Alkali metal salts of 4-hydroxybenzoic acid: a structural and educational study.

As part of an educational exercise designed to introduce school students to the technique of single-crystal X-ray diffraction and enhance their understanding of primary and secondary bonding, a group of nine secondary school students was given the opportunity to prepare new compounds and to solve and refine data collected on the crystalline materials they had prepared. Their investigation of the alkali metal salts of 4-hydroxybenzoic acid (H2hba) yielded nine new compounds and their structures are described in this article. Whilst the salts might be expected to have similar atomic arrangements, there are significant differences in their structures. Although H2hba is a relatively simple organic molecule, it displays remarkable coordinative flexibility, forming ionic solids containing the uncharged molecule, the monoanion Hhba- or the dianion hba2-. A common feature of the structures is their layered arrangement: alternating hydrophilic layers made up of closely packed metal-oxygen polyhedra separated by the hydrophobic component of the hydroxybenzoate linking units. Close packing of these units seems to be a dominant influence in determining the overall structure. The hydroxybenzoate units are usually both parallel and antiparallel with their immediate neighbours, with packing that can be edge-to-face, face-to-face or a mixture of the two. Hydrogen bonding plays a key role in the structure of most compounds and a short strong hydrogen bond (SSHB) is observed in two of the networks. The compounds of 4-hydroxybenzoic acid, C7H6O3, described here are: poly[di-µ-aqua-µ-4-oxidobenzoato-dilithium], [Li2(C7H4O3)(H2O)2]n, 1, poly[triaqua-µ-4-oxidobenzoato-dilithium], [Li2(C7H4O3)(H2O)3]n, 2, poly[µ-4-hydroxybenzoato-lithium], [Li(C7H5O3)]n, 3, catena-poly[4-hydroxybenzoate [[diaquasodium]-di-µ-aqua]], {[Na(H2O)4](C7H5O3)}n, 4, poly[di-µ-aqua-aqua-µ-4-hydroxybenzoato-potassium], [K(C7H5O3)(H2O)3]n, 5, poly[µ-aqua-µ-4-hydroxybenzoato-potassium], [K(C7H5O3)(H2O)]n, 6, poly[aqua-µ-4-hydroxybenzoato-rubidium], [Rb(C7H5O3)(H2O)]n, 7, poly[aqua-µ-4-hydroxybenzoato-caesium], [Cs(C7H5O3)(H2O)]n, 8, poly[[µ-aqua-aqua(µ-4-hydroxybenzoato)(4-hydroxybenzoic acid)sodium] monohydrate], {[Na(C7H5O3)(C7H6O3)(H2O)2]·H2O}n, 9, poly[[(µ-4-hydroxybenzoato)(µ-4-hydroxybenzoic acid)rubidium] monohydrate], {[K(C7H5O3)(C7H6O3)]·H2O}n, 10, and poly[[(µ-4-hydroxybenzoato)(µ-4-hydroxybenzoic acid)rubidium] monohydrate], {[Rb(C7H5O3)(C7H6O3)]·H2O}n, 11.

The Effect of Preoperative Administration of Intravenous Tranexamic Acid During Revision Hip Arthroplasty: A Retrospective Study.

BACKGROUND: Revision hip arthroplasty poses several challenges, including the management of perioperative blood loss. Recent studies have validated the use of tranexamic acid in primary total hip arthroplasty, showing reduced blood loss and decreased number of allogenic blood transfusions. The effectiveness of tranexamic acid has not been well studied in the revision hip arthroplasty setting. METHODS: We performed a retrospective review of 1,072 patients who underwent revision hip arthroplasty at our institution from 2008 to 2016. A total of 634 patients met the inclusion criteria, and comparisons were made between 232 consecutive patients without the use of tranexamic acid and 402 consecutive patients with the use of tranexamic acid. Patients were subdivided into 4 groups based on the complexity of revision surgical procedures: (1) major revision, (2) isolated femoral component revision, (3) isolated acetabular component revision, and (4) isolated femoral head and acetabular liner exchange. Within these groups, we compared the demographic data, estimated intraoperative blood loss, perioperative blood units transfused, postoperative hemoglobin drop, and thromboembolic complications between patients receiving either tranexamic acid or no antifibrinolytic therapy. RESULTS: The primary outcomes of our study (estimated intraoperative blood loss, postoperative hemoglobin drop, and perioperative blood transfusion) were all reduced in patients who received tranexamic acid compared with patients who received no antifibrinolytic therapy. When analyzed on the basis of the complexity of surgical revision, there was a decrease in estimated intraoperative blood loss following tranexamic acid administration in the major revision group (845 compared with 1,095 mL; p < 0.001). The postoperative drop in hemoglobin was lower in the major revision group with tranexamic acid administration (by 8.9 g/L; p < 0.01) and the isolated acetabular component revision group with tranexamic acid administration (by 11.9 g/L; p < 0.001). The need for perioperative blood transfusion was reduced across all revisions treated with tranexamic acid (major revision group, 1.79 compared with 3.33 units, p < 0.001; femoral revision only, 0.97 compared with 2.25 units, p < 0.01; acetabular revision only, 0.73 compared with 1.72 units, p < 0.001; and head and liner exchange, 0.15 compared with 0.89 unit, p < 0.05). CONCLUSIONS: Based on this study, preoperative administration of intravenous tranexamic acid in revision hip arthroplasty reduces allogenic blood transfusions and perioperative blood loss. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.