nitrogen matrices, but the assigned bands are consistent with M06-2X predictions for the short-bond, minimum-energy structures. None of the observed IR bands could be assigned to the metastable, long-bond structures.

RESUMEN

The 1:1 and 2:1 complexes of FCH2CN and ClCH2CN with GeF4 have been investigated by M06/aug-cc-pVTZ calculations, low-temperature, thin-film IR spectroscopy, and an x-ray structure has been obtained for (FCH2CN)2-GeF4. Theoretical structures and binding energies for FCH2CN-GeF4 and ClCH2CN-GeF4 demonstrate that halogen substitution significantly weakens the Ge-N dative bonds. The Ge-N distances for the F-and Cl-complexes (2.447 and 2.407 Å, respectively) are about 0.2 Å longer than in CH3CN-GeF4, and the binding energies (6.5 and 6.9 kcal/mol) are 2 to 3 kcal/mol less. Furthermore, the Ge-N potential curves are flatter for the halogenated complexes, exhibit a greater response to dielectric media, and thus these systems are more prone to structural change in condensed-phases. For the 2:1 complexes, experimental and theoretical structure and frequency data are consistent with differences in the (calculated) gas-phase and solid-state structures. For (FCH2CN)2-GeF4 the calculated gas-phase structure has Ge-N distances about 0.3 Å longer those in the x-ray structure (2.366 Å vs. 2.059 Å (ave)). Also, low-temperature IR spectra of CH3CN/GeF4, FCH2CN/GeF4, and ClCH2CN/GeF4 thin films are consistent with the presence of 2:1 nitrile:GeF4 complexes, and the splitting patterns of the GeF-stretching bands (~700 cm-1) match predictions for the corresponding complexes, but are red-shifted relative to the gas-phase predictions, and reflect Ge-N bonds that are compressed in the solid-state, relative to predicted gas-phase structures.

RESUMEN

We have characterized the structural and energetic properties of CH3CN-BCl3via computations and matrix-IR spectroscopy. We find two equilibrium structures of the complex via computations. At the MP2/aug-cc-pVTZ level, the global minimum energy structure has a B-N distance of 1.601 Å, and a binding energy of 12.0 kcal mol(-1). The secondary structure lies 7.1 kcal mol(-1) higher in energy with a B-N distance of 2.687 Å and a binding energy of 4.9 kcal mol(-1). Computational scans of the B-N potential curve using both DFT and post-HF methods indicate that a significant barrier exists between these structures, and that it lies 1 to 2 kcal mol(-1) above the secondary minimum at a B-N distance of about 2.2 Å. We also observed several key, structurally-sensitive IR bands for six isotopic forms of the complex in neon matrices, including: the B-Cl asymmetric stretching band (ν) at 792 cm(-1) and the C-N stretching band (νCN) at 2380 cm(-1) (for the primary isotopomer, CH3C(14)N-(11)BCl3). These frequencies are consistent with computational predictions for the minimum-energy form of the complex. Energy decomposition analyses were conducted for CH3CN-BCl3 and also two related complexes, CH3CN-BF3 and CH3CN-BH3. These provide insight into the trend in Lewis acidity of the BX3 acceptors toward nitriles. Furthermore, these analyses indicate that the barrier along the B-N potential of CH3CN-BCl3 results from Pauli repulsion between the π electrons on the nitrile moiety and the chlorine atoms in BCl3, which is significant at relatively long distances where attractive bonding interactions fail to overcome it.

Asunto(s)

Boranos/química , Cloruros/química , Cianuros/química , Teoría Cuántica , Espectrofotometría Infrarroja/métodos

RESUMEN

We have conducted an extensive computational study of the structural and energetic properties of select acetonitrile-Group IV (A & B) tetrahalide complexes, both CH3CN-MX4 and (CH3CN)2-MX4 (M = Si, Ge, Ti; X = F, Cl). We have also examined the reactivity of CH3CN with SiF4, SiCl4, GeCl4, and TiCl4, and measured low-temperature IR spectra of thin films containing CH3CN with SiF4, GeCl4, or TiCl4. The six 1:1 complexes fall into two general structural classes. CH3CN-TiCl4, CH3CN-TiF4, and CH3CN-GeF4, exhibit relatively short M-N bonds (~2.3 Å), an intermediate degree of distortion in the MX4 subunit, and binding energies ranging from 11.0 to 13.0 kcal/mol. Conversely, CH3CN-GeCl4, CH3CN-SiF4, and CH3CN-SiCl4, are weakly bonded systems, with long M-N distances (>3.0 Å), little distortion in the MX4 subunit, and binding energies ranging from 3.0 to 4.4 kcal/mol. The structural features of analogous 2:1 systems resemble those of their 1:1 counterparts, whereas the binding energies (relative to three isolated fragments) are roughly twice as large. Calculated M-N potential curves in the gas phase and bulk, dielectric media are reported for all 1:1 complexes, and for two systems, CH3CN-GeF4 and CH3CN-SiF4, these data predict significant condensed-phase structural changes. The effect on the CH3CN-SiF4 potential is extreme; the curve becomes quite flat over a broad range in dielectric media, and at higher ε values, the global minimum shifts inward by about 1.0 Å. In bulk reactivity experiments, no reaction was observed between CH3CN and SiF4, SiCl4, or GeCl4, whereas CH3CN and TiCl4 were found to react immediately upon contact. Also, thin-film IR spectra indicate a strong interaction between CH3CN and TiCl4, yet only weak interactions between CH3CN and GeCl4 or SiF4 in the solid state.

RESUMEN

We have measured several IR bands of FCH2CN-BF3 and ClCH2CN-BF3 in solid nitrogen, argon, and neon. These bands include the B-F asymmetric stretch (νBF(a)), the B-F symmetric stretch (νBF(s)), the BF3 symmetric deformation or "umbrella" mode (δBF(s)), and the CN stretch (νCN). For both complexes, the frequencies of these modes shift across the various media, particularly the B-F asymmetric stretching band, and thus they indicate that the inert gas matrix environments significantly alter the structural properties of FCH2CN-BF3 and ClCH2CN-BF3. Furthermore, the frequencies shift in a manner that parallels the dielectric constant of these media, which suggests a progressive contraction of the B-N distances in these systems and also that it parallels the ability of the medium to stabilize the increase in polarity that accompanies the bond contraction. We have also mapped the B-N distance potentials for FCH2CN-BF3 and ClCH2CN-BF3 using several density functional and post-Hartree-Fock methods, all of which reveal a flat, shelflike region that extends from the gas-phase minimum (near 2.4 Å) toward the inner wall (to about 1.7 Å). Furthermore, we were able to rationalize the medium effects on the structure by constructing hybrid bond potentials composed of the electrostatic component of the solvation free energy and the gas-phase electronic energy. These curves indicate that the solvation energies are greatest at short B-N distances (at which the complex is more polar), and ultimately, the potential minima shift inward as the dielectric constant of the medium increases.

RESUMEN

We performed a systematic review and meta-analysis to examine whether a difficult embryo transfer or the presence of blood on the transfer catheter affects assisted reproduction outcomes. We searched the following databases: Cochrane Central Register of Controlled Trials (CENTRAL), Database of Abstracts of Reviews of Effects (DARE), MEDLINE, Embase, PsycINFO, Cumulative Index to Nursing and Allied Health Literature (CINAHL), and Literatura Latino-Americana e do Caribe em Ciências da Saúde (LILACS). We aimed to determine the risk ratio (RR) associated with difficult embryo transfer or the presence of blood on the transfer catheter for the following outcomes: live birth, clinical pregnancy, and miscarriage. We identified 3066 papers, of which 194 were reviewed and nine were included. The outcome of live birth was not reported in any of the included studies and the effect on miscarriage was too imprecise for any conclusions. Pooled analysis of five studies demonstrated lower clinical pregnancy rates following a non-easy embryo transfer (RR=0.75; 95% CI=0.66-0.86). This included three studies showing subjectively difficult transfers reducing clinical pregnancies (RR=0.67; 95% CI=0.51-0.87) and two studies in which the need for additional manoeuvers reduced clinical pregnancies (RR=0.78; 95% CI=0.67-0.91). The presence of blood on the transfer catheter did not affect clinical pregnancy rates (RR=0.96; 95% CI=0.82-1.14) in five studies. We concluded that low quality evidence suggests that a difficult embryo transfer but not a bloody catheter reduces the chance of achieving a clinical pregnancy. More good quality studies are needed to evaluate the effect of difficult embryo transfer and the presence of blood on the catheter on the main outcomes of assisted reproduction.

Asunto(s)

Transferencia de Embrión/efectos adversos , Contaminación de Equipos , Infertilidad Femenina/terapia , Técnicas Reproductivas Asistidas/efectos adversos , Aborto Espontáneo/etiología , Sangre , Catéteres , Implantación del Embrión , Transferencia de Embrión/instrumentación , Femenino , Humanos , Infertilidad Masculina/terapia , Masculino , Embarazo , Resultado del Embarazo , Índice de Embarazo , Técnicas Reproductivas Asistidas/instrumentación

RESUMEN

PURPOSE: Compare outcomes with vaginal gel versus intramuscular progesterone replacement in donor oocyte recipients. METHODS: A single-center retrospective analysis (January 2004-December 2006) evaluated pregnancy outcomes (serum human chorionic gonadotropin, implantation, clinical pregnancy, delivery, total pregnancy loss rates) for 225 recipients of embryos from donor (aged <32 years) oocytes. Vaginal progesterone gel (Crinone® 8%; 90 mg twice daily; n = 105) or intramuscular progesterone (50 mg once daily; n = 120) was started the afternoon of oocyte retrieval and continued until a negative pregnancy test or 10 weeks' gestation. RESULTS: There were no statistically significant differences between groups for the five pregnancy outcomes; numerical results favored vaginal progesterone in all cases. Confidence intervals showed vaginal gel was within, or <1% from, a noninferiority limit of 10% versus intramuscular progesterone for four of five pregnancy outcomes. CONCLUSIONS: Pregnancy outcomes were comparable for progesterone replacement with vaginal gel and intramuscular progesterone in an oocyte donation program.

Asunto(s)

Transferencia de Embrión , Terapia de Reemplazo de Hormonas , Infertilidad/terapia , Donación de Oocito , Progesterona/administración & dosificación , Adulto , Gonadotropina Coriónica/sangre , Preparaciones de Acción Retardada/administración & dosificación , Preparaciones de Acción Retardada/uso terapéutico , Femenino , Fertilización In Vitro , Humanos , Infertilidad/sangre , Inyecciones Intramusculares , Persona de Mediana Edad , Embarazo , Resultado del Embarazo , Índice de Embarazo , Progesterona/análogos & derivados , Progesterona/uso terapéutico , Estudios Retrospectivos , Inyecciones de Esperma Intracitoplasmáticas , Cremas, Espumas y Geles Vaginales

RESUMEN

The structural and energetic properties of CH(3)CN-BH(3), HCN-BH(3), FCH(2)CN-BH(3), and F(3)CCN-BH(3) have been examined via density functional theory and post-Hartree-Fock calculations. The B-N distances in these systems are notably short, less than 1.6 Å, and the binding energies are substantial, about 20 kcal/mol. The properties of these systems do vary as a result of the nitrile substituent, but surprisingly, more electronegative substituents result in shorter B-N distances. For example, the B-N distance for F(3)CCN-BH(3) is 1.576 Å via MP2/aug-cc-pVTZ, while that for CH(3)CN-BH(3) is 1.584 Å. However, the binding energies vary as expected, from 17.4 kcal/mol in the case of F(3)CCN-BH(3) to 22.6 kcal/mol for CH(3)CN-BH(3) (via MP2/aug-cc-pVTZ). The extent of charge transfer and the degree of covalent character in the B-N bonds were explored by a natural bond orbital analysis, and the atoms in molecules formalism, respectively, and do provide some rationale for the substituent effects. Frequency calculations indicate that BH(3)-localized vibrational modes do shift appreciably upon complex formation, especially the BH(3) asymmetric stretch. For CH(3)CN-BH(3), experimental and calculated frequency shifts compare well for the asymmetric BH(3) bending mode, but the observed shift for the BH(3) asymmetric stretch, the most structurally sensitive mode, is about 40 cm(-1) larger than the predictions. While this may suggest a very slight contraction of the B-N bond upon formation of solid CH(3)CN-BH(3) (for which experimental data are available) the balance of evidence indicates that no significant medium effects occur in these complexes. We also discuss the distinct differences between these complexes and their BF(3) analogs. The underlying reasons for the markedly different structural properties are illustrated through an energy decomposition analysis applied to HCN-BH(3) and HCN-BF(3). These data indicate that less Pauli repulsion of the electrons on each respective subunit is the most significant factor that favors the overall stability of the BH(3) complex.

RESUMEN

The structure, bonding, and energetic properties of the N(2)-BH(3) complex are reported as characterized by density functional theory (DFT) and post-Hartree-Fock (HF) calculations. The equilibrium structure of the complex exhibits a short B-N distance near 1.6 A, comparable to that of a strong acid-base complex like H(3)N-BH(3). However, the binding energy is only 5.7 kcal/mol at the CCSD(T)/6-311+G(2df,2dp) level of theory, which is reminiscent of a weak, nonbonded complex. Natural bond orbital (NBO) and atoms in molecules (AIM) analyses of the electron density from both DFT and post-HF calculations do indicate that the extent of charge transfer and covalent character in the B-N dative bond is only somewhat less than in comparable systems with fairly large binding energies (e.g., H(3)N-BH(3) and OC-BH(3)). Energy decomposition analysis indicates key differences between the N(2), CO, and NH(3) complexes, primarily associated with the natures of the lone pairs involved (sp vs sp(3)) and the donor/acceptor characteristics of the relevant occupied and virtual orbitals, both sigma and pi. Also, CCSD/6-311+G(2df,2dp) calculations indicate that the B-N distance potential is rather anharmonic and exhibits a flat, shelf-like region ranging from 2.1 to 2.5 A that lies about 1.5 kcal/mol above the minimum at 1.67 A. However, this region is more sloped and lies about 2.5 kcal/mol above the equilibrium region according to the CCSD(T)/6-311+G(2df,2dp)//CCSD/6-311+G(2df,2dp) potential. A 1D analysis of the vibrational motion along the B-N stretching coordinate in the CCSD/6-311+G(2df,2dp) potential indicates that the average B-N distance in the ground vibrational state is 1.71 A, about 0.04 A longer than the equilibrium distance. Furthermore, the vibrationally averaged distance obtained via an analysis of the CCSD(T)/6-311+G(2df,2dp)//CCSD/6-311+G(2df,2dp) potential was found to be 0.03 A longer than the CCSD(T)/6-311+G(2df,2dp) minimum.

RESUMEN

OBJECTIVE: To perform an analysis of data with consideration for the current clinically accepted vaginal progesterone (P) or intramuscular (IM) P dosing regimens and the clinically relevant randomized clinical trials published during the time frame 1992 to 2008. DESIGN: Meta-analysis of progesterone luteal support in IVF cycles using odds ratios (OR) and 95% confidence intervals (CI). SETTING: Previously conducted randomized clinical trials meeting acceptance criteria. PATIENT(S): Infertility patients. INTERVENTION(S): Progesterone (50 mg) IM daily or 200 mg P-in-oil capsules three times a day vaginally or 90 mg P in bioadhesive gel daily vaginally. MAIN OUTCOME MEASURE(S): Clinical pregnancy, ongoing pregnancy, miscarriage. RESULT(S): This analysis showed a comparable effect between vaginal progesterone as an oil-in-capsule or as a bioadhesive gel and IM P administration on the endpoints of clinical pregnancy (OR = 0.91, 95% [CI 0.74, 1.13]) and ongoing pregnancy (OR = 0.94, 95% [CI 0.71, 1.26]). A nominally significantly lower rate of miscarriage was observed with vaginal P compared with IM P (OR = 0.54, 95% [CI 0.29, 1.02]). CONCLUSION(S): Administration of vaginal P is comparable to administration of IM P for luteal phase support in assisted reproductive technology.

Asunto(s)

Cuerpo Lúteo/fisiología , Fertilización In Vitro/métodos , Progesterona/administración & dosificación , Progesterona/uso terapéutico , Técnicas Reproductivas Asistidas/normas , Administración Intravaginal , Administración Oral , Cápsulas , Cuerpo Lúteo/efectos de los fármacos , Femenino , Humanos , Inyecciones Intramusculares , Oportunidad Relativa , Embarazo , Ensayos Clínicos Controlados Aleatorios como Asunto

RESUMEN

Combined experimental and computational studies suggest that the iron-mediated aziridination of cis-1-phenylpropene proceeds along two mechanistic pathways that share a common imidoiron(IV) intermediate. One pathway involves a second species, proposed to be an azametallacyclobutane intermediate, which collapses to provide the syn-aziridine product. A second, parallel pathway is responsible for the formation of an anti-aziridine.

RESUMEN

We sought to compare frequency and duration of hepatic encephalopathy-related hospitalizations during rifaximin versus lactulose treatment. Hospitalizations, clinical efficacy data, and adverse events obtained from charts of 145 patients with hepatic encephalopathy who received lactulose (30 cc twice daily) for > or = 6 months and then rifaximin (400 mg 3 times a day) for > or = 6 months compared last 6 months on lactulose (lactulose period) to first 6 months on rifaximin (rifaximin period). Fewer hospitalizations (0.5 versus 1.6; P < .001), fewer days hospitalized (2.5 versus 7.3; P < .001), fewer total weeks hospitalized (0.4 versus 1.8; P < .001), and lower hospitalization charges per patient ($14,222 versus $56,635) were reported during the rifaximin period. More patients had asterixis, diarrhea, flatulence, and abdominal pain during the lactulose period (P < .001). Treatment of hepatic encephalopathy with rifaximin was associated with lower hospitalization frequency and duration, lower hospital charges, better clinical status, and fewer adverse events.

Asunto(s)

Fármacos Gastrointestinales/uso terapéutico , Encefalopatía Hepática/tratamiento farmacológico , Hospitalización/estadística & datos numéricos , Lactulosa/uso terapéutico , Rifamicinas/uso terapéutico , Adulto , Femenino , Fármacos Gastrointestinales/economía , Encefalopatía Hepática/economía , Hospitalización/economía , Humanos , Lactulosa/economía , Tiempo de Internación , Cirrosis Hepática/complicaciones , Masculino , Persona de Mediana Edad , New Jersey , Rifamicinas/economía , Rifaximina

RESUMEN

We have re-examined the B-N distance potential of CH3CN-BF3 using MP2, DFT, and high-accuracy multicoefficient methods (MCG3 and MC-QCISD). In addition, we have solved a 1-D Schrödinger equation for nuclear motion along the B-N stretching coordinate, thereby obtaining vibrational energy levels, wave functions, and vibrationally averaged B-N distances. For the gas-phase, MCG3//MP2/aug-cc-pVTZ potential, we find an average B-N distance of 1.95 A, which is 0.13 A longer than the corresponding equilibrium value. In turn, this provides solid evidence that the long-standing discrepancy between the experimental (R(B-N) = 2.01 A) and theoretical (R(B-N) = 1.8 A or R(B-N) = 2.2-2.3 A) distances may be genuine, stemming from large amplitude vibrational motion in the B-N stretching coordinate. Furthermore, we have examined the effects of low-dielectric media (epsilon = 1.1-5.0) on the structure of CH3CN-BF3 by calculating solvation free energies (PCM/B97-2/aug-cc-pVTZ) and adding them to the gas-phase, MCG3 potential. These calculations demonstrate that the inner region of the potential is stabilized to a greater extent by these media, and correspondingly, the equilibrium and average B-N distances decrease with increasing dielectric constant. We find that the crystallographic structural result (R(B-N) = 1.63 A) is nearly reproduced with a dielectric constant of only 5.0, and also predict significant structural changes for epsilon values of 1.1-1.5, consistent with results from matrix-isolation-IR experiments.

RESUMEN

We have observed several IR bands of CH3CN-BF3 in neon and nitrogen matrices. For the 11B isotopomer in neon matrices, we observed the BF3 symmetric deformation band (nu7) as a doublet at 600 and 603 cm(-1), the BF3 symmetric stretching band (nu6) as a doublet at 833 and 838 cm(-1), the BF3 asymmetric stretching mode (nu13) at 1281 cm(-1) (partially obscured), and the C-N stretching mode (nu2) as a doublet at 2352 and 2356 cm(-1). The nitrogen matrix data are largely consistent with those reported recently, though we do propose a refinement of one band assignment. Comparisons of the frequencies of a few key, structurally sensitive vibrational modes either observed in various condensed-phase environments or calculated for two minimum-energy gas-phase structures indicate that inert matrix media significantly alter the structural properties of CH3CN-BF3. Specifically, the B-N dative bond compresses relative to the gas phase and other concomitant changes occur as well. Furthermore, the frequency shifts depict structural changes that occur across the various matrix hosts in a manner that largely parallels the degree of stabilization offered by these inert media.

RESUMEN

BACKGROUND: Suppressive therapy has not been studied during the first year after acquisition of genital herpes, the time of maximum frequency of reactivation, potential for transmission, and impact on quality of life. OBJECTIVE: The objective of this study was to evaluate the effectiveness of suppressive therapy with valacyclovir initiated within 3 months of infection. STUDY DESIGN: The authors conducted a double-blind, randomized, controlled trial of 1.0 g valacyclovir daily versus placebo for 6 months in 119 patients. RESULTS: Herpes simplex virus (HSV) type 2 and HSV-1 were documented in 75 and 22 patients, respectively. In intention-to-treat analysis, annualized rates of symptomatic recurrences for valacyclovir and placebo, respectively, were 1.7 +/- 2.7 (mean +/- standard deviation) and 3.4 +/- 4.0 outbreaks per year (P = 0.012). Time to first recurrence was 80 +/- 47 days for valacyclovir and 54 +/- 49 days for placebo (P = 0.001). The differences in favor of valacyclovir were greatest in patients with confirmed HSV-2 infection. The Recurrent Genital Herpes Quality of Life score in HSV-2 infected patients rose 11.9 +/- 11.1 points for valacyclovir and 5.9 +/- 9.1 points for placebo (P = 0.040). CONCLUSIONS: Early suppressive therapy with valacyclovir reduces symptomatic recurrent outbreaks, especially in patients with HSV-2 infection. Valacyclovir therapy was associated with improved herpes-related quality of life.

Asunto(s)

Aciclovir/análogos & derivados , Antivirales/uso terapéutico , Herpes Genital/tratamiento farmacológico , Herpes Genital/psicología , Calidad de Vida , Valina/análogos & derivados , Aciclovir/administración & dosificación , Aciclovir/uso terapéutico , Adolescente , Adulto , Instituciones de Atención Ambulatoria , Antivirales/administración & dosificación , Método Doble Ciego , Esquema de Medicación , Femenino , Herpes Genital/patología , Herpesvirus Humano 1 , Herpesvirus Humano 2 , Humanos , Masculino , Oregon , Proyectos Piloto , Recurrencia , Resultado del Tratamiento , Valaciclovir , Valina/administración & dosificación , Valina/uso terapéutico , Washingtón

RESUMEN

The structural properties of the singly halogenated derivatives of CH(3)CN-BF(3) (X-CH(2)CN-BF(3): X = F, Cl, Br, I) have been investigated via single-crystal X-ray crystallography, solid-state infrared spectroscopy, and correlated electronic-structure theory. Taken together, these data illustrate large differences between the gas-phase and solid-state structures of these systems. Calculated gas-phase structures (B3PW91/aug-cc-pVTZ) of FCH(2)CN-BF(3), ClCH(2)CN-BF(3), and BrCH(2)CN-BF(3) indicate that the B-N dative bonds in these systems are quite weak, with distances of 2.422, 2.374, and 2.341 A, respectively. However, these distances, as well as other calculated structural parameters and normal-mode vibrational frequencies, indicate that the dative interactions do become slightly stronger in proceeding from F- to Br-CH(2)CN-BF(3). In contrast, solid-state structures for FCH(2)CN-BF(3), ClCH(2)CN-BF(3), and ICH(2)CN-BF(3) from X-ray crystallography all have B-N distances that are quite short, about 1.65 A. Thus, the B-N distances of the F- and Cl-containing derivatives contract by over 0.7 A upon crystallization. Large shifts in the vibrational modes involving motions of the BF(3) subunit parallel these structural changes. An X-ray crystal structure could not be determined for BrCH(2)CN-BF(3)(s), but the solid-state IR spectrum is consistent with those obtained previously for related complexes and suggests that the solid-state structure resembles those of the others, and in turn, implicates a large gas-solid structural difference for this species as well.

RESUMEN

The structure, dipole moment, binding energy, and vibrational frequencies of HCN-BF3 are investigated via 12 DFT methods as well as MP2, MC-QCISD, and MCG3 calculations. By comparing the DFT results to both experimental data and results from post-Hartree-Fock molecular orbital methods, we gauge the effectiveness of various density functionals in modeling this fairly weak donor-acceptor system. For structural data, B3PW91, B98, and mPWPW91 provide results that compare favorably with experiment. All DFT methods that yield a reasonable structure predict dipole moments that are only slightly larger than the experimental value by 0.1 to 0.2 D. Moreover, to ensure that a comparison of calculated (equilibrium) and experimental (vibrationally averaged) data is indeed valid for this system, the B-N distance potential is calculated using B3PW91, MP2, and MCG3, and the one-dimensional Schrödinger equation for motion along this bond-stretching coordinate is solved to obtain vibrational energy levels, wave functions, and expectation values of the B-N distance and dipole moment. In every instance, average bond lengths differ by only a few thousandths of an angstrom from the corresponding equilibrium values, and dipole moments are unchanged to within hundredths of a debye. For vibrational frequencies, B3PW91 agrees most closely with gas-phase experimental data for BF3 and also with MP2 calculations of the BF3-localized modes in the complex; mPW1PW91 and B3LYP agree nearly as well. However, despite the effectiveness of DFT for structure, dipole moment, and vibrational frequencies, all DFT methods fail to predict a binding energy that compares favorably to the MCG3//MC-QCISD result of -5.7 kcal/mol.