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P Langan

Publications and source records attributed to P Langan.

At least 19 recordsLinked to original sources
PubMed2001

A low-temperature neutron diffraction study of Mn12-acetate.

In the low-temperature region, where the dodecanuclear mixed-valence manganese carboxylate hexadecaacetatotetraaquadodecaoxododecamanganese bis(acetic acid) tetrahydrate, [Mn(12)O(12)(C(2)D(3)O(2))(16)(H(2)O)(4)].2C(2)HD(3)O(2).4H(2)O, displays unusual magnetic properties, its structure is similar to that previously determined at room temperature [Lis (1980). Acta Cryst. B36, 2042-2046], differing only by a small change in the configuration of one of the coordinated acetate groups, related to the formation of additional hydrogen bonds, and by the orientation of the methyl groups. Since most of the magnetization density of this system resides on the Mn atoms, the consequences of these rearrangements for the magnetic properties of the compound are small.

Journal Article↗
PubMed2001

X-ray structure of mercerized cellulose II at 1 a resolution.

A revised crystal structure for mercerized cellulose based on high-resolution synchrotron X-ray data collected from ramie fibers is reported (space group P2(1), a = 8.10(3) A, b = 9.03(3) A, c = 10.31(5) A, gamma = 117.10(5) degrees; 751 reflections in 304 composite spots; theta < 21.11 degrees; lambda = 0.7208 A; LALS refinement with d > 1.5 A, R' ' = 0.16; SHELX97 refinement with d > 1 A, R = 0.21). As with regenerated cellulose the crystal structure consists of antiparallel chains with different conformations but with the hydroxymethyl groups of both chains near the gt position. However, the conformation of the hydroxymethyl group of the center chain in the structure reported here differs significantly from the conformation in regenerated cellulose. This may be related to a large observed difference in the amount of hydroxymethyl group disorder: approximately 30% for regenerated cellulose and approximately 10% for mercerized cellulose.

Boehmeria↗
PubMed1999

High resolution neutron fibre diffraction data on hydrogenated and deuterated cellulose.

High-resolution fibre neutron diffraction data were recorded from cellulose samples on a D19 diffractometer at the Institut Laue-Langevin (Grenoble). Highly crystalline cellulose I samples from Cladophora (cellulose I alpha + I beta) or Halocynthia (cellulose I beta) origin were prepared in the form of oriented films. Samples were studied in a hydrogenated form and in a hydrogen-deuterium exchanged deuterated form corresponding to all OH moieties being replaced by ODs. These samples, which diffracted to a resolution of around 0.9 A, gave diffraction diagrams consisting of several hundred independent diffraction spots. Crystalline cellulose II fibres resulting from the mercerization of flax were also studied in a hydrogenated form using NaOH/H2O as mercerizing medium and in a deuterated form using NaOD/D2O. Both of these samples diffracted to around 1.2 A, giving fibre diffraction diagrams slightly less resolved than those of cellulose I, but still consisting of more than one hundred independent diffraction spots. For cellulose I as well as for cellulose II, significant differences between the hydrogenated and deuterated patterns were observed and recorded. These new data should lead to improved structures for cellulose and direct identification of the position of hydrogen atoms involved in hydrogen bonding.

Cellulose↗
PubMed1999

Neutron Laue diffraction studies of coenzyme cob(II)alamin.

Using a recently designed neutron single-crystal diffractometer utilizing a narrow-band Laue concept (LADI), diffraction data were collected from a crystal of the coenzyme cob(II)alamin (B12r), crystallized from a mixture of D2O and perdeuterated acetone. The instrument was placed at the end of a cold neutron guide at the Institute Laue Langevin (ILL, Grenoble, France), and data collection with neutrons of 1.8-8.0 A wavelength to a crystallographic resolution of 1.43 A was complete after about 36 h. This compares favourably with a previous experiment utilizing the same crystal specimen, where more than four weeks were required to collect monochromatic diffraction data to about 1 A resolution. Using the Laue data, the structure was solved by molecular replacement with the known X-ray crystal structure. Difference density maps revealed the atomic positions (including deuterium atoms) of seven ordered solvent water molecules and two (partially disordered) acetone molecules. These density maps were compared with corresponding maps computed with monochromatic neutron-diffraction data collected to 1. 0 A resolution using the same crystal specimen, as well as to maps derived from high-resolution (0.90 A) synchrotron X-ray data. In spite of the better definition of atomic positions in the two high-resolution maps, the 1.43 A LADI maps show considerable power for the determination of the location of hydrogen and deuterium positions.

Coenzymes↗
PubMed1999

Negative-pressure pulmonary edema: a complication of shoulder arthroscopy.

Negative-pressure pulmonary edema has been increasingly reported in surgical literature since 1977, yet there are no references to this condition in current orthopedic textbooks. We report a case of negative-pressure pulmonary edema occurring during arthroscopic surgery of the shoulder. The patient required reintubation for 5 days and hospitalization for 1 week. Because arthroscopic surgery is widely believed to be without complications, we want to make orthopedic surgeons aware of the possibility of negative-pressure pulmonary edema.

Adult↗
PubMed1997

A high-angle neutron fibre diffraction study of the hydration of deuterated A-DNA.

A high-angle neutron fibre diffraction study of the hydration of A-DNA has been performed using the single-crystal diffractometer D19 at the Institut Laue-Langevin (Grenoble, France). The sample was prepared using deuterated DNA extracted from E. Coli cells cultured on deuterated nutrients. In common with our previous neutron fibre diffraction studies of DNA, this work exploits the ability to isotopically replace H2O around the DNA by D2O. However this study benefitted additionally from the fact that the hydrogen atoms which are covalently bonded to carbon atoms in the DNA sugars and bases were replaced by deuterium so that incoherent scattering and absorption effects were minimised. Successive cycles of Fourier synthesis and Fourier difference synthesis allowed water peaks to be identified and their positional and occupancy parameters to be refined against the observed diffraction data. The results confirm the main hydration features noted in our earlier studies with a clear network of water running along the inside edge of the major groove linking successive OI phosphate oxygen atoms. The central core of water running along the axis of the double helix is very much clearer in this work. Additionally this study shows chains of ordered water lying in the centre of the major groove.

Crystallography↗
PubMed1996

DNA hydration studied by neutron fiber diffraction.

The development of neutron high angle fiber diffraction to investigate the location of water around the deoxyribonucleic acid (DNA) double-helix is described. The power of the technique is illustrated by its application to the D and A conformations of DNA using the single crystal diffractometer, D19, at the Institut Laue-Langevin. Grenoble and the time of flight diffractometer, SXD, at the Rutherford Appleton ISIS Spallation Neutron Source. These studies show the existence of bound water closely associated with the DNA. The patterns of hydration in these two DNA conformations are quite distinct and are compared to those observed in X-ray single crystal studies of two-stranded oligodeoxynucleotides. Information on the location of water around the DNA double-helix from the neutron fiber diffraction studies is combined with that on the location of alkali metal cations from complementary X-ray high angle fiber diffraction studies at the Daresbury Laboratory SRS using synchrotron radiation. These analyses emphasize the importance of viewing DNA, water and ions as a single system with specific interactions between the three components and provide a basis for understanding the effect of changes in the concentration of water and ions in inducing conformational transitions in the DNA double-helix.

Crystallography↗
PubMed1996

Time-of-flight Laue fiber diffraction studies of perdeuterated DNA.

The diffractometer SXD at the Rutherford Appleton Laboratory ISIS pulsed neutron source has been used to record high resolution time-of-flight Laue fiber diffraction data from DNA. These experiments, which are the first of their kind, were undertaken using fibers of DNA in the A conformation and prepared using deuterated DNA in order to minimise incoherent background scattering. These studies complement previous experiments on instrument D19 at the Institut Laue Langevin using monochromatic neutrons. Sample preparation involved drawing large numbers of these deuterated DNA fibers and mounting them in a parallel array. The strategy of data collection is discussed in terms of camera design, sample environment and data collection. The methods used to correct the recorded time-of-flight data and map it into the final reciprocal space fiber diffraction dataset are also discussed. Difference Fourier maps showing the distribution of water around A-DNA calculated on the basis of these data are compared with results obtained using data recorded from hydrogenated A-DNA on D19. Since the methods used for sample preparation, data collection and data processing are fundamentally different for the monochromatic and Laue techniques, the results of these experiments also afford a valuable opportunity to independently test the data reduction and analysis techniques used in the two methods.

Crystallography↗
PubMed1995

Comparison of home and laboratory based monitoring of NPT using the Rigiscan; a preliminary report.

Laboratory based and home based monitoring of nocturnal penile tumescence (NPT) with the Rigiscan device was compared in a consecutive series of 100 men monitored in the laboratory, and a further consecutive series of 100 men monitored at home. Recordings at home were significantly shorter and involved more interruptions than laboratory based records. With subgroups, matched for diagnosis or the reporting of waking erections as well as age, laboratory monitoring tended to produce more sustained erections. However, in spite of the matching of subgroups, this trend may have resulted from aetiological rather than methodological differences, and further comparison of the two methods in the same subjects is now warranted. In the meantime, home monitoring should be used with diagnostic caution.

Adult↗
PubMed1992

A high angle neutron fibre diffraction study of the hydration of the A conformation of the DNA double helix.

A high angle neutron fibre diffraction study of the distribution of water around the A-form of DNA has been performed using the diffractometer D19 at the Institut Laue-Langevin, Grenoble. These experiments have exploited the ability to replace H2O surrounding the DNA by D2O so that isotopic difference Fourier maps can be computed in which peaks are identified with the distribution of water in the unit cell. All peaks of significant height have been accounted for by four families of water molecules whose positions and occupancies have been determined using least squares refinement. The coordinates of the water peaks making up each family do not deviate significantly from a regular helical arrangement with the same parameters as the DNA. Two of these families are of particular interest. The first consists of water molecules in the major groove linking successive charged phosphate oxygens along the polynucleotide chains. The second is associated with bases in the major groove and forms a central core of density along the helix axis. These two families provide a layer of hydration lining the interior wall of the major groove leaving a central channel to accommodate cations. The relationship between these observations and conformational stability is discussed.

DNA↗
PubMed1989

Surgical disassembly of the Sivash hip.

Due to the constrained nature of the Sivash type total hip, revision of the acetabular component without revision of the stem depends on the ability to separate the unit. Where the stem is tight in the shaft of the femur, it is preferable not to revise the stem if separation of the components is possible. This report describes a simple method of component separation.

Female↗
PubMed1987

Rupture of the patellar tendon after use of its central third.

The authors, in performing anterior cruciate ligament reconstruction, have been using the central third of the patella tendon with a connected piece of patella for a transfer. In this paper they report a case in which the residual patella tendon itself ruptured and required a subsequent repair. The technique of repair is described. Diagnosis of the rupture was difficult. The authors also describe an experimental technique for assessing derangement of the knee.

Adult↗
PubMed1986

Reduction of dislocated hip with transepiphyseal fracture.

A case report of a 12-year-old boy who suffered a dislocated hip in a football game. He was unable to walk and was in severe pain when seen in the emergency room. Efforts at closed reduction of the displacement were complicated by the development of a transepiphyseal fracture.

Athletic Injuries↗
PubMed1986

Magnetic imaging of lumbar spine.

The author compares the use of magnetic resonance imaging (MRI) scanning with other modalities in the diagnosis of lumbar disk pathology. As a result of his study, he cites three advantages of magnetic scanning: no ionizing radiation, visualization of the entire lumbar spine and more distinctly obvious image differences in the disks, adjacent tissue, nerve roots and epidural fat. He also notes greater physician satisfaction in assessing results of magnetic scanning.

Adult↗
PubMed1979

The Giliberty bipolar prosthesis: a clinical and radiographical review.

An interim report of 65 Giliberty bipolar hip units followed for an average of 19 months shows excellent short-term results in regard to their clinical condition. Radiographic study of the prosthesis with special attention to cup movement portends a favorable long-term result. Nevertheless, the snap-fit mechanism of the prosthetic head in the cup and the moving cup justify a cautious attitude until a larger series of a longer term can be completed.

Aged↗
PubMed1977

Changes in the calcar femoris in relation to cement technology in total hip replacement.

Radiological changes in the calcar femoris after total hip replacement, in 97 hips where an extreme valgus position of the prosthesis had been achieved, were compared with 119 hips where the alignment of the prosthesis ranged from varus to only a moderate degree of valgus. In the series with extreme valgus there was a minimum of 1 cm of cement between the calcar femoris and the prosthesis, whereas in the other series the thickness of cement averaged 4.5 mm. In the series with thick cement destructive changes in the calcar were reduced by a factor of 10 and there were no examples of incipient subsidence of the femoral prosthesis. This comparison was based on a follow-up of only 2 years.

Acrylic Resins↗