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PubMed1999

The supramolecular organisation of fibrillin-rich microfibrils determines the mechanical properties of bovine zonular filaments.

The zonular filaments from the eyes of cows are rich in microfibrils containing fibrillin. Tensile tests, stress-relaxation tests and X-ray diffraction studies were used to study the relationship between the mechanical behaviour of zonular filaments and the molecular packing and structure of the fibrillin-rich microfibrils. Zonular filaments show a non-linear (J-shaped) stress-strain curve and appreciable stress-relaxation. It is proposed that the non-linear properties are due to local variations in waviness in the microfibrils or assemblies of microfibrils, which straighten out and become more regularly aligned with strain. Previous and current X-ray diffraction results consistently show a partial ordering of microfibrils in zonular filaments into staggered aggregates which become more ordered and laterally aligned on stretching. Although the removal and re-addition of Ca(2+) is known to change the molecular structure of fibrillin, no effect was observed on the tensile properties of the zonular filaments. It is hypothesised that strain-induced deformation in the supramolecular aggregate packing may not be Ca(2+)-sensitive but could dominate the mechanical behaviour of microfibrillar arrays in zonular filaments.

Animals↗
PubMed2003

Experience in 100 cases with the Nuss procedure using a technique for stabilization of the pectus bar.

The Nuss procedure is a new, minimally invasive technique for the repair of pectus excavatum. We describe our experience with this operation, in a relatively large series in a single institution, and introduce our technical modification for stabilizing the pectus bar. In 107 patients (75 male and 32 female) with pectus excavatum who underwent the Nuss procedure, age at operation ranged from 3 to 23 years old (mean: 7.5+/-4.1) and Haller's CT index ranged from 33 to 2.6 (mean: 6.1+/-3.5). To stabilize the pectus bars, we tied the rib and both edges of the bars with surgical steel wire, 0.8 mm in diameter, using a Duchenne needle to guide the wire behind the rib. Average operating time with this technique (n=100) was 48+/-20 min. The stability of pectus bars after the operation was assessed by lateral chest X-ray films. The position of the center of the pectus bars, facing the sternum at right angles, was classified as excellent. A minimal bar displacement of less than 45 degrees was classified as incomplete. The position of the bars that had rotated 90 degrees was classified as poor. The post-operative course was uneventful in all cases except for three patients who showed wound infection, hemothorax or pneumothorax, independently. Two patients required wire removal due to skin irritation as a late complication. Five patients underwent re-operations due to bar displacement. Among them, only two cases were included in the group of wire fixation. Only five teen-aged patients required a lateral stabilizing bar. Lateral chest X-ray films of 100 patients showed that the position of the pectus bar was excellent in 86 cases, incomplete in 12 cases and poor in two cases. In 70 patients aged less than 10 years, the position in 91% was excellent and in 9% was incomplete. In 30 patients aged 10 years and older, 14 required two pectus bars and the results were excellent in all cases. The other 16 patients with a single bar showed excellent results in eight (50%) cases, incomplete in six (37.5%) and poor in two (12.5%). The wire-fixation technique was safe, effective and time efficient to perform in young cases. Teen-aged patients, however, were at high risk of bar displacement. Therefore, the use of two bars and lateral stabilizing bars are recommended for these high-risk patients.

Adolescent↗
PubMedDate not supplied

[Radiotherapy of the inoperable kidney tumours in the adult (author's transl)].

Radiotherapy as the sole method of treatment or as a preoperative measure is an important tool against the inoperable tumours of the kidney in the adult. Several techniques of irradiation are possible, for all of which the CT is an invaluable means of efficiency. The author describes the case of a huge renal tumour in a patient aged 76, exclusively treated by cobalt therapy, who is alive and well at more than 3 years. Four main conclusions are drawn: 1) the treatment must be versatile and continuously adapted to the clinical, radiological and CT modifications; 2) in the first phase of treatment a large tumour must be irradiated through a grid (gamma or high energy X-rays); 3) the fractionation must be very slow (2 sessions a week or several cycles in an overall time of some months, with periods of rest); in order to getting a good re-oxygenation of the large anoxic parts of the tumour mass; 4) the involution of the tumour must be graphically evaluated, as the rate of shrinkage may be very slow, continuing many months after completion of the treatment.

Adenocarcinoma↗
PubMedDate not supplied

Mixed-ligand technetium(III) complexes with tetradendate/monodendate NS(3)/isocyanide coordination: a new nonpolar technetium chelate system for the design of neutral and lipophilic complexes stable in vivo.

Starting from the tripodal ligand 2,2',2' '-nitrilotris(ethanethiol) (NS(3)) and isocyanides (CNR) as co-ligands, neutral mixed-ligand technetium(III) complexes of the general formulation [Tc(NS(3))(CNR)] have been synthesized and characterized. The (99)Tc complexes can be( )()obtained by a two-step reduction/substitution procedure starting from [TcO(4)](-) via the phosphine-containing precursor complex [Tc(NS(3))(PMe(2)Ph)]. As shown by X-ray structural analyses, the complexes adopt a nearly ideal trigonal-bipyramidal geometry with the trigonal plane formed by the three thiolate sulfurs of the tripodal ligand. The central nitrogen atom of the chelate ligand and the monodendate isocyanides occupy the apical positions. The no-carrier-added preparation of the corresponding (99m)Tc complexes was performed by a one-step procedure starting from (99m)[TcO(4)](-) with stannous chloride as reducing agent. Biodistribution studies in the rat demonstrated for the nonpolar, lipophilic compounds a significant initial brain uptake. In vitro challenge experiments with glutathione clearly indicated that no transchelation reaction occurs. Furthermore, there were no indications for reoxidation of Tc(III) to Tc(V) species or pertechnetate. We propose this type of complexes as a useful tool in the design of lipophilic (99m)Tc or (186)Re/(188)Re radiopharmaceuticals.

Animals↗
PubMed1992

An analysis of reported discomfort caused by mammographic X-ray amongst attenders at an Australian pilot breast screening program.

The aims of the study were to describe levels of discomfort experienced by women undergoing screening mammography; examine correlates of discomfort experienced and to examine whether the degree of discomfort experienced was perceived as a deterrent for re-screening. The study involved ninety five attenders at the pilot mammography screening program in Melbourne, Victoria. Women completed a questionnaire one or two days after having a screening mammogram. Pain was assessed on a seven point scale. Information was obtained on a number of possible correlates such as breast tenderness, perceptions of the service received and expectations of discomfort. Eighty-eight women were re-interviewed three months later about recall of discomfort and whether this would deter them from future mammography. Results were as follows: Thirty per cent of women reported no discomfort, 60% mild or moderate discomfort and 10% severe discomfort or worse. The degree of discomfort reported was not significantly related to age, breast tenderness in the previous three days, previous symptoms, previous mammographic experience, or outcome of visit. The degree of discomfort was related to retrospectively reported expectation of discomfort (r = .336; p = .001); reported lack of confidence in the staff taking the X-ray (r = .184; p = .039); perceptions of awkwardness (r = .175; p = .049) and unpleasantness (r = .297; p = .002) of the examination position. No woman said discomfort would definitely stop her having another screening mammogram. Three per cent said that it might stop them, while 97% of women said that it would not stop them at all.(ABSTRACT TRUNCATED AT 250 WORDS)

Breast↗
PubMed2000

Radiation-induced arrest of cells in G2 phase elicits hypersensitivity to DNA double-strand break inducers and an altered pattern of DNA cleavage upon re-irradiation.

PURPOSE: To determine how radiation-induced arrest in G2 affects the response of mammalian cells to a challenging dose of radiation or to antitumour drugs producing DNA double-strand breaks. MATERIALS AND METHODS: V79 fibroblast survival to 5 Gy gamma-rays followed at intervals by 3 Gy irradiation or by contact with an equitoxic dose of neocarzinostatin or etoposide, was measured by clonogenic assays. The pattern of radiation-induced DNA double-strand breaks was determined by filter elution and CFGE (continuous field gel electrophoresis) or PFGE (pulsed-field gel electrophoresis) in G2-arrested cells as well as in nonpre-irradiated asynchronous or synchronized cells. The cell-cycle phase specificity of drug susceptibility was determined in synchronized HeLa cells. RESULTS: Cell kill by radiation-drug combined treatment varied markedly with the time elapsed after priming irradiation. Pre-irradiated, G2-arrested V79 fibroblasts demonstrated excess double-stranded DNA cleavage upon re-irradiation and hypersensitivity to drugs and radiation, although maximum resistance to both neocarzinostatin and etoposide in synchronized HeLa cells was in G2. This effect occurred in the megabase range only, with a peak around 4 Mbp; no change in the electrophoretic migration profile of DNA was observed below 1 Mbp. Moreover, the DNA migration profile and the yield of DNA cleavage in G2-arrested cells were close to those expected from S-phase cells. CONCLUSION: The available data suggest that mechanisms operating within the radiation-induced G2 block promote susceptibility to DNA double-strand break inducers at this stage. It is also proposed that the conformation of DNA in cells accumulated in G2 following irradiation bears resemblance to that for cells in S phase, due either to active repair mechanisms or to inhibition of chromosome disentanglement at the S-G2 transition.

Animals↗
PubMed2006

Phosphato, chromato, and perrhenato complexes of titanium(IV) and zirconium(IV) containing Kläui's tripodal ligand.

Treatment of titanyl sulfate in dilute sulfuric acid with 1 equiv of NaL(OEt) (L(OEt)(-) = [(eta(5)-C(5)H(5))Co{P(O)(OEt)(2)](3)](-)) in the presence of Na(3)PO(4) and Na(4)P(2)O(7) led to isolation of [(L(OEt)Ti)(3)(mu-O)(3)(mu(3-)PO(4))] (1) and [(L(OEt)Ti)(2)(mu-O)(mu-P(2)O(7))] (2), respectively. The structure of 1 consists of a Ti(3)O(3) core capped by a mu(3)-phosphato group. In 2, the [P(2)O(7)](4-) ligands binds to the two Ti's in a mu:eta(2),eta(2) fashion. Treatment of titanyl sulfate in dilute sulfuric acid with NaL(OEt) and 1.5 equiv of Na(2)Cr(2)O(7) gave [(L(OEt)Ti)(2)(mu-CrO(4))(3)] (3) that contains two L(OEt)Ti(3+) fragments bridged by three mu-CrO(4)(2-)-O,O' ligands. Complex 3 can act as a 6-electron oxidant and oxidize benzyl alcohol to give ca. 3 equiv of benzaldehyde. Treatment of [L(OEt)Ti(OTf)(3)] (OTf(-) = triflate) with [n-Bu(4)N][ReO(4)] afforded [[L(OEt)Ti(ReO(4))(2)](2)(mu-O)] (4). Treatment of [L(OEt)MF(3)] (M = Ti and Zr) with 3 equiv of [ReO(3)(OSiMe(3))] afforded [L(OEt)Ti(ReO(4))(3)] (5) and [L(OEt)Zr(ReO(4))(3)(H(2)O)] (6), respectively. Treatment of [L(OEt)MF(3)] with 2 equiv of [ReO(3)(OSiMe(3))] afforded [L(OEt)Ti(ReO(4))(2)F] (7) and [[L(OEt)Zr(ReO(4))(2)](2)(mu-F)(2)] (8), respectively, which reacted with Me(3)SiOTf to give [L(OEt)M(ReO(4))(2)(OTf)] (M = Ti (9), Zr (10)). Hydrolysis of [L(OEt)Zr(OTf)(3)] (11) with Na(2)WO(4).xH(2)O and wet CH(2)Cl(2) afforded the hydroxo-bridged complexes [[L(OEt)Zr(H(2)O)](3)(mu-OH)(3)(mu(3)-O)][OTf](4) (12) and [[L(OEt)Zr(H(2)O)(2)](2)(mu-OH)(2)][OTf](4) (13), respectively. The solid-state structures of 1-3, 6, and 11-13 have been established by X-ray crystallography. The L(OEt)Ti(IV) complexes can catalyze oxidation of methyl p-tolyl sulfide with tert-butyl hydroperoxide. The bimetallic Ti/ Re complexes 5 and 9 were found to be more active catalysts for the sulfide oxidation than other Ti(IV) complexes presumably because Re alkylperoxo species are involved as the reactive intermediates.

Journal Article↗
PubMed2005

Preparation and characterization of diarylphosphazene and diarylphosphinohydrazide complexes of titanium, tungsten and ruthenium and phosphorylketimido complexes of rhenium.

Reaction of the proligand Ph2PN(SiMe3)2 (L1) with WCl6 gives the oligomeric phosphazene complex [WCl4(NPPh2)]n, 1 and subsequent reaction with PMe2Ph or NBu4Cl gives [WCl4(NPPh2)(PMe2Ph)] (2) or [WCl5(NPPh2)][NBu4] (3), respectively. DF calculations on [WCl5(NPPh2)][NBu4] show a W=N double bond (1.756 A) and a P-N bond distance of 1.701 A, which combined with the geometry about the P atom suggests, there is no P-N multiple bonding. Reaction of L1 with [ReOX3(PPh3)2] in MeCN (X = Cl or Br) gives [ReX2(NC(CH3)P(O)Ph2)(MeCN)(PPh3)](X = Cl, 4, X = Br, 5) which contains the new phosphorylketimido ligand. It is bound to the rhenium centre with a virtually linear Re-N-C arrangement (Re-N-C angle = 176.6 degrees, when X = Cl) and there is multiple bonding between Re and N (Re-N = 1.809(7) A when X = Cl). The proligand Ph2PNHNMe2(L2H) reacts with [(C5H5)TiCl3] to give [(C5H5)TiCl2(Me2NNPPh2)] (6). An X-ray crystal structure of the complex shows the ligand (L2) is bound by both nitrogen atoms. Reaction of the proligands Ph2PNHNR2[R2 = Me2 (L2H), -(CH2CH2)2NCH3 (L3H), (CH2CH2)2CH2 (L4H)] with [{RuCl(mu-Cl)(eta6-p-MeC6H4iPr)}2] gave [RuCl2(eta6-p-MeC6H4iPr)L] {L = L2H (7), L3H (8), L4H (9)}. The X-ray crystal structures of 7-9 confirmed that the phosphinohydrazine ligand is neutral and bound via the phosphorus only. Reaction of complexes 7-9 with AgBF4 resulted in chloride ion abstraction and the formation of the cationic species [RuCl(6-p-MeC6H4iPr)(L)]+ BF4- {(L = L2H (10), L3H (11), L4H (12)}. Finally, reaction of complex 6 with [{RuCl(mu-Cl)(eta6-p-MeC6H4iPr)}2] gave the binuclear species [(eta6-p-MeC6H4iPr)Cl2Ru(mu2,eta3-Ph2PNNMe2)TiCl2(C5H5)], 13.

Journal Article↗
PubMed1998

Low leptin gene expression and hyperleptinemia in chronic renal failure.

BACKGROUND: The ob gene product leptin is thought to be a key regulator of food intake and body weight. Patients having advanced chronic renal failure (CRF) have markedly higher serum leptin levels. It is not known whether the increase in leptin levels in CRF is caused by a decreased plasma clearance and/or increased production. METHODS: In the present study serum leptin levels and glomerular filtration rate (GFR) were measured in 219 patients having various degrees of renal failure. In addition, serum leptin levels, C-reactive protein (CRP), body composition (by dual-energy x-ray absorptiometry) and ob gene expression (by in situ hybridization histochemistry) were determined in 15 patients with advanced CRF. Seven of the patients were re-evaluated following 12 months of peritoneal dialysis (PD) treatment. RESULTS: Serum leptin levels correlated negatively to GFR (r = -0.26; P < 0.0001). The ob gene expression was significantly lower in patients with CRF than in healthy controls. A negative correlation between serum leptin levels and ob gene expression (r = -0.66; P < 0.05) was found in patients with CRP < 25 mg/liter. The ob gene expression (20.0 +/- 1.8 vs. 15.0 +/- 1.0 nCi/g; P < 0.05) was significantly higher in 5 patients with CRP > 25 mg/liter than in 10 patients with CRP < 25 mg/liter. Following 12 months of PD, the amount of body fat increased by 30% while the ob gene expression remained unchanged. CONCLUSION: The present study shows a correlation between serum leptin levels and GFR, and our results suggest that elevated leptin levels, due to a decreased plasma clearance, down-regulate the expression of the ob gene. We also found that an ongoing inflammation stimulates ob gene expression in patients with CRF. Therefore, it is suggested that the hyperleptinemia induced feedback inhibition of ob gene expression is overcome by inflammatory cytokines.

Adipose Tissue↗
PubMed1997

Serum immunoreactive leptin concentration and its relation to the body fat content in chronic renal failure.

Leptin, secreted from fat cells, functions as a lipostat mechanism through modulation of satiety signals. The role of leptin in humans has been only partly revealed. However, obese patients have markedly elevated levels of this hormone, and in both normal-weight and obese subjects there is a direct correlation between serum leptin levels and the percentage of body fat. The aim of the present study was to investigate the role of leptin and its relation to body fat content in chronic renal failure (CRF), a disorder associated with decreased appetite. Serum leptin levels and body composition (dual-energy x-ray absorptiometry) were measured in a cohort of 59 patients with terminal CRF (creatinine clearance rate, 8 +/- 1 ml/min). Sixteen of the patients were re-evaluated after 12 mo of peritoneal dialysis treatment, and eight patients were re-evaluated after 12 mo of hemodialysis treatment. The mean serum leptin concentrations were markedly higher (mean +/- SEM) in patients with CRF than in healthy control subjects matched for gender and body mass index (25.7 +/- 5.2 ng/ml versus 8.4 +/- 0.9 ng/ml; P < 0.001). Patients with ongoing signs of inflammation (C-reactive protein > 10 mg/L) demonstrated higher serum leptin levels (41.9 +/- 13.7 ng/ml versus 18.6 +/- 4.2 ng/ml; P < 0.05) than patients with normal C-reactive protein. A strong positive correlation (rho = 0.83; P < 0.0001) was found between serum leptin concentrations and the percentage of body fat. After 12 mo of peritoneal dialysis, the amount of body fat increased markedly (19.0 +/- 1.5 to 25.1 +/- 2.2 kg; P < 0.001), and the changes in serum leptin concentrations correlated significantly (rho = 0.69; P < 0.01) to the changes in the body fat content. In contrast, no significant changes in either body fat content or serum leptin levels were recorded in the eight patients that were re-evaluated after 12 mo of hemodialysis. Serum leptin concentrations are approximately three times higher in patients with CRF compared with healthy control subjects with a similar body mass index. In this study, it is also demonstrated that serum leptin is a good marker for the body fat content in CRF patients and correlates strongly to changes in body fat during 12 mo of peritoneal dialysis. These findings suggest that serum leptin could serve as a valuable clinical marker for the body fat content in patients with CRF. Further studies are needed to verify the hypothesis that increased serum leptin concentrations may contribute to uremic anorexia.

Adipose Tissue↗
PubMed2004

[Revision hip arthroplasty after prosthesis removal in septic loosening].

The author presents the therapeutic protocol in "hanging hip" after prosthesis removal in septic loosening, basing on a series of 11 patients--7 females and 4 males--age ranging from 31 to 67 years. On average the primary prosthesis was removed 2.5 years after implantation, while patients remained with a "hanging hip" for an average period of 2.2 years (limb shortening before revision arthroplasty was on average 4.5cm). When qualifying patients for revision arthroplasty the following parameters were taken into account: sedimentation rate, CRP reactive protein levels, bacteriological blood culture results, cultures from the hip punctate, every-day life activity and post-op patient compliance with the therapy. Acetabular roof defects were managed according to Zuk's method. Clinical assessment of the patients was performed 6 weeks, 3, 6 and 12 months using Merle-d'Aubigne and Postel classification, while X-rays were used to assess proper prosthesis implantation. During follow-up proper prosthesis implantation was found in all cases, while no signs of re-infection, nor radiological and clinical signs of implant loosening were noted. Clinical assessment of the patients yielded 1 very good result, 7 good results and 3 satisfactory. The presented material indicates that good results can be obtained in prosthesis reimplantation after removal of the primary prosthesis because of its septic loosening.

Adult↗
PubMed1993

[TV-assisted thoracoscopic surgery with a lung forceps combined with thoracoscope under local anesthesia for spontaneous pneumothorax with a persistent air leak--a single access port approach].

TV-assisted thoracoscopic surgery was performed under local anesthesia by through a single access port to control a continuing air leak in spontaneous pneumotorax. A 75-year-old man was admitted with severe dyspnea and right-sided chest pain. The chest X-ray film showed right lung collapse. A right spontaneous pneumothorax was diagnosed and was treated by chest tube drainage. However, the lung did not re-expand because of a continuing air leak and subcutaneous emphysema developed. TV-assisted thoracoscopic surgery was performed under local anesthesia to treat the persistent air leak on day 12. By endoscopy, the ruptured bulla was double-ligated with an Endoloop through a single access port using lung forceps combined with endoscope. The air leak subsequently ceased and the lung re-expanded. This method is minimally invasive and is very suitable for controlling a continuing air-leak causing spontaneous pneumothorax in a patient.

Aged↗
PubMed2005

Dual modes of modification of hepatitis A virus 3C protease by a serine-derived beta-lactone: selective crystallization and formation of a functional catalytic triad in the active site.

Hepatitis A virus (HAV) 3C proteinase is a member of the picornain cysteine proteases responsible for the processing of the viral polyprotein, a function essential for viral maturation and infectivity. This and its structural similarity to other 3C and 3C-like proteases make it an attractive target for the development of antiviral drugs. Previous solution NMR studies have shown that a Cys24Ser (C24S) variant of HAV 3C protein, which displays catalytic properties indistinguishable from the native enzyme, is irreversibly inactivated by N-benzyloxycarbonyl-l-serine-beta-lactone (1a) through alkylation of the sulfur atom at the active site Cys172. However, crystallization of an enzyme-inhibitor adduct from the reaction mixture followed by X-ray structural analysis shows only covalent modification of the epsilon2-nitrogen of the surface His102 by the beta-lactone with no reaction at Cys172. Re-examination of the heteronuclear multiple quantum coherence (HMQC) NMR spectra of the enzyme-inhibitor mixture indicates that dual modes of single covalent modification occur with a >/=3:1 ratio of S-alkylation of Cys172 to N-alkylation of His102. The latter product crystallizes readily, probably due to the interaction between the phenyl ring of the N-benzyloxycarbonyl (N-Cbz) moiety and a hydrophobic pocket of a neighboring protein molecule in the crystal. Furthermore, significant structural changes are observed in the active site of the 3C protease, which lead to the formation of a functional catalytic triad with Asp84 accepting one hydrogen bond from His44. Although the 3C protease modified at Cys172 is catalytically inactive, the singly modified His102 N(epsilon2)-alkylated protein displays a significant level of enzymatic activity, which can be further modified/inhibited by N-iodoacetyl-valine-phenylalanine-amide (IVF) (in solution and in crystal) or excessive amount of the same beta-lactone inhibitor (in solution). The success of soaking IVF into HAV 3C-1a crystals demonstrates the usefulness of this new crystal form in the study of enzyme-inhibitor interactions in the proteolytic active site.

3C Viral Proteases↗
PubMed2005

Ligand-to-diimine/metal-to-diimine charge-transfer excited states of [Re(NCS)(CO)3(alpha-diimine)] (alpha-diimine = 2,2'-bipyridine, di-iPr-N,N-1,4-diazabutadiene). A spectroscopic and computational study.

Two new complexes fac-[Re(NCS)(CO)3(N,N)] (N,N = 2,2'-bipyridine (bpy), di-iPr-N,N-1,4-diazabutadiene (iPr-DAB)) were synthesized and their molecular structures determined by X-ray diffraction. UV-vis absorption, resonance Raman, emission, and picosecond time-resolved IR spectra were measured experimentally and calculated with TD-DFT. A good agreement between experimental and calculated ground- and excited-state spectra is obtained, but only if the solvent (MeCN) is included into calculations and excited state structures are fully optimized at the TD-DFT level. The lowest excited states of the bpy and iPr-DAB complexes are assigned by TD-DFT as 3aA' by comparison of calculated and experimental IR spectra. Excited-state lifetimes of 23 ns and ca. 625 ps were determined for the bpy and DAB complex, respectively, in a fluid solution at room temperature. Biexponential emission decay (1.3, 2.7 micros) observed for [Re(NCS)(CO)3(bpy)] in a 77 K glass indicates the presence of two unequilibrated emissive states. Low-lying electronic transitions and excited states of both complexes have a mixed NCS --> N,N ligand-to-ligand and Re --> N,N metal-to-ligand charge-transfer character (LLCT/MLCT). It originates in mixing between Re d(pi) and NCS pi characters in high-lying occupied MOs. Experimentally, the LLCT/MLCT mixing in the lowest excited state is manifested by shifting the nu(CO) and nu(NC) IR bands to higher and lower wavenumbers, respectively, upon excitation. Resonant enhancement of both nu(CO) and nu(NC) Raman bands indicates that the same LLCT/MLCT character mixing occurs in the lowest allowed electronic transition.

2,2'-Dipyridyl↗
PubMed1993

Fourier transform infrared spectroscopy characterization of the lamellar and nonlamellar structures of free lipid A and Re lipopolysaccharides from Salmonella minnesota and Escherichia coli.

The structural polymorphism of free lipid A and deep rough mutant lipopolysaccharide (LPS Re) from Salmonella minnesota strain R595 and Escherichia coli strain F515 was characterized by Fourier transform infrared (IR) spectroscopy. For this, the beta <--> alpha phase states and the three-dimensional supramolecular structures, the latter deduced from small-angle synchrotron radiation x-ray diffraction, were investigated at different water contents, Mg2+ concentrations, and temperatures. The analysis of the IR data for vibrations originating from the hydrophobic moiety shows that the beta <--> alpha acyl chain melting is strongly expressed only for the stretching and scissoring modes of the methylene groups. Vibrational groups originating from the interface region sense the acyl chain melting well (ester carbonyl bands) or only weakly (amide bands), and those resulting from the pure polar moiety not at all. From the x-ray data, the existence of lamellar (L), different cubic, and, for lipid A and LPS R595, also inverted hexagonal (HII) structures could be proven in the temperature range 20-80 degrees C with cubic <--> cubic and cubic <--> HII transitions for the Mg(2+)-free and L <--> HII transitions for the Mg(2+)-containing samples. These structural transitions can be characterized most readily by specific changes of the vibrational bands resulting from the interface region: the ester carbonyl and the amide bands. The magnitude of the changes corresponds to that of the structural rearrangement, i.e., is highest for the L <--> HII, lower for the cubic <--> HII, and lowest for the cubic <--> cubic transitions. The structural transitions are only marginally expressed for vibrational bands of the hydrophobic moiety. Similarly, the band contours of vibrations from the hydrophilic region are no indicators of the structural reorientations except for the carboxylate bands of LPS Re. Particularly the stretching vibrations of the phosphate groups are nearly completely invariant; the absolute values of their half bandwidths, however, differ significantly for lipid A and LPS Re, which seems to be of biological relevance. The ability of IR spectroscopy to detect supramolecular changes also beyond the measurability by x-ray diffraction, i.e., at water contents > 95 to 99.5%, is demonstrated.

Biophysical Phenomena↗