The Rich Solid-State Phase Behavior of l-Phenylalanine: Disappearing Polymorphs and High Temperature Forms.

After years of controversy over the solid state structure of the essential amino acid l-phenylalanine, four different polymorphic forms were published recently. The common form I has symmetry P21 with four molecules in the asymmetric unit (Z' = 4), similar to form III, but with a different arrangement of molecular bilayers. Form II, obtained from the hydrate at very low humidity, is unrelated to forms I and III, as is the high-density form IV. The present investigation demonstrates that this prototype aromatic amino acid has two additional high-temperature phases Ih and IIIh obtained from form I and form III above 458 and 440 K, respectively, when flipping between two alternative side-chain conformations becomes dynamic and causes pairs of molecules, initially crystallographically independent, to become equivalent above a sharp transition temperature. These abrupt and reversible phase changes occur with a reduction of Z' from 4 (low T) to 2 (high T) and modified crystal symmetry. We furthermore experienced an example of disappearing polymorph for form I which after growing form III in one of our laboratories could no longer be crystallized at room temperature. In contrast, form III crystals may be irreversibly converted to form I crystals as a result of sliding of molecular bilayers in the crystal at elevated temperature. No conversions between the high-temperature forms Ih and IIIh were found. The remarkable crystallographic results are here corroborated by Molecular Dynamics and metadynamics simulations of the form I - form III system.

The Rich Solid-State Phase Behavior of dl-Aminoheptanoic Acid: Five Polymorphic Forms and Their Phase Transitions.

The rich landscape of enantiotropically related polymorphic forms and their solid-state phase transitions of dl-2-aminoheptanoic acid (dl-AHE) has been explored using a range of complementary characterization techniques, and is largely exemplary of the polymorphic behavior of linear aliphatic amino acids. As many as five new polymorphic forms were found, connected by four fully reversible solid-state phase transitions. Two low temperature forms were refined in a high Z' crystal structure, which is a new phenomenon for linear aliphatic amino acids. All five structures consist of two-dimensional hydrogen-bonded bilayers interconnected by weak van der Waals interactions. The single-crystal-to-single-crystal phase transitions involve shifts of bilayers and/or conformational changes in the aliphatic chain. Compared to two similar phase transitions of the related amino acid dl-norleucine, the enthalpies of transition and NMR chemical shift differences are notably smaller in dl-aminoheptanoic acid. This is explained to be a result of both the nature of the conformational changes and the increased chain length, weakening the interactions between the bilayers.

The structure of PbCl2 on the {100} surface of NaCl and its consequences for crystal growth.

The role that additives play in the growth of sodium chloride is a topic which has been widely researched but not always fully understood at an atomic level. Lead chloride (PbCl2) is one such additive which has been reported to have growth inhibition effects on NaCl {100} and {111}; however, no definitive evidence has been reported which details the mechanism of this interaction. In this investigation, we used the technique of surface x-ray diffraction to determine the interaction between PbCl2 and NaCl {100} and the structure at the surface. We find that Pb2+ replaces a surface Na+ ion, while a Cl- ion is located on top of the Pb2+. This leads to a charge mismatch in the bulk crystal, which, as energetically unfavourable, leads to a growth blocking effect. While this is a similar mechanism as in the anticaking agent ferrocyanide, the effect of PbCl2 is much weaker, most likely due to the fact that the Pb2+ ion can more easily desorb. Moreover, PbCl2 has an even stronger effect on NaCl {111}.

Concentration-Dependent Adsorption of CsI at the Muscovite-Electrolyte Interface.

The interfacial structure of muscovite in contact with aqueous CsI solutions was measured using surface X-ray diffraction for several CsI concentrations (2-1000 mM). At CsI concentrations up to 200 mM, Cs+ adsorption is likely hindered by H3O+, as both cations compete for the adsorption site above the muscovite hexagonal cavity. Above this concentration, more Cs+ adsorbs than is required to compensate the negatively charged muscovite surface, which means that coadsorption of an anion takes place. The I- anion does not coadsorb in an ordered manner. Moreover, the hydration ring and water layers do not change significantly as a function of the CsI concentration.

Do solid-to-solid polymorphic transitions in DL-norleucine proceed through nucleation?

DL-Norleucine is a molecular crystal exhibiting two enantiotropic phase transitions. The high temperature α ↔ γ transition has been shown to proceed through nucleation and growth [Mnyukh et al., J. Phys. Chem. Solids, 1975, 36, 127]. We focus on the low temperature ß â†” α transition in a combined computational and experimental study. The temperature dependence of the structural and energetic properties of both polymorphic forms is nearly identical. Molecular dynamics simulations and nudged elastic band calculations of the transition process itself, suggest that the transition is governed by cooperative movements of bilayers over relatively large energy barriers.

High risk for neoplastic transformation of endometriosis in a carrier of Lynch syndrome.

Lynch syndrome is an autosomal dominant cancer-susceptibility disorder caused by mutations in DNA mismatch repair genes. Women with Lynch syndrome have an increased lifetime risk for endometrial and ovarian cancers. While there is evidence of efficacy for prophylactic surgery, no standard recommendations have been developed to support screening for premalignant endometrial and ovarian epithelial lesions in high-risk women. Here, we report a case of a healthy woman carrying a germline mutation in MLH1 gene with endometrial intra-epithelial neoplasia and ovarian endometriotic lesions exhibiting a loss of MLH1 protein expression. This case report illustrates the malignant potential of endometriosis, and highlights the need for a meticulous management of gynecologic premalignant precursor lesions in reducing cancer risk among related Lynch syndrome women.

Surgical management of endometriosis.

The efficacy of medical and surgical treatment of endometriosis-associated infertility and pelvic pain is a source of ongoing controversy. Complete resolution of endometriosis is not yet possible and current therapy has three main objectives: (1) to reduce pain; (2) to increase the possibility of pregnancy; and (3) to delay recurrence for as long as possible. It is possible that a consensus will never be reached on the optimal treatment of minimal and mild endometriosis. In case of moderate and severe endometriosis-associated infertility, the combined approach (operative laparoscopy with a gonadotropin-releasing hormone (GnRH) agonist) should be considered as 'first-line' treatment. The mean pregnancy rate of 50% reported in the literature following surgery provides scientific proof that operative treatment should first be undertaken to give our patients the best chance of conceiving naturally. In case of rectovaginal adenomyotic nodules, surgery must be considered as first-line therapy, medical therapy being relatively in-efficacious.

Pelvic mass in a woman with Mayer-Rokitansky-Kuster-Hauser syndrome.

Magnetic resonance imaging and laparoscopy demonstrated the presence of a myoma in a woman with Rokitansky syndrome.

Laparoscopic management of peritoneal endometriosis, endometriotic cysts, and rectovaginal adenomyosis.

Peritoneal endometriosis is probably caused by the implantation of regurgitated menstrual cells. The ovarian endometrioma is the consequence of non-hormone-regulated bleeding from intraovarian epithelial inclusions after they have undergone metaplasia into endometrial-like tissue. Rectovaginal adenomyosis is, in fact, an adenomyotic lesion and can develop from Müllerian rests. In conclusion, peritoneal endometriosis, ovarian endometriosis, and rectovaginal adenomyotic nodules must be considered as three separate entities with different pathogeneses that require a different therapeutic approach.

Pre- and post-surgical management of endometriosis.

The efficacy of medical and surgical treatment of endometriosis-associated infertility and pelvic pain is a source of questions and controversies. Complete resolution of endometriosis is not yet possible, but therapy has essentially three main objectives: (1) to reduce pain, (2) to increase the possibility of pregnancy, and (3) to delay recurrence for as long as possible. It could be concluded that a consensus will probably never be reached on minimal and mild endometriosis. In cases of moderate and severe endometriosis-associated infertility, the combined approach (operative laparoscopy with gonadotropin-releasing hormone agonist) must be considered as first-line treatment. The mean pregnancy rate of 50% reported in the literature following surgery provides scientific proof that operative treatment should first be undertaken to give our patients the best chance of conceiving naturally. In cases of rectovaginal adenomyotic nodule, surgery must be considered as first-line therapy, medical therapy being relatively inefficacious.

Safety of conservative management and fertility outcome in women with borderline tumors of the ovary.

OBJECTIVE: To assess the safety of fertility-sparing treatment and the remaining chance of childbearing after surgery. DESIGN: Retrospective clinical study. DESIGN: Gynecology department of a university teaching hospital. PATIENT(S): Seventy-five women underwent surgical management in our institution between 1986 and 2001 for borderline tumors of the ovary. INTERVENTION(S): Fifty-nine patients were treated by radical, fertility-compromising surgery. The remaining 16 patients underwent conservative surgery, preserving the uterus and at least some functional ovarian tissue. Seven unilateral adnexectomies, one simple cystectomy, and two adnexectomies associated with contralateral cystectomy were performed. MAIN OUTCOME MEASURE(S): Recurrence, survival, and pregnancy rates. RESULT(S): The observed recurrence rates after radical and conservative surgery were 0.0% and 18.7%, respectively. No disease-related deaths occurred in any group; there is no significant difference in survival rates. We can report 12 pregnancies in 7 of 11 women who underwent fertility-sparing management and who wished to become pregnant. CONCLUSION(S): In certain circumstances, conservative management offers a safe solution for borderline tumors of the ovary. Recurrence is noted significantly more often after this type of treatment, but all cases of recurrent disease can be detected with close follow-up and can be treated accordingly. No significant change in survival rates was found. Moreover, the pregnancy rate in women desiring pregnancy, those treated conservatively, was as high as 63.6%.

The efficacy of medical and surgical treatment of endometriosis-associated infertility and pelvic pain.

This article is a review of the efficacy of medical and surgical treatment of endometriosis-associated infertility and pelvic pain. Endometriosis is the cause of pelvic pain (dysmenorrhea, dyspareunia) and infertility in more than 35% of women of reproductive age. Complete resolution of endometriosis is not yet possible but therapy has essentially three main objectives: (1) to reduce pain; (2) to increase the possibility of pregnancy; (3) to delay recurrence for as long as possible. It could be concluded that a consensus will probably never be reached on minimal and mild endometriosis. Nevertheless, because the Canadian study reported a large number of cases, we strongly support the view that visible endometriosis must be removed at the time of surgery. In cases of moderate and severe endometriosis-associated infertility, the combined approach (operative laparoscopy with GnRH-a) must be considered as 'first-line' treatment. The mean pregnancy rate of 50% reported in the literature following surgery provides scientific proof that operative treatment should be undertaken first to give our patients the best chance of conceiving naturally.